Interactions of thyroid hormone and FSH in the regulation of rat granulosa cell apoptosis.

Thyroid hormone (TH) is important for normal reproductive function. Our previous studies indicate that FSH increases preantral follicle growth in vitro, a response markedly enhanced by triiodothyronine (T3). However, the nature of this hormonal interaction is poorly understood. The objective of this study was to determine if and how T3 modulate FSH-induced expression and actions of granulosa cell intracellular survival and death intermediates. We investigated the possible involvement of Src and PI3K/Akt pathway in the regulation of granulosa cell survival. We demonstrated that, while ineffective alone (0.1-100 nM), T3 markedly enhanced FSH (100 ng/ml)-induced granulosa cell phospho-Src and phospho-Akt contents and Xiap expression in vitro. The effects of T3 were concentration-dependent, with maximal responses at 1.0 nM. FSH alone decreased Fas Ligand (FasL) content irrespective of the presence of T3. Co-treatment of cell with T3 and FSH decreased Fas content, although neither hormone alone elicited a significant response. Taken together, the present study demonstrates that T3 potentiates the cell survival action of FSH through Src- and PI3K-mediated Xiap up-regulation and decreased Fas and FasL expression.