Exercise training enhanced SIRT1 longevity signaling replaces the IGF1 survival pathway to attenuate aging-induced rat heart apoptosis

Abstract

Cardiovascular disease is the second leading cause of death (9.1 %) in Taiwan. Heart function deteriorates with age at a rate of 1 % per year. As society ages, we must study the serious problem of cardiovascular disease. SIRT1 regulates important cellular processes, including anti-apoptosis, neuronal protection, cellular senescence, aging, and longevity. In our previous studies, rats with obesity, high blood pressure, and diabetes exhibiting slowed myocardial performance and induced cell apoptosis were reversed via sports training through IGF1 survival signaling compensation. This study designed a set of experiments with rats, in aging and exercise groups, to identify changes in myocardial cell signaling transduction pathways. Three groups of three different aged rats, 3, 12, and 18 months old, were randomly divided into aging groups (C3, A12, and A18) and exercise groups (E3, AE12, and AE18). The exercise training consisted of swimming five times a week with gradual increases from the first week from 20 to 60 min for 12 weeks. After the sports training process was completed, tissue sections were taken to observe cell organization (hematoxylin and eosin (H&E) stain) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays) and to observe any changes in the myocardial tissues and proteins (Western blotting). The experimental results show that cardiomyocyte apoptotic pathway protein expression increased with age in the aging groups (C3, A12, and A18), with improvement in the exercise group (E3, AE12, and AE18). However, the expression of the pro-survival p-Akt protein decreased significantly with age and reduced performance. The IGF1R/PI3K/Akt survival pathway in the heart of young rats can indeed be increased through exercise training. As rats age, this pathway loses its original function, even with increasing upstream IGF1. However, levels of SIRT1 and its downstream target PGC-1α were found to increase with age and compensatory performance. Moreover, exercise training enhanced the SIRT longevity pathway compensation instead of IGF1 survival signaling to improve cardiomyocyte survival.

Fig. 1

Hematoxylin and eosin staining (H&E staining). Cardiac tissue sections stained with hematoxylin and eosin. The myocardial architecture images were magnified ×400. The scale bar is 100 μm

Fig. 2

a Representative apoptotic cells in cardiac sections from the left ventricles of SD rats, in the aging (C3, A12, and A18) and exercise (E3, AE12, and AE18) groups, measured using DAPI staining (upper panels, blue spots) and the TUNEL assay (lower panels, green spots). The images were magnified ×400. The scale bar is 100 μm. b Bars present the percentage of TUNEL-positive cells relative to total cells. *p < 0.05; **p < 0.01; ***p < 0.001, significant differences between the C3 and A12 or A18 groups. ^# p < 0.05; ^## p < 0.01; ^### p < 0.001, significant differences between the aging (C3, A12, and A18) and exercise (E3, AE12, and AE18) groups

Fig. 3

a The representative protein products of the Fas receptor, FADD, caspase-8, and caspase-3 extracted from the left ventricles of two rats in each group, SD rats (C3), aging rats (A12, A18), and aging, exercise-trained rats (E3, AE12, AE18), measured using Western blotting. b The representative cytochrome c, caspase-9, and caspase-3 protein products extracted from the left ventricles of two rats in each group, SD rats (C3), aging rats (A12, A18), and aging, exercise-trained rats (E3, AE12, AE18), measured using Western blotting. c The representative protein products of IGF1, pIGF1R, pPI3K, and pAkt extracted from the left ventricles of two rats in each group, SD rats (C3), aging rats (A12, A18), and aging, exercise-trained rats (E3, AE12, AE18), measured using Western blotting. α-Tubulin was used as an internal control. *p < 0.05; **p < 0.01; ***p < 0.001, significant differences between the aging (C3, A12, and A18) and exercise (E3, AE12, and AE18) groups

Fig. 4

The representative protein products of pAMPK, SIRT1, and PGC-1α extracted from the left ventricles of two rats in each group, SD rats (C3), aging rats (A12, A18), and aging, exercise-trained rats (E3, AE12, AE18) were measured using Western blotting. α-Tubulin was used as an internal control. *p < 0.05; **p < 0.01; ***p < 0.001, significant differences between the aging (C3, A12, and A18) and exercise (E3, AE12, and AE18) groups

Fig. 5

The summary of SIRT1 regulating the apoptotic upstream pathways within a cardiomyocyte in exercise-trained SD rats