Metabolism of Non-Enzymatically Derived Oxysterols: Clues from sterol metabolic disorders.

Cholestane-3ß,5α,6ß-triol (3ß,5α,6ß-triol) is formed from cholestan-5,6-epoxide (5,6-EC) in a reaction catalysed by cholesterol epoxide hydrolase, following formation of 5,6-EC through free radical oxidation of cholesterol. 7-Oxocholesterol (7-OC) and 7ß-hydroxycholesterol (7ß-HC) can also be formed by free radical oxidation of cholesterol. Here we investigate how 3ß,5α,6ß-triol, 7-OC and 7ß-HC are metabolised to bile acids. We show, by monitoring oxysterol metabolites in plasma samples rich in 3ß,5α,6ß-triol, 7-OC and 7ß-HC, that these three oxysterols fall into novel branches of the acidic pathway of bile acid biosynthesis becoming (25R)26-hydroxylated then carboxylated, 24-hydroxylated and side-chain shortened to give the final products 3ß,5α,6ß-trihydroxycholanoic, 3ß-hydroxy-7-oxochol-5-enoic and 3ß,7ß-dihydroxychol-5-enoic acids, respectively. The intermediates in these pathways may be causative of some phenotypical features of, and/or have diagnostic value for, the lysosomal storage diseases, Niemann Pick types C and B and lysosomal acid lipase deficiency. Free radical derived oxysterols are metabolised in human to unusual bile acids via novel branches of the acidic pathway, intermediates in these pathways are observed in plasma.

MLN64 induces mitochondrial dysfunction associated with increased mitochondrial cholesterol content.

MLN64 is a late endosomal cholesterol-binding membrane protein that has been implicated in cholesterol transport from endosomal membranes to the plasma membrane and/or mitochondria, in toxin-induced resistance, and in mitochondrial dysfunction. Down-regulation of MLN64 in Niemann-Pick C1 deficient cells decreased mitochondrial cholesterol content, suggesting that MLN64 functions independently of NPC1. However, the role of MLN64 in the maintenance of endosomal cholesterol flow and intracellular cholesterol homeostasis remains unclear. We have previously described that hepatic MLN64 overexpression increases liver cholesterol content and induces liver damage. Here, we studied the function of MLN64 in normal and NPC1-deficient cells and we evaluated whether MLN64 overexpressing cells exhibit alterations in mitochondrial function. We used recombinant-adenovirus-mediated MLN64 gene transfer to overexpress MLN64 in mouse liver and hepatic cells; and RNA interference to down-regulate MLN64 in NPC1-deficient cells. In MLN64-overexpressing cells, we found increased mitochondrial cholesterol content and decreased glutathione (GSH) levels and ATPase activity. Furthermore, we found decreased mitochondrial membrane potential and mitochondrial fragmentation and increased mitochondrial superoxide levels in MLN64-overexpressing cells and in NPC1-deficient cells. Consequently, MLN64 expression was increased in NPC1-deficient cells and reduction of its expression restore mitochondrial membrane potential and mitochondrial superoxide levels. Our findings suggest that MLN64 overexpression induces an increase in mitochondrial cholesterol content and consequently a decrease in mitochondrial GSH content leading to mitochondrial dysfunction. In addition, we demonstrate that MLN64 expression is increased in NPC cells and plays a key role in cholesterol transport into the mitochondria.

Quantitative evaluation of orofacial motor function in mice: The pasta gnawing test, a voluntary and stress-free behavior test.

BACKGROUND: Evaluation of motor deficits in rodents is mostly restricted to limb motor tests that are often high stressors for the animals. NEW METHOD: To test rodents for orofacial motor impairments in a stress-free environment, we established the pasta gnawing test by measuring the biting noise of mice that eat a piece of spaghetti. Two parameters were evaluated, the biting speed and the biting peaks per biting episode. To evaluate the power of this test compared to commonly used limb motor and muscle strength tests, three mouse models of Parkinson's disease, amyotrophic lateral sclerosis and Niemann-Pick disease were tested in the pasta gnawing test, RotaRod and wire suspension test. RESULTS: Our results show that the pasta gnawing test reliably displays orofacial motor deficits. COMPARISON WITH EXISTING METHODS: The test is especially useful as additional motor test in early onset disease models, since it shows first deficits later than the RotaRod or wire suspension test. The test depends on a voluntary eating behavior of the animal with only a short-time food deprivation and should thus be stress-free. CONCLUSIONS: The pasta gnawing test represents a valuable tool to analyze orofacial motor deficits in different early onset disease models.

