244 - Perinatal nicotine exposure disrupts circadian rhythm and induces premature lung senescence

Cigarette smoke (CS)-induced cellular senescence predisposes to aging and chronic lung disease in adult smokers. Nicotine, a major component of both tobacco smoke and electronic cigarettes, has been implicated in chronic lung disease; however, the risk of nicotine-induced lung senescence following its exposure during development is unknown.

Objective:

To test the hypothesis that perinatal nicotine exposure induces premature lung senescence in offspring and that this effect is associated with a dysregulated circadian clock, which is being increasingly recognized as an independent mediator of cellular senescence.

Design/Methods:

Pregnant pair-fed Sprague-Dawley rat dams were treated once daily with either 1 mg/kg nicotine or saline from embryonic day 6 to postnatal day 21 (PND21). At PND21, pups were either sacrificed or weaned for later sacrifice at PND60. Lungs were collected 12-hours apart (8 AM/8 PM) and snap-frozen for later analysis. Senescence-associated markers p16, p21, p53, and Pai1 and core circadian clock components Bmal1, Reverbα, and Ck1δ/ε were assessed through RT-qPCR and western blot analysis.

Results:

Protein analysis of lungs from nicotine exposed PND60 rats exhibited significantly increased expression of p16 and p53 compared to saline controls of both sexes (N=4; p< 0.05), indicating premature lung senescence. However, the mRNA expression of senescence markers showed no significant changes in both sexes, with only Pai1 expression in male lungs showing a modest, but statistically insignificant increase. At PND60, core circadian clock markers Bmal1 and Reverbα exhibited significant differences in the nicotine-exposed lungs collected at the 8 PM timepoint in both sexes (N=4; p< 0.05). Ck1δ/ε, a key component that phosphorylates core clock proteins, was downregulated in nicotine-exposed lungs. Nicotine’s effect on Reverbα at PND21 was like that observed at PND60 for 8 PM samples, but the 8 AM samples exhibited an opposite effect, i.e., Reverbα expression in nicotine-treated lungs was upregulated at the 8 AM timepoint but downregulated at 8 PM in both sexes.

Conclusion(s):

Perinatal nicotine exposure predisposes premature lung cellular senescence and is associated with a dysregulated circadian clock. Nicotine-induced differential expression of Bmal1 and Reverbα persisted from the weaning age (PND21) to young adulthood (PND60) and was time-of-the-day dependent, indicating a long-term impact on altered phase oscillations. The cause-and-effect relationship between the disrupted circadian rhythm and premature lung senescence following perinatal nicotine exposure remains to be established.