Niemann-Pick Type C1 Mutant Research Articles

Annexin A6 and NPC1 regulate LDL-inducible cell migration and distribution of focal adhesions

Cholesterol is considered indispensable for cell motility, but how physiological cholesterol pools enable cells to move forward remains to be clarified. The majority of cells obtain cholesterol from the uptake of Low-Density lipoproteins (LDL) and here we demonstrate that LDL stimulates A431 squamous epithelial carcinoma and Chinese hamster ovary (CHO) cell migration and invasion. LDL also potentiated epidermal growth factor (EGF) -stimulated A431 cell migration as well as A431 invasion in 3-dimensional environments, using organotypic assays. Blocking cholesterol export from late endosomes (LE), using Niemann Pick Type C1 (NPC1) mutant cells, pharmacological NPC1 inhibition or overexpression of the annexin A6 (AnxA6) scaffold protein, compromised LDL-inducible migration and invasion. Nevertheless, NPC1 mutant cells established focal adhesions (FA) that contain activated focal adhesion kinase (pY397FAK, pY861FAK), vinculin and paxillin. Compared to controls, NPC1 mutants display increased FA numbers throughout the cell body, but lack LDL-inducible FA formation at cell edges. Strikingly, AnxA6 depletion in NPC1 mutant cells, which restores late endosomal cholesterol export in these cells, increases their cell motility and association of the cholesterol biosensor D4H with active FAK at cell edges, indicating that AnxA6-regulated transport routes contribute to cholesterol delivery to FA structures, thereby improving NPC1 mutant cell migratory behaviour.

HSP90 inhibitors reduce cholesterol storage in Niemann-Pick type C1 mutant fibroblasts

Niemann-Pick type C1 (NPC1) disease is a lysosomal lipid storage disorder caused by mutations of the NPC1 gene. More than 300 disease-associated mutations are reported in patients, resulting in abnormal accumulation of unesterified cholesterol, glycosphingolipids, and other lipids in late endosomes and lysosomes (LE/Ly) of many cell types. Previously, we showed that treatment of many different NPC1 mutant fibroblasts with histone deacetylase inhibitors resulted in reduction of cholesterol storage, and we found that this was associated with enhanced exit of the NPC1 protein from the endoplasmic reticulum and delivery to LE/Ly. This suggested that histone deacetylase inhibitors may work through changes in protein chaperones to enhance the folding of NPC1 mutants, allowing them to be delivered to LE/Ly. In this study, we evaluated the effect of several HSP90 inhibitors on NPC1I1061T skin fibroblasts. We found that HSP90 inhibition resulted in clearance of cholesterol from LE/Ly, and this was associated with enhanced delivery of the mutant NPC1I1061T protein to LE/Ly. We also observed that inhibition of HSP90 increased the expression of HSP70, and overexpression of HSP70 also reduced cholesterol storage in NPC1I1061T fibroblasts. However, we did not see correction of cholesterol storage by arimoclomol, a drug that is reported to increase HSP70 expression, at doses up to 0.5 mM. The increase in other chaperones as a consequence of HSP90 improves folding of NPC1 protein and relieves cholesterol accumulation in NPC1 mutant fibroblasts.

Selective Degradation Permits a Feedback Loop Controlling Annexin A6 and Cholesterol Levels in Endolysosomes of NPC1 Mutant Cells.

We recently identified elevated annexin A6 (AnxA6) protein levels in Niemann–Pick-type C1 (NPC1) mutant cells. In these cells, AnxA6 depletion rescued the cholesterol accumulation associated with NPC1 deficiency. Here, we demonstrate that elevated AnxA6 protein levels in NPC1 mutants or upon pharmacological NPC1 inhibition, using U18666A, were not due to upregulated AnxA6 mRNA expression, but caused by defects in AnxA6 protein degradation. Two KFERQ-motifs are believed to target AnxA6 to lysosomes for chaperone-mediated autophagy (CMA), and we hypothesized that the cholesterol accumulation in endolysosomes (LE/Lys) triggered by the NPC1 inhibition could interfere with the CMA pathway. Therefore, AnxA6 protein amounts and cholesterol levels in the LE/Lys (LE-Chol) compartment were analyzed in NPC1 mutant cells ectopically expressing lysosome-associated membrane protein 2A (Lamp2A), which is well known to induce the CMA pathway. Strikingly, AnxA6 protein amounts were strongly decreased and coincided with significantly reduced LE-Chol levels in NPC1 mutant cells upon Lamp2A overexpression. Therefore, these findings suggest Lamp2A-mediated restoration of CMA in NPC1 mutant cells to lower LE-Chol levels with concomitant lysosomal AnxA6 degradation. Collectively, we propose CMA to permit a feedback loop between AnxA6 and cholesterol levels in LE/Lys, encompassing a novel mechanism for regulating cholesterol homeostasis in NPC1 disease.

