Hypertension is a serious risk factor for myocardial infarction, heart failure, vascular disease, stroke, and renal failure. Angiotensinogen (AGT) gene locus is associated with human essential hypertension and its expression is increased by glucocorticoid and IL-6 treatment. Previous studies have shown that variant -6A of the AGT gene is associated with increased plasma AGT level and increased blood pressure in Caucasian and Japanese population. However, transgenic mice containing 1.2 Kb of the promoter with -6A allele of the hAGT gene neither show increased transcription nor increased blood pressure compared to transgenic mice containing -6G allele. We have found that hAGT gene has three additional SNPs (A/G at -1670, C/G at -1562 and T/G at -1561) and variants -1670A, - 1562C, and -1561T almost always occur with variant -6A. Therefore hAGT gene may be subdivided in either -6A haplotype (containing -6A, -1561T, -1562C, -1670A) or -6G haplotype (containing -6G, -1561G, -15652, -1670G). Our transient transfection assays show that reporter construct with -6A haplotype has four fold increased glucocorticoid and five fold increased IL-6 induced promoter activity as compared to the reporter construct with -6G haplotype in liver and kidney cells. In order to understand the role of glucocorticoids and IL-6 on transcription of -6A and -6G haplotypes of the hAGT gene and on the regulation of blood pressure in an in vivo situation, we have re-combineered 180 Kb long BAC DNA (containing 116 Kb of the 5'-flanking region, all five exons and four introns, and 54 Kb of the 3'-UTR of the hAGT gene) and produced double transgenic mice containing either -6A or - 6G haplotype of the hAGT gene and human renin gene. Our studies suggest that: (a) blood pressure and (b) hAGT mRNA in the liver and kidney is increased in transgenic mice containing -6A haplotype as compared to -6G haplotype. We will now use these transgenic mice to understand the role of glucocorticoids and IL-6 on hAGT gene expression and blood pressure in an in vivo situation. These studies will provide new strategies to reduce blood pressure in hypertensive subjects.
Hypertension is a serious risk factor for myocardial infarction, heart failure, vascular disease, stroke, and renal failure. It is estimated that hypertension affects 50 million Americans with a prevalence rate of 25-30% in the adult Caucasian population. Angiotensinogen gene plays an important role in human hypertension. Variants of angiotensinogen gene have been associated with hypertension in Caucasian subjects. Our studies will help us understand molecular mechanism involved in expression of human angiotensinogen gene by these variants in an in vivo situation using transgenic mice.
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