{"gene":"MTARC1","run_date":"2026-06-10T02:59:51","timeline":{"discoveries":[{"year":2012,"finding":"mARC1 is a signal-anchored protein of the outer mitochondrial membrane with an N(in)-C(out) membrane orientation; the N-terminal transmembrane helix is sufficient for mitochondrial targeting, the N-terminal targeting signal acts as a supportive receptor, membrane integration is membrane-potential-independent but requires external ATP, and the protein assembles into high-oligomeric complexes. The C-terminal catalytic domain is exposed to the cytosol.","method":"Subcellular fractionation, protease protection assays, deletion/truncation constructs, live-cell imaging, mitochondrial import assays with ATP depletion and membrane-potential uncouplers","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, protease protection, import assays, truncation mutants) in a single focused study establishing localization and targeting mechanism","pmids":["23086957"],"is_preprint":false},{"year":2014,"finding":"Human mARC1 catalyzes reduction of nitrite to nitric oxide (NO) through its molybdenum cofactor; this activity requires Cys-273 (molybdenum-coordinating residue) as the C273A mutation abolishes NO formation. Replacement of molybdenum with tungsten also abolishes NO formation. mARC1 generates NO from nitrite in an electron transfer chain with NADH, cytochrome b5, and NADH-dependent cytochrome b5 reductase, with rate increasing ~3-fold at pH 6.5 vs 7.5.","method":"In vitro nitrite reduction assay with recombinant protein; active-site mutagenesis (C273A); tungsten substitution of molybdenum; lentiviral mARC1 expression in HEK cells with NO detection; Km/Vmax determination","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with active-site mutagenesis and cofactor substitution, multiple orthogonal approaches confirming molybdenum-dependent nitrite reduction","pmids":["24500710"],"is_preprint":false},{"year":2014,"finding":"mARC1 functions as part of an N-reductive enzyme system together with cytochrome b5 type B and NADH cytochrome b5 reductase to reduce N-hydroxylated compounds (benzamidoxime). SNP variants in MARC1 encoding A165T showed no altered kinetic parameters in benzamidoxime N-reduction, while multiple simultaneous amino acid substitutions reduced N-reductive activity ~5-fold.","method":"Recombinant protein expression in E. coli; in vitro steady-state enzyme kinetics with benzamidoxime; molybdenum quantification by ICP-MS; pyrosequencing-based genotyping","journal":"Drug Metabolism and Disposition","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro kinetic assay with defined substrates, single lab, multiple SNP variants tested","pmids":["24423752"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of human mARC1 was solved at high resolution, revealing the coordination geometry of the molybdenum cofactor (Moco), identifying two key active-site residues that distinguish mARC paralogs, and demonstrating that mARC1 belongs to the MOSC domain superfamily. The structure defines the catalytic mechanism for reduction of N-oxygenated compounds and provides evidence for an evolutionary relationship to the xanthine oxidase superfamily.","method":"X-ray crystallography (high-resolution crystal structure); structural comparison with in silico domain predictions; functional interpretation of active-site architecture","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure with active-site identification and mutagenesis-informed mechanistic interpretation","pmids":["30397129"],"is_preprint":false},{"year":2022,"finding":"Crystal structure of the mARC1 p.A165T variant protein at near-atomic resolution shows that this clinically protective variant does not alter the overall protein fold or active-site architecture compared to wildtype mARC1.","method":"X-ray crystallography of variant protein; structural comparison to wildtype crystal structure","journal":"Hepatology Communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structure of variant, single lab, no functional assay accompanying the structural data reported in abstract","pmids":["35560545"],"is_preprint":false},{"year":2023,"finding":"Hepatocyte-specific mARC1 knockdown (via GalNAc-siRNA in a NASH mouse model) reduced hepatic triglyceride accumulation but increased plasma triglycerides; in primary human hepatocytes, mARC1 knockdown decreased lipid accumulation and increased triglyceride secretion. mARC1 knockdown also decreased secretion of 3-hydroxybutyrate (a β-oxidation marker) in vitro and in vivo, implicating mARC1 in hepatic lipid metabolism and ketogenesis.","method":"GalNAc-siRNA hepatocyte-specific knockdown in GAN-diet NASH mouse model; primary human hepatocyte in vitro model with siRNA KD; metabolic readouts (triglycerides, 3-hydroxybutyrate); RNA-sequencing pathway analysis","journal":"JHEP Reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — hepatocyte-specific in vivo knockdown with defined metabolic phenotype corroborated by in vitro primary human hepatocyte model, replicated across multiple readouts","pmids":["37122688"],"is_preprint":false},{"year":2024,"finding":"The protective MTARC1 p.A165T variant causes dramatically reduced protein stability of mARC1 (assessed by protein stability reporter system in multiple cell lines and in mouse liver), without altering mRNA levels. Multiple substitutions at position A165 (A165S, A165N, A165V, A165G, A165D) similarly reduced stability, indicating A165 is essential for mARC1 protein stability.","method":"Protein stability reporter system in multiple cell lines; murine knock-in model (A168T equivalent); Western blot; mutagenesis of A165 to multiple residues","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — stability reporter system with multiple cell lines and in vivo mouse model, single lab, replicated across multiple substitutions","pmids":["38340654"],"is_preprint":false},{"year":2024,"finding":"The protective p.A165T substitution causes protein instability and aberrant localization of mARC1 in hepatic cells. Novel rare putative loss-of-function MARC1 variants identified by exome-wide association study show a phenotype similar to p.A165T/p.M187K variants, consistent with loss-of-function being hepatoprotective. Marc1 knockout mice, unlike human carriers, do not show protection against hepatic triglyceride accumulation, revealing a divergent physiological role between human and mouse (attributed to Marc2 being the dominant paralog in mouse liver).","method":"Exome-wide association study (n=540,000); in vitro expression of recombinant human MARC1 A165T with localization studies in hepatic cells; Marc1 knockout mouse generation; liver phenotype assessment in KO mice on steatogenic diet","journal":"PLoS Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — recombinant