Annexin A6 modulates TBC1D15/Rab7/StARD3 axis to control endosomal cholesterol export in NPC1 cells

Cholesterol accumulation in late endosomes is a prevailing phenotype of Niemann-Pick type C1 (NPC1) mutant cells. Likewise, annexin A6 (AnxA6) overexpression induces a phenotype reminiscent of NPC1 mutant cells. Here, we demonstrate that this cellular cholesterol imbalance is due to AnxA6 promoting Rab7 inactivation via TBC1D15, a Rab7-GAP. In NPC1 mutant cells, AnxA6 depletion and eventual Rab7 activation was associated with peripheral distribution and increased mobility of late endosomes. This was accompanied by an enhanced lipid accumulation in lipid droplets in an acyl-CoA:cholesterol acyltransferase (ACAT)-dependent manner. Moreover, in AnxA6-deficient NPC1 mutant cells, Rab7-mediated rescue of late endosome-cholesterol export required the StAR-related lipid transfer domain-3 (StARD3) protein. Electron microscopy revealed a significant increase of membrane contact sites (MCS) between late endosomes and ER in NPC1 mutant cells lacking AnxA6, suggesting late endosome-cholesterol transfer to the ER via Rab7 and StARD3-dependent MCS formation. This study identifies AnxA6 as a novel gatekeeper that controls cellular distribution of late endosome-cholesterol via regulation of a Rab7-GAP and MCS formation.

Altered myelination in the Niemann-Pick type C1 mutant mouse.

Niemann-Pick type C1 (NPC1) disease is a lysosomal storage disorder caused by mutation of Npc1 or Npc2 gene, resulting in various progressive pathological features. Myelin defection is a major pathological problem in Npc1 mutant mice; however, impairment of myelin proteins in the developing brain is still incompletely understood. In this study, we showed that the expression of myelin genes and proteins is strongly inhibited from postnatal day 35 onwards including reduced myelin basic protein (MBP) expression in the brain. Furthermore, myelination characterized by MBP immunohistochemistry was strongly perturbed in the forebrain, moderately in the midbrain and cerebellum, and slightly in the hindbrain. Our results demonstrate that mutation of the Npc1 gene is sufficient to cause severe and progressive defects in myelination in the mouse brain.

Improvement of impaired electrical activity in NPC1 mutant cortical neurons upon DHPG stimulation detected by micro-electrode array

Niemann-Pick Type C1 (NPC1) disease is an autosomal recessive neurodegenerative disease characterized by an excessive accumulation of unesterified cholesterol in late endosomes/lysosomes. Patients with NPC1 disease show a series of symptoms in neuropathology, including a gradually increased loss of motor control and seizures. However, mechanism of the neurological manifestations in NPC1 disease is not fully understood yet. In this study, we utilized the micro-electrode array (MEA) to analyze the spontaneous extracellular electrical activity in cultivated cortical neurons of the NPC1 mutant (NPC1−/−) mouse. Our results show a decrease of the spontaneous electrical activity in NPC1−/− neuronal network when compared to wild type neurons, as indicated by the decreased spike rate, burst rate, event rate, and the increased burst period and event period. Application of 3,5-dihydroxyphenylglycine (DHPG), a specific agonist of group I metabotropic glutamate receptors, improved the electrical activity of the NPC1−/− neuronal network, suggesting that DHPG can be used as a potential therapeutic strategy for recovery of the electrical activity in NPC1 disease.

