{"gene":"HAPLN1","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2007,"finding":"HAPLN1 (Crtl1) stabilizes the interaction between hyaluronan (HA) and versican in the extracellular matrix; Crtl1-deficient mice display cardiac malformations including AV septal and myocardial defects, accompanied by significant reduction in versican protein levels, establishing HAPLN1 as required for versican stability and cardiac development.","method":"Knockout mouse (Crtl1-/-), immunohistochemistry, expression analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with specific cardiac phenotypic readout, reduction in versican levels confirmed, replicated across multiple embryonic stages","pmids":["17822691"],"is_preprint":false},{"year":2018,"finding":"HAPLN1, together with lumican and collagen I (HLC), causes hyaluronic acid (HA)-dependent folding of the developing human neocortex. HLC addition to human fetal neocortex cultures induced local tissue stiffness changes, cortical plate folding, and increased HA levels; these effects required the HA receptor CD168 and downstream ERK signaling, and loss of HA reduced HLC-induced folding.","method":"Ex vivo human fetal neocortex culture, ECM protein addition, HA receptor blocking, ERK inhibition, functional folding assay","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal interventions (protein addition, receptor blockade, signaling inhibition, HA depletion) in a single rigorous study with defined mechanistic pathway","pmids":["30078576"],"is_preprint":false},{"year":2018,"finding":"Age-related decrease in HAPLN1 in the lymphatic ECM increases endothelial permeability via modulation of VE-cadherin junctions. Recombinant HAPLN1 added to aged fibroblast ECMs reduced endothelial permeability, while HAPLN1 knockdown in young fibroblasts increased permeability. In vivo reconstitution of HAPLN1 in aged mice increased lymph node metastases but reduced visceral metastases.","method":"Recombinant protein addition, siRNA knockdown, endothelial permeability assay, VE-cadherin junction imaging, in vivo mouse reconstitution experiment","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments in vitro and in vivo with defined molecular readout (VE-cadherin junctions)","pmids":["30279172"],"is_preprint":false},{"year":2009,"finding":"The SP-IgV domain of HAPLN1 is sufficient to increase tumorigenic properties (proliferation, motility, invasion, soft-agar colony formation) of mesothelioma cells, identifying the IgV domain as the functionally active domain for pro-tumorigenic activity.","method":"Transfection of full-length HAPLN1 and domain constructs into mesothelioma cells, proliferation/motility/invasion/soft-agar assays","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mutagenesis/truncation with multiple functional readouts in a single lab","pmids":["19351750"],"is_preprint":false},{"year":2010,"finding":"LH/hCG-induced Hapln1 expression in rat granulosa cells is mediated by RUNX1 and RUNX2 transcription factors binding directly to the Hapln1 promoter; this induction requires PKA, PI3K, p38 MAPK, EGF signaling, and prostaglandin synthesis. HAPLN1 promotes granulosa cell survival and reduces apoptosis.","method":"siRNA knockdown of Runx1/2, dominant-negative RUNX, chromatin immunoprecipitation (ChIP), luciferase reporter with RUNX site mutation, pharmacological inhibitors, cell viability assay","journal":"Molecular endocrinology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP confirms in vivo binding, reporter mutagenesis abolishes activity, multiple orthogonal methods in single study","pmids":["20339004"],"is_preprint":false},{"year":2003,"finding":"FSH and IGF-I synergistically induce Crtl1 (HAPLN1) production in rat granulosa cells via PI3K/Akt signaling; inhibition of PI3K (LY294002, wortmannin) abrogated FSH- and IGF-I-dependent Crtl1 production, while p38 MAPK inhibition caused partial (~30%) reduction.","method":"Primary granulosa cell culture, pharmacological inhibitors (PI3K, p38 MAPK), immunoblotting, RT-PCR","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological pathway dissection with two inhibitor classes, single lab","pmids":["12586755"],"is_preprint":false},{"year":2017,"finding":"HAPLN1, produced by bone marrow stromal cells, activates a bortezomib-resistant atypical NF-κB pathway in multiple myeloma cells involving IκBα degradation that is resistant to proteasome inhibition, thereby promoting drug resistance.","method":"HAPLN1 protein treatment of MM cells, NF-κB reporter assays, IκBα degradation assay, bortezomib proteasome activity assay, cell survival assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined pathway mechanism (IκBα degradation despite proteasome inhibition), single lab, multiple biochemical readouts","pmids":["29279332"],"is_preprint":false},{"year":2021,"finding":"Gastric cancer cells activate fibroblasts to upregulate HAPLN1 expression via TGF-β1/Smad2/3 signaling. CAF-derived HAPLN1 promotes tumor migration and invasion through ECM remodeling, as demonstrated by SHG imaging of collagen fiber changes.","method":"Spheroid cell invasion assay, xenograft model, second harmonic generation (SHG) imaging, TGF-β1/Smad2/3 pathway analysis","journal":"Gastric cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional assays with signaling pathway identification, single lab","pmids":["34724589"],"is_preprint":false},{"year":2022,"finding":"In zebrafish, hapln1b-expressing epicardial cells deposit hyaluronic acid at cardiac injury sites to support cardiomyocyte proliferation and heart regeneration. Genetic depletion of hapln1-expressing cells or inactivation of hapln1b disrupted HA deposition and inhibited cardiomyocyte proliferation. hapln1-expressing epicardial cells also direct cardiomyocyte expansion during juvenile cardiac wall maturation.","method":"Single-cell RNA sequencing, induced genetic cell depletion, genetic inactivation of hapln1b, HA deposition assay, cardiomyocyte proliferation assay (zebrafish)","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic loss-of-function with defined molecular (HA deposition) and cellular (cardiomyocyte proliferation) readouts, multiple genetic approaches","pmids":["35652354"],"is_preprint":false},{"year":2023,"finding":"HAPLN1 promotes perineuronal net (PNN) formation and stabilizes chondroitin sulfate proteoglycan (CSPG) condensation; Crtl1-KO mice display normal CSPG levels but disrupted CSPG condensation into PNNs. This PNN disruption renders fear memories susceptible to erasure after extinction protocol and abolishes amygdala neural activation (Zif268) following extinction in conditioned mice.","method":"Crtl1 knockout mouse, fear extinction behavioral assay, Zif268 immunostaining in amygdala, pupil dynamics analysis","journal":"Molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with specific PNN structural and behavioral/neural readouts, single lab","pmids":["37022587"],"is_preprint":false},{"year":2022,"finding":"The proteoglycan tandem repeat 1 (PTR1) domain of HAPLN1 induces cell survival gene expression and confers resistance to multiple drug classes (proteasome inhibitors, steroids, immunomodulatory drugs, DNA damaging agents) in multiple myeloma cells.","method":"PTR1 domain protein treatment of MM cell lines, cell survival assays, gene