A Distinct Population of Mitochondrial miRNA in Human Male Skeletal Muscle Assessed Before and After Exercise

Initially thought to localize at the cytosol and nucleus only, emerging evidence indicates that miRNAs also localize within mitochondria where they could regulate diverse pathological and physiological processes. Therefore, the aim of the current study was to profile the population of miRNAs in isolated mitochondria and whole-tissue from human skeletal muscle at rest and in response to acute endurance exercise. Twelve healthy males (age 26 ± 4 years, mean ± SD) cycled for 60 min at 70% VO2_peak and muscle biopsies were collected at rest, immediately after and 3 h after exercise. The mitochondria were isolated by immunoprecipitation, enzymatically purified, then the resident RNA was sequenced to assess the mitochondrial transcriptome. Small RNA sequencing revealed that mitochondria isolated from male skeletal muscle tissue contain a distinct population of miRNAs. Of the approximately 127 mature miRNAs detected in skeletal muscle mitochondria at each time point, the canonical muscle-specific miRs (myo-miRs) miR-1, miR-133 and miR-206 families constituted on average 45% of total mitochondria miRNA reads. However, none of these canonical myo-miRs were differentially expressed in mitochondria following endurance exercise. One miRNA, hsa-miR-146b-5p, was differentially expressed 3 h after exercise when compared to pre-exercise in both mitochondria (log2 fold-change = 5.4, p = 0.003, FDR = 0.82) and whole muscle tissue (log2 fold-change = 2.3, p < 0.0001, FDR = 0.060) but not when adjusted for multiple testing. Future research is now required to investigate miRNA-mRNA interactions in the mitochondria of skeletal muscle tissue.