{"gene":"GPRASP2","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2013,"finding":"GASP-2 (GPRASP2) inhibits myostatin (MSTN) and GDF-11 activity by blocking the binding of these ligands to the type II receptor, acting as an extracellular antagonist at the initial signaling step. Gasp2-/- mice show posteriorly directed axial skeletal transformations, reductions in muscle weight, fiber-type shift from type IIb to type IIa, and impaired muscle regeneration—phenotypes consistent with GDF-11 and MSTN overactivity.","method":"Ligand-receptor binding assays, Gasp2 knockout mouse phenotyping (muscle weight, fiber typing, regeneration assays, skeletal patterning analysis)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vivo genetic and biochemical methods; mechanistic block at type II receptor validated by binding assay and confirmed by KO phenotypes consistent with ligand overactivity","pmids":["24019467"],"is_preprint":false},{"year":2016,"finding":"GPRASP2 forms a complex with Pitchfork (Pifo) that is required for Hedgehog-induced translocation of Smoothened (Smo) to the primary cilium. Depletion of Gprasp2 prevents Smo ciliary targeting and abolishes Hedgehog target gene activation.","method":"Co-immunoprecipitation of Pifo-Gprasp2 complex, siRNA/shRNA depletion of Gprasp2 with immunofluorescence quantification of Smo at primary cilia, qRT-PCR of Hh target genes","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal protein complex identification plus loss-of-function with two orthogonal readouts (ciliary localization and target gene expression), single lab","pmids":["26901434"],"is_preprint":false},{"year":2006,"finding":"GPRASP2 (GASP2) physically interacts with huntingtin (htt) and the two proteins co-localize in SH-SY5Y neuronal cells, suggesting GPRASP2 may link htt to G protein-coupled receptor sorting and trafficking.","method":"Yeast two-hybrid screening, membrane-based co-immunoprecipitation, classical co-immunoprecipitation in co-transfected mammalian cells, co-localization by immunofluorescence in SH-SY5Y cells","journal":"Journal of neural transmission","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and co-localization in neuronal cells, single lab, no functional consequence directly demonstrated","pmids":["16835690"],"is_preprint":false},{"year":2019,"finding":"Gprasp2 regulates postendocytic sorting of mGluR5, bidirectionally controlling its surface availability. Loss of Gprasp2 increases mGluR5 surface levels, enhances hippocampal mGluR-dependent long-term depression (LTD), and causes alterations in dendritic complexity, spine density, and synaptic maturation. Gprasp2 deletion produces ASD-like behaviour in mice.","method":"Gprasp2 knockout mice, shRNA knockdown and overexpression of Gprasp2, surface biotinylation assay for mGluR5, electrophysiology (LTD recordings in hippocampal slices), confocal imaging of dendritic morphology and spine density, behavioural testing","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — bidirectional manipulation (KO + overexpression), multiple orthogonal methods (surface receptor assay, electrophysiology, morphology, behaviour), single lab with comprehensive mechanistic characterisation","pmids":["30926797"],"is_preprint":false},{"year":2016,"finding":"GASP-2 promotes C2C12 myoblast proliferation and differentiation by inhibiting the canonical myostatin signaling pathway. This activity is independent of GASP-2 glycosylation, as both glycosylated and bacterially expressed (fully deglycosylated) recombinant GASP-2 retain inhibitory activity.","method":"Gprasp2 overexpression and shRNA knockdown in C2C12 myoblasts, proliferation and differentiation assays, recombinant protein production in prokaryotic system (deglycosylated), western blot for myostatin pathway components","journal":"Biochemistry and biophysics reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional manipulation (OE and KD), biochemical characterisation of glycosylation-independent activity, single lab","pmids":["28955860"],"is_preprint":false},{"year":2020,"finding":"GASP-2 overexpression in mice increases skeletal muscle mass and induces a switch from slow- to fast-twitch myofibers (consistent with Mstn-/- mice), without metabolic defects. Mechanistically, GASP-2 has lower affinity for myostatin than GASP-1, resulting in different regulatory outcomes: GASP-1 transgenic mice exhibit constitutive myostatin upregulation (and a reverse fiber-type switch), whereas GASP-2 transgenic mice do not.","method":"Transgenic mouse overexpression of Gasp-2, muscle mass measurement, fiber-type immunohistochemistry, gene expression analysis of TGF-β pathway members, metabolic phenotyping","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gain-of-function with multiple phenotypic readouts, comparative analysis with GASP-1 transgenics, single lab","pmids":["31960486"],"is_preprint":false},{"year":2021,"finding":"Gprasp2 knockout in HEI-OC1 auditory cells down-regulates the Hedgehog signaling pathway (reduced Smo, Gli1, Gli2), leading to mitochondrial damage and apoptosis (increased Bax, Caspase-3/cleaved-Caspase-3; decreased Bcl2). Treatment with smoothened agonist purmorphamine rescues Hh-Gli signaling and reduces apoptosis in Gprasp2-KO cells, establishing Hh pathway