Identification of HE1 as the second gene of Niemann-Pick C disease

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

Niemann-Pick Type C (NPC) disease is an autosomal recessive disorder caused by mutations in either the NPC1 or HE1 genes. Hallmarks of this presently incurable disease include abnormal intracellular accumulation of cholesterol and glycosphingolipids, progressive neuropathology and neurodegeneration, and premature death. There have been increased efforts to understand the effects of NPC disease on neurons of the brain, in part due to the recent development of improved research tools and reagents, and in part due to the rapidly growing appreciation of the importance of cholesterol and lipoproteins in the brain during neuronal development, function, and degeneration. Here, we highlight fundamental aspects of neurons that appear to be affected by NPC disease, including their morphology, metabolism, intracellular transport, electrical signaling, and response to environmental factors, and suggest other potentially important areas for future investigation. This provides a framework for acquiring additional insight to this disorder and shaping new therapeutic approaches to NPC disease.

Metazoan and microbial models of Niemann-Pick Type C disease

Niemann-Pick Type C (NP-C) disease compellingly provides insight into lipid transport and the association of this process with severe neuronal dysfunction. The two genes that define this syndrome, NPC1 and NPC2, are conserved throughout much of eukaryotic evolution, to the extent that the yeast and mammalian NPC1 genes are functionally interchangeable. We present here an evolutionary perspective of the genes defective in NP-C disease. We will describe how conservation of sequences and their biological roles in a variety of microbial and metazoan model systems may act as roadmaps to understanding this syndrome in humans.

NCR-1 and NCR-2, theC. eleganshomologs of the human Niemann-Pick type C1 disease protein, function upstream of DAF-9 in the dauer formation pathways

Mutations in the human NPC1 gene cause most cases of Niemann-Pick type C(NP-C) disease, a fatal autosomal recessive neurodegenerative disorder. NPC1 is implicated in intracellular trafficking of cholesterol and glycolipids, but its exact function remains unclear. The C. elegans genome contains two homologs of NPC1, ncr-1 and ncr-2, and an ncr-2;ncr-1 double deletion mutant forms dauer larvae constitutively (Daf-c). We have analyzed the phenotypes of ncr single and double mutants in detail, and determined the ncr gene expression patterns. We find that the ncr genes function in a hormonal branch of the dauer formation pathway upstream of daf-9 and daf-12, which encode a cytochrome P450 enzyme and a nuclear hormone receptor, respectively. ncr-1 is expressed broadly in tissues with high levels of cholesterol, whereas expression of ncr-2 is restricted to a few cells. Both Ncr genes are expressed in the XXX cells, which are implicated in regulating dauer formation via the daf-9 pathway. Only the ncr-1 mutant is hypersensitive to cholesterol deprivation and to progesterone, an inhibitor of intracellular cholesterol trafficking. Our results support the hypothesis that ncr-1 and ncr-2 are involved in intracellular cholesterol processing in C. elegans, and that a sterol-signaling defect is responsible for the Daf-c phenotype of the ncr-2; ncr-1 mutant.

Structure and function of the NPC2 protein

Somatic cell hydridization and linkage studies indicated the implication of a second gene as a cause of Niemann-Pick C disease in a minority (5%) of patients. A study of the lysosomal proteome led to the identification of a previously known gene, HE1, as the NPC2 gene. The mature NPC2/HE1 protein is a ubiquitous soluble small 132-amino-acid glycoprotein, first characterized as a major secretory protein in the human epididymis, but also detected in most tissues. Seventeen families with mutations in the NPC2 gene are known. Good genotype-phenotype correlations were observed. No distinction can be made between the biochemical phenotypes of NPC1 or NPC2 mutants. The NPC2 protein binds cholesterol with submicromolar affinity at neutral and acidic pH. The bovine protein has been crystallized, and the cholesterol-binding site assigned to a hydrophobic loosely packed region. There is strong evidence that the NPC1 and NPC2 proteins must function in a closely related fashion. Current data have led to the hypothesis that NPC2 would bind cholesterol from internal lysosomal membranes, enabling a physical interaction with NPC1 (or another protein) and allowing postlysosomal export of cholesterol. In this model, the activity of NPC1 would depend on that of NPC2. The precise function of the NPC2 protein has, however, not been fully elucidated.

Secretion of Sterols and the NPC2 Protein from Primary Astrocytes

Astrocytes secrete cholesterol in lipoprotein particles. Here we show that primary murine embryonic astrocytes secrete endogenously synthesized cholesterol but also the cholesterol precursors desmosterol and lathosterol. In astrocyte membranes, desmosterol and cholesterol were the predominant sterols. Astrocytes derived from Niemann-Pick type C lipidosis (NPC1-/-) mice displayed late endosomal cholesterol deposits, but the secretion of biosynthetic sterols from the cells was not inhibited. Both wild-type and NPC1-/- astrocytes secreted the NPC2 protein. Size-exclusion chromatography combined with electron microscopy showed that the majority of sterols were secreted separately from NPC2 in heterogeneous spherical particles with an average diameter of 20 nm. These data suggest that NPC2 and the majority of sterols secreted from astrocytes are not released together and that the secretion of neither sterols nor NPC2 requires NPC1 function. In addition, the findings reveal a complexity of sterol species in astrocytes and bring up the possibility that some of the effects assigned to astrocyte cholesterol may be attributed to its penultimate precursors.

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.

Therapy of Niemann–Pick disease, type C

Niemann-Pick disease, type C (NPC) is a progressive autosomal recessive neurodegenerative disease, characterized by late endosomal-lysosomal accumulation of multiple lipid molecules in association with abnormal tubulovesicular trafficking. The major gene product, NPC1 protein, is not suitable for transduction therapies, and gene replacement or repair is not yet practicable for NPC and related disorders. Attempts at therapy to date have focused on reduction of the accumulating molecules that are presumed to have direct or indirect toxic effects. More recent insights into the pathophysiology of NPC raise the possibility of small molecule therapies to interdict pathways triggering apoptosis and related routes to cell death and dysfunction.

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.

The pathophysiology and mechanisms of NP-C disease

The molecular isolation of NPC1 and NPC2, the genes defective in patients with Niemann-Pick disease type C (NP-C), has heralded in an exponential increase in our understanding of this syndrome and thus of human intracellular sterol transport. Despite this, neither the mechanisms of action nor the substrates for these putative transporters have been defined. In this overview, we describe our perspectives on the current awareness of the genetic determination and cellular biology of this syndrome, with emphasis on the underlying events that lead to neurodegeneration and the manner in which they might eventually be treated.

