Background-Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that metabolizes Ang II into Ang 1-7, thereby functioning as a negative regulator of the renin-angiotensin system. We hypothesized that ACE2 deficiency may compromise the cardiac response to myocardial infarction (MI). Methods and Results-In response to MI (induced by left anterior descending artery ligation), there was a persistent increase in ACE2 protein in the infarct zone in wild-type mice, whereas loss of ACE2

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... nced the susceptibility to MI, with increased mortality, infarct expansion, and adverse ventricular remodeling characterized by ventricular dilation and systolic dysfunction. In ACE2-deficient hearts, elevated myocardial levels of Ang II and decreased levels of Ang 1-7 in the infarct-related zone was associated with increased production of reactive oxygen species. ACE2 deficiency leads to increased matrix metalloproteinase (MMP) 2 and MMP9 levels with MMP2 activation in the infarct and peri-infarct regions, as well as increased gelatinase activity leading to a disrupted extracellular matrix structure after MI. Loss of ACE2 also leads to increased neutrophilic infiltration in the infarct and peri-infarct regions, resulting in upregulation of inflammatory cytokines, interferon-␥, interleukin-6, and the chemokine, monocyte chemoattractant protein-1, as well as increased phosphorylation of ERK1/2 and JNK1/2 signaling pathways. Treatment of Ace2 Ϫ/y -MI mice with irbesartan, an AT1 receptor blocker, reduced nicotinamide-adenine dinucleotide phosphate oxidase activity, infarct size, MMP activation, and myocardial inflammation, ultimately resulting in improved post-MI ventricular function. Conclusions-We conclude that loss of ACE2 facilitates adverse post-MI ventricular remodeling by potentiation of Ang II effects by means of the AT1 receptors, and supplementing ACE2 can be a potential therapy for ischemic heart disease. (Circ Heart Fail. 2009;2:446-455.)