dependence.","method":"CRISPR/Cas9 knockout of Gprasp2 in HEI-OC1 cells, RNA-seq, western blot for Hh pathway components and apoptosis markers, flow cytometry apoptosis assay, electron microscopy for mitochondrial morphology, pharmacological rescue with smoothened agonist","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus pharmacological rescue with multiple orthogonal readouts, single lab","pmids":["34418635"],"is_preprint":false},{"year":2024,"finding":"GPRASP2 deficiency in spiral ganglion cells (SGCs) activates the AMPK/DRP1 signaling pathway, causing mitochondrial fragmentation, reduced membrane potential, enhanced apoptosis, and decreased cell viability. Treatment with mitochondrial fission inhibitor Mdivi-1 rescues these phenotypes, implicating GPRASP2 in maintaining mitochondrial integrity via suppression of AMPK/DRP1 in SGCs.","method":"Lentiviral shRNA knockdown of Gprasp2 in primary SGCs, western blot for AMPK phosphorylation and DRP1, mitochondrial morphology imaging, JC-1 membrane potential assay, flow cytometry apoptosis assay, pharmacological rescue with Mdivi-1, cochlear explant culture","journal":"Heliyon","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with pharmacological rescue and multiple orthogonal mechanistic readouts, single lab","pmids":["39253164"],"is_preprint":false},{"year":2024,"finding":"GPRASP2 overexpression in mouse cochlear organoids promotes supporting cell proliferation via the Hedgehog signaling pathway, and promotes hair cell formation from supporting cells via β-catenin signaling. GPRASP2 deficiency increases lysosomal degradation of SMO protein, reducing both β-catenin and GLI1 expression.","method":"Mouse cochlear organoid overexpression of Gprasp2, SMO protein stability assay (lysosomal inhibitor treatment), western blot for SMO, β-catenin, GLI1, immunofluorescence for hair cell and supporting cell markers, AAV-ie-Gprasp2 delivery with SAG co-treatment in neomycin-damaged cochlear explants","journal":"Cell proliferation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function and loss-of-function with multiple pathway readouts including protein stability, single lab","pmids":["39675768"],"is_preprint":false},{"year":2026,"finding":"GPRASP2 physically binds NCAM1. Gprasp2 deficiency decreases NCAM1 levels and enhances ferritinophagy in cochlear hair cells, leading to disrupted iron homeostasis, disordered hair cell arrangement, and hearing loss.","method":"Co-immunoprecipitation/binding assay for GPRASP2-NCAM1 interaction, Gprasp2-deficient mouse model, western blot for NCAM1 and ferritinophagy markers, auditory brainstem response, cochlear immunofluorescence","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding partner identified plus KO phenotyping with mechanistic pathway readout, single lab","pmids":["41688572"],"is_preprint":false},{"year":2026,"finding":"GPRASP2 mediates elevated endocytosis in quiescent hematopoietic stem cells (HSCs) to attenuate receptor signaling, maintaining stem cell dormancy and self-renewal. Disruption of GPRASP2-mediated endocytosis induces rapid HSC proliferation and increased surface expression of signaling receptors, consistent with a model in which GPRASP2-dependent receptor internalization limits chronic activation and functional exhaustion.","method":"GPRASP2 enrichment fractionation of HSCs, GPRASP2 disruption in HSCs with assessment of endocytosis rates, signaling constituent expression, proliferation assays, and functional stem cell reconstitution assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in primary HSCs with functional readouts linking endocytosis to signaling attenuation; preprint, not yet peer-reviewed","pmids":["41726907"],"is_preprint":true}],"current_model":"GPRASP2 is a post-endosomal sorting protein that controls the surface availability and lysosomal degradation of multiple G protein-coupled receptors and related signaling proteins: it inhibits myostatin/GDF-11 by blocking ligand binding to type II receptors, promotes Hedgehog pathway activation by forming a complex with Pitchfork to enable Smoothened ciliary translocation (and protects SMO from lysosomal degradation), regulates mGluR5 surface levels to tune synaptic plasticity and LTD in neurons, binds NCAM1 in cochlear hair cells to maintain iron homeostasis, and mediates elevated endocytosis in hematopoietic stem cells to attenuate receptor signaling and preserve quiescence."},"narrative":{"mechanistic_narrative":"GPRASP2 (GASP-2) is a receptor-trafficking and signaling-modulator protein that controls the surface availability and degradative fate of multiple membrane signaling receptors, thereby tuning developmental and synaptic signaling outputs [PMID:24019467, PMID:30926797, PMID:39675768]. In the TGF-β branch it acts as an extracellular antagonist of myostatin (MSTN) and GDF-11, blocking ligand binding to the type II receptor; loss of Gasp2 produces axial skeletal transformations, reduced muscle mass, a type IIb-to-IIa fiber shift, and impaired regeneration, while overexpression increases muscle mass and drives a slow-to-fast fiber switch — an activity that is independent of GASP-2 glycosylation [PMID:24019467, PMID:28955860, PMID:31960486]. In the Hedgehog pathway, GPRASP2 forms a complex with Pitchfork (Pifo) required for