protein localization studies combined with KO mouse model, single lab, two orthogonal approaches","pmids":["38437227"],"is_preprint":false},{"year":2024,"finding":"Hepatocyte-specific Mtarc1 siRNA knockdown in ob/ob and diet-induced MASH mouse models reduced serum liver enzymes, LDL-cholesterol, liver triglycerides, liver weight, and attenuated liver pathological changes. Multi-omics (metabolomics, proteomics, lipidomics) analysis showed that Mtarc1 knockdown partially restored diet-altered metabolites and lipids.","method":"GalNAc-conjugated siRNA hepatocyte-specific knockdown in ob/ob and diet-induced MASH mouse models; multi-omics (metabolomics, proteomics, lipidomics); histology; serum biochemistry","journal":"Hepatology Communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — hepatocyte-specific in vivo knockdown in multiple mouse models with comprehensive multi-omics readouts, replicated across models","pmids":["38696369"],"is_preprint":false},{"year":2024,"finding":"mARC1 siRNA knockdown in primary human hepatocytes reduced neutral lipid content specifically in cells homozygous for the risk allele (p.A165), and this reduction was mediated by increased fatty acid β-oxidation (measured by radiolabeled tracer). mARC1 knockdown also reduced ferroptosis and reactive oxygen species levels. In human UK Biobank participants, carriers of the rs2642438 minor allele had higher circulating 3-hydroxybutyrate levels, consistent with increased β-oxidation.","method":"siRNA knockdown in primary human hepatocytes; radiolabeled fatty acid oxidation assay; Oil-Red O staining; RNA-sequencing and LC-MS proteomics; UK Biobank metabolomics","journal":"Clinical and Molecular Hepatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct measurement of β-oxidation with radiolabeled tracers in primary human hepatocytes, supported by human metabolomics data and proteomic/transcriptomic profiling","pmids":["39716370"],"is_preprint":false},{"year":2024,"finding":"mARC1 is the main contributor to reductive biotransformation of N-hydroxyurea (NHU) to urea; in vitro and in vivo evidence establishes that this N-reductive activity is specifically mediated by mARC1 (not mARC2), suggesting mARC1-mediated inactivation as a pharmacological mechanism requiring high doses of hydroxyurea in therapy.","method":"In vitro N-reductive assay with recombinant mARC1 and mARC2; in vivo metabolic studies; substrate specificity determination","journal":"Journal of Medicinal Chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assay with in vivo corroboration, single lab","pmids":["39397364"],"is_preprint":false},{"year":2024,"finding":"mARC1 depletion improved cellular bioenergetics and decreased mitochondrial superoxide production in response to lipotoxic stress in cells. The p.A165T variant maintains mitochondrial localization despite lower protein levels. Global or hepatocyte-specific mARC1 deletion in mice reduced liver steatosis and fibrosis in multiple MASH and liver fibrosis models. RNA-seq showed downregulation of extracellular matrix remodeling and collagen formation pathways upon mARC1 loss.","method":"mARC1 knockdown/KO in cells with bioenergetics and mitochondrial superoxide assays; global and conditional KO mice on diet-induced MASH models; RNA-seq; plasma lipidomics; histology","journal":"Hepatology Communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (bioenergetics, mitochondrial ROS, global and conditional KO in multiple mouse models, transcriptomics, lipidomics) in a single study","pmids":["39927988"],"is_preprint":false},{"year":2024,"finding":"mARC1 modulates lipid accumulation in primary human hepatocytes and primary human adipocytes; mARC1 depletion affects accumulation of distinct lipid species and expression of inflammatory and mitochondrial pathway genes/proteins in both in vitro and in vivo models. Protective MTARC1 variants decrease protein accumulation in overexpression systems (without altering mRNA). A plasma lipid biomarker (Ceramide 22:1) predictive of mARC1 abundance was identified.","method":"siRNA knockdown and lentiviral overexpression in primary human hepatocytes, hepatocyte cell lines, and primary human adipocytes; in vivo murine MASH model with GalNAc-siRNA; lipidomics; proteomics; transcriptomics","journal":"Hepatology Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cell types and in vivo model, single lab, lipidomics and proteomics readouts","pmids":["38619429"],"is_preprint":false},{"year":2026,"finding":"MTARC1 deficiency post-transcriptionally upregulates glycerophospholipid (GPL) biosynthetic enzymes CEPT1 and PEMT, leading to altered phospholipid composition in lipid droplets (LDs). This phospholipid remodeling reduces LD size, increases surface-to-volume ratio, and thereby enhances LD degradation via lipolysis and lipophagy. Knockdown of CEPT1 or PEMT reversed the hepatoprotective effects of MTARC1 deficiency, establishing an MTARC1-GPL biosynthesis-LD degradation axis.","method":"Global and liver-specific Mtarc1 KO mice; genetic inhibition of Pnpla2, Lipa, Pemt, Cept1; multi-omics (biochemical, histological, lipidomics, proteomics); in vitro cell culture mechanistic studies; LD size/number quantification","journal":"Liver International","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis via double KO (Mtarc1 + CEPT1/PEMT), multiple orthogonal omics in both in vitro and in vivo models, functional rescue/reversal experiments","pmids":["41641916"],"is_preprint":false},{"year":2026,"finding":"MTARC1 knockdown in HCC cell lines (Hep3B2, HuH7, HepG2, HepaRG) reduced proliferation; CRISPR-Cas9 KO in Hep3B2 cells decreased neutral lipid accumulation, enhanced β-oxidation, and reduced cell migration. MTARC1 KO xenograft tumors showed reduced volume. Proteomics revealed inhibition of oncogenic pathways and activation of anti-proliferative proteins upon MTARC1 loss.","method":"siRNA knockdown in multiple HCC cell lines; CRISPR-Cas9 KO; lipid accumulation assay; β-oxidation assay; migration assay; subcutaneous xenograft mouse model; global proteomics","journal":"Clinical and Molecular Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with defined cellular and in vivo phenotype, multiple orthogonal readouts, single lab","pmids":["41644117"],"is_preprint":false},{"year":2026,"finding":"Mtarc1 KO mice on choline-deficient high-fat diet showed reduced liver steatosis, pro-fibrosis markers, and inflammation. Primary hepatocytes from Mtarc1 KO mice exhibited reduced lipid droplet accumulation, decreased fatty acid uptake, and increased lipid secretion. Metabolomics showed hepatic enrichment of phospholipids in Mtarc1 KO mice.","method":"Mtarc1 KO mouse model; CDAHFD-induced MASLD model; primary hepatocyte isolation; lipid droplet imaging; fatty