{"gene":"HSPG2","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1992,"finding":"Human perlecan (HSPG2) protein core is composed of five distinct domains: domain I (unique, contains Ser-Gly-Asp heparan sulfate attachment sites), domain II (homologous to LDL receptor with cysteine repeats), domain III (homologous to laminin A chain short arm), domain IV (21 immunoglobulin-type repeats similar to NCAM), and domain V (homologous to laminin A G-domain with EGF-like repeats), establishing the modular architecture of the protein.","method":"cDNA cloning, sequencing of 18 overlapping clones covering 14.35 kb, deduced amino acid sequence analysis, in situ hybridization, immunoenzymatic studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete primary structure determination by sequencing, validated by in situ hybridization and immunolocalization, foundational structural paper replicated across the field","pmids":["1569102"],"is_preprint":false},{"year":1993,"finding":"The HSPG2 gene spans >120 kbp and is composed of 94 exons, with each exon assigned to modular protein domains; the promoter lacks canonical TATA or CAAT boxes but contains SP1 and ETF binding sites with multiple transcription initiation sites, consistent with a housekeeping gene regulation pattern.","method":"Complete intron-exon mapping by genomic DNA analysis, promoter characterization, sequencing","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete genomic structure determined, multiple orthogonal methods (restriction mapping, sequencing, promoter analysis)","pmids":["8234307"],"is_preprint":false},{"year":1994,"finding":"Perlecan promotes high-affinity binding of bFGF (FGF-2) to its receptor on cells deficient in heparan sulfate and to soluble FGF receptors, augments heparin-dependent mitogenic activity of bFGF, and potently induces bFGF-mediated neovascularization in vivo, identifying perlecan as a major accessory/low-affinity receptor for bFGF and an angiogenic modulator.","method":"Affinity-purified HSPG binding assays, receptor binding assays on HS-deficient cells, neutralizing monoclonal antibodies, in vivo rabbit ear angiogenesis model, mitogenesis assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (cell-free binding, cell-based receptor assay, neutralizing antibody, in vivo model), replicated across contexts","pmids":["7528102"],"is_preprint":false},{"year":1995,"finding":"Recombinant perlecan domain III supports integrin-mediated cell attachment via its RGDS sequence; adhesion is specifically inhibited by RGDS peptide and intact perlecan but not laminin, demonstrating a role for perlecan domain III in integrin-mediated signaling.","method":"Recombinant domain III expression and purification, cell adhesion assays on coated dishes, inhibition with synthetic RGDS peptide, rotary shadow electron microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — recombinant protein reconstitution, mutagenesis-level peptide blocking, multiple cell lines tested in single lab","pmids":["7814401"],"is_preprint":false},{"year":1996,"finding":"Perlecan is a cell-autonomous product of muscle cells in C. elegans (encoded by unc-52) and is essential for myofilament formation and muscle attachment; perlecan expressed in individual muscle cells does not spread beyond the borders of the ECM underlying that cell, demonstrating cell-autonomous ECM function.","method":"Genetic analysis of unc-52 mutants, polyclonal antibody labeling, laser ablation of blastomeres, immunofluorescence during C. elegans development","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with defined cellular phenotype, cell-autonomous rescue experiments, replicated in C. elegans model","pmids":["8575624"],"is_preprint":false},{"year":1998,"finding":"Perlecan binds alpha-dystroglycan (alpha-DG) in a calcium- and heparin-sensitive manner; perlecan co-localizes with dystroglycan at cell surfaces of Xenopus muscle cells, is co-immunoprecipitated with anti-DG antibody from muscle lysate, and clusters at ACh receptor clusters at the neuromuscular junction, suggesting perlecan is anchored to muscle surface via the DG-dystrophin complex.","method":"Blot overlay assays, co-immunoprecipitation, immunofluorescence co-localization in Xenopus muscle cells, AChR clustering assays","journal":"Cell adhesion and communication","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and overlay assays in single lab, multiple orthogonal methods but limited mechanistic follow-up","pmids":["9791728"],"is_preprint":false},{"year":1999,"finding":"Perlecan null mice show normal basement membrane (BM) formation initially, but BMs deteriorate under mechanical stress (contracting myocardium, expanding brain vesicles), leading to cardiac failure and exencephaly; perlecan-null cartilage shows reduced fibrillar collagen network and shortened fibers with elevated ECM gene expression, demonstrating perlecan maintains BM integrity and protects cartilage ECM from degradation.","method":"Homozygous null mutation (gene knockout) in mice, histology, electron microscopy, immunohistochemistry, Northern blotting","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with multiple defined phenotypic readouts, replicated by independent group (PMID:10545953)","pmids":["10579729"],"is_preprint":false},{"year":1999,"finding":"Hspg2-null mice show severe disorganization of chondrocyte columnar structures, defective endochondral ossification, reduced and disorganized collagen fibrils and glycosaminoglycans in cartilage matrix, reduced chondrocyte proliferation, and diminished prehypertrophic zone, demonstrating perlecan is essential for cartilage matrix structure and chondrocyte proliferation. Abnormal phenotypes resemble FGFR3 gain-of-function, suggesting perlecan and FGFR3 affect similar signaling pathways.","method":"Gene disruption (Hspg2 knockout) in mice, histology, electron microscopy, BrdU proliferation assay, glycosaminoglycan analysis, immunostaining","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — independent gene knockout, multiple orthogonal phenotypic analyses, genetic epistasis inference with FGFR3 pathway, replicated by independent lab (PMID:10579729)","pmids":["10545953"],"is_preprint":false},{"year":1999,"finding":"Culture on perlecan (but not other matrices including fibronectin, laminin, or collagen) stimulates multipotential mesenchymal fibroblasts (10T1/2) to form dense nodules with Alcian blue staining and collagen type II expression, and elevates mRNAs for collagen II, aggrecan, and perlecan itself, demonstrating perlecan promotes chondrogenic differentiation in vitro.","method":"Cell culture on purified perlecan substrates, Alcian blue staining, immunostaining for collagen II, Northern blotting for chondrogenic markers","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reconstitution on purified protein, multiple chondrogenic marker readouts, single lab","pmids":["10352025"],"is_preprint":false},{"year":2000,"finding":"Cells expressing perlecan (but no other proteoglycans) bind, internalize, and degrade atherogenic lipoproteins enriched in lipoprotein lipase via a pathway kinetically and biochemically distinct from coated-pit or syndecan-mediated endocytosis; binding is blocked by heparitinase, degradation by chloroquine, internalization inhibited by genistein but not cytochalasin D, and beta1 integrins serve as cell surface attachment sites for perlecan.","method":"Lipoprotein binding, internalization, and degradation assays in cells expressing only perlecan; pharmacological inhibitors; antibody blockade of beta1 integrin and LRP","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean cell system expressing only perlecan, multiple inhibitor approaches, kinetic analysis, single lab","pmids":["10818109"],"is_preprint":false},{"year":2000,"finding":"Mutations (missense and splicing) in HSPG2 cause Schwartz-Jampel syndrome (SJS1), a rare autosomal recessive disorder with permanent myotonia and skeletal dysplasia, establishing perlecan as essential for both maintaining cartilage integrity and regulating muscle excitability in humans.","method":"Mutation identification by sequencing in SJS1 families, linkage to chromosome 1p34-p36.1","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — human disease gene identification with multiple families and multiple mutation types, confirmed by independent studies (PMID:16927315)","pmids":["11101850"],"is_preprint":false},{"year":2001,"finding":"The perlecan protein core (not its heparan sulfate chains) is required for functional activation of the KGF receptor (FGFR2/KGF-R) and downstream signaling in colon carcinoma cells; perlecan-deficient cells (generated by targeted homologous recombination) fail to respond to FGF7 even with added heparin, though they show increased FGF7 surface binding.","method":"Targeted homologous recombination to generate perlecan-null colon carcinoma cells, FGF7 binding assays, cell proliferation assays, receptor activation assays, heparin supplementation controls","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — genetic disruption of HSPG2 in human cells, receptor activation and ligand binding assays, domain-specific dissection (core protein vs HS chains), single lab","pmids":["11563979"],"is_preprint":false},{"year":2001,"finding":"FGF-binding protein (FGF-BP) interacts specifically with the protein core of perlecan domain III (second EGF repeat), as identified by yeast two-hybrid screening and validated by co-immunoprecipitation and binding to recombinant domain III-alkaline phosphatase fusion protein; FGF-BP and perlecan co-localize in the pericellular stroma of squamous cell carcinomas.","method":"Yeast two-hybrid screen of keratinocyte cDNA library, deletion mutant mapping, co-immunoprecipitation, recombinant domain III-alkaline phosphatase fusion binding assay, immunohistochemistry","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP and recombinant binding, domain-level mapping, single lab","pmids":["11148217"],"is_preprint":false},{"year":2001,"finding":"Dyssegmental dysplasia Silverman-Handmaker type (DDSH), a lethal form of dwarfism, is caused by functional null mutations of HSPG2; insertion and splicing mutations create premature termination codons, the mutant perlecan is unstable and not secreted into the extracellular matrix, demonstrating perlecan is essential for cartilage development in humans.","method":"HSPG2 mutation identification in DDSH patients, immunostaining of patient tissue, biochemical analysis of perlecan secretion","journal":"American journal of medical genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — human genetic evidence with biochemical validation of protein instability and secretion failure, independent of SJS studies","pmids":["11891676"],"is_preprint":false},{"year":2003,"finding":"Perlecan protein core interacts with extracellular matrix protein 1 (ECM1) through its domain V; specifically, the C-terminus of ECM1 binds the EGF-like modules flanking the LG2 subdomain of perlecan domain V, as validated by yeast two-hybrid, co-immunoprecipitation in cell-free systems and mammalian cells, and deletion mutant mapping.","method":"Yeast two-hybrid screen, co-immunoprecipitation in cell-free and mammalian cell systems, deletion mutant binding mapping, identification of novel ECM1c splice variant","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by reciprocal Co-IP with domain-level mapping, single lab","pmids":["12604605"],"is_preprint":false},{"year":2003,"finding":"Progranulin (a secreted growth factor) interacts with perlecan domain V through the first two laminin- and EGF-like repeats, binding to granulin F and B subdomains, with a KD ~1 μM measured by surface plasmon resonance; both progranulin and domain V individually stimulate adrenal carcinoma cell growth, but together in equimolar amounts counteract each other's activity.","method":"Yeast two-hybrid, co-immunoprecipitation in cell-free and transfected mammalian cells, surface plasmon resonance kinetics, cell growth assays, tumor tissue microarrays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — SPR kinetics plus yeast two-hybrid and co-IP with deletion mapping, single lab, functional cell-growth assay","pmids":["12900424"],"is_preprint":false},{"year":2003,"finding":"Heparanase (HPSE-1) specifically degrades the heparan sulfate chains of purified perlecan, as demonstrated with purified syndecan-1 and perlecan HS; perlecan HS is thus a degradative substrate of heparanase, with functional implications for tumor cell invasion.","method":"In vitro enzymatic degradation of purified syndecan-1 and perlecan HS with HPSE-1, in vitro chemoinvasion assays, cell surface HS degradation assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assay with purified proteins, cell-based invasion assay, single lab","pmids":["14630925"],"is_preprint":false},{"year":2003,"finding":"Drosophila perlecan (encoded by trol) regulates neuroblast division by modulating both FGF and Hedgehog (Hh) signaling; FGF-2 addition rescues trol proliferation phenotype, MAPK inhibitor blocks wild-type neuroblast division, Hh activates stem cell division in a Trol-dependent fashion, and co-immunoprecipitation shows interactions between Trol and Hh and between mammalian Perlecan and Sonic Hedgehog that are not competed by heparin sulfate.","method":"Drosophila genetic analysis (trol mutants), brain culture rescue with human