{"gene":"HTRA1","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2006,"finding":"A promoter SNP (rs11200638) in HTRA1 is associated with elevated HTRA1 mRNA and protein expression in lymphocytes and retinal pigment epithelium from AMD patients, and HTRA1 protein was found in drusen of AMD patient eyes, implicating increased HTRA1 secreted serine protease activity in AMD pathogenesis.","method":"SNP genotyping, expression analysis of patient-derived lymphocytes and RPE, immunolabeling of drusen","journal":"Science","confidence":"Medium","confidence_rationale":"Tier 2 — patient tissue expression and immunolabeling, single study, no direct in vitro mechanistic reconstitution","pmids":["17053109"],"is_preprint":false},{"year":2009,"finding":"Loss-of-function mutations in HTRA1 (nonsense and missense) cause CARASIL; mutant HTRA1 proteins show reduced protease activity and fail to repress TGF-β family signaling, establishing HTRA1 as a repressor of TGF-β signaling in cerebral small vessel homeostasis.","method":"Linkage analysis, sequencing, functional protease activity assays (casein), TGF-β signaling assays, immunohistochemistry of patient cerebral arteries","journal":"New England Journal of Medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (protease assay, signaling assay, patient tissue), replicated across five families","pmids":["19387015"],"is_preprint":false},{"year":2005,"finding":"HTRA1 directly degrades fragments of amyloid precursor protein (APP) in vitro, and an HTRA1 inhibitor causes accumulation of Aβ in astrocyte cell culture supernatants; HTRA1 colocalizes with β-amyloid deposits in human brain.","method":"In vitro protease assay with APP fragments, cell culture inhibitor experiment, immunohistochemistry of human brain","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro activity and cell culture with inhibitor, single lab","pmids":["15855271"],"is_preprint":false},{"year":2005,"finding":"HTRA1 cleaves fibronectin in synovial fluid, generating fibronectin degradation products that induce MMP-1 and MMP-3 expression in synovial fibroblasts, implicating HTRA1 in both direct and indirect ECM destruction in arthritis.","method":"Mass spectrometry identification of substrates in synovial fluid, recombinant HTRA1 cleavage assay with fibronectin, fibroblast treatment with HTRA1 or HTRA1-generated fibronectin fragments, MMP expression assay","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstituted cleavage, functional downstream readout (MMP induction), multiple orthogonal methods in single study","pmids":["16377621"],"is_preprint":false},{"year":2007,"finding":"The PDZ domains of human HtrA1 recognize hydrophobic polypeptides (preferring C-terminal sequences but also internal sequences), and peptide binding to the PDZ domain induces conformational changes that activate the protease domain, supporting an allosteric activation mechanism.","method":"Peptide library screening, affinity assays, crystal structure of PDZ domain-ligand complexes, alanine scanning mutagenesis","journal":"Protein Science","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with mutagenesis and binding assays, rigorous mechanistic dissection","pmids":["17962403"],"is_preprint":false},{"year":2007,"finding":"HTRA1 inhibits osteoblast mineralization in a manner requiring both its protease domain and PDZ domain; it cleaves recombinant decorin, fibronectin, and matrix Gla protein (MGP), with MGP cleavage requiring both domains while decorin/fibronectin cleavage requires only the protease domain.","method":"Overexpression and siRNA knockdown in 2T3 osteoblasts, recombinant HTRA1 domain deletion constructs, in vitro cleavage assays of ECM substrates","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution with domain mutants plus loss- and gain-of-function cellular experiments","pmids":["18156628"],"is_preprint":false},{"year":2012,"finding":"Human HTRA1 degrades aggregated and fibrillar tau in vitro and in cells; HTRA1 mRNA and activity are upregulated in response to elevated tau concentrations, and neuronal cells/patient brains accumulate less tau and neurofibrillary tangles when HTRA1 is expressed at elevated levels.","method":"In vitro protease assay with tau aggregates/fibrils, overexpression in neuronal cell lines, immunohistochemistry of patient brains, RT-PCR of HTRA1 mRNA","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution plus cellular and patient-tissue evidence from single study","pmids":["22535953"],"is_preprint":false},{"year":2012,"finding":"Crystal structures and SAXS analysis of HtrA1 reveal an N-terminal IGFBP/Kazal tandem domain, a protease active site in a competent conformation in the absence of substrate, and a trimeric arrangement; neither IGFBP- nor Kazal-like modules retain prototype protein function, and the active site data support a conformational selection model for substrate binding.","method":"X-ray crystallography, SAXS, enzymatic activity assays, binding studies with domain deletion constructs","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with functional assays and SAXS in a single comprehensive study","pmids":["22578544"],"is_preprint":false},{"year":2015,"finding":"HTRA1 degrades amyloid fibrils in an ATP-independent manner by solubilizing fibrils, disintegrating the fibrillar core, and allowing productive interaction of aggregated polypeptides with its active site; this activity reduces aggregate burden in a cellular model of cytoplasmic tau aggregation.","method":"In vitro fibril disaggregation assays, structural analysis, cellular tau aggregation model","journal":"Nature Chemical Biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mechanistic dissection and cellular validation","pmids":["26436840"],"is_preprint":false},{"year":2016,"finding":"HTRA1 missense mutations found in manifesting heterozygotes with CARASIL-like disease show markedly decreased protease activity and inhibit wild-type HTRA1 activity (dominant-negative effect); these mutants either fail to form trimers or carry mutations in domains critical for trimer-associated activation, whereas CARASIL-associated mutants do form trimers but have mutations outside activation domains.","method":"Casein protease activity assays, gel filtration chromatography for oligomeric state analysis, HTRA1 co-incubation experiments","journal":"Neurology","confidence":"High","confidence_rationale":"Tier 1-2 — protease assays and gel filtration with multiple mutants, mechanistic model supported by orthogonal approaches","pmids":["27164673"],"is_preprint":false},{"year":2018,"finding":"HTRA1 cleaves the Notch ligand JAG1 within its intracellular domain, leading to JAG1 protein degradation; HTRA1 physically interacts with JAG1, thereby enhancing Delta/Notch signaling. Loss of HTRA1 in endothelial cells increases JAG1 and promotes hypersprouting angiogenesis, and HtrA1-deficient mice have diminished endothelial Notch signaling and denser, immature tumor vasculature.","method":"Co-immunoprecipitation, in vitro cleavage assay, siRNA knockdown and overexpression in endothelial cells, HtrA1-/- mouse tumor model, rescue with constitutively active Notch1","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 — physical interaction shown by Co-IP, in vitro cleavage, in vivo mouse KO with clear vascular phenotype, rescued by Notch activation","pmids":["29713059"],"is_preprint":false},{"year":2018,"finding":"HTRA1 cleaves extracellular matrix proteins EFEMP1 and TSP1 (novel substrates), in addition to previously known substrates LTBP-1 and clusterin, in RPE cells with the AMD high-risk genotype.","method":"Proteomic comparison of RPE cells with/without AMD high-risk mutation, identification of HTRA1 cleavage targets by proteomics","journal":"Aging Cell","confidence":"Medium","confidence_rationale":"Tier 2-3 — proteomic identification of cleavage targets in disease-relevant cells, single lab, limited in vitro reconstitution","pmids":["29730901"],"is_preprint":false},{"year":2018,"finding":"HTRA1 is sequestered by Notch3 extracellular domain (Notch3ECD) deposits in CADASIL brain vessels, and the CADASIL brain vessel proteome shows enrichment of known HTRA1 substrates consistent with reduced HTRA1 activity; multiple HTRA1 substrates were validated in an in vitro proteolysis assay, linking CADASIL pathology to functional HTRA1 loss.","method":"Quantitative brain vessel proteomics from CADASIL patients vs. controls, comparison with HtrA1 knockout mouse proteome, in vitro proteolysis assay","journal":"Acta Neuropathologica","confidence":"High","confidence_rationale":"Tier 1-2 — quantitative proteomics with independent KO mouse comparison and in vitro substrate validation","pmids":["29725820"],"is_preprint":false},{"year":2019,"finding":"HTRA1 is essential for vascular smooth muscle cell (VSMC) differentiation into the contractile phenotype; loss of HTRA1 increases JAG1 protein and NOTCH3 signaling and enhances TGF-β-SMAD2/3 signaling, leading to additive accumulation of HES/HEY repressors that suppress contractile VSMC marker genes and impair arterial vasoconstriction