The role of sFRP4, a secreted frizzled-related protein, in ovulation

Ovulation is a complex, multi-factorial event that involves the degeneration of a specific area of the follicular and ovarian surface via apoptosis. Many apoptosis related genes have been identified in the ovary. Secreted Frizzled Related Protein 4 (sFRP4) is a protein that appears to antagonize a molecular pathway for cell survival. sFRP4 gene expression is known to be upregulated with apoptosis in the ovarian corpus luteum. In this study, ovulation was hormonally induced in immature Wistar rats and their ovaries collected for analysis of apoptosis and sFRP4. TUNEL staining identified a greater amount of dying cells in the thecal layer of treated rat ovaries compared to controls. The results of 3'-end labelling revealed a significant increase (p < 0.01) in apoptosis at 12 hours following treatment compared to other time points and control. In situ hybridization exhibited a visible increase in amounts of sFRP4 mRNA expression in the thecal layers of follicles from treated rats compared to controls. Quantitative RT-PCR revealed no significant difference in sFRP4 expression levels between treated and control tissues although a clear trend towards an increase was observed in the treated group. This study demonstrates an association between sFRP4 and apoptosis in rat ovulation.