{"gene":"ATP6V1H","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":1993,"finding":"VMA13 (the yeast ortholog of ATP6V1H) encodes the 54-kDa subunit of the V-ATPase. This subunit is essential for ATPase activity but not for assembly or membrane targeting of other V-ATPase subunits. Null mutants lacking Vma13p retain other subunits on the vacuolar membrane but form a less stable, inactive complex.","method":"Genetic complementation, null mutant characterization, subcellular fractionation, enzyme activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (complementation, fractionation, activity assays) in foundational paper; widely cited","pmids":["8349704"],"is_preprint":false},{"year":1998,"finding":"NBP1, the human homolog of yeast Vma13p (i.e., the human ATP6V1H/subunit H), directly interacts with HIV-1 Nef in vitro and in vivo. This interaction facilitates Nef-mediated internalization of CD4, linking ATP6V1H to the endocytic pathway. Antisense suppression of NBP1 abolished Nef-mediated CD4 downregulation.","method":"Co-immunoprecipitation, yeast two-hybrid, yeast complementation assay, antisense knockdown with functional readout (CD4 surface expression)","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, yeast complementation, functional antisense knockdown with defined phenotypic readout","pmids":["9620685"],"is_preprint":false},{"year":1999,"finding":"The human SFD (Sub Fifty-eight-kDa Doublet) polypeptides—isoforms of the ATP6V1H subunit arising by alternative splicing—are both required to activate ATPase and proton-pumping activities of the V-ATPase holoenzyme. Recombinant SFDα (57 kDa) and SFDβ (50 kDa) are functionally interchangeable in restoring activity to SFD-depleted enzyme. These subunits interact structurally with both V1 and V0 domains, indicating roles in coupling ATP hydrolysis to proton translocation.","method":"Recombinant protein expression, reconstitution with SFD-depleted holoenzyme, ATPase activity assay, proton pumping assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with activity assays; multiple isoforms tested across multiple enzyme preparations","pmids":["10336497"],"is_preprint":false},{"year":2016,"finding":"Haploinsufficiency of ATP6V1H in mice (CRISPR/Cas9 knockout) causes osteoporosis via impaired bone remodeling. Atp6v1h-deficient osteoclasts show increased intracellular pH, which downregulates TGF-β1 activation, thereby reducing osteoblast induction. Bone resorption is increased and bone formation decreased, with a net bone matrix loss.","method":"CRISPR/Cas9 knockout mouse model, micro-CT, histomorphometry, intracellular pH measurement, TGF-β1 signaling analysis, GWAS SNP association","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular and molecular phenotype, pathway placement via TGF-β1, multiple orthogonal assays","pmids":["27924156"],"is_preprint":false},{"year":2017,"finding":"Loss of atp6v1h function in zebrafish (CRISPR/Cas9) severely reduces mature calcified bone cells and dramatically increases expression of mmp9 and mmp13. Small molecule inhibitors of MMP9 and MMP13 restore bone mass in mutants, placing ATP6V1H upstream of MMP9/MMP13 in a pathway regulating bone formation.","method":"CRISPR/Cas9 zebrafish knockout, bone staining, gene expression analysis, pharmacological rescue with MMP inhibitors","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis established by pharmacological rescue; multiple orthogonal assays in vivo","pmids":["28158191"],"is_preprint":false},{"year":2018,"finding":"ATP6V1H is expressed in bone marrow stromal cells (BMSCs), and Atp6v1h+/- BMSCs show reduced proliferation, cell cycle arrest, decreased osteogenic differentiation, and increased adipogenic potential. Loss of ATP6V1H downregulates TGF-β1 receptor mRNA and the TGF-β receptor binding molecule AP-2 (subunit β of adaptor protein complex 2), suggesting ATP6V1H regulates BMSC differentiation via interaction with TGF-β receptor I and AP-2 complex.","method":"Heterozygous knockout mouse (Atp6v1h+/-), cell proliferation assays, cell cycle analysis, osteogenic/adipogenic differentiation assays, histology, qPCR","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO model with defined cellular phenotype; pathway placement by gene expression only (Tier 3 for molecular mechanism)","pmids":["29782852"],"is_preprint":false},{"year":2019,"finding":"In MC3T3-E1 osteoblastic cells under high-glucose/free-fatty-acid conditions simulating T2DM, ATP6V1H overexpression promotes osteogenic differentiation and inhibits the Akt/GSK3β signaling pathway, while ATP6V1H knockdown activates Akt/GSK3β signaling. This places ATP6V1H upstream of Akt/GSK3β in regulating osteogenic differentiation.","method":"Overexpression and siRNA knockdown, Alizarin Red staining, western blot (Akt/GSK3β phosphorylation), CCK8 viability assay","journal":"Organogenesis","confidence":"Medium","confidence_rationale":"Tier 2-3 — OE/KD with pathway readout; single lab, single cell-line model","pmids":["31272281"],"is_preprint":false},{"year":2022,"finding":"ATP6V1H deficiency in Atp6v1h+/- mice fed a high-fat diet worsens glucose tolerance by augmenting endoplasmic reticulum (ER) stress in pancreatic β-cells, thereby impairing insulin secretion. Transcriptome sequencing identified ER stress pathway upregulation, and alternative splicing of ATP6V1H transcripts may also be involved.","method":"Atp6v1h+/- mouse HFD model, glucose tolerance testing, insulin measurement, transcriptome sequencing, qPCR, western blot","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 — defined genetic model with pathway placement via transcriptomics and functional metabolic readout; single lab","pmids":["34990584"],"is_preprint":false},{"year":2024,"finding":"In simulated microgravity (tail-suspension) mouse model, Atp6v1h+/- mice do not show aggravated bone loss beyond that from Atp6v1h deficiency alone. Transcriptomic analysis revealed upregulation of Fos, Jun, Src, and integrin subunits. Co-immunoprecipitation demonstrated direct interactions between ATP6V1H protein and integrin beta 1, beta 3, beta 5, alpha 2b, and alpha 5, placing ATP6V1H in a Fos-Jun-Src-Integrin pathway that modulates osteoclast activity.","method":"Mouse tail-suspension model, micro-CT, TRAP staining, transcriptomic sequencing, RT-qPCR, co-immunoprecipitation","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP identifies novel binding partners (integrins); transcriptomics provides pathway context; single lab","pmids":["38203808"],"is_preprint":false},{"year":2024,"finding":"The lncRNA lnc-TCEA1-3 positively regulates