expression analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain-specific functional assay with multiple drug classes tested, single lab","pmids":["36480501"],"is_preprint":false},{"year":2022,"finding":"Cell surface chaperonin 60 (CH60) acts as a direct binding partner of HAPLN1 on multiple myeloma cells, and CH60 specifically interacts with TLR4 to evoke HAPLN1-induced NF-κB signaling, anti-apoptotic gene transcription, and drug resistance.","method":"Unbiased cell surface biotinylation assay, co-immunoprecipitation, NF-κB reporter assay, apoptosis assay, drug resistance assay","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — unbiased receptor identification by biotinylation plus Co-IP confirming CH60-TLR4 interaction, single lab","pmids":["36625202"],"is_preprint":false},{"year":2023,"finding":"A HAPLN1-derived matrikine activates STAT1 in multiple myeloma cells via NF-κB-induced IFN-β signaling, promoting MM cell adhesion to fibronectin, endothelial cells, and stromal cells, and inducing chemotactic/chemokinetic migration and bone marrow homing in a mouse xenograft model.","method":"Matrikine peptide treatment of MM cells, xenograft BM homing assay, STAT1 activation assay, NF-κB assay, IFN-β measurement, adhesion and migration assays","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional assays with defined NF-κB–IFN-β–STAT1 signaling pathway, single lab","pmids":["37647592"],"is_preprint":false},{"year":2023,"finding":"HAPLN1 promotes peritoneal metastasis of pancreatic cancer by upregulating tumor necrosis factor receptor 2 (TNFR2) on cancer cells, which facilitates TNF-mediated upregulation of hyaluronan (HA) production, thereby promoting EMT, stemness, invasion, and immunomodulation.","method":"Mouse peritoneal carcinomatosis model, TNFR2 receptor expression analysis, HA production assay, EMT/stemness markers, in vivo tumor spreading assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse model with mechanistic pathway (TNFR2/TNF/HA) identified, single lab","pmids":["37095087"],"is_preprint":false},{"year":2023,"finding":"Recombinant HAPLN1 increases TGF-β receptor I (but not TGF-β RII) protein levels in human alveolar epithelial cells in a CD44-dependent manner, and enhances Smad3 (but not Smad2) phosphorylation upon TGF-β1 stimulation. HAPLN1 also increases SIRT1/2/6 levels and regulates cellular senescence markers (p53, p21, p16).","method":"Recombinant protein treatment of alveolar epithelial cells, western blotting of receptor and signaling components, CD44-dependent blocking experiment, mouse emphysema model","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro receptor specificity established with receptor-subtype discrimination and receptor-dependence (CD44) test, in vivo mouse model corroboration, single lab","pmids":["37587649"],"is_preprint":false},{"year":2020,"finding":"HAPLN1 localizes to pericellular matrices in human lung fibroblasts, associating with both versican and hyaluronan. Exogenous HAPLN1 (together with aggrecan G1 domain) promotes myofibroblast conversion (α-SMA upregulation) and compaction of hyaluronan-rich ECM. Nuclear HAPLN1 staining increases after myofibroblast induction and redistributes to cytosol during mitosis.","method":"Immunocytochemistry, confocal microscopy, exogenous HAPLN1 protein addition, α-SMA quantification, TGF-β1-free myofibroblast induction assay","journal":"The journal of histochemistry and cytochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — direct localization by confocal microscopy with functional consequence (myofibroblast conversion), single lab","pmids":["33064036"],"is_preprint":false},{"year":2023,"finding":"Hapln1 promotes dedifferentiation and proliferation of iPSC-derived cardiomyocytes by binding to versican, which traps GDF11; this complex is required for rhHapln1-mediated activation of TGF-β/SMAD2/3 signaling that stimulates cardiomyocyte dedifferentiation and proliferation.","method":"Recombinant Hapln1 treatment of hiPSC-CMs, versican-GDF11 interaction assay, GDF11 requirement test, TGF-β/SMAD2/3 signaling western blot, adult mouse myocardial infarction model","journal":"Journal of pharmaceutical analysis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — physical binding mechanism (versican-GDF11 trapping) linked to downstream signaling, in vitro and in vivo corroboration, single lab","pmids":["38618242"],"is_preprint":false},{"year":2024,"finding":"HAPLN1 in the dermal ECM maintains melanoma-associated blood vessel integrity by increasing hyaluronic acid and decreasing endothelial ICAM1 expression in an indirect, matrix-dependent manner. ICAM1 phosphorylates and internalizes VE-cadherin, causing vascular permeability; HAPLN1 loss with aging leads to increased ICAM1 and compromised vascular integrity.","method":"Recombinant HAPLN1 addition to ECM, ICAM1 expression analysis, VE-cadherin phosphorylation/internalization assay, ICAM1 blocking in vivo mouse experiment","journal":"Nature aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined molecular cascade (HAPLN1→HA→ICAM1→VE-cadherin internalization) with in vitro and in vivo validation, single lab","pmids":["38472454"],"is_preprint":false},{"year":2023,"finding":"HAPLN1 inhibits the NLRP3 inflammasome through stimulation of the Nrf2/ARE pathway in spinal cord injury models; HAPLN1 administration increased Nrf2/HO-1/NQO-1, decreased NLRP3/ASC/caspase-1/IL-1β, and improved motor neuron survival. Inhibition of Nrf2 with ML385 abolished these protective effects.","method":"In vitro (H2O2-treated PC12 cells) and in vivo SCI mouse model, HAPLN1 administration, Nrf2 inhibition (ML385), western blot, ELISA, Nissl staining, TUNEL assay","journal":"Biotechnology and applied biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological rescue experiment (Nrf2 inhibitor reverses HAPLN1 effects) in vitro and in vivo, single lab","pmids":["38607990"],"is_preprint":false},{"year":2024,"finding":"N-glycosylation of HAPLN1 at two sites (Asn 6 and Asn 41) differs in composition and function: Asn 6 bears predominantly tri- and tetra-sialylated glycans (protecting HAPLN1 from proteolysis, extending half-life), while Asn 41 (located in the Ig-like domain that interacts with proteoglycan) bears predominantly di-fucosylated glycans and sialyl-Lewis X/a epitopes (supporting molecular interactions).","method":"Nano-LC-MS/MS of trypsin-treated recombinant human HAPLN1 from CHO cells, site-specific N-glycopeptide identification","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — rigorous mass spectrometry-based structural characterization, single lab, functional interpretation is inferred from glycan composition rather than direct binding assay","pmids":["38246450"],"is_preprint":false},{"year":2024,"finding":"HaloTag-HAPLN1 fusion probe reveals spatial and temporal regulation of hyaluronan-scaffolded ECM deposition in neurons; excitatory neurons possess previously unidentified ECM architecture, and ECM assembly around dendrites is developmentally regulated. Dual-color birthdating demonstrates ECM assembly dynamics in vitro and in vivo.","method":"HaloTag-HAPLN1 fusion protein expression in primary rat neuronal cultures and mouse brain, live imaging, dual-color birthdating, confocal microscopy","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live-imaging