Before the loss: neuronal dysfunction in Niemann-Pick Type C disease

Model construction of Niemann-Pick type C disease in zebrafish

Niemann-Pick type C disease (NPC) is a rare human disease, with limited effective treatment options. Most cases of NPC disease are associated with inactivating mutations of the NPC1 gene. However, cellular and molecular mechanisms responsible for the NPC1 pathogenesis remain poorly defined. This is partly due to the lack of a suitable animal model to monitor the disease progression. In this study, we used CRISPR to construct an NPC1-/- zebrafish model, which faithfully reproduced the cardinal pathological features of this disease. In contrast to the wild type (WT), the deletion of NPC1 alone caused significant hepatosplenomegaly, ataxia, Purkinje cell death, increased lipid storage, infertility and reduced body length and life span. Most of the NPC1-/- zebrafish died within the first month post fertilization, while the remaining specimens developed slower than the WT and died before reaching 8 months of age. Filipin-stained hepatocytes of the NPC1-/- zebrafish were clear, indicating abnormal accumulation of unesterified cholesterol. Lipid profiling showed a significant difference between NPC1-/- and WT zebrafish. An obvious accumulation of seven sphingolipids was detected in livers of NPC1-/- zebrafish. In summary, our results provide a valuable model system that could identify promising therapeutic targets and treatments for the NPC disease.

Hepatic and neuronal phenotype of NPC1-/- mice

Niemann-Pick type C disease (NPC) is a fatal autosomal recessive disorder characterized by a defect in the intracellular transport of lipoproteins leading to the accumulation of lipids in diverse tissues. A visceral and neuronal phenotype mimicking human NPC1 disease has been described in NPC1 mutant mice. These mice are by now the most widely used NPC1 rodent model to study NPC and developmental compounds against this devastating disease. Here we characterized NPC1-/- mice for their hepatic and neuronal phenotype to confirm the stability of the phenotype, provide a characterization of disease progression and pinpoint the age of robust phenotype onset. Animals of 4-10 weeks of age were analyzed for general health, motor deficits as well as hepatic and neuronal alterations with a special focus on cerebellar pathology. Our results show that NPC1-/- mice have a reduced general health at the age of 9-10 weeks. Robust motor deficits can be observed even earlier at 8 weeks of age. Hepatic changes included increased organ weight and cholesterol levels at 6 weeks of age accompanied by severely increased liver enzyme levels. Analysis of NPC1-/- brain pathology showed decreased cholesterol and increased Aβ levels in the hippocampus at the age of 6 weeks. Further analysis revealed a decrease of the cytokine IL-12p70 in the cerebellum along with a very early increase of astrocytosis. Hippocampal IL-12p70 levels were increased at the age of 6 weeks followed by increased activated microglia levels. By the age of 10 weeks, also cerebellar Aβ levels were increased along with strongly reduced Calbindin D-28k levels. Our results validate and summarize the progressive development of the hepatic and neuronal phenotype of NPC1-/- mice that starts with cerebellar astrocytosis, making this mouse model a valuable tool for the development of new compounds against NPC.

Defects in the retina of Niemann-pick type C 1 mutant mice

Background

Niemann-Pick type C1 (NPC1) disease is an inherited lysosomal storage disease caused by mutation of the Npc1 gene, resulting in a progressive accumulation of unesterified cholesterol and glycolipids in lysosomes of multiple tissues and leading to neurodegeneration and other disease. In Npc1 mutant mice, retinal degeneration including impaired visual function, lipofuscin accumulation in the pigment epithelium and ganglion cells as well as photoreceptor defects has been found. However, the pathologies of other individual cell types of the retina in Npc1 mutant mice are still not fully clear. We hypothesized that horizontal cells, amacrine cells, bipolar cells and glial cells are also affected in the retina of Npc1 mutant mice.

Results

Immunohistochemistry and electron microscopy were used to investigate pathologies of ganglion cells, horizontal cells, amacrine cells, bipolar cells, and optic nerves as well as altered activity of glial cells in Npc1 mutant mice.

Electron microscopy reveals that electron-dense inclusions are generally accumulated in ganglion cells, bipolar cells, Müller cells, and in the optic nerve. Furthermore, abnormal arborisation and ectopic processes of horizontal and amacrine cells as well as defective bipolar cells are observed by immunohistochemistry for specific cellular markers. Furthermore, hyperactivity of glial cells, including astrocytes, microglial cells, and Müller cells, is also revealed.

Conclusions

Our data extend previous findings to show multiple defects in the retina of Npc1 mutant mice, suggesting an important role of Npc1 protein in the normal function of the retina.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-014-0126-2) contains supplementary material, which is available to authorized users.

