{"gene":"GPC6","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2009,"finding":"Loss-of-function mutations in GPC6 (point mutations and larger genomic rearrangements causing protein truncation) abolish both the heparan sulfate-binding site and the GPI-bearing membrane-associated domain, impairing endochondral ossification and causing recessive omodysplasia. Gpc6 is expressed in proliferative chondrocytes of the mouse growth plate, establishing its role in skeletal growth at this cellular locus.","method":"Human genetics (mutation identification), protein domain analysis, microdissected mouse growth plate expression studies","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human loss-of-function genetics with domain-level mechanistic interpretation and expression localization, single study but multiple orthogonal methods","pmids":["19481194"],"is_preprint":false},{"year":1999,"finding":"GPC6 encodes a 554-amino-acid GPI-anchored heparan sulfate proteoglycan most structurally related to GPC4, expressed most abundantly in ovary, liver, and kidney. It is a cell-surface proteoglycan of the glypican family implicated in cellular growth control and differentiation.","method":"cDNA cloning, sequence analysis, Northern blot tissue expression profiling, radiation hybrid mapping","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct molecular characterization of the protein product with structural and expression data, single study","pmids":["10329016"],"is_preprint":false},{"year":2023,"finding":"A missense variant in GPC6 (p.Arg171Trp) results in significantly reduced stimulation of Hedgehog (Hh) signaling activity compared to wild-type GPC6 protein, as measured by a Hedgehog reporter assay, establishing that GPC6 normally stimulates Hh pathway activity and that partial loss of this function causes a milder skeletal dysplasia phenotype.","method":"Hedgehog reporter assay with wild-type vs. mutant GPC6 comparison","journal":"American journal of medical genetics. Part A","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct functional reporter assay comparing wild-type and mutant protein, single lab, single method","pmids":["37353964"],"is_preprint":false},{"year":2021,"finding":"In a Drosophila model of TDP-43 proteinopathy, dlp mRNA (encoding Dlp/GPC6, a Wnt signaling regulator) is insolubilized and shows altered ribosome association. Dlp/GPC6 protein forms puncta in the Drosophila neuropil and is reduced at the neuromuscular synapse, and genetic interaction data establish Dlp/GPC6 as a physiologically relevant target of TDP-43 proteinopathy affecting synaptic compartments.","method":"Tagged ribosome affinity purification (TRAP), immunofluorescence, genetic interaction analysis in Drosophila TDP-43 proteinopathy model","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (TRAP, localization, genetics) in a single study using Drosophila ortholog","pmids":["33762006"],"is_preprint":false},{"year":2026,"finding":"In Drosophila mushroom body neurons expressing C9orf72 G4C2 repeats, Dlp (GPC6 ortholog) is reduced in an age- and repeat-length-dependent manner. Restoring Dlp expression mitigated locomotor and working-memory deficits and loss of presynaptic active zones, but did not rescue axonal degeneration or TDP-43 mislocalization. A CRISPRi screen in TDP-43 knockdown iNeurons identified GPC6 as a significant contributor to TDP-43-dependent synaptic loss, placing GPC6 in a Wnt-related signaling axis relevant to synaptic maintenance.","method":"Drosophila genetic rescue experiments, behavioral assays, CRISPRi screen in human iPSC-derived neurons","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (in vivo rescue, CRISPRi screen) across fly and human neuronal models; preprint not yet peer-reviewed","pmids":["42182325"],"is_preprint":true},{"year":2025,"finding":"GDE2, a surface GPI-anchor cleaving enzyme, negatively regulates GPC6 surface expression in neurons. Excessive GPC6 surface expression potentiates canonical Wnt signaling in vivo, causing nuclear pore complex (NPC) disruption, alterations in Ran-dependent nucleocytoplasmic trafficking, and TDP-43 mislocalization. Genetic reduction of GPC6 in GDE2-deficient mice rescues NPC integrity, nucleocytoplasmic trafficking, and TDP-43 nuclear localization, defining a GDE2–GPC6–Wnt signaling axis controlling NPC integrity in neurons.","method":"In vivo mouse genetics (GDE2 KO, GPC6 genetic reduction), nuclear pore complex integrity assays, nucleocytoplasmic trafficking assays, TDP-43 localization studies","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo epistasis with genetic rescue using multiple cellular readouts; preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.09.24.678385"],"is_preprint":true},{"year":2026,"finding":"GPC6 promotes cell proliferation, migration, and invasion in SHH-subgroup medulloblastoma cell lines (DAOY and ONS-76). GPC6 enhances