Progressive neuronal loss in the ventral posterior lateral and medial nuclei of thalamus in Niemann-Pick disease type C mouse brain

Early onset ataxia with comorbid myoclonus and epilepsy: A disease spectrum with shared molecular pathways and cortico-thalamo-cerebellar network involvement

OBJECTIVES

Early onset ataxia (EOA) concerns a heterogeneous disease group, often presenting with other comorbid phenotypes such as myoclonus and epilepsy. Due to genetic and phenotypic heterogeneity, it can be difficult to identify the underlying gene defect from the clinical symptoms. The pathological mechanisms underlying comorbid EOA phenotypes remain largely unknown. The aim of this study is to investigate the key pathological mechanisms in EOA with myoclonus and/or epilepsy.

METHODS

For 154 EOA-genes we investigated (1) the associated phenotype (2) reported anatomical neuroimaging abnormalities, and (3) functionally enriched biological pathways through in silico analysis. We assessed the validity of our in silico results by outcome comparison to a clinical EOA-cohort (80 patients, 31 genes).

RESULTS

EOA associated gene mutations cause a spectrum of disorders, including myoclonic and epileptic phenotypes. Cerebellar imaging abnormalities were observed in 73-86% (cohort and in silico respectively) of EOA-genes independently of phenotypic comorbidity. EOA phenotypes with comorbid myoclonus and myoclonus/epilepsy were specifically associated with abnormalities in the cerebello-thalamo-cortical network. EOA, myoclonus and epilepsy genes shared enriched pathways involved in neurotransmission and neurodevelopment both in the in silico and clinical genes. EOA gene subgroups with myoclonus and epilepsy showed specific enrichment for lysosomal and lipid processes.

CONCLUSIONS

The investigated EOA phenotypes revealed predominantly cerebellar abnormalities, with thalamo-cortical abnormalities in the mixed phenotypes, suggesting anatomical network involvement in EOA pathogenesis. The studied phenotypes exhibit a shared biomolecular pathogenesis, with some specific phenotype-dependent pathways. Mutations in EOA, epilepsy and myoclonus associated genes can all cause heterogeneous ataxia phenotypes, which supports exome sequencing with a movement disorder panel over conventional single gene panel testing in the clinical setting.

The Cerebellum in Niemann-Pick C1 Disease: Mouse Versus Man

Selective neuronal vulnerability is common to most degenerative disorders, including Niemann-Pick C (NPC), a rare genetic disease with altered intracellular trafficking of cholesterol. Purkinje cell dysfunction and loss are responsible for cerebellar ataxia, which is among the prevailing neurological signs of the NPC disease. In this review, we focus on some questions that are still unresolved. First, we frame the cerebellar vulnerability in the context of the extended postnatal time length by which the development of this structure is completed in mammals. In line with this thought, the much later development of cerebellar symptoms in humans is due to the later development and/or maturation of the cerebellum. Hence, the occurrence of developmental events under a protracted condition of defective intracellular cholesterol mobilization hits the functional maturation of the various cell types generating the ground of increased vulnerability. This is particularly consistent with the high cholesterol demand required for cell proliferation, migration, differentiation, and synapse formation/remodeling. Other major questions we address are why the progression of Purkinje cells loss is always from the anterior to the posterior lobes and why cerebellar defects persist in the mouse model even when genetic manipulations can lead to nearly normal survival.

Organ Weights in NPC1 Mutant Mice Partly Normalized by Various Pharmacological Treatment Approaches

Niemann-Pick Type C1 (NPC1, MIM 257220) is a rare, progressive, lethal, inherited autosomal-recessive endolysosomal storage disease caused by mutations in the NPC1 leading to intracellular lipid storage. We analyzed mostly not jet known alterations of the weights of 14 different organs in the BALB/cNctr-Npc1^m1N/-J Jackson Npc1 mice in female and male Npc1^+/+ and Npc1^-/- mice under various treatment strategies. Mice were treated with (i) no therapy, (ii) vehicle injection, (iii) a combination of miglustat, allopregnanolone, and 2-hydroxypropyl-ß-cyclodextrin (HPßCD), (iv) miglustat, and (v) HPßCD alone starting at P7 and repeated weekly throughout life. The 12 respective male and female wild-type mice groups were evaluated in parallel. In total, 351 mice (176 Npc1^+/+, 175 Npc1^-/-) were dissected at P65. In both sexes, the body weights of None and Sham Npc1^-/- mice were lower than those of respective Npc1^+/+ mice. The influence of the Npc1 mutation and/or sex on the weights of various organs, however, differed considerably. In males, Npc1^+/+ and Npc1^-/- mice had comparable absolute weights of lungs, spleen, and adrenal glands. In Npc1^-/- mice, smaller weights of hearts, livers, kidneys, testes, vesicular, and scent glands were found. In female Npc1^-/- mice, ovaries, and uteri were significantly smaller. In Npc1^-/- mice, relative organ weights, i.e., normalized with body weights, were sex-specifically altered to different extents by the different therapies. The combination of miglustat, allopregnanolone, and the sterol chelator HPßCD partly normalized the weights of more organs than miglustat or HPßCD mono-therapies.

