Influência do exercício físico sobre a via da miostatina e o fenótipo muscular em ratos submetidos a alimentação intermitente

Abstract

Intermittent feeding (IF) is a dietary intervention often used as an alternative to caloric restriction (CR) and characterized by cycles alternating ad libitum feeding and fasting. The main consequence of CR on skeletal muscle is fiber size reduction, which can be attenuated by physical exercise. However, the effects of IF on skeletal muscle phenotype and its related molecular mechanisms are not well studied. Myostatin is a growth factor that correlates negatively to muscle mass. The present study aimed to evaluate the influence of exercise on myostatin signaling and skeletal muscle phenotype in rats submitted to intermitent feeding. Male Wistar rats (n=40) were allocated into four groups: sedentary control (C-S), control + physical exercise (C-Ex), sedentary intermitent feeding (IF-S), and intermitent feeding + physical exercise (IF-Ex). The C-S and C-Ex groups were fed ad libitum (AL), and IF-S and IF-Ex groups had ad libitum access to food on alternating days. Rats from C-Ex and IF-Ex underwent into a treadmill-exercise protocol for 90 days. Myostatin and follistatin protein expression was assessed by Western blot in soleus and gastrocnemius (white portion) muscles. Exercise improved functional capacity, assessed by maximal exercise test on treadmill. Concerning skeletal muscle analysis, soleus muscle mass was lower in IF-S group than in C-S group. Gastrocnemius muscle mass was lower in IF-S and IF-Ex groups in comparison to C-S and C-Ex, respectively; however, it was higher in IF-Ex group than in IF-S. Gastrocnemius muscle fiber cross-sectional area was significantly lower in IF-S than in C-S, and lower in IF-Ex than in C-Ex group. In soleus muscle, fiber cross-sectional area was lower in IF-S than in C-S group, and higher in IF-Ex than in IF-S group. Exercise influenced myostatin protein expression in gastrocnemius muscle; additionally, myostatin was significantly lower in C-Ex group than in C-S. There was no significantly difference between the groups for myostatin expression in soleus muscle, and follistatin expression in both gastrocnemius and soleus muscle. In conclusion, intermittent feeding promotes a physical exercise-reversible atrophy in soleus and gastrocnemius muscles of rats. Although myostatin can be modulated by physical exercise, it does not seem to participate on intermittent feeding-induced muscle atrophy.