Recent advances in elucidating Niemann-Pick C disease

Differently increased volumes of multiple brain areas in Npc1 mutant mice following various drug treatments

Background

Niemann-Pick disease type C1 (NPC1, MIM 257220) is a heritable lysosomal storage disease characterized by a progressive neurological degeneration that causes disability and premature death. A murine model of Npc1-/- displays a rapidly progressing form of Npc1 disease, which is characterized by weight loss, ataxia, and increased cholesterol storage. Npc1-/- mice receiving a combined therapy (COMBI) of miglustat (MIGLU), the neurosteroid allopregnanolone (ALLO) and the cyclic oligosaccharide 2-hydroxypropyl-β-cyclodextrin (HPßCD) showed prevention of Purkinje cell loss, improved motor function and reduced intracellular lipid storage. Although therapy of Npc1-/- mice with COMBI, MIGLU or HPßCD resulted in the prevention of body weight loss, reduced total brain weight was not positively influenced.

Methods

In order to evaluate alterations of different brain areas caused by pharmacotherapy, fresh volumes (volumes calculated from the volumes determined from paraffin embedded brain slices) of various brain structures in sham- and drug-treated wild type and mutant mice were measured using stereological methods.

Results

In the wild type mice, the volumes of investigated brain areas were not significantly altered by either therapy. Compared with the respective wild types, fresh volumes of specific brain areas, which were significantly reduced in sham-treated Npc1-/- mice, partly increased after the pharmacotherapies in all treatment strategies; most pronounced differences were found in the CA1 area of the hippocampus and in olfactory structures.

Discussion

Volumes of brain areas of Npc1-/- mice were not specifically changed in terms of functionality after administering COMBI, MIGLU, or HPßCD. Measurements of fresh volumes of brain areas in Npc1-/- mice could monitor region-specific changes and response to drug treatment that correlated, in part, with behavioral improvements in this mouse model.

The point mutation of the cholesterol trafficking membrane protein NPC1 may affect its proper function in more than a single step: Molecular dynamics simulation study

The Niemann-Pick type C1 (NPC1) protein is one of the key players of cholesterol trafficking from the lysosome and its function is closely coupled with the Niemann-Pick type C2 (NPC2) protein. The dysfunction of one of these proteins can cause problems in the overall cholesterol homeostasis and leads to a disease, which is called the Niemann-Pick type C (NPC) disease. The parts of the cholesterol transport mechanism by NPC1 have begun to recently emerge, especially after the full-length NPC1 structure was determined from a cryo-EM study. However, many details about the overall cholesterol trafficking process by NPC1 still remain to be elucidated. Notably, the NPC1 could act as one of the target proteins for the control of infectious diseases due to its role as the virus entry point into the cells as well as for cancer treatment due to the inhibitory effect of tumor growth. A mutation of NPC1 can leads to dysfunctions and understanding this process can provide valuable insights into the mechanisms of the corresponding protein and the therapeutic strategies against the disease that are caused by the mutation. It has been found that patients with the point mutation R518W (or R518Q) on the NPC1 show the accumulation of lipids within the lysosomal lumen. In this paper, we report how the corresponding mutation can affect the cholesterol transport process by NPC1 in the different stages by the molecular dynamics simulations. The simulation results show that the point mutation intervenes at least at two different steps during the cholesterol transport by NPC1 and NPC2 in combination, which includes the association step of NPC2 with the NPC1, the cholesterol transfer step from NPC2 to NPC1-NTD while the cholesterol passage within the NPC1 via a channel is relatively unaffected by R518W mutation. The detailed analysis of the resulting simulation trajectories reveals the important structural features that are essential for the proper functioning of the NPC1 for the cholesterol transport, and it shows how the overall structure, which thereby includes the function, can be affected by a single mutation.

Increased exosome secretion in neurons aging in vitro by NPC1-mediated endosomal cholesterol buildup

The present study unveils the molecular mechanism through which neurons in vitro compensate age-associated proteostasis defects by increasing exosome release.

As neurons age, they show a decrease in their ability to degrade proteins and membranes. Because undegraded material is a source of toxic products, defects in degradation are associated with reduced cell function and survival. However, there are very few dead neurons in the aging brain, suggesting the action of compensatory mechanisms. We show in this work that ageing neurons in culture show large multivesicular bodies (MVBs) filled with intralumenal vesicles (ILVs) and secrete more small extracellular vesicles than younger neurons. We also show that the high number of ILVs is the consequence of the accumulation of cholesterol in MVBs, which in turn is due to decreased levels of the cholesterol extruding protein NPC1. NPC1 down-regulation is the consequence of a combination of upregulation of the NPC1 repressor microRNA 33, and increased degradation, due to Akt-mTOR targeting of NPC1 to the phagosome. Although releasing more exosomes can be beneficial to old neurons, other cells, neighbouring and distant, can be negatively affected by the waste material they contain.

Ultrastructure of spinal anterior horn cells in human Niemann-Pick type C (NPC) patient and mouse model of NPC with retroposon insertion in NPC1 genes

Niemann-Pick disease type C (NPC) is a neurovisceral lipid-storage disease. Although NPC patients show lipid storage in anterior horn cells of the spinal cord, little information is available regarding the electron microscopic analyses of the morphologies of intra-endosomal lipid like-materials in the anterior horn cells of NPC patients. In this study, we elucidated the intra-endosomal ultrastructures in spinal anterior horn cells in an NPC patient, as well as in mutant BALB/c NPC1^-/- mice with a retroposon insertion in the NPC1 gene. These morphologies were classified into four types: vesicle, multiple concentric sphere (MCS), membrane, and rose flower. The percentages of the composition in the NPC patient and NPC1^-/- mice were: vesicle (55.5% and 14.9%), MCS (15.7% and 3.4%), membrane (23.6% and 57.1%), and rose flower (5.2% and 24.6%), respectively. Formation of the intra-endosomal structures could proceed as follows: (i) a vesicle or MCS buds off the endosome into the lumen; (ii) when a vesicle breaks down, a membrane is formed; and (iii) after an MCS breaks down, a rose flower structure is formed. Our new finding in this study is that ultrastructural morphology is the same between the NPC patient and NPC1^-/- mice, although there are differences in the composition.

Recent neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC

Niemann–Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder with extensive biological, molecular, and clinical heterogeneity. Recently, numerous studies have tried to shed light on the pathophysiology of the disease, highlighting possible disease pathways common to other neurodegenerative disorders, such as Alzheimer’s disease and frontotemporal dementia, and identifying possible candidate biomarkers for disease staging and response to treatment. Miglustat, which reversibly inhibits glycosphingolipid synthesis, has been licensed in the European Union and elsewhere for the treatment of NPC in both children and adults. A number of ongoing clinical trials might hold promise for the development of new treatments for NPC. The objective of the present work is to review and evaluate recent literature data in order to highlight the latest neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC pathophysiology. Furthermore, ongoing developments in disease-modifying treatments will be briefly discussed.

