141. METHYLATION OF GENES OF THE RENIN ANGIOTENSIN SYSTEM (RAS) IN EARLY HUMAN AMNION

Abstract

The renin angiotensin system (RAS) genes angiotensin converting enzyme (ACE), angiotensin II type 1 receptor (AGTR1) and prorenin receptor (ATP6AP2) have CpG islands at their promoters, so these genes may be regulated by CpG island methylation as may the expression of two proteases implicated in prorenin activation (cathepsin D {CTSD} and kallikrein 1 {KLK1}). We measured CpG island methylation of 3 RAS genes and of CTSD and KLK1 in amnion using the Methyl-Profiler assay (SA Biosciences), which discriminates methyl-CpG density between hypermethylated, intermediately methylated and unmethylated CpG islands. DNA from human amnion collected between 10–17.8 weeks gestation, at elective caesarean section and after labour at term was analysed. The bulk (>80%) of CpG islands in all genes examined except for KLK1 was unmethylated and without intermediate methylation throughout gestation, while the rest was hypermethylated. There was no change in methylation density with labour (Table 1). In early gestation KLK1 methylation was greater than ACE, AGTR1 and ATP6AP2 (P < 0.05). KLKI methylation shifted towards the unmethylated state after labour (P < 0.05). There were correlations between methylation of ACE, AGTR1 and ATP6AP2 (P < 0.02) but not between RAS genes and KLKI. This suggests that the 3 RAS genes in amnion are not controlled by CpG island methylation. It is likely, however, that KLK1 is silenced in early gestation amnion partially by CpG island methylation, which is reduced by term. Since Kallikrein 1 can activate prorenin, the methylation status of this gene may regulate RAS activity in amnion during gestation.