{"gene":"SORCS2","run_date":"2026-06-10T07:46:38","timeline":{"discoveries":[{"year":2014,"finding":"SorCS2 functions as a proneurotrophin (proNT) receptor that mediates both trophic and apoptotic signals in conjunction with p75NTR. In CNS neurons, SorCS2 exists as a single-chain protein required for proBDNF-induced growth cone collapse in developing dopaminergic processes. In PNS glia (Schwann cells), proteolytic processing produces a two-chain SorCS2 isoform that mediates proNT-dependent apoptosis; sciatic nerve injury triggers generation of two-chain SorCS2 in p75NTR-positive dying Schwann cells, with apoptosis profoundly attenuated in Sorcs2−/− mice.","method":"Knockout mouse phenotyping (Sorcs2−/− and p75NTR−/−), biochemical characterization of SorCS2 processing (single- vs two-chain isoforms), growth cone collapse assay, dopamine level measurements, behavioral assays","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic and biochemical evidence across CNS and PNS compartments, multiple orthogonal methods including KO phenotyping, biochemical processing assays, and functional cell biology assays","pmids":["24908487"],"is_preprint":false},{"year":2016,"finding":"SorCS2 forms complexes with p75NTR (static interaction) and with TrkB (activity-dependent interaction) in hippocampal neurons. The SorCS2-p75NTR complex is required for proBDNF-induced long-term depression, and the SorCS2-TrkB complex facilitates TrkB translocation to postsynaptic densities for synaptic tagging and maintenance of long-term potentiation. Neurons lacking SorCS2 fail to respond to BDNF by TrkB autophosphorylation and activation of downstream signaling cascades, impairing neurite outgrowth and spine formation.","method":"Co-immunoprecipitation, synaptic plasticity recordings (LTP/LTD) in Sorcs2−/− hippocampal slices, TrkB phosphorylation assays, subcellular fractionation, behavioral testing","journal":"Molecular psychiatry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, electrophysiological recordings, biochemical phosphorylation assays, and behavioral phenotyping across multiple orthogonal methods","pmids":["27457814"],"is_preprint":false},{"year":2018,"finding":"Crystal structures of the SorCS2 ectodomain (unliganded and in complex with NGF) reveal cross-braced SorCS2 homodimers with two NGF dimers bound in a 2:4 stoichiometry. Five of six SorCS2 domains contribute to dimer formation; a C-terminal membrane-proximal domain with an RNA recognition motif fold locks the dimer in an intermolecular head-to-tail interaction. Both NGF dimer chains interact exclusively with the top face of the SorCS2 β-propeller, which serves as the ligand-binding platform. Biophysical experiments confirmed that NGF, proNGF, and proBDNF all bind at this β-propeller site.","method":"X-ray crystallography of SorCS2–NGF complex and unliganded SorCS2 ectodomain; biophysical binding experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure determination with biophysical validation of ligand binding, multiple orthogonal methods in a single rigorous study","pmids":["30061605"],"is_preprint":false},{"year":2019,"finding":"SorCS2 acts as a sorting receptor that sustains cell-surface expression of the neuronal amino acid transporter EAAT3, facilitating cysteine import required for glutathione synthesis. Loss of SorCS2 depletes EAAT3 from the plasma membrane, impairs neuronal cysteine uptake, causes oxidative brain damage, and increases neuronal cell death and mortality during epilepsy.","method":"Surface biotinylation/fractionation to measure EAAT3 plasma membrane levels, cysteine uptake assays, oxidative stress markers, epilepsy survival assays in Sorcs2−/− mice","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — surface fractionation, functional transport assays, in vivo KO phenotyping with multiple orthogonal readouts in a single study","pmids":["30840898"],"is_preprint":false},{"year":2017,"finding":"SorCS2 interacts with VPS35 (a core retromer component) and regulates surface trafficking of the NMDA receptor subunit NR2A in medium spiny neurons (MSNs) of the striatum. In zQ175 HD mice, SorCS2 is markedly decreased in an age- and allele-dependent manner and is mislocalized to perinuclear clusters. SorCS2 selectively interacts with mutant huntingtin (mtHTT) but not wild-type huntingtin. Genetic deficiency of SorCS2 accelerates onset and exacerbates motor coordination deficits in HD mice.","method":"Co-immunoprecipitation of SorCS2 with VPS35 and mtHTT, immunofluorescence localization, surface receptor analysis, behavioral testing in double-mutant mice","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for protein interactions, in vivo localization, and genetic epistasis (SorCS2 KO × zQ175) with behavioral readout, single lab","pmids":["28469074"],"is_preprint":false},{"year":2020,"finding":"SorCS2 is a selective regulator of NMDA receptor (but not AMPA receptor) surface trafficking in hippocampal neurons, localizing to the postsynaptic density and endosomes within dendritic spines of CA2 neurons. SorCS2 deficiency reduces dendritic spine density in CA2 neurons and impairs social memory without affecting sociability or other hippocampal-dependent behaviors.","method":"Surface receptor trafficking assays (distinguishing NMDA vs AMPA), immunolocalization to postsynaptic density/endosomes, dendritic spine analysis, behavioral testing in novel Sorcs2−/− mice","journal":"Molecular psychiatry","confidence":"High","confidence_rationale":"Tier 2 / Strong — selective trafficking assays with receptor specificity controls, subcellular localization experiments, and behavioral phenotyping with multiple specificity controls in a single rigorous study","pmids":["31988435"],"is_preprint":false},{"year":2020,"finding":"In astrocytes surrounding ischemic brain injury, SorCS2 expression is induced by TGF-β1 and controls secretion of endostatin. Loss of SorCS2 in mice abolishes the acute post-stroke endostatin response and impairs vascularization of the ischemic brain, identifying SorCS2 as a sorting receptor for endostatin release from reactive astrocytes.","method":"Mouse stroke models (in vivo), TGF-β1 stimulation of astrocytes in vitro, endostatin secretion assays, vascularization quantification in Sorcs2−/− mice","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO phenotyping combined with in vitro secretion assays and TGF-β1 stimulation, single lab","pmids":["31898841"],"is_preprint":false},{"year":2017,"finding":"Disruption of SorCS2 in mice causes severe stereociliary bundle defects in cochlear and vestibular macular hair cells. SorCS2 loss disrupts the intrinsic polarity pathway: LGN and Gαi3 were largely absent and aPKC lost its asymmetric distribution in affected hair cells, placing SorCS2 upstream of the intrinsic polarity pathway controlling hair bundle formation.","method":"Transgenic disruption of SorCS2 locus confirmed by whole-genome sequencing and qPCR; immunolabeling of polarity markers LGN, Gαi3, aPKC in cochlear/vestibular tissue; hair bundle morphology analysis","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with specific molecular pathway readouts (polarity markers), single lab with multiple cellular markers","pmids":["28346477"],"is_preprint":false},{"year":2023,"finding":"SorCS2 is a progranulin (PGRN) receptor required for motor neuron (MN) diversification and axon outgrowth. SorCS2 binds PGRN to control its secretion, intracellular signaling, and conversion into granulins. In zebrafish, SorCS2 knockdown impairs neuromuscular junction morphology and motility. In mice, SorCS2 deficiency perturbs