Peripheral nerve pathology in Niemann-Pick type C mouse

The History of the Neurosciences at the Albert Einstein Medical Center and Montefiore Medical Center-Science at the Heart of Medicine

"Science at the heart of medicine," the ethos of the Albert Einstein College of Medicine and its university hospital, Montefiore Medical Center, has shaped the institution's legacy of pivotal contributions in the neurosciences. From its inception to the present day, the leaders of these institutions have epitomized the integration of clinical medicine, technical excellence, and multidisciplinary basic research. Over time these skills have become increasingly imperative for addressing neurological disorders and overcoming obstacles hindering progress in the field. This article aims to provide a summarized history of the work and achievements of these interdisciplinary surgical and scientific pioneers and departments, in the hopes of inspiring future generations of surgeons and physician scientists and documenting the institution's legacy in the neurosciences. Here we provide a summarized history of the life, work, and achievements of the physicians and scientists on which the institution's legacy in the neurosciences was built.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Elovl5 is required for proper action potential conduction along peripheral myelinated fibers

Elovl5 elongates fatty acids with 18 carbon atoms and in cooperation with other enzymes guarantees the normal levels of very long‐chain fatty acids, which are necessary for a proper membrane structure. Action potential conduction along myelinated axons depends on structural integrity of myelin, which is maintained by a correct amount of fatty acids and a proper interaction between fatty acids and myelin proteins. We hypothesized that in Elovl5^−/− mice, the lack of elongation of Elovl5 substrates might cause alterations of myelin structure. The analysis of myelin ultrastructure showed an enlarged periodicity with reduced G‐ratio across all axonal diameters. We hypothesized that the structural alteration of myelin might affect the conduction of action potentials. The sciatic nerve conduction velocity was significantly reduced without change in the amplitude of the nerve compound potential, suggesting a myelin defect without a concomitant axonal degeneration. Since Elovl5 is important in attaining normal amounts of polyunsaturated fatty acids, which are the principal component of myelin, we performed a lipidomic analysis of peripheral nerves of Elovl5‐deficient mice. The results revealed an unbalance, with reduction of fatty acids longer than 18 carbon atoms relative to shorter ones. In addition, the ratio of saturated to unsaturated fatty acids was strongly increased. These findings point out the essential role of Elovl5 in the peripheral nervous system in supporting the normal structure of myelin, which is the key element for a proper conduction of electrical signals along myelinated nerves.

Niemann-Pick disease, type C and Roscoe Brady

The Niemann-Pick family of diseases was poorly understood until Roscoe Brady and his colleagues began their investigations in the 1960s. Following Brady's discovery of the defect in acid sphingomyelinase in Niemann-Pick disease, types A and B, Peter Pentchev, a senior scientist in the group, launched a series of investigations of an unusual lipid storage disease in a spontaneous mouse model. These led initially to identification of the cholesterol trafficking defect in the mouse, and then in human Niemann-Pick disease, type C (NPC). This discovery formed the basis of the standard diagnostic test for NPC for the next three decades. Subsequently, an international collaboration was established, based at the Brady lab at NIH, which culminated in discovery of the NPC1 gene. Roscoe Brady, Peter Pentchev and their colleagues defined and refined the clinical biochemical and pathological phenotypes of NPC in a series of elegant parallel studies. They also identified abnormal oxysterols in NPC; later work has proved such compounds to be sensitive biomarkers of the disease. The dedication of the Brady lab to NPC, and the discoveries that flowed therefrom, provided critical foundations for the current explosion of progress in this disease.

