221 CYSTIC BOVINE FOLLICLES ARE ASSOCIATED WITH AN ALTERATION IN LOCAL GENE AND PROTEIN EXPRESSION

Abstract

Formation of persistent follicular cysts is a prevalent problem for producers of domestic agricultural animals in North America. The most common group of animals affected is dairy cattle. This condition is problematic as it renders cattle anovulatory and infertile for the duration of the cyst. Various studies have assessed the incidence of follicular cysts in dairy cattle, revealing a range of prevalence of 9–26%. Although there is information regarding the incidence of this disorder, little is known of the etiology. It is known that a complex interaction occurs between the hypothalamus, anterior pituitary, and ovary to regulate normal reproductive function. Dysregulation at any of these sites could contribute to the formation of persistent follicular cysts. The objective of this study was to determine whether local changes in gene and protein expression are present in cystic follicles. Transvaginal aspirations from follicles that had been greater than 2.5-cm diameter for at least 10 days were collected. Aspirates were centrifuged, and granulosa cells and follicular fluid were separated. Granulosa cells were lysed, and RNA and protein was isolated. For immunohistochemistry, bovine slaughterhouse ovaries with follicles greater than 2.5 cm in diameter were dissected, fixed, and processed. Western blot analysis and RT-PCR were performed on protein and RNA samples, respectively. Cystic and control follicles were analyzed for expression of vascular endothelial growth factor (VEGF) and its receptor VEGF-R2 and members of the insulin-like growth factor (IGF) family, which are known to mediate a host of cellular events during follicular development. Cystic follicles exhibited a significant increase in VEGF and IGF-I protein concentrations and a reduction in VEGF-R2 and the type 1 IGF receptor. Immunohistochemical analysis demonstrated increased ligand staining and reduced receptor expression in granulosa cells of cystic follicles. These results indicate that there is an altered growth factor profile in cystic follicles and suggest that intra- as well as extra-follicular dysregulation is important in the etiology of this reproductive disorder.