Perspectives in Pediatric Pathology, Chapter 21. Testicular Pathology in Heritable Metabolic Disease

Inborn errors of metabolism have wide and profound effects in many or all organs, and especially so in those with endocrine functions. The testes are greatly affected by systemic metabolic disorders, leading to specific histological findings that generally reveal the nature of the underlying disorder. Here we describe the main testicular changes seen in the setting of metabolic disease.

LC-MS/MS based assay and reference intervals in children and adolescents for oxysterols elevated in Niemann-Pick diseases

BACKGROUND

Niemann-Pick type C (NP-C) is a rare progressive neurodegenerative lipid storage disorder with heterogeneous clinical presentation and challenging diagnostic procedures. Recently oxysterols have been reported to be specific biomarkers for NP-C but knowledge on the intra-individual variation and on reference intervals in children and adolescents are lacking.

METHODS

We established a LC-MS/MS assay to measure Cholestane-3β, 5α, 6β-triol (C-triol) and 7-Ketocholesterol (7-KC) following Steglich esterification. To assess reference intervals and intra-individual variation we determined oxysterols in 148 children and adolescents from 0 to 18 years and repeat measurements in 19 of them.

RESULTS

The reported method is linear (r>0.99), sensitive (detection limit of 0.03 ng/mL [0.07 nM] for C-triol, and 0.54 ng/mL [1.35 nM] for 7-KC) and precise, with an intra-day imprecision of 4.8% and 4.1%, and an inter-day imprecision of 7.0% and 11.0% for C-triol (28 ng/ml, 67 nM) and 7-KC (32 ng/ml, 80 nM), respectively. Recoveries for 7-KC and C-triol range between 93% and 107%. The upper reference limit obtained for C-triol is 40.4 ng/mL (95% CI: 26.4-61.7 ng/mL, 96.0 nM, 95% CI: 62.8-146.7 nM) and 75.0 ng/mL for 7-KC (95% CI: 55.5-102.5 ng/mL, 187.2 nM, 95% CI: 138.53-255.8 nM), with no age or gender dependency. Both oxysterols have a broad intra-individual variation of 46%±23% for C-triol and 52%±29% for 7-KC. Nevertheless, all Niemann-Pick patients showed increased C-triol levels including Niemann-Pick type A and B patients.

CONCLUSIONS

The LC-MS/MS assay is a robust assay to quantify C-triol and 7-KC in plasma with well documented reference intervals in children and adolescents to screen for NP-C in the pediatric population. In addition our results suggest that especially the C-triol is a biomarker for all three Niemann-Pick diseases.

Laboratory diagnosis of Niemann-Pick disease type C: the filipin staining test

Niemann-Pick disease type C (NPC) is an atypical neurovisceral lysosomal storage disorder resulting from mutations in either the NPC1 or the NPC2 gene, currently conceived as a lipid trafficking disorder. Impaired egress of cholesterol from the late endosomal/lysosomal (LE/L) compartment is a key element of the pathogenesis. The resulting accumulation of unesterified cholesterol in the LE/L compartment can be visualized by fluorescence microscopy after staining with filipin. The "filipin test," performed on cultured fibroblasts, is the historical gold standard method to establish the diagnosis in patients. The authors provide methodological details of the protocol developed and used in their laboratory since 1988, in which two sources of low-density lipoproteins (LDL) (total serum and pure LDL) are used in parallel to facilitate the final interpretation. Methodological caveats and variability of patterns encountered in patients with proven Niemann-Pick C disease (typical "classic" or "intermediate," atypical "variant") are described. An overview of the past 5 years referrals (533 subjects tested, 57 NPC cases, but also 74 mildly/weakly positive tests not due to NPC) is discussed, leading to a proposed algorithm for interpretation of results in the filipin test. This tool takes into account the limits of the method. In up to 15% of all referrals, the filipin test was inconclusive in absence of molecular analysis. Patients diagnosed in the adult age preferentially showed an "intermediate" or "variant" pattern. Well conducted, the filipin test remains an efficient approach for diagnosing NPC, and it is a good functional test to study the pathogenicity of novel mutations.

Focused metabolomics using liquid chromatography/electrospray ionization tandem mass spectrometry for analysis of urinary conjugated cholesterol metabolites from patients with Niemann-Pick disease type C and 3β-hydroxysteroid dehydrogenase deficiency

BACKGROUND

Various conjugated cholesterol metabolites are excreted in urine of the patients with metabolic abnormalities and hepatobiliary diseases. We aimed to examine the usefulness of precursor ion scan and neutral loss scan for the characterization of conjugated cholesterol metabolites in urine.

METHODS

A mixture of authentic standards of conjugated cholesterol metabolites was used for investigating the performance of the present method. The urine of patients with Niemann-Pick diseases type C and 3β-hydroxysteroid dehydrogenase deficiency were analysed by precursor ion scan of m/z 97, 74, and 124.

RESULTS

A precursor ion scan of m/z 97 was effective for identifying conjugates with ester sulphates on hydroxyl groups whereas ester sulphates on phenolic alcohols were signalled by a neutral loss scan of 80 Da. Monosaccharide-conjugated cholesterol metabolites were signalled by a precursor ion scan of m/z 113. Although precursor ion scan of m/z 74 and 124 was effective for finding glycine- and taurine-conjugated metabolites, high intensity of product ions (m/z 74 and 124) disturbed measurement of other multiply conjugated metabolites. The urine samples contained many conjugated cholesterol metabolites, and there were several disease-specific intense peaks. We found several unknown intense peaks with three known peaks in urine of the Niemann-Pick type C patient. In the patient with 3β-hydroxysteroid dehydrogenase deficiency, intense peaks that were tentatively identified as 5-cholenoic acid sulphates and their glycine and taurine conjugates were present.

CONCLUSION

The method should lead to the discovery of new urinary biomarkers for these disturbances of cholesterol catabolism and transport.

Complex lipid trafficking in Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is an atypical lysosomal storage disease resulting from mutations in one of two genes, either NPC1 or NPC2. Although a neurovisceral disorder, it is above all a neurodegenerative disease in the vast majority of patients. Not an enzyme deficiency, it is currently conceived as a lipid trafficking disorder. Impaired egress of cholesterol from the late endosomal/lysosomal (LE/L) compartment is a specific and key element of the pathogenesis, but other lipids, more specially sphingolipids, are also involved, and there are indications for further abnormalities. The full function of the NPC1 and NPC2 proteins is still unclear. This review provides a reappraisal of lipid storage and lysosomal enzymes activities in tissues/cells from NPC patients and animal models. It summarizes the current knowledge on the NPC1 and NPC2 proteins and their function in transport of cholesterol within the late endosomal-lysosomal compartment, with emphasis on differences between systemic organs and the brain; it also discusses regulation by membrane lipids of the NPC2-mediated cholesterol trafficking, interplay between cholesterol and sphingomyelin, the metabolic origin of glycosphingolipids stored in brain, and the putative role of free sphingoid bases in pathogenesis. Brief mention is finally made of diseases affecting other genes that were very recently shown to impact the "NPC pathway".

