Effects of ceramide, the Fas signal intermediate, on apoptosis and phospholipase D activity in mouse ovarian granulosa cells in vitro

Although recent studies have demonstrated that ovarian follicular atresia occurs by apoptosis of granulosa cells, the intracellular signaling pathways involved in apoptotic cell death are still poorly characterized. We examined the role of ceramide as a candidate intracellular mediator of Fas-mediated signaling in cultured granulosa cells. Expression of Fas antigen was demonstrated by Western blot of granulosa cell lysates and immunostaining of cultured granulosa cells. Exposure of granulosa cells to anti-Fas monoclonal antibody (anti-Fas mAb) resulted in significant sphingomyelin hydrolysis, which was accompanied by a progressive increase in endogenous levels of ceramide. The addition of exogenous C6-ceramide induced drastic morphological change, including nuclear fragmentation and typical apoptotic DNA degradation. Furthermore, both anti-Fas mAb and C6-ceramide decreased phospholipase D (PLD) activity and diacylglycerol (DAG) concentrations in a time- or a dose-dependent manner. In addition, treatment with phorbol 12-myristate 13-acetate completely attenuated the ceramide-induced inhibition of PLD activity and partially suppressed ceramide-induced apoptosis. These results indicate that the Fas/ceramide signaling pathway might play a role in granulosa cell apoptosis and suggest that the PLD/DAG pathway might be cross-linked to the Fas/ceramide pathway in apoptotic processes of granulosa cells.