FGF-2, MAPK inhibitor treatment, co-immunoprecipitation of Trol/Hh and Perlecan/Shh, genetic epistasis of trol/hh/ttv","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in Drosophila, biochemical co-IP, pharmacological rescue, multiple orthogonal methods, extended by PMID:17980035","pmids":["12645928"],"is_preprint":false},{"year":2006,"finding":"HSPG2 mutations causing SJS show a hypomorphic effect; truncating mutations cause HSPG2 mRNA instability via nonsense-mediated mRNA decay, whereas missense mutations involving cysteine residues cause intracellular retention of perlecan, likely through quality control pathways, establishing distinct molecular consequences of different mutation classes.","method":"HSPG2 mRNA analysis, perlecan immunostaining on patient cells, sequencing of 22 new mutations in 23 SJS families","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mRNA and protein analysis in patient cells with multiple mutation types, mechanistic distinction between truncating vs missense mutations established, single group","pmids":["16927315"],"is_preprint":false},{"year":2007,"finding":"A peptide sequence (TWSKVGGHLRPGIVQSG) from an immunoglobulin repeat in perlecan domain IV supports rapid cell adhesion, spreading, and focal adhesion kinase (FAK) activation in a divalent cation-independent, heparin-sensitive manner; cell adhesion is receptor-specific and differs between cell lines.","method":"Bioinformatics-based peptide identification, cell adhesion assays, focal adhesion and actin cytoskeleton visualization, FAK activation assays","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — peptide-based functional assay with multiple cell lines, FAK activation readout, heparin competition, single lab","pmids":["17997086"],"is_preprint":false},{"year":2009,"finding":"Perlecan is required for proper endothelial cell migration and proliferation during developmental angiogenesis; perlecan knockdown causes abnormal increase and redistribution of total VEGF-A protein, perlecan binds VEGF-A165 in a heparan sulfate-dependent manner, and perlecan enhances VEGF-mediated VEGFR2 activation of human endothelial cells; the morphant phenotype is rescued by VEGF-A165 microinjection.","method":"Zebrafish perlecan morpholino knockdown, endothelial cell behavior analysis, VEGF-A localization by immunostaining, VEGF-A/perlecan binding assay (heparan sulfate dependence), VEGFR2 phosphorylation assays in human endothelial cells, mRNA rescue experiments","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — zebrafish KD with defined cellular phenotype, biochemical binding assay, VEGFR2 activation, mRNA rescue, multiple orthogonal methods, single lab","pmids":["19422911"],"is_preprint":false},{"year":2010,"finding":"Perlecan deficiency in skeletal muscle (Hspg2(-/-)-Tg mice) causes muscle hypertrophy with increased type IIb fiber cross-sectional area, substantially decreased myostatin and its type I receptor (ALK4) expression, reduced myostatin-induced Smad activation in myotubes, and altered fiber composition including increased type IIx fibers, demonstrating perlecan regulates fast muscle mass and fiber composition through myostatin signaling.","method":"Perlecan-deficient mouse model (Hspg2(-/-)-Tg), fiber cross-sectional area measurements, myosin heavy chain fiber typing, myostatin and ALK4 expression analysis, Smad activation assay in cultured myotubes, tenotomy overload/unload experiments","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined muscle phenotype, in vitro Smad signaling assay, single lab","pmids":["20541011"],"is_preprint":false},{"year":2011,"finding":"Perlecan/Hspg2 localizes to the osteocyte lacunocanalicular system of cortical bone; perlecan deficiency results in diminished canalicular pericellular area, reduced canalicular density, and fewer transverse tethering elements per canaliculus, demonstrating perlecan maintains the pericellular space of the lacunocanalicular system for interstitial fluid movement.","method":"Immunofluorescence, immunogold/TEM localization, ultrastructural measurements by electron microscopy in perlecan-deficient mice","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization tied to functional pericellular space measurement in KO mice, single lab","pmids":["20814969"],"is_preprint":false},{"year":2011,"finding":"Perlecan HS chains interact with tropoelastin electrostatically through heparan sulfate and core protein; these interactions promote tropoelastin coacervation and deposition of elastin onto immobilized perlecan, demonstrated by quartz crystal microbalance with dissipation studies, with co-localization of elastin, fibrillin-1, and perlecan in connective tissues.","method":"Quartz crystal microbalance with dissipation (QCM-D) solid-phase binding, co-localization by immunofluorescence in multiple connective tissues","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — solid-phase biophysical binding assay with dissipation monitoring, in vivo co-localization, single lab","pmids":["21874555"],"is_preprint":false},{"year":2012,"finding":"Drosophila perlecan (trol) is required for Sema-1a-PlexA-mediated repulsive axon guidance; trol mutations suppress Sema-1a-mediated motor axon defasciculation, trol genetically interacts with PlexA and Sema-1a, perlecan augments Sema-1a-induced reduction of phospho-FAK in insect cells, and restoring perlecan to mutant motor neurons rescues guidance defects, revealing ECM proteoglycan modulation of transmembrane guidance cue signaling.","method":"Drosophila genetic analysis (trol mutants, genetic interactions), in vitro Sema-1a treatment of insect cells with phospho-FAK measurement, rescue experiments by motor neuron-specific perlecan restoration","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis, in vitro biochemical assay, cell-type-specific rescue, multiple orthogonal methods, single lab","pmids":["23028146"],"is_preprint":false},{"year":2013,"finding":"Perlecan is required for FGF-2 signaling in the adult neural stem cell niche; perlecan deficiency reduces GFAP/CD133-positive neural stem cells in the SVZ and new neurons in the olfactory bulb; in the absence of perlecan, FGF-2 fails to promote neurosphere formation or activate Akt/Erk1/2 pathways and cyclin D2 expression, demonstrating perlecan is a niche component regulating FGF-2-dependent neural stem cell self-renewal.","method":"Hspg2-null mice, immunohistochemistry, neurosphere formation assay, Western blot for Akt/Erk1/2 phosphorylation and cyclin D2, FGF-2 treatment of wild-type and perlecan-deficient cells","journal":"Stem cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse phenotype plus in vitro signaling pathway dissection, single lab","pmids":["24434631"],"is_preprint":false},{"year":2014,"finding":"MMP-7 (matrilysin) cleaves perlecan/HSPG2 at multiple sites within domain IV immunoglobulin repeats, even when fully decorated with HS or in native BM context; domain IV-3 fragment induces PCa cell clustering (anti-invasive), whereas MMP-7 digestion of domain IV-3 reverses clustering to favor cell dispersion, acting as a molecular switch altering PCa cell behavior and promoting invasion through perlecan-rich BM.","method":"In vitro digestion of purified perlecan with MMP-7 and other proteases, recombinant domain IV subdomains, Transwell invasion assays, PCa cell clustering/dispersion assays with pre-digested BM extract","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with purified proteins, recombinant domain fragments, functional cell invasion assay, in silico + in vitro + in vivo contexts, single lab","pmids":["24833109"],"is_preprint":false},{"year":2014,"finding":"Perlecan domain V promotes niche function via α5β1 integrin; Drosophila intestinal stem cells (ISCs) that lose Pcan fail to adhere to ECM, lose identity, and fail to proliferate; these defects are cell-autonomous (loss from ISCs but not surrounding cells causes the phenotype) and depend partially on integrin signaling, not EGFR or JAK/STAT pathways.","method":"Drosophila genetic analysis with cell-type-specific Pcan knockdown, ISC identity and proliferation assays, epistasis with integrin/EGFR/JAK-STAT pathways","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-autonomous genetic analysis in Drosophila, pathway epistasis, clean phenotypic readout, single lab","pmids":["24936464"],"is_preprint":false},{"year":2014,"finding":"Smooth muscle cell-derived perlecan is decorated with both heparan sulfate and chondroitin sulfate, while endothelial cell-derived perlecan contains exclusively heparan sulfate; smooth muscle cells bind the perlecan protein core (domain III and domain V/endorepellin) only when glycosaminoglycans are removed via α2β1 integrin, whereas endothelial cells adhere to perlecan core in the presence of GAGs; perlecan HS from SMCs promotes FGF2 but not FGF1 signaling, while endothelial perlecan promotes both.","method":"Isolation of perlecan from primary human coronary artery SMCs and ECs, GAG characterization, cell adhesion assays with GAG-removed perlecan, integrin blocking antibodies, FGF1/FGF2 signaling assays","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-type-specific perlecan isolation with biochemical characterization and functional assays, single lab","pmids":["24509440"],"is_preprint":false},{"year":2014,"finding":"TNF-α activates NF-κB, which binds conserved sites in the distal HSPG2 promoter (2.6 kb upstream) to upregulate perlecan transcription in prostate cancer stromal and cancer cells; TNF-α but not TGFβ1 is identified as the major cytokine regulator of perlecan production, with p65 nuclear translocation and binding to HSPG2 regulatory region confirmed.","method":"HSPG2 promoter reporter constructs (up to 2.6 kb), TNF-α and TGFβ1 treatment, p65 nuclear translocation assay, ChIP for p65 binding to HSPG2 promoter region","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter deletion mapping, ChIP, nuclear translocation, single lab","pmids":["24700612"],"is_preprint":false},{"year":2014,"finding":"Perlecan domain II (LDLR-like domain) interacts with LDL through O-linked glycans present only in secreted DII; the negatively charged sialic acid caps on O-glycans are critical for LDL binding; HS chains and DII have an additive effect on LDL binding; unlike LDLR, this interaction mediates lipoprotein retention rather than endocytosis.","method":"Recombinant domain II binding assays, glycan analysis, deglycosylation experiments, surface plasmon resonance or related binding assays, sialic acid dependency assays","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — recombinant domain binding with biochemical characterization of glycan-dependence, single lab","pmids":["25528754"],"is_preprint":false},{"year":2015,"finding":"Perlecan heparan sulfate chains are required for formation of the HS-FGF2-FGFR1 ternary complex; Hspg2(Δ3/Δ3) mice (HS-deficient) have reduced pericytes and muscularization of pulmonary vessels, attenuated hypoxic pulmonary hypertension with lower FGFR1 phosphorylation and reduced PASMC proliferation; ligand and carbohydrate engagement assay confirmed perlecan HS is required for HS-FGF2-FGFR1 complex formation.","method":"Hspg2(Δ3/Δ3) mice (exon 3 deletion, HS-deficient), pulmonary angiography, RVSP measurement, FGFR1 phosphorylation analysis, ligand and carbohydrate engagement assay (LACE), in vitro PASMC proliferation and adhesion assays, FGFR1 inhibitor treatment","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 / Strong — HS-specific KO mouse, LACE assay for ternary complex, in vivo phenotype plus in vitro mechanistic validation, multiple methods, single lab","pmids":["25952902"],"is_preprint":false},{"year":2015,"finding":"Perlecan deficiency in slow-twitch soleus muscle enhances autophagic activity (increased LC3II, decreased p62), accompanied by reduced phosphorylation of p70S6k and Akt and increased AMPK phosphorylation, suggesting perlecan inhibits autophagy through the mTORC1 pathway in skeletal muscle.","method":"Perlecan-deficient mice (Hspg2(-/-)-Tg), mechanical unloading (tenotomy), Western blot for autophagy markers (LC3II, p62), mTORC1 pathway analysis (p70S6k, Akt phosphorylation), AMPKα phosphorylation","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with pathway analysis, multiple signaling readouts, single lab","pmids":["26319110"],"is_preprint":false},{"year":2015,"finding":"Perlecan domain V promotes pericyte migration by interacting with α5β1 integrin to enhance PDGF-BB-induced phosphorylation of PDGFRβ, Src homology region 2 domain-containing phosphatase-2 (SHP-2), and focal adhesion kinase (FAK), supporting blood-brain barrier repair after ischemic stroke.","method":"Recombinant domain V treatment, phosphorylation assays for PDGFRβ/SHP-2/FAK, integrin α5β1 interaction assays, pericyte migration assays","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant domain functional assay, specific signaling molecule readouts, single lab (cited in PMID:32947020)","pmids":["32947020"],"is_preprint":false},{"year":2016,"finding":"Perlecan interacts with type VI collagen pericellularly in intervertebral disc; this interaction is confirmed by surface plasmon resonance; translamellar cross-bridges are significantly less abundant in HS-deficient Hspg2 exon 3 null mice than in wild type, demonstrating perlecan HS chains contribute to type VI collagen pericellular organization and IVD