{"gene":"CTSD","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2020,"finding":"Autophagy triggers CTSD maturation and localization inside cells to promote apoptosis. Glycosylation of asparagine 233 (N233) determines pro-CTSD secretion outside cells (for proliferative signaling), while autophagy-mediated maturation retains CTSD inside cells where it activates caspase-3 and promotes apoptosis, establishing a dual-function regulatory mechanism.","method":"RNAi knockdown, pharmacological autophagy modulation, PNGase F glycosylation assay, immunofluorescence localization, caspase-3 activity assay in Helicoverpa armigera model","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (RNAi, glycosylation assay, localization imaging, caspase activity), single lab, insect model system","pmids":["32324083"],"is_preprint":false},{"year":2020,"finding":"CTSD is an essential lysosomal protease in neurons; shRNA-mediated knockdown of CTSD alone is sufficient to cause lysosomal dysfunction, and lentiviral restoration of CTSD activity rescues lysosomal function and cell viability in oxygen-glucose deprivation (OGD) conditions, establishing a direct causal role for CTSD in maintaining neuronal lysosomal homeostasis.","method":"shRNA knockdown, lentiviral transduction, lysosomal function assays, cell death assays in mouse cortical neurons and MCAO stroke model","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined lysosomal phenotype, single lab, two orthogonal approaches (KD + rescue)","pmids":["32450052"],"is_preprint":false},{"year":2006,"finding":"A missense mutation (Met199Ile) in CTSD reduces cathepsin D-specific enzymatic activity to 36% of normal in affected American Bulldogs while leaving 15 other lysosomal enzyme activities unchanged, causing neuronal ceroid lipofuscinosis (NCL), establishing that CTSD enzymatic activity is specifically required for preventing NCL pathology.","method":"Enzymatic activity assays for cathepsin D and 15 other lysosomal enzymes, genetic linkage analysis, histopathology","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct enzymatic assay with enzyme-specific substrate, replicated across multiple affected animals with appropriate controls for 15 other lysosomal enzymes","pmids":["16386934"],"is_preprint":false},{"year":2019,"finding":"Recombinant human pro-CTSD is taken up by cells via mannose-6-phosphate receptor-mediated endocytosis, correctly targeted to lysosomes, and processed to the active mature form, where it corrects defective proteolysis and restores autophagic flux in CTSD-deficient CLN10 disease models in vitro and in vivo.","method":"Recombinant protein uptake assays, lysosomal targeting by immunofluorescence/fractionation, enzymatic activity assay, autophagic flux measurement, murine CLN10 model in vivo dosing","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution of enzyme activity in deficient cells, multiple model systems (cell lines, hippocampal slices, retinal cells, whole animal), multiple orthogonal readouts","pmids":["31282275"],"is_preprint":false},{"year":2022,"finding":"CTSD is the major lysosomal protease responsible for SNCA/α-synuclein degradation; recombinant human pro-CTSD is endocytosed by neuronal cells, trafficked to lysosomes, matured to active enzyme, and reduces insoluble SNCA conformers in PD patient-derived iPSC dopaminergic neurons and in ctsd-deficient mouse brains.","method":"rHsCTSD uptake and lysosomal targeting assays, SNCA solubility fractionation (Triton-soluble/insoluble), iPSC-derived neurons from A53T SNCA PD patients, ctsd-knockout mouse model, structured illumination microscopy","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1 / Strong — enzyme reconstitution in multiple human and murine neuronal models, multiple orthogonal readouts, disease-relevant genetic model","pmids":["35287553"],"is_preprint":false},{"year":2008,"finding":"Estrogen receptor alpha (ERα) up-regulates CTSD expression through a distal enhancer element located 9 kb upstream of the CTSD transcription start site via a chromatin looping mechanism, with ERα and phosphorylated RNA Pol II recruited to this distal ERE, and transient CpG methylation occurring at both the proximal promoter and the distal enhancer upon estrogen stimulation.","method":"Chromatin immunoprecipitation (ChIP) for ERα and phospho-Pol II, bisulfite sequencing for CpG methylation kinetics, chromosome conformation capture or looping assay in MCF-7 cells","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP with multiple targets plus methylation kinetics, single lab, MCF-7 cell model","pmids":["19383337"],"is_preprint":false},{"year":2020,"finding":"CTSD inhibition (siRNA or pepstatin A) attenuates autophagy by blocking autophagosome-lysosome fusion, resulting in increased autophagosomes and decreased autolysosomes, and this impaired autophagy increases radiosensitivity of glioblastoma cells. CTSD expression positively correlates with the autophagy marker LC3-II/I and negatively with p62 after ionizing radiation.","method":"siRNA knockdown, pepstatin A inhibition, Western blot, immunofluorescence for autophagosome/autolysosome quantification in radioresistant GBM cells","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — two methods (siRNA + pharmacological inhibition) with consistent phenotype, single lab, defined cellular mechanism","pmids":["32253787"],"is_preprint":false},{"year":2024,"finding":"N-glycosylation of CTSD at residue N263, regulated by the glycosyltransferase complex DDOST/STT3B, affects CTSD protease activity; glycosylated CTSD cleaves ACADM, and ACADM in turn regulates ferroptosis-related proteins (ACSL4, SLC7A11, GPX4) to influence invasion and metastasis of colorectal cancer cells.","method":"N-glycoproteomics, site-directed mutagenesis (N263), DDOST/STT3B manipulation, ACADM substrate identification, ferroptosis marker (ACSL4/SLC7A11/GPX4) quantification, invasion/metastasis assays","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (proteomics, mutagenesis, functional substrate assay), single lab","pmids":["39716927"],"is_preprint":false},{"year":2023,"finding":"Swainsonine reduces O-GlcNAcylation of CTSD, which impairs CTSD maturation (reducing mature CTSD levels), leading to lysosomal dysfunction and inhibition of autophagy degradation; pharmacological increase of O-GlcNAcylation (with TMG) promotes autophagy while decrease (with OSMI) inhibits it, implicating O-GlcNAcylation as a post-translational modification that regulates CTSD maturation.","method":"Immunoprecipitation, Western blot for mature/pro CTSD forms, OGA inhibitor (TMG) and OGT inhibitor (OSMI) treatments, proteomics, lysosomal function assays","journal":"Chemico-biological interactions","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — IP plus pharmacological modulation of O-GlcNAcylation with functional readouts, single lab","pmids":["37442287"],"is_preprint":false},{"year":2024,"finding":"CLN5 release from Dictyostelium discoideum cells is regulated by extracellular CtsD levels; autophagy induction promotes release of both Cln5 and CtsD; release requires signal peptides, autophagy proteins (Atg1, Atg5, Atg9 for Cln5; Atg1 and Atg5 for CtsD), autophagosomal-lysosomal fusion, microfilaments, and lysosomal exocytosis components (AP-3, LYST, mucopilin-1, WASH); sortilin and cation-independent mannose-6-phosphate receptor homologs regulate intracellular/extracellular distribution of CtsD.","method":"Genetic