Abstract 251: Dexamethasone Promotes Hypertension In Transgenic Mice By Haplotype-Dependent Regulation Of The Human Angiotensinogen Gene

Abstract

Human angiotensinogen gene (hAGT) gene has polymorphisms in its 2.5Kb promoter that forms two haplotype (Hap) blocks: -6A/G (-1670A/G, -1562C/T, -1561T/C) and -217A/G (-532T/C, -793A/G, -1074T/C, and -1178G/A). Hap -6A/-217A (Hap -6A) is associated with human hypertension whereas, Hap -6G/-217G (Hap -6G) reduces cardiovascular risk. In vitro, transient transfection shows that Hap -6A has increased promoter activity with a glucocorticoid receptor (GR) agonist (4.7 fold higher) when compared to the Hap -6G. Here, we examine the physiological significance of GR-mediated allele-specific regulation of the hAGT gene, in vivo, with consequential effects on the renin angiotensin system (RAS) in double transgenic (TG) mice engineered with human renin and either haplotype of the hAGT gene. TG mice were treated with and without low dose of a GR agonist, dexamethasone (DEX, 10μg/mL), for 72 hours. In untreated mice, ChIP assay shows greater chromatin-GR binding (Hap -6A- 0.46±0.02 vs. Hap -6G- 0.23±0.01 A.U., p<0.05) and immunoblot shows increased hAGT expression in liver of the Hap -6A-TG mice (Hap -6A- 0.90±0.04 vs. Hap -6G- 0.33±0.03 A.U., p<0.05). However, DEX treatment elicited increased chromatin binding (Hap -6A- 0.80±0.04 vs. Hap -6G- 0.26±0.06 A.U., p<0.05), higher hepatic hAGT expression (Hap -6A- 1.88±0.1 vs. Hap -6G- 0.38±0.09 A.U., p<0.05), increased plasma hAGT (Hap -6A- 1.40±0.11 vs. Hap -6G- 0.42±0.05 A.U., p<0.05) and elevated angiotensin II levels (Hap -6A- 870±45 vs. Hap -6G- 630±47 pg/mL, p<0.05) only in Hap -6A TG mice. No significant change was observed in the endogenous mAGT gene with or without DEX. Similar results were obtained from renal tissues of the two TG lines. Importantly, the GR agonist brought about greater increase in blood pressure (ΔSBP: Hap -6A- 14.5±1.2 vs. Hap -6G- 8.1±1.0 mm Hg, p<0.05) in mice with Hap -6A. Complementary experiments show upregulation of renal redox marker NOX1 (Hap -6A- 1.72±0.13 vs. Hap -6G- 0.45±0.06 A.U., p<0.05) in the -6A TG mice. Taken together, our results show that SNPs in the hAGT Hap -6A favor agonist-induced GR binding that lead to DEX-induced increased expression of the hAGT. This activates the RAS with pathophysiological implications including, increase in blood pressure and tissue oxidative stress.