Platform Session 9. Signaling Pathways in the Ovarian Follicle
Monday, July 25, 2005
2:00 PM–4:00 PM
Location: CCQ 204AB
(69) REGULATION OF RAT GRANULOSA CELL APOPTOSIS BY NODAL/ALK7-SIGNALING PATHWAY.
Wang, Hongmei1, Peng, Chun2, Tsang, Benjamin1, 1 University of Ottawa, Ottawa Health Research Institute, Ottawa, ON, Canada2 York University, Toronto, ON, Canada
ABSTRACT- Apoptosis, an essential process involved in the maintenance of ovarian homeostatic function, is regulated by the coordinated actions and interactions of endocrine, paracrine, and autocrine factors, including members of the transforming growth factor (TGF) family. Although growth differentiation factor-9 and bone morphogenetic protein-15 have been shown to be important regulators of folliculogenesis, little is known about the role of TGF family member Nodal in the control of granulosa cell apoptosis and follicular atresia. In this study, we have examined the expression of Nodal and its type I receptor ALK7 and their role and mechanism involved in the regulation of granulosa cell apoptosis. Nodal and ALK7 expression at different stages of follicular development was assessed by immunohistochemistry in ovaries from immature rats treated with eCG (10 IU). In addition, granulosa cells (GCs) from eCG-primed (48h) rats were cultured and activation of the Nodal/ALK7 pathway was achieved by addition of Nodal or infection with adenoviral Nodal and constitutively active ALK7. Phospho-Smad2 (P-Smad2), Xiap, phospho-Akt (P-Akt) in whole cell, Smac and Omi content in mitochondria and cytosolic fractions were determined by Western blot, and apoptosis was assessed by nuclear morphology (Hoechst staining). While Nodal was expressed mainly in GCs of preantral follicles and theca cells of early antral and large antral follicles, ALK7 was detected mainly in GCs of the antral follicles. GCs treated with Nodal or overexpressed with activated ALK7 exhibited increased P-Smad2 content, Smad2 nuclear import, and decreased Xiap and P-Akt content. These responses were associated with increased mitochondrial release of Smac and Omi and apoptosis. In conclusion, Nodal and ALK7 are expressed in the rat follicle in a cell-specific and follicular stage-dependent manner. Activation of Nodal/ALK7 signaling pathway induces apoptosis in rat GCs. This response is associated with downregulation of the cell survival factors Xiap and Akt, and activation of the mitochondria death pathway. (Supported by CIHR and STIRRHS)
KEY WORDS: nodal/ALK7-signaling pathway, rat, granulosa cell, apoptosis