Pilot study of newborn screening for six lysosomal storage diseases using Tandem Mass Spectrometry.

BACKGROUND: There is current expansion of newborn screening (NBS) programs to include lysosomal storage disorders because of the availability of treatments that produce an optimal clinical outcome when started early in life. OBJECTIVE: To evaluate the performance of a multiplex-tandem mass spectrometry (MS/MS) enzymatic activity assay of 6 lysosomal enzymes in a NBS laboratory for the identification of newborns at risk for developing Pompe, Mucopolysaccharidosis-I (MPS-I), Fabry, Gaucher, Niemann Pick-A/B, and Krabbe diseases. METHODS AND RESULTS: Enzyme activities (acid α-glucosidase (GAA), galactocerebrosidase (GALC), glucocerebrosidase (GBA), α-galactosidase A (GLA), α-iduronidase (IDUA) and sphingomyeline phosphodiesterase-1 (SMPD-1)) were measured on ~43,000 de-identified dried blood spot (DBS) punches, and screen positive samples were submitted for DNA sequencing to obtain genotype confirmation of disease risk. The 6-plex assay was efficiently performed in the Washington state NBS laboratory by a single laboratory technician at the bench using a single MS/MS instrument. The number of screen positive samples per 100,000 newborns were as follows: GAA (4.5), IDUA (13.6), GLA (18.2), SMPD1 (11.4), GBA (6.8), and GALC (25.0). DISCUSSION: A 6-plex MS/MS assay for 6 lysosomal enzymes can be successfully performed in a NBS laboratory. The analytical ranges (enzyme-dependent assay response for the quality control HIGH sample divided by that for all enzyme-independent processes) for the 6-enzymes with the MS/MS is 5- to 15-fold higher than comparable fluorimetric assays using 4-methylumbelliferyl substrates. The rate of screen positive detection is consistently lower for the MS/MS assay compared to the fluorimetric assay using a digital microfluidics platform.

Role of ACAT1-positive late endosomes in macrophages: cholesterol metabolism and therapeutic applications for Niemann-Pick disease type C.

Macrophages in hyperlipidemic conditions accumulate cholesterol esters and develop into foamy transformed macrophages. During this transformation, macrophages demonstrate endoplasmic reticulum fragmentation and consequently produce acyl coenzyme A: cholesterol acyltransferase 1 (ACAT1)-positive late endosomes (ACAT1-LE). ACAT1-LE-positive macrophages effectively esterify modified or native low-density lipoprotein-derived free cholesterol, which results in efficient cholesterol esterification as well as atherosclerotic plaque formation. These macrophages show significant cholesterol ester formation even when free cholesterol egress from late endosomes is impaired, which indicates that free cholesterol is esterified at ACAT1-LE. Genetic blockade of cholesterol egress from late endosomes causes Niemann-Pick disease type C (NPC), an inherited lysosomal storage disease with progressive neurodegeneration. Induction of ACAT1-LE in macrophages with the NPC phenotype led to significant recovery of cholesterol esterification. In addition, in vivo ACAT1-LE induction significantly extended the lifespan of mice with the NPC phenotype. Thus, ACAT1-LE not only regulates intracellular cholesterol metabolism but also ameliorates NPC pathophysiology.

Lysosomal storage diseases as differential diagnosis of hepatosplenomegaly.

In adults, elevated transaminases and hepatomegaly, often mild, with moderate to massive idiopathic splenomegaly might hint to a lysosomal storage disease (LSD). In most of these cases, hepatosplenomegaly does not eventually lead to cirrhosis, hepatocellular carcinoma or cholestasis. Nevertheless, the hepatic clinical findings might be the incentive for the patient to present at the physician's office. Many of the currently known >50 lysosomal storage diseases might manifest in liver: out of these, the most important ones in adults are: Gaucher disease, cholesterol ester storage disease (CESD) and the Niemann-Pick diseases. An increase of plasma chitotriosidase should alert the physician for the presence of an LSD. For Gaucher's disease, enzyme supplementation and substrate deprivation constitute effective therapeutic options. Fabry's disease, the most prevalent lysosomal storage disease, does usually not affect the liver, but causes painful episodes of hands' or feet pain (acroparesthesias), left ventricular hypertrophy, renal failure, early stroke and decreased life expectancy. The emerging advent of effective therapeutic options and the cumulative prevalence of lysosomal storage diseases urge the hepatologist to add these diagnostic pathways to the clinical repertoire.

