CHARACTERIZING THE ACUTE MITOCHONDRIAL RESPONSE TO RESISTANCE EXERCISE IN AGING

Abstract

<p>Introduction: Mitochondrial dysfunction and oxidative stress increase with aging and may contribute to age-associated muscle atrophy (sarcopenia). Resistance exercise (RE) can promote the accretion of muscle mass, increase strength, and ultimately improve function in the elderly. Such beneficial effects are thought to be mitigated solely by increased muscle mass and strength; however, the contribution of the mitochondria to the beneficial effects of RE in aging have not been thoroughly characterized. While mitochondrial benefits have been established separately in both young and aged adults following chronic RE, the acute effects have not been well characterized. Methods: Sedentary young and aged adult males completed either an acute bout of fatiguing RE or endurance exercise (EE), and muscle biopsies were obtained at 3, 24 and 48 h post- exercise depending on the study. Results: Despite equivalent lean-body mass, increased age was associated with elevated mtDNA deletions, indicating potential for mitochondrial dysfunction. RE was associated with reduced mitochondrial content (transcripts, protein, and mtDNA copy number) at 48 h post-exercise, a response that did not differ with increasing age. Paradoxically, reduced mitochondrial content occurred alongside elevated total peroxisome proliferator-activated receptor γ coactivator one α (PGC-1α) mRNA; however, RE altered only the PGC-1α4 isoform post-exercise, a transcript that regulates myostatin and insulin-like growth factor one (IGF1) signalling and ultimately muscle hypertrophy and not mitochondrial adaptations. In addition, PGC-1α modulates the unfolded protein response (UPR), and RE was subsequently shown to elevate endoplasmic reticulum stress and elicit the UPR. Conclusion: PGC-1α mRNA increases regardless of exercise mode; however, differential expression or regulation of alternate PGC-1α isoforms or transcriptional binding partners co-activated by PGC-1α may dictate the specific phenotypic adaptations that occur following divergent modes of exercise. Furthermore, RE acutely decreases mitochondrial content despite elevated PGC-1α mRNA, and this response is not influenced by age.</p>