title: Cathepsin D, a lysosomal protease, regulates ABCA1-mediated lipid efflux.
abstract: To identify genes involved in the regulation of plasma high density lipoprotein (HDL) cholesterol (HDL-C) levels, patients with low HDL-C and age- and sex-matched controls (normal HDL-C) were extensively characterized. Comparative transcriptome analysis was carried out in cholesterol-loaded monocyte-derived macrophages from low HDL subjects segregated into groups with or without cholesterol efflux defects or ABCA1 mutations. Clusters of differentially regulated genes were evident in the low HDL groups as compared with controls. Of particular note, expression of cathepsin D (CTSD), a lysosomal proteinase, was reduced by approximately 50% in monocyte-derived macrophages of low HDL-C subjects, most significantly those with cholesterol efflux defects but without mutations in ABCA1 (p < 0.01). These results were verified by reverse transcription-PCR and replicated in a second cohort. We show here that blocking the activity or expression of CTSD, by pepstatin or CTSD small interfering RNA, respectively, reduced ABCA1 expression and protein abundance in both macrophages and CHO cells and apolipoprotein A-I-mediated lipid efflux by more than 70%. Conversely, expression of CTSD increased both ABCA1 mRNA expression and cellular ABCA1 protein. Consistent with its role in the proteolytic processing of prosaposin, inactivation of CTSD function resulted in the accumulation of glycosphingo-lipid and free cholesterol in late endosomes/lysosomes, a phenotype similar to NPC1 deficiency. Inhibition of CTSD also caused retention of ABCA1 in lysosomal compartments, reducing its trafficking to the plasma membrane. These studies demonstrate a novel and potentially important role for CTSD in intracellular cholesterol trafficking and ABCA1-mediated efflux. Therefore, decreased CTSD expression may contribute to low plasma HDL-C levels.
authors.affiliation: Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ottawa, Ontario, K1Y 4W7, Canada.
authors.forename: Bassam
authors.initials: B
authors.lastname: Haidar
authors.forename: Robert S
authors.initials: RS
authors.lastname: Kiss
authors.forename: Lea
authors.initials: L
authors.lastname: Sarov-Blat
authors.forename: Roch
authors.initials: R
authors.lastname: Brunet
authors.forename: Christopher
authors.initials: C
authors.lastname: Harder
authors.forename: Ruth
authors.initials: R
authors.lastname: McPherson
authors.forename: Yves L
authors.initials: YL
authors.lastname: Marcel
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D016466:CHO Cells; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002522:Chlorocebus aethiops; D008076:Cholesterol, HDL / Q000378:metabolism; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D007424:Intracellular Fluid / Q000201:enzymology; D050356:Lipid Metabolism / Q000502:physiology*; D008075:Lipoproteins, HDL / Q000096:biosynthesis / Q000378:metabolism; D008247:Lysosomes / Q000201:enzymology*; D008264:Macrophages / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009000:Monocytes / Q000201:enzymology / Q000378:metabolism; D010447:Peptide Hydrolases / Q000502:physiology*
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008076:Cholesterol, HDL; D008075:Lipoproteins, HDL; D010447:Peptide Hydrolases; D002402:Cathepsin D