{"gene":"VMA21","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2009,"finding":"VMA21 is an essential assembly chaperone of the vacuolar ATPase (V-ATPase), the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH, reduces lysosomal degradative ability, blocks autophagy, reduces cellular free amino acids, upregulates mTOR-dependent macroautophagy, and results in proliferation of large ineffective autolysosomes that vacuolate the cell — establishing the disease mechanism of XMEA.","method":"Genetic identification of hypomorphic VMA21 alleles in XMEA patients, functional studies in patient cells including lysosomal pH measurement, autophagic flux assays, amino acid quantification, and mTOR pathway analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (genetic, cell biological, biochemical) in a single rigorous study, replicated in a follow-up paper (PMID:23315026)","pmids":["19379691"],"is_preprint":false},{"year":2013,"finding":"VMA21 is confirmed as the diverged human ortholog of yeast Vma21p and functions as an essential V-ATPase assembly chaperone. VMA21 deficiency causes autophagic vacuolar myopathy through lysosomal pH increase, reduced lysosomal degradation, blocked autophagy, reduced free amino acids, downregulation of mTORC1, and consequent macroautophagic overcompensation.","method":"Analysis of XMEA patient muscle biopsies and cells with hypomorphic VMA21 alleles; lysosomal pH measurement, autophagy assays, mTORC1 pathway analysis","journal":"Acta neuropathologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — independent replication of PMID:19379691 findings with multiple orthogonal methods across patient samples","pmids":["23315026"],"is_preprint":false},{"year":2020,"finding":"Pathogenic VMA21 variants cause V-ATPase misassembly and dysfunction, impairing lysosomal acidification and degradation of phagocytosed materials, leading to lipid droplet accumulation in autolysosomes, ER stress, sequestration of unesterified cholesterol in lysosomes, and activation of SREBP-mediated cholesterol synthesis pathways — establishing a liver-specific CDG phenotype.","method":"Patient-derived cells with VMA21 variants; V-ATPase assembly assays, lysosomal acidification assays, lipidomics, ER stress markers, cholesterol trafficking experiments","journal":"Hepatology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays in patient-derived cells establishing mechanistic pathway","pmids":["32145091"],"is_preprint":false},{"year":2022,"finding":"Follicular lymphoma-associated VMA21 hotspot mutation p.93X removes a C-terminal non-canonical ER retrieval signal, causing VMA21 mislocalization to lysosomes, impairing V-ATPase activity, preventing full lysosomal acidification and pH-dependent protein degradation (shown by lysosomal metabolomics), depleting cytoplasmic amino acids, and driving compensatory autophagy activation that creates a survival dependency on ULK1.","method":"Identification of FL patient mutations, cellular mislocalization studies, lysosomal metabolomics, V-ATPase activity assays, autophagy assays in human and yeast cells, ULK1 inhibitor sensitivity assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple complementary assays (metabolomics, localization, V-ATPase activity, autophagy flux) in both human and yeast cells","pmids":["35287545"],"is_preprint":false},{"year":2022,"finding":"In yeast, the FL-associated Vma21[Δ66-77] mutation (corresponding to human p.93X) reduces V-ATPase assembly, shown by decreased vacuolar levels of V0 subunits and a Vph1 stability assay, and significantly reduces vacuolar levels of histidine, lysine, and arginine, explaining autophagy activation.","method":"Yeast genetic model with Vma21[Δ66-77]; V0 subunit vacuolar fractionation, Vph1 stability assay, vacuolar amino acid metabolomics","journal":"Autophagy reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical assays in yeast model, single lab, consistent with human data in PMID:35287545","pmids":["37389034"],"is_preprint":false},{"year":2023,"finding":"VMA21 encodes two protein isoforms: a ubiquitous short isoform (VMA21-101) and a muscle-specific long isoform (VMA21-120). VMA21-120 is predominantly expressed in skeletal muscle, rapidly upregulated upon differentiation of mouse and human muscle precursors, and accumulates during muscle