SHH pathway activity by upregulating GLI1 expression, supports ciliogenesis required for signal transduction, and facilitates SHH ligand expression via extracellular vesicles, establishing GPC6 as a regulator of Hedgehog secretion and signaling.","method":"Cell line knockdown/overexpression assays, GLI1 expression measurement, ciliogenesis assays, extracellular vesicle analysis","journal":"Journal of biomedical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular assays in cancer cell lines establishing mechanism, single lab study","pmids":["41320180"],"is_preprint":false},{"year":2021,"finding":"Running exercise increases STAT3 and Gpc6 expression in astrocytes, and mechanistically targets Gpc6 through the STAT3 pathway to regulate synapse number, promoting synapse proliferation via transformation of astrocytes toward a neuroprotective phenotype.","method":"In vivo MCAO model with exercise, in vitro oxygen-glucose deprivation of astrocytes, gene expression analysis, pathway analysis","journal":"Frontiers in physiology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, primarily expression-based with limited direct mechanistic validation of GPC6 function","pmids":["34122124"],"is_preprint":false},{"year":2019,"finding":"GPC6 promotes migration, invasion, and proliferation of nasopharyngeal carcinoma (NPC) cells in vitro, as demonstrated by functional experiments following identification of GPC6 mutations in NPC by whole-genome sequencing.","method":"Cell proliferation, migration, and invasion assays in NPC cell lines with GPC6 manipulation","journal":"Journal of Cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, cell-based functional assays without defined molecular mechanism or pathway placement","pmids":["31417636"],"is_preprint":false}],"current_model":"GPC6 is a GPI-anchored heparan sulfate proteoglycan expressed on the cell surface that modulates Hedgehog (Hh) and Wnt signaling: it stimulates Hh pathway activity (required for endochondral ossification and skeletal growth) and potentiates canonical Wnt signaling in neurons, where its surface levels are negatively regulated by the GPI-anchor cleaving enzyme GDE2; excessive GPC6-driven Wnt activation disrupts nuclear pore complex integrity, nucleocytoplasmic trafficking, and TDP-43 nuclear localization, linking GPC6 to neurodegenerative pathomechanisms including TDP-43 proteinopathy."},"narrative":{"mechanistic_narrative":"GPC6 is a GPI-anchored, heparan sulfate-bearing glypican that acts at the cell surface to modulate developmental morphogen signaling, with roles spanning skeletal growth, oncogenic proliferation, and neuronal homeostasis [PMID:10329016, PMID:19481194]. Recessive loss-of-function mutations that disrupt both the heparan sulfate-binding site and the GPI-membrane anchor impair endochondral ossification and cause omodysplasia, consistent with Gpc6 expression in proliferative growth-plate chondrocytes [PMID:19481194]. Mechanistically, GPC6 stimulates Hedgehog pathway activity, and a missense variant that diminishes this stimulation produces a milder skeletal phenotype [PMID:37353964]; in SHH-subgroup medulloblastoma cells GPC6 upregulates GLI1, supports the ciliogenesis required for signal transduction, and facilitates SHH ligand release via extracellular vesicles, driving proliferation, migration, and invasion [PMID:41320180]. In the nervous system GPC6 instead potentiates canonical Wnt signaling: its surface levels are restrained by the GPI-anchor-cleaving enzyme GDE2, and excess GPC6 disrupts nuclear pore complex integrity, Ran-dependent nucleocytoplasmic trafficking, and TDP-43 nuclear localization, with genetic reduction of GPC6 in GDE2-deficient neurons rescuing these defects—defining a GDE2–GPC6–Wnt axis controlling NPC integrity [PMID:bio_10.1101_2025.09.24.678385]. The Drosophila ortholog Dlp is a target of TDP-43 and C9orf72 proteinopathy whose restoration mitigates synaptic and behavioral deficits, and a CRISPRi screen confirmed GPC6 as a contributor to TDP-43-dependent synaptic loss in human neurons [PMID:33762006, PMID:42182325].","teleology":[{"year":1999,"claim":"Defined the basic identity of GPC6 as a member of the glypican family, establishing it as a candidate cell-surface regulator of growth and differentiation before any functional role was known.","evidence":"cDNA cloning, sequence analysis, and Northern blot tissue profiling","pmids":["10329016"],"confidence":"Medium","gaps":["No functional pathway assignment","No identification of signaling partners or substrates"]},{"year":2009,"claim":"Established GPC6 as essential for skeletal growth by linking loss-of-function mutations that ablate both the heparan sulfate and GPI-anchor domains to recessive omodysplasia and localizing expression to proliferative growth-plate chondrocytes.","evidence":"Human mutation identification, protein domain analysis, and microdissected mouse