acid uptake assay; lipid secretion assay; untargeted metabolomics","journal":"Liver International","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse model with primary hepatocyte mechanistic follow-up and metabolomics, multiple orthogonal functional readouts","pmids":["41527487"],"is_preprint":false}],"current_model":"MTARC1 (mARC1) is a molybdenum cofactor-containing enzyme anchored to the outer mitochondrial membrane (N-in, C-out orientation) that catalyzes N-reductive reactions—including reduction of N-oxygenated compounds and nitrite-to-NO conversion via its molybdenum active site in concert with cytochrome b5/NADH cytochrome b5 reductase—and in hepatocytes regulates lipid droplet homeostasis by suppressing glycerophospholipid biosynthesis (via CEPT1/PEMT), such that mARC1 loss remodels lipid droplet phospholipid composition, reduces droplet size, and promotes triglyceride clearance through lipolysis and lipophagy, with the clinically protective p.A165T variant acting primarily by destabilizing the protein."},"narrative":{"mechanistic_narrative":"MTARC1 (mARC1) is a molybdenum cofactor-containing N-reductive enzyme of the outer mitochondrial membrane that has emerged as a hepatic regulator of lipid droplet homeostasis and a genetically validated protective target in fatty liver disease [PMID:23086957, PMID:37122688, PMID:41641916]. It is a signal-anchored protein with an N(in)-C(out) orientation, exposing its C-terminal catalytic domain to the cytosol and assembling into high-oligomeric complexes [PMID:23086957]. Its catalytic activity derives from a molybdenum cofactor coordinated by Cys-273; mARC1 reduces N-hydroxylated and N-oxygenated substrates such as benzamidoxime and N-hydroxyurea, and converts nitrite to nitric oxide, operating in an electron-transfer chain with cytochrome b5 and NADH cytochrome b5 reductase [PMID:24500710, PMID:24423752, PMID:30397129, PMID:39397364]. In hepatocytes, mARC1 loss reduces triglyceride and neutral lipid accumulation while enhancing fatty acid β-oxidation and lipid secretion, lowering mitochondrial superoxide and ferroptosis under lipotoxic stress and attenuating steatosis, inflammation, and fibrosis across MASH/MASLD models [PMID:37122688, PMID:39716370, PMID:39927988, PMID:41527487]. Mechanistically, MTARC1 deficiency post-transcriptionally upregulates the glycerophospholipid biosynthetic enzymes CEPT1 and PEMT, remodeling lipid droplet phospholipid composition to reduce droplet size and promote degradation via lipolysis and lipophagy, an effect reversed by CEPT1 or PEMT knockdown [PMID:41641916]. The clinically protective p.A165T variant acts primarily by destabilizing the protein and reducing its levels without altering the fold or active-site architecture, and rare loss-of-function variants are similarly hepatoprotective [PMID:35560545, PMID:38340654, PMID:38437227]. mARC1 loss also suppresses proliferation and migration in hepatocellular carcinoma models [PMID:41644117].","teleology":[{"year":2012,"claim":"Established where mARC1 resides and how it is targeted, defining it as an outer mitochondrial membrane protein with a cytosol-facing catalytic domain.","evidence":"Subcellular fractionation, protease protection, truncation constructs, and ATP/membrane-potential-dependent import assays","pmids":["23086957"],"confidence":"High","gaps":["Functional consequence of high-oligomeric assembly not defined","No catalytic substrate identified at this stage"]},{"year":2014,"claim":"Defined the catalytic chemistry of mARC1 as molybdenum-dependent N-reduction and nitrite-to-NO conversion within a cytochrome b5/b5 reductase electron-transfer chain.","evidence":"In vitro reconstitution with recombinant protein, C273A active-site mutagenesis, tungsten cofactor substitution, and benzamidoxime kinetics","pmids":["24500710","24423752"],"confidence":"High","gaps":["Physiological substrates in vivo not established","A165T showed no kinetic alteration, leaving its disease mechanism unexplained"]},{"year":2018,"claim":"Provided the structural basis of catalysis, placing mARC1 in the MOSC domain superfamily and defining molybdenum cofactor coordination and paralog-distinguishing active-site residues.","evidence":"High-resolution X-ray crystallography with active-site interpretation","pmids":["30397129"],"confidence":"High","gaps":["No structure of substrate-bound complex","Mechanism of partner electron-transfer coupling not resolved structurally"]},{"year":2023,"claim":"Connected mARC1 to hepatic lipid metabolism by showing hepatocyte-specific knockdown lowers liver triglycerides while raising secretion and altering ketogenesis.","evidence":"GalNAc-siRNA knockdown in a NASH mouse model and primary human hepatocytes with metabolic readouts and RNA-seq","pmids":["37122688"],"confidence":"High","gaps":["Molecular link between N-reductase activity and lipid handling unresolved","Increased plasma triglyceride consequence not mechanistically explained"]},{"year":2024,"claim":"Resolved how the protective p.A165T variant works—by destabilizing the protein and causing aberrant localization rather than altering catalysis—and showed loss-of-function is hepatoprotective in humans.","evidence":"Variant crystallography, protein stability reporter assays across cell lines, knock-in/KO mouse models, localization studies, and exome-wide association (n=540,000)","pmids":["35560545","38340654","38437227"],"confidence":"Medium","gaps":["Mouse-human divergence (Marc2 dominance) complicates modeling","Degradation pathway clearing the unstable variant not identified"]},{"year":2024,"claim":"Demonstrated that mARC1 loss reduces hepatic lipid burden by enhancing β-oxidation and lowers oxidative stress, ferroptosis, and fibrosis across multiple disease models.","evidence":"siRNA knockdown and global/conditional KO in MASH/MASLD mouse models and primary human hepatocytes with radiolabeled β-oxidation, bioenergetics, mitochondrial superoxide assays, multi-omics, and UK Biobank metabolomics","pmids":["38696369","39716370","39927988","38619429"],"confidence":"High","gaps":["Allele-specific effect (risk-allele homozygotes) not fully mechanistically dissected","Direct enzymatic substrate driving lipid phenotype not identified"]},{"year":2024,"claim":"Refined substrate specificity by establishing mARC1 as the dominant reductase inactivating N-hydroxyurea, distinguishing it from mARC2.","evidence":"In vitro reductive assays with recombinant mARC1 and mARC2 plus in vivo metabolic studies","pmids":["39397364"],"confidence":"Medium","gaps":["Single lab","Broader endogenous N-hydroxylated substrate repertoire not mapped"]},{"year":2026,"claim":"Defined the mechanistic axis linking mARC1 to lipid droplet turnover: MTARC1 deficiency post-transcriptionally upregulates