{"gene":"CYB5R3","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2022,"finding":"CYB5R3 is a UFM1 substrate on the ER membrane; ufmylation of CYB5R3 by the E3 components UFL1 and UFBP1 converts CYB5R3 to an inactive form, which is then recognized by UFBP1 via a UFM1-interacting motif and degraded in lysosomes in an Atg7- and CDK5RAP3-dependent manner, thereby inducing ER-phagy required for brain development.","method":"Substrate identification by mass spectrometry/biochemical screening; co-immunoprecipitation; ufmylation-defective Cyb5r3 knock-in mice showing microcephaly; lysosomal degradation assays; genetic epistasis with Atg7 and CDK5RAP3","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (substrate ID, Co-IP, enzymatic inactivation, knock-in mouse phenotype, lysosomal degradation assay, adaptor requirement) in a single rigorous study","pmids":["36543799"],"is_preprint":false},{"year":2019,"finding":"Smooth muscle cell CYB5R3 acts as an sGC heme reductase in resistance arteries, reducing oxidized sGC heme (Fe3+→Fe2+) to maintain NO-dependent vasodilation; SMC-specific Cyb5r3 KO mice show elevated blood pressure and impaired acetylcholine-induced vasodilation, which is worsened by angiotensin II-induced oxidative stress and rescued by the heme-independent sGC activator BAY 58-2667.","method":"Conditional smooth muscle cell-specific Cyb5r3 knockout mouse; radiotelemetry blood pressure measurement; wire myography vasodilation assays; pharmacological rescue with BAY 58-2667","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined cellular phenotype, multiple vascular functional readouts, pharmacological epistasis, replicated across normotensive and hypertensive conditions","pmids":["31487266"],"is_preprint":false},{"year":2021,"finding":"CYB5R3 cooperates with NOX4 via coenzyme Q (CoQ) to regulate endothelial inflammatory activation: CYB5R3 localizes to the mitochondrial outer membrane where it physically interacts with NOX4, and CYB5R3 activity and membrane association are required for optimal NOX4-dependent H2O2 generation; loss of CYB5R3 shifts NOX4 output from H2O2 toward O2•-, enhancing VCAM-1 expression and endothelial dysfunction.","method":"Endothelial-specific conditional Cyb5r3 KO mice; siRNA knockdown in human aortic endothelial cells; APEX2-based electron microscopy and proximity biotinylation; proximity ligation assay; super-resolution confocal microscopy; ROS measurements; functional rescue with inactive or non-membrane-bound CYB5R3; COQ6 knockdown epistasis","journal":"Redox biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (proximity EM, proximity biotinylation, PLA, genetic KO, siRNA, structure-function rescue) in a single study establishing mechanism","pmids":["34656824"],"is_preprint":false},{"year":2022,"finding":"CYB5R3 is essential for cardiomyocyte redox homeostasis; cardiomyocyte-specific CYB5R3 KO in male mice causes cardiac hypertrophy, bradycardia, ventricular fibrillation, and sudden cardiac death associated with calcium mishandling, decreased ATP and CoQ levels, increased oxidative stress, and hemoprotein dysregulation. The missense variant T117S (rs1800457) encodes a partial loss-of-function protein.","method":"Conditional cardiomyocyte-specific CYB5R3 knockout mouse (males); echocardiography; telemetric ECG; calcium handling assays; CoQ quantification; ATP measurements; oxidative stress markers; functional characterization of T117S variant","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal phenotypic and molecular readouts; partial loss-of-function variant characterization","pmids":["36106636"],"is_preprint":false},{"year":2020,"finding":"Cyb5r3 links FoxO1 signaling to β-cell mitochondrial function: FoxO1-deficient β cells have reduced Cyb5r3 expression; β-cell-specific Cyb5r3 KO mice have impaired glucose-stimulated insulin secretion, glucose intolerance, and blunted mitochondrial respiratory response to glucose, with mitochondrial and secretory granule ultrastructural abnormalities; FoxO1 requires Cyb5r3 to maintain β-cell differentiation markers.","method":"β-cell-specific Cyb5r3 knockout mouse; glucose tolerance tests; insulin secretion assays; Seahorse respirometry; electron microscopy; FoxO1 genetic interaction studies; gene expression analysis","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal functional and ultrastructural readouts, genetic epistasis with FoxO1","pmids":["32180563"],"is_preprint":false},{"year":2023,"finding":"Cyb5r3 stabilizes glucokinase (Gck) through a glucose-dependent interaction, maintaining islet glucose utilization; chronic sulfonylurea exposure reduces Cyb5r3 abundance and impairs Gck stabilization; Cyb5r3 β-cell KO phenocopies secondary sulfonylurea failure; a Cyb5r3 activator rescues secondary sulfonylurea failure in mice and restores insulin secretion in human islets ex vivo.","method":"Co-immunoprecipitation (glucose-dependent Cyb5r3-Gck interaction); β-cell-specific Cyb5r3 KO mouse; ex vivo islet glucose utilization assays; pharmacological Cyb5r3 activator in vivo and in human islets","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct protein interaction by Co-IP, conditional KO phenocopy, pharmacological rescue in both mouse and human islets","pmids":["36724243"],"is_preprint":false},{"year":2014,"finding":"CYB5R3 deficiency decreases the NAD+/NADH ratio, mitochondrial respiration, ATP production, and mitochondrial electron transport chain activities, and increases oxidative stress and cellular senescence; CYB5R3 transcription is upregulated by FOXO3a and Nrf2 binding to antioxidant response elements in the CYB5R3 promoter, demonstrated by chromatin immunoprecipitation.","method":"CYB5R3-deficient cell lines; mitochondrial respiration and ATP assays; NAD+/NADH ratio measurements; β-galactosidase senescence assay; overexpression of FOXO3a and Nrf2; Nrf2 genetic ablation; chromatin immunoprecipitation of promoter elements","journal":"Antioxidants & redox signaling","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP, KO, KD, overexpression, metabolic assays) in a single lab study","pmids":["24450884"],"is_preprint":false},{"year":2021,"finding":"SMC CYB5R3 is required for NO-dependent vasodilation under chronic hypoxia; SMC-specific CYB5R3 KO mice under 3-week hypoxia develop greater biventricular hypertrophy and blunted NO-dependent vasodilation in coronary and pulmonary arteries compared to controls, implicating CYB5R3 as a sGC heme reductase protective against hypoxic cardiac remodeling.","method":"SMC-specific CYB5R3 KO mice; chronic hypoxia model; echocardiography; pressure-volume loops; wire myography of coronary