ATP6V1H expression in osteoclasts: overexpression of lnc-TCEA1-3 upregulates ATP6V1H mRNA in HEK293 cells, HOS cells, and primary osteoclasts, and increases osteoclast number. This establishes a post-transcriptional regulatory axis upstream of ATP6V1H in bone cells.","method":"Lentivirus-mediated overexpression, qPCR, primary osteoclast culture, Atp6v1h knockout mice for validation","journal":"Critical reviews in eukaryotic gene expression","confidence":"Low","confidence_rationale":"Tier 3 — single lab, primarily expression-level readout; mechanism of lncRNA-mediated regulation not fully defined","pmids":["37824389"],"is_preprint":false},{"year":2025,"finding":"In larval zebrafish, the v-ATPase subunit Atp6v1h co-localizes with Aspergillus fumigatus spores inside macrophages in vivo. CRISPR/Cas9 targeting of atp6v1h does not reduce macrophage spore killing but abolishes macrophage-mediated inhibition of spore germination and extracellular hyphal growth, demonstrating that v-ATPase (via Atp6v1h) is required for controlling fungal germination but not spore killing.","method":"Live imaging in larval zebrafish, CRISPR/Cas9 knockout of atp6v1h, co-localization imaging, fungal germination/killing assays in vivo","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — clean genetic KO with specific functional dissection (killing vs. germination) using live in vivo imaging; preprint only","pmids":["bio_10.1101_2025.07.14.664761"],"is_preprint":true}],"current_model":"ATP6V1H (subunit H of the V1 domain) is essential for V-ATPase catalytic activity by stabilizing the holoenzyme and coupling ATP hydrolysis to proton translocation across membranes; in bone, it regulates osteoclast and osteoblast function through TGF-β1 and MMP9/MMP13 pathways to maintain bone homeostasis, and it physically interacts with integrin subunits and the HIV-1 Nef binding protein NBP1 to link endosomal acidification to membrane trafficking and immune pathogen control."},"narrative":{"teleology":[{"year":1993,"claim":"The foundational question of whether V-ATPase subunit H is needed for complex assembly or for catalytic activity was resolved: Vma13p (yeast ATP6V1H ortholog) is dispensable for V-ATPase assembly and membrane targeting but is strictly required for ATPase enzymatic activity, establishing its role as a catalytic activator rather than a structural scaffold.","evidence":"Yeast VMA13 null mutant characterization with subcellular fractionation and enzyme activity assays","pmids":["8349704"],"confidence":"High","gaps":["Mechanism by which subunit H activates hydrolysis/translocation coupling was not defined","Relevance of yeast findings to mammalian V-ATPase not yet tested"]},{"year":1998,"claim":"The unexpected finding that HIV-1 Nef directly binds the human ATP6V1H homolog (NBP1) and requires it for CD4 downregulation revealed that subunit H operates at the interface of endosomal acidification and pathogen-hijacked membrane trafficking.","evidence":"Reciprocal co-immunoprecipitation, yeast two-hybrid, and antisense knockdown with CD4 surface expression readout","pmids":["9620685"],"confidence":"High","gaps":["Structural basis of the Nef–subunit H interaction was not resolved","Whether Nef binding alters V-ATPase proton pumping activity was not tested"]},{"year":1999,"claim":"Reconstitution of human subunit H isoforms into SFD-depleted V-ATPase established that two alternatively spliced variants (SFDα/SFDβ) are functionally interchangeable and that subunit H bridges the V1 and V0 sectors to activate both ATPase and proton-pumping activities.","evidence":"In vitro reconstitution of purified recombinant SFDα and SFDβ with SFD-depleted holoenzyme, ATPase and proton transport assays","pmids":["10336497"],"confidence":"High","gaps":["Tissue- or context-specific roles of SFDα versus SFDβ were not examined","No structural data on how H subunit contacts V1-V0 interface"]},{"year":2016,"claim":"The first in vivo mammalian loss-of-function study demonstrated that ATP6V1H haploinsufficiency causes osteoporosis by raising osteoclast intracellular pH, impairing TGF-β1 activation, and thereby reducing osteoblast recruitment — connecting V-ATPase proton pumping to bone remodeling.","evidence":"CRISPR/Cas9 Atp6v1h knockout mice with micro-CT, histomorphometry, intracellular pH measurements, and TGF-β1 pathway analysis","pmids":["27924156"],"confidence":"High","gaps":["Whether TGF-β1 is the sole downstream mediator of the bone phenotype was not established","Human genetic validation for osteoporosis susceptibility was correlative (GWAS SNP) rather than causal"]},{"year":2017,"claim":"Zebrafish atp6v1h knockout placed ATP6V1H genetically upstream of MMP9/MMP13 in bone formation, with pharmacological rescue by MMP inhibitors providing epistasis evidence for a V-ATPase–MMP axis distinct from the TGF-β1 pathway identified in mice.","evidence":"CRISPR/Cas9 zebrafish mutants with bone staining, expression analysis, and chemical rescue with MMP9/MMP13 inhibitors","pmids":["28158191"],"confidence":"High","gaps":["Whether MMP upregulation reflects direct transcriptional control or is secondary to pH changes was unclear","Relationship between TGF-β1 and MMP9/MMP13 pathways downstream of ATP6V1H was not integrated"]},{"year":2018,"claim":"Extension of the heterozygous mouse model to bone marrow stromal cells showed that ATP6V1H deficiency biases mesenchymal progenitor differentiation away from osteogenesis and toward adipogenesis, with downregulation of TGF-β receptor I and AP-2 complex components, broadening the bone phenotype to a progenitor cell-autonomous defect.","evidence":"Atp6v1h+/− mouse BMSCs with proliferation, cell cycle, and differentiation assays; qPCR for pathway markers","pmids":["29782852"],"confidence":"Medium","gaps":["Pathway placement relied on gene expression changes without direct protein interaction or rescue data","Whether the adipogenic shift contributes to the in vivo osteoporosis phenotype was not shown"]},{"year":2019,"claim":"Gain- and loss-of-function experiments in osteoblastic cells under diabetic-mimicking conditions placed ATP6V1H upstream of Akt/GSK3β signaling in promoting osteogenic differentiation, suggesting a second signaling axis in addition to TGF-β1.","evidence":"Overexpression and siRNA knockdown of ATP6V1H in MC3T3-E1 cells; western blot for phospho-Akt/GSK3β","pmids":["31272281"],"confidence":"Medium","gaps":["Whether Akt/GSK3β modulation is direct or secondary to altered intracellular pH was not tested","Single cell-line study under non-physiological high-glucose/FFA conditions"]},{"year":2022,"claim":"ATP6V1H