cell-fate decisions of brachial MNs and slows adult motor nerve regeneration. Primitive macrophage-derived PGRN interacts with SorCS2-positive motor axons during pathfinding.","method":"Zebrafish knockdown (morpholino/CRISPR), mouse knockout analysis, co-expression studies, PGRN binding/secretion/processing assays, cell-fate tracing, nerve segmentation","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — ligand binding established biochemically, multiple model organisms (zebrafish and mouse), functional assays for secretion and granulin conversion, genetic KO phenotyping","pmids":["37897724"],"is_preprint":false},{"year":2023,"finding":"SorCS2 undergoes alternative splicing that generates four variants differing in insertion of an acidic cluster motif and/or a serine residue in the intracellular domain (ICD), each undergoing proteolytic processing to give eight protein isoforms. Variants lacking the serine (but not those with it) rescued BDNF-induced neuronal branching in SorCS2 KO neurons. Variants without the acidic cluster show increased interactions with clathrin-associated adaptors AP-1, AP-2, and AP-3. Yeast two-hybrid screens revealed that all variants bound dynein light chain Tctex-type 3, but only variants with the acidic cluster motif bound kinesin light chain 1, giving variants distinct trafficking routes and subcellular localizations.","method":"Alternative splicing characterization, rescue assays in SorCS2 KO hippocampal neurons, co-immunoprecipitation with AP complexes, yeast two-hybrid screening for Tctex-type 3 and kinesin light chain 1, subcellular localization assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional rescue assays, Co-IP with multiple AP complexes, yeast two-hybrid, and subcellular localization, multiple orthogonal methods in a single study","pmids":["37507021"],"is_preprint":false},{"year":2023,"finding":"SorCS2 is predominantly expressed in pancreatic islet alpha cells and controls osteopontin production/secretion; loss of SorCS2 prevents alpha cells from producing osteopontin, a secreted factor that facilitates insulin release from stressed beta cells, leading to defective insulin granule maturation and blunted glucose response in beta cells.","method":"Metabolic studies in SORCS2-deficient mice, ex vivo functional islet analyses, single-cell transcriptomics of pancreatic tissue, osteopontin secretion assays","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse metabolic phenotyping combined with ex vivo functional analyses and single-cell transcriptomics, single lab","pmids":["38226160"],"is_preprint":false},{"year":2021,"finding":"Loss of SorCS2 in mice results in elevated DNA double-strand break (DSB) levels in the dentate gyrus. Knockout of SORCS2 in a human neuronal cell line increased Topoisomerase IIβ-dependent DSB formation and reduced neuronal viability, linking SorCS2 to regulation of DNA integrity via a Topoisomerase IIβ-dependent pathway.","method":"γH2AX immunostaining for DSBs in mouse dentate gyrus, SORCS2 CRISPR KO in human neuronal cell line, Topoisomerase IIβ inhibitor experiments, viability assays","journal":"Cellular and molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO and in vitro KO with mechanistic inhibitor experiments, single lab","pmids":["34741697"],"is_preprint":false},{"year":2025,"finding":"The SorCS2 intracellular domain (ICD) contains a triple serine motif that functions as a signaling switch. Serine-to-alanine substitution renders neurons less responsive to BDNF, whereas phosphomimetic mutations induce neurotrophic effects independently of the SorCS2 extracellular domain and BDNF. Triple serine motif-based cell-penetrating peptides activate intracellular signaling that partially overlaps with the BDNF pathway and ultimately activates the transcription factor CREB.","method":"Site-directed mutagenesis (serine→alanine and phosphomimetic substitutions), BDNF response assays in hippocampal neurons, cell-penetrating peptide experiments, CREB activation assays","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — active-site mutagenesis with functional readouts in neurons, single lab but multiple orthogonal mutations tested","pmids":["40520096"],"is_preprint":false},{"year":2025,"finding":"A heterozygous SORCS2 variant (arginine-to-tryptophan substitution in the 10CC region of the extracellular Vps10p domain) found in ADHD patients causes aberrant posttranslational receptor processing, altered subcellular localization, impaired ligand binding, and abrogates BDNF signaling in a dominant-negative manner.","method":"Biochemical characterization of variant processing (Western blot), subcellular localization assays, ligand binding assays, BDNF signaling assays in cells expressing the variant","journal":"Molecular psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical readouts (processing, localization, binding, signaling) for a specific variant, single lab","pmids":["40968259"],"is_preprint":false},{"year":2025,"finding":"SorCS2 is important for astrocytic neurovascular coupling. SorCS2 is strongly expressed in astrocyte endfeet at P8 but sparse in adult brain. Sorcs2−/− mice show reduced neurovascular coupling associated with reduced astrocytic calcium response to neuronal excitation. In Sorcs2−/− astrocytes, AQP4 abundance is increased in bulk lysate but reduced in the cell surface fraction, indicating impaired AQP4 trafficking; glutamate metabotropic receptor 3 (mGluR3) is also increased.","method":"Immunostaining for SorCS2/GFAP/AQP4, laser speckle contrast imaging for neurovascular coupling in vivo, calcium imaging in live brain slices, cell surface fraction proteomics, Western blot, qPCR","journal":"Acta physiologica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo functional imaging combined with surface proteomics and in vitro validation, single lab, multiple methods","pmids":["40342271"],"is_preprint":false},{"year":2024,"finding":"Hippocampal SorCS2 overexpression (via AAV) reverses chronic stress-induced depression-like behaviors in mice and restores SorCS2-TrkB binding, BDNF signaling cascade activation, and hippocampal neurogenesis. Chronic stress reduces SorCS2-TrkB complex formation specifically in the hippocampus.","method":"AAV-mediated SorCS2 overexpression in hippocampus of CSDS/CUMS mice, Co-IP of SorCS2-TrkB, BDNF pathway phosphorylation assays, immunofluorescence for immature neurons, behavioral testing","journal":"Pharmacology, biochemistry, and behavior","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function rescue with Co-IP and pathway assays, single lab","pmids":["38996926"],"is_preprint":false},{"year":2025,"finding":"SorCS2-derived macrocyclic peptides (TT-P34) activate CREB and AMPK in a CAMKK2-dependent manner, upregulating PGC1α and TFEB and inducing mitochondrial biogenesis. In zQ175 HD mice, TT-P34 rescues motor behavioral deficits and preserves synaptic and mitochondrial signatures. In MPTP-induced Parkinson's Disease mice, TT-P34 ameliorates behavioral deficits and reduces dopaminergic loss. TT-P34 crosses the blood-brain barrier in non-human primates.","method":"Macrocyclic peptide design, CREB/AMPK/PGC1α/TFEB pathway assays, CAMKK2 inhibitor epistasis, behavioral testing in zQ175 and MPTP mouse models, non-human primate pharmacokinetics","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vitro and in vivo models with mechanistic pathway analysis; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.09.17.676723"],"is_preprint":true}],"current_model":"SorCS2 is a Vps10p-domain sorting receptor that functions as a co-receptor for proneurotrophins (proBDNF, proNGF) and mature neurotrophins via p75NTR and TrkB complexes, regulating dopaminergic axon guidance, hippocampal synaptic plasticity (LTP/LTD), and NMDA receptor surface trafficking through retromer (VPS35)-dependent and clathrin adaptor (AP-1/2/3)-dependent routes; its intracellular domain harbors a phosphorylatable triple-serine motif and splice-variant-specific acidic cluster/motor-protein binding sites that dictate cell-type-specific trafficking; it also acts as a sorting receptor sustaining plasma membrane levels of EAAT3 for oxidative stress protection and AQP4 in astrocytes for neurovascular coupling, as a progranulin receptor controlling motor neuron fate and axon pathfinding, and as a stress-response factor in astrocytes and pancreatic alpha cells that controls endostatin and osteopontin secretion, respectively."