growth-plate expression","pmids":["19481194"],"confidence":"Medium","gaps":["Did not define which signaling pathway GPC6 acts through in chondrocytes","Mechanism connecting surface proteoglycan to ossification unresolved"]},{"year":2019,"claim":"Extended GPC6 beyond development by showing it promotes a malignant phenotype in nasopharyngeal carcinoma, raising the possibility of a proliferative signaling role in cancer.","evidence":"Proliferation, migration, and invasion assays in NPC cell lines with GPC6 manipulation","pmids":["31417636"],"confidence":"Low","gaps":["No molecular mechanism or pathway placement","Single-lab cell-line evidence only"]},{"year":2021,"claim":"First implicated the GPC6 ortholog in neurodegenerative proteinopathy by identifying Dlp/GPC6 as a TDP-43 target affecting synaptic compartments, connecting the gene to Wnt-related synaptic biology.","evidence":"TRAP, immunofluorescence, and genetic interaction analysis in a Drosophila TDP-43 proteinopathy model","pmids":["33762006"],"confidence":"Medium","gaps":["Ortholog-based; human GPC6 not directly tested here","Causal direction between Dlp loss and synaptic dysfunction not isolated"]},{"year":2023,"claim":"Pinned the disease-relevant molecular activity of GPC6 to Hedgehog pathway stimulation by showing a hypomorphic missense variant reduces Hh reporter activity and yields a milder skeletal phenotype.","evidence":"Hedgehog reporter assay comparing wild-type and mutant GPC6","pmids":["37353964"],"confidence":"Medium","gaps":["Did not resolve how GPC6 mechanistically engages the Hh pathway","Single method and lab"]},{"year":2025,"claim":"Defined a GDE2–GPC6–Wnt axis in neurons, showing GPC6 surface levels are restrained by GDE2 and that GPC6 excess disrupts nuclear pore integrity and TDP-43 localization, providing a mechanistic bridge between glypican signaling and neurodegeneration.","evidence":"In vivo mouse genetics (GDE2 KO, GPC6 reduction), NPC integrity and nucleocytoplasmic trafficking assays, TDP-43 localization (preprint)","pmids":["bio_10.1101_2025.09.24.678385"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Molecular link between Wnt potentiation and NPC disruption not defined"]},{"year":2026,"claim":"Resolved how GPC6 stimulates Hedgehog signaling in cancer—via GLI1 upregulation, ciliogenesis support, and EV-mediated SHH ligand release—while also confirming its synaptic role in human neurons through CRISPRi.","evidence":"Cancer cell-line knockdown/overexpression with GLI1, ciliogenesis and EV assays; Drosophila rescue and CRISPRi in TDP-43 knockdown iNeurons (one preprint)","pmids":["41320180","42182325"],"confidence":"Medium","gaps":["One source is a preprint","Direct biochemical interaction between GPC6 and Hh/Wnt components not demonstrated","Mechanism distinguishing Hh vs Wnt context-specificity unresolved"]},{"year":null,"claim":"How a single surface glypican selectively engages Hedgehog signaling in skeletal/tumor contexts versus canonical Wnt in neurons, and the structural basis of these interactions, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of GPC6 with Hh or Wnt ligands","No direct binding data for proposed pathway partners","Context-determining factors for Hh vs Wnt output unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[2,5,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,5,6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,5,6]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,2]}],"complexes":[],"partners":["GDE2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y625","full_name":"Glypican-6","aliases":[],"length_aa":555,"mass_kda":62.7,"function":"Cell surface proteoglycan that bears heparan sulfate. Putative cell surface coreceptor for growth factors, extracellular matrix proteins, proteases and anti-proteases (By similarity). Enhances migration and invasion of cancer cells through WNT5A signaling","subcellular_location":"Secreted, extracellular space","url":"https://www.uniprot.org/uniprotkb/Q9Y625/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPC6","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":[{"gene":"SRP9","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/GPC6","total_profiled":1310},"omim":[{"mim_id":"604404","title":"GLYPICAN 6; GPC6","url":"https://www.omim.org/entry/604404"},{"mim_id":"300168","title":"GLYPICAN 4; GPC4","url":"https://www.omim.org/entry/300168"},{"mim_id":"258315","title":"OMODYSPLASIA 1; OMOD1","url":"https://www.omim.org/entry/258315"},{"mim_id":"138248","title":"GLUTAMATE RECEPTOR, IONOTROPIC, AMPA 1; GRIA1","url":"https://www.omim.org/entry/138248"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GPC6"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9Y625","domains":[{"cath_id":"-","chopping":"103-250_263-348_375-483","consensus_level":"medium","plddt":93.0122,"start":103,"end":483}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y625","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y625-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y625-F1-predicted_aligned_error_v6.png","plddt_mean":82.