Targeting molecular chaperone HSP90 to treat Niemann‐Pick type C1 disease

NPC1 is a fatal, lysosomal neurovisceral storage disease caused by mutations in the npc1 gene. More than 200 different disease‐associated mutations are reported in patients, resulting in abnormal accumulation of unesterified cholesterol, glycosphingolipids and other lipids in late endosome/ lysosomes (LE/Ly) of many cell types. There is no FDA‐approved therapy to treat NPC1 disease. A limited initial human trial of hydroxyl propyl cyclodextrin (HPCD) is currently in progress, but HPCD does not cross the BBB. Based on our previous findings on NPC1I1061T skin fibroblast, a small clinical trial is also in progress on the treatment of histone deacetylase inhibitor (HDACi), Vorinostat. Our data suggested that HDACi treatment on skin fibroblasts results in increased expression of the Niemann‐Pick type C1 (NPC1) protein in mutant cells. Using an engineered human cell line, we have also observed that HDACis, can correct the NPC1 cholesterol storage defect in 60 of the 81 NPC1 mutants tested. Although significant progress has been made in understanding the pathology of NPC1 disease, the mechanisms governing the proteostatic control of NPC1 protein is not completely understood. However, being an epigenetic modifier, HDACi is known to alter the pattern of gene expression. As a result, off‐target effects are of a major concern in using HDACi's as a therapy. In order to understand the molecular mechanism of HDACi on NPC1, we considered potential cellular targets of HDACi other than histones. Disruption of molecular chaperone HSP90 (via hyperacetylation) is one of the many consequences of HDACi treatment.We, therefore, evaluated the effect of direct inhibition of HSP90 family of proteins on NPC1 skin fibroblasts in terms of lowering lysosomal cholesterol accumulation. Our results indicated that out of the three HSP90 family proteins, selectively HSP90A and not HSP90B or TRAP inhibition resulted in clearance of cholesterol from lysosomes as well as aided in mobilizing unfolded mutant NPC1 protein from ER to lysosomes. Hence the data on the effect of several different HSP90 inhibitors on multiple human patient‐derived skin fibroblast in lowering lysosomal cholesterol burden using microscopy based filipin assay will be presented. Our previous published work using HDACi and recent preliminary results using heat shock protein HSP90 inhibitors suggests that cytosolic HSP90 and associated chaperones may be a target and indicates that protein folding quality control plays a critical role in NPC1 diseases. An attempt will be made to elucidate the role of cytosolic HSP90 and its associated co‐chaperones in the regulation of NPC1 mutant protein stability.Support or Funding InformationAra Parseghian Medical Research FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

1H NMR-Linked Metabolomics Analysis of Liver from a Mouse Model of NP-C1 Disease.

Clinical manifestations of Niemann-Pick type C1 (NP-C1) disease include neonatal hepatosplenomegaly and in some patients progressive liver dysfunction and failure. This study involved a 1H NMR-linked metabolomics analysis of liver samples collected from a NP-C1 disease mutant mouse model in order to explore time-dependent imbalances in metabolic pathways associated with NP-C1 liver dysfunction, including fibrosis. NP-C1 mutant (Npc1-/-; NP-C1), control (Npc1+/+; WT), and NP-C1 heterozygous mice (Npc1+/-; HET) were generated from heterozygote matings. Aqueous extracts of these liver samples collected at time points of 3, 6, 9, and 11 weeks were subjected to high-resolution NMR analysis, and multivariate (MV) metabolomics analyses of data sets acquired were performed. A MV random forests (RFs) model effectively discriminated between NP-C1 and a combined WT/HET hepatic NMR profiles with very high predictive accuracy and reliability. Key distinguishing features included significant upregulations in the hepatic concentrations of phenylalanine, tyrosine, glutamate, lysine/ornithine, valine, threonine, and hypotaurine/methionine, and diminished levels of nicotinate/niacinamide, inosine, phosphoenolpyruvate, and 3-hydroxyphenylacetate. Quantitative pathway topological analysis confirmed that imbalances in tyrosine biosynthesis, and hepatic phenylalanine, tyrosine, glutamate/glutamine, and nicotinate/niacinamide metabolism were involved in the pathogenesis of NP-C1 disease-associated liver dysfunction/damage. 1H NMR-linked metabolomics analysis provides valuable biomarker information regarding hepatic dysfunction or damage in NP-C1 disease.