Intracellular trafficking of Niemann–Pick C proteins 1 and 2: obligate components of subcellular lipid transport

Niemann-Pick C 1 (NPC1) is a large integral membrane glycoprotein that resides in late endosomes, whereas NPC2 is a small soluble protein found in the lumen of lysosomes. Mutations in either NPC1 or NPC2 result in aberrant lipid transport from endocytic compartments, which results in lysosomal storage of a complex mixture of lipids, primarily cholesterol and glycosphingolipids. What are the biological functions of the NPC1 and NPC2 proteins? Here we review what is known about the intracellular itinerary of these two proteins as they facilitate lipid transport. We propose that the intracellular trafficking patterns of these proteins will provide clues about their function.

Differential Mass Spectrometry: A Label-Free LC−MS Method for Finding Significant Differences in Complex Peptide and Protein Mixtures

Efficiently identifying and quantifying disease- or treatment-related changes in the abundance of proteins is an important area of research for the pharmaceutical industry. Here we describe an automated, label-free method for finding differences in complex mixtures using complete LC-MS data sets, rather than subsets of extracted peaks or features. The method selectively finds statistically significant differences in the intensity of both high-abundance and low-abundance ions, accounting for the variability of measured intensities and the fact that true differences will persist in time. The method was used to compare two complex peptide mixtures with known peptide differences. This controlled experiment allowed us to assess the validity of each difference found and so to analyze the method's sensitivity and specificity. The method detects both presence versus absence and a 2-fold change in peptide concentration near the limit of detection of the instrument used, where chromatographic peaks may not be sufficiently well defined to be detected in individual samples. The method is more sensitive and gives fewer false positives than subtractive methods that ignore signal variability. Differential mass spectrometry combined with targeted MS/MS analysis of only identified differences may save both computation time and human effort compared to shotgun proteomics approaches.

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.

Disturbed cholesterol traffic but normal proteolytic function in LAMP-1/LAMP-2 double-deficient fibroblasts

Mice double deficient in LAMP-1 and -2 were generated. The embryos died between embryonic days 14.5 and 16.5. An accumulation of autophagic vacuoles was detected in many tissues including endothelial cells and Schwann cells. Fibroblast cell lines derived from the double-deficient embryos accumulated autophagic vacuoles and the autophagy protein LC3II after amino acid starvation. Lysosomal vesicles were larger and more peripherally distributed and showed a lower specific density in Percoll gradients in double deficient when compared with control cells. Lysosomal enzyme activities, cathepsin D processing and mannose-6-phosphate receptor expression levels were not affected by the deficiency of both LAMPs. Surprisingly, LAMP-1 and -2 deficiencies did not affect long-lived protein degradation rates, including proteolysis due to chaperone-mediated autophagy. The LAMP-1/2 double-deficient cells and, to a lesser extent, LAMP-2 single-deficient cells showed an accumulation of unesterified cholesterol in endo/lysosomal, rab7, and NPC1 positive compartments as well as reduced amounts of lipid droplets. The cholesterol accumulation in LAMP-1/2 double-deficient cells could be rescued by overexpression of murine LAMP-2a, but not by LAMP-1, highlighting the more prominent role of LAMP-2. Taken together these findings indicate partially overlapping functions for LAMP-1 and -2 in lysosome biogenesis, autophagy, and cholesterol homeostasis.

Niemann-Pick type C disease involves disrupted neurosteroidogenesis and responds to allopregnanolone

Niemann-Pick type C (NP-C) disease is a fatal, autosomal recessive, childhood neurodegenerative disease. The NP-C mouse recapitulates the cholesterol and sphingolipid storage, onset of neurological deficits, histopathological lesions, Purkinje cell loss and early death typical of the most severe form of human NP-C. Neurosteroids, steroids made in the brain, affect neuronal growth and differentiation, and modulate neurotransmitter receptors. Disordered cholesterol trafficking might disrupt neurosteroidogenesis, thereby contributing to the NP-C phenotype. Here we show that NP-C mouse brain contains substantially less neurosteroid than wild-type brain and has an age-related decrease in the ability to synthesize 5alpha-dihydroprogesterone and allopregnanolone. Immunohistochemical assessment confirms a decrease in expression of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase, especially in cerebellum. Neonatal administration of allopregnanolone delays the onset of neurological symptoms, increases Purkinje and granule cell survival, reduces cortical GM2 and GM3 ganglioside accumulation and doubles the lifespan of NP-C mice. Earlier administration increases effectiveness of treatment. Decreased production of allopregnanolone apparently contributes to the pathology of NP-C; thus, neurosteroid treatment may be useful in ameliorating progression of the disease.

In vivo interaction between the human dehydrodolichyl diphosphate synthase and the Niemann-Pick C2 protein revealed by a yeast two-hybrid system

Dehydrodolichyl diphosphate (DedolPP) synthase catalyzes the sequential condensation of isopentenyl diphosphate with farnesyl diphosphate to synthesize DedolPP, a biosynthetic precursor for dolichol which plays an important role as a sugar-carrier lipid in the biosynthesis of glycoprotein in eukaryotic cells. During certain pathological processes like Alzheimer's disease or some neurological disorders, dolichol has been shown to accumulate in human brain. In order to understand the regulatory mechanism of dolichol in eukaryotes, we performed a yeast two-hybrid screen using full length human DedolPP synthase gene [Endo et al. BBA 1625 (2003) 291] as a bait to find some proteins specifically interacting with the enzyme. We identified Niemann-Pick Type C2 protein (NPC2) to show a specific interaction with human DedolPP synthase. This interaction was further confirmed by in vitro co-immunoprecipitation experiment, indicating the possible physiological interaction between NPC2 and DedolPP synthase proteins in human.

Aberrant phosphorylation of alpha-synuclein in human Niemann-Pick type C1 disease

Niemann-Pick type C1 disease (NPC1) is an autosomal recessive neurovisceral storage disease caused by the mutation of NPC1 gene, resulting in perturbed intracellular transport of unesterified cholesterol. In NPC1, early-onset tauopathy is a constant feature. In addition, in NPC1 patients with ApoE epsilon4 homozygosity, deposition of A beta occurs mimicking Alzheimer disease (AD). Since AD is frequently associated with neuronal expression of alpha-synuclein, we investigated phosphorylated alpha-synuclein (psyn) immunoreactivity in the brains of 12 NPC1 patients, ages at death ranging from 9 months to 55 years. Psyn immunoreactivity was demonstrated in the perikarya of storage neurons and oligodendroglia in 10 cases. The immunoreactivity appeared more intense in subjects who had the ApoE epsilon4 allele. Lewy bodies were found in the substantia nigra in 2 of these cases. The psyn immunoreactivity was most intense in the substantia nigra where tauopathy was most severe. Phosphorylated tau and alpha-synuclein frequently colocalized. This study first documents alpha-synucleinopathy in NPC1. This observation suggests that the defect in intracellular cholesterol trafficking in NPC1 may provoke aberrant phosphorylation of alpha-synuclein and tau, and that this phosphorylation is enhanced by the ApoE epsilon4 allele. Thus, elucidation of metabolic pathways in NPC1 could provide clues to common mechanisms associated with neurodegeneration.