matrix stability.","method":"Confocal laser scanning microscopy co-localization, surface plasmon resonance binding assay, Hspg2 exon 3 null mouse (HS-deficient) histology and cross-bridge quantification","journal":"European cells & materials","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — SPR binding plus HS-specific KO phenotype for structural role, single lab","pmids":["27377666"],"is_preprint":false},{"year":2018,"finding":"Domain IV-3 of perlecan interacts directly with semaphorin 3A (Sema3A) on prostate cancer cells to deactivate FAK (dephosphorylation) and stabilize cell-cell interactions (tumoroid formation); MMP-7 cleavage of perlecan disrupts the perlecan-Sema3A complex, allowing FAK re-phosphorylation and cell dispersion; Sema3A antibody mimics Domain IV-3 clustering activity and Sema3A knockdown prevents Domain IV-3-induced tumoroid formation.","method":"Direct binding experiments (Domain IV-3/Sema3A), Sema3A antibody treatment, Sema3A siRNA knockdown, FAK phosphorylation assays, tumoroid formation assays, MMP-7 digestion of complex","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated, genetic knockdown plus antibody confirmation, signaling readout, single lab","pmids":["29740048"],"is_preprint":false},{"year":2019,"finding":"Perlecan/HSPG2 deficiency impairs osteocyte calcium signaling in response to mechanical loading; perlecan-deficient osteocytes show decreased overall Ca2+ response rate, peaks, and recovery speed; RNA sequencing identifies suppression of calcium signaling, ECM-receptor interaction, and focal adhesion pathways; specific defects in ER calcium cycling regulators (Ryr1/ryanodine receptors and Atp2a1/Serca1 pumps) are identified in Hypo bones.","method":"Real-time Ca2+ imaging in situ in murine tibiae under cyclic loading, RNA sequencing with pathway analysis, perlecan-deficient (Hypo) mouse model","journal":"Bone","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — real-time in situ calcium imaging plus transcriptome pathway analysis in KO mouse, single lab","pmids":["31715337"],"is_preprint":false},{"year":2023,"finding":"TNFSF13 binds HSPG2 (perlecan) at the cell surface and activates the NF-κB signaling pathway to promote hypertrophic scar fibroblast proliferation, migration, fibrosis, and inflammation; silencing of HSPG2 eliminates the promoting effects of TNFSF13 and inhibition of NF-κB blocks these effects; MSC-derived exosomes reduce TNFSF13 and HSPG2 to inhibit fibroblast activity.","method":"Co-binding assay (TNFSF13/HSPG2 interaction), HSPG2 siRNA knockdown, recombinant TNFSF13 protein stimulation, NF-κB inhibition, CCK-8/EdU/Transwell assays, Western blot","journal":"International journal of nanomedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding shown, siRNA knockdown with defined phenotype, NF-κB pathway epistasis, single lab","pmids":["38046235"],"is_preprint":false},{"year":2024,"finding":"Perlecan (HSPG2) promotes cardiomyocyte structural, contractile, and metabolic maturation; perlecan-haploinsufficient hPSC-CMs show immature features including reduced α-actinin expression, increased glycolytic metabolism and proliferation; perlecan-haploinsufficient engineered heart tissues have reduced thickness and force generation; hPSC-CMs on perlecan-peptide substrate show hypertrophic growth; perlecan signaling is mediated via the dystroglycan complex.","method":"HSPG2+/- hPSC haploinsufficient lines, hPSC-CM differentiation, structural/contractile/metabolic characterization, engineered heart tissue force measurement, perlecan peptide substrate culture, dystroglycan complex interaction assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — haploinsufficient human cell model plus engineered tissue functional assay, dystroglycan complex interaction, single lab","pmids":["38198277"],"is_preprint":false}],"current_model":"Perlecan (HSPG2) is a large, modular heparan sulfate proteoglycan with a five-domain protein core that functions at basement membranes and pericellular matrices as: (1) an accessory co-receptor for FGF family members (bFGF/FGF-2, FGF-7/KGF, FGF-1) and VEGF-A, where its HS chains form ternary complexes with growth factors and their receptors to potentiate signaling; (2) a structural scaffold maintaining basement membrane and cartilage ECM integrity under mechanical stress, partly through interactions with collagen IV, laminins, type VI collagen, and elastin/tropoelastin; (3) a cell adhesion substrate via multiple domain-specific integrin-binding sites (domain III RGDS/α integrins, domain IV TWSKVGG peptide/heparin-sensitive receptor, domain V/α2β1 and α5β1 integrins); (4) a Hedgehog and semaphorin signaling modulator through direct protein-core interactions; (5) a regulator of muscle physiology through myostatin signaling and neuromuscular junction organization via dystroglycan binding; and (6) a mechanosensor in osteocyte lacunocanalicular systems and vascular endothelium; its C-terminal domain V (endorepellin) antagonizes VEGFR2 and α2β1 integrin to inhibit angiogenesis, while MMP-7 cleavage of domain IV acts as a molecular switch altering cell behavior from cohesion to invasion."},"narrative":{"mechanistic_narrative":"Perlecan (HSPG2) is a large modular heparan sulfate proteoglycan built from five distinct protein-core domains—an HS-attachment domain I, an LDL-receptor-like domain II, a laminin-like domain III, a domain IV of immunoglobulin repeats, and a laminin G-like domain V—that organizes basement membranes and pericellular matrices and modulates growth-factor signaling [PMID:1569102]. Its HS chains act as accessory co-receptors that potentiate FGF and VEGF signaling: perlecan promotes high-affinity bFGF–receptor binding and bFGF-driven angiogenesis [PMID:7528102], its HS is required to assemble the HS–FGF2–FGFR1 ternary complex [PMID:25952902], and it binds VEGF-A165 to enhance VEGFR2 activation during developmental angiogenesis [PMID:19422911]. Beyond its glycan chains, the perlecan protein core itself transduces signals, being required for KGF/FGFR2 activation independently of HS [PMID:11563979] and supporting integrin-mediated cell adhesion through a domain III RGDS site and a domain IV immunoglobulin-repeat peptide that drives FAK activation [PMID:7814401, PMID:17997086]. Structurally, perlecan maintains basement membrane and cartilage integrity under mechanical stress, with null mice showing stress-induced BM deterioration, cardiac failure, exencephaly, and disorganized chondrocyte columns and collagen fibrils [PMID:10579729, PMID:10545953], phenotypes mirrored in humans where HSPG2 mutations cause Schwartz-Jampel syndrome (myotonia with skeletal dysplasia) [PMID:11101850] and functional-null mutations cause lethal dyssegmental dysplasia Silverman-Handmaker type [PMID:11891676]. In muscle, perlecan anchors to the cell surface via alpha-dystroglycan and organizes the neuromuscular junction [PMID:9791728], and regulates fast muscle mass through myostatin signaling [PMID:20541011]. Domain V (endorepellin) engages alpha5beta1 integrin to drive pericyte and stem-cell behaviors [PMID:32947020, PMID:24936464], while MMP-7 cleavage of domain IV acts as a molecular switch—disrupting domain IV-3/Sema3A-mediated FAK deactivation to convert prostate cancer cells from cohesion to invasion [PMID:24833109, PMID:29740048].","teleology":[{"year":1992,"claim":"Establishing the five-domain modular architecture of the perlecan core defined the structural basis for its multifunctionality, assigning candidate functions to each domain (HS attachment, LDL-receptor homology, laminin/NCAM-like adhesion modules).","evidence":"cDNA cloning and full-length sequence determination with in situ hybridization and immunolocalization","pmids":["1569102"],"confidence":"High","gaps":["Domain-level functions inferred from homology, not yet functionally tested","No structural model of the assembled core"]},{"year":1993,"claim":"Complete genomic mapping correlated 94 exons to protein domains and revealed a TATA-less, SP1/ETF promoter, indicating constitutive housekeeping-style regulation.","evidence":"Intron-exon mapping and promoter characterization from genomic DNA","pmids":["8234307"],"confidence":"High","gaps":["Cell-type-specific and inducible regulation not addressed","Alternative splicing of functional variants not catalogued"]},{"year":1994,"claim":"Identifying perlecan as a low-affinity/accessory bFGF receptor that potentiates mitogenesis and neovascularization assigned its HS chains a direct role in growth-factor signaling rather than purely structural support.","evidence":"Receptor binding on HS-deficient cells, neutralizing antibodies, in vivo rabbit ear angiogenesis","pmids":["7528102"],"confidence":"High","gaps":["Ternary complex stoichiometry not resolved at the time","Did not distinguish HS- vs core-dependent contributions"]},{"year":1995,"claim":"Demonstrating that domain III supports RGDS-dependent integrin adhesion established the protein core (not just HS) as a direct cell-adhesion substrate.","evidence":"Recombinant domain III adhesion assays with RGDS peptide inhibition","pmids":["7814401"],"confidence":"High","gaps":["Specific integrin heterodimer not pinned down","Downstream signaling not characterized"]},{"year":1996,"claim":"C. elegans unc-52 work showed perlecan is a cell-autonomous muscle ECM product essential for myofilament assembly and muscle attachment, linking the proteoglycan to muscle architecture.","evidence":"unc-52 genetic analysis, antibody labeling, laser ablation in C. elegans","pmids":["8575624"],"confidence":"High","gaps":["Molecular receptor mediating attachment not identified in worm","Mammalian conservation of mechanism untested here"]},{"year":1998,"claim":"Identifying alpha-dystroglycan as a calcium/heparin-sensitive perlecan partner provided a surface-anchoring mechanism linking perlecan to the DG-dystrophin complex and AChR clustering at the NMJ.","evidence":"Blot overlay, co-IP, and immunofluorescence in Xenopus muscle","pmids":["9791728"],"confidence":"Medium","gaps":["Binding domain on perlecan not mapped","Limited mechanistic follow-up beyond single lab"]},{"year":1999,"claim":"Two independent knockouts established perlecan as essential for stress-resistant basement membranes and cartilage matrix integrity, with the chondrocyte phenotype resembling FGFR3 gain-of-function and implicating shared signaling.","evidence":"Hspg2-null mouse histology, EM, BrdU proliferation, GAG analysis","pmids":["10579729","10545953"],"confidence":"High","gaps":["Whether BM failure is purely mechanical vs signaling-driven not separated","FGFR3 epistasis was inferential, not direct"]},{"year":1999,"claim":"Perlecan substrates were shown to drive chondrogenic differentiation of mesenchymal cells, indicating an instructive, not merely scaffolding, role in cartilage formation.","evidence":"Culture of 10T1/2 cells on purified perlecan with chondrogenic marker readouts","pmids":["10352025"],"confidence":"Medium","gaps":["Receptor/signal mediating differentiation not identified","Single lab, in vitro only"]},{"year":2000,"claim":"Human SJS1 mutation discovery established HSPG2 as a disease gene controlling both cartilage integrity and muscle excitability, validating the mouse phenotypes in humans.","evidence":"Mutation sequencing and linkage in SJS1 families","pmids":["11101850"],"confidence":"High","gaps":["Mechanism linking perlecan loss to myotonia not resolved","Genotype-phenotype relationships incomplete"]},{"year":2000,"claim":"A perlecan-only cell system revealed a distinct beta1-integrin-dependent endocytic pathway for atherogenic lipoprotein uptake and degradation, expanding perlecan's role into lipid handling.","evidence":"Lipoprotein binding/internalization/degradation assays with inhibitors and integrin/LRP blockade","pmids":["10818109"],"confidence":"Medium","gaps":["In vivo relevance to atherosclerosis untested","Molecular machinery of the pathway incompletely defined"]},{"year":2001,"claim":"Genetic disruption in human carcinoma cells showed the perlecan protein core, not its HS chains, is required for KGF/FGFR2 activation, distinguishing core-dependent from HS-dependent growth-factor functions.","evidence":"Targeted HSPG2 knockout colon carcinoma cells with FGF7 binding/activation assays and heparin controls","pmids":["11563979"],"confidence":"High","gaps":["Core domain mediating FGFR2 activation not localized","Direct core-FGF7 binding not demonstrated"]},{"year":2001,"claim":"Mapping FGF-binding protein to a specific EGF repeat in domain III provided a molecular basis for perlecan core participation in FGF signaling in tumor stroma.","evidence":"Yeast two-hybrid, co-IP, recombinant domain III-AP binding, IHC in squamous carcinoma","pmids":["11148217"],"confidence":"Medium","gaps":["Functional consequence of the interaction in vivo unproven","Single lab"]},{"year":2002,"claim":"DDSH mutation work showed functional-null perlecan that is unstable and unsecreted causes lethal dwarfism, demonstrating that secretion into the ECM is essential for cartilage development.","evidence":"HSPG2 mutation identification with tissue immunostaining and secretion analysis in DDSH patients","pmids":["11891676"],"confidence":"High","gaps":["Cellular quality-control pathway retaining mutant protein not defined here","Relationship to milder SJS allelic series unresolved at the time"]},{"year":2003,"claim":"Drosophila trol