Muscle specific microRNAs are regulated by endurance exercise in human skeletal muscle

Abstract

Muscle specific miRNAs, myomiRs, have been shown to control muscle development in vitro and are differentially expressed at rest in diabetic skeletal muscle. Therefore, we investigated the expression of these myomiRs, including miR-1, miR-133a, miR-133b and miR-206 in muscle biopsies from vastus lateralis of healthy young males (n = 10) in relation to a hyperinsulinaemic–euglycaemic clamp as well as acute endurance exercise before and after 12 weeks of endurance training. The subjects increased their endurance capacity, VO2max (l min−1) by 17.4% (P < 0.001), and improved insulin sensitivity by 19% (P < 0.01). While myomiR expression remained stable during a hyperinsulinaemic–euglycaemic clamp, an acute bout of exercise increased mir-1 (P < 0.05) and mir-133a (P < 0.05) expression before, but not after, training. In resting biopsies, endurance training for 12 weeks decreased basal expression of all four myomiRs (P < 0.05). Interestingly, all myomiRs reverted to their pre-training expression levels 14 days after ceasing the training programme. Components of major pathways involved in endurance adaptation such as MAPK and TGF-β were predicted to be targeted by the myomiRs examined. Tested predicted target proteins included Cdc42 and ERK 1/2. Although these proteins were downregulated between post-training period and 2 weeks of cessation, an inverse correlation between myomiR and target proteins was not found. In conclusion, our data suggest myomiRs respond to physiological stimuli, but their role in regulating human skeletal muscle adaptation remains unknown.

Figures

Figure 1. Schematic overview of the study design

Downward arrows indicate the days during which biopsies were taken. Resting biopsies on trial exercise before training were compared to before the euglycaemic–hyperinsulinaemic clamp to obtain training effect and compared to the acute exercise trial post-training to obtain a comparison following cessation.

Figure 4. Myomir expression in response to euglycaemic–hyperinsulinaemic before and after endurance training

MyomiR expression in response to euglycaemic–hyperinsulinaemic clamp before and after a 12 week training period. A paired t test did not show a significant effect of insulin infusion in the expression of all four myomiRs (P > 0.05) before (A) or after the training period (B).

Figure 2. Myomir expression in response to endurance exercise

MyomiR expression in response to a single 60 min bout at 65% Pmax of endurance exercise before and after 12 weeks of high intensity endurance training. A one-way (RM) ANOVA demonstrated a significant effect of exercise for two myomiRs (mir-1: P < 0.05; mir-133a: P < 0.05) before the training period. None of the myomiRs were differentially altered in response to acute endurance exercise after 12 weeks of training. *Main effect of exercise, P < 0.05.

Figure 3. Myomir expression at rest in response to endurance training

MyomiR expression in resting samples following 12 weeks of training and 2 weeks of cessation of training. Healthy, young men (n = 10) performed a 12 week endurance-training programme. Muscle biopsies were obtained at rest before and after the training period. A one way (RM) ANOVA demonstrated a significant effect of training in the expression of all four myomiRs. A Bonferroni multiple comparison post hoc test revealed a training induced downregulation of mir-1 (P < 0.05), mir-133a (P < 0.01), mir-133b (P < 0.05) and mir-206(P < 0.01) and an upregulation of mir-1 (P < 0.05), mir-133a (P < 0.01), mir-133a (P < 0.05), and mir-206 (P < 0.05) in the following cessation period. *Main effect of exercise, P < 0.05; **main effect of exercise, P < 0.01.

Figure 5. MyomiR targeted protein levels at rest in response to endurance training

Protein expression at rest of Cdc42, representing the MAPK pathway and ERK1/2, representing the TGF-β pathway, based on the prediction analysis of the myomiRs. A one way (RM) ANOVA demonstrated a significant change in the Cdc42 and ERK1/2 levels (A and B) (P < 0.05) in the experimental period. A post hoc analysis demonstrated a significant difference between the post training and cessation period. Main effect of endurance training period is indicated: *P < 0.05, **P < 0.01.