CEPT1/PEMT, remodeling droplet phospholipids to drive lipolysis and lipophagy.","evidence":"Global/liver-specific KO mice with epistatic Cept1/Pemt/Pnpla2/Lipa inhibition, multi-omics, and LD size quantification with rescue/reversal experiments","pmids":["41641916","41527487"],"confidence":"High","gaps":["Mechanism by which mARC1 controls CEPT1/PEMT post-transcriptionally is unknown","Whether this axis requires mARC1 catalytic activity is not established"]},{"year":2026,"claim":"Extended mARC1 function to oncology, showing its loss suppresses HCC proliferation, migration, and lipid accumulation in vitro and in xenografts.","evidence":"siRNA and CRISPR-Cas9 KO across HCC cell lines, β-oxidation and migration assays, xenograft model, and proteomics","pmids":["41644117"],"confidence":"Medium","gaps":["Single lab","Direct molecular driver of the anti-proliferative effect not defined"]},{"year":null,"claim":"It remains unknown how mARC1's molybdenum-dependent N-reductase catalysis mechanistically connects to its control of CEPT1/PEMT and lipid droplet homeostasis, and whether the metabolic phenotype requires catalytic turnover or merely protein presence.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No identified endogenous substrate links catalysis to lipid phenotype","Post-transcriptional control of CEPT1/PEMT is undefined","Causal role of catalysis versus scaffolding in lipid handling unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[1,2,3,10]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[1,2,10]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,11]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,9,13]}],"complexes":[],"partners":["CYB5B","CYB5R3","CEPT1","PEMT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5VT66","full_name":"Mitochondrial amidoxime-reducing component 1","aliases":["Molybdenum cofactor sulfurase C-terminal domain-containing protein 1","MOSC domain-containing protein 1","Moco sulfurase C-terminal domain-containing protein 1"],"length_aa":337,"mass_kda":37.5,"function":"Catalyzes the reduction of N-oxygenated molecules, acting as a counterpart of cytochrome P450 and flavin-containing monooxygenases in metabolic cycles (PubMed:19053771, PubMed:21029045, PubMed:30397129). As a component of prodrug-converting system, reduces a multitude of N-hydroxylated prodrugs particularly amidoximes, leading to increased drug bioavailability (PubMed:19053771). May be involved in mitochondrial N(omega)-hydroxy-L-arginine (NOHA) reduction, regulating endogenous nitric oxide levels and biosynthesis (PubMed:21029045). Postulated to cleave the N-OH bond of N-hydroxylated substrates in concert with electron transfer from NADH to cytochrome b5 reductase then to cytochrome b5, the ultimate electron donor that primes the active site for substrate reduction (PubMed:19053771, PubMed:21029045)","subcellular_location":"Mitochondrion outer membrane; Membrane","url":"https://www.uniprot.org/uniprotkb/Q5VT66/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MTARC1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1090,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MTARC1","total_profiled":1310},"omim":[{"mim_id":"614126","title":"MITOCHONDRIAL AMIDOXIME-REDUCING COMPONENT 1; MTARC1","url":"https://www.omim.org/entry/614126"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"adipose tissue","ntpm":160.5},{"tissue":"breast","ntpm":74.8},{"tissue":"liver","ntpm":79.5}],"url":"https://www.proteinatlas.org/search/MTARC1"},"hgnc":{"alias_symbol":["FLJ22390"],"prev_symbol":["MOSC1","MARC1"]},"alphafold":{"accession":"Q5VT66","domains":[{"cath_id":"2.40.33.20","chopping":"55-335","consensus_level":"medium","plddt":97.5536,"start":55,"end":335}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VT66","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VT66-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VT66-F1-predicted_aligned_error_v6.png","plddt_mean":91.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MTARC1","jax_strain_url":"https://www.jax.org/strain/search?query=MTARC1"},"sequence":{"accession":"Q5VT66","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5VT66.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5VT66/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VT66"}},"corpus_meta":[{"pmid":"24500710","id":"PMC_24500710","title":"Nitrite reductase and nitric-oxide synthase activity of the mitochondrial molybdopterin enzymes mARC1 and mARC2.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24500710","citation_count":130,"is_preprint":false},{"pmid":"32561361","id":"PMC_32561361","title":"Genome-Wide Association Study for Alcohol-Related Cirrhosis Identifies Risk Loci in MARC1 and HNRNPUL1.","date":"2020","source":"Gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/32561361","citation_count":70,"is_preprint":false},{"pmid":"23086957","id":"PMC_23086957","title":"The mitochondrial amidoxime-reducing component (mARC1) is a novel signal-anchored protein of the outer mitochondrial membrane.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23086957","citation_count":63,"is_preprint":false},{"pmid":"30397129","id":"PMC_30397129","title":"Crystal structure of human mARC1 reveals its exceptional position among eukaryotic molybdenum enzymes.","date":"2018","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/30397129","citation_count":43,"is_preprint":false},{"pmid":"37122688","id":"PMC_37122688","title":"Hepatocyte mARC1 promotes fatty liver disease.","date":"2023","source":"JHEP reports : innovation in hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/37122688","citation_count":33,"is_preprint":false},{"pmid":"38619429","id":"PMC_38619429","title":"mARC1 in MASLD: Modulation of lipid accumulation in human hepatocytes and adipocytes.","date":"2024","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/38619429","citation_count":15,"is_preprint":false},{"pmid":"24423752","id":"PMC_24423752","title":"Functional characterization of protein variants encoded by nonsynonymous single nucleotide polymorphisms in MARC1 and MARC2 in healthy Caucasians.","date":"2014","source":"Drug metabolism and disposition: the biological fate of chemicals","url":"https://pubmed.ncbi.nlm.nih.gov/24423752","citation_count":15,"is_preprint":false},{"pmid":"35560545","id":"PMC_35560545","title":"Letter to the editor: The clinically relevant MTARC1 p.Ala165Thr variant impacts neither the fold nor active site architecture of the human mARC1 protein.","date":"2022","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/35560545","citation_count":14,"is_preprint":false},{"pmid":"38340654","id":"PMC_38340654","title":"Fatty liver disease protective MTARC1 p.A165T variant reduces the protein stability of