Abstract P151: Adam17 in the Paraventricular Nucleus Contributes to Activation of Pre-Autonomic Neurons and Maintenance of Baseline Blood Pressure

Abstract

We previously reported that over-activation of the classical arm ( i.e. ACE/Ang-II/AT1 receptor) of the brain renin-angiotensin system (RAS) up-regulates ADAM17, a disintegrin and metalloprotease. ADAM17 cleaves angiotensin converting enzyme 2 (ACE2) from the cell surface, leading to a compromised compensatory RAS axis ( i.e. ACE2/Ang-(1-7)/Mas receptor) and neurogenic hypertension. We hypothesized that ADAM17 within the paraventricular nucleus of the hypothalamus (PVN) intrinsically regulate neuronal activity, thus contributing to sustained sympathetic drive and the development of neurogenic hypertension. To test this hypothesis, a new transgenic mouse line, named SAT, was generated to selectively knockdown ADAM17 in pre-autonomic Sim1 neurons within the PVN, using cre-loxP technology. Mean arterial pressure recorded in conscious mice (telemetry) showed a significant reduction at baseline (ΔMAP: -8 ±2 mmHg, N=3, P <0.05) and an increased vagal tone (Heart rate: 231 ±19 vs. 160 ±11 bpm, N=10, P<0.05) in SAT vs. control (NT) litter-mates. To address the impact of ADAM17 deletion on neuronal excitability, c-Fos immunohistochemistry was performed. SAT mice exhibited a significant reduction of c-Fos expression in the PVN compared to NT (14 ±2 vs. 124 ±8 neurons, N=3, P <0.001). Retrograde labeling (pseudorabies virus-eGFP) confirmed that a sub-population of these neurons projected to the kidney. In addition, mRNA expression of the GABAa receptor was higher in the hypothalamus of SAT compared to NT mice (1.3 ±0.1 vs. 1.0 ±0.1, N=7, P <0.05). ADAM17 knockdown from the PVN had a positive effect on the compensatory RAS, as evidenced by a rise in hypothalamic ACE2 activity compared to NT mice (82.3 ±4.2 vs. 69.7 ±3.3, N=7, P <0.05). Interestingly, this was also extended downstream of the PVN, with an increase in ACE2 activity (96.7 ± 3.8 vs. 82.0 ± 3.4, N=7, P <0.05), as well as Mas receptor gene expression (0.28 ±0.03 vs. 0.17 ± 0.01, N=6, P <0.01) in the brainstem of SAT compared to NT mice. Altogether, our data highlight a new role for ADAM17 in neuronal excitability and the maintenance of baseline blood pressure. Potential mechanisms opposing ADAM17-mediated neuronal excitability of PVN neurons include GABAergic pathways and the compensatory axis of the brain RAS.