PGC-1α and PGC-1β have both similar and distinct effects on myofiber switching toward an oxidative phenotype

Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha and -1 beta (PGC-1 alpha and PGC-1 beta) were overexpressed by adenovirus-mediated gene transfer in cultures of primary rat skeletal muscle cells derived from neonatal myoblasts. Effects on muscle fiber type transition and metabolism were studied from days 5 to 22 of culture. PGC-1 alpha and PGC-1 beta overexpression caused a three- to fourfold increase in mRNA level, a doubling of enzymatic activity of citrate synthase, a slight increase in short-chain acyl-CoA dehydrogenase mRNA, a doubling of the mRNA level, and a 30-50% increase in enzymatic activity of glyceraldehyde-3- phosphate dehydrogenase. Lactate dehydrogenase or creatine kinase activity was unchanged. PGC-1 alpha enhanced glycogen buildup twofold at 5 or 25 mM glucose, whereas PGC-1 beta caused a decrease. Both PGC-1 alpha and PGC-1 beta overexpression caused a faster maturation of myotubes, as seen by mRNA downregulation of the immature embryonal and perinatal myosin heavy-chain (MHC) isoforms. PGC-1 alpha or PGC-1 beta overexpression enhanced mRNA of the slow oxidative-associated MHC isoform MHCIb and downregulated mRNA levels of the fast glycolytic-associated MHC isoforms MHCIIX and MHCIIB. Only PGC-1 beta overexpression caused an increase in mRNA of the intermediary fast oxidative-associated MHC isoform MHCIIA. PGC-1 alpha or PGC-1 beta overexpression upregulated GLUT4 mRNA and downregulated myocyte enhancer factor 2C transcription factor mRNA; only PGC-beta 1 overexpression caused an increase in the mRNA expression of TRB3, a negative regulator of insulin signaling. These results show that both PGC-1 alpha and PGC-1 beta are involved in the regulation of skeletal muscle fiber transition and metabolism and that they have both overlapping and differing effects.