Functional promoter polymorphisms govern the differential expression of HMG-CoA Reductase gene in rat models of essential hypertension

Abstract

3-Hydroxy-3-methyl glutaryl-coenzyme A reductase (Hmgcr) encoding the rate-limiting enzyme in the cholesterol biosynthesis pathway is a candidate gene for essential hypertension (EH). However, the regulation of Hmgcr in rat models of hypertension (viz. Spontaneously Hypertensive Rats [SHR] and its normotensive control Wistar/Kyoto [WKY] strain) is unknown. Here, we show that Hmgcr transcript and protein levels are diminished in liver tissues of SHR as compared to WKY. Consistently, a number of other rat models of hypertension display diminished cholesterol levels as compared to corresponding control strains. Sequencing of the Hmgcr promoter in SHR/WKY reveals three variations: A-405G, C-62T and a 11 bp insertion (-393_-382insTGCGGTCCTCC) in SHR. Moreover, SHR-Hmgcr promoter displays higher activity than WKY-Hmgcr promoter in various cell lines. Transient transfections of Hmgcr-promoter mutants and in silico analysis suggest altered binding of Runx3 and Srebf1 across A-405G and -393_-382insTGCGGTCCTCC sites. Indeed, chromatin immunoprecipitation assays confirm differential binding of Runx3/Srebf1 to Hmgcr promoter leading to diminished expression of Hmgcr in SHR as compared to WKY under basal/cholesterol-modulated conditions. Taken together, this study provides mechanistic insights for the altered Hmgcr expression in these models of EH, thereby unravelling the links of this gene to hypertension and associated cardiovascular disease states.