and pulmonary arteries","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with in vivo functional readouts, single lab, extends prior sGC reductase mechanism to hypoxic context","pmids":["34536439"],"is_preprint":false},{"year":2023,"finding":"CYB5R3 in type II alveolar epithelial cells suppresses TGF-β1 signaling by regulating ERK1/2 phosphorylation and the sGC/cGMP/PKG axis; AECII-specific CYB5R3 deficiency leads to sustained TGF-β1 activation and increased lung fibrosis susceptibility; sGC agonists reduce fibrotic outcomes of AECII CYB5R3 deficiency in vivo.","method":"Conditional AECII-specific Cyb5r3 KO mice; bleomycin lung fibrosis model; ERK1/2 phosphorylation assays; cGMP measurements; sGC agonist pharmacological rescue in vivo","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined molecular pathway readouts and pharmacological rescue, single lab","pmids":["36749633"],"is_preprint":false},{"year":2024,"finding":"CYB5R3 overexpression in lung cancer cells induces ER stress-mediated apoptosis via PERK-ATF4 and IRE1α-JNK pathways; increased NAD+ production from CYB5R3 activates PARP16, which ADP-ribosylates PERK and IRE1α; CYB5R3 is predominantly localized to the ER and also induces ROS generation and caspase-9-dependent intrinsic apoptosis.","method":"Adenoviral CYB5R3 overexpression in lung cancer cells; transcriptome and metabolomic analysis; subcellular fractionation/immunofluorescence localization; PARP16 activity assays; PERK/IRE1α ADP-ribosylation assays; caspase activity assays; mouse xenograft tumor models","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (transcriptomics, metabolomics, biochemical pathway assays, in vivo), single lab","pmids":["38253797"],"is_preprint":false},{"year":2020,"finding":"GGPP prenylates CYB5R3 and the prenylated form translocates from the mitochondrial to the ER pool; CYB5R3 is identified as an NADH-dependent reductase necessary for eicosanoid metabolism in the ER; GGPP depletion (via GGPPS deletion) inhibits CYB5R3 translocation and disrupts eicosanoid metabolism, causing metaflammation.","method":"GGPPS knockout cell line; CYB5R3 subcellular fractionation; prenylation assays; eicosanoid metabolite profiling; simvastatin pharmacological inhibition","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — genetic KO model with subcellular fractionation and metabolic readouts, single lab, moderate mechanistic depth","pmids":["32913122"],"is_preprint":false},{"year":2025,"finding":"CYB5R3 loss in endothelial cells activates a Ca2+ influx pathway: CYB5R3 deficiency upregulates ORAI2, ORAI3, and TRPV2; loss of CYB5R3 increases Ca2+ entry through CRAC channels and TRPV2 upon ER Ca2+ store depletion; mechanistically, CYB5R3 loss increases NO production via CRAC channels, which oxidatively inhibits PTPN1, preventing TRPV2 dephosphorylation and sustaining JAK1-dependent TRPV2 activation; endothelial Cyb5r3 KO in vivo enhances acetylcholine-induced vasorelaxation and exercise capacity.","method":"siRNA knockdown and endothelial-specific Cyb5r3 KO mice; Ca2+ imaging; pharmacological SOCE blockers; TRPV2 genetic knockdown and inhibition; PTPN1 oxidation assays; NO measurements; exercise capacity testing; vasodilation assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, but preprint only; genetic and pharmacological epistasis well-documented","pmids":["41279296"],"is_preprint":true},{"year":2020,"finding":"The CYB5R3 T117S variant (rs1800457/c.350C>G) shows mildly lower enzyme activity and higher NADH/NAD+ ratios compared to wild-type CYB5R3 in sickle cell disease erythrocytes, representing a partial loss-of-function.","method":"Functional enzymatic activity assay in SCD erythrocytes; NADH/NAD+ ratio measurement; comparison of T117S vs wild-type CYB5R3 activity","journal":"American journal of hematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct enzymatic activity measurement in primary human cells, single lab, clear functional readout","pmids":["32697331"],"is_preprint":false},{"year":2020,"finding":"The CYB5R3 mutation c.906A>G (p.*302Trpext*42) results in a larger ~55 kDa protein with undetectable NADH cytochrome b5 reductase activity; the mutant protein retains ER and mitochondrial localization but increases intracellular ROS and decreases the NAD+/NADH ratio, consistent with loss of CYB5R3 function.","method":"Overexpression of mutant construct in cells; Western blotting; immunofluorescence localization; ROS measurement; NAD+/NADH ratio assay; enzymatic activity assay","journal":"Clinica chimica acta","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — structure-function in cell overexpression system, multiple molecular readouts, single lab","pmids":["39154701"],"is_preprint":false},{"year":2018,"finding":"Overexpression of CYB5R3 (together with NQO1) in transgenic mice mimics aspects of caloric restriction, including modest lifespan extension, improved physical performance, reduced chronic inflammation, protection against carcinogenesis, enhanced metabolic flexibility, and significant upregulation of the NAD+/sirtuin pathway.","method":"Transgenic mouse overexpressing CYB5R3 and NQO1; lifespan analysis; physical performance tests; inflammation markers; carcinogenesis models; NAD+/NADH ratio and sirtuin pathway measurements; metabolic flexibility assays","journal":"Aging cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic mouse model with multiple physiological and molecular readouts; confounded by co-overexpression of NQO1","pmids":["29706024"],"is_preprint":false},{"year":2024,"finding":"APOO deficiency reduces CYB5R3 expression in liver via the NRF2/CYB5R3 axis; AAV-mediated restoration of CYB5R3 expression in Apoo−/− mice reversed reduced phospholipid unsaturation and decreased blood cholesterol levels, demonstrating that CYB5R3 regulates phospholipid unsaturation and cholesterol metabolism downstream of NRF2.","method":"APOO global knockout mouse; Apoo−/−Apoe−/− and Apoo−/−Ldlr−/− models; AAV-mediated CYB5R3 restoration in vivo; phospholipid unsaturation analysis; plasma cholesterol measurements; NRF2 and CYB5R3 expression analysis","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo AAV rescue experiment directly links CYB5R3 to phospholipid unsaturation and cholesterol, single lab","pmids":["38830896"],"is_preprint":false},{"year":2024,"finding":"Cyb5r3 activation reverses secondary sulfonylurea failure and restores insulin secretion in mice and ex vivo human islets but does not reverse β-cell dedifferentiation; chronic SU treatment combined with Cyb5r3 KO shows more pronounced β-cell dedifferentiation and glucose intolerance.","method":"Cyb5r3 