work placed perlecan as a modulator of both FGF and Hedgehog signaling in neuroblast division, with direct perlecan-Shh binding not competed by heparin, indicating core-mediated Hh interaction.","evidence":"trol genetics, FGF-2 rescue, MAPK inhibition, Trol/Hh and Perlecan/Shh co-IP","pmids":["12645928"],"confidence":"High","gaps":["Perlecan domain binding Hh not mapped","Mammalian Shh modulation tested only biochemically"]},{"year":2003,"claim":"Domain V was shown to bind ECM1 and progranulin, with the progranulin interaction functionally counteracting domain V's growth-promoting activity, establishing domain V as a hub for partner-modulated signaling.","evidence":"Yeast two-hybrid, co-IP, SPR kinetics, cell growth assays","pmids":["12604605","12900424"],"confidence":"Medium","gaps":["In vivo significance of these interactions untested","Single lab for each interaction"]},{"year":2003,"claim":"Heparanase was shown to specifically degrade perlecan HS chains, linking perlecan HS turnover to tumor cell invasion.","evidence":"In vitro HPSE-1 digestion of purified perlecan HS and chemoinvasion assays","pmids":["14630925"],"confidence":"Medium","gaps":["Released HS fragment activities not characterized","In vivo invasion link correlative"]},{"year":2007,"claim":"A domain IV TWSKVGG peptide was shown to drive cation-independent, heparin-sensitive adhesion and FAK activation, adding a distinct adhesion module to the perlecan core.","evidence":"Peptide adhesion/spreading assays with FAK activation across cell lines","pmids":["17997086"],"confidence":"Medium","gaps":["Receptor mediating peptide adhesion not identified","Relevance of peptide to intact perlecan unproven"]},{"year":2006,"claim":"Distinguishing mutation classes in SJS established hypomorphic mechanisms—NMD for truncating alleles and intracellular retention for cysteine missense alleles—explaining graded disease severity.","evidence":"mRNA and immunostaining analysis of 22 new mutations in SJS patient cells","pmids":["16927315"],"confidence":"Medium","gaps":["Quality-control machinery retaining missense protein not identified","Quantitative dose-phenotype relationships incomplete"]},{"year":2009,"claim":"Zebrafish work established perlecan as required for developmental angiogenesis, binding and concentrating VEGF-A165 in an HS-dependent manner to enhance VEGFR2 activation.","evidence":"Morpholino knockdown, VEGF-A binding assay, VEGFR2 phosphorylation, VEGF-A165 mRNA rescue","pmids":["19422911"],"confidence":"High","gaps":["Whether perlecan core also contributes to VEGF signaling not addressed","Endothelial vs matrix source of perlecan not separated"]},{"year":2010,"claim":"Perlecan deficiency was shown to cause fast-fiber muscle hypertrophy via reduced myostatin/ALK4-Smad signaling, defining a role in muscle mass regulation distinct from its structural functions.","evidence":"Hspg2(-/-)-Tg mouse fiber analysis and myotube Smad activation assays","pmids":["20541011"],"confidence":"Medium","gaps":["Direct perlecan-myostatin binding not demonstrated","Single lab"]},{"year":2011,"claim":"Localization to the osteocyte lacunocanalicular system and tropoelastin binding established perlecan as a pericellular structural organizer supporting interstitial fluid spaces and elastogenesis.","evidence":"Immunogold/TEM ultrastructure in KO bone; QCM-D tropoelastin binding with tissue co-localization","pmids":["20814969","21874555"],"confidence":"Medium","gaps":["Functional consequence for bone mechanotransduction not yet linked here","Tropoelastin binding determinants only partially mapped"]},{"year":2012,"claim":"Drosophila trol was shown to modulate Sema-1a/PlexA repulsive axon guidance via phospho-FAK regulation, revealing ECM proteoglycan tuning of transmembrane guidance-cue signaling.","evidence":"trol genetics with Sema-1a/PlexA, in vitro phospho-FAK assays, motor-neuron-specific rescue","pmids":["23028146"],"confidence":"High","gaps":["Direct perlecan-Sema/Plexin binding not shown in fly","Mammalian conservation untested here"]},{"year":2013,"claim":"Perlecan was established as a neural stem cell niche component required for FGF-2-dependent self-renewal via Akt/Erk and cyclin D2 activation.","evidence":"Hspg2-null mouse SVZ analysis and neurosphere/FGF-2 signaling assays","pmids":["24434631"],"confidence":"Medium","gaps":["Whether HS or core mediates the niche effect not separated","Single lab"]},{"year":2014,"claim":"A series of studies dissected cell-type-specific perlecan glycosylation, domain V/alpha5beta1 stem-cell niche function, TNF-alpha/NF-kappaB transcriptional control, and domain II glycan-dependent LDL retention, refining how perlecan composition tailors its function.","evidence":"SMC/EC perlecan isolation and GAG analysis; Drosophila ISC genetics; HSPG2 promoter ChIP; recombinant domain II LDL binding","pmids":["24509440","24936464","24700612","25528754"],"confidence":"Medium","gaps":["In vivo integration of these context-specific functions incomplete","Each finding from a single lab"]},{"year":2014,"claim":"Identifying MMP-7 cleavage of domain IV as a molecular switch from clustering (anti-invasive) to dispersion (pro-invasive) defined a regulated mechanism converting perlecan from cohesion to invasion-permissive.","evidence":"In vitro MMP-7 digestion of perlecan, recombinant domain IV subdomains, invasion and clustering assays","pmids":["24833109"],"confidence":"High","gaps":["In vivo demonstration of the switch limited","Receptor for intact domain IV-3 clustering not yet identified here"]},{"year":2015,"claim":"HS-specific knockouts and domain V studies dissected perlecan HS as essential for the HS-FGF2-FGFR1 ternary complex in pulmonary vascular remodeling, while domain V/alpha5beta1 promotes PDGF-driven pericyte migration and perlecan suppresses muscle autophagy via mTORC1.","evidence":"Hspg2(Δ3/Δ3) HS-deficient mice with LACE assay; recombinant domain V pericyte signaling; KO muscle autophagy pathway analysis","pmids":["25952902","32947020","26319110"],"confidence":"High","gaps":["Crosstalk between HS-dependent and core-dependent functions not unified","Domain V pericyte mechanism from single lab"]},{"year":2016,"claim":"Perlecan HS chains were shown to organize type VI collagen pericellularly and stabilize intervertebral disc matrix, extending its pericellular structural role to translamellar cross-bridges.","evidence":"SPR binding and HS-deficient mouse cross-bridge quantification","pmids":["27377666"],"confidence":"Medium","gaps":["Mechanism by which HS organizes collagen VI not detailed","Single lab"]},{"year":2018,"claim":"Domain IV-3 was shown to bind Sema3A directly to deactivate FAK and stabilize tumor cell-cell interactions, with MMP-7 cleavage disrupting the complex—mechanistically explaining the cohesion-to-invasion switch.","evidence":"Direct binding, Sema3A antibody/siRNA, FAK phosphorylation, tumoroid assays, MMP-7 digestion","pmids":["29740048"],"confidence":"Medium","gaps":["In vivo prostate cancer relevance not established here","Single lab"]},{"year":2019,"claim":"Perlecan deficiency was shown to impair osteocyte calcium signaling under mechanical load, with transcriptomic suppression of calcium signaling, ECM-receptor, and focal adhesion pathways, defining a mechanosensory role in bone.","evidence":"In situ real-time Ca2+ imaging in loaded tibiae and RNA-seq in KO mice","pmids":["31715337"],"confidence":"Medium","gaps":["Direct link between pericellular perlecan and Ca2+ machinery not mechanistically resolved","Single lab"]},{"year":2023,"claim":"TNFSF13 was shown to bind cell-surface HSPG2 to activate NF-kappaB and drive fibroblast proliferation/fibrosis, identifying perlecan as a co-receptor in hypertrophic scar pathology.","evidence":"Co-binding assay, HSPG2 siRNA, NF-kappaB inhibition, proliferation/migration assays","pmids":["38046235"],"confidence":"Medium","gaps":["Binding domain on perlecan not mapped","In vivo scar model not tested"]},{"year":2024,"claim":"Perlecan haploinsufficiency was shown to impair cardiomyocyte structural, contractile, and metabolic maturation via the dystroglycan complex, extending its role to cardiac tissue maturation.","evidence":"HSPG2+/- hPSC-CM and engineered heart tissue assays with peptide substrate and dystroglycan interaction studies","pmids":["38198277"],"confidence":"Medium","gaps":["Specific perlecan domain driving maturation not pinned down","Single lab; human in vitro model only"]},{"year":null,"claim":"It remains unresolved how perlecan's distinct functional modules—HS-dependent growth-factor co-receptor activity, core-protein integrin/adhesion signaling, and dystroglycan anchoring—are integrated and prioritized in a given tissue context, and which receptor mediates several core-domain effects (KGF/FGFR2 activation, domain IV peptide adhesion, domain IV-3 clustering).","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model of the assembled five-domain core with bound partners","Receptors for several core-domain functions remain unidentified","Tissue-specific division of labor between HS and core not systematically defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,31,20,11]},{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[3,19,27]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[6,7,23,34]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,6,22]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[6,7,34]},{"term_id":"GO:0030312","term_label":"external encapsulating structure","supporting_discovery_ids":[6,7]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,20,31,11]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[6,7,23,34]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[7,17,25,27]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,13]}],"complexes":["dystroglycan-dystrophin complex","HS-FGF2-FGFR1 ternary complex"],"partners":["DAG1","FGF2","VEGFA","FGFBP1","ECM1","GRN","COL6","SEMA3A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P98160","full_name":"Basement membrane-specific heparan sulfate proteoglycan core protein","aliases":["Perlecan","PLC"],"length_aa":4391,"mass_kda":468.8,"function":"Integral component of basement membranes. Component of the glomerular basement membrane (GBM), responsible for the fixed negative electrostatic membrane charge, and which provides a barrier which is both size- and charge-selective. It serves as an attachment substrate for cells. Plays essential roles in vascularization. Critical for normal heart development and for regulating the vascular response to injury. Also required for avascular cartilage development (PubMed:12435733, PubMed:15591058, PubMed:19789387). In muscle, it is essential for localizing acetylcholinesterase (AChE) at the neuromuscular junctions (NMJ), most probably acting as an adapter that links the acetylcholinesterase collagenic tail peptide (COLQ) to alpha-dystroglycan, and is therefore involved in the down-regulation of colinergic synaptic transmission (By similarity) Anti-angiogenic and anti-tumor peptide that inhibits endothelial cell migration, collagen-induced endothelial tube morphogenesis and blood vessel growth in the chorioallantoic membrane. Blocks endothelial cell adhesion to fibronectin and type I collagen. Anti-tumor agent in neovascularization. Interaction with its ligand, integrin alpha2/beta1, is required for the anti-angiogenic properties. Evokes a reduction in phosphorylation of receptor tyrosine kinases via alpha2/beta1 integrin-mediated activation of the tyrosine phosphatase, PTPN6 Has anti-angiogenic properties that require binding of calcium ions for full activity","subcellular_location":"Secreted, extracellular space, extracellular matrix, basement membrane; Secreted","url":"https://www.uniprot.org/uniprotkb/P98160/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HSPG2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HSPG2","total_profiled":1310},"omim":[{"mim_id":"621182","title":"NEURODEVELOPMENTAL DISORDER WITH POOR OR ABSENT SPEECH, DYSMORPHIC FACIES, AND BEHAVIORAL ABNORMALITIES; NEDSFB","url":"https://www.omim.org/entry/621182"},{"mim_id":"611901","title":"VON WILLEBRAND FACTOR A DOMAIN-CONTAINING PROTEIN 1; VWA1","url":"https://www.omim.org/entry/611901"},{"mim_id":"607737","title":"FIBROBLAST GROWTH FACTOR-BINDING PROTEIN 1; FGFBP1","url":"https://www.omim.org/entry/607737"},{"mim_id":"605399","title":"NIDOGEN 2; NID2","url":"https://www.omim.org/entry/605399"},{"mim_id":"601559","title":"STUVE-WIEDEMANN SYNDROME 1; STWS1","url":"https://www.omim.org/entry/601559"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"blood vessel","ntpm":245.5}],"url":"https://www.proteinatlas.org/search/HSPG2"},"hgnc":{"alias_symbol":["perlecan","PRCAN"],"prev_symbol":["SJS1"]},"alphafold":{"accession":"P98160","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P98160","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HSPG2","jax_strain_url":"https://www.jax.org/strain/search?query=HSPG2"},"sequence":{"accession":"P98160","fasta_url":"https://rest.uniprot.org/uniprotkb/P98160.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P98160/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P98160"}},"corpus_meta":[{"pmid":"10579729","id":"PMC_10579729","title":"Perlecan maintains the integrity of cartilage and some basement membranes.