title: Cholesterol efflux via HDL resecretion occurs when cholesterol transport out of the lysosome is impaired.
abstract: Recently, we showed that holo HDL particle uptake and resecretion occur in physiologically relevant cell lines and that HDL uptake is mediated by scavenger receptor class B type I (SR-BI). Furthermore, we established that HDL resecretion is accompanied by [(3)H]cholesterol efflux. This study shows that HDL uptake and resecretion occur even when LDL uptake and cholesterol trafficking are disturbed. First, we used a set of inhibitors that block cholesterol transport out of the lysosome: chloroquine, imipramine, U18666A, and monensin. In all cases, HDL retroendocytosis occurred and HDL resecretion mediated [(3)H]cholesterol efflux, although to a lesser extent. Second, cell lines carrying somatic mutations in intracellular cholesterol transport were used: CHO 2-2 and CHO 3-6 cells accumulated LDL-derived lipid in the lysosome but showed all components of HDL retroendocytosis. SR-BI overexpression increased HDL uptake and resecretion and [(3)H]cholesterol efflux in these mutant cells. Finally, we used Niemann-Pick type C (NPC) patient fibroblast cells, which carry a defect in cholesterol transfer out of the lysosome. NPC fibroblast cells accumulate cholesterol in the lysosome as a result of a mutation in the NPC1 gene. Despite disturbed intracellular cholesterol transfer, NPC fibroblast cells exhibited HDL retroendocytosis and [(3)H]cholesterol efflux via HDL resecretion, although to a lesser extent. Thus, [(3)H]cholesterol efflux via HDL resecretion is independent of the cholesterol uptake pathway via the LDL receptor and may be an alternative way to remove excess cholesterol.
authors.affiliation: Center for Physiology and Pathophysiology, Department of Medical Chemistry, Medical University of Vienna, A-1090, Vienna, Austria.
authors.forename: Tamara A
authors.initials: TA
authors.lastname: Pagler
authors.forename: Angelika
authors.initials: A
authors.lastname: Neuhofer
authors.forename: Hildegard
authors.initials: H
authors.lastname: Laggner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Strobl
authors.forename: Herbert
authors.initials: H
authors.lastname: Stangl
mesh_terms: D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000378:metabolism; D002738:Chloroquine / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007099:Imipramine / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D000077296:Niemann-Pick C1 Protein; D051122:Scavenger Receptors, Class B / Q000378:metabolism
chemical_list: D000736:Androstenes; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008075:Lipoproteins, HDL; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; C495124:SCARB1 protein, human; D051122:Scavenger Receptors, Class B; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; D002738:Chloroquine; D008985:Monensin; D002784:Cholesterol; D007099:Imipramine