Mechanisms and consequences of impaired lipid trafficking in Niemann–Pick type C1-deficient mammalian cells

Department of Medicine and Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, AB, Canada
Biochimica et Biophysica Acta (Impact Factor: 4.66). 07/2009; 1791(7):659-670. DOI: 10.1016/j.bbalip.2009.01.025
Source: PubMed


Niemann–Pick C disease is a fatal progressive neurodegenerative disorder caused in 95% of cases by mutations in the NPC1 gene; the remaining 5% of cases result from mutations in the NPC2 gene. The major biochemical manifestation of NPC1 deficiency is an abnormal sequestration of lipids, including cholesterol and glycosphingolipids, in late endosomes/lysosomes (LE/L) of all cells. In this review, we summarize the current knowledge of the NPC1 protein in mammalian cells with particular focus on how defects in NPC1 alter lipid trafficking and neuronal functions. NPC1 is a protein of LE/L and is predicted to contain thirteen transmembrane domains, five of which constitute a sterol-sensing domain. The precise function of NPC1, and the mechanism by which NPC1 and NPC2 (both cholesterol binding proteins) act together to promote the movement of cholesterol and other lipids out of the LE/L, have not yet been established. Recent evidence suggests that the sequestration of cholesterol in LE/L of cells of the brain (neurons and glial cells) contributes to the widespread death and dysfunction of neurons in the brain. Potential therapies include treatments that promote the removal of cholesterol and glycosphingolipids from LE/L. Currently, the most promising approach for extending life-span and improving the quality of life for NPC patients is a combination of several treatments each of which individually modestly slows disease progression.