Reduced cerebellar neurodegeneration after combined therapy with cyclodextrin/allopregnanolone and miglustat in NPC1: a mouse model of Niemann-Pick type C1 disease.

Niemann-Pick type C1 (NPC1) disease is a lysosomal storage disease characterized by a deficiency of NPC1 gene function. The malfunction of protein results in a progressive accumulation of lipids in many organs. A combined approach with substrate-reduction therapy (SRT) and byproduct therapy (BPT) has been shown to ameliorate the disease course in a mutant mouse model (NPC1(-/-)). The present study examines the morphological parameters underlying these changes. For the combined SRT/BPT treatment, NPC1(-/-) mutant mice (NPC1(-/-SRT/BPT)) were injected with allopregnanolone/cyclodextrin weekly, starting at postnatal day (P) 7. Starting at P10, a miglustat injection was administered daily until P23. Thereafter, miglustat was added to the powdered chow. For the sham treatment, both mutant NPC1(-/-) (NPC1(-/-sham)) and wild-type (NPC1(+/+sham)) mice received an NaCl injection and were fed powdered chow without miglustat. Analysis was performed on cerebellar slices by histology and immunohistochemistry. The volumes and cell counts of cerebellar structures were quantified. Additionally, ultrastructural analysis was performed with transmission electron microscopy. In agreement with previous studies, the current study demonstrates Purkinje cell degeneration in the mutant mice, which was partially abrogated by SRT/BPT. The volumes of cerebellar white matter and molecular layer were reduced as well. Also, the number of neurons was reduced in granular and molecular layers. However, only the molecular layer benefited from the therapy, as shown by an increase in the volume and the amount of neurons. The volume and number of neurons of the deep cerebellar nuclei were significantly decreased in mutant mice; an appreciable therapeutic benefit could be demonstrated for the nucleus interpositus.

Cholesterol Regulates Syntaxin 6 Trafficking at trans-Golgi Network Endosomal Boundaries

Inhibition of cholesterol export from late endosomes causes cellular cholesterol imbalance, including cholesterol depletion in the trans-Golgi network (TGN). Here, using Chinese hamster ovary (CHO) Niemann-Pick type C1 (NPC1) mutant cell lines and human NPC1 mutant fibroblasts, we show that altered cholesterol levels at the TGN/endosome boundaries trigger Syntaxin 6 (Stx6) accumulation into VAMP3, transferrin, and Rab11-positive recycling endosomes (REs). This increases Stx6/VAMP3 interaction and interferes with the recycling of αVβ3 and α5β1 integrins and cell migration, possibly in a Stx6-dependent manner. In NPC1 mutant cells, restoration of cholesterol levels in the TGN, but not inhibition of VAMP3, restores the steady-state localization of Stx6 in the TGN. Furthermore, elevation of RE cholesterol is associated with increased amounts of Stx6 in RE. Hence, the fine-tuning of cholesterol levels at the TGN-RE boundaries together with a subset of cholesterol-sensitive SNARE proteins may play a regulatory role in cell migration and invasion.

Combined therapy with cyclodextrin/allopregnanolone and miglustat improves motor but not cognitive functions in Niemann–Pick Type C1 mice