development, regeneration, and denervation. Both isoforms localize to the sarcoplasmic reticulum of muscle cells and interact with the V-ATPase. XMEA-associated mutations cause loss of both VMA21-101 and VMA21-120.","method":"Isoform identification by molecular cloning; immunofluorescence/fractionation for localization to sarcoplasmic reticulum; co-immunoprecipitation with V-ATPase; expression analysis in mouse/human muscle differentiation models; XMEA patient samples","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, direct localization by fractionation, functional validation in differentiation models and patient samples, multiple orthogonal methods in single study","pmids":["37756622"],"is_preprint":false},{"year":2023,"finding":"Aerobic exercise upregulates VMA21 levels via ADRB2/β2-adrenergic receptor activation and the AMPK-MTOR signaling pathway, thereby restoring V-ATPase function and reversing autophagy-lysosomal deficits in APP-PSEN1 Alzheimer disease mice. Inhibition of ADRB2 by propranolol blocked this VMA21 upregulation and the associated reduction in amyloid-β pathology.","method":"In vivo aerobic exercise intervention in APP-PSEN1 mice; propranolol pharmacological inhibition of ADRB2; VMA21 protein level measurement; V-ATPase activity assays; autophagy flux assays; Aβ pathology assessment","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic/pharmacological epistasis with multiple functional readouts, single lab","pmids":["37964627"],"is_preprint":false},{"year":2000,"finding":"X-linked myopathy with excessive autophagy (XMEA) maps to chromosome Xq28 by genetic linkage analysis using polymorphic markers across the X chromosome in multiple affected families.","method":"Two-point and multipoint linkage analysis with 32 polymorphic X-chromosome markers in four XMEA families; maximum lod score 2.74 at DXS1183","journal":"European journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic linkage in multiple families, establishes disease locus but not direct protein mechanism","pmids":["10757644"],"is_preprint":false},{"year":2024,"finding":"VMA21 stabilizes TCIRG1 protein expression in triple-negative breast cancer cells by binding to TCIRG1 and inhibiting its ubiquitination-mediated degradation, thereby promoting TNBC cell proliferation, invasion, and immune evasion.","method":"Co-immunoprecipitation of VMA21 and TCIRG1; ubiquitination assay after VMA21 knockdown; functional assays (clone formation, scratch, Transwell) in TNBC cells; in vivo xenograft with CD8+ T cell immune infiltration analysis","journal":"American journal of cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and ubiquitination assay establish binding and mechanism, but single lab, single study","pmids":["39267677"],"is_preprint":false}],"current_model":"VMA21 is an ER-resident assembly chaperone essential for the proper assembly of the vacuolar H+-ATPase (V-ATPase) proton pump complex; it exists as two isoforms (ubiquitous VMA21-101 and muscle-specific VMA21-120) that both localize to the sarcoplasmic/endoplasmic reticulum and interact with V-ATPase, and VMA21 deficiency impairs lysosomal acidification and autophagic degradation, triggering compensatory macroautophagy, ER stress, and lipid/cholesterol dysregulation — causing X-linked myopathy with excessive autophagy (XMEA) in skeletal muscle or a congenital disorder of glycosylation with liver disease depending on the mutation context."},"narrative":{"mechanistic_narrative":"VMA21 is an endoplasmic/sarcoplasmic reticulum-resident assembly chaperone essential for the proper assembly of the vacuolar H+-ATPase (V-ATPase) proton pump, the principal driver of lysosomal acidification [PMID:19379691, PMID:23315026]. Loss of VMA21 function causes V-ATPase misassembly that raises lysosomal pH, impairs lysosomal degradation and autophagic flux, depletes cytoplasmic free amino acids, and dysregulates mTORC1, driving compensatory macroautophagy [PMID:19379691, PMID:23315026, PMID:35287545]. This core defect underlies X-linked myopathy with excessive autophagy (XMEA), caused by hypomorphic VMA21 alleles, in which the resulting failure of autolysosomal degradation produces vacuolating autolysosomes in skeletal muscle [PMID:19379691, PMID:23315026]; distinct pathogenic variants instead produce a liver-specific congenital disorder