A single bout of resistance exercise triggers mitophagy, potentially involving the ejection of mitochondria in human skeletal muscle

Aim The present study aimed to investigate the effects of a single bout of resistance exercise on mitophagy in human skeletal muscle (SkM). Methods Eight healthy men were recruited to complete an acute bout of one‐leg resistance exercise. SkM biopsies were obtained one hour after exercise in the resting leg (Rest‐leg) and the contracting leg (Ex‐leg). Mitophagy was assessed using protein‐related abundance, transmission electron microscopy (TEM), and fluorescence microscopy. Results Our results show that acute resistance exercise increased pro‐fission protein phosphorylation (DRP1Ser616) and decreased mitophagy markers such as PARKIN and BNIP3L/NIX protein abundance in the Ex‐leg. Additionally, mitochondrial complex IV decreased in the Ex‐leg when compared to the Rest‐leg. In the Ex‐leg, TEM and immunofluorescence images showed mitochondrial cristae abnormalities, a mitochondrial fission phenotype, and increased mitophagosome‐like structures in both subsarcolemmal and intermyofibrillar mitochondria. We also observed increased mitophagosome‐like structures on the subsarcolemmal cleft and mitochondria in the extracellular space of SkM in the Ex‐leg. We stimulated human primary myotubes with CCCP, which mimics mitophagy induction in the Ex‐leg, and found that BNIP3L/NIX protein abundance decreased independently of lysosomal degradation. Finally, in another human cohort, we found a negative association between BNIP3L/NIX protein abundance with both mitophagosome‐like structures and mitochondrial cristae density in the SkM. Conclusion The findings suggest that a single bout of resistance exercise can initiate mitophagy, potentially involving mitochondrial ejection, in human skeletal muscle. BNIP3L/NIX is proposed as a sensitive marker for assessing mitophagy flux in SkM.