Resistance Exercise Inhibits Cardiomyocyte Apoptosis Through Stimulating the Skeletal Muscle FSTL1 Secretion in Myocardial Infarction Rats and its Mechanisms

Objective: To investigate the effects of resistance exercise on cardiomyocyte apoptosis through stimulating the skeletal muscle Follistatin-like protein 1(FSTL1) secretion in myocardial infarction rats and its mechanisms.Methods: Animal experiment:the male Sprague-Dawley rats were randomly divided into 5 groups(n=10 in each group): sham-operated group(S), sedentary MI group(MI), MI with resistance exercise group(MR), MI with adeno-associated virus(AAV) empty vector group(MV), and MI with FSTL1-AAV vector group(MF) after the MI model was established by left anterior descending coronary artery ligation. The S group underwent threading without ligation. 1 week after MI, rats in MR group were conducted a resistance exercise program for 4 weeks,and rats in MV and MF group were injected AAV empty vector or FSTL1-AAV vector in tibialis anterior of the left limb,respectively. The next day after the whole training program, the heart function was measured after anesthesia, and then the heart and tibialis anterior of the left limb were collected. Collagen volume fraction(%) of myocardium were observed and calculated by Masson staining; cardiomyocyte apoptosis was measured by TUNEL; the protein expression of skeletal muscle and serum FSTL1 and myocardium FSTL1, DIP2A, p-Akt/Akt, p-mTOR/mTOR and Bcl2/Bax were measured by Western blotting. Cell experiment:H9C2 cells were divided into 8 groups: H9C2 cells control group, H9C2+LPS(Lipopolysaccharide) group, H9C2+LPS+AICAR(AMPK activator) group, H9C2+LPS+LY294002(PI3 K inhibitor) group, H9C2+LPS+AICAR+LY294002 group, H9C2+LPS+rhFSTL1 group, H9C2 +LPS+rhFSTL1+AICAR group, H9C2+LPS+rhFSTL1+LY294002 group. The apoptosis of H9C2 cell was detected by TUNEL; the H9C2 cell viability was determined by CCK8 assay; the protein expression of FSTL1, DIP2A, p-Akt/Akt,p-mTOR/mTOR and Bcl2/Bax in each group were determined by Western blotting. Results: After MI, the skeletal muscle FSTL1 gene and protein expression were decreased, the myocardium and serum FSTL1 protein level were significantly increased, the cardiomyocyte apoptosis and myocardial fibrosis were significantly increased, and the heart function was declined; however, no significant changes were observed in the myocardium FSTL1 gene expression. After resistance exercise or injection of FSTL1-AAV vector, the skeletal muscle and serum FSTL1 protein level and myocardium FSTL1, DIP2A, p-Akt, p-mTOR and Bcl2/Bax protein expression were significantly increased, the cardiomyocyte apoptosis and myocardial fibrosis were decreased and the heart function was significantly improved; meanwhile, resistance exercise significantly up-regulated the FSTL1 gene expression in skeletal muscle,but there was no significant difference in myocardium FSTL1 gene expression. FSTL1 and AICAR inhibited LPS-induced H9C2 cells apoptosis significantly, and increased the FSTL1, DIP2A, p-Akt, p-mTOR, Bcl2/Bax protein expression level and H9C2 cell viability; however, the LY294002 expressed opposite effects. Conclusion: The skeletal muscle-derived FSTL1 plays an important role in resistance exercise up-regulates myocardium FSTL1 expression and inhibited cardiomyocyte apoptosis in MI rats. Skeletal muscle-derived FSTL1 can reach the heart through blood circulation, and then bind to its receptor DIP2A and activate the AktmTOR signaling pathway, which inhibiting the cardiomyocyte apoptosis, reducing myocardial fibrosis and improving heart function in MI rats.