Vitamin E dietary supplementation improves neurological symptoms and decreases c-Abl/p73 activation in Niemann-Pick C mice

Niemann-Pick C (NPC) disease is a fatal neurodegenerative disorder characterized by the accumulation of free cholesterol in lysosomes. We have previously reported that oxidative stress is the main upstream stimulus activating the proapoptotic c-Abl/p73 pathway in NPC neurons. We have also observed accumulation of vitamin E in NPC lysosomes, which could lead to a potential decrease of its bioavailability. Our aim was to determine if dietary vitamin E supplementation could improve NPC disease in mice. NPC mice received an alpha-tocopherol (α-TOH) supplemented diet and neurological symptoms, survival, Purkinje cell loss, α-TOH and nitrotyrosine levels, astrogliosis, and the c-Abl/p73 pathway functions were evaluated. In addition, the effect of α-TOH on the c-Abl/p73 pathway was evaluated in an in vitro NPC neuron model. The α-TOH rich diet delayed loss of weight, improved coordination and locomotor function and increased the survival of NPC mice. We found increased Purkinje neurons and α-TOH levels and reduced astrogliosis, nitrotyrosine and phosphorylated p73 in cerebellum. A decrease of c-Abl/p73 activation was also observed in the in vitro NPC neurons treated with α-TOH. In conclusion, our results show that vitamin E can delay neurodegeneration in NPC mice and suggest that its supplementation in the diet could be useful for the treatment of NPC patients.

MicroRNA 375 mediates palmitate-induced enteric neuronal damage and high-fat diet-induced delayed intestinal transit in mice

BACKGROUND & AIMS

A high-fat diet (HFD) can cause serious health problems, including alteration of gastrointestinal transit, the exact mechanism of which is not clear. Several microRNAs (miRNAs) are involved in energy homeostasis, lipid metabolism, and HFD-induced weight gain. We investigated the role of miRNAs in HFD-induced damage to the enteric nervous system.

METHODS

Male mice were fed a HFD (60% calories from fat) or regular diets (18% calories from fat) for 11 weeks. Mice on regular diets and HFDs were given intraperitoneal injections of Mir375 inhibitor or a negative control. Body weights, food intake, stool indices, and gastrointestinal transit (following Evans blue gavage) were measured. An enteric neuronal cell line (immorto-fetal enteric neuronal) and primary enteric neurons were used for in vitro studies.

RESULTS

HFD delayed intestinal transit, which was associated with increased apoptosis and loss of colonic myenteric neurons. Mice fed a low-palmitate HFD did not develop a similar phenotype. Palmitate caused apoptosis of enteric neuronal cells associated with mitochondrial dysfunction and endoplasmic reticulum stress. Palmitate significantly increased the expression of Mir375 in vitro; transfection of cells with a Mir375 inhibitor prevented the palmitate-induced enteric neuronal cell apoptosis. Mir375 expression was increased in myenteric ganglia of mice fed HFD and associated with decreased levels of Mir375 target messenger RNAs, including Pdk1. Systemic injection of a Mir375 inhibitor for 5 weeks prevented HFD-induced delay in intestinal transit and morphologic changes.

CONCLUSIONS

HFDs delay colonic transit, partly by inducing apoptosis in enteric neuronal cells. This effect is mediated by Mir375 and is associated with reduced levels of Pdk1. Mir375 might be targeted to increase survival of enteric neurons and gastrointestinal motility.

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.

Abnormal accumulation and recycling of glycoproteins visualized in Niemann-Pick type C cells using the chemical reporter strategy

Niemann-Pick type C (NPC) disease is characterized by impaired cholesterol efflux from late endosomes and lysosomes and secondary accumulation of lipids. Although impaired trafficking of individual glycoproteins and glycolipids has been noted in NPC cells and other storage disorders, there is currently no effective way to monitor their localization and movement en masse. Using a chemical reporter strategy in combination with pharmacologic treatments, we demonstrate a disease-specific and previously unrecognized accumulation of a diverse set of glycoconjugates in NPC1-null and NPC2-deficient fibroblasts within endocytic compartments. These labeled vesicles do not colocalize with the cholesterol-laden compartments of NPC cells. Experiments using the endocytic uptake marker dextran show that the endosomal accumulation of sialylated molecules can be largely attributed to impaired recycling as opposed to altered fusion of vesicles. Treatment of either NPC1-null or NPC2-deficient cells with cyclodextrin was effective in reducing cholesterol storage as well as the endocytic accumulation of sialoglycoproteins, demonstrating a direct link between cholesterol storage and abnormal recycling. Our data further demonstrate that this accumulation is largely glycoproteins, given that inhibitors of O-glycan initiation or N-glycan processing led to a significant reduction in staining intensity. Taken together, our results provide a unique perspective on the trafficking defects in NPC cells, and highlight the utility of this methodology in analyzing cells with altered recycling and turnover of glycoproteins.

Alterations in gene expression in mutant amyloid precursor protein transgenic mice lacking Niemann-Pick type C1 protein

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.

Cerebellar volume correlates with saccadic gain and ataxia in adult Niemann-Pick type C

BACKGROUND AND PURPOSE

Cerebellar Purkinje cells are known to be highly vulnerable to neuronal pathology in Niemann-Pick type C (NPC), a disease where widespread white matter changes have also been reported. We sought to determine the relationship between white and grey matter cerebellar changes and clinical variables in NPC.

MATERIALS AND METHODS

Ten adult patients with NPC were matched to control subjects (n=27) on age and gender. Patients were rated for symptom duration and severity, degree of ataxia, and were assessed for saccadic eye measures. Cerebellar white and grey matter volumes were automatically segmented using the Freesurfer software package.

RESULTS

NPC patients had a significant reduction in both grey and white matter volumes. Volume did not correlate with symptom duration or severity, but did correlate with saccadic gain and ataxia measures.

CONCLUSIONS

Both cerebellar grey and white matter volume decreases in adult NPC, and these changes are associated with impairments in saccadic gain and in motor control.

