{"gene":"NEU1","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2023,"finding":"Crystal/cryo-EM structure of murine NEU1 was determined, revealing that the enzyme oligomerizes through two self-association interfaces, displays a wide substrate-binding cavity, and contains a catalytic loop that adopts an inactive conformation. A mechanism of activation was proposed involving a conformational change in this loop upon binding to its protective protein PPCA/cathepsin A.","method":"Structure determination (3D structural analysis), biochemical characterization","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Moderate — first experimentally determined 3D structure of NEU1, with structural data supporting mechanistic model of activation; single study but rigorous structural method","pmids":["37205763"],"is_preprint":false},{"year":2009,"finding":"NEU1 (and not NEU2, NEU3, or NEU4) forms a complex with TLR-2, -3, and -4 on the cell surface of naïve macrophages. Ligand binding to TLR4 (LPS) induces NEU1 sialidase activity, which hydrolyzes alpha-2,3-sialyl residues on TLR4, removing steric hindrance to TLR4 dimerization, MyD88/TLR4 complex formation, and subsequent NFκB activation. This was confirmed using primary Neu1-deficient macrophages (which fail to respond), catalytically inactive trans-sialidase mutant (which cannot substitute), and the neuraminidase inhibitor Tamiflu.","method":"Co-immunoprecipitation, live-cell sialidase assay, pharmacological inhibition (Tamiflu/DANA/zanamivir), lectin blocking, primary Neu1-deficient macrophages, HEK293 reconstitution with TLR4/MD2","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, primary KO macrophages, pharmacological inhibition, catalytic mutant controls, replicated across multiple cell types and labs","pmids":["19796680","19430901"],"is_preprint":false},{"year":2009,"finding":"NEU1 forms a stable heterodimer with protective protein/cathepsin A (PPCA). PPCA acts as a molecular chaperone that prevents premature self-oligomerization of NEU1 by competing for a NEU1 self-association interface. In the absence of PPCA (as in galactosialidosis), NEU1 self-associates into chain-like oligomers. PPCA binding reverses NEU1 self-oligomerization by disassembling NEU1 oligomers into a PPCA-NEU1 heterodimer.","method":"Hydrodynamic analysis (analytical ultracentrifugation), binding site mapping, structural modeling, biochemical reconstitution","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution-level biochemistry with multiple biophysical methods in a single rigorous study; identifies binding sites on both proteins","pmids":["19666471"],"is_preprint":false},{"year":2006,"finding":"During monocyte-to-macrophage differentiation, NEU1 relocalizes from lysosomes to the cell surface via LAMP-2-negative, MHC class II-positive vesicles that merge with the plasma membrane. Cathepsin A, which forms a complex with and activates NEU1 in lysosomes, is co-sorted to the plasma membrane. siRNA suppression of NEU1 or anti-NEU1 antibodies reduced macrophage phagocytosis of bacteria and cytokine production.","method":"Immunofluorescence, subcellular fractionation, siRNA knockdown, anti-Neu1 antibody blocking, flow cytometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with functional consequence (phagocytosis, cytokine production) using multiple orthogonal methods in one study","pmids":["16835219"],"is_preprint":false},{"year":2007,"finding":"The catalytic sialidase activity of the NEU1 subunit of the elastin receptor complex (ERC) is responsible for ERK1/2 activation and pro-MMP-1 production induced by elastin peptide binding. A catalytically inactive NEU1 mutant and siRNA-mediated NEU1 knockdown both abolished elastin peptide-induced ERK1/2 activation and pro-MMP-1 production in skin fibroblasts. N-acetyl neuraminic acid (sialic acid) could reproduce the elastin peptide effects.","method":"Pharmacological inhibition, catalytically inactive NEU1 mutant, siRNA knockdown, ERK1/2 activation assay, pro-MMP-1 production assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — catalytic mutant + siRNA + pharmacological inhibition in a single study; multiple orthogonal methods establishing catalytic mechanism","pmids":["17327233"],"is_preprint":false},{"year":2011,"finding":"On the surface of naive macrophage cells, NEU1 forms a complex with MMP-9, both of which are constitutively bound to TLR4. LPS binding to TLR4 activates Gαi GPCR signaling, which activates MMP-9, which in turn activates NEU1 sialidase. NEU1-mediated TLR4 desialylation and NFκB activation are blocked by specific MMP-9 inhibition, Gαi-pathway inhibition, MMP-9 shRNA/siRNA knockdown, and are absent in MMP-9 knockout macrophages.","method":"Co-immunoprecipitation, siRNA/shRNA knockdown, MMP-9 KO macrophages, lentiviral transduction, pharmacological inhibition, live-cell sialidase assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic and pharmacological approaches, KO validation, reciprocal Co-IP, replicated across different cell lines","pmids":["21873432"],"is_preprint":false},{"year":2010,"finding":"Neu1 and MMP-9 form a complex bound to TrkA on the surface of naive neurons and TrkA-expressing cells. NGF binding to TrkA activates GPCR Gαi signaling → MMP-9 activation → Neu1 sialidase activation. Tamiflu (oseltamivir phosphate) blocks NGF-induced Neu1 activity and subsequent Trk receptor activation and neurite outgrowth in TrkA-PC12 cells.","method":"Co-immunoprecipitation, live-cell sialidase assay, pharmacological inhibition (Tamiflu), TrkA-PC12 cell lines, primary neurons","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, pharmacological inhibition, functional readout (neurite outgrowth); single lab, but multiple orthogonal approaches","pmids":["20347965"],"is_preprint":false},{"year":2009,"finding":"NEU1 overexpression in human colon cancer HT-29 cells desialylates integrin beta4 (removing alpha-2,3 and O-glycan sialic acids), reduces integrin beta4 phosphorylation, attenuates focal adhesion kinase (FAK) and Erk1/2 signaling, and downregulates MMP-7, leading to suppressed cell migration, invasion, adhesion, and in vivo liver metastasis.","method":"NEU1 overexpression and siRNA knockdown, lectin blotting of integrin beta4 immunoprecipitates, immunofluorescence, biotinylation assay, O-glycosylation inhibitor (GalNAc-α-O-benzyl), in vivo transsplenic injection model","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal biochemical approaches (OE + KD), direct substrate identification by immunoprecipitation + lectin blotting, in vivo validation","pmids":["19151752"],"is_preprint":false},{"year":2012,"finding":"In human airway epithelial cells, NEU1 sialidase directly associates with EGFR and MUC1 and accounts for >70% of cellular sialidase activity. NEU1 overexpression diminishes EGF-stimulated EGFR Tyr-1068 autophosphorylation, while NEU1 depletion increases EGFR activation. NEU1 also desialylates MUC1, enhancing MUC1-dependent Pseudomonas aeruginosa adhesion and flagellin-stimulated ERK1/2 activation.","method":"Co-immunoprecipitation, NEU1 overexpression/siRNA, lectin blotting (MAL-2/PNA), EGFR phosphorylation assay, bacterial adhesion assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP identifies substrates, functional phosphorylation assays, multiple orthogonal readouts in one study","pmids":["22247545"],"is_preprint":false},{"year":2013,"finding":"NEU1 deficiency in mice leads to accumulation and amyloidogenic processing of an oversialylated amyloid precursor protein (APP) in lysosomes, followed by excessive lysosomal exocytosis that releases Aβ peptides extracellularly. Cerebral injection of NEU1 into an established AD mouse model substantially reduces β-amyloid plaques.","method":"NEU1-deficient mouse model, APP processing analysis, lysosomal fractionation, Aβ ELISA, cerebral NEU1 injection rescue experiment","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic mouse model combined with rescue experiment and biochemical analysis of lysosomal exocytosis pathway; multiple orthogonal approaches in one study","pmids":["24225533"],"is_preprint":false},{"year":2014,"finding":"TLR4 activation triggers NEU1 translocation to the cell surface, where NEU1 disrupts the inhibitory TLR4:Siglec-E interaction by desialylating TLR4. Sialidase inhibitor Neu5Gc2en prevents TLR4 ligand-induced disruption of TLR4:Siglec-E/F interactions. Absence of NEU1 in hematopoietic cells protects mice against endotoxemia, demonstrating that NEU1-mediated de-repression of TLR4 from Siglec inhibition is a positive feedback mechanism for TLR activation during infection.","method":"Cell surface translocation assay, sialidase inhibitor treatment (Neu5Gc2en), Neu1-conditional hematopoietic KO mice, TLR4:Siglec interaction co-IP/pulldown, endotoxemia mouse model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO mouse model, pharmacological inhibition, direct TLR-Siglec interaction assays, in vivo endotoxemia validation; replicated mechanisms from prior NEU1-TLR studies","pmids":["25187624"],"is_preprint":false},{"year":2014,"finding":"Catalytically active NEU1 inhibits in vitro angiogenesis (capillary-like tube formation) through desialylation of its substrate CD31 in postconfluent human pulmonary microvascular endothelial cells. A catalytically dead NEU1 mutant (G68V) did not inhibit tube formation. Prior CD31 silencing or use of CD31-null ECs abrogated NEU1's inhibitory effect, and forced CD31 sialylation (via sialyltransferase ST6GAL-I overexpression) counteracted NEU1-mediated inhibition.","method":"NEU1 overexpression with catalytic mutant control (G68V), siRNA knockdown of NEU1/CD31, CD31-null ECs, lectin blotting (SNA/PNA), Matrigel tube formation assay, wounding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — catalytic mutant controls, substrate identification by lectin blotting, genetic rescue experiments; multiple orthogonal approaches","pmids":["24550400"],"is_preprint":false},{"year":1998,"finding":"A single amino acid substitution L209I in the Neu1 protein is responsible for the partial neuraminidase deficiency in SM/J mice. The mutant enzyme is correctly localized to lysosomes and retains the ability to associate with its activating protein PPCA, but the reduced activity is caused by altered substrate affinity rather than changed substrate specificity or turnover rate.","method":"Genetic analysis, sequencing, site-directed mutagenesis, enzyme activity assays, lysosomal fractionation, PPCA binding assay","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct mutagenesis + enzyme activity assay + localization + PPCA interaction analysis in one study establishing structure-function relationship","pmids":["9425240"],"is_preprint":false},{"year":2004,"finding":"Five novel NEU1 mutations (R225P, A298V, M1?, R341G, W23X) in type II sialidosis patients abolish enzymatic sialidase activity when expressed via recombinant adenovirus. The R341G mutation perturbs substrate binding, while A298V and R225P impair enzyme folding, as determined by activity assay and immunofluorescence localization analysis.","method":"Adenoviral expression of mutant sialidases in primary cell cultures, sialidase activity assay, intracellular localization (immunofluorescence)","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct expression of mutant alleles with enzymatic activity assays and localization, identifying distinct mutant mechanisms (substrate binding vs. folding)","pmids":["14695530"],"is_preprint":false},{"year":2012,"finding":"NEU1 is the dominant sialidase in human lung microvascular endothelial cells (expressed ~2700-fold more than NEU2/3/4), localizes to both plasma membrane and perinuclear regions, and restrains endothelial cell migration. NEU1 overexpression reduced EC migration into wounds by >40%, whereas NEU3 overexpression did not. siRNA knockdown of NEU1 decreased >65% of total sialidase activity for 4-MU-NANA substrate.","method":"Real-time RT-PCR, Western blot, confocal microscopy/flow cytometry (localization), siRNA knockdown, wound-healing migration assay, sialidase activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with functional consequence (migration), siRNA validation, quantitative activity assays; multiple orthogonal methods","pmids":["22403397"],"is_preprint":false},{"year":2010,"finding":"Neu1 sialidase is required for hyaluronic acid receptor function of CD44 on CD4+ T cells. Antigen stimulation induces Neu1 expression on splenic CD4+ T cells from asthmatic mice, and increased Neu1 activity removes inhibitory sialic acid residues from CD44 to enable HA binding and T helper type 2-mediated airway inflammation. Sialidase inhibitor treatment suppressed HA binding, and Neu1-deficient SM/J mice showed reduced Th2 airway inflammation and airway hyperresponsiveness.","method":"Flow cytometry (HA-binding), real-time RT-PCR, pharmacological sialidase inhibition, Neu1-deficient SM/J mouse model, cytokine analysis, airway hyperresponsiveness measurement","journal":"Clinical and experimental immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Neu1-deficient mouse model with functional readout; pharmacological inhibition corroborates genetic data; substrate (CD44) inferred but not directly demonstrated by immunoprecipitation","pmids":["20491786"],"is_preprint":false},{"year":2013,"finding":"NEU1 and MMP-9 form a tripartite complex with neuromedin B GPCR, TLR-7, and TLR-9. Ligand-induced activation of endosomal TLR-7 and TLR-9 requires this NMBR-MMP9-Neu1 cross-talk signaling platform. siRNA silencing of Neu1, MMP-9, or NMBR each significantly reduced nucleic acid-induced NFκB activation and TNFα/MCP-1 cytokine responses.","method":"siRNA knockdown, complex formation (immunoprecipitation), NFκB reporter assay, SEAP reporter, pharmacological inhibitors (Tamiflu, MMP-9 inhibitor, BIM23127, BIM-46174)","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA of three complex components with consistent phenotype; pharmacological inhibition corroborates; single lab","pmids":["23827939"],"is_preprint":false},{"year":2012,"finding":"GPCR agonists (bombesin, bradykinin, LPA, cholesterol, angiotensin-1 and -2) induce Neu1 sialidase activity in macrophages via a neuromedin B receptor (NMBR)-MMP9 signaling platform, transactivating TLR receptors and inducing NFκB activation. Bombesin receptor (NMBR) forms a complex with TLR4 and MMP9. MMP9 siRNA knockdown or MMP9 absence abolishes this GPCR-induced Neu1 activity.","method":"Live-cell sialidase assay, siRNA knockdown, co-immunoprecipitation, NFκB-SEAP