},"narrative":{"mechanistic_narrative":"SorCS2 is a Vps10p-domain sorting receptor that governs neurotrophin signaling, receptor trafficking, and regulated secretion across neurons, glia, and pancreatic islet cells [PMID:24908487, PMID:27457814, PMID:30840898]. It serves as a co-receptor for proneurotrophins and mature neurotrophins, forming a static complex with p75NTR that mediates proBDNF-induced growth cone collapse and long-term depression, and an activity-dependent complex with TrkB that drives TrkB autophosphorylation, postsynaptic translocation, neurite outgrowth, and maintenance of long-term potentiation [PMID:24908487, PMID:27457814]. Crystal structures show the SorCS2 ectodomain forms cross-braced homodimers that bind NGF, proNGF, and proBDNF dimers in a 2:4 stoichiometry through the top face of its β-propeller [PMID:30061605]. As a sorting receptor, SorCS2 sustains plasma-membrane levels of the cysteine transporter EAAT3 to support glutathione synthesis and protect against oxidative damage, selectively controls surface trafficking of NMDA receptor subunits (but not AMPA receptors) in hippocampal and striatal neurons via an interaction with the retromer component VPS35, and maintains AQP4 surface trafficking in astrocyte endfeet for neurovascular coupling [PMID:30840898, PMID:28469074, PMID:31988435, PMID:40342271]. Its intracellular domain encodes a signaling switch: a phosphorylatable triple-serine motif whose phosphomimetic state drives neurotrophic, CREB-activating signaling independently of the ectodomain and BDNF, and splice-variant-specific acidic-cluster and serine elements that confer differential binding to clathrin adaptors AP-1/2/3 and to dynein and kinesin light chains, dictating cell-type-specific trafficking routes [PMID:37507021, PMID:40520096]. Beyond the nervous system, SorCS2 acts as a progranulin receptor controlling motor neuron diversification and axon outgrowth and as a stress-induced sorting receptor for regulated secretion of endostatin from reactive astrocytes and osteopontin from pancreatic alpha cells [PMID:31898841, PMID:37897724, PMID:38226160]. A heterozygous SORCS2 variant in the extracellular Vps10p domain identified in ADHD patients impairs receptor processing and ligand binding and abrogates BDNF signaling in a dominant-negative manner [PMID:40968259].","teleology":[{"year":2014,"claim":"Established SorCS2 as a proneurotrophin receptor whose processing state determines whether it transmits trophic or apoptotic signals, defining its core role with p75NTR.","evidence":"Knockout mouse phenotyping with biochemical isoform characterization and growth cone collapse assays across CNS and PNS","pmids":["24908487"],"confidence":"High","gaps":["Did not resolve the structural basis of ligand binding","Mechanism of single- vs two-chain processing not defined at the protease level"]},{"year":2016,"claim":"Distinguished two functional SorCS2 complexes—static with p75NTR and activity-dependent with TrkB—linking the receptor to bidirectional control of synaptic plasticity.","evidence":"Reciprocal Co-IP, LTP/LTD recordings, and TrkB phosphorylation assays in Sorcs2−/− hippocampal slices","pmids":["27457814"],"confidence":"High","gaps":["How activity triggers the SorCS2-TrkB interaction is unresolved","Trafficking machinery directing TrkB to postsynaptic densities not identified here"]},{"year":2018,"claim":"Resolved the molecular architecture of ligand recognition, showing SorCS2 homodimers present a β-propeller platform that binds NGF, proNGF, and proBDNF.","evidence":"X-ray crystallography of liganded and unliganded ectodomain with biophysical binding validation","pmids":["30061605"],"confidence":"High","gaps":["Structures do not include the transmembrane or intracellular domains","How dimer geometry couples to p75NTR/TrkB complexes not shown"]},{"year":2017,"claim":"Extended SorCS2 function beyond neurotrophin signaling by placing it upstream of the intrinsic polarity pathway controlling cochlear and vestibular hair bundle formation.","evidence":"Genetic disruption with immunolabeling of polarity markers LGN, Gαi3, and aPKC","pmids":["28346477"],"confidence":"Medium","gaps":["Molecular link between SorCS2 and the LGN/Gαi3 polarity machinery undefined","Whether a ligand drives this function is unknown"]},{"year":2017,"claim":"Identified SorCS2 as a VPS35/retromer-associated regulator of NMDA receptor surface trafficking and a selective binding partner of mutant huntingtin, connecting it to striatal pathology.","evidence":"Co-IP with VPS35 and mtHTT, localization, and genetic epistasis in zQ175 HD mice","pmids":["28469074"],"confidence":"Medium","gaps":["Single-lab Co-IP without reciprocal structural validation","Mechanism by which mtHTT mislocalizes SorCS2 not resolved"]},{"year":2019,"claim":"Demonstrated a sorting-receptor role sustaining surface EAAT3 to drive cysteine import and glutathione-dependent oxidative protection, broadening SorCS2 function to metabolite transport.","evidence":"Surface fractionation, cysteine uptake assays, and epilepsy survival readouts in Sorcs2−/− mice","pmids":["30840898"],"confidence":"High","gaps":["Direct SorCS2-EAAT3 binding interface not mapped","Trafficking adaptors involved not identified here"]},{"year":2020,"claim":"Refined receptor-trafficking specificity, showing SorCS2 selectively controls NMDA but not AMPA receptor surface levels in CA2 neurons and is required for social memory.","evidence":"Receptor-specific surface trafficking assays, PSD/endosome localization, spine analysis, and behavior in Sorcs2−/− mice","pmids":["31988435"],"confidence":"High","gaps":["Molecular basis of NMDA-receptor selectivity unknown","How endosomal SorCS2 sorts receptors not mechanistically detailed"]},{"year":2020,"claim":"Identified SorCS2 as a TGF-β1-induced sorting receptor for endostatin secretion from reactive astrocytes, coupling it to post-stroke vascularization.","evidence":"Stroke models, in vitro TGF-β1 stimulation, and endostatin secretion/vascularization assays in Sorcs2−/− mice","pmids":["31898841"],"confidence":"Medium","gaps":["Direct SorCS2-endostatin binding not demonstrated","Secretory route used remains undefined"]},{"year":2021,"claim":"Linked SorCS2 loss to genomic instability via Topoisomerase IIβ-dependent DNA double-strand breaks in neurons, a function outside its receptor roles.","evidence":"γH2AX staining in dentate gyrus, CRISPR KO in human neuronal cells, and Topoisomerase IIβ inhibitor experiments","pmids":["34741697"],"confidence":"Medium","gaps":["Mechanistic connection between a surface sorting receptor and nuclear DSB formation unexplained","Single lab without orthogonal DSB assays"]},{"year":2023,"claim":"Established SorCS2 as a progranulin receptor controlling its