of glycosylation marked by lysosomal lipid and unesterified cholesterol accumulation, ER stress, and SREBP-driven cholesterol synthesis [PMID:32145091]. The protein carries a C-terminal non-canonical ER retrieval signal whose loss (the follicular-lymphoma hotspot p.93X) mislocalizes VMA21 to lysosomes, impairing V-ATPase activity and creating a compensatory-autophagy dependence on ULK1 [PMID:35287545]. VMA21 is expressed as a ubiquitous short isoform (VMA21-101) and a muscle-specific long isoform (VMA21-120) that is upregulated during muscle differentiation, regeneration, and denervation; both localize to the sarcoplasmic reticulum and interact with the V-ATPase [PMID:37756622]. Beyond V-ATPase chaperoning, VMA21 stabilizes TCIRG1 by binding it and blocking its ubiquitination-mediated degradation [PMID:39267677].","teleology":[{"year":2000,"claim":"Before any gene was identified, the question was where the XMEA disease locus resided; mapping it established the genomic interval that would later pinpoint VMA21.","evidence":"Two-point and multipoint linkage analysis with X-chromosome markers in four XMEA families","pmids":["10757644"],"confidence":"Medium","gaps":["Localizes the locus to Xq28 but does not identify the causative gene or any protein mechanism","No functional or molecular characterization"]},{"year":2009,"claim":"Identified VMA21 as the XMEA gene and defined its molecular role as a V-ATPase assembly chaperone, linking proton-pump assembly failure to a defined autophagy-lysosomal disease mechanism.","evidence":"Genetic identification of hypomorphic alleles in XMEA patients plus lysosomal pH, autophagic flux, amino acid, and mTOR assays in patient cells","pmids":["19379691"],"confidence":"High","gaps":["Does not define the structural basis of VMA21–V-ATPase interaction","Isoform diversity not resolved","Tissue-specific manifestations not yet explained"]},{"year":2013,"claim":"Independently confirmed VMA21 as the diverged human ortholog of yeast Vma21p and reproduced the lysosomal-pH/autophagy/mTORC1 cascade in patient muscle, solidifying the disease mechanism.","evidence":"Analysis of XMEA patient muscle biopsies and cells with hypomorphic alleles; lysosomal pH, autophagy, and mTORC1 assays","pmids":["23315026"],"confidence":"High","gaps":["Does not address non-muscle phenotypes","No direct biochemical reconstitution of assembly chaperone activity"]},{"year":2020,"claim":"Extended the VMA21 phenotypic spectrum by showing distinct pathogenic variants cause a liver CDG, revealing how impaired lysosomal acidification feeds into lipid and cholesterol dysregulation and ER stress.","evidence":"Patient-derived cells with VMA21 variants; V-ATPase assembly, lysosomal acidification, lipidomics, ER-stress, and cholesterol-trafficking assays","pmids":["32145091"],"confidence":"High","gaps":["Does not explain why these variants give a liver rather than muscle phenotype","SREBP activation mechanism downstream of cholesterol sequestration not fully dissected"]},{"year":2022,"claim":"Defined a C-terminal non-canonical ER retrieval signal and showed its loss (p.93X) mislocalizes VMA21 to lysosomes and creates a therapeutically exploitable ULK1 dependency in follicular lymphoma.","evidence":"FL patient mutation analysis, localization studies, lysosomal metabolomics, V-ATPase activity and autophagy assays in human and yeast cells, ULK1 inhibitor sensitivity","pmids":["35287545"],"confidence":"High","gaps":["Retrieval-signal receptor/machinery not identified","ULK1 dependency tested in a limited set of models"]},{"year":2022,"claim":"Reconstituted the FL-associated mutation in yeast to causally link reduced V0-subunit assembly to depletion of specific vacuolar amino acids, providing cross-species mechanistic support for autophagy activation.","evidence":"Yeast Vma21[Δ66-77] model; V0 vacuolar fractionation, Vph1 stability assay, vacuolar amino-acid metabolomics","pmids":["37389034"],"confidence":"Medium","gaps":["Single lab; yeast surrogate of the human mutation","Does not establish direct chaperone binding stoichiometry"]},{"year":2023,"claim":"Resolved VMA21 isoform diversity, identifying a muscle-specific long isoform regulated by differentiation and denervation, addressing why VMA21 loss particularly affects skeletal muscle.","evidence":"Molecular