ABCA1-dependent mobilization of lysosomal cholesterol requires functional Niemann-Pick C2 but not Niemann-Pick C1 protein

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• 作者：Emmanuel Boadu^a ; Randy C. Nelson^b ; Gordon A. Francis^a ; ^{gordon.francis@hli.ubc.ca}
• 关键词：ApoA-I ; apolipoprotein A-1 ; ABCA1 ; ATP-binding cassette transporter A1 ; EGFP ; enhanced green fluorescent protein ; HDL ; high density lipoprotein ; LDL ; low density lipoprotein ; LXR ; liver X receptor ; NPC ; Niemann&ndash ; Pick type C
• 刊名：Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids
• 出版年：2012
• 期刊代码：18_13881981
• 类别：bio
• 出版时间：March, 2012
• 卷：1821
• 期：3
• 页码：396-404
• 文件大小：856 K

摘要

Niemann-Pick disease type C (NPC) is caused by mutations leading to loss of function of NPC1 or NPC2 proteins, resulting in accumulation of unesterified cholesterol in late endosomes and lysosomes. We previously reported that expression of the ATP-binding cassette transporter A1 (ABCA1) is impaired in human NPC1^{鈭?鈭?/sup> fibroblasts, resulting in reduced HDL particle formation and providing a mechanism for the reduced plasma HDL cholesterol seen in the majority of NPC1 patients. We also found that treatment of NPC1鈭?鈭?/sup> fibroblasts with an agonist of liver X-receptor corrects ABCA1 expression and HDL formation and reduces lysosomal cholesterol accumulation. We have confirmed that ABCA1 expression is also reduced in NPC2鈭?鈭?/sup> cells, and found that 伪-HDL particle formation is impaired in these cells. To determine whether selective up-regulation of ABCA1 can correct lysosomal cholesterol accumulation in NPC disease cells and HDL particle formation, we produced and infected NPC1鈭?鈭?/sup> and NPC2鈭?鈭?/sup> fibroblasts with an adenovirus expressing full-length ABCA1 and enhanced green fluorescent protein (AdABCA1-EGFP). ABCA1-EGFP expression in NPC1鈭?鈭?/sup> fibroblasts resulted in normalization of cholesterol efflux to apolipoprotein A-I (apoA-I) and 伪-HDL particle formation, plus a marked reduction in filipin staining of unesterified cholesterol in late endosomes/lysosomes. In contrast, AdABCA1-EGFP treatment of NPC2鈭?鈭?/sup> fibroblasts to normalize ABCA1 expression had no effect on cholesterol efflux to apoA-I or accumulation of excess cholesterol in lysosomes, and only partially corrected 伪-HDL formation by these cells. These results suggest that correction of ABCA1 expression can bypass the mutation of NPC1 but not NPC2 to mobilize excess cholesterol from late endosomes and lysosomes in NPC disease cells. Expression of ABCA1-EGFP in NPC1鈭?鈭?/sup> cells increased cholesterol available for esterification and reduced levels of HMG-CoA reductase protein, effects that were abrogated by co-incubation with apoA-I. A model can be generated in which ABCA1 is able to mobilize cholesterol, to join the intracellular regulatory pool or to be effluxed for HDL particle formation, either directly or indirectly from the lysosomal membrane, but not from the lysosomal lumen. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).}