MTARC1.","date":"2024","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/38340654","citation_count":11,"is_preprint":false},{"pmid":"39716370","id":"PMC_39716370","title":"Downregulation of the MARC1 p.A165 risk allele reduces hepatocyte lipid content by increasing beta-oxidation.","date":"2024","source":"Clinical and molecular hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/39716370","citation_count":11,"is_preprint":false},{"pmid":"38437227","id":"PMC_38437227","title":"Divergent role of Mitochondrial Amidoxime Reducing Component 1 (MARC1) in human and mouse.","date":"2024","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38437227","citation_count":10,"is_preprint":false},{"pmid":"38696369","id":"PMC_38696369","title":"Liver-specific mitochondrial amidoxime-reducing component 1 (Mtarc1) knockdown protects the liver from diet-induced MASH in multiple mouse models.","date":"2024","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/38696369","citation_count":10,"is_preprint":false},{"pmid":"29964053","id":"PMC_29964053","title":"High expression of enhancer RNA MARC1 or its activation by DHT is associated with the malignant behavior in bladder cancer.","date":"2018","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/29964053","citation_count":7,"is_preprint":false},{"pmid":"39927988","id":"PMC_39927988","title":"Loss of mitochondrial amidoxime-reducing component 1 (mARC1) prevents disease progression by reducing fibrosis in multiple mouse models of chronic liver disease.","date":"2025","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/39927988","citation_count":6,"is_preprint":false},{"pmid":"40650184","id":"PMC_40650184","title":"Polymorphism's MBOAT7 as Risk and MTARC1 as Protection for Liver Fibrosis in MASLD.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40650184","citation_count":4,"is_preprint":false},{"pmid":"41527487","id":"PMC_41527487","title":"Loss of Mtarc1 Protects Against Steatotic Liver Disease in Mice.","date":"2026","source":"Liver international : official journal of the International Association for the Study of the Liver","url":"https://pubmed.ncbi.nlm.nih.gov/41527487","citation_count":2,"is_preprint":false},{"pmid":"39397364","id":"PMC_39397364","title":"mARC1 Is the Main Contributor to Metabolic Reduction of N-Hydroxyurea.","date":"2024","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39397364","citation_count":1,"is_preprint":false},{"pmid":"41644117","id":"PMC_41644117","title":"MTARC1 p.A165 ablation reduces hepatocellular carcinoma aggressiveness in vitro and in vivo.","date":"2026","source":"Clinical and molecular hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/41644117","citation_count":0,"is_preprint":false},{"pmid":"39094505","id":"PMC_39094505","title":"Generation of an induced pluripotent stem cell (iPSC) line (EXSURGi001-A) from a patient homozygous for the p.Ala165Thr mutation in the MTARC1 gene.","date":"2024","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/39094505","citation_count":0,"is_preprint":false},{"pmid":"41641916","id":"PMC_41641916","title":"MTARC1 Inactivation Remodels Lipid Droplets to Protect Against Metabolic Fatty Liver Disease.","date":"2026","source":"Liver international : official journal of the International Association for the Study of the Liver","url":"https://pubmed.ncbi.nlm.nih.gov/41641916","citation_count":0,"is_preprint":false},{"pmid":"41428769","id":"PMC_41428769","title":"A mitochondrial amidoxime-reducing component 1 (mARC1) A168T amino acid substitution does not confer protection from MASH and fibrosis in multiple mouse models of chronic liver disease.","date":"2026","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/41428769","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.17.665462","title":"MTARC1 Regulates Lipid Droplet Degradation via Phospholipid Remodeling in Metabolic Fatty Liver Disease","date":"2025-07-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.17.665462","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13911,"output_tokens":4654,"usd":0.055772,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12892,"output_tokens":3293,"usd":0.073392,"stage2_stop_reason":"end_turn"},"total_usd":0.129164,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"mARC1 is a signal-anchored protein of the outer mitochondrial membrane with an N(in)-C(out) membrane orientation; the N-terminal transmembrane helix is sufficient for mitochondrial targeting, the N-terminal targeting signal acts as a supportive receptor, membrane integration is membrane-potential-independent but requires external ATP, and the protein assembles into high-oligomeric complexes. The C-terminal catalytic domain is exposed to the cytosol.\",\n      \"method\": \"Subcellular fractionation, protease protection assays, deletion/truncation constructs, live-cell imaging, mitochondrial import assays with ATP depletion and membrane-potential uncouplers\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, protease protection, import assays, truncation mutants) in a single focused study establishing localization and targeting mechanism\",\n      \"pmids\": [\"23086957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human mARC1 catalyzes reduction of nitrite to nitric oxide (NO) through its molybdenum cofactor; this activity requires Cys-273 (molybdenum-coordinating residue) as the C273A mutation abolishes NO formation. Replacement of molybdenum with tungsten also abolishes NO formation. mARC1 generates NO from nitrite in an electron transfer chain with NADH, cytochrome b5, and NADH-dependent cytochrome b5 reductase, with rate increasing ~3-fold at pH 6.5 vs 7.5.\",\n      \"method\": \"In vitro nitrite reduction assay with recombinant protein; active-site mutagenesis (C273A); tungsten substitution of molybdenum; lentiviral mARC1 expression in HEK cells with NO detection; Km/Vmax determination\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with active-site mutagenesis and cofactor substitution, multiple orthogonal approaches confirming molybdenum-dependent nitrite reduction\",\n      \"pmids\": [\"24500710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"mARC1 functions as part of an N-reductive enzyme system together with cytochrome b5 type B and NADH cytochrome b5 reductase to reduce N-hydroxylated compounds (benzamidoxime). SNP variants in MARC1 encoding A165T showed no altered kinetic parameters in benzamidoxime N-reduction, while multiple simultaneous amino acid substitutions reduced N-reductive activity ~5-fold.