Role of lysosomal acid ceramidase in the metabolism of ceramide in human skin fibroblasts

A 2.8-fold accumulation of ceramide was demonstrated in cultured skin ftbroblasts from a patient with Farber's disease, an inborn error of metabolism in which acid ceramidase activity is deficient. To investigate the role of acid ceramidase in the metabolism of ceramide in fibroblasts, we have investigated the lysosomal degradation of ceramide that was taken up by fibroblasts from an exogenous lipid suspension. Fluorescent 4-nitrobenz-2-oxa-1,3-diazole-7-aminododecanoyl-sphingosine (NBD-ceramide) from an exogenous ceramide suspension was incorporated into the intracellular structures of fibroblasts at 37 °C. Study of the cellular uptake of exogenous [³H]oleylsphingosine showed that the rate of ceramide accumulation was nearly identical in Farber's disease and normal fibroblasts. The deficiency of acid ceramidase in Farber's fibroblasts resulted in the decrease of cellular degradation and uptake of ceramide and the increase of retention time of ceramide in these diseased cells. Studies of subcellular fractionation of these fibroblasts showed that the accumulated ceramide was located in the lysosomal fraction. As a result, the density of the lysosomal fraction of Farber's fibroblasts was found to be less than that of controls. These results suggest the defect of cellular metabolism in this inherited disease is located within the lysosome.