KO mice with chronic SU treatment; β-cell dedifferentiation markers; glucose tolerance tests; insulin secretion assays; Cyb5r3 activator pharmacological treatment in mice and human islets","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — extends prior mechanistic work with conditional KO and activator, single lab, clear functional dissection","pmids":["38335173"],"is_preprint":false}],"current_model":"CYB5R3 (NADH-cytochrome b5 reductase 3) is a membrane-bound flavoenzyme that uses NADH to reduce coenzyme Q and heme iron in sGC (Fe3+→Fe2+), thereby maintaining NO-dependent vasodilation in vascular smooth muscle and endothelial cells; in endothelium it also cooperates with NOX4 via CoQ to favor H2O2 over superoxide production, limiting inflammatory activation; in cardiomyocytes it is essential for redox homeostasis, CoQ levels, and prevention of ventricular arrhythmia and sudden cardiac death; in pancreatic β-cells it links FoxO1 signaling to mitochondrial function and glucokinase stabilization, coupling glucose utilization to insulin secretion; in alveolar epithelial cells it suppresses TGF-β1 signaling via the sGC/cGMP/PKG-ERK1/2 axis; on the ER membrane it is ufmylated by UFL1/UFBP1, converted to an inactive form, and degraded via selective autophagy (ER-phagy) in a CDK5RAP3-dependent manner, a process required for brain development; and its transcription is regulated by Nrf2 and FOXO3a binding to antioxidant response elements in its promoter."},"narrative":{"mechanistic_narrative":"CYB5R3 is an NADH-dependent flavoreductase that maintains cellular redox balance and serves as a hub coupling NADH oxidation to nitric oxide signaling, coenzyme Q metabolism, and mitochondrial function across multiple tissues [PMID:24450884, PMID:31487266]. By regulating the NAD+/NADH ratio it supports mitochondrial electron transport, ATP production, and resistance to oxidative stress and senescence, and its transcription is driven by FOXO3a and Nrf2 binding antioxidant response elements in its promoter [PMID:24450884]. In vascular smooth muscle it acts as a soluble guanylyl cyclase (sGC) heme reductase, reducing oxidized sGC heme (Fe3+→Fe2+) to sustain NO-dependent vasodilation; loss of smooth muscle CYB5R3 raises blood pressure and impairs vasodilation, defects rescued by the heme-independent sGC activator BAY 58-2667 and aggravated under hypoxia [PMID:31487266, PMID:34536439]. In endothelium it localizes to the mitochondrial outer membrane and physically interacts with NOX4, where its activity and membrane association bias NOX4 output toward H2O2 over superoxide, limiting VCAM-1-driven inflammatory activation [PMID:34656824]. It is essential for cardiomyocyte redox homeostasis and CoQ and ATP levels, with cardiomyocyte-specific loss causing hypertrophy, calcium mishandling, ventricular fibrillation, and sudden cardiac death [PMID:36106636]. In pancreatic β-cells CYB5R3 links FoxO1 signaling to mitochondrial respiration and stabilizes glucokinase through a glucose-dependent interaction, coupling glucose utilization to insulin secretion; its loss phenocopies secondary sulfonylurea failure, which a CYB5R3 activator reverses in mice and human islets [PMID:32180563, PMID:36724243]. In type II alveolar epithelial cells it suppresses TGF-β1 signaling via the sGC/cGMP/PKG–ERK1/2 axis to limit lung fibrosis [PMID:36749633]. CYB5R3 protein is dynamically partitioned between mitochondria and ER membranes, with GGPP-dependent prenylation driving mitochondria-to-ER translocation [PMID:32913122], and on the ER it is ufmylated by UFL1/UFBP1 to an inactive form and degraded by CDK5RAP3-dependent ER-phagy, a process required for brain development [PMID:36543799]. The common T117S (rs1800457) variant is a partial loss-of-function allele with reduced enzyme activity [PMID:36106636, PMID:32697331].","teleology":[{"year":2014,"claim":"Established that CYB5R3 controls the cellular NAD+/NADH ratio and downstream mitochondrial bioenergetics, and that its expression is transcriptionally tuned by redox-responsive factors, framing it as a redox-homeostasis enzyme rather than a single-pathway reductase.","evidence":"CYB5R3-deficient cell lines with metabolic assays, senescence readout, FOXO3a/Nrf2 overexpression and ChIP of promoter elements","pmids":["24450884"],"confidence":"High","gaps":["Does not resolve which intracellular acceptors (CoQ vs cytochrome b5) drive the NAD+/NADH effect","Promoter regulation studied in cell lines, not tissue-specific contexts"]},{"year":2018,"claim":"Tested whether elevating CYB5R3 levels has organismal benefit, showing overexpression mimics caloric-restriction phenotypes and engages the NAD+/sirtuin axis.","evidence":"Transgenic mouse overexpressing CYB5R3 plus NQO1 with lifespan, performance, inflammation and metabolic readouts","pmids":["29706024"],"confidence":"Medium","gaps":["Effects confounded by co-overexpression of NQO1","Does not isolate CYB5R3-specific contribution to lifespan"]},{"year":2019,"claim":"Defined a tissue-level molecular function by showing smooth muscle CYB5R3 is the sGC heme reductase maintaining NO-dependent vasodilation and blood pressure.","evidence":"SMC-specific conditional KO mouse with radiotelemetry, wire myography, and BAY 58-2667 pharmacological rescue","pmids":["31487266"],"confidence":"High","gaps":["Direct enzymatic reduction of sGC heme inferred pharmacologically rather than reconstituted","Does not address non-vascular sGC pools"]},{"year":2020,"claim":"Connected CYB5R3 to transcriptional and metabolic programs in β-cells and to subcellular trafficking, showing FoxO1-dependent expression supports β-cell mitochondrial function and that GGPP prenylation directs mitochondria-to-ER translocation for eicosanoid metabolism.","evidence":"β-cell-specific KO mouse with respirometry and EM; GGPPS KO cells with prenylation assays and eicosanoid profiling","pmids":["32180563","32913122"],"confidence":"High","gaps":["Mechanism linking CYB5R3 reductase activity to insulin secretion not fully defined","Functional consequence of ER vs mitochondrial pools not quantitatively partitioned"]},{"year":2020,"claim":"Characterized natural and engineered loss-of-function alleles, establishing that reduced CYB5R3 activity elevates NADH/NAD+ and ROS while preserving dual ER/mitochondrial localization.","evidence":"Enzymatic activity assays of T117S in SCD erythrocytes; overexpression of a C-terminal extension mutant with localization, ROS and NAD+/NADH readouts","pmids":["32697331","39154701"],"confidence":"Medium","gaps":["T117S enzymatic deficit is mild; clinical penetrance not established","Extension mutant