Human umbilical cord blood-derived mesenchymal stem cells improve neurological abnormalities of Niemann-Pick type C mouse by modulation of neuroinflammatory condition.

Niemann-Pick type C (NP-C) disease is a devastating developmental disorder with progressive and fatal neurodegeneration. We have used a mouse model of Niemann-Pick type C (NP-C) disease to evaluate the effects of direct intracerebral transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) on the progression of neurological disease in this order. Here, we show that hUCB-MSCs transplantation into NP-C mice prevents the loss of Purkinje neurons and inhibits cerebellar apoptotic cell death. Interestingly, these effects were associated with the modulation of inflammatory responses, as evidenced by increased anti-inflammatory cytokine IL-10, and reduced abnormal astrocytic activation. Furthermore, our results show that the hUCB-MSCs transplantation reduced the cholesterol accumulation level in neurons in NP-C mice compared with sham-transplanted animals. This study provides the first evidence that hUCB-MSCs can improve neurological symptoms in NP-C disease, suggesting it as a potential therapeutic agent against neurodegenerative diseases.

Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion.

We examined the effect of Niemann-Pick disease type 2 (NPC2) protein and some late endosomal lipids [sphingomyelin, ceramide and bis(monoacylglycero)phosphate (BMP)] on cholesterol transfer and membrane fusion. Of all lipid-binding proteins tested, only NPC2 transferred cholesterol at a substantial rate, with no transfer of ceramide, GM3, galactosylceramide, sulfatide, phosphatidylethanolamine, or phosphatidylserine. Cholesterol transfer was greatly stimulated by BMP, little by ceramide, and strongly inhibited by sphingomyelin. Cholesterol and ceramide were also significantly transferred in the absence of protein. This spontaneous transfer of cholesterol was greatly enhanced by ceramide, slightly by BMP, and strongly inhibited by sphingomyelin. In our transfer assay, biotinylated donor liposomes were separated from fluorescent acceptor liposomes by streptavidin-coated magnetic beads. Thus, the loss of fluorescence indicated membrane fusion. Ceramide induced spontaneous fusion of lipid vesicles even at very low concentrations, while BMP and sphingomyelin did so at about 20 mol% and 10 mol% concentrations, respectively. In addition to transfer of cholesterol, NPC2 induced membrane fusion, although less than saposin-C. In this process, BMP and ceramide had a strong and mild stimulating effect, and sphingomyelin an inhibiting effect, respectively. Note that the effects of the lipids on cholesterol transfer mediated by NPC2 were similar to their effect on membrane fusion induced by NPC2 and saposin-C.

Defects of synaptic vesicle turnover at excitatory and inhibitory synapses in Niemann-Pick C1-deficient neurons.

Niemann-Pick disease type C (NPC) is a progressive neurodegenerative disorder characterized by accumulation of free cholesterol in late endosomes/lysosomes. The pathological basis for the disease is poorly understood. In the present study, electrophysiological and fluorescent dye studies were applied to examine neuron-specific functions of Niemann-Pick disease type C1 (NPC1) and to determine whether excitatory and inhibitory synapses are differentially impaired by NPC1 deficiency. Densities of spines and postsynaptic receptor clusters were not affected by NPC1 deficiency over the period examined. However, drastic defects on exocytosis were found both in glutamatergic and GABAergic synapses. The defects were caused in part by a delay in the time required for replacement of excytosed vesicles with new fusion-competent ones. Moreover, we found that the delay of synaptic vesicle turnover was longer in inhibitory synapses (>3 s) than in excitatory synapses (<0.2 s). These defects may be early indicators, and could provide a potential explanation for key features of the disease, such as dystonia and seizures.

Expression of Npc1 in glial cells corrects sterility in Npc1(-/-) mice.

Niemann-Pick type C1 (NPC) disease is an autosomal recessive neurodegenerative disorder. One feature of the mouse model of NPC1 is it's infertility. We have made transgenic mice which express the Npc1 protein exclusively in fibrillary astrocytes, using the glial fibrillary acidic protein (GFAP) promoter. This selective expression of Npc1 corrects sterility in GFAP-Npc1(-/-), Npc1(-/-) mice. Counts of acidophils in the pituitary of GFAP-Npc1E, Npc1(-/-) mice, as compared Npc1(-/-) mice, and measurements of dopamine D2 receptor (DRD2) mRNA in the pituitary, suggest mechanisms for fertility enhancement. We conclude that the correction of sterility in GFAP-Npc1E, Npc1(-/-) mice is a result of restoring hypothalamic control of the pituitary.

