Bioenergetic remodeling during cellular differentiation: changes in cytochromecoxidase regulation do not affect the metabolic phenotype

Abstract

Myogenesis induces mitochondrial proliferation, a decrease in reactive oxygen species (ROS) production, and an increased reliance upon oxidative phosphorylation. While muscles typically possess 20%-40% excess capacity of cytochrome c oxidase (COX), undifferentiated myoblasts have only 5%-20% of the mitochondrial content of myotubes and muscles. We used two muscle lines (C2C12, Sol8) and 3T3-L1 pre-adipocytes to examine if changes in COX regulation or activity with differentiation cause a shift in metabolic phenotype (i.e., more oxidative, less glycolytic, less ROS). COX activity in vivo can be suppressed by its inhibitor, nitric oxide, or sub-optimal substrate (cytochrome c) concentrations. Inhibition of nitric oxide synthase via L-NAME had no effect on the respiration of adherent undifferentiated cells, although it did stimulate respiration of myoblasts in suspension. While cytochrome c content increased during differentiation, there was no correlation with respiratory rate or reliance on oxidative metabolism. There was no correlation between COX specific activity and oxidative metabolism between cell type or in relation to differentiation. These studies show that, despite the very low activities of COX, undifferentiated myoblasts and pre-adipocytes possess a reserve of COX capacity and changes in COX with differentiation do not trigger the shift in metabolic phenotype.

Isoform-specific regulation of Akt by PDGF-induced reactive oxygen species

“…S9A (Lower). Insulin-induced ROS was shown to be important for differentiation of myoblasts into myotubes (24)(25)(26). In accordance with these studies, insulin treatment induced Akt2 oxidation and decreased Akt2 activity in myoblasts, unlike the results in myotubes (Fig.…”

Oxidation of Akt2 kinase promotes cell migration and regulates G1-S transition in the cell cycle

“…For instance, Akt2 regulates differentiation of myoblasts to myotubes and both, oxidative stress and Akt2 knock down are suggested to impair this differentiation process. [38][39][40][41] We reported in our earlier findings that insulin-stimulated ROS inhibits Akt2 only in the C2C12 myoblasts and not in the differentiated myotubes. We have also observed lack of differentiation in that fine-tunes Akt signaling with consequences on various cellular functions such as migration, glucose uptake and cell cycle.…”

Control of muscle bioenergetic gene expression: implications for allometric scaling relationships of glycolytic and oxidative enzymes

“…Two weeks post-differentiation, myotubes have increased mitochondrial content about fivefold, but glycolytic enzymes do not change (Moyes et al, 1997). The reason for this metabolic shift in the first few days of differentiation remains enigmatic because it occurs well before major changes in mitochondrial enzymes (Lyons et al, 2004). In any case, the changes in mitochondrial enzymes during myogenesis appear to arise independent of metabolic changes, arguing against a role for the intrinsic regulators in myogenic mitochondrial proliferation.…”