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.

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.

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.

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.

Sphingomyelin lipidosis variant with cirrhosis in the pediatric age group.

Two children with a variant of sphingomyelin lipidosis had otherwise unexplained cirrhosis that was histologically inactive and appeared to run an indolent course. The primary clinical problems involved the central nervous system, with vertical supranuclear ophthalmoplegia being the most distinctive feature. Biochemical analysis of cultured skin fibroblasts obtained from one of the children revealed that sphingomyelinase activity was 42% of control values. The typical inconspicuous hepatic storage and cirrhosis, coupled with the important morphologic finding of sea-blue histiocytes in the marrow, suggested that in cases of unexplained infantile or childhood cirrhosis the marrow should be closely examined for such histiocytes. Likewise, in cases of sea-blue histiocytes without evident etiology, with or without cirrhosis, this disease should be considered.