Cholinergic abnormalities, endosomal alterations and up-regulation of nerve growth factor signaling in Niemann-Pick type C disease

BACKGROUND

Neurotrophins and their receptors regulate several aspects of the developing and mature nervous system, including neuronal morphology and survival. Neurotrophin receptors are active in signaling endosomes, which are organelles that propagate neurotrophin signaling along neuronal processes. Defects in the Npc1 gene are associated with the accumulation of cholesterol and lipids in late endosomes and lysosomes, leading to neurodegeneration and Niemann-Pick type C (NPC) disease. The aim of this work was to assess whether the endosomal and lysosomal alterations observed in NPC disease disrupt neurotrophin signaling. As models, we used i) NPC1-deficient mice to evaluate the central cholinergic septo-hippocampal pathway and its response to nerve growth factor (NGF) after axotomy and ii) PC12 cells treated with U18666A, a pharmacological cellular model of NPC, stimulated with NGF.

RESULTS

NPC1-deficient cholinergic cells respond to NGF after axotomy and exhibit increased levels of choline acetyl transferase (ChAT), whose gene is under the control of NGF signaling, compared to wild type cholinergic neurons. This finding was correlated with increased ChAT and phosphorylated Akt in basal forebrain homogenates. In addition, we found that cholinergic neurons from NPC1-deficient mice had disrupted neuronal morphology, suggesting early signs of neurodegeneration. Consistently, PC12 cells treated with U18666A presented a clear NPC cellular phenotype with a prominent endocytic dysfunction that includes an increased size of TrkA-containing endosomes and reduced recycling of the receptor. This result correlates with increased sensitivity to NGF, and, in particular, with up-regulation of the Akt and PLC-γ signaling pathways, increased neurite extension, increased phosphorylation of tau protein and cell death when PC12 cells are differentiated and treated with U18666A.

CONCLUSIONS

Our results suggest that the NPC cellular phenotype causes neuronal dysfunction through the abnormal up-regulation of survival pathways, which causes the perturbation of signaling cascades and anomalous phosphorylation of the cytoskeleton.

Increased excitability and compromised long-term potentiation in the neocortex of NPC1(-/-) mice

Niemann-Pick type C1 (NPC1) disease is a neurodegenerative lysosomal storage disorder caused by mutations in the NPC1 gene which encodes a transmembrane protein of the acidic compartment. Albeit the NPC1(-/-) mouse is available serving as an appropriate animal model of the human disease, the precise function of this protein remains obscure. Here, we investigated the synaptic consequences of this disease and explored long-term potentiation (LTP) in slices taken from the hippocampal CA1 region, the dorsomedial striatum as well as the somatosensory neocortex in NPC1(-/-) mice using extracellular field potential recordings. We did not observe significant changes in synaptic excitability as well as LTP in the hippocampal CA1 region and the dorsomedial striatum of NPC1(-/-) mice when compared to wildtype littermates. However, neocortical excitability was significantly enhanced while LTP was abolished. These results suggest that at least in the somatosensory neocortex NPC1 protein is instrumental in synaptic function.

Decreased expression of myelin gene regulatory factor in Niemann-Pick type C 1 mouse

Niemann-Pick type C 1 (NPC1) disease is an autosomal recessive cholesterol transport defect resulting in a neurodegenerative process in patients mainly at an early age, although some patients may start with manifestation in adult. Since loss of myelin is considered as a main pathogenetic factor, the precise mechanism inducing dysmylination in NPC1 disease is still unclear. In the present study, a quantitative evaluation on the myelin protein and its regulatory factors of oligodendrocytes, such as SRY-related HMG-box 10 (Sox10), Yin Yang 1 factor (YY1) and myelin gene regulatory factor (MRF), in different parts of the brain and spinal cord was performed in NPC1-mutant mice. The results showed that NPC1 protein was expressed in oligodendrocytes and the amount of myelin protein was generally decreased in all parts of the brain and spinal cord in NPC1-mutant mice. Compared to wild type, the amount of Sox10 and YY1 was not different in NPC1-mutant mice, but MRF was significantly decreased, suggesting a possible mechanism perturbing differentiation of oligodendrocytes and the myelination process in the NPC1-mutant mouse.

Morphological alterations of the cornea in the mouse model of niemann-pick disease type c1

PURPOSE

Niemann-Pick disease type C1 (NPC1) is a genetic neurovisceral disorder characterized by abnormalities in intracellular sterol trafficking. A knockout mouse model (NPC1) is an important tool for the study of pathogenesis and treatment strategies. In the present study, NPC1 mice were examined for pathological changes in the cornea.

METHODS

Fifteen inbred homozygous NPC1 knockout mice (NPC1, 5-10 weeks old), 5 age-matched heterozygous mice (NPC1), and 14 wild-type control mice (NPC1) were examined. In vivo confocal laser scanning microscopy (CLSM) was performed on both eyes of each animal; afterward, the eyes were processed for histology, electron microscopy, and lipid analysis.

RESULTS

In vivo CLSM disclosed hyperreflective intracellular deposits in the intermediate and basal cell layers of corneal epithelium in all NPC1 mice. At the electron microscopy level, however, vacuolated cytoplasmic structures, 200-500 nm in diameter, with electron-dense material appeared in all structures investigated, including all epithelial layers and stromal keratocytes. These deposits were negative for filipin, a marker for unesterified cholesterol. Lipid analysis showed a marked increase in disialotetrahexosylganglioside 2 (GM2) level in NPC1 mice corneas, whereas no changes were detected in free cholesterol and disialotetrahexosylganglioside 3 (GM3) levels when compared with controls.

