Circulating Levels of Select Micro-RNA Are Not Impacted by Manipulating Nutrient Intake Following High-Intensity Cycling

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Circulating microRNAs (ci-miRNA) may facilitate intercellular communication as well as fine-tune phenotype adaptations to exercise through post-transcriptional regulation. Ci- miRNA levels are sensitive to acute aerobic exercise, yet much less is known about the influence of high-intensity interval type exercise. Further, almost nothing is known about the impact of post-exercise nutrition (carbohydrate and/or protein) on ci-miRNA levels. PURPOSE: To examine the effects of high-intensity interval cycling and different post-exercise nutrition treatments on select ci-miRNA levels. METHODS: Eight recreationally active males (age 22 ± 2 yrs; VO2max 50 ± 4 mL/kg/min) completed 3 trials, each consisting of 4 sets of 3-min intervals (90% Wmax) flanked by 30-sec Wingate intervals. Placebo (PLA; water), carbohydrate (CHO; 65 g), and carbohydrate (65 g) + protein (20 g) (PRO) beverages (600 mL) were consumed immediately following exercise. Serum levels of 9 miRNA (miR-1, -21, -126, -146a, -150, -210, -221, -222, and -486) were measured pre-exercise (Pre), immediately post (Post-0), Post-1hr, and Post-4hr. miRNA levels were expressed as fold changes relative to baseline and analyzed with repeated measures ANOVAs. RESULTS: With the exception of a 1.3-fold increase (p<0.05) in ci-miRNA-486 there was no main effect of time for any of the target ci-miRNA from Pre to Post-0 (i.e. prior to any nutritional intervention). There was a main effect of time for Ci-miRNA-150 from Pre to Post-1hr (0.6 fold-change, p<0.05) and from Pre to Post-4hr (0.7 fold-change, p<0.05), but there were no detectable nutritional effects. Further, ci-miRNA-1 increased from Pre to Post-4hr (3.1-fold-change, p<0.05) but again with no nutrition effect. No other differences, across time or between treatments, were detected. CONCLUSION: In general, high-intensity cycling had a subtle impact on serum levels of miRNA. However, mi-RNA associated with skeletal muscle (miRNA-1 and -486) and cardiac physiology (miRNA-1 and -150) were affected by exercise. Post-exercise nutrition had no consequences on any of the targets of interest. However, the extent to which ci-miRNA reflects intracellular miRNA activity is poorly understood and future work should investigate how nutrition may influence intracellular mi-RNA levels.