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Mitofusin 2 mRNA and mitochondrial DNA increase with exercise but not training

Exercise increases mRNA for genes involved in mitochondrial biogenesis. A common measure of changes in mitochondrial capacity is the ratio between mitochondrial DNA (mtDNA) to genomic DNA (gDNA). In addition, little is known about the role of mitochondrial fusion in exercise training and mitochondrial development. The purpose was to examine the effects of acute and chronic exercise on mtDNA/gDNA ratio and mitofusin 2 (Mfn2) mRNA. Ten trained cyclists cycled ~100 miles a day for 21 days at a self selected workrate in the field. Muscle biopsies were obtained from the vastus lateralis immediately pre‐ and post‐exercise on days 1, 11 and 21. Muscle samples were analyzed for gene expression of Mfn2 and mtDNA/gDNA. Data were analyzed using a 2 (exercise) × 3 (day) repeated measures ANOVA. Exercise caused an increase in Mfn2 mRNA (P=0.038) and mtDNA/gDNA ratio (P=0.03). There was not a significant effect of day on either of these two outcomes (P=0.44 and P=0.99 respectively). Acute exercise caused an increase in the mRNA for Mfn2, a protein involved in mitochondrial fusion. This may explain the increase observed in mtDNA/gDNA following one 5 hr bout of exercise. Mitochondrial fusion‐fission may artificially alter the mtDNA/gDNA ratio making this measure difficult to interpret after exercise training.