cloning, immunofluorescence/fractionation for sarcoplasmic reticulum localization, reciprocal Co-IP with V-ATPase, muscle differentiation models, XMEA patient samples","pmids":["37756622"],"confidence":"High","gaps":["Functional difference between VMA21-101 and VMA21-120 not defined","Whether the long isoform has V-ATPase-independent roles unknown"]},{"year":2023,"claim":"Placed VMA21 downstream of a regulable signaling axis, showing aerobic exercise upregulates VMA21 via ADRB2 and AMPK-MTOR to restore V-ATPase function and reduce amyloid pathology, suggesting VMA21 is a tunable node in neurodegeneration.","evidence":"Aerobic exercise and propranolol intervention in APP-PSEN1 mice; VMA21 protein, V-ATPase activity, autophagy flux, and Aβ pathology readouts","pmids":["37964627"],"confidence":"Medium","gaps":["Direct transcriptional/post-translational mechanism of VMA21 induction not defined","Single lab; correlative coupling between VMA21 levels and Aβ reduction"]},{"year":2024,"claim":"Uncovered a V-ATPase-assembly-independent role: VMA21 binds and stabilizes TCIRG1 by inhibiting its ubiquitination, promoting tumor cell proliferation, invasion, and immune evasion in TNBC.","evidence":"Co-IP of VMA21 and TCIRG1, ubiquitination assay after VMA21 knockdown, functional and xenograft assays with CD8+ T-cell infiltration analysis","pmids":["39267677"],"confidence":"Medium","gaps":["Single lab, single study","Whether stabilization is direct or via the V-ATPase complex not resolved","E3 ligase acting on TCIRG1 not identified"]},{"year":null,"claim":"The structural mechanism by which VMA21 chaperones V-ATPase assembly, and how distinct mutations and isoforms produce tissue-specific muscle, liver, lymphoma, and neurodegenerative phenotypes, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the VMA21–V-ATPase assembly intermediate","Mechanistic basis of tissue-specific phenotypes not defined","Functional distinction between isoforms unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,1,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,8]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0,1,3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,2,3]}],"complexes":["V-ATPase"],"partners":["TCIRG1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q3ZAQ7","full_name":"Vacuolar ATPase assembly integral membrane protein VMA21","aliases":["Myopathy with excessive autophagy protein"],"length_aa":101,"mass_kda":11.4,"function":"Required for the assembly of the V0 complex of the vacuolar ATPase (V-ATPase) in the endoplasmic reticulum","subcellular_location":"Endoplasmic reticulum membrane; Endoplasmic reticulum-Golgi intermediate compartment membrane; Cytoplasmic vesicle, COPII-coated vesicle membrane","url":"https://www.uniprot.org/uniprotkb/Q3ZAQ7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/VMA21","classification":"Not Classified","n_dependent_lines":381,"n_total_lines":1208,"dependency_fraction":0.31539735099337746},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ATP6V0A2","stoichiometry":10.0},{"gene":"CANX","stoichiometry":4.0},{"gene":"ATP6V1F","stoichiometry":0.2},{"gene":"TMED10","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/VMA21","total_profiled":1310},"omim":[{"mim_id":"310440","title":"MYOPATHY, X-LINKED, WITH EXCESSIVE AUTOPHAGY; MEAX","url":"https://www.omim.org/entry/310440"},{"mim_id":"300913","title":"VACUOLAR ATPase ASSEMBLY FACTOR VMA21; VMA21","url":"https://www.omim.org/entry/300913"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/VMA21"},"hgnc":{"alias_symbol":["XMEA"],"prev_symbol":["MEAX"]},"alphafold":{"accession":"Q3ZAQ7","domains":[{"cath_id":"1.10.287","chopping":"23-97","consensus_level":"high","plddt":72.6215,"start":23,"end":97}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q3ZAQ7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q3ZAQ7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q3ZAQ7-F1-predicted_aligned_error_v6.png","plddt_mean":70.