The highly conserved Leptin-Melanocortin signaling pathway plays a central role in the regulation of body weight and energy expenditure. Mutations in POMC and MC-4R lead to dosage dependent monogenetic obesity. However, several evidences suggest an epigenetic impact on the regulation of body weight. Moreover it has been shown recently that variants of the FTO gene, which affects ss DNA methylation in the arcuate nucleus, correlate with increased body weight in children and adults. We therefore investigated the epigenetic state of the MC-4R and POMC gene in different, obese and normal individuals, in different tissues and in different species. We analysed the DNA methylation pattern of the POMC and MC-4R gene with bisulfite cloning technique in human peripheral blood cells, microdissected human ß-MSH expressing cells in the arcuate nucleus and in mice peripheral blood cells. Promoter activity has been analysed with Luciferase-Reporter-Gene-Assays. Comparing DNA from non-expressing peripheral blood cells and expressing arcuate neurons we observed a non-tissue specific POMC DNA methylation pattern, which was also conserved in mouse peripheral blood cells. We obtained a significant over-all hypermethylation in one CpG island of the POMC gene in peripheral blood cells in obese compared to normal weight individuals. In in vitro studies we could demonstrate that expression of the MC-4R gene was decreased after methylation of the promoter fragment. This study reveals a distinct evolutionary conserved DNA methylation pattern of the POMC and MC-4R gene, suggesting a functional role of methylation in melanocortin gene function. In aggreement with that the MC-4R promoter can be silenced by DNA methylation in vitro. In obese individuals we observed significant differences in the DNA methylation pattern of the POMC gene, which might lead to altered gene function and might contribute as an epigenetic alteration to the onset of obesity.
03 - 07 May 2008
European Society of Endocrinology