51
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Xu S, Chen X, Wei X, Liu G, Wang Q. Presynaptic impairment in Niemann-Pick C1-deficient neurons: not dependent on presence of glial cells. Neurosci Lett 2011; 496:54-9. [PMID: 21507342 DOI: 10.1016/j.neulet.2011.03.097] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Revised: 03/28/2011] [Accepted: 03/29/2011] [Indexed: 11/16/2022]
Abstract
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 has been poorly understood yet. In our previous study, we have demonstrated that synaptic function is impaired in this disease. In the current study, electrophysiological and fluorescent dyes studies were used to determine whether the synaptic defects result from presynaptic or postsynaptic contributions. Furthermore, we would like to ascertain whether such defects are caused by direct effect of NPC1 deficiency in neurons or indirect effect of NPC1 deficiency in glial cells. Both mean inter-event interval of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) were significantly larger in NPC1(-/-) neurons than those in the wild-type neurons, while the amplitudes and the receptor kinetics were not different compared with those in wild-type controls. Synaptic vesicle exocytosis was also slower in the NPC1(-/-) neurons. The mean time constant of destaining was larger in NPC1(-/-) neurons than in wild-type controls both in the presence and absence of glial cells. All these results indicated a general presynaptic functional impairment in the NPC1(-/-) neurons and such defects were not dependent of glial cells. Therefore, neuropathology characteristics of NPC diseases may be a more possible consequence of neuronal presynaptic dysfunction than indirect defects in glial cells.
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Affiliation(s)
- Shujun Xu
- Department of Physiology and Pharmacology, Ningbo University School of Medicine, Fenghua Road 818, Jiangbei District, Ningbo 315211, Zhejiang, China.
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52
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Abstract
The last 10 years have seen a rebirth of interest in lipid biology in the fields of Drosophila development and neurobiology, and sphingolipids have emerged as controlling many processes that have not previously been studied from the viewpoint of lipid biochemistry. Mutations in sphingolipid regulatory enzymes have been pinpointed as affecting cell survival and growth in tissues ranging from muscle to retina. Specification of cell types are also influenced by sphingolipid regulatory pathways, as genetic interactions of glycosphingolipid biosynthetic enzymes with many well-known signaling receptors such as Notch and epidermal growth factor receptor reveal. Furthermore, studies in flies are now uncovering unexpected roles of sphingolipids in controlling lipid storage and response to nutrient availability. The sophisticated genetics of Drosophila is particularly well suited to uncover the roles of sphingolipid regulatory enzymes in development and metabolism, especially in light of conserved pathways that are present in both flies and mammals. The challenges that remain in the field of sphingolipid biology in Drosophila are to combine traditional developmental genetics with more analytical biochemical and biophysical methods, to quantify and localize the responses of these lipids to genetic and metabolic perturbations.
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Affiliation(s)
- Rachel Kraut
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
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53
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Wang C, Ma Z, Scott MP, Huang X. The cholesterol trafficking protein NPC1 is required for Drosophila spermatogenesis. Dev Biol 2011; 351:146-55. [PMID: 21215267 DOI: 10.1016/j.ydbio.2010.12.042] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 12/21/2010] [Accepted: 12/27/2010] [Indexed: 10/25/2022]
Abstract
Niemann-Pick C (NPC) disease is a lethal neurodegenerative disorder affecting cellular sterol trafficking. Besides neurodegeneration, NPC patients also exhibit other pleiotropic conditions, indicating that NPC protein is required for other physiological processes. Previous studies indicated that a sterol shortage that in turn leads to a shortage of steroid hormones (for example, ecdysone in Drosophila) is likely to be the cause of NPC disease pathology. We have shown that mutations in Drosophila npc1, one of the two NPC disease-related genes, leads to larval lethal and male infertility. Here, we reported that npc1 mutants are defective in spermatogenesis and in particular in the membrane-remodeling individualization process. Interestingly, we found that ecdysone, the steroid hormone responsible for the larval lethal phenotype in npc1 mutants, is not required for individualization. However, supplying 7-dehydrocholesterol can partially rescue the male infertility of npc1 mutants, suggesting that a sterol shortage is responsible for the spermatogenesis defects. In addition, the individualization defects of npc1 mutants were enhanced at high temperature, suggesting that the sterol shortage may lead to temperature-sensitive defects in the membrane-remodeling process. Together, our study reveals a sterol-dependent, ecdysone-independent mechanism of NPC1 function in Drosophila spermatogenesis.