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=VMA21","jax_strain_url":"https://www.jax.org/strain/search?query=VMA21"},"sequence":{"accession":"Q3ZAQ7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q3ZAQ7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q3ZAQ7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q3ZAQ7"}},"corpus_meta":[{"pmid":"29343508","id":"PMC_29343508","title":"Circular RNA VMA21 protects against intervertebral disc degeneration through targeting miR-200c and X linked inhibitor-of-apoptosis protein.","date":"2018","source":"Annals of the rheumatic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/29343508","citation_count":244,"is_preprint":false},{"pmid":"23315026","id":"PMC_23315026","title":"VMA21 deficiency prevents vacuolar ATPase assembly and causes autophagic vacuolar myopathy.","date":"2013","source":"Acta neuropathologica","url":"https://pubmed.ncbi.nlm.nih.gov/23315026","citation_count":111,"is_preprint":false},{"pmid":"32827242","id":"PMC_32827242","title":"Circular RNA VMA21 ameliorates sepsis-associated acute kidney injury by regulating miR-9-3p/SMG1/inflammation axis and oxidative stress.","date":"2020","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32827242","citation_count":66,"is_preprint":false},{"pmid":"31297866","id":"PMC_31297866","title":"lncRNA ZFPM2-AS1 promotes proliferation via miR-18b-5p/VMA21 axis in lung 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disease","date":"2025-05-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.18.654701","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16550,"output_tokens":2563,"usd":0.044048,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9759,"output_tokens":3491,"usd":0.068035,"stage2_stop_reason":"end_turn"},"total_usd":0.112083,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"VMA21 is an essential assembly chaperone of the vacuolar ATPase (V-ATPase), the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH, reduces lysosomal degradative ability, blocks autophagy, reduces cellular free amino acids, upregulates mTOR-dependent macroautophagy, and results in proliferation of large ineffective autolysosomes that vacuolate the cell — establishing the disease mechanism of XMEA.\",\n      \"method\": \"Genetic identification of hypomorphic VMA21 alleles in XMEA patients, functional studies in patient cells including lysosomal pH measurement, autophagic flux assays, amino acid quantification, and mTOR pathway analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (genetic, cell biological, biochemical) in a single rigorous study, replicated in a follow-up paper (PMID:23315026)\",\n      \"pmids\": [\"19379691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"VMA21 is confirmed as the diverged human ortholog of yeast Vma21p and functions as an essential V-ATPase assembly chaperone. VMA21 deficiency causes autophagic vacuolar myopathy through lysosomal pH increase, reduced lysosomal degradation, blocked autophagy, reduced free amino acids, downregulation of mTORC1, and consequent macroautophagic overcompensation.\",\n      \"method\": \"Analysis of XMEA patient muscle biopsies and cells with hypomorphic VMA21 alleles; lysosomal pH measurement, autophagy assays, mTORC1 pathway analysis\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independent replication of PMID:19379691 findings with multiple orthogonal methods across patient samples\",\n      \"pmids\": [\"23315026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Pathogenic VMA21 variants cause V-ATPase misassembly and dysfunction, impairing lysosomal acidification and degradation of phagocytosed materials, leading to lipid droplet accumulation in autolysosomes, ER stress, sequestration of unesterified cholesterol in lysosomes, and activation of SREBP-mediated cholesterol synthesis pathways — establishing a liver-specific CDG phenotype.\",\n      \"method\": \"Patient-derived cells with VMA21 variants; V-ATPase assembly assays, lysosomal acidification assays, lipidomics, ER stress markers, cholesterol trafficking experiments\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays in patient-derived cells establishing mechanistic pathway\",\n      \"pmids\": [\"32145091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Follicular lymphoma-associated VMA21 hotspot mutation p.93X removes a C-terminal non-canonical ER retrieval signal, causing VMA21 mislocalization to lysosomes, impairing V-ATPase activity, preventing full lysosomal acidification and pH-dependent protein degradation (shown by lysosomal metabolomics), depleting cytoplasmic amino acids, and driving compensatory autophagy activation that creates a survival dependency on ULK1.