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

Abstract

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.