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Affiliation(s)
- Chao Wang
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
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54
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Tessier CR, Broadie K. The fragile X mental retardation protein developmentally regulates the strength and fidelity of calcium signaling in Drosophila mushroom body neurons. Neurobiol Dis 2011; 41:147-59. [PMID: 20843478 PMCID: PMC2982942 DOI: 10.1016/j.nbd.2010.09.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Revised: 08/17/2010] [Accepted: 09/03/2010] [Indexed: 11/20/2022] Open
Abstract
Fragile X syndrome (FXS) is a broad-spectrum neurological disorder characterized by hypersensitivity to sensory stimuli, hyperactivity and severe cognitive impairment. FXS is caused by loss of the fragile X mental retardation 1 (FMR1) gene, whose FMRP product regulates mRNA translation downstream of synaptic activity to modulate changes in synaptic architecture, function and plasticity. Null Drosophila FMR1 (dfmr1) mutants exhibit reduced learning and loss of protein synthesis-dependent memory consolidation, which is dependent on the brain mushroom body (MB) learning and memory center. We targeted a transgenic GFP-based calcium reporter to the MB in order to analyze calcium dynamics downstream of neuronal activation. In the dfmr1 null MB, there was significant augmentation of the calcium transients induced by membrane depolarization, as well as elevated release of calcium from intracellular organelle stores. The severity of these calcium signaling defects increased with developmental age, although early stages were characterized by highly variable, low fidelity calcium regulation. At the single neuron level, both calcium transient and calcium store release defects were exhibited by dfmr1 null MB neurons in primary culture. Null dfmr1 mutants exhibit reduced brain mRNA expression of calcium-binding proteins, including calcium buffers calmodulin and calbindin, predicting that the inability to appropriately sequester cytosolic calcium may be the common mechanistic defect causing calcium accumulation following both influx and store release. Changes in the magnitude and fidelity of calcium signals in the absence of dFMRP likely contribute to defects in neuronal structure/function, leading to the hallmark learning and memory dysfunction of FXS.
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Affiliation(s)
- Charles R Tessier
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37232, USA
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55
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Abstract
Synaptic vesicles have a high sterol content, but the importance of vesicular sterols during vesicle recycling is unclear. We used the Drosophila temperature-sensitive dynamin mutant, shibire-ts1, to block endocytosis of recycling synaptic vesicles and to trap them reversibly at the plasma membrane where they were accessible to sterol extraction. Depletion of sterols from trapped vesicles prevented recovery of synaptic transmission after removal of the endocytic block. Measurement of vesicle recycling with synaptopHluorin, FM1-43, and FM4-64 demonstrated impaired membrane retrieval after vesicular sterol depletion. When plasma membrane sterols were extracted before vesicle trapping, no vesicle recycling defects were observed. Ultrastructural analysis indicated accumulation of endosomes and a defect in the formation of synaptic vesicles in synaptic terminals subjected to vesicular sterol depletion. Our results demonstrate the importance of a high vesicular sterol concentration for endocytosis and suggest that vesicular and membrane sterol pools do not readily intermingle during vesicle recycling.