reporter, pharmacological inhibitors, Neu1-deficient primary macrophages as negative control","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP identifies complex, siRNA validates mechanism, Neu1-deficient macrophages as genetic control; single lab","pmids":["22759791"],"is_preprint":false},{"year":2013,"finding":"Elastin-derived peptides (EDP) binding to the elastin receptor complex (ERC, which contains NEU1) activate monocyte migration and ROS production through a neuraminidase activity-dependent PI3Kγ signaling pathway. The absence of the cathepsin A-NEU1 complex in hematopoietic cells abolished atherosclerotic plaque progression in LDLR-/- mice. In vitro, PI3Kγ was required for EDP-induced monocyte migration and this was dependent upon neuraminidase activity.","method":"In vivo atherosclerosis mouse models, PI3Kγ KO bone marrow chimeras, cathepsin A-NEU1 complex-deficient hematopoietic cells, neuraminidase activity inhibition, monocyte migration assay, ROS production assay","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse models with hematopoietic-specific deletion and functional in vitro assays; pathway positioning via epistasis","pmids":["24357053"],"is_preprint":false},{"year":2015,"finding":"NEU1-driven MUC1 ectodomain desialylation increases binding affinity of P. aeruginosa flagellin to MUC1, promotes bacterial adhesion and invasion, and triggers MUC1-ED shedding. The shed desialylated MUC1-ED functions as a hyperadhesive decoy receptor that competitively blocks bacterial adhesion. NEU1 association with MUC1 increases upon flagellin stimulation, and NEU1 co-associates with MUC1's chaperone PPCA in this context.","method":"Scatchard binding analysis, NEU1/MUC1 co-immunoprecipitation, lectin blotting, NEU1 overexpression/siRNA, bacterial adhesion/invasion assay, ex vivo BAL fluid analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical approaches, Scatchard analysis quantifying binding affinity, ex vivo patient sample validation; multiple functional readouts","pmids":["25963144"],"is_preprint":false},{"year":2021,"finding":"NEU1 directly associates with the MUC1 cytoplasmic domain (CD) at its juxtamembranous 36 amino acid region, independently of NEU1 catalytic activity and independently of PPCA chaperone. This NEU1-MUC1-CD interaction does not require NEU1 enzymatic activity for MUC1-ED desialylation. However, both wild-type NEU1 and the catalytically dead NEU1-G68V mutant inhibit PI3K binding to MUC1-CD and reduce downstream Akt phosphorylation, indicating NEU1 inhibits PI3K-Akt signaling through its scaffold function independent of catalytic activity.","method":"Reciprocal co-immunoprecipitation, in vitro binding assays (GST pull-down with deletion mutants), cell-free binding assay with purified proteins, catalytic dead mutant (G68V), NEU1-selective inhibitor C9-BA-DANA","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cell-free reconstitution with purified proteins, deletion mapping, catalytic mutant controls, multiple orthogonal binding assays in one rigorous study","pmids":["34688655"],"is_preprint":false},{"year":2017,"finding":"As human pulmonary microvascular endothelial cells (HPMECs) achieve confluence, Src family kinases (SFKs) are activated and phosphorylate p120 catenin. Tyrosine-phosphorylated p120 catenin functions as an adaptor molecule that physically couples NEU1 to CD31, enabling NEU1-mediated CD31 desialylation. SFK inhibition blocks both p120ctn phosphorylation and NEU1-CD31 association. Direct protein-protein interactions between NEU1, CD31, and p120ctn were demonstrated in a cell-free system with purified recombinant proteins.","method":"Co-immunoprecipitation, siRNA knockdown of individual SFKs/CD31/p120ctn, SFK pharmacological inhibitors (PP2, SU6656), cell-free binding assay with purified recombinant proteins, pull-down assays","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — cell-free reconstitution with purified proteins + co-IP + genetic knockdown; multiple orthogonal methods establish scaffolding mechanism","pmids":["28343945"],"is_preprint":false},{"year":2018,"finding":"Membrane NEU1 interacts with CD36 (class B scavenger receptor) in human macrophages. Elastin-derived peptides (EDP) binding to the elastin receptor complex desialylate CD36 via NEU1. EDP-induced desialylation of CD36 increases uptake of oxidized LDL by macrophages, an effect blocked by both V14 peptide (blocking EDP-ERC interaction) and the sialidase inhibitor DANA.","method":"Proteomic purification (LC-MS/MS), co-immunoprecipitation validation, sialidase activity assay, oxidized LDL uptake assay, pharmacological inhibition (V14 peptide, DANA)","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomic identification of interaction partner confirmed by co-IP, functional readout (oxLDL uptake) with pharmacological controls; single lab","pmids":["30498996"],"is_preprint":false},{"year":2021,"finding":"In L. donovani-infected macrophages, Neu1 translocation to the plasma membrane is impaired due to reduced tyrosine-phosphorylation of Neu1 and diminished Neu1-cathepsin A association. Reduced membrane-bound Neu1 results in hypersialylated TLR4 (enhanced alpha-2,3-linked sialic acids), reduced Neu1-TLR4 association, impaired MyD88 recruitment, and suppressed downstream MAP kinase/NFκB signaling. NEU1 overexpression rescued TLR4 desialylation, MyD88 association, and cytokine production, reducing parasite burden.","method":"Immunoprecipitation, phosphorylation analysis, NEU1 overexpression, NEU1 silencing, flow cytometry, confocal microscopy, ELISA cytokine assay","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — NEU1 overexpression and knockdown with multiple readouts; phosphorylation requirement for translocation is novel finding; single lab","pmids":["33763070"],"is_preprint":false},{"year":2005,"finding":"Lysosomal sialidase (Neu1) activity is induced ~6-fold in the first 24 h of C2C12 myoblast differentiation, driven by MyoD transcriptional activation through a mechanism dependent on MyoD's chromatin remodeling domain. Inappropriate Neu1 overexpression 48 h after differentiation onset downregulates myogenin and myosin heavy chain expression and halts the myogenic differentiation cascade.","method":"C2C12 myoblast differentiation, sialidase activity assay, MyoD overexpression/reporter assay, Neu1 overexpression, Western blot (myogenin/MHC)","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic overexpression with specific myogenic marker readouts; transcriptional regulation by MyoD established via reporter; single lab","pmids":["16216242"],"is_preprint":false},{"year":2022,"finding":"Activated microglia release Neu1 into culture medium by lysosomal exocytosis (blocked by lysosomal exocytosis inhibitors). Released/extracellular Neu1 and Neu1 overexpression increase microglial phagocytosis, while Neu1 knockdown decreases phagocytosis. Microglial activation desialylates phagocytic receptors Trem2 and MerTK via Neu1, increasing Trem2 ligand (galectin-3) binding. Conditioned medium from activated microglia containing Neu1 desialylates neurons and sensitizes them to glutamate-induced death.","method":"Neu1 knockdown, exocytosis inhibitor treatment, Neu1 overexpression, phagocytosis assay, co-immunoprecipitation of Trem2/MerTK, galectin-3 binding assay, neuronal desialylation and toxicity assay","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional readouts with genetic and pharmacological validation; demonstrates secreted active NEU1 can act on distinct cell types; single lab","pmids":["35693885"],"is_preprint":false},{"year":2017,"finding":"NEU1 interacts with perilipin 1 (Plin1) on lipid droplets under basal conditions in 3T3-L1 adipocytes, as shown by co-immunoprecipitation and co-localization. Neu1 knockdown increases glycerol release (lipolysis), Plin1 phosphorylation, and Plin1-HSL interaction upon β-adrenergic stimulation, indicating that NEU1 inhibits lipolysis by interacting with Plin1 on lipid droplets.","method":"siRNA knockdown, co-immunoprecipitation, immunofluorescent co-localization, glycerol concentration measurement, Plin1 phosphorylation analysis, Plin1-HSL interaction assay","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and co-localization identify direct interaction, functional lipolysis assay with genetic validation; single lab","pmids":["28429532"],"is_preprint":false},{"year":2022,"finding":"Cardiomyocyte-specific NEU1 deficiency in mice post-myocardial infarction reduces cardiac dysfunction, hypertrophy, fibrosis, mitochondrial dysfunction, and oxidative stress. The mechanism involves NEU1 deficiency increasing SIRT1 and PGC-1α expression; SIRT1 activity inhibition or PGC-1α knockout abolished the beneficial effects of NEU1 deficiency, placing NEU1 upstream of the SIRT1/PGC-1α axis in post-MI cardiac metabolism.","method":"Cardiomyocyte-specific NEU1 KO mice (MI model), SIRT1 activity inhibitor, PGC-1α KO mice, echocardiography, Western blot, mitochondrial metabolic assays, oxidative stress assays","journal":"Frontiers in cardiovascular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis established with KO + inhibitor + double KO approach; functional pathway placement via multiple rescue experiments; single lab","pmids":["35548408"],"is_preprint":false},{"year":2023,"finding":"NEU1 regulates coronavirus replication by controlling sialylation on the coronavirus nucleocapsid protein. Coronavirus nucleocapsid proteins from COVID-19 patients and HCoV-OC43-infected cells are heavily sialylated, and this sialylation controls RNA-binding activity and viral replication. NEU1 overexpression increased HCoV-OC43 replication, while NEU1 knockdown reduced it. A NEU1 inhibitor (Neu5Ac2en-OAcOMe) dramatically reduced HCoV-OC43 and SARS-CoV-2 replication in vitro and rescued mice from HCoV-OC43 infection-induced death.","method":"NEU1 overexpression and knockdown, NEU1 inhibitor treatment, nucleocapsid protein sialylation analysis, RNA-binding assay, in vivo mouse infection model, in vitro SARS-CoV-2 replication assay","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic gain/loss of function, biochemical sialylation analysis, in vivo rescue; identifies viral nucleocapsid as NEU1 substrate; single lab","pmids":["36714013"],"is_preprint":false},{"year":2021,"finding":"NEU1 associates with and desialylates CD31 only when CD31 ectodomains are homophilically engaged in postconfluent endothelial cells. Prior NEU1 silencing completely protected against CD31 desialylation in postconfluent cells. NEU1 sialidase activity is required for inhibiting tube formation, while catalytically dead NEU1-G68V had no effect.","method":"siRNA knockdown, adenoviral overexpression of WT and catalytic dead mutant G68V, lectin blotting (SNA/PNA), tube formation assay, wound migration assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — catalytic mutant controls, genetic knockdown, lectin blotting substrate identification; single lab extending prior work","pmids":["24550400"],"is_preprint":false},{"year":2009,"finding":"A regulatory mutation (-519G→A) in the Neu1 promoter generates a consensus binding site for Nkx3 family repressors. Recombinant Nkx3.2 binds strongly to and preferentially represses the mutant promoter. This tissue-specific epigenetic mechanism causes reduced Neu1 expression in SM/J mice, contributing to impaired immune response and altered leukocyte adhesion/rolling.","method":"Reporter assays, recombinant Nkx3.2 binding and repression assays, intravital hepatic microcirculation imaging, SM/J mouse model","journal":"Molecular genetics and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct transcription factor binding and repression demonstrated in reporter assay; in vivo validation via SM/J model; single lab","pmids":["19217813"],"is_preprint":false},{"year":2022,"finding":"NEU1 haploinsufficiency drives a model of pleomorphic rhabdomyosarcoma through increased lysosomal exocytosis downstream of reduced NEU1. This is evidenced by redistribution of LAMP1 to the plasma membrane of tumor and stromal cells, establishing NEU1's negative regulation of lysosomal exocytosis as a tumor-suppressor mechanism in muscle.","method":"NEU1 haploinsufficient mouse model (Ptch1+/-/ETV7TG+/-), LAMP1 immunolocalization, single-cell analysis of exocytic cells","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse model with defined mechanistic readout (LAMP1 redistribution); demonstrates NEU1 as negative regulator of lysosomal exocytosis in vivo","pmids":["36127469"],"is_preprint":false},{"year":2023,"finding":"NEU1 desialylates ATG5, an autophagy protein, under hypoxic conditions. Desialylation of ATG5 by NEU1 enhances ATG5 protein stability (via altered charge effects), promotes formation of the ATG5-ATG12-ATG16L complex, and increases autophagosome formation. NEU1 was identified as a direct interacting protein of ATG5 by co-immunoprecipitation. NEU1 knockdown or inhibition reversed hypoxia-induced autophagy and inflammatory responses in macrophages.","method":"Co-immunoprecipitation (NEU1-ATG5 interaction), NEU1 knockdown/inhibition, ATG5 sialylation analysis, autophagosome formation assay, ATG5-ATG12-ATG16L complex analysis","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP identifies interaction, functional autophagy assays, genetic/pharmacological validation; single lab, novel substrate identification","pmids":["37844713"],"is_preprint":false},{"year":2021,"finding":"NEU1 interacts with and desialylates β2 integrin in human monocytes and desialylates ICAM-1 in endothelial cells, downstream of EDP binding to the elastin receptor complex. These desialylation events are associated with increased monocyte adhesion to and transendothelial migration across endothelial cells.","method":"Proteomic validation, co-immunoprecipitation, sialidase activity assay, monocyte adhesion assay, transendothelial migration assay","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP validates proteomic hits, functional adhesion/migration assays; single lab extending NEU1 substrate repertoire","pmids":["34903296"],"is_preprint":false},{"year":2018,"finding":"NEU1 exists on the surface of mouse thymocytes and CD5 is a natural substrate for this cell-surface NEU1. The activity was identified by PNA-blot analysis of anti-CD5 immunoprecipitate and inhibited by the NEU1-selective inhibitor C9-butyl-amide-DANA.","method":"PNA-blot of anti-CD5 immunoprecipitate, NEU1-selective inhibitor (C9-BA-DANA), SM/J (Neu1-deficient) mouse comparison, real-time