knockouts of autophagy and trafficking genes in Dictyostelium, secretion assays, glycosylation analysis, pharmacological autophagy induction","journal":"Traffic","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic knockouts with consistent trafficking phenotypes in model organism, single lab","pmids":["38272448"],"is_preprint":false},{"year":2025,"finding":"LRP6 interacts with HSP90α and CTSD in cardiomyocytes under mechanical stress; LRP6 facilitates CTSD-mediated degradation of HSP90α, which consequently inhibits β-catenin activation and reduces cardiac hypertrophy; pepstatin A (CTSD inhibitor) partly abolishes the cardioprotective effect of LRP6 overexpression, establishing CTSD as a downstream effector in the LRP6/CTSD/HSP90α/β-catenin axis.","method":"Mass spectrometry co-immunoprecipitation, cardiomyocyte-specific LRP6 overexpression mice, TAC model, pepstatin A pharmacological inhibition, recombinant HSP90α rescue, echocardiography","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-based interaction identification plus genetic (overexpression) and pharmacological (pepstatin A) validation in vivo, single lab","pmids":["39779966"],"is_preprint":false},{"year":2025,"finding":"SAMHD1 deficiency impairs lysosomal function in macrophages by enhancing MITF nuclear translocation, which suppresses CTSD expression; pharmacological inhibition of PI3K/AKT/mTOR restores MITF-CTSD signaling and lysosomal function, placing CTSD downstream of the mTOR-MITF axis in macrophage autophagy-lysosomal homeostasis.","method":"Myeloid-specific SAMHD1-KO mice, scRNA-seq, mTOR pathway inhibition (rapamycin), MITF nuclear translocation assay, CTSD expression and lysosomal flux measurements","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus pharmacological rescue with pathway-specific reagents, single lab","pmids":["40886983"],"is_preprint":false},{"year":2026,"finding":"Snapin binds cystathionine β-synthase (CBS) in neurons after mild TBI, disrupting H2S metabolic homeostasis and reducing endogenous H2S levels; decreased H2S limits S-sulfhydration of pro-CTSD, promoting its maturation into active CTSD which induces PANoptosis; both pepstatin A (CTSD inhibitor) and NaHS (H2S donor) are neuroprotective, establishing that H2S-dependent S-sulfhydration of pro-CTSD is a post-translational modification that regulates CTSD maturation.","method":"AAV-shSnapin conditional knockdown, co-immunoprecipitation (Snapin-CBS interaction), modified biotin switch assay for S-sulfhydration of CTSD, endogenous H2S measurement by sulfide ion-selective electrode, pepstatin A and NaHS treatment, behavioral tests","journal":"Journal of advanced research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (co-IP, biotin switch, pharmacological inhibition/rescue), single lab, novel PTM identification","pmids":["41558604"],"is_preprint":false},{"year":2026,"finding":"Circulatory pro-CTSD binds the Cluster II domain of LRP1 on brain endothelial cells, triggering LRP1 endocytosis and lysosomal degradation, which reduces endothelial LRP1 levels and impairs brain-to-blood Aβ clearance in Alzheimer's disease mouse models.","method":"Western blot for LRP1 in pro-CTSD-treated brain endothelial cells, transgenic mice with high circulatory pro-CTSD, confocal and TIRF microscopy for pro-CTSD internalization and LRP1 co-localization, immunostaining for Aβ deposition, Cluster II domain binding specificity assay","journal":"Alzheimer's & dementia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding domain identified, in vitro and in vivo models with multiple imaging methods, single lab","pmids":["42162956"],"is_preprint":false},{"year":2026,"finding":"In macrophages, KIF13B deficiency impairs proteasome-dependent degradation of the glycosyltransferase STT3A, thereby enhancing CTSD glycosylation and secretion, which promotes lipid accumulation and inflammatory responses in hepatocytes through interaction with the hepatocyte membrane protein THBS1, establishing the STT3A/CTSD glycosylation/secretion axis as downstream of KIF13B.","method":"Myeloid-specific Kif13b KO mice, diet-induced MASLD model, STT3A degradation assay, CTSD glycosylation and secretion measurements, CTSD-THBS1 interaction analysis, ZNF384 transcription factor binding to KIF13B promoter","journal":"Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with mechanistic follow-up on glycosylation and protein interactions, single lab","pmids":["41746601"],"is_preprint":false},{"year":2008,"finding":"A novel CTSD missense mutation (c.299C>T, p.Ser100Phe) reduces cathepsin D enzymatic activity to marginal levels in patient fibroblasts while the protein remains stable and normally processed, causing congenital neuronal ceroid lipofuscinosis (CLN10), confirming that catalytic activity rather than protein stability is critical for CTSD function.","method":"Cathepsin D enzymatic activity assay in patient fibroblasts, overexpression studies, protein stability and processing analysis","journal":"Acta neuropathologica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct enzymatic activity assay plus overexpression rescue in human patient cells, single lab","pmids":["18762956"],"is_preprint":false},{"year":2023,"finding":"miR-1912-3p directly targets CTSD in fetal chondrocytes; dexamethasone activates glucocorticoid receptor (GR) to increase H3K9ac and miR-1912-3p expression, which suppresses CTSD expression and inhibits autophagic flux; overexpression of CTSD rescues autophagic flux inhibited by dexamethasone, placing CTSD downstream of the GR/H3K9ac/miR-1912-3p axis in chondrocyte autophagy regulation.","method":"CTSD overexpression rescue experiments, miR-1912-3p target validation, H3K9ac ChIP, GR pathway inhibition, autophagic flux assays (autolysosome accumulation), in vivo PDE rat model","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function rescue plus epigenetic mechanism characterization, in vivo and in vitro concordant results, single lab","pmids":["37249374"],"is_preprint":false},{"year":2025,"finding":"Cathepsin D (CtsD) in astrocytes cleaves α-synuclein pre-formed fibrils (PFFs) into C-terminally truncated, seeding-competent species; these truncated species are transferred to neurons where they promote Lewy neurite-like aggregate growth. α-syn PFF exposure disrupts lysosomal membrane integrity in astrocytes, leading to CtsD upregulation in a feed-forward mechanism.","method":"Neuron-astrocyte co-culture system, lysosomal protease identification (CtsD), α-syn PFF truncation assay, aggregate seeding assay in neurons, lysosomal membrane integrity assessment","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, mechanistic details of truncation assay not fully described in abstract","pmids":[],"is_preprint":true},{"year":2025,"finding":"CtsD deletion in mice dramatically decreases bone mass with decreased osteoblast number/activity and increased osteoclast number/activity; siRNA-mediated CTSD inactivation in osteoblasts (MC3T3E1) attenuates osteoblastic differentiation and decreases LC3B and P62 expression, while inactivation in osteoclasts (RAW264.7) increases osteoclast differentiation with decreased LC3B but upregulated P62, demonstrating that CTSD mediates autophagy through distinct mechanisms in osteoblasts versus osteoclasts.","method":"CtsD conditional KO mice, microCT, histomorphometry, siRNA knockdown in MC3T3E1 and RAW264.7 cells, LC3B and P62 expression, differentiation