REGULATION OF INTRACELLULAR CHOLESTEROL-METABOLISM IS DEFECTIVE IN LYMPHOBLASTS FROM NIEMANN-PICK TYPE-C AND TYPE-D PATIENTS

Regulation of intracellular cholesterol metabolism has been studied in Epstein-Barr virus-transformed lymphoblasts from patients with Nieman n-Pick type C (NPC) and the Nova Scotia type D (NPD) disease. Addition of LDL to normal lymphoblasts cultured in lipoprotein-deficient mediu m increased cholesterol esterification 10-fold (to a maximum of 1.0 nm ol/h/mg protein at 15 h), while little stimulation was seen in NPC cel ls. The response by NPD lymphoblasts was intermediate, reaching approx imately half of normal values by 14-24 h. Lymphoblasts from both NPC a nd NPD obligate heterozygotes exhibited 50% of normal LDL-stimulated c holesterol esterification at 6 h, when activity was < 10% of normal va lues in patient cells. Fluorescence staining with filipin indicated ex cessive intracellular accumulation of LDL-derived cholesterol in both NPC and NPD lymphoblasts. Downregulation of LDL receptor mRNA levels b y LDL, measured by SI. nuclease protection assay, was also impaired in NP lymphoblasts and fibroblasts (NPC > NPD), although a similar rate of receptor protein down-regulation by LDL (t(1/2) 10-15 h) was observ ed in normal and NP lymphoblasts. In contrast, LDL down-regulation of 3-hydroxy-3-methylglutaryl-CoA reductase mRNA did not appear to be aff ected in NP cells: LDL produced a S-fold (lymphoblasts) or > 10-fold ( fibroblasts) decrease by 12 h in both normal and affected cells. Thus, NPC and NPD lymphoblasts exhibit distinct defects in cholesterol este rification and storage, similar to those observed in mutant fibroblast s. Other regulatory responses are also impaired in NPC lymphoblasts bu t appear to be less affected in NPD cells. Lymphoblasts should provide a valuable immortalized cell line model-for study of defective regula tion of cholesterol esterification and transport in Niemann-Pick type II disease, and may also be suitable for diagnosis and carrier detecti on.