secretion and granulin conversion, required for motor neuron diversification and axon pathfinding.","evidence":"PGRN binding/secretion/processing assays with zebrafish knockdown and mouse KO phenotyping","pmids":["37897724"],"confidence":"High","gaps":["Structural basis of PGRN binding versus neurotrophin binding not compared","Intracellular signaling downstream of PGRN-SorCS2 not detailed"]},{"year":2023,"claim":"Showed alternative splicing of the SorCS2 intracellular domain encodes distinct trafficking codes, with variant-specific binding to AP adaptors and motor protein light chains determining localization and BDNF responsiveness.","evidence":"Splice-variant rescue assays, Co-IP with AP-1/2/3, and yeast two-hybrid against Tctex-type 3 and kinesin light chain 1","pmids":["37507021"],"confidence":"High","gaps":["In vivo functional consequences of individual variants untested","How variant trafficking maps to cell types not resolved"]},{"year":2023,"claim":"Extended SorCS2 function to endocrine tissue, showing it drives osteopontin secretion from pancreatic alpha cells to support insulin granule maturation in beta cells.","evidence":"Metabolic phenotyping, ex vivo islet analysis, single-cell transcriptomics, and osteopontin secretion assays in SORCS2-deficient mice","pmids":["38226160"],"confidence":"Medium","gaps":["Direct SorCS2-osteopontin binding not shown","Secretory pathway and adaptors used in alpha cells undefined"]},{"year":2024,"claim":"Demonstrated that restoring hippocampal SorCS2 reverses chronic stress depression phenotypes by re-establishing SorCS2-TrkB binding and BDNF signaling, tying the receptor to mood regulation.","evidence":"AAV overexpression in CSDS/CUMS mice with Co-IP, BDNF pathway assays, and behavior","pmids":["38996926"],"confidence":"Medium","gaps":["How chronic stress disrupts SorCS2-TrkB complex molecularly unknown","Gain-of-function only; endogenous regulation not addressed"]},{"year":2025,"claim":"Identified a triple-serine signaling switch in the SorCS2 ICD whose phosphomimetic state drives CREB-activating neurotrophic signaling independently of the ectodomain and BDNF.","evidence":"Serine-to-alanine and phosphomimetic mutagenesis with cell-penetrating peptide and CREB activation assays in neurons","pmids":["40520096"],"confidence":"Medium","gaps":["Kinase phosphorylating the triple-serine motif not identified","Single lab; in vivo relevance untested"]},{"year":2025,"claim":"Provided human genetic evidence that a Vps10p-domain SORCS2 variant disrupts processing, localization, and ligand binding to abrogate BDNF signaling dominant-negatively, linking the gene to ADHD.","evidence":"Biochemical characterization of an arginine-to-tryptophan variant: processing, localization, binding, and BDNF signaling assays","pmids":["40968259"],"confidence":"Medium","gaps":["Patient cohort and segregation evidence limited","Structural impact on the 10CC region not directly resolved"]},{"year":2025,"claim":"Showed SorCS2 endfeet expression maintains AQP4 surface trafficking for astrocytic neurovascular coupling, extending its sorting role to gliovascular function.","evidence":"Immunostaining, in vivo laser speckle imaging, calcium imaging, and surface fraction proteomics in Sorcs2−/− mice","pmids":["40342271"],"confidence":"Medium","gaps":["Direct SorCS2-AQP4 interaction not mapped","Developmental versus adult role distinction not fully resolved"]},{"year":null,"claim":"How a single sorting receptor integrates ligand binding, splice-variant trafficking codes, and ICD phosphorylation into the diverse cell-type-specific outcomes (synaptic, secretory, metabolic, gliovascular) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking ICD phosphorylation to specific trafficking routes in vivo","Substrate/cargo-selection rules across tissues not defined","Kinases and proteases governing the receptor's signaling switch unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,3,8]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[2]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,12]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,5,14]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5,9]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,12]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[3,5,14]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[6,10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[7,8]}],"complexes":["SorCS2-p75NTR proneurotrophin co-receptor complex","SorCS2-TrkB complex","SorCS2 homodimer"],"partners":["P75NTR","TRKB","VPS35","GRN","AP-2","HUNTINGTIN","DYNLT3","KLC1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96PQ0","full_name":"VPS10 domain-containing receptor SorCS2","aliases":[],"length_aa":1159,"mass_kda":128.2,"function":"The heterodimer formed by NGFR and SORCS2 functions as receptor for the precursor forms of NGF (proNGF) and BDNF (proBDNF) (PubMed:22155786, PubMed:24908487). ProNGF and proBDNF binding both promote axon growth cone collapse (in vitro) (PubMed:22155786, PubMed:24908487). Plays a role in the regulation of dendritic spine density in hippocampus neurons (By similarity). Required for normal neurite branching and extension in response to BDNF (PubMed:27457814). Plays a role in BDNF-dependent hippocampal synaptic plasticity. Together with NGFR and NTRK2, is required both for BDNF-mediated synaptic long-term depression and long-term potentiation (PubMed:27457814). ProNGF binding promotes dissociation of TRIO from the heterodimer, which leads to inactivation of RAC1 and/or RAC2 and subsequent reorganization of the actin cytoskeleton (PubMed:22155786). Together with the retromer complex subunit VPS35, required for normal expression of GRIN2A at synapses and dendritic cell membranes. Required for normal expression of the amino acid transporter SLC1A1 at the cell membrane, and thereby contributes to protect cells against oxidative stress (By similarity) Does not promote Schwann cell apoptosis in response to proBDNF SorCS2 104 kDa chain and SorCS2 18 kDa chain together promote Schwann cell apoptosis in response to proBDNF","subcellular_location":"Cell membrane; Cell projection; Cytoplasmic vesicle membrane; Early endosome membrane; Recycling endosome membrane; Synapse, synaptosome; Perikaryon; Cell projection, dendrite; Cell projection, dendritic spine; Postsynaptic density membrane","url":"https://www.uniprot.org/uniprotkb/Q96PQ0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SORCS2","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/SORCS2","total_profiled":1310},"omim":[{"mim_id":"606285","title":"SORTILIN-RELATED VPS10 DOMAIN-CONTAINING RECEPTOR 3; SORCS3","url":"https://www.omim.org/entry/606285"},{"mim_id":"606284","title":"SORTILIN-RELATED VPS10 DOMAIN-CONTAINING RECEPTOR 2; SORCS2","url":"https://www.omim.org/entry/606284"},{"mim_id":"606283","title":"SORTILIN-RELATED VPS10 DOMAIN-CONTAINING RECEPTOR 1; SORCS1","url":"https://www.omim.org/entry/606283"},{"mim_id":"602458","title":"SORTILIN; SORT1","url":"https://www.omim.org/entry/602458"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in 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overexpression represses chronic stress-induced depressive-like behaviors by promoting the BDNF-TrkB system.","date":"2024","source":"Pharmacology, biochemistry, and behavior","url":"https://pubmed.ncbi.nlm.nih.gov/38996926","citation_count":3,"is_preprint":false},{"pmid":"37507021","id":"PMC_37507021","title":"Alternative splicing regulates adaptor protein binding, trafficking, and activity of the Vps10p domain receptor SorCS2 in neuronal