A C57BL/KsJ mouse model of Niemann-Pick disease (spm) belongs to the same complementation group as the major childhood type of Niemann-Pick disease type C

Early steps in steroidogenesis: intracellular cholesterol trafficking

Steroid hormones are made from cholesterol, primarily derived from lipoproteins that enter cells via receptor-mediated endocytosis. In endo-lysosomes, cholesterol is released from cholesterol esters by lysosomal acid lipase (LAL; disordered in Wolman disease) and exported via Niemann-Pick type C (NPC) proteins (disordered in NPC disease). These diseases are characterized by accumulated cholesterol and cholesterol esters in most cell types. Mechanisms for trans-cytoplasmic cholesterol transport, membrane insertion, and retrieval from membranes are less clear. Cholesterol esters and "free" cholesterol are enzymatically interconverted in lipid droplets. Cholesterol transport to the cholesterol-poor outer mitochondrial membrane (OMM) appears to involve cholesterol transport proteins. Cytochrome P450scc (CYP11A1) then initiates steroidogenesis by converting cholesterol to pregnenolone on the inner mitochondrial membrane (IMM). Acute steroidogenic responses are regulated by cholesterol delivery from OMM to IMM, triggered by the steroidogenic acute regulatory protein (StAR). Chronic steroidogenic capacity is determined by CYP11A1 gene transcription. StAR mutations cause congenital lipoid adrenal hyperplasia, with absent steroidogenesis, potentially lethal salt loss, and 46,XY sex reversal. StAR mutations initially destroy most, but not all steroidogenesis; low levels of StAR-independent steroidogenesis are lost later due to cellular damage, explaining the clinical findings. Rare P450scc mutations cause a similar syndrome. This review addresses these early steps in steroid biosynthesis.

Npc1 deficiency in the C57BL/6J genetic background enhances Niemann-Pick disease type C spleen pathology

Niemann-Pick type C (NPC) disease is an autosomal recessive neurovisceral lipid storage disorder. The affected genes are NPC1 and NPC2. Mutations in either gene lead to intracellular cholesterol accumulation. There are three forms of the disease, which are categorized based on the onset and severity of the disease: the infantile form, in which the liver and spleen are severely affected, the juvenile form, in which the liver and brain are affected, and the adult form, which affects the brain. In mice, a spontaneous mutation in the Npc1 gene originated in the BALB/c inbred strain mimics the juvenile form of the disease. To study the influence of genetic background on the expression of NPC disease in mice, we transferred the Npc1 mutation from the BALB/c to C57BL/6J inbred background. We found that C57BL/6J-Npc1(-/-) mice present with a much more aggressive form of the disease, including a shorter lifespan than BALB/c-Npc1(-/-) mice. Surprisingly, there was no difference in the amount of cholesterol in the brains of Npc1(-/-) mice of either mouse strain. However, Npc1(-/-) mice with the C57BL/6J genetic background showed striking spleen damage with a marked buildup of cholesterol and phospholipids at an early age, which correlated with large foamy cell clusters. In addition, C57BL/6J Npc1(-/-) mice presented red cell abnormalities and abundant ghost erythrocytes that correlated with a lower hemoglobin concentration. We also found abnormalities in white cells, such as cytoplasmic granulation and neutrophil hypersegmentation that included lymphopenia and atypias. In conclusion, Npc1 deficiency in the C57BL6/J background is associated with spleen, erythrocyte, and immune system abnormalities that lead to a reduced lifespan.

Cerebellar long-term depression is deficient in Niemann-Pick type C disease mice

Niemann-Pick type C disease (NPC) is an autosomal recessive lipidosis characterized by progressive neurodegeneration. Although several studies have revealed unusual accumulation of unesterfied cholesterol in astrocytic lysosome of NPC, pathophysiological basis of cerebellar neuronal dysfunction remains unclear. We compared parallel fiber-Purkinje cell synaptic transmission and long-term depression (LTD) in +/+npc (nih) (npc(+/+)) and -/-npc(nih) (npc(-/-)) mice. Our data showed that adenosine A1 receptor agonists decreased parallel fiber excitatory postsynaptic current (EPSC) amplitude and mEPSC frequency while its antagonists increased EPSC amplitude and mEPSC frequency in wild type and mutant mice. Furthermore, parallel fiber LTD was deficient in npc(-/-) mice and supplement of adenosine triphosphate (ATP) rescued the impaired LTD. Taken together, these experiments suggest that synaptic strength and LTD are altered in npc(-/-) mice due to the decrease of ATP/adenosine release and deactivation of A1 receptors in parallel fiber terminals. The enhanced synaptic transmission and the decreased LTD might result in progressive neurotoxicity of Purkinje cells in npc(-/-) mice.