CONCLUSIONS

Morphological changes characteristic for the NPC1 mouse cornea were visualized in all epithelial layers and keratocytes. In vivo CLSM findings were confirmed by other techniques. In vivo detection of ocular manifestations and analysis of ocular tissue have the potential to aid the diagnosis of NPC1 disease and to monitor the efficacy of treatment.

Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells Protect against Neuronal Cell Death and Ameliorate Motor Deficits in Niemann Pick Type C1 Mice

Niemann Pick disease type C1 (NPC) is an autosomal recessive disease characterized by progressive neurological deterioration leading to premature death. In this study, we hypothesized that human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have the multifunctional abilities to ameliorate NPC symptoms in the brain. To test this hypothesis, hUCB-MSCs were transplanted into the hippocampus of NPC mice in the early asymptomatic stage. This transplantation resulted in the recovery of motor function in the Rota Rod test and impaired cholesterol homeostasis leading to increased levels of cholesterol efflux-related genes such as LXRα, ABCA1, and ABCG5 while decreased levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase were observed in NPC mice. In the cerebrum, hUCB-MSCs enhanced neuronal cell survival and proliferation, where they directly differentiated into electrically active MAP2-positive neurons as demonstrated by whole-cell patch clamping. In addition, we observed that hUCB-MSCs reduced Purkinje neuronal loss by suppression of inflammatory and apoptotic signaling in the cerebellum as shown by immunohistochemistry. We further investigated how hUCB-MSCs enhance cellular survival and inhibit apoptosis in NPC mice. Neuronal cell survival was associated with increased PI3K/AKT and JAK2/STAT3 signaling; moreover, hUCB-MSCs modulated the levels of GABA/glutamate transporters such as GAT1, EAAT2, EAAT3, and GAD6 in NPC mice as assessed by Western blot analysis. Taken together, our findings suggest that hUCB-MSCs might play multifunctional roles in neuronal cell survival and ameliorating motor deficits of NPC mice.

In vivo quantification of brain injury in adult Niemann-Pick Disease Type C

Development of surrogate markers is necessary to assess the potential efficacy of new therapeutics in Niemann-Pick Disease Type C (NP-C). In the present study, magnetization transfer ratio (MTR) imaging, a quantitative MRI imaging technique sensitive to subtle brain microstructural changes, was applied in two patients suffering from adult NP-C. Statistical mapping analysis was performed to compare each patient's MTR maps with those of a group of 34 healthy controls to quantify and localize the extent of brain injury of each patient. Using this method, pathological changes were evidenced in the cerebellum, the thalami and the lenticular nuclei in both patients and also in the fronto-temporal cortices in the patient with the worse functional deficit. In addition, white matter changes were located in the midbrain, the cerebellum and the fronto-temporal lobes in the patient with the higher level of disability and in only one limited periventricular white matter region in the other patient. A 6-month follow-up was performed in the patient with the lower functional deficit and evidenced significant extension of grey matter (GM) and white matter (WM) injuries during the following period (14% of increased injury for GM and 53% for WM). This study demonstrates that significant brain injury related to clinical deficit can be assessed in vivo in adult NP-C using MTR imaging. Although preliminary, these findings suggest that MTR imaging may be a relevant candidate for the development of biomarker in NP-C.

Cerebellar long-term depression is deficient in Niemann-Pick type C disease mice

Niemann-Pick type C disease (NPC) is an autosomal recessive lipidosis characterized by progressive neurodegeneration. Although several studies have revealed unusual accumulation of unesterfied cholesterol in astrocytic lysosome of NPC, pathophysiological basis of cerebellar neuronal dysfunction remains unclear. We compared parallel fiber-Purkinje cell synaptic transmission and long-term depression (LTD) in +/+npc (nih) (npc(+/+)) and -/-npc(nih) (npc(-/-)) mice. Our data showed that adenosine A1 receptor agonists decreased parallel fiber excitatory postsynaptic current (EPSC) amplitude and mEPSC frequency while its antagonists increased EPSC amplitude and mEPSC frequency in wild type and mutant mice. Furthermore, parallel fiber LTD was deficient in npc(-/-) mice and supplement of adenosine triphosphate (ATP) rescued the impaired LTD. Taken together, these experiments suggest that synaptic strength and LTD are altered in npc(-/-) mice due to the decrease of ATP/adenosine release and deactivation of A1 receptors in parallel fiber terminals. The enhanced synaptic transmission and the decreased LTD might result in progressive neurotoxicity of Purkinje cells in npc(-/-) mice.

Size and shape of the corpus callosum in adult Niemann-Pick type C reflects state and trait illness variables

BACKGROUND AND PURPOSE

Variable alterations to the structure of the corpus callosum have been described in adults with NPC, a neurometabolic disorder known to result in both white and gray matter pathology. This study sought to examine the structure of the callosum in a group of adult patients with NPC and compared callosal structure with a group of matched controls, and to relate callosal structure with state and trait illness variables.