Cytokine profile and cholesterol levels in patients with Niemann-Pick type C disease presenting neurological symptoms: The in vivo effect of miglustat and the in vitro effect of N-acetylcysteine and Coenzyme Q10

Niemann Pick type C is an inborn error of metabolism (IEM), classified as a lysosomal storage disease (LSD) caused by a dysfunction in NPC transport protein, that leads to intracellular accumulation of non-esterified cholesterol and other lipids. Clinical manifestations are ample, with visceral and neurological symptoms. Miglustat, a molecule that reversibly inhibits glucosylceramide synthase is used as treatment for this disorder. Studies demonstrated the influence of oxidative stress and inflammation in IEM, as well in animal model of NP-C disease. Nonetheless, literature lacks data on patients, so our work aimed to investigate if there is influence of chronic inflammation in the pathophysiology of NP-C disease, and the effect of miglustat, N-acetylcysteine (NAC) and Coenzyme Q10 (CoQ10). We evaluated the plasmatic cytokines in NPC patients at diagnosis and during the treatment with miglustat. Additionally, we performed an in vitro study with antioxidants NAC (1 mM and 2.5 mM) and CoQ10 (5 μM and 10 μM), where we could verify its effect on inflammatory parameters, as well as in cholesterol accumulation. Our results showed that NP-C patients have higher plasmatic levels of pro and anti-inflammatory cytokines (IL-6, IL-8, and IL-10) at diagnosis and the treatment with miglustat was able to restore it. In vitro study showed that treatment with antioxidants in higher concentrations significantly decrease cholesterol accumulation, and NAC at 2.5 mM normalized the level of pro-inflammatory cytokines. Although the mechanism is not completely clear, it can be related to restoration in lipid traffic and decrease in oxidative stress caused by antioxidants.

Induced neural stem cells from human patient-derived fibroblasts attenuate neurodegeneration in Niemann-Pick type C mice

Background

Niemann-Pick disease type C (NPC) is caused by the mutation of NPC genes, which leads to the abnormal accumulation of unesterified cholesterol and glycolipids in lysosomes. This autosomal recessive disease is characterized by liver dysfunction, hepatosplenomegaly, and progressive neurodegeneration. Recently, the application of induced neural stem cells (iNSCs), converted from fibroblasts using specific transcription factors, to repair degenerated lesions has been considered a novel therapy.

Objectives

The therapeutic effects on NPC by human iNSCs generated by our research group have not yet been studied in vivo; in this study, we investigate those effects.

Methods

We used an NPC mouse model to efficiently evaluate the therapeutic effect of iNSCs, because neurodegeneration progress is rapid in NPC. In addition, application of human iNSCs from NPC patient-derived fibroblasts in an NPC model in vivo can give insight into the clinical usefulness of iNSC treatment. The iNSCs, generated from NPC patient-derived fibroblasts using the SOX2 and HMGA2 reprogramming factors, were transplanted by intracerebral injection into NPC mice.

Results

Transplantation of iNSCs showed positive results in survival and body weight change in vivo. Additionally, iNSC-treated mice showed improved learning and memory in behavior test results. Furthermore, through magnetic resonance imaging and histopathological assessments, we observed delayed neurodegeneration in NPC mouse brains.

Conclusions

iNSCs converted from patient-derived fibroblasts can become another choice of treatment for neurodegenerative diseases such as NPC.

Rodent somatosensory thalamocortical circuitry: Neurons, synapses, and connectivity

As our understanding of the thalamocortical system deepens, the questions we face become more complex. Their investigation requires the adoption of novel experimental approaches complemented with increasingly sophisticated computational modeling. In this review, we take stock of current data and knowledge about the circuitry of the somatosensory thalamocortical loop in rodents, discussing common principles across modalities and species whenever appropriate. We review the different levels of organization, including the cells, synapses, neuroanatomy, and network connectivity. We provide a complete overview of this system that should be accessible for newcomers to this field while nevertheless being comprehensive enough to serve as a reference for seasoned neuroscientists and computational modelers studying the thalamocortical system. We further highlight key gaps in data and knowledge that constitute pressing targets for future experimental work. Filling these gaps would provide invaluable information for systematically unveiling how this system supports behavioral and cognitive processes.

Psychiatric and Cognitive Symptoms Associated with Niemann-Pick Type C Disease: Neurobiology and Management

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder that presents with a spectrum of clinical manifestations from infancy and childhood or in early or mid-adulthood. Progressive neurological symptoms including ataxia, dystonia and vertical gaze palsy are a hallmark of the disease, and psychiatric symptoms such as psychosis and mood disorders are common. These latter symptoms often present early in the course of NPC and thus these patients are often diagnosed with a major psychotic or affective disorder before neurological and cognitive signs present and the diagnosis is revised. The commonalities and characteristics of psychotic symptoms in both NPC and schizophrenia may share neuronal pathways and mechanisms and provide potential targets for research in both disorders. The neurobiology of NPC and its relationship to the pattern of neuropsychiatric and cognitive symptoms is described in this review. A number of neurobiological models are proposed as mechanisms by which NPC causes psychiatric and cognitive symptoms, informed from models proposed in schizophrenia and other metabolic disorders. There are a number of symptomatic and illness-modifying treatments for NPC currently available. The current evidence is discussed; focussing on two medications which have shown promise, miglustat and hydroxypropyl-β-cyclodextrin.

Cell Densities in the Mouse Brain: A Systematic Review

The mouse brain is the most extensively studied brain of all species. We performed an exhaustive review of the literature to establish our current state of knowledge on cell numbers in mouse brain regions, arguably the most fundamental property to measure when attempting to understand a brain. The synthesized information, collected in one place, can be used by both theorists and experimentalists. Although for commonly-studied regions cell densities could be obtained for principal cell types, overall we know very little about how many cells are present in most brain regions and even less about cell-type specific densities. There is also substantial variation in cell density values obtained from different sources. This suggests that we need a new approach to obtain cell density datasets for the mouse brain.

