Abstract 074: Epigenetic Regulation of Brain (Pro)renin Receptor by Benzamil-sensitive Sodium Channel in DOCA-salt Hypertension

Abstract

Increased expression of the brain (pro)renin receptor (PRR) contributes to the development of salt-sensitive hypertension (SSH). Yet, the mechanisms that drive this increase in PRR expression are not known. We previously reported an increase in histone 3 lysine 4 trimethylation (H3K4me3), an epigenetic marker for gene activation, on the PRR promoter in SSH mice. We hypothesized that the increase in brain PRR expression is driven by epigenetic modifications linked to high-salt intake. To test our hypothesis, C57Bl/6J mice were treated with Sham (sham pellet + tap water for drinking) or DOCA-salt (50mg DOCA pellet + 0.9% saline) with chronic intracerebroventricular (ICV) infusion of the epithelial sodium channel (ENaC) blocker Benzamil (2.64μg/day, 0.5μl/h) or aCSF for 3 days. Hypothalamic tissues were used to examine the chromatin modifiers activity (ng/h/mg of protein) responsible for the methylation or demethylation of H3K4 including the histone methyltransferase (HMT) and histone demethylase (HDM). Water intake and PRR mRNA level were monitored. In mice receiving ICV aCSF, DOCA-Salt treatment increased the activity of H3K4 HMT (18.5 ± 1.2 vs. 6.6 ± 0.3, P<0.001) and HDM (0.55 ± 0.03 vs. 0.37 ± 0.05, P<0.05) compared to Sham respectively. HMT activity was blunted by ICV infusion of Benzamil (14.2 ± 0.5, P<0.01) compared to ICV infusion of aCSF following 3 days of DOCA-salt treatment. Interestingly, HDM activity was further elevated with the treatment of ICV Benzamil compared to ICV infusion of aCSF (0.84 ± 0.03, P<0.01). ICV infusion of Benzamil also reduced the PRR mRNA levels in the hypothalamus of mice treated with DOCA-salt from (1.43 ± 0.09, P<0.05) to (1.07 ± 0.02 P>0.05) relative to Sham (1.00). In addition, the saline intake amount (ml/day) was lower (P<0.05) in mice receiving ICV infusion of Benzamil (17 ± 3) compared to ICV aCSF (32 ± 9) following DOCA-salt treatment. In summary, ICV infusion of Benzamil attenuates the elevation in HMT activity, water and sodium intake, and the PRR mRNA levels, while increasing HDM activity in DOCA-salt treated mice. We conclude the Benzamil-sensitive sodium channel, possibly ENaC, may be a key channel regulating the epigenetic modifications governing the increased expression of brain PRR in SSH.