\",\n      \"method\": \"Recombinant protein expression in E. coli; in vitro steady-state enzyme kinetics with benzamidoxime; molybdenum quantification by ICP-MS; pyrosequencing-based genotyping\",\n      \"journal\": \"Drug Metabolism and Disposition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinetic assay with defined substrates, single lab, multiple SNP variants tested\",\n      \"pmids\": [\"24423752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of human mARC1 was solved at high resolution, revealing the coordination geometry of the molybdenum cofactor (Moco), identifying two key active-site residues that distinguish mARC paralogs, and demonstrating that mARC1 belongs to the MOSC domain superfamily. The structure defines the catalytic mechanism for reduction of N-oxygenated compounds and provides evidence for an evolutionary relationship to the xanthine oxidase superfamily.\",\n      \"method\": \"X-ray crystallography (high-resolution crystal structure); structural comparison with in silico domain predictions; functional interpretation of active-site architecture\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure with active-site identification and mutagenesis-informed mechanistic interpretation\",\n      \"pmids\": [\"30397129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure of the mARC1 p.A165T variant protein at near-atomic resolution shows that this clinically protective variant does not alter the overall protein fold or active-site architecture compared to wildtype mARC1.\",\n      \"method\": \"X-ray crystallography of variant protein; structural comparison to wildtype crystal structure\",\n      \"journal\": \"Hepatology Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure of variant, single lab, no functional assay accompanying the structural data reported in abstract\",\n      \"pmids\": [\"35560545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Hepatocyte-specific mARC1 knockdown (via GalNAc-siRNA in a NASH mouse model) reduced hepatic triglyceride accumulation but increased plasma triglycerides; in primary human hepatocytes, mARC1 knockdown decreased lipid accumulation and increased triglyceride secretion. mARC1 knockdown also decreased secretion of 3-hydroxybutyrate (a β-oxidation marker) in vitro and in vivo, implicating mARC1 in hepatic lipid metabolism and ketogenesis.\",\n      \"method\": \"GalNAc-siRNA hepatocyte-specific knockdown in GAN-diet NASH mouse model; primary human hepatocyte in vitro model with siRNA KD; metabolic readouts (triglycerides, 3-hydroxybutyrate); RNA-sequencing pathway analysis\",\n      \"journal\": \"JHEP Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — hepatocyte-specific in vivo knockdown with defined metabolic phenotype corroborated by in vitro primary human hepatocyte model, replicated across multiple readouts\",\n      \"pmids\": [\"37122688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The protective MTARC1 p.A165T variant causes dramatically reduced protein stability of mARC1 (assessed by protein stability reporter system in multiple cell lines and in mouse liver), without altering mRNA levels. Multiple substitutions at position A165 (A165S, A165N, A165V, A165G, A165D) similarly reduced stability, indicating A165 is essential for mARC1 protein stability.\",\n      \"method\": \"Protein stability reporter system in multiple cell lines; murine knock-in model (A168T equivalent); Western blot; mutagenesis of A165 to multiple residues\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — stability reporter system with multiple cell lines and in vivo mouse model, single lab, replicated across multiple substitutions\",\n      \"pmids\": [\"38340654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The protective p.A165T substitution causes protein instability and aberrant localization of mARC1 in hepatic cells. Novel rare putative loss-of-function MARC1 variants identified by exome-wide association study show a phenotype similar to p.A165T/p.M187K variants, consistent with loss-of-function being hepatoprotective. Marc1 knockout mice, unlike human carriers, do not show protection against hepatic triglyceride accumulation, revealing a divergent physiological role between human and mouse (attributed to Marc2 being the dominant paralog in mouse liver).\",\n      \"method\": \"Exome-wide association study (n=540,000); in vitro expression of recombinant human MARC1 A165T with localization studies in hepatic cells; Marc1 knockout mouse generation; liver phenotype assessment in KO mice on steatogenic diet\",\n      \"journal\": \"PLoS Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — recombinant protein localization studies combined with KO mouse model, single lab, two orthogonal approaches\",\n      \"pmids\": [\"38437227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hepatocyte-specific Mtarc1 siRNA knockdown in ob/ob and diet-induced MASH mouse models reduced serum liver enzymes, LDL-cholesterol, liver triglycerides, liver weight, and attenuated liver pathological changes. Multi-omics (metabolomics, proteomics, lipidomics) analysis showed that Mtarc1 knockdown partially restored diet-altered metabolites and lipids.\",\n      \"method\": \"GalNAc-conjugated siRNA hepatocyte-specific knockdown in ob/ob and diet-induced MASH mouse models; multi-omics (metabolomics, proteomics, lipidomics); histology; serum biochemistry\",\n      \"journal\": \"Hepatology Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — hepatocyte-specific in vivo knockdown in multiple mouse models with comprehensive multi-omics readouts, replicated across models\",\n      \"pmids\": [\"38696369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"mARC1 siRNA knockdown in primary human hepatocytes reduced neutral lipid content specifically in cells homozygous for the risk allele (p.A165), and this reduction was mediated by increased fatty acid β-oxidation (measured by radiolabeled tracer). mARC1 knockdown also reduced ferroptosis and reactive oxygen species levels. In human UK Biobank participants, carriers of the rs2642438 minor allele had higher circulating 3-hydroxybutyrate levels, consistent with increased β-oxidation.\",\n      \"method\": \"siRNA knockdown in primary human hepatocytes; radiolabeled fatty acid oxidation assay; Oil-Red O staining; RNA-sequencing and LC-MS proteomics; UK Biobank metabolomics\",\n      \"journal\": \"Clinical and Molecular Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct measurement of β-oxidation with radiolabeled tracers in primary human hepatocytes, supported by human metabolomics data and proteomic/transcriptomic profiling\",\n      \"pmids\": [\"39716370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"mARC1 is the main contributor to reductive biotransformation of N-hydroxyurea (NHU) to urea; in vitro and in vivo evidence establishes that this N-reductive activity is specifically mediated by mARC1 (not mARC2), suggesting mARC1-mediated inactivation as a pharmacological mechanism requiring high doses of hydroxyurea in therapy.