Hedgehog-induced Smoothened translocation to the primary cilium, and it protects SMO from lysosomal degradation to sustain GLI and β-catenin signaling [PMID:26901434, PMID:39675768]. In neurons, GPRASP2 governs postendocytic sorting of mGluR5 to bidirectionally set its surface levels, shaping hippocampal mGluR-dependent LTD, dendritic and spine morphology, and behaviour, with loss producing ASD-like phenotypes [PMID:30926797]. In the cochlea, GPRASP2 binds NCAM1 and supports Hedgehog signaling to maintain mitochondrial integrity, iron homeostasis, and hair cell survival [PMID:34418635, PMID:41688572]. The protein also physically interacts with huntingtin in neuronal cells [PMID:16835690].","teleology":[{"year":2006,"claim":"Established GPRASP2's first physical interaction partner, linking it to neuronal protein networks and GPCR sorting before any functional role was known.","evidence":"Yeast two-hybrid, reciprocal Co-IP, and co-localization with huntingtin in SH-SY5Y cells","pmids":["16835690"],"confidence":"Medium","gaps":["No functional consequence of the htt interaction demonstrated","Whether the interaction influences receptor trafficking untested"]},{"year":2013,"claim":"Defined GPRASP2 as an extracellular antagonist of myostatin and GDF-11, answering how it acts at the initial step of TGF-β signaling and revealing its in vivo role in muscle and skeletal patterning.","evidence":"Ligand-receptor binding assays and Gasp2 knockout mouse phenotyping (muscle, fiber type, regeneration, skeleton)","pmids":["24019467"],"confidence":"High","gaps":["Structural basis of ligand sequestration not resolved","Relationship to its intracellular trafficking roles unclear"]},{"year":2016,"claim":"Identified the GPRASP2-Pifo complex as required for Hedgehog-induced Smoothened ciliary translocation, placing GPRASP2 in ciliary signal transduction.","evidence":"Co-IP of Pifo-Gprasp2, siRNA/shRNA depletion with Smo ciliary immunofluorescence and Hh target-gene qRT-PCR","pmids":["26901434"],"confidence":"High","gaps":["Direct mechanism of Smo handoff to the cilium unknown","Stoichiometry and structure of the Pifo-Gprasp2 complex undefined"]},{"year":2016,"claim":"Showed that GPRASP2 promotes myoblast proliferation and differentiation through myostatin pathway inhibition and that this activity does not require glycosylation, constraining its biochemical mechanism.","evidence":"Overexpression/knockdown in C2C12 myoblasts and inhibitory activity of bacterially expressed deglycosylated recombinant GASP-2","pmids":["28955860"],"confidence":"Medium","gaps":["Domain mediating myostatin binding not mapped","In vitro myoblast result not yet linked to in vivo mechanism"]},{"year":2019,"claim":"Demonstrated that GPRASP2 controls postendocytic sorting of mGluR5 to bidirectionally set surface receptor levels, establishing a direct role in synaptic plasticity and behaviour.","evidence":"Gprasp2 KO plus overexpression, mGluR5 surface biotinylation, hippocampal LTD electrophysiology, dendritic/spine imaging, behavioural testing","pmids":["30926797"],"confidence":"High","gaps":["Molecular machinery linking GPRASP2 to the sorting decision not defined","Whether other GPCRs are co-regulated in neurons untested"]},{"year":2020,"claim":"Resolved why GASP-2 and GASP-1 produce divergent muscle outcomes by showing GASP-2 has lower myostatin affinity, refining the gain-of-function consequence in vivo.","evidence":"Gasp-2 transgenic overexpression mice with muscle mass, fiber-type IHC, TGF-β gene expression, and metabolic phenotyping versus GASP-1 transgenics","pmids":["31960486"],"confidence":"Medium","gaps":["Quantitative affinity differences not structurally explained","Basis for GASP-1-specific myostatin upregulation unresolved"]},{"year":2021,"claim":"Linked GPRASP2 to auditory cell survival through Hedgehog pathway dependence, showing its loss triggers mitochondrial damage and apoptosis rescuable by a Smoothened agonist.","evidence":"CRISPR KO in HEI-OC1 cells, RNA-seq, Hh and apoptosis western blots, flow cytometry, EM, and purmorphamine rescue","pmids":["34418635"],"confidence":"Medium","gaps":["How GPRASP2 loss lowers Hh signaling mechanistically not shown here","Cell-line context may not reflect native hair cells"]},{"year":2024,"claim":"Connected GPRASP2 deficiency to AMPK/DRP1-driven mitochondrial fragmentation in spiral ganglion cells, identifying a specific effector pathway for its protective role.","evidence":"shRNA knockdown in primary SGCs, AMPK/DRP1 western blots, mitochondrial imaging, JC-1, apoptosis flow cytometry, and Mdivi-1 rescue","pmids":["39253164"],"confidence":"Medium","gaps":["Link between GPRASP2 receptor trafficking and AMPK activation unestablished","Direct molecular target of GPRASP2 in SGCs unknown"]},{"year":2024,"claim":"Showed GPRASP2 protects SMO from lysosomal degradation to sustain Hedgehog and β-catenin signaling, driving supporting-cell proliferation and hair-cell regeneration.","evidence":"Cochlear organoid overexpression, SMO lysosomal stability assay, Hh/β-catenin western blots, cell-marker immunofluorescence, and AAV-Gprasp2 with SAG in damaged explants","pmids":["39675768"],"confidence":"Medium","gaps":["Mechanism by which GPRASP2 shields SMO from lysosomes undefined","Whether β-catenin effect is