FUNCTIONAL COMPARTMENTS OF SULFATIDE METABOLISM IN CULTURED LIVING CELLS - EVIDENCE FOR THE INVOLVEMENT OF A NOVEL SULFATIDE-DEGRADING PATHWAY

The modes of uptake and degradation of radiolabelled cerebroside sulph ate (CS or sulphatide) were investigated in cultured living skin fibro blasts and Epstein-Barr virus-transformed lymphoblastoid cell lines es tablished from control individuals and patients affected with metachro matic leucodystrophy (cerebroside sulphatase deficiency), multiple sul phatase deficiency and low-density-lipoprotein-receptor-negative famil ial hypercholesterolaemia. In both cell types, CS was taken up through a non-receptor-mediated process. In fibroblasts, CS degradation occur red intralysosomally as was evident from the findings that fibroblasts from metachromatic leucodystrophic patients accumulated the sulphatid e and that chloroquine inhibited its degradation by normal cells. In c ontrast, under similar conditions of CS availability, lymphoblastoid c ell lines from patients with metachromatic leucodystrophy could degrad e the incorporated sulphatide exactly as their normal counterparts. Th is metabolic pathway was also fully active in lymphoblastoid cells fro m patients with multiple sulphatase deficiency and was not inhibited b y chloroquine treatment. These data are consistent with a non-lysosoma l type of hydrolysis. In addition to the lysosomal and non-lysosomal c ompartments, a third compartment was identified in the two cell types which is probably formed by the pool of the sulphatide molecules incor porated into the plasma membrane. This is the first report on the exis tence of a CS-degrading pathway in intact cells with deficient lysosom al cerebroside sulphatase activity.