Electrodiagnostic testing and histopathologic changes confirm peripheral nervous system myelin abnormalities in the feline model of niemann-pick disease type C

Niemann-Pick disease type C (NPC disease) is an incurable, neurodegenerative, autosomal recessive disease caused by mutations in either the NPC1 or the NPC2 gene. These mutations affect the intracellular trafficking of lipids and cholesterol, resulting in the intralysosomal accumulation of unesterified cholesterol and glycosphingolipids. These abnormalities are associated with clinical ataxia and impaired motor and intellectual development, and death frequently occurs in adolescence. The incidence of peripheral neuropathy in NPC patients is not known. We investigated peripheral nerves in the naturally occurring feline model of NPC disease, which has proven to be critical for understanding both disease pathogenesis and for evaluating experimental therapies. Electrodiagnostic studies revealed significantly slowed motor and sensory nerve conduction velocities in affected cats in the absence of altered M-wave amplitude. Histologic and ultrastructural analyses showed thin myelin sheaths, membranous debris, myelin figures, lipid vacuolization of Schwann cell cytoplasm, and expanded paranodal areas. Axonal degeneration was not identified. There was a shift to small myelinated fibers in affected cats, and there were significant decreases in fiber diameter, axon diameter, and myelin thickness. These changes were similar to those described in the murine NPC disease model and in rare patients in whom nerve biopsy has been performed. Characterization of the demyelinating neuropathy is necessary for evaluating clinical trials that target only the CNS aspects of NPC.

Morphological alterations of the cornea in the mouse model of niemann-pick disease type c1

PURPOSE

Niemann-Pick disease type C1 (NPC1) is a genetic neurovisceral disorder characterized by abnormalities in intracellular sterol trafficking. A knockout mouse model (NPC1) is an important tool for the study of pathogenesis and treatment strategies. In the present study, NPC1 mice were examined for pathological changes in the cornea.

METHODS

Fifteen inbred homozygous NPC1 knockout mice (NPC1, 5-10 weeks old), 5 age-matched heterozygous mice (NPC1), and 14 wild-type control mice (NPC1) were examined. In vivo confocal laser scanning microscopy (CLSM) was performed on both eyes of each animal; afterward, the eyes were processed for histology, electron microscopy, and lipid analysis.

RESULTS

In vivo CLSM disclosed hyperreflective intracellular deposits in the intermediate and basal cell layers of corneal epithelium in all NPC1 mice. At the electron microscopy level, however, vacuolated cytoplasmic structures, 200-500 nm in diameter, with electron-dense material appeared in all structures investigated, including all epithelial layers and stromal keratocytes. These deposits were negative for filipin, a marker for unesterified cholesterol. Lipid analysis showed a marked increase in disialotetrahexosylganglioside 2 (GM2) level in NPC1 mice corneas, whereas no changes were detected in free cholesterol and disialotetrahexosylganglioside 3 (GM3) levels when compared with controls.

CONCLUSIONS

Morphological changes characteristic for the NPC1 mouse cornea were visualized in all epithelial layers and keratocytes. In vivo CLSM findings were confirmed by other techniques. In vivo detection of ocular manifestations and analysis of ocular tissue have the potential to aid the diagnosis of NPC1 disease and to monitor the efficacy of treatment.

Defective cholesterol trafficking in Niemann-Pick C-deficient cells

Pathways of intracellular cholesterol trafficking are poorly understood at the molecular level. Mutations in Niemann-Pick C (NPC) proteins, NPC1 and NPC2, however, have led to insights into the mechanism by which endocytosed cholesterol is exported from late endosomes/lysosomes (LE/L). Mutations in NPC1, a multi-spanning membrane protein of LE/L, or mutations in NPC2, a soluble luminal protein of LE/L, cause the neurodegenerative disorder NPC disease. This review focuses on data supporting a model in which movement of cholesterol out of LE/L is mediated by the sequential action of the two NPC proteins. We also discuss potential therapies for NPC disease, including evidence that treatment of NPC-deficient mice with the cholesterol-binding compound, cyclodextrin, markedly attenuates neurodegeneration, and increases life-span, of NPC1-deficient mice.

