Apoptosis induction in synovial fibroblasts by ceramide: in vitro and in vivo effects.

Several lipid second messengers are important mediators of extracellular signals. Among them ceramide, which is formed by cell membrane sphingomyelin, influences the apoptotic signal pathway through Fas antigen. We examined the apoptotic effect of cell-permeable C2-ceramide on rheumatoid synovial fibroblasts in vitro and in vivo. Exposure of cultured human rheumatoid synovial fibroblasts to C2-ceramide for 24 hours produced internucleosomal DNA fragmentation and morphologic changes characteristic of apoptosis. This C2-ceramide-mediated apoptosis was dose dependent as confirmed by analysis of cytosolic oligonucleosome-bound DNA of treated synovial fibroblasts. We also demonstrated that intra-articular administration of C2-ceramide into Fas-deficient MRL lpr/lpr mice produced a profound reduction of synovial hyperplasia within 24 hours. In situ nick end labeling analysis confirmed the induction of apoptosis in synovial lining cells. Our results indicate that C2-ceramide may function as a potent inducer of apoptosis in the synovium and suggest that pharmacologically-induced apoptosis may be useful as a new therapeutic modality for rheumatoid arthritis.