MATERIALS AND METHODS

Nine adult patients with NPC were matched to control subjects (n = 26) on age and sex. The corpus callosum was segmented from the midsagittal section of T1-weighted images on all subjects, and total area, length, bending angle, and mean thickness were calculated. In addition, 39 regional thickness measures were derived by using a previously published method. All measures were compared between groups, and analyzed alongside symptom measures, biochemical parameters, and ocular-motor measures.

RESULTS

The callosal area and mean thickness were significantly reduced in the patient group, and regional thickness differences were greatest in the genu, posterior body, isthmus, and anterior splenium. Global callosal measures correlated significantly with duration of illness and symptom score, and at trend level with degree of filipin staining. Measures of reflexive saccadic peak velocity and gain, and self-paced saccades, correlated strongly with total callosal area.

CONCLUSIONS

Callosal structure and size reflect both state and trait markers in adult NPC, and they may be useful biomarkers to index both white and gray matter changes that reflect illness severity and progression.

Decreased purinergic inhibition of synaptic activity in a mouse model of Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is a progressive neurodegenerative disorder characterized by accumulation of free cholesterol in lysosomes, mainly due to a mutation in the NPC1 gene. The pathophysiological basis of the neural disorders in NPC, however, is not well understood. We found that the hippocampal field excitatory postsynaptic potential (fEPSP) was enhanced in NPC1 mutant mice. A1-receptor antagonist or adenosine degrading enzyme enhanced the fEPSP in both types of mice, but had a much weaker effect in the mutant mice, suggesting less tonic inhibition of synaptic transmission by endogenous adenosine in the mutant. Further evidence showed impaired hippocampal long term potentiation (LTP) in mutant mice. Supplement of A1 agonist N6-Cyclopentyladenosine (CPA) partially rescued the impaired LTP in mutant mice. Moreover, adenosine release from hippocampal slices was significantly decreased in the mutant. The enhanced excitatory synaptic transmission and the decreased synaptic plasticity due to the decreased adenosine release in NPC brain may partially contribute to the neural disorders of NPC disease, such as seizures, neurodegeneration, and dementia.

Post-ictal psychosis in adolescent Niemann-Pick disease type C

We describe the presentation of an adolescent with juvenile-onset Niemann-Pick disease type C (NPC) who presented with post-ictal psychosis in the context of a developing seizure disorder. After demonstrating mild gait disturbance beginning at the age of 4 years, he was diagnosed with NPC at age 12 on the basis of 95% of cultured fibroblasts staining positive for filipin and a reduced fibroblast cholesterol esterification rate. He then developed a seizure disorder at age 15, where clusters of seizures produced typical psychotic symptoms, including hallucinations and delusions. His seizure disorder responded to valproate, which resulted in a settling of his psychotic symptoms. Whilst post-ictal psychosis is rarely reported prior to the age of 16, NPC in adolescents and adults is particularly psychotogenic and may increase the risk for post-ictal psychosis in the pediatric population.

The ins and outs of cholesterol in the vertebrate retina

The vertebrate retina has multiple demands for utilization of cholesterol and must meet those demands either by synthesizing its own supply of cholesterol or by importing cholesterol from extraretinal sources, or both. Unlike the blood-brain barrier, the blood-retina barrier allows uptake of cholesterol from the circulation via a lipoprotein-based/receptor-mediated mechanism. Under normal conditions, cholesterol homeostasis is tightly regulated; also, cholesterol exists in the neural retina overwhelmingly in unesterified form, and sterol intermediates are present in minimal to negligible quantities. However, under certain pathological conditions, either due to an inborn error in cholesterol biosynthesis or as a consequence of exposure to selective inhibitors of enzymes in the cholesterol pathway, the ratio of sterol intermediates to cholesterol in the retina can rise dramatically and persist, in some cases resulting in progressive degeneration that significantly compromises the structure and function of the retina. Although the relative contributions of de novo synthesis versus extraretinal uptake are not yet known, herein we review what is known about these processes and the dynamics of cholesterol in the vertebrate retina and indicate some future avenues of research in this area.

Altered levels and distribution of amyloid precursor protein and its processing enzymes in Niemann-Pick type C1-deficient mouse brains

Niemann-Pick type C (NPC) disease is an autosomal recessive neurodegenerative disorder characterized by intracellular accumulation of cholesterol and glycosphingolipids in many tissues including the brain. The disease is caused by mutations of either NPC1 or NPC2 gene and is accompanied by a severe loss of neurons in the cerebellum, but not in the hippocampus. NPC pathology exhibits some similarities with Alzheimer's disease, including increased levels of amyloid beta (Abeta)-related peptides in vulnerable brain regions, but very little is known about the expression of amyloid precursor protein (APP) or APP secretases in NPC disease. In this article, we evaluated age-related alterations in the level/distribution of APP and its processing enzymes, beta- and gamma-secretases, in the hippocampus and cerebellum of Npc1(-/-) mice, a well-established model of NPC pathology. Our results show that levels and expression of APP and beta-secretase are elevated in the cerebellum prior to changes in the hippocampus, whereas gamma-secretase components are enhanced in both brain regions at the same time in Npc1(-/-) mice. Interestingly, a subset of reactive astrocytes in Npc1(-/-) mouse brains expresses high levels of APP as well as beta- and gamma-secretase components. Additionally, the activity of beta-secretase is enhanced in both the hippocampus and cerebellum of Npc1(-/-) mice at all ages, while the level of C-terminal APP fragments is increased in the cerebellum of 10-week-old Npc1(-/-) mice. These results, taken together, suggest that increased level and processing of APP may be associated with the development of pathology and/or degenerative events observed in Npc1(-/-) mouse brains.