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56
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Fliesler SJ, Bretillon L. The ins and outs of cholesterol in the vertebrate retina. J Lipid Res 2010; 51:3399-413. [PMID: 20861164 DOI: 10.1194/jlr.r010538] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The vertebrate retina has multiple demands for utilization of cholesterol and must meet those demands either by synthesizing its own supply of cholesterol or by importing cholesterol from extraretinal sources, or both. Unlike the blood-brain barrier, the blood-retina barrier allows uptake of cholesterol from the circulation via a lipoprotein-based/receptor-mediated mechanism. Under normal conditions, cholesterol homeostasis is tightly regulated; also, cholesterol exists in the neural retina overwhelmingly in unesterified form, and sterol intermediates are present in minimal to negligible quantities. However, under certain pathological conditions, either due to an inborn error in cholesterol biosynthesis or as a consequence of exposure to selective inhibitors of enzymes in the cholesterol pathway, the ratio of sterol intermediates to cholesterol in the retina can rise dramatically and persist, in some cases resulting in progressive degeneration that significantly compromises the structure and function of the retina. Although the relative contributions of de novo synthesis versus extraretinal uptake are not yet known, herein we review what is known about these processes and the dynamics of cholesterol in the vertebrate retina and indicate some future avenues of research in this area.
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Affiliation(s)
- Steven J Fliesler
- Research Service, Veterans Administration Western New York Healthcare System, University at Buffalo, The State University of New York, Buffalo, NY, USA.
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57
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Strauss K, Goebel C, Runz H, Möbius W, Weiss S, Feussner I, Simons M, Schneider A. Exosome secretion ameliorates lysosomal storage of cholesterol in Niemann-Pick type C disease. J Biol Chem 2010; 285:26279-88. [PMID: 20554533 DOI: 10.1074/jbc.m110.134775] [Citation(s) in RCA: 175] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Niemann-Pick type C1 disease is an autosomal-recessive lysosomal storage disorder. Loss of function of the npc1 gene leads to abnormal accumulation of free cholesterol and sphingolipids within the late endosomal and lysosomal compartments resulting in progressive neurodegeneration and dysmyelination. Here, we show that oligodendroglial cells secrete cholesterol by exosomes when challenged with cholesterol or U18666A, which induces late endosomal cholesterol accumulation. Up-regulation of exosomal cholesterol release was also observed after siRNA-mediated knockdown of NPC1 and in fibroblasts derived from NPC1 patients and could be reversed by expression of wild-type NPC1. We provide evidence that exosomal cholesterol secretion depends on the presence of flotillin. Our findings indicate that exosomal release of cholesterol may serve as a cellular mechanism to partially bypass the traffic block that results in the toxic lysosomal cholesterol accumulation in Niemann-Pick type C1 disease. Furthermore, we suggest that secretion of cholesterol by exosomes contributes to maintain cellular cholesterol homeostasis.
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Affiliation(s)
- Katrin Strauss
- Max-Planck-Institute for Experimental Medicine, Goettingen, Germany
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58
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Drosophila as a lipotoxicity model organism — more than a promise? Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1801:215-21. [DOI: 10.1016/j.bbalip.2009.09.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 09/04/2009] [Accepted: 09/13/2009] [Indexed: 12/13/2022]
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59
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Hortsch R, Lee E, Erathodiyil N, Hebbar S, Steinert S, Lee JY, Chua DSK, Kraut R. Glycolipid trafficking in Drosophila undergoes pathway switching in response to aberrant cholesterol levels. Mol Biol Cell 2010; 21:778-90. [PMID: 20053687 PMCID: PMC2828964 DOI: 10.1091/mbc.e09-01-0005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Revised: 11/24/2009] [Accepted: 12/22/2009] [Indexed: 01/29/2023] Open
Abstract
In lipid storage diseases, the intracellular trafficking of sphingolipids is altered by conditions of aberrant cholesterol accumulation. Drosophila has been used recently to model lipid storage diseases, but the effects of sterol accumulation on sphingolipid trafficking are not known in the fly, and the trafficking of sphingolipids in general has not been studied in this model organism. Here, we examined the uptake and intracellular distribution of a fluorescent glycolipid analog, BODIPY-lactosyl-ceramide, in Drosophila neurons. The uptake mechanism and intracellular trafficking route of this simple glycolipid are largely conserved. Our principle finding is that cholesterol steers trafficking of the glycolipid between Golgi, lysosome, and recycling compartments. Our analyses support the idea that cholesterol storage in Drosophila triggers a switch in glycolipid trafficking from the biosynthetic to the degradative endolysosomal pathway, whereas cholesterol depletion eliminates recycling of the glycolipid. Unexpectedly, we observe a novel phenomenon we term "hijacking," whereby lactosyl-ceramide diverts the trafficking pathway of an endocytic cargo, dextran, completely away from its lysosomal target. This work establishes that glycolipid trafficking in Drosophila undergoes changes similar to those seen in mammalian cells under conditions of cholesterol storage and therefore validates Drosophila as a suitable model organism in which to study lipid storage diseases.