Reversal of Pathologic Lipid Accumulation in NPC1-Deficient Neurons by Drug-Promoted Release of LAMP1-Coated Lamellar Inclusions

Aging and pathologic conditions cause intracellular aggregation of macromolecules and the dysfunction and degeneration of neurons, but the mechanisms are largely unknown. Prime examples are lysosomal storage disorders such as Niemann-Pick type C (NPC) disease, where defects in the endosomal-lysosomal protein NPC1 or NPC2 cause intracellular accumulation of unesterified cholesterol and other lipids leading to neurodegeneration and fatal neurovisceral symptoms. Here, we investigated the impact of NPC1 deficiency on rodent neurons using pharmacologic and genetic models of the disease. Improved ultrastructural detection of lipids and correlative light and electron microscopy identified lamellar inclusions as the subcellular site of cholesterol accumulation in neurons with impaired NPC1 activity. Immunogold labeling combined with transmission electron microscopy revealed the presence of CD63 on internal lamellae and of LAMP1 on the membrane surrounding the inclusions, indicating their origins from intraluminal vesicles of late endosomes and of a lysosomal compartment, respectively. Lamellar inclusions contained cell-intrinsic cholesterol and surface-labeled GM1, indicating the incorporation of plasma membrane components. Scanning electron microscopy revealed that the therapeutic drug candidate β-cyclodextrin induces the subplasmalemmal location of lamellar inclusions and their subsequent release to the extracellular space. In parallel, β-cyclodextrin mediated the NPC1-independent redistribution of cholesterol within neurons and thereby abolished a deleterious cycle of enhanced cholesterol synthesis and its intracellular accumulation, which was indicated by neuron-specific transcript analysis. Our study provides new mechanistic insight into the pathologic aggregation of macromolecules in neurons and suggests exocytosis as cellular target for its therapeutic reversal.

SIGNIFICANCE STATEMENT

Many neurodegenerative diseases involve pathologic accumulation of molecules within neurons, but the subcellular location and the cellular impact are often unknown and therapeutic approaches lacking. We investigated these questions in the lysosomal storage disorder Niemann-Pick type C (NPC), where a defect in intracellular cholesterol transport causes loss of neurons and fatal neurovisceral symptoms. Here, we identify lamellar inclusions as the subcellular site of lipid accumulation in neurons, we uncover a vicious cycle of cholesterol synthesis and accretion, which may cause gradual neurodegeneration, and we reveal how β-cyclodextrin, a potential therapeutic drug, reverts these changes. Our study provides new mechanistic insight in NPC disease and uncovers new targets for therapeutic approaches.

Quantitative magnetic resonance imaging of brain atrophy in a mouse model of Niemann-Pick type C disease

In vivo magnetic resonance imaging (MRI) was used to investigate regional and global brain atrophy in the neurodegenerative Niemann Pick Type C1 (NPC1) disease mouse model. Imaging experiments were conducted with the most commonly studied mouse model of NPC1 disease at early and late disease states. High-resolution in vivo images were acquired at early and late stages of the disease and analyzed with atlas-based registration to obtain measurements of twenty brain region volumes. A two-way ANOVA analysis indicated eighteen of these regions were different due to genotype and thirteen showed a significant interaction with age and genotype. The ability to measure in vivo neurodegeneration evidenced by brain atrophy adds to the ability to monitor disease progression and treatment response in the mouse model.

Severe demyelination in a patient with a late infantile form of Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is a cholesterol storage disease caused by defective cellular cholesterol transportation. The onset and progression of NPC are variable, and autopsy findings have mainly been reported for the adult and juvenile forms of this disease. Here we report the clinical and pathological findings from a 9-year-old female patient with the late infantile form of NPC due to NPC1 gene mutation. She had notable splenomegaly at 4 months of age. She lost the ability to speak at 18 months of age. She learned to walk, but often fell and could no longer walk after 30 months. At 3 years of age, she was diagnosed with NPC. Sequence analysis of the NPC1 gene revealed compound heterozygous mutation of T2108C (F703S) and C2348G (S813X) (both novel). Thereafter, the patient suffered repeated respiratory infections and died of respiratory failure at 9 years of age. Pathological findings included cerebral atrophy (particularly of white matter), severe demyelination, and the loss of neurons from the cerebrum and from the nuclei of the brain stem. Remnant neuronal cells and microglia in the cerebrum, cerebellum, and brain stem had become swollen and foamy. Neurons of the hippocampal CA1 and Purkinje cells were relatively spared, and senile plaques and axonal spheroids were not present. Foamy cells were also observed in other organs, especially the spleen and bone marrow. The F703S mutation in this patient was localized in a sterol-sensing domain (SSD). Severe neurological phenotypes have been previously reported in patients with missense mutations in an SSD. It is considered that the combination of a nonsense mutation and missense mutation in an SSD was responsible for the severe neurological phenotype of our present patient. While pathological findings of adult/juvenile forms of NPC have included swollen neurons and glia, neuronal cell loss, and NFTs, demyelination may be a predominant finding in the infantile form of NPC.