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10579729","citation_count":515,"is_preprint":false},{"pmid":"7528102","id":"PMC_7528102","title":"Perlecan, basal lamina proteoglycan, promotes basic fibroblast growth factor-receptor binding, mitogenesis, and angiogenesis.","date":"1994","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/7528102","citation_count":476,"is_preprint":false},{"pmid":"10545953","id":"PMC_10545953","title":"Perlecan is essential for cartilage and cephalic development.","date":"1999","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10545953","citation_count":411,"is_preprint":false},{"pmid":"1569102","id":"PMC_1569102","title":"Primary structure of the human heparan sulfate proteoglycan from basement membrane (HSPG2/perlecan). A chimeric molecule with multiple domains homologous to the low density lipoprotein receptor, laminin, neural cell adhesion molecules, and epidermal growth factor.","date":"1992","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/1569102","citation_count":281,"is_preprint":false},{"pmid":"18826258","id":"PMC_18826258","title":"Diverse cell signaling events modulated by perlecan.","date":"2008","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18826258","citation_count":214,"is_preprint":false},{"pmid":"11101850","id":"PMC_11101850","title":"Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia).","date":"2000","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/11101850","citation_count":207,"is_preprint":false},{"pmid":"27613501","id":"PMC_27613501","title":"A current view of perlecan in physiology and pathology: A mosaic of 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the promoter lacks canonical TATA or CAAT boxes but contains SP1 and ETF binding sites with multiple transcription initiation sites, consistent with a housekeeping gene regulation pattern.\",\n      \"method\": \"Complete intron-exon mapping by genomic DNA analysis, promoter characterization, sequencing\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete genomic structure determined, multiple orthogonal methods (restriction mapping, sequencing, promoter analysis)\",\n      \"pmids\": [\"8234307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Perlecan promotes high-affinity binding of bFGF (FGF-2) to its receptor on cells deficient in heparan sulfate and to soluble FGF receptors, augments heparin-dependent mitogenic activity of bFGF, and potently induces bFGF-mediated neovascularization in vivo, identifying perlecan as a major accessory/low-affinity receptor for bFGF and an angiogenic modulator.\",\n      \"method\": \"Affinity-purified HSPG binding assays, receptor binding assays on HS-deficient cells, neutralizing monoclonal antibodies, in vivo rabbit ear angiogenesis model, mitogenesis assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (cell-free binding, cell-based receptor assay, neutralizing antibody, in vivo model), replicated across contexts\",\n      \"pmids\": [\"7528102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Recombinant perlecan domain III supports integrin-mediated cell attachment via its RGDS sequence; adhesion is specifically inhibited by RGDS peptide and intact perlecan but not laminin, demonstrating a role for perlecan domain III in integrin-mediated signaling.\",\n      \"method\": \"Recombinant domain III expression and purification, cell adhesion assays on coated dishes, inhibition with synthetic RGDS peptide, rotary shadow electron microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — recombinant protein reconstitution, mutagenesis-level peptide blocking, multiple cell lines tested in single lab\",\n      \"pmids\": [\"7814401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Perlecan is a cell-autonomous product of muscle cells in C. elegans (encoded by unc-52) and is essential for myofilament formation and muscle attachment; perlecan expressed in individual muscle cells does not spread beyond the borders of the ECM underlying that cell, demonstrating cell-autonomous ECM function.\",\n      \"method\": \"Genetic analysis of unc-52 mutants, polyclonal antibody labeling, laser ablation of blastomeres, immunofluorescence during C. elegans development\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with defined cellular phenotype, cell-autonomous rescue experiments, replicated in C. elegans model\",\n      \"pmids\": [\"8575624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Perlecan binds alpha-dystroglycan (alpha-DG) in a calcium- and heparin-sensitive manner; perlecan co-localizes with dystroglycan at cell surfaces of Xenopus muscle cells, is co-immunoprecipitated with anti-DG antibody from muscle lysate, and clusters at ACh receptor clusters at the neuromuscular junction, suggesting perlecan is anchored to muscle surface via the DG-dystrophin complex.\",\n      \"method\": \"Blot overlay assays, co-immunoprecipitation, immunofluorescence co-localization in Xenopus muscle cells, AChR clustering assays\",\n      \"journal\": \"Cell adhesion and communication\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and overlay assays in single lab, multiple orthogonal methods but limited mechanistic follow-up\",\n      \"pmids\": [\"9791728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Perlecan null mice show normal basement membrane (BM) formation initially, but BMs deteriorate under mechanical stress (contracting myocardium, expanding brain vesicles), leading to cardiac failure and exencephaly; perlecan-null cartilage shows reduced fibrillar collagen network and shortened fibers with elevated ECM gene expression, demonstrating perlecan maintains BM integrity and protects cartilage ECM from degradation.\",\n      \"method\": \"Homozygous null mutation (gene knockout) in mice, histology, electron microscopy, immunohistochemistry, Northern blotting\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with multiple defined phenotypic readouts, replicated by independent group (PMID:10545953)\",\n      \"pmids\": [\"10579729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Hspg2-null mice show severe disorganization of chondrocyte columnar structures, defective endochondral ossification, reduced and disorganized collagen fibrils and glycosaminoglycans in cartilage matrix, reduced chondrocyte proliferation, and diminished prehypertrophic zone, demonstrating perlecan is essential for cartilage matrix structure and chondrocyte proliferation. Abnormal phenotypes resemble FGFR3 gain-of-function, suggesting perlecan and FGFR3 affect similar signaling pathways.\",\n      \"method\": \"Gene disruption (Hspg2 knockout) in mice, histology, electron microscopy, BrdU proliferation assay, glycosaminoglycan analysis, immunostaining\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independent gene knockout, multiple orthogonal phenotypic analyses, genetic epistasis inference with FGFR3 pathway, replicated by independent lab (PMID:10579729)\",\n      \"pmids\": [\"10545953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Culture on perlecan (but not other matrices including fibronectin, laminin, or collagen) stimulates multipotential mesenchymal fibroblasts (10T1/2) to form dense nodules with Alcian blue staining and collagen type II expression, and elevates mRNAs for collagen II, aggrecan, and perlecan itself, demonstrating perlecan promotes chondrogenic differentiation in vitro.\",\n      \"method\": \"Cell culture on purified perlecan substrates, Alcian blue staining, immunostaining for collagen II, Northern blotting for chondrogenic markers\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reconstitution on purified protein, multiple chondrogenic marker readouts, single lab\",\n      \"pmids\": [\"10352025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Cells expressing perlecan (but no other proteoglycans) bind, internalize, and degrade atherogenic lipoproteins enriched in lipoprotein lipase via a pathway kinetically and biochemically distinct from coated-pit or syndecan-mediated endocytosis; binding is blocked by heparitinase, degradation by chloroquine, internalization inhibited by genistein but not cytochalasin D, and beta1 integrins serve as cell surface attachment sites for perlecan.\",\n      \"method\": \"Lipoprotein binding, internalization, and degradation assays in cells expressing only perlecan; pharmacological inhibitors; antibody blockade of beta1 integrin and LRP\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean cell system expressing only perlecan, multiple inhibitor approaches, kinetic analysis, single lab\",\n      \"pmids\": [\"10818109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Mutations (missense and splicing) in HSPG2 cause Schwartz-Jampel syndrome (SJS1), a rare autosomal recessive disorder with permanent myotonia and skeletal dysplasia, establishing perlecan as essential for both maintaining cartilage integrity and regulating muscle excitability in humans.\",\n      \"method\": \"Mutation identification by sequencing in SJS1 families, linkage to chromosome 1p34-p36.1\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human disease gene identification with multiple families and multiple mutation types, confirmed by independent studies (PMID:16927315)\",\n      \"pmids\": [\"11101850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The perlecan protein core (not its heparan sulfate chains) is required for functional activation of the KGF receptor (FGFR2/KGF-R) and downstream signaling in colon carcinoma cells; perlecan-deficient cells (generated by targeted homologous recombination) fail to respond to FGF7 even with added heparin, though they show increased FGF7 surface binding.\",\n      \"method\": \"Targeted homologous recombination to generate perlecan-null colon carcinoma cells, FGF7 binding assays, cell proliferation assays, receptor activation assays, heparin supplementation controls\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — genetic disruption of HSPG2 in human cells, receptor activation and ligand binding assays, domain-specific dissection (core protein vs HS chains), single lab\",\n      \"pmids\": [\"11563979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"FGF-binding protein (FGF-BP) interacts specifically with the protein core of perlecan domain III (second EGF repeat), as identified by yeast two-hybrid screening and validated by co-immunoprecipitation and binding to recombinant domain III-alkaline phosphatase fusion protein; FGF-BP and perlecan co-localize in the pericellular stroma of squamous cell carcinomas.\",\n      \"method\": \"Yeast two-hybrid screen of keratinocyte cDNA library, deletion mutant mapping, co-immunoprecipitation, recombinant domain III-alkaline phosphatase fusion binding assay, immunohistochemistry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP and recombinant binding, domain-level mapping, single lab\",\n      \"pmids\": [\"11148217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Dyssegmental dysplasia Silverman-Handmaker type (DDSH), a lethal form of dwarfism, is caused by functional null mutations of HSPG2; insertion and splicing mutations create premature termination codons, the mutant perlecan is unstable and not secreted into the extracellular matrix, demonstrating perlecan is essential for cartilage development in humans.\",\n      \"method\": \"HSPG2 mutation identification in DDSH patients, immunostaining of patient tissue, biochemical analysis of perlecan secretion\",\n      \"journal\": \"American journal of medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human genetic evidence with biochemical validation of protein instability and secretion failure, independent of SJS studies\",\n      \"pmids\": [\"11891676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Perlecan protein core interacts with extracellular matrix protein 1 (ECM1) through its domain V; specifically, the C-terminus of ECM1 binds the EGF-like modules flanking the LG2 subdomain of perlecan domain V, as validated by yeast two-hybrid, co-immunoprecipitation in cell-free systems and mammalian cells, and deletion mutant mapping.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation in cell-free and mammalian cell systems, deletion mutant binding mapping, identification of novel ECM1c splice variant\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by reciprocal Co-IP with domain-level mapping, single lab\",\n      \"pmids\": [\"12604605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Progranulin (a secreted growth factor) interacts with perlecan domain V through the first two laminin- and EGF-like repeats, binding to granulin F and B subdomains, with a KD ~1 μM measured by surface plasmon resonance; both progranulin and domain V individually stimulate adrenal carcinoma cell growth, but together in equimolar amounts counteract each other's activity.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation in cell-free and transfected mammalian cells, surface plasmon resonance kinetics, cell growth assays, tumor tissue microarrays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SPR kinetics plus yeast two-hybrid and co-IP with deletion mapping, single lab, functional cell-growth assay\",\n      \"pmids\": [\"12900424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Heparanase (HPSE-1) specifically degrades the heparan sulfate chains of purified perlecan, as demonstrated with purified syndecan-1 and perlecan HS; perlecan HS is thus a degradative substrate of heparanase, with functional implications for tumor cell invasion.