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPC6","jax_strain_url":"https://www.jax.org/strain/search?query=GPC6"},"sequence":{"accession":"Q9Y625","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y625.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y625/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y625"}},"corpus_meta":[{"pmid":"28869591","id":"PMC_28869591","title":"Identification of 153 new loci associated with heel bone mineral density and functional involvement of GPC6 in osteoporosis.","date":"2017","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28869591","citation_count":353,"is_preprint":false},{"pmid":"19481194","id":"PMC_19481194","title":"Mutations in the heparan-sulfate proteoglycan glypican 6 (GPC6) impair endochondral ossification and cause recessive omodysplasia.","date":"2009","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19481194","citation_count":91,"is_preprint":false},{"pmid":"10329016","id":"PMC_10329016","title":"GPC6, a novel member of the glypican gene family, encodes a product structurally related to GPC4 and is colocalized with GPC5 on human chromosome 13.","date":"1999","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10329016","citation_count":60,"is_preprint":false},{"pmid":"31417636","id":"PMC_31417636","title":"GPC6 Promotes Cell Proliferation, Migration, and Invasion in Nasopharyngeal Carcinoma.","date":"2019","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31417636","citation_count":33,"is_preprint":false},{"pmid":"26448945","id":"PMC_26448945","title":"Overexpression of GPC6 and TMEM132D in Early Stage Ovarian Cancer Correlates with CD8+ T-Lymphocyte Infiltration and Increased Patient Survival.","date":"2015","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/26448945","citation_count":22,"is_preprint":false},{"pmid":"33762006","id":"PMC_33762006","title":"TDP-43 proteinopathy alters the ribosome association of multiple mRNAs including the glypican Dally-like protein (Dlp)/GPC6.","date":"2021","source":"Acta neuropathologica communications","url":"https://pubmed.ncbi.nlm.nih.gov/33762006","citation_count":16,"is_preprint":false},{"pmid":"19726429","id":"PMC_19726429","title":"Allelic imbalance at 13q31 is associated with reduced GPC6 in Chinese with sporadic retinoblastoma.","date":"2009","source":"The British journal of ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/19726429","citation_count":13,"is_preprint":false},{"pmid":"34122124","id":"PMC_34122124","title":"Running Promotes Transformation of Brain Astrocytes Into Neuroprotective Reactive Astrocytes and Synaptic Formation by Targeting Gpc6 Through the STAT3 Pathway.","date":"2021","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/34122124","citation_count":11,"is_preprint":false},{"pmid":"11566272","id":"PMC_11566272","title":"A 4-Mb BAC/PAC contig and complete genomic structure of the GPC5/GPC6 gene cluster on chromosome 13q32.","date":"2001","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/11566272","citation_count":4,"is_preprint":false},{"pmid":"36110408","id":"PMC_36110408","title":"PFKP and GPC6 Variants Were Correlated with Alcohol-Induced Femoral Head Necrosis Risk in the Chinese Han Population.","date":"2022","source":"Pharmacogenomics and personalized medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36110408","citation_count":3,"is_preprint":false},{"pmid":"37353964","id":"PMC_37353964","title":"Five siblings expand the spectrum of GPC6-related skeletal dysplasia.","date":"2023","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/37353964","citation_count":1,"is_preprint":false},{"pmid":"42135908","id":"PMC_42135908","title":"Natural variation of a transcriptional repressor encoding gene GPC6 confers grain protein content in rice.","date":"2026","source":"Journal of integrative plant biology","url":"https://pubmed.ncbi.nlm.nih.gov/42135908","citation_count":0,"is_preprint":false},{"pmid":"42182325","id":"PMC_42182325","title":"C9orf72 -associated G4C2 hexanucleotide repeat expression in Drosophila mushroom bodies causes age dependent TDP-43 pathology and dementia relevant phenotypes mediated in part by the glypican Dlp/GPC6.