Increased Regenerative Capacity of the Olfactory Epithelium in Niemann-Pick Disease Type C1

Niemann–Pick disease type C1 (NPC1) is a fatal neurovisceral lysosomal lipid storage disorder. The mutation of the NPC1 protein affects the homeostasis and transport of cholesterol and glycosphingolipids from late endosomes/lysosomes to the endoplasmic reticulum resulting in progressive neurodegeneration. Since olfactory impairment is one of the earliest symptoms in many neurodegenerative disorders, we focused on alterations of the olfactory epithelium in an NPC1 mouse model. Previous findings revealed severe morphological and immunohistochemical alterations in the olfactory system of NPC1^−/− mutant mice compared with healthy controls (NPC1^+/+). Based on immunohistochemical evaluation of the olfactory epithelium, we analyzed the impact of neurodegeneration in the olfactory epithelium of NPC1^−/− mice and observed considerable loss of mature olfactory receptor neurons as well as an increased number of proliferating and apoptotic cells. Additionally, after administration of two different therapy approaches using either a combination of miglustat, 2-hydroxypropyl-β-cyclodextrin (HPβCD) and allopregnanolone or a monotherapy with HPβCD, we recorded a remarkable reduction of morphological damages in NPC1^−/− mice and an up to four-fold increase of proliferating cells within the olfactory epithelium. Numbers of mature olfactory receptor neurons doubled after both therapy approaches. Interestingly, we also observed therapy-induced alterations in treated NPC1^+/+ controls. Thus, olfactory testing may provide useful information to monitor pharmacologic treatment approaches in human NPC1.

Neurological Dysfunction in Early Maturity of a Model for Niemann-Pick C1 Carrier Status

Autosomal recessive inheritance of NPC1 with loss-of-function mutations underlies Niemann-Pick disease, type C1 (NP-C1), a lysosomal storage disorder with progressive neurodegeneration. It is uncertain from limited biochemical studies and patient case reports whether NPC1 haploinsufficiency can cause a partial NP-C1 phenotype in carriers. In the present study, we examined this possibility in heterozygotes of a natural loss-of-function mutant Npc1 mouse model. We found partial motor dysfunction and increased anxiety-like behavior in Npc1 (+/-) mice by 9 weeks of age. Relative to Npc1 (+/+) mice, Npc1 (+/-) mice failed to show neurodevelopmental improvements in motor coordination and balance on an accelerating Rotarod. In the open-field test, Npc1 (+/-) mice showed an intermediate phenotype in spontaneous locomotor activity compared with Npc1 (+/+) and Npc1 (-/-) mice, as well as decreased center tendency. Together with increased stride length under anxiogenic conditions on the DigiGait treadmill, these findings are consistent with heightened anxiety. Our findings indicate that pathogenic NPC1 allele carriers, who represent about 0.66 % of humans, could be vulnerable to motor and anxiety disorders.

Stimulation of adenosine A2A receptors reduces intracellular cholesterol accumulation and rescues mitochondrial abnormalities in human neural cell models of Niemann-Pick C1

Niemann Pick C 1 (NPC1) disease is an incurable, devastating lysosomal-lipid storage disorder characterized by hepatosplenomegaly, progressive neurological impairment and early death. Current treatments are very limited and the research of new therapeutic targets is thus mandatory. We recently showed that the stimulation of adenosine A2A receptors (A2ARs) rescues the abnormal phenotype of fibroblasts from NPC1 patients suggesting that A2AR agonists could represent a therapeutic option for this disease. However, since all NPC1 patients develop severe neurological symptoms which can be ascribed to the complex pathology occurring in both neurons and oligodendrocytes, in the present paper we tested the effects of the A2AR agonist CGS21680 in human neuronal and oligodendroglial NPC1 cell lines (i.e. neuroblastoma SH-SY5Y and oligodendroglial MO3.13 transiently transfected with NPC1 small interfering RNA). The down-regulation of the NPC1 protein effectively resulted in intracellular cholesterol accumulation and altered mitochondrial membrane potential. Both effects were significantly attenuated by CGS21680 (500 nM). The protective effects of CGS were prevented by the selective A2AR antagonist ZM241385 (500 nM). The involvement of calcium modulation was demonstrated by the ability of Bapta-AM (5-7 μM) in reverting the effect of CGS. The A2A-dependent activity was prevented by the PKA-inhibitor KT5720, thus showing the involvement of the cAMP/PKA signaling. These findings provide a clear in vitro proof of concept that A2AR agonists are promising potential drugs for NPC disease.

The pleiotropic roles of sphingolipid signaling in autophagy

The autophagic process involves encompassing damaged proteins and organelles within double- or multi-membraned structures and delivering these molecules to the lytic compartments of vacuoles. Sphingolipids (SLs), which are ubiquitous membrane lipids in eukaryotes, participate in the generation of various membrane structures, including rafts, caveolae, and cytosolic vesicles. SLs are a complex family of molecules that have a growing number of members, including ceramide, sphingosine-1-phosphate, and dihydroceramide, which have been associated with the essential cellular process of autophagy. This review highlights recent studies focusing on the regulation and function of SL-associated autophagy and its role in cell fate, diseases, and therapeutic interventions.

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.

Altered transition metal homeostasis in Niemann-Pick disease, type C1

The loss of NPC1 protein function is the predominant cause of Niemann-Pick type C1 disease (NP-C1), a systemic and neurodegenerative disorder characterized by late-endosomal/lysosomal accumulation of cholesterol and other lipids. Limited evidence from post-mortem human tissues, an Npc1(-/-) mouse model, and cell culture studies also suggest failure of metal homeostasis in NP-C1. To investigate these findings, we performed a comprehensive transition metal analysis of cerebrospinal fluid (CSF), plasma and tissue samples from human NP-C1 patients and an Npc1(-/-) mouse model. NPC1 deficiency in the Npc1(-/-) mouse model resulted in a perturbation of transition metal homeostasis in the plasma and key organs (brain, liver, spleen, heart, lungs, and kidneys). Analysis of human patient CSF, plasma and post-mortem brain tissues also indicated disrupted metal homeostasis. There was a disparity in the direction of metal changes between the human and the Npc1(-/-) mouse samples, which may reflect species-specific metal metabolism. Nevertheless, common to both species is brain zinc accumulation. Furthermore, treatment with the glucosylceramide synthase inhibitor miglustat, the only drug shown in a controlled clinical trial to have some efficacy for NP-C1, did not correct the alterations in CSF and plasma transition metal and ceruloplasmin (CP) metabolism in NP-C1 patients. These findings highlight the importance of NPC1 function in metal homeostasis, and indicate that metal-targeting therapy may be of value as a treatment for NP-C.

