Abstract 033: Neuronal Knock-out of AT1 Receptor Attenuates the Development of Doca-salt-induced Hypertension

Abstract

We previously reported that neurogenic hypertension is associated with an increase in A Disintegrin And Metalloprotease 17 (ADAM17) activity and a reduction of Angiotensin Converting Enzyme 2 (ACE2) activity in the hypothalamus. In addition, we showed that silencing ADAM17 or blocking Angiotensin (Ang)-II type 1 receptors (AT1R) in the central nervous system (CNS) prevented DOCA-salt hypertension, confirming the pivotal role of AT1R and ADAM17 in neurogenic hypertension. However, the interaction between AT1R, ADAM17, and ACE2 is still unclear. Since ADAM17 is known to be expressed in multiple cell types and can be activated by various receptors, we tested the hypothesis that neuronal AT1R are necessary for ADAM17-mediated ACE2 shedding in neurogenic hypertension. Male neuronal AT1R knockout (AT1R floxed crossed with Nefh-cre recombinase mice, 12-16 week-old, n=5) and littermate mice (n=8) were implanted with telemetry probes for continuous recording of blood pressure (BP) and heart rate (HR). Following DOCA-salt treatment, both strains developed hypertension, however mean arterial pressure (MAP; 123.9 ±6.4 vs. 138.4 ±4.3 mmHg) and HR (483.9 ±24.1 vs. 520.3 ±22.5 bmp) were significantly lower in neuronal AT1R knockout mice after 2 weeks of treatment, compared to controls. Western blot and enzyme activity assays from the hypothalamus of these DOCA-salt-treated mice revealed that the expression of pro-ADAM17 (inactive form) was significantly increased (+17.0 ±5.3%, P<0.05), while the activity of ADAM17 was decreased (-37.4 ±10.5%) in neuronal AT1R knockout animals. Concomitant to the down-regulation of ADAM17, both the expression and activity of ACE2 were found to be significantly (P<0.05) up-regulated in the hypothalamus of neuronal AT1R knockout mice, by +20.7 ±8.5% and +32.3 ±10.1%, respectively. These results suggest that activation of neuronal AT1R is responsible for ADAM17-mediated ACE2 shedding and the maintenance of neurogenic hypertension.