Conditional Niemann-Pick C mice demonstrate cell autonomous Purkinje cell neurodegeneration

Pathways regulating neuronal vulnerability are poorly understood, yet are central to identifying therapeutic targets for degenerative neurological diseases. Here, we characterize mechanisms underlying neurodegeneration in Niemann-Pick type C (NPC) disease, a lysosomal storage disorder characterized by impaired cholesterol trafficking. To date, the relative contributions of neuronal and glial defects to neuron loss are poorly defined. Using gene targeting, we generate Npc1 conditional null mutant mice. Deletion of Npc1 in mature cerebellar Purkinje cells leads to an age-dependent impairment in motor tasks, including rotarod and balance beam performance. Surprisingly, these mice did not show the early death or weight loss that are characteristic of global Npc1 null mice, suggesting that Purkinje cell degeneration does not underlie these phenotypes. Histological examination revealed the progressive loss of Purkinje cells in an anterior-to-posterior gradient. This cell autonomous neurodegeneration occurs in a spatiotemporal pattern similar to that of global knockout mice. A subpopulation of Purkinje cells in the posterior cerebellum exhibits marked resistance to cell death despite Npc1 deletion. To explore this selective response, we investigated the electrophysiological properties of vulnerable and susceptible Purkinje cell subpopulations. Unexpectedly, Purkinje cells in both subpopulations displayed no electrophysiological abnormalities prior to degeneration. Our data establish that Npc1 deficiency leads to cell autonomous, selective neurodegeneration and suggest that the ataxic symptoms of NPC disease arise from Purkinje cell death rather than cellular dysfunction.

Increased activity and altered subcellular distribution of lysosomal enzymes determine neuronal vulnerability in Niemann-Pick type C1-deficient mice

Niemann-Pick disease type C (NPC), caused by mutations in the Npc1 or Npc2 genes, is a progressive neurodegenerative disorder characterized by intracellular accumulation/redistribution of cholesterol in a number of tissues including the brain. This is accompanied by a severe loss of neurons in selected brain regions. In this study, we evaluated the role of lysosomal enzymes, cathepsins B and D, in determining neuronal vulnerability in NPC1-deficient (Npc1(-/-)) mouse brains. Our results showed that Npc1(-/-) mice exhibit an age-dependent degeneration of neurons in the cerebellum but not in the hippocampus. The cellular level/expression and activity of cathepsins B and D are increased more predominantly in the cerebellum than in the hippocampus of Npc1(-/-) mice. In addition, the cytosolic levels of cathepsins, cytochrome c, and Bax2 are higher in the cerebellum than in the hippocampus of Npc1(-/-) mice, suggesting a role for these enzymes in the degeneration of neurons. This suggestion is supported by our observation that degeneration of cultured cortical neurons treated with U18666A, which induces an NPC1-like phenotype at the cellular level, can be attenuated by inhibition of cathepsin B or D enzyme activity. These results suggest that the increased level/activity and altered subcellular distribution of cathepsins may be associated with the underlying cause of neuronal vulnerability in Npc1(-/-) brains. Therefore, their inhibitors may have therapeutic potential in attenuating NPC pathology.

Mitochondrial cholesterol loading exacerbates amyloid beta peptide-induced inflammation and neurotoxicity

The role of cholesterol in Alzheimer's disease (AD) has been linked to the generation of toxic amyloid beta peptides (Abeta). Using genetic mouse models of cholesterol loading, we examined whether mitochondrial cholesterol regulates Abeta neurotoxicity and AD pathology. Isolated mitochondria from brain or cortical neurons of transgenic mice overexpressing SREBP-2 (sterol regulatory element binding protein 2) or NPC1 (Niemann-Pick type C1) knock-out mice exhibited mitochondrial cholesterol accumulation, mitochondrial glutathione (mGSH) depletion and increased susceptibility to Abeta1-42-induced oxidative stress and release of apoptogenic proteins. Similar findings were observed in pharmacologically GSH-restricted rat brain mitochondria, while selective mGSH depletion sensitized human neuronal and glial cell lines to Abeta1-42-mediated cell death. Intracerebroventricular human Abeta delivery colocalized with mitochondria resulting in oxidative stress, neuroinflammation and neuronal damage that were enhanced in Tg-SREBP-2 mice and prevented upon mGSH recovery by GSH ethyl ester coinfusion, with a similar protection observed by intraperitoneal administration of GSH ethyl ester. Finally, APP/PS1 (amyloid precursor protein/presenilin 1) mice, a transgenic AD mouse model, exhibited mitochondrial cholesterol loading and mGSH depletion. Thus, mitochondrial cholesterol accumulation emerges as a novel pathogenic factor in AD by modulating Abeta toxicity via mGSH regulation; strategies boosting the particular pool of mGSH may be of relevance to slow down disease progression.