deficiency was linked to glucose intolerance through augmented ER stress in pancreatic β-cells, extending the phenotypic spectrum beyond bone to metabolic homeostasis.","evidence":"Atp6v1h+/− mice on high-fat diet with glucose tolerance tests, insulin measurement, and transcriptome sequencing","pmids":["34990584"],"confidence":"Medium","gaps":["Causal link between V-ATPase dysfunction and ER stress was correlative (transcriptomic)","Whether β-cell phenotype is cell-autonomous or secondary to systemic changes was not resolved"]},{"year":2024,"claim":"Co-immunoprecipitation identified integrin β1, β3, β5, α2b, and α5 as direct physical partners of ATP6V1H in osteoclasts, connecting V-ATPase to a Fos-Jun-Src-integrin signaling axis and providing the first evidence of non-V-ATPase binding partners beyond HIV-1 Nef.","evidence":"Atp6v1h+/− mice in tail-suspension model; co-immunoprecipitation, transcriptomics, micro-CT","pmids":["38203808"],"confidence":"Medium","gaps":["Integrin interactions detected by Co-IP only; reciprocal validation and domain mapping not reported","Functional consequence of integrin–ATP6V1H binding on V-ATPase activity or integrin signaling was not tested"]},{"year":null,"claim":"Key open questions remain: the structural basis for how subunit H bridges V1 and V0 sectors to activate proton pumping; whether the integrin, TGF-β1, MMP, and Akt/GSK3β downstream pathways converge or represent context-dependent outputs of luminal pH changes; and whether ATP6V1H loss-of-function mutations cause Mendelian skeletal or metabolic disease in humans.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of human subunit H in the holoenzyme context","No integration of the multiple downstream signaling pathways into a unified model","No human Mendelian disease causally attributed to ATP6V1H mutations"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005773","term_label":"vacuole","supporting_discovery_ids":[0]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[3,10]}],"pathway":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4,6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,10]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,7]}],"complexes":["V-ATPase (V1 domain)"],"partners":["ITGB1","ITGB3","ITGB5","ITGA2B","ITGA5","NEF (HIV-1)"],"other_free_text":[]},"mechanistic_narrative":"ATP6V1H encodes the H subunit of the V1 domain of the vacuolar H⁺-ATPase (V-ATPase) and is essential for coupling ATP hydrolysis to proton translocation across endomembranes; it is not required for V-ATPase assembly but is indispensable for catalytic activation of the holoenzyme [PMID:8349704, PMID:10336497]. Two alternatively spliced human isoforms (SFDα and SFDβ) are functionally interchangeable in reconstituting ATPase and proton-pumping activity, and the subunit bridges the V1 and V0 sectors [PMID:10336497]. In bone, ATP6V1H haploinsufficiency causes osteoporosis by elevating osteoclast intracellular pH, reducing TGF-β1 activation and osteoblast induction, and de-repressing MMP9/MMP13, while it also regulates osteoblast differentiation through Akt/GSK3β signaling and physically interacts with integrin β1/β3/β5 subunits in osteoclasts [PMID:27924156, PMID:28158191, PMID:31272281, PMID:38203808]. ATP6V1H additionally participates in HIV-1 Nef-mediated CD4 endocytosis through direct interaction with Nef, linking V-ATPase-dependent endosomal acidification to pathogen-driven membrane trafficking [PMID:9620685]."},"prefetch_data":{"uniprot":{"accession":"Q9UI12","full_name":"V-type proton ATPase subunit H","aliases":["Nef-binding protein 1","NBP1","Protein VMA13 homolog","V-ATPase 50/57 kDa subunits","Vacuolar proton pump subunit H","Vacuolar proton pump subunit SFD"],"length_aa":483,"mass_kda":55.9,"function":"Subunit of the V1 complex of vacuolar(H+)-ATPase (V-ATPase), a multisubunit enzyme composed of a peripheral complex (V1) that hydrolyzes ATP and a membrane integral complex (V0) that translocates protons (PubMed:33065002). V-ATPase is responsible for acidifying and maintaining the pH of intracellular compartments and in some cell types, is targeted to the plasma membrane, where it is responsible for acidifying the extracellular environment (By similarity). Subunit H is essential for V-ATPase activity, but not for the assembly of the complex (By similarity). Involved in the endocytosis mediated by clathrin-coated pits, required for the formation of endosomes (PubMed:12032142)","subcellular_location":"Cytoplasmic vesicle, clathrin-coated vesicle membrane","url":"https://www.uniprot.org/uniprotkb/Q9UI12/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/ATP6V1H","classification":"Common Essential","n_dependent_lines":843,"n_total_lines":1208,"dependency_fraction":0.6978476821192053},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000047249","cell_line_id":"CID001652","localizations":[{"compartment":"vesicles","grade":3},{"compartment":"cytoplasmic","grade":2}],"interactors":[{"gene":"ATP6AP2","stoichiometry":10.0},{"gene":"ATP6V1A","stoichiometry":10.0},{"gene":"ATP6V1B2","stoichiometry":10.0},{"gene":"ATP6V1D","stoichiometry":10.0},{"gene":"ATP6V1E1","stoichiometry":10.0},{"gene":"ATP6V1F","stoichiometry":10.0},{"gene":"ATP6V1G1","stoichiometry":10.0},{"gene":"WDR7","stoichiometry":4.0},{"gene":"ATP6V0A1","stoichiometry":0.2},{"gene":"ATP6V0D1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001652","total_profiled":1310},"omim":[{"mim_id":"608861","title":"ATPase, H+ TRANSPORTING, LYSOSOMAL, 50/57-KD, V1 SUBUNIT H; ATP6V1H","url":"https://www.omim.org/entry/608861"},{"mim_id":"600669","title":"EPILEPSY, IDIOPATHIC GENERALIZED; EIG","url":"https://www.omim.org/entry/600669"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Actin filaments","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATP6V1H"},"hgnc":{"alias_symbol":["CGI-11","SFD","VMA13","SFDalpha","SFDbeta"],"prev_symbol":[]},"alphafold":{"accession":"Q9UI12","domains":[{"cath_id":"1.25.10","chopping":"14-174_195-219","consensus_level":"medium","plddt":92.7906,"start":14,"end":219},{"cath_id":"1.25.10.10","chopping":"222-349","consensus_level":"medium","plddt":93.6272,"start":222,"end":349},{"cath_id":"1.25.40.150","chopping":"376-466","consensus_level":"high","plddt":92.5537,"start":376,"end":466}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UI12","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UI12-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UI12-F1-predicted_aligned_error_v6.png","plddt_mean":87.