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/42182325","citation_count":0,"is_preprint":false},{"pmid":"41320180","id":"PMC_41320180","title":"GPC6 facilitates progression of SHH-subgroup medulloblastoma by enhancing Hedgehog secretion and signaling responses.","date":"2026","source":"Journal of biomedical research","url":"https://pubmed.ncbi.nlm.nih.gov/41320180","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.24.678385","title":"Regulation of Glypican 6-mediated Wnt activation maintains TDP-43 nuclear localization in neurons","date":"2025-09-25","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.24.678385","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.03.06.25323506","title":"Molecular architecture of human atherosclerosis revealed through integrative human genetics","date":"2025-03-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.06.25323506","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.19.24317547","title":"Interpretable machine learning classifiers implicate GPC6 in Parkinson's disease from single-nuclei midbrain transcriptomes","date":"2024-11-20","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.19.24317547","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10153,"output_tokens":2363,"usd":0.032952,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9566,"output_tokens":2788,"usd":0.058765,"stage2_stop_reason":"end_turn"},"total_usd":0.091717,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss-of-function mutations in GPC6 (point mutations and larger genomic rearrangements causing protein truncation) abolish both the heparan sulfate-binding site and the GPI-bearing membrane-associated domain, impairing endochondral ossification and causing recessive omodysplasia. Gpc6 is expressed in proliferative chondrocytes of the mouse growth plate, establishing its role in skeletal growth at this cellular locus.\",\n      \"method\": \"Human genetics (mutation identification), protein domain analysis, microdissected mouse growth plate expression studies\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human loss-of-function genetics with domain-level mechanistic interpretation and expression localization, single study but multiple orthogonal methods\",\n      \"pmids\": [\"19481194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GPC6 encodes a 554-amino-acid GPI-anchored heparan sulfate proteoglycan most structurally related to GPC4, expressed most abundantly in ovary, liver, and kidney. It is a cell-surface proteoglycan of the glypican family implicated in cellular growth control and differentiation.\",\n      \"method\": \"cDNA cloning, sequence analysis, Northern blot tissue expression profiling, radiation hybrid mapping\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct molecular characterization of the protein product with structural and expression data, single study\",\n      \"pmids\": [\"10329016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A missense variant in GPC6 (p.Arg171Trp) results in significantly reduced stimulation of Hedgehog (Hh) signaling activity compared to wild-type GPC6 protein, as measured by a Hedgehog reporter assay, establishing that GPC6 normally stimulates Hh pathway activity and that partial loss of this function causes a milder skeletal dysplasia phenotype.\",\n      \"method\": \"Hedgehog reporter assay with wild-type vs. mutant GPC6 comparison\",\n      \"journal\": \"American journal of medical genetics. Part A\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct functional reporter assay comparing wild-type and mutant protein, single lab, single method\",\n      \"pmids\": [\"37353964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In a Drosophila model of TDP-43 proteinopathy, dlp mRNA (encoding Dlp/GPC6, a Wnt signaling regulator) is insolubilized and shows altered ribosome association. Dlp/GPC6 protein forms puncta in the Drosophila neuropil and is reduced at the neuromuscular synapse, and genetic interaction data establish Dlp/GPC6 as a physiologically relevant target of TDP-43 proteinopathy affecting synaptic compartments.\",\n      \"method\": \"Tagged ribosome affinity purification (TRAP), immunofluorescence, genetic interaction analysis in Drosophila TDP-43 proteinopathy model\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (TRAP, localization, genetics) in a single study using Drosophila ortholog\",\n      \"pmids\": [\"33762006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In Drosophila mushroom body neurons expressing C9orf72 G4C2 repeats, Dlp (GPC6 ortholog) is reduced in an age- and repeat-length-dependent manner. Restoring Dlp expression mitigated locomotor and working-memory deficits and loss of presynaptic active zones, but did not rescue axonal degeneration or TDP-43 mislocalization. A CRISPRi screen in TDP-43 knockdown iNeurons identified GPC6 as a significant contributor to TDP-43-dependent synaptic loss, placing GPC6 in a Wnt-related signaling axis relevant to synaptic maintenance.