assays","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, genetic KO with cellular mechanistic follow-up, single lab, cell-type-specific distinction is novel","pmids":[],"is_preprint":true},{"year":2026,"finding":"miR-214-3p directly targets CTSD (validated by luciferase assay); overexpression of CTSD reverses the protective effects of miR-214-3p mimic on lysosomal acidification and LAMP1 levels in porcine intestinal epithelial cells, establishing CTSD as a direct functional target of miR-214-3p in regulating lysosomal homeostasis.","method":"Luciferase reporter assay for miR-214-3p/CTSD interaction, CTSD overexpression rescue, lysosomal acidification measurement, LAMP1 expression, cell viability assays in IPEC-J2 cells","journal":"Biology","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — luciferase validation plus functional rescue, single lab, non-human cellular model","pmids":["42117833"],"is_preprint":false},{"year":2024,"finding":"N-glycosylation of CTSD at residue N258 (CTSD-N258A mutant) promotes lysosomal localization of CTSD and affects lysosomal membrane permeability and apoptosis in BMSCs; the N258A mutant reduces CTSD levels in cytoplasm and lysosomes and inhibits BMSC apoptosis in a dexamethasone-induced model.","method":"CTSD N258A site-directed mutagenesis, flow cytometry for apoptosis, confocal microscopy for lysosomal colocalization, AO staining for lysosomal membrane permeability, Western blot for apoptosis-related proteins","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single mutagenesis study with functional readouts, single lab, abstract-level description","pmids":["41931502"],"is_preprint":false}],"current_model":"CTSD (cathepsin D) is a lysosomal aspartic protease that is synthesized as a pro-enzyme, secreted extracellularly as pro-CTSD (where it can act as a ligand to promote cell proliferation), or retained intracellularly and matured to its active form through autophagy-dependent and post-translational modification-dependent mechanisms (including N-glycosylation, O-GlcNAcylation, and H2S-dependent S-sulfhydration of pro-CTSD) to perform proteolytic functions; inside lysosomes, mature CTSD maintains proteostasis by degrading substrates including SNCA/α-synuclein, HSP90α, and ACADM, sustains autophagic flux by enabling autophagosome-lysosome fusion, and is transcriptionally regulated via ERα-mediated chromatin looping to a distal enhancer; loss of CTSD enzymatic activity causes lysosomal storage disorder (CLN10/neuronal ceroid lipofuscinosis), while circulatory pro-CTSD can bind the Cluster II domain of endothelial LRP1 to trigger its lysosomal degradation and impair brain Aβ clearance, and in macrophages CTSD secretion is regulated by STT3A-dependent N-glycosylation downstream of the KIF13B/mTOR-MITF axis."},"narrative":{"mechanistic_narrative":"CTSD (cathepsin D) is a lysosomal aspartic protease that maintains neuronal and cellular proteostasis and autophagic flux by degrading substrates in the lysosome [PMID:32450052, PMID:35287553]. It is synthesized as an inactive pro-enzyme that is matured to its catalytically active form, and this maturation is the decisive step controlling its function: missense mutations that specifically reduce catalytic activity (Met199Ile; Ser100Phe) — without altering protein stability or other lysosomal enzyme activities — cause neuronal ceroid lipofuscinosis (CLN10), establishing that enzymatic activity, not protein abundance, is required to prevent lysosomal storage pathology [PMID:16386934, PMID:18762956]. Mature CTSD sustains autophagy by enabling autophagosome–lysosome fusion, and its loss causes lysosomal dysfunction and impaired autophagic degradation [PMID:32450052, PMID:32253787]. Among its substrates, CTSD is the major lysosomal protease degrading SNCA/α-synuclein, and recombinant pro-CTSD delivered via mannose-6-phosphate receptor-mediated endocytosis is correctly trafficked to lysosomes, matured, and restores defective proteolysis and autophagic flux in CTSD-deficient disease models, reducing insoluble α-synuclein conformers in patient-derived neurons and ctsd-deficient mouse brains [PMID:31282275, PMID:35287553]. Its maturation and trafficking are governed by post-translational modifications — N-glycosylation (controlling secretion of pro-CTSD versus intracellular retention, and protease activity), O-GlcNAcylation, and H2S-dependent S-sulfhydration of pro-CTSD — which collectively partition CTSD between an intracellular pro-apoptotic/proteostatic role and a secreted extracellular pool [PMID:32324083, PMID:39716927, PMID:37442287, PMID:41558604]. CTSD transcription is induced by estrogen receptor alpha through chromatin looping to a distal enhancer 9 kb upstream of its start site [PMID:19383337], and it is suppressed downstream of an mTOR–MITF axis in macrophages [PMID:40886983]. Beyond the lysosome, secreted or circulatory pro-CTSD acts in trans: it binds the Cluster II domain of endothelial LRP1 to trigger LRP1 lysosomal degradation and impair brain Aβ clearance [PMID:42162956], and engages LRP6 to mediate degradation of HSP90α in cardiomyocytes [PMID:39779966]. Loss of CTSD enzymatic activity causes CLN10/neuronal ceroid lipofuscinosis [PMID:16386934, PMID:18762956].","teleology":[{"year":2006,"claim":"Established that it is CTSD catalytic activity specifically — not general lysosomal enzyme deficiency — that prevents neuronal ceroid lipofuscinosis, defining CTSD as a disease gene through its enzymatic function.","evidence":"Enzyme-specific activity assays comparing CTSD to 15 other lysosomal enzymes plus genetic linkage in Met199Ile American Bulldogs","pmids":["16386934"],"confidence":"High","gaps":["Did not identify the physiological substrates whose accumulation drives NCL pathology","Canine model; human variant spectrum addressed separately"]},{"year":2008,"claim":"Distinguished catalytic activity from protein stability as the critical determinant, showing a stable, normally processed CTSD protein with marginal activity still causes congenital CLN10.","evidence":"Enzymatic activity assay and processing/stability analysis in patient fibroblasts carrying p.Ser100Phe, with overexpression studies","pmids":["18762956"],"confidence":"Medium","gaps":["Mechanism linking marginal activity to congenital lethality not resolved","Single patient genotype"]},{"year":2008,"claim":"Defined how CTSD is transcriptionally controlled, identifying ERα-driven induction via long-range chromatin looping to a distal enhancer.","evidence":"ChIP for ERα and phospho-Pol II, bisulfite sequencing, and chromatin looping assays in MCF-7 cells","pmids":["19383337"],"confidence":"Medium","gaps":["Functional consequence of transient CpG methylation not established","Restricted to one breast cancer cell line"]},{"year":2020,"claim":"Resolved the localization-versus-function switch, showing autophagy drives intracellular CTSD maturation toward apoptosis while N233 glycosylation routes pro-CTSD to secretion for proliferative signaling.","evidence":"RNAi, autophagy modulation, PNGase F glycosylation assay, and caspase-3 activity in an insect (Helicoverpa armigera) model","pmids":["32324083"],"confidence":"Medium","gaps":["Demonstrated in an insect model; mammalian generality not shown here","Glycosite numbering and mechanism differ across mammalian studies"]},{"year":2020,"claim":"Established CTSD as causally required for neuronal lysosomal homeostasis and autophagic flux, with knockdown