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATP6V1H","jax_strain_url":"https://www.jax.org/strain/search?query=ATP6V1H"},"sequence":{"accession":"Q9UI12","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UI12.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UI12/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UI12"}},"corpus_meta":[{"pmid":"8349704","id":"PMC_8349704","title":"VMA13 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The Vma13 polypeptide co-purifies with the active V-ATPase complex on the vacuolar membrane, is essential for V-ATPase activity, but is not required for assembly or membrane targeting of other V-ATPase subunits. Deletion of VMA13 produces an inactive, less stable V-ATPase complex.\",\n      \"method\": \"Genetic complementation, null mutant analysis, vacuolar membrane fractionation, co-purification with active complex\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (fractionation, co-purification, activity assay, null mutant) in a highly-cited foundational paper\",\n      \"pmids\": [\"8349704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The SFD (Sub Fifty-eight-kDa Doublet) isoforms SFDα (57 kDa) and SFDβ (50 kDa) — the mammalian ATP6V1H isoforms arising by alternative splicing — are functionally interchangeable in restoring both ATPase and proton-pumping activities when reassembled with SFD-depleted holoenzyme. Both isoforms interact structurally with both the V1 and V0 sectors, suggesting roles in coupling ATP hydrolysis to proton flow.\",\n      \"method\": \"Recombinant protein expression in E. coli, reconstitution with SFD-depleted native holoenzyme, ATPase activity assay, proton-pumping assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with activity assays and structural interaction data, replicated across two native enzyme preparations (clathrin-coated vesicles and chromaffin granules)\",\n      \"pmids\": [\"10336497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Haploinsufficiency of ATP6V1H in mice (Atp6v1h+/- CRISPR/Cas9 knockout) impairs osteoclast function by raising intracellular pH, which downregulates TGF-β1 activation, thereby reducing osteoblast induction and causing net bone matrix loss (osteoporosis). Bone resorption is also increased, but bone formation is reduced more, producing a net bone loss phenotype.\",\n      \"method\": \"CRISPR/Cas9 mouse knockout, intracellular pH measurement, TGF-β1 activation assay, histomorphometry, bone mineral density measurement\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO mouse with defined cellular and molecular phenotype; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27924156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of ATP6V1H function in zebrafish (atp6v1h CRISPR/Cas9 knockout) severely reduces mature calcified bone cells and dramatically increases expression of mmp9 and mmp13. Pharmacological inhibition of MMP9 and MMP13 significantly restores bone mass in atp6v1h mutants, placing ATP6V1H upstream of MMP9/MMP13 in a bone formation pathway.\",\n      \"method\": \"CRISPR/Cas9 zebrafish knockout, bone staining, mmp9/mmp13 expression analysis, small-molecule MMP inhibitor rescue experiment\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with defined molecular phenotype confirmed by chemical epistasis rescue; published in high-impact journal with strong evidence\",\n      \"pmids\": [\"28158191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ATP6V1H regulates proliferation and differentiation of bone marrow stromal cells (BMSCs): Atp6v1h+/- BMSCs show reduced proliferation, cell cycle arrest, reduced osteogenic differentiation, and increased adipogenic potential. Mechanistically, loss of ATP6V1H downregulates mRNA levels of TGF-β1 receptor and its binding molecule, the AP-2 complex subunit β, suggesting ATP6V1H regulates BMSC fate through TGF-β receptor I and AP-2 complex interactions.\",\n      \"method\": \"Heterozygous knockout mouse BMSCs, proliferation assay, osteogenic/adipogenic differentiation assay, qPCR, histological analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — defined cellular phenotypes in primary knockout cells with molecular pathway identification, single lab\",\n      \"pmids\": [\"29782852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATP6V1H promotes osteogenic differentiation of MC3T3-E1 cells through inhibition of the Akt/GSK3β signaling pathway: overexpression of ATP6V1H inhibits Akt/GSK3β signaling and promotes osteogenic differentiation, while knockdown promotes Akt/GSK3β signaling and reduces osteogenic differentiation.\",\n      \"method\": \"Overexpression and knockdown in MC3T3-E1 cells, Alizarin Red staining, western blot for Akt/GSK3β pathway components, CCK8 viability assay\",\n      \"journal\": \"Organogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — gain- and loss-of-function in cell line with pathway readout; single lab\",\n      \"pmids\": [\"31272281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ATP6V1H deficiency augments endoplasmic reticulum (ER) stress in pancreatic β-cells and worsens high-fat diet-induced glucose intolerance in Atp6v1h+/- mice; transcriptome sequencing revealed that alternative splicing of ATP6V1H transcripts may be involved in regulating insulin secretion.\",\n      \"method\": \"Atp6v1h+/- mouse HFD model, transcriptome sequencing, qPCR, western blot for ER stress markers\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mouse knockout with transcriptomic and biochemical characterization; single lab\",\n      \"pmids\": [\"34990584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Atp6v1h deficiency in mice modulates bone loss under simulated microgravity through the Fos-Jun-Src-Integrin pathway. Co-immunoprecipitation identified physical interactions between ATP6V1H and integrin subunits β1, β3, β5, α2b, and α5, linking ATP6V1H to osteoclast activity and bone resorption via integrin-mediated signaling.\",\n      \"method\": \"Mouse tail suspension model, micro-CT, TRAP assay, transcriptomic sequencing, RT-qPCR, co-immunoprecipitation\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vivo model with transcriptomics and co-IP validation; single lab\",\n      \"pmids\": [\"38203808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Long noncoding RNA lnc-TCEA1-3 positively regulates ATP6V1H expression in osteoclasts; overexpression of lnc-TCEA1-3 upregulates ATP6V1H mRNA and protein and increases osteoclast numbers. The lncRNA exerts differential effects on the two ATP6V1H transcript isoforms.