development.","date":"2023","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37507021","citation_count":3,"is_preprint":false},{"pmid":"36996265","id":"PMC_36996265","title":"Blood transcriptome of Rasa Aragonesa rams with different sexual behavior phenotype reveals CRYL1 and SORCS2 as genes associated with this trait.","date":"2023","source":"Journal of animal science","url":"https://pubmed.ncbi.nlm.nih.gov/36996265","citation_count":3,"is_preprint":false},{"pmid":"40342271","id":"PMC_40342271","title":"SorCS2 Is Important for Astrocytic Function in Neurovascular Signaling.","date":"2025","source":"Acta physiologica (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/40342271","citation_count":2,"is_preprint":false},{"pmid":"35114376","id":"PMC_35114376","title":"Expression, purification and characterization of SORCS2 intracellular domain for structural studies.","date":"2022","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/35114376","citation_count":1,"is_preprint":false},{"pmid":"40968259","id":"PMC_40968259","title":"A low frequency damaging SORCS2 variant identified in a family with ADHD compromises receptor stability and quenches activity.","date":"2025","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/40968259","citation_count":1,"is_preprint":false},{"pmid":"40520096","id":"PMC_40520096","title":"A triple serine motif in the intracellular domain of SorCS2 impacts its cellular 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neurodegeneration","date":"2025-09-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.17.676723","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15981,"output_tokens":5202,"usd":0.062987,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13657,"output_tokens":5252,"usd":0.099793,"stage2_stop_reason":"end_turn"},"total_usd":0.16278,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"SorCS2 functions as a proneurotrophin (proNT) receptor that mediates both trophic and apoptotic signals in conjunction with p75NTR. In CNS neurons, SorCS2 exists as a single-chain protein required for proBDNF-induced growth cone collapse in developing dopaminergic processes. In PNS glia (Schwann cells), proteolytic processing produces a two-chain SorCS2 isoform that mediates proNT-dependent apoptosis; sciatic nerve injury triggers generation of two-chain SorCS2 in p75NTR-positive dying Schwann cells, with apoptosis profoundly attenuated in Sorcs2−/− mice.\",\n      \"method\": \"Knockout mouse phenotyping (Sorcs2−/− and p75NTR−/−), biochemical characterization of SorCS2 processing (single- vs two-chain isoforms), growth cone collapse assay, dopamine level measurements, behavioral assays\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic and biochemical evidence across CNS and PNS compartments, multiple orthogonal methods including KO phenotyping, biochemical processing assays, and functional cell biology assays\",\n      \"pmids\": [\"24908487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SorCS2 forms complexes with p75NTR (static interaction) and with TrkB (activity-dependent interaction) in hippocampal neurons. The SorCS2-p75NTR complex is required for proBDNF-induced long-term depression, and the SorCS2-TrkB complex facilitates TrkB translocation to postsynaptic densities for synaptic tagging and maintenance of long-term potentiation. Neurons lacking SorCS2 fail to respond to BDNF by TrkB autophosphorylation and activation of downstream signaling cascades, impairing neurite outgrowth and spine formation.\",\n      \"method\": \"Co-immunoprecipitation, synaptic plasticity recordings (LTP/LTD) in Sorcs2−/− hippocampal slices, TrkB phosphorylation assays, subcellular fractionation, behavioral testing\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, electrophysiological recordings, biochemical phosphorylation assays, and behavioral phenotyping across multiple orthogonal methods\",\n      \"pmids\": [\"27457814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structures of the SorCS2 ectodomain (unliganded and in complex with NGF) reveal cross-braced SorCS2 homodimers with two NGF dimers bound in a 2:4 stoichiometry. Five of six SorCS2 domains contribute to dimer formation; a C-terminal membrane-proximal domain with an RNA recognition motif fold locks the dimer in an intermolecular head-to-tail interaction. Both NGF dimer chains interact exclusively with the top face of the SorCS2 β-propeller, which serves as the ligand-binding platform. Biophysical experiments confirmed that NGF, proNGF, and proBDNF all bind at this β-propeller site.\",\n      \"method\": \"X-ray crystallography of SorCS2–NGF complex and unliganded SorCS2 ectodomain; biophysical binding experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure determination with biophysical validation of ligand binding, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"30061605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SorCS2 acts as a sorting receptor that sustains cell-surface expression of the neuronal amino acid transporter EAAT3, facilitating cysteine import required for glutathione synthesis. Loss of SorCS2 depletes EAAT3 from the plasma membrane, impairs neuronal cysteine uptake, causes oxidative brain damage, and increases neuronal cell death and mortality during epilepsy.\",\n      \"method\": \"Surface biotinylation/fractionation to measure EAAT3 plasma membrane levels, cysteine uptake assays, oxidative stress markers, epilepsy survival assays in Sorcs2−/− mice\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — surface fractionation, functional transport assays, in vivo KO phenotyping with multiple orthogonal readouts in a single study\",\n      \"pmids\": [\"30840898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SorCS2 interacts with VPS35 (a core retromer component) and regulates surface trafficking of the NMDA receptor subunit NR2A in medium spiny neurons (MSNs) of the striatum. In zQ175 HD mice, SorCS2 is markedly decreased in an age- and allele-dependent manner and is mislocalized to perinuclear clusters. SorCS2 selectively interacts with mutant huntingtin (mtHTT) but not wild-type huntingtin. Genetic deficiency of SorCS2 accelerates onset and exacerbates motor coordination deficits in HD mice.\",\n      \"method\": \"Co-immunoprecipitation of SorCS2 with VPS35 and mtHTT, immunofluorescence localization, surface receptor analysis, behavioral testing in double-mutant mice\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for protein interactions, in vivo localization, and genetic epistasis (SorCS2 KO × zQ175) with behavioral readout, single lab\",\n      \"pmids\": [\"28469074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SorCS2 is a selective regulator of NMDA receptor (but not AMPA receptor) surface trafficking in hippocampal neurons, localizing to the postsynaptic density and endosomes within dendritic spines of CA2 neurons. SorCS2 deficiency reduces dendritic spine density in CA2 neurons and impairs social memory without affecting sociability or other hippocampal-dependent behaviors.\",\n      \"method\": \"Surface receptor trafficking assays (distinguishing NMDA vs AMPA), immunolocalization to postsynaptic density/endosomes, dendritic spine analysis, behavioral testing in novel Sorcs2−/− mice\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — selective trafficking assays with receptor specificity controls, subcellular localization experiments, and behavioral phenotyping with multiple specificity controls in a single rigorous study\",\n      \"pmids\": [\"31988435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In astrocytes surrounding ischemic brain injury, SorCS2 expression is induced by TGF-β1 and controls secretion of endostatin. Loss of SorCS2 in mice abolishes the acute post-stroke endostatin response and impairs vascularization of the ischemic brain, identifying SorCS2 as a sorting receptor for endostatin release from reactive astrocytes.