Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC241

Poster Communications

Dynamics of ovarian follicular development and atresia are regulated by the balance of pro- and anti-angiogenic isoforms of vascular endothelial growth factor (VEGF)

J. Castle-Miller2, M. Cengarle2, D. Bates1, Y. Qiu1, D. Tortonese2

1. Microvascular Research Laboratories, School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom. 2. Centre for Comparative and Clinical Anatomy, University of Bristol, Bristol, United Kingdom.

Vascular endothelial growth factor (VEGF) moderates angiogenesis and vascular permeability in the ovary. It is expressed as a pro-angiogenic (e.g. VEGF165) or anti-angiogenic (e.g. VEGF165b) isoform according to splice site selection in the terminal exon. Angiogenesis provides follicles with the hormonal milieu required to reach pre-ovulatory stage, whereas anti-angiogenesis accompanies atresia. VEGF165b over-expression in the ovary(1) has been shown to reduce litter size and the number of ovulated embryos in the oviduct, but it is not known whether this was due to reduced angiogenesis in the ovaries of these mice or reduced follicle stimulating hormone (FSH) signalling. Here we examined the number and size of healthy follicles, incidence of FSH receptor expression, number and size of CL, and the quantity of atretic follicles, in the ovaries of transgenic (TG) mice over-expressing VEGF165b in the ovary under control of the MMTV promoter(1) and in wild type (WT) littermate controls. Animals (n = 6/group) were mated with wild type mice and killed by a schedule 1 method at 0.5 days post coitus. Using immunohistochemistry and morphometric analysis, we determined that the total number of healthy follicles was significantly reduced in TG mice compared to WT controls (4.39±1.31 vs 8.25±0.90 /section, respectively; p<0.05). TG mice had a significant decrease in the number (0.61±0.33 vs 2.25±0.38 /section; p<0.05) and size (p<0.05) of secondary antral follicles, and a significant reduction in the ratio of tertiary to secondary-antral follicles (0.037±0.02) in comparison to WT controls (0.65±0.28; p<0.05). Furthermore, the diameter of tertiary follicles was significantly smaller in TG when compared to WT controls (p<0.05). However, TG and WT mice showed no significant difference in FSH-R expression (4.15±0.89 vs 4.02±0.34 %, respectively; p>0.05). TG mice were found to have a highly significant reduction in the number of CL (1.83±0.53 vs 4.70±1.09 /section; p<0.01), and a significant reduction in the size of the CL (p<0.05), compared to WT littermates. Finally, we observed a significant increase in the number of atretic follicles in the ovaries of TG mice (4.69±0.02 /section), compared to WT controls (1.24±0.56 /section; p<0.05). These results confirm that VEGF is a key regulator of follicular and CL angiogenesis, and show that inhibition by VEGF165b results in reduced growth and quantity of follicles and CL. This study also provides evidence that VEGF inhibition by VEGF165b does not affect FSH-R expression, and that VEGF regulates follicle atresia.

Where applicable, experiments conform with Society ethical requirements