\",\n      \"method\": \"Lentiviral overexpression in HEK293, HOS cells, and primary osteoclasts; qPCR; Atp6v1h knockout mice as controls\",\n      \"journal\": \"Critical reviews in eukaryotic gene expression\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, transcriptional regulation via lncRNA with limited mechanistic detail\",\n      \"pmids\": [\"37824389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In zebrafish macrophages, Atp6v1h (the V-ATPase subunit H) co-localizes with internalized Aspergillus fumigatus spores in vivo. V-ATPase deficiency (atp6v1h CRISPR/Cas9 knockout) does not reduce macrophage spore killing but impairs macrophage-mediated inhibition of spore germination and hyphal growth, demonstrating that these two macrophage defense functions are mechanistically decoupled by V-ATPase activity.\",\n      \"method\": \"Live imaging in larval zebrafish, CRISPR/Cas9 knockout of atp6v1h, fluorescence co-localization, survival assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo live imaging with genetic knockout and functional dissection; preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.07.14.664761\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"ATP6V1H (subunit H of the vacuolar H+-ATPase V1 domain) is essential for V-ATPase catalytic activity and proton pumping — but not complex assembly — by structurally bridging the V1 and V0 sectors; in bone, it regulates osteoclast acidification, TGF-β1 activation, MMP9/MMP13 expression, and integrin signaling to coordinate bone resorption and formation, while in other cell types it controls ER stress in pancreatic β-cells, BMSC fate via TGF-β/AP-2, and macrophage control of fungal germination.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"VMA13 (the yeast ortholog of ATP6V1H) encodes the 54-kDa subunit of the V-ATPase. This subunit is essential for ATPase activity but not for assembly or membrane targeting of other V-ATPase subunits. Null mutants lacking Vma13p retain other subunits on the vacuolar membrane but form a less stable, inactive complex.\",\n      \"method\": \"Genetic complementation, null mutant characterization, subcellular fractionation, enzyme activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (complementation, fractionation, activity assays) in foundational paper; widely cited\",\n      \"pmids\": [\"8349704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"NBP1, the human homolog of yeast Vma13p (i.e., the human ATP6V1H/subunit H), directly interacts with HIV-1 Nef in vitro and in vivo. This interaction facilitates Nef-mediated internalization of CD4, linking ATP6V1H to the endocytic pathway. Antisense suppression of NBP1 abolished Nef-mediated CD4 downregulation.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, yeast complementation assay, antisense knockdown with functional readout (CD4 surface expression)\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, yeast complementation, functional antisense knockdown with defined phenotypic readout\",\n      \"pmids\": [\"9620685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The human SFD (Sub Fifty-eight-kDa Doublet) polypeptides—isoforms of the ATP6V1H subunit arising by alternative splicing—are both required to activate ATPase and proton-pumping activities of the V-ATPase holoenzyme. Recombinant SFDα (57 kDa) and SFDβ (50 kDa) are functionally interchangeable in restoring activity to SFD-depleted enzyme. These subunits interact structurally with both V1 and V0 domains, indicating roles in coupling ATP hydrolysis to proton translocation.\",\n      \"method\": \"Recombinant protein expression, reconstitution with SFD-depleted holoenzyme, ATPase activity assay, proton pumping assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with activity assays; multiple isoforms tested across multiple enzyme preparations\",\n      \"pmids\": [\"10336497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Haploinsufficiency of ATP6V1H in mice (CRISPR/Cas9 knockout) causes osteoporosis via impaired bone remodeling. Atp6v1h-deficient osteoclasts show increased intracellular pH, which downregulates TGF-β1 activation, thereby reducing osteoblast induction. Bone resorption is increased and bone formation decreased, with a net bone matrix loss.\",\n      \"method\": \"CRISPR/Cas9 knockout mouse model, micro-CT, histomorphometry, intracellular pH measurement, TGF-β1 signaling analysis, GWAS SNP association\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular and molecular phenotype, pathway placement via TGF-β1, multiple orthogonal assays\",\n      \"pmids\": [\"27924156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of atp6v1h function in zebrafish (CRISPR/Cas9) severely reduces mature calcified bone cells and dramatically increases expression of mmp9 and mmp13. Small molecule inhibitors of MMP9 and MMP13 restore bone mass in mutants, placing ATP6V1H upstream of MMP9/MMP13 in a pathway regulating bone formation.\",\n      \"method\": \"CRISPR/Cas9 zebrafish knockout, bone staining, gene expression analysis, pharmacological rescue with MMP inhibitors\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis established by pharmacological rescue; multiple orthogonal assays in vivo\",\n      \"pmids\": [\"28158191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ATP6V1H is expressed in bone marrow stromal cells (BMSCs), and Atp6v1h+/- BMSCs show reduced proliferation, cell cycle arrest, decreased osteogenic differentiation, and increased adipogenic potential. Loss of ATP6V1H downregulates TGF-β1 receptor mRNA and the TGF-β receptor binding molecule AP-2 (subunit β of adaptor protein complex 2), suggesting ATP6V1H regulates BMSC differentiation via interaction with TGF-β receptor I and AP-2 complex.\",\n      \"method\": \"Heterozygous knockout mouse (Atp6v1h+/-), cell proliferation assays, cell cycle analysis, osteogenic/adipogenic differentiation assays, histology, qPCR\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO model with defined cellular phenotype; pathway placement by gene expression only (Tier 3 for molecular mechanism)\",\n      \"pmids\": [\"29782852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In MC3T3-E1 osteoblastic cells under high-glucose/free-fatty-acid conditions simulating T2DM, ATP6V1H overexpression promotes osteogenic differentiation and inhibits the Akt/GSK3β signaling pathway, while ATP6V1H knockdown activates Akt/GSK3β signaling. This places ATP6V1H upstream of Akt/GSK3β in regulating osteogenic differentiation.