Inflammation and Apoptosis Factors in Mares’ Follicular Fluid Regarding Seasonal Cyclicity

Background: The in vitro production of human and animal embryos rapidly has been developed in recent years. The year-round practice of obtaining oocytes from valuable mares does not account for seasonal changes in the oocyte microenvironment or their potential impact on oocyte quality. Objectives: This study aimed to assess levels of inflammation and apoptosis markers in the follicular fluid (FF) of mares during the transitional anovulatory period and the breeding season with normal estrous cycles. Methods: The experimental samples included clinically healthy crossbred mares aged 6-12 years. The expression of inflammation and apoptosis factors (interleukin [IL]-1α, IL-1β, Tumor necrosis factor alpha (TNF-α), nuclear factor kappa B [NF-kB], B-cell lymphoma-2 [BCL2], FAS, Bcl-2–associated X protein (Bax), caspase 3) in FF samples from the transitional and ovulatory phases was assessed by Western Blotting. Results: The inflammation and apoptosis developed in large FFs (≥31-35 mm) in both periods, evidenced by an increase in the levels of IL-1α, IL-1β, TNFα, FAS, and caspase-3. In luteinizing follicles during the transitional period, anti-apoptotic markers NF-kB and BCL2 reached their peak level, while in large estrous follicles, the level of these markers significantly decreased. This indicated that apoptosis in large FFs is not triggered by TNFα. In hormonally stimulated preovulatory follicles, the level of all inflammation and apoptosis markers decreased except for NF-kB and TNFα. On the contrary, the TNFa reached a maximum level, which could indicate preparation for follicle rupture and the release of a mature oocyte (ovulation). Conclusion: The findings indicate the presence of specific regulatory pro- and antiapoptotic mechanisms involved in the preparation of mature follicles for ovulation.