Clinical, electrophysiological, and serum biochemical measures of progressive neurological and hepatic dysfunction in feline Niemann-Pick type C disease.

Niemann-Pick type C (NP-C) disease is a neurovisceral lysosomal storage disease characterized by neurologic dysfunction, hepatosplenomegaly, and early death. Natural history studies are very difficult to perform due to the low incidence and high heterogeneity of disease in the human population. Sixteen cats with a spontaneously occurring missense mutation in NPC1 were evaluated over time to define the progression of neurologic and hepatic disease. Affected cats had remarkably regular onsets of specific signs of cerebellar and vestibular system dysfunction with progressive severity of dysfunction quantified by postrotatory nystagmus and brain stem auditory evoked response measures. NP-C disease cats also showed increasing serum activity of alanine aminotransferase, asparate aminotransferase, and cholesterol with advancing age. Affected cats lived to a mean age of 20.5 +/- 4.8 wk. CNS and hepatic lesions were similar to those described in human patients. These data are the first to document progressive hepatic disease in the feline model and demonstrate the importance of liver disease as part of the NP-C disease phenotype. Both neurologic and hepatic measures of disease onset and severity can be used as a baseline with which to assess the efficacy of experimental therapies of NP-C disease in the feline model.

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

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

Cholesterol accumulation is associated with lysosomal dysfunction and autophagic stress in Npc1 -/- mouse brain.

Niemann-Pick type C (NPC) disease is an autosomal recessive disorder caused by mutations of NPC1 and NPC2 genes. Progressive neurodegeneration that accompanies NPC is fatal, but the underlying mechanisms are still poorly understood. In the present study, we characterized the association of autophagic-lysosomal dysfunction with cholesterol accumulation in Npc1(-/-) mice during postnatal development. Brain levels of lysosomal cathepsin D were significantly higher in mutant than in wild-type mice. Increases in cathepsin D occurred first in neurons and later in astrocytes and microglia and were both spatially and temporally associated with intracellular cholesterol accumulation and neurodegeneration. Furthermore, levels of ubiquitinated proteins were higher in endosomal/lysosomal fractions of brains from Npc1(-/-) mice than from wild-type mice. Immunoblotting results showed that levels of LC3-II were significantly higher in brains of mutant than wild-type mice. Combined LC3 immunofluorescence and filipin staining showed that LC3 accumulated within filipin-labeled cholesterol clusters inside Purkinje cells. Electron microscopic examination revealed the existence of autophagic vacuole-like structures and multivesicles in brains from Npc1(-/-) mice. These results provide strong evidence that cholesterol accumulation-induced changes in autophagy-lysosome function are closely associated with neurodegeneration in NPC.

Cholesterol accumulation sequesters Rab9 and disrupts late endosome function in NPC1-deficient cells.

Niemann-Pick type C disease is an autosomal recessive disorder that leads to massive accumulation of cholesterol and glycosphingolipids in late endosomes and lysosomes. To understand how cholesterol accumulation influences late endosome function, we investigated the effect of elevated cholesterol on Rab9-dependent export of mannose 6-phosphate receptors from this compartment. Endogenous Rab9 levels were elevated 1.8-fold in Niemann-Pick type C cells relative to wild type cells, and its half-life increased 1.6-fold, suggesting that Rab9 accumulation is caused by impaired protein turnover. Reduced Rab9 degradation was accompanied by stabilization on endosome membranes, as shown by a reduction in the capacity of Rab9 for guanine nucleotide dissociation inhibitor-mediated extraction from Niemann-Pick type C membranes. Cholesterol appeared to stabilize Rab9 directly, as liposomes loaded with prenylated Rab9 showed decreased extractability with increasing cholesterol content. Rab9 is likely sequestered in an inactive form on Niemann-Pick type C membranes, as cation-dependent mannose 6-phosphate receptors were missorted to the lysosome for degradation, a process that was reversed by overexpression of GFP-tagged Rab9. In addition to using primary fibroblasts isolated from Niemann-Pick type C patients, RNA interference was utilized to recapitulate the disease phenotype in cultured cells, greatly facilitating the analysis of cholesterol accumulation and late endosome function. We conclude that cholesterol contributes directly to the sequestration of Rab9 on Niemann-Pick type C cell membranes, which in turn, disrupts mannose 6-phosphate receptor trafficking.