PCR","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — substrate identified by immunoprecipitation + lectin blot, pharmacological inhibition and genetic NEU1-deficient control; single lab","pmids":["29897583"],"is_preprint":false},{"year":2017,"finding":"GPCR agonists (bombesin, bradykinin, angiotensin I and II) activate Neu1 sialidase and insulin receptor (IR) signaling independently of insulin, via a biased GPCR signaling platform involving neuromedin B receptor (NMBR)-MMP9-Neu1 cross-talk. The angiotensin II receptor (type I) forms a multimeric complex with Neu1, IRβ, and NMBR in both naïve and stimulated HTC-IR cells.","method":"Co-immunoprecipitation, live-cell sialidase assay, IR phosphorylation analysis, NMBR inhibitor (BIM-23127), oseltamivir phosphate (NEU1 inhibitor)","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP identifies multiprotein complex, pharmacological blocking of specific components, phosphorylation readout; single lab","pmids":["29277445"],"is_preprint":false},{"year":2016,"finding":"NEU1 overexpression in pulmonary fibroblasts provokes increased collagen types I and III, accelerated MMP-14 degradation, and global gene expression changes. In lung microvascular endothelial cells, NEU1 overexpression increases T cell adhesion and disrupts capillary-like tube formation. NEU1 adenoviral delivery to mice induces lymphocyte (predominantly CD8+ T cell) accumulation in bronchoalveolar lavage and lung, plus pulmonary TGF-β and collagen elevation, recapitulating key features of lung fibrosis.","method":"Adenoviral NEU1 gene delivery (in vitro and in vivo), collagen assay, MMP-14 analysis, wounding assay, T cell adhesion assay, tube formation assay, BAL cell counting","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gene delivery with functional readouts in multiple cell types; single lab, multiple orthogonal endpoints","pmids":["26993524"],"is_preprint":false},{"year":2025,"finding":"Epididymal epithelial cells secrete and transfer NEU1 onto the sperm surface, where it regulates α-2,6 sialylation to influence sperm maturation, energy metabolism, and capacitation. Inhibition of NEU1 activity markedly reduced sperm motility and fertilization capacity. NEU1 expression was lower in asthenozoospermic individuals and correlated with sperm kinematic parameters.","method":"Immunofluorescence, Western blot, flow cytometry, NEU1 activity inhibition, IVF assay, murine transfer model, sialylation analysis","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional inhibition with clear readout, in vitro and in vivo (murine) transfer model, human clinical correlation; single lab","pmids":["41329355"],"is_preprint":false},{"year":2024,"finding":"In the periosteum, fibroblast-derived NEU1 desialylates α2,3-linked sialic acid residues on osteoclasts, disrupting cell-cell recognition and maintaining osteoclasts in a mononuclear state, thereby maintaining low cortical bone metabolic activity. Targeted NEU1 inhibition in mouse models accelerated fracture healing by up to 30%. Identified by single-cell RNA sequencing of human periosteum combined with in vitro and in vivo NEU1 inhibition experiments.","method":"Single-cell RNA sequencing, NEU1 inhibition (in vitro and in vivo), osteoclast mononuclear state analysis, fracture healing mouse model, bone quality/mechanical strength assessment","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition with in vivo rescue, scRNA-seq identifies cell-type source; substrate (osteoclast glycoproteins) identified functionally; single lab","pmids":["41356197"],"is_preprint":false}],"current_model":"NEU1 is a lysosomal and plasma membrane sialidase that is transported to lysosomes via its chaperone/activator PPCA (cathepsin A)—which prevents premature NEU1 self-oligomerization—where it catabolizes sialylated glycoconjugates; at the plasma membrane, NEU1 operates within multiprotein complexes (e.g., with TLR2/3/4, MMP-9, GPCR, or the elastin receptor complex) to desialylate specific substrates including TLR4, integrin β4, CD31, EGFR, MUC1, CD44, CD5, CD36, β2 integrin, ATG5, coronavirus nucleocapsid, and others, thereby regulating receptor dimerization and downstream signaling pathways (NFκB, ERK1/2, FAK, PI3K-Akt, TrkA, SIRT1/PGC-1α) in immunity, inflammation, cancer metastasis, angiogenesis, neurodegeneration, and lysosomal exocytosis."},"narrative":{"mechanistic_narrative":"NEU1 is a sialidase that catabolizes sialylated glycoconjugates in lysosomes and, when relocalized to the plasma membrane, desialylates a defined set of cell-surface glycoproteins to control receptor signaling across immunity, inflammation, vascular biology, and tissue remodeling [PMID:19796680, PMID:19430901, PMID:16835219, PMID:22403397]. Its structure reveals self-association interfaces and a catalytic loop that adopts an inactive conformation, and stable heterodimerization with the chaperone PPCA/cathepsin A both reverses NEU1 self-oligomerization and provides the conformational activation needed for catalysis and lysosomal targeting [PMID:37205763, PMID:19666471]. At the cell surface, NEU1 acts within multiprotein platforms: it forms a complex with TLR2/3/4 and removes alpha-2,3-sialyl residues from TLR4, relieving steric hindrance to receptor dimerization and MyD88 recruitment and de-repressing TLR4 from inhibitory Siglec interaction to drive NFκB activation [PMID:19796680, PMID:19430901, PMID:25187624]. This sialidase activity is gated by a GPCR–MMP-9 cascade, in which ligand engagement of neuromedin B receptor or TrkA triggers Gαi and MMP-9 activation that in turn activates NEU1 [PMID:21873432, PMID:20347965, PMID:23827939, PMID:22759791]. NEU1 desialylates a broad substrate repertoire—integrin β4, CD31, EGFR, MUC1, CD44, CD5, CD36, β2 integrin, and the viral coronavirus nucleocapsid—to modulate FAK/ERK, PI3K, and downstream signaling that governs cancer cell migration and metastasis, angiogenesis, monocyte adhesion, and viral replication [PMID:19151752, PMID:22247545, PMID:24550400, PMID:25963144, PMID:36714013, PMID:34903296, PMID:29897583]. NEU1 substrate engagement is spatially controlled, requiring homophilic CD31 engagement and a Src-kinase/p120-catenin adaptor bridge to couple NEU1 to its target [PMID:28343945, PMID:24550400]. Beyond catalysis, NEU1 acts as a non-enzymatic scaffold, binding the MUC1 cytoplasmic domain to block PI3K–Akt signaling independently of its sialidase activity [PMID:34688655]. NEU1 also negatively regulates lysosomal exocytosis, and its loss drives pathological exocytosis underlying amyloidogenic APP processing in Alzheimer-model brain and a tumor-suppressor phenotype in rhabdomyosarcoma [PMID:24225533, PMID:36127469]. Loss-of-function NEU1 mutations cause type II sialidosis [PMID:14695530].","teleology":[{"year":1998,"claim":"Establishing that a single residue controls NEU1 catalytic competence without disrupting trafficking or chaperone binding linked enzyme structure to enzymatic deficiency.","evidence":"Site-directed mutagenesis, enzyme activity assays, lysosomal fractionation and PPCA binding in SM/J mice","pmids":["9425240"],"confidence":"High","gaps":["Does not resolve the atomic basis of altered substrate affinity","Tested a single naturally occurring variant"]},{"year":2004,"claim":"Mapping disease mutations to distinct mechanistic defects established NEU1 loss-of-function as causative for type II sialidosis.","evidence":"Adenoviral expression of patient mutant alleles, sialidase activity and localization assays","pmids":["14695530"],"confidence":"High","gaps":["Folding-vs-substrate-binding assignment is inferential without structural data","Genotype–phenotype severity correlations not addressed"]},{"year":2005,"claim":"Linking NEU1 induction to MyoD-driven myogenic differentiation showed that regulated sialidase activity is required for proper differentiation timing.","evidence":"C2C12 differentiation with MyoD reporter and NEU1 overexpression, myogenic marker Westerns","pmids":["16216242"],"confidence":"Medium","gaps":["Relevant NEU1 substrates in myoblasts not identified","Single cell line"]},{"year":2006,"claim":"Demonstrating NEU1 relocalization from lysosome to plasma membrane during macrophage differentiation revealed a surface pool with immune function.","evidence":"Immunofluorescence, fractionation, siRNA and antibody blocking with phagocytosis/cytokine readouts","pmids":["16835219"],"confidence":"High","gaps":["Trafficking machinery for surface delivery not fully defined","Surface substrates not yet identified in this study"]},{"year":2009,"claim":"Defining NEU1–PPCA heterodimerization clarified how premature self-oligomerization is prevented and NEU1 is activated and trafficked.","evidence":"Analytical ultracentrifugation, binding-site mapping, biochemical reconstitution","pmids":["19666471"],"confidence":"High","gaps":["High-resolution structure of the heterodimer not resolved here","Dynamics of oligomer disassembly in vivo not measured"]},{"year":2009,"claim":"Identifying the NEU1–TLR4 complex and TLR4 desialylation as a requirement for TLR4 dimerization and NFκB activation established NEU1 as a positive regulator of innate immune signaling.","evidence":"Reciprocal co-IP, live-cell sialidase assay, Neu1-deficient macrophages, catalytic mutant, pharmacological inhibition","pmids":["19796680","19430901"],"confidence":"High","gaps":["Precise sialoglycan sites on TLR4 not mapped","Mechanism of NEU1 surface activation not addressed in this study"]},{"year":2009,"claim":"Showing NEU1 desialylates integrin β4 to suppress FAK/ERK signaling and metastasis positioned NEU1 as a regulator of cancer cell invasion.","evidence":"NEU1 overexpression/knockdown, lectin blotting of integrin β4, in vivo transsplenic metastasis model","pmids":["19151752"],"confidence":"High","gaps":["Whether surface NEU1 acts within a defined complex on integrin β4 unknown","Single tumor model"]},{"year":2009,"claim":"Identifying an Nkx3-binding promoter mutation explained reduced Neu1 expression and immune phenotypes in SM/J mice.","evidence":"Reporter assays, recombinant Nkx3.2 binding/repression, intravital microcirculation imaging","pmids":["19217813"],"confidence":"Medium","gaps":["Relevance to human NEU1 regulation not established","In vivo TF occupancy not directly shown"]},{"year":2007,"claim":"Demonstrating that the NEU1 subunit of the elastin receptor complex drives ERK1/2 and pro-MMP-1 responses established NEU1 catalysis as the effector of elastin-peptide signaling.","evidence":"Catalytic-dead mutant, siRNA, ERK1/2 and pro-MMP-1 assays in fibroblasts","pmids":["17327233"],"confidence":"High","gaps":["Direct desialylation substrate within the ERC pathway not identified here","Single cell type"]},{"year":2010,"claim":"Extending the GPCR–MMP-9–NEU1 module to TrkA/NGF signaling generalized the surface activation cascade beyond TLR4.","evidence":"Co-IP, live-cell sialidase assay, Tamiflu inhibition, neurite outgrowth in TrkA-PC12 cells","pmids":["20347965"],"confidence":"Medium","gaps":["Direct TrkA desialylation not biochemically demonstrated","Single lab"]},{"year":2010,"claim":"Linking NEU1 to CD44 desialylation in CD4+ T cells connected NEU1 to HA-receptor function and Th2 airway inflammation.","evidence":"HA-binding flow cytometry, sialidase inhibition, Neu1-deficient SM/J mice, airway hyperresponsiveness","pmids":["20491786"],"confidence":"Medium","gaps":["CD44 substrate inferred rather than shown by immunoprecipitation","Indirect effects of global Neu1 deficiency not excluded"]},{"year":2011,"claim":"Placing MMP-9 between Gαi-GPCR signaling and NEU1 activation defined the molecular order of TLR4-coupled sialidase induction.","evidence":"Co-IP, MMP-9 KO macrophages, shRNA/siRNA, live-cell sialidase assay, pharmacological inhibition","pmids":["21873432"],"confidence":"High","gaps":["Direct mechanism by which MMP-9 activates NEU1 not resolved","Stoichiometry of the TLR4–MMP9–NEU1 complex unknown"]},{"year":2012,"claim":"Identifying EGFR and MUC1 as NEU1-associated substrates in airway epithelium showed NEU1 restrains EGFR autophosphorylation and modulates host–pathogen interactions.","evidence":"Co-IP, NEU1 overexpression/siRNA, lectin blotting, EGFR phosphorylation and bacterial adhesion assays","pmids":["22247545"],"confidence":"High","gaps":["Direct desialylation sites on EGFR not mapped","In vivo relevance not tested in this study"]},{"year":2012,"claim":"Quantifying NEU1 as the dominant endothelial sialidase that restrains migration tied NEU1 expression level to vascular cell behavior.","evidence":"RT-PCR, Western, confocal localization, siRNA, wound-healing and activity assays","pmids":["22403397"],"confidence":"High","gaps":["Endothelial substrates not identified in this study","Mechanism of perinuclear vs surface pools unclear"]},{"year":2012,"claim":"Generalizing NMBR-MMP9-NEU1 to multiple GPCR agonists established a broad transactivation platform for TLR signaling.","evidence":"Live-cell sialidase assay, siRNA, co-IP, NFκB reporter, Neu1-deficient macrophages","pmids":["22759791"],"confidence":"Medium","gaps":["Direct receptor desialylation events not all demonstrated","Single lab"]},{"year":2013,"claim":"Connecting NEU1 deficiency to oversialylated APP, lysosomal exocytosis, and Aβ release, with rescue by NEU1 injection, implicated NEU1 in amyloid pathology.","evidence":"NEU1-deficient mice, APP/Aβ analysis, lysosomal fractionation, cerebral NEU1 rescue","pmids":["24225533"],"confidence":"High","gaps":["Direct desialylation of APP by NEU1 not shown biochemically","Human relevance not established"]},{"year":2013,"claim":"Extending the NMBR-MMP9-Neu1 platform to endosomal TLR7/9 broadened NEU1's role to nucleic-acid sensing.","evidence":"siRNA of complex components, co-IP, NFκB reporter, cytokine readouts","pmids":["23827939"],"confidence":"Medium","gaps":["Endosomal substrate of NEU1 not identified","Single lab"]},{"year":2013,"claim":"Demonstrating cathepsin A–NEU1–dependent PI3Kγ signaling in monocytes linked the elastin receptor complex to atherosclerotic plaque progression.","evidence":"Atherosclerosis mouse models, hematopoietic-specific complex deletion, neuraminidase inhibition, migration/ROS assays","pmids":["24357053"],"confidence":"Medium","gaps":["Direct NEU1 substrate upstream of PI3Kγ not defined here","Catalysis-vs-scaffold contribution not separated"]},{"year":2014,"claim":"Identifying CD31 as a NEU1 substrate whose desialylation inhibits angiogenesis established a catalysis-dependent anti-angiogenic role.","evidence":"Catalytic-dead