sufficient to cause dysfunction and rescue restoring viability.","evidence":"shRNA knockdown plus lentiviral rescue with lysosomal and cell-death assays in mouse cortical neurons and an MCAO stroke model; siRNA/pepstatin A blocking autophagosome-lysosome fusion in glioblastoma","pmids":["32450052","32253787"],"confidence":"Medium","gaps":["Direct molecular step at which CTSD enables fusion not defined","Substrate(s) mediating the fusion phenotype unidentified"]},{"year":2022,"claim":"Identified α-synuclein as a key CTSD substrate and demonstrated therapeutic enzyme reconstitution, showing recombinant pro-CTSD reduces insoluble SNCA in human and murine neuronal models.","evidence":"rHsCTSD uptake/lysosomal targeting, SNCA solubility fractionation, A53T PD iPSC neurons, ctsd-knockout mice; earlier CLN10 reconstitution work established M6P-receptor uptake and autophagy rescue","pmids":["35287553","31282275"],"confidence":"High","gaps":["Cleavage sites and kinetics on SNCA not fully mapped","Long-term in vivo efficacy and delivery not addressed"]},{"year":2024,"claim":"Defined N-glycosylation as a regulator of CTSD protease activity and downstream substrate processing, linking glycosylated CTSD to ACADM cleavage and ferroptosis-related signaling in cancer.","evidence":"N-glycoproteomics, N263 site-directed mutagenesis, DDOST/STT3B manipulation, and ferroptosis-marker assays in colorectal cancer cells","pmids":["39716927"],"confidence":"Medium","gaps":["Relationship between distinct reported glycosites (N233/N258/N263) unresolved","Single cancer-cell context"]},{"year":2023,"claim":"Extended PTM control of CTSD maturation to O-GlcNAcylation, showing reduced O-GlcNAcylation impairs maturation and autophagic degradation.","evidence":"IP, mature/pro CTSD Western blots, and OGT/OGA inhibitor (OSMI/TMG) modulation with lysosomal function assays","pmids":["37442287"],"confidence":"Medium","gaps":["Direct O-GlcNAc site on CTSD not mapped","Whether effect is direct or via trafficking machinery unclear"]},{"year":2023,"claim":"Placed CTSD downstream of microRNA and epigenetic control, showing GR/H3K9ac-driven miR-1912-3p suppresses CTSD to inhibit chondrocyte autophagic flux, reversible by CTSD overexpression.","evidence":"miR target validation, H3K9ac ChIP, CTSD overexpression rescue, and autophagic flux assays in vitro and in a PDE rat model; complementary miR-214-3p targeting validated in porcine intestinal epithelial cells","pmids":["37249374","42117833"],"confidence":"Medium","gaps":["Physiological contexts where each miRNA dominates not defined","miR-214-3p evidence is Low-confidence, non-human"]},{"year":2025,"claim":"Connected CTSD to upstream signaling controlling its expression, placing it downstream of an mTOR-MITF axis in macrophage lysosomal homeostasis.","evidence":"Myeloid-specific SAMHD1-KO mice, scRNA-seq, rapamycin treatment, and MITF nuclear translocation/CTSD expression assays","pmids":["40886983"],"confidence":"Medium","gaps":["Whether MITF binds the CTSD locus directly not shown","Single disease context"]},{"year":2025,"claim":"Identified an extracellular/trans CTSD function in cardiomyocytes, where LRP6 facilitates CTSD-mediated HSP90α degradation to limit β-catenin-driven hypertrophy.","evidence":"MS co-IP, cardiomyocyte LRP6 overexpression mice, TAC model, pepstatin A inhibition, and recombinant HSP90α rescue","pmids":["39779966"],"confidence":"Medium","gaps":["Direct CTSD cleavage of HSP90α versus indirect effect not fully separated","Subcellular compartment of the degradation event unclear"]},{"year":2026,"claim":"Established H2S-dependent S-sulfhydration of pro-CTSD as a maturation brake, with loss of sulfhydration promoting active CTSD that drives PANoptosis after TBI.","evidence":"AAV-shSnapin knockdown, Snapin-CBS co-IP, biotin switch S-sulfhydration assay, H2S measurement, and pepstatin A/NaHS rescue with behavioral tests","pmids":["41558604"],"confidence":"Medium","gaps":["Sulfhydrated cysteine residue on pro-CTSD not mapped","Single injury model"]},{"year":2026,"claim":"Defined a pathogenic trans action of circulatory pro-CTSD, showing it binds the LRP1 Cluster II domain to trigger LRP1 degradation and impair brain Aβ clearance.","evidence":"Western blot, domain-specific binding assay, transgenic mice with high circulatory pro-CTSD, and confocal/TIRF imaging of internalization in Alzheimer's models","pmids":["42162956"],"confidence":"Medium","gaps":["Whether pro-CTSD enzymatic activity is required for LRP1 degradation not resolved","Source of elevated circulatory pro-CTSD in disease unclear"]},{"year":2026,"claim":"Linked macrophage CTSD secretion to a glycosylation-trafficking circuit, showing KIF13B loss stabilizes STT3A to enhance CTSD glycosylation and secretion, promoting hepatocyte lipid accumulation via THBS1.","evidence":"Myeloid-specific Kif13b-KO mice, MASLD model, STT3A degradation assays, and CTSD-THBS1 interaction analysis","pmids":["41746601"],"confidence":"Medium","gaps":["Whether CTSD acts as protease or ligand on hepatocytes not separated","Direct CTSD-THBS1 binding interface not mapped"]},{"year":null,"claim":"How distinct N-glycosites (N233/N258/N263), O-GlcNAcylation, and S-sulfhydration are integrated to set the balance between intracellular maturation, secretion, and substrate selectivity remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model reconciling the multiple reported glycosites and PTMs","Structural basis of pro-CTSD maturation control not defined","Quantitative partitioning between lysosomal and secreted pools across cell types unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[2,4,15]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,7,10]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,6]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,3,4]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,13,14]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[1,6,8]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,7,10]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,4,13,15]}],"complexes":[],"partners":["LRP1","LRP6","HSP90A1","ACADM","SNCA","THBS1","STT3A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07339","full_name":"Cathepsin D","aliases":[],"length_aa":412,"mass_kda":44.6,"function":"Acid protease active in intracellular protein breakdown. Plays a role in APP processing following cleavage and activation by ADAM30 which leads to APP degradation (PubMed:27333034). Involved in the pathogenesis of several diseases such as breast cancer and possibly Alzheimer disease","subcellular_location":"Lysosome; Melanosome; Secreted, extracellular space","url":"https://www.uniprot.org/uniprotkb/P07339/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CTSD","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":[{"gene":"CANX","stoichiometry":0.2},{"gene":"LDHB","stoichiometry":0.2},{"gene":"VASP","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CTSD","total_profiled":1310},"omim":[{"mim_id":"621024","title":"PROTEIN PRENYLTRANSFERASE ALPHA SUBUNIT REPEAT-CONTAINING PROTEIN 1; PTAR1","url":"https://www.omim.org/entry/621024"},{"mim_id":"620937","title":"KARIMINEJAD NEURODEVELOPMENTAL SYNDROME; KAREVS","url":"https://www.omim.org/entry/620937"},{"mim_id":"619628","title":"AFTIPHILIN; AFTPH","url":"https://www.omim.org/entry/619628"},{"mim_id":"619517","title":"NEURODEVELOPMENTAL DISORDER WITH SEIZURES AND BRAIN ABNORMALITIES; NEDSBA","url":"https://www.omim.org/entry/619517"},{"mim_id":"617366","title":"COILED-COIL DOMAIN-CONTAINING PROTEIN 91; CCDC91","url":"https://www.omim.org/entry/617366"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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Glycosylation of asparagine 233 (N233) determines pro-CTSD secretion outside cells (for proliferative signaling), while autophagy-mediated maturation retains CTSD inside cells where it activates caspase-3 and promotes apoptosis, establishing a dual-function regulatory mechanism.