Niemann-Pick C Variant Detection by Altered Sphingolipid Trafficking and Correlation with Mutations within a Specific Domain of NPC1

Thoracic Diseases Research Unit, Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, MN 55905, USA.
The American Journal of Human Genetics (Impact Factor: 10.93). 07/2001; 68(6):1361-72. DOI: 10.1086/320599
Source: PubMed


Niemann-Pick disease type C (NPC) is a fatal, autosomal recessive lipidosis characterized by lysosomal accumulation of unesterified cholesterol and multiple neurological symptoms, such as vertical supranuclear ophthalmoplegia, progressive ataxia, and dementia. More than 90% of cases of NPC are due to a defect in Niemann-Pick C1 (NPC1), a late endosomal, integral membrane protein that plays a role in cholesterol transport or homeostasis. Biochemical diagnosis of NPC has relied on the use of patient skin fibroblasts in an assay to demonstrate delayed low-density lipoprotein (LDL)-derived cholesterol esterification and a cytological technique-filipin staining-to demonstrate the intracellular accumulation of cholesterol. A small percentage of patients, referred to as "NPC variants," present with clinical symptoms of NPC but show near-normal results of these biochemical tests, making laboratory confirmation of NPC disease problematic. Here, we demonstrate that NPC-variant fibroblast samples can be detected as sphingolipid storage disease cells, using a fluorescent sphingolipid analog, BODIPY-lactosylceramide. This lipid accumulated in endosomes/lysosomes in variant cells preincubated with LDL cholesterol but targeted to the Golgi complex in normal cells under these conditions. The reproducibility of this technique was validated in a blinded study. In addition, we performed mutation analysis of the NPC1 gene in NPC variant and "classical" NPC cell samples and found a high incidence of specific mutations within the cysteine-rich region of NPC1 in variants. We also found that 5 of the 12 variant cell samples had no apparent defect in NPC1 but were otherwise indistinguishable from other variant cells. This is a surprising result, since, in general, approximately 90% of patients with NPC possess defects in NPC1. Our findings should be useful for the detection of NPC variants and also may provide significant new insight regarding NPC1 genotype/phenotype correlations.