Niemann–Pick Type C1 (NPC1) is an autosomal recessive disorder characterized by the accumulation of cholesterol and glycosphingolipids. Combination-treatment utilizing cyclodextrin, allopregnanolone and miglustat (CYCLO/ALLO/miglustat) can ameliorate NPC1 disease in a mutant mouse model. The present study was designed to add behavioral analysis in NPC1 mutant mice upon CYCLO/ALLO/miglustat therapy.NPC1 mutant (BALB/cJ NPC1NIH) and control mice were used. For the combination treatment mice were injected with CYCLO/ALLO weekly, starting at P7. The miglustat injection was performed daily from P10 till P23. Starting at P23, miglustat was added to the powdered chow. For the sham treatment of control and mutant mice the same schedule was used with 0.9% NaCl injection. Locomotor activity was assessed in open field, elevated plus maze and accelerod tests. For assessment of spatial learning and memory the Morris water maze test was conducted. Electron microscopy has been performed to support the behavioral data.The sham-treated mutant mice exhibited motor impairments in all performed tests. In the water maze the sham-treated mutants exhibited impairment in remembering the location of the hidden platform. CYCLO/ALLO/miglustat treatment positively influenced motor dysfunction: total distance and number of visits significantly increased, and accelerod performance improved. The spatial learning, however, did not benefit from therapy.At the morphological level, an excessive accumulation of electron-dense material was seen in the cerebellar Purkinje cells of mutant mice. A regression of these autophagosomal inclusions was seen upon therapy.CYCLO/ALLO/miglustat therapy ameliorates motor but not cognitive deficits in NPC1 mutant mice, suggesting unequal vulnerability of different brain areas to the treatment.

Pulmonary Abnormalities in Animal Models Due to Niemann-Pick Type C1 (NPC1) or C2 (NPC2) Disease

Niemann-Pick C (NPC) disease is due to loss of NPC1 or NPC2 protein function that is required for unesterified cholesterol transport from the endosomal/lysosomal compartment. Though lung involvement is a recognized characteristic of Niemann-Pick type C disease, the pathological features are not well understood. We investigated components of the surfactant system in both NPC1 mutant mice and felines and in NPC2 mutant mice near the end of their expected life span. Histological analysis of the NPC mutant mice demonstrated thickened septae and foamy macrophages/leukocytes. At the level of electron microscopy, NPC1-mutant type II cells had uncharacteristically larger lamellar bodies (LB, mean area 2-fold larger), while NPC2-mutant cells had predominantly smaller lamellar bodies (mean area 50% of normal) than wild type. Bronchoalveolar lavage from NPC1 and NPC2 mutant mice had an approx. 4-fold and 2.5-fold enrichment in phospholipid, respectively, and an approx. 9-fold and 35-fold enrichment in cholesterol, consistent with alveolar lipidosis. Phospholipid and cholesterol also were elevated in type II cell LBs and lung tissue while phospholipid degradation was reduced. Enrichment of surfactant protein-A in the lung and surfactant of the mutant mice was found. Immunocytochemical results showed that cholesterol accumulated in the LBs of the type II cells isolated from the affected mice. Alveolar macrophages from the NPC1 and NPC2 mutant mice were enlarged compared to those from wild type mice and were enriched in phospholipid and cholesterol. Pulmonary features of NPC1 mutant felines reflected the disease described in NPC1 mutant mice. Thus, with the exception of lamellar body size, the lung phenotype seen in the NPC1 and NPC2 mutant mice were similar. The lack of NPC1 and NPC2 proteins resulted in a disruption of the type II cell surfactant system contributing to pulmonary abnormalities.

Dynamic movements of organelles containing Niemann-Pick C1 protein: NPC1 involvement in late endocytic events.

People homozygous for mutations in the Niemann-Pick type C1 (NPC1) gene have physiological defects, including excess accumulation of intracellular cholesterol and other lipids, that lead to drastic neural and liver degeneration. The NPC1 multipass transmembrane protein is resident in late endosomes and lysosomes, but its functions are unknown. We find that organelles containing functional NPC1-fluorescent protein fusions undergo dramatic movements, some in association with extending strands of endoplasmic reticulum. In NPC1 mutant cells the NPC1-bearing organelles that normally move at high speed between perinuclear regions and the periphery of the cell are largely absent. Pulse-chase experiments with dialkylindocarbocyanine low-density lipoprotein showed that NPC1 organelles function late in the endocytic pathway; NPC1 protein may aid the partitioning of endocytic and lysosomal compartments. The close connection between NPC1 and the drug U18666A, which causes NPC1-like organelle defects, was established by rescuing drug-treated cells with overproduced NPC1. U18666A inhibits outward movements of NPC1 organelles, trapping membranes and cholesterol in perinuclear organelles similar to those in NPC1 mutant cells, even when cells are grown in lipoprotein-depleted serum. We conclude that NPC1 protein promotes the creation and/or movement of particular late endosomes, which rapidly transport materials to and from the cell periphery.