Abstract P280: Novel Insights into Transcriptional Regulation of the Human Angiotensinogen Gene by High-salt: A Study in Transgenic Mice

Abstract

Angiotensinogen is the substrate for the entire RAS cascade and polymorphisms leading to its overexpression are linked to hypertension. SNPs in the promoter of the hAGT gene are associated with hypertension. Importantly, these SNPs can further modulate the gene of interest in various physiological/environmental settings like the high-sodium diet. In this regard, the human angiotensinogen (hAGT) gene has polymorphisms in its 2.5Kb promoter that form 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 is associated with human hypertension whereas Hap -6G/-217G reduces cardiovascular risk. We have engineered transgenic (TG) mice with these haplotypes (Hap -6A: -6A/-217A and Hap -6G: -6G/-217G) so as to examine the transcriptional regulation of the hAGT in an in vivo setting. This study is designed to study the effects of a high-sodium diet on the transcriptional milieu of renal tissues with consequential effects on the hAGT expression in our two haplotypes. Male TG mice were placed on 4% Na + diet for a period of 8 weeks. High-salt diet induces mineralocorticoid receptor (MR) and SGK-kinase expression in both haplotypes, equally. MR has been shown to bind to GRE elements in the hAGT gene. Importantly, MR-binding (ChIP assay) and hAGT induction are significantly (p<0.05) greater in the -6A haplotype males as compared to -6G males. High-salt also increased the expression of transcriptional regulators including CEBPβ and HNF4 (p<0.05) that are independent of haplotype. Complementary ChIP assay confirmed enhanced transcription factor (TF) binding to the chromatin of male -6A TG mice as compared to their -6G counterparts after high-salt diet treatment. Thus, we show here an effect of high-salt on cellular transcriptional apparatus that is haplotype-independent. However, increased TF affinity of the chromatin in -6A TG mice leads to higher salt-induced AGT levels in this haplotype than -6G. These observations could partly account for increased salt-sensitivity of some adult males that, in turn, is governed by the “risk” haplotype. Identifying these individuals with the -6A haplotype will help guide therapeutic lifestyle changes in patients with essential hypertension.