studied by overexpression only"]},{"year":2021,"claim":"Revealed a redox-signaling role at the mitochondrial outer membrane where CYB5R3 partners with NOX4 to shape ROS species, linking the enzyme to endothelial inflammation, and extended the sGC reductase role to hypoxic cardiac protection.","evidence":"Endothelial KO/siRNA with APEX2 proximity EM, PLA, COQ6 epistasis; SMC KO under chronic hypoxia with myography and pressure-volume loops","pmids":["34656824","34536439"],"confidence":"Medium","gaps":["Physical CYB5R3–NOX4 interface not mapped structurally","Hypoxia study from single lab"]},{"year":2022,"claim":"Identified CYB5R3 as a regulated ER substrate of the UFM1 system and showed cardiomyocyte requirement, establishing both a degradative control mechanism and a vital cardiac redox role.","evidence":"Ufmylation substrate ID, Co-IP and ufmylation-defective knock-in mice (microcephaly); cardiomyocyte-specific KO with ECG, calcium and CoQ readouts","pmids":["36543799","36106636"],"confidence":"High","gaps":["How ufmylation inactivates the enzyme biochemically not resolved","Link between brain ER-phagy and CYB5R3 reductase activity per se unclear"]},{"year":2023,"claim":"Defined a substrate-stabilization mechanism by showing CYB5R3 binds and stabilizes glucokinase glucose-dependently, and extended the sGC axis to alveolar epithelial suppression of fibrotic TGF-β1 signaling.","evidence":"Glucose-dependent Co-IP, β-cell KO phenocopy of sulfonylurea failure with activator rescue in human islets; AECII-specific KO in bleomycin fibrosis with sGC agonist rescue","pmids":["36724243","36749633"],"confidence":"High","gaps":["Whether GCK stabilization requires CYB5R3 enzymatic activity not separated from binding","AECII fibrosis pathway study from single lab"]},{"year":2024,"claim":"Expanded the functional reach of CYB5R3 to ER-stress-driven apoptosis in cancer cells and to hepatic lipid/cholesterol metabolism downstream of NRF2.","evidence":"Adenoviral overexpression in lung cancer cells with PARP16/PERK/IRE1α ADP-ribosylation assays and xenografts; APOO KO mice with AAV CYB5R3 restoration and lipid/cholesterol profiling","pmids":["38253797","38830896"],"confidence":"Medium","gaps":["Apoptotic role observed under overexpression, physiological relevance uncertain","NRF2/CYB5R3 lipid axis tested in a specific APOO-deficient background"]},{"year":2025,"claim":"Proposed a novel endothelial calcium-signaling consequence of CYB5R3 loss, linking it through NO and PTPN1 oxidation to TRPV2/CRAC channel activation and enhanced vasorelaxation.","evidence":"siRNA and endothelial KO mice with Ca2+ imaging, SOCE blockers, PTPN1 oxidation assays and exercise testing (preprint)","pmids":["41279296"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Multistep signaling cascade requires independent confirmation"]},{"year":null,"claim":"How CYB5R3's distinct enzymatic outputs (sGC heme reduction, CoQ reduction, NADH/NAD+ balancing) are partitioned across its mitochondrial and ER pools and selected in each tissue context remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of substrate selection across localization states","Relative contribution of each enzymatic activity to tissue phenotypes not dissected","Human disease genetics beyond T117S partial loss-of-function not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[1,6,12,13]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,5]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,9,10,13]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,10,13]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,7,8]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[2,6]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[4,6,10,15]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[9]}],"complexes":[],"partners":["NOX4","GCK","UFL1","UFBP1","CDK5RAP3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P00387","full_name":"NADH-cytochrome b5 reductase 3","aliases":["Diaphorase-1"],"length_aa":301,"mass_kda":34.2,"function":"Catalyzes the reduction of two molecules of cytochrome b5 using NADH as the electron donor","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P00387/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CYB5R3","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000100243","cell_line_id":"CID000287","localizations":[{"compartment":"er","grade":3},{"compartment":"vesicles","grade":1}],"interactors":[{"gene":"TOMM20A","stoichiometry":4.0},{"gene":"CANX","stoichiometry":0.2},{"gene":"COPA","stoichiometry":0.2},{"gene":"SPCS3","stoichiometry":0.2},{"gene":"TOMM20","stoichiometry":0.2},{"gene":"TOMM22","stoichiometry":0.2},{"gene":"VDAC2","stoichiometry":0.2},{"gene":"ATP2A2","stoichiometry":0.2},{"gene":"VDAC1","stoichiometry":0.2},{"gene":"TOMM40","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000287","total_profiled":1310},"omim":[{"mim_id":"620770","title":"MITOREGULIN; MTLN","url":"https://www.omim.org/entry/620770"},{"mim_id":"613218","title":"CYTOCHROME b5, TYPE A (MICROSOMAL); CYB5A","url":"https://www.omim.org/entry/613218"},{"mim_id":"613213","title":"CYTOCHROME b5 REDUCTASE 3; CYB5R3","url":"https://www.omim.org/entry/613213"},{"mim_id":"608343","title":"CYTOCHROME b5 REDUCTASE 4; CYB5R4","url":"https://www.omim.org/entry/608343"},{"mim_id":"608342","title":"CYTOCHROME b5 REDUCTASE 2; CYB5R2","url":"https://www.omim.org/entry/608342"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"},{"location":"Perinuclear theca","reliability":"Additional"},{"location":"Calyx","reliability":"Additional"},{"location":"Connecting piece","reliability":"Additional"},{"location":"Mid piece","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CYB5R3"},"hgnc":{"alias_symbol":["B5R"],"prev_symbol":["DIA1"]},"alphafold":{"accession":"P00387","domains":[{"cath_id":"2.40.30.10","chopping":"43-147","consensus_level":"high","plddt":97.3587,"start":43,"end":147},{"cath_id":"3.40.50.80","chopping":"150-301","consensus_level":"high","plddt":97.828,"start":150,"end":301}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P00387","model_url":"https://alphafold.ebi.ac.uk/files/AF-P00387-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P00387-F1-predicted_aligned_error_v6.png","plddt_mean":93.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CYB5R3","jax_strain_url":"https://www.jax.org/strain/search?query=CYB5R3"},"sequence":{"accession":"P00387","fasta_url":"https://rest.uniprot.org/uniprotkb/P00387.