Effect of Exercise Intensity on Isoform-Specific Expressions of NT-PGC-1 alpha mRNA in Mouse Skeletal Muscle

PGC-1 alpha is an inducible transcriptional coactivator that regulates mitochondrial biogenesis and cellular energy metabolism in skeletal muscle. Recent studies have identified two additional PGC-1 alpha transcripts that are derived from an alternative exon 1 (exon 1b) and induced by exercise. Given that the PGC-1 alpha gene also produces NT-PGC-1 alpha transcript by alternative 3' splicing between exon 6 and exon 7, we have investigated isoform-specific expression of NT-PGC-1 alpha mRNA in mouse skeletal muscle during physical exercise with different intensities. We report here that NT-PGC-1 alpha-a mRNA expression derived from a canonical exon 1 (exon 1a) is increased by high-intensity exercise and AMPK activator AICAR in mouse skeletal muscle but not altered by low- and medium-intensity exercise and beta(2)-adrenergic receptor agonist clenbuterol. In contrast, the alternative exon 1b-driven NT-PGC-1 alpha-b (PGC-1 alpha 4) and NT-PGC-1 alpha-c are highly induced by low-, medium-, and high-intensity exercise, AICAR, and clenbuterol. Ectopic expression of NT-PGC-1 alpha-a in C2C12 myotube cells upregulates myosin heavy chain (MHC I, MHC II a) and Glut4, which represent oxidative fibers, and promotes the expression of mitochondrial genes (Cyc1, COX5B, and ATP5B). In line with gene expression data, citrate synthase activity was significantly increased by NT-PGC-1 alpha-a in C2C12 myotube cells. Our results indicate the regulatory role for NT-PGC-1 alpha-a in mitochondrial biogenesis and adaptation of skeletal muscle to endurance exercise.