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    • "Studies using these models have neither revealed the mechanisms leading to the selective massive degeneration of neurons nor found drugs, which can efficiently halt disease progression. Although the function of NPC1 in lipid trafficking is evolutionary highly conserved [27], the widely used murine BALB/c NPC1 model [28] cannot exactly reproduce human pathology. For example, neurofibrillary tangles composed of tau protein, which are seen in human NPC1 neurons, are absent in this model reflecting obvious biochemical and physiological differences [29]. "
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    ABSTRACT: Niemann-Pick type C1 disease (NPC1) is a rare progressive neurodegenerative disorder caused by mutations in the NPC1 gene. In this lysosomal storage disorder the intracellular transport and sequestration of several lipids like cholesterol is severely impaired, resulting in an accumulation of lipids in late endosomes and lysosomes. The neurological manifestation of the disease is caused by dysfunction and cell death in the central nervous system. Several animal models were used to analyze the impaired pathways. However, the underlying pathogenic mechanisms are still not completely understood and the genetic variability in humans cannot be reflected in these models. Therefore, a human model using patient-specific induced pluripotent stem cells provides a promising approach. We reprogrammed human fibroblasts from a NPC1 patient and a healthy control by retroviral transduction with Oct4, Klf4, Sox2 and c-Myc. The obtained human induced pluripotent stem cells (hiPSCs) were characterized by immunocytochemical analyses. Neural progenitor cells were generated and patch clamp recordings were performed for a functional analysis of derived neuronal cells. Filipin stainings and the Amplex Red assay were used to demonstrate and quantify cholesterol accumulation. The hiPSCs expressed different stem cell markers, e.g. Nanog, Tra-1-81 and SSEA4. Using the embryoid body assay, the cells were differentiated in cells of all three germ layers and induced teratoma in immunodeficient mice, demonstrating their pluripotency. In addition, neural progenitor cells were derived and differentiated into functional neuronal cells. Patch clamp recordings revealed voltage dependent channels, spontaneous action potentials and postsynaptic currents. The accumulation of cholesterol in different tissues is the main hallmark of NPC1. In this study we found an accumulation of cholesterol in fibroblasts of a NPC1 patient, derived hiPSCs, and neural progenitor cells, but not in cells derived from fibroblasts of a healthy individual. These findings were quantified by the Amplex Red assay, demonstrating a significantly elevated cholesterol level in cells derived from fibroblasts of a NPC1 patient. We generated a neuronal model based on induced pluripotent stem cells derived from patient fibroblasts, providing a human in vitro model to study the pathogenic mechanisms of NPC1 disease.
    Full-text · Article · Sep 2013 · Orphanet Journal of Rare Diseases
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    • "Cholesterol accumulation in NPC1-deficient cells has been shown to interfere with the transport of proteins between various cellular compartments. Consequently, proteins involved in membrane trafficking including those regulating biogenesis/function of lysosomes are up-regulated to compensate for the defects [44], [45]. In keeping with these data, we observed a significant increase in the expression of genes encoding lysosomal enzymes such as Ctsb, Ctsd and Gusb, both at transcript and protein levels, in the Npc1-null and ANPC mouse brains. "
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    ABSTRACT: Niemann-Pick type C (NPC) disease, a rare autosomal recessive disorder caused mostly by mutation in NPC1 gene, is pathologically characterized by the accumulation of free cholesterol in brain and other tissues. This is accompanied by gliosis and loss of neurons in selected brain regions, including the cerebellum. Recent studies have shown that NPC disease exhibits intriguing parallels with Alzheimer's disease, including the presence of neurofibrillary tangles and increased levels of amyloid precursor protein (APP)-derived β-amyloid (Aβ) peptides in vulnerable brain neurons. To evaluate the role of Aβ in NPC disease, we determined the gene expression profile in selected brain regions of our recently developed bigenic ANPC mice, generated by crossing APP transgenic (Tg) mice with heterozygous Npc1-deficient mice. The ANPC mice exhibited exacerbated neuronal and glial pathology compared to other genotypes [i.e., APP-Tg, double heterozygous (Dhet), Npc1-null and wild-type mice]. Analysis of expression profiles of 86 selected genes using real-time RT-PCR arrays showed a wide-spectrum of alterations in the four genotypes compared to wild-type controls. The changes observed in APP-Tg and Dhet mice are limited to only few genes involved mostly in the regulation of cholesterol metabolism, whereas Npc1-null and ANPC mice showed alterations in the expression profiles of a number of genes regulating cholesterol homeostasis, APP metabolism, vesicular trafficking and cell death mechanism in both hippocampus and cerebellum compared to wild-type mice. Intriguingly, ANPC and Npc1-null mice, with some exceptions, exhibited similar changes, although more genes were differentially expressed in the affected cerebellum than the relatively spared hippocampus. The altered gene profiles were found to match with the corresponding protein levels. These results suggest that lack of Npc1 protein can alter the expression profile of selected transcripts as well as proteins, and APP overexpression influences cerebral pathology by enhancing changes triggered by Npc1 deficiency in the bigenic line.
    Full-text · Article · Jan 2013 · PLoS ONE
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    • "Cholesterol and sphingolipids are especially enriched in ILVs at early stages, whereas ILVs in older LEs and lysosomes contain high concentrations of BMP/LBPA and ceramide (Mobius et al, 2003). The decrease in cholesterol is due to extraction and transport to the ER through the action of NPC1 and NPC2, mutant forms of which cause Niemann-Pick disease, a lysosomal storage disorder in which cholesterol accumulates in LEs and endolysosomes (Karten et al, 2009). NPC2 is a soluble protein that extracts cholesterol from ILVs, while NPC1 resides in the limiting membrane and transfers cholesterol across. "
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    ABSTRACT: Being deeply connected to signalling, cell dynamics, growth, regulation, and defence, endocytic processes are linked to almost all aspects of cell life and disease. In this review, we focus on endosomes in the classical endocytic pathway, and on the programme of changes that lead to the formation and maturation of late endosomes/multivesicular bodies. The maturation programme entails a dramatic transformation of these dynamic organelles disconnecting them functionally and spatially from early endosomes and preparing them for their unidirectional role as a feeder pathway to lysosomes.
    Full-text · Article · Aug 2011 · The EMBO Journal
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