of ECM organization using genetically encoded HAPLN1 probe, both in vitro and in vivo, single lab","pmids":["39251350"],"is_preprint":false},{"year":2023,"finding":"HAPLN1 interacts with ASPN (asporin) in bone marrow mesenchymal stromal cells; combined knockdown of ASPN and HAPLN1 synergistically increases osteogenic marker expression (ALP, OPN, OCN, COL1A1) and ECM mineralization in BMSCs, while decreasing osteoclast markers (Nfatc1, c-Fos).","method":"Co-immunoprecipitation (ASPN-HAPLN1 interaction), siRNA knockdown (single and dual), osteogenic differentiation assays, ECM mineralization assay in OVX mouse-derived BMSCs","journal":"Orthopaedic surgery","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP for interaction, functional assays from single lab without rigorous mechanistic follow-up","pmids":["37427673"],"is_preprint":false},{"year":2022,"finding":"HAPLN1 secreted by RA fibroblast-like synoviocytes promotes macrophage polarization towards the M1 (pro-inflammatory) phenotype, increasing M1/Mϕ ratio and expression of IL-1β, TNF-α, and iNOS.","method":"Recombinant HAPLN1 (rHAPLN1) treatment of THP-1-derived macrophages, HAPLN1OE/si-HAPLN1 transfection of RA-FLS co-cultured with macrophages, flow cytometry, qPCR, western blot","journal":"Xi bao yu fen zi mian yi xue za zhi","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, co-culture system without deep pathway mechanistic follow-up","pmids":["40415620"],"is_preprint":false},{"year":2023,"finding":"Recombinant HAPLN1 selectively increases TGF-β receptor II (not TGF-β RI) levels in human hair matrix cells and activates the ERK1/2 signaling pathway, promoting hair matrix cell proliferation and accelerating entry of hair follicles into the anagen phase.","method":"Recombinant HAPLN1 treatment of human hair matrix cells, western blotting of TGF-β receptors, ERK1/2 phosphorylation assay, mouse hair cycle experiment","journal":"Biomolecules & therapeutics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method per endpoint, TGF-β RI vs RII distinction is the opposite of what was found in alveolar epithelial cells (potential context-dependence)","pmids":["37551604"],"is_preprint":false},{"year":2026,"finding":"In zebrafish spinal cord injury, hapln1 is upregulated in progenitor cells and is required for hyaluronic acid-CD44b-mediated progenitor cell proliferation and spontaneous spinal cord regeneration; loss of hapln1a/b or ablation of hapln1+ cells reduced progenitor activation and hindered recovery.","method":"Single-cell RNA sequencing, loss-of-function genetics (hapln1a/b), cell ablation, in vivo and in vitro CD44b signaling assays (zebrafish)","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic loss-of-function approaches with defined HA-CD44b mechanistic axis, preprint not yet peer-reviewed","pmids":["41959443"],"is_preprint":true}],"current_model":"HAPLN1 is an extracellular matrix protein that non-covalently links hyaluronan and proteoglycans (particularly versican and aggrecan) to stabilize the pericellular and interstitial ECM; it acts as a structural scaffold whose functional consequences span multiple contexts: in cartilage and cardiac development it is required for versican stability and normal organogenesis; in the brain it organizes hyaluronan-scaffolded perineuronal nets that regulate neuronal plasticity and fear memory consolidation; in the ovary its expression is transcriptionally driven by LH via RUNX1/2 binding at its promoter and PI3K/Akt signaling; in cancer and aging contexts it modulates vascular and lymphatic permeability (via VE-cadherin and ICAM1), drives tumor invasion and metastasis (via TNFR2/TNF/HA and TGF-β/SMAD pathways), and in multiple myeloma it promotes drug resistance through an atypical, bortezomib-resistant NF-κB pathway initiated by a CH60-TLR4 cell surface receptor complex and by a matrikine that signals through NF-κB–IFN-β–STAT1 to promote bone marrow homing."},"narrative":{"mechanistic_narrative":"HAPLN1 is a secreted extracellular matrix link protein that non-covalently stabilizes the association between hyaluronan (HA) and proteoglycans, organizing the pericellular and interstitial matrix across cartilage, heart, brain, and tumor microenvironments [PMID:17822691, PMID:33064036]. It is required for versican stability during cardiac development, and its loss produces atrioventricular septal and myocardial defects [PMID:17822691]. The same HA-scaffolding activity underlies organized ECM architecture in the nervous system: HAPLN1 drives condensation of chondroitin sulfate proteoglycans into perineuronal nets that consolidate fear memories, and live-imaging probes reveal that it templates developmentally regulated HA-scaffolded ECM around neurons [PMID:37022587, PMID:39251350]. In tissue mechanics and morphogenesis it contributes, with lumican and collagen I, to HA-dependent stiffening and folding of the developing human neocortex via CD168 and ERK signaling, and in regenerating zebrafish heart and spinal cord hapln1-expressing cells deposit HA to support progenitor and cardiomyocyte proliferation through CD44 signaling [PMID:30078576, PMID:35652354, PMID:41959443]. Functional activity maps to specific domains: the SP-IgV (Ig-like) domain confers pro-tumorigenic properties, and the proteoglycan tandem repeat 1 (PTR1) domain induces survival gene expression [PMID:19351750, PMID:36480501]. HAPLN1 expression is transcriptionally induced in granulosa cells by LH via RUNX1/RUNX2 binding at its promoter and by FSH/IGF-I through PI3K/Akt signaling, where it promotes cell survival [PMID:20339004, PMID:12586755]. In aging and cancer, declining matrix HAPLN1 raises endothelial and lymphatic permeability through a HA-dependent cascade that lowers ICAM1 and stabilizes VE-cadherin junctions, while in tumors it drives invasion and metastasis through TGF-β/SMAD signaling, TNFR2/TNF/HA-mediated EMT, and versican-GDF11 trapping that activates SMAD2/3 [PMID:30279172, PMID:38472454, PMID:34724589, PMID:37095087, PMID:38618242]. In multiple myeloma, stroma-derived HAPLN1 engages a cell-surface CH60–TLR4 complex to activate an atypical, bortezomib-resistant NF-κB pathway, and a HAPLN1-derived matrikine signals through NF-κB–IFN-β–STAT1 to promote bone marrow homing and drug resistance [PMID:29279332, PMID:36625202, PMID:37647592].","teleology":[{"year":2003,"claim":"Established that HAPLN1 is a regulated gene product downstream of gonadotropin signaling, answering how hormonal cues control its production in the ovary.","evidence":"Pharmacological PI3K and p38 inhibition in primary rat granulosa cells treated with FSH and IGF-I","pmids":["12586755"],"confidence":"Medium","gaps":["Transcription factors mediating induction not identified here","Functional consequence in ovary not addressed"]},{"year":2007,"claim":"Defined the core structural function of HAPLN1 by showing it stabilizes the HA-versican interaction and is required for normal cardiac morphogenesis.","evidence":"Crtl1-/- knockout mouse with immunohistochemistry and versican expression analysis","pmids":["17822691"],"confidence":"High","gaps":["Molecular basis of versican destabilization not resolved","Whether the cardiac role generalizes to other organs untested here"]},{"year":2009,"claim":"Localized pro-tumorigenic activity to a