Relationships Between Circulating MicroRNA and Muscular Performance Responses to a 30 Day Bed Rest Protocol

Abstract

Microgravity is known to have detrimental effects on muscle tissue, leading to atrophy and a decline in performance. Although underlying mechanisms are not clear, microRNAs (miRNA) may play a role as they have regulatory effects on skeletal muscle gene expression. PURPOSE: To determine the effects of a 30 day six-degree head-down bed rest protocol at an ambient 0.5% CO2 on lower body muscular performance. Relationships between circulating miRNAs and changes in muscle variables were also examined. METHODS: 11 healthy subjects, 5 males and 6 females, were recruited for this study. The intervention involved a 30 day, six-degree head-down bed rest platform to simulate International Space Station flight. Maximal muscular performance was assessed for isokinetic knee extension (IsokKE), isokinetic knee flexion (IsokKF), isometric knee extension (IsomKE), isometric knee flexion (IsomKF), jump velocity (JV), absolute jump power (AbJP), and relative jump power (RelJP) 5 days before and 2 days after bed rest. Serum miRNAs (miR-21-5p, -100-5p, -125b-5p, -126-3p) were assessed by qPCR and fold changes (FC) were correlated with muscle performance variables. RESULTS: All muscular performance measures decreased (p<0.05) after bed rest (absolute changes: IsokKE -36±27N, IsokKF -16±17N, IsomKE -28±22N, IsomKF -12±14N, JV -0.21±0.08m/s, AbsJP -0.45±0.19kW, RelJP Power -5.23±1.88W/kg). Pre bed rest miR-100-5p relative expression was positively correlated with Pre strength measures and jump power (r=0.603 to 0.727, p<0.05). MiR-126-3p FC was negatively related to absolute change in relative power (r=-0.705, p<0.05), and miR-125b-5p FC was positively correlated (p<0.05) with absolute changes in IsomKE (r=0.627), IsomKF (r=0.817), and JV (r=0.700). MiR-100-5p FC was positively correlated (p<0.05) with absolute changes in IsomKE (r=0.652) and IsomKF (r=0.759). CONCLUSION: As expected, muscle performance significantly declined after 30 days of bed rest. Significant relationships were found between miRNAs and muscle variables at baseline (miR-100-5p), and miRNA fold changes (miR-100-5p, -125b-5p, -126-3p) were correlated with absolute changes in muscle strength and power. These miRNAs require further investigation to explore their possible mechanistic roles in muscle performance declines after bed rest.