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Affiliation(s)
- Ralf Hortsch
- Institute of Bioengineering and Nanotechnology, Agency for Science, Technology, and Research, Singapore 138669; and
| | - Esther Lee
- Institute of Bioengineering and Nanotechnology, Agency for Science, Technology, and Research, Singapore 138669; and
| | - Nandanan Erathodiyil
- Institute of Bioengineering and Nanotechnology, Agency for Science, Technology, and Research, Singapore 138669; and
| | - Sarita Hebbar
- Institute of Bioengineering and Nanotechnology, Agency for Science, Technology, and Research, Singapore 138669; and
| | - Steffen Steinert
- Institute of Bioengineering and Nanotechnology, Agency for Science, Technology, and Research, Singapore 138669; and
| | - Jun Yu Lee
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Doreen See Kin Chua
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
| | - Rachel Kraut
- School of Biological Sciences, Nanyang Technological University, Singapore 639798
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60
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Xu S, Zhou S, Xia D, Xia J, Chen G, Duan S, Luo J. Defects of synaptic vesicle turnover at excitatory and inhibitory synapses in Niemann-Pick C1-deficient neurons. Neuroscience 2010; 167:608-20. [PMID: 20167265 DOI: 10.1016/j.neuroscience.2010.02.033] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 02/09/2010] [Accepted: 02/11/2010] [Indexed: 01/27/2023]
Abstract
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.
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Affiliation(s)
- S Xu
- Department of Neurobiology, Institute of Neuroscience, Zhejiang University School of Medicine, Hangzhou, Zhejiang, PR China
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61
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Harris JR, Milton NGN. Cholesterol in Alzheimer's disease and other amyloidogenic disorders. Subcell Biochem 2010; 51:47-75. [PMID: 20213540 DOI: 10.1007/978-90-481-8622-8_2] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The complex association of cholesterol metabolism and Alzheimer's disease is presented in depth, including the possible benefits to be gained from cholesterol-lowering statin therapy. Then follows a survey of the role of neuronal membrane cholesterol in Abeta pore formation and Abeta fibrillogenesis, together with the link with membrane raft domains and gangliosides. The contribution of structural studies to Abeta fibrillogenesis, using TEM and AFM, is given some emphasis. The role of apolipoprotein E and its isoforms, in particular ApoE4, in cholesterol and Abeta binding is presented, in relation to genetic risk factors for Alzheimer's disease. Increasing evidence suggests that cholesterol oxidation products are of importance in generation of Alzheimer's disease, possibly induced by Abeta-produced hydrogen peroxide. The body of evidence for a link between cholesterol in atherosclerosis and Alzheimer's disease is increasing, along with an associated inflammatory response. The possible role of cholesterol in tau fibrillization, tauopathies and in some other non-Abeta amyloidogenic disorders is surveyed.
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Affiliation(s)
- J Robin Harris
- Institute of Zoology, University of Mainz, D-55099, Mainz, Germany.
