The truncated splice variants, NT-PGC-1α and PGC-1α4, increase with both endurance and resistance exercise in human skeletal muscle

Recently, a truncated peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) splice variant, PGC-1 alpha 4, that originates from the alternative promoter was shown to be induced by resistance exercise and to elicit muscle hypertrophy without coactivation of classical PGC-1 alpha targets involved in mitochondrial biogenesis and angiogenesis. In order to test if distinct physiological adaptations are characterized by divergent induction of PGC-1 alpha splice variants, we investigated the expression of truncated and nontruncated PGC-1 alpha splice variants and PGC-1 alpha transcripts originating from the alternative and the proximal promoter, in human skeletal muscle in response to endurance and resistance exercise. Both total PGC-1 alpha and truncated PGC-1 alpha mRNA expression were increased 2 h after endurance (P < 0.01) and resistance exercise (P < 0.01), with greater increases after endurance exercise (P < 0.05). Expression of nontruncated PGC-1 alpha increased significantly in both exercise groups (P < 0.01 for both groups) without any significant differences between the groups. Both endurance and resistance exercise induced truncated as well as nontruncated PGC-1 alpha transcripts from both the alternative and the proximal promoter. Further challenging the hypothesis that induction of distinct PGC-1 alpha splice variants controls exercise adaptation, both nontruncated and truncated PGC-1 alpha transcripts were induced in AICAR-treated human myotubes (P < 0.05). Thus, contrary to our hypothesis, resistance exercise did not specifically induce the truncated forms of PGC-1 alpha. Induction of truncated PGC-1 alpha splice variants does not appear to underlie distinct adaptations to resistance versus endurance exercise. Further studies on the existence of numerous splice variants originating from different promoters are needed.