\",\n      \"method\": \"RNAi knockdown, pharmacological autophagy modulation, PNGase F glycosylation assay, immunofluorescence localization, caspase-3 activity assay in Helicoverpa armigera model\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (RNAi, glycosylation assay, localization imaging, caspase activity), single lab, insect model system\",\n      \"pmids\": [\"32324083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CTSD is an essential lysosomal protease in neurons; shRNA-mediated knockdown of CTSD alone is sufficient to cause lysosomal dysfunction, and lentiviral restoration of CTSD activity rescues lysosomal function and cell viability in oxygen-glucose deprivation (OGD) conditions, establishing a direct causal role for CTSD in maintaining neuronal lysosomal homeostasis.\",\n      \"method\": \"shRNA knockdown, lentiviral transduction, lysosomal function assays, cell death assays in mouse cortical neurons and MCAO stroke model\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined lysosomal phenotype, single lab, two orthogonal approaches (KD + rescue)\",\n      \"pmids\": [\"32450052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A missense mutation (Met199Ile) in CTSD reduces cathepsin D-specific enzymatic activity to 36% of normal in affected American Bulldogs while leaving 15 other lysosomal enzyme activities unchanged, causing neuronal ceroid lipofuscinosis (NCL), establishing that CTSD enzymatic activity is specifically required for preventing NCL pathology.\",\n      \"method\": \"Enzymatic activity assays for cathepsin D and 15 other lysosomal enzymes, genetic linkage analysis, histopathology\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct enzymatic assay with enzyme-specific substrate, replicated across multiple affected animals with appropriate controls for 15 other lysosomal enzymes\",\n      \"pmids\": [\"16386934\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Recombinant human pro-CTSD is taken up by cells via mannose-6-phosphate receptor-mediated endocytosis, correctly targeted to lysosomes, and processed to the active mature form, where it corrects defective proteolysis and restores autophagic flux in CTSD-deficient CLN10 disease models in vitro and in vivo.\",\n      \"method\": \"Recombinant protein uptake assays, lysosomal targeting by immunofluorescence/fractionation, enzymatic activity assay, autophagic flux measurement, murine CLN10 model in vivo dosing\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution of enzyme activity in deficient cells, multiple model systems (cell lines, hippocampal slices, retinal cells, whole animal), multiple orthogonal readouts\",\n      \"pmids\": [\"31282275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CTSD is the major lysosomal protease responsible for SNCA/α-synuclein degradation; recombinant human pro-CTSD is endocytosed by neuronal cells, trafficked to lysosomes, matured to active enzyme, and reduces insoluble SNCA conformers in PD patient-derived iPSC dopaminergic neurons and in ctsd-deficient mouse brains.\",\n      \"method\": \"rHsCTSD uptake and lysosomal targeting assays, SNCA solubility fractionation (Triton-soluble/insoluble), iPSC-derived neurons from A53T SNCA PD patients, ctsd-knockout mouse model, structured illumination microscopy\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — enzyme reconstitution in multiple human and murine neuronal models, multiple orthogonal readouts, disease-relevant genetic model\",\n      \"pmids\": [\"35287553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Estrogen receptor alpha (ERα) up-regulates CTSD expression through a distal enhancer element located 9 kb upstream of the CTSD transcription start site via a chromatin looping mechanism, with ERα and phosphorylated RNA Pol II recruited to this distal ERE, and transient CpG methylation occurring at both the proximal promoter and the distal enhancer upon estrogen stimulation.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for ERα and phospho-Pol II, bisulfite sequencing for CpG methylation kinetics, chromosome conformation capture or looping assay in MCF-7 cells\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP with multiple targets plus methylation kinetics, single lab, MCF-7 cell model\",\n      \"pmids\": [\"19383337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CTSD inhibition (siRNA or pepstatin A) attenuates autophagy by blocking autophagosome-lysosome fusion, resulting in increased autophagosomes and decreased autolysosomes, and this impaired autophagy increases radiosensitivity of glioblastoma cells. CTSD expression positively correlates with the autophagy marker LC3-II/I and negatively with p62 after ionizing radiation.\",\n      \"method\": \"siRNA knockdown, pepstatin A inhibition, Western blot, immunofluorescence for autophagosome/autolysosome quantification in radioresistant GBM cells\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — two methods (siRNA + pharmacological inhibition) with consistent phenotype, single lab, defined cellular mechanism\",\n      \"pmids\": [\"32253787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"N-glycosylation of CTSD at residue N263, regulated by the glycosyltransferase complex DDOST/STT3B, affects CTSD protease activity; glycosylated CTSD cleaves ACADM, and ACADM in turn regulates ferroptosis-related proteins (ACSL4, SLC7A11, GPX4) to influence invasion and metastasis of colorectal cancer cells.\",\n      \"method\": \"N-glycoproteomics, site-directed mutagenesis (N263), DDOST/STT3B manipulation, ACADM substrate identification, ferroptosis marker (ACSL4/SLC7A11/GPX4) quantification, invasion/metastasis assays\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (proteomics, mutagenesis, functional substrate assay), single lab\",\n      \"pmids\": [\"39716927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Swainsonine reduces O-GlcNAcylation of CTSD, which impairs CTSD maturation (reducing mature CTSD levels), leading to lysosomal dysfunction and inhibition of autophagy degradation; pharmacological increase of O-GlcNAcylation (with TMG) promotes autophagy while decrease (with OSMI) inhibits it, implicating O-GlcNAcylation as a post-translational modification that regulates CTSD maturation.\",\n      \"method\": \"Immunoprecipitation, Western blot for mature/pro CTSD forms, OGA inhibitor (TMG) and OGT inhibitor (OSMI) treatments, proteomics, lysosomal function assays\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — IP plus pharmacological modulation of O-GlcNAcylation with functional readouts, single lab\",\n      \"pmids\": [\"37442287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CLN5 release from Dictyostelium discoideum cells is regulated by extracellular CtsD levels; autophagy induction promotes release of both Cln5 and CtsD; release requires signal peptides, autophagy proteins (Atg1, Atg5, Atg9 for Cln5; Atg1 and Atg5 for CtsD), autophagosomal-lysosomal fusion, microfilaments, and lysosomal exocytosis components (AP-3, LYST, mucopilin-1, WASH); sortilin and cation-independent mannose-6-phosphate receptor homologs regulate intracellular/extracellular distribution of CtsD.