discrete protein module, showing the SP-IgV domain is sufficient for transformed-cell behavior.","evidence":"Domain construct transfection into mesothelioma cells with proliferation, motility, invasion, and soft-agar assays","pmids":["19351750"],"confidence":"Medium","gaps":["Receptor or binding partner for the IgV domain not identified","Single cell-type, single lab"]},{"year":2010,"claim":"Identified the direct transcriptional control of HAPLN1, showing RUNX1/2 bind its promoter to drive LH-induced expression and granulosa cell survival.","evidence":"ChIP, luciferase reporter with RUNX-site mutation, RUNX siRNA and dominant-negative constructs in rat granulosa cells","pmids":["20339004"],"confidence":"High","gaps":["Downstream survival effectors of HAPLN1 not defined","Relevance beyond ovarian follicle untested"]},{"year":2017,"claim":"Revealed an unexpected signaling role for stroma-derived HAPLN1, showing it activates a proteasome-inhibitor-resistant atypical NF-κB pathway driving myeloma drug resistance.","evidence":"HAPLN1 protein treatment of MM cells with NF-κB reporter, IκBα degradation, and bortezomib survival assays","pmids":["29279332"],"confidence":"Medium","gaps":["Surface receptor not yet identified at this stage","Mechanism of proteasome-independent IκBα degradation unresolved"]},{"year":2018,"claim":"Connected HAPLN1 to tissue mechanics and to age-related barrier function, showing it drives HA-dependent cortical folding and modulates endothelial permeability via VE-cadherin.","evidence":"Ex vivo human neocortex culture with CD168 blockade and ERK inhibition; reciprocal recombinant-protein and siRNA permeability assays plus in vivo reconstitution","pmids":["30078576","30279172"],"confidence":"High","gaps":["Direct biochemical link between HAPLN1 and VE-cadherin not established","Cell-type specificity of mechanical effects incomplete"]},{"year":2020,"claim":"Defined HAPLN1 subcellular and pericellular distribution and a TGF-β-independent route to myofibroblast conversion.","evidence":"Confocal immunocytochemistry and exogenous HAPLN1 plus aggrecan G1 addition with α-SMA quantification in lung fibroblasts","pmids":["33064036"],"confidence":"Medium","gaps":["Function of nuclear HAPLN1 staining unknown","Mechanism of myofibroblast induction not dissected"]},{"year":2021,"claim":"Placed HAPLN1 in the tumor stroma as a CAF-derived effector, showing TGF-β1/Smad2/3-driven HAPLN1 remodels collagen to promote invasion.","evidence":"Spheroid invasion, xenograft, and SHG collagen imaging in gastric cancer with TGF-β1/Smad2/3 pathway analysis","pmids":["34724589"],"confidence":"Medium","gaps":["Direct molecular target of HAPLN1 in collagen remodeling unclear","Single tumor type"]},{"year":2022,"claim":"Identified the myeloma surface receptor and a second active domain, defining a CH60–TLR4 complex and the PTR1 module as drivers of HAPLN1 signaling and multi-drug resistance.","evidence":"Cell-surface biotinylation and Co-IP identifying CH60-TLR4; PTR1 domain protein treatment with survival and gene-expression assays in MM cells","pmids":["36625202","36480501"],"confidence":"Medium","gaps":["Stoichiometry and direct binding affinity of HAPLN1-CH60-TLR4 not quantified","Single lab for both findings"]},{"year":2022,"claim":"Demonstrated an in vivo regenerative role, showing hapln1-expressing epicardial cells deposit HA to drive cardiomyocyte proliferation in zebrafish.","evidence":"scRNA-seq, induced cell depletion, and hapln1b genetic inactivation with HA deposition and cardiomyocyte proliferation readouts","pmids":["35652354"],"confidence":"High","gaps":["Mammalian conservation of the regenerative role untested","Signaling axis downstream of HA deposition not defined here"]},{"year":2023,"claim":"Expanded the mechanistic repertoire across neural, vascular, metastatic, and protective contexts, defining distinct HA- and proteoglycan-coupled effector pathways.","evidence":"Crtl1-KO fear extinction and PNN analysis; TNFR2/TNF/HA peritoneal metastasis model; NF-κB–IFN-β–STAT1 matrikine BM-homing assays; CD44-dependent TGF-βRI/Smad3 and SIRT/senescence analysis; Nrf2/ARE-mediated NLRP3 inhibition in spinal cord injury","pmids":["37022587","37095087","37647592","37587649","38607990"],"confidence":"Medium","gaps":["Whether one biochemical activity underlies these divergent outputs is unresolved","TGF-β receptor-subtype selectivity differs between tissues","Several pathways rest on single-lab evidence"]},{"year":2024,"claim":"Refined the vascular-integrity and regenerative mechanisms and characterized site-specific glycosylation, linking HAPLN1 to HA-ICAM1-VE-cadherin control, versican-GDF11 trapping, and glycan-dependent stability.","evidence":"Recombinant HAPLN1 ECM addition with ICAM1/VE-cadherin assays; versican-GDF11 binding and SMAD2/3 signaling in hiPSC-CMs; HaloTag-HAPLN1 live imaging of neuronal ECM; nano-LC-MS/MS site-specific N-glycopeptide analysis","pmids":["38472454","38618242","39251350","38246450"],"confidence":"Medium","gaps":["Functional roles of Asn6/Asn41 glycans inferred from composition, not directly tested","Direct versican-GDF11-HAPLN1 ternary structure not resolved"]},{"year":null,"claim":"It remains unresolved whether the diverse signaling outputs attributed to HAPLN1 (NF-κB, STAT1, TGF-β/SMAD, ERK, Nrf2, TNFR2) arise from a single conserved biochemical activity (HA/proteoglycan organization) or from distinct, context-specific receptor engagements by released matrikine fragments.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying receptor model across tissues","Relationship between full-length link function and matrikine signaling untested","Structural basis of domain-specific activities not determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,15]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[13,16,17]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,15]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[9,15,20]}],"pathway":[],"complexes":["perineuronal net","hyaluronan-proteoglycan complex"],"partners":["VCAN","HMMR","CD44","TLR4","HSPD1","GDF11","ASPN","TNFRSF1B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P10915","full_name":"Hyaluronan and proteoglycan link protein 1","aliases":["Cartilage-linking protein 1","Cartilage-link protein","Proteoglycan link protein"],"length_aa":354,"mass_kda":40.2,"function":"Stabilizes the aggregates of proteoglycan monomers with hyaluronic acid in the extracellular cartilage matrix","subcellular_location":"Secreted, extracellular space, extracellular matrix","url":"https://www.uniprot.org/uniprotkb/P10915/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HAPLN1","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HAPLN1","total_profiled":1310},"omim":[{"mim_id":"619726","title":"HYALURONAN AND PROTEOGLYCAN LINK PROTEIN 2; HAPLN2","url":"https://www.omim.org/entry/619726"},{"mim_id":"619710","title":"HYALURONAN AND PROTEOGLYCAN LINK PROTEIN 4; HAPLN4","url":"https://www.omim.org/entry/619710"},{"mim_id":"614161","title":"PR DOMAIN-CONTAINING PROTEIN 5; PRDM5","url":"https://www.omim.org/entry/614161"},{"mim_id":"612078","title":"ZINC FINGER PROTEIN 469; ZNF469","url":"https://www.omim.org/entry/612078"},{"mim_id":"605702","title":"LYMPHATIC VESSEL ENDOTHELIAL HYALURONAN RECEPTOR 1; LYVE1","url":"https://www.omim.org/entry/605702"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in 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cardiac development.