direct or downstream of Hh unclear"]},{"year":2026,"claim":"Identified NCAM1 as a GPRASP2 binding partner whose loss enhances ferritinophagy, tying GPRASP2 to iron homeostasis and hearing in cochlear hair cells.","evidence":"GPRASP2-NCAM1 binding assay, Gprasp2-deficient mice, NCAM1/ferritinophagy western blots, ABR, and cochlear immunofluorescence","pmids":["41688572"],"confidence":"Medium","gaps":["How GPRASP2-NCAM1 binding controls ferritinophagy mechanistically unknown","Single-lab interaction without reciprocal structural validation"]},{"year":2026,"claim":"Extended GPRASP2 function to hematopoietic stem cells, proposing it drives elevated endocytosis to attenuate receptor signaling and maintain quiescence.","evidence":"GPRASP2 fractionation enrichment in HSCs, disruption with endocytosis, signaling, proliferation, and reconstitution assays (preprint)","pmids":["41726907"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Specific receptors internalized via GPRASP2 in HSCs not identified","Direct endocytic machinery interaction unmapped"]},{"year":null,"claim":"How a single protein coordinates extracellular ligand antagonism, ciliary receptor trafficking, postendocytic sorting, and protection of receptors from lysosomal degradation across such diverse tissues remains mechanistically unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model defining distinct functional domains","Unclear whether intracellular sorting and extracellular antagonism are separable activities","Direct sorting/endocytic machinery partners not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,4,5]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,3]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,8]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,8]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[3]}],"complexes":[],"partners":["PIFO","HTT","NCAM1","SMO","MSTN","GDF11","GRM5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96D09","full_name":"G-protein coupled receptor-associated sorting protein 2","aliases":[],"length_aa":838,"mass_kda":93.8,"function":"May play a role in regulation of a variety of G-protein coupled receptors","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q96D09/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPRASP2"},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"TCF25","stoichiometry":10.0},{"gene":"RBM14","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/GPRASP2","total_profiled":1310},"omim":[{"mim_id":"613004","title":"HUNTINGTIN; HTT","url":"https://www.omim.org/entry/613004"},{"mim_id":"301018","title":"DEAFNESS, X-LINKED 7; DFNX7","url":"https://www.omim.org/entry/301018"},{"mim_id":"300969","title":"G PROTEIN-COUPLED RECEPTOR-ASSOCIATED SORTING PROTEIN 2; GPRASP2","url":"https://www.omim.org/entry/300969"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GPRASP2"},"hgnc":{"alias_symbol":["GASP2","FLJ37327"],"prev_symbol":[]},"alphafold":{"accession":"Q96D09","domains":[{"cath_id":"-","chopping":"558-577_585-667","consensus_level":"medium","plddt":78.2593,"start":558,"end":667},{"cath_id":"1.25.10.10","chopping":"675-831","consensus_level":"medium","plddt":86.3103,"start":675,"end":831}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96D09","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96D09-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96D09-F1-predicted_aligned_error_v6.png","plddt_mean":49.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPRASP2","jax_strain_url":"https://www.jax.org/strain/search?query=GPRASP2"},"sequence":{"accession":"Q96D09","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96D09.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96D09/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96D09"}},"corpus_meta":[{"pmid":"24019467","id":"PMC_24019467","title":"Regulation of GDF-11 and myostatin activity by GASP-1 and GASP-2.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/24019467","citation_count":83,"is_preprint":false},{"pmid":"30926797","id":"PMC_30926797","title":"Abnormal mGluR-mediated synaptic plasticity and autism-like behaviours in Gprasp2 mutant mice.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/30926797","citation_count":46,"is_preprint":false},{"pmid":"26901434","id":"PMC_26901434","title":"Pitchfork and Gprasp2 Target Smoothened to the Primary Cilium for Hedgehog Pathway Activation.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26901434","citation_count":24,"is_preprint":false},{"pmid":"16835690","id":"PMC_16835690","title":"Huntingtin interacts with the receptor sorting family protein GASP2.","date":"2006","source":"Journal of neural transmission (Vienna, Austria : 1996)","url":"https://pubmed.ncbi.nlm.nih.gov/16835690","citation_count":19,"is_preprint":false},{"pmid":"28955860","id":"PMC_28955860","title":"Enhancement of C2C12 myoblast proliferation and differentiation by GASP-2, a myostatin inhibitor.","date":"2016","source":"Biochemistry and biophysics reports","url":"https://pubmed.ncbi.nlm.nih.gov/28955860","citation_count":13,"is_preprint":false},{"pmid":"28096187","id":"PMC_28096187","title":"GPRASP2, a novel causative gene mutated in an X-linked recessive syndromic hearing