Human muscular mitochondrial fusion in athletes during exercise

The main objective of this work was to investigate whether mitochondrial fusion occurs in the skeletal muscle of well‐trained athletes in response to high‐intensity exercise. Well‐trained swimmers ( n = 9) performed a duration‐matched sprint interval training (SIT) and high‐intensity high‐volume training (HIHVT) session on separate days. Muscle samples from triceps brachii were taken before, immediately after, and 3 h after the training sessions. Transmission electron microscopy (TEM) was applied to assess mitochondrial morphology. Moreover, expression of genes coding for regulators of mitochondrial fusion and fission were assessed by real‐time quantitative PCR. In addition, mitofusin (MFN)2 and optic atrophy 1 (OPA1) were quantified by Western blot analysis. TEM analyses showed that mitochondrial morphology remained altered for 3 h after HIHVT, whereas SIT‐induced changes were only evident immediately after exercise. Only SIT increased MFN1 and MFN2 mRNA expression, whereas SIT and HIHVT both increased MFN2 protein content 3 h after exercise. Notably, only HIHVT increased OPA1 protein content. Mitochondrial morphologic changes that suggest fusion occurs in well‐adapted athletes during exercise. However, HIHVT appears as a more robust inducer of mitochondrial fusion events than SIT. Indeed, SIT induces a rapid and transient change in mitochondrial morphology.—Huertas, J. R., Ruiz‐Ojeda, F. J., Plaza‐Díaz, J., Nordsborg, N. B., Martín‐Albo, J., Rueda‐Robles, A., Casuso, R. A. Human muscular mitochondrial fusion in athletes during exercise. FASEB J. 33, 12087‐12098 (2019). www.fasebj.org