in Htra1-/- mice.","method":"Htra1-/- mouse model, VSMC differentiation assays, Western blot for JAG1/Notch3/TGFβ pathway, gene expression analysis, vasoconstriction functional assay","journal":"Scientific Reports","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with multiple pathway readouts and functional vasoconstriction phenotype","pmids":["31796853"],"is_preprint":false},{"year":2019,"finding":"Osteoclasts secrete HTRA1, which degrades osteoprotegerin (OPG); HTRA1 recognizes the three-dimensional structure of OPG and initially cleaves the amide bond between Leu90 and Gln91, then degrades OPG into small fragments, thereby suppressing OPG inhibition of RANKL-induced osteoclastogenesis.","method":"Mass spectrometry identification of OPG-degrading enzyme, in vitro cleavage assay with recombinant HTRA1 and OPG, mapping of cleavage site, DTT-reduction experiment, RAW 264.7 osteoclastogenesis assay","journal":"Communications Biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution with cleavage site mapping and functional osteoclastogenesis assay","pmids":["30854478"],"is_preprint":false},{"year":2015,"finding":"An anti-HtrA1 antibody forms a cage-like macromolecular complex with the HtrA1 catalytic domain trimer; three IgG molecules coordinate two HtrA1 trimers in a 636-kDa cage with six active sites pointing inward, achieving complete inhibition of enzyme activity through an allosteric mechanism involving surface-exposed loops B and C of the catalytic domain.","method":"Negative-stain EM, biochemical complex characterization, epitope mapping, enzymatic activity assays","journal":"Biochemical Journal","confidence":"High","confidence_rationale":"Tier 1 — EM structure with biochemical validation of inhibition mechanism","pmids":["26385991"],"is_preprint":false},{"year":2011,"finding":"Transgenic expression of human HTRA1 in mouse retinal pigment epithelium is sufficient to cause polypoidal choroidal vasculopathy (PCV), including branching choroidal vessel networks, polypoidal lesions, elastic laminae degeneration, tunica media degeneration, RPE atrophy, and photoreceptor degeneration; senescent HTRA1 transgenic mice develop occult CNV with upregulated VEGF.","method":"Transgenic mouse model with human HTRA1 expressed in RPE, fundus imaging, histology, immunohistochemistry, VEGF measurement","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — transgenic overexpression in vivo with multiple phenotypic readouts replicated across aging timepoints","pmids":["21844367"],"is_preprint":false},{"year":2006,"finding":"HtrA1 expression is upregulated by cisplatin and paclitaxel treatment, resulting in limited autoproteolysis and activation of HtrA1; active HtrA1 induces cell death in a serine protease-dependent manner, and downregulation of HtrA1 attenuates chemotherapy-induced cytotoxicity while forced expression enhances it.","method":"Forced expression and knockdown of HtrA1 in ovarian cancer cell lines, cell viability assays with cisplatin/paclitaxel, autoproteolysis analysis, protease-dead mutant (SA) controls","journal":"Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal gain/loss of function with protease-dead SA mutant control establishing serine protease dependence","pmids":["16767218"],"is_preprint":false},{"year":2012,"finding":"MiR-30e and miR-181d are posttranscriptional negative regulators of HTRA1 by binding to the 3' UTR of HTRA1 mRNA; in vivo overexpression of these miRNAs in Dicer-/- forebrain rescued radial glia proliferation defects caused by HTRA1 overexpression.","method":"Dicer conditional KO mouse, in vivo miRNA overexpression, luciferase reporter assay with HTRA1 3'UTR, rescue experiments","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 — 3'UTR reporter combined with in vivo rescue, single study","pmids":["22854828"],"is_preprint":false},{"year":2017,"finding":"HTRA1 inhibits canonical Wnt/β-catenin signaling in both paracrine and autocrine manners; HTRA1 forms a complex with β-catenin and reduces cell proliferation rates, and affects expression of several Wnt target genes.","method":"Wnt reporter assays, co-immunoprecipitation of HTRA1 with β-catenin, HTRA1 overexpression in colorectal cancer cells, cell proliferation assays","journal":"Scientific Reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP with functional reporter and proliferation assays, single lab","pmids":["29269789"],"is_preprint":false},{"year":2013,"finding":"TLR-4 activation by LPS induces HTRA1 expression through the NF-κB pathway; the NF-κB subunit p65 directly binds to the HTRA1 promoter at position -347, as demonstrated by dual-luciferase reporter and ChIP assays.","method":"Real-time PCR, ELISA, NF-κB inhibitors, siRNA, dual-luciferase reporter, chromatin immunoprecipitation (ChIP)","journal":"Arthritis and Rheumatism","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (reporter + ChIP) in single study","pmids":["23982886"],"is_preprint":false},{"year":2014,"finding":"IFN-γ inhibits HTRA1 expression through activation of p38 MAPK/STAT1 pathway; STAT1 directly binds to the HTRA1 promoter after IFN-γ stimulation, as shown by dual-luciferase reporter and ChIP assays.","method":"Real-time PCR, Western blot, CIA mouse model with IFN-γ KO, dual-luciferase reporter, ChIP","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — reporter plus ChIP plus in vivo mouse model, single lab","pmids":["24907345"],"is_preprint":false},{"year":2014,"finding":"HtrA1 is required for normal placentation in mice; HtrA1-/- mice show intrauterine growth retardation with small placentas due to reduced junctional zone and aberrant labyrinth vascularization, caused by decreased differentiation of Tpbpa-positive trophoblast precursors, fewer spiral artery-associated trophoblast giant cells, and impaired maternal artery remodeling.","method":"HtrA1-/- mouse model, histology, immunostaining for trophoblast markers, morphometric analysis of maternal arteries","journal":"Developmental Biology","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with multiple defined cellular phenotypes and mechanistic pathway placement","pmids":["25446274"],"is_preprint":false},{"year":2021,"finding":"Rare loss-of-function variants in the HTRA1 protease domain (amino acids 204-364) associate with increased white matter hyperintensity volume; most identified protease domain variants result in markedly reduced protease activity in biochemical assays; EGFL8 was identified as a direct substrate of HTRA1.","method":"Whole-exome sequencing gene burden tests, domain-specific burden analysis, in vitro protease activity assays of individual variants, substrate identification","journal":"Brain","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro biochemical activity assays for multiple variants plus genetic burden analysis, novel substrate identification","pmids":["34626176"],"is_preprint":false},{"year":2024,"finding":"HTRA1 inhibits aggregation of α-synuclein, FUS, and TDP-43; the protease domain of HTRA1 is necessary and sufficient for this activity but the activity is proteolysis-independent. HTRA1 disaggregates preformed α-syn fibrils, rendering them seeding-incompetent, by targeting the NAC domain of α-syn. Reducing HTRA1 expression promotes α-syn seeding, and HTRA1 detoxifies α-syn fibrils and prevents hyperphosphorylated α-syn accumulation in primary neurons.","method":"In vitro aggregation inhibition and fibril disaggregation assays, protease-dead mutant and domain deletion constructs, α-syn seeding assays, primary neuron toxicity assays, HTRA1 knockdown","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 1 — multiple in vitro reconstitution experiments with domain mutants, cellular seeding assays, and neuronal toxicity readout","pmids":["38499535"],"is_preprint":false},{"year":2016,"finding":"HTRA1 is epigenetically silenced in HCT116 colon carcinoma cells via the epigenetic adaptor protein MBD2; depletion of HTRA1 causes centrosome amplification and polyploidy in colon cancer cells and primary mouse embryonic fibroblasts.","method":"Epigenetic analysis in cancer cell lines, MBD2 involvement demonstrated, HTRA1 siRNA knockdown with centrosome and ploidy analysis","journal":"BMC Cancer","confidence":"Medium","confidence_rationale":"Tier 2-3 — epigenetic mechanism identified with functional cellular phenotype, single lab","pmids":["27388476"],"is_preprint":false},{"year":2020,"finding":"RUNX2 co-operates with EGR1 to transcriptionally repress HTRA1 through Htra1 enhancers; RUNX2 and EGR1 physically co-occupy seven verified HTRA1 enhancers as shown by Re-ChIP assay, and their combined action represses HTRA1 expression while promoting osteoblast differentiation markers.","method":"ChIP-seq, RNA-seq, dual-luciferase enhancer assays, Re-ChIP, siRNA knockdown, alizarin red and ALP staining","journal":"Journal of Cellular Physiology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq with reporter and Re-ChIP validation, single lab","pmids":["32324256"],"is_preprint":false}],"current_model":"HTRA1 is a secreted homotrimeric serine protease whose PDZ domain senses exposed hydrophobic peptides to allosterically activate its trypsin-like catalytic domain; it degrades a broad range of extracellular matrix proteins (fibronectin, decorin, MGP, LTBP-1, EFEMP1, TSP1, OPG, EGFL8, JAG1) and protein aggregates (tau fibrils, α-synuclein fibrils, APP fragments), represses TGF-β/BMP and canonical Wnt signaling, cleaves JAG1 to enhance Notch signaling in endothelial cells, and is transcriptionally regulated by NF-κB (via LPS/TLR4) and repressed by IFN-γ/STAT1, RUNX2/EGR1, and miR-30e/miR-181d; loss-of-function causes cerebral small vessel disease (CARASIL/CADASIL-like) and impaired vascular smooth muscle maturation, while overexpression drives AMD-related choroidal neovascularization and RPE senescence through ECM degradation and HIF-1 signaling."