Characterization of transforming growth factor beta superfamily, growth factors, transcriptional factors, and lipopolysaccharide in bovine cystic ovarian follicles

Abstract

The process of transformation of growing bovine follicles into cysts is still a mystery. Local expression of proteins or factors, including transforming growth factor β, growth factors, and transcription factors, plays a central role in mammals. Therefore, in abattoir-derived cystic ovarian follicles and follicular fluid, the role of some transforming growth factor β superfamily proteins, insulinlike growth factor-1 (IGF-1) and GATA-4 and GATA-6, were investigated. The relationship between intrafollicular lipopolysaccharide (LPS) and etiopathogenesis of ovarian cysts was also assessed. Data on the preovulatory follicle and the largest follicle (F1) were compared. The number of intrafollicular LPS-positive samples and LPS concentrations were higher in cysts. Immunohistochemical staining was mildly positive for IGF-1, inhibin alpha, and GATA-4 in thecal cells. Staining for anti-Müllerian hormone (AMH), growth differentiation factor-9, bone morphogenetic protein-6 (BMP-6), and GATA-6 was insufficient for their quantitation, and oocytes could not be stained for any of the proteins tested in the cystic follicles. Expression of BMP-6, inhibin alpha, and IGF-1 was moderately higher in granulosa cells of F1 follicles, and all the proteins were moderately expressed in granulosa cells in preovulatory follicles. However, loss of GATA-6 staining was significant in F1 follicles. Intrafollicular progesterone, IGF-1, and AMH concentrations in cysts and F1 follicles were significantly higher than those in preovulatory follicles. Western blot analyses revealed that follicular fluid inhibin-α was strongly expressed, whereas expression of growth differentiation factor-9, BMP-6, GATA-4 and GATA-6 was lower in cysts than in preovulatory follicles. Also, high intrafollicular AMH concentration and low BMP-6 expression were closely associated with cystic degeneration and atresia. In conclusion, immunohistochemical loss of BMP-6 and GATA-6 in the granulosa cells together with high intrafollicular LPS levels may play important roles in disruption of the ovulatory mechanism and steroidogenic reactions in type 2 cyst. Also, high intrafollicular AMH concentration along with low BMP-6 expression may be used as indicators of the bovine degenarative ovarian follicles.

Keywords: Bone morphogenetic protein-6; Bovine ovarian cyst; GATA-4; GATA-6; Insulinlike growth factor-1; Lipopolysaccharide.