Neuronal cell death caused by inhibition of intracellular cholesterol trafficking is caspase dependent and associated with activation of the mitochondrial apoptosis pathway.

An elevated level of cholesterol in mitochondrial membranes of Niemann-Pick disease type C1 (NPC1) mouse brains and neural cells has been found to cause mitochondrial dysfunction. In this study, we demonstrate that inhibition of intracellular cholesterol trafficking in primary neurons by class 2 amphiphiles, which mimics the major biochemical and cellular feature of NPC1, led to not only impaired mitochondrial function but also activation of the mitochondrial apoptosis pathway. In activation of this pathway both cytochrome c and Smac/Diablo were released but apoptosis-inducing factor (AIF) was not involved. Treatment of the neurons with taurine, a caspase 9-specific inhibitor, could prevent the amphiphile-induced apoptotic cell death, suggesting that formation of apoptosome, followed by caspase 9 and caspase 3 activation, might play a critical role in the neuronal death pathway. Taken together, the mitochondria-dependent death cascade induced by blocking intracellular cholesterol trafficking was caspase dependent. The findings provide clues for both understanding the molecular basis of neurodegeneration in NPC1 disease and developing therapeutic strategies for treatment of this disorder.

Natural history of Type A Niemann-Pick disease: possible endpoints for therapeutic trials.

OBJECTIVE: To describe the disease course and natural history of Type A Niemann-Pick disease (NPD). METHODS: Ten patients with NPD-A (six male, four female; age range at entry: 3 to 6 months) were serially evaluated including clinical neurologic, ophthalmologic, and physical examinations, and assessment of development. Laboratory analyses, abdominal and brain ultrasounds, and chest radiographs also were obtained and information on intercurrent illnesses and cause of mortality was collected. RESULTS: All affected infants had a normal neonatal course and early development. The first symptom detected in all patients was hepatosplenomegaly. Developmental age did not progress beyond 10 months for adaptive behavior, 12 months for expressive language, 9 months for gross motor skills, and 10 months for fine motor skills. Non-neurologic symptoms included frequent vomiting, failure to thrive, respiratory infections, irritability, and sleep disturbance. Neurologic examination at the time of presentation was normal in most patients. Later neurologic examinations revealed progressive hypotonia with loss of the deep tendon reflexes. All patients had cherry red spots by 12 months. The median time from diagnosis to death was 21 months. The cause of death was respiratory failure in nine patients and complications from bleeding in the tenth. CONCLUSIONS: The clinical course in Type A Niemann-Pick disease is similar among affected patients and is characterized by a relentless neurodegenerative course that leads to death, usually within 3 years.

Type B Niemann-Pick disease: findings at chest radiography, thin-section CT, and pulmonary function testing.

PURPOSE: To evaluate findings at radiography, computed tomography (CT), and pulmonary function testing in patients with type B Niemann-Pick disease. MATERIALS AND METHODS: The study was approved by the institutional review board or ethics committee at each study site and was compliant with HIPAA at the U.S. site. Written informed consent was obtained from each patient or guardian and minor assent was obtained from all children before any study-related procedures. Pulmonary involvement in 53 patients (27 male and 26 female patients; age range, 7-65 years; mean age, 23.3 years) with type B Niemann-Pick disease was evaluated with imaging and pulmonary function tests. All patients underwent chest radiography and thin-section CT, and images were independently interpreted by one of two radiologists. Spirometry (forced vital capacity [FVC] and forced expiratory volume in 1 second [FEV1]) was performed and diffusing capacity of lung for carbon monoxide (Dlco) was evaluated in all patients who could comply. A score for the degree of interstitial lung disease was derived at both radiography and CT, and the CT scores were then compared with results of pulmonary function testing and patient age by means of linear regression. CT scores were compared between the upper and lower lung zones by using the Wilcoxon signed rank test. RESULTS: Chest radiography and CT, respectively, revealed interstitial lung disease in 47 (90%) and 51 (98%) of the 52 patients who completed both imaging examinations. There was a basilar predominance of interstitial lung disease at CT. Six patients had pulmonary nodules, one of which was calcified at chest radiography. There were no statistically significant correlations between interstitial lung disease score at CT and age or percentage predicted FVC, FEV1, or Dlco values. CONCLUSION: Although pulmonary function test indexes may be abnormal, imaging findings do not necessarily correlate with pulmonary function in patients with type B Niemann-Pick disease.