Impact of participating to a 330 km long ultra-trail versus a 67 km short ultra-trail on muscular and cardiac genetic regulation by microRNAs

INTRODUCTION: Even though endurance exercise has always shown beneficial action on cardiovascular diseases, the impact of an ultra-endurance experience on the human body has not been studied enough yet. Indeed, the consequences of such effort could represent a major issue to the organism and particularly to the myocardial muscle, could lead to sudden cardiac death when experienced too many times - a phenomenon which is more and more linked to the athletic world. The main objective of this study was to measure the impact of high level physical activity on the expression of different microRNAs such as specific to muscular and cardiac suffering (miR-1, miR 133a and miR 208b), specific to muscular suffering (miR 133b, miR 206, miR 499a and miR 499b) specific to cardiac suffering (miR 208a) and specific to fibrosis (miR 21 and miR 29b).
METHODS: The study was conducted on two different trails participants: the “Tor des Géants” (TDG), 330 km long and the “Ultra Tour de Liège” (UTL), 67km long. Blood samples were collected at different timings. Timing of sampling were respectively: 4 days before starting (t0), after completing 148 km (t2), finish line (t3) and 3 days after the end of the race for the TDG (t4) , and for the UTL : just before the starting (t0), at the finish line( t2) : and 3 hours after finishing (t3). There was a number of 12 TDG studied volunteers and 10 from the UTL. MicroRNAs were extracted by using miRneasy® Serum/Plasma kit and qRT-PCR has been employed to measure their expression.
RESULTS: Only miR-1, miR-133a, miR-133b, miR-206 and miR-499a showed significant variation in their expression during both races. The variation was found to be linked to the exhaustion during the race. From these data, four out of the five miRNAs showed a higher expression level during the shorter trail (UTL). No correlation was found between miR-208a and frequently used cardiac biomarkers (hs-TnT, sST2 and NT-proBNP). No significant variation was found in fibrosis specific microRNAs (miR-21 and miR-29b).
CONCLUSION: From the amount of microRNAs tested, the expression of five of them increased significantly during both the races, which showed myocardial and muscular cellular suffering. Moreover, the levels of miRNA never came back to the baseline during recovery times. However, the fibrotic miRNA did not show any significant increase during in any race, suggesting there was no permanent damage of the heart, but this point needs further investigations.