Intracellular cholesterol transport

Intracellular cholesterol transport is essential for the maintenance of cholesterol homeostasis. Many aspects of cholesterol metabolism are well-known, including its synthesis in the endoplasmic reticulum, its extracellular transport in plasma lipoproteins, its uptake by the low-density lipoprotein receptor, and its regulation of SREBP and LXR transcription factors. These fundamental pathways in cholesterol metabolism all rely on its proper intracellular distribution among subcellular organelles and the plasma membrane. Transport involving the ER and endosomes is essential for cholesterol synthesis, uptake, and esterification, whereas cholesterol catabolism by enzymes in mitochondria and ER generates steroids, bile acids, and oxysterols. Cholesterol is a highly hydrophobic lipid that requires specialized transport in the aqueous cytosol, involving either vesicles or nonvesicular mechanisms. The latter includes hydrophobic cavity transporters such as StAR-related lipid transfer (START) proteins. Molecular understanding of intracellular cholesterol trafficking has lagged somewhat behind other aspects of cholesterol metabolism, but recent advances have defined some transport pathways and candidate proteins. In this review, we discuss cholesterol transport among specific intracellular compartments, emphasizing the relevance of these pathways to cholesterol homeostasis.

Accumulation of glycosphingolipids in Niemann-Pick C disease disrupts endosomal transport

Glycosphingolipids are endocytosed and targeted to the Golgi apparatus but are mistargeted to lysosomes in sphingolipid storage disorders. Substrate reduction therapy utilizes imino sugars to inhibit glucosylceramide synthase and potentially abrogate the effects of storage. Niemann-Pick type C (NPC) disease is a disorder of intracellular transport where glycosphingolipids (GSLs) and cholesterol accumulate in endosomal compartments. The mechanisms of altered intracellular trafficking are not known but may involve the mistargeting and disrupted function of proteins associated with GSL membrane microdomains. Membrane microdomains were isolated by Triton X-100 and sucrose density gradient ultracentrifugation. High pressure liquid chromatography and mass spectrometric analysis of NPC1(-/-) mouse brain revealed large increases in GSL. Sphingosine was also found to be a component of membrane microdomains, and in NPC liver and spleen, large increases in cholesterol and sphingosine were found. GSL and cholesterol levels were increased in mutant NPC1-null Chinese hamster ovary cells as well as U18666A and progesterone induced NPC cell culture models. However, inhibition of GSL synthesis in NPC cells with N-butyldeoxygalactonojirimycin led to marked decreases in GSL but only small decreases in cholesterol levels. Both annexin 2 and 6, membrane-associated proteins that are important in endocytic trafficking, show distorted distributions in NPC cells. Altered BODIPY lactosylceramide targeting, decreased endocytic uptake of a fluid phase marker, and mistargeting of annexin 2 (phenotypes associated with NPC) are reversed by inhibition of GSL synthesis. It is suggested that accumulating GSL is part of a mislocalized membrane microdomain and is responsible for the deficit in endocytic trafficking found in NPC disease.

Niemann-Pick Type C disease and Alzheimer's disease: the APP-endosome connection fattens up

Niemann-Pick Type C (NPC) is an inherited neurodegenerative disease of childhood and adolescence that develops from a failure of cholesterol trafficking within the endosomal-lysosomal pathway. Although NPC differs in major respects from Alzheimer's disease (AD), intriguing parallels exist in the cellular pathology of these two diseases, including neurofibrillary tangle formation, prominent lysosome system dysfunction, and influences of apolipoprotein E epsilon4 genotype. Added to these similarities are new findings that some neuronal populations develop abnormalities of endosomes resembling those seen at the earliest stages of AD and also accumulate beta-cleaved amyloid precursor protein (APP) and Abeta peptides within endosomes. In this commentary, the common features of endosome dysfunction are reviewed. Emerging evidence that endosome dysfunction may lead to beta-amyloidogenic APP processing or neurodegeneration by several different means is discussed.

Adult onset Niemann-Pick type C disease: A clinical, neuroimaging and molecular genetic study

We report on a patient with adult-onset Niemann-Pick type C (NPC) disease, carrying the mutations P1007 and I1061T in the NPC1 gene, presenting with marked psychiatric changes followed by dystonia and cognitive impairment. Filipin staining, single photon emission computed tomography perfusional, positron emission tomography metabolic, conventional magnetic resonance imaging, and magnetic resonance spectroscopy findings suggested a pathophysiological correlation with phenotype expression. This case expands the clinical and genetic spectrum of the rare adult-onset NPC disease phenotype.

Immortalization by large T-antigen of the adult epididymal duct epithelium

The SV40 large T-antigen has been widely used to convert various cell types to a transformed phenotype, and also to induce progressive tumours in transgenic animals. The objectives of this review are to compare and discuss three different approaches to generate epididymal epithelial cell lines using the large T-antigen. In the first approach, retroviral transfection of primary cultures was used to immortalize canine epididymal cells in vitro; the other two approaches used transgenic mice expressing the large T-antigen. In one of these in vivo approaches, a construct consisting of the coding sequence of a temperature sensitive (ts) SV40 large T-antigen was inserted in a mouse genome. When the cells are exposed to the permissive temperature of 33 degrees C, functional expression of the large T-antigen occurs and cells start to proliferate. In the second in vivo approach a tissue-specific promoter, the 5kb GPX5 promoter, was used to direct expression of the large T-antigen to the epididymal duct epithelium.

Targeted mutation of the MLN64 START domain causes only modest alterations in cellular sterol metabolism

The StAR-related lipid transfer (START) domain, first identified in the steroidogenic acute regulatory protein (StAR), is involved in the intracellular trafficking of lipids. Sixteen mammalian START domain-containing proteins have been identified to date. StAR, a protein targeted to mitochondria, stimulates the movement of cholesterol from the outer to the inner mitochondrial membranes, where it is metabolized into pregnenolone in steroidogenic cells. MLN64, the START domain protein most closely related to StAR, is localized to late endosomes along with other proteins involved in sterol trafficking, including NPC1 and NPC2, where it has been postulated to participate in sterol distribution to intracellular membranes. To investigate the role of MLN64 in sterol metabolism, we created mice with a targeted mutation in the Mln64 START domain, expecting to find a phenotype similar to that in humans and mice lacking NPC1 or NPC2 (progressive neurodegenerative symptoms, free cholesterol accumulation in lysosomes). Unexpectedly, mice homozygous for the Mln64 mutant allele were viable, neurologically intact, and fertile. No significant alterations in plasma lipid levels, liver lipid content and distribution, and expression of genes involved in sterol metabolism were observed, except for an increase in sterol ester storage in mutant mice fed a high fat diet. Embryonic fibroblast cells transfected with the cholesterol side-chain cleavage system and primary cultures of granulosa cells from Mln64 mutant mice showed defects in sterol trafficking as reflected in reduced conversion of endogenous cholesterol to steroid hormones. These observations suggest that the Mln64 START domain is largely dispensable for sterol metabolism in mice.

