Regulation of low density lipoprotein receptor and 3-hydroxy-3-methyl-glutaryl-CoA reductase activities are differentially affected in Niemann-Pick type C and type D fibroblasts.
Defective regulation of intracellular cholesterol metabolism has been investigated in cultured fibroblasts from two subtypes of Niemann-Pick type II disease: the panethnic Niemann-Pick type C (NPC) and the Nova Scotia type D (NPD). Cell extracts from NPC and NPD fibroblasts cultured in lipoprotein-deficient medium exhibited activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase that were two-fold greater than in normal cells. Addition of serum resulted in only a 15% decrease in HMG-CoA reductase activity within 6 h in these cells, compared with a decrease of 80% in normal fibroblasts. The initial rate of return to maximal values for the first 6 h after removal of serum was similar in all three cell types; thereafter, the rate was faster in the mutant fibroblasts. Binding and internalization of 125I-labeled low density lipoprotein (LDL) was not decreased within 12 h of incubation of NPC fibroblasts with serum, while a decrease of 50% was observed for both NPD and normal fibroblasts over this time period. Northern blot analysis also indicated a slower decrease in steady-state LDL receptor mRNA in NPC relative to normal and NPD cells. In all three cell types, inhibition of HMG-CoA reductase with mevinolin had no effect on serum-stimulated cholesterol esterification, while inhibition of acyl-CoA:cholesterol acyltransferase with Sandoz 58-035 did not influence HMG-CoA reductase activity, indicating that defects in these regulatory mechanisms are independent.(ABSTRACT TRUNCATED AT 250 WORDS)
Sidhu
H S
HS
Atlantic Research Centre, Department of Pediatrics, Dalhousie University, Halifax, NS, Canada.
Rastogi
S A
SA
Byers
D M
DM
Guernsey
D L
DL
Cook
H W
HW
Palmer
F B
FB
Spence
M W
MW
D001769:Blood; D015152:Blotting, Northern; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism; D004951:Esterification; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000378:metabolism; D008148:Lovastatin / Q000494:pharmacology; D009542:Niemann-Pick Diseases / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D002785:Sterol O-Acyltransferase / Q000037:antagonists & inhibitors
D002788:Cholesterol Esters; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D011973:Receptors, LDL; D002784:Cholesterol; D008148:Lovastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D002785:Sterol O-Acyltransferase