\",\n      \"method\": \"Identification of FL patient mutations, cellular mislocalization studies, lysosomal metabolomics, V-ATPase activity assays, autophagy assays in human and yeast cells, ULK1 inhibitor sensitivity assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple complementary assays (metabolomics, localization, V-ATPase activity, autophagy flux) in both human and yeast cells\",\n      \"pmids\": [\"35287545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In yeast, the FL-associated Vma21[Δ66-77] mutation (corresponding to human p.93X) reduces V-ATPase assembly, shown by decreased vacuolar levels of V0 subunits and a Vph1 stability assay, and significantly reduces vacuolar levels of histidine, lysine, and arginine, explaining autophagy activation.\",\n      \"method\": \"Yeast genetic model with Vma21[Δ66-77]; V0 subunit vacuolar fractionation, Vph1 stability assay, vacuolar amino acid metabolomics\",\n      \"journal\": \"Autophagy reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical assays in yeast model, single lab, consistent with human data in PMID:35287545\",\n      \"pmids\": [\"37389034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VMA21 encodes two protein isoforms: a ubiquitous short isoform (VMA21-101) and a muscle-specific long isoform (VMA21-120). VMA21-120 is predominantly expressed in skeletal muscle, rapidly upregulated upon differentiation of mouse and human muscle precursors, and accumulates during muscle development, regeneration, and denervation. Both isoforms localize to the sarcoplasmic reticulum of muscle cells and interact with the V-ATPase. XMEA-associated mutations cause loss of both VMA21-101 and VMA21-120.\",\n      \"method\": \"Isoform identification by molecular cloning; immunofluorescence/fractionation for localization to sarcoplasmic reticulum; co-immunoprecipitation with V-ATPase; expression analysis in mouse/human muscle differentiation models; XMEA patient samples\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, direct localization by fractionation, functional validation in differentiation models and patient samples, multiple orthogonal methods in single study\",\n      \"pmids\": [\"37756622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Aerobic exercise upregulates VMA21 levels via ADRB2/β2-adrenergic receptor activation and the AMPK-MTOR signaling pathway, thereby restoring V-ATPase function and reversing autophagy-lysosomal deficits in APP-PSEN1 Alzheimer disease mice. Inhibition of ADRB2 by propranolol blocked this VMA21 upregulation and the associated reduction in amyloid-β pathology.\",\n      \"method\": \"In vivo aerobic exercise intervention in APP-PSEN1 mice; propranolol pharmacological inhibition of ADRB2; VMA21 protein level measurement; V-ATPase activity assays; autophagy flux assays; Aβ pathology assessment\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic/pharmacological epistasis with multiple functional readouts, single lab\",\n      \"pmids\": [\"37964627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"X-linked myopathy with excessive autophagy (XMEA) maps to chromosome Xq28 by genetic linkage analysis using polymorphic markers across the X chromosome in multiple affected families.\",\n      \"method\": \"Two-point and multipoint linkage analysis with 32 polymorphic X-chromosome markers in four XMEA families; maximum lod score 2.74 at DXS1183\",\n      \"journal\": \"European journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic linkage in multiple families, establishes disease locus but not direct protein mechanism\",\n      \"pmids\": [\"10757644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"VMA21 stabilizes TCIRG1 protein expression in triple-negative breast cancer cells by binding to TCIRG1 and inhibiting its ubiquitination-mediated degradation, thereby promoting TNBC cell proliferation, invasion, and immune evasion.