Functional status of STAT3 and MAPK3/1 signaling pathways in granulosa cells during bovine follicular deviation

Follicle development is coordinated by gonadotropins, steroids, and growth factors, which activate multiple signaling pathways. Phosphorylated-MAPK (pMAPK) level was indicated as an early marker of follicle dominance, whereas phosphorylated STAT3 (pSTAT3) was increased in granulosa cells of hypophysectomized rats. We hypothesized that MAPK3/1 and STAT3 pathways are regulated in granulosa cells during follicle deviation in cattle. Cyclic beef cows were synchronized and ovariectomized to recover the two largest follicles. Follicular diameter did not differ on Day 2 but was significantly greater in dominant follicles (DFs) than that in subordinate follicles (SFs) on Days 3 and 4 of the follicular wave. The elevated abundance of CYP19A1 mRNA expression in granulosa cells of DFs and cleaved caspase 3 in Day-4 SFs further validated our in vivo model. Before deviation, pMAPK3/1 levels were significantly higher in granulosa cells of the future DF. STAT3 mRNA and total protein (tSTAT3) were higher in granulosa cells of SFs collected on Day 4. Furthermore, levels of pSTAT3 were dramatically increased in granulosa cells of Day-4 SFs. In conclusion, pMAPK3/1 was increased in the future DF, but such differential abundance between the DF and SF was not evident after deviation. The higher abundance of pSTAT3 in granulosa cells of SFs after deviation suggests that this pathway may be involved in granulosa cell death and follicular atresia.