Niemann-Pick Disease Type C: from molecule to clinic

1. Niemann-Pick Type C disease (NPC) is an incurable cholesterol-storage disorder that stems from inherited deficiencies of lysosomal proteins involved in intracellular lipid-trafficking proteins. The condition manifests as progressive neurological impairment and leads to death at an early age. 2. To improve clinical recognization and investigate therapeutic strategies, recent studies using molecular and genetic approaches have led to significant advances in the creation of animal models of NPC, as well as in the understanding of the cellular and molecular mechanisms underlying the pathogenesis of NPC. 3. Patients with NPC are divided into four groups based on age at presentation, whereas the clinical features of NPC can be divided into five categories based on the severity of the disease. Progressive neuronal loss, especially of cerebellar Purkinje cells, is a hallmark of NPC. Ballooned neurons, axonal abnormalities and astroglyosis are among the pathological changes seen. Severe demyelination is also present in the mouse model of NPC. 4. Mutations in the NPC1 gene cause approximately 95% of cases of NPC, whereas mutations in the NPC2 gene account for the remainder of cases. NPC1 is a transmembrane protein and NPC2 is a soluble protein involved in lipid trafficking in lysosomes. Loss-of-function mutations in the NPC1 gene lead to a failure of the calcium-mediated fusion of endosomes with lysosomes, resulting in the accumulation of cholesterol and other lipids in late endosomes and lysosomes. 5. The present review updates the disorders of NPC from clinical features to animal models and molecular mechanisms.

Ethanol-related increases in degenerating bodies in the Purkinje neuron dendrites of aging rats

Chronic ethanol consumption in aging rats results in regression of Purkinje neuron (PN) dendritic arbors ([Pentney, 1995 Measurements of dendritic pathlengths provide evidence that ethanol-induced lengthening of terminal dendritic segments may result from dendritic regression. Alcohol Alcohol. 30, 87-96]), loss of synapses (Dlugos and Pentney, 1997), dilation of the smooth endoplasmic reticulum (SER), and the formation of degenerating bodies within PN dendrites ([Dlugos, C.A., 2006a. Ethanol-Related Smooth Endoplasmic Reticulum Dilation in Purkinje Dendrites of Aging Rats. Alcohol., Clin. Exp. Res. 30, 883-891,Dlugos, C.A., 2006b. Smooth endoplasmic reticulum dilation and degeneration in Purkinje neuron dendrites of aging ethanol-fed female rats. Cerebellum. 5, 155-162]). Dilation of the SER and the formation of degenerating bodies may be a predictor of dendritic regression. Ethanol-induced effects on mitochondria may be involved as mitochondria cooperate with the SER to maintain calcium homeostasis. The purpose of this study was to determine whether degenerating body number and mitochondrial density and structure are altered by chronic ethanol treatment in PN dendrites. Male, Fischer 344 rats, 12 months of age, were fed an ethanol or pair-fed liquid diet, or rat chow for a period of 10, 20, or 40 weeks (15 rats/treatment; 45 rats/treatment duration). Ethanol-fed rats received 35% of their calories as ethanol. At the end of treatment, all animals were euthanized, perfused, and tissue prepared for electron microscopy. The densities of degenerating bodies and mitochondria, mitochondrial areas, and the distance between the SER and the mitochondria were measured. Results showed that there was an ethanol-related increase in degenerating bodies compared to controls at 40 weeks. Ethanol-induced alterations to mitochondria were absent. Correlation of the present results with those of previous studies suggest that degenerating bodies may be formed from membrane reabsorption during dendritic regression or from degenerating SER whose function has been compromised by dilation.

Endogenous and synthetic neurosteroids in treatment of Niemann-Pick Type C disease