Atypical multisensory integration in Niemann-Pick type C disease - towards potential biomarkers

Background

Niemann-Pick type C (NPC) is an autosomal recessive disease in which cholesterol and glycosphingolipids accumulate in lysosomes due to aberrant cell-transport mechanisms. It is characterized by progressive and ultimately terminal neurological disease, but both pre-clinical studies and direct human trials are underway to test the safety and efficacy of cholesterol clearing compounds, with good success already observed in animal models. Key to assessing the effectiveness of interventions in patients, however, is the development of objective neurobiological outcome measures. Multisensory integration mechanisms present as an excellent candidate since they necessarily rely on the fidelity of long-range neural connections between the respective sensory cortices (e.g. the auditory and visual systems).

Methods

A simple way to test integrity of the multisensory system is to ask whether individuals respond faster to the occurrence of a bisensory event than they do to the occurrence of either of the unisensory constituents alone. Here, we presented simple auditory, visual, and audio-visual stimuli in random sequence. Participants responded as fast as possible with a button push. One 11-year-old and two 14-year-old boys with NPC participated in the experiment and their results were compared to those of 35 age-matched neurotypical boys.

Results

Reaction times (RTs) to the stimuli when presented simultaneously were significantly faster than when they were presented alone in the neurotypical children, a facilitation that could not be accounted for by probability summation, as evidenced by violation of the so-called ‘race’ model. In stark contrast, the NPC boys showed no such speeding, despite the fact that their unisensory RTs fell within the distribution of RTs observed in the neurotypicals.

Conclusions

These results uncover a previously undescribed deficit in multisensory integrative abilities in NPC, with implications for ongoing treatment of the clinical symptoms of these children. They also suggest that multisensory processes may represent a good candidate biomarker against which to test the efficacy of therapeutic interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0149-x) contains supplementary material, which is available to authorized users.

Niemann-Pick C disease and mobilization of lysosomal cholesterol by cyclodextrin

Niemann-Pick type C (NPC) disease is a lysosomal storage disease in which endocytosed cholesterol becomes sequestered in late endosomes/lysosomes (LEs/Ls) because of mutations in either the NPC1 or NPC2 gene. Mutations in either of these genes can lead to impaired functions of the NPC1 or NPC2 proteins and progressive neurodegeneration as well as liver and lung disease. NPC1 is a polytopic protein of the LE/L limiting membrane, whereas NPC2 is a soluble protein in the LE/L lumen. These two proteins act in tandem and promote the export of cholesterol from LEs/Ls. Consequently, a defect in either NPC1 or NPC2 causes cholesterol accumulation in LEs/Ls. In this review, we summarize the molecular mechanisms leading to NPC disease, particularly in the CNS. Recent exciting data on the mechanism by which the cholesterol-sequestering agent cyclodextrin can bypass the functions of NPC1 and NPC2 in the LEs/Ls, and mobilize cholesterol from LEs/Ls, will be highlighted. Moreover, the possible use of cyclodextrin as a valuable therapeutic agent for treatment of NPC patients will be considered.

Autobiography: Kinuko Suzuki, MD

EDITORS' INTRODUCTION

The following reminiscence by Kinuko Suzuki is the 9th autobiography in a series published in the Journal of Neuropathology and Experimental Neurology. These have been solicited from senior members of the neuropathology community who have been noted leaders and contributors to neuroscience and to the American Association of Neuropathologists (AANP) and have a historical perspective of the importance of neuropathology in diagnosis, education, and research. It is hoped that this series will entertain, enlighten, and present members of the AANP with a better sense of the legacy that we have inherited, as well as reintroduce our respected neuroscientists as humans having interesting lives filled with joys and sorrows and allowing them to present their lives in their own words.MNH, RAS.

Changes of calcium binding proteins, c-Fos and COX in hippocampal formation and cerebellum of Niemann-Pick, type C mouse

Niemann-Pick disease, type C (NPC) is an intractable disease that is accompanied by ataxia, dystonia, neurodegeneration, and dementia due to an NPC gene defect. Disruption of calcium homeostasis in neurons is important in patients with NPC. Thus, we used immunohistochemistry to assess the expression levels of calcium binding proteins (calbindin D28K, parvalbumin, and calretinin), c-Fos and cyclooxygenase-1,2 (COX-1,2) in the hippocampal formation and cerebellum of 4 and 8 week old NPC+/+, NPC+/-, and NPC-/- mice. General expression of these proteins decreased in the hippocampus and cerebellum of NPC-/- compared to that in both young and adult NPC+/+ or NPC+/- mice. Parvalbumin, COX-1,2 or c-Fos-immunoreactive neurons were widely detected in the CA1, CA3, and DG of the hippocampus, but the immunoreactivities were decreased sharply in all areas of hippocampus of NPC-/- compared to NPC+/+ and NPC+/- mice. Taken together, reduction of these proteins may be one of the strong phenotypes related to the neuronal degeneration in NPC-/- mice.

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.

Recommendations for the diagnosis and management of Niemann-Pick disease type C: an update

Niemann-Pick disease type C (NP-C) is a rare inherited neurovisceral disease caused by mutations in either the NPC1 (in 95% of cases) or the NPC2 gene (in around 5% of cases), which lead to impaired intracellular lipid trafficking and accumulation of cholesterol and glycosphingolipids in the brain and other tissues. Characteristic neurological manifestations of NP-C include saccadic eye movement (SEM) abnormalities or vertical supranuclear gaze palsy (VSGP), cerebellar signs (ataxia, dystonia/dysmetria, dysarthria and dysphagia) and gelastic cataplexy. Epileptic seizures are also common in affected patients. Typically, neurological disease onset occurs during childhood, although an increasing number of cases are being detected and diagnosed during adulthood based on late-onset neurological signs and psychiatric manifestations. Categorization of patients according to age at onset of neurological manifestations (i.e. early-infantile, late-infantile, juvenile and adolescent/adult-onset) can be useful for the evaluation of disease course and treatment responses. The first international guidelines for the clinical management of NP-C in children and adults were published in 2009. Since that time a significant amount of data regarding the epidemiology, detection/diagnosis, and treatment of NP-C has been published. Here, we report points of consensus among experts in the diagnosis and treatment of NP-C based on a follow-up meeting in Paris, France in September 2011. This article serves as an update to the original guidelines providing, among other things, further information on detection/diagnostic methods, potential new methods of monitoring disease progression, and therapy. Treatment goals and the application of disease-specific therapy with miglustat are also re-evaluated.

