Author(s): GEDYE, M., HIAM, D., BERNARDO, B., LAMON, S., WADLEY, G., Institution: DEAKIN UNIVERSITY, Country: AUSTRALIA, Abstract-ID: 1501

INTRODUCTION:
Mitochondria play a pivotal role in cell biology and are essential to overall metabolic health. Skeletal muscle is a highly metabolic tissue, containing a particularly rich volume of mitochondria that can be further enhanced with exercise. While this process is well known, the regulatory mechanisms remain elusive. microRNAs (miRNAs), however, have shown potential as regulators of cellular function, including mitochondrial dynamics. Additionally, miRNAs have been shown to localise to the mitochondria. Though, their function remains elusive. The aim of the MATRX (Mitochondrial And Transcriptomic Response to eXercise) study was to investigate the regulation of miRNAs localised to the skeletal muscle mitochondria of young, healthy males and observe changes in miRNA expression following an acute bout of sub-maximal exercise.
METHODS:
Ethics was obtained prior to recruitment (2024-191). 13 young, healthy males were included in the study. Participants were required to cycle for 60 minutes at submaximal intensity with muscle biopsies taken before, after and at three hours after exercise. Mitochondria were isolated with Magnetic-Activated Cell Sorting and treated with RNAse-A and Proteinase K prior to RNA extraction (1). Mitochondrial RNA libraries were sequenced and differential expression analysis performed on the resulting transcripts using DEseq2. Wald tests were used for pairwise contrasts to assess acute (post vs pre), recovery (post vs recovery) and sustained (recovery vs pre) responses. P-values were adjusted for multiple testing using the Benjamini-Hochberg false discovery rate procedure with an adjusted p-value < 0.05 considered statistically significant.
RESULTS:
314 miRNAs were identified in the mitochondria of skeletal muscle. A subset of these were significantly differentially expressed following an acute bout of endurance exercise. Pairwise Wald contrasts identified three distinct response patterns and included 23 miRNAs that were uniquely regulated in the acute phase, 25 miRNAs that were uniquely regulated in the recovery phase and 59 miRNAs that showed sustained regulation across the exercise-recovery time course. Canonical myomiRs including miR-1, miR-133a, miR-133b and miR-206 were identified, though none were significantly differentially expressed.
CONCLUSION:
Nuclear-encoded miRNAs localise to skeletal muscle mitochondria in humans and exhibit distinct temporal regulation following acute endurance exercise. The identification of multiple exercise-induced mitochondrial-associated miRNAs highlights a potential regulatory layer underlying mitochondrial adaptation. While the mode of mitochondrial localisation and function of these miRNAs were not addressed in the present study, these findings identify candidate miRNAs for future studies integrating mitochondrial gene expression and functional manipulation.
References:
1. Silver et al.  FASEB J, 38(23): e70223, 2024.