Neuronal activation of ADAM17 by AT1A receptors contributes to neurogenic hypertension

We previously reported that neurogenic hypertension is associated with a reduction of Angiotensin Converting Enzyme 2 (ACE2) activity and an increase in A Disintegrin And Metalloprotease 17 (ADAM17) activity in the hypothalamus. In addition, we showed that silencing ADAM17 or blocking Angiotensin (Ang)‐II type 1 (AT1) receptors 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 AT1 receptors, 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 AT1a receptors (AT1aR) are necessary for ADAM17‐mediated ACE2 shedding in neurogenic hypertension. Male neuronal AT1aR knock‐down (AT1aR floxed crossed with Nefh‐cre recombinase mice, 12–16 week‐old, n=10) and control littermates (n=10) were implanted with telemetry probes for continuous recording of blood pressure (BP) and heart rate (HR). Following DOCA‐salt treatment (DOCA 1mg/g body weight sc + 1% saline po for 3 weeks), both strains showed increased BP, however mean arterial pressure and HR were significantly lower in neuronal AT1aR knock‐down mice after 19 days of treatment, compared to the controls. Meanwhile, autonomic function and urinary norepinephrine levels were assessed in conscious mice before and after 19 days of treatment. At baseline level, autonomic function and urinary norepinephrine levels were identical between AT1aR knock‐down and their wild type (WT) counterparts. However, the deleterious changes caused by DOCA‐salt administration on sympathetic drive and vagal tone were partially reverted by neuronal AT1aR knock‐down ( P <0.05), whereas DOCA‐salt‐induced cardiac and renal hypertrophy were not corrected. Furthermore, enzyme activity assays from the hypothalamus of these DOCA‐salt‐treated mice revealed that ADAM17 activity was significantly decreased (−37.4 ±10.5%, P <0.05) in neuronal AT1aR knock‐down animals. Unlike WT group, there was no marked difference in ADAM17 activity between DOCA‐salt treated and sham AT1aR knock‐down mice, which remained at baseline levels. 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 AT1aR knock‐down mice, by +20.7 ±8.5% and +32.3 ±10.1%, respectively. Preliminary results show an increasing tendency for ADAM17 inhibitory protein, TIMP‐3, in the hypothalamus of AT1aR knock‐down mice. To further confirm the pivotal role of neuronal AT1R, hypothalamic primary neurons isolated from neonates were exposed to Ang‐II (300 nM, 24 h) after 14 days of culture. Western blotting reveals that Ang‐II significantly increased the expression of mature ADAM17 and this effect could be blocked by pre‐treatment with the AT1R antagonist, Losartan (10 μM, 30 min prior). Together our data provide strong evidence that activation of neuronal AT1aR is responsible for ADAM17‐mediated ACE2 shedding and the maintenance of neurogenic hypertension. Support or Funding Information American Heart Association Postdoctoral Fellowship (15POST25000010) NIH/NHLBI 2R01HL093178‐06A1 NIH COBRE P30GM106392