title: Quantitative role of LAL, NPC2, and NPC1 in lysosomal cholesterol processing defined by genetic and pharmacological manipulations.
abstract: Lipoprotein cholesterol taken up by cells is processed in the endosomal/lysosomal (E/L) compartment by the sequential action of lysosomal acid lipase (LAL), Niemann-Pick C2 (NPC2), and Niemann-Pick C1 (NPC1). Inactivation of NPC2 in mouse caused sequestration of unesterified cholesterol (UC) and expanded the whole animal sterol pool from 2,305 to 4,337 mg/kg. However, this pool increased to 5,408 and 9,480 mg/kg, respectively, when NPC1 or LAL function was absent. The transport defect in mutants lacking NPC2 or NPC1, but not in those lacking LAL, was reversed by cyclodextrin (CD), and the ED₅₀ values for this reversal varied from ~40 mg/kg in kidney to >20,000 mg/kg in brain in both groups. This reversal occurred only with a CD that could interact with UC. Further, a CD that could interact with, but not solubilize, UC still overcame the transport defect. These studies showed that processing and export of sterol from the late E/L compartment was quantitatively different in mice lacking LAL, NPC2, or NPC1 function. In both npc2(-/-) and npc1(-/-) mice, the transport defect was reversed by a CD that interacted with UC, likely at the membrane/bulk-water interface, allowing sterol to move rapidly to the export site of the E/L compartment.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical School, Dallas, TX 75390-9151, USA.
authors.forename: Charina M
authors.initials: CM
authors.lastname: Ramirez
authors.forename: Benny
authors.initials: B
authors.lastname: Liu
authors.forename: Amal
authors.initials: A
authors.lastname: Aqul
authors.forename: Anna M
authors.initials: AM
authors.lastname: Taylor
authors.forename: Joyce J
authors.initials: JJ
authors.lastname: Repa
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Turley
authors.forename: John M
authors.initials: JM
authors.lastname: Dietschy
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D002784:Cholesterol / Q000378:metabolism*; D003505:Cyclodextrins / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D050356:Lipid Metabolism / Q000187:drug effects; D008111:Liver Function Tests; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008817:Mice, Mutant Strains; D000077296:Niemann-Pick C1 Protein; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D002787:Sterol Esterase / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D003505:Cyclodextrins; D047908:Intracellular Signaling Peptides and Proteins; D000077296:Niemann-Pick C1 Protein; C106831:Npc1 protein, mouse; C497045:Npc2 protein, mouse; D011506:Proteins; D033921:Vesicular Transport Proteins; D002784:Cholesterol; D002787:Sterol Esterase