[Disorder of cholesterol metabolism: regulation of intracellular cholesterol and membrane trafficking].

It has been clarified that several transcription factors and functioning proteins play important roles regulating intracellular cholesterol levels. They bind to the ER membrane and sense changes in cholesterol levels in the membrane through SSD. An important membrane-binding transcription factor, SREBP, is retained in the ER membrane, forming an SREBP/SCAP/INSIG trimer when cellular cholesterol levels are abundant. This complex blocks the transport of SREBPs to the Golgi apparatus, thus preventing subsequent transcriptional activation. When cellular cholesterol levels are low, the ER cholesterol concentration is below a threshold value ( <5 mol %). Under these conditions, SCAP escorts SREBPs from the ER to Golgi apparatus by binding to a component of the CopII protein coat. Once in the Golgi apparatus, the SREBPs are proteolytically processed to generate their nuclear form, the bHLH leucine zipper, that activates genes for cholesterol synthesis and uptake. HMG-CoA reductase is also post-transcriptionally regulated by sterol, with INSIG binding of the protein leading to its proteosomal degradation. We demonstrated that Tangier disease and Niemann-Pick disease type B and type C are metabolic disorders of membrane cholesterol. These diseases are not so common in clinical medicine; however, it is very important to understand membrane lipid metabolism, especially in the ER. It will be clarified in the near future disorders of membrane cholesterol trafficking contribute to the pathogeneses of many kinds of disease affecting through ER functioning.

The pathogenesis and treatment of acid sphingomyelinase-deficient Niemann-Pick disease.

Patients with Niemann-Pick disease (NPD) Types A and B have an inherited deficiency of acid sphingomyelinase (ASM) activity. The clinical spectrum of this disorder ranges from the infantile neurological form that results in death by 3 years of age (NPD Type A) to the non-neurological form that is compatible with survival into adulthood (NPD Type B). Intermediate cases have also been reported, and the disease is best thought of as a single entity with a spectrum of phenotypes. ASM deficiency is panethnic, but appears to be more frequent in individuals of Middle Eastern and North African descent. Current estimates of the disease incidence range from 0.5 to 1 per 100,000 births, although these approximations are thought to underestimate the true frequency of the disorder. The gene encoding ASM--SMPD1--has been studied extensively, and over 100 mutations in SMPD1 have been found to cause ASM-deficient NPD. Based on these findings, DNA-based carrier screening has been implemented in the Ashkenazi Jewish community. ASM-knockout mouse models also have been generated and used to investigate disease pathogenesis and treatment with stem cell transplantation, gene therapy and enzyme replacement therapy (ERT). Based on these studies, clinical trials of ERT are underway in patients with non-neurological ASM-deficient NPD.

TNF-{alpha} plays a role in hepatocyte apoptosis in Niemann-Pick type C liver disease.

Niemann-Pick type C (NPC) is a fatal autosomal recessive lysosomal storage disease clinically characterized by neurodegeneration and liver disease. Heterogeneous mutations in the NPC1 and NPC2 genes cause impaired egress of free cholesterol from lysosomes, leading to accumulation of cholesterol and glycosphingolipids. Key features of NPC liver disease include hepatic apoptosis, inflammation, and fibrosis. It is unclear what signaling events regulate these disease processes in NPC. We hypothesize that tumor necrosis factor alpha (TNF-alpha), which is involved in both proinflammatory and apoptotic signaling cascades, is a key mediator of inflammation, apoptosis, and fibrosis in NPC liver disease. In this study, we evaluated the role of TNF-alpha signaling in NPC liver disease by utilizing NPC1-specific antisense oligonucleotides to knock down NPC1 expression in control and TNF-alpha knockout mice. In the absence of TNF-alpha, NPC1 knockdown produced liver disease with significantly less inflammation, apoptosis, and fibrosis.

