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

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.