The steroidal analog GW707 activates the SREBP pathway through disruption of intracellular cholesterol trafficking

Recently, a new class of lipid-lowering agents has been described that upregulate LDL receptor (LDLr) activity. These agents are proposed to activate sterol-regulated gene expression through binding to the sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP). Here, we show that the steroidal LDLr upregulator, GW707, induces accumulation of lysosomal free cholesterol and inhibits LDL-stimulated cholesterol esterification, similar to that observed in U18666A-treated cells and in Niemann-Pick type C1 (NPC1) mutants. Moreover, we demonstrate that induction of the NPC-like phenotype by GW707 is independent of SCAP function. We find that treatment with GW707 does not increase SREBP-dependent gene expression above that observed in lipoprotein-starved cells. Rather, we show that the apparent increase in SREBP-dependent activity in GW707-treated cells is attributable to a failure to appropriately suppress sterol-regulated gene expression, as has been shown previously for U18666A-treated cells and NPC mutant fibroblasts. We further demonstrate that cells treated with either GW707 or U18666A fail to appropriately generate 27-hydroxycholesterol in response to LDL cholesterol. Taken together, these findings support a mechanism in which GW707 exerts its hypolipidemic effects through disruption of late endosomal/lysosomal sterol trafficking and subsequent stimulation of LDLr activity.

Plasticity and the spread of Alzheimer's disease-like changes

Tangles are a major histopathological feature of Alzheimer's disease and their regional location and number correlate significantly with the individual's cognitive decline. Intriguingly, these tangles are formed only in a small subset of nerve cell types and are practically absent in most animal species examined so far. In humans, tangle formation seemingly starts decades before clinical signs of dementia are seen and spread over cortical areas in a regular manner described by the Braak classification. In the present article the role of plasticity-related molecules and mechanisms are discussed considering their putative role in neuronal vulnerability and spread of tangles. Special emphasis is given to some aspects of lipid metabolism, that is, apolipoprotein E polymorphism, statin effects, and lysosomal dysfunction in Alzheimer's and Niemann-Pick C's diseases.

A novel cholesterol stain reveals early neuronal cholesterol accumulation in the Niemann-Pick type C1 mouse brain

Niemann-Pick type C (NPC) is a neurodegenerative disorder characterized by progressive accumulation of cholesterol, gangliosides, and other lipids in the central nervous system and visceral organs. In the NPC1 mouse model, neurodegeneration and neuronal cell loss occur before postnatal day 21. Whether neuronal cholesterol accumulation occurs in vivo before the first signs of neuronal cell loss has not been demonstrated. In this report, we used the NPC1 mouse model and employed a novel cholesterol binding reagent, BC theta, that enabled us to visualize cellular cholesterol accumulation at a level previously unattainable. The results demonstrate the superiority of BC theta staining over conventional filipin staining in confocal microscopy and highlight several new findings. We show that at postnatal day 9, although only mild signs of neurodegeneration are detectable, significant neuronal cholesterol accumulation has already occurred throughout the NPC1 brain. In addition, although NPC1 Purkinje neurons exhibit a normal morphology at day 9, significant cholesterol accumulation within their extensive dendritic trees has occurred. We also show that in the thalamus and cortex of NPC1 mice, activated glial cells first appear at postnatal day 9 and heavily populate by day 22, suggesting that in NPC1 mice, neuronal cholesterol accumulation precedes neuronal injury and neuronal cell loss.

Enzyme therapy for lysosomal storage disease: principles, practice, and prospects

Over the past three decades, enzyme therapy for lysosomal storage diseases has moved from an academic pursuit to direct delivery of effective clinical care for affected patients and families. This success is based on understanding the complexities of lysosomal biogenesis, lysosomal hydrolase sorting and hydrolytic requirements, and the target sites of pathology of these diseases. This article reviews these concepts and their application to the treatment of affected patients with Gaucher disease, Fabry disease, and mucopolysaccharidosis I. The principles, progress, and practice in these diseases provide prototypes for expansion of enzyme therapy to a growing set of these diseases.

Differential trafficking of the Niemann-Pick C1 and 2 proteins highlights distinct roles in late endocytic lipid trafficking

The cellular location of Niemann-Pick C2 protein (NPC2) in cultured human fibroblasts and Chinese hamster ovary cells was examined immunocytochemically and in living cells by expression of a functional red fluorescent protein chimeric analogue.

RESULTS

NPC2 is present in the lysosomes of both cholesterol-depleted and -replenished cells, unlike Niemann-Pick C1 protein (NPC1) which is recruited to late endosomes only upon uptake of low-density lipoprotein. With mobilization of cholesterol from lysosomes, immunocytochemical detection of NPC2 in lysosomes is greatly diminished, whereas NPC1 remains in the late endosomal compartment. We found a partial overlap in the trafficking and organellar sites of accumulation of NPC2 and NPC1. In living cells, NPC2 traffics with NPC1 in late endosomal tubules. However, in contrast to NPC1, which remains either in late endosomal vesicles and tubules or at the peripheries of cholesterol-laden lysosomes, NPC2 moves into the central core of lysosomes. Glycolipid analysis reveals that, in contrast to null mutant NPC1 cells, which accumulate GM2 ganglioside only at the plasma membrane, with no endocytic storage, absence of NPC2 protein in null mutant NPC2 cells does not block internalization of GM2 into endocytic vesicles. This difference in the cellular distribution of GM2 in NPC1 and NPC2 null mutants is the first report of a variation in the phenotypic expression of these genotypically distinct lesions.

CONCLUSION

We speculate that while NPC1 may play a major role in the sorting of glycolipids as well as cholesterol within the late endosomes, NPC2 primarily plays a role in the egress of cholesterol and, potentially, glycolipids from lysosomes. These proteins appear not to be integrated into a tightly bound biological complex, but rather represent separate functional entities that complement each other.

A Riddle Wrapped in a Mystery: Understanding Niemann-Pick Disease, Type C

BACKGROUND

Niemann-Pick disease, type C (NPC), is a lipid storage disease that may present at any age from fetal life to the seventh decade. Its protean manifestations include hepatic and pulmonary failure, as well as a range of progressive neuropsychiatric phenotypes. Late onset disease has been increasingly recognized as the biochemical diagnosis of NPC has been more widely applied.