Niemann-Pick type C1 protein influences the delivery of cholesterol to the SREBP: SCAP complex

The proposed role of Niemann-Pick type C1 protein (NPC1) in the delivery of low-density lipoprotein (LDL) cholesterol to the sterol regulatory element binding protein (SREBP):SREBP cleavage activation protein (SCAP) complex in the endoplasmic reticulum has been largely based on indirect studies and remains contentious. The major aim of the present study was to assess whether NPC1 is involved in the delivery of LDL cholesterol to the SREBP:SCAP complex. A cell line stably expressing green fluorescence protein-SCAP was cultured in the presence of U18666A, which can induce a Niemann-Pick type C disease phenotype, in order to locate the SREBP:SCAP complex by fluorescence microscopy. Our major finding was that defective NPC1 caused a delay in the ability of LDL cholesterol to suppress SREBP processing. This was shown in a time-course experiment by the effect of LDL on green fluorescence protein-SCAP movement when cells were treated with pharmacological agents to induce a Niemann-Pick type C disease phenotype. We demonstrated directly by fluorescence microscopy that defective NPC1 causes a delay in LDL cholesterol delivery to the endoplasmic reticulum where SCAP senses cholesterol.

Niemann-Pick type C1 protein influences the delivery of cholesterol to the SREBP:SCAP complex.

The proposed role of Niemann-Pick type C1 protein (NPC1) in the delivery of low-density lipoprotein (LDL) cholesterol to the sterol regulatory element binding protein (SREBP):SREBP cleavage activation protein (SCAP) complex in the endoplasmic reticulum has been largely based on indirect studies and remains contentious. The major aim of the present study was to assess whether NPC1 is involved in the delivery of LDL cholesterol to the SREBP:SCAP complex. A cell line stably expressing green fluorescence protein-SCAP was cultured in the presence of U18666A, which can induce a Niemann-Pick type C disease phenotype, in order to locate the SREBP:SCAP complex by fluorescence microscopy. Our major finding was that defective NPC1 caused a delay in the ability of LDL cholesterol to suppress SREBP processing. This was shown in a time-course experiment by the effect of LDL on green fluorescence protein-SCAP movement when cells were treated with pharmacological agents to induce a Niemann-Pick type C disease phenotype. We demonstrated directly by fluorescence microscopy that defective NPC1 causes a delay in LDL cholesterol delivery to the endoplasmic reticulum where SCAP senses cholesterol.

Altered cholesterol metabolism in Niemann-Pick type C1 mouse brains affects mitochondrial function.

Niemann-Pick type C1 (NPC1) disease is a fatal hereditary disorder characterized by a defect in cholesterol trafficking and progressive neurodegeneration. Although the NPC1 gene has been identified, the molecular mechanism responsible for neuronal dysfunction in brains of patients with NPC1 disease remains unknown. This study demonstrates that the amount of cholesterol within mitochondria membranes is significantly elevated in NPC1 mouse brains and neural cells. In addition, the mitochondrial membrane potential, the activity of ATP synthase, and henceforth the level of ATP are markedly decreased in NPC1 mouse brains and neurons. Importantly, reducing the level of cholesterol within mitochondrial membranes using methyl-beta-cyclodextrin can restore the activity of ATP synthase. Finally, NPC1 neurons show an impaired neurite outgrowth, which can be rescued by exogenous ATP. These results suggest that mitochondrial dysfunctions and subsequent ATP deficiency, which are induced by altered cholesterol metabolism in mitochondria, may be responsible for neuronal impairment in NPC1 disease.

Comparative effects of recombinant acid sphingomyelinase administration by different routes in niemann-pick disease mice.

An inherited deficiency of acid sphingomyelinase (ASM) activity results in the Type A and B forms of Niemann-Pick disease (NPD). The aim of this study was to evaluate the effects of recombinant human ASM (rhASM) replacement therapy on the mouse model, by comparing different routes of administration. Eight NPD mice received rhASM via an intravenous injection (IV) administered at a dose of 1 mg/kg and another group of 8 NPD mice received the same dose by subcutaneous injection (SC). The plasma levels of ASM activity in intravenously administered mice were significantly elevated immediately after injection. In contrast, in the subcutaneously injected mice, the level of ASM activity was maximal 6 h after injection. The levels of ASM activity in both groups had declined substantially by 2 days after injection. It was concluded that rhASM administered by subcutaneous injection is completely absorbed, and offers a similar efficacy to intravenously administered recombinant enzyme.

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.