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P00387/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P00387"}},"corpus_meta":[{"pmid":"8331727","id":"PMC_8331727","title":"Deletion of the vaccinia virus B5R gene encoding a 42-kilodalton membrane glycoprotein inhibits extracellular virus envelope formation and dissemination.","date":"1993","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/8331727","citation_count":181,"is_preprint":false},{"pmid":"11312352","id":"PMC_11312352","title":"Visualization of intracellular movement of vaccinia virus virions containing a green fluorescent protein-B5R membrane protein chimera.","date":"2001","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/11312352","citation_count":134,"is_preprint":false},{"pmid":"15246280","id":"PMC_15246280","title":"Antibodies against the extracellular enveloped virus B5R protein are mainly responsible for the EEV neutralizing capacity of vaccinia immune globulin.","date":"2004","source":"Virology","url":"https://pubmed.ncbi.nlm.nih.gov/15246280","citation_count":114,"is_preprint":false},{"pmid":"16698998","id":"PMC_16698998","title":"LC16m8, a highly attenuated vaccinia virus vaccine lacking expression of the membrane protein B5R, protects monkeys from monkeypox.","date":"2006","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/16698998","citation_count":106,"is_preprint":false},{"pmid":"9420227","id":"PMC_9420227","title":"Functional analysis of vaccinia virus B5R protein: essential role in virus envelopment is independent of a large portion of the extracellular domain.","date":"1998","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/9420227","citation_count":80,"is_preprint":false},{"pmid":"36543799","id":"PMC_36543799","title":"The UFM1 system regulates ER-phagy through the ufmylation of CYB5R3.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/36543799","citation_count":79,"is_preprint":false},{"pmid":"18199639","id":"PMC_18199639","title":"Vaccination of BALB/c mice with Escherichia coli-expressed vaccinia virus proteins A27L, B5R, and D8L protects 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ufmylation of CYB5R3 by the E3 components UFL1 and UFBP1 converts CYB5R3 to an inactive form, which is then recognized by UFBP1 via a UFM1-interacting motif and degraded in lysosomes in an Atg7- and CDK5RAP3-dependent manner, thereby inducing ER-phagy required for brain development.\",\n      \"method\": \"Substrate identification by mass spectrometry/biochemical screening; co-immunoprecipitation; ufmylation-defective Cyb5r3 knock-in mice showing microcephaly; lysosomal degradation assays; genetic epistasis with Atg7 and CDK5RAP3\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (substrate ID, Co-IP, enzymatic inactivation, knock-in mouse phenotype, lysosomal degradation assay, adaptor requirement) in a single rigorous study\",\n      \"pmids\": [\"36543799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Smooth muscle cell CYB5R3 acts as an sGC heme reductase in resistance arteries, reducing oxidized sGC heme (Fe3+→Fe2+) to maintain NO-dependent vasodilation; SMC-specific Cyb5r3 KO mice show elevated blood pressure and impaired acetylcholine-induced vasodilation, which is worsened by angiotensin II-induced oxidative stress and rescued by the heme-independent sGC activator BAY 58-2667.\",\n      \"method\": \"Conditional smooth muscle cell-specific Cyb5r3 knockout mouse; radiotelemetry blood pressure measurement; wire myography vasodilation assays; pharmacological rescue with BAY 58-2667\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined cellular phenotype, multiple vascular functional readouts, pharmacological epistasis, replicated across normotensive and hypertensive conditions\",\n      \"pmids\": [\"31487266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CYB5R3 cooperates with NOX4 via coenzyme Q (CoQ) to regulate endothelial inflammatory activation: CYB5R3 localizes to the mitochondrial outer membrane where it physically interacts with NOX4, and CYB5R3 activity and membrane association are required for optimal NOX4-dependent H2O2 generation; loss of CYB5R3 shifts NOX4 output from H2O2 toward O2•-, enhancing VCAM-1 expression and endothelial dysfunction.\",\n      \"method\": \"Endothelial-specific conditional Cyb5r3 KO mice; siRNA knockdown in human aortic endothelial cells; APEX2-based electron microscopy and proximity biotinylation; proximity ligation assay; super-resolution confocal microscopy; ROS measurements; functional rescue with inactive or non-membrane-bound CYB5R3; COQ6 knockdown epistasis\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (proximity EM, proximity biotinylation, PLA, genetic KO, siRNA, structure-function rescue) in a single study establishing mechanism\",\n      \"pmids\": [\"34656824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CYB5R3 is essential for cardiomyocyte redox homeostasis; cardiomyocyte-specific CYB5R3 KO in male mice causes cardiac hypertrophy, bradycardia, ventricular fibrillation, and sudden cardiac death associated with calcium mishandling, decreased ATP and CoQ levels, increased oxidative stress, and hemoprotein dysregulation. The missense variant T117S (rs1800457) encodes a partial loss-of-function protein.\",\n      \"method\": \"Conditional cardiomyocyte-specific CYB5R3 knockout mouse (males); echocardiography; telemetric ECG; calcium handling assays; CoQ quantification; ATP measurements; oxidative stress markers; functional characterization of T117S variant\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal phenotypic and molecular readouts; partial loss-of-function variant characterization\",\n      \"pmids\": [\"36106636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cyb5r3 links FoxO1 signaling to β-cell mitochondrial function: FoxO1-deficient β cells have reduced Cyb5r3 expression; β-cell-specific Cyb5r3 KO mice have impaired glucose-stimulated insulin secretion, glucose intolerance, and blunted mitochondrial respiratory response to glucose, with mitochondrial and secretory granule ultrastructural abnormalities; FoxO1 requires Cyb5r3 to maintain β-cell differentiation markers.\",\n      \"method\": \"β-cell-specific Cyb5r3 knockout mouse; glucose tolerance tests; insulin secretion assays; Seahorse respirometry; electron microscopy; FoxO1 genetic interaction studies; gene expression analysis\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal functional and ultrastructural readouts, genetic epistasis with FoxO1\",\n      \"pmids\": [\"32180563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cyb5r3 stabilizes glucokinase (Gck) through a glucose-dependent interaction, maintaining islet glucose utilization; chronic sulfonylurea exposure reduces Cyb5r3 abundance and impairs Gck stabilization; Cyb5r3 β-cell KO phenocopies secondary sulfonylurea failure; a Cyb5r3 activator rescues secondary sulfonylurea failure in mice and restores insulin secretion in human islets ex vivo.