Acute and Chronic High-Intensity Exercise Differentially Regulate the miRNA Biogenesis Pathway in Human Skeletal Muscle.

Background/Objectives: MicroRNAs (miRNAs) are key regulators of skeletal muscle adaptation; however, the extent to which exercise modulates the miRNA biogenesis pathway remains poorly understood. To investigate the impact of acute and chronic high-intensity exercise on components of miRNA biogenesis, and whether such changes are reflected in miRNA expression across stages of their biogenesis, we performed secondary analyses of muscle biopsy samples from two previously published studies. Methods: Muscle biopsies were analyzed from the following protocols: nine men and eight women pre- and 3 h post- a bout of high-intensity interval cycling exercise (HIIE), and eleven men and eight women pre- and post- a 6-week period of high-intensity interval training (HIIT) or non-exercise control. mRNA expression of components of miRNA biogenesis including Drosha, Exportin-5, Dicer, and Ago2 were assessed following HIIE using RT-qPCR and their protein abundance was measured following HIIT using Western blotting. Primary (pri-miR-133a1, -133a2, -133b) and mature (miR-133a-3p, -133a-5p, -133b) miRNA expression were quantified following HIIT. Results: An acute bout of HIIE significantly decreased Drosha mRNA (p < 0.05) and resulted in a reduction in Dicer mRNA that approached significance (p < 0.10). Following 6 weeks of HIIT, no significant changes were detected in the protein abundance of Drosha, Exportin-5, Dicer, or Ago2. HIIT did not alter miR-133 expression at either the primary or mature transcript level across all isoforms. Conclusions: This study highlights the complexity of miRNA regulation in skeletal muscle and underscores the need for further research examining the temporal and mechanistic control of miRNA biogenesis in response to exercise.