\",\n      \"method\": \"Genetic knockouts of autophagy and trafficking genes in Dictyostelium, secretion assays, glycosylation analysis, pharmacological autophagy induction\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic knockouts with consistent trafficking phenotypes in model organism, single lab\",\n      \"pmids\": [\"38272448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LRP6 interacts with HSP90α and CTSD in cardiomyocytes under mechanical stress; LRP6 facilitates CTSD-mediated degradation of HSP90α, which consequently inhibits β-catenin activation and reduces cardiac hypertrophy; pepstatin A (CTSD inhibitor) partly abolishes the cardioprotective effect of LRP6 overexpression, establishing CTSD as a downstream effector in the LRP6/CTSD/HSP90α/β-catenin axis.\",\n      \"method\": \"Mass spectrometry co-immunoprecipitation, cardiomyocyte-specific LRP6 overexpression mice, TAC model, pepstatin A pharmacological inhibition, recombinant HSP90α rescue, echocardiography\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-based interaction identification plus genetic (overexpression) and pharmacological (pepstatin A) validation in vivo, single lab\",\n      \"pmids\": [\"39779966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SAMHD1 deficiency impairs lysosomal function in macrophages by enhancing MITF nuclear translocation, which suppresses CTSD expression; pharmacological inhibition of PI3K/AKT/mTOR restores MITF-CTSD signaling and lysosomal function, placing CTSD downstream of the mTOR-MITF axis in macrophage autophagy-lysosomal homeostasis.\",\n      \"method\": \"Myeloid-specific SAMHD1-KO mice, scRNA-seq, mTOR pathway inhibition (rapamycin), MITF nuclear translocation assay, CTSD expression and lysosomal flux measurements\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus pharmacological rescue with pathway-specific reagents, single lab\",\n      \"pmids\": [\"40886983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Snapin binds cystathionine β-synthase (CBS) in neurons after mild TBI, disrupting H2S metabolic homeostasis and reducing endogenous H2S levels; decreased H2S limits S-sulfhydration of pro-CTSD, promoting its maturation into active CTSD which induces PANoptosis; both pepstatin A (CTSD inhibitor) and NaHS (H2S donor) are neuroprotective, establishing that H2S-dependent S-sulfhydration of pro-CTSD is a post-translational modification that regulates CTSD maturation.\",\n      \"method\": \"AAV-shSnapin conditional knockdown, co-immunoprecipitation (Snapin-CBS interaction), modified biotin switch assay for S-sulfhydration of CTSD, endogenous H2S measurement by sulfide ion-selective electrode, pepstatin A and NaHS treatment, behavioral tests\",\n      \"journal\": \"Journal of advanced research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (co-IP, biotin switch, pharmacological inhibition/rescue), single lab, novel PTM identification\",\n      \"pmids\": [\"41558604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Circulatory pro-CTSD binds the Cluster II domain of LRP1 on brain endothelial cells, triggering LRP1 endocytosis and lysosomal degradation, which reduces endothelial LRP1 levels and impairs brain-to-blood Aβ clearance in Alzheimer's disease mouse models.\",\n      \"method\": \"Western blot for LRP1 in pro-CTSD-treated brain endothelial cells, transgenic mice with high circulatory pro-CTSD, confocal and TIRF microscopy for pro-CTSD internalization and LRP1 co-localization, immunostaining for Aβ deposition, Cluster II domain binding specificity assay\",\n      \"journal\": \"Alzheimer's & dementia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding domain identified, in vitro and in vivo models with multiple imaging methods, single lab\",\n      \"pmids\": [\"42162956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In macrophages, KIF13B deficiency impairs proteasome-dependent degradation of the glycosyltransferase STT3A, thereby enhancing CTSD glycosylation and secretion, which promotes lipid accumulation and inflammatory responses in hepatocytes through interaction with the hepatocyte membrane protein THBS1, establishing the STT3A/CTSD glycosylation/secretion axis as downstream of KIF13B.\",\n      \"method\": \"Myeloid-specific Kif13b KO mice, diet-induced MASLD model, STT3A degradation assay, CTSD glycosylation and secretion measurements, CTSD-THBS1 interaction analysis, ZNF384 transcription factor binding to KIF13B promoter\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with mechanistic follow-up on glycosylation and protein interactions, single lab\",\n      \"pmids\": [\"41746601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A novel CTSD missense mutation (c.299C>T, p.Ser100Phe) reduces cathepsin D enzymatic activity to marginal levels in patient fibroblasts while the protein remains stable and normally processed, causing congenital neuronal ceroid lipofuscinosis (CLN10), confirming that catalytic activity rather than protein stability is critical for CTSD function.\",\n      \"method\": \"Cathepsin D enzymatic activity assay in patient fibroblasts, overexpression studies, protein stability and processing analysis\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct enzymatic activity assay plus overexpression rescue in human patient cells, single lab\",\n      \"pmids\": [\"18762956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"miR-1912-3p directly targets CTSD in fetal chondrocytes; dexamethasone activates glucocorticoid receptor (GR) to increase H3K9ac and miR-1912-3p expression, which suppresses CTSD expression and inhibits autophagic flux; overexpression of CTSD rescues autophagic flux inhibited by dexamethasone, placing CTSD downstream of the GR/H3K9ac/miR-1912-3p axis in chondrocyte autophagy regulation.\",\n      \"method\": \"CTSD overexpression rescue experiments, miR-1912-3p target validation, H3K9ac ChIP, GR pathway inhibition, autophagic flux assays (autolysosome accumulation), in vivo PDE rat model\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function rescue plus epigenetic mechanism characterization, in vivo and in vitro concordant results, single lab\",\n      \"pmids\": [\"37249374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cathepsin D (CtsD) in astrocytes cleaves α-synuclein pre-formed fibrils (PFFs) into C-terminally truncated, seeding-competent species; these truncated species are transferred to neurons where they promote Lewy neurite-like aggregate growth. α-syn PFF exposure disrupts lysosomal membrane integrity in astrocytes, leading to CtsD upregulation in a feed-forward mechanism.\",\n      \"method\": \"Neuron-astrocyte co-culture system, lysosomal protease identification (CtsD), α-syn PFF truncation assay, aggregate seeding assay in neurons, lysosomal membrane integrity assessment\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, mechanistic details of truncation assay not fully described in abstract\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CtsD deletion in mice dramatically decreases bone mass with decreased osteoblast number/activity and increased osteoclast number/activity; siRNA-mediated CTSD inactivation in osteoblasts (MC3T3E1) attenuates osteoblastic differentiation and decreases LC3B and P62 expression, while inactivation in osteoclasts (RAW264.7) increases osteoclast differentiation with decreased LC3B but upregulated P62, demonstrating that CTSD mediates autophagy through distinct mechanisms in osteoblasts versus osteoclasts.