Corneal alterations during combined therapy with cyclodextrin/allopregnanolone and miglustat in a knock-out mouse model of NPC1 disease

Background

Niemann Pick disease type C1 is a neurodegenerative disease caused by mutations in the NPC1 gene, which result in accumulation of unesterified cholesterol and glycosphingolipids in the endosomal-lysosomal system as well as limiting membranes. We have previously shown the corneal involvement in NPC1 pathology in form of intracellular inclusions in epithelial cells and keratocytes. The purpose of the present study was to clarify if these inclusions regress during combined substrate reduction- and by-product therapy (SRT and BPT).

Methodology/Principal Findings

Starting at postnatal day 7 (P7) and thereafter, NPC1 knock-out mice (NPC1^−/−) and wild type controls (NPC1^+/+) were injected with cyclodextrin/allopregnanolone weekly. Additionally, a daily miglustat injection started at P10 until P23. Starting at P23 the mice were fed powdered chow with daily addition of miglustat. The sham group was injected with 0.9% NaCl at P7, thereafter daily starting at P10 until P23, and fed powdered chow starting at P23. For corneal examination, in vivo confocal laser-scanning microscopy (CLSM) was performed one day before experiment was terminated. Excised corneas were harvested for lipid analysis (HPLC/MS) and electron microscopy.

In vivo CLSM demonstrated a regression of hyperreflective inclusions in all treated NPC1^−/−mice. The findings varied between individual mice, demonstrating a regression, ranging from complete absence to pronounced depositions. The reflectivity of inclusions, however, was significantly lower when compared to untreated and sham-injected NPC1^−/− mice. These confocal findings were confirmed by lipid analysis and electron microscopy. Another important CLSM finding revealed a distinct increase of mature dendritic cell number in corneas of all treated mice (NPC1^−/− and NPC1^+/+), including sham-treated ones.

Conclusions/Significance

The combined substrate reduction- and by-product therapy revealed beneficial effects on the cornea. In vivo CLSM is a non-invasive tool to monitor disease progression and treatment effects in NPC1 disorder.

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.

Bone marrow-derived mesenchymal stem cells prevent the loss of Niemann-Pick type C mouse Purkinje neurons by correcting sphingolipid metabolism and increasing sphingosine-1-phosphate

Niemann-Pick type C (NP-C) disease exhibits neuronal sphingolipid storage and cerebellar Purkinje neuron (PN) loss. Although it is clear that PNs are compromised in this disorder, it remains to be defined how neuronal lipid storage causes the PN loss. Our previous studies have shown that bone marrow-derived mesenchymal stem cells (BM-MSCs) transplantation prevent PN loss in NP-C mice. The aim of the present study was therefore to examine the neuroprotective mechanism of BM-MSCs on PNs. We found that NP-C PNs exhibit abnormal sphingolipid metabolism and defective lysosomal calcium store compared to wild-type mice PNs. BM-MSCs promote the survival of NP-C PNs by correction of the altered calcium homeostasis, restoration of the sphingolipid imbalance, as evidenced by increased sphingosine-1-phosphate levels and decreased sphingosine, and ultimately, inhibition of apoptosis pathways. These effects suggest that BM-MSCs modulate sphingolipid metabolism of endogenous NP-C PNs, resulting in their survival and improved clinical outcome in mice.

Roles of cholesterol and lipids in the etiopathogenesis of Alzheimer's disease

Alzheimer's disease is the principal cause of dementia throughout the world and the fourth cause of death in developed economies.This brain disorder is characterized by the formation of brain protein aggregates, namely, the paired helical filaments and senile plaques. Oxidative stress during life, neuroinflamamtion, and alterations in neuron-glia interaction patterns have been also involved in the etiopathogenesis of this disease. In recent years, cumulative evidence has been gained on the involvement of alteration in neuronal lipoproteins activity, as well as on the role of cholesterol and other lipids in the pathogenesis of this neurodegenerative disorder. In this review, we analyze the links between changes in cholesterol homeostasis, and the changes of lipids of major importance for neuronal activity and Alheimer's disease. The investigation on the fine molecular mechanisms underlying the lipids influence in the etiopathogenesis of Alzheimer's disease may shed light into its treatment and medical management.

Niemann-Pick disease type C

Niemann-Pick C disease (NP-C) is a neurovisceral atypical lysosomal lipid storage disorder with an estimated minimal incidence of 1/120 000 live births. The broad clinical spectrum ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease. The neurological involvement defines the disease severity in most patients but is typically preceded by systemic signs (cholestatic jaundice in the neonatal period or isolated spleno- or hepatosplenomegaly in infancy or childhood). The first neurological symptoms vary with age of onset: delay in developmental motor milestones (early infantile period), gait problems, falls, clumsiness, cataplexy, school problems (late infantile and juvenile period), and ataxia not unfrequently following initial psychiatric disturbances (adult form). The most characteristic sign is vertical supranuclear gaze palsy. The neurological disorder consists mainly of cerebellar ataxia, dysarthria, dysphagia, and progressive dementia. Cataplexy, seizures and dystonia are other common features. NP-C is transmitted in an autosomal recessive manner and is caused by mutations of either the NPC1 (95% of families) or the NPC2 genes. The exact functions of the NPC1 and NPC2 proteins are still unclear. NP-C is currently described as a cellular cholesterol trafficking defect but in the brain, the prominently stored lipids are gangliosides. Clinical examination should include comprehensive neurological and ophthalmological evaluations. The primary laboratory diagnosis requires living skin fibroblasts to demonstrate accumulation of unesterified cholesterol in perinuclear vesicles (lysosomes) after staining with filipin. Pronounced abnormalities are observed in about 80% of the cases, mild to moderate alterations in the remainder ("variant" biochemical phenotype). Genotyping of patients is useful to confirm the diagnosis in the latter patients and essential for future prenatal diagnosis. The differential diagnosis may include other lipidoses; idiopathic neonatal hepatitis and other causes of cholestatic icterus should be considered in neonates, and conditions with cerebellar ataxia, dystonia, cataplexy and supranuclear gaze palsy in older children and adults. Symptomatic management of patients is crucial. A first product, miglustat, has been granted marketing authorization in Europe and several other countries for specific treatment of the neurological manifestations. The prognosis largely correlates with the age at onset of the neurological manifestations.