\",\n      \"method\": \"Mouse stroke models (in vivo), TGF-β1 stimulation of astrocytes in vitro, endostatin secretion assays, vascularization quantification in Sorcs2−/− mice\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO phenotyping combined with in vitro secretion assays and TGF-β1 stimulation, single lab\",\n      \"pmids\": [\"31898841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Disruption of SorCS2 in mice causes severe stereociliary bundle defects in cochlear and vestibular macular hair cells. SorCS2 loss disrupts the intrinsic polarity pathway: LGN and Gαi3 were largely absent and aPKC lost its asymmetric distribution in affected hair cells, placing SorCS2 upstream of the intrinsic polarity pathway controlling hair bundle formation.\",\n      \"method\": \"Transgenic disruption of SorCS2 locus confirmed by whole-genome sequencing and qPCR; immunolabeling of polarity markers LGN, Gαi3, aPKC in cochlear/vestibular tissue; hair bundle morphology analysis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with specific molecular pathway readouts (polarity markers), single lab with multiple cellular markers\",\n      \"pmids\": [\"28346477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SorCS2 is a progranulin (PGRN) receptor required for motor neuron (MN) diversification and axon outgrowth. SorCS2 binds PGRN to control its secretion, intracellular signaling, and conversion into granulins. In zebrafish, SorCS2 knockdown impairs neuromuscular junction morphology and motility. In mice, SorCS2 deficiency perturbs cell-fate decisions of brachial MNs and slows adult motor nerve regeneration. Primitive macrophage-derived PGRN interacts with SorCS2-positive motor axons during pathfinding.\",\n      \"method\": \"Zebrafish knockdown (morpholino/CRISPR), mouse knockout analysis, co-expression studies, PGRN binding/secretion/processing assays, cell-fate tracing, nerve segmentation\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ligand binding established biochemically, multiple model organisms (zebrafish and mouse), functional assays for secretion and granulin conversion, genetic KO phenotyping\",\n      \"pmids\": [\"37897724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SorCS2 undergoes alternative splicing that generates four variants differing in insertion of an acidic cluster motif and/or a serine residue in the intracellular domain (ICD), each undergoing proteolytic processing to give eight protein isoforms. Variants lacking the serine (but not those with it) rescued BDNF-induced neuronal branching in SorCS2 KO neurons. Variants without the acidic cluster show increased interactions with clathrin-associated adaptors AP-1, AP-2, and AP-3. Yeast two-hybrid screens revealed that all variants bound dynein light chain Tctex-type 3, but only variants with the acidic cluster motif bound kinesin light chain 1, giving variants distinct trafficking routes and subcellular localizations.\",\n      \"method\": \"Alternative splicing characterization, rescue assays in SorCS2 KO hippocampal neurons, co-immunoprecipitation with AP complexes, yeast two-hybrid screening for Tctex-type 3 and kinesin light chain 1, subcellular localization assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional rescue assays, Co-IP with multiple AP complexes, yeast two-hybrid, and subcellular localization, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"37507021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SorCS2 is predominantly expressed in pancreatic islet alpha cells and controls osteopontin production/secretion; loss of SorCS2 prevents alpha cells from producing osteopontin, a secreted factor that facilitates insulin release from stressed beta cells, leading to defective insulin granule maturation and blunted glucose response in beta cells.\",\n      \"method\": \"Metabolic studies in SORCS2-deficient mice, ex vivo functional islet analyses, single-cell transcriptomics of pancreatic tissue, osteopontin secretion assays\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse metabolic phenotyping combined with ex vivo functional analyses and single-cell transcriptomics, single lab\",\n      \"pmids\": [\"38226160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Loss of SorCS2 in mice results in elevated DNA double-strand break (DSB) levels in the dentate gyrus. Knockout of SORCS2 in a human neuronal cell line increased Topoisomerase IIβ-dependent DSB formation and reduced neuronal viability, linking SorCS2 to regulation of DNA integrity via a Topoisomerase IIβ-dependent pathway.\",\n      \"method\": \"γH2AX immunostaining for DSBs in mouse dentate gyrus, SORCS2 CRISPR KO in human neuronal cell line, Topoisomerase IIβ inhibitor experiments, viability assays\",\n      \"journal\": \"Cellular and molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO and in vitro KO with mechanistic inhibitor experiments, single lab\",\n      \"pmids\": [\"34741697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The SorCS2 intracellular domain (ICD) contains a triple serine motif that functions as a signaling switch. Serine-to-alanine substitution renders neurons less responsive to BDNF, whereas phosphomimetic mutations induce neurotrophic effects independently of the SorCS2 extracellular domain and BDNF. Triple serine motif-based cell-penetrating peptides activate intracellular signaling that partially overlaps with the BDNF pathway and ultimately activates the transcription factor CREB.\",\n      \"method\": \"Site-directed mutagenesis (serine→alanine and phosphomimetic substitutions), BDNF response assays in hippocampal neurons, cell-penetrating peptide experiments, CREB activation assays\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — active-site mutagenesis with functional readouts in neurons, single lab but multiple orthogonal mutations tested\",\n      \"pmids\": [\"40520096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A heterozygous SORCS2 variant (arginine-to-tryptophan substitution in the 10CC region of the extracellular Vps10p domain) found in ADHD patients causes aberrant posttranslational receptor processing, altered subcellular localization, impaired ligand binding, and abrogates BDNF signaling in a dominant-negative manner.\",\n      \"method\": \"Biochemical characterization of variant processing (Western blot), subcellular localization assays, ligand binding assays, BDNF signaling assays in cells expressing the variant\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical readouts (processing, localization, binding, signaling) for a specific variant, single lab\",\n      \"pmids\": [\"40968259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SorCS2 is important for astrocytic neurovascular coupling. SorCS2 is strongly expressed in astrocyte endfeet at P8 but sparse in adult brain. Sorcs2−/− mice show reduced neurovascular coupling associated with reduced astrocytic calcium response to neuronal excitation. In Sorcs2−/− astrocytes, AQP4 abundance is increased in bulk lysate but reduced in the cell surface fraction, indicating impaired AQP4 trafficking; glutamate metabotropic receptor 3 (mGluR3) is also increased.