Paternal nicotine exposure induces hyperactivity in next-generation via down-regulating the expression of DAT

Many substances in cigarette smoke can induce changes in DNA methylation. Our previous studies have confirmed paternal nicotine exposure causes hyperactivity in the offspring via mmu-miR-15b. The main aim of the present study is to explore the molecular mechanism underlying the cross-generation effects of paternal nicotine exposure more comprehensively. The male C57BL/6 mice were exposed to 2 mg/kg/d nicotine for 5 weeks, and then mated with wild-type females. The offspring male mice were subjected to behavioral tests at 8 weeks after birth. The results suggested that, paternal nicotine exposure led to hyperactivity in the offspring. An analysis of the changes in DNA methylation revealed that nicotine exposure induced a rise in the total DNA methylation level of Dat in murine spermatozoa, and the hyper-methylation could imprint in the brains of the offspring mice. Then these epigenetic modifications reduced the expression of DAT in the brain of the offspring, resulting in a rise in the level of extracellular dopamine. The activation of D2 receptors caused the dephosphorylation of AKT, which led to increased activation of GSK3 alpha/beta, and ultimately caused hyperactivity in the offspring mice. Further, in wild-type mice, injection of DAT inhibitors simulated this hyperactive phenotype, while the injection of D2s inhibitors reversed the hyperactivity of the offspring caused by paternal nicotine exposure. In conclusion, all results indicated that paternal nicotine exposure could induce hyperactivity in the offspring via the hyper-methylation of Dat. Consequently, Dat may be one of the genes that mediate the cross-generation effects of nicotine besides mmu-mmiR-15b.