Increased expression of cholesterol transporter ABCA1 is highly correlated with severity of dementia in AD hippocampus

To gain insight into ATP-binding cassette transporter A1 (ABCA1) function and its potential role in AD pathology, we analyzed the expression of the cholesterol transporter ABCA1 in postmortem hippocampus from persons at different stages of dementia and AD associated neuropathology relative to cognitively intact normal donors by quantitative polymerase chain reaction (qPCR) and Western blot. In this study clinical dementia rating (CDR) scores were used as a measure of dementia severity, whereas, Braak neuropathological staging and neuritic plaque density were used as an index of the neuropathological progression of AD. Correlation analysis showed that ABCA1 mRNA expression was significantly elevated at the earliest recognizable stage of dementia compared to persons with intact cognition. ABCA1 mRNA was also positively correlated with Braak neuropathological stages and neuritic plaque density counts. Additionally, ABCA1 mRNA levels showed robust correlation with dementia severity even after controlling for the confounding contribution of accompanying neuropathological parameters to ABCA1 mRNA expression. Western blot analyses showed that the differential expression observed at the transcriptional level is also reflected at the protein level. Thus, our study provides transcriptional and translational evidence that the expression of ABCA1, a key modulator of cholesterol transport across the plasma membrane, is dysregulated in the AD brain and that this dysregulation is associated with increasing severity of AD, whether measured functionally as dementia severity or neuropathologically as increased neuritic plaque and neurofibrillary tangle density.

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.

A neurodegenerative disease affecting synaptic connections in Drosophila mutant for the tumor suppressor morphogen Patched

The tumor suppressor morphogen, Patched (Ptc), has an extensive homology to the Niemann-Pick-C 1 (NPC1) protein. The NPC disease is a paediatric, progressive and fatal neurodegenerative disorder thought to be due to an abnormal accumulation of cholesterol in neurons. Here, we report that patched mutant adults develop a progressive neurodegenerative disease and their brain contains membranous and lamellar inclusions. There is also a significant reduction in the number of synaptic terminals in the brain of the mutant adults. Interestingly, feeding cholesterol to wild type flies generates inclusions in the brain, but does not cause the disease. However, feeding cholesterol to mutant flies increases synaptic connections and suppresses the disease. Our results suggest that sequestration of cholesterol in the mutant brain in the form of membranous material and inclusions affects available pool of cholesterol for cellular functions. This, in turn, negatively affects the synaptic number and contributes to the disease-state. Consistent with this, in ptc mutants there is a reduction in the pool of cholesterol esters, and cholesterol-mediated suppression of the disease accompanies an increase in cholesterol esters. We further show that Ptc does not function directly in this process since gain of function for Hedgehog also induces the same disease with a reduction in the level of cholesterol esters. We believe that loss of function for ptc causes neurodegeneration via two distinct ways: de-repression of genes that interfere with lipid trafficking, and de-repression of genes outside of the lipid trafficking; the functions of both classes of genes ultimately converge on synaptic connections.

Niemann-Pick Disease Type C: from molecule to clinic

1. Niemann-Pick Type C disease (NPC) is an incurable cholesterol-storage disorder that stems from inherited deficiencies of lysosomal proteins involved in intracellular lipid-trafficking proteins. The condition manifests as progressive neurological impairment and leads to death at an early age. 2. To improve clinical recognization and investigate therapeutic strategies, recent studies using molecular and genetic approaches have led to significant advances in the creation of animal models of NPC, as well as in the understanding of the cellular and molecular mechanisms underlying the pathogenesis of NPC. 3. Patients with NPC are divided into four groups based on age at presentation, whereas the clinical features of NPC can be divided into five categories based on the severity of the disease. Progressive neuronal loss, especially of cerebellar Purkinje cells, is a hallmark of NPC. Ballooned neurons, axonal abnormalities and astroglyosis are among the pathological changes seen. Severe demyelination is also present in the mouse model of NPC. 4. Mutations in the NPC1 gene cause approximately 95% of cases of NPC, whereas mutations in the NPC2 gene account for the remainder of cases. NPC1 is a transmembrane protein and NPC2 is a soluble protein involved in lipid trafficking in lysosomes. Loss-of-function mutations in the NPC1 gene lead to a failure of the calcium-mediated fusion of endosomes with lysosomes, resulting in the accumulation of cholesterol and other lipids in late endosomes and lysosomes. 5. The present review updates the disorders of NPC from clinical features to animal models and molecular mechanisms.

Mitotic epitopes are incorporated into age-dependent neurofibrillary tangles in Niemann-Pick disease type C

The mechanism underlying neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) and other neurodegenerative disorders remains elusive. Niemann-Pick disease type C (NPC) is a kind of genetic neurovisceral disorder in which the intracellular sequestration of cholesterol and other lipids in neurons, NFT formation and neuronal degeneration in brain are the neuropathology hallmarks. The age of onset and progression of the disease vary dramatically. We have analyzed the hippocampus from 17 NPC cases, aged from 7 months to 55 years, to depict the temporal characteristics of NFT formation. Unexpectedly, classic NFT was observed in about 4-year-old NPC brain, suggesting that NFT is not aging dependent, and that juvenile brain neurons satisfy the requirements for NFT formation. NFT in the hippocampus of NPC was significantly increased in number with the advance of age. More importantly, multiple mitotic phase markers, which are not usually found in normal mature neurons, were abundant in the affected neurons and incorporated into NFT. The unusual activation of cdc2/cyclin B kinase and downstream mitotic indices are closely associated with the age-dependent NFT formation, signifying the contribution of abortive cell cycle to neurodegeneration. The cdc2 inhibitors may be therapeutically used for early intervention of neurodegeneration and NFT formation in NPC.

Lentivector-mediated RNAi efficiently downregulates expression of murine TNF-alpha gene in vitro and in vivo

In order to explore the role of TNF-alpha in Niemann-Pick type C (NPC) disease, lentiviral-delivered RNA interference (RNAi) was used to silence the expression of murine TNF-alpha gene in vitro and in npc mice. Interference efficiency of the lentivirus expressing TNF-alpha-siRNA, previously constructed with the concentration of 2 x 10(8) ifu/mL, was determined by RT-PCR and ELISA in BV-2 cells and astrocytes. At the same time, the constructed Lenti-TNF-alpha-siRNA was intracerebroventricularly infused into 4-week old npc mice for a 4-week period, and the mice were divided into 3 groups: Lenti-TNF-alpha-siRNA (n=6), control lentivirus (n=6), and NPC mice without any intervention (n=4). By using immunohistochemistry and real-time PCR, the down-regulation of the target genes was detected. The Lenti-TNF-alpha-siRNA downregulated the expression of murine TNF-alpha gene efficiently in vitro and the interference efficiency was 66.7%. Lentivirus could be expressed stably for long-term in the npc mice brain. Immunohistochemistry and real-time PCR revealed that, as compared with non-intervention group and Lenti-control group, Lenti-TNF-alpha-siRNA efficiently down-regulated the expression of murine TNF-alpha gene with the interference efficiency being 66.9%. TNF-alpha-siRNA down-regulated the expression of TNF-alpha gene in vitro and in vivo, which provided a potential tool for studying and treating neurodegenerative diseases and TNF-alpha-related diseases.

