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.

Abstract 324: In Vivo Cross-talk Between Mineralocorticoid Receptor and Ang-(1-7) Enhances Ca2+ Signaling in Ventricular Myocytes

Mineralocorticoids have been implicated in the pathogenesis of cardiac diseases. In contraposition, Angiotensin (Ang)-(1-7) has been shown to attenuate cardiac dysfunction induced by excessive mineralocorticoid receptor (MR) activation in vivo , suggesting a possible interaction between these two signaling pathways in the heart. Here, we investigated whether there is a cross-talk between MR signaling and Ang-(1-7) and its consequences for cardiomyocyte function. For this, we used a transgenic rat that overexpress an Ang-(1-7)-producing fusion protein, TGR(A1-7)3292 (TG), which induces an increase in circulating levels of this peptide, treated or not with deoxycorticosterone acetate (DOCA). After six weeks of DOCA-salt, rats presented increased blood pressure and cardiac ejection fraction when compared to SD control rats. Marked cardiac hypertrophy was also observed at six weeks of DOCA-salt treatment. In contrast, TG DOCA rats did not develop cardiac hypertrophy or changes in ventricular function. qPCR analysis of ventricular myocytes from SD DOCA-salt rats revealed a six fold increase in MR and a three fold increase in ß-myosin heavy chain mRNA transcripts. These changes were significantly attenuated in cardiomyocytes from TG DOCA rats. We also examined intracellular Ca 2+ levels in freshly isolated Fluo-4-loaded cells. The amplitude of the [Ca 2+ ] i transient was reduced in SD DOCA cardiomyocytes (F/F 0 =5.12+ 0.1 n=56 in SD versus F/F 0 =3.75+0.1 n=65 in SD DOCA myocytes, p<0.05). These changes were at least partly explained by reduced SERCA2 protein and altered PLN phosphorylation in these cells. In contrast, TG DOCA cardiomyocytes presented enhanced Ca 2+ transient (F/F 0 =8.02+ 0.2 n=68 myocytes) and increased SERCA2 expression. Cardiomyocytes from TG rats presented Ca 2+ transient comparable to SD cells. SD DOCA rats also showed increased PP1 and PKC alpha expression in comparison to SD and TG DOCA cells. These results suggest that Ang-(1-7) and MR signaling pathways cross-talk to enhance Ca 2+ transient in cardiomyocytes preventing the Ca 2+ signaling dysfunction characteristic of excessive MR activation. These data provide a better understanding of the cardioprotective effects of this putative therapeutic peptide.

Abstract 312: Activation of GPR30 Attenuates Cardiac Injury in the Ovariectomized Diabetic mRen2.Lewis Rat

Our previous study demonstrated that the exacerbation of hypertension as well as alterations in the angiotensin II type 1 receptor (AT1) and endothelial nitric oxide synthase (eNOS) pathways were associated with the development of cardiac remodeling in the diabetic, ovariectomized (OVX-D) mRen2.Lewis rats. The present study evaluated the cardiovascular effects of G-1, a selective agonist of the estrogen receptor GPR30, in insulin- and estrogen-depleted mRen.Lewis rats. Hemizygous littermates were divided into 3 groups: intact controls (C); OVX-D, and OVX-D treated with G1 (G-1). Ovariectomy was performed at 10 weeks of age and diabetes subsequently induced at 11 weeks with streptozotocin (65 mg/kg). G-1 was given by osmotic minipump implanted 2 days after STZ injection (0.2 mg/kg/day; ip). After four weeks blood pressure was measured and heart removed for analysis of AT1 receptor and eNOS protein expression as well as immunohistochemical identification of GPR30. Left ventricle (LV) wet weight was measured and cardiac tissue fibrosis was analyzed from the LV sections stained with picrosirius red. Immunohistochemical staining for GPR30 was evident in both coronary vessels and cardiac myocyte of the OVX-D rats. Chronic treatment with G1 decreased the systolic blood pressure (C: 142 ± 3; OVX-D: 184 ± 3*; G-1: 167 ± 6* # mmHg; *p<0.05 vs C; # p<0.05 vs OVX-D) and the incidence of microinfractions but did not reduce LV weight of OVX-D mRen2.Lewis rats (C: 0.57 ± 0.01; OVX-D: 0.62 ± 0.02*; G-1: 0.63 ± 0.01*g). G-1 treatment was associated with an increase in the cardiac expression of eNOS (C: 100 ± 6%; OVX-D: 59 ± 2%*; G-1: 86 ± 2% # ) but the agonist did not alter cardiac AT1 receptor expression (C: 100 ± 14%; OVX-D: 163 ± 11%*; G-1: 174 ± 9%*). We detected no change in uterine weight of the OVX-D rats treated with G-1 suggesting no crossover of the agonist with the steroid receptors ERα or ERβ (C: 0.68 ± 0.07; OVX-D: 0.14 ± 0.01*; G-1: 0.14 ± 0.01*g). In conclusion, the present study suggests that selective activation of a novel GPR30 receptor may attenuate cardiac injury in estrogen- and insulin-depleted mRen2.Lewis rats by reducing blood pressure and preserving eNOS pathway.

Chronic infusion of angiotensin-(1-7) into the lateral ventricle of the brain attenuates hypertension in DOCA-salt rats

Angiotensin-(ANG)-(1-7) is known by its central and peripheral actions, which mainly oppose the deleterious effects induced by accumulation of ANG II during pathophysiological conditions. In the present study we evaluated whether a chronic increase in ANG-(1-7) levels in the brain would modify the progression of hypertension. After DOCA-salt hypertension was induced for seven days, Sprague-Dawley rats were subjected to 14 days of intracerebroventricular (ICV) infusion of ANG-(1-7) (200 ng/h, DOCA-A7) or 0.9% sterile saline. As expected, on the 21st day, DOCA rats presented increased mean arterial pressure (MAP) (≈40%), and impaired baroreflex control of heart rate (HR) and baroreflex renal sympathetic nerve activity (RSNA) in comparison with that in normotensive control rats (CTL). These changes were followed by an overactivity of the cardiac sympathetic tone and reduction of the cardiac parasympathetic tone, and exaggerated mRNA expression of collagen type I (≈9-fold) in the left ventricle. In contrast, DOCA rats treated with ANG-(1-7) ICV had an improvement of baroreflex control of HR, which was even higher than that in CTL, and a restoration of the baroreflex control of RSNA, the balance of cardiac autonomic tone, and normalized mRNA expression of collagen type I in the left ventricle. Furthermore, DOCA-A7 had MAP lowered significantly. These effects were not accompanied by significant circulating or cardiac changes in angiotensin levels. Taken together, our data show that chronic increase in ANG-(1-7) in the brain attenuates the development of DOCA-salt hypertension, highlighting the importance of this peptide in the brain for the treatment of cardiovascular diseases.