Molecular consequences of altered neuronal cholesterol biosynthesis

The first dedicated step in de novo cholesterol biosynthesis begins with formation of squalene and ends with the reduction of 7-dehydrocholesterol by 7-dehydrocholesterol reductase (Dhcr7) into cholesterol, which is an essential structural and signaling molecule. Mutations in the Dhcr7 gene lead to Smith-Lemli-Opitz syndrome (SLOS), which is characterized by developmental deformities, incomplete myelination, and mental retardation. To understand better the molecular consequences of Dhcr7 deficiency in neuronal tissue, we analyzed the effect of cholesterol deficiency on the transcriptome in Neuro2a cells. Transient down-regulation of Dhcr7 by siRNA led to altered expression of multiple molecules that play critical roles in intracellular signaling or vesicular transport or are inserted into membrane rafts (e.g. Egr1, Snx, and Adam19). A similar down-regulation was also observed in stable Dhrc7-shRNA-transfected cell lines, and the findings were verified by qPCR. Furthermore, we investigated the Dhcr7-deficient and control cells for the expression of several critical genes involved in lipid biosynthesis. Among these, fatty acid synthase, sterol-regulatory element binding protein 2, SREBF chaperone, site-1 protease, and squalene synthase showed a significant down-regulation, suggesting that, in a neuronal cell line, Dhcr7 is a potent regulator of lipid biosynthesis. Importantly, the gene expression changes were present in both lipid-containing and cholesterol-deficient media, suggesting that intrinsic cholesterol biosynthesis is necessary for normal neuronal function and cannot be supplemented from extrinsic sources.

Neuronal loss of Drosophila NPC1a causes cholesterol aggregation and age-progressive neurodegeneration

The mistrafficking and consequent cytoplasmic accumulation of cholesterol and sphingolipids is linked to multiple neurodegenerative diseases. One class of disease, the sphingolipid storage diseases, includes Niemann-Pick disease type C (NPC), caused predominantly (95%) by mutation of the NPC1 gene. A disease model has been established through mutation of Drosophila NPC1a (dnpc1a). Null mutants display early lethality attributable to loss of cholesterol-dependent ecdysone steroid hormone production. Null mutants rescued to adults by restoring ecdysone production mimic human NPC patients with progressive motor defects and reduced life spans. Analysis of dnpc1a null brains shows elevated overall cholesterol levels and progressive accumulation of filipin-positive cholesterol aggregates within brain and retina, as well as isolated cultured brain neurons. Ultrastructural imaging of dnpc1a mutant brains reveals age-progressive accumulation of striking multilamellar and multivesicular organelles, preceding the onset of neurodegeneration. Consistently, electroretinogram recordings show age-progressive loss of phototransduction and photoreceptor synaptic transmission. Early lethality, movement impairments, neuronal cholesterol deposits, accumulation of multilamellar bodies, and age-dependent neurodegeneration are all rescued by targeted neuronal expression of a wild-type dnpc1a transgene. Interestingly, targeted expression of dnpc1a in glia also provides limited rescue of adult lethality. Generation of dnpc1a null mutant neuron clones in the brain reveals cell-autonomous requirements for dNPC1a in cholesterol and membrane trafficking. These data demonstrate a requirement for dNPC1a in the maintenance of neuronal function and viability and show that loss of dNPC1a in neurons mimics the human neurodegenerative condition.

NRIF is a regulator of neuronal cholesterol biosynthesis genes

Cholesterol is a critical component of neuronal membranes, required for normal signal transduction. We showed previously that adult hippocampal neurons co-express high levels of cholesterogenic enzymes, and that their expression is under the control of the p75 neurotrophin receptor (p75NTR). Most of the cellular effects of p75NTR are mediated via interacting proteins, including neurotrophin receptor interacting factor (NRIF). In this study, we tested the hypothesis that p75NTR-dependent regulation of cholesterol and lipid biosynthesis genes is mediated by NRIF. We found that in vitro down regulation of NRIF expression decreased the mRNA for two main cholesterogenic enzymes, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (Hmgcr; EC 2.3.3.10) and 7-dehydrocholesterol reductase (Dhcr7; EC 1.3.1.21). Further analyses revealed that NRIF-dependent and Dhcr7-dependent transcriptional changes show a high degree of overlap, and that NRIF reduction resulted in reduced expression of sterol-sensing domain protein SCAP, followed by a decrease in mRNA levels of SRE-motif containing genes (HMGCR, FASN, SREBP2, S1P, and SQS1). Finally, a reduction in cholesterol biosynthesis-related gene expression was also observed in hippocampal tissue of mice with NRIF deletion. Our combined in vitro and in vivo studies suggest that hippocampal neuronal cholesterol biosynthesis is regulated through the p75NTR interacting factor NRIF.

The Niemann-Pick C1 protein in recycling endosomes of presynaptic nerve terminals

Niemann-Pick type C (NPC) disease is a fatal, neurodegenerative disorder caused in 95% of cases by loss of function of NPC1, a ubiquitous endosomal transmembrane protein. A biochemical hallmark of NPC deficiency is cholesterol accumulation in the endocytic pathway. Although cholesterol trafficking defects are observed in all cell types, neurons are the most vulnerable to NPC1 deficiency, suggesting a specialized function for NPC1 in neurons. We investigated the subcellular localization of NPC1 in neurons to gain insight into the mechanism of action of NPC1 in neuronal metabolism. We show that NPC1 is abundant in axons of sympathetic neurons and is present in recycling endosomes in presynaptic nerve terminals. NPC1 deficiency causes morphological and biochemical changes in the presynaptic nerve terminal. Synaptic vesicles from Npc1(-/-) mice have normal cholesterol content but altered protein composition. We propose that NPC1 plays a previously unrecognized role in the presynaptic nerve terminal and that NPC1 deficiency at this site might contribute to the progressive neurological impairment in NPC disease.