The autophagic defect in Niemann-Pick disease type C neurons differs from somatic cells and reduces neuronal viability

Niemann-Pick disease type C (NPC) is a fatal, progressive neurovisceral disorder. Several studies report that the autophagic flux is disturbed in NPC1-deficient (NPC1-/-) cells. Since it has been suggested that the autophagic defect may contribute to the neurodegeneration, we used cell cultures of NPC1-deficient and NPC1-wildtype neurons to investigate whether the disturbance influences neuronal survival. We found a genotype-dependent difference in survival, when autophagy is induced during culturing. NPC1-deficient neurons are more sensitive to rapamycin treatment and starvation than wildtype neurons. The subsequent search for defects in regulatory components of the autophagic pathway and the autophagic flux brought up results which differ from previous reports on somatic cells in one essential aspect: we exclude that an enhanced formation of autophagosomes contributes to the imbalanced autophagic flux in NPC1 deficient neurons. We found that solely the clearance of autophagosomes is delayed in these cells, which leads to an accumulation of autophagic vacuoles within the lysosomal compartment. Lowering the abnormal lipid load of the acidic organelles with cyclodextrin is sufficient to correct the autophagic flux and prevents premature death of NPC1-/- neurons under autophagic stress. From our results, we conclude that a pharmacological intervention in the neuropathology of NPC-disease should focus on the restoration of the lysosomal degradation capacity of cells.

Olfactory deficits in Niemann-Pick type C1 (NPC1) disease

Background

Niemann-Pick type C disease (NPC) is a rare autosomal recessive lipid storage disease characterized by progressive neurodegeneration. As only a few studies have been conducted on the impact of NPC on sensory systems, we used a mutant mouse model (NPC1^−/−) to examine the effects of this disorder to morphologically distinct regions of the olfactory system, namely the olfactory epithelium (OE) and olfactory bulb (OB).

Methodology/Principal findings

For structural and functional analysis immunohistochemistry, electron microscopy, western blotting, and electrophysiology have been applied. For histochemistry and western blotting, we used antibodies against a series of neuronal and glia marker proteins, as well as macrophage markers.

NPC1^−/− animals present myelin-like lysosomal deposits in virtually all types of cells of the peripheral and central olfactory system. Especially supporting cells of the OE and central glia cells are affected, resulting in pronounced astrocytosis and microgliosis in the OB and other olfactory cortices. Up-regulation of Galectin-3, Cathepsin D and GFAP in the cortical layers of the OB underlines the critical role and location of the OB as a possible entrance gate for noxious substances. Unmyelinated olfactory afferents of the lamina propria seem less affected than ensheathing cells. Supporting the structural findings, electro-olfactometry of the olfactory mucosa suggests that NPC1^−/− animals exhibit olfactory and trigeminal deficits.

Conclusions/Significance

Our data demonstrate a pronounced neurodegeneration and glia activation in the olfactory system of NPC1^−/−, which is accompanied by sensory deficits.

Subcortical volumetric reductions in adult Niemann-Pick disease type C: a cross-sectional study

BACKGROUND AND PURPOSE

Voxel-based analysis has suggested that deep gray matter rather than cortical regions is initially affected in adult Niemann-Pick type C. We sought to examine a range of deep gray matter structures in adults with NPC and relate these to clinical variables.

MATERIALS AND METHODS

Ten adult patients with NPC (18-49 years of age) were compared with 27 age- and sex-matched controls, and subcortical structures were automatically segmented from normalized T1-weighted MR images. Absolute volumes (in cubic millimeters) were generated for a range of deep gray matter structures and were compared between groups and correlated with illness variables.

RESULTS

Most structures were smaller in patients with NPC compared with controls. The thalamus, hippocampus, and striatum showed the greatest and most significant reductions, and left hippocampal volume correlated with symptom score and cognition. Vertex analysis of the thalamus, hippocampus, and caudate implicated regions involved in memory, executive function, and motor control.

CONCLUSIONS

Thalamic and hippocampal reductions may underpin the memory and executive deficits seen in adult NPC. Volume losses in other subcortical regions may also be involved in the characteristic range of motor, psychiatric, and cognitive deficits seen in the disease.

Early glial activation, synaptic changes and axonal pathology in the thalamocortical system of Niemann-Pick type C1 mice

Niemann–Pick disease type C (NPC) is an inherited lysosomal storage disease characterised by accumulation of cholesterol and glycosphingolipids. NPC patients suffer a progressive neurodegenerative phenotype presenting with motor dysfunction, mental retardation and cognitive decline. To examine the onset and progression of neuropathological insults in NPC we have systematically examined the CNS of a mouse model of NPC1 (Npc1^−/− mice) at different stages of the disease course. This revealed a specific spatial and temporal pattern of neuropathology in Npc1^−/− mice, highlighting that sensory thalamic pathways are particularly vulnerable to loss of NPC1 resulting in neurodegeneration in Npc1^−/− mice. Examination of markers of astrocytosis and microglial activation revealed a particularly pronounced reactive gliosis in the thalamus early in the disease, which subsequently also occurred in interconnected cortical laminae at later ages. Our examination of the precise staging of events demonstrate that the relationship between glia and neurons varies between brain regions in Npc1^−/− mice, suggesting that the cues causing glial reactivity may differ between brain regions. In addition, aggregations of pre-synaptic markers are apparent in white matter tracts and the thalamus and are likely to be formed within axonal spheroids. Our data provide a new perspective, revealing a number of events that occur prior to and alongside neuron loss and highlighting that these occur in a pathway dependent manner.