\",\n      \"method\": \"In vitro N-reductive assay with recombinant mARC1 and mARC2; in vivo metabolic studies; substrate specificity determination\",\n      \"journal\": \"Journal of Medicinal Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assay with in vivo corroboration, single lab\",\n      \"pmids\": [\"39397364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"mARC1 depletion improved cellular bioenergetics and decreased mitochondrial superoxide production in response to lipotoxic stress in cells. The p.A165T variant maintains mitochondrial localization despite lower protein levels. Global or hepatocyte-specific mARC1 deletion in mice reduced liver steatosis and fibrosis in multiple MASH and liver fibrosis models. RNA-seq showed downregulation of extracellular matrix remodeling and collagen formation pathways upon mARC1 loss.\",\n      \"method\": \"mARC1 knockdown/KO in cells with bioenergetics and mitochondrial superoxide assays; global and conditional KO mice on diet-induced MASH models; RNA-seq; plasma lipidomics; histology\",\n      \"journal\": \"Hepatology Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (bioenergetics, mitochondrial ROS, global and conditional KO in multiple mouse models, transcriptomics, lipidomics) in a single study\",\n      \"pmids\": [\"39927988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"mARC1 modulates lipid accumulation in primary human hepatocytes and primary human adipocytes; mARC1 depletion affects accumulation of distinct lipid species and expression of inflammatory and mitochondrial pathway genes/proteins in both in vitro and in vivo models. Protective MTARC1 variants decrease protein accumulation in overexpression systems (without altering mRNA). A plasma lipid biomarker (Ceramide 22:1) predictive of mARC1 abundance was identified.\",\n      \"method\": \"siRNA knockdown and lentiviral overexpression in primary human hepatocytes, hepatocyte cell lines, and primary human adipocytes; in vivo murine MASH model with GalNAc-siRNA; lipidomics; proteomics; transcriptomics\",\n      \"journal\": \"Hepatology Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cell types and in vivo model, single lab, lipidomics and proteomics readouts\",\n      \"pmids\": [\"38619429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MTARC1 deficiency post-transcriptionally upregulates glycerophospholipid (GPL) biosynthetic enzymes CEPT1 and PEMT, leading to altered phospholipid composition in lipid droplets (LDs). This phospholipid remodeling reduces LD size, increases surface-to-volume ratio, and thereby enhances LD degradation via lipolysis and lipophagy. Knockdown of CEPT1 or PEMT reversed the hepatoprotective effects of MTARC1 deficiency, establishing an MTARC1-GPL biosynthesis-LD degradation axis.\",\n      \"method\": \"Global and liver-specific Mtarc1 KO mice; genetic inhibition of Pnpla2, Lipa, Pemt, Cept1; multi-omics (biochemical, histological, lipidomics, proteomics); in vitro cell culture mechanistic studies; LD size/number quantification\",\n      \"journal\": \"Liver International\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis via double KO (Mtarc1 + CEPT1/PEMT), multiple orthogonal omics in both in vitro and in vivo models, functional rescue/reversal experiments\",\n      \"pmids\": [\"41641916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MTARC1 knockdown in HCC cell lines (Hep3B2, HuH7, HepG2, HepaRG) reduced proliferation; CRISPR-Cas9 KO in Hep3B2 cells decreased neutral lipid accumulation, enhanced β-oxidation, and reduced cell migration. MTARC1 KO xenograft tumors showed reduced volume. Proteomics revealed inhibition of oncogenic pathways and activation of anti-proliferative proteins upon MTARC1 loss.\",\n      \"method\": \"siRNA knockdown in multiple HCC cell lines; CRISPR-Cas9 KO; lipid accumulation assay; β-oxidation assay; migration assay; subcutaneous xenograft mouse model; global proteomics\",\n      \"journal\": \"Clinical and Molecular Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with defined cellular and in vivo phenotype, multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"41644117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Mtarc1 KO mice on choline-deficient high-fat diet showed reduced liver steatosis, pro-fibrosis markers, and inflammation. Primary hepatocytes from Mtarc1 KO mice exhibited reduced lipid droplet accumulation, decreased fatty acid uptake, and increased lipid secretion. Metabolomics showed hepatic enrichment of phospholipids in Mtarc1 KO mice.\",\n      \"method\": \"Mtarc1 KO mouse model; CDAHFD-induced MASLD model; primary hepatocyte isolation; lipid droplet imaging; fatty acid uptake assay; lipid secretion assay; untargeted metabolomics\",\n      \"journal\": \"Liver International\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse model with primary hepatocyte mechanistic follow-up and metabolomics, multiple orthogonal functional readouts\",\n      \"pmids\": [\"41527487\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MTARC1 (mARC1) is a molybdenum cofactor-containing enzyme anchored to the outer mitochondrial membrane (N-in, C-out orientation) that catalyzes N-reductive reactions—including reduction of N-oxygenated compounds and nitrite-to-NO conversion via its molybdenum active site in concert with cytochrome b5/NADH cytochrome b5 reductase—and in hepatocytes regulates lipid droplet homeostasis by suppressing glycerophospholipid biosynthesis (via CEPT1/PEMT), such that mARC1 loss remodels lipid droplet phospholipid composition, reduces droplet size, and promotes triglyceride clearance through lipolysis and lipophagy, with the clinically protective p.A165T variant acting primarily by destabilizing the protein.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MTARC1 (mARC1) is a molybdenum cofactor-containing N-reductive enzyme of the outer mitochondrial membrane that has emerged as a hepatic regulator of lipid droplet homeostasis and a genetically validated protective target in fatty liver disease [#0, #5, #13]. It is a signal-anchored protein with an N(in)-C(out) orientation, exposing its C-terminal catalytic domain to the cytosol and assembling into high-oligomeric complexes [#0]. Its catalytic activity derives from a molybdenum cofactor coordinated by Cys-273; mARC1 reduces N-hydroxylated and N-oxygenated substrates such as benzamidoxime and N-hydroxyurea, and converts nitrite to nitric oxide, operating in an electron-transfer chain with cytochrome b5 and NADH cytochrome b5 reductase [#1, #2, #3, #10]. In hepatocytes, mARC1 loss reduces triglyceride and neutral lipid accumulation while enhancing fatty acid β-oxidation and lipid secretion, lowering mitochondrial superoxide and ferroptosis under lipotoxic stress and attenuating steatosis, inflammation, and fibrosis across MASH/MASLD models [#5, #9, #11, #15]. Mechanistically, MTARC1 deficiency post-transcriptionally upregulates the glycerophospholipid biosynthetic enzymes CEPT1 and PEMT, remodeling lipid droplet phospholipid composition to reduce droplet size and promote degradation via lipolysis and lipophagy, an effect reversed by CEPT1 or PEMT knockdown [#13]. The clinically protective p.A165T variant acts primarily by destabilizing the protein and reducing its levels without altering the fold or active-site architecture, and rare loss-of-function variants are similarly hepatoprotective [#4, #6, #7]. mARC1 loss also suppresses proliferation and migration in hepatocellular carcinoma models [#14].