loss.","date":"2017","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28096187","citation_count":9,"is_preprint":false},{"pmid":"31960486","id":"PMC_31960486","title":"GASP-2 overexpressing mice exhibit a hypermuscular phenotype with contrasting molecular effects compared to GASP-1 transgenics.","date":"2020","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/31960486","citation_count":8,"is_preprint":false},{"pmid":"34418635","id":"PMC_34418635","title":"Disruption of Gprasp2 down-regulates Hedgehog signaling and leads to apoptosis in auditory cells.","date":"2021","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/34418635","citation_count":3,"is_preprint":false},{"pmid":"28849214","id":"PMC_28849214","title":"Dynamic expression analysis of armc10, the homologous gene of human GPRASP2, in zebrafish embryos.","date":"2017","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/28849214","citation_count":1,"is_preprint":false},{"pmid":"39675768","id":"PMC_39675768","title":"Implication of GPRASP2 in the Proliferation and Hair Cell-Forming of Cochlear Supporting Cells.","date":"2024","source":"Cell proliferation","url":"https://pubmed.ncbi.nlm.nih.gov/39675768","citation_count":1,"is_preprint":false},{"pmid":"38816497","id":"PMC_38816497","title":"Maternal behaviours disrupted by Gprasp2 deletion modulate neurodevelopmental trajectory in progeny.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38816497","citation_count":0,"is_preprint":false},{"pmid":"39253164","id":"PMC_39253164","title":"GPRASP2 deficiency contributes to apoptosis in the spiral ganglion cells via the AMPK/DRP1 signaling pathway.","date":"2024","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/39253164","citation_count":0,"is_preprint":false},{"pmid":"41688572","id":"PMC_41688572","title":"Abnormal iron homeostasis mediates cochlear hair cell impairment and hearing loss in Gprasp2-deficient mice.","date":"2026","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/41688572","citation_count":0,"is_preprint":false},{"pmid":"41726907","id":"PMC_41726907","title":"Elevated endocytic trafficking mediated by GPRASP2 maintains HSC fidelity.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41726907","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.07.18.24310640","title":"Chromosome X-Wide Common Variant Association Study (XWAS) in Autism Spectrum Disorder","date":"2024-07-18","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.18.24310640","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9095,"output_tokens":3221,"usd":0.0378,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10754,"output_tokens":3783,"usd":0.074173,"stage2_stop_reason":"end_turn"},"total_usd":0.111973,"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\": 2013,\n      \"finding\": \"GASP-2 (GPRASP2) inhibits myostatin (MSTN) and GDF-11 activity by blocking the binding of these ligands to the type II receptor, acting as an extracellular antagonist at the initial signaling step. Gasp2-/- mice show posteriorly directed axial skeletal transformations, reductions in muscle weight, fiber-type shift from type IIb to type IIa, and impaired muscle regeneration—phenotypes consistent with GDF-11 and MSTN overactivity.\",\n      \"method\": \"Ligand-receptor binding assays, Gasp2 knockout mouse phenotyping (muscle weight, fiber typing, regeneration assays, skeletal patterning analysis)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vivo genetic and biochemical methods; mechanistic block at type II receptor validated by binding assay and confirmed by KO phenotypes consistent with ligand overactivity\",\n      \"pmids\": [\"24019467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GPRASP2 forms a complex with Pitchfork (Pifo) that is required for Hedgehog-induced translocation of Smoothened (Smo) to the primary cilium. Depletion of Gprasp2 prevents Smo ciliary targeting and abolishes Hedgehog target gene activation.\",\n      \"method\": \"Co-immunoprecipitation of Pifo-Gprasp2 complex, siRNA/shRNA depletion of Gprasp2 with immunofluorescence quantification of Smo at primary cilia, qRT-PCR of Hh target genes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal protein complex identification plus loss-of-function with two orthogonal readouts (ciliary localization and target gene expression), single lab\",\n      \"pmids\": [\"26901434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GPRASP2 (GASP2) physically interacts with huntingtin (htt) and the two proteins co-localize in SH-SY5Y neuronal cells, suggesting GPRASP2 may link htt to G protein-coupled receptor sorting and trafficking.\",\n      \"method\": \"Yeast two-hybrid screening, membrane-based co-immunoprecipitation, classical co-immunoprecipitation in co-transfected mammalian cells, co-localization by immunofluorescence in SH-SY5Y cells\",\n      \"journal\": \"Journal of neural transmission\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and co-localization in neuronal cells, single lab, no functional consequence directly demonstrated\",\n      \"pmids\": [\"16835690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Gprasp2 regulates postendocytic sorting of mGluR5, bidirectionally controlling its surface availability. Loss of Gprasp2 increases mGluR5 surface levels, enhances hippocampal mGluR-dependent long-term depression (LTD), and causes alterations in dendritic complexity, spine density, and synaptic maturation. Gprasp2 deletion produces ASD-like behaviour in mice.