Ceramide accumulation is associated with increased apoptotic cell death incultured fibroblasts of sphingolipid activator protein-deficient mouse butnot in fibroblasts of patients with Farber disease

Ceramide is recognized as an intracellular mediator of cell growth, differe ntiation and apoptosis. Tumour necrosis factor, anti-fas antibody, radiatio n and anticancer drugs such as actinomycin D are known to induce apoptosis in several cell types through generation of ceramide by activation of the s phingomyelinase pathway or ceramide synthetase. In this study, we examined the occurrence of apoptosis in fibroblasts from patients with Farber diseas e and from sphingolipid activator protein-deficient (sap -/-) mouse. These cells accumulate ceramide as the result of genetic deficiency of acid ceram idase and the ceramidase activator (sap-D), respectively. Amounts of cerami de in fibroblasts from Farber patients and in fibroblasts from sap -/- mous e were increased 2.9-fold and 2.8-fold, respectively, over the level of con trols. Despite the similar degree of ceramide accumulation, cells exhibitin g apoptotic features were increased only in fibroblasts from the sap -/- mo use but not those from the Farber patients. Thymidine uptake of Farber fibr oblasts was normal while that of sap -/- mouse fibroblasts was twice normal , consistent with the apparently normal growth and the different rates of a poptotic cell death in these two cell lines. These data suggest that intral ysosomal accumulation of ceramide due to defective acid ceramidase or its a ctivator may not play an important role as a mediator of apoptosis. The inc reased apoptosis in the cultured fibroblasts from the sap -/- mouse may be caused by mechanisms other than the ceramide accumulation. Although more fr equent than normal, significant apoptotic cell death was not observed in sa p -/- mouse brain in vivo.