Cigarette Smoke Exposure Triggers Autophagy-Mediated Ovarian Follicle Loss in a Mouse Model.

Delayed conception, decreased success in assisted reproductive technologies and premature ovarian failure have all been reported in female smokers compared with non-smokers. Recently we reported that exposure to cigarette smoke resulted in significant primordial follicle loss that was not associated with activation of either the intrinsic or extrinsic apoptosis pathways as shown by absence of an effect on TUNEL staining, DNA laddering, Bax expression and activated caspase-3 expression compared to controls. However, a significant decrease in the expression of the inhibitor of apoptosis B-cell lymphoma-2 (Bcl-2) in ovaries of exposed mice vs. controls was found. Intriguingly, while Bcl-2 is a key regulatory protein in the apoptosis pathway inhibiting cell death by blocking the action of Bax, it has also been implicated in inhibiting cell death by preventing Beclin-1 from performing its role in another cell death pathway, autophagy (self-digestion). Although cigarette smoking in humans and cigarette smoke (CS) exposure in mice depletes the primordial follicle population, the mechanism of action is unknown. Therefore, the effect of cigarette smoke exposure, at concentrations representative of human exposure, on selective stage-dependent destruction of follicles in mouse ovaries was studied. In the present study, mice were exposed to CS or room air (control) for 8 weeks. Ovaries were excised and processed for electron microscopy (EM), Western blotting, immunohistochemistry (IHC) and quantitative real time-PCR (q-PCR). Markers of survival were decreased, as was the ovary's ability to cope with the production of reactive oxygen species. Increased expression of loxI and lc3, markers if autophagy, and an increase in the presence of autophagosomes in the granulosa cells of smoke exposed ovaries compared to controls were documented. The results of the present study suggest that exposure to cigarette smoke causes significant primordial follicle loss following the production of reactive oxygen species and the triggering of the autophagy pathway through a decrease in Bcl-2 expression. (platform)