Angiotensin-converting Enzyme 2 Over-expression in the Central Nervous System Reduces Angiotensin-II-mediated Cardiac Hypertrophy

Angiotensin-converting enzyme type 2 (ACE2) has been shown to be an important member of the renin angiotensin system. Previously, we observed that central ACE2 reduces the development of hypertension following chronic angiotensin II (Ang-II) infusion in syn-hACE2 transgenic (SA) mice, in which the human ACE2 transgene is selectively targeted to neurons. To study the physiological consequences of central ACE2 over-expression on cardiac function and cardiac hypertrophy, SA and non-transgenic (NT) mice were infused with Ang-II (600 ng/kg/min, sc) for 14 days, and cardiac function was assessed by echocardiography. Blood pressure (BP), hemodynamic parameters, left ventricle (LV) mass/tibia length, relative ventricle wall thickness (2PW/LVD), cardiomyocyte diameters and collagen deposition were similar (P>0.05) between NT and SA mice during saline infusion. After a 2-week infusion, BP was elevated in NT but not in SA mice. Although ejection fraction and fractional shortening were not altered, Ang-II infusion increased 2PW/LVD compared to saline infusion in NT mice. Interestingly, the 2PW/LVD and LV mass/tibia ratios were significantly lower in SA compared to NT mice at the end of infusion. Moreover, Ang-II infusion significantly increased arterial collagen deposition and cardiomyocytes diameter in NT mice but not in transgenic animals (P<0.05). More importantly, ACE2 over expression significantly reduced the Ang-II-mediated increase in urine norepinephrine levels in SA compared to NT mice. The protective effect of ACE2 appears to involve reductions in Ang-II-mediated hypertension and sympathetic nerve activity.