Angiotensin-converting enzyme 2 over-expression in the central nervous system reduces angiotensin-II-mediated cardiac hypertrophy

Abstract

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.

Figure 1. ACE2 over expression decreases Ang II-induced left ventricle cardiac hypotrophy.

2 weeks after Ang II or saline infusion, echocardiography were performed on 3 different cardiac cycles, the values averaged and used to calculate 2PW/LVD; then, mice left ventricle were collected and tibia length were measured for calculation of LV mass/Tibia ratio. ACE2 over expression significantly reduced the increase of 2PW/LVD (A) and LV mass/Tibia ratio (B) in SA compare to NT mice following Ang II infusion (P<0.05). N = 8/group. Statistical significance: *P<0.05 vs. NT with the same treatment; ^# P<0.05 vs. saline with the same genotype.

Figure 2. Brain-targeted ACE2 over expression prevents the increase in cardiomyocyte diameters following Ang II infusion.

Mice were anesthetized and hearts were processed for H&E staining at the end of 2 weeks Ang II or saline infusion. The average cardiomyocyte diameters were quantized by using Image-Pro Plus software. The cardiomyocyte diameters were not different between NT (A) and SA (B) mice following 2 weeks of saline infusion (P>0.05). Ang II infusion significantly increased the cardiomyocyte diameters in NT (C) compared to saline infusion (P<0.05). However, it was smaller in SA (D) compared to NT mice at the end of 2 weeks Ang II infusion (P<0.05). N = 5/group. Statistical significance: *P<0.05 vs. NT with the same treatment; ^# P<0.05 vs. saline with the same genotype.

Figure 3. ACE2 over expression in the brain reduces Ang II-induced collagen deposition in aortas and coronary arteries.

Mice were anesthetized and hearts were processed for Masson's Trichrome staining at the end of 2 weeks Ang II or saline infusion. The average trichrome staining densities were quantified by using Image-Pro Plus software. Brain-targeted ACE2 over expression significantly reduces collagen deposition in coronary arteries (A, B) and aortas (C, D) following 2 weeks of Ang II infusion. N = 5/group. Statistical significance: *P<0.05 vs. NT with the same treatment; ^# P<0.05 vs. saline with the same genotype.

Figure 4. Urine NE levels.

Mice were infused with Ang II or saline for 2 weeks. Urine were collected in 6 N HCl and processed for NE measurements using ELISA methods. Two weeks of Ang II infusion significantly increase urine NE levels compared to saline infusion in NT mice. However, the NE levels is significantly lower in SA compared NT at the end of 2 weeks infusion. N = 4/group. Statistical significance: *P<0.05 vs. NT with the same treatment; ^# P<0.05 vs. saline with the same genotype.