Deregulation of the phosphatidylinositol-3 kinase signaling cascade is associated with neurodegeneration in Npc1-/- mouse brain

Niemann-Pick type C (NPC) disease is caused by mutations to genes that encode proteins critical to intracellular lipid homeostasis. The events underlying NPC progressive neurodegeneration are poorly understood but include neurofibrillary tangles of the type found in Alzheimer's disease. Here we investigated possible contributions of a phosphatidylinositol-3 kinase cascade [PI3K, Akt, glycogen synthase kinase-3beta (GSK-3beta)] that is linked to apoptosis and various degenerative conditions. Brain concentrations of phosphorylated Akt, which phosphorylates and inactivates GSK-3beta, were significantly elevated in Npc1-/- mice relative to Npc1+/+ mice. Accordingly, levels of inactive GSK-3beta were 50 to 100% higher in mutant brains than in controls. Increases in inactive GSK-3beta occurred early in postnatal development, well before neuronal loss, and were most prominent in structures with intracellular cholesterol accumulation, suggesting a contribution to subsequent degeneration. Perturbations of nuclear factor (NF)-kappaB, which is regulated by GSK-3beta, occurred in Npc1-/- mouse brains. Nuclear concentrations and DNA binding activity of NF-kappaB's transactivation subunit, p65, were significantly reduced in Npc1-/- mice compared to Npc1+/+ mice. Cytoplasmic levels of the p50 subunit and its precursor, p105, were higher in Npc1-/- mice. These results suggest that excessive activity in the PI3K-Akt pathway depresses GSK-3beta, thereby disrupting the formation and/or nuclear import of p50/p65 NF-kappaB dimers and contributing to neuronal degeneration.

A Yeast Model System for Functional Analysis of the Niemann-Pick Type C Protein 1 Homolog, Ncr1p

Niemann-Pick disease type C (NP-C) is a progressive, ultimately fatal, autosomal recessive neurodegenerative disorder. The major biochemical hallmark of the disease is the endocytic accumulation of low-density lipoprotein-derived cholesterol. The majority of NP-C patients have mutations in the Niemann-Pick type C1 gene, NPC1. This study focuses on the Saccharomyces cerevisiae homolog of the human NPC1 protein encoded by the NCR1 gene. Ncr1p localizes to the vacuole, the yeast equivalent to the mammalian endosome-lysosome system. Here, we identify the first phenotype caused by deletion of NCR1 from the yeast genome, resistance to the ether lipid drug, edelfosine. Our results indicate that edelfosine has a cytotoxic, rather than cytostatic, effect on wildtype yeast cells. We exploit the edelfosine resistance phenotype to assess the function of yeast Ncr1 proteins carrying amino acid changes corresponding to human NPC1 patient mutations. We find that one of these amino acid changes severely compromises Ncr1p function as assessed using the edelfosine resistance assay. These findings establish S. cerevisiae as a model system that can be exploited to analyze the molecular consequences of patient mutations in NPC1 and provide the basis for future genetic studies using yeast.

Cholesterol homeostasis in neurons and glial cells

Cholesterol is highly enriched in the brain compared to other tissues. Essentially all cholesterol in the brain is synthesized endogenously since plasma lipoproteins are unable to cross the blood-brain barrier. Cholesterol is transported within the central nervous system in the form of apolipoprotein E-containing lipoprotein particles that are secreted mainly by glial cells. Cholesterol is excreted from the brain in the form of 24-hydroxycholesterol. Apolipoprotein E and cholesterol have been implicated in the formation of amyloid plaques in Alzheimer's disease. In addition, the progressive neurodegenerative disorder Niemann-Pick C disease is characterized by defects in intracellular trafficking of cholesterol.

Adenovirus expressing an NPC1-GFP fusion gene corrects neuronal and nonneuronal defects associated with Niemann pick type C disease

Niemann Pick type C (NPC) disease is an autosomal recessive disorder characterized by abnormal cholesterol metabolism and accumulation in lysosomal and endosomal compartments. Although peripheral organs are affected, the progressive neurodegeneration in the brain is typically most deleterious, leading to dystonia, ataxia, seizures, and premature death. Although the two genes underlying this disorder in humans and mouse models of the disease have been identified (NPC1 in 95% and NPC2/HE1 in 5% of human cases), their cellular roles have not Been fully defined, and there is currently no effective treatment for this disorder. To help address these issues, we constructed a recombinant adenovirus, Ad(NPC1-GFP), which contains a cDNA encoding a mouse NPC1 protein with a green fluorescent protein (GFP) fused to its C-terminus. Fluorescence microscopy and cholesterol trafficking assays demonstrate that the GFP-tagged NPC1 protein is functional and detectable in cells from different species (hamster, mouse, human) and of different types (ovary-derived cells, fibroblasts, astrocytes, neurons from peripheral and central nervous systems) in vitro. Combined with results from time-lapse microscopy and in vivo brain injections, our findings suggest that this adenovirus offers advantages for expressing NPC1 and analyzing its cellular localization, movement, functional properties, and beneficial effects in vitro and in vivo.