\",\n      \"method\": \"Immunostaining for SorCS2/GFAP/AQP4, laser speckle contrast imaging for neurovascular coupling in vivo, calcium imaging in live brain slices, cell surface fraction proteomics, Western blot, qPCR\",\n      \"journal\": \"Acta physiologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo functional imaging combined with surface proteomics and in vitro validation, single lab, multiple methods\",\n      \"pmids\": [\"40342271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hippocampal SorCS2 overexpression (via AAV) reverses chronic stress-induced depression-like behaviors in mice and restores SorCS2-TrkB binding, BDNF signaling cascade activation, and hippocampal neurogenesis. Chronic stress reduces SorCS2-TrkB complex formation specifically in the hippocampus.\",\n      \"method\": \"AAV-mediated SorCS2 overexpression in hippocampus of CSDS/CUMS mice, Co-IP of SorCS2-TrkB, BDNF pathway phosphorylation assays, immunofluorescence for immature neurons, behavioral testing\",\n      \"journal\": \"Pharmacology, biochemistry, and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function rescue with Co-IP and pathway assays, single lab\",\n      \"pmids\": [\"38996926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SorCS2-derived macrocyclic peptides (TT-P34) activate CREB and AMPK in a CAMKK2-dependent manner, upregulating PGC1α and TFEB and inducing mitochondrial biogenesis. In zQ175 HD mice, TT-P34 rescues motor behavioral deficits and preserves synaptic and mitochondrial signatures. In MPTP-induced Parkinson's Disease mice, TT-P34 ameliorates behavioral deficits and reduces dopaminergic loss. TT-P34 crosses the blood-brain barrier in non-human primates.\",\n      \"method\": \"Macrocyclic peptide design, CREB/AMPK/PGC1α/TFEB pathway assays, CAMKK2 inhibitor epistasis, behavioral testing in zQ175 and MPTP mouse models, non-human primate pharmacokinetics\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vitro and in vivo models with mechanistic pathway analysis; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.09.17.676723\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SorCS2 is a Vps10p-domain sorting receptor that functions as a co-receptor for proneurotrophins (proBDNF, proNGF) and mature neurotrophins via p75NTR and TrkB complexes, regulating dopaminergic axon guidance, hippocampal synaptic plasticity (LTP/LTD), and NMDA receptor surface trafficking through retromer (VPS35)-dependent and clathrin adaptor (AP-1/2/3)-dependent routes; its intracellular domain harbors a phosphorylatable triple-serine motif and splice-variant-specific acidic cluster/motor-protein binding sites that dictate cell-type-specific trafficking; it also acts as a sorting receptor sustaining plasma membrane levels of EAAT3 for oxidative stress protection and AQP4 in astrocytes for neurovascular coupling, as a progranulin receptor controlling motor neuron fate and axon pathfinding, and as a stress-response factor in astrocytes and pancreatic alpha cells that controls endostatin and osteopontin secretion, respectively.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SorCS2 is a Vps10p-domain sorting receptor that governs neurotrophin signaling, receptor trafficking, and regulated secretion across neurons, glia, and pancreatic islet cells [#0, #1, #3]. It serves as a co-receptor for proneurotrophins and mature neurotrophins, forming a static complex with p75NTR that mediates proBDNF-induced growth cone collapse and long-term depression, and an activity-dependent complex with TrkB that drives TrkB autophosphorylation, postsynaptic translocation, neurite outgrowth, and maintenance of long-term potentiation [#0, #1]. Crystal structures show the SorCS2 ectodomain forms cross-braced homodimers that bind NGF, proNGF, and proBDNF dimers in a 2:4 stoichiometry through the top face of its β-propeller [#2]. As a sorting receptor, SorCS2 sustains plasma-membrane levels of the cysteine transporter EAAT3 to support glutathione synthesis and protect against oxidative damage, selectively controls surface trafficking of NMDA receptor subunits (but not AMPA receptors) in hippocampal and striatal neurons via an interaction with the retromer component VPS35, and maintains AQP4 surface trafficking in astrocyte endfeet for neurovascular coupling [#3, #4, #5, #14]. Its intracellular domain encodes a signaling switch: a phosphorylatable triple-serine motif whose phosphomimetic state drives neurotrophic, CREB-activating signaling independently of the ectodomain and BDNF, and splice-variant-specific acidic-cluster and serine elements that confer differential binding to clathrin adaptors AP-1/2/3 and to dynein and kinesin light chains, dictating cell-type-specific trafficking routes [#9, #12]. Beyond the nervous system, SorCS2 acts as a progranulin receptor controlling motor neuron diversification and axon outgrowth and as a stress-induced sorting receptor for regulated secretion of endostatin from reactive astrocytes and osteopontin from pancreatic alpha cells [#6, #8, #10]. A heterozygous SORCS2 variant in the extracellular Vps10p domain identified in ADHD patients impairs receptor processing and ligand binding and abrogates BDNF signaling in a dominant-negative manner [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established SorCS2 as a proneurotrophin receptor whose processing state determines whether it transmits trophic or apoptotic signals, defining its core role with p75NTR.\",\n      \"evidence\": \"Knockout mouse phenotyping with biochemical isoform characterization and growth cone collapse assays across CNS and PNS\",\n      \"pmids\": [\"24908487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of ligand binding\", \"Mechanism of single- vs two-chain processing not defined at the protease level\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Distinguished two functional SorCS2 complexes—static with p75NTR and activity-dependent with TrkB—linking the receptor to bidirectional control of synaptic plasticity.\",\n      \"evidence\": \"Reciprocal Co-IP, LTP/LTD recordings, and TrkB phosphorylation assays in Sorcs2−/− hippocampal slices\",\n      \"pmids\": [\"27457814\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How activity triggers the SorCS2-TrkB interaction is unresolved\", \"Trafficking machinery directing TrkB to postsynaptic densities not identified here\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the molecular architecture of ligand recognition, showing SorCS2 homodimers present a β-propeller platform that binds NGF, proNGF, and proBDNF.\",\n      \"evidence\": \"X-ray crystallography of liganded and unliganded ectodomain with biophysical binding validation\",\n      \"pmids\": [\"30061605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures do not include the transmembrane or intracellular domains\", \"How dimer geometry couples to p75NTR/TrkB complexes not shown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended SorCS2 function beyond neurotrophin signaling by placing it upstream of the intrinsic polarity pathway controlling cochlear and vestibular hair bundle formation.\",\n      \"evidence\": \"Genetic disruption with immunolabeling of polarity markers LGN, Gαi3, and aPKC\",\n      \"pmids\": [\"28346477\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between SorCS2 and the LGN/Gαi3 polarity machinery undefined\", \"Whether a ligand drives this function is unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified SorCS2 as a VPS35/retromer-associated regulator of NMDA receptor surface trafficking and a selective binding partner of mutant huntingtin, connecting it to striatal pathology.