\",\n      \"method\": \"Knockout mouse (Crtl1-/-), immunohistochemistry, expression analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with specific cardiac phenotypic readout, reduction in versican levels confirmed, replicated across multiple embryonic stages\",\n      \"pmids\": [\"17822691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HAPLN1, together with lumican and collagen I (HLC), causes hyaluronic acid (HA)-dependent folding of the developing human neocortex. HLC addition to human fetal neocortex cultures induced local tissue stiffness changes, cortical plate folding, and increased HA levels; these effects required the HA receptor CD168 and downstream ERK signaling, and loss of HA reduced HLC-induced folding.\",\n      \"method\": \"Ex vivo human fetal neocortex culture, ECM protein addition, HA receptor blocking, ERK inhibition, functional folding assay\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal interventions (protein addition, receptor blockade, signaling inhibition, HA depletion) in a single rigorous study with defined mechanistic pathway\",\n      \"pmids\": [\"30078576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Age-related decrease in HAPLN1 in the lymphatic ECM increases endothelial permeability via modulation of VE-cadherin junctions. Recombinant HAPLN1 added to aged fibroblast ECMs reduced endothelial permeability, while HAPLN1 knockdown in young fibroblasts increased permeability. In vivo reconstitution of HAPLN1 in aged mice increased lymph node metastases but reduced visceral metastases.\",\n      \"method\": \"Recombinant protein addition, siRNA knockdown, endothelial permeability assay, VE-cadherin junction imaging, in vivo mouse reconstitution experiment\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments in vitro and in vivo with defined molecular readout (VE-cadherin junctions)\",\n      \"pmids\": [\"30279172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The SP-IgV domain of HAPLN1 is sufficient to increase tumorigenic properties (proliferation, motility, invasion, soft-agar colony formation) of mesothelioma cells, identifying the IgV domain as the functionally active domain for pro-tumorigenic activity.\",\n      \"method\": \"Transfection of full-length HAPLN1 and domain constructs into mesothelioma cells, proliferation/motility/invasion/soft-agar assays\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mutagenesis/truncation with multiple functional readouts in a single lab\",\n      \"pmids\": [\"19351750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"LH/hCG-induced Hapln1 expression in rat granulosa cells is mediated by RUNX1 and RUNX2 transcription factors binding directly to the Hapln1 promoter; this induction requires PKA, PI3K, p38 MAPK, EGF signaling, and prostaglandin synthesis. HAPLN1 promotes granulosa cell survival and reduces apoptosis.\",\n      \"method\": \"siRNA knockdown of Runx1/2, dominant-negative RUNX, chromatin immunoprecipitation (ChIP), luciferase reporter with RUNX site mutation, pharmacological inhibitors, cell viability assay\",\n      \"journal\": \"Molecular endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP confirms in vivo binding, reporter mutagenesis abolishes activity, multiple orthogonal methods in single study\",\n      \"pmids\": [\"20339004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"FSH and IGF-I synergistically induce Crtl1 (HAPLN1) production in rat granulosa cells via PI3K/Akt signaling; inhibition of PI3K (LY294002, wortmannin) abrogated FSH- and IGF-I-dependent Crtl1 production, while p38 MAPK inhibition caused partial (~30%) reduction.\",\n      \"method\": \"Primary granulosa cell culture, pharmacological inhibitors (PI3K, p38 MAPK), immunoblotting, RT-PCR\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological pathway dissection with two inhibitor classes, single lab\",\n      \"pmids\": [\"12586755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HAPLN1, produced by bone marrow stromal cells, activates a bortezomib-resistant atypical NF-κB pathway in multiple myeloma cells involving IκBα degradation that is resistant to proteasome inhibition, thereby promoting drug resistance.\",\n      \"method\": \"HAPLN1 protein treatment of MM cells, NF-κB reporter assays, IκBα degradation assay, bortezomib proteasome activity assay, cell survival assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined pathway mechanism (IκBα degradation despite proteasome inhibition), single lab, multiple biochemical readouts\",\n      \"pmids\": [\"29279332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Gastric cancer cells activate fibroblasts to upregulate HAPLN1 expression via TGF-β1/Smad2/3 signaling. CAF-derived HAPLN1 promotes tumor migration and invasion through ECM remodeling, as demonstrated by SHG imaging of collagen fiber changes.\",\n      \"method\": \"Spheroid cell invasion assay, xenograft model, second harmonic generation (SHG) imaging, TGF-β1/Smad2/3 pathway analysis\",\n      \"journal\": \"Gastric cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional assays with signaling pathway identification, single lab\",\n      \"pmids\": [\"34724589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In zebrafish, hapln1b-expressing epicardial cells deposit hyaluronic acid at cardiac injury sites to support cardiomyocyte proliferation and heart regeneration. Genetic depletion of hapln1-expressing cells or inactivation of hapln1b disrupted HA deposition and inhibited cardiomyocyte proliferation. hapln1-expressing epicardial cells also direct cardiomyocyte expansion during juvenile cardiac wall maturation.\",\n      \"method\": \"Single-cell RNA sequencing, induced genetic cell depletion, genetic inactivation of hapln1b, HA deposition assay, cardiomyocyte proliferation assay (zebrafish)\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic loss-of-function with defined molecular (HA deposition) and cellular (cardiomyocyte proliferation) readouts, multiple genetic approaches\",\n      \"pmids\": [\"35652354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HAPLN1 promotes perineuronal net (PNN) formation and stabilizes chondroitin sulfate proteoglycan (CSPG) condensation; Crtl1-KO mice display normal CSPG levels but disrupted CSPG condensation into PNNs. This PNN disruption renders fear memories susceptible to erasure after extinction protocol and abolishes amygdala neural activation (Zif268) following extinction in conditioned mice.\",\n      \"method\": \"Crtl1 knockout mouse, fear extinction behavioral assay, Zif268 immunostaining in amygdala, pupil dynamics analysis\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with specific PNN structural and behavioral/neural readouts, single lab\",\n      \"pmids\": [\"37022587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The proteoglycan tandem repeat 1 (PTR1) domain of HAPLN1 induces cell survival gene expression and confers resistance to multiple drug classes (proteasome inhibitors, steroids, immunomodulatory drugs, DNA damaging agents) in multiple myeloma cells.