\",\n      \"method\": \"Co-immunoprecipitation of VMA21 and TCIRG1; ubiquitination assay after VMA21 knockdown; functional assays (clone formation, scratch, Transwell) in TNBC cells; in vivo xenograft with CD8+ T cell immune infiltration analysis\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and ubiquitination assay establish binding and mechanism, but single lab, single study\",\n      \"pmids\": [\"39267677\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"VMA21 is an ER-resident assembly chaperone essential for the proper assembly of the vacuolar H+-ATPase (V-ATPase) proton pump complex; it exists as two isoforms (ubiquitous VMA21-101 and muscle-specific VMA21-120) that both localize to the sarcoplasmic/endoplasmic reticulum and interact with V-ATPase, and VMA21 deficiency impairs lysosomal acidification and autophagic degradation, triggering compensatory macroautophagy, ER stress, and lipid/cholesterol dysregulation — causing X-linked myopathy with excessive autophagy (XMEA) in skeletal muscle or a congenital disorder of glycosylation with liver disease depending on the mutation context.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"VMA21 is an endoplasmic/sarcoplasmic reticulum-resident assembly chaperone essential for the proper assembly of the vacuolar H+-ATPase (V-ATPase) proton pump, the principal driver of lysosomal acidification [#0, #1]. Loss of VMA21 function causes V-ATPase misassembly that raises lysosomal pH, impairs lysosomal degradation and autophagic flux, depletes cytoplasmic free amino acids, and dysregulates mTORC1, driving compensatory macroautophagy [#0, #1, #3]. This core defect underlies X-linked myopathy with excessive autophagy (XMEA), caused by hypomorphic VMA21 alleles, in which the resulting failure of autolysosomal degradation produces vacuolating autolysosomes in skeletal muscle [#0, #1]; distinct pathogenic variants instead produce a liver-specific congenital disorder of glycosylation marked by lysosomal lipid and unesterified cholesterol accumulation, ER stress, and SREBP-driven cholesterol synthesis [#2]. The protein carries a C-terminal non-canonical ER retrieval signal whose loss (the follicular-lymphoma hotspot p.93X) mislocalizes VMA21 to lysosomes, impairing V-ATPase activity and creating a compensatory-autophagy dependence on ULK1 [#3]. VMA21 is expressed as a ubiquitous short isoform (VMA21-101) and a muscle-specific long isoform (VMA21-120) that is upregulated during muscle differentiation, regeneration, and denervation; both localize to the sarcoplasmic reticulum and interact with the V-ATPase [#5]. Beyond V-ATPase chaperoning, VMA21 stabilizes TCIRG1 by binding it and blocking its ubiquitination-mediated degradation [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Before any gene was identified, the question was where the XMEA disease locus resided; mapping it established the genomic interval that would later pinpoint VMA21.\",\n      \"evidence\": \"Two-point and multipoint linkage analysis with X-chromosome markers in four XMEA families\",\n      \"pmids\": [\"10757644\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localizes the locus to Xq28 but does not identify the causative gene or any protein mechanism\", \"No functional or molecular characterization\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified VMA21 as the XMEA gene and defined its molecular role as a V-ATPase assembly chaperone, linking proton-pump assembly failure to a defined autophagy-lysosomal disease mechanism.\",\n      \"evidence\": \"Genetic identification of hypomorphic alleles in XMEA patients plus lysosomal pH, autophagic flux, amino acid, and mTOR assays in patient cells\",\n      \"pmids\": [\"19379691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define the structural basis of VMA21–V-ATPase interaction\", \"Isoform diversity not resolved\", \"Tissue-specific manifestations not yet explained\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Independently confirmed VMA21 as the diverged human ortholog of yeast Vma21p and reproduced the lysosomal-pH/autophagy/mTORC1 cascade in patient muscle, solidifying the disease mechanism.\",\n      \"evidence\": \"Analysis of XMEA patient muscle biopsies and cells with hypomorphic alleles; lysosomal pH, autophagy, and mTORC1 assays\",\n      \"pmids\": [\"23315026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address non-muscle phenotypes\", \"No direct biochemical reconstitution of assembly chaperone activity\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the VMA21 phenotypic spectrum by showing distinct pathogenic variants cause a liver CDG, revealing how impaired lysosomal acidification feeds into lipid and cholesterol dysregulation and ER stress.