Expression and localisation of vascular endothelial growth factor and basic fibroblast growth factor during the final growth of bovine ovarian follicles

Abstract

Locally produced growth factors may have important modulatory roles in final ovarian follicular growth. The aim of this study was to investigate the possible participation of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF2) in bovine follicles during final growth. Ovaries were collected from a slaughterhouse within 10-20 min after exsanguination. A classification of follicles into five groups (<0·5; >0·5-5; >5-20; >20-180; >180 ng/ml) was performed according to the follicular fluid (FF) oestradiol-17 content. For a better characterisation of classes the mRNA expressions of FSH receptor, LH receptor and aromatase cytochrome P450 in theca interna (TI) and granulosa cells (GC) were determined. Analysis of VEGF transcript by RT-PCR showed that GC and theca cells express predominantly the smallest isoforms (VEGF 121 and VEGF 165 ). VEGF mRNA expression in both tissues (TI and GC) and VEGF protein concentration in total follicle tissue increased significantly (and correlated) with developmental stages of follicle growth. The expression of mRNA for VEGF receptor (VEGFR)-1 and VEGFR-2 was very weak in GC, without any regulatory change during final follicle growth. In contrast, TI showed strong expression of mRNA for both receptors in all follicle classes examined. VEGF protein concentrations in FF increased significantly and continuously to maximum levels in preovulatory follicles. As shown by immunohistochemistry, VEGF protein was clearly localised in TI and GC of preovulatory follicles. FGF2 and FGF receptor (FGFR) mRNA expression in TI increased significantly during final growth of follicles. In contrast, the FGF2 and FGFR mRNA expression in GC was very weak and without any regulatory change during follicle growth. Histological observation revealed that FGF2 protein was localised in theca tissue (cytoplasm of endothelial cells and pericytes) but not in GC.Our results suggest that VEGF and FGF families are involved in the proliferation of capillaries that accompanies the selection of the preovulatory follicle resulting in an increased supply of nutrients and precursors, and therefore supporting the growth of the dominant follicle.

Expression and possible role of fibroblast growth factor family members in porcine antral follicles during final maturation

“…In contrast with the cow (Berisha et al 2000a), the FSHR mRNA expression trended to decrease during porcine follicle maturation. This agrees with findings by Cardenas & Pope (2002).…”

“…Zeleznik et al (1981) suggested that the selected follicles possess more elaborate microvasculature than other follicles. We concluded from studies in cow that vascular endothelial growth factor (VEGFA) and fibroblast growth factor 2 (FGF2) are involved in the proliferation of capillaries that accompany the selection of the preovulatory follicle resulting in an increased supply of nutrients, precursors and hormones, and therefore supporting the growth of the dominant follicle (Berisha et al 2000a, Yamashita et al 2008.…”

“…The distinct immunohistochemical localisation of FGF2 in selected bovine dominant follicles in cytoplasm of capillary endothelial cells (Berisha et al 2000a(Berisha et al , 2006a suggests an important role of FGF2 for the selection process in monovulatory bovine species. If this hypothesis is correct, we should see differences in FGF2 expression and localisation in polyovulatory species.…”

Follicle selection in cattle and horses: role of intrafollicular factors

“…An increase in VEGF, an angiogenic factor, occurred in the follicles of cattle (Berisha et al 2000) and pigs (Barboni et al 2000) as diameter increased. The synthesis and secretion of VEGF increased in cultures of granulosa cells in cattle (Schams et al 2001) and monkeys (Martinez-Chequer et al 2003) when exposed to IGF-I.…”

Changes in fibroblast growth factor 2 and its receptors in bovine follicles before and after GnRH application and after ovulation

“…Recently, it has been shown that vascular endothelial growth factor and FGF families are involved in the proliferation of capillaries that accompanies the selection of the preovulatory follicle. This results in an increased supply of nutrients and precursors, therefore supporting the growth of the dominant follicle in bovine ovaries (Berisha et al 2000a). In addition, FGF2 may play a significant role in bovine granulosa cell steroidogenesis (Vernon & Spicer 1994), anti-apoptotic action (Peluso et al 2001) and differentiation of granulosa cells (GCs) into luteal cells during the process of luteinisation (Lavranos et al 1994).…”