Adeno-associated virus-mediated expression of β-hexosaminidase prevents neuronal loss in the Sandhoff mouse brain

Sandhoff disease, a GM2 gangliosidosis caused by a deficiency in β-hexosaminidase, is characterized by progressive neurodegeneration. Although loss of neurons in association with lysosomal storage of glycosphingolipids occurs in patients with this disease, the molecular pathways that lead to the accompanying neurological defects are unclear. Using an authentic murine model of GM2 gangliosidosis, we examined the pattern of neuronal loss in the central nervous system and investigated the effects of gene transfer using recombinant adeno-associated viral vectors expressing β-hexosaminidase subunits (rAAV2/1-Hex). In 4-month-old Sandhoff mice with neurological deficits, cells staining positively for the apoptotic signature in the TUNEL reaction were found in the ventroposterior medial and ventroposterior lateral (VPM/VPL) nuclei of the thalamus. There was progressive loss of neuronal density in this region with age. Comparable loss of neuronal density was identified in the lateral vestibular nucleus of the brainstem and a small but statistically significant loss was present in the ventral spinal cord. Loss of neurons was not detected in other regions that were analysed. Administration of rAAV2/1-Hex into the brain of Sandhoff mice prevented the decline in neuronal density in the VPM/VPL. Preservation of neurons in the VPM/VPL was variable at the humane endpoint in treated animals, but correlated directly with increased lifespan. Loss of neurons was localized to only a few regions in the Sandhoff brain and was prevented by rAAV-mediated transfer of β-hexosaminidase gene function at considerable distances from the site of vector administration.

Cholesterol metabolism in neurons and astrocytes

Cells in the mammalian body must accurately maintain their content of cholesterol, which is an essential membrane component and precursor for vital signalling molecules. Outside the brain, cholesterol homeostasis is guaranteed by a lipoprotein shuttle between the liver, intestine and other organs via the blood circulation. Cells inside the brain are cut off from this circuit by the blood-brain barrier and must regulate their cholesterol content in a different manner. Here, we review how this is accomplished by neurons and astrocytes, two cell types of the central nervous system, whose cooperation is essential for normal brain development and function. The key observation is a remarkable cell-specific distribution of proteins that mediate different steps of cholesterol metabolism. This form of metabolic compartmentalization identifies astrocytes as net producers of cholesterol and neurons as consumers with unique means to prevent cholesterol overload. The idea that cholesterol turnover in neurons depends on close cooperation with astrocytes raises new questions that need to be addressed by new experimental approaches to monitor and manipulate cholesterol homeostasis in a cell-specific manner. We conclude that an understanding of cholesterol metabolism in the brain and its role in disease requires a close look at individual cell types.

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.

Anatomically defined neuron-based rescue of neurodegenerative Niemann-Pick type C disorder

Niemann-Pick type C disease is a fatal lysosomal storage disorder caused by loss of NPC1 function. The disorder severely affects multiple body systems, particularly the nervous system. To test whether rescue of NPC1 activity in neurons, astrocytes, or other cell types can correct the neurological defects, a Tet-inducible Npc1-YFP transgene was introduced into Npc1(-/-) mice for the cell type-specific rescue of NPC1 loss. NPC1-YFP produced in neurons prevented neuron degeneration, slowed reactive glial activity, and ameliorated the disease. NPC1-YFP produced in astrocytes or in cells of visceral tissue did not. These results suggest that loss of NPC1 activity from neurons is the primary cause of the neuropathology and that rescue of NPC1 function in neurons is sufficient to mitigate the disease. The ability of neurons to survive and function in a cell-autonomous fashion allowed the use of this newly engineered rescue system to further define the brain regions or neuron populations required to ameliorate a neurological symptom. NPC1-YFP produced specifically in cerebellar Purkinje neurons reduced ataxia, increased weight, and prolonged life, but it did not prevent the eventual decline and premature death of Npc1(-/-) mice. Significant increase in lifespan correlated with sustained reduction of inflammation in the thalamus. Neuron rescue of other forebrain areas provided little benefit. Future work targeting increasingly discrete neuronal networks should reveal which CNS areas are critical for survival. This work may have broad implications for understanding the anatomical and cellular basis of neurological signs and symptoms of other neurodegenerative and lysosomal disorders.

Altered vitamin E status in Niemann-Pick type C disease

Vitamin E (α-tocopherol) is the major lipid-soluble antioxidant in many species. Niemann-Pick type C (NPC) disease is a lysosomal storage disorder caused by mutations in the NPC1 or NPC2 gene, which regulates lipid transport through the endocytic pathway. NPC disease is characterized by massive intracellular accumulation of unesterified cholesterol and other lipids in lysosomal vesicles. We examined the roles that NPC1/2 proteins play in the intracellular trafficking of tocopherol. Reduction of NPC1 or NPC2 expression or function in cultured cells caused a marked lysosomal accumulation of vitamin E in cultured cells. In vivo, tocopherol significantly accumulated in murine Npc1-null and Npc2-null livers, Npc2-null cerebella, and Npc1-null cerebral cortices. Plasma tocopherol levels were within the normal range in Npc1-null and Npc2-null mice, and in plasma samples from human NPC patients. The binding affinity of tocopherol to the purified sterol-binding domain of NPC1 and to purified NPC2 was significantly weaker than that of cholesterol (measurements kindly performed by R. Infante, University of Texas Southwestern Medical Center, Dallas, TX). Taken together, our observations indicate that functionality of NPC1/2 proteins is necessary for proper bioavailability of vitamin E and that the NPC pathology might involve tissue-specific perturbations of vitamin E status.