Lipid and cholesterol trafficking in NPC.

Niemann-Pick type C, or NPC for short, is an early childhood disease exhibiting progressive neurological degeneration, associated with hepatosplenomegaly in some cases. The disease, at the cellular level, is a result of improper trafficking of lipids such as cholesterol and glycosphingolipids (GSLs) to lysosome-like storage organelles (LSOs), which become engorged with these lipids. It is believed that the initial defect in trafficking, whether of cholesterol or a GSL, results in an eventual traffic jam in these LSOs. This leads to the retention of not only other lipids, but also of transmembrane proteins that transiently associate with the late endosomes (LE) in normal cells, on their way to other cellular destinations such as the trans-Golgi network (TGN). In this review, we discuss the biophysical properties of lipids and cholesterol that might determine their intracellular itineraries, and how these itineraries are altered in NPC cells, which have defects in the proteins NPC1 or NPC2. We also discuss some potential therapeutic directions being suggested by recent research.

Cellular pathology of Niemann-Pick type C disease.

Niemann-Pick type C (NPC) is a lysosomal storage disorder that results in the accumulation of cholesterol and sphingolipids. Mutations in the NPC1 or NPC2 gene are responsible for the disease but the precise functions of the encoded proteins remain unresolved. Recent observations have challenged the traditional concept of NPC as a primary cholesterol transport defect. This review updates the recent NPC literature, summarizing the increasing insight into the cholesterol trafficking circuits and also addressing the contribution of other lipids in the cellular pathogenesis. The importance of NPC as a model for subcellular lipid imbalance in studying more common diseases, such as Alzheimer's and cardiovascular diseases, is discussed.

Neurodegenerative disorders and cholesterol.

It has been suggested that a high serum cholesterol level is a risk factor for Alzheimer's disease (AD), that treatment with cholesterol-lowering drugs (statins) reduces the frequency of AD development, and that the polymorpholism of genes encoding proteins regulating cholesterol metabolism is associated with the frequency of AD development. However, the mechanism by which high serum cholesterol level leads to AD, still remains unclarified. Several recent studies have shown the results challenging the above notions. Here another notion is proposed, that is, a low high-density lipoprotein (HDL) level in serum and cerebro-spinal fluid (CSF) is a risk factor for the development of AD; moreover, the possibility that AD and Niemann-Pick type C disease share a common cascade, by which altered cholesterol metabolism leads to neurodegeneration (tauopathy) is discussed. In this review, the association between cholesterol and AD pathogenesis is discussed from different viewpoints and several basic issues are delineated and addressed to fully understand the mechanisms underlying this relationship.

Multidrug permeases and subcellular cholesterol transport.

Studies of Niemann-Pick C (NPC) and Tangier diseases have led to the identification of the causative genes, NPC1 and ABCA1, respectively. Characterization of their protein products shows that NPC1 and ABCA1 are permeases that belong to two different superfamilies of efflux pumps, which might be important in subcellular lipid and cholesterol transport.

Manifestaçäo hemorrágica no recém nascido como sinal precoce da doença de Niemann-Pick / Bleeding in newborn as early signal of Niemann-Pick

A Doença de Niemann-Pick é um distúrbio de armazenamento hereditário cujo problema principal reside na deficiência parcial ou total de esfingomielinase e/ou de suas isoenzimas, levando ao acúmulo de esfingomielina em todos os orgäos, principalmente no fígado, rins e cérebro. As alteraçöes da coagulaçäo na Doença de Niemann-Pick ainda säo pouco descritas, porém podem apresentar-se precose e isoladamente nos neonatos, precedendo os sinais e sintomas mais frequentes. Os autores apresentam neste relato um caso de paciente do sexo feminino, cinco meses de vida, com quadro de hemorragia grave aos 13 dias de vida após realizaçäo do Teste do Pezinho e aumento do volume abdominal progressivo desde o nascimento. O diagnóstico de Doença de Niemann-Pick foi dado após exclusäo das principais patologias com quadro semelhante e pelo achado de células histiocíticas com depósito citoplasmático espumoso no aspirado de medula óssea. Os autores destacam ainda suas características clínico-laboratoriais e diagnósticos diferenciais.