G68V mutant, NEU1/CD31 knockdown, CD31-null cells, lectin blotting, tube formation assay","pmids":["24550400"],"confidence":"High","gaps":["Spatial trigger for CD31 desialylation not yet defined in this study","In vivo angiogenesis not tested"]},{"year":2014,"claim":"Showing NEU1 disrupts inhibitory TLR4:Siglec-E interactions defined a positive-feedback de-repression mechanism for TLR activation in vivo.","evidence":"Surface translocation assay, sialidase inhibitor, conditional hematopoietic Neu1 KO, endotoxemia model","pmids":["25187624"],"confidence":"High","gaps":["Quantitative kinetics of Siglec disengagement not measured","Other Siglec partners not surveyed"]},{"year":2015,"claim":"Defining NEU1-driven MUC1 ectodomain desialylation and shedding revealed a decoy-receptor mechanism in bacterial defense.","evidence":"Scatchard binding, NEU1/MUC1 co-IP, lectin blotting, adhesion/invasion assays, ex vivo BAL fluid","pmids":["25963144"],"confidence":"High","gaps":["In vivo contribution to infection outcome not tested here","Role of PPCA co-association mechanistically unresolved"]},{"year":2016,"claim":"Showing NEU1 overexpression recapitulates lung fibrosis features positioned NEU1 as a driver of fibrotic tissue remodeling.","evidence":"Adenoviral NEU1 delivery in vitro/in vivo, collagen/MMP-14 assays, T-cell adhesion, BAL analysis","pmids":["26993524"],"confidence":"Medium","gaps":["Causal substrates underlying fibrosis not identified","Overexpression may not reflect physiologic levels"]},{"year":2017,"claim":"Identifying the SFK/p120-catenin adaptor bridge explained how NEU1 is spatially coupled to CD31 only under confluence.","evidence":"Co-IP, siRNA of SFKs/CD31/p120ctn, SFK inhibitors, cell-free reconstitution with purified proteins","pmids":["28343945"],"confidence":"High","gaps":["Whether similar adaptors gate other NEU1 substrates unknown","Stoichiometry of the assembled scaffold not determined"]},{"year":2017,"claim":"Demonstrating NEU1 interaction with Plin1 on lipid droplets identified a non-immune role restraining lipolysis.","evidence":"siRNA, co-IP, co-localization, glycerol release and Plin1 phosphorylation assays in adipocytes","pmids":["28429532"],"confidence":"Medium","gaps":["Whether the effect is catalytic or scaffold not resolved","Single cell model"]},{"year":2017,"claim":"Showing GPCR agonists activate NEU1 and insulin-receptor signaling via NMBR-MMP9-Neu1 extended the platform to metabolic receptor crosstalk.","evidence":"Co-IP of AT1R–Neu1–IRβ–NMBR complex, live-cell sialidase assay, IR phosphorylation, pharmacological inhibition","pmids":["29277445"],"confidence":"Medium","gaps":["Direct IR desialylation not demonstrated","Single lab"]},{"year":2018,"claim":"Identifying CD36 as a NEU1 substrate downstream of the ERC linked NEU1 to macrophage oxLDL uptake and foam-cell biology.","evidence":"LC-MS/MS, co-IP, sialidase assay, oxLDL uptake assay with pharmacological controls","pmids":["30498996"],"confidence":"Medium","gaps":["CD36 desialylation sites not mapped","Single lab"]},{"year":2018,"claim":"Establishing CD5 as a cell-surface NEU1 substrate on thymocytes added a lymphocyte target to the NEU1 repertoire.","evidence":"PNA-blot of anti-CD5 IP, NEU1-selective inhibitor, SM/J-deficient comparison","pmids":["29897583"],"confidence":"Medium","gaps":["Functional consequence of CD5 desialylation not defined","Single lab"]},{"year":2021,"claim":"Discovering a catalysis-independent scaffold function at the MUC1 cytoplasmic domain showed NEU1 can inhibit PI3K–Akt signaling without sialidase activity.","evidence":"Reciprocal co-IP, GST pull-down deletion mapping, cell-free binding with purified proteins, G68V catalytic-dead mutant","pmids":["34688655"],"confidence":"High","gaps":["Structural basis of the NEU1–MUC1-CD interaction unknown","Generality of scaffold mode across substrates unclear"]},{"year":2021,"claim":"Showing CD31 desialylation requires homophilic CD31 engagement refined the spatial logic of NEU1 substrate selection.","evidence":"siRNA, WT and catalytic-dead G68V overexpression, lectin blotting, tube formation/migration assays","pmids":["24550400"],"confidence":"Medium","gaps":["Conformational sensing mechanism not defined","Single lab extension"]},{"year":2021,"claim":"Identifying β2 integrin and ICAM-1 as ERC-downstream NEU1 substrates linked NEU1 to monocyte adhesion and transendothelial migration.","evidence":"Proteomics, co-IP, sialidase assay, adhesion and transmigration assays","pmids":["34903296"],"confidence":"Medium","gaps":["In vivo relevance not established","Single lab"]},{"year":2021,"claim":"Showing pathogen-induced suppression of Neu1 phosphorylation/translocation defined a host-evasion mechanism via TLR4 hypersialylation.","evidence":"IP, phosphorylation analysis, NEU1 overexpression/silencing, confocal, cytokine ELISA in Leishmania-infected macrophages","pmids":["33763070"],"confidence":"Medium","gaps":["Kinase responsible for Neu1 phosphorylation not identified","Single lab"]},{"year":2022,"claim":"Demonstrating that secreted active Neu1 from microglia desialylates Trem2/MerTK and neurons connected NEU1 to phagocytosis and neuronal vulnerability.","evidence":"Neu1 knockdown/overexpression, exocytosis inhibitors, phagocytosis and co-IP, galectin-3 binding, neuronal toxicity assays","pmids":["35693885"],"confidence":"Medium","gaps":["In vivo relevance to neurodegeneration not established","Single lab"]},{"year":2022,"claim":"Placing NEU1 upstream of the SIRT1/PGC-1α axis defined a role in post-MI cardiac metabolism and oxidative stress.","evidence":"Cardiomyocyte-specific NEU1 KO, SIRT1 inhibitor, PGC-1α KO epistasis, echocardiography and metabolic assays","pmids":["35548408"],"confidence":"Medium","gaps":["Molecular link between NEU1 and SIRT1/PGC-1α not defined","Single lab"]},{"year":2022,"claim":"Showing NEU1 haploinsufficiency increases lysosomal exocytosis and drives rhabdomyosarcoma established a tumor-suppressor function via exocytosis control.","evidence":"NEU1 haploinsufficient mouse model, LAMP1 redistribution, single-cell exocytosis analysis","pmids":["36127469"],"confidence":"Medium","gaps":["Substrate driving exocytosis suppression not identified","Single model"]},{"year":2023,"claim":"The first 3D structure of NEU1 revealed self-association interfaces and an inactive catalytic loop, providing a structural model for PPCA-dependent activation.","evidence":"Crystal/cryo-EM structure determination and biochemical characterization of murine NEU1","pmids":["37205763"],"confidence":"High","gaps":["Structure of the activated PPCA-bound state not resolved","Human NEU1 structure inferred from murine"]},{"year":2023,"claim":"Identifying ATG5 as a hypoxia-dependent NEU1 substrate connected NEU1 to autophagosome formation and inflammatory responses.","evidence":"Co-IP, NEU1 knockdown/inhibition, ATG5 sialylation and complex-formation analysis, autophagosome assay","pmids":["37844713"],"confidence":"Medium","gaps":["Whether ATG5 sialylation occurs at the lysosome or elsewhere unclear","Single lab"]},{"year":2023,"claim":"Showing NEU1 controls sialylation of the coronavirus nucleocapsid to regulate replication identified a viral substrate and antiviral target.","evidence":"NEU1 overexpression/knockdown, NEU1 inhibitor, nucleocapsid sialylation and RNA-binding assays, in vivo HCoV-OC43 rescue","pmids":["36714013"],"confidence":"Medium","gaps":["Mechanism of nucleocapsid sialylation/desialylation balance unclear","Single lab"]},{"year":2024,"claim":"Demonstrating fibroblast-derived NEU1 keeps osteoclasts mononuclear linked NEU1 to cortical bone metabolism and fracture healing.","evidence":"scRNA-seq of human periosteum, NEU1 inhibition in vitro/in vivo, osteoclast fusion analysis, fracture healing model","pmids":["41356197"],"confidence":"Medium","gaps":["Specific osteoclast glycoprotein substrate not identified","Single lab"]},{"year":2025,"claim":"Showing epididymal cells transfer NEU1 to sperm to regulate α-2,6 sialylation tied NEU1 to sperm maturation and fertility.","evidence":"Immunofluorescence, Western, NEU1 inhibition, IVF, murine transfer model, clinical correlation","pmids":["41329355"],"confidence":"Medium","gaps":["Direct sperm-surface substrate not identified","Single lab"]},{"year":null,"claim":"How NEU1 substrate selectivity is encoded—distinguishing catalytic versus scaffold modes and the structural basis of activation in the PPCA-bound state—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the activated human PPCA-NEU1 complex","General rules governing which substrates require adaptor bridges vs direct association not defined","Relative physiologic contribution of lysosomal vs surface vs secreted NEU1 pools unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,1,4,7,8,11,19]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,4,11]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[20,21]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5,20]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[2,3,9,12]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,3,5,14,34]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[26]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[25,37]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,5,10,16,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,8,20,35]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[32]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[9,31]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,2]}],"complexes":["NEU1-PPCA/cathepsin A heterodimer","TLR4-MMP-9-NEU1 surface complex","elastin receptor complex (ERC)","NMBR-MMP9-NEU1 GPCR signaling platform"],"partners":["PPCA/CTSA","TLR4","MMP9","MUC1","CD31/PECAM1","EGFR","CD36","ATG5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q99519","full_name":"Sialidase-1","aliases":["Acetylneuraminyl hydrolase","G9 sialidase","Lysosomal sialidase","N-acetyl-alpha-neuraminidase 1"],"length_aa":415,"mass_kda":45.5,"function":"Catalyzes the removal of sialic acid (N-acetylneuraminic acid) moieties from glycoproteins and glycolipids. To be active, it is strictly dependent on its presence in the multienzyme complex. Appears to have a preference for alpha 2-3 and alpha 2-6 sialyl linkage","subcellular_location":"Lysosome membrane; Lysosome lumen; Cell membrane; Cytoplasmic vesicle; Lysosome","url":"https://www.uniprot.org/uniprotkb/Q99519/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NEU1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NEU1","total_profiled":1310},"omim":[{"mim_id":"613111","title":"CATHEPSIN A; CTSA","url":"https://www.omim.org/entry/613111"},{"mim_id":"611458","title":"GALACTOSIDASE, BETA-1; GLB1","url":"https://www.omim.org/entry/611458"},{"mim_id":"608527","title":"NEURAMINIDASE 4; NEU4","url":"https://www.omim.org/entry/608527"},{"mim_id":"608272","title":"NEURAMINIDASE 1; NEU1","url":"https://www.omim.org/entry/608272"},{"mim_id":"606107","title":"SOLUTE CARRIER FAMILY 44, MEMBER 4; SLC44A4","url":"https://www.omim.org/entry/606107"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Cell Junctions","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NEU1"},"hgnc":{"alias_symbol":[],"prev_symbol":["NEU"]},"alphafold":{"accession":"Q99519","domains":[{"cath_id":"2.120.10.10","chopping":"56-409","consensus_level":"medium","plddt":95.6316,"start":56,"end":409}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99519","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99519-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99519-F1-predicted_aligned_error_v6.png","plddt_mean":89.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NEU1","jax_strain_url":"https://www.jax.org/strain/search?query=NEU1"},"sequence":{"accession":"Q99519","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99519.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99519/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99519"}},"corpus_meta":[{"pmid":"19796680","id":"PMC_19796680","title":"Neu1 desialylation of sialyl alpha-2,3-linked beta-galactosyl residues of TOLL-like receptor 4 is essential for receptor activation and cellular signaling.","date":"2009","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/19796680","citation_count":160,"is_preprint":false},{"pmid":"19151752","id":"PMC_19151752","title":"Contribution of sialidase NEU1 to suppression of metastasis of human colon cancer cells through desialylation of integrin beta4.","date":"2009","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/19151752","citation_count":153,"is_preprint":false},{"pmid":"25187624","id":"PMC_25187624","title":"Broad and direct interaction between TLR and Siglec families of pattern recognition receptors and its regulation by Neu1.","date":"2014","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/25187624","citation_count":124,"is_preprint":false},{"pmid":"24225533","id":"PMC_24225533","title":"Lysosomal NEU1 deficiency affects amyloid precursor protein levels and amyloid-β secretion via deregulated lysosomal exocytosis.","date":"2013","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/24225533","citation_count":123,"is_preprint":false},{"pmid":"16835219","id":"PMC_16835219","title":"Monocyte differentiation up-regulates the expression of the lysosomal sialidase, Neu1, and triggers its targeting to the plasma membrane via major histocompatibility complex class II-positive compartments.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16835219","citation_count":121,"is_preprint":false},{"pmid":"14517945","id":"PMC_14517945","title":"Molecular pathology of NEU1 gene in sialidosis.","date":"2003","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/14517945","citation_count":113,"is_preprint":false},{"pmid":"19430901","id":"PMC_19430901","title":"Dependence of pathogen molecule-induced toll-like receptor activation and cell function on Neu1 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Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/40573316","citation_count":2,"is_preprint":false},{"pmid":"39314239","id":"PMC_39314239","title":"Stenotrophomonas maltophilia provokes NEU1-mediated release of a flagellin-binding decoy receptor that protects against lethal infection.","date":"2024","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/39314239","citation_count":2,"is_preprint":false},{"pmid":"34421504","id":"PMC_34421504","title":"Clinical Exome Sequencing Enables Congenital Sialidosis Type II Diagnosis in Two Siblings Presenting with Unreported Clinical Features from a Rare Homozygous Sequence Variant p.