\",\n      \"method\": \"Drosophila genetic rescue experiments, behavioral assays, CRISPRi screen in human iPSC-derived neurons\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (in vivo rescue, CRISPRi screen) across fly and human neuronal models; preprint not yet peer-reviewed\",\n      \"pmids\": [\"42182325\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GDE2, a surface GPI-anchor cleaving enzyme, negatively regulates GPC6 surface expression in neurons. Excessive GPC6 surface expression potentiates canonical Wnt signaling in vivo, causing nuclear pore complex (NPC) disruption, alterations in Ran-dependent nucleocytoplasmic trafficking, and TDP-43 mislocalization. Genetic reduction of GPC6 in GDE2-deficient mice rescues NPC integrity, nucleocytoplasmic trafficking, and TDP-43 nuclear localization, defining a GDE2–GPC6–Wnt signaling axis controlling NPC integrity in neurons.\",\n      \"method\": \"In vivo mouse genetics (GDE2 KO, GPC6 genetic reduction), nuclear pore complex integrity assays, nucleocytoplasmic trafficking assays, TDP-43 localization studies\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo epistasis with genetic rescue using multiple cellular readouts; preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.09.24.678385\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GPC6 promotes cell proliferation, migration, and invasion in SHH-subgroup medulloblastoma cell lines (DAOY and ONS-76). GPC6 enhances SHH pathway activity by upregulating GLI1 expression, supports ciliogenesis required for signal transduction, and facilitates SHH ligand expression via extracellular vesicles, establishing GPC6 as a regulator of Hedgehog secretion and signaling.\",\n      \"method\": \"Cell line knockdown/overexpression assays, GLI1 expression measurement, ciliogenesis assays, extracellular vesicle analysis\",\n      \"journal\": \"Journal of biomedical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular assays in cancer cell lines establishing mechanism, single lab study\",\n      \"pmids\": [\"41320180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Running exercise increases STAT3 and Gpc6 expression in astrocytes, and mechanistically targets Gpc6 through the STAT3 pathway to regulate synapse number, promoting synapse proliferation via transformation of astrocytes toward a neuroprotective phenotype.\",\n      \"method\": \"In vivo MCAO model with exercise, in vitro oxygen-glucose deprivation of astrocytes, gene expression analysis, pathway analysis\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, primarily expression-based with limited direct mechanistic validation of GPC6 function\",\n      \"pmids\": [\"34122124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPC6 promotes migration, invasion, and proliferation of nasopharyngeal carcinoma (NPC) cells in vitro, as demonstrated by functional experiments following identification of GPC6 mutations in NPC by whole-genome sequencing.\",\n      \"method\": \"Cell proliferation, migration, and invasion assays in NPC cell lines with GPC6 manipulation\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, cell-based functional assays without defined molecular mechanism or pathway placement\",\n      \"pmids\": [\"31417636\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPC6 is a GPI-anchored heparan sulfate proteoglycan expressed on the cell surface that modulates Hedgehog (Hh) and Wnt signaling: it stimulates Hh pathway activity (required for endochondral ossification and skeletal growth) and potentiates canonical Wnt signaling in neurons, where its surface levels are negatively regulated by the GPI-anchor cleaving enzyme GDE2; excessive GPC6-driven Wnt activation disrupts nuclear pore complex integrity, nucleocytoplasmic trafficking, and TDP-43 nuclear localization, linking GPC6 to neurodegenerative pathomechanisms including TDP-43 proteinopathy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPC6 is a GPI-anchored, heparan sulfate-bearing glypican that acts at the cell surface to modulate developmental morphogen signaling, with roles spanning skeletal growth, oncogenic proliferation, and neuronal homeostasis [#1, #0]. Recessive loss-of-function mutations that disrupt both the heparan sulfate-binding site and the GPI-membrane anchor impair endochondral ossification and cause omodysplasia, consistent with Gpc6 expression in proliferative growth-plate chondrocytes [#0]. Mechanistically, GPC6 stimulates Hedgehog pathway activity, and a missense variant that diminishes this stimulation produces a milder skeletal phenotype [#2]; in SHH-subgroup medulloblastoma cells GPC6 upregulates GLI1, supports the ciliogenesis required for signal transduction, and facilitates SHH ligand release via extracellular vesicles, driving proliferation, migration, and invasion [#6]. In the nervous system GPC6 instead potentiates canonical Wnt signaling: its surface levels are restrained by the GPI-anchor-cleaving enzyme GDE2, and excess GPC6 disrupts nuclear pore complex integrity, Ran-dependent nucleocytoplasmic trafficking, and TDP-43 nuclear localization, with genetic reduction of GPC6 in GDE2-deficient neurons rescuing these defects—defining a GDE2–GPC6–Wnt axis controlling NPC integrity [#5]. The Drosophila ortholog Dlp is a target of TDP-43 and C9orf72 proteinopathy whose restoration mitigates synaptic and behavioral deficits, and a CRISPRi screen confirmed GPC6 as a contributor to TDP-43-dependent synaptic loss in human neurons [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the basic identity of GPC6 as a member of the glypican family, establishing it as a candidate cell-surface regulator of growth and differentiation before any functional role was known.