Our long range objective is to understand molecular mechanisms involved in human hypertension. The octapeptide, angiotensin-II, is one of the most potent vasoactive substances, and is produced from its precursor molecule, angiotensinogen (AG). Recent linkage analysis has suggested that AG gene locus is involved in human essential hypertension and a point mutation that converts methionine to threonine at amino acid 235 is associated with increased plasma AG levels and increased blood pressure. However, this mutation is located far away from the renin cleavage site and does not explain the mechanism involved in increased plasma AG levels. The nucleotide sequence of the promoter of the G gene of some hypertensive patients contains a mutations that converts nucleoside G to A at-6. Our studies show that reporter constructs containing nucleoside A at -6 have increased promoter activity on transient transfection in HepG2 cells. In addition, liver enriched transcription factor HNF4 binds to this region of the promoter and co- transfection of an expression vector containing HNF4 coding sequence increases the promoter activity of reporter constructs when nucleoside A is present at -6. The clinical relevance of this mutation has been shown by recent studies that molecular variants 235T and -6(A) are in complete association or in other words AG gene that has threonine at amino acid 235 also contains nucleoside A at -6. Based on these observations, our hypothesis is that mutation G to A at-6 in the promoter of AG gene of some hypertensive patients increases its transcription that leads to its increased plasma and/or tissue specific AG levels. We will now study the mechanism involved in increased transcription activity by mutation A at -6. Finally, we will develop transgenic mice to understand the role of this polymorphism on transcriptional regulation of the human angiotensinogen gen in an in vivo setting.