REVIEW SUMMARY

The phenotypes, biochemical, and molecular bases of NPC are reviewed. Indistinguishable phenotypes are produced by mutations in two distinct genes, designated NPC 1 and NPC 2, that play key roles in the intracellular trafficking of lipids. The diagnosis of NPC is challenging as the characteristic vertical supranuclear gaze palsy is difficult to recognize, organomegaly is often absent, and standard biochemical screening studies are usually normal. Definitive diagnosis requires demonstration of the trafficking defect in cultured fibroblasts, supplemented in selected cases by genotyping. Animal studies have shown that inhibition of glycosphingolipid synthesis may delay the onset of disease and prolong survival; a human trial of this approach is underway.

CONCLUSIONS

NPC is a model for inborn errors of metabolism whose gene product mediates molecular trafficking rather than catabolizing macromolecules, as in classic lipid storage diseases. NPC should be considered in the differential diagnosis of progressive neurodegenerative disorders at any age. The astute clinician can provide great comfort to families afflicted by NPC by making an accurate diagnosis, notwithstanding the absence of definitive treatment.

Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral lipid storage with a wide spectrum of clinical phenotypes. At the cellular level, the disorder is characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system. Approximatively 95% of patients have mutations in the NPC1 gene (mapped at 18q11) which encodes a large membrane glycoprotein primarily located to late endosomes. The remainder have mutations in the NPC2 gene (mapped at 14q24.3) which encodes a small soluble lysosomal protein with cholesterol-binding properties. The identical biochemical patterns observed in NPC1 and NPC2 mutants suggest that the two proteins function in a coordinate fashion. Identification of mutations revealed a complex picture of molecular heterogeneity, allowing genotype - phenotype correlations for both genes and providing insights into structure - function relationships for the NPC1 protein. Although a whole body of evidence suggests that the NPC1 and NPC2 proteins are involved in the cellular postlysosomal/late endosomal transport of cholesterol, glycolipids and other cargo, their precise functions and relationship remain unclear and are currently the subject of intense investigation. These studies, conducted in various models, should ultimately lead to a better understanding of the pathophysiology of NPC and new therapeutic approaches.

Identification of 58 novel mutations in Niemann-Pick disease type C: correlation with biochemical phenotype and importance of PTC1-like domains in NPC1

The two known complementation groups of Niemann-Pick Type C disease, NPC1 and NPC2, result from non-allelic protein defects. Both the NPC1 and NPC2 (HE1) gene products are intimately involved in cholesterol and glycolipid trafficking and/or transport. We describe mutation analysis on samples from 143 unrelated affected NPC patients using conformation sensitive gel electrophoresis and DNA sequencing as the primary mutation screening methods for NPC1 and NPC2, respectively. These methods are robust, sensitive, and do not require any specialized laboratory equipment. Analyses identified two NPC1 mutations for 115 (80.4%) patients, one NPC1 mutation for 10 (7.0%) patients, two NPC2 mutations for five (3.5%) patients, one NPC2 mutation for one (0.7%) patient, and no mutations for 12 (8.4%) patients. Thus, mutations were identified on 251 of 286 (88%) disease alleles, including 121 different mutations (114 in NPC1 and seven in NPC2), 58 of which are previously unreported. The most common NPC1 mutation, I1061T, was detected on 18% of NPC alleles. Other NPC1 mutations were mostly private, missense mutations located throughout the gene with clustering in the cysteine-rich luminal domain. Correlation with biochemical data suggests classification of several mutations as severe and others as moderate or variable. The region between amino acids 1038 and 1253, which shares 35% identity with Patched 1, appears to be a hot spot for mutations. Additionally, a high percentage of mutations were located at amino acids identical to the NPC1 homolog, NPC1L1. Biochemical complementation analysis of cases negative for mutations revealed a high percentage of equivocal results where the complementation group appeared to be non-NPC1 and non-NPC2. This raises the possibilities of an additional NPC complementation group(s) or non-specificity of the biochemical testing for NPC. These caveats must be considered when offering mutation testing as a clinical service.

Niemann-Pick type C disease associated with peripheral neuropathy

Niemann-Pick type C disease is an autosomal-recessive, inherited neurovisceral lipid storage disorder. This disease results from either protein NPC1 or HE1 deficiency, which leads to cholesterol metabolism disturbance and is characterized by early hepatosplenomegaly and progressive ataxia, dystonia, cataplexy, dysarthria, and dementia. We describe a 3 1/2-year-old patient with Niemann-Pick type C disease, who presented with regression in both cognitive and motor domains. Almost 10 months before admission to the hospital, the child developed progressive speech and behavioral changes, as well as gait disturbances with frequent falls. The examination demonstrated hepatosplenomegaly, ataxia, and vertical gaze palsy. Nerve conduction velocities demonstrated mild demyelinating peripheral neuropathy. Bone marrow examination revealed foam cells, and cholesterol esterification studies found massive accumulation of unesterified cholesterol and very low intracellular esterification of exogenous lipoprotein-derived cholesterol. These results indicate Niemann-Pick type C disease. Peripheral neuropathy is a rare complication in patients with Niemann-Pick type C disease, which certainly contributes to their neurologic deterioration.

NPC1 and NPC2 regulate cellular cholesterol homeostasis through generation of low density lipoprotein cholesterol-derived oxysterols

Mutations in the Niemann-Pick disease genes cause lysosomal cholesterol accumulation and impaired low density lipoprotein (LDL) cholesterol esterification. These findings have been attributed to a block in cholesterol movement from lysosomes to the site of the sterol regulatory machinery. In this study we show that Niemann-Pick type C1 (NPC1) and Niemann-Pick type C2 (NPC2) mutants have increased cellular cholesterol, yet they are unable to suppress LDL receptor activity and cholesterol biosynthesis. Cholesterol overload in both NPC1 and NPC2 mutants results from the failure of LDL cholesterol tobothsuppresssterolregulatoryelement-bindingprotein-dependent gene expression and promote liver X receptor-mediated responses. However, the severity of the defect in regulation of sterol homeostasis does not correlate with endoplasmic reticulum cholesterol levels, but rather with the degree to which NPC mutant fibroblasts fail to appropriately generate 25-hydroxycholesterol and 27-hydroxycholesterol in response to LDL cholesterol. Moreover, we demonstrate that treatment with oxysterols reduces cholesterol in NPC mutants and is able to correct the NPC1I1061T phenotype, the most prevalent NPC1 disease genotype. Our findings support a role for NPC1 and NPC2 in the regulation of sterol homeostasis through generation of LDL cholesterol-derived oxysterols and have important implications for the treatment of NPC disease.

