Expression and distribution patterns of VEGF, TGF‐β(1) and HIF‐1α in the ovarian follicles of Tibetan sheep

BACKGROUND: Hypoxia‐inducible factor‐1α (HIF‐1α), vascular endothelial growth factor (VEGF) and transforming growth factor β(1) (TGF‐β(1)) are multifunctional growth factors that play an important role in follicular growth and development. However, its biological function in the follicular development of Tibetan sheep at different stages has not been described. OBJECTIVES: The purpose of this study was to investigate the effect of VEGF, TGF‐β(1) and HIF‐1α expression and distribution on the development of follicles of different sizes. METHODS: Immunohistochemistry (IHC), western blot (WB) and quantification real‐time polymerase chain reaction (qRT‐PCR) were used to detect the localisation and quantitative expression of VEGF, TGF‐β(1) and HIF‐1α proteins and mRNA in small‐ (< 3 mm), medium‐ (3 mm < diameter < 5 mm)‐, and large‐ (> 5 mm) sized follicles. RESULTS: The results showed that the proteins VEGF, TGF‐β(1) and HIF‐1α, as well as their mRNA, were expressed in follicles. However, the expression in medium‐sized follicles was significantly higher than that in large‐ and small‐sized follicles (p <0.05). IHC also showed that the proteins VEGF, TGF‐β(1), and HIF‐1α were distributed in granulosa cells (GCs) in small‐, medium‐, and large‐sized follicles. CONCLUSIONS: This study indicates that VEGF, TGF‐β(1) and HIF‐1α, which operate in an autocrine or paracrine manner with the GCs, influence the follicular progressive growth, suggesting that these growth factors are closely associated with the follicular growth and development in ovarian.