Sutrina S L, Chen W W
J Biol Chem. 1982 Mar 25;257(6):3039-44.
Two isoenzymes of ceramidase, including lysosomal acid ceramidase and nonlysosomal alkaline ceramidase, catalyze the degradation of ceramide in cultured human skin fibroblasts. A genetically determined disorder of sphingolipid metabolism (Farber's-disease) is characterized by the deficiency of acid ceramidase and by the pathological accumulation of ceramide. In this report, we take advantage of this genetic deficiency to study the intracellular transport of reconstituted low density lipoprotein (LDL) containing ceramide and of ceramide-containing liposomes into lysosomes. Our findings show that there is decreased incorporation of LDL in Farber's diseased fibroblasts, presumably related to the lack of lysosomal degradation of ceramide. In turnover experiments, the deficiency of lysosomal acid ceramidase in Farber's disease fibroblasts leads to the complete lack of degradation of ceramide internalized through the LDL uptake process. In contrast, this genetic defect does not affect either the uptake or turnover of ceramide-containing phosphatidylcholine liposomes. Comparison of these results suggests that in cultured skin fibroblasts the coated vesicles containing ceramide-LDL are designated for lysosomal delivery and are clearly distinguished from endocytotic vesicles involved in the uptake of ceramide-containing liposomes, which may be destined to be transported into subcellular organelles other than lysosomes.
神经酰胺酶的两种同工酶，包括溶酶体酸性神经酰胺酶和非溶酶体碱性神经酰胺酶，催化培养的人皮肤成纤维细胞中神经酰胺的降解。一种由基因决定的鞘脂代谢紊乱疾病（法伯病）的特征是酸性神经酰胺酶缺乏以及神经酰胺的病理性蓄积。在本报告中，我们利用这种基因缺陷来研究含有神经酰胺的重组低密度脂蛋白（LDL）以及含神经酰胺脂质体向溶酶体的细胞内转运。我们的研究结果表明，法伯病成纤维细胞中LDL的掺入减少，这可能与神经酰胺缺乏溶酶体降解有关。在周转实验中，法伯病成纤维细胞中溶酶体酸性神经酰胺酶的缺乏导致通过LDL摄取过程内化的神经酰胺完全缺乏降解。相比之下，这种基因缺陷既不影响含神经酰胺的磷脂酰胆碱脂质体的摄取也不影响其周转。这些结果的比较表明，在培养的皮肤成纤维细胞中，含有神经酰胺-LDL的被膜小泡被指定用于溶酶体递送，并且与参与摄取含神经酰胺脂质体的内吞小泡明显不同，后者可能注定要被转运到溶酶体以外的亚细胞细胞器中。
