Impairments in SHMT2 expression or cellular folate availability reduce oxidative phosphorylation and pyruvate kinase activity.

backgroundSerine hydroxymethyltransferase 2 (SHMT2) catalyzes the reversible conversion of tetrahydrofolate (THF) and serine-producing THF-conjugated one-carbon units and glycine in the mitochondria. Biallelic SHMT2 variants were identified in humans and suggested to alter the protein's active site, potentially disrupting enzymatic function. SHMT2 expression has also been shown to decrease with aging in human fibroblasts. Immortalized cell models of total SHMT2 loss or folate deficiency exhibit decreased oxidative capacity and impaired mitochondrial complex I assembly and protein levels, suggesting folate-mediated one-carbon metabolism (FOCM) and the oxidative phosphorylation system are functionally coordinated. This study examined the role of SHMT2 and folate availability in regulating mitochondrial function, energy metabolism, and cellular proliferative capacity in both heterozygous and homozygous cell models of reduced SHMT2 expression. In this study, primary mouse embryonic fibroblasts (MEF) were isolated from a C57Bl/6J dam crossed with a heterozygous Shmt2

resultsHomozygous loss of SHMT2 in HAP1 cells impaired cellular folate accumulation and altered mitochondrial DNA content, formate production, membrane potential, and basal respiration. Formate rescued proliferation in HAP1, but not ΔSHMT2, cells cultured in low-folate medium. Pyruvate kinase activity and protein levels were impaired in ΔSHMT2 cells and in MEF cells exposed to low-folate medium. Mitochondrial biogenesis protein levels were elevated in Shmt2

conclusionsThe results from this study indicate disrupted mitochondrial FOCM impairs mitochondrial folate accumulation and respiration, mitochondrial formate production, glycolytic activity, and cellular proliferation. These changes persist even after a potentially compensatory increase in mitochondrial biogenesis as a result of decreased SHMT2 levels.