Coordinated expression of the VEGF system components in granulosa cells to develop a pro-angiogenic autocrine milieu during ovarian follicle development.

In the present study we investigated the temporal relationship between angiogenic and anti-angiogenic vascular endothelial growth factor isoforms (VEGFxxxa and VEGFxxxb respectively), the receptors VEGFR1 and VEGFR2, their soluble forms, and the kinases and the splicing factors regulating the synthesis of VEGF isoforms in healthy and atretic antral follicles. The results show a higher (P<0.05) mRNA expression of VEGF120a, VEGF164a and VEGF120b in healthy than in atretic follicles, but the mRNA expression of VEGF164b was not detected. The mRNA of serine-arginine protein kinase 1 (SRPK1) was higher (P<0.05) in large healthy follicles than in large atretic follicles. In contrast, atretic follicles had higher mRNA expression of soluble form of the receptor 2 of VEGF (sVEGFR2) than healthy follicles (P<0.05). Additionally we observed a positive relationship (P<0.05) between SRPK1 and serine-arginine-rich splicing factor 1 (SRSF1) with the angiogenic isoforms VEGF120a and VEGF164a and between CDC-like kinases-1 (CLK1) and SRSF6 with the antiangiogenic VEGF120b isoform. Principal components analysis (PCA) resulted in two PC explaining 71% of the variation, which were formed by the VEGF isoforms, the kinases and the splicing factor (PC1) and by the VEGF receptors (PC2). When PC analysis was carried out within follicular health status, there were no differences for PC1 between follicular status, whereas PC2 differed between healthy and atretic follicles. In conclusion, the higher mRNA expression for VEGF120a and VEGF164a, the low expression of sVEGFR2 and absent expression of mRNA for VEGF164b provide evidence of a pro-angiogenic autocrine milieu to support granulosa cells during follicle development. This article is protected by copyright. All rights reserved.