\",\n      \"method\": \"Overexpression and siRNA knockdown, Alizarin Red staining, western blot (Akt/GSK3β phosphorylation), CCK8 viability assay\",\n      \"journal\": \"Organogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — OE/KD with pathway readout; single lab, single cell-line model\",\n      \"pmids\": [\"31272281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ATP6V1H deficiency in Atp6v1h+/- mice fed a high-fat diet worsens glucose tolerance by augmenting endoplasmic reticulum (ER) stress in pancreatic β-cells, thereby impairing insulin secretion. Transcriptome sequencing identified ER stress pathway upregulation, and alternative splicing of ATP6V1H transcripts may also be involved.\",\n      \"method\": \"Atp6v1h+/- mouse HFD model, glucose tolerance testing, insulin measurement, transcriptome sequencing, qPCR, western blot\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined genetic model with pathway placement via transcriptomics and functional metabolic readout; single lab\",\n      \"pmids\": [\"34990584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In simulated microgravity (tail-suspension) mouse model, Atp6v1h+/- mice do not show aggravated bone loss beyond that from Atp6v1h deficiency alone. Transcriptomic analysis revealed upregulation of Fos, Jun, Src, and integrin subunits. Co-immunoprecipitation demonstrated direct interactions between ATP6V1H protein and integrin beta 1, beta 3, beta 5, alpha 2b, and alpha 5, placing ATP6V1H in a Fos-Jun-Src-Integrin pathway that modulates osteoclast activity.\",\n      \"method\": \"Mouse tail-suspension model, micro-CT, TRAP staining, transcriptomic sequencing, RT-qPCR, co-immunoprecipitation\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP identifies novel binding partners (integrins); transcriptomics provides pathway context; single lab\",\n      \"pmids\": [\"38203808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The lncRNA lnc-TCEA1-3 positively regulates ATP6V1H expression in osteoclasts: overexpression of lnc-TCEA1-3 upregulates ATP6V1H mRNA in HEK293 cells, HOS cells, and primary osteoclasts, and increases osteoclast number. This establishes a post-transcriptional regulatory axis upstream of ATP6V1H in bone cells.\",\n      \"method\": \"Lentivirus-mediated overexpression, qPCR, primary osteoclast culture, Atp6v1h knockout mice for validation\",\n      \"journal\": \"Critical reviews in eukaryotic gene expression\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, primarily expression-level readout; mechanism of lncRNA-mediated regulation not fully defined\",\n      \"pmids\": [\"37824389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In larval zebrafish, the v-ATPase subunit Atp6v1h co-localizes with Aspergillus fumigatus spores inside macrophages in vivo. CRISPR/Cas9 targeting of atp6v1h does not reduce macrophage spore killing but abolishes macrophage-mediated inhibition of spore germination and extracellular hyphal growth, demonstrating that v-ATPase (via Atp6v1h) is required for controlling fungal germination but not spore killing.\",\n      \"method\": \"Live imaging in larval zebrafish, CRISPR/Cas9 knockout of atp6v1h, co-localization imaging, fungal germination/killing assays in vivo\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with specific functional dissection (killing vs. germination) using live in vivo imaging; preprint only\",\n      \"pmids\": [\"bio_10.1101_2025.07.14.664761\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"ATP6V1H (subunit H of the V1 domain) is essential for V-ATPase catalytic activity by stabilizing the holoenzyme and coupling ATP hydrolysis to proton translocation across membranes; in bone, it regulates osteoclast and osteoblast function through TGF-β1 and MMP9/MMP13 pathways to maintain bone homeostasis, and it physically interacts with integrin subunits and the HIV-1 Nef binding protein NBP1 to link endosomal acidification to membrane trafficking and immune pathogen control.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ATP6V1H encodes subunit H of the vacuolar H+-ATPase (V-ATPase), a structural bridge between the catalytic V1 and membrane-embedded V0 sectors that is essential for ATPase activity and proton pumping but dispensable for complex assembly [PMID:8349704, PMID:10336497]. In bone, ATP6V1H controls osteoclast acidification and resorption while coupling these processes to bone formation through activation of TGF-β1, regulation of MMP9/MMP13 expression, integrin-mediated signaling via the Fos-Jun-Src pathway, and modulation of BMSC osteogenic versus adipogenic fate through TGF-β/AP-2 and Akt/GSK3β pathways [PMID:27924156, PMID:28158191, PMID:38203808, PMID:29782852, PMID:31272281]. Beyond bone, ATP6V1H deficiency in pancreatic β-cells augments ER stress and worsens glucose intolerance [PMID:34990584]. Two mammalian splice isoforms (SFDα and SFDβ) are functionally interchangeable in reconstituting V-ATPase catalytic and proton-transport activities [PMID:10336497].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of VMA13/ATP6V1H as the V-ATPase subunit H established that this polypeptide is essential for enzymatic activity and complex stability but not for assembly or membrane targeting of other subunits, defining its non-catalytic yet indispensable role.\",\n      \"evidence\": \"Yeast VMA13 null mutant analysis with vacuolar membrane fractionation, co-purification, and activity assays\",\n      \"pmids\": [\"8349704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which subunit H activates the holoenzyme was not defined\", \"No mammalian data at this point\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Reconstitution experiments demonstrated that both mammalian splice isoforms (SFDα/SFDβ) are functionally interchangeable and interact with both V1 and V0 sectors, establishing subunit H as a physical bridge that couples ATP hydrolysis to proton translocation.\",\n      \"evidence\": \"Recombinant protein reconstitution with SFD-depleted native holoenzyme from clathrin-coated vesicles and chromaffin granules, ATPase and proton-pumping assays\",\n      \"pmids\": [\"10336497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of V1–V0 bridging by subunit H not resolved\", \"Physiological significance of isoform choice unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Mouse haploinsufficiency revealed that ATP6V1H regulates osteoclast intracellular pH and TGF-β1 activation, coupling bone resorption to osteoblast induction; loss produced net bone loss due to disproportionately reduced bone formation.