Phosphorylation of MDH2 at S246 renders cardioprotection against hypoxia/reoxygenation injury

Mitochondrial malate dehydrogenase (MDH2) regulates the conversion of malate/NAD+ to oxaloacetate/NADH. Proteomic studies show that MDH2 is involved in cardiovascular diseases wherein the expression of specific mitochondrial proteins is altered under ischemia/reperfusion conditions. Screening of phosphorylation sites of MDH2 revealed several posttranslational modifications occurring in the protein. However, it is still unclear how alterations of these sites lead to the altered activity and function of the system under pathologic models. This study focuses on the importance of MDH2 phosphorylation and how it regulates mitochondrial biogenesis and mitochondrial function. Phosphorylation occurs at various conserved sites, specifically Y56, Y80, Y161 and S246. Phosphorylation mutants based on these sites were manufactured using expression vectors and were transfected into cellular models for analysis. Phosphomutants decreased cell viability, ATP production, and MDH2 activity. Mitochondrial biogenesis marker expressions were also altered by phosphomutants under hypoxia/reoxygenation conditions. Overall, this study demonstrates the novel findings suggesting the unique role of the phosphorylation of mitochondrial MDH2 in the cardiac setting. We have identified phosphomutations in MDH2 which can be potential targets for future in vivo cardiac investigations. The protective mechanism of how MDH2 confers cardioprotection still remains unclear. Further studies on the role of MDH2 phosphorylation in mitochondrial biogenesis can elucidate the importance of MDH2 in cardiovascular disease models and treatment modalities.