Short-Duration Swimming Exercise after Myocardial Infarction Attenuates Cardiac Dysfunction and Regulates Mitochondrial Quality Control in Aged Mice

Abstract

Background: Exercise benefits to cardiac rehabilitation (CR) following stable myocardial infarction (MI). The suitable exercise duration for aged patients with coronary heart disease (CHD) remains controversial, and the underlying molecular mechanism is still unclear.

Methods and results: 18-Month-old mice after stable MI were randomly submitted to different durations of exercise, including 15 and 60 min swimming training (ST) once per day, five times a week for 8 weeks. Compared to sedentary mice, 15 min ST, rather than 60 min ST, significantly augmented left ventricular function, increased survival rate, and suppressed myocardial fibrosis and apoptosis. 15 min ST improved mitochondrial morphology via regulating mitochondrial fission-fusion signaling. 15 min ST regulated mitophagy signaling via inhibiting LC3-II and P62 levels and increasing PINK/Parkin expression. 15 min ST also inhibited ROS production and enhanced antioxidant SOD2 activity. Notably, 15 min ST significantly increased sirtuin (SIRT) 3 level (2.7-fold) in vivo while the inhibition of SIRT3 exacerbated senescent H9c2 cellular LDH release and ROS production under hypoxia. In addition, SIRT3 silencing impairs mitochondrial dynamics and mitophagy in senescent cardiomyocytes against simulated ischemia (SI) injury.

Conclusion: Collectively, our study demonstrated for the first time that sustained short-duration exercise, rather than long-duration exercise, attenuates cardiac dysfunction after MI in aged mice. It is likely that the positive regulation induced by a short-duration ST regimen on the elevated SIRT3 protein level improved mitochondrial quality control and decreased apoptosis and fibrosis contributed to the observed more resistant phenotype.

Figure 1

Short-duration exercise after MI promotes left ventricular ejection fraction (LVEF) and reduces mortality in aged mice. (a) Statistics of mouse body weight before and after 8-week swimming training (ST). (b) LVEF analysis. (c) Echocardiography of aged mice after 8-week ST. (d) Survival curves. ^∗ P < 0.05 versus the sham group; ^# P < 0.05, ^## P < 0.01 versus the MI-sedentary group; ^&& P < 0.01 versus the MI + 15' ST group. N = 21–23 for survival rate analysis and N = 8–9 for other assessments.

Figure 2

Short-duration exercise after MI inhibits cardiac fibrosis and apoptosis in aged mice. (a, b) Myocardial interstitial fibrosis determined by Masson trichrome staining. Black arrows indicate the ligation of left coronary artery. Scale bars, 50 μm. (c, d) Cardiomyocyte apoptosis determined by TUNEL staining. Scale bars, 30 μm. ^∗∗ P < 0.01 versus the sham group; ^# P < 0.05, ^## P < 0.01 versus the MI-sedentary group; ^&& P < 0.01 versus the MI + 15' ST group. N = 6–8.

Figure 3

Short-duration exercise after MI modulates mitochondrial morphology and dynamics in aged heart. (a) Representative transmission electron micrographs of cardiac mitochondria. Scale bars, 1 μm. (b) Frequency distribution (% total mitochondria) of the mitochondrial surface area. N = 243–251. (c–i) Western blot analysis of mitochondrial fission and fusion markers. ^∗∗ P < 0.01 versus the sham group; ^# P < 0.05, ^## P < 0.01 versus the MI-sedentary group; ^&& P < 0.01 versus the MI + 15' ST group. N = 6–8.

Figure 4

Short-duration exercise after MI regulates mitophagy signaling in aged mice. (a–c) Western blot analysis of mitophagy markers LC3 and P62. (d-e) Western blot analysis of PINK1 and Parkin. ^∗ P < 0.05, ^∗∗ P < 0.01 versus the sham group; ^# P < 0.05, ^## P < 0.01 versus the MI-sedentary group; ^&& P < 0.01 versus the MI + 15' ST group. N = 6–8.

Figure 5

Short-duration exercise after MI attenuates oxidative stress and increases SIRT3 expression in aged heart. (a) ROS production determined by DHE staining. Scale bars, 50 μm. (b) Statistical analysis of DHE positive cells. (c) Ac-SOD2 to SOD2 ratio. (d) Western blot analysis of mitochondrial SIRT3. ^∗ P < 0.05; ^∗∗ P < 0.01 versus the sham group; ^## P < 0.01 versus the MI-sedentary group; ^&& P < 0.01 versus the MI + 15' ST group. N = 6–8.

Figure 6

SIRT3 deficiency exacerbates SI-induced cardiomyocyte apoptosis and oxidative stress. (a) Effect of SIRT3 silencing on cell death, determined by LDH release assay. (b) Effect of SIRT3 silencing on apoptotic events, determined by caspase-3 activity assay. (c–e) Effect of SIRT3 silencing on mitochondrial ROS production, determined by MitoSOX Red dye. Scale bars, 10 μm. (f) Ac-SOD2 to SOD2 ratio upon SIRT3 inhibition. ^∗ P < 0.05, ^∗∗ P < 0.01 versus the SI + NC group. N = 3–6.

Figure 7

SIRT3 regulates cardiomyocytes mitochondrial dynamics under SI injury. (a–c) Western blot analysis of fission proteins Drp1 and Fis1 upon SIRT3 silencing. (d–g) Western blot analysis of fusion proteins Mfn1, Mfn2, and Opa1 upon SIRT3 silencing. ^∗ P < 0.05 versus the SI + NC group. N = 3–6.

Figure 8

SIRT3 regulates SI-induced mitophagy signaling in vitro. (a–c) Western blot analysis of mitophagy makers LC3 and P62 upon SIRT3 silencing. (d-e) Western blot analysis of PINK1 and Parkin upon SIRT3 silencing. ^∗ P < 0.05, ^∗∗ P < 0.01 versus the SI + NC group. N = 3–6.