Role of lipoylation in mitochondrial supercomplex formation during C2C12 cell differentiation

In mitochondria, the pyruvate dehydrogenase complex (PDHC) serves as a key metabolic regulatorGraphical Abstract by converting glycolysis-derived pyruvate into acetyl-CoA, thereby controlling carbon flux into the tricarboxylic acid cycle. PDHC activity is tightly regulated by two post-translational modifications: phosphorylation of the E1 subunit and lipoylation of the E2 subunit. While phosphorylation of E1 reversibly suppresses pyruvate dehydrogenase (PDH) activity, lipoylation of E2 is essential for intra-complex electron transfer reactions, and together these modifications define PDHC enzymatic activity. Mitochondrial respiratory supercomplexes (SCs) play a critical role in efficient electron transfer during mitochondrial respiration, and PDH has been reported to regulate SC organization. However, it remains unclear whether this regulatory mechanism, including subunit phosphorylation, is linked to protein lipoylation. In this study, we examined the impact of protein lipoylation on the phosphorylation status of the PDHC E1 subunit and on mitochondrial respiratory SC formation during C2C12 differentiation. To this end, suppression of lipoic acid synthase, a key enzyme responsible for mitochondrial protein lipoylation, in C2C12 cells resulted in dephosphorylation of the PDHC E1 subunit and formation of specific mitochondrial respiratory SCs. These findings suggest that PDHC E1 dephosphorylation and specific mitochondrial respiratory SC assembly can occur under conditions of impaired E2 lipoylation.