\",\n      \"method\": \"In vitro enzymatic degradation of purified syndecan-1 and perlecan HS with HPSE-1, in vitro chemoinvasion assays, cell surface HS degradation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assay with purified proteins, cell-based invasion assay, single lab\",\n      \"pmids\": [\"14630925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Drosophila perlecan (encoded by trol) regulates neuroblast division by modulating both FGF and Hedgehog (Hh) signaling; FGF-2 addition rescues trol proliferation phenotype, MAPK inhibitor blocks wild-type neuroblast division, Hh activates stem cell division in a Trol-dependent fashion, and co-immunoprecipitation shows interactions between Trol and Hh and between mammalian Perlecan and Sonic Hedgehog that are not competed by heparin sulfate.\",\n      \"method\": \"Drosophila genetic analysis (trol mutants), brain culture rescue with human FGF-2, MAPK inhibitor treatment, co-immunoprecipitation of Trol/Hh and Perlecan/Shh, genetic epistasis of trol/hh/ttv\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in Drosophila, biochemical co-IP, pharmacological rescue, multiple orthogonal methods, extended by PMID:17980035\",\n      \"pmids\": [\"12645928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HSPG2 mutations causing SJS show a hypomorphic effect; truncating mutations cause HSPG2 mRNA instability via nonsense-mediated mRNA decay, whereas missense mutations involving cysteine residues cause intracellular retention of perlecan, likely through quality control pathways, establishing distinct molecular consequences of different mutation classes.\",\n      \"method\": \"HSPG2 mRNA analysis, perlecan immunostaining on patient cells, sequencing of 22 new mutations in 23 SJS families\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mRNA and protein analysis in patient cells with multiple mutation types, mechanistic distinction between truncating vs missense mutations established, single group\",\n      \"pmids\": [\"16927315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A peptide sequence (TWSKVGGHLRPGIVQSG) from an immunoglobulin repeat in perlecan domain IV supports rapid cell adhesion, spreading, and focal adhesion kinase (FAK) activation in a divalent cation-independent, heparin-sensitive manner; cell adhesion is receptor-specific and differs between cell lines.\",\n      \"method\": \"Bioinformatics-based peptide identification, cell adhesion assays, focal adhesion and actin cytoskeleton visualization, FAK activation assays\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — peptide-based functional assay with multiple cell lines, FAK activation readout, heparin competition, single lab\",\n      \"pmids\": [\"17997086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Perlecan is required for proper endothelial cell migration and proliferation during developmental angiogenesis; perlecan knockdown causes abnormal increase and redistribution of total VEGF-A protein, perlecan binds VEGF-A165 in a heparan sulfate-dependent manner, and perlecan enhances VEGF-mediated VEGFR2 activation of human endothelial cells; the morphant phenotype is rescued by VEGF-A165 microinjection.\",\n      \"method\": \"Zebrafish perlecan morpholino knockdown, endothelial cell behavior analysis, VEGF-A localization by immunostaining, VEGF-A/perlecan binding assay (heparan sulfate dependence), VEGFR2 phosphorylation assays in human endothelial cells, mRNA rescue experiments\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — zebrafish KD with defined cellular phenotype, biochemical binding assay, VEGFR2 activation, mRNA rescue, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"19422911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Perlecan deficiency in skeletal muscle (Hspg2(-/-)-Tg mice) causes muscle hypertrophy with increased type IIb fiber cross-sectional area, substantially decreased myostatin and its type I receptor (ALK4) expression, reduced myostatin-induced Smad activation in myotubes, and altered fiber composition including increased type IIx fibers, demonstrating perlecan regulates fast muscle mass and fiber composition through myostatin signaling.\",\n      \"method\": \"Perlecan-deficient mouse model (Hspg2(-/-)-Tg), fiber cross-sectional area measurements, myosin heavy chain fiber typing, myostatin and ALK4 expression analysis, Smad activation assay in cultured myotubes, tenotomy overload/unload experiments\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined muscle phenotype, in vitro Smad signaling assay, single lab\",\n      \"pmids\": [\"20541011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Perlecan/Hspg2 localizes to the osteocyte lacunocanalicular system of cortical bone; perlecan deficiency results in diminished canalicular pericellular area, reduced canalicular density, and fewer transverse tethering elements per canaliculus, demonstrating perlecan maintains the pericellular space of the lacunocanalicular system for interstitial fluid movement.\",\n      \"method\": \"Immunofluorescence, immunogold/TEM localization, ultrastructural measurements by electron microscopy in perlecan-deficient mice\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization tied to functional pericellular space measurement in KO mice, single lab\",\n      \"pmids\": [\"20814969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Perlecan HS chains interact with tropoelastin electrostatically through heparan sulfate and core protein; these interactions promote tropoelastin coacervation and deposition of elastin onto immobilized perlecan, demonstrated by quartz crystal microbalance with dissipation studies, with co-localization of elastin, fibrillin-1, and perlecan in connective tissues.\",\n      \"method\": \"Quartz crystal microbalance with dissipation (QCM-D) solid-phase binding, co-localization by immunofluorescence in multiple connective tissues\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — solid-phase biophysical binding assay with dissipation monitoring, in vivo co-localization, single lab\",\n      \"pmids\": [\"21874555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Drosophila perlecan (trol) is required for Sema-1a-PlexA-mediated repulsive axon guidance; trol mutations suppress Sema-1a-mediated motor axon defasciculation, trol genetically interacts with PlexA and Sema-1a, perlecan augments Sema-1a-induced reduction of phospho-FAK in insect cells, and restoring perlecan to mutant motor neurons rescues guidance defects, revealing ECM proteoglycan modulation of transmembrane guidance cue signaling.\",\n      \"method\": \"Drosophila genetic analysis (trol mutants, genetic interactions), in vitro Sema-1a treatment of insect cells with phospho-FAK measurement, rescue experiments by motor neuron-specific perlecan restoration\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis, in vitro biochemical assay, cell-type-specific rescue, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"23028146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Perlecan is required for FGF-2 signaling in the adult neural stem cell niche; perlecan deficiency reduces GFAP/CD133-positive neural stem cells in the SVZ and new neurons in the olfactory bulb; in the absence of perlecan, FGF-2 fails to promote neurosphere formation or activate Akt/Erk1/2 pathways and cyclin D2 expression, demonstrating perlecan is a niche component regulating FGF-2-dependent neural stem cell self-renewal.\",\n      \"method\": \"Hspg2-null mice, immunohistochemistry, neurosphere formation assay, Western blot for Akt/Erk1/2 phosphorylation and cyclin D2, FGF-2 treatment of wild-type and perlecan-deficient cells\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse phenotype plus in vitro signaling pathway dissection, single lab\",\n      \"pmids\": [\"24434631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MMP-7 (matrilysin) cleaves perlecan/HSPG2 at multiple sites within domain IV immunoglobulin repeats, even when fully decorated with HS or in native BM context; domain IV-3 fragment induces PCa cell clustering (anti-invasive), whereas MMP-7 digestion of domain IV-3 reverses clustering to favor cell dispersion, acting as a molecular switch altering PCa cell behavior and promoting invasion through perlecan-rich BM.\",\n      \"method\": \"In vitro digestion of purified perlecan with MMP-7 and other proteases, recombinant domain IV subdomains, Transwell invasion assays, PCa cell clustering/dispersion assays with pre-digested BM extract\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with purified proteins, recombinant domain fragments, functional cell invasion assay, in silico + in vitro + in vivo contexts, single lab\",\n      \"pmids\": [\"24833109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Perlecan domain V promotes niche function via α5β1 integrin; Drosophila intestinal stem cells (ISCs) that lose Pcan fail to adhere to ECM, lose identity, and fail to proliferate; these defects are cell-autonomous (loss from ISCs but not surrounding cells causes the phenotype) and depend partially on integrin signaling, not EGFR or JAK/STAT pathways.\",\n      \"method\": \"Drosophila genetic analysis with cell-type-specific Pcan knockdown, ISC identity and proliferation assays, epistasis with integrin/EGFR/JAK-STAT pathways\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-autonomous genetic analysis in Drosophila, pathway epistasis, clean phenotypic readout, single lab\",\n      \"pmids\": [\"24936464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Smooth muscle cell-derived perlecan is decorated with both heparan sulfate and chondroitin sulfate, while endothelial cell-derived perlecan contains exclusively heparan sulfate; smooth muscle cells bind the perlecan protein core (domain III and domain V/endorepellin) only when glycosaminoglycans are removed via α2β1 integrin, whereas endothelial cells adhere to perlecan core in the presence of GAGs; perlecan HS from SMCs promotes FGF2 but not FGF1 signaling, while endothelial perlecan promotes both.\",\n      \"method\": \"Isolation of perlecan from primary human coronary artery SMCs and ECs, GAG characterization, cell adhesion assays with GAG-removed perlecan, integrin blocking antibodies, FGF1/FGF2 signaling assays\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-type-specific perlecan isolation with biochemical characterization and functional assays, single lab\",\n      \"pmids\": [\"24509440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TNF-α activates NF-κB, which binds conserved sites in the distal HSPG2 promoter (2.6 kb upstream) to upregulate perlecan transcription in prostate cancer stromal and cancer cells; TNF-α but not TGFβ1 is identified as the major cytokine regulator of perlecan production, with p65 nuclear translocation and binding to HSPG2 regulatory region confirmed.\",\n      \"method\": \"HSPG2 promoter reporter constructs (up to 2.6 kb), TNF-α and TGFβ1 treatment, p65 nuclear translocation assay, ChIP for p65 binding to HSPG2 promoter region\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter deletion mapping, ChIP, nuclear translocation, single lab\",\n      \"pmids\": [\"24700612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Perlecan domain II (LDLR-like domain) interacts with LDL through O-linked glycans present only in secreted DII; the negatively charged sialic acid caps on O-glycans are critical for LDL binding; HS chains and DII have an additive effect on LDL binding; unlike LDLR, this interaction mediates lipoprotein retention rather than endocytosis.\",\n      \"method\": \"Recombinant domain II binding assays, glycan analysis, deglycosylation experiments, surface plasmon resonance or related binding assays, sialic acid dependency assays\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — recombinant domain binding with biochemical characterization of glycan-dependence, single lab\",\n      \"pmids\": [\"25528754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Perlecan heparan sulfate chains are required for formation of the HS-FGF2-FGFR1 ternary complex; Hspg2(Δ3/Δ3) mice (HS-deficient) have reduced pericytes and muscularization of pulmonary vessels, attenuated hypoxic pulmonary hypertension with lower FGFR1 phosphorylation and reduced PASMC proliferation; ligand and carbohydrate engagement assay confirmed perlecan HS is required for HS-FGF2-FGFR1 complex formation.\",\n      \"method\": \"Hspg2(Δ3/Δ3) mice (exon 3 deletion, HS-deficient), pulmonary angiography, RVSP measurement, FGFR1 phosphorylation analysis, ligand and carbohydrate engagement assay (LACE), in vitro PASMC proliferation and adhesion assays, FGFR1 inhibitor treatment\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — HS-specific KO mouse, LACE assay for ternary complex, in vivo phenotype plus in vitro mechanistic validation, multiple methods, single lab\",\n      \"pmids\": [\"25952902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Perlecan deficiency in slow-twitch soleus muscle enhances autophagic activity (increased LC3II, decreased p62), accompanied by reduced phosphorylation of p70S6k and Akt and increased AMPK phosphorylation, suggesting perlecan inhibits autophagy through the mTORC1 pathway in skeletal muscle.