DIFFERENTIAL ACCUMULATION OF CHOLESTEROL IN GOLGI COMPARTMENTS OF NORMAL AND NIEMANN-PICK TYPE-C FIBROBLASTS INCUBATED WITH LDL - A CYTOCHEMICAL FREEZE-FRACTURE STUDY

Cholesterol accumulation in the Golgi of normal and Niemann-Pick Type C (NP-C) fibroblasts was shown by freeze-fracture electron microscopy using filipin as a probe for unesterified cholesterol. The specific di stribution of cholesterol within individual Golgi compartments could b e examined because membrane cholesterol forms complexes with filipin t hat are visible as membrane deformations (pits and protuberances) in f reeze-fracture replicas. The density of filipin-cholesterol deformatio ns, quantitated for cis, medial, and trans Golgi cisternae and trans G olgi vacuoles, was shown to increase in a cis to trans direction. Afte r addition of low density lipoproteins (LDL) to cultured fibroblasts f or 24 h, the cholesterol content increased within specific compartment s of the Golgi. Normal cells showed an increase in filipin-cholesterol deformations in membranes of cis/medial cisternae and trans Golgi vac uoles, whereas NP-C cells showed only an increase in membranes of tran s Golgi cisternae. LDL uptake by cells appears to induce a disparate c holesterol enrichment of Golgi compartments of normal and mutant cells . The ability of cells to process endocytosed cholesterol may in part depend on modulation of cholesterol-enriched membrane transport throug h the Golgi, a function which appears to be defective in NP-C cells.