Investigating the roles of miR-206 and miR-486 on skeletal muscle growth and myogenesis in response to in in vitro beta-2 adrenergic receptor stimulation
In response to exercise, SKM mass can be increased and new tissue can also be regenerated for growth or repair (i.e., myogenesis). These processes are regulated, in part, by small noncoding RNAs, referred to as microRNA (miRNA). The purpose of this study was to utilize an in vitro cell culture model to determine how miRNA and genes regulating SKM growth and myogenesis are influenced in response to both acute and chronic exercise stimulation using the exercise mimetic, formoterol. Human SKM cells (n = 5 per group) were proliferated and differentiated for six days. Three experimental conditions were utilized: a) control media (CON), b) acute formoterol (ACF), and c) chronic formoterol (CHF). For ACF, mature myotubes were treated with 30nM of formoterol for 3h at day 6 (D6) and this was immediately followed by RNA extraction. Similarly, for CHF, mature myotubes were treated with 30nM of formoterol for 3h at day 6 (D6), day 7 (D7), and day 8 (D8). During each day of CHF (D6, D7, D8), RNA was extracted immediately following the 3h formoterol treatment. CON utilized the same differentiation media as ACF and CHF but did not include formoterol treatment. Gene expression was assessed for the following categories: (A) myogenesis, (B) skeletal muscle growth, (C) cell and mitochondrial function, and (D) miRNA. Statistical analysis was done using one-way repeated measures analysis of variance (ANOVA) and Bonferroni post-hoc testing. Acute and chronic formoterol stimulation resulted in an increase in miR-206 and no change in miR-486 expression. Additionally, acute formoterol had stimulatory effects on genes related to myogenesis, promoting expression of early-to-mid stage MRFs (Myf5), but this effect was lost with chronic formoterol stimulation. Lastly, there was an increase in expression of genes that promote metabolic adaptations, mitochondrial biogenesis and activity, as well as muscle protein degradation with acute formoterol stimulation. These effects were no longer observed with chronic formoterol stimulation. Gene expression reflective of muscle protein synthesis was also reduced following formoterol stimulation. Acute formoterol stimulation stimulates myogenesis, metabolic and mitochondrial activity, as well as muscle protein degradation, with miRNA appearing to mediate some of these effects.