\",\n      \"evidence\": \"CRISPR/Cas9 Atp6v1h+/− mouse with intracellular pH measurement, TGF-β1 activation assay, histomorphometry, bone mineral density analysis\",\n      \"pmids\": [\"27924156\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism linking pH change to TGF-β1 activation not established\", \"Homozygous knockout phenotype not characterized (likely lethal)\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Zebrafish knockout showed ATP6V1H acts upstream of MMP9/MMP13 in bone formation, and pharmacological MMP inhibition rescued the bone defect, establishing a genetic epistasis relationship.\",\n      \"evidence\": \"CRISPR/Cas9 zebrafish atp6v1h knockout with bone staining, mmp9/mmp13 expression analysis, and MMP inhibitor rescue\",\n      \"pmids\": [\"28158191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MMP upregulation is a direct transcriptional consequence or secondary to pH dysregulation is unknown\", \"Relevance of this pathway in mammals not confirmed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"ATP6V1H was shown to regulate bone marrow stromal cell fate — promoting osteogenesis over adipogenesis — through TGF-β receptor I and AP-2 complex signaling, extending its bone-related roles beyond osteoclasts to mesenchymal progenitors.\",\n      \"evidence\": \"Atp6v1h+/− mouse BMSCs with proliferation, differentiation assays, and qPCR for TGF-β pathway components\",\n      \"pmids\": [\"29782852\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"AP-2 complex interaction is inferred from mRNA changes, not direct binding\", \"Whether V-ATPase activity per se or a non-canonical function of ATP6V1H drives BMSC fate is unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Gain- and loss-of-function studies in osteoblast-lineage cells placed ATP6V1H as a negative regulator of Akt/GSK3β signaling, adding an additional signaling axis through which it promotes osteogenic differentiation.\",\n      \"evidence\": \"Overexpression and knockdown in MC3T3-E1 cells with western blot for Akt/GSK3β pathway\",\n      \"pmids\": [\"31272281\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting V-ATPase/proton pumping to Akt/GSK3β is not established\", \"Single cell line study\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"ATP6V1H deficiency was linked to pancreatic β-cell ER stress and glucose intolerance, demonstrating a non-skeletal physiological role and raising the possibility that alternative splicing of ATP6V1H isoforms regulates insulin secretion.\",\n      \"evidence\": \"Atp6v1h+/− mouse on high-fat diet with transcriptome sequencing and ER stress marker analysis\",\n      \"pmids\": [\"34990584\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from V-ATPase dysfunction to ER stress not defined\", \"Alternative splicing regulation of insulin secretion is correlative\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Co-immunoprecipitation identified direct physical interactions between ATP6V1H and multiple integrin subunits (β1, β3, β5, α2b, α5), connecting ATP6V1H to osteoclast bone resorption via a Fos-Jun-Src-integrin signaling axis under mechanical unloading.\",\n      \"evidence\": \"Mouse tail suspension model with micro-CT, transcriptomics, and co-immunoprecipitation\",\n      \"pmids\": [\"38203808\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Integrin interactions await reciprocal validation and domain mapping\", \"Whether integrin binding reflects V-ATPase-dependent or -independent function is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the structural basis of subunit H's bridging function at atomic resolution, whether bone and metabolic phenotypes are driven by acidification defects versus non-canonical signaling roles, and whether ATP6V1H mutations cause human skeletal or metabolic disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of mammalian V-ATPase subunit H in holoenzyme context\", \"No human genetic disease association reported from direct evidence\", \"Relative contributions of proton-pumping versus scaffolding/signaling functions remain unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005773\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005773\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 4, 5, 7]}\n    ],\n    \"complexes\": [\"V-ATPase (vacuolar H+-ATPase)\"],\n    \"partners\": [\"ITGB1\", \"ITGB3\", \"ITGB5\", \"ITGA2B\", \"ITGA5\"],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"ATP6V1H encodes the H subunit of the V1 domain of the vacuolar H⁺-ATPase (V-ATPase) and is essential for coupling ATP hydrolysis to proton translocation across endomembranes; it is not required for V-ATPase assembly but is indispensable for catalytic activation of the holoenzyme [PMID:8349704, PMID:10336497]. Two alternatively spliced human isoforms (SFDα and SFDβ) are functionally interchangeable in reconstituting ATPase and proton-pumping activity, and the subunit bridges the V1 and V0 sectors [PMID:10336497]. In bone, ATP6V1H haploinsufficiency causes osteoporosis by elevating osteoclast intracellular pH, reducing TGF-β1 activation and osteoblast induction, and de-repressing MMP9/MMP13, while it also regulates osteoblast differentiation through Akt/GSK3β signaling and physically interacts with integrin β1/β3/β5 subunits in osteoclasts [PMID:27924156, PMID:28158191, PMID:31272281, PMID:38203808]. ATP6V1H additionally participates in HIV-1 Nef-mediated CD4 endocytosis through direct interaction with Nef, linking V-ATPase-dependent endosomal acidification to pathogen-driven membrane trafficking [PMID:9620685].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"The foundational question of whether V-ATPase subunit H is needed for complex assembly or for catalytic activity was resolved: Vma13p (yeast ATP6V1H ortholog) is dispensable for V-ATPase assembly and membrane targeting but is strictly required for ATPase enzymatic activity, establishing its role as a catalytic activator rather than a structural scaffold.\",\n      \"evidence\": \"Yeast VMA13 null mutant characterization with subcellular fractionation and enzyme activity assays\",\n      \"pmids\": [\"8349704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which subunit H activates hydrolysis/translocation coupling was not defined\",\n        \"Relevance of yeast findings to mammalian V-ATPase not yet tested\"\n      ]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"The unexpected finding that HIV-1 Nef directly binds the human ATP6V1H homolog (NBP1) and requires it for CD4 downregulation revealed that subunit H operates at the interface of endosomal acidification and pathogen-hijacked membrane trafficking.