Nicotine attenuates global genomic DNA methylation by influencing DNMTs gene expression in human endometrial stromal cells.

There is increasing evidence indicating an incidence of infertility and also the risk of endometrial cancers among smokers. However, the mechanism underlying nicotine adverse effect on female reproduction remains unclear. Growing evidence has suggested that environmental exposures such as nicotine could modulate the epigenome. No study has yet been published to evaluate the direct effect of nicotine on the epigenome profiling of human endometrial stromal cells (HESC). Herein, we decided to examine the direct effects of nicotine on global genomic DNA methylation status and DNA methyl- transferases (DNMTs) gene expression in HESC. HESC were treated with different doses of nicotine (0 or control, 10^{- 11}, 10^{- 8} and 10^{- 6}) M for 24 h and their genomic global DNA methylation and gene expression of DNMTs (DNMT1, DNMT3A, and DNMT3B) were investigated using ELISA and real-time PCR, respectively.

Nicotine treatments reduced the average level of DNMTs gene expression by 90, 79, and 73.4% in 10^{- 11}, 10^{- 8} and 10^{- 6} M of nicotine treated cells as compared to control cells, respectively (p < 0.05). Also, 10^{- 8} and 10^{- 6} M of nicotine concentrations effectively reduced the amounts of 5-methylated cytosine (5-mC) by 1.09 and 1.87% compared to control cells, respectively (p < 0.05). The 5-mC percentages were positively correlated with the relative cellular DNMTs expression in HESC as verified by the Pearson correlation test.

An interesting possibility raised by the current study is that the reduced genomic global DNA methylation level in HESC may be partly due to the suppression of DNMTs gene expression caused by nicotine in these cells.