Recent advances in elucidating Niemann-Pick C disease

Lysosomal sequestration of endocytosed LDL-derived cholesterol, premature and abnormal enrichment of cholesterol in trans Golgi cisternae and accompanying anomalies in intracellular sterol trafficking are the hallmark phenotypic features of the Niemann-Pick C (NPC) lesion. A variable severity of these alterations has been observed, with only partial correlation between clinical and biochemical phenotypes. NPC also affects the metabolism of sphingolipids, and other biochemical abnormalities have been reported. Occurrence of neurofibrillary tangles in the brain of patients with a slowly progressive course is a recent intriguing observation. Genetic heterogeneity was established by cell hybridization and linkage studies. The two complementation groups could not be distinguished from each other by clinical, cellular or biochemical criteria, suggesting that the two gene products may interact or function sequentially. The major (> 90% of patients) NPC1 gene was mapped to 18q11 and recently isolated by positional cloning. The cDNA sequence predicts a 1278-amino acid protein, with 13 to 16 possible transmembrane regions and a putative cholesterol-sensing domain. Two murine models of the disease involving the same gene are known. The murine cDNA and the npc(nih) mutation have been characterized. Described homologies of the NPC1 protein are in line with its putative involvement in cellular cholesterol traffic.

Substance P immunoreactive cell reductions in cerebral cortex of Niemann-Pick disease type C mouse

Niemann-Pick disease type C (NPC) is characterized by progressive neurodegeneration and arises from mutations in the NPC1 gene. Cholesterol has received most attention in the pathogenesis of NPC, but normalizing lipid levels in humans or mouse does not prevent neurodegeneration. In NPC mouse, neuronal degeneration in the cerebellum is the most commonly detected change, and thus previous studies have tended to focus on the cerebellum, especially Purkinje cells. Although numerous peptides have been found in the mammalian central nervous system, little data on neurotransmitters in NPC are available, and information on neurotransmitter system abnormalities could explain the complex and characteristic deficits of NPC. Thus, we performed an immunohistochemical study on NPC mouse cortices to compare cell numbers exhibiting vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and substance P (SP) immunoreactivity. In terms of VIP and NPY-immunoreactive (ir) cell numbers in the cerebral cortex, SP-ir cells were significantly reduced by about 90% in NPC (-/-) versus NPC (+/+) mouse, and were also mildly decreased in frontal and parietal NPC (+/-) versus NPC (+/+) mouse cortex. This study demonstrates for the first time, reduced number of SP-ir cells in the NPC mouse cortex.

Increased NPC1 mRNA in skin fibroblasts from Niemann-Pick disease type C patients

Niemann-Pick disease type C (NP-C) is an autosomal recessive lipid-storage disease that is characterized by progressive neurodegeneration and hepatosplenomegaly. Since identification of the NPC1 gene in 1997, a total of 120 disease-causing mutations have been reported. In this study, two novel mutations were identified, namely c.2508[-2509]A del (837Fs-838X) in exon 16 and T3194G (V1065G) in exon 21. To explore the impact of NPC1 mutations on transcription of this gene, we analyzed NPC1 mRNA levels in skin fibroblasts derived from NP-C patients. Fibroblasts from patients with missense mutations showed increased levels of NPC1 mRNA while fibroblasts from patients with a specific frameshift mutation showed mRNA levels similar to those of normal control subjects. These results suggest that NPC1 transcription levels are altered in cells with mutations in the NPC1 gene.

Patterned Purkinje cell degeneration in mouse models of Niemann-Pick type C disease

Niemann Pick disease type C1 (NPC1) is an inherited, autosomal recessive, lipid-storage disorder with major neurological involvement. Purkinje cell death is a prominent feature of the neuropathology of NPC. We have investigated Purkinje cell death in two murine models of NPC1, BALB/c npc(nih) and C57BLKS/J spm. In both cases, extensive Purkinje cell death was found in the cerebellum. The pattern of Purkinje cell death is complex. First, zebrin II-negative Purkinje cells disappear, to leave survivors aligned in stripes that closely resemble the pattern revealed by using zebrin II immunocytochemistry. Subsequently, as the disease progresses, additional Purkinje cells die. At the terminal stages of the disease, the surviving Purkinje cells are concentrated in lobules IX and X of the posterior lobe vermis. Purkinje cell degeneration is accompanied by the ectopic expression of tyrosine hydroxylase and the small heat shock protein HSP25, both associated preferentially with the surviving cells. The pattern of cell death thus reflects the fundamental compartmentation of the cerebellum into zones and stripes.

