| Background: Pathological left ventricular hypertrophy is the response of heart to various stimuli or diseases such as hypertension, myocardial infarction, strain and aortic stenosis, heart failure or neurohormones. These inappropriate burdens initially stimulate proteosynthesis and improve cardiac output, namely compensatory cardiac hypertrophy, while sustained cardiac hypertrophy ultimately decompensates with progressive cell death and fibrosis, leading to heart failure, sudden death and stroke. Thus exploring strategies to treat cardiac hypertrophy and elucidating the underlying mechanisms are of great interest. Melatonin(N-acetyl-5-Methoxytryptamine), a ubiquitous and versatile molecule, is believed to function in practically every living organism. Experimental evidences obtained from both human and rodent studies demonstrated that melatonin influences the cardiovascular system, such as limiting the loss of critical heart tissue resulting from ischemia/reperfusion injury, retarding the progression of atherosclerosis, ameliorating nocturnal hypertension,protecting against pathological cardiac hypertrophy induced by hyperthyroidism or chronic hypoxia, and reducing ischemic heart damage induced by isoproterenol. Although the short-term effect of melatonin on pressure overload-induced cardiac hypertrophy has already been investigated in spontaneously hypertensive rats, the long-term effect of melatonin administration on cardiac hypertrophy as well as the underlying mechanis m remain unclear. Cardiac hypertrophy is reported to be associated with mitochondrial energy metabolism abnormalities, and PGC-1? plays a vital role in regulating mitochondrial energy metabolism. Many studies also suggest that melatonin can improve mitochondrial metabolism in various pathological conditions. In this study, the effect of melatonin on pathological cardiac hypertrophy was discussed in vivo and in vitro, and the related mechanism was studied in primary cultured neonatal rat cardiomyocytes.Objective: 1) To explore the protective effect of melatonin on pressure overload-induced cardiac hypertrophy and angiotensin?-induced cardiomyocyte hypertrophy. 2) To illuminate whether PGC-1? was participated into the anti-hypertrophic role of melatonin.Methods: 1) We introduced novel minimally invasive transverse aortic constriction surgery to create pressure overload-induced cardiac hypertrophy. 2) We use angiotensin? to induce cardiomyocyte hypertrophy. 3) Eight-week survival rate and death causes were ananlyzed. 4) The cardiac function in each group was determined by transthoracic ultrasonography. 5) The mean cross-sectional area of the hearts in each group were determined by HE staining. 6) The degree of collagen deposition, namely cardiac fibrosis, were determined by Masson staining and hydroxyproline level measurement. 7) The protein levels of markers of cardiac hypertrophy were determined by western blot. 8) The RNA levels of markers of cardiac hypertrophy were determined by real-time quantitative polymerase chain reaction(RT-PCR). 9) ?-actinin staining was used to measure the mean area of primary cultured neonatal rat ventricular myocytes. 10) The expression of PGC-1? in primary cultured neonatal rat ventricular myocytes in was downregulated by PGC-1?-targeted Si RNA.Results: 1) Melatonin administration significantly improved the 8-week survival rate of mice underwent TAC surgery. The 8-week survival rate of both Sham and melatonin-treated normal mice was 100%. Melatonin supplementation significantly enhanced survival to 91.43%(32 of the 35 mice survived for 8 weeks) in comparison with 72.50%(29 of the 40 mice survived for 8 weeks) survival in vehicle-treated TAC mice(P < 0.05). B y daily observation of the mice and performing autopsy of the dead mice, we found that acute pulmonary oedema/hae morrhage acted as the major cause of early post-TAC death. The majority of mice died late after TAC surgery were presented with pulmonary consolidation, which may acted as the major cause of late post-TAC death. 2) Treatment with melatonin for 8 weeks significantly reversed TAC-induced cardiac hypertrophy, while 4-week treatment not. The sham operation and melatonin alone did not cause cardiac hypertrophy. Four and 8 weeks after TAC surgery, the HW/BW ratios increased by 42.83%(vs. Sham 4W, P < 0.05) and 60.31%(vs. Sham 8W, P < 0.05) respectively. Eight-week melatonin administration significantly reversed the enhanced HW/BW ratio caused by TAC surgery(vs. TAC 8W, P < 0.05), while 4-week melatonin treatment showed no benefit on cardiac enlargement( vs. TAC 4W, P > 0.05). Besides, the mean cross-sectional area of left ventricle cardiomyocytes was remarkably increased 4 and 8 weeks after TAC(P < 0.05). Four-week melatonin administration showed no beneficial effect on cardiac enlargement( P > 0.05), while 8-week melatonin administration greatly reduced the mean cross-sectional area of left ventricle compared with TAC 8W mice(P < 0.05). 3) Melatonin protected hearts against long-lasting pressure overload induced cardiac fibrosis. Four weeks after TAC, mice submitted to TAC procedure showed a moderate increase in perivascular but interstitial collagen content compared with Sham 4W mice, while melatonin administration prevented the development of cardiac fibrosis caused by TAC(P < 0.05). Instead of the mild cardiac collagen deposition 4 weeks after TAC, 8-week TAC caused a severe fibrotic response both in the perivascular and interstitial parts of heart tissue. Melatonin administration(8 weeks) significantly attenuated the collagen accumulation in the heart tissues following TAC(P < 0.05). 4) Melatonin treatment significantly reversed angiotensin ? –induced cardiomyocyte hypertrophy. Cellular immunofluorescence(?-actinin staining) was used to determine the mean area of primary cultured rat neonatal cardiomyocytes. Angiotensin ? caused a significant increase in cell area compared with the control gro up, while melatonin treatment revered the increase in cell area caused by angiotensin?. 5) Both in vivo and in vitro studies showed that melatonin supplementation attenuated the pathological alterations in protein and m RNA levels of ?-myosin heavy chain(?-MHC) and ?-myosin heavy chain(?-MHC), alleviated the elevation of m RNA level of atrial natriuretic factor(ANF) and upregulated the expression of PGC-1?. 6) Downregulation of PGC-1? largely abolished these anti-hypertrophic roles of melatonin on primary cultured rat neonatal cardiomyocytes.Conclusion: 1) We firstly confirmed that melatonin showed a protective role against TAC-induced pathological cardiac hypertrophy and angiotensin ?-incued cardiomyocyte hypertrophy. 2) Melatonin protects cardiomyocytes from angiote nsin ?-incued cardiomyocyte hypertrophy largely by activating PGC-1?. |
PDF Full Text Request