(Tyr370Cys) in NEU1.","date":"2021","source":"Molecular syndromology","url":"https://pubmed.ncbi.nlm.nih.gov/34421504","citation_count":2,"is_preprint":false},{"pmid":"38505872","id":"PMC_38505872","title":"HDAC1-Mediated Downregulation of NEU1 Exacerbates the Aggressiveness of Cervical Cancer.","date":"2024","source":"Critical reviews in eukaryotic gene expression","url":"https://pubmed.ncbi.nlm.nih.gov/38505872","citation_count":1,"is_preprint":false},{"pmid":"41329355","id":"PMC_41329355","title":"Epididymal epithelial cells facilitate NEU1 loading to modulate sperm α-2,6 sialylation, enhance maturation and motility.","date":"2025","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/41329355","citation_count":1,"is_preprint":false},{"pmid":"41356197","id":"PMC_41356197","title":"Fibroblast-derived NEU1 as a therapeutic target for improving cortical bone integrity and fracture healing.","date":"2026","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/41356197","citation_count":1,"is_preprint":false},{"pmid":"39566266","id":"PMC_39566266","title":"H1N1 swine influenza viruses upregulate NEU1 expression through histone H3 acetylation regulated by HDAC2.","date":"2024","source":"Virology","url":"https://pubmed.ncbi.nlm.nih.gov/39566266","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54859,"output_tokens":11557,"usd":0.168966,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":22660,"output_tokens":9825,"usd":0.179462,"stage2_stop_reason":"end_turn"},"total_usd":0.348428,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"Crystal/cryo-EM structure of murine NEU1 was determined, revealing that the enzyme oligomerizes through two self-association interfaces, displays a wide substrate-binding cavity, and contains a catalytic loop that adopts an inactive conformation. A mechanism of activation was proposed involving a conformational change in this loop upon binding to its protective protein PPCA/cathepsin A.\",\n      \"method\": \"Structure determination (3D structural analysis), biochemical characterization\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — first experimentally determined 3D structure of NEU1, with structural data supporting mechanistic model of activation; single study but rigorous structural method\",\n      \"pmids\": [\"37205763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NEU1 (and not NEU2, NEU3, or NEU4) forms a complex with TLR-2, -3, and -4 on the cell surface of naïve macrophages. Ligand binding to TLR4 (LPS) induces NEU1 sialidase activity, which hydrolyzes alpha-2,3-sialyl residues on TLR4, removing steric hindrance to TLR4 dimerization, MyD88/TLR4 complex formation, and subsequent NFκB activation. This was confirmed using primary Neu1-deficient macrophages (which fail to respond), catalytically inactive trans-sialidase mutant (which cannot substitute), and the neuraminidase inhibitor Tamiflu.\",\n      \"method\": \"Co-immunoprecipitation, live-cell sialidase assay, pharmacological inhibition (Tamiflu/DANA/zanamivir), lectin blocking, primary Neu1-deficient macrophages, HEK293 reconstitution with TLR4/MD2\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, primary KO macrophages, pharmacological inhibition, catalytic mutant controls, replicated across multiple cell types and labs\",\n      \"pmids\": [\"19796680\", \"19430901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NEU1 forms a stable heterodimer with protective protein/cathepsin A (PPCA). PPCA acts as a molecular chaperone that prevents premature self-oligomerization of NEU1 by competing for a NEU1 self-association interface. In the absence of PPCA (as in galactosialidosis), NEU1 self-associates into chain-like oligomers. PPCA binding reverses NEU1 self-oligomerization by disassembling NEU1 oligomers into a PPCA-NEU1 heterodimer.\",\n      \"method\": \"Hydrodynamic analysis (analytical ultracentrifugation), binding site mapping, structural modeling, biochemical reconstitution\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution-level biochemistry with multiple biophysical methods in a single rigorous study; identifies binding sites on both proteins\",\n      \"pmids\": [\"19666471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"During monocyte-to-macrophage differentiation, NEU1 relocalizes from lysosomes to the cell surface via LAMP-2-negative, MHC class II-positive vesicles that merge with the plasma membrane. Cathepsin A, which forms a complex with and activates NEU1 in lysosomes, is co-sorted to the plasma membrane. siRNA suppression of NEU1 or anti-NEU1 antibodies reduced macrophage phagocytosis of bacteria and cytokine production.\",\n      \"method\": \"Immunofluorescence, subcellular fractionation, siRNA knockdown, anti-Neu1 antibody blocking, flow cytometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with functional consequence (phagocytosis, cytokine production) using multiple orthogonal methods in one study\",\n      \"pmids\": [\"16835219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The catalytic sialidase activity of the NEU1 subunit of the elastin receptor complex (ERC) is responsible for ERK1/2 activation and pro-MMP-1 production induced by elastin peptide binding. A catalytically inactive NEU1 mutant and siRNA-mediated NEU1 knockdown both abolished elastin peptide-induced ERK1/2 activation and pro-MMP-1 production in skin fibroblasts. N-acetyl neuraminic acid (sialic acid) could reproduce the elastin peptide effects.\",\n      \"method\": \"Pharmacological inhibition, catalytically inactive NEU1 mutant, siRNA knockdown, ERK1/2 activation assay, pro-MMP-1 production assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — catalytic mutant + siRNA + pharmacological inhibition in a single study; multiple orthogonal methods establishing catalytic mechanism\",\n      \"pmids\": [\"17327233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"On the surface of naive macrophage cells, NEU1 forms a complex with MMP-9, both of which are constitutively bound to TLR4. LPS binding to TLR4 activates Gαi GPCR signaling, which activates MMP-9, which in turn activates NEU1 sialidase. NEU1-mediated TLR4 desialylation and NFκB activation are blocked by specific MMP-9 inhibition, Gαi-pathway inhibition, MMP-9 shRNA/siRNA knockdown, and are absent in MMP-9 knockout macrophages.\",\n      \"method\": \"Co-immunoprecipitation, siRNA/shRNA knockdown, MMP-9 KO macrophages, lentiviral transduction, pharmacological inhibition, live-cell sialidase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic and pharmacological approaches, KO validation, reciprocal Co-IP, replicated across different cell lines\",\n      \"pmids\": [\"21873432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Neu1 and MMP-9 form a complex bound to TrkA on the surface of naive neurons and TrkA-expressing cells. NGF binding to TrkA activates GPCR Gαi signaling → MMP-9 activation → Neu1 sialidase activation. Tamiflu (oseltamivir phosphate) blocks NGF-induced Neu1 activity and subsequent Trk receptor activation and neurite outgrowth in TrkA-PC12 cells.\",\n      \"method\": \"Co-immunoprecipitation, live-cell sialidase assay, pharmacological inhibition (Tamiflu), TrkA-PC12 cell lines, primary neurons\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, pharmacological inhibition, functional readout (neurite outgrowth); single lab, but multiple orthogonal approaches\",\n      \"pmids\": [\"20347965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NEU1 overexpression in human colon cancer HT-29 cells desialylates integrin beta4 (removing alpha-2,3 and O-glycan sialic acids), reduces integrin beta4 phosphorylation, attenuates focal adhesion kinase (FAK) and Erk1/2 signaling, and downregulates MMP-7, leading to suppressed cell migration, invasion, adhesion, and in vivo liver metastasis.\",\n      \"method\": \"NEU1 overexpression and siRNA knockdown, lectin blotting of integrin beta4 immunoprecipitates, immunofluorescence, biotinylation assay, O-glycosylation inhibitor (GalNAc-α-O-benzyl), in vivo transsplenic injection model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal biochemical approaches (OE + KD), direct substrate identification by immunoprecipitation + lectin blotting, in vivo validation\",\n      \"pmids\": [\"19151752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In human airway epithelial cells, NEU1 sialidase directly associates with EGFR and MUC1 and accounts for >70% of cellular sialidase activity. NEU1 overexpression diminishes EGF-stimulated EGFR Tyr-1068 autophosphorylation, while NEU1 depletion increases EGFR activation. NEU1 also desialylates MUC1, enhancing MUC1-dependent Pseudomonas aeruginosa adhesion and flagellin-stimulated ERK1/2 activation.\",\n      \"method\": \"Co-immunoprecipitation, NEU1 overexpression/siRNA, lectin blotting (MAL-2/PNA), EGFR phosphorylation assay, bacterial adhesion assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP identifies substrates, functional phosphorylation assays, multiple orthogonal readouts in one study\",\n      \"pmids\": [\"22247545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NEU1 deficiency in mice leads to accumulation and amyloidogenic processing of an oversialylated amyloid precursor protein (APP) in lysosomes, followed by excessive lysosomal exocytosis that releases Aβ peptides extracellularly. Cerebral injection of NEU1 into an established AD mouse model substantially reduces β-amyloid plaques.\",\n      \"method\": \"NEU1-deficient mouse model, APP processing analysis, lysosomal fractionation, Aβ ELISA, cerebral NEU1 injection rescue experiment\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse model combined with rescue experiment and biochemical analysis of lysosomal exocytosis pathway; multiple orthogonal approaches in one study\",\n      \"pmids\": [\"24225533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR4 activation triggers NEU1 translocation to the cell surface, where NEU1 disrupts the inhibitory TLR4:Siglec-E interaction by desialylating TLR4. Sialidase inhibitor Neu5Gc2en prevents TLR4 ligand-induced disruption of TLR4:Siglec-E/F interactions. Absence of NEU1 in hematopoietic cells protects mice against endotoxemia, demonstrating that NEU1-mediated de-repression of TLR4 from Siglec inhibition is a positive feedback mechanism for TLR activation during infection.\",\n      \"method\": \"Cell surface translocation assay, sialidase inhibitor treatment (Neu5Gc2en), Neu1-conditional hematopoietic KO mice, TLR4:Siglec interaction co-IP/pulldown, endotoxemia mouse model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO mouse model, pharmacological inhibition, direct TLR-Siglec interaction assays, in vivo endotoxemia validation; replicated mechanisms from prior NEU1-TLR studies\",\n      \"pmids\": [\"25187624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Catalytically active NEU1 inhibits in vitro angiogenesis (capillary-like tube formation) through desialylation of its substrate CD31 in postconfluent human pulmonary microvascular endothelial cells. A catalytically dead NEU1 mutant (G68V) did not inhibit tube formation. Prior CD31 silencing or use of CD31-null ECs abrogated NEU1's inhibitory effect, and forced CD31 sialylation (via sialyltransferase ST6GAL-I overexpression) counteracted NEU1-mediated inhibition.\",\n      \"method\": \"NEU1 overexpression with catalytic mutant control (G68V), siRNA knockdown of NEU1/CD31, CD31-null ECs, lectin blotting (SNA/PNA), Matrigel tube formation assay, wounding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — catalytic mutant controls, substrate identification by lectin blotting, genetic rescue experiments; multiple orthogonal approaches\",\n      \"pmids\": [\"24550400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"A single amino acid substitution L209I in the Neu1 protein is responsible for the partial neuraminidase deficiency in SM/J mice. The mutant enzyme is correctly localized to lysosomes and retains the ability to associate with its activating protein PPCA, but the reduced activity is caused by altered substrate affinity rather than changed substrate specificity or turnover rate.\",\n      \"method\": \"Genetic analysis, sequencing, site-directed mutagenesis, enzyme activity assays, lysosomal fractionation, PPCA binding assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct mutagenesis + enzyme activity assay + localization + PPCA interaction analysis in one study establishing structure-function relationship\",\n      \"pmids\": [\"9425240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Five novel NEU1 mutations (R225P, A298V, M1?, R341G, W23X) in type II sialidosis patients abolish enzymatic sialidase activity when expressed via recombinant adenovirus. The R341G mutation perturbs substrate binding, while A298V and R225P impair enzyme folding, as determined by activity assay and immunofluorescence localization analysis.\",\n      \"method\": \"Adenoviral expression of mutant sialidases in primary cell cultures, sialidase activity assay, intracellular localization (immunofluorescence)\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct expression of mutant alleles with enzymatic activity assays and localization, identifying distinct mutant mechanisms (substrate binding vs. folding)\",\n      \"pmids\": [\"14695530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"NEU1 is the dominant sialidase in human lung microvascular endothelial cells (expressed ~2700-fold more than NEU2/3/4), localizes to both plasma membrane and perinuclear regions, and restrains endothelial cell migration. NEU1 overexpression reduced EC migration into wounds by >40%, whereas NEU3 overexpression did not. siRNA knockdown of NEU1 decreased >65% of total sialidase activity for 4-MU-NANA substrate.\",\n      \"method\": \"Real-time RT-PCR, Western blot, confocal microscopy/flow cytometry (localization), siRNA knockdown, wound-healing migration assay, sialidase activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with functional consequence (migration), siRNA validation, quantitative activity assays; multiple orthogonal methods\",\n      \"pmids\": [\"22403397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Neu1 sialidase is required for hyaluronic acid receptor function of CD44 on CD4+ T cells. Antigen stimulation induces Neu1 expression on splenic CD4+ T cells from asthmatic mice, and increased Neu1 activity removes inhibitory sialic acid residues from CD44 to enable HA binding and T helper type 2-mediated airway inflammation. Sialidase inhibitor treatment suppressed HA binding, and Neu1-deficient SM/J mice showed reduced Th2 airway inflammation and airway hyperresponsiveness.