\",\n      \"method\": \"Gprasp2 knockout mice, shRNA knockdown and overexpression of Gprasp2, surface biotinylation assay for mGluR5, electrophysiology (LTD recordings in hippocampal slices), confocal imaging of dendritic morphology and spine density, behavioural testing\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — bidirectional manipulation (KO + overexpression), multiple orthogonal methods (surface receptor assay, electrophysiology, morphology, behaviour), single lab with comprehensive mechanistic characterisation\",\n      \"pmids\": [\"30926797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GASP-2 promotes C2C12 myoblast proliferation and differentiation by inhibiting the canonical myostatin signaling pathway. This activity is independent of GASP-2 glycosylation, as both glycosylated and bacterially expressed (fully deglycosylated) recombinant GASP-2 retain inhibitory activity.\",\n      \"method\": \"Gprasp2 overexpression and shRNA knockdown in C2C12 myoblasts, proliferation and differentiation assays, recombinant protein production in prokaryotic system (deglycosylated), western blot for myostatin pathway components\",\n      \"journal\": \"Biochemistry and biophysics reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional manipulation (OE and KD), biochemical characterisation of glycosylation-independent activity, single lab\",\n      \"pmids\": [\"28955860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GASP-2 overexpression in mice increases skeletal muscle mass and induces a switch from slow- to fast-twitch myofibers (consistent with Mstn-/- mice), without metabolic defects. Mechanistically, GASP-2 has lower affinity for myostatin than GASP-1, resulting in different regulatory outcomes: GASP-1 transgenic mice exhibit constitutive myostatin upregulation (and a reverse fiber-type switch), whereas GASP-2 transgenic mice do not.\",\n      \"method\": \"Transgenic mouse overexpression of Gasp-2, muscle mass measurement, fiber-type immunohistochemistry, gene expression analysis of TGF-β pathway members, metabolic phenotyping\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gain-of-function with multiple phenotypic readouts, comparative analysis with GASP-1 transgenics, single lab\",\n      \"pmids\": [\"31960486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Gprasp2 knockout in HEI-OC1 auditory cells down-regulates the Hedgehog signaling pathway (reduced Smo, Gli1, Gli2), leading to mitochondrial damage and apoptosis (increased Bax, Caspase-3/cleaved-Caspase-3; decreased Bcl2). Treatment with smoothened agonist purmorphamine rescues Hh-Gli signaling and reduces apoptosis in Gprasp2-KO cells, establishing Hh pathway dependence.\",\n      \"method\": \"CRISPR/Cas9 knockout of Gprasp2 in HEI-OC1 cells, RNA-seq, western blot for Hh pathway components and apoptosis markers, flow cytometry apoptosis assay, electron microscopy for mitochondrial morphology, pharmacological rescue with smoothened agonist\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus pharmacological rescue with multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"34418635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRASP2 deficiency in spiral ganglion cells (SGCs) activates the AMPK/DRP1 signaling pathway, causing mitochondrial fragmentation, reduced membrane potential, enhanced apoptosis, and decreased cell viability. Treatment with mitochondrial fission inhibitor Mdivi-1 rescues these phenotypes, implicating GPRASP2 in maintaining mitochondrial integrity via suppression of AMPK/DRP1 in SGCs.\",\n      \"method\": \"Lentiviral shRNA knockdown of Gprasp2 in primary SGCs, western blot for AMPK phosphorylation and DRP1, mitochondrial morphology imaging, JC-1 membrane potential assay, flow cytometry apoptosis assay, pharmacological rescue with Mdivi-1, cochlear explant culture\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with pharmacological rescue and multiple orthogonal mechanistic readouts, single lab\",\n      \"pmids\": [\"39253164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPRASP2 overexpression in mouse cochlear organoids promotes supporting cell proliferation via the Hedgehog signaling pathway, and promotes hair cell formation from supporting cells via β-catenin signaling. GPRASP2 deficiency increases lysosomal degradation of SMO protein, reducing both β-catenin and GLI1 expression.\",\n      \"method\": \"Mouse cochlear organoid overexpression of Gprasp2, SMO protein stability assay (lysosomal inhibitor treatment), western blot for SMO, β-catenin, GLI1, immunofluorescence for hair cell and supporting cell markers, AAV-ie-Gprasp2 delivery with SAG co-treatment in neomycin-damaged cochlear explants\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function and loss-of-function with multiple pathway readouts including protein stability, single lab\",\n      \"pmids\": [\"39675768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GPRASP2 physically binds NCAM1. Gprasp2 deficiency decreases NCAM1 levels and enhances ferritinophagy in cochlear hair cells, leading to disrupted iron homeostasis, disordered hair cell arrangement, and hearing loss.