The role of glutamate transporters in neurodegenerative diseases and potential opportunities for intervention

Extracellular concentrations of the predominant excitatory neurotransmitter, glutamate, and related excitatory amino acids are maintained at relatively low levels to ensure an appropriate signal-to-noise ratio and to prevent excessive activation of glutamate receptors that can result in cell death. The latter phenomenon is known as 'excitotoxicity' and has been associated with a wide range of acute and chronic neurodegenerative disorders, as well as disorders that result in the loss of non-neural cells such as oligodendroglia in multiple sclerosis. Unfortunately clinical trials with glutamate receptor antagonists that would logically seem to prevent the effects of excessive receptor activation have been associated with untoward side effects or little clinical benefit. In the mammalian CNS, the extracellular concentrations of glutamate are controlled by two types of transporters; these include a family of Na(+)-dependent transporters and a cystine-glutamate exchange process, referred to as system X(c)(-). In this review, we will focus primarily on the Na(+)-dependent transporters. A brief introduction to glutamate as a neurotransmitter will be followed by an overview of the properties of these transporters, including a summary of the presumed physiologic mechanisms that regulate these transporters. Many studies have provided compelling evidence that impairing the function of these transporters can increase the sensitivity of tissue to deleterious effects of aberrant activation of glutamate receptors. Over the last decade, it has become clear that many neurodegenerative disorders are associated with a change in localization and/or expression of some of the subtypes of these transporters. This would suggest that therapies directed toward enhancing transporter expression might be beneficial. However, there is also evidence that glutamate transporters might increase the susceptibility of tissue to the consequences of insults that result in a collapse of the electrochemical gradients required for normal function such as stroke. In spite of the potential adverse effects of upregulation of glutamate transporters, there is recent evidence that upregulation of one of the glutamate transporters, GLT-1 (also called EAAT2), with beta-lactam antibiotics attenuates the damage observed in models of both acute and chronic neurodegenerative disorders. While it seems somewhat unlikely that antibiotics specifically target GLT-1 expression, these studies identify a potential strategy to limit excitotoxicity. If successful, this type of approach could have widespread utility given the large number of neurodegenerative diseases associated with decreases in transporter expression and excitotoxicity. However, given the massive effort directed at developing glutamate receptor agents during the 1990s and the relatively modest advances to date, one wonders if we will maintain the patience needed to carefully understand the glutamatergic system so that it will be successfully targeted in the future.

Receptor-mediated and bulk-phase endocytosis cause macrophage and cholesterol accumulation in Niemann-Pick C disease

These studies explored the roles of receptor-mediated and bulk-phase endocytosis as well as macrophage infiltration in the accumulation of cholesterol in the mouse with Niemann-Pick type C (NPC) disease. Uptake of LDL-cholesterol varied from 514 microg/day in the liver to zero in the central nervous system. In animals lacking LDL receptors, liver uptake remained about the same (411 microg/day), but more cholesterol was taken up in extrahepatic organs. This uptake was unaffected by the reductive methylation of LDL and consistent with bulk-phase endocytosis. All tissues accumulated cholesterol in mice lacking NPC1 function, but this accumulation was decreased in adrenal, unchanged in liver, and increased in organs like spleen and lung when LDL receptor function was also deleted. Over 56 days, the spleen and lung accumulated amounts of cholesterol greater than predicted, and these organs were heavily infiltrated with macrophages. This accumulation of both cholesterol and macrophages was increased by deleting LDL receptor function. These observations indicate that both receptor-mediated and bulk-phase endocytosis of lipoproteins, as well as macrophage infiltration, contribute to the cholesterol accumulation seen in NPC disease. These macrophages may also play a role in parenchymal cell death in this syndrome.

Niemann-Pick C disease: functional characterization of three NPC2 mutations and clinical and molecular update on patients with NPC2

Niemann-Pick type C disease (NPC), a neurovisceral disorder characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system, is due to mutations on either the NPC1 or the NPC2 genes. We report the diagnosis of six unrelated patients with NPC2, all with homozygous mutations. We further attempted functional characterization of the p.P120S, p.Q146X and IVS1 + 2 t>c mutations under native conditions. This was achieved by immunoblotting and immunocytofluorescence microscopy on cultured skin fibroblasts and in silico modeling. IVS1 + 2 t>c led to multiple transcripts, with only abnormally spliced cDNAs. Among the three NPC2 variants, only p.P120S led to detectable amounts of an immunoreactive protein. This protein showed a normal lysosomal localization. Our results suggest that the p.P120S mutation, the first naturally occurring missense mutation located in the cholesterol-binding Evolutionarily Constrained Regions D domain, results in reduced amounts of a protein capable to reach the lysosome, but unable to efficiently bind cholesterol. The patient had a juvenile neurological onset form of the disease. An update of the 22 families with mutations in the NPC2 gene, currently known to us, confirms the good genotype-phenotype correlations seen in this disorder. Characterization of more naturally occurring NPC2 mutations may help to dissect further the functional domains of the protein.

Niemann-Pick type C disease: subcellular location and functional characterization of NPC2 proteins with naturally occurring missense mutations

Niemann-Pick disease type C (NPC), a severe neurovisceral lysosomal disorder, is due to mutations on the NPC1 gene or, in a minority of families, the NPC2 gene. Few investigations have been devoted to the NPC2 protein, for which only 13 different disease-causing mutations (including three novel ones in this report) have been described. Among the currently known NPC2 mutant alleles, six resulted in a premature stop codon. Only five missense mutations, c.115G>A (p.V39M), c.140G>T (p.C47F), c.199T>C (p.S67P), c.278G>T (p.C93F), and (this report) c.295T>C (p.C99R) were identified. In the present study, we generated cDNA constructs harboring each of these missense mutations and, upon overexpression in human fibroblasts with a nonsense NPC2 mutation, characterized the mutated proteins by immunoblotting, immunocytofluorescence microscopy, and complementation. Mutation p.V39M, described in the homozygous state in two patients with an adult-onset neurological disease, resulted in the synthesis of apparently functional recombinant proteins correctly targeted to lysosomes. Although a mild functional impact could possibly be overlooked in our overexpression system, comparative studies with NPC1 mutants indicated that mild mutations might not necessarily affect localization of the protein or its quantity in the native state. Conversely, mutations p.C47F, p.C93R, p.C99R but also, less predictably, p.S67P, led to the synthesis of misfolded recombinant proteins that colocalized with an endoplasmic reticulum marker. The four latter proteins were normally secreted but were unable to correct cholesterol storage in NPC2(-/-) cells. Functional characterization of the mutant proteins showed an excellent genotype-phenotype correlation in the three cases for whom a clinical history was available.