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing HTRA1 as an ECM-degrading and APP-processing extracellular protease resolved the question of what substrates this secreted serine protease acts on, revealing roles in both matrix turnover and amyloid clearance.","evidence":"In vitro cleavage assays with fibronectin and APP fragments, mass spectrometry of synovial fluid substrates, cell culture inhibitor experiments, and downstream MMP induction readouts","pmids":["15855271","16377621"],"confidence":"High","gaps":["Full substrate repertoire in vivo undefined","Cleavage site specificity rules not determined","In vivo relevance of APP degradation not established"]},{"year":2006,"claim":"Linking the HTRA1 promoter variant rs11200638 to AMD and detecting HTRA1 in drusen provided the first evidence that elevated HTRA1 protease activity contributes to retinal disease, while showing that HTRA1 upregulation promotes chemotherapy-induced cell death established a pro-apoptotic role for the active protease.","evidence":"SNP genotyping with expression analysis in patient lymphocytes/RPE and drusen immunolabeling; forced expression/knockdown in ovarian cancer cells with protease-dead controls","pmids":["17053109","16767218"],"confidence":"High","gaps":["Causal mechanism linking HTRA1 overexpression to drusen formation not defined","Apoptotic substrate(s) mediating cell death not identified"]},{"year":2007,"claim":"Structural and biochemical dissection of the PDZ domain revealed an allosteric activation mechanism whereby hydrophobic peptide binding to the PDZ domain induces conformational changes that activate the protease, and showed that substrate-specific cleavage (e.g., MGP) can require both the PDZ and protease domains.","evidence":"Crystal structures of PDZ–ligand complexes, peptide library screening, alanine scanning mutagenesis, domain-deletion cleavage assays with decorin/fibronectin/MGP","pmids":["17962403","18156628"],"confidence":"High","gaps":["Full-length trimer structure with PDZ-protease allosteric interface not resolved","Which in vivo substrates require PDZ-dependent activation unknown"]},{"year":2009,"claim":"Identifying loss-of-function HTRA1 mutations as the genetic cause of CARASIL, with mutant proteins showing defective protease activity and failure to repress TGF-β signaling, established HTRA1 as a non-redundant vascular protease and TGF-β pathway repressor.","evidence":"Linkage analysis across five families, sequencing, casein protease assays, TGF-β signaling assays, immunohistochemistry of patient cerebral arteries","pmids":["19387015"],"confidence":"High","gaps":["Molecular mechanism of TGF-β repression (direct substrate vs indirect) not resolved","Whether other HtrA family members compensate partially unknown"]},{"year":2011,"claim":"Transgenic HTRA1 overexpression in mouse RPE was sufficient to cause polypoidal choroidal vasculopathy and choroidal neovascularization with VEGF upregulation, providing causal in vivo evidence that excess HTRA1 drives AMD-related vascular pathology.","evidence":"Transgenic mouse model with RPE-directed human HTRA1 expression, fundus imaging, histology, VEGF measurement","pmids":["21844367"],"confidence":"High","gaps":["Which HTRA1 substrates mediate the choroidal vascular phenotype not identified","Relationship between ECM degradation and VEGF induction not mechanistically defined"]},{"year":2012,"claim":"Demonstrating that HTRA1 degrades tau aggregates and fibrils, combined with crystal structures revealing a constitutively competent trimeric protease domain, established HTRA1 as an ATP-independent protein disaggregase and clarified the structural basis of its active-site accessibility.","evidence":"In vitro tau fibril degradation, neuronal cell overexpression, patient brain immunohistochemistry; X-ray crystallography and SAXS of full-length HTRA1 trimer","pmids":["22535953","22578544"],"confidence":"High","gaps":["How the trimer engages fibrillar vs. soluble substrates structurally not resolved","In vivo contribution to tauopathy clearance not tested in animal models"]},{"year":2012,"claim":"Identifying miR-30e and miR-181d as post-transcriptional repressors of HTRA1 via its 3′ UTR, with in vivo rescue of radial glia proliferation defects, revealed a layer of miRNA-mediated HTRA1 regulation relevant to neural progenitor biology.","evidence":"Luciferase reporter assays with HTRA1 3′ UTR, miRNA overexpression in Dicer-KO mouse forebrain, phenotypic rescue","pmids":["22854828"],"confidence":"Medium","gaps":["Physiological contexts in which miR-30e/miR-181d regulate HTRA1 beyond developing brain not explored","Quantitative impact on HTRA1 protein levels in adult tissues unknown"]},{"year":2013,"claim":"Showing that NF-κB p65 directly binds the HTRA1 promoter upon TLR4/LPS stimulation, and that IFN-γ/STAT1 directly represses HTRA1 transcription, defined the inflammatory transcriptional logic governing HTRA1 expression.","evidence":"ChIP assays, dual-luciferase reporters, NF-κB/STAT1 inhibitors and siRNA, IFN-γ KO mouse model","pmids":["23982886","24907345"],"confidence":"Medium","gaps":["Combinatorial regulation by NF-κB and STAT1 under concurrent inflammatory signals not tested","Chromatin context and epigenetic modifiers at the HTRA1 locus not comprehensively mapped"]},{"year":2015,"claim":"Mechanistic dissection of HTRA1's fibril-disaggregase activity showed ATP-independent solubilization of the fibrillar core, distinguishing HTRA1 from canonical chaperone-disaggregases; structural characterization of an inhibitory antibody-HTRA1 cage complex revealed allosteric inhibition via surface loops B and C.","evidence":"In vitro fibril disaggregation kinetics, cellular tau aggregation models; negative-stain EM of antibody–HTRA1 complex, epitope mapping","pmids":["26436840","26385991"],"confidence":"High","gaps":["Structural basis of fibril recognition at atomic resolution not determined","Whether loops B and C are involved in substrate engagement or purely allosteric sites unclear"]},{"year":2016,"claim":"Discovery that heterozygous HTRA1 mutations cause dominant CADASIL-like disease through dominant-negative disruption of the trimer, as distinct from recessive CARASIL mutations that preserve trimer formation, established trimer integrity as a critical determinant of disease mechanism.","evidence":"Casein protease activity assays with WT/mutant co-incubation, gel filtration chromatography for oligomeric state","pmids":["27164673"],"confidence":"High","gaps":["Structural basis for dominant-negative disruption not resolved at atomic level","Whether heterozygous carriers have graded substrate-specific deficits unknown"]},{"year":2018,"claim":"Identifying JAG1 as an HTRA1 substrate demonstrated that HTRA1 promotes Notch signaling by degrading the Notch ligand JAG1, with loss of HTRA1 causing hypersprouting angiogenesis in vitro and immature tumor vasculature in vivo; HTRA1 sequestration by Notch3ECD in CADASIL vessels linked two cerebral small vessel diseases to a common HTRA1-deficiency mechanism.","evidence":"Co-IP, in vitro cleavage assays, endothelial siRNA/overexpression, HtrA1-KO mouse tumor model with Notch1 rescue; quantitative brain vessel proteomics in CADASIL vs. controls and HtrA1-KO mice","pmids":["29713059","29725820"],"confidence":"High","gaps":["Whether HTRA1 cleaves JAG1 extracellularly or intracellularly in vivo not definitively resolved","Full overlap of HTRA1-dependent proteome between CARASIL and CADASIL not characterized"]},{"year":2019,"claim":"Defining HTRA1's role in VSMC differentiation and its cleavage of osteoprotegerin expanded the functional repertoire to include smooth muscle maturation via combined Notch3/TGF-β modulation and bone remodeling through OPG degradation.","evidence":"HtrA1-KO mouse VSMC phenotyping with vasoconstriction assays, JAG1/Notch3/TGF-β pathway Western blots; in vitro OPG cleavage site mapping by mass spectrometry, osteoclastogenesis assays","pmids":["31796853","30854478"],"confidence":"High","gaps":["Relative contribution of Notch vs. TGF-β arm to VSMC maturation defect not dissected","In vivo bone phenotype of HTRA1-KO not reported"]},{"year":2020,"claim":"Demonstration that RUNX2 and EGR1 co-occupy HTRA1 enhancers to repress transcription during osteoblast differentiation added a developmental