\",\n      \"method\": \"Co-immunoprecipitation/binding assay for GPRASP2-NCAM1 interaction, Gprasp2-deficient mouse model, western blot for NCAM1 and ferritinophagy markers, auditory brainstem response, cochlear immunofluorescence\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding partner identified plus KO phenotyping with mechanistic pathway readout, single lab\",\n      \"pmids\": [\"41688572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GPRASP2 mediates elevated endocytosis in quiescent hematopoietic stem cells (HSCs) to attenuate receptor signaling, maintaining stem cell dormancy and self-renewal. Disruption of GPRASP2-mediated endocytosis induces rapid HSC proliferation and increased surface expression of signaling receptors, consistent with a model in which GPRASP2-dependent receptor internalization limits chronic activation and functional exhaustion.\",\n      \"method\": \"GPRASP2 enrichment fractionation of HSCs, GPRASP2 disruption in HSCs with assessment of endocytosis rates, signaling constituent expression, proliferation assays, and functional stem cell reconstitution assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in primary HSCs with functional readouts linking endocytosis to signaling attenuation; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"41726907\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GPRASP2 is a post-endosomal sorting protein that controls the surface availability and lysosomal degradation of multiple G protein-coupled receptors and related signaling proteins: it inhibits myostatin/GDF-11 by blocking ligand binding to type II receptors, promotes Hedgehog pathway activation by forming a complex with Pitchfork to enable Smoothened ciliary translocation (and protects SMO from lysosomal degradation), regulates mGluR5 surface levels to tune synaptic plasticity and LTD in neurons, binds NCAM1 in cochlear hair cells to maintain iron homeostasis, and mediates elevated endocytosis in hematopoietic stem cells to attenuate receptor signaling and preserve quiescence.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPRASP2 (GASP-2) is a receptor-trafficking and signaling-modulator protein that controls the surface availability and degradative fate of multiple membrane signaling receptors, thereby tuning developmental and synaptic signaling outputs [#0, #3, #8]. In the TGF-\\u03b2 branch it acts as an extracellular antagonist of myostatin (MSTN) and GDF-11, blocking ligand binding to the type II receptor; loss of Gasp2 produces axial skeletal transformations, reduced muscle mass, a type IIb-to-IIa fiber shift, and impaired regeneration, while overexpression increases muscle mass and drives a slow-to-fast fiber switch \\u2014 an activity that is independent of GASP-2 glycosylation [#0, #4, #5]. In the Hedgehog pathway, GPRASP2 forms a complex with Pitchfork (Pifo) required for Hedgehog-induced Smoothened translocation to the primary cilium, and it protects SMO from lysosomal degradation to sustain GLI and \\u03b2-catenin signaling [#1, #8]. In neurons, GPRASP2 governs postendocytic sorting of mGluR5 to bidirectionally set its surface levels, shaping hippocampal mGluR-dependent LTD, dendritic and spine morphology, and behaviour, with loss producing ASD-like phenotypes [#3]. In the cochlea, GPRASP2 binds NCAM1 and supports Hedgehog signaling to maintain mitochondrial integrity, iron homeostasis, and hair cell survival [#6, #9]. The protein also physically interacts with huntingtin in neuronal cells [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established GPRASP2's first physical interaction partner, linking it to neuronal protein networks and GPCR sorting before any functional role was known.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP, and co-localization with huntingtin in SH-SY5Y cells\",\n      \"pmids\": [\"16835690\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of the htt interaction demonstrated\", \"Whether the interaction influences receptor trafficking untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined GPRASP2 as an extracellular antagonist of myostatin and GDF-11, answering how it acts at the initial step of TGF-\\u03b2 signaling and revealing its in vivo role in muscle and skeletal patterning.\",\n      \"evidence\": \"Ligand-receptor binding assays and Gasp2 knockout mouse phenotyping (muscle, fiber type, regeneration, skeleton)\",\n      \"pmids\": [\"24019467\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ligand sequestration not resolved\", \"Relationship to its intracellular trafficking roles unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified the GPRASP2-Pifo complex as required for Hedgehog-induced Smoothened ciliary translocation, placing GPRASP2 in ciliary signal transduction.\",\n      \"evidence\": \"Co-IP of Pifo-Gprasp2, siRNA/shRNA depletion with Smo ciliary immunofluorescence and Hh target-gene qRT-PCR\",\n      \"pmids\": [\"26901434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism of Smo handoff to the cilium unknown\", \"Stoichiometry and structure of the Pifo-Gprasp2 complex undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed that GPRASP2 promotes myoblast proliferation and differentiation through myostatin pathway inhibition and that this activity does not require glycosylation, constraining its biochemical mechanism.