Effects Of Aerobic Exercise On Cardiomyocyte Proliferation During Cardiac Hypertrophy And Its Regulatory Mechanism

Objective:To explore exercise on the activation of cardiomyocyte proliferation in cardiac hypertrophy and the role of cyclic-AMP-responsive element binding protein binding protein (CBP) in it by in vivo and in vitro experiments.Method:The exercise-induced cardiac hypertrophy model was made by swim training, and the pathological model was made by transverse aortic constriction (TAC).12-week-old C57B1/6J mice were divided randomly into control group, swim group, sham group and TAC group. By the end of experiments, cardiac hypertrophy, contractility were evaluated by echocardiography, heart weight/body weight rasio (HW/BW) and left ventricular weight/tibial length ratio (LVW/TL) were calculated to evaluate the degree of myocardiac hypertrophy. Myocardial fibrosis were detected by Masson staining. The expression level of myocardial PCNA were examined by Western Blot, ANP and BNP mRNA expression were detected by real time PCR (RT-PCR), the expression level of myocardial CBP were examined by RT-PCR, Western Blot and immunohistochemical methods. To verify the effect of CBP on activation of cardiomyocytes proliferation, we did in vitro experiment on primary cardiomyocytes. In this experiment, cardiomyocyte hypertrophy were induced by phenylephrine (PE), and C646was used to inhibit the expression of CBP. Meanwhile, cardiomyocyte hypertrophy was detected by a-actin immunofluorescence, CBP mRNA expression were detected by RT-PCR, the expression level of Ki67was detected by immunofluorescence to evaluate the degree of cardiomyocyte proliferation.Results:1. Compared with corresponding control groups, inter ventricular septum thickness (IVS) and left ventricular posterior wall thickness (LVPW) of exercise-induced and pathological cardiac hypertrophy models were significantly increased (p<0.05). Heart weight/body weight ratio (HW/BW), left ventricular weight/tibia length ratio (LVW/TL) were also increased significantly (p<0.05) compared with corresponding control groups. The area of cardiomyocytes were significantly increased of two cardiac hypertrophy models (p<0.01) compared with corresponding control groups.2. The myocardial fibrosis of TAC group was significantly heavier than Swim group, ANP and BNP mRNA expression of TAC group were higher than those of Sham group obviously (p<0.01). ANP mRNA expression of Swim group was higher than that of Control group (p<0.05), while BNP mRNA expression did not change significantly.3. The protein expression levels of PCNA in Swim group was higher than that of Control group (p<0.05) and TAC group (p<0.01).4. CBP mRNA expression of Swim group was increased significantly than that of Control (p<0.01) and TAC group (p<0.05). CBP protein expression of TAC was decreased significantly than that of Sham (p<0.05), and the level of Swim were higher obviously than those of Control (p<0.05) and TAC (p<0.01). The immunohistochemistry of CBP showed that CBP-positive cells of Swim was significantly more than Control (p<0.01) and TAC group (p<0.01).5. In vitro experiment, the primary cardiomyocytes performanced hypertrophy induced by PE (p <0.05), and use of C646could decrease cardiomyocyte hypertrophy (p<0.05) significangtly than that of PE. CBP mRNA expression of PE was significantly increased compared with Control (p<0.05), and this level was obviously inhibited by C646(p<0.01). The immunofluorescence of Ki67showed that PE could increase Ki67-positive cells obviously (p<0.01), and cardiomyocytes proliferation were inhibited (p<0.05) when CBP activity were suppressed.Conclusion:1. Aerobic exercise promotes myocardial proliferation of ischemic myocardium.2. Aerobic exercise promotes myocardial proliferation through activating CBP possibly. Cardiomyocytes proliferation was inhibited when CBP activity were suppressed.