\",\n      \"method\": \"Flow cytometry (HA-binding), real-time RT-PCR, pharmacological sialidase inhibition, Neu1-deficient SM/J mouse model, cytokine analysis, airway hyperresponsiveness measurement\",\n      \"journal\": \"Clinical and experimental immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Neu1-deficient mouse model with functional readout; pharmacological inhibition corroborates genetic data; substrate (CD44) inferred but not directly demonstrated by immunoprecipitation\",\n      \"pmids\": [\"20491786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NEU1 and MMP-9 form a tripartite complex with neuromedin B GPCR, TLR-7, and TLR-9. Ligand-induced activation of endosomal TLR-7 and TLR-9 requires this NMBR-MMP9-Neu1 cross-talk signaling platform. siRNA silencing of Neu1, MMP-9, or NMBR each significantly reduced nucleic acid-induced NFκB activation and TNFα/MCP-1 cytokine responses.\",\n      \"method\": \"siRNA knockdown, complex formation (immunoprecipitation), NFκB reporter assay, SEAP reporter, pharmacological inhibitors (Tamiflu, MMP-9 inhibitor, BIM23127, BIM-46174)\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA of three complex components with consistent phenotype; pharmacological inhibition corroborates; single lab\",\n      \"pmids\": [\"23827939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GPCR agonists (bombesin, bradykinin, LPA, cholesterol, angiotensin-1 and -2) induce Neu1 sialidase activity in macrophages via a neuromedin B receptor (NMBR)-MMP9 signaling platform, transactivating TLR receptors and inducing NFκB activation. Bombesin receptor (NMBR) forms a complex with TLR4 and MMP9. MMP9 siRNA knockdown or MMP9 absence abolishes this GPCR-induced Neu1 activity.\",\n      \"method\": \"Live-cell sialidase assay, siRNA knockdown, co-immunoprecipitation, NFκB-SEAP reporter, pharmacological inhibitors, Neu1-deficient primary macrophages as negative control\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP identifies complex, siRNA validates mechanism, Neu1-deficient macrophages as genetic control; single lab\",\n      \"pmids\": [\"22759791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Elastin-derived peptides (EDP) binding to the elastin receptor complex (ERC, which contains NEU1) activate monocyte migration and ROS production through a neuraminidase activity-dependent PI3Kγ signaling pathway. The absence of the cathepsin A-NEU1 complex in hematopoietic cells abolished atherosclerotic plaque progression in LDLR-/- mice. In vitro, PI3Kγ was required for EDP-induced monocyte migration and this was dependent upon neuraminidase activity.\",\n      \"method\": \"In vivo atherosclerosis mouse models, PI3Kγ KO bone marrow chimeras, cathepsin A-NEU1 complex-deficient hematopoietic cells, neuraminidase activity inhibition, monocyte migration assay, ROS production assay\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse models with hematopoietic-specific deletion and functional in vitro assays; pathway positioning via epistasis\",\n      \"pmids\": [\"24357053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NEU1-driven MUC1 ectodomain desialylation increases binding affinity of P. aeruginosa flagellin to MUC1, promotes bacterial adhesion and invasion, and triggers MUC1-ED shedding. The shed desialylated MUC1-ED functions as a hyperadhesive decoy receptor that competitively blocks bacterial adhesion. NEU1 association with MUC1 increases upon flagellin stimulation, and NEU1 co-associates with MUC1's chaperone PPCA in this context.\",\n      \"method\": \"Scatchard binding analysis, NEU1/MUC1 co-immunoprecipitation, lectin blotting, NEU1 overexpression/siRNA, bacterial adhesion/invasion assay, ex vivo BAL fluid analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical approaches, Scatchard analysis quantifying binding affinity, ex vivo patient sample validation; multiple functional readouts\",\n      \"pmids\": [\"25963144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NEU1 directly associates with the MUC1 cytoplasmic domain (CD) at its juxtamembranous 36 amino acid region, independently of NEU1 catalytic activity and independently of PPCA chaperone. This NEU1-MUC1-CD interaction does not require NEU1 enzymatic activity for MUC1-ED desialylation. However, both wild-type NEU1 and the catalytically dead NEU1-G68V mutant inhibit PI3K binding to MUC1-CD and reduce downstream Akt phosphorylation, indicating NEU1 inhibits PI3K-Akt signaling through its scaffold function independent of catalytic activity.\",\n      \"method\": \"Reciprocal co-immunoprecipitation, in vitro binding assays (GST pull-down with deletion mutants), cell-free binding assay with purified proteins, catalytic dead mutant (G68V), NEU1-selective inhibitor C9-BA-DANA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cell-free reconstitution with purified proteins, deletion mapping, catalytic mutant controls, multiple orthogonal binding assays in one rigorous study\",\n      \"pmids\": [\"34688655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"As human pulmonary microvascular endothelial cells (HPMECs) achieve confluence, Src family kinases (SFKs) are activated and phosphorylate p120 catenin. Tyrosine-phosphorylated p120 catenin functions as an adaptor molecule that physically couples NEU1 to CD31, enabling NEU1-mediated CD31 desialylation. SFK inhibition blocks both p120ctn phosphorylation and NEU1-CD31 association. Direct protein-protein interactions between NEU1, CD31, and p120ctn were demonstrated in a cell-free system with purified recombinant proteins.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of individual SFKs/CD31/p120ctn, SFK pharmacological inhibitors (PP2, SU6656), cell-free binding assay with purified recombinant proteins, pull-down assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — cell-free reconstitution with purified proteins + co-IP + genetic knockdown; multiple orthogonal methods establish scaffolding mechanism\",\n      \"pmids\": [\"28343945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Membrane NEU1 interacts with CD36 (class B scavenger receptor) in human macrophages. Elastin-derived peptides (EDP) binding to the elastin receptor complex desialylate CD36 via NEU1. EDP-induced desialylation of CD36 increases uptake of oxidized LDL by macrophages, an effect blocked by both V14 peptide (blocking EDP-ERC interaction) and the sialidase inhibitor DANA.\",\n      \"method\": \"Proteomic purification (LC-MS/MS), co-immunoprecipitation validation, sialidase activity assay, oxidized LDL uptake assay, pharmacological inhibition (V14 peptide, DANA)\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic identification of interaction partner confirmed by co-IP, functional readout (oxLDL uptake) with pharmacological controls; single lab\",\n      \"pmids\": [\"30498996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In L. donovani-infected macrophages, Neu1 translocation to the plasma membrane is impaired due to reduced tyrosine-phosphorylation of Neu1 and diminished Neu1-cathepsin A association. Reduced membrane-bound Neu1 results in hypersialylated TLR4 (enhanced alpha-2,3-linked sialic acids), reduced Neu1-TLR4 association, impaired MyD88 recruitment, and suppressed downstream MAP kinase/NFκB signaling. NEU1 overexpression rescued TLR4 desialylation, MyD88 association, and cytokine production, reducing parasite burden.\",\n      \"method\": \"Immunoprecipitation, phosphorylation analysis, NEU1 overexpression, NEU1 silencing, flow cytometry, confocal microscopy, ELISA cytokine assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — NEU1 overexpression and knockdown with multiple readouts; phosphorylation requirement for translocation is novel finding; single lab\",\n      \"pmids\": [\"33763070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Lysosomal sialidase (Neu1) activity is induced ~6-fold in the first 24 h of C2C12 myoblast differentiation, driven by MyoD transcriptional activation through a mechanism dependent on MyoD's chromatin remodeling domain. Inappropriate Neu1 overexpression 48 h after differentiation onset downregulates myogenin and myosin heavy chain expression and halts the myogenic differentiation cascade.\",\n      \"method\": \"C2C12 myoblast differentiation, sialidase activity assay, MyoD overexpression/reporter assay, Neu1 overexpression, Western blot (myogenin/MHC)\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic overexpression with specific myogenic marker readouts; transcriptional regulation by MyoD established via reporter; single lab\",\n      \"pmids\": [\"16216242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Activated microglia release Neu1 into culture medium by lysosomal exocytosis (blocked by lysosomal exocytosis inhibitors). Released/extracellular Neu1 and Neu1 overexpression increase microglial phagocytosis, while Neu1 knockdown decreases phagocytosis. Microglial activation desialylates phagocytic receptors Trem2 and MerTK via Neu1, increasing Trem2 ligand (galectin-3) binding. Conditioned medium from activated microglia containing Neu1 desialylates neurons and sensitizes them to glutamate-induced death.\",\n      \"method\": \"Neu1 knockdown, exocytosis inhibitor treatment, Neu1 overexpression, phagocytosis assay, co-immunoprecipitation of Trem2/MerTK, galectin-3 binding assay, neuronal desialylation and toxicity assay\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional readouts with genetic and pharmacological validation; demonstrates secreted active NEU1 can act on distinct cell types; single lab\",\n      \"pmids\": [\"35693885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NEU1 interacts with perilipin 1 (Plin1) on lipid droplets under basal conditions in 3T3-L1 adipocytes, as shown by co-immunoprecipitation and co-localization. Neu1 knockdown increases glycerol release (lipolysis), Plin1 phosphorylation, and Plin1-HSL interaction upon β-adrenergic stimulation, indicating that NEU1 inhibits lipolysis by interacting with Plin1 on lipid droplets.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, immunofluorescent co-localization, glycerol concentration measurement, Plin1 phosphorylation analysis, Plin1-HSL interaction assay\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and co-localization identify direct interaction, functional lipolysis assay with genetic validation; single lab\",\n      \"pmids\": [\"28429532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cardiomyocyte-specific NEU1 deficiency in mice post-myocardial infarction reduces cardiac dysfunction, hypertrophy, fibrosis, mitochondrial dysfunction, and oxidative stress. The mechanism involves NEU1 deficiency increasing SIRT1 and PGC-1α expression; SIRT1 activity inhibition or PGC-1α knockout abolished the beneficial effects of NEU1 deficiency, placing NEU1 upstream of the SIRT1/PGC-1α axis in post-MI cardiac metabolism.\",\n      \"method\": \"Cardiomyocyte-specific NEU1 KO mice (MI model), SIRT1 activity inhibitor, PGC-1α KO mice, echocardiography, Western blot, mitochondrial metabolic assays, oxidative stress assays\",\n      \"journal\": \"Frontiers in cardiovascular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis established with KO + inhibitor + double KO approach; functional pathway placement via multiple rescue experiments; single lab\",\n      \"pmids\": [\"35548408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NEU1 regulates coronavirus replication by controlling sialylation on the coronavirus nucleocapsid protein. Coronavirus nucleocapsid proteins from COVID-19 patients and HCoV-OC43-infected cells are heavily sialylated, and this sialylation controls RNA-binding activity and viral replication. NEU1 overexpression increased HCoV-OC43 replication, while NEU1 knockdown reduced it. A NEU1 inhibitor (Neu5Ac2en-OAcOMe) dramatically reduced HCoV-OC43 and SARS-CoV-2 replication in vitro and rescued mice from HCoV-OC43 infection-induced death.\",\n      \"method\": \"NEU1 overexpression and knockdown, NEU1 inhibitor treatment, nucleocapsid protein sialylation analysis, RNA-binding assay, in vivo mouse infection model, in vitro SARS-CoV-2 replication assay\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic gain/loss of function, biochemical sialylation analysis, in vivo rescue; identifies viral nucleocapsid as NEU1 substrate; single lab\",\n      \"pmids\": [\"36714013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NEU1 associates with and desialylates CD31 only when CD31 ectodomains are homophilically engaged in postconfluent endothelial cells. Prior NEU1 silencing completely protected against CD31 desialylation in postconfluent cells. NEU1 sialidase activity is required for inhibiting tube formation, while catalytically dead NEU1-G68V had no effect.\",\n      \"method\": \"siRNA knockdown, adenoviral overexpression of WT and catalytic dead mutant G68V, lectin blotting (SNA/PNA), tube formation assay, wound migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — catalytic mutant controls, genetic knockdown, lectin blotting substrate identification; single lab extending prior work\",\n      \"pmids\": [\"24550400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A regulatory mutation (-519G→A) in the Neu1 promoter generates a consensus binding site for Nkx3 family repressors. Recombinant Nkx3.2 binds strongly to and preferentially represses the mutant promoter. This tissue-specific epigenetic mechanism causes reduced Neu1 expression in SM/J mice, contributing to impaired immune response and altered leukocyte adhesion/rolling.\",\n      \"method\": \"Reporter assays, recombinant Nkx3.2 binding and repression assays, intravital hepatic microcirculation imaging, SM/J mouse model\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct transcription factor binding and repression demonstrated in reporter assay; in vivo validation via SM/J model; single lab\",\n      \"pmids\": [\"19217813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NEU1 haploinsufficiency drives a model of pleomorphic rhabdomyosarcoma through increased lysosomal exocytosis downstream of reduced NEU1. This is evidenced by redistribution of LAMP1 to the plasma membrane of tumor and stromal cells, establishing NEU1's negative regulation of lysosomal exocytosis as a tumor-suppressor mechanism in muscle.