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and Northern blot tissue profiling\",\n      \"pmids\": [\"10329016\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional pathway assignment\", \"No identification of signaling partners or substrates\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established GPC6 as essential for skeletal growth by linking loss-of-function mutations that ablate both the heparan sulfate and GPI-anchor domains to recessive omodysplasia and localizing expression to proliferative growth-plate chondrocytes.\",\n      \"evidence\": \"Human mutation identification, protein domain analysis, and microdissected mouse growth-plate expression\",\n      \"pmids\": [\"19481194\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not define which signaling pathway GPC6 acts through in chondrocytes\", \"Mechanism connecting surface proteoglycan to ossification unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended GPC6 beyond development by showing it promotes a malignant phenotype in nasopharyngeal carcinoma, raising the possibility of a proliferative signaling role in cancer.\",\n      \"evidence\": \"Proliferation, migration, and invasion assays in NPC cell lines with GPC6 manipulation\",\n      \"pmids\": [\"31417636\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No molecular mechanism or pathway placement\", \"Single-lab cell-line evidence only\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"First implicated the GPC6 ortholog in neurodegenerative proteinopathy by identifying Dlp/GPC6 as a TDP-43 target affecting synaptic compartments, connecting the gene to Wnt-related synaptic biology.\",\n      \"evidence\": \"TRAP, immunofluorescence, and genetic interaction analysis in a Drosophila TDP-43 proteinopathy model\",\n      \"pmids\": [\"33762006\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ortholog-based; human GPC6 not directly tested here\", \"Causal direction between Dlp loss and synaptic dysfunction not isolated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Pinned the disease-relevant molecular activity of GPC6 to Hedgehog pathway stimulation by showing a hypomorphic missense variant reduces Hh reporter activity and yields a milder skeletal phenotype.\",\n      \"evidence\": \"Hedgehog reporter assay comparing wild-type and mutant GPC6\",\n      \"pmids\": [\"37353964\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not resolve how GPC6 mechanistically engages the Hh pathway\", \"Single method and lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a GDE2–GPC6–Wnt axis in neurons, showing GPC6 surface levels are restrained by GDE2 and that GPC6 excess disrupts nuclear pore integrity and TDP-43 localization, providing a mechanistic bridge between glypican signaling and neurodegeneration.\",\n      \"evidence\": \"In vivo mouse genetics (GDE2 KO, GPC6 reduction), NPC integrity and nucleocytoplasmic trafficking assays, TDP-43 localization (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.09.24.678385\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Molecular link between Wnt potentiation and NPC disruption not defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Resolved how GPC6 stimulates Hedgehog signaling in cancer—via GLI1 upregulation, ciliogenesis support, and EV-mediated SHH ligand release—while also confirming its synaptic role in human neurons through CRISPRi.\",\n      \"evidence\": \"Cancer cell-line knockdown/overexpression with GLI1, ciliogenesis and EV assays; Drosophila rescue and CRISPRi in TDP-43 knockdown iNeurons (one preprint)\",\n      \"pmids\": [\"41320180\", \"42182325\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"One source is a preprint\", \"Direct biochemical interaction between GPC6 and Hh/Wnt components not demonstrated\", \"Mechanism distinguishing Hh vs Wnt context-specificity unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single surface glypican selectively engages Hedgehog signaling in skeletal/tumor contexts versus canonical Wnt in neurons, and the structural basis of these interactions, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of GPC6 with Hh or Wnt ligands\", \"No direct binding data for proposed pathway partners\", \"Context-determining factors for Hh vs Wnt output unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [2, 5, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 5, 6]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GDE2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}