\",\n      \"method\": \"CtsD conditional KO mice, microCT, histomorphometry, siRNA knockdown in MC3T3E1 and RAW264.7 cells, LC3B and P62 expression, differentiation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, genetic KO with cellular mechanistic follow-up, single lab, cell-type-specific distinction is novel\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"miR-214-3p directly targets CTSD (validated by luciferase assay); overexpression of CTSD reverses the protective effects of miR-214-3p mimic on lysosomal acidification and LAMP1 levels in porcine intestinal epithelial cells, establishing CTSD as a direct functional target of miR-214-3p in regulating lysosomal homeostasis.\",\n      \"method\": \"Luciferase reporter assay for miR-214-3p/CTSD interaction, CTSD overexpression rescue, lysosomal acidification measurement, LAMP1 expression, cell viability assays in IPEC-J2 cells\",\n      \"journal\": \"Biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — luciferase validation plus functional rescue, single lab, non-human cellular model\",\n      \"pmids\": [\"42117833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"N-glycosylation of CTSD at residue N258 (CTSD-N258A mutant) promotes lysosomal localization of CTSD and affects lysosomal membrane permeability and apoptosis in BMSCs; the N258A mutant reduces CTSD levels in cytoplasm and lysosomes and inhibits BMSC apoptosis in a dexamethasone-induced model.\",\n      \"method\": \"CTSD N258A site-directed mutagenesis, flow cytometry for apoptosis, confocal microscopy for lysosomal colocalization, AO staining for lysosomal membrane permeability, Western blot for apoptosis-related proteins\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single mutagenesis study with functional readouts, single lab, abstract-level description\",\n      \"pmids\": [\"41931502\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CTSD (cathepsin D) is a lysosomal aspartic protease that is synthesized as a pro-enzyme, secreted extracellularly as pro-CTSD (where it can act as a ligand to promote cell proliferation), or retained intracellularly and matured to its active form through autophagy-dependent and post-translational modification-dependent mechanisms (including N-glycosylation, O-GlcNAcylation, and H2S-dependent S-sulfhydration of pro-CTSD) to perform proteolytic functions; inside lysosomes, mature CTSD maintains proteostasis by degrading substrates including SNCA/α-synuclein, HSP90α, and ACADM, sustains autophagic flux by enabling autophagosome-lysosome fusion, and is transcriptionally regulated via ERα-mediated chromatin looping to a distal enhancer; loss of CTSD enzymatic activity causes lysosomal storage disorder (CLN10/neuronal ceroid lipofuscinosis), while circulatory pro-CTSD can bind the Cluster II domain of endothelial LRP1 to trigger its lysosomal degradation and impair brain Aβ clearance, and in macrophages CTSD secretion is regulated by STT3A-dependent N-glycosylation downstream of the KIF13B/mTOR-MITF axis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CTSD (cathepsin D) is a lysosomal aspartic protease that maintains neuronal and cellular proteostasis and autophagic flux by degrading substrates in the lysosome [#1, #4]. It is synthesized as an inactive pro-enzyme that is matured to its catalytically active form, and this maturation is the decisive step controlling its function: missense mutations that specifically reduce catalytic activity (Met199Ile; Ser100Phe) — without altering protein stability or other lysosomal enzyme activities — cause neuronal ceroid lipofuscinosis (CLN10), establishing that enzymatic activity, not protein abundance, is required to prevent lysosomal storage pathology [#2, #15]. Mature CTSD sustains autophagy by enabling autophagosome–lysosome fusion, and its loss causes lysosomal dysfunction and impaired autophagic degradation [#1, #6]. Among its substrates, CTSD is the major lysosomal protease degrading SNCA/α-synuclein, and recombinant pro-CTSD delivered via mannose-6-phosphate receptor-mediated endocytosis is correctly trafficked to lysosomes, matured, and restores defective proteolysis and autophagic flux in CTSD-deficient disease models, reducing insoluble α-synuclein conformers in patient-derived neurons and ctsd-deficient mouse brains [#3, #4]. Its maturation and trafficking are governed by post-translational modifications — N-glycosylation (controlling secretion of pro-CTSD versus intracellular retention, and protease activity), O-GlcNAcylation, and H2S-dependent S-sulfhydration of pro-CTSD — which collectively partition CTSD between an intracellular pro-apoptotic/proteostatic role and a secreted extracellular pool [#0, #7, #8, #12]. CTSD transcription is induced by estrogen receptor alpha through chromatin looping to a distal enhancer 9 kb upstream of its start site [#5], and it is suppressed downstream of an mTOR–MITF axis in macrophages [#11]. Beyond the lysosome, secreted or circulatory pro-CTSD acts in trans: it binds the Cluster II domain of endothelial LRP1 to trigger LRP1 lysosomal degradation and impair brain Aβ clearance [#13], and engages LRP6 to mediate degradation of HSP90α in cardiomyocytes [#10]. Loss of CTSD enzymatic activity causes CLN10/neuronal ceroid lipofuscinosis [#2, #15].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that it is CTSD catalytic activity specifically — not general lysosomal enzyme deficiency — that prevents neuronal ceroid lipofuscinosis, defining CTSD as a disease gene through its enzymatic function.\",\n      \"evidence\": \"Enzyme-specific activity assays comparing CTSD to 15 other lysosomal enzymes plus genetic linkage in Met199Ile American Bulldogs\",\n      \"pmids\": [\"16386934\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the physiological substrates whose accumulation drives NCL pathology\", \"Canine model; human variant spectrum addressed separately\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Distinguished catalytic activity from protein stability as the critical determinant, showing a stable, normally processed CTSD protein with marginal activity still causes congenital CLN10.\",\n      \"evidence\": \"Enzymatic activity assay and processing/stability analysis in patient fibroblasts carrying p.Ser100Phe, with overexpression studies\",\n      \"pmids\": [\"18762956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking marginal activity to congenital lethality not resolved\", \"Single patient genotype\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined how CTSD is transcriptionally controlled, identifying ERα-driven induction via long-range chromatin looping to a distal enhancer.\",\n      \"evidence\": \"ChIP for ERα and phospho-Pol II, bisulfite sequencing, and chromatin looping assays in MCF-7 cells\",\n      \"pmids\": [\"19383337\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of transient CpG methylation not established\", \"Restricted to one breast cancer cell line\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the localization-versus-function switch, showing autophagy drives intracellular CTSD maturation toward apoptosis while N233 glycosylation routes pro-CTSD to secretion for proliferative signaling.