Xia, Q.; Tang, J.; Casas-Martinez, J. C.; Li, P.; Quinlan, L. R.; Goljanek-Whysall, K.; McDonagh, B.

Exercise can help mitigate age-related muscle atrophy, promoting mitochondrial function, Ca2+ homeostasis and regulating gene expression. MicroRNAs (miRs) are crucial post-transcriptional regulators of gene expression, fine tuning protein levels to maintain cellular homeostasis. In C. elegans, a 5-day swimming regimen increased mitochondrial content, lifespan and fitness. Small RNA sequencing identified exercise specific miRs, including increased levels of cel-miR-57-5p and cel-miR-249-3p, and decreased cel-miR-72-3p and cel-miR-77-5p. mir-57 and mir-249 mutant strains had enhanced fertility, survival and lifespan, whereas mir-72 and mir-77 mutant strains had diminished fertility, survival and lifespan. Interestingly both miR-77 and mir-249 mutant strains had disrupted mitochondrial morphology and reduced fitness following exercise. The exercise related miRs identified in C. elegans did not have conserved mammalian orthologs. Exercise regulated mammalian miRs were identified from the literature including mmu-miR-181a-5p, mmu-miR-199a-5p and mmu-miR-378a-3p. Treatment of murine myoblasts with mmu-miR-181a-5p and mmu-miR-378a-3p enhanced mitochondrial content, autophagy markers and myogenesis, while mmu-miR-199a-5p impaired these processes. However, the exercise related miRs identified in C. elegans although not conserved in mammals shared common target genes which regulate Ca2+ homeostasis such as ipp-5 (inositol Polyphosphate-5-phosphatase), sca-1 (Ca2+ transporting ATPase) and ncx-2 (mitochondrial Na+/Ca2+ antiporter). Treatment of myoblasts with mmu-miR181a-5p mimics (miR181) improved myogenesis and antogmiRs (AM181) altered Ca2+ handling in myotubes. Similarly, mmu-miR-378a-3p and cel-miR-249-3p target Kinase Suppressor of Ras (Ksr1)/ksr-2, involved in the MAPK pathway. Despite direct conservation of exercise related miRs from nematodes to mammals there are common regulatory pathways, contributing to exercise-induced adaptations.