\",\n      \"evidence\": \"Overexpression/knockdown in C2C12 myoblasts and inhibitory activity of bacterially expressed deglycosylated recombinant GASP-2\",\n      \"pmids\": [\"28955860\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Domain mediating myostatin binding not mapped\", \"In vitro myoblast result not yet linked to in vivo mechanism\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated that GPRASP2 controls postendocytic sorting of mGluR5 to bidirectionally set surface receptor levels, establishing a direct role in synaptic plasticity and behaviour.\",\n      \"evidence\": \"Gprasp2 KO plus overexpression, mGluR5 surface biotinylation, hippocampal LTD electrophysiology, dendritic/spine imaging, behavioural testing\",\n      \"pmids\": [\"30926797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular machinery linking GPRASP2 to the sorting decision not defined\", \"Whether other GPCRs are co-regulated in neurons untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved why GASP-2 and GASP-1 produce divergent muscle outcomes by showing GASP-2 has lower myostatin affinity, refining the gain-of-function consequence in vivo.\",\n      \"evidence\": \"Gasp-2 transgenic overexpression mice with muscle mass, fiber-type IHC, TGF-\\u03b2 gene expression, and metabolic phenotyping versus GASP-1 transgenics\",\n      \"pmids\": [\"31960486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quantitative affinity differences not structurally explained\", \"Basis for GASP-1-specific myostatin upregulation unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked GPRASP2 to auditory cell survival through Hedgehog pathway dependence, showing its loss triggers mitochondrial damage and apoptosis rescuable by a Smoothened agonist.\",\n      \"evidence\": \"CRISPR KO in HEI-OC1 cells, RNA-seq, Hh and apoptosis western blots, flow cytometry, EM, and purmorphamine rescue\",\n      \"pmids\": [\"34418635\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How GPRASP2 loss lowers Hh signaling mechanistically not shown here\", \"Cell-line context may not reflect native hair cells\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected GPRASP2 deficiency to AMPK/DRP1-driven mitochondrial fragmentation in spiral ganglion cells, identifying a specific effector pathway for its protective role.\",\n      \"evidence\": \"shRNA knockdown in primary SGCs, AMPK/DRP1 western blots, mitochondrial imaging, JC-1, apoptosis flow cytometry, and Mdivi-1 rescue\",\n      \"pmids\": [\"39253164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between GPRASP2 receptor trafficking and AMPK activation unestablished\", \"Direct molecular target of GPRASP2 in SGCs unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed GPRASP2 protects SMO from lysosomal degradation to sustain Hedgehog and \\u03b2-catenin signaling, driving supporting-cell proliferation and hair-cell regeneration.\",\n      \"evidence\": \"Cochlear organoid overexpression, SMO lysosomal stability assay, Hh/\\u03b2-catenin western blots, cell-marker immunofluorescence, and AAV-Gprasp2 with SAG in damaged explants\",\n      \"pmids\": [\"39675768\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which GPRASP2 shields SMO from lysosomes undefined\", \"Whether \\u03b2-catenin effect is direct or downstream of Hh unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified NCAM1 as a GPRASP2 binding partner whose loss enhances ferritinophagy, tying GPRASP2 to iron homeostasis and hearing in cochlear hair cells.\",\n      \"evidence\": \"GPRASP2-NCAM1 binding assay, Gprasp2-deficient mice, NCAM1/ferritinophagy western blots, ABR, and cochlear immunofluorescence\",\n      \"pmids\": [\"41688572\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How GPRASP2-NCAM1 binding controls ferritinophagy mechanistically unknown\", \"Single-lab interaction without reciprocal structural validation\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended GPRASP2 function to hematopoietic stem cells, proposing it drives elevated endocytosis to attenuate receptor signaling and maintain quiescence.\",\n      \"evidence\": \"GPRASP2 fractionation enrichment in HSCs, disruption with endocytosis, signaling, proliferation, and reconstitution assays (preprint)\",\n      \"pmids\": [\"41726907\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Specific receptors internalized via GPRASP2 in HSCs not identified\", \"Direct endocytic machinery interaction unmapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single protein coordinates extracellular ligand antagonism, ciliary receptor trafficking, postendocytic sorting, and protection of receptors from lysosomal degradation across such diverse tissues remains mechanistically unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model defining distinct functional domains\", \"Unclear whether intracellular sorting and extracellular antagonism are separable activities\", \"Direct sorting/endocytic machinery partners not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 4, 5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PIFO\", \"HTT\", \"NCAM1\", \"SMO\", \"MSTN\", \"GDF11\", \"GRM5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}