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Available from: Marc Patterson, Jul 17, 2014
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    • "Mutations in the NPC1 gene occur in 95% of cases [3] [4]. Niemann-Pick disease is fatal [5], hereditary, and autosomal recessive [2] [6] [7]. The disease occurs in 1/120,000 live births [4]. "
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    ABSTRACT: Objective. This case report describes the changes in caries risk and activity and dental treatment of a 9-year-old patient who presented with signs and symptoms of Niemann-Pick disease type C (NPC). Treatment. The preventive dental treatment included instructions to caregivers for oral hygiene and diet. A calcium hydroxide pulpotomy and restorative dental treatments were performed in a dental office with desensitization techniques and behavioral management. The patient was attended every 3 months for the control of dental plaque biofilm, for topical fluoride application, and for observing the pulpotomized tooth. Results. The bacterial plaque biofilm was being adequately controlled by the caregiver. After 2 years, the clinical and radiographic examination of the pulpotomized tooth showed the absence of internal root resorption and bone rarefaction, and clinical examination showed tooth sensitivity, dental pain, and gingival swelling. Conclusion. The pulpotomy prevented clinical and radiographic success. Dentists must be aware of and be able to identify systemic and local aspects associated with caries risk of children with NPC disease. Furthermore, dentists must employ stringent preventive measures and provide instructions to caregivers to reduce caries risk.
    Full-text · Article · Feb 2015
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    • "Moreover, in a more recent study, the IGL of a Npc1 −/− cat was found to be thinner compared to that of wild-type controls, opening the possibility that GNs were generated in a lower number during postnatal cerebellar development or died because of an increased level of apoptosis (Vite et al., 2008). An additional line of evidence enlightening the possible contribution of a GN defect to NPC neuropathology derives from a recent study showing that the synaptic transmission from parallel fibers to PCs is increased and that long-term depression (LTD) is deficient in 3- week-old Npc1 −/− mice (Sun et al., 2001). "
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    ABSTRACT: In this study we show that postnatal development of cerebellar granule neurons (GNs) is defective in Npc1−/− mice. Compared to age-matched wild-type littermates, there is an accelerated disappearance of the external granule layer (EGL) in these mice. This is due to a premature exit from the cell cycle of GN precursors residing at the level of the EGL. As a consequence, the size of cerebellar lobules of these mice displays a 20%–25% reduction compared to that of age-matched wild-type mice. This size reduction is detectable at post-natal day 28 (PN28), when cerebellar GN development is completed while signs of neuronal atrophy are not yet apparent. Based on the analysis of EGL thickness and the determination of proliferating GN fractions at increasing developmental times (PN8–PN14), we trace the onset of this GN developmental defect during the second postnatal week. We also show that during this developmental time Shh transcripts undergo a significant reduction in Npc1−/− mice compared to age-matched wild-type mice. In light of the mitogenic activity of Shh on GNs, this observation further supports the presence of defective GN proliferation in Npc1−/− mice. A single injection of hydroxypropyl-β-cyclodextrin at PN7 rescues this defect, restoring the normal patterns of granule neuron proliferation and cerebellar lobule size. To our knowledge, these findings identify a novel developmental defect that was underappreciated in previous studies. This defect was probably overlooked because Npc1 loss-of-function does not affect cerebellar foliation and causes the internal granule layer and molecular layer to decrease proportionally, giving rise to a normally appearing, yet harmoniously smaller, cerebellum.
    Full-text · Article · Jun 2014 · Neurobiology of Disease
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    • "NPC1 is a transmembrane lysosomal protein while NPC2 is localized in the lumen of lysosomes [10,11]. The NPC1 and NPC2 proteins are engaged in transporting free cholesterol and some accompanying glycolipids from lysosomes to other cellular compartments [6,12,13]. In addition to cholesterol accumulation in lysosomes its synthesis and metabolism are also affected leading to disturbances in the synthesis of steroid hormones and in the assembly of cellular membranes. "
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    ABSTRACT: Niemann-Pick disease type C (NPC) is caused by defects in cholesterol efflux from lysosomes due to mutations of genes coding for NPC1 and NPC2 proteins. As a result, massive accumulation of unesterified cholesterol in late endosomes/lysosomes is observed. At the level of the organism these cholesterol metabolism disorders are manifested by progressive neurodegeneration and hepatosplenomegaly. Until now filipin staining of cholesterol deposits in cells has been widely used for NPC diagnostics. In this report we present an alternative method for cholesterol visualization and estimation using a cholesterol-binding bacterial toxin, perfringolysin O. To detect cholesterol deposits, a recombinant probe, perfringolysin O fused with glutathione S-transferase (GST-PFO) was prepared. GST-PFO followed by labeled antibodies or streptavidin was applied for immunofluorescence and immunoelectron microscopy to analyze cholesterol distribution in cells derived from NPC patients. The identity of GST-PFO-positive structures was revealed by a quantitative analysis of their colocalization with several organelle markers. Cellular ELISA using GST-PFO was developed to estimate the level of unesterified cholesterol in NPC cells. GST-PFO recognized cholesterol with high sensitivity and selectivity, as demonstrated by a protein/lipid overlay assay and surface plasmon resonance analysis. When applied to stain NPC cells, GST-PFO decorated abundant deposits of cholesterol in intracellular vesicles that colocalized with filipin-positive structures. These cholesterol deposits were resistant to 0.05%-0.2% Triton X-100 used for cells permeabilization in the staining procedure. GST-PFO-stained organelles were identified as late endosomes/lysosomes based on their colocalization with LAMP-1 and lysobisphosphatidic acid. On the other hand, GST-PFO did not colocalize with markers of the Golgi apparatus, endoplasmic reticulum, peroxisomes or with actin filaments. Only negligible GST-PFO staining was seen in fibroblasts of healthy individuals. When applied to cellular ELISA, GST-PFO followed by anti-GST-peroxidase allowed a semiquantitative analysis of cholesterol level in cells of NPC patients. Binding of GST-PFO to NPC cells was nearly abolished after extraction of cholesterol with methyl-beta-cyclodextrin. Our data indicate that a recombinant protein GST-PFO can be used to detect cholesterol accumulated in NPC cells by immunofluorescence and cellular ELISA. GST-PFO can be a convenient and reliable probe for revealing cholesterol deposits in cells and can be useful in diagnostics of NPC disease.
    Full-text · Article · Apr 2014 · Orphanet Journal of Rare Diseases
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