| Background and Objectives:Cardiovascular diseases were seriously threat to human health, which have become the leading cause of death worldwide. Heart failure is a serious and terminal stage of various heart diseases, which is one of the most important cardiovascular diseases today. Cardiac hypertrophy is the adaptive response of heart to the hemodynamic overload that leads to hyperplasia, which is an independent risk factor for cardiovascular disease. Prolonged cardiac hypertrophy leads to congestive heart failure, coronary heart disease, sudden death and stroke. Many risk factors are implicated in the development of heart failure. The genetic factors including gender, age, race, belong to an irreversible factors. Other factors such as high blood pressure, diabetes, obesity, insulin resistance, alcohol abuse, high salt intake and low potassium, are associated with unhealthy lifestyles.Since 2200 B.C.E., salt as a condiment has been widely used in China, and high salt intake becomes a part of Chinese food culture. Epidemiological survey showed that the people in northern China have higher daily salt intakes(>15g/day) than southern China(>10g/day) in average, while both are far higher than the recommendations from world health organization(<5g/day).Meanwhile, epidemiological studies have shown that the incidence of high blood pressure and coronary heart disease(CHD) in northern China is significantly higher than those in southern China.Since the populations in northern China like to eat salty diet, and the southwestern people like to eat spicy diet, differences in dietary habits may have important effects on cardiovascular metabolic diseases.Capsaicin, a major pungent ingredient in chili peppers, is a highly selective agonist for the transient receptor potential vanilloid receptor 1(TRPV1).TRPV1 is mainly expressed in the sensory neurons and brain,and also expressed in various non-neuronal tissues including smooth muscle cell,epithelial cell,vascular endothelial cell,adipose tissue.Our previous studies confirmed that activation of TRPV1 can lower blood pressure, alleviate atherosclerosis, improve glucose metabolism and prevent obesity.By activating TRPV1, capsaicin increases exercise tolerance, oxygen consumption, and type I fiber content of skeletal muscle in mice to improve the energy metabolism of skeletal muscle. Nocturnal high blood pressure is the major cause of cardiac hypertrophy caused by high salt intake.Our previous study showed that activation of TRPV1 lowers high salt-mediated blood pressure increment.These studies indicate that capsaicin plays a protective role in cardiovascular system.Clinical and experimental studies suggest that long-term high salt intake is an independent risk factor for cardiac hypertrophy. The pathophysiology mechanism between high salt and cardiac hypertrophy remains unknown. The findings from both clinical and experimental studies suggest that dysfunction of mitochondrial energetic may contribute to the development of cardiac hypertrophy.Fatty acids are the main substrates used by mitochondria to provide myocardial energy under normal conditions.Before the development of left ventricular hypertrophy and heart failure, pressure load leads to the change in energy metabolism of myocardial mitochondria. It would use glucose as substrate of energy production. In the early stages of cardiac remodeling, changes in energy metabolism play a crucial role in protecting the heart from irreversible damage.Uncoupling protein 3, belongs to the mitochondrial anion carrier family, mainly regulates energy metabolism and free fatty acid metabolism. UCP3 has a protective role in the heart through improving mitochondrial function and alleviating ROS-induced oxidative stress. High salt intake leads to the increase of pressure load, leading to the cardiac remodeling at first. It remains unknown whether the increase of pressure load caused by high salt intake leads to myocardial energy metabolism changes and consequent mitochondrial dysfunction. Therefore, we hypothesized that mitochondrial dysfunction contributes to high salt-induced cardiac hypertrophy and some ion channels, such as TRPV1 and UCP3 might participate in the development of high salt-induced cardiac remodeling.To test the above hypothesis, this study was divided into two parts. Part one: we sought to examine the hypothesis that TRPV1 activation by capsaicin prevents high salt-induced cardiac hypertrophy through improving cardiac mitochondrial function. First of all, we confirmed that the activation of TRPV1 by dietary capsaicin attenuated high salt-induced cardiac