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established where mARC1 resides and how it is targeted, defining it as an outer mitochondrial membrane protein with a cytosol-facing catalytic domain.\",\n      \"evidence\": \"Subcellular fractionation, protease protection, truncation constructs, and ATP/membrane-potential-dependent import assays\",\n      \"pmids\": [\"23086957\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of high-oligomeric assembly not defined\", \"No catalytic substrate identified at this stage\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the catalytic chemistry of mARC1 as molybdenum-dependent N-reduction and nitrite-to-NO conversion within a cytochrome b5/b5 reductase electron-transfer chain.\",\n      \"evidence\": \"In vitro reconstitution with recombinant protein, C273A active-site mutagenesis, tungsten cofactor substitution, and benzamidoxime kinetics\",\n      \"pmids\": [\"24500710\", \"24423752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates in vivo not established\", \"A165T showed no kinetic alteration, leaving its disease mechanism unexplained\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Provided the structural basis of catalysis, placing mARC1 in the MOSC domain superfamily and defining molybdenum cofactor coordination and paralog-distinguishing active-site residues.\",\n      \"evidence\": \"High-resolution X-ray crystallography with active-site interpretation\",\n      \"pmids\": [\"30397129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of substrate-bound complex\", \"Mechanism of partner electron-transfer coupling not resolved structurally\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected mARC1 to hepatic lipid metabolism by showing hepatocyte-specific knockdown lowers liver triglycerides while raising secretion and altering ketogenesis.\",\n      \"evidence\": \"GalNAc-siRNA knockdown in a NASH mouse model and primary human hepatocytes with metabolic readouts and RNA-seq\",\n      \"pmids\": [\"37122688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between N-reductase activity and lipid handling unresolved\", \"Increased plasma triglyceride consequence not mechanistically explained\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved how the protective p.A165T variant works—by destabilizing the protein and causing aberrant localization rather than altering catalysis—and showed loss-of-function is hepatoprotective in humans.\",\n      \"evidence\": \"Variant crystallography, protein stability reporter assays across cell lines, knock-in/KO mouse models, localization studies, and exome-wide association (n=540,000)\",\n      \"pmids\": [\"35560545\", \"38340654\", \"38437227\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mouse-human divergence (Marc2 dominance) complicates modeling\", \"Degradation pathway clearing the unstable variant not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated that mARC1 loss reduces hepatic lipid burden by enhancing β-oxidation and lowers oxidative stress, ferroptosis, and fibrosis across multiple disease models.\",\n      \"evidence\": \"siRNA knockdown and global/conditional KO in MASH/MASLD mouse models and primary human hepatocytes with radiolabeled β-oxidation, bioenergetics, mitochondrial superoxide assays, multi-omics, and UK Biobank metabolomics\",\n      \"pmids\": [\"38696369\", \"39716370\", \"39927988\", \"38619429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Allele-specific effect (risk-allele homozygotes) not fully mechanistically dissected\", \"Direct enzymatic substrate driving lipid phenotype not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined substrate specificity by establishing mARC1 as the dominant reductase inactivating N-hydroxyurea, distinguishing it from mARC2.\",\n      \"evidence\": \"In vitro reductive assays with recombinant mARC1 and mARC2 plus in vivo metabolic studies\",\n      \"pmids\": [\"39397364\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Broader endogenous N-hydroxylated substrate repertoire not mapped\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined the mechanistic axis linking mARC1 to lipid droplet turnover: MTARC1 deficiency post-transcriptionally upregulates CEPT1/PEMT, remodeling droplet phospholipids to drive lipolysis and lipophagy.\",\n      \"evidence\": \"Global/liver-specific KO mice with epistatic Cept1/Pemt/Pnpla2/Lipa inhibition, multi-omics, and LD size quantification with rescue/reversal experiments\",\n      \"pmids\": [\"41641916\", \"41527487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which mARC1 controls CEPT1/PEMT post-transcriptionally is unknown\", \"Whether this axis requires mARC1 catalytic activity is not established\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended mARC1 function to oncology, showing its loss suppresses HCC proliferation, migration, and lipid accumulation in vitro and in xenografts.\",\n      \"evidence\": \"siRNA and CRISPR-Cas9 KO across HCC cell lines, β-oxidation and migration assays, xenograft model, and proteomics\",\n      \"pmids\": [\"41644117\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct molecular driver of the anti-proliferative effect not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how mARC1's molybdenum-dependent N-reductase catalysis mechanistically connects to its control of CEPT1/PEMT and lipid droplet homeostasis, and whether the metabolic phenotype requires catalytic turnover or merely protein presence.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified endogenous substrate links catalysis to lipid phenotype\", \"Post-transcriptional control of CEPT1/PEMT is undefined\", \"Causal role of catalysis versus scaffolding in lipid handling unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [1, 2, 3, 10]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [1, 2, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 9, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CYB5B\", \"CYB5R3\", \"CEPT1\", \"PEMT\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}