Influence of physical exercise on cardiac remodeling, oxidative stress, MAPK and NF-kB pathways signaling in spontaneously hypertensive rats

Abstract

Heart failure (HF) is a clinical problem of extreme importance due to its high prevalence, the severity of clinical manifestations and its high morbidity and mortality. Systemic arterial hypertension is a major cause of HF. Chronic hemodynamic overloads such as hypertension induce genetic, molecular, cellular and interstitial alterations, which manifest clinically through changes in the heart size, shape and function a process known as cardiac remodeling. The pressure overload caused by hypertension may produce changes in collagen architecture and induce fibrosis, as well as imbalance between production of reactive oxygen species (ROS) and antioxidant capacity. Increased ROS leads to the activation of signaling pathways such as nuclear factor kappa B (NF-kB) and mitogen-activated protein kinases (MAPK), which may be involved in the response of cardiac muscle to oxidative stress. Changes in extracellular matrix and ROS generation may influence the signaling pathways involved in myocyte growth, fibrosis, inflammation and contraction. These processes contribute to the damage of the cardiac muscle, with consequent cardiac remodeling. Exercise plays important role in mitigating cardiovascular risk factors such as hypertension. In addition, exercise has been shown as a beneficial supportive measure in HF treatment, but its effect on cardiac remodeling, particularly associated with uncontrolled hypertension, remains unclear. Therefore, the aim of this study is to evaluate the influence of exercise training on cardiac remodeling in spontaneously hypertensive rats, at the preceding stage of HF development. Four experimental groups of rats will be used: sedentary normotensive (n=20); trained normotensive (n=20); and sedentary (n=20) and exercised (n=20) spontaneously hypertensive rats (SHR). From 13 months of age, the animals from exercise groups will undergo protocol of treadmill exercise, five days a week for four months. Structural and functional assessment in vivo of the heart will be performed by echocardiography. Myocardial function in vitro will be evaluated through preparations of isolated papillary muscle of the left ventricle. Tissue samples from the rats left ventricle will be obtained for biochemical and histological analysis, as well as from the signaling pathways. The assessment of total myocardial collagen will be performed through histology and hydroxyproline quantification. The size of the myocytes will be measured by histological sections of the left ventricle. The activity of antioxidant enzymes will be quantified by spectrophotometry. The NADPH oxidase activity and total ROS generation will be assessed through quantification of products derived from oxidation of dihidroetídio by HPLC. The protein quantification of collagen I, collagen III, lysyl oxidase, MAPK and NF-kB, and metalloproteinases tissue inhibitors 1 and 2 will be performed by Western blot. The activity of metalloproteinases 2 and 9 will be performed by zymography. Comparisons between groups will be performed by two factors analysis of variance (ANOVA), complemented with the Bonferroni multiple comparison test (normal distribution) or Kruskal-Wallis test complemented with Dunn multiple comparison test (non normal distribution). The statistical conclusions will be discussed at a significance level of 5%. (AU)