\",\n      \"method\": \"PTR1 domain protein treatment of MM cell lines, cell survival assays, gene expression analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-specific functional assay with multiple drug classes tested, single lab\",\n      \"pmids\": [\"36480501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cell surface chaperonin 60 (CH60) acts as a direct binding partner of HAPLN1 on multiple myeloma cells, and CH60 specifically interacts with TLR4 to evoke HAPLN1-induced NF-κB signaling, anti-apoptotic gene transcription, and drug resistance.\",\n      \"method\": \"Unbiased cell surface biotinylation assay, co-immunoprecipitation, NF-κB reporter assay, apoptosis assay, drug resistance assay\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased receptor identification by biotinylation plus Co-IP confirming CH60-TLR4 interaction, single lab\",\n      \"pmids\": [\"36625202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A HAPLN1-derived matrikine activates STAT1 in multiple myeloma cells via NF-κB-induced IFN-β signaling, promoting MM cell adhesion to fibronectin, endothelial cells, and stromal cells, and inducing chemotactic/chemokinetic migration and bone marrow homing in a mouse xenograft model.\",\n      \"method\": \"Matrikine peptide treatment of MM cells, xenograft BM homing assay, STAT1 activation assay, NF-κB assay, IFN-β measurement, adhesion and migration assays\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional assays with defined NF-κB–IFN-β–STAT1 signaling pathway, single lab\",\n      \"pmids\": [\"37647592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HAPLN1 promotes peritoneal metastasis of pancreatic cancer by upregulating tumor necrosis factor receptor 2 (TNFR2) on cancer cells, which facilitates TNF-mediated upregulation of hyaluronan (HA) production, thereby promoting EMT, stemness, invasion, and immunomodulation.\",\n      \"method\": \"Mouse peritoneal carcinomatosis model, TNFR2 receptor expression analysis, HA production assay, EMT/stemness markers, in vivo tumor spreading assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse model with mechanistic pathway (TNFR2/TNF/HA) identified, single lab\",\n      \"pmids\": [\"37095087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Recombinant HAPLN1 increases TGF-β receptor I (but not TGF-β RII) protein levels in human alveolar epithelial cells in a CD44-dependent manner, and enhances Smad3 (but not Smad2) phosphorylation upon TGF-β1 stimulation. HAPLN1 also increases SIRT1/2/6 levels and regulates cellular senescence markers (p53, p21, p16).\",\n      \"method\": \"Recombinant protein treatment of alveolar epithelial cells, western blotting of receptor and signaling components, CD44-dependent blocking experiment, mouse emphysema model\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro receptor specificity established with receptor-subtype discrimination and receptor-dependence (CD44) test, in vivo mouse model corroboration, single lab\",\n      \"pmids\": [\"37587649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HAPLN1 localizes to pericellular matrices in human lung fibroblasts, associating with both versican and hyaluronan. Exogenous HAPLN1 (together with aggrecan G1 domain) promotes myofibroblast conversion (α-SMA upregulation) and compaction of hyaluronan-rich ECM. Nuclear HAPLN1 staining increases after myofibroblast induction and redistributes to cytosol during mitosis.\",\n      \"method\": \"Immunocytochemistry, confocal microscopy, exogenous HAPLN1 protein addition, α-SMA quantification, TGF-β1-free myofibroblast induction assay\",\n      \"journal\": \"The journal of histochemistry and cytochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — direct localization by confocal microscopy with functional consequence (myofibroblast conversion), single lab\",\n      \"pmids\": [\"33064036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Hapln1 promotes dedifferentiation and proliferation of iPSC-derived cardiomyocytes by binding to versican, which traps GDF11; this complex is required for rhHapln1-mediated activation of TGF-β/SMAD2/3 signaling that stimulates cardiomyocyte dedifferentiation and proliferation.\",\n      \"method\": \"Recombinant Hapln1 treatment of hiPSC-CMs, versican-GDF11 interaction assay, GDF11 requirement test, TGF-β/SMAD2/3 signaling western blot, adult mouse myocardial infarction model\",\n      \"journal\": \"Journal of pharmaceutical analysis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — physical binding mechanism (versican-GDF11 trapping) linked to downstream signaling, in vitro and in vivo corroboration, single lab\",\n      \"pmids\": [\"38618242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HAPLN1 in the dermal ECM maintains melanoma-associated blood vessel integrity by increasing hyaluronic acid and decreasing endothelial ICAM1 expression in an indirect, matrix-dependent manner. ICAM1 phosphorylates and internalizes VE-cadherin, causing vascular permeability; HAPLN1 loss with aging leads to increased ICAM1 and compromised vascular integrity.\",\n      \"method\": \"Recombinant HAPLN1 addition to ECM, ICAM1 expression analysis, VE-cadherin phosphorylation/internalization assay, ICAM1 blocking in vivo mouse experiment\",\n      \"journal\": \"Nature aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined molecular cascade (HAPLN1→HA→ICAM1→VE-cadherin internalization) with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"38472454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HAPLN1 inhibits the NLRP3 inflammasome through stimulation of the Nrf2/ARE pathway in spinal cord injury models; HAPLN1 administration increased Nrf2/HO-1/NQO-1, decreased NLRP3/ASC/caspase-1/IL-1β, and improved motor neuron survival. Inhibition of Nrf2 with ML385 abolished these protective effects.\",\n      \"method\": \"In vitro (H2O2-treated PC12 cells) and in vivo SCI mouse model, HAPLN1 administration, Nrf2 inhibition (ML385), western blot, ELISA, Nissl staining, TUNEL assay\",\n      \"journal\": \"Biotechnology and applied biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological rescue experiment (Nrf2 inhibitor reverses HAPLN1 effects) in vitro and in vivo, single lab\",\n      \"pmids\": [\"38607990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"N-glycosylation of HAPLN1 at two sites (Asn 6 and Asn 41) differs in composition and function: Asn 6 bears predominantly tri- and tetra-sialylated glycans (protecting HAPLN1 from proteolysis, extending half-life), while Asn 41 (located in the Ig-like domain that interacts with proteoglycan) bears predominantly di-fucosylated glycans and sialyl-Lewis X/a epitopes (supporting molecular interactions).\",\n      \"method\": \"Nano-LC-MS/MS of trypsin-treated recombinant human HAPLN1 from CHO cells, site-specific N-glycopeptide identification\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — rigorous mass spectrometry-based structural characterization, single lab, functional interpretation is inferred from glycan composition rather than direct binding assay\",\n      \"pmids\": [\"38246450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HaloTag-HAPLN1 fusion probe reveals spatial and temporal regulation of hyaluronan-scaffolded ECM deposition in neurons; excitatory neurons possess previously unidentified ECM architecture, and ECM assembly around dendrites is developmentally regulated. Dual-color birthdating demonstrates ECM assembly dynamics in vitro and in vivo.