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Abstract 048: Epigenetic Regulation of the Human Angiotensinogen Gene: Role of Individual SNPs and Implication for Hypertension

Hypertension is a complex disease caused by a combination of genetic and environmental factors. Renin angiotensin system (RAS) dysfunction is a frequent accompaniment of essential hypertension. In this regard, polymorphisms in the angiotensinogen (AGT) gene increase RAS activity and cause blood pressure elevation. We have identified two distinct haplotypes of the human AGT gene constituted by a group of four SNPs in linkage disequilibrium. Variants -1670A, -1562C, and -1561T always occur with -6A and form the haplotype-I (Hap-I), while variants -1670G, -1562G, and -1561G always occur with -6G and constitute haplotype-II (Hap-II). 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 alter gene transcription at an epigenetic level and this, in turn, could be dependent on individual polymorphisms. hAGT promoter CpG sites in the kidney are more methylated as compared to liver and fat. In the Kidney, the hAGT promoter CpG sites are methylated at -460, -434, -386, -346, -282, -261, -245, -229, -218, -185, -144, -18, -11, -7, +10, +42, +65 in Hap-II whereas, in Hap-I the promoter DNA methylation is observed at -460, -434, -401, -386 positions. Further, in both liver and fat the CpG sites were methylated at -11, +42, +65 positions in Hap-II TG mice, whereas in the Hap-I there were no methylation sites detected. The hAGT gene mRNA levels from these tissues were quantitated by qPCR and were 2.1 (kidney), 2.5 (liver) and 4.28 (fat) fold higher in haplotype-I vs. haplotype-II (p<0.05). Our results indicate that, in Hap-II TG mice liver, kidney and fat tissues having more CpG sites methylated in the promoter of the hAGT, and thus having less gene expression. On the other hand, Hap-I has either less or no methylation of CpG sites in the hAGT promoter and hence high gene expression. Thus, we show here for the first time that SNP blocks in the hAGT gene alter its methylation pattern in a tissue-dependent manner. This shifts the paradigm in favor of an interdependent system where epigenetic regulation is reliant on the gene haplotypes; together, these regulate protein expression and associated physiological outcomes.