Activation of the sphingomyelinase/ceramide signal transduction pathway in insulin-secreting beta-cells: role in cytokine-induced beta-cell death.

Activation of the sphingomyelin/ceramide pathway may mediate interleukin-1-induced beta-cell death (Welsh, N: Interleuken-1beta-induced ceramide and diacylglycerol generation may lead to activation of the c-Jun NH2-terminal kinase and the transcription factor ATF-2 in the insulin-producing cell line RINm5F. J Biol Chem 271: 8307-8312, 1996). In this report, we have examined this pathway in more detail. Culture of beta-TC3 cells with 25 micromol/l ceramide analogs (N-acetyl- and N-hexanoylsphingosine) for 72 h did not significantly affect glucose- and carbachol-induced insulin secretion. Dihydroceramide (N-acetyl- or N-hexanoylsphinganine), a structurally similar analog, had no effect on agonist-induced secretion. However, ceramide analogs both time- and dose-dependently decreased cell viability, while the dihydroceramide analog had no effect. The ceramide effect on cell viability mimicked the effect of the cytokines TNF-alpha, IL-1beta, and IFN-gamma, reported stimulators of sphingomyelin hydrolysis. Cytokines, however, failed to stimulate sphingomyelin metabolism. Furthermore, using two different methods to quantitate ceramide, cytokines failed to cause an increase in beta-cell ceramide content versus unstimulated or time-matched vehicle controls. Taken together, these data suggest that although ceramide analogs mimic the cytotoxic effect of cytokines, activation of the sphingomyelin/ceramide signaling pathway is not involved in cytokine-induced beta-cell death.