The functions for neurosteroids during development and in response to nervous system injury are beginning to be identified. We focused on a mouse model in which we believed neurosteroid production would be altered, and which had a neurodegenerative phenotype. Niemann-Pick Type-C (NP-C) is an autosomal recessive neurodegenerative disease caused by mutations in NPC1 (95%) or NPC2 (5%), resulting in lysosomal accumulation of unesterified cholesterol and glycolipids. The NIH mouse model of NP-C has a mutation in the NPC1 gene, and exhibits several pathological features of the most severe NP-C patients. How lysosomal storage and trafficking defects lead to neurodegeneration is unknown. We found that these mice had normal neurosteroidogenic enzyme activity during development, but lost this activity in the early neonatal period, prior to onset of neurological symptoms. Neurons that expressed P450scc, 3beta HSD, as well as those that expressed 3alpha HSD and 5alpha reductase were lost in adult NP-C brains, resulting in diminished concentrations of allopregnanolone. We treated NP-C mice with allopregnanolone and found that a single dose in the neonatal period resulted in a doubling of life span, substantial delay in onset of neurological symptoms, survival of cerebellar Purkinje and granule cell neurons, and reduction in cholesterol and ganglioside accumulation. The mechanism by which allopregnanolone elicited these effects is unknown. Our in vitro studies showed that Purkinje cell survival promoted by allopregnanolone was lost by treatment with bicuculline, suggesting GABA(A) receptors may play a role. We treated NP-C mice with a synthetic GABA(A) neurosteroid, ganaxolone (3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one). Ganaxolone treatment of NP-C mice produced beneficial neurological effects, but these effects were not as robust as those obtained using allopregnanolone. Thus, allopregnanolone may elicit its effects through GABA(A) receptors and through other mechanisms. Additional studies also suggest that allopregnanolone may elicit its effects through pregnane-X-receptors (PXR). Our data suggest that mouse models of neurodegeneration may be beneficial in establishing both physiologic and pharmacologic actions of neurosteroids. These animal models further establish the wide range of functions of these compounds, which may ultimately be useful for treatment of human diseases.

Behavioural characterisation of the robotic mouse mutant

The ataxic mouse mutant robotic is characterised by progressive adult-onset Purkinje cell loss that occurs in a distinctive region-specific pattern. We report the first behavioural characterisation of this mutant and quantify its performance on tests of motor function, locomotor and exploratory activity over a time course that reflects specific stages of cell loss in the cerebellum. Robotic mutants are significantly impaired on the rotarod and static rod tests of coordination and their performance declined during aging. In addition, gait analysis revealed an increase in the severity of the ataxia displayed by mutants over time. Interestingly, spontaneous alternation testing in a T-maze was not significantly affected in robotic mice, unlike other ataxic mutants with more rapid and extensive cerebellar degeneration; robotic therefore provides an opportunity to investigate the necessity of specific Purkinje cell populations for various behavioural tasks.

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.

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.

Ultrastructural analysis of climbing fiber-Purkinje cell synaptogenesis in the rat cerebellum

Previous reports have described the transient expression of the neuropeptides calcitonin gene-related peptide and neuropeptide Y in selected subsets of rat olivocerebellar compartments during embryonic and postnatal development. Using these neuropeptides as endogenous markers for olivocerebellar fibers, the aim of this electron microscopic analysis was to reveal the synaptogenetic processes occurring between climbing fibers and their target Purkinje cells, from embryonic day 19 to postnatal day 16, the period during which Purkinje cells undergo intense emission and retraction of dendrites, and climbing fibers translocate their synapses along Purkinje cell membrane surfaces. The present findings provide the first direct evidence that climbing fiber synaptogenesis starts on embryonic day 19 and that these first synapses mainly involve the Purkinje cell embryonic dendrite rather than the Purkinje cell soma. At the same age, the presence of unlabeled synapses resembling calcitonin gene-related peptide-labeled synapses in the Purkinje cell plate makes it possible to conclude that climbing fibers form a major synaptic investment on embryonic Purkinje cells, a finding that strongly supports the hypothesis of an early differentiating role of climbing fibers on cerebellar development. Furthermore, during the period of intense dendritic remodeling of Purkinje cells, 'myelin figures' were often detected in Purkinje cell dendrites suggesting that they may at least in part represent real ultrastructural markers of membrane turnover that identifies the sites where Purkinje cell dendritic rearrangement is taking place. Finally the finding that the climbing fiber terminals apposed to degenerating dendrites did not generally show signs of degeneration leads us to suggests that climbing fiber translocation from a perisomatic to a dendritic location may be driven by the Purkinje cell dendritic remodeling.