\",\n      \"method\": \"NEU1 haploinsufficient mouse model (Ptch1+/-/ETV7TG+/-), LAMP1 immunolocalization, single-cell analysis of exocytic cells\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse model with defined mechanistic readout (LAMP1 redistribution); demonstrates NEU1 as negative regulator of lysosomal exocytosis in vivo\",\n      \"pmids\": [\"36127469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NEU1 desialylates ATG5, an autophagy protein, under hypoxic conditions. Desialylation of ATG5 by NEU1 enhances ATG5 protein stability (via altered charge effects), promotes formation of the ATG5-ATG12-ATG16L complex, and increases autophagosome formation. NEU1 was identified as a direct interacting protein of ATG5 by co-immunoprecipitation. NEU1 knockdown or inhibition reversed hypoxia-induced autophagy and inflammatory responses in macrophages.\",\n      \"method\": \"Co-immunoprecipitation (NEU1-ATG5 interaction), NEU1 knockdown/inhibition, ATG5 sialylation analysis, autophagosome formation assay, ATG5-ATG12-ATG16L complex analysis\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP identifies interaction, functional autophagy assays, genetic/pharmacological validation; single lab, novel substrate identification\",\n      \"pmids\": [\"37844713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NEU1 interacts with and desialylates β2 integrin in human monocytes and desialylates ICAM-1 in endothelial cells, downstream of EDP binding to the elastin receptor complex. These desialylation events are associated with increased monocyte adhesion to and transendothelial migration across endothelial cells.\",\n      \"method\": \"Proteomic validation, co-immunoprecipitation, sialidase activity assay, monocyte adhesion assay, transendothelial migration assay\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP validates proteomic hits, functional adhesion/migration assays; single lab extending NEU1 substrate repertoire\",\n      \"pmids\": [\"34903296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NEU1 exists on the surface of mouse thymocytes and CD5 is a natural substrate for this cell-surface NEU1. The activity was identified by PNA-blot analysis of anti-CD5 immunoprecipitate and inhibited by the NEU1-selective inhibitor C9-butyl-amide-DANA.\",\n      \"method\": \"PNA-blot of anti-CD5 immunoprecipitate, NEU1-selective inhibitor (C9-BA-DANA), SM/J (Neu1-deficient) mouse comparison, real-time PCR\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — substrate identified by immunoprecipitation + lectin blot, pharmacological inhibition and genetic NEU1-deficient control; single lab\",\n      \"pmids\": [\"29897583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPCR agonists (bombesin, bradykinin, angiotensin I and II) activate Neu1 sialidase and insulin receptor (IR) signaling independently of insulin, via a biased GPCR signaling platform involving neuromedin B receptor (NMBR)-MMP9-Neu1 cross-talk. The angiotensin II receptor (type I) forms a multimeric complex with Neu1, IRβ, and NMBR in both naïve and stimulated HTC-IR cells.\",\n      \"method\": \"Co-immunoprecipitation, live-cell sialidase assay, IR phosphorylation analysis, NMBR inhibitor (BIM-23127), oseltamivir phosphate (NEU1 inhibitor)\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP identifies multiprotein complex, pharmacological blocking of specific components, phosphorylation readout; single lab\",\n      \"pmids\": [\"29277445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"NEU1 overexpression in pulmonary fibroblasts provokes increased collagen types I and III, accelerated MMP-14 degradation, and global gene expression changes. In lung microvascular endothelial cells, NEU1 overexpression increases T cell adhesion and disrupts capillary-like tube formation. NEU1 adenoviral delivery to mice induces lymphocyte (predominantly CD8+ T cell) accumulation in bronchoalveolar lavage and lung, plus pulmonary TGF-β and collagen elevation, recapitulating key features of lung fibrosis.\",\n      \"method\": \"Adenoviral NEU1 gene delivery (in vitro and in vivo), collagen assay, MMP-14 analysis, wounding assay, T cell adhesion assay, tube formation assay, BAL cell counting\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gene delivery with functional readouts in multiple cell types; single lab, multiple orthogonal endpoints\",\n      \"pmids\": [\"26993524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Epididymal epithelial cells secrete and transfer NEU1 onto the sperm surface, where it regulates α-2,6 sialylation to influence sperm maturation, energy metabolism, and capacitation. Inhibition of NEU1 activity markedly reduced sperm motility and fertilization capacity. NEU1 expression was lower in asthenozoospermic individuals and correlated with sperm kinematic parameters.\",\n      \"method\": \"Immunofluorescence, Western blot, flow cytometry, NEU1 activity inhibition, IVF assay, murine transfer model, sialylation analysis\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional inhibition with clear readout, in vitro and in vivo (murine) transfer model, human clinical correlation; single lab\",\n      \"pmids\": [\"41329355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In the periosteum, fibroblast-derived NEU1 desialylates α2,3-linked sialic acid residues on osteoclasts, disrupting cell-cell recognition and maintaining osteoclasts in a mononuclear state, thereby maintaining low cortical bone metabolic activity. Targeted NEU1 inhibition in mouse models accelerated fracture healing by up to 30%. Identified by single-cell RNA sequencing of human periosteum combined with in vitro and in vivo NEU1 inhibition experiments.\",\n      \"method\": \"Single-cell RNA sequencing, NEU1 inhibition (in vitro and in vivo), osteoclast mononuclear state analysis, fracture healing mouse model, bone quality/mechanical strength assessment\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition with in vivo rescue, scRNA-seq identifies cell-type source; substrate (osteoclast glycoproteins) identified functionally; single lab\",\n      \"pmids\": [\"41356197\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NEU1 is a lysosomal and plasma membrane sialidase that is transported to lysosomes via its chaperone/activator PPCA (cathepsin A)—which prevents premature NEU1 self-oligomerization—where it catabolizes sialylated glycoconjugates; at the plasma membrane, NEU1 operates within multiprotein complexes (e.g., with TLR2/3/4, MMP-9, GPCR, or the elastin receptor complex) to desialylate specific substrates including TLR4, integrin β4, CD31, EGFR, MUC1, CD44, CD5, CD36, β2 integrin, ATG5, coronavirus nucleocapsid, and others, thereby regulating receptor dimerization and downstream signaling pathways (NFκB, ERK1/2, FAK, PI3K-Akt, TrkA, SIRT1/PGC-1α) in immunity, inflammation, cancer metastasis, angiogenesis, neurodegeneration, and lysosomal exocytosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NEU1 is a sialidase that catabolizes sialylated glycoconjugates in lysosomes and, when relocalized to the plasma membrane, desialylates a defined set of cell-surface glycoproteins to control receptor signaling across immunity, inflammation, vascular biology, and tissue remodeling [#1, #3, #14]. Its structure reveals self-association interfaces and a catalytic loop that adopts an inactive conformation, and stable heterodimerization with the chaperone PPCA/cathepsin A both reverses NEU1 self-oligomerization and provides the conformational activation needed for catalysis and lysosomal targeting [#0, #2]. At the cell surface, NEU1 acts within multiprotein platforms: it forms a complex with TLR2/3/4 and removes alpha-2,3-sialyl residues from TLR4, relieving steric hindrance to receptor dimerization and MyD88 recruitment and de-repressing TLR4 from inhibitory Siglec interaction to drive NF\\u03baB activation [#1, #10]. This sialidase activity is gated by a GPCR\\u2013MMP-9 cascade, in which ligand engagement of neuromedin B receptor or TrkA triggers G\\u03b1i and MMP-9 activation that in turn activates NEU1 [#5, #6, #16, #17]. NEU1 desialylates a broad substrate repertoire\\u2014integrin \\u03b24, CD31, EGFR, MUC1, CD44, CD5, CD36, \\u03b22 integrin, and the viral coronavirus nucleocapsid\\u2014to modulate FAK/ERK, PI3K, and downstream signaling that governs cancer cell migration and metastasis, angiogenesis, monocyte adhesion, and viral replication [#7, #8, #11, #19, #28, #33, #34]. NEU1 substrate engagement is spatially controlled, requiring homophilic CD31 engagement and a Src-kinase/p120-catenin adaptor bridge to couple NEU1 to its target [#21, #29]. Beyond catalysis, NEU1 acts as a non-enzymatic scaffold, binding the MUC1 cytoplasmic domain to block PI3K\\u2013Akt signaling independently of its sialidase activity [#20]. NEU1 also negatively regulates lysosomal exocytosis, and its loss drives pathological exocytosis underlying amyloidogenic APP processing in Alzheimer-model brain and a tumor-suppressor phenotype in rhabdomyosarcoma [#9, #31]. Loss-of-function NEU1 mutations cause type II sialidosis [#13].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that a single residue controls NEU1 catalytic competence without disrupting trafficking or chaperone binding linked enzyme structure to enzymatic deficiency.\",\n      \"evidence\": \"Site-directed mutagenesis, enzyme activity assays, lysosomal fractionation and PPCA binding in SM/J mice\",\n      \"pmids\": [\"9425240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve the atomic basis of altered substrate affinity\", \"Tested a single naturally occurring variant\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapping disease mutations to distinct mechanistic defects established NEU1 loss-of-function as causative for type II sialidosis.\",\n      \"evidence\": \"Adenoviral expression of patient mutant alleles, sialidase activity and localization assays\",\n      \"pmids\": [\"14695530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Folding-vs-substrate-binding assignment is inferential without structural data\", \"Genotype\\u2013phenotype severity correlations not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Linking NEU1 induction to MyoD-driven myogenic differentiation showed that regulated sialidase activity is required for proper differentiation timing.\",\n      \"evidence\": \"C2C12 differentiation with MyoD reporter and NEU1 overexpression, myogenic marker Westerns\",\n      \"pmids\": [\"16216242\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relevant NEU1 substrates in myoblasts not identified\", \"Single cell line\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating NEU1 relocalization from lysosome to plasma membrane during macrophage differentiation revealed a surface pool with immune function.\",\n      \"evidence\": \"Immunofluorescence, fractionation, siRNA and antibody blocking with phagocytosis/cytokine readouts\",\n      \"pmids\": [\"16835219\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trafficking machinery for surface delivery not fully defined\", \"Surface substrates not yet identified in this study\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defining NEU1\\u2013PPCA heterodimerization clarified how premature self-oligomerization is prevented and NEU1 is activated and trafficked.\",\n      \"evidence\": \"Analytical ultracentrifugation, binding-site mapping, biochemical reconstitution\",\n      \"pmids\": [\"19666471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the heterodimer not resolved here\", \"Dynamics of oligomer disassembly in vivo not measured\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying the NEU1\\u2013TLR4 complex and TLR4 desialylation as a requirement for TLR4 dimerization and NF\\u03baB activation established NEU1 as a positive regulator of innate immune signaling.\",\n      \"evidence\": \"Reciprocal co-IP, live-cell sialidase assay, Neu1-deficient macrophages, catalytic mutant, pharmacological inhibition\",\n      \"pmids\": [\"19796680\", \"19430901\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise sialoglycan sites on TLR4 not mapped\", \"Mechanism of NEU1 surface activation not addressed in this study\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showing NEU1 desialylates integrin \\u03b24 to suppress FAK/ERK signaling and metastasis positioned NEU1 as a regulator of cancer cell invasion.\",\n      \"evidence\": \"NEU1 overexpression/knockdown, lectin blotting of integrin \\u03b24, in vivo transsplenic metastasis model\",\n      \"pmids\": [\"19151752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether surface NEU1 acts within a defined complex on integrin \\u03b24 unknown\", \"Single tumor model\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying an Nkx3-binding promoter mutation explained reduced Neu1 expression and immune phenotypes in SM/J mice.\",\n      \"evidence\": \"Reporter assays, recombinant Nkx3.2 binding/repression, intravital microcirculation imaging\",\n      \"pmids\": [\"19217813\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relevance to human NEU1 regulation not established\", \"In vivo TF occupancy not directly shown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that the NEU1 subunit of the elastin receptor complex drives ERK1/2 and pro-MMP-1 responses established NEU1 catalysis as the effector of elastin-peptide signaling.\",\n      \"evidence\": \"Catalytic-dead mutant, siRNA, ERK1/2 and pro-MMP-1 assays in fibroblasts\",\n      \"pmids\": [\"17327233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct desialylation substrate within the ERC pathway not identified here\", \"Single cell type\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extending the GPCR\\u2013MMP-9\\u2013NEU1 module to TrkA/NGF signaling generalized the surface activation cascade beyond TLR4.\",\n      \"evidence\": \"Co-IP, live-cell sialidase assay, Tamiflu inhibition, neurite outgrowth in TrkA-PC12 cells\",\n      \"pmids\": [\"20347965\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct TrkA desialylation not biochemically demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linking NEU1 to CD44 desialylation in CD4+ T cells connected NEU1 to HA-receptor function and Th2 airway inflammation.