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.

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

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

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.

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.

Regulation of hippocampal cholesterol metabolism by apoE and environmental stimulation

Alzheimer's disease is associated with genetic risk factors, of which the allele E4 of apolipoprotein E (apoE4) is the most prevalent, and it is also affected by environmental factors such as early life education. We have recently shown, utilizing apoE-deficient and apoE transgenic mice, that synaptogenesis in the hippocampus following environmental stimulation is affected by apoE. In view of the pivotal role of cholesterol in synaptic plasticity, and of its suggested role in synaptogenesis, we presently examined the effects of apoE and environmental stimulation on brain cholesterol homeostasis. The hippocampal levels of cholesterol and its precursors and metabolites in control mice were not affected by exposure to environmental stimulation. In contrast, the hippocampal levels of cholesterol and its precursors lathosterol and desmosterol and metabolite 24S-hydroxycholesterol were lower in apoE-deficient mice that were maintained in a regular environmental than those of corresponding control mice, whereas they were markedly elevated following environmental stimulation. Histological and immunohistochemical experiments revealed that the combined stimulatory effects of apoE deficiency and environmental stimulation on cholesterol metabolism were associated with marked activation of hippocampal astrocytes and with the abnormal accumulation of cholesterol in neurons and astrocytes. These effects were rescued similarly in apoE3 and apoE4 transgenic mice. These findings suggest that apoE plays an important role in the translocation of cholesterol from astrocytes to neurons in vivo and in the regulation and homeostasis of this process.

Neurodegeneration Augments the Ability of Bone Marrow-Derived Mesenchymal Stem Cells to Fuse with Purkinje Neurons in Niemann–Pick Type C Mice

After transplantation, adult bone marrow-derived mesenchymal stem cells (BM-MSCs) may undergo transdifferentiation and/or cell fusion in response to new environments. However, the mechanism(s) that govern these cell fate switches remain unknown. Here we demonstrate that the pathology associated with murine Niemann-Pick disease type C (NP-C) cerebellum augments the ability of BM-MSCs to fuse with Purkinje neurons. The results suggest that the degenerative microenvironment of Purkinje neurons in the NP-C cerebellum modulates the cell fate switch of BM-MSCs via cell fusion.

Cell-autonomous death of cerebellar purkinje neurons with autophagy in Niemann-Pick type C disease

Niemann-Pick type C is a neurodegenerative lysosomal storage disorder caused by mutations in either of two genes, npc1 and npc2. Cells lacking Npc1, which is a transmembrane protein related to the Hedgehog receptor Patched, or Npc2, which is a secreted cholesterol-binding protein, have aberrant organelle trafficking and accumulate large quantities of cholesterol and other lipids. Though the Npc proteins are produced by all cells, cerebellar Purkinje neurons are especially sensitive to loss of Npc function. Since Niemann-Pick type C disease involves circulating molecules such as sterols and steroids and a robust inflammatory response within the brain parenchyma, it is crucial to determine whether external factors affect the survival of Purkinje cells (PCs). We investigated the basis of neurodegeneration in chimeric mice that have functional npc1 in only some cells. Death of mutant npc1 cells was not prevented by neighboring wild-type cells, and wild-type PCs were not poisoned by surrounding mutant npc1 cells. PCs undergoing cell-autonomous degeneration have features consistent with autophagic cell death. Chimeric mice exhibited a remarkable delay and reduction of wasting and ataxia despite their substantial amount of mutant tissue and dying cells, revealing a robust mechanism that partially compensates for massive PC death.

Niemann-Pick disease type C is a deadly neurodegenerative disease that is most often due to mutations in a gene called npc1. As a consequence of intracellular lipid trafficking defects, patients with Niemann-Pick type C, and mice with the same disease, lose an important class of cerebellar neurons called Purkinje cells (PCs). Npc1 (the protein coded by npc1) might be needed in other cell types to produce substances that nourish PCs or within the PCs themselves. To see which is true, the researchers constructed genetically mosaic mice in which some cells have mutant Npc1 and some have normal Npc1 function. In the cerebella of these mosaic mice, PCs lacking Npc1 continued to die even while surrounded by normal cells, while normal PCs appeared unaffected by their partially mutant surroundings. From these findings, the researchers concluded that the neurodegeneration is due to a problem within PCs and not due to a lack of supporting factors provided by other cells or an extrinsic toxic or inflammatory insult. Npc1 probably functions within PCs to allow critical transport processes necessary for cell survival. The researchers also found that the degenerating PCs undergo a complex process called autophagy in which the cells sense a lack of key nutrients and start to break down their own structures to feed themselves. By identifying exactly which cells require Npc1 function, the researchers set the stage for investigating the exact molecular roles of Npc1 protein in the cells where it is most needed.

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.

