关键词: n-3多不饱和脂肪酸, 肥胖, DNA甲基化, DNA甲基化转移酶, 甲基化CpG结合蛋白

Abstract: Obejective To investigate the epigenetic mechanisms linking n-3 polyunsaturated fatty acids (n-3 PUFAs) and the increased leptin expression in obesity. Methods Thirty 3~4 week-old male C57BL/6J mice were randomly divided into 3 groups and fed 4 months with two different high-fat diets (34.9% of fat providing 40% of total energy), high-fat diets (lard oil and sunflower oil) and fish oil high-fat diet (lard oil and fish oil), and one lean control diet (lard oil and sunflower oil, 4.3% of fat providing 10% of total energy).After fasted for 12 hours, mice were sacrificed and epididymal fat was collected.The mRNA expression of leptin in fat was assessed by real-time PCR (RT-PCR).Bisulfite sequencing-PCR (BSP) was used to determine the methylation level of CpG sites in the leptin promoter.Chromatin immunoprecipitation (ChIP) and RT-PCR were used to determine the amount of DNA methyltransferase (DNMTs), methyl CpG binding protein 2 (MeCP-2) and RNA polymerase II (Poly II) associated with the leptin promoter. Results As compared to the lean control diet group, the leptin mRNA expression in fat from the high-fat diet group was increased, whereas no change was found in the fish oil high-fat diet group.The methylation level of CpG sites in the leptin promoter and the associated proteins, DNMT1, DNMT3a, DNMT3b, MeCP-2 were higher than the lean control diet group with reduced binding of Poly II.In the fish oil high-fat group, increased DNMT3a, DNMT3b and MeCP-2 binding to the leptin promoter were found and the extent of MeCP-2 increase was less compared to the high-fat diet group.No changes were found in the associated DNMT1 and Poly II, and methylation of the leptin promoter in the fish oil high-fat diet group. Conclusion Our findings suggest that the leptin expression may be associated with the promoter methylation of the gene and the binding proteins and RNA polymerase in obesity, and n-3 PUFAs regulate the leptin expression through these pathways.

Key words: n-3 polyunsaturated fatty acids, obesity, DNA methylation, DNA methyltransferase, methyl CpG binding protein