\",\n      \"evidence\": \"HA-binding flow cytometry, sialidase inhibition, Neu1-deficient SM/J mice, airway hyperresponsiveness\",\n      \"pmids\": [\"20491786\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CD44 substrate inferred rather than shown by immunoprecipitation\", \"Indirect effects of global Neu1 deficiency not excluded\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placing MMP-9 between G\\u03b1i-GPCR signaling and NEU1 activation defined the molecular order of TLR4-coupled sialidase induction.\",\n      \"evidence\": \"Co-IP, MMP-9 KO macrophages, shRNA/siRNA, live-cell sialidase assay, pharmacological inhibition\",\n      \"pmids\": [\"21873432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism by which MMP-9 activates NEU1 not resolved\", \"Stoichiometry of the TLR4\\u2013MMP9\\u2013NEU1 complex unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying EGFR and MUC1 as NEU1-associated substrates in airway epithelium showed NEU1 restrains EGFR autophosphorylation and modulates host\\u2013pathogen interactions.\",\n      \"evidence\": \"Co-IP, NEU1 overexpression/siRNA, lectin blotting, EGFR phosphorylation and bacterial adhesion assays\",\n      \"pmids\": [\"22247545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct desialylation sites on EGFR not mapped\", \"In vivo relevance not tested in this study\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Quantifying NEU1 as the dominant endothelial sialidase that restrains migration tied NEU1 expression level to vascular cell behavior.\",\n      \"evidence\": \"RT-PCR, Western, confocal localization, siRNA, wound-healing and activity assays\",\n      \"pmids\": [\"22403397\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endothelial substrates not identified in this study\", \"Mechanism of perinuclear vs surface pools unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Generalizing NMBR-MMP9-NEU1 to multiple GPCR agonists established a broad transactivation platform for TLR signaling.\",\n      \"evidence\": \"Live-cell sialidase assay, siRNA, co-IP, NF\\u03baB reporter, Neu1-deficient macrophages\",\n      \"pmids\": [\"22759791\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor desialylation events not all demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connecting NEU1 deficiency to oversialylated APP, lysosomal exocytosis, and A\\u03b2 release, with rescue by NEU1 injection, implicated NEU1 in amyloid pathology.\",\n      \"evidence\": \"NEU1-deficient mice, APP/A\\u03b2 analysis, lysosomal fractionation, cerebral NEU1 rescue\",\n      \"pmids\": [\"24225533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct desialylation of APP by NEU1 not shown biochemically\", \"Human relevance not established\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extending the NMBR-MMP9-Neu1 platform to endosomal TLR7/9 broadened NEU1's role to nucleic-acid sensing.\",\n      \"evidence\": \"siRNA of complex components, co-IP, NF\\u03baB reporter, cytokine readouts\",\n      \"pmids\": [\"23827939\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endosomal substrate of NEU1 not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating cathepsin A\\u2013NEU1\\u2013dependent PI3K\\u03b3 signaling in monocytes linked the elastin receptor complex to atherosclerotic plaque progression.\",\n      \"evidence\": \"Atherosclerosis mouse models, hematopoietic-specific complex deletion, neuraminidase inhibition, migration/ROS assays\",\n      \"pmids\": [\"24357053\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct NEU1 substrate upstream of PI3K\\u03b3 not defined here\", \"Catalysis-vs-scaffold contribution not separated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying CD31 as a NEU1 substrate whose desialylation inhibits angiogenesis established a catalysis-dependent anti-angiogenic role.\",\n      \"evidence\": \"Catalytic-dead G68V mutant, NEU1/CD31 knockdown, CD31-null cells, lectin blotting, tube formation assay\",\n      \"pmids\": [\"24550400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial trigger for CD31 desialylation not yet defined in this study\", \"In vivo angiogenesis not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showing NEU1 disrupts inhibitory TLR4:Siglec-E interactions defined a positive-feedback de-repression mechanism for TLR activation in vivo.\",\n      \"evidence\": \"Surface translocation assay, sialidase inhibitor, conditional hematopoietic Neu1 KO, endotoxemia model\",\n      \"pmids\": [\"25187624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative kinetics of Siglec disengagement not measured\", \"Other Siglec partners not surveyed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining NEU1-driven MUC1 ectodomain desialylation and shedding revealed a decoy-receptor mechanism in bacterial defense.\",\n      \"evidence\": \"Scatchard binding, NEU1/MUC1 co-IP, lectin blotting, adhesion/invasion assays, ex vivo BAL fluid\",\n      \"pmids\": [\"25963144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution to infection outcome not tested here\", \"Role of PPCA co-association mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing NEU1 overexpression recapitulates lung fibrosis features positioned NEU1 as a driver of fibrotic tissue remodeling.\",\n      \"evidence\": \"Adenoviral NEU1 delivery in vitro/in vivo, collagen/MMP-14 assays, T-cell adhesion, BAL analysis\",\n      \"pmids\": [\"26993524\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal substrates underlying fibrosis not identified\", \"Overexpression may not reflect physiologic levels\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying the SFK/p120-catenin adaptor bridge explained how NEU1 is spatially coupled to CD31 only under confluence.\",\n      \"evidence\": \"Co-IP, siRNA of SFKs/CD31/p120ctn, SFK inhibitors, cell-free reconstitution with purified proteins\",\n      \"pmids\": [\"28343945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether similar adaptors gate other NEU1 substrates unknown\", \"Stoichiometry of the assembled scaffold not determined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating NEU1 interaction with Plin1 on lipid droplets identified a non-immune role restraining lipolysis.\",\n      \"evidence\": \"siRNA, co-IP, co-localization, glycerol release and Plin1 phosphorylation assays in adipocytes\",\n      \"pmids\": [\"28429532\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the effect is catalytic or scaffold not resolved\", \"Single cell model\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing GPCR agonists activate NEU1 and insulin-receptor signaling via NMBR-MMP9-Neu1 extended the platform to metabolic receptor crosstalk.\",\n      \"evidence\": \"Co-IP of AT1R\\u2013Neu1\\u2013IR\\u03b2\\u2013NMBR complex, live-cell sialidase assay, IR phosphorylation, pharmacological inhibition\",\n      \"pmids\": [\"29277445\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct IR desialylation not demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying CD36 as a NEU1 substrate downstream of the ERC linked NEU1 to macrophage oxLDL uptake and foam-cell biology.\",\n      \"evidence\": \"LC-MS/MS, co-IP, sialidase assay, oxLDL uptake assay with pharmacological controls\",\n      \"pmids\": [\"30498996\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CD36 desialylation sites not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Establishing CD5 as a cell-surface NEU1 substrate on thymocytes added a lymphocyte target to the NEU1 repertoire.\",\n      \"evidence\": \"PNA-blot of anti-CD5 IP, NEU1-selective inhibitor, SM/J-deficient comparison\",\n      \"pmids\": [\"29897583\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of CD5 desialylation not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovering a catalysis-independent scaffold function at the MUC1 cytoplasmic domain showed NEU1 can inhibit PI3K\\u2013Akt signaling without sialidase activity.\",\n      \"evidence\": \"Reciprocal co-IP, GST pull-down deletion mapping, cell-free binding with purified proteins, G68V catalytic-dead mutant\",\n      \"pmids\": [\"34688655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the NEU1\\u2013MUC1-CD interaction unknown\", \"Generality of scaffold mode across substrates unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing CD31 desialylation requires homophilic CD31 engagement refined the spatial logic of NEU1 substrate selection.\",\n      \"evidence\": \"siRNA, WT and catalytic-dead G68V overexpression, lectin blotting, tube formation/migration assays\",\n      \"pmids\": [\"24550400\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conformational sensing mechanism not defined\", \"Single lab extension\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying \\u03b22 integrin and ICAM-1 as ERC-downstream NEU1 substrates linked NEU1 to monocyte adhesion and transendothelial migration.\",\n      \"evidence\": \"Proteomics, co-IP, sialidase assay, adhesion and transmigration assays\",\n      \"pmids\": [\"34903296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing pathogen-induced suppression of Neu1 phosphorylation/translocation defined a host-evasion mechanism via TLR4 hypersialylation.\",\n      \"evidence\": \"IP, phosphorylation analysis, NEU1 overexpression/silencing, confocal, cytokine ELISA in Leishmania-infected macrophages\",\n      \"pmids\": [\"33763070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase responsible for Neu1 phosphorylation not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that secreted active Neu1 from microglia desialylates Trem2/MerTK and neurons connected NEU1 to phagocytosis and neuronal vulnerability.\",\n      \"evidence\": \"Neu1 knockdown/overexpression, exocytosis inhibitors, phagocytosis and co-IP, galectin-3 binding, neuronal toxicity assays\",\n      \"pmids\": [\"35693885\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to neurodegeneration not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placing NEU1 upstream of the SIRT1/PGC-1\\u03b1 axis defined a role in post-MI cardiac metabolism and oxidative stress.\",\n      \"evidence\": \"Cardiomyocyte-specific NEU1 KO, SIRT1 inhibitor, PGC-1\\u03b1 KO epistasis, echocardiography and metabolic assays\",\n      \"pmids\": [\"35548408\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between NEU1 and SIRT1/PGC-1\\u03b1 not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showing NEU1 haploinsufficiency increases lysosomal exocytosis and drives rhabdomyosarcoma established a tumor-suppressor function via exocytosis control.\",\n      \"evidence\": \"NEU1 haploinsufficient mouse model, LAMP1 redistribution, single-cell exocytosis analysis\",\n      \"pmids\": [\"36127469\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate driving exocytosis suppression not identified\", \"Single model\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The first 3D structure of NEU1 revealed self-association interfaces and an inactive catalytic loop, providing a structural model for PPCA-dependent activation.\",\n      \"evidence\": \"Crystal/cryo-EM structure determination and biochemical characterization of murine NEU1\",\n      \"pmids\": [\"37205763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the activated PPCA-bound state not resolved\", \"Human NEU1 structure inferred from murine\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying ATG5 as a hypoxia-dependent NEU1 substrate connected NEU1 to autophagosome formation and inflammatory responses.\",\n      \"evidence\": \"Co-IP, NEU1 knockdown/inhibition, ATG5 sialylation and complex-formation analysis, autophagosome assay\",\n      \"pmids\": [\"37844713\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ATG5 sialylation occurs at the lysosome or elsewhere unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showing NEU1 controls sialylation of the coronavirus nucleocapsid to regulate replication identified a viral substrate and antiviral target.\",\n      \"evidence\": \"NEU1 overexpression/knockdown, NEU1 inhibitor, nucleocapsid sialylation and RNA-binding assays, in vivo HCoV-OC43 rescue\",\n      \"pmids\": [\"36714013\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of nucleocapsid sialylation/desialylation balance unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrating fibroblast-derived NEU1 keeps osteoclasts mononuclear linked NEU1 to cortical bone metabolism and fracture healing.\",\n      \"evidence\": \"scRNA-seq of human periosteum, NEU1 inhibition in vitro/in vivo, osteoclast fusion analysis, fracture healing model\",\n      \"pmids\": [\"41356197\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific osteoclast glycoprotein substrate not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showing epididymal cells transfer NEU1 to sperm to regulate \\u03b1-2,6 sialylation tied NEU1 to sperm maturation and fertility.\",\n      \"evidence\": \"Immunofluorescence, Western, NEU1 inhibition, IVF, murine transfer model, clinical correlation\",\n      \"pmids\": [\"41329355\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct sperm-surface substrate not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How NEU1 substrate selectivity is encoded\\u2014distinguishing catalytic versus scaffold modes and the structural basis of activation in the PPCA-bound state\\u2014remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the activated human PPCA-NEU1 complex\", \"General rules governing which substrates require adaptor bridges vs direct association not defined\", \"Relative physiologic contribution of lysosomal vs surface vs secreted NEU1 pools unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 1, 4, 7, 8, 11, 19]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 4, 11]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [20, 21]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [2, 3, 9, 12]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 3, 5, 14, 34]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [26]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [25, 37]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 5, 10, 16, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 8, 20, 35]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [9, 31]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\n      \"NEU1-PPCA/cathepsin A heterodimer\",\n      \"TLR4-MMP-9-NEU1 surface complex\",\n      \"elastin receptor complex (ERC)\",\n      \"NMBR-MMP9-NEU1 GPCR signaling platform\"\n    ],\n    \"partners\": [\n      \"PPCA/CTSA\",\n      \"TLR4\",\n      \"MMP9\",\n      \"MUC1\",\n      \"CD31/PECAM1\",\n      \"EGFR\",\n      \"CD36\",\n      \"ATG5\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}