Hypertension is a serious risk factor for myocardial infarction, heart failure, vascular disease, stroke, and renal failure. The renin-angiotensin system plays an important role in the regulation of blood pressure. Previous studies have suggested that: (a) angiotensinogen (AGT) gene locus is associated with human essential hypertension, (b) variant -6A of the AGT gene is associated with hypertension in Caucasian and Japanese subjects and (c) over-expression of the AGT gene increases blood pressure in transgenic mice. We have found an A/G polymorphism at -217 in the human AGT gene promoter and have shown that frequency of allele A at -217 is significantly increased in African-American hypertensive patients. AGT gene is primarily expressed in the liver and we have shown that reporter constructs containing AGT gene promoter with nucleoside A at -217 have increased basal and IL-6 induced promoter activity on transient transfection in human liver cells. Although hAGT gene has seven polymorphic sites in 1.2Kb region of its promoter, variants -217A almost always occurs with -532T, -793A, and -1074T and variants -217G, -532C, -793G, and -1074G always occur together forming two haplotypes. Since allele - 6A is the predominant allele (frequency 0.85) in African-Americans, AGT gene can be subdivided into four haplotypes -6A:-217A (AA);-6A:-217G (AG);-6G:-217A (GA) and -6G:-217G (GG). However, haplotypes GA and GG are very rare leaving AA and AG as two prominent haplotypes. We have shown that: (a) frequency of AA haplotype is increased in hypertensive patients as compared to the AG haplotype and (b) reporter constructs containing AA haplotype have increased basal as well as IL-6 induced promoter activity as compared to AG haplotype. Since inflammation plays an important role in hypertension, our hypothesis is that increased transcription of AA haplotype of the AGT gene plays an important role in the development of hypertension. In order to prove this hypothesis, we have generated transgenic mice containing human renin gene and either AA or AG haplotype of the hAGT gene using knock-in strategy at the HPRT locus. We have shown that AGT mRNA and protein level is increased in double transgenic mice containing AA haplotype of the AGT gene as compared to the AG haplotype. We have also shown that double transgenic mice containing AA haplotype of the hAGT gene and hRen gene have increased blood pressure as compared to transgenic mice containing AG haplotype of the hAGT gene and hRen gene. We will now study the role of these haplotypes on blood pressure regulation in an in vivo situation in transgenic mice containing either AA or AG haplotype of the hAGT gene and hRen gene but devoid of mAGT gene.
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. The incidence of hypertension and complications due to hypertension are even greater in the African American population. Our studies will help us understand molecular mechanism involved in hypertension.
