Abnormal processing of Golgi elements and lysosomes in Tangier disease.

Abstract

It has been demonstrated that the cellular defect in Tangier disease is associated with morphological abnormalities in the lysosomal compartment and in the Golgi apparatus of mononuclear phagocytes (MNPs) after lipid loading by exposure to acetylated low density lipoproteins (acetyl-LDLs). On exposure to acetyl-LDL, Tangier MNPs accumulate two unusual types of vacuoles that were not observed in control MNPs. The electron-lucent type I vacuoles are round or ovoid, form aggregates, and are filled with fine flocculent or fibrillar material. Type II vacuoles are filled with more electron-dense material, are larger, and contain scrolls and lamellae with varying degrees of electron opacity. By immunoelectron microscopy both types of vacuoles could be identified as lysosomes. This abnormality of the lysosomal compartment in Tangier MNPs was not observed in Tangier fibroblasts, where the few lysosomes detected were found to be similar to those of controls. Morphological analysis of the Golgi apparatus in Tangier MNPs revealed numerous dilated Golgi cisternae, which were distributed more widely throughout the cell. However, both Tangier MNPs and especially Tangier fibroblasts showed a marked hyperplasia of the Golgi complex. Specific staining of the Golgi apparatus with the fluorescent ceramide analogue N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]-6-aminocaproylsphingosine (C6-NBD-ceramide) showed that Tangier fibroblasts incorporated significantly higher amounts of C6-NBD-ceramide than did control fibroblasts. Moreover, the Tangier fibroblasts that appear generally larger than normal fibroblasts also show significant staining along the cytoskeleton, which may indicate the association of fluorescent ceramide and sphingomyelin to cytoskeletal elements. Phospholipid synthesis and catabolism were studied in Tangier fibroblasts from five patients with the use of tritiated choline as a tracer. A significantly higher incorporation rate was measured for sphingomyelin (176 +/- 18% of control) and phosphatidylcholine (144 +/- 12% of control). A moderate increase in catabolism was found for sphingomyelin (20 +/- 8% of control) and phosphatidylcholine (11 +/- 4% of control). These data are principally in agreement with our former studies of the abnormalities of phospholipid metabolism in Tangier MNPs (G. Schmitz et al, Arteriosclerosis 1990; 10:1010-1019). It is concluded that the defect in Tangier disease that we have recently described as a "disorder of intracellular traffic" (G. Schmitz et al, Proc Natl Acad Sci U S A 1985;82:6305-6309) is also expressed in Tangier fibroblasts. Tangier disease seems to be associated with morphological abnormalities of intracellular organelles, thus strongly indicating that the translocation disorder in this disease affects the Golgi apparatus and the regular processing of lysosomes and shows abnormalities in cellular lipid metabolism.