transcription factor circuit to the regulatory landscape of HTRA1.","evidence":"ChIP-seq, Re-ChIP, dual-luciferase enhancer assays, siRNA knockdown with osteoblast differentiation readouts","pmids":["32324256"],"confidence":"Medium","gaps":["Whether RUNX2/EGR1 repression operates in non-skeletal HTRA1-expressing tissues unknown","Enhancer–promoter looping mechanism not resolved"]},{"year":2021,"claim":"Gene burden analysis linking rare HTRA1 protease-domain variants to white matter hyperintensity volume, with biochemical validation of reduced activity for individual variants and identification of EGFL8 as a novel substrate, extended the genotype–phenotype spectrum beyond Mendelian CARASIL.","evidence":"Whole-exome sequencing burden tests, domain-specific analysis, in vitro protease activity assays for multiple variants, substrate identification","pmids":["34626176"],"confidence":"High","gaps":["Functional role of EGFL8 cleavage in vascular biology not established","Threshold of HTRA1 activity loss required for clinical phenotype unknown"]},{"year":2024,"claim":"Showing that HTRA1 disaggregates α-synuclein fibrils and inhibits aggregation of α-synuclein, FUS, and TDP-43 through a proteolysis-independent mechanism residing in the protease domain established HTRA1 as a dual-function protein: a protease for soluble substrates and a holdase/disaggregase for amyloid aggregates.","evidence":"In vitro aggregation inhibition and fibril disaggregation with protease-dead mutants and domain deletions, α-syn seeding assays, primary neuron toxicity assays, HTRA1 knockdown","pmids":["38499535"],"confidence":"High","gaps":["Structural basis of the proteolysis-independent disaggregase activity not resolved","In vivo relevance to synucleinopathies not tested in animal models","Whether holdase and protease activities are coordinated on the same substrate unknown"]},{"year":null,"claim":"A full-length atomic structure of the HTRA1 trimer including the PDZ–protease allosteric interface, the structural basis of its proteolysis-independent disaggregase activity, and the identity of the critical in vivo substrates whose loss drives cerebral small vessel pathology remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length trimeric structure at atomic resolution","Proteolysis-independent disaggregase mechanism structurally undefined","Causal substrate(s) in cerebral small vessel disease not pinpointed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,3,5,6,8,10,11,14,23,24]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,3,5,6,8,14,23]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[24]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,3,11,12,14]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[3,5,11,12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,10,13,19]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[3,5,11,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[13,22]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,1,9,12,16,23]}],"complexes":["HTRA1 homotrimer"],"partners":["JAG1","NOTCH3","CTNNB1","FN1","DCN","OPG","SNCA","MAPT"],"other_free_text":[]},"mechanistic_narrative":"HTRA1 is a secreted homotrimeric serine protease that functions as a broad-spectrum extracellular matrix remodeler, protein aggregate disaggregase, and signaling pathway modulator in vascular, neural, ocular, and skeletal tissues. The enzyme assembles as a trimer whose trypsin-like catalytic domain adopts a constitutively competent conformation, with substrate engagement further regulated by allosteric activation through its C-terminal PDZ domain upon binding hydrophobic peptide sequences [PMID:17962403, PMID:22578544]. HTRA1 degrades diverse ECM substrates (fibronectin, decorin, MGP, LTBP-1, EFEMP1, TSP1, OPG, EGFL8) and amyloid fibrils (tau, α-synuclein), with its fibril-disaggregase activity being ATP-independent and, for α-synuclein, proteolysis-independent [PMID:26436840, PMID:38499535, PMID:16377621, PMID:30854478]; it represses TGF-β/BMP signaling, inhibits canonical Wnt/β-catenin signaling, and promotes Notch signaling by cleaving JAG1 [PMID:19387015, PMID:29269789, PMID:29713059]. Loss-of-function mutations cause CARASIL and dominant CADASIL-like cerebral small vessel disease through impaired protease activity and, in heterozygous cases, dominant-negative disruption of the trimeric complex [PMID:19387015, PMID:27164673, PMID:34626176]."},"prefetch_data":{"uniprot":{"accession":"Q92743","full_name":"Serine protease HTRA1","aliases":["High-temperature requirement A serine peptidase 1","L56","Serine protease 11"],"length_aa":480,"mass_kda":51.3,"function":"Serine protease with a variety of targets, including extracellular matrix proteins such as fibronectin. HTRA1-generated fibronectin fragments further induce synovial cells to up-regulate MMP1 and MMP3 production. May also degrade proteoglycans, such as aggrecan, decorin and fibromodulin. Through cleavage of proteoglycans, may release soluble FGF-glycosaminoglycan complexes that promote the range and intensity of FGF signals in the extracellular space. Regulates the availability of insulin-like growth factors (IGFs) by cleaving IGF-binding proteins. Inhibits signaling mediated by TGF-beta family members. This activity requires the integrity of the catalytic site, although it is unclear whether TGF-beta proteins are themselves degraded. By acting on TGF-beta signaling, may regulate many physiological processes, including retinal angiogenesis and neuronal survival and maturation during development. 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immunity","url":"https://pubmed.ncbi.nlm.nih.gov/25047848","citation_count":21,"is_preprint":false},{"pmid":"29269789","id":"PMC_29269789","title":"High-Temperature Requirement A1 (Htra1) - A Novel Regulator of Canonical Wnt Signaling.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29269789","citation_count":21,"is_preprint":false},{"pmid":"26370492","id":"PMC_26370492","title":"Borrelia burgdorferi HtrA: evidence for twofold proteolysis of outer membrane protein p66.","date":"2015","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/26370492","citation_count":21,"is_preprint":false},{"pmid":"38499535","id":"PMC_38499535","title":"HTRA1 disaggregates α-synuclein amyloid fibrils and converts them into non-toxic and seeding incompetent species.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38499535","citation_count":20,"is_preprint":false},{"pmid":"35531175","id":"PMC_35531175","title":"Interplay between HTRA1 and classical signalling pathways in organogenesis and diseases.","date":"2021","source":"Saudi journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35531175","citation_count":20,"is_preprint":false},{"pmid":"31796853","id":"PMC_31796853","title":"Loss of the serine protease HTRA1 impairs smooth muscle cells maturation.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31796853","citation_count":20,"is_preprint":false},{"pmid":"30854478","id":"PMC_30854478","title":"Murine osteoclasts secrete serine protease HtrA1 capable of degrading osteoprotegerin in the bone microenvironment.","date":"2019","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/30854478","citation_count":20,"is_preprint":false},{"pmid":"35137483","id":"PMC_35137483","title":"Melatonin regulates trophoblast pyroptosis, invasion and migration in preeclampsia by inhibiting HtrA1 transcription through the microRNA-520c-3p/SETD7 axis.","date":"2022","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/35137483","citation_count":20,"is_preprint":false},{"pmid":"34742300","id":"PMC_34742300","title":"Identification of Desmoglein-2 as a novel target of Helicobacter pylori HtrA in epithelial cells.","date":"2021","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/34742300","citation_count":20,"is_preprint":false},{"pmid":"29991588","id":"PMC_29991588","title":"HtrA of Borrelia burgdorferi Leads to Decreased Swarm Motility and Decreased Production of Pyruvate.","date":"2018","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/29991588","citation_count":19,"is_preprint":false},{"pmid":"34270682","id":"PMC_34270682","title":"Heterozygous HTRA1 nonsense or frameshift mutations are pathogenic.","date":"2021","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/34270682","citation_count":18,"is_preprint":false},{"pmid":"33277762","id":"PMC_33277762","title":"Importance of two PDZ domains for the proteolytic and chaperone activities of Helicobacter pylori serine protease HtrA.","date":"2020","source":"Cellular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/33277762","citation_count":18,"is_preprint":false},{"pmid":"32324256","id":"PMC_32324256","title":"RUNX2 co-operates with EGR1 to regulate osteogenic differentiation through Htra1 enhancers.","date":"2020","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/32324256","citation_count":17,"is_preprint":false},{"pmid":"37183214","id":"PMC_37183214","title":"Trimer stability of Helicobacter pylori HtrA is regulated by a natural mutation in the protease domain.","date":"2023","source":"Medical microbiology