\",\n      \"evidence\": \"Patient-derived cells with VMA21 variants; V-ATPase assembly, lysosomal acidification, lipidomics, ER-stress, and cholesterol-trafficking assays\",\n      \"pmids\": [\"32145091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not explain why these variants give a liver rather than muscle phenotype\", \"SREBP activation mechanism downstream of cholesterol sequestration not fully dissected\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a C-terminal non-canonical ER retrieval signal and showed its loss (p.93X) mislocalizes VMA21 to lysosomes and creates a therapeutically exploitable ULK1 dependency in follicular lymphoma.\",\n      \"evidence\": \"FL patient mutation analysis, localization studies, lysosomal metabolomics, V-ATPase activity and autophagy assays in human and yeast cells, ULK1 inhibitor sensitivity\",\n      \"pmids\": [\"35287545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Retrieval-signal receptor/machinery not identified\", \"ULK1 dependency tested in a limited set of models\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Reconstituted the FL-associated mutation in yeast to causally link reduced V0-subunit assembly to depletion of specific vacuolar amino acids, providing cross-species mechanistic support for autophagy activation.\",\n      \"evidence\": \"Yeast Vma21[\\u039466-77] model; V0 vacuolar fractionation, Vph1 stability assay, vacuolar amino-acid metabolomics\",\n      \"pmids\": [\"37389034\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; yeast surrogate of the human mutation\", \"Does not establish direct chaperone binding stoichiometry\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved VMA21 isoform diversity, identifying a muscle-specific long isoform regulated by differentiation and denervation, addressing why VMA21 loss particularly affects skeletal muscle.\",\n      \"evidence\": \"Molecular cloning, immunofluorescence/fractionation for sarcoplasmic reticulum localization, reciprocal Co-IP with V-ATPase, muscle differentiation models, XMEA patient samples\",\n      \"pmids\": [\"37756622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional difference between VMA21-101 and VMA21-120 not defined\", \"Whether the long isoform has V-ATPase-independent roles unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed VMA21 downstream of a regulable signaling axis, showing aerobic exercise upregulates VMA21 via ADRB2 and AMPK-MTOR to restore V-ATPase function and reduce amyloid pathology, suggesting VMA21 is a tunable node in neurodegeneration.\",\n      \"evidence\": \"Aerobic exercise and propranolol intervention in APP-PSEN1 mice; VMA21 protein, V-ATPase activity, autophagy flux, and A\\u03b2 pathology readouts\",\n      \"pmids\": [\"37964627\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional/post-translational mechanism of VMA21 induction not defined\", \"Single lab; correlative coupling between VMA21 levels and Aβ reduction\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Uncovered a V-ATPase-assembly-independent role: VMA21 binds and stabilizes TCIRG1 by inhibiting its ubiquitination, promoting tumor cell proliferation, invasion, and immune evasion in TNBC.\",\n      \"evidence\": \"Co-IP of VMA21 and TCIRG1, ubiquitination assay after VMA21 knockdown, functional and xenograft assays with CD8+ T-cell infiltration analysis\",\n      \"pmids\": [\"39267677\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, single study\", \"Whether stabilization is direct or via the V-ATPase complex not resolved\", \"E3 ligase acting on TCIRG1 not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural mechanism by which VMA21 chaperones V-ATPase assembly, and how distinct mutations and isoforms produce tissue-specific muscle, liver, lymphoma, and neurodegenerative phenotypes, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the VMA21–V-ATPase assembly intermediate\", \"Mechanistic basis of tissue-specific phenotypes not defined\", \"Functional distinction between isoforms unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005790\", \"supporting_discovery_ids\": []}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"complexes\": [\"V-ATPase\"],\n    \"partners\": [\"TCIRG1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}