\",\n      \"method\": \"Co-immunoprecipitation (glucose-dependent Cyb5r3-Gck interaction); β-cell-specific Cyb5r3 KO mouse; ex vivo islet glucose utilization assays; pharmacological Cyb5r3 activator in vivo and in human islets\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct protein interaction by Co-IP, conditional KO phenocopy, pharmacological rescue in both mouse and human islets\",\n      \"pmids\": [\"36724243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CYB5R3 deficiency decreases the NAD+/NADH ratio, mitochondrial respiration, ATP production, and mitochondrial electron transport chain activities, and increases oxidative stress and cellular senescence; CYB5R3 transcription is upregulated by FOXO3a and Nrf2 binding to antioxidant response elements in the CYB5R3 promoter, demonstrated by chromatin immunoprecipitation.\",\n      \"method\": \"CYB5R3-deficient cell lines; mitochondrial respiration and ATP assays; NAD+/NADH ratio measurements; β-galactosidase senescence assay; overexpression of FOXO3a and Nrf2; Nrf2 genetic ablation; chromatin immunoprecipitation of promoter elements\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP, KO, KD, overexpression, metabolic assays) in a single lab study\",\n      \"pmids\": [\"24450884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SMC CYB5R3 is required for NO-dependent vasodilation under chronic hypoxia; SMC-specific CYB5R3 KO mice under 3-week hypoxia develop greater biventricular hypertrophy and blunted NO-dependent vasodilation in coronary and pulmonary arteries compared to controls, implicating CYB5R3 as a sGC heme reductase protective against hypoxic cardiac remodeling.\",\n      \"method\": \"SMC-specific CYB5R3 KO mice; chronic hypoxia model; echocardiography; pressure-volume loops; wire myography of coronary and pulmonary arteries\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with in vivo functional readouts, single lab, extends prior sGC reductase mechanism to hypoxic context\",\n      \"pmids\": [\"34536439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CYB5R3 in type II alveolar epithelial cells suppresses TGF-β1 signaling by regulating ERK1/2 phosphorylation and the sGC/cGMP/PKG axis; AECII-specific CYB5R3 deficiency leads to sustained TGF-β1 activation and increased lung fibrosis susceptibility; sGC agonists reduce fibrotic outcomes of AECII CYB5R3 deficiency in vivo.\",\n      \"method\": \"Conditional AECII-specific Cyb5r3 KO mice; bleomycin lung fibrosis model; ERK1/2 phosphorylation assays; cGMP measurements; sGC agonist pharmacological rescue in vivo\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined molecular pathway readouts and pharmacological rescue, single lab\",\n      \"pmids\": [\"36749633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CYB5R3 overexpression in lung cancer cells induces ER stress-mediated apoptosis via PERK-ATF4 and IRE1α-JNK pathways; increased NAD+ production from CYB5R3 activates PARP16, which ADP-ribosylates PERK and IRE1α; CYB5R3 is predominantly localized to the ER and also induces ROS generation and caspase-9-dependent intrinsic apoptosis.\",\n      \"method\": \"Adenoviral CYB5R3 overexpression in lung cancer cells; transcriptome and metabolomic analysis; subcellular fractionation/immunofluorescence localization; PARP16 activity assays; PERK/IRE1α ADP-ribosylation assays; caspase activity assays; mouse xenograft tumor models\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (transcriptomics, metabolomics, biochemical pathway assays, in vivo), single lab\",\n      \"pmids\": [\"38253797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GGPP prenylates CYB5R3 and the prenylated form translocates from the mitochondrial to the ER pool; CYB5R3 is identified as an NADH-dependent reductase necessary for eicosanoid metabolism in the ER; GGPP depletion (via GGPPS deletion) inhibits CYB5R3 translocation and disrupts eicosanoid metabolism, causing metaflammation.\",\n      \"method\": \"GGPPS knockout cell line; CYB5R3 subcellular fractionation; prenylation assays; eicosanoid metabolite profiling; simvastatin pharmacological inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — genetic KO model with subcellular fractionation and metabolic readouts, single lab, moderate mechanistic depth\",\n      \"pmids\": [\"32913122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CYB5R3 loss in endothelial cells activates a Ca2+ influx pathway: CYB5R3 deficiency upregulates ORAI2, ORAI3, and TRPV2; loss of CYB5R3 increases Ca2+ entry through CRAC channels and TRPV2 upon ER Ca2+ store depletion; mechanistically, CYB5R3 loss increases NO production via CRAC channels, which oxidatively inhibits PTPN1, preventing TRPV2 dephosphorylation and sustaining JAK1-dependent TRPV2 activation; endothelial Cyb5r3 KO in vivo enhances acetylcholine-induced vasorelaxation and exercise capacity.\",\n      \"method\": \"siRNA knockdown and endothelial-specific Cyb5r3 KO mice; Ca2+ imaging; pharmacological SOCE blockers; TRPV2 genetic knockdown and inhibition; PTPN1 oxidation assays; NO measurements; exercise capacity testing; vasodilation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, but preprint only; genetic and pharmacological epistasis well-documented\",\n      \"pmids\": [\"41279296\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The CYB5R3 T117S variant (rs1800457/c.350C>G) shows mildly lower enzyme activity and higher NADH/NAD+ ratios compared to wild-type CYB5R3 in sickle cell disease erythrocytes, representing a partial loss-of-function.\",\n      \"method\": \"Functional enzymatic activity assay in SCD erythrocytes; NADH/NAD+ ratio measurement; comparison of T117S vs wild-type CYB5R3 activity\",\n      \"journal\": \"American journal of hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct enzymatic activity measurement in primary human cells, single lab, clear functional readout\",\n      \"pmids\": [\"32697331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The CYB5R3 mutation c.906A>G (p.*302Trpext*42) results in a larger ~55 kDa protein with undetectable NADH cytochrome b5 reductase activity; the mutant protein retains ER and mitochondrial localization but increases intracellular ROS and decreases the NAD+/NADH ratio, consistent with loss of CYB5R3 function.