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.

Cholesterol storage and tau pathology in Niemann-Pick type C disease in the brain

Niemann-Pick type C disease is an inherited neurovisceral storage disorder with intracellular accumulation of cholesterol. In affected brains, many ballooned neurons are seen. Considerable nerve cell loss of unknown pathogenesis leads to neurological deterioration and dementia. Chemical examination of brains has failed to demonstrate increased levels of cholesterol. Using filipin fluorometry of neuronal cells in tissue slices, we found massive accumulation of cholesterol in neurons in four out of five human Niemann-Pick type C cases including adult patients. Neurofibrillary tangles composed of aggregates of the otherwise highly soluble protein tau were present in three Niemann-Pick type C cases and were also immunologically identical to those associated with Alzheimer's disease. However, only a thin slab of spinal cord or a tiny piece of isocortex was available for examination in the two cases without tangles. In a further semi-quantitative analysis of 576 neurons, we determined higher cholesterol content in tangle-bearing neurons than in adjacent tangle-free neurons. The association of cholesterol accumulation with neurofibrillary degeneration in Niemann-Pick type C disease and Alzheimer's disease awakens interest in the role of impaired cholesterol metabolism in the development of neurofibrillary tangles in both diseases.

Trafficking defects in endogenously synthesized cholesterol in fibroblasts, macrophages, hepatocytes, and glial cells from Niemann-Pick type C1 mice

Niemann-Pick type C1 disease (NPC1) is an inherited neurovisceral lipid storage disorder, hallmarked by the intracellular accumulation of unesterified cholesterol and glycolipids in endocytic organelles. Cells acquire cholesterol through exogenous uptake and endogenous biosynthesis. NPC1 participation in the trafficking of LDL-derived cholesterol has been well studied; however, its role in the trafficking of endogenously synthesized cholesterol (endoCHOL) has received much less attention. Previously, using mutant Chinese hamster ovary cells, we showed that endoCHOL moves from the endoplasmic reticulum (ER) to the plasma membrane (PM) independent of NPC1. After arriving at the PM, it moves between the PM and internal compartments. The movement of endoCHOL from internal membranes back to the PM and the ER for esterification was shown to be defective in NPC1 cells. To test the generality of these findings, we have examined the trafficking of endoCHOL in four different physiologically relevant cell types isolated from wild-type, heterozygous, and homozygous BALB/c NPC1NIH mice. The results show that all NPC1 homozygous cell types (embryonic fibroblasts, peritoneal macrophages, hepatocytes, and cerebellar glial cells) exhibit partial trafficking defects, with macrophages and glial cells most prominently affected. Our findings suggest that endoCHOL may contribute significantly to the overall cholesterol accumulation observed in selective tissues affected by Niemann-Pick type C disease.

START domain proteins and the intracellular trafficking of cholesterol in steroidogenic cells

The intracellular trafficking of cholesterol in steroidogenic cells plays an important role in the regulation of hormone synthesis. Recent evidence indicates that a family of proteins related to the steroidogenic acute regulatory protein (StAR) perform critical functions in moving the sterol substrate to the mitochondrial inner membrane where the first committed step in steroid hormone synthesis occurs. StAR, the prototype of the family, is known to promote the translocation of cholesterol from the outer to the inner mitochondrial membrane. Mutations in StAR cause congenital lipoid adrenal hyperplasia, a cholesterol storage disorder in which synthesis of all gonadal and adrenocortical steroid hormones is severely impaired, and the cholesterol that is not efficiently moved into the mitochondria accumulates in cytoplasmic lipid droplets. The StAR-related lipid transfer (START) domain consists of an approximately 210 amino acid residue sequence that forms a compact alpha/beta structure, a helix-grip fold, with a hydrophobic tunnel that can accommodate a sterol molecule. START domains can bind sterol, facilitate the transfer of cholesterol from sterol-rich unilammelar liposomes to acceptor membranes, and stimulate steroidogenesis when expressed in cells co-expressing the cholesterol side-chain cleavage system or when added to isolated steroidogenic mitochondria. Sixteen human START domain proteins have been identified to date. Of these, StAR and MLN64 consist of one subfamily and newly described proteins named StarD4, StarD5, and StarD6 represent a closely related second subfamily. MLN64 is incorporated into the late endosomal compartment and is involved in the movement of cholesterol acquired from endocytosed LDL out of these vesicles. Expression of a dominant negative form of MLN64 causes accumulation of free cholesterol in lysosomes. The roles of StarD4, StarD5, and StarD6 in sterol movement remain to be determined. These genes have tissue-specific patterns of expression that may predict specialized roles.

Storage diseases: new insights into sphingolipid functions

Studying human diseases can help us to uncover important processes in normal cells. Cell biologists have recently focused on inherited sphingolipid-storage diseases. Eukaryotic life is characterized by internal membranes of various compositions, and sphingolipids are a small but important part of these membranes. Compositional differences between cellular membranes are maintained by sorting and sphingolipids are thought to organize this process by forming ordered domains of increased thickness in the bilayer. Here, we describe the impact of sphingolipid accumulation on the sorting of endocytic membranes and discuss the proposed basis for the pathology of these diseases at the cellular level.

Myofibroblastic conversion of mesothelial cells

BACKGROUND

The continuous chemical, physical, and inflammatory insults of prolonged continuous ambulatory peritoneal dialysis (CAPD) incite mesothelial cell responses, which may result in peritoneal fibrosis. The transforming growth factor-beta (TGF-beta), especially the isoform TGF-beta 1, has long been known to play crucial role in the fibrogenic process. Although several studies have implicated TGF-beta in peritoneal fibrosis, the underlying mechanism has not been completely elucidated.

METHODS

To test the effects of exogenous TGF-beta 1 on mesothelial cells, we assessed cytoarchitectural changes of human peritoneal mesothelial cells (HPMC) in in vitro culture by light, immunofluorescent, electron and immunoelectron microscopy, and differential gene expression analysis using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and cDNA expression array assays.

RESULTS

The TGF-beta 1-induced myofibroblastic conversion was a transdifferentiation process resulting in characteristic myofibroblastic phenotype that included prominent rough endoplasmic reticuli (rER) with dilated cisternas, conspicuous smooth muscle actin (SMA) myofilaments, frequent intercellular intermediate and gap junctions, and active deposition of extracellular matrix (ECM) and formation of fibronexus. The gene expression array analysis revealed complex modulation of gene expression involving cytoskeletal organization, cell adhesion, ECM production, cell proliferation, innate immunity, cytokine/growth factor signaling, cytoprotection, stress response, and many other essential metabolic processes in mesothelial cells.

