Activin A promotes bovine pituitary FSH synthesis and secretion through the cooperative action of the SMAD signaling pathway and FOXO3

Abstract The pituitary gland is an important endocrine organ in living organisms and is divided into two parts: the adenohypophysis and the neurohypophysis. Follicle-stimulating hormone (FSH) secreted by the adenohypophysis can act on the granulosa cells of the ovary to promote follicle development and maturation. Activin A is a dimeric protein belonging to the transforming growth factor beta superfamily that promotes FSH secretion from the pituitary gland. Recent studies on the mechanisms of pituitary FSH regulation have focused on species such as mice, rats, pigs, and sheep, and the specific mechanisms of FSH synthesis and secretion in the bovine pituitary are not known. In our study, we demonstrated that activin A also promotes FSH synthesis and secretion in bovine adenohypophysis by isolating and culturing bovine adenohypophysis primary cells. Mechanistically, activin A binds to cell surface receptors, activates the SMAD signaling pathway, and promotes the expression of the transcription factor FOXO3, which enters the nucleus and binds to the FSHB promoter. Additionally, knockdown of FOXL2 did not affect the regulatory effects of activin A on bovine FSH, so we hypothesized that bovine FSHB may be regulated by the FOX protein FOXO3, which is different from the FSHB promoter in other species. Finally, dual luciferase and co-immunoprecipitation experiments revealed that FOXO3 and SMAD2/3 form a complex that synergistically mediates the transcriptional activation of activin A. Overall, this study confirmed the promoting effect of activin A on FSH synthesis and secretion in the bovine pituitary gland and explored the specific molecular mechanism involved.