Nicotine exposure declines quality of early embryos and disrupts placental structure by destabilizing Notch signaling pathway

Nicotine is a common environmental pollution which is diffused into the air in the form of cigarette smoke fumes. Due to its lipophilic nature, nicotine can rapidly transport through membrane barriers and spread throughout the body which leads to abnormalities in the human brain, heart and even the fatal. However, the effects of nicotine on early embryonic development remains elusive. In this study, we found that nicotine significantly affected early embryonic development with decreased blastocyst formation. In addition, embryos treated with nicotine caused increased level of ROS, DNA damage and cell apoptosis. By RNA sequencing analysis, we demonstrated that nicotine affected the expression of placental development genes. Consistently, we found that the placental development at E17.5 was impaired by nicotine exposure, with increased placental weight and disrupted placental structure. This was due to excessive activation of the Notch signaling pathway, since blocking Notch signal by DAPT treatment recovered abnormal placental weight and structure induced by nicotine exposure. We also observed that nicotine exposure could specifically cause promoter hypermethylation of Phlda2 (a maternally expressed imprinted gene associated with placental development) and lead to its abnormal expression. Overall, this study provides evidence that nicotine causes the declining quality of early embryo and leads to placental abnormalities related with over-activation of the Notch signaling pathway. The RNA-Seq experiments of the control and nicotine treated embryos at the morula, ICM and TE stage.