Abstract 116: Epigenetic Regulation of Human Angiotensinogen (hAGT) Gene by SNPs.

Hypertension is a complex disease caused by a combination of genetic and environmental factors. Renin angiotensin system (RAS) dysfunction leads to essential hypertension. Polymorphisms in the AGT gene increase RAS activity and cause blood pressure elevation. We and others have shown that SNPs in the promoter of hAGT gene can be arranged mainly in two haplotypes. Variants -1670A, -1562C, and -1561T always occur with -6A and form the haplotype-l (Hap-l), while variants -1670G, -1562G, and -1561G always occur with -6G and constitute haplotype-ll (Hap-ll). We have made transgenic animals containing these two haplotype blocks and shown that Haplotype-I is the risk haplotype and increases hAGT expression in TG animals. We hypothesized that these SNPs, when present together as Hap-I or Hap-II in transgenic mice (TG) may lead to haplotype dependent DNA methylation of CpG sites in the promoter of the hAGT gene. Methylation patterns may modulate gene transcription at an epigenetic level and this, in turn, could be dependent on individual polymorphisms. Hypo-methylation is associated with higher gene expression and hyper methylation is associated with lower gene expression. We have found that the number of methylated CpG sites in the hAGT promoter is decreased after high salt (HS) treatment in the liver of Hap-I TG animals as compared to the liver of Hap-I animals. In the liver of Hap-I animals, the hAGT promoter CpG sites are methylated at -460,-434,-386,-261,+42, whereas after high salt treatment, the promoter DNA methylation is observed at -460,-386,+65. On the other hand methylation of hAGT promoter CpG sites in the liver of Hap-II are increased as compared to the liver of Hap-II after high salt treatment. In the liver of Hap-II animals, the CpG sites are methylated at -386,-346,+65, whereas after high salt treatment, methylate sites are observed at -386,-261. Results of this experiment show that methylation of CpG sites is reduced in the DNA obtained from high salt treated liver of both haplotypes. However, DNA from high salt treated liver of Hap-II animals had least number of methylated CpG sites and therefore open chromatin that leads to higher expression of the hAGT gene in this haplotype.