Angiotensin(1-7) Blunts Hypertensive Cardiac Remodeling by a Direct Effect on the Heart

Angiotensin-converting enzyme 2 (ACE2) converts the vasopressor angiotensin II (Ang II) into angiotensin (1-7) [Ang(1-7)], a peptide reported to have vasodilatory and cardioprotective properties. Inactivation of the ACE2 gene in mice has been reported by one group to result in an accumulation of Ang II in the heart and an age-related defect in cardiac contractility. A second study confirmed the role of ACE2 as an Ang II clearance enzyme but failed to reproduce the contractility defects previously reported in ACE2-deficient mice. The reasons for these differences are unclear but could include differences in the accumulation of Ang II or the deficiencies in Ang(1-7) in the mouse models used. As a result, the roles of ACE2, Ang II, and Ang(1-7) in the heart remain controversial. Using a novel strategy, we targeted the chronic overproduction of either Ang II or Ang(1-7) in the heart of transgenic mice and tested their effect on age-related contractility and on cardiac remodeling in response to a hypertensive challenge. We demonstrate that a chronic accumulation of Ang II in the heart does not result in cardiac contractility defects, even in older (8-month-old) mice. Likewise, transgenic animals with an 8-fold increase in Ang(1-7) peptide in the heart exhibited no differences in resting blood pressure or cardiac contractility as compared to age- matched controls, but they had significantly less ventricular hypertrophy and fibrosis than their nontransgenic littermates in response to a hypertensive challenge. Analysis of downstream signaling cascades demonstrates that cardiac Ang(1-7) selectively modulates some of the downstream signaling effectors of cardiac remodeling. These results suggest that Ang(1-7) can reduce hypertension-induced cardiac remodeling through a direct effect on the heart and raise the possibility that pathologies associated with ACE2 inactivation are mediated in part by a decrease in production of Ang(1-7). (Circ Res. 2008; 103: 1319-1326.)