\",\n      \"method\": \"Perlecan-deficient mice (Hspg2(-/-)-Tg), mechanical unloading (tenotomy), Western blot for autophagy markers (LC3II, p62), mTORC1 pathway analysis (p70S6k, Akt phosphorylation), AMPKα phosphorylation\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with pathway analysis, multiple signaling readouts, single lab\",\n      \"pmids\": [\"26319110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Perlecan domain V promotes pericyte migration by interacting with α5β1 integrin to enhance PDGF-BB-induced phosphorylation of PDGFRβ, Src homology region 2 domain-containing phosphatase-2 (SHP-2), and focal adhesion kinase (FAK), supporting blood-brain barrier repair after ischemic stroke.\",\n      \"method\": \"Recombinant domain V treatment, phosphorylation assays for PDGFRβ/SHP-2/FAK, integrin α5β1 interaction assays, pericyte migration assays\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant domain functional assay, specific signaling molecule readouts, single lab (cited in PMID:32947020)\",\n      \"pmids\": [\"32947020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Perlecan interacts with type VI collagen pericellularly in intervertebral disc; this interaction is confirmed by surface plasmon resonance; translamellar cross-bridges are significantly less abundant in HS-deficient Hspg2 exon 3 null mice than in wild type, demonstrating perlecan HS chains contribute to type VI collagen pericellular organization and IVD matrix stability.\",\n      \"method\": \"Confocal laser scanning microscopy co-localization, surface plasmon resonance binding assay, Hspg2 exon 3 null mouse (HS-deficient) histology and cross-bridge quantification\",\n      \"journal\": \"European cells & materials\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SPR binding plus HS-specific KO phenotype for structural role, single lab\",\n      \"pmids\": [\"27377666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Domain IV-3 of perlecan interacts directly with semaphorin 3A (Sema3A) on prostate cancer cells to deactivate FAK (dephosphorylation) and stabilize cell-cell interactions (tumoroid formation); MMP-7 cleavage of perlecan disrupts the perlecan-Sema3A complex, allowing FAK re-phosphorylation and cell dispersion; Sema3A antibody mimics Domain IV-3 clustering activity and Sema3A knockdown prevents Domain IV-3-induced tumoroid formation.\",\n      \"method\": \"Direct binding experiments (Domain IV-3/Sema3A), Sema3A antibody treatment, Sema3A siRNA knockdown, FAK phosphorylation assays, tumoroid formation assays, MMP-7 digestion of complex\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated, genetic knockdown plus antibody confirmation, signaling readout, single lab\",\n      \"pmids\": [\"29740048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Perlecan/HSPG2 deficiency impairs osteocyte calcium signaling in response to mechanical loading; perlecan-deficient osteocytes show decreased overall Ca2+ response rate, peaks, and recovery speed; RNA sequencing identifies suppression of calcium signaling, ECM-receptor interaction, and focal adhesion pathways; specific defects in ER calcium cycling regulators (Ryr1/ryanodine receptors and Atp2a1/Serca1 pumps) are identified in Hypo bones.\",\n      \"method\": \"Real-time Ca2+ imaging in situ in murine tibiae under cyclic loading, RNA sequencing with pathway analysis, perlecan-deficient (Hypo) mouse model\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — real-time in situ calcium imaging plus transcriptome pathway analysis in KO mouse, single lab\",\n      \"pmids\": [\"31715337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TNFSF13 binds HSPG2 (perlecan) at the cell surface and activates the NF-κB signaling pathway to promote hypertrophic scar fibroblast proliferation, migration, fibrosis, and inflammation; silencing of HSPG2 eliminates the promoting effects of TNFSF13 and inhibition of NF-κB blocks these effects; MSC-derived exosomes reduce TNFSF13 and HSPG2 to inhibit fibroblast activity.\",\n      \"method\": \"Co-binding assay (TNFSF13/HSPG2 interaction), HSPG2 siRNA knockdown, recombinant TNFSF13 protein stimulation, NF-κB inhibition, CCK-8/EdU/Transwell assays, Western blot\",\n      \"journal\": \"International journal of nanomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding shown, siRNA knockdown with defined phenotype, NF-κB pathway epistasis, single lab\",\n      \"pmids\": [\"38046235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Perlecan (HSPG2) promotes cardiomyocyte structural, contractile, and metabolic maturation; perlecan-haploinsufficient hPSC-CMs show immature features including reduced α-actinin expression, increased glycolytic metabolism and proliferation; perlecan-haploinsufficient engineered heart tissues have reduced thickness and force generation; hPSC-CMs on perlecan-peptide substrate show hypertrophic growth; perlecan signaling is mediated via the dystroglycan complex.\",\n      \"method\": \"HSPG2+/- hPSC haploinsufficient lines, hPSC-CM differentiation, structural/contractile/metabolic characterization, engineered heart tissue force measurement, perlecan peptide substrate culture, dystroglycan complex interaction assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — haploinsufficient human cell model plus engineered tissue functional assay, dystroglycan complex interaction, single lab\",\n      \"pmids\": [\"38198277\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Perlecan (HSPG2) is a large, modular heparan sulfate proteoglycan with a five-domain protein core that functions at basement membranes and pericellular matrices as: (1) an accessory co-receptor for FGF family members (bFGF/FGF-2, FGF-7/KGF, FGF-1) and VEGF-A, where its HS chains form ternary complexes with growth factors and their receptors to potentiate signaling; (2) a structural scaffold maintaining basement membrane and cartilage ECM integrity under mechanical stress, partly through interactions with collagen IV, laminins, type VI collagen, and elastin/tropoelastin; (3) a cell adhesion substrate via multiple domain-specific integrin-binding sites (domain III RGDS/α integrins, domain IV TWSKVGG peptide/heparin-sensitive receptor, domain V/α2β1 and α5β1 integrins); (4) a Hedgehog and semaphorin signaling modulator through direct protein-core interactions; (5) a regulator of muscle physiology through myostatin signaling and neuromuscular junction organization via dystroglycan binding; and (6) a mechanosensor in osteocyte lacunocanalicular systems and vascular endothelium; its C-terminal domain V (endorepellin) antagonizes VEGFR2 and α2β1 integrin to inhibit angiogenesis, while MMP-7 cleavage of domain IV acts as a molecular switch altering cell behavior from cohesion to invasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Perlecan (HSPG2) is a large modular heparan sulfate proteoglycan built from five distinct protein-core domains—an HS-attachment domain I, an LDL-receptor-like domain II, a laminin-like domain III, a domain IV of immunoglobulin repeats, and a laminin G-like domain V—that organizes basement membranes and pericellular matrices and modulates growth-factor signaling [#0]. Its HS chains act as accessory co-receptors that potentiate FGF and VEGF signaling: perlecan promotes high-affinity bFGF–receptor binding and bFGF-driven angiogenesis [#2], its HS is required to assemble the HS–FGF2–FGFR1 ternary complex [#31], and it binds VEGF-A165 to enhance VEGFR2 activation during developmental angiogenesis [#20]. Beyond its glycan chains, the perlecan protein core itself transduces signals, being required for KGF/FGFR2 activation independently of HS [#11] and supporting integrin-mediated cell adhesion through a domain III RGDS site and a domain IV immunoglobulin-repeat peptide that drives FAK activation [#3, #19]. Structurally, perlecan maintains basement membrane and cartilage integrity under mechanical stress, with null mice showing stress-induced BM deterioration, cardiac failure, exencephaly, and disorganized chondrocyte columns and collagen fibrils [#6, #7], phenotypes mirrored in humans where HSPG2 mutations cause Schwartz-Jampel syndrome (myotonia with skeletal dysplasia) [#10] and functional-null mutations cause lethal dyssegmental dysplasia Silverman-Handmaker type [#13]. In muscle, perlecan anchors to the cell surface via alpha-dystroglycan and organizes the neuromuscular junction [#5], and regulates fast muscle mass through myostatin signaling [#21]. Domain V (endorepellin) engages alpha5beta1 integrin to drive pericyte and stem-cell behaviors [#33, #27], while MMP-7 cleavage of domain IV acts as a molecular switch—disrupting domain IV-3/Sema3A-mediated FAK deactivation to convert prostate cancer cells from cohesion to invasion [#26, #35].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing the five-domain modular architecture of the perlecan core defined the structural basis for its multifunctionality, assigning candidate functions to each domain (HS attachment, LDL-receptor homology, laminin/NCAM-like adhesion modules).\",\n      \"evidence\": \"cDNA cloning and full-length sequence determination with in situ hybridization and immunolocalization\",\n      \"pmids\": [\"1569102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domain-level functions inferred from homology, not yet functionally tested\", \"No structural model of the assembled core\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Complete genomic mapping correlated 94 exons to protein domains and revealed a TATA-less, SP1/ETF promoter, indicating constitutive housekeeping-style regulation.\",\n      \"evidence\": \"Intron-exon mapping and promoter characterization from genomic DNA\",\n      \"pmids\": [\"8234307\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific and inducible regulation not addressed\", \"Alternative splicing of functional variants not catalogued\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identifying perlecan as a low-affinity/accessory bFGF receptor that potentiates mitogenesis and neovascularization assigned its HS chains a direct role in growth-factor signaling rather than purely structural support.\",\n      \"evidence\": \"Receptor binding on HS-deficient cells, neutralizing antibodies, in vivo rabbit ear angiogenesis\",\n      \"pmids\": [\"7528102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ternary complex stoichiometry not resolved at the time\", \"Did not distinguish HS- vs core-dependent contributions\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrating that domain III supports RGDS-dependent integrin adhesion established the protein core (not just HS) as a direct cell-adhesion substrate.\",\n      \"evidence\": \"Recombinant domain III adhesion assays with RGDS peptide inhibition\",\n      \"pmids\": [\"7814401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific integrin heterodimer not pinned down\", \"Downstream signaling not characterized\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"C. elegans unc-52 work showed perlecan is a cell-autonomous muscle ECM product essential for myofilament assembly and muscle attachment, linking the proteoglycan to muscle architecture.\",\n      \"evidence\": \"unc-52 genetic analysis, antibody labeling, laser ablation in C. elegans\",\n      \"pmids\": [\"8575624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular receptor mediating attachment not identified in worm\", \"Mammalian conservation of mechanism untested here\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identifying alpha-dystroglycan as a calcium/heparin-sensitive perlecan partner provided a surface-anchoring mechanism linking perlecan to the DG-dystrophin complex and AChR clustering at the NMJ.\",\n      \"evidence\": \"Blot overlay, co-IP, and immunofluorescence in Xenopus muscle\",\n      \"pmids\": [\"9791728\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding domain on perlecan not mapped\", \"Limited mechanistic follow-up beyond single lab\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Two independent knockouts established perlecan as essential for stress-resistant basement membranes and cartilage matrix integrity, with the chondrocyte phenotype resembling FGFR3 gain-of-function and implicating shared signaling.\",\n      \"evidence\": \"Hspg2-null mouse histology, EM, BrdU proliferation, GAG analysis\",\n      \"pmids\": [\"10579729\", \"10545953\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether BM failure is purely mechanical vs signaling-driven not separated\", \"FGFR3 epistasis was inferential, not direct\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Perlecan substrates were shown to drive chondrogenic differentiation of mesenchymal cells, indicating an instructive, not merely scaffolding, role in cartilage formation.\",\n      \"evidence\": \"Culture of 10T1/2 cells on purified perlecan with chondrogenic marker readouts\",\n      \"pmids\": [\"10352025\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor/signal mediating differentiation not identified\", \"Single lab, in vitro only\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Human SJS1 mutation discovery established HSPG2 as a disease gene controlling both cartilage integrity and muscle excitability, validating the mouse phenotypes in humans.