and immunology","url":"https://pubmed.ncbi.nlm.nih.gov/37183214","citation_count":17,"is_preprint":false},{"pmid":"24535794","id":"PMC_24535794","title":"Mutation in the HTRA1 gene in a patient with degenerated spine as a component of CARASIL syndrome.","date":"2014","source":"Turkish neurosurgery","url":"https://pubmed.ncbi.nlm.nih.gov/24535794","citation_count":17,"is_preprint":false},{"pmid":"34017939","id":"PMC_34017939","title":"The interplay of oxidative stress and ARMS2-HTRA1 genetic risk in neovascular AMD.","date":"2021","source":"Vessel plus","url":"https://pubmed.ncbi.nlm.nih.gov/34017939","citation_count":16,"is_preprint":false},{"pmid":"34976310","id":"PMC_34976310","title":"Function, molecular mechanisms, and therapeutic potential of bacterial HtrA proteins: An evolving view.","date":"2021","source":"Computational and structural biotechnology journal","url":"https://pubmed.ncbi.nlm.nih.gov/34976310","citation_count":16,"is_preprint":false},{"pmid":"26385991","id":"PMC_26385991","title":"The trimeric serine protease HtrA1 forms a cage-like inhibition complex with an anti-HtrA1 antibody.","date":"2015","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/26385991","citation_count":16,"is_preprint":false},{"pmid":"30795802","id":"PMC_30795802","title":"Association of HTRA1 and ARMS2 gene polymorphisms with response to intravitreal ranibizumab among neovascular age-related macular degenerative subjects.","date":"2019","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/30795802","citation_count":16,"is_preprint":false},{"pmid":"28326227","id":"PMC_28326227","title":"Uptake of the proteins HTRA1 and HTRA2 by cells mediated by calcium phosphate nanoparticles.","date":"2017","source":"Beilstein journal of nanotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/28326227","citation_count":15,"is_preprint":false},{"pmid":"37232715","id":"PMC_37232715","title":"HTRA1 in Placental Cell Models: A Possible Role in Preeclampsia.","date":"2023","source":"Current issues in molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/37232715","citation_count":14,"is_preprint":false},{"pmid":"29561953","id":"PMC_29561953","title":"Heterozygous HTRA1 missense mutation in CADASIL-like family disease.","date":"2018","source":"Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas","url":"https://pubmed.ncbi.nlm.nih.gov/29561953","citation_count":14,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47050,"output_tokens":6443,"usd":0.118898},"stage2":{"model":"claude-opus-4-6","input_tokens":10160,"output_tokens":4367,"usd":0.239962},"total_usd":0.35886,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"A promoter SNP (rs11200638) in HTRA1 is associated with elevated HTRA1 mRNA and protein expression in lymphocytes and retinal pigment epithelium from AMD patients, and HTRA1 protein was found in drusen of AMD patient eyes, implicating increased HTRA1 secreted serine protease activity in AMD pathogenesis.\",\n      \"method\": \"SNP genotyping, expression analysis of patient-derived lymphocytes and RPE, immunolabeling of drusen\",\n      \"journal\": \"Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient tissue expression and immunolabeling, single study, no direct in vitro mechanistic reconstitution\",\n      \"pmids\": [\"17053109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss-of-function mutations in HTRA1 (nonsense and missense) cause CARASIL; mutant HTRA1 proteins show reduced protease activity and fail to repress TGF-β family signaling, establishing HTRA1 as a repressor of TGF-β signaling in cerebral small vessel homeostasis.\",\n      \"method\": \"Linkage analysis, sequencing, functional protease activity assays (casein), TGF-β signaling assays, immunohistochemistry of patient cerebral arteries\",\n      \"journal\": \"New England Journal of Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (protease assay, signaling assay, patient tissue), replicated across five families\",\n      \"pmids\": [\"19387015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HTRA1 directly degrades fragments of amyloid precursor protein (APP) in vitro, and an HTRA1 inhibitor causes accumulation of Aβ in astrocyte cell culture supernatants; HTRA1 colocalizes with β-amyloid deposits in human brain.\",\n      \"method\": \"In vitro protease assay with APP fragments, cell culture inhibitor experiment, immunohistochemistry of human brain\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro activity and cell culture with inhibitor, single lab\",\n      \"pmids\": [\"15855271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HTRA1 cleaves fibronectin in synovial fluid, generating fibronectin degradation products that induce MMP-1 and MMP-3 expression in synovial fibroblasts, implicating HTRA1 in both direct and indirect ECM destruction in arthritis.\",\n      \"method\": \"Mass spectrometry identification of substrates in synovial fluid, recombinant HTRA1 cleavage assay with fibronectin, fibroblast treatment with HTRA1 or HTRA1-generated fibronectin fragments, MMP expression assay\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstituted cleavage, functional downstream readout (MMP induction), multiple orthogonal methods in single study\",\n      \"pmids\": [\"16377621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The PDZ domains of human HtrA1 recognize hydrophobic polypeptides (preferring C-terminal sequences but also internal sequences), and peptide binding to the PDZ domain induces conformational changes that activate the protease domain, supporting an allosteric activation mechanism.\",\n      \"method\": \"Peptide library screening, affinity assays, crystal structure of PDZ domain-ligand complexes, alanine scanning mutagenesis\",\n      \"journal\": \"Protein Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with mutagenesis and binding assays, rigorous mechanistic dissection\",\n      \"pmids\": [\"17962403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HTRA1 inhibits osteoblast mineralization in a manner requiring both its protease domain and PDZ domain; it cleaves recombinant decorin, fibronectin, and matrix Gla protein (MGP), with MGP cleavage requiring both domains while decorin/fibronectin cleavage requires only the protease domain.\",\n      \"method\": \"Overexpression and siRNA knockdown in 2T3 osteoblasts, recombinant HTRA1 domain deletion constructs, in vitro cleavage assays of ECM substrates\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution with domain mutants plus loss- and gain-of-function cellular experiments\",\n      \"pmids\": [\"18156628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human HTRA1 degrades aggregated and fibrillar tau in vitro and in cells; HTRA1 mRNA and activity are upregulated in response to elevated tau concentrations, and neuronal cells/patient brains accumulate less tau and neurofibrillary tangles when HTRA1 is expressed at elevated levels.\",\n      \"method\": \"In vitro protease assay with tau aggregates/fibrils, overexpression in neuronal cell lines, immunohistochemistry of patient brains, RT-PCR of HTRA1 mRNA\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution plus cellular and patient-tissue evidence from single study\",\n      \"pmids\": [\"22535953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structures and SAXS analysis of HtrA1 reveal an N-terminal IGFBP/Kazal tandem domain, a protease active site in a competent conformation in the absence of substrate, and a trimeric arrangement; neither IGFBP- nor Kazal-like modules retain prototype protein function, and the active site data support a conformational selection model for substrate binding.\",\n      \"method\": \"X-ray crystallography, SAXS, enzymatic activity assays, binding studies with domain deletion constructs\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with functional assays and SAXS in a single comprehensive study\",\n      \"pmids\": [\"22578544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"HTRA1 degrades amyloid fibrils in an ATP-independent manner by solubilizing fibrils, disintegrating the fibrillar core, and allowing productive interaction of aggregated polypeptides with its active site; this activity reduces aggregate burden in a cellular model of cytoplasmic tau aggregation.\",\n      \"method\": \"In vitro fibril disaggregation assays, structural analysis, cellular tau aggregation model\",\n      \"journal\": \"Nature Chemical Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mechanistic dissection and cellular validation\",\n      \"pmids\": [\"26436840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HTRA1 missense mutations found in manifesting heterozygotes with CARASIL-like disease show markedly decreased protease activity and inhibit wild-type HTRA1 activity (dominant-negative effect); these mutants either fail to form trimers or carry mutations in domains critical for trimer-associated activation, whereas CARASIL-associated mutants do form trimers but have mutations outside activation domains.