Beneficial effects of angiotensin-(1-7) against deoxycorticosterone acetate-induced diastolic dysfunction occur independently of changes in blood pressure.

Mineralocorticoids have been implicated in the pathogenesis of diastolic heart failure. On the contrary, angiotensin (Ang)-(1-7) has emerged as a potential strategy for treatment of cardiac dysfunction induced by excessive mineralocorticoid receptor activation. A critical question about the cardioprotective effect of Ang-(1-7) in hypertensive models is its dependence on blood pressure (BP) reduction. Here, we addressed this question by investigating the mechanisms involved in Ang-(1-7) cardioprotection against mineralocorticoid receptor activation. Sprague-Dawley (SD) and transgenic (TG) rats that overexpress an Ang-(1-7) producing fusion protein (TG(A1-7)3292) were treated with deoxycorticosterone acetate (DOCA) for 6 weeks. After treatment, SD rats became hypertensive and developed ventricular hypertrophy. These parameters were attenuated in TG-DOCA. SD-DOCA rats developed diastolic dysfunction which was associated at the cellular level with reduced Ca(2+) transient. Oppositely, TG-DOCA myocytes presented enhanced Ca(2+) transient. Moreover, higher extracellular signal-regulated kinase phosphorylation, type 1 phosphatase, and protein kinase Cα levels were found in SD-DOCA cells. In vivo, pressor effects of DOCA can contribute to the diastolic dysfunction, raising the question of whether protection in TG was a consequence of reduced BP. To address this issue, BP in SD-DOCA was kept at TG-DOCA level by giving hydralazine or by reducing the DOCA amount given to rats (Low-DOCA). Under similar BP, diastolic dysfunction and molecular changes were still evident in DOCA-hydralazine and SD-low-DOCA, but not in TG-DOCA. In conclusion, Ang-(1-7) protective signaling against DOCA-induced diastolic dysfunction occurs independently of BP attenuation and is mediated by the activation of pathways involved in Ca(2+) handling, hypertrophy, and survival.

The cardiac expression of Mas receptor is responsive to different physiological and pathological stimuli.

The Mas protooncogene encodes a G protein-coupled receptor that has been described as a functional receptor for the cardioprotective fragment of the renin-angiotensin system (RAS), Angiotensin (Ang)-(1-7). The aim of this current study was to evaluate the responsiveness of Mas expression in hearts during different physiological and pathological conditions in rats. Physical training was considered a physiological condition, while isoproterenol-induced hypertrophy, myocardial infarction and DOCA-salt model of hypertension were used as pathological models of heart injury. The expression of Mas was analyzed by western blotting. Although swim-trained rats presented significant cardiac hypertrophy, our physical training protocol was unable to induce changes in the expression of Mas. On the other hand, cardiac hypertrophy and damage elicited by isoproterenol treatment led to a reduction in Mas expression. Myocardial infarction also significantly decreased the expression of Mas after 21 days of myocardial ischemia. Additionally, Mas expression levels were increased in hearts of DOCA-salt rats. Our present data indicate that Mas expression is responsive to different pathological stimuli, thereby suggesting that Mas receptor is involved in the homeostasis of the heart, as well as in the establishment and progression of cardiac diseases.

Molecular mechanisms involved in the angiotensin-(1-7)/Mas signaling pathway in cardiomyocytes.

Recently there has been growing evidence suggesting that beneficial effects of angiotensin-(1-7) [Ang-(1-7)] in the heart are mediated by its receptor Mas. However, the signaling pathways involved in these effects in cardiomyocytes are unknown. Here, we investigated the involvement of the Ang-(1-7)/Mas axis in NO generation and Ca(2+) handling in adult ventricular myocytes using a combination of molecular biology, intracellular Ca(2+) imaging, and confocal microscopy. Acute Ang-(1-7) treatment (10 nmol/L) leads to NO production and activates endothelial NO synthase and Akt in cardiomyocytes. Ang-(1-7)-dependent NO raise was abolished by pretreatment with A-779 (1 micromol/L). To confirm that Ang-(1-7) action is mediated by Mas, we used cardiomyocytes isolated from Mas-deficient mice. In Mas-deficient cardiomyocytes, Ang-(1-7) failed to increase NO levels. Moreover, Mas-ablation was accompanied by significant alterations in the proteins involved in the regulation of endothelial NO synthase activity, indicating that endothelial NO synthase and its binding partners are important effectors of the Mas-mediated pathway in cardiomyocytes. We then investigated the role of the Ang-(1-7)/Mas axis on Ca(2+) signaling. Cardiomyocytes treated with 10 nmol/L of Ang-(1-7) did not show changes in Ca(2+)-transient parameters such as peak Ca(2+) transients and kinetics of decay. Nevertheless, cardiomyocytes from Mas-deficient mice presented reduced peak and slower [Ca(2+)](i) transients when compared with wild-type cardiomyocytes. Lower Ca(2+) ATPase of the sarcoplasmic reticulum expression levels accompanied the reduced Ca(2+) transient in Mas-deficient cardiomyocytes. Therefore, chronic Mas-deficiency leads to impaired Ca(2+) handling in cardiomyocytes. Collectively, these observations reveal a key role for the Ang-(1-7)/Mas axis as a modulator of cardiomyocyte function.