MDH1

MDH1 is a cytosolic NAD(H)-dependent malate dehydrogenase that catalyzes the reversible interconversion of malate and oxaloacetate as a core component of the malate-aspartate shuttle, coupling cytosolic and mitochondrial redox state (PMID:8786100, PMID:31538237). Loss of MDH1 disrupts this shuttle, elevating glycerol-3-phosphate (a compensatory glycerol-phosphate shuttle response), aspartate, and lowering fumarate, with a homozygous missense variant in its NAD+-binding domain causing severely diminished protein expression (PMID:31538237). Its enzymatic output is tuned by multiple post-translational modifications: CARM1/PRMT4 methylates Arg248 to block dimerization and inhibit activity, restraining a glutamine-driven NADPH-generating pathway in pancreatic cancer (PMID:27840030); HDAC6-mediated deacetylation at K121/K298 and at K118 lowers activity and impairs NADPH/redox homeostasis, driving oxidative neuronal injury and, in liver, NETosis, ER-stress-dependent PANoptosis, and cGAS-STING inflammatory signaling (PMID:35678904, PMID:38172700, PMID:38851781, PMID:38660411, PMID:40388861); and oxidative trioxidation at the active-zone residue Cys137 reduces activity in aged brain (PMID:32175745). Beyond core metabolism, MDH1 sustains levels of the autophagy-initiating kinase ULK1 to promote autophagosome formation (PMID:30765601) and acts downstream of STAT3, which transactivates MDH1 to maintain malate-aspartate shuttle flux required for fetal liver hematopoietic stem cell self-renewal (PMID:32396938). In yeast, the mitochondrial ortholog forms a pH- and metabolite-regulated metabolon with citrate synthase that channels oxaloacetate [PMID:bio_10.1101_2025.06.16.659985].

1. 1996 Medium

   Establishing the molecular identity of human MDH1 was the prerequisite for all mechanistic work, defining it as a cytosolic malate dehydrogenase, its gene locus, and its tissue distribution.

   Evidence cDNA cloning, Northern blot, and FISH mapping to 2p15

   PMID:8786100

   Open questions at the time

   • No catalytic or structural mechanism addressed
   • Physiological role inferred from expression, not function
2. 2016 High

   Resolved how MDH1 activity is post-translationally restrained, showing CARM1 methylation of R248 disrupts dimerization to inhibit the enzyme and a glutamine-derived NADPH pathway supporting pancreatic cancer growth.

   Evidence In vitro methylation, methylation-mimetic mutagenesis, dimerization Co-IP, and metabolic rescue in PDAC cells

   PMID:27840030

   Open questions at the time

   • Demethylase not identified
   • Extent of regulation outside PDAC unknown
3. 2019 Medium

   Identified a non-canonical role for MDH1 in autophagy, linking it to maintenance of ULK1 levels and early autophagosome formation.

   Evidence Genome-wide siRNA screen with knockdown validation and ULK1 protein measurement in PDAC cells

   PMID:30765601

   Open questions at the time

   • No direct MDH1-ULK1 biochemical interaction shown
   • Mechanism connecting MDH1 to ULK1 stability unresolved
4. 2019 Medium

   Demonstrated the metabolic consequence of MDH1 loss, defining its role in the malate-aspartate shuttle through a disease-associated NAD+-binding-domain variant.

   Evidence CRISPR MDH1 KO HEK293 cells and untargeted metabolomics on patient dried blood spots

   PMID:31538237

   Open questions at the time

   • Clinical phenotype-to-metabolite causality not fully resolved
   • Single patient/cell-line context
5. 2020 Medium

   Placed MDH1 in developmental hematopoiesis as a STAT3-induced effector sustaining malate-aspartate shuttle flux for fetal liver HSC self-renewal.

   Evidence In vivo SoNar NADH/NAD+ sensor mice, STAT3-MDH1 transactivation reporters, and HSC functional assays

   PMID:32396938

   Open questions at the time

   • Direct STAT3 binding to the MDH1 promoter not detailed
   • Relevance to adult HSC unaddressed
6. 2020 Medium

   Showed MDH1 activity declines with age via oxidative modification, identifying trioxidation of active-zone Cys137 as a mechanism dysregulating brain bioenergetics.

   Evidence LC-MS/MS, MRM-MS, structural modeling, and enzymatic kinetics of MDH1 from old vs young mouse brain

   PMID:32175745

   Open questions at the time

   • Causal link to neurodegenerative phenotype not established
   • Reversibility of trioxidation unknown
7. 2022 High

   Defined HDAC6 as an upstream regulator of MDH1, with deacetylation at K121/K298 controlling NADPH/redox homeostasis and neuronal survival after hemorrhage.

   Evidence Reciprocal Co-IP, acetylation-site mutants, HDAC6 KO mice, and MDH1 knockdown rescue with NADPH/ROS readouts

   PMID:35678904

   Open questions at the time

   • Acetyltransferase counterpart not identified
   • Quantitative stoichiometry of site occupancy unknown
8. 2024 Medium

   Extended MDH1 deacetylation signaling to acute liver failure, linking K118 deacetylation to NETosis, ER-stress-driven PANoptosis, mitochondrial dynamics/autophagy, and cGAS-STING inflammation.

   Evidence K118 acetylation mutants, AAV delivery, ER stress and HDAC6 inhibitor rescue, DNase 1 NET degradation, and LPS/D-gal ALF mouse model

   PMID:38172700 PMID:38660411 PMID:38851781 PMID:39353390 PMID:40388861

   Open questions at the time

   • Direct enzymatic basis linking MDH1 activity loss to downstream effectors not fully dissected
   • Findings concentrated in a single lab's ALF model
9. 2025 Medium

   Demonstrated MDH1 can be pharmacologically activated, with covalent engagement of Cys137 by HSYA restoring enzymatic activity and mitochondrial energetics in cardiac ischemia/reperfusion.

   Evidence rdTOP-ABPP chemoproteomics, cellular thermal shift assay, enzymatic profiling, and siRNA rescue in a MIRI mouse model

   PMID:40513321

   Open questions at the time

   • Specificity of HSYA for MDH1 over other Cys-containing targets not fully bounded
   • Translational dosing unaddressed
10. 2025 Medium

    Provided structural-functional insight into MDH1 organization, showing the ortholog forms a metabolite- and pH-regulated metabolon with citrate synthase that channels oxaloacetate.

    Evidence In vitro reconstitution and affinity assays under varying pH/metabolite conditions in yeast (preprint)

    PMID:bio_10.1101_2025.06.16.659985

    Open questions at the time

    • Demonstrated in yeast mitochondrial ortholog, not human cytosolic MDH1
    • Preprint, not peer-reviewed
11. 2025 Medium

    Tested the in vivo requirement for MDH1 in erythropoiesis, finding the malate-aspartate shuttle via MDH1 dispensable for red cell development unlike GOT1/GOT2.

    Evidence Erythroid-specific conditional Mdh1 knockout mouse with blood and progenitor analysis (preprint)

    PMID:bio_10.1101_2025.09.16.675844

    Open questions at the time

    • Negative result; compensatory pathways not mapped
    • Preprint, not peer-reviewed

• How the converging post-translational modifications (methylation, acetylation, oxidation) are integrated to set MDH1 activity in any single physiological context, and the identities of the writer enzymes opposing HDAC6 deacetylation, remain unresolved.
• No acetyltransferase or demethylase identified for MDH1
• Cross-talk among R248 methylation, K118/K121/K298 acetylation, and C137 oxidation not jointly studied
• Human structural model of the metabolon lacking