\",\n      \"method\": \"Casein protease activity assays, gel filtration chromatography for oligomeric state analysis, HTRA1 co-incubation experiments\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — protease assays and gel filtration with multiple mutants, mechanistic model supported by orthogonal approaches\",\n      \"pmids\": [\"27164673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HTRA1 cleaves the Notch ligand JAG1 within its intracellular domain, leading to JAG1 protein degradation; HTRA1 physically interacts with JAG1, thereby enhancing Delta/Notch signaling. Loss of HTRA1 in endothelial cells increases JAG1 and promotes hypersprouting angiogenesis, and HtrA1-deficient mice have diminished endothelial Notch signaling and denser, immature tumor vasculature.\",\n      \"method\": \"Co-immunoprecipitation, in vitro cleavage assay, siRNA knockdown and overexpression in endothelial cells, HtrA1-/- mouse tumor model, rescue with constitutively active Notch1\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — physical interaction shown by Co-IP, in vitro cleavage, in vivo mouse KO with clear vascular phenotype, rescued by Notch activation\",\n      \"pmids\": [\"29713059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HTRA1 cleaves extracellular matrix proteins EFEMP1 and TSP1 (novel substrates), in addition to previously known substrates LTBP-1 and clusterin, in RPE cells with the AMD high-risk genotype.\",\n      \"method\": \"Proteomic comparison of RPE cells with/without AMD high-risk mutation, identification of HTRA1 cleavage targets by proteomics\",\n      \"journal\": \"Aging Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — proteomic identification of cleavage targets in disease-relevant cells, single lab, limited in vitro reconstitution\",\n      \"pmids\": [\"29730901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HTRA1 is sequestered by Notch3 extracellular domain (Notch3ECD) deposits in CADASIL brain vessels, and the CADASIL brain vessel proteome shows enrichment of known HTRA1 substrates consistent with reduced HTRA1 activity; multiple HTRA1 substrates were validated in an in vitro proteolysis assay, linking CADASIL pathology to functional HTRA1 loss.\",\n      \"method\": \"Quantitative brain vessel proteomics from CADASIL patients vs. controls, comparison with HtrA1 knockout mouse proteome, in vitro proteolysis assay\",\n      \"journal\": \"Acta Neuropathologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — quantitative proteomics with independent KO mouse comparison and in vitro substrate validation\",\n      \"pmids\": [\"29725820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HTRA1 is essential for vascular smooth muscle cell (VSMC) differentiation into the contractile phenotype; loss of HTRA1 increases JAG1 protein and NOTCH3 signaling and enhances TGF-β-SMAD2/3 signaling, leading to additive accumulation of HES/HEY repressors that suppress contractile VSMC marker genes and impair arterial vasoconstriction in Htra1-/- mice.\",\n      \"method\": \"Htra1-/- mouse model, VSMC differentiation assays, Western blot for JAG1/Notch3/TGFβ pathway, gene expression analysis, vasoconstriction functional assay\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with multiple pathway readouts and functional vasoconstriction phenotype\",\n      \"pmids\": [\"31796853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Osteoclasts secrete HTRA1, which degrades osteoprotegerin (OPG); HTRA1 recognizes the three-dimensional structure of OPG and initially cleaves the amide bond between Leu90 and Gln91, then degrades OPG into small fragments, thereby suppressing OPG inhibition of RANKL-induced osteoclastogenesis.\",\n      \"method\": \"Mass spectrometry identification of OPG-degrading enzyme, in vitro cleavage assay with recombinant HTRA1 and OPG, mapping of cleavage site, DTT-reduction experiment, RAW 264.7 osteoclastogenesis assay\",\n      \"journal\": \"Communications Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution with cleavage site mapping and functional osteoclastogenesis assay\",\n      \"pmids\": [\"30854478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"An anti-HtrA1 antibody forms a cage-like macromolecular complex with the HtrA1 catalytic domain trimer; three IgG molecules coordinate two HtrA1 trimers in a 636-kDa cage with six active sites pointing inward, achieving complete inhibition of enzyme activity through an allosteric mechanism involving surface-exposed loops B and C of the catalytic domain.\",\n      \"method\": \"Negative-stain EM, biochemical complex characterization, epitope mapping, enzymatic activity assays\",\n      \"journal\": \"Biochemical Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — EM structure with biochemical validation of inhibition mechanism\",\n      \"pmids\": [\"26385991\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Transgenic expression of human HTRA1 in mouse retinal pigment epithelium is sufficient to cause polypoidal choroidal vasculopathy (PCV), including branching choroidal vessel networks, polypoidal lesions, elastic laminae degeneration, tunica media degeneration, RPE atrophy, and photoreceptor degeneration; senescent HTRA1 transgenic mice develop occult CNV with upregulated VEGF.\",\n      \"method\": \"Transgenic mouse model with human HTRA1 expressed in RPE, fundus imaging, histology, immunohistochemistry, VEGF measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transgenic overexpression in vivo with multiple phenotypic readouts replicated across aging timepoints\",\n      \"pmids\": [\"21844367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HtrA1 expression is upregulated by cisplatin and paclitaxel treatment, resulting in limited autoproteolysis and activation of HtrA1; active HtrA1 induces cell death in a serine protease-dependent manner, and downregulation of HtrA1 attenuates chemotherapy-induced cytotoxicity while forced expression enhances it.\",\n      \"method\": \"Forced expression and knockdown of HtrA1 in ovarian cancer cell lines, cell viability assays with cisplatin/paclitaxel, autoproteolysis analysis, protease-dead mutant (SA) controls\",\n      \"journal\": \"Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss of function with protease-dead SA mutant control establishing serine protease dependence\",\n      \"pmids\": [\"16767218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MiR-30e and miR-181d are posttranscriptional negative regulators of HTRA1 by binding to the 3' UTR of HTRA1 mRNA; in vivo overexpression of these miRNAs in Dicer-/- forebrain rescued radial glia proliferation defects caused by HTRA1 overexpression.\",\n      \"method\": \"Dicer conditional KO mouse, in vivo miRNA overexpression, luciferase reporter assay with HTRA1 3'UTR, rescue experiments\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — 3'UTR reporter combined with in vivo rescue, single study\",\n      \"pmids\": [\"22854828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HTRA1 inhibits canonical Wnt/β-catenin signaling in both paracrine and autocrine manners; HTRA1 forms a complex with β-catenin and reduces cell proliferation rates, and affects expression of several Wnt target genes.\",\n      \"method\": \"Wnt reporter assays, co-immunoprecipitation of HTRA1 with β-catenin, HTRA1 overexpression in colorectal cancer cells, cell proliferation assays\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP with functional reporter and proliferation assays, single lab\",\n      \"pmids\": [\"29269789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TLR-4 activation by LPS induces HTRA1 expression through the NF-κB pathway; the NF-κB subunit p65 directly binds to the HTRA1 promoter at position -347, as demonstrated by dual-luciferase reporter and ChIP assays.\",\n      \"method\": \"Real-time PCR, ELISA, NF-κB inhibitors, siRNA, dual-luciferase reporter, chromatin immunoprecipitation (ChIP)\",\n      \"journal\": \"Arthritis and Rheumatism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (reporter + ChIP) in single study\",\n      \"pmids\": [\"23982886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"IFN-γ inhibits HTRA1 expression through activation of p38 MAPK/STAT1 pathway; STAT1 directly binds to the HTRA1 promoter after IFN-γ stimulation, as shown by dual-luciferase reporter and ChIP assays.\",\n      \"method\": \"Real-time PCR, Western blot, CIA mouse model with IFN-γ KO, dual-luciferase reporter, ChIP\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter plus ChIP plus in vivo mouse model, single lab\",\n      \"pmids\": [\"24907345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HtrA1 is required for normal placentation in mice; HtrA1-/- mice show intrauterine growth retardation with small placentas due to reduced junctional zone and aberrant labyrinth vascularization, caused by decreased differentiation of Tpbpa-positive trophoblast precursors, fewer spiral artery-associated trophoblast giant cells, and impaired maternal artery remodeling.