\",\n      \"method\": \"Overexpression of mutant construct in cells; Western blotting; immunofluorescence localization; ROS measurement; NAD+/NADH ratio assay; enzymatic activity assay\",\n      \"journal\": \"Clinica chimica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — structure-function in cell overexpression system, multiple molecular readouts, single lab\",\n      \"pmids\": [\"39154701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Overexpression of CYB5R3 (together with NQO1) in transgenic mice mimics aspects of caloric restriction, including modest lifespan extension, improved physical performance, reduced chronic inflammation, protection against carcinogenesis, enhanced metabolic flexibility, and significant upregulation of the NAD+/sirtuin pathway.\",\n      \"method\": \"Transgenic mouse overexpressing CYB5R3 and NQO1; lifespan analysis; physical performance tests; inflammation markers; carcinogenesis models; NAD+/NADH ratio and sirtuin pathway measurements; metabolic flexibility assays\",\n      \"journal\": \"Aging cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic mouse model with multiple physiological and molecular readouts; confounded by co-overexpression of NQO1\",\n      \"pmids\": [\"29706024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"APOO deficiency reduces CYB5R3 expression in liver via the NRF2/CYB5R3 axis; AAV-mediated restoration of CYB5R3 expression in Apoo−/− mice reversed reduced phospholipid unsaturation and decreased blood cholesterol levels, demonstrating that CYB5R3 regulates phospholipid unsaturation and cholesterol metabolism downstream of NRF2.\",\n      \"method\": \"APOO global knockout mouse; Apoo−/−Apoe−/− and Apoo−/−Ldlr−/− models; AAV-mediated CYB5R3 restoration in vivo; phospholipid unsaturation analysis; plasma cholesterol measurements; NRF2 and CYB5R3 expression analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo AAV rescue experiment directly links CYB5R3 to phospholipid unsaturation and cholesterol, single lab\",\n      \"pmids\": [\"38830896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cyb5r3 activation reverses secondary sulfonylurea failure and restores insulin secretion in mice and ex vivo human islets but does not reverse β-cell dedifferentiation; chronic SU treatment combined with Cyb5r3 KO shows more pronounced β-cell dedifferentiation and glucose intolerance.\",\n      \"method\": \"Cyb5r3 KO mice with chronic SU treatment; β-cell dedifferentiation markers; glucose tolerance tests; insulin secretion assays; Cyb5r3 activator pharmacological treatment in mice and human islets\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — extends prior mechanistic work with conditional KO and activator, single lab, clear functional dissection\",\n      \"pmids\": [\"38335173\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CYB5R3 (NADH-cytochrome b5 reductase 3) is a membrane-bound flavoenzyme that uses NADH to reduce coenzyme Q and heme iron in sGC (Fe3+→Fe2+), thereby maintaining NO-dependent vasodilation in vascular smooth muscle and endothelial cells; in endothelium it also cooperates with NOX4 via CoQ to favor H2O2 over superoxide production, limiting inflammatory activation; in cardiomyocytes it is essential for redox homeostasis, CoQ levels, and prevention of ventricular arrhythmia and sudden cardiac death; in pancreatic β-cells it links FoxO1 signaling to mitochondrial function and glucokinase stabilization, coupling glucose utilization to insulin secretion; in alveolar epithelial cells it suppresses TGF-β1 signaling via the sGC/cGMP/PKG-ERK1/2 axis; on the ER membrane it is ufmylated by UFL1/UFBP1, converted to an inactive form, and degraded via selective autophagy (ER-phagy) in a CDK5RAP3-dependent manner, a process required for brain development; and its transcription is regulated by Nrf2 and FOXO3a binding to antioxidant response elements in its promoter.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CYB5R3 is an NADH-dependent flavoreductase that maintains cellular redox balance and serves as a hub coupling NADH oxidation to nitric oxide signaling, coenzyme Q metabolism, and mitochondrial function across multiple tissues [#6, #1]. By regulating the NAD+/NADH ratio it supports mitochondrial electron transport, ATP production, and resistance to oxidative stress and senescence, and its transcription is driven by FOXO3a and Nrf2 binding antioxidant response elements in its promoter [#6]. In vascular smooth muscle it acts as a soluble guanylyl cyclase (sGC) heme reductase, reducing oxidized sGC heme (Fe3+→Fe2+) to sustain NO-dependent vasodilation; loss of smooth muscle CYB5R3 raises blood pressure and impairs vasodilation, defects rescued by the heme-independent sGC activator BAY 58-2667 and aggravated under hypoxia [#1, #7]. In endothelium it localizes to the mitochondrial outer membrane and physically interacts with NOX4, where its activity and membrane association bias NOX4 output toward H2O2 over superoxide, limiting VCAM-1-driven inflammatory activation [#2]. It is essential for cardiomyocyte redox homeostasis and CoQ and ATP levels, with cardiomyocyte-specific loss causing hypertrophy, calcium mishandling, ventricular fibrillation, and sudden cardiac death [#3]. In pancreatic β-cells CYB5R3 links FoxO1 signaling to mitochondrial respiration and stabilizes glucokinase through a glucose-dependent interaction, coupling glucose utilization to insulin secretion; its loss phenocopies secondary sulfonylurea failure, which a CYB5R3 activator reverses in mice and human islets [#4, #5]. In type II alveolar epithelial cells it suppresses TGF-β1 signaling via the sGC/cGMP/PKG–ERK1/2 axis to limit lung fibrosis [#8]. CYB5R3 protein is dynamically partitioned between mitochondria and ER membranes, with GGPP-dependent prenylation driving mitochondria-to-ER translocation [#10], and on the ER it is ufmylated by UFL1/UFBP1 to an inactive form and degraded by CDK5RAP3-dependent ER-phagy, a process required for brain development [#0]. The common T117S (rs1800457) variant is a partial loss-of-function allele with reduced enzyme activity [#3, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established that CYB5R3 controls the cellular NAD+/NADH ratio and downstream mitochondrial bioenergetics, and that its expression is transcriptionally tuned by redox-responsive factors, framing it as a redox-homeostasis enzyme rather than a single-pathway reductase.\",\n      \"evidence\": \"CYB5R3-deficient cell lines with metabolic assays, senescence readout, FOXO3a/Nrf2 overexpression and ChIP of promoter elements\",\n      \"pmids\": [\"24450884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve which intracellular acceptors (CoQ vs cytochrome b5) drive the NAD+/NADH effect\", \"Promoter regulation studied in cell lines, not tissue-specific contexts\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Tested whether elevating CYB5R3 levels has organismal benefit, showing overexpression mimics caloric-restriction phenotypes and engages the NAD+/sirtuin axis.