hypertrophy. The cardiac function indexes and endurance capacity of mice were assessed. Then energy expenditure and physical performance were monitored using the Comprehensive Laboratory Animal Monitoring System(CLAMS). We then further confirmed that mitochondrial dysfunction was implicated in the development of cardiac hypertrophy caused by high salt intake. Mitochondrial respiration and oxygen consumption were measured using high-resolution respirometry. The protein expression levels of TRPV1, sirtuin 3 and NDUFA9 were detected in cardiac cells and tissues. Part two: we investigated the role of uncoupling protein 3 in the development of cardiac hypertrophy caused by high salt intake.Material and methods:This study includes in vitro and in vivo experiments. In vitro experiments were performed on cultured rat myocardial cells(H9C2 cells).In vivo models including TRPV1 knockout(TRPV1-/-) mice and their wild type littermates, were randomly grouped and treated with normal-salt diet(0.05% salt,NS), high-salt diet(8% salt,HS) and high salt plus capsaicin diet(8% salt plus 0.01% capsaicin,HC) for 24 weeks.In addition, UCP3 knockout(UCP3-/-)mice and C57 BL / 6 mice were randomly grouped and fed with normal-salt diet(0.05% salt,NS), high-salt diet(8% salt,HS) for 24 weeks.1.Animal experiment study:1) Body weight, blood pressure, heart rate, food intake, water intake were measured.2) Echocardiography and endurance test were performed to evaluate the changes of heart structure and function in mice.3) Energy expenditure and physical performance were monitored by CLAMS.4) Mitochondrial function test determined the changes of mitochondrial respiration function, enzyme activity of respiration chain, and the ATP level.5) The protein expression of TRPV1, Sirt3, NDUFA9 in cardiac mitochondria of mice was detected by immunoblotting.2.Cell experiment study: The protein expression of TRPV1, Sirt3 and NDUFA9 in cultured rat myocardial cells was detected by immunoblotting.Results:1.Long-term high salt intake led to elevated systolic BP, left ventricular hypertrophy and cardiac function lesion. The activation of TRPV1 by dietary capsaicin can lower blood pressure, alleviate left ventricular hypertrophy and improve cardiac dysfunction.2. Long-term high salt intake led to energy metabolism disorder, performance abnormal and endurance capacity reduction of mice. The activation of TRPV1 by dietary capsaicin improved energy metabolism, increased locomotor activity and enhanced endurance capacity.3.TRPV1 existed in both cardiac mitochondria of mice and mitochondria of rat myocardial cells(H9C2 cells). The knockout of TRPV1 and long-term high salt intake led to mitochondrial dysfuncition, the activation of TRPV1 by dietary capsaicin improved mitochondrial dysfuntion caused by high salt intake, enhanced the oxidative phosphorylation(OXPHOS) capacity of CⅠ and CⅠ+Ⅱ as well as electron transfer system(ETS)capacity of CⅠ and CⅠ+Ⅱ.4.The knockout of TRPV1 and high salt intake decreased the enzyme activity of mitochondrial CⅠand citrate synthase but there was no effect on Complex Ⅱ(CⅡ).Chronic dietary capsaicin significantly enhanced the enzyme activity of CⅠand citrate synthase, but these effects were absent in CⅡ.5.The knockout of TRPV1 and high salt intake reduced the level of ATP, and the activation of TRPV1 by chronic dietary capsaicin markedly increased the level of ATP.6.The activation of TRPV1 by capsaicin upregulated the protein expression of Sirt3 and NDUFA9 in both cardiac mitochondria of mice and mitochondria of rat myocardial cells.7.High salt intake induced left ventricular hypertrophy and diastolic dysfunction independent of elevated systolic BP. UCP3-/- mice were more sensitive to salt than C57BL/ 6 mice. The knockout of UCP3 exacerbated cardiac hypertrophy and cardiac lesions caused by high salt intake.Conclusion:1.Long-term high salt intake led to cardiac hypertrophy and dysfunction through either blood pressure dependent or independent manner. 2.Long-term high salt intake led to cardiac mitochondrial respiratory dysfunction. The knockout of TRPV1 and UCP3 exacerbates high salt-induced mitochondrial respiratory dysfunction. The activation of TRPV1 by capsaicin upregulated the protein expression of Sirt3 and NDUFA9, increased complex Ⅰ enzyme activity and mitochondrial content, enhanced ATP production, and thereby improved cardiac mitochondrial dysfunction caused by high salt intake.3.The knockout of UCP3 increased salt sensitivity. UCP3 had a protective effect on the heart through improving myocardial mitochondrial function. |
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