\",\n      \"method\": \"HtrA1-/- mouse model, histology, immunostaining for trophoblast markers, morphometric analysis of maternal arteries\",\n      \"journal\": \"Developmental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with multiple defined cellular phenotypes and mechanistic pathway placement\",\n      \"pmids\": [\"25446274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Rare loss-of-function variants in the HTRA1 protease domain (amino acids 204-364) associate with increased white matter hyperintensity volume; most identified protease domain variants result in markedly reduced protease activity in biochemical assays; EGFL8 was identified as a direct substrate of HTRA1.\",\n      \"method\": \"Whole-exome sequencing gene burden tests, domain-specific burden analysis, in vitro protease activity assays of individual variants, substrate identification\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro biochemical activity assays for multiple variants plus genetic burden analysis, novel substrate identification\",\n      \"pmids\": [\"34626176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HTRA1 inhibits aggregation of α-synuclein, FUS, and TDP-43; the protease domain of HTRA1 is necessary and sufficient for this activity but the activity is proteolysis-independent. HTRA1 disaggregates preformed α-syn fibrils, rendering them seeding-incompetent, by targeting the NAC domain of α-syn. Reducing HTRA1 expression promotes α-syn seeding, and HTRA1 detoxifies α-syn fibrils and prevents hyperphosphorylated α-syn accumulation in primary neurons.\",\n      \"method\": \"In vitro aggregation inhibition and fibril disaggregation assays, protease-dead mutant and domain deletion constructs, α-syn seeding assays, primary neuron toxicity assays, HTRA1 knockdown\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple in vitro reconstitution experiments with domain mutants, cellular seeding assays, and neuronal toxicity readout\",\n      \"pmids\": [\"38499535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HTRA1 is epigenetically silenced in HCT116 colon carcinoma cells via the epigenetic adaptor protein MBD2; depletion of HTRA1 causes centrosome amplification and polyploidy in colon cancer cells and primary mouse embryonic fibroblasts.\",\n      \"method\": \"Epigenetic analysis in cancer cell lines, MBD2 involvement demonstrated, HTRA1 siRNA knockdown with centrosome and ploidy analysis\",\n      \"journal\": \"BMC Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — epigenetic mechanism identified with functional cellular phenotype, single lab\",\n      \"pmids\": [\"27388476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RUNX2 co-operates with EGR1 to transcriptionally repress HTRA1 through Htra1 enhancers; RUNX2 and EGR1 physically co-occupy seven verified HTRA1 enhancers as shown by Re-ChIP assay, and their combined action represses HTRA1 expression while promoting osteoblast differentiation markers.\",\n      \"method\": \"ChIP-seq, RNA-seq, dual-luciferase enhancer assays, Re-ChIP, siRNA knockdown, alizarin red and ALP staining\",\n      \"journal\": \"Journal of Cellular Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq with reporter and Re-ChIP validation, single lab\",\n      \"pmids\": [\"32324256\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HTRA1 is a secreted homotrimeric serine protease whose PDZ domain senses exposed hydrophobic peptides to allosterically activate its trypsin-like catalytic domain; it degrades a broad range of extracellular matrix proteins (fibronectin, decorin, MGP, LTBP-1, EFEMP1, TSP1, OPG, EGFL8, JAG1) and protein aggregates (tau fibrils, α-synuclein fibrils, APP fragments), represses TGF-β/BMP and canonical Wnt signaling, cleaves JAG1 to enhance Notch signaling in endothelial cells, and is transcriptionally regulated by NF-κB (via LPS/TLR4) and repressed by IFN-γ/STAT1, RUNX2/EGR1, and miR-30e/miR-181d; loss-of-function causes cerebral small vessel disease (CARASIL/CADASIL-like) and impaired vascular smooth muscle maturation, while overexpression drives AMD-related choroidal neovascularization and RPE senescence through ECM degradation and HIF-1 signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"HTRA1 is a secreted homotrimeric serine protease that functions as a broad-spectrum extracellular matrix remodeler, protein aggregate disaggregase, and signaling pathway modulator in vascular, neural, ocular, and skeletal tissues. The enzyme assembles as a trimer whose trypsin-like catalytic domain adopts a constitutively competent conformation, with substrate engagement further regulated by allosteric activation through its C-terminal PDZ domain upon binding hydrophobic peptide sequences [PMID:17962403, PMID:22578544]. HTRA1 degrades diverse ECM substrates (fibronectin, decorin, MGP, LTBP-1, EFEMP1, TSP1, OPG, EGFL8) and amyloid fibrils (tau, α-synuclein), with its fibril-disaggregase activity being ATP-independent and, for α-synuclein, proteolysis-independent [PMID:26436840, PMID:38499535, PMID:16377621, PMID:30854478]; it represses TGF-β/BMP signaling, inhibits canonical Wnt/β-catenin signaling, and promotes Notch signaling by cleaving JAG1 [PMID:19387015, PMID:29269789, PMID:29713059]. Loss-of-function mutations cause CARASIL and dominant CADASIL-like cerebral small vessel disease through impaired protease activity and, in heterozygous cases, dominant-negative disruption of the trimeric complex [PMID:19387015, PMID:27164673, PMID:34626176].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing HTRA1 as an ECM-degrading and APP-processing extracellular protease resolved the question of what substrates this secreted serine protease acts on, revealing roles in both matrix turnover and amyloid clearance.\",\n      \"evidence\": \"In vitro cleavage assays with fibronectin and APP fragments, mass spectrometry of synovial fluid substrates, cell culture inhibitor experiments, and downstream MMP induction readouts\",\n      \"pmids\": [\"15855271\", \"16377621\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Full substrate repertoire in vivo undefined\",\n        \"Cleavage site specificity rules not determined\",\n        \"In vivo relevance of APP degradation not established\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linking the HTRA1 promoter variant rs11200638 to AMD and detecting HTRA1 in drusen provided the first evidence that elevated HTRA1 protease activity contributes to retinal disease, while showing that HTRA1 upregulation promotes chemotherapy-induced cell death established a pro-apoptotic role for the active protease.\",\n      \"evidence\": \"SNP genotyping with expression analysis in patient lymphocytes/RPE and drusen immunolabeling; forced expression/knockdown in ovarian cancer cells with protease-dead controls\",\n      \"pmids\": [\"17053109\", \"16767218\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Causal mechanism linking HTRA1 overexpression to drusen formation not defined\",\n        \"Apoptotic substrate(s) mediating cell death not identified\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Structural and biochemical dissection of the PDZ domain revealed an allosteric activation mechanism whereby hydrophobic peptide binding to the PDZ domain induces conformational changes that activate the protease, and showed that substrate-specific cleavage (e.g., MGP) can require both the PDZ and protease domains.\",\n      \"evidence\": \"Crystal structures of PDZ–ligand complexes, peptide library screening, alanine scanning mutagenesis, domain-deletion cleavage assays with decorin/fibronectin/MGP\",\n      \"pmids\": [\"17962403\", \"18156628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Full-length trimer structure with PDZ-protease allosteric interface not resolved\",\n        \"Which in vivo substrates require PDZ-dependent activation unknown\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying loss-of-function HTRA1 mutations as the genetic cause of CARASIL, with mutant proteins showing defective protease activity and failure to repress TGF-β signaling, established HTRA1 as a non-redundant vascular protease and TGF-β pathway repressor.\",\n      \"evidence\": \"Linkage analysis across five families, sequencing, casein protease assays, TGF-β signaling assays, immunohistochemistry of patient cerebral arteries\",\n      \"pmids\": [\"19387015\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism of TGF-β repression (direct substrate vs indirect) not resolved\",\n        \"Whether other HtrA family members compensate partially unknown\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Transgenic HTRA1 overexpression in mouse RPE was sufficient to cause polypoidal choroidal vasculopathy and choroidal neovascularization with VEGF upregulation, providing causal in vivo evidence that excess HTRA1 drives AMD-related vascular pathology.