\",\n      \"method\": \"HaloTag-HAPLN1 fusion protein expression in primary rat neuronal cultures and mouse brain, live imaging, dual-color birthdating, confocal microscopy\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live-imaging of ECM organization using genetically encoded HAPLN1 probe, both in vitro and in vivo, single lab\",\n      \"pmids\": [\"39251350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HAPLN1 interacts with ASPN (asporin) in bone marrow mesenchymal stromal cells; combined knockdown of ASPN and HAPLN1 synergistically increases osteogenic marker expression (ALP, OPN, OCN, COL1A1) and ECM mineralization in BMSCs, while decreasing osteoclast markers (Nfatc1, c-Fos).\",\n      \"method\": \"Co-immunoprecipitation (ASPN-HAPLN1 interaction), siRNA knockdown (single and dual), osteogenic differentiation assays, ECM mineralization assay in OVX mouse-derived BMSCs\",\n      \"journal\": \"Orthopaedic surgery\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP for interaction, functional assays from single lab without rigorous mechanistic follow-up\",\n      \"pmids\": [\"37427673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HAPLN1 secreted by RA fibroblast-like synoviocytes promotes macrophage polarization towards the M1 (pro-inflammatory) phenotype, increasing M1/Mϕ ratio and expression of IL-1β, TNF-α, and iNOS.\",\n      \"method\": \"Recombinant HAPLN1 (rHAPLN1) treatment of THP-1-derived macrophages, HAPLN1OE/si-HAPLN1 transfection of RA-FLS co-cultured with macrophages, flow cytometry, qPCR, western blot\",\n      \"journal\": \"Xi bao yu fen zi mian yi xue za zhi\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, co-culture system without deep pathway mechanistic follow-up\",\n      \"pmids\": [\"40415620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Recombinant HAPLN1 selectively increases TGF-β receptor II (not TGF-β RI) levels in human hair matrix cells and activates the ERK1/2 signaling pathway, promoting hair matrix cell proliferation and accelerating entry of hair follicles into the anagen phase.\",\n      \"method\": \"Recombinant HAPLN1 treatment of human hair matrix cells, western blotting of TGF-β receptors, ERK1/2 phosphorylation assay, mouse hair cycle experiment\",\n      \"journal\": \"Biomolecules & therapeutics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method per endpoint, TGF-β RI vs RII distinction is the opposite of what was found in alveolar epithelial cells (potential context-dependence)\",\n      \"pmids\": [\"37551604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In zebrafish spinal cord injury, hapln1 is upregulated in progenitor cells and is required for hyaluronic acid-CD44b-mediated progenitor cell proliferation and spontaneous spinal cord regeneration; loss of hapln1a/b or ablation of hapln1+ cells reduced progenitor activation and hindered recovery.\",\n      \"method\": \"Single-cell RNA sequencing, loss-of-function genetics (hapln1a/b), cell ablation, in vivo and in vitro CD44b signaling assays (zebrafish)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic loss-of-function approaches with defined HA-CD44b mechanistic axis, preprint not yet peer-reviewed\",\n      \"pmids\": [\"41959443\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HAPLN1 is an extracellular matrix protein that non-covalently links hyaluronan and proteoglycans (particularly versican and aggrecan) to stabilize the pericellular and interstitial ECM; it acts as a structural scaffold whose functional consequences span multiple contexts: in cartilage and cardiac development it is required for versican stability and normal organogenesis; in the brain it organizes hyaluronan-scaffolded perineuronal nets that regulate neuronal plasticity and fear memory consolidation; in the ovary its expression is transcriptionally driven by LH via RUNX1/2 binding at its promoter and PI3K/Akt signaling; in cancer and aging contexts it modulates vascular and lymphatic permeability (via VE-cadherin and ICAM1), drives tumor invasion and metastasis (via TNFR2/TNF/HA and TGF-β/SMAD pathways), and in multiple myeloma it promotes drug resistance through an atypical, bortezomib-resistant NF-κB pathway initiated by a CH60-TLR4 cell surface receptor complex and by a matrikine that signals through NF-κB–IFN-β–STAT1 to promote bone marrow homing.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HAPLN1 is a secreted extracellular matrix link protein that non-covalently stabilizes the association between hyaluronan (HA) and proteoglycans, organizing the pericellular and interstitial matrix across cartilage, heart, brain, and tumor microenvironments [#0, #15]. It is required for versican stability during cardiac development, and its loss produces atrioventricular septal and myocardial defects [#0]. The same HA-scaffolding activity underlies organized ECM architecture in the nervous system: HAPLN1 drives condensation of chondroitin sulfate proteoglycans into perineuronal nets that consolidate fear memories, and live-imaging probes reveal that it templates developmentally regulated HA-scaffolded ECM around neurons [#9, #20]. In tissue mechanics and morphogenesis it contributes, with lumican and collagen I, to HA-dependent stiffening and folding of the developing human neocortex via CD168 and ERK signaling, and in regenerating zebrafish heart and spinal cord hapln1-expressing cells deposit HA to support progenitor and cardiomyocyte proliferation through CD44 signaling [#1, #8, #24]. Functional activity maps to specific domains: the SP-IgV (Ig-like) domain confers pro-tumorigenic properties, and the proteoglycan tandem repeat 1 (PTR1) domain induces survival gene expression [#3, #10]. HAPLN1 expression is transcriptionally induced in granulosa cells by LH via RUNX1/RUNX2 binding at its promoter and by FSH/IGF-I through PI3K/Akt signaling, where it promotes cell survival [#4, #5]. In aging and cancer, declining matrix HAPLN1 raises endothelial and lymphatic permeability through a HA-dependent cascade that lowers ICAM1 and stabilizes VE-cadherin junctions, while in tumors it drives invasion and metastasis through TGF-β/SMAD signaling, TNFR2/TNF/HA-mediated EMT, and versican-GDF11 trapping that activates SMAD2/3 [#2, #17, #7, #13, #16]. In multiple myeloma, stroma-derived HAPLN1 engages a cell-surface CH60–TLR4 complex to activate an atypical, bortezomib-resistant NF-κB pathway, and a HAPLN1-derived matrikine signals through NF-κB–IFN-β–STAT1 to promote bone marrow homing and drug resistance [#6, #11, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established that HAPLN1 is a regulated gene product downstream of gonadotropin signaling, answering how hormonal cues control its production in the ovary.\",\n      \"evidence\": \"Pharmacological PI3K and p38 inhibition in primary rat granulosa cells treated with FSH and IGF-I\",\n      \"pmids\": [\"12586755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcription factors mediating induction not identified here\", \"Functional consequence in ovary not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the core structural function of HAPLN1 by showing it stabilizes the HA-versican interaction and is required for normal cardiac morphogenesis.