Acute exercise activates p38 MAPK and increases the expression of telomere-protective genes in cardiac muscle

Abstract

What is the central question of this study? A positive association between telomere length and exercise training has been shown in cardiac tissue of mice. It is currently unknown how each bout of exercise influences telomere-length-regulating proteins. We sought to determine how a bout of exercise altered the expression of telomere-length-regulating genes and a related signalling pathway in cardiac tissue of mice. What is the main finding and its importance? Acute exercise altered the expression of telomere-length-regulating genes in cardiac tissue and might be related to altered mitogen-activated protein kinase signalling. These findings are important in understanding how exercise provides a cardioprotective phenotype with ageing. Age is the greatest risk factor for cardiovascular disease. Telomere length is shorter in the hearts of aged mice compared with young mice, and short telomere length has been associated with an increased risk of cardiovascular disease. One year of voluntary wheel-running exercise attenuates the age-associated loss of telomere length and results in altered gene expression of telomere-length-maintaining and genome-stabilizing proteins in heart tissue of mice. Understanding the early adaptive response of the heart to an endurance exercise bout is paramount to understanding the impact of endurance exercise on heart tissue and cells. To this end, we studied mice before (BL), immediately after (TP1) and 1 h after a treadmill running bout (TP2). We measured the changes in expression of telomere-related genes (shelterin components), DNA-damage-sensing (p53 and Chk2) and DNA-repair genes (Ku70 and Ku80) and mitogen-activated protein kinase (MAPK) signalling. The TP1 animals had increased TRF1 and TRF2 protein and mRNA levels, greater expression of DNA-repair and -response genes (Chk2 and Ku80) and greater protein content of phosphorylated p38 MAPK compared with both BL and TP2 animals. These data provide insights into how physiological stressors remodel the heart tissue and how an early adaptive response mediated by exercise may be maintaining telomere length and/or stabilizing the heart genome through the upregulation of telomere-protective genes.

Keywords: gene expression; telomerase; telomere.

Figure 1. Acute treadmill running increased shelterin gene expression in cardiac muscle

mRNA abundance was assessed by RT-PCR and target genes were normalized to 18S and expressed relative to BL. Results of densitometric analysis are shown. Data are presented as means ± S.D. BL: baseline (n = 6); TP1: immediately after the exercise bout (n = 8); TP2: one-hour after the exercise bout (n = 8). * TP1 significantly different than BL (p < 0.05). ^# TP1 significantly different than TP2 (p < 0.05). ^§ TP2 significantly different than BL (p < 0.05).

Figure 2. TRF1 and TRF2 protein content were increased following acute treadmill running

Results of densitometric analysis and representative immunoblots of TRF1, TRF2, and GAPDH are shown; GADPH was a loading reference. Data are presented as means ± S.D. BL: baseline (n = 6); TP1: immediately after the exercise bout (n = 8); TP2: one-hour after the exercise bout (n = 8). GAPDH: glyceraldehyde 3-phosphate dehydrogenase. * TP1 significantly different than BL (p < 0.05). ^# TP1 significantly different than TP2.

Figure 3. Activity and expression of telomerase increased after acute treadmill running

Telomerase enzyme activity (left) and mTert gene expression (right) are shown. mRNA abundance for mTert was assessed with RT-PCR, normalized to 18S and expressed relative to BL. Results of densitometric analysis are shown. Data are presented as means ± S.D. BL: baseline (n = 4); TP1: immediately after the exercise bout (n = 6); TP2: one-hour after the exercise bout (n = 6). mTert = mouse telomerase reverse transcriptase.

Figure 4. Acute exercise increases gene expression of DNA damage repair and response factors

mRNA abundance was assessed by RT-PCR and target genes were normalized to 18S and expressed relative to BL. Results of densitometric analysis are shown. Data are presented as means ± S.D. BL: baseline (n = 6); TP1: immediately after the exercise bout (n = 8); TP2: one-hour after the exercise bout (n = 8). * TP1 significantly different than BL (p < 0.05). ^§ TP2 significantly different than BL (p < 0.05).

Figure 5. p38 MAPK phosphorylation in cardiac muscle is increased following acute treadmill running

Results of densitometric analysis and representative immunoblots of MAPKs (total and phosphorylated) and GAPDH are shown; GADPH was a loading reference. Phosphorylated to total protein ratios were derived and expressed relative to BL. Data are presented as means ± S.D. BL: baseline; TP1: immediately after the exercise bout; TP2: one-hour after the exercise bout. * TP1 significantly different than BL (p < 0.05). ^# TP1 significantly different than TP2 (p < 0.05). ^§ TP2 tended to be different than BL (p < 0.1).