Cognitive deficit and development of motor impairment in a mouse model of Niemann-Pick type C disease

Niemann-Pick disease type C (NPC) is a fatal, autosomal recessive lipidosis characterized by a unique error in cellular trafficking of cholesterol. In the disease, unesterified cholesterol as well as sphingolipids accumulate in the late endosomes/lysosomes due to mutations in either of two recently isolated genes, NPC1 or NPC2. A metabolic and neurological disorder reminiscent of human NPC disease has been described in Balb/C mice, and it was recently shown that the mutation in the NPC mice resides in the orthologous murine Npc1 gene. Here we have followed the growth rate and applied behavioural methods in order to establish the onset and development of the major symptoms in the NPC mouse model. Wild type and NPC mice were studied during 28-59 days of age. Both male and female NPC mice displayed retarded growth at the age between 25 and 35 days. At the age of 35-45 days the weight was similar to controls and thereafter very rapidly decreased. The battery of coordination tests (vertical screen, beam balancing, coat hanger and rotating rod) established motor impairment of the NPC mice already at the age of 28-42 days, well before the onset of visually detectable ataxia. Decreased exploratory activity and lack of habituation was revealed in the NPC mice by open field test. The diseased mice were unable to learn and remember the location of the hidden escape platform in spatial water maze task suggesting cognitive impairment. In several tests the male NPC mice were more affected than the females. The present study represents the first behavioural analysis of the NPC mice. The battery of behavioural tests employed here should be valuable in the assessment of effective approaches to treat NPC, for which no preventive or curative measures have so far been established.

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

Niemann-Pick disease type C (NP-C) disease is a progressive and fatal neurological disorder characterized by accumulation of cholesterol and glycosphingolipids in peripheral tissues and that of glycosphingolipids in the brain. A C57BL/KsJ-npc1(spm) mutant strain is a genetically authentic model of NP-C. This study investigated neuronal cell loss and lipid accumulation in the npc1(spm) mouse brain. Nissl-staining revealed abundant swollen neurons in the neocortex, piriform cortex, hippocampus and basal ganglia at 3-4 wk of age. In addition to loss of the Purkinje cells, we found a conspicuous cell loss in the ventral posterial lateral (VPL) and medial (VPM) nuclei of thalamus, which became apparent after 4-5 wk. Biochemical analyses revealed no increase of cholesterol in the lipid extracts whereas a substantial accumulation of cholesterol was detectable in most of the large neurons by filipin staining in the brain of homozygous mice. In contrast to the diffuse staining pattern in normal brains, the neuropils of the neurons in the brain of homozygous mice were stained in a punctate pattern. The ubiquitous accumulation excludes a direct role of cholesterol in the progressive neuronal loss in the Purkinje cell layer and in the VPL and VPM of the thalamus.

Decreased membrane fluidity and unsaturated fatty acids in Niemann-Pick disease type C fibroblasts

Niemann-Pick disease type C (NP-C) is an autosomal recessive disorder characterized by the sequestration and trapping of endocytosed cholesterol in lysosomes. The NPC1 gene on chromosome 18 was recently identified but its physiological function remains unknown. We have studied the lipid compositions of cultured human NP-C fibroblasts and mouse SPM-3T3 cell line derived from the C57BL/KsJ NP-C model mouse, which belongs to the same complementation group. Fibroblasts derived from apparently normal age-matched individuals and a subline of SPM-3T3 cells which restores cholesterol metabolism by transfer of human chromosome 18 were used as controls. Levels of free cholesterol in whole cell homogenates increased about 1.5-fold in human NP-C fibroblasts and mouse SPM-3T3 cells, while in the plasma membrane, cholesterol content did not significantly change in NP-C fibroblasts but rather decreased in SPM-3T3 cells. The total phospholipid content did not significantly change; however, among phospholipid head groups, increases in sphingomyelin and decreases in other classes were observed in human NP-C fibroblasts and mouse SPM-3T3 cells. The ratios of saturated fatty acids to unsaturated fatty acids increased in both human and mouse cells. The increase was also confirmed in the plasma membrane fraction of SPM-3T3 cells. Membrane fluidity was examined using a 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescent probe. The DPH anisotropy values were markedly increased in NP-C fibroblasts and in SPM-3T3 cells. The results suggest that a NP-C mutation causes complex alterations in cellular lipid contents and biophysical properties of the membrane.

Murine model of Niemann-Pick C disease: mutation in a cholesterol homeostasis gene

An integrated human-mouse positional candidate approach was used to identify the gene responsible for the phenotypes observed in a mouse model of Niemann-Pick type C (NP-C) disease. The predicted murine NPC1 protein has sequence homology to the putative transmembrane domains of the Hedgehog signaling molecule Patched, to the cholesterol-sensing regions of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and SREBP cleavage-activating protein (SCAP), and to the NPC1 orthologs identified in human, the nematode Caenorhabditis elegans, and the yeast Saccharomyces cerevisiae. The mouse model may provide an important resource for studying the role of NPC1 in cholesterol homeostasis and neurodegeneration and for assessing the efficacy of new drugs for NP-C disease.