\",\n      \"evidence\": \"RNAi, autophagy modulation, PNGase F glycosylation assay, and caspase-3 activity in an insect (Helicoverpa armigera) model\",\n      \"pmids\": [\"32324083\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Demonstrated in an insect model; mammalian generality not shown here\", \"Glycosite numbering and mechanism differ across mammalian studies\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established CTSD as causally required for neuronal lysosomal homeostasis and autophagic flux, with knockdown sufficient to cause dysfunction and rescue restoring viability.\",\n      \"evidence\": \"shRNA knockdown plus lentiviral rescue with lysosomal and cell-death assays in mouse cortical neurons and an MCAO stroke model; siRNA/pepstatin A blocking autophagosome-lysosome fusion in glioblastoma\",\n      \"pmids\": [\"32450052\", \"32253787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular step at which CTSD enables fusion not defined\", \"Substrate(s) mediating the fusion phenotype unidentified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified α-synuclein as a key CTSD substrate and demonstrated therapeutic enzyme reconstitution, showing recombinant pro-CTSD reduces insoluble SNCA in human and murine neuronal models.\",\n      \"evidence\": \"rHsCTSD uptake/lysosomal targeting, SNCA solubility fractionation, A53T PD iPSC neurons, ctsd-knockout mice; earlier CLN10 reconstitution work established M6P-receptor uptake and autophagy rescue\",\n      \"pmids\": [\"35287553\", \"31282275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cleavage sites and kinetics on SNCA not fully mapped\", \"Long-term in vivo efficacy and delivery not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined N-glycosylation as a regulator of CTSD protease activity and downstream substrate processing, linking glycosylated CTSD to ACADM cleavage and ferroptosis-related signaling in cancer.\",\n      \"evidence\": \"N-glycoproteomics, N263 site-directed mutagenesis, DDOST/STT3B manipulation, and ferroptosis-marker assays in colorectal cancer cells\",\n      \"pmids\": [\"39716927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between distinct reported glycosites (N233/N258/N263) unresolved\", \"Single cancer-cell context\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended PTM control of CTSD maturation to O-GlcNAcylation, showing reduced O-GlcNAcylation impairs maturation and autophagic degradation.\",\n      \"evidence\": \"IP, mature/pro CTSD Western blots, and OGT/OGA inhibitor (OSMI/TMG) modulation with lysosomal function assays\",\n      \"pmids\": [\"37442287\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct O-GlcNAc site on CTSD not mapped\", \"Whether effect is direct or via trafficking machinery unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed CTSD downstream of microRNA and epigenetic control, showing GR/H3K9ac-driven miR-1912-3p suppresses CTSD to inhibit chondrocyte autophagic flux, reversible by CTSD overexpression.\",\n      \"evidence\": \"miR target validation, H3K9ac ChIP, CTSD overexpression rescue, and autophagic flux assays in vitro and in a PDE rat model; complementary miR-214-3p targeting validated in porcine intestinal epithelial cells\",\n      \"pmids\": [\"37249374\", \"42117833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological contexts where each miRNA dominates not defined\", \"miR-214-3p evidence is Low-confidence, non-human\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected CTSD to upstream signaling controlling its expression, placing it downstream of an mTOR-MITF axis in macrophage lysosomal homeostasis.\",\n      \"evidence\": \"Myeloid-specific SAMHD1-KO mice, scRNA-seq, rapamycin treatment, and MITF nuclear translocation/CTSD expression assays\",\n      \"pmids\": [\"40886983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MITF binds the CTSD locus directly not shown\", \"Single disease context\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified an extracellular/trans CTSD function in cardiomyocytes, where LRP6 facilitates CTSD-mediated HSP90α degradation to limit β-catenin-driven hypertrophy.\",\n      \"evidence\": \"MS co-IP, cardiomyocyte LRP6 overexpression mice, TAC model, pepstatin A inhibition, and recombinant HSP90α rescue\",\n      \"pmids\": [\"39779966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CTSD cleavage of HSP90α versus indirect effect not fully separated\", \"Subcellular compartment of the degradation event unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established H2S-dependent S-sulfhydration of pro-CTSD as a maturation brake, with loss of sulfhydration promoting active CTSD that drives PANoptosis after TBI.\",\n      \"evidence\": \"AAV-shSnapin knockdown, Snapin-CBS co-IP, biotin switch S-sulfhydration assay, H2S measurement, and pepstatin A/NaHS rescue with behavioral tests\",\n      \"pmids\": [\"41558604\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sulfhydrated cysteine residue on pro-CTSD not mapped\", \"Single injury model\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined a pathogenic trans action of circulatory pro-CTSD, showing it binds the LRP1 Cluster II domain to trigger LRP1 degradation and impair brain Aβ clearance.\",\n      \"evidence\": \"Western blot, domain-specific binding assay, transgenic mice with high circulatory pro-CTSD, and confocal/TIRF imaging of internalization in Alzheimer's models\",\n      \"pmids\": [\"42162956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether pro-CTSD enzymatic activity is required for LRP1 degradation not resolved\", \"Source of elevated circulatory pro-CTSD in disease unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Linked macrophage CTSD secretion to a glycosylation-trafficking circuit, showing KIF13B loss stabilizes STT3A to enhance CTSD glycosylation and secretion, promoting hepatocyte lipid accumulation via THBS1.\",\n      \"evidence\": \"Myeloid-specific Kif13b-KO mice, MASLD model, STT3A degradation assays, and CTSD-THBS1 interaction analysis\",\n      \"pmids\": [\"41746601\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CTSD acts as protease or ligand on hepatocytes not separated\", \"Direct CTSD-THBS1 binding interface not mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct N-glycosites (N233/N258/N263), O-GlcNAcylation, and S-sulfhydration are integrated to set the balance between intracellular maturation, secretion, and substrate selectivity remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model reconciling the multiple reported glycosites and PTMs\", \"Structural basis of pro-CTSD maturation control not defined\", \"Quantitative partitioning between lysosomal and secreted pools across cell types unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [2, 4, 15]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 7, 10]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 3, 4]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 13, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [1, 6, 8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 7, 10]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 4, 13, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"LRP1\", \"LRP6\", \"HSP90A1\", \"ACADM\", \"SNCA\", \"THBS1\", \"STT3A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}