CONCLUSION

This report describes myofibroblastic conversion of mesothelial cells, a previously undefined, yet frequently speculated, cell adaptive or pathogenic process. Our study helps to elucidate the complex molecular and cellular events involved in myofibroblastic conversion of mesothelial cells. We propose that differentiated epithelial cells of mesothelium convert or transdifferentiate into myofibroblasts, which implies the recruitment of fibrogenic cells from mesothelium during serosal inflammation and wound healing.

Recycling compartments and the internal vesicles of multivesicular bodies harbor most of the cholesterol found in the endocytic pathway

We employed our recently developed immuno-electron microscopic method (W. Möbius, Y. Ohno-Iwashita, E. G. van Donselaar, V. M. Oorschot, Y. Shimada, T. Fujimoto, H. F. Heijnen, H. J. Geuze and J. W. Slot, J Histochem Cytochem 2002; 50: 43-55) to analyze the distribution of cholesterol in the endocytic pathway of human B lymphocytes. We could distinguish 6 categories of endocytic compartments on the basis of morphology, BSA gold uptake kinetics and organelle marker analysis. Of all cholesterol detected in the endocytic pathway, we found 20% in the recycling tubulo-vesicles and 63% present in two types of multivesicular bodies. In the multivesicular bodies, most of the cholesterol was contained in the internal membrane vesicles, the precursors of exosomes secreted by B cells. Cholesterol was almost absent from lysosomes, that contained the bulk of the lipid bis(monoacylglycero)phosphate, also termed lysobisphosphatidic acid. Thus, cholesterol displays a highly differential distribution in the various membrane domains of the endocytic pathway.

The integrity of a cholesterol-binding pocket in Niemann-Pick C2 protein is necessary to control lysosome cholesterol levels

The neurodegenerative disease Niemann-Pick Type C2 (NPC2) results from mutations in the NPC2 (HE1) gene that cause abnormally high cholesterol accumulation in cells. We find that purified NPC2, a secreted soluble protein, binds cholesterol specifically with a much higher affinity (K(d) = 30-50 nM) than previously reported. Genetic and biochemical studies identified single amino acid changes that prevent both cholesterol binding and the restoration of normal cholesterol levels in mutant cells. The amino acids that affect cholesterol binding surround a hydrophobic pocket in the NPC2 protein structure, identifying a candidate sterol-binding location. On the basis of evolutionary analysis and mutagenesis, three other regions of the NPC2 protein emerged as important, including one required for efficient secretion.

Structure of a cholesterol-binding protein deficient in Niemann-Pick type C2 disease

Niemann-Pick disease type C2 (NP-C2) is a fatal hereditary disease characterized by accumulation of low-density lipoprotein-derived cholesterol in lysosomes. Here we report the 1.7-A resolution crystal structure of the cholesterol-binding protein deficient in this disease, NPC2, and the characterization of its ligand binding properties. Human NPC2 binds the cholesterol analog dehydroergosterol with submicromolar affinity at both acidic and neutral pH. NPC2 has an Ig-like fold stabilized by three disulfide bonds. The structure of the bovine protein reveals a loosely packed region penetrating from the surface into the hydrophobic core that forms adjacent small cavities with a total volume of approximately 160 A(3). We propose that this region represents the incipient cholesterol-binding site that dilates to accommodate an approximately 740-A(3) cholesterol molecule.

Childhood dystonia

Childhood dystonias are a heterogeneous group of disorders with strong inherited basis. This review describes the clinical characteristics, classification, genetic basis, pathophysiology, biochemistry, pathology, and treatment of dystonias, including the primary dystonias, the dystonia-plus syndromes, secondary dystonias, and heredodegenerative disorders. Conditions discussed in detail include idiopathic torsion dystonia, dopa-responsive dystonia, Wilson's disease, myoclonus dystonia, rapid-onset dystonia parkinsonism, neurodegeneration with brain iron accumulation (Hallervorden-Spatz syndrome), mitochondrial dystonias, Niemann-Pick type C, and neuroacanthocytosis.

Concurrent increase of cholesterol, sphingomyelin and glucosylceramide in the spleen from non-neurologic Niemann-Pick type C patients but also patients possibly affected with other lipid trafficking disorders

Niemann-Pick type C disease (NPC) is a neurovisceral (or, extremely rarely, only visceral) lipidosis caused by mutations in the NPC1 gene or, in a few patients, the HE1 gene, which encode sterol regulating proteins. NPC is characterised by a complex lipid anomaly including a disturbed cellular trafficking of cholesterol but also multi-lipid storage in visceral organs and brain. Lipids were studied using conventional methods in enlarged spleens that had been removed from five patients for different therapeutic and diagnostic reasons and found to have microscopic signs of lysosomal storage disease not suspected clinically. The spleen lipid findings with a concurrent accumulation of cholesterol, sphingomyelin and glucosylceramide (Acc-CSG) allowed us to suggest NPC diagnoses for these patients, who were free of neurologic symptoms. From two patients no material for confirmatory studies was available, but in two other patients NPC diagnoses could be confirmed with the filipin cytochemical cholesterol assay and NPC1 gene analysis, respectively. However, these tests and also HE1 gene analysis were negative in a third patient. Since the Acc-CSG lipid pattern seems to indicate a multi-lipid trafficking defect rather than being highly specific for NPC, this patient, if not affected with very atypical NPC, may be a candidate for a different lipid trafficking disorder. The Acc-CSG pattern was considered to be similar to the lipid pattern known for the lipid rafts, these functional cell structures being probably disorganised and accumulated in late endosomes and lysosomes of NPC cells.

The DNA sequence and analysis of human chromosome 14

Chromosome 14 is one of five acrocentric chromosomes in the human genome. These chromosomes are characterized by a heterochromatic short arm that contains essentially ribosomal RNA genes, and a euchromatic long arm in which most, if not all, of the protein-coding genes are located. The finished sequence of human chromosome 14 comprises 87,410,661 base pairs, representing 100% of its euchromatic portion, in a single continuous segment covering the entire long arm with no gaps. Two loci of crucial importance for the immune system, as well as more than 60 disease genes, have been localized so far on chromosome 14. We identified 1,050 genes and gene fragments, and 393 pseudogenes. On the basis of comparisons with other vertebrate genomes, we estimate that more than 96% of the chromosome 14 genes have been annotated. From an analysis of the CpG island occurrences, we estimate that 70% of these annotated genes are complete at their 5' end.