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, yeast two-hybrid, and antisense knockdown with CD4 surface expression readout\",\n      \"pmids\": [\"9620685\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the Nef–subunit H interaction was not resolved\",\n        \"Whether Nef binding alters V-ATPase proton pumping activity was not tested\"\n      ]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Reconstitution of human subunit H isoforms into SFD-depleted V-ATPase established that two alternatively spliced variants (SFDα/SFDβ) are functionally interchangeable and that subunit H bridges the V1 and V0 sectors to activate both ATPase and proton-pumping activities.\",\n      \"evidence\": \"In vitro reconstitution of purified recombinant SFDα and SFDβ with SFD-depleted holoenzyme, ATPase and proton transport assays\",\n      \"pmids\": [\"10336497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Tissue- or context-specific roles of SFDα versus SFDβ were not examined\",\n        \"No structural data on how H subunit contacts V1-V0 interface\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The first in vivo mammalian loss-of-function study demonstrated that ATP6V1H haploinsufficiency causes osteoporosis by raising osteoclast intracellular pH, impairing TGF-β1 activation, and thereby reducing osteoblast recruitment — connecting V-ATPase proton pumping to bone remodeling.\",\n      \"evidence\": \"CRISPR/Cas9 Atp6v1h knockout mice with micro-CT, histomorphometry, intracellular pH measurements, and TGF-β1 pathway analysis\",\n      \"pmids\": [\"27924156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether TGF-β1 is the sole downstream mediator of the bone phenotype was not established\",\n        \"Human genetic validation for osteoporosis susceptibility was correlative (GWAS SNP) rather than causal\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Zebrafish atp6v1h knockout placed ATP6V1H genetically upstream of MMP9/MMP13 in bone formation, with pharmacological rescue by MMP inhibitors providing epistasis evidence for a V-ATPase–MMP axis distinct from the TGF-β1 pathway identified in mice.\",\n      \"evidence\": \"CRISPR/Cas9 zebrafish mutants with bone staining, expression analysis, and chemical rescue with MMP9/MMP13 inhibitors\",\n      \"pmids\": [\"28158191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether MMP upregulation reflects direct transcriptional control or is secondary to pH changes was unclear\",\n        \"Relationship between TGF-β1 and MMP9/MMP13 pathways downstream of ATP6V1H was not integrated\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extension of the heterozygous mouse model to bone marrow stromal cells showed that ATP6V1H deficiency biases mesenchymal progenitor differentiation away from osteogenesis and toward adipogenesis, with downregulation of TGF-β receptor I and AP-2 complex components, broadening the bone phenotype to a progenitor cell-autonomous defect.\",\n      \"evidence\": \"Atp6v1h+/− mouse BMSCs with proliferation, cell cycle, and differentiation assays; qPCR for pathway markers\",\n      \"pmids\": [\"29782852\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Pathway placement relied on gene expression changes without direct protein interaction or rescue data\",\n        \"Whether the adipogenic shift contributes to the in vivo osteoporosis phenotype was not shown\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Gain- and loss-of-function experiments in osteoblastic cells under diabetic-mimicking conditions placed ATP6V1H upstream of Akt/GSK3β signaling in promoting osteogenic differentiation, suggesting a second signaling axis in addition to TGF-β1.\",\n      \"evidence\": \"Overexpression and siRNA knockdown of ATP6V1H in MC3T3-E1 cells; western blot for phospho-Akt/GSK3β\",\n      \"pmids\": [\"31272281\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether Akt/GSK3β modulation is direct or secondary to altered intracellular pH was not tested\",\n        \"Single cell-line study under non-physiological high-glucose/FFA conditions\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"ATP6V1H deficiency was linked to glucose intolerance through augmented ER stress in pancreatic β-cells, extending the phenotypic spectrum beyond bone to metabolic homeostasis.\",\n      \"evidence\": \"Atp6v1h+/− mice on high-fat diet with glucose tolerance tests, insulin measurement, and transcriptome sequencing\",\n      \"pmids\": [\"34990584\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Causal link between V-ATPase dysfunction and ER stress was correlative (transcriptomic)\",\n        \"Whether β-cell phenotype is cell-autonomous or secondary to systemic changes was not resolved\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Co-immunoprecipitation identified integrin β1, β3, β5, α2b, and α5 as direct physical partners of ATP6V1H in osteoclasts, connecting V-ATPase to a Fos-Jun-Src-integrin signaling axis and providing the first evidence of non-V-ATPase binding partners beyond HIV-1 Nef.\",\n      \"evidence\": \"Atp6v1h+/− mice in tail-suspension model; co-immunoprecipitation, transcriptomics, micro-CT\",\n      \"pmids\": [\"38203808\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Integrin interactions detected by Co-IP only; reciprocal validation and domain mapping not reported\",\n        \"Functional consequence of integrin–ATP6V1H binding on V-ATPase activity or integrin signaling was not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions remain: the structural basis for how subunit H bridges V1 and V0 sectors to activate proton pumping; whether the integrin, TGF-β1, MMP, and Akt/GSK3β downstream pathways converge or represent context-dependent outputs of luminal pH changes; and whether ATP6V1H loss-of-function mutations cause Mendelian skeletal or metabolic disease in humans.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of human subunit H in the holoenzyme context\",\n        \"No integration of the multiple downstream signaling pathways into a unified model\",\n        \"No human Mendelian disease causally attributed to ATP6V1H mutations\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005773\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [3, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4, 6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 10]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"complexes\": [\n      \"V-ATPase (V1 domain)\"\n    ],\n    \"partners\": [\n      \"ITGB1\",\n      \"ITGB3\",\n      \"ITGB5\",\n      \"ITGA2B\",\n      \"ITGA5\",\n      \"NEF (HIV-1)\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}