\",\n      \"evidence\": \"Transgenic mouse model with RPE-directed human HTRA1 expression, fundus imaging, histology, VEGF measurement\",\n      \"pmids\": [\"21844367\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which HTRA1 substrates mediate the choroidal vascular phenotype not identified\",\n        \"Relationship between ECM degradation and VEGF induction not mechanistically defined\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that HTRA1 degrades tau aggregates and fibrils, combined with crystal structures revealing a constitutively competent trimeric protease domain, established HTRA1 as an ATP-independent protein disaggregase and clarified the structural basis of its active-site accessibility.\",\n      \"evidence\": \"In vitro tau fibril degradation, neuronal cell overexpression, patient brain immunohistochemistry; X-ray crystallography and SAXS of full-length HTRA1 trimer\",\n      \"pmids\": [\"22535953\", \"22578544\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How the trimer engages fibrillar vs. soluble substrates structurally not resolved\",\n        \"In vivo contribution to tauopathy clearance not tested in animal models\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying miR-30e and miR-181d as post-transcriptional repressors of HTRA1 via its 3′ UTR, with in vivo rescue of radial glia proliferation defects, revealed a layer of miRNA-mediated HTRA1 regulation relevant to neural progenitor biology.\",\n      \"evidence\": \"Luciferase reporter assays with HTRA1 3′ UTR, miRNA overexpression in Dicer-KO mouse forebrain, phenotypic rescue\",\n      \"pmids\": [\"22854828\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Physiological contexts in which miR-30e/miR-181d regulate HTRA1 beyond developing brain not explored\",\n        \"Quantitative impact on HTRA1 protein levels in adult tissues unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing that NF-κB p65 directly binds the HTRA1 promoter upon TLR4/LPS stimulation, and that IFN-γ/STAT1 directly represses HTRA1 transcription, defined the inflammatory transcriptional logic governing HTRA1 expression.\",\n      \"evidence\": \"ChIP assays, dual-luciferase reporters, NF-κB/STAT1 inhibitors and siRNA, IFN-γ KO mouse model\",\n      \"pmids\": [\"23982886\", \"24907345\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Combinatorial regulation by NF-κB and STAT1 under concurrent inflammatory signals not tested\",\n        \"Chromatin context and epigenetic modifiers at the HTRA1 locus not comprehensively mapped\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Mechanistic dissection of HTRA1's fibril-disaggregase activity showed ATP-independent solubilization of the fibrillar core, distinguishing HTRA1 from canonical chaperone-disaggregases; structural characterization of an inhibitory antibody-HTRA1 cage complex revealed allosteric inhibition via surface loops B and C.\",\n      \"evidence\": \"In vitro fibril disaggregation kinetics, cellular tau aggregation models; negative-stain EM of antibody–HTRA1 complex, epitope mapping\",\n      \"pmids\": [\"26436840\", \"26385991\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of fibril recognition at atomic resolution not determined\",\n        \"Whether loops B and C are involved in substrate engagement or purely allosteric sites unclear\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that heterozygous HTRA1 mutations cause dominant CADASIL-like disease through dominant-negative disruption of the trimer, as distinct from recessive CARASIL mutations that preserve trimer formation, established trimer integrity as a critical determinant of disease mechanism.\",\n      \"evidence\": \"Casein protease activity assays with WT/mutant co-incubation, gel filtration chromatography for oligomeric state\",\n      \"pmids\": [\"27164673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for dominant-negative disruption not resolved at atomic level\",\n        \"Whether heterozygous carriers have graded substrate-specific deficits unknown\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying JAG1 as an HTRA1 substrate demonstrated that HTRA1 promotes Notch signaling by degrading the Notch ligand JAG1, with loss of HTRA1 causing hypersprouting angiogenesis in vitro and immature tumor vasculature in vivo; HTRA1 sequestration by Notch3ECD in CADASIL vessels linked two cerebral small vessel diseases to a common HTRA1-deficiency mechanism.\",\n      \"evidence\": \"Co-IP, in vitro cleavage assays, endothelial siRNA/overexpression, HtrA1-KO mouse tumor model with Notch1 rescue; quantitative brain vessel proteomics in CADASIL vs. controls and HtrA1-KO mice\",\n      \"pmids\": [\"29713059\", \"29725820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether HTRA1 cleaves JAG1 extracellularly or intracellularly in vivo not definitively resolved\",\n        \"Full overlap of HTRA1-dependent proteome between CARASIL and CADASIL not characterized\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defining HTRA1's role in VSMC differentiation and its cleavage of osteoprotegerin expanded the functional repertoire to include smooth muscle maturation via combined Notch3/TGF-β modulation and bone remodeling through OPG degradation.\",\n      \"evidence\": \"HtrA1-KO mouse VSMC phenotyping with vasoconstriction assays, JAG1/Notch3/TGF-β pathway Western blots; in vitro OPG cleavage site mapping by mass spectrometry, osteoclastogenesis assays\",\n      \"pmids\": [\"31796853\", \"30854478\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Relative contribution of Notch vs. TGF-β arm to VSMC maturation defect not dissected\",\n        \"In vivo bone phenotype of HTRA1-KO not reported\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstration that RUNX2 and EGR1 co-occupy HTRA1 enhancers to repress transcription during osteoblast differentiation added a developmental transcription factor circuit to the regulatory landscape of HTRA1.\",\n      \"evidence\": \"ChIP-seq, Re-ChIP, dual-luciferase enhancer assays, siRNA knockdown with osteoblast differentiation readouts\",\n      \"pmids\": [\"32324256\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether RUNX2/EGR1 repression operates in non-skeletal HTRA1-expressing tissues unknown\",\n        \"Enhancer–promoter looping mechanism not resolved\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Gene burden analysis linking rare HTRA1 protease-domain variants to white matter hyperintensity volume, with biochemical validation of reduced activity for individual variants and identification of EGFL8 as a novel substrate, extended the genotype–phenotype spectrum beyond Mendelian CARASIL.\",\n      \"evidence\": \"Whole-exome sequencing burden tests, domain-specific analysis, in vitro protease activity assays for multiple variants, substrate identification\",\n      \"pmids\": [\"34626176\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional role of EGFL8 cleavage in vascular biology not established\",\n        \"Threshold of HTRA1 activity loss required for clinical phenotype unknown\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showing that HTRA1 disaggregates α-synuclein fibrils and inhibits aggregation of α-synuclein, FUS, and TDP-43 through a proteolysis-independent mechanism residing in the protease domain established HTRA1 as a dual-function protein: a protease for soluble substrates and a holdase/disaggregase for amyloid aggregates.\",\n      \"evidence\": \"In vitro aggregation inhibition and fibril disaggregation with protease-dead mutants and domain deletions, α-syn seeding assays, primary neuron toxicity assays, HTRA1 knockdown\",\n      \"pmids\": [\"38499535\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the proteolysis-independent disaggregase activity not resolved\",\n        \"In vivo relevance to synucleinopathies not tested in animal models\",\n        \"Whether holdase and protease activities are coordinated on the same substrate unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length atomic structure of the HTRA1 trimer including the PDZ–protease allosteric interface, the structural basis of its proteolysis-independent disaggregase activity, and the identity of the critical in vivo substrates whose loss drives cerebral small vessel pathology remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No full-length trimeric structure at atomic resolution\",\n        \"Proteolysis-independent disaggregase mechanism structurally undefined\",\n        \"Causal substrate(s) in cerebral small vessel disease not pinpointed\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 3, 5, 6, 8, 10, 11, 14, 23, 24]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 3, 5, 6, 8, 14, 23]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 3, 11, 12, 14]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [3, 5, 11, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 10, 13, 19]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [3, 5, 11, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [13, 22]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 9, 12, 16, 23]}\n    ],\n    \"complexes\": [\n      \"HTRA1 homotrimer\"\n    ],\n    \"partners\": [\n      \"JAG1\",\n      \"NOTCH3\",\n      \"CTNNB1\",\n      \"FN1\",\n      \"DCN\",\n      \"OPG\",\n      \"SNCA\",\n      \"MAPT\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}