ABSTRACT
Vitamin E (α-tocopherol) is the major lipid-soluble antioxidant in many species. Niemann-Pick type C (NPC) disease is a lysosomal storage disorder caused by mutations in the NPC1 or NPC2 gene, which regulates lipid transport through the endocytic pathway. NPC disease is characterized by massive intracellular accumulation of unesterified cholesterol and other lipids in lysosomal vesicles. We examined the roles that NPC1/2 proteins play in the intracellular trafficking of tocopherol. Reduction of NPC1 or NPC2 expression or function in cultured cells caused a marked lysosomal accumulation of vitamin E in cultured cells. In vivo, tocopherol significantly accumulated in murine Npc1-null and Npc2-null livers, Npc2-null cerebella, and Npc1-null cerebral cortices. Plasma tocopherol levels were within the normal range in Npc1-null and Npc2-null mice, and in plasma samples from human NPC patients. The binding affinity of tocopherol to the purified sterol-binding domain of NPC1 and to purified NPC2 was significantly weaker than that of cholesterol (measurements kindly performed by R. Infante, University of Texas Southwestern Medical Center, Dallas, TX). Taken together, our observations indicate that functionality of NPC1/2 proteins is necessary for proper bioavailability of vitamin E and that the NPC pathology might involve tissue-specific perturbations of vitamin E status.
Subject(s)
Niemann-Pick Disease, Type C/metabolism , alpha-Tocopherol/metabolism , Alleles , Animals , Biological Transport , Carrier Proteins/genetics , Carrier Proteins/metabolism , Cell Line , Extracellular Space/metabolism , Fibroblasts/metabolism , Fibroblasts/pathology , Gene Expression Regulation/genetics , Gene Knockdown Techniques , Glycoproteins/deficiency , Glycoproteins/genetics , Glycoproteins/metabolism , Hepatocytes/cytology , Hepatocytes/metabolism , Humans , Intracellular Signaling Peptides and Proteins , Ligands , Lysosomes/metabolism , Membrane Glycoproteins/deficiency , Membrane Glycoproteins/genetics , Membrane Glycoproteins/metabolism , Mice , Niemann-Pick C1 Protein , Niemann-Pick Disease, Type C/genetics , Niemann-Pick Disease, Type C/pathology , Vesicular Transport ProteinsABSTRACT
OBJECTIVE: Niemann-Pick disease type C (NPC) is an inherited disorder characterized by intracellular accumulation of lipids such as cholesterol and glycosphingolipids in endosomes and lysosomes. This accumulation induces progressive degeneration of the nervous system. NPC shows some intriguing similarities with Alzheimer disease (AD), including neurofibrillary tangles, but patients with NPC generally lack amyloid-ß (Aß) plaques. Lipids affect γ-secretase-dependent amyloid precursor protein (APP) metabolism that generates Aß in vitro, but this has been difficult to prove in vivo. Our aim was to assess the effect of altered lipid constituents in neuronal membranes on amyloidogenic APP processing in humans. METHODS: We examined Aß in CSF from patients with NPC (n = 38) and controls (n = 14). CSF was analyzed for Aß(38), Aß(40), Aß(42), α-cleaved soluble APP, ß-cleaved soluble APP, total-tau, and phospho-tau. RESULTS: Aß release was markedly increased in NPC, with a shift toward the Aß(42) isoform. Levels of α- and ß-cleaved soluble APP were similar in patients and controls. Patients with NPC had increased total-tau. Patients on treatment with miglustat (n = 18), a glucosylceramide synthase blocker, had lower Aß(42) and total-tau than untreated patients. CONCLUSION: Increased CSF levels of Aß(38), Aß(40), and Aß(42) and unaltered levels of ß-cleaved soluble APP are consistent with increased γ-secretase-dependent Aß release in the brains of patients with NPC. These results provide the first in vivo evidence that neuronal lipid accumulation facilitates γ-secretase-dependent Aß production in humans and may be of relevance to AD pathogenesis.