\",\n      \"evidence\": \"Crtl1-/- knockout mouse with immunohistochemistry and versican expression analysis\",\n      \"pmids\": [\"17822691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of versican destabilization not resolved\", \"Whether the cardiac role generalizes to other organs untested here\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Localized pro-tumorigenic activity to a discrete protein module, showing the SP-IgV domain is sufficient for transformed-cell behavior.\",\n      \"evidence\": \"Domain construct transfection into mesothelioma cells with proliferation, motility, invasion, and soft-agar assays\",\n      \"pmids\": [\"19351750\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor or binding partner for the IgV domain not identified\", \"Single cell-type, single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the direct transcriptional control of HAPLN1, showing RUNX1/2 bind its promoter to drive LH-induced expression and granulosa cell survival.\",\n      \"evidence\": \"ChIP, luciferase reporter with RUNX-site mutation, RUNX siRNA and dominant-negative constructs in rat granulosa cells\",\n      \"pmids\": [\"20339004\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream survival effectors of HAPLN1 not defined\", \"Relevance beyond ovarian follicle untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed an unexpected signaling role for stroma-derived HAPLN1, showing it activates a proteasome-inhibitor-resistant atypical NF-κB pathway driving myeloma drug resistance.\",\n      \"evidence\": \"HAPLN1 protein treatment of MM cells with NF-κB reporter, IκBα degradation, and bortezomib survival assays\",\n      \"pmids\": [\"29279332\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Surface receptor not yet identified at this stage\", \"Mechanism of proteasome-independent IκBα degradation unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected HAPLN1 to tissue mechanics and to age-related barrier function, showing it drives HA-dependent cortical folding and modulates endothelial permeability via VE-cadherin.\",\n      \"evidence\": \"Ex vivo human neocortex culture with CD168 blockade and ERK inhibition; reciprocal recombinant-protein and siRNA permeability assays plus in vivo reconstitution\",\n      \"pmids\": [\"30078576\", \"30279172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between HAPLN1 and VE-cadherin not established\", \"Cell-type specificity of mechanical effects incomplete\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined HAPLN1 subcellular and pericellular distribution and a TGF-β-independent route to myofibroblast conversion.\",\n      \"evidence\": \"Confocal immunocytochemistry and exogenous HAPLN1 plus aggrecan G1 addition with α-SMA quantification in lung fibroblasts\",\n      \"pmids\": [\"33064036\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function of nuclear HAPLN1 staining unknown\", \"Mechanism of myofibroblast induction not dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed HAPLN1 in the tumor stroma as a CAF-derived effector, showing TGF-β1/Smad2/3-driven HAPLN1 remodels collagen to promote invasion.\",\n      \"evidence\": \"Spheroid invasion, xenograft, and SHG collagen imaging in gastric cancer with TGF-β1/Smad2/3 pathway analysis\",\n      \"pmids\": [\"34724589\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target of HAPLN1 in collagen remodeling unclear\", \"Single tumor type\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the myeloma surface receptor and a second active domain, defining a CH60–TLR4 complex and the PTR1 module as drivers of HAPLN1 signaling and multi-drug resistance.\",\n      \"evidence\": \"Cell-surface biotinylation and Co-IP identifying CH60-TLR4; PTR1 domain protein treatment with survival and gene-expression assays in MM cells\",\n      \"pmids\": [\"36625202\", \"36480501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and direct binding affinity of HAPLN1-CH60-TLR4 not quantified\", \"Single lab for both findings\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated an in vivo regenerative role, showing hapln1-expressing epicardial cells deposit HA to drive cardiomyocyte proliferation in zebrafish.\",\n      \"evidence\": \"scRNA-seq, induced cell depletion, and hapln1b genetic inactivation with HA deposition and cardiomyocyte proliferation readouts\",\n      \"pmids\": [\"35652354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian conservation of the regenerative role untested\", \"Signaling axis downstream of HA deposition not defined here\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Expanded the mechanistic repertoire across neural, vascular, metastatic, and protective contexts, defining distinct HA- and proteoglycan-coupled effector pathways.\",\n      \"evidence\": \"Crtl1-KO fear extinction and PNN analysis; TNFR2/TNF/HA peritoneal metastasis model; NF-κB–IFN-β–STAT1 matrikine BM-homing assays; CD44-dependent TGF-βRI/Smad3 and SIRT/senescence analysis; Nrf2/ARE-mediated NLRP3 inhibition in spinal cord injury\",\n      \"pmids\": [\"37022587\", \"37095087\", \"37647592\", \"37587649\", \"38607990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether one biochemical activity underlies these divergent outputs is unresolved\", \"TGF-β receptor-subtype selectivity differs between tissues\", \"Several pathways rest on single-lab evidence\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined the vascular-integrity and regenerative mechanisms and characterized site-specific glycosylation, linking HAPLN1 to HA-ICAM1-VE-cadherin control, versican-GDF11 trapping, and glycan-dependent stability.\",\n      \"evidence\": \"Recombinant HAPLN1 ECM addition with ICAM1/VE-cadherin assays; versican-GDF11 binding and SMAD2/3 signaling in hiPSC-CMs; HaloTag-HAPLN1 live imaging of neuronal ECM; nano-LC-MS/MS site-specific N-glycopeptide analysis\",\n      \"pmids\": [\"38472454\", \"38618242\", \"39251350\", \"38246450\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional roles of Asn6/Asn41 glycans inferred from composition, not directly tested\", \"Direct versican-GDF11-HAPLN1 ternary structure not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved whether the diverse signaling outputs attributed to HAPLN1 (NF-κB, STAT1, TGF-β/SMAD, ERK, Nrf2, TNFR2) arise from a single conserved biochemical activity (HA/proteoglycan organization) or from distinct, context-specific receptor engagements by released matrikine fragments.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying receptor model across tissues\", \"Relationship between full-length link function and matrikine signaling untested\", \"Structural basis of domain-specific activities not determined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 15]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [13, 16, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 2, 15]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [9, 15, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [\"perineuronal net\", \"hyaluronan-proteoglycan complex\"],\n    \"partners\": [\"VCAN\", \"HMMR\", \"CD44\", \"TLR4\", \"HSPD1\", \"GDF11\", \"ASPN\", \"TNFRSF1B\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}