\",\n      \"evidence\": \"Co-IP with VPS35 and mtHTT, localization, and genetic epistasis in zQ175 HD mice\",\n      \"pmids\": [\"28469074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab Co-IP without reciprocal structural validation\", \"Mechanism by which mtHTT mislocalizes SorCS2 not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated a sorting-receptor role sustaining surface EAAT3 to drive cysteine import and glutathione-dependent oxidative protection, broadening SorCS2 function to metabolite transport.\",\n      \"evidence\": \"Surface fractionation, cysteine uptake assays, and epilepsy survival readouts in Sorcs2−/− mice\",\n      \"pmids\": [\"30840898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SorCS2-EAAT3 binding interface not mapped\", \"Trafficking adaptors involved not identified here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Refined receptor-trafficking specificity, showing SorCS2 selectively controls NMDA but not AMPA receptor surface levels in CA2 neurons and is required for social memory.\",\n      \"evidence\": \"Receptor-specific surface trafficking assays, PSD/endosome localization, spine analysis, and behavior in Sorcs2−/− mice\",\n      \"pmids\": [\"31988435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of NMDA-receptor selectivity unknown\", \"How endosomal SorCS2 sorts receptors not mechanistically detailed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified SorCS2 as a TGF-β1-induced sorting receptor for endostatin secretion from reactive astrocytes, coupling it to post-stroke vascularization.\",\n      \"evidence\": \"Stroke models, in vitro TGF-β1 stimulation, and endostatin secretion/vascularization assays in Sorcs2−/− mice\",\n      \"pmids\": [\"31898841\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SorCS2-endostatin binding not demonstrated\", \"Secretory route used remains undefined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked SorCS2 loss to genomic instability via Topoisomerase IIβ-dependent DNA double-strand breaks in neurons, a function outside its receptor roles.\",\n      \"evidence\": \"γH2AX staining in dentate gyrus, CRISPR KO in human neuronal cells, and Topoisomerase IIβ inhibitor experiments\",\n      \"pmids\": [\"34741697\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic connection between a surface sorting receptor and nuclear DSB formation unexplained\", \"Single lab without orthogonal DSB assays\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established SorCS2 as a progranulin receptor controlling its secretion and granulin conversion, required for motor neuron diversification and axon pathfinding.\",\n      \"evidence\": \"PGRN binding/secretion/processing assays with zebrafish knockdown and mouse KO phenotyping\",\n      \"pmids\": [\"37897724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PGRN binding versus neurotrophin binding not compared\", \"Intracellular signaling downstream of PGRN-SorCS2 not detailed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed alternative splicing of the SorCS2 intracellular domain encodes distinct trafficking codes, with variant-specific binding to AP adaptors and motor protein light chains determining localization and BDNF responsiveness.\",\n      \"evidence\": \"Splice-variant rescue assays, Co-IP with AP-1/2/3, and yeast two-hybrid against Tctex-type 3 and kinesin light chain 1\",\n      \"pmids\": [\"37507021\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo functional consequences of individual variants untested\", \"How variant trafficking maps to cell types not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended SorCS2 function to endocrine tissue, showing it drives osteopontin secretion from pancreatic alpha cells to support insulin granule maturation in beta cells.\",\n      \"evidence\": \"Metabolic phenotyping, ex vivo islet analysis, single-cell transcriptomics, and osteopontin secretion assays in SORCS2-deficient mice\",\n      \"pmids\": [\"38226160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SorCS2-osteopontin binding not shown\", \"Secretory pathway and adaptors used in alpha cells undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated that restoring hippocampal SorCS2 reverses chronic stress depression phenotypes by re-establishing SorCS2-TrkB binding and BDNF signaling, tying the receptor to mood regulation.\",\n      \"evidence\": \"AAV overexpression in CSDS/CUMS mice with Co-IP, BDNF pathway assays, and behavior\",\n      \"pmids\": [\"38996926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How chronic stress disrupts SorCS2-TrkB complex molecularly unknown\", \"Gain-of-function only; endogenous regulation not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified a triple-serine signaling switch in the SorCS2 ICD whose phosphomimetic state drives CREB-activating neurotrophic signaling independently of the ectodomain and BDNF.\",\n      \"evidence\": \"Serine-to-alanine and phosphomimetic mutagenesis with cell-penetrating peptide and CREB activation assays in neurons\",\n      \"pmids\": [\"40520096\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase phosphorylating the triple-serine motif not identified\", \"Single lab; in vivo relevance untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided human genetic evidence that a Vps10p-domain SORCS2 variant disrupts processing, localization, and ligand binding to abrogate BDNF signaling dominant-negatively, linking the gene to ADHD.\",\n      \"evidence\": \"Biochemical characterization of an arginine-to-tryptophan variant: processing, localization, binding, and BDNF signaling assays\",\n      \"pmids\": [\"40968259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Patient cohort and segregation evidence limited\", \"Structural impact on the 10CC region not directly resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed SorCS2 endfeet expression maintains AQP4 surface trafficking for astrocytic neurovascular coupling, extending its sorting role to gliovascular function.\",\n      \"evidence\": \"Immunostaining, in vivo laser speckle imaging, calcium imaging, and surface fraction proteomics in Sorcs2−/− mice\",\n      \"pmids\": [\"40342271\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SorCS2-AQP4 interaction not mapped\", \"Developmental versus adult role distinction not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single sorting receptor integrates ligand binding, splice-variant trafficking codes, and ICD phosphorylation into the diverse cell-type-specific outcomes (synaptic, secretory, metabolic, gliovascular) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking ICD phosphorylation to specific trafficking routes in vivo\", \"Substrate/cargo-selection rules across tissues not defined\", \"Kinases and proteases governing the receptor's signaling switch unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 3, 8]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 12]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 5, 14]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 12]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [3, 5, 14]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [6, 10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"complexes\": [\n      \"SorCS2-p75NTR proneurotrophin co-receptor complex\",\n      \"SorCS2-TrkB complex\",\n      \"SorCS2 homodimer\"\n    ],\n    \"partners\": [\n      \"p75NTR\",\n      \"TrkB\",\n      \"VPS35\",\n      \"GRN\",\n      \"AP-2\",\n      \"huntingtin\",\n      \"DYNLT3\",\n      \"KLC1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}