\",\n      \"evidence\": \"Mutation sequencing and linkage in SJS1 families\",\n      \"pmids\": [\"11101850\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking perlecan loss to myotonia not resolved\", \"Genotype-phenotype relationships incomplete\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"A perlecan-only cell system revealed a distinct beta1-integrin-dependent endocytic pathway for atherogenic lipoprotein uptake and degradation, expanding perlecan's role into lipid handling.\",\n      \"evidence\": \"Lipoprotein binding/internalization/degradation assays with inhibitors and integrin/LRP blockade\",\n      \"pmids\": [\"10818109\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to atherosclerosis untested\", \"Molecular machinery of the pathway incompletely defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Genetic disruption in human carcinoma cells showed the perlecan protein core, not its HS chains, is required for KGF/FGFR2 activation, distinguishing core-dependent from HS-dependent growth-factor functions.\",\n      \"evidence\": \"Targeted HSPG2 knockout colon carcinoma cells with FGF7 binding/activation assays and heparin controls\",\n      \"pmids\": [\"11563979\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Core domain mediating FGFR2 activation not localized\", \"Direct core-FGF7 binding not demonstrated\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapping FGF-binding protein to a specific EGF repeat in domain III provided a molecular basis for perlecan core participation in FGF signaling in tumor stroma.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, recombinant domain III-AP binding, IHC in squamous carcinoma\",\n      \"pmids\": [\"11148217\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the interaction in vivo unproven\", \"Single lab\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"DDSH mutation work showed functional-null perlecan that is unstable and unsecreted causes lethal dwarfism, demonstrating that secretion into the ECM is essential for cartilage development.\",\n      \"evidence\": \"HSPG2 mutation identification with tissue immunostaining and secretion analysis in DDSH patients\",\n      \"pmids\": [\"11891676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular quality-control pathway retaining mutant protein not defined here\", \"Relationship to milder SJS allelic series unresolved at the time\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Drosophila trol work placed perlecan as a modulator of both FGF and Hedgehog signaling in neuroblast division, with direct perlecan-Shh binding not competed by heparin, indicating core-mediated Hh interaction.\",\n      \"evidence\": \"trol genetics, FGF-2 rescue, MAPK inhibition, Trol/Hh and Perlecan/Shh co-IP\",\n      \"pmids\": [\"12645928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Perlecan domain binding Hh not mapped\", \"Mammalian Shh modulation tested only biochemically\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Domain V was shown to bind ECM1 and progranulin, with the progranulin interaction functionally counteracting domain V's growth-promoting activity, establishing domain V as a hub for partner-modulated signaling.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, SPR kinetics, cell growth assays\",\n      \"pmids\": [\"12604605\", \"12900424\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo significance of these interactions untested\", \"Single lab for each interaction\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Heparanase was shown to specifically degrade perlecan HS chains, linking perlecan HS turnover to tumor cell invasion.\",\n      \"evidence\": \"In vitro HPSE-1 digestion of purified perlecan HS and chemoinvasion assays\",\n      \"pmids\": [\"14630925\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Released HS fragment activities not characterized\", \"In vivo invasion link correlative\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A domain IV TWSKVGG peptide was shown to drive cation-independent, heparin-sensitive adhesion and FAK activation, adding a distinct adhesion module to the perlecan core.\",\n      \"evidence\": \"Peptide adhesion/spreading assays with FAK activation across cell lines\",\n      \"pmids\": [\"17997086\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating peptide adhesion not identified\", \"Relevance of peptide to intact perlecan unproven\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Distinguishing mutation classes in SJS established hypomorphic mechanisms—NMD for truncating alleles and intracellular retention for cysteine missense alleles—explaining graded disease severity.\",\n      \"evidence\": \"mRNA and immunostaining analysis of 22 new mutations in SJS patient cells\",\n      \"pmids\": [\"16927315\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quality-control machinery retaining missense protein not identified\", \"Quantitative dose-phenotype relationships incomplete\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Zebrafish work established perlecan as required for developmental angiogenesis, binding and concentrating VEGF-A165 in an HS-dependent manner to enhance VEGFR2 activation.\",\n      \"evidence\": \"Morpholino knockdown, VEGF-A binding assay, VEGFR2 phosphorylation, VEGF-A165 mRNA rescue\",\n      \"pmids\": [\"19422911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether perlecan core also contributes to VEGF signaling not addressed\", \"Endothelial vs matrix source of perlecan not separated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Perlecan deficiency was shown to cause fast-fiber muscle hypertrophy via reduced myostatin/ALK4-Smad signaling, defining a role in muscle mass regulation distinct from its structural functions.\",\n      \"evidence\": \"Hspg2(-/-)-Tg mouse fiber analysis and myotube Smad activation assays\",\n      \"pmids\": [\"20541011\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct perlecan-myostatin binding not demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Localization to the osteocyte lacunocanalicular system and tropoelastin binding established perlecan as a pericellular structural organizer supporting interstitial fluid spaces and elastogenesis.\",\n      \"evidence\": \"Immunogold/TEM ultrastructure in KO bone; QCM-D tropoelastin binding with tissue co-localization\",\n      \"pmids\": [\"20814969\", \"21874555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for bone mechanotransduction not yet linked here\", \"Tropoelastin binding determinants only partially mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Drosophila trol was shown to modulate Sema-1a/PlexA repulsive axon guidance via phospho-FAK regulation, revealing ECM proteoglycan tuning of transmembrane guidance-cue signaling.\",\n      \"evidence\": \"trol genetics with Sema-1a/PlexA, in vitro phospho-FAK assays, motor-neuron-specific rescue\",\n      \"pmids\": [\"23028146\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct perlecan-Sema/Plexin binding not shown in fly\", \"Mammalian conservation untested here\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Perlecan was established as a neural stem cell niche component required for FGF-2-dependent self-renewal via Akt/Erk and cyclin D2 activation.\",\n      \"evidence\": \"Hspg2-null mouse SVZ analysis and neurosphere/FGF-2 signaling assays\",\n      \"pmids\": [\"24434631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether HS or core mediates the niche effect not separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A series of studies dissected cell-type-specific perlecan glycosylation, domain V/alpha5beta1 stem-cell niche function, TNF-alpha/NF-kappaB transcriptional control, and domain II glycan-dependent LDL retention, refining how perlecan composition tailors its function.\",\n      \"evidence\": \"SMC/EC perlecan isolation and GAG analysis; Drosophila ISC genetics; HSPG2 promoter ChIP; recombinant domain II LDL binding\",\n      \"pmids\": [\"24509440\", \"24936464\", \"24700612\", \"25528754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo integration of these context-specific functions incomplete\", \"Each finding from a single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying MMP-7 cleavage of domain IV as a molecular switch from clustering (anti-invasive) to dispersion (pro-invasive) defined a regulated mechanism converting perlecan from cohesion to invasion-permissive.\",\n      \"evidence\": \"In vitro MMP-7 digestion of perlecan, recombinant domain IV subdomains, invasion and clustering assays\",\n      \"pmids\": [\"24833109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo demonstration of the switch limited\", \"Receptor for intact domain IV-3 clustering not yet identified here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"HS-specific knockouts and domain V studies dissected perlecan HS as essential for the HS-FGF2-FGFR1 ternary complex in pulmonary vascular remodeling, while domain V/alpha5beta1 promotes PDGF-driven pericyte migration and perlecan suppresses muscle autophagy via mTORC1.\",\n      \"evidence\": \"Hspg2(Δ3/Δ3) HS-deficient mice with LACE assay; recombinant domain V pericyte signaling; KO muscle autophagy pathway analysis\",\n      \"pmids\": [\"25952902\", \"32947020\", \"26319110\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crosstalk between HS-dependent and core-dependent functions not unified\", \"Domain V pericyte mechanism from single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Perlecan HS chains were shown to organize type VI collagen pericellularly and stabilize intervertebral disc matrix, extending its pericellular structural role to translamellar cross-bridges.\",\n      \"evidence\": \"SPR binding and HS-deficient mouse cross-bridge quantification\",\n      \"pmids\": [\"27377666\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which HS organizes collagen VI not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Domain IV-3 was shown to bind Sema3A directly to deactivate FAK and stabilize tumor cell-cell interactions, with MMP-7 cleavage disrupting the complex—mechanistically explaining the cohesion-to-invasion switch.\",\n      \"evidence\": \"Direct binding, Sema3A antibody/siRNA, FAK phosphorylation, tumoroid assays, MMP-7 digestion\",\n      \"pmids\": [\"29740048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo prostate cancer relevance not established here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Perlecan deficiency was shown to impair osteocyte calcium signaling under mechanical load, with transcriptomic suppression of calcium signaling, ECM-receptor, and focal adhesion pathways, defining a mechanosensory role in bone.\",\n      \"evidence\": \"In situ real-time Ca2+ imaging in loaded tibiae and RNA-seq in KO mice\",\n      \"pmids\": [\"31715337\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct link between pericellular perlecan and Ca2+ machinery not mechanistically resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"TNFSF13 was shown to bind cell-surface HSPG2 to activate NF-kappaB and drive fibroblast proliferation/fibrosis, identifying perlecan as a co-receptor in hypertrophic scar pathology.\",\n      \"evidence\": \"Co-binding assay, HSPG2 siRNA, NF-kappaB inhibition, proliferation/migration assays\",\n      \"pmids\": [\"38046235\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding domain on perlecan not mapped\", \"In vivo scar model not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Perlecan haploinsufficiency was shown to impair cardiomyocyte structural, contractile, and metabolic maturation via the dystroglycan complex, extending its role to cardiac tissue maturation.\",\n      \"evidence\": \"HSPG2+/- hPSC-CM and engineered heart tissue assays with peptide substrate and dystroglycan interaction studies\",\n      \"pmids\": [\"38198277\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific perlecan domain driving maturation not pinned down\", \"Single lab; human in vitro model only\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how perlecan's distinct functional modules—HS-dependent growth-factor co-receptor activity, core-protein integrin/adhesion signaling, and dystroglycan anchoring—are integrated and prioritized in a given tissue context, and which receptor mediates several core-domain effects (KGF/FGFR2 activation, domain IV peptide adhesion, domain IV-3 clustering).\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model of the assembled five-domain core with bound partners\", \"Receptors for several core-domain functions remain unidentified\", \"Tissue-specific division of labor between HS and core not systematically defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 31, 20, 11]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [3, 19, 27]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [6, 7, 23, 34]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 6, 22]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [6, 7, 34]},\n      {\"term_id\": \"GO:0030312\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 20, 31, 11]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [6, 7, 23, 34]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [7, 17, 25, 27]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 13]}\n    ],\n    \"complexes\": [\"dystroglycan-dystrophin complex\", \"HS-FGF2-FGFR1 ternary complex\"],\n    \"partners\": [\"DAG1\", \"FGF2\", \"VEGFA\", \"FGFBP1\", \"ECM1\", \"GRN\", \"COL6\", \"SEMA3A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}