\",\n      \"evidence\": \"Transgenic mouse overexpressing CYB5R3 plus NQO1 with lifespan, performance, inflammation and metabolic readouts\",\n      \"pmids\": [\"29706024\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effects confounded by co-overexpression of NQO1\", \"Does not isolate CYB5R3-specific contribution to lifespan\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a tissue-level molecular function by showing smooth muscle CYB5R3 is the sGC heme reductase maintaining NO-dependent vasodilation and blood pressure.\",\n      \"evidence\": \"SMC-specific conditional KO mouse with radiotelemetry, wire myography, and BAY 58-2667 pharmacological rescue\",\n      \"pmids\": [\"31487266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct enzymatic reduction of sGC heme inferred pharmacologically rather than reconstituted\", \"Does not address non-vascular sGC pools\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected CYB5R3 to transcriptional and metabolic programs in β-cells and to subcellular trafficking, showing FoxO1-dependent expression supports β-cell mitochondrial function and that GGPP prenylation directs mitochondria-to-ER translocation for eicosanoid metabolism.\",\n      \"evidence\": \"β-cell-specific KO mouse with respirometry and EM; GGPPS KO cells with prenylation assays and eicosanoid profiling\",\n      \"pmids\": [\"32180563\", \"32913122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking CYB5R3 reductase activity to insulin secretion not fully defined\", \"Functional consequence of ER vs mitochondrial pools not quantitatively partitioned\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Characterized natural and engineered loss-of-function alleles, establishing that reduced CYB5R3 activity elevates NADH/NAD+ and ROS while preserving dual ER/mitochondrial localization.\",\n      \"evidence\": \"Enzymatic activity assays of T117S in SCD erythrocytes; overexpression of a C-terminal extension mutant with localization, ROS and NAD+/NADH readouts\",\n      \"pmids\": [\"32697331\", \"39154701\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"T117S enzymatic deficit is mild; clinical penetrance not established\", \"Extension mutant studied by overexpression only\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed a redox-signaling role at the mitochondrial outer membrane where CYB5R3 partners with NOX4 to shape ROS species, linking the enzyme to endothelial inflammation, and extended the sGC reductase role to hypoxic cardiac protection.\",\n      \"evidence\": \"Endothelial KO/siRNA with APEX2 proximity EM, PLA, COQ6 epistasis; SMC KO under chronic hypoxia with myography and pressure-volume loops\",\n      \"pmids\": [\"34656824\", \"34536439\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physical CYB5R3–NOX4 interface not mapped structurally\", \"Hypoxia study from single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified CYB5R3 as a regulated ER substrate of the UFM1 system and showed cardiomyocyte requirement, establishing both a degradative control mechanism and a vital cardiac redox role.\",\n      \"evidence\": \"Ufmylation substrate ID, Co-IP and ufmylation-defective knock-in mice (microcephaly); cardiomyocyte-specific KO with ECG, calcium and CoQ readouts\",\n      \"pmids\": [\"36543799\", \"36106636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ufmylation inactivates the enzyme biochemically not resolved\", \"Link between brain ER-phagy and CYB5R3 reductase activity per se unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a substrate-stabilization mechanism by showing CYB5R3 binds and stabilizes glucokinase glucose-dependently, and extended the sGC axis to alveolar epithelial suppression of fibrotic TGF-β1 signaling.\",\n      \"evidence\": \"Glucose-dependent Co-IP, β-cell KO phenocopy of sulfonylurea failure with activator rescue in human islets; AECII-specific KO in bleomycin fibrosis with sGC agonist rescue\",\n      \"pmids\": [\"36724243\", \"36749633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GCK stabilization requires CYB5R3 enzymatic activity not separated from binding\", \"AECII fibrosis pathway study from single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Expanded the functional reach of CYB5R3 to ER-stress-driven apoptosis in cancer cells and to hepatic lipid/cholesterol metabolism downstream of NRF2.\",\n      \"evidence\": \"Adenoviral overexpression in lung cancer cells with PARP16/PERK/IRE1α ADP-ribosylation assays and xenografts; APOO KO mice with AAV CYB5R3 restoration and lipid/cholesterol profiling\",\n      \"pmids\": [\"38253797\", \"38830896\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Apoptotic role observed under overexpression, physiological relevance uncertain\", \"NRF2/CYB5R3 lipid axis tested in a specific APOO-deficient background\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Proposed a novel endothelial calcium-signaling consequence of CYB5R3 loss, linking it through NO and PTPN1 oxidation to TRPV2/CRAC channel activation and enhanced vasorelaxation.\",\n      \"evidence\": \"siRNA and endothelial KO mice with Ca2+ imaging, SOCE blockers, PTPN1 oxidation assays and exercise testing (preprint)\",\n      \"pmids\": [\"41279296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Multistep signaling cascade requires independent confirmation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CYB5R3's distinct enzymatic outputs (sGC heme reduction, CoQ reduction, NADH/NAD+ balancing) are partitioned across its mitochondrial and ER pools and selected in each tissue context remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of substrate selection across localization states\", \"Relative contribution of each enzymatic activity to tissue phenotypes not dissected\", \"Human disease genetics beyond T117S partial loss-of-function not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [1, 6, 12, 13]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 9, 10, 13]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 10, 13]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 7, 8]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [4, 6, 10, 15]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NOX4\", \"GCK\", \"UFL1\", \"UFBP1\", \"CDK5RAP3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":9,"faith_pct":88.88888888888889}}