Production and characterization of a monoclonal antibody against Niemann Pick type C protein

Niemann Pick type C is a severe, incurable disease caused, in the majority of cases, by mutations in the Niemann Pick type C protein 1 (NPC1). The pathology and biochemical changes associated with the disease have been extensively studied. However, the function of the protein is still unknown, and recent studies challenge the established concept that a defect in cholesterol and sphingolipids transport is the primary cause of this human lipidosis. Clearly defining the mechanisms by which defects in this protein lead to the disease phenotype will require further studies on the structure and function of this protein. Therefore, the development of a well-characterized monoclonal antibody (MAb) against this protein to facilitate such studies is an important goal. Here, we describe the production and characterization of such a MAb. The antibody is demonstrated to be highly specific and species cross-reactive. Function studies show that the antibody induces the NPC1 disease phenotype in cells, making it highly likely that the antibody blocks function of the NPC1 protein.

Degeneration of cholecystokinin-immunoreactive afferents to the VPL thalamus in a mouse model of Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a progressive neurological disorder of lipid metabolism. The Balb/C npc1 mutant strain is a genetically authentic murine model of NPC, which reproduce the clinical and histologic features of human NP-C. In the present study, we show that cholecystokinin (CCK)-immunoreactive fibers in the thalamic VPL nuclei, which are densely distributed in controls, degenerate in NPC mice. This degeneration is associated with the appearance of CCK-immunoreactive axonal spheroids containing characteristic intracellular inclusions of NP-C. These observations provide supportive evidence of the occurrence of dying-back axonopathy of neurons in the dorsal column nuclei in this mouse model.

Alteration of the glutamate and GABA transporters in the hippocampus of the Niemann-Pick disease, type C mouse using proteomic analysis

Niemann-Pick disease type C (NPC) is a fatal autosomal recessive cholesterol disorder characterized by severe progressive neurodegeneration. To unveil the mechanism of neurodegeneration, proteomic and morphological approaches were applied to the hippocampus in NPC -/- mouse. Two-DE was utilized to resolve the hippocampal protein expression profiles of 4- and 8-week-old NPC +/+ and -/- mice. Differentially expressed protein spots were identified by MALDI-TOF MS and database searching. At 4 weeks of age, there was no significant difference in protein profiles between NPC +/+ and -/- mice. However, at the age of 8 weeks, NPC +/+ and -/- mice showed marked difference in protein expressions. Among these, glutamate receptor 2 precursor was identified. The immunohistochemical study on neurotransporters showed that glial GABA transporter (GAT-3) increased in both 4- and 8-week-old NPC -/- mouse and glutamic acid decarboxylase (GAD-6) increased in 8-week-old NPC -/- mouse. Glial glutamate transporter, excitatory amino acids carrier-1 (EAAC1), decreased in 8-week-old NPC -/- mouse. In conclusion, our data may provide insight into the understanding of the basic mechanism through perturbation of protein networks and neurotransporter systems in a single gene knockout model of NPC disease.

Automated microscopy screening for compounds that partially revert cholesterol accumulation in Niemann-Pick C cells

Niemann-Pick disease type C (NPC) is an autosomal recessive genetic disorder manifested by abnormal accumulation of unesterified cholesterol and other lipids. We screened combinatorially synthesized chemical libraries to identify compounds that would partially revert cholesterol accumulation. Cultured CHO cells with NPC phenotypes (CT60 and CT43) were used for screening along with normal CHO cells as a control. We developed an automated microscopy assay based on imaging of filipin fluorescence for estimating cholesterol accumulation in lysosomal storage organelles. Our primary screen of 14,956 compounds identified 14 hit compounds that caused significant reduction in cellular cholesterol accumulation at 10 microM. We then screened a secondary library of 3,962 compounds selected based on chemical similarity to the initial hits and identified 7 compounds that demonstrated greater efficacy and lower toxicity than the original hits. These compounds are effective at concentrations of 123 nM to 3 microM in reducing the cholesterol accumulation in cells with a NPC1 phenotype.

Cholesterol accumulation and liver cell death in mice with Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease develops as a result of mutations in the NPC1 gene that encodes a protein involved in the net movement of unesterified cholesterol from the late endosomal/lysosomal compartment to the metabolically active pool of sterol in the cytosol of virtually every cell in the body. Although early publications emphasized the neurodegeneration occurring in children with this mutation, more recent clinical information suggests that serious liver disease also is an important part of this syndrome. These studies, therefore, were undertaken to characterize the liver dysfunction seen in mice with this same mutation. The NPC mouse develops significant hepatomegaly that reaches 8% of body weight at 5 to 6 weeks of age. This increase in liver size is associated with a linear increase in cholesterol content and with accumulation of amorphous cellular inclusions in both hepatocytes and macrophages. During the few weeks after birth, significant elevation of the plasma alkaline phosphatase level occurs, as also is seen in the human infant with this disease. At 4 to 5 weeks of age, plasma aminotransferase levels also rise abruptly. Histologically, at this time there is apoptosis, but no excess deposition of collagen or glycogen. mRNA expression is elevated for caspase 1, caspase 6, and several enzymes associated with sterol biosynthesis and bile acid formation. In conclusion, the NPC mouse has liver disease similar to that seen in the NPC infant and represents a relevant model for exploring the molecular events occurring in this form of liver disease.

Substance P immunoreactive cell reductions in cerebral cortex of Niemann-Pick disease type C mouse

Niemann-Pick disease type C (NPC) is characterized by progressive neurodegeneration and arises from mutations in the NPC1 gene. Cholesterol has received most attention in the pathogenesis of NPC, but normalizing lipid levels in humans or mouse does not prevent neurodegeneration. In NPC mouse, neuronal degeneration in the cerebellum is the most commonly detected change, and thus previous studies have tended to focus on the cerebellum, especially Purkinje cells. Although numerous peptides have been found in the mammalian central nervous system, little data on neurotransmitters in NPC are available, and information on neurotransmitter system abnormalities could explain the complex and characteristic deficits of NPC. Thus, we performed an immunohistochemical study on NPC mouse cortices to compare cell numbers exhibiting vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and substance P (SP) immunoreactivity. In terms of VIP and NPY-immunoreactive (ir) cell numbers in the cerebral cortex, SP-ir cells were significantly reduced by about 90% in NPC (-/-) versus NPC (+/+) mouse, and were also mildly decreased in frontal and parietal NPC (+/-) versus NPC (+/+) mouse cortex. This study demonstrates for the first time, reduced number of SP-ir cells in the NPC mouse cortex.

Recent advances in experimental modeling of the assembly of tau filaments

Intracellular assembly of microtubule-associated protein tau into filamentous inclusions is central to Alzheimer's disease and related disorders collectively known as tauopathies. Although tau mutations, posttranslational modifications and degradations have been the focus of investigations, the mechanism of tau fibrillogenesis in vivo still remains elusive. Different strategies have been undertaken to generate animal and cellular models for tauopathies. Some are used to study the molecular events leading to the assembly and accumulation of tau filaments, and others to identify potential therapeutic agents that are capable of impeding tauopathy. This review highlights the latest developments in new models and how their utility improves our understanding of the sequence of events leading to human tauopathy.