Combinatorial evolution of high-affinity peptides that bind to the Thomsen-Friedenreich carcinoma antigen

Thomsen-Friedenreich (TF) antigen occurs on approximately 90% of human carcinomas, is likely involved in carcinoma cell homotypic aggregation, and has clinical value as a prognostic indicator and marker of metastasized cells. Previously, we isolated anti-TF antigen peptides from bacteriophage display libraries. These bound to TF antigen on carcinoma cells but were of low affinity and solubility. We hypothesized that peptide amino acid sequence changes would result in increased affinity and solubility, which would translate into improved carcinoma cell binding and increased inhibition of aggregation. The new peptides were more soluble and exhibited up to fivefold increase in affinity (Kd approximately equal to 60 nM). They bound cultured human breast and prostate carcinoma cells at low concentrations, whereas the earlier peptides did not. Moreover, the new peptides were potent inhibitors of homotypic aggregation. The maturated peptides will have expanded applications in basic studies of the TF antigen and particular utility as clinical carcinoma-targeting agents.

Telomerase immortalization upregulates Rab9 expression and restores LDL cholesterol egress from Niemann-Pick C1 late endosomes

Niemann-Pick C (NPC) disease is a rare recessive lipidosis marked by excessive accumulation of LDL-derived free cholesterol and glycosphingolipids in the late endosomal-lysosomal (E-L) system. Here we report that ectopic expression of human telomerase reverse transcriptase (hTeRT) in human cells leads to an upregulation of the small GTPase Rab9 and its effector p40. Expression of hTeRT in NPC1 cells results in a correction of their cellular phenotype, including clearance of accumulated cholesterol from their E-L system. Specifically, in NPC1-TeRT cells, the transport of cholesterol from the E-L system to the plasma membrane is restored with a concomitant increase in cholesterol esterification. This effect is Rab9-specific since expression of Rab9 in untransformed NPC1 cells also leads to a reversal of their disease phenotype. These effects are also seen in normal TeRT-immortalized cells and it appears that TeRT expression leads to an increase in the transport of molecules, including cholesterol, from the E-L system, and may play a role in increasing cellular proliferation. These results suggest the existence of alternative endogenous therapeutic targets that can be modulated to reverse the NPC1 disease phenotype.

Macrophage cholesterol transport: a critical player in foam cell formation

Mammalian cells have evolved complex feedback mechanisms to ensure sufficient supply of cholesterol and to prevent its excessive accumulation. During the process of atherosclerosis, these homeostatic mechanisms fail in macrophages. Uncontrolled cholesterol deposition is promoted by scavenger functions of the macrophages and the adaptive mechanisms elicited are not sufficient to process the lipid load. Consequently, a lipid-laden 'foam cell' is formed. In this review, we summarize key aspects of intracellular cholesterol processing in the special case of macrophages, including mechanisms of lipoprotein cholesterol uptake, fate of the internalized cholesterol and mechanisms implicated in cholesterol efflux. The importance of inflammatory cues, the cellular compartmentalization of cholesterol homeostatic responses and the increasing information on the transcriptional control of cholesterol balance are discussed.

MENTHO, a MLN64 homologue devoid of the START domain

MLN64 is a late endosomal membrane protein containing a carboxyl-terminal cholesterol binding START domain and is presumably involved in intracellular cholesterol transport. In the present study, we have cloned a human cDNA encoding a novel protein that we called MENTHO as an acronym for MLN64 N-terminal domain homologue because this protein is closely related to the amino-terminal half of MLN64. MLN64 and MENTHO share 70% identity and 83% similarity in an original protein domain encompassing 171 amino acids that we designated as the MENTAL (MLN64 N-terminal) domain. By translation initiation scanning MENTHO is synthesized as two isoforms of 234 (alpha) and 227 (beta) amino acids that can be phosphorylated. As MLN64, MENTHO is ubiquitously expressed and is located in the membrane of late endosomes, its amino and carboxyl-terminal extremities projecting toward the cytoplasm. We show that MENTHO overexpression does not rescue the Niemann-Pick type C lipid storage phenotype. However, MENTHO overexpression alters severely the endocytic compartment by leading at steady state to the accumulation of enlarged endosomes. These results indicate that in addition to its previously established function in addressing and anchoring proteins to the membrane of late endosomes, the MENTAL domain possesses an intrinsic biological function in endocytic transport.

Frontal lobe atrophy due to a mutation in the cholesterol binding protein HE1/NPC2

This is the first description of slowly progressive Niemann-Pick disease type C (NPC) without the typical lysosomal storage in bone marrow and viscera in two descendants of a group of 17th century French-Canadians. The index patient was a married 43-year-old woman with onset of dementia in her thirties, later followed by the development of ataxia and athetoid movements. Her autopsy disclosed frontal lobe atrophy, neurolysosomal storage with oligolamellar inclusion and tau-positive neurofibrillary tangles. Of the 119 family members screened, only a married 42-year-old sister displayed symptoms of a dementia. Both women displayed vertical supranuclear ophthalmoplegia; expressive aphasia; concrete, stimulus-bound, perseverative behavior; and impaired conceptualization and planning. Cultured fibroblasts showed decreased cholesterol esterification and positive filipin staining, but no mutation was detected in coding or promoter regions of the NPC1 gene using conformation sensitive gel electrophoresis and sequencing. Sequencing showed a homozygous gene mutation that is predicted to result in an amino acid substitution, V39M, in the cholesterol binding protein HE1 (NPC2). Adult-onset NPC2 with lysosomal storage virtually restricted to neurons represents a novel phenotypic and genotypic variant with diffuse cognitive impairment and focal frontal involvement described for the first time.

Cholesterol accumulates in cell bodies, but is decreased in distal axons, of Niemann-Pick C1-deficient neurons

Niemann-Pick type-C (NPC) disease is characterized by a progressive loss of neurons and an accumulation of unesterified cholesterol within the endocytic pathway. Unlike other tissues, however, NPC1-deficient brains do not accumulate cholesterol but whether or not NPC1-deficient neurons accumulate cholesterol is not clear. Therefore, as most studies on cholesterol homeostasis in NPC1-deficient cells have been performed in fibroblasts we have investigated cholesterol homeostasis in cultured murine sympathetic neurons lacking functional NPC1. These neurons did not display obvious abnormalities in growth or morphology and appeared to respond normally to nerve growth factor. Filipin staining revealed numerous cholesterol-filled endosomes/lysosomes in NPC1-deficient neurons and the mass of cholesterol in cell bodies was greater than in wild-type neurons. Surprisingly, however, the cholesterol content of NPC1-deficient and wild-type neurons as a whole was the same. This apparent paradox was resolved when the cholesterol content of NPC1-deficient distal axons was found to be less than of wild-type axons. Cholesterol sequestration in cell bodies did not depend on exogenously supplied cholesterol since the cholesterol accumulated before birth and did not disperse when neurons were cultured without exogenous cholesterol. The altered cholesterol distribution between cell bodies and axons suggests that transport of cholesterol, particularly that synthesized endogenously, from cell bodies to distal axons is impaired in NPC1-deficient neurons.