Abstract MP49: Central Angiotensin II Mediates Neurogenic Hypertension Through Hif1-Alpha/NMDAR Axis In The Paraventricular Nucleus Of The Hypothalamus (PVN)

Abstract

Listen

Translate article

Central activation of the renin-angiotensin system and subsequent sympathoexcitation plays a pivotal role in the pathogenesis of hypertension. The specific neural substrates and the possible molecular mechanisms for the sympathoexcitation remain unclear. The glutamatergic activation via N-methyl-d-aspartate receptors (NMDAR) in the PVN enhances sympathetic outflow in hypertension. Previously, using Chromatin immunoprecipitation assay (ChiP) we have shown that Hypoxia-Inducible Factor-1 (heterodimer of HIF-1 α and HIF-1 β subunits ) binds to HREs elements in the NMDA-NR1(structural subunit of NMDAR) promoter in nucleus and increases transcription. In this study, central infusion of Ang II (20 ng/min, 14days, 0.5μl/h, i.c.v) through osmotic mini-pumps in Sprague-Dawley rats increased renal sympathetic nerve activity (20.5 ± 2.3 vs. 6.4 ± 1.9 % of Max) and mean arterial pressure (126 ± 9 vs. 84 ± 4 mmHg). At the same time, there was an increased expression of HIF-1α mRNA (2.79 fold) and HIF-1α protein (1.54 fold), as well as the expression of NMDA-NR1 mRNA (3.17 fold) and NMDA-NR1 protein levels (1.52 fold) in the PVN of Ang II infused group. Direct application of Ang II (1μM) induced an increase in the expression of HIF-1α protein (0.74 ± 0.03* vs. 0.50 ± 0.04) as well as decreased expression of prolyl hydroxylase domain protein 2 (an enzyme hydroxylating the proline residues of HIF-α, inducing subsequent ubiquitination and proteasomal degradation) (1.47 ± 0.14* vs. 0.50 ± 0.03) in NG108-15 neuronal cells. Tandem Ubiquitin-Binding Entities assay showed decreased HIF-α -Ub conjugates in Ang II-treated cells (0.65 ± 0.09* vs. 1.31 ± 0.10) suggesting a role for Ang II in post-translational stabilization of HIF-α. Further, silencing of HIF-1α (~60%) with siRNA in NG108-15 cells leads to a decrease in the expression of NMDA-NR1 induced by Ang II, compared with scrambled siRNA (0.47 ± 0.05* vs 0.80 ± 0.04). Taken together, these studies suggest that elevated central Ang II upregulates the expression of HIF-1α at transcriptional as well as post-translational level, which potentiates glutamatergic tone by enhanced expression of NMDA-NR1 in the PVN leading to heightened glutamatergic tone with a consequent increase in sympathetic outflow resulting in hypertension.