News and views in Histochemistry and Cell Biology

Advances in histochemical methodology and ingenious applications of novel and improved methods continue to confirm the standing of morphological means and approaches in research efforts, and contribute significantly to increasing our knowledge about structures and functions in all areas of the life sciences from cell biology to pathology. Reports published during recent months documenting this progress are summarized in the present review.

Axon-dominant localization of cell-surface cholesterol in cultured hippocampal neurons and its disappearance in Niemann-Pick type C model cells

There is growing evidence showing the important role of cholesterol in maintaining neuronal function. In particular, much attention has been paid to the role of the cholesterol-rich microdomains called lipid rafts. However, the cholesterol distribution on neurons is not clear. Here, we investigated localization of cholesterol in cultured rat hippocampal neurons, using filipin and a novel cholesterol-binding reagent BCtheta. In our culture system, BCtheta detects only cell-surface cholesterol, whereas filipin stains both intracellular and cell-surface cholesterol. BCtheta staining appeared visible in a maturation-dependent manner and showed axon-dominant distribution of cell-surface cholesterol in fully matured neurons. A part of this cholesterol on axons was resistant to detergents at 4 degrees C, and thus might be involved in lipid rafts. Interestingly, Niemann-Pick type C model neurons induced by class 2 amphiphiles lost the cell-surface but not the intracellular cholesterol staining. Niemann-Pick type C disease is caused by the disruption of intracellular cholesterol transport and is known to induce neurodegeneration in brains accompanied by formation of neurofibrillary tangles. Our observations suggest the important role of cell-surface cholesterol in maintaining a functional axonal membrane and indicate that the observed defect in axonal surface cholesterol might lead to neurodegeneration.

Niemann-Pick type C disease: importance of N-glycosylation sites for function and cellular location of the NPC2 protein

Niemann-Pick disease type C (NPC), a neurovisceral disorder characterized by accumulation of cholesterol and glycolipids in the lysosomal/late endosomal system, is due to mutations on either the NPC1 or the NPC2 genes. Although NPC1 and NPC2 proteins appear essential for proper cellular cholesterol trafficking, their precise functions and relationship have remained elusive. Mutation identification in NPC2 patients did not provide insights into structure-function relationships, but recent studies brought important information on the cholesterol-binding site of the NPC2 protein. The present work was focused on localization and N-glycosylation of NPC2, considering that glycosylation is often essential for targeting, stability and biological function of proteins. Using immunocytofluorescence in cultured human fibroblasts, we found that the native NPC2 protein is essentially lysosomal, at variance with the late endosomal location of NPC1. Expression of cDNA mutants affecting each of the three potential NPC2 N-glycosylation sites in NPC2-/- fibroblasts showed that only two sites are used. The intracellular human NPC2 protein occurred as two N-glycosylated forms, with either one single oligosaccharide chain attached to Asn 58 or two oligosaccharides attached to Asn 58 and 135. The oligosaccharidic chains were of the hybrid and/or high mannose type, with no complex chains. Further studies on the cellular location of Asn 58 and Asn 135 mutant proteins and their respective effect on restoration of normal cholesterol traficking in NPC2-/- cells led to the conclusion that only the oligosaccharide chain carried by Asn 58 is responsible for proper targeting of NPC2 to lysosomes, and is crucial for NPC2 function.

Binding between the Niemann-Pick C1 protein and a photoactivatable cholesterol analog requires a functional sterol-sensing domain

Niemann-Pick type C (NPC) 1 protein plays important roles in moving cholesterol and other lipids out of late endosomes by means of vesicular trafficking, but it is not known whether NPC1 directly interacts with cholesterol. We performed photoaffinity labeling of intact cells expressing fluorescent protein (FP)-tagged NPC1 by using [(3)H]7,7-azocholestanol ([(3)H]AC). After immunoprecipitation, (3)H-labeled NPC1-GFP appeared as a single band. Including excess unlabeled sterol to the labeling reaction significantly diminished the labeling. Altering the NPC1 sterol-sensing domain (SSD) with loss-of-function mutations (P692S and Y635C) severely reduced the extent of labeling. To further demonstrate the specificity of labeling, we show that NPC2, a late endosomal/lysosomal protein that binds to cholesterol with high affinity, is labeled, whereas mutant NPC2 proteins inactive in binding cholesterol are not. Vamp7, an abundant late endosomal membrane protein without an SSD but with one transmembrane domain, cannot be labeled. Binding between [(3)H]AC and NPC1 does not require NPC2. Treating cells with either U-18666A, a compound that creates an NPC-like phenotype, or with bafilomycin A1, a compound that raises late endosomal pH, has no effect on labeling of NPC1-YFP, suggesting that both drugs affect processes other than NPC1 binding to cholesterol. We also developed a procedure to label the NPC1-YFP by [(3)H]AC in vitro and showed that cholesterol is more effective in protection against labeling than its analogs epicholesterol or 5-alpha-cholestan. Overall, the results demonstrate that there is direct binding between NPC1 and azocholestanol; the binding does not require NPC2 but requires a functional SSD within NPC1.

Reduced sensitivity of Niemann-Pick C1-deficient cells to theta-toxin (perfringolysin O): sequestration of toxin to raft-enriched membrane vesicles

Theta-toxin (perfringolysin O) binds to cell surface cholesterol and forms oligomeric pores that cause membrane damage. Both in cytotoxicity and cell survival assays, a mutant Chinese hamster ovary cell line NPC1(-) that lacked Niemann-Pick C1 showed reduced sensitivity to theta-toxin, compared with wild-type (wt) cells. BCtheta is a derivative of theta-toxin that retains cholesterol-binding activity but lacks cytotoxicity. Confocal and electron microscopy revealed the presence of multiple vesicles which bound BCtheta, both on the cell surface and in the extracellular space of these cells. BCtheta binding to raft microdomains was verified by its resistance to 1% Triton X-100 at 4 degrees C and recovery of bound BCtheta in floating low-density fractions on sucrose density gradient fractionation. BCtheta-labeled vesicles were abolished when NPC1(-) cells were depleted of lipoproteins and also when treated with a Rho-associated kinase inhibitor Y-27632. In addition, similar vesicles were observed in wt cells treated with progesterone. In parallel with these results, theta-toxin sensitivity of NPC1(-) cells was increased when cells were depleted of lipoproteins or treated with Y-27632, whereas that of wt cells was decreased by progesterone. Our findings suggest that sequestration of toxin to raft-enriched cell surface vesicles may underlie reduced sensitivity of NPC1-deficient cells to theta-toxin.