Consequences of NPC1 and NPC2 loss of function in mammalian neurons

Genetic deficiency of NPC1 or NPC2 results in a devastating cholesterol-glycosphingolipidosis of brain and other organs known as Niemann-Pick type C (NPC) disease. While NPC1 is a transmembrane protein believed involved in retroendocytic shuttling of substrate(s) to the Golgi and possibly elsewhere in cells as part of an essential recycling/homeostatic control mechanism, NPC2 is a soluble lysosomal protein known to bind cholesterol. The precise role(s) of NPC1 and NPC2 in endosomal-lysosomal function remain unclear, nor is it known whether the two proteins directly interact as part of this function. The pathologic features of NPC disease, however, are well documented. Brain cells undergo massive intracellular accumulation of glycosphingolipids (lactosylceramide, glucosylceramide, GM2 and GM3 gangliosides) and cholesterol and concomitant distortion of neuron shape (meganeurite formation). In neurons from humans with NPC disease the metabolic defects and storage often lead to extensive growth of new, ectopic dendrites (possibly linked to ganglioside sequestration) as well as formation of neurofibrillary tangles (NFTs) (possibly linked to dysregulation of cholesterol metabolism). Other features of cellular pathology in NPC disease include fragmentation of the Golgi apparatus and neuroaxonal dystrophy, though reasons for these changes remain largely unknown. As the disease progresses, neurodegeneration is also apparent for neurons in some brain regions, particularly Purkinje cells of the cerebellum, but the basis of this selective neuronal vulnerability is unknown. The NPC1 protein is evolutionarily conserved with homologues reported in yeast to humans; NPC2 is reported in C. elegans to humans. While neurons in mammalian models of NPC1 and NPC2 diseases exhibit many changes that are remarkably similar to those in humans (e.g., endosomal/lysosomal storage, Golgi fragmentation, neuroaxonal dystrophy, neurodegeneration), a reduced degree of ectopic dendritogenesis and an absence of NFTs in these species suggest important differences in the way lower mammalian neurons respond to NPC1/NPC2 loss of function.

Postnatal development of inflammation in a murine model of Niemann–Pick type C disease: immunohistochemical observations of microglia and astroglia

Niemann-Pick type C (NPC) is a rare and fatal neurovisceral storage disorder that is currently untreatable. In most cases, NPC is caused by mutations of the NPC1 gene, which encodes a glycoprotein playing an important role in cholesterol transport. Mice lacking the NPC1 gene exhibit several pathological features of NPC patients and have been widely used to provide insights into the mechanisms of the disease. In the present study, we analyzed the postnatal development of pathological manifestations of inflammation in several brain regions of NPC1-/- mice. Brain sections from NPC1-/- and wild-type (NPC1+/+) mice were immunostained with the MAC1 antibody, which recognizes microglia, with antibodies against glial fibrillary acidic protein (GFAP), which recognize astrocytes, and with antibodies against the cytokine interleukin-1beta (IL-1beta). Numbers of MAC1 immunopositive cells were markedly increased in several brain regions of NPC1-/- mice as early as 2 weeks of age. This effect was particularly evident in globus pallidus, ventral lateral thalamus, medial geniculate nucleus, and cerebellum. MAC1-immunopositive cells had enlarged cell bodies and shorter processes, suggesting they were in an active state. By 4 weeks, most brain structures exhibited enhanced microglial activation in NPC1-/- mice, and this was maintained at 12 weeks. At 2 weeks, reactive astrocytes were only observed in the ventral lateral thalamus while they were present throughout the brain of NPC1-/- mice at 4 weeks of age. Moreover, the astroglial reaction coincided with up-regulation of the cytokine, interleukin-1beta, in most, but not all brain regions. In particular, no interleukin-1beta up-regulation was observed in regions devoid of neuronal degeneration. These results suggest that microglial activation precedes and might be causally related to neuronal degeneration, while astrocyte activation might be a consequence of neuronal degeneration.

Spatial and temporal distribution of intracellular free cholesterol in brains of a Niemann-Pick type C mouse model showing hyperphosphorylated tau protein. Implications for Alzheimer's disease

Niemann-Pick type C (NPC) disease is a fatal hereditary neurovisceral disorder with diagnostically relevant intracellular accumulation of cholesterol in non-brain tissue, for example the spleen and fibroblasts. In the brain, many ballooned neurons are seen. Using filipin microfluorodensitometry, significant accumulations of free cholesterol in specified neurons have been described in NPC patients. The present study demonstrates spatial and temporal accumulation of free cholesterol in the brains of homozygous NPC (-(npc)/-(npc)) mice, a widely acknowledged mouse model, and in primarily cultured neurons therefrom. Intraneuronal storage of free cholesterol was already prominent at a pre-clinical stage in various grey matter areas of the murine cerebral cortex. Hippocampal areas showed differential development of the pathological distribution of free cholesterol. The pyramidal cells in the CA3 sector of Ammon's horn were affected much earlier than in CA1. Some of the deeper cerebral nuclei were affected only slightly, even at the final stage. Neurons (E15-E17) cultured in a cholesterol-free medium also showed massive accumulation of intracellular free cholesterol. In addition, brains from the murine NPC model for Alzheimer's disease (AD)-like changes in the microtubule-associated protein tau were tested using the Gallyas silver technique and AT8-immunolabelling, since both human diseases are accompanied by intraneuronal tangles made up of tau protein aggregations. Although the analysis failed to show classical silver-stainable tangles of the AD type in the NPC mice, tau protein phosphorylated at epitopes considered to represent early stages of AD was found. This further strengthens the concept that an alteration in cholesterol metabolism may play an important role in AD. The NPC mouse model may thus serve as a tool to analyse the role of cholesterol in initial changes of tau that eventually lead to the formation of tangles in both NPC and AD.