Differential expression of genes controlling mitochondrial biogenesis during C2C12 differentiation

Abstract

Myogenesis involves the fusion of myoblasts into myotubes. Mitochondrial biogenesis plays an important role in myogenesis, but the molecular mechanisms that govern the changes in mitochondria during differentiation have yet to be fully elucidated. Thus, we sought to describe the regulation of mitochondrial biogenesis during 8 days of C2C12 myoblast differentiation in culture. Cytochrome c oxidase (COX) activity, a marker of biogenesis, was increased by 2.6-fold during differentiation. The mRNAs encoding the fusion protein mitofusin-2 (Mfn2) increased by 20–30 fold by day 4, while no changes were observed in Fis1, a fission protein. This coincided with an increase in mitochondrial network formation, and a decrease in organelle granularity. Mitochondrial transcription factor A (Tfam) and COX subunit IV (COX IV) protein levels increased during differentiation, but no changes in mRNA levels were evident. Thus, differentiation of C2C12 cells promotes mitochondrial biogenesis via: mitochondrial fusion through an increase in the Mfn2-to-Fis1 ratio, increases in Tfam, the regulator of mtDNA gene transcription and translation. These changes contribute to the increase in mitochondrial function and content, evident from the changes in COX enzyme activity. These data suggest a well regulated pattern of gene expression that occurs during differentiation leading to mitochondrial biogenesis.