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62
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Elrick MJ, Pacheco CD, Yu T, Dadgar N, Shakkottai VG, Ware C, Paulson HL, Lieberman AP. Conditional Niemann-Pick C mice demonstrate cell autonomous Purkinje cell neurodegeneration. Hum Mol Genet 2009; 19:837-47. [PMID: 20007718 DOI: 10.1093/hmg/ddp552] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Pathways regulating neuronal vulnerability are poorly understood, yet are central to identifying therapeutic targets for degenerative neurological diseases. Here, we characterize mechanisms underlying neurodegeneration in Niemann-Pick type C (NPC) disease, a lysosomal storage disorder characterized by impaired cholesterol trafficking. To date, the relative contributions of neuronal and glial defects to neuron loss are poorly defined. Using gene targeting, we generate Npc1 conditional null mutant mice. Deletion of Npc1 in mature cerebellar Purkinje cells leads to an age-dependent impairment in motor tasks, including rotarod and balance beam performance. Surprisingly, these mice did not show the early death or weight loss that are characteristic of global Npc1 null mice, suggesting that Purkinje cell degeneration does not underlie these phenotypes. Histological examination revealed the progressive loss of Purkinje cells in an anterior-to-posterior gradient. This cell autonomous neurodegeneration occurs in a spatiotemporal pattern similar to that of global knockout mice. A subpopulation of Purkinje cells in the posterior cerebellum exhibits marked resistance to cell death despite Npc1 deletion. To explore this selective response, we investigated the electrophysiological properties of vulnerable and susceptible Purkinje cell subpopulations. Unexpectedly, Purkinje cells in both subpopulations displayed no electrophysiological abnormalities prior to degeneration. Our data establish that Npc1 deficiency leads to cell autonomous, selective neurodegeneration and suggest that the ataxic symptoms of NPC disease arise from Purkinje cell death rather than cellular dysfunction.
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Affiliation(s)
- Matthew J Elrick
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109-0605, USA
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63
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Claudepierre T, Paques M, Simonutti M, Buard I, Sahel J, Maue RA, Picaud S, Pfrieger FW. Lack of Niemann-Pick type C1 induces age-related degeneration in the mouse retina. Mol Cell Neurosci 2009; 43:164-76. [PMID: 19883762 DOI: 10.1016/j.mcn.2009.10.007] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Accepted: 10/17/2009] [Indexed: 11/26/2022] Open
Abstract
Niemann-Pick type C (NPC) disease is an inherited lysosomal storage disease and caused by mutations in Npc1 or Npc2, which mediate cooperatively the egress of cholesterol from lysosomes. The disease entails progressive neurodegeneration, whose cause is poorly understood. Here, we report that Npc1 is distributed in distinct layers of the mouse retina and that its deficiency causes striking retinal degeneration in 2-month-old mice with signs of age-related maculopathies. This includes impaired visual function, accumulation of lipofuscin in the retinal pigment epithelium layer, degeneration of photoreceptor outer segments, disruption of synaptic layers and an increase in autophagy markers in the ganglion cell layer. Moreover, the lack of Npc1 results in the upregulation of proteins that mediate cellular cholesterol release in the retina. Our findings suggest that Npc1 is required for normal retinal function and that its absence may serve as model to study age-related degeneration of the retina.
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Affiliation(s)
- Thomas Claudepierre
- CNRS UPR 3212, University of Strasbourg, Institute of Cellular and Integrative Neurosciences (INCI), 5, rue Blaise Pascal, F-67084 Strasbourg, France
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64
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Tessier CR, Broadie K. Activity-dependent modulation of neural circuit synaptic connectivity. Front Mol Neurosci 2009; 2:8. [PMID: 19668708 PMCID: PMC2724028 DOI: 10.3389/neuro.02.008.2009] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Accepted: 07/15/2009] [Indexed: 01/10/2023] Open
Abstract
In many nervous systems, the establishment of neural circuits is known to proceed via a two-stage process; (1) early, activity-independent wiring to produce a rough map characterized by excessive synaptic connections, and (2) subsequent, use-dependent pruning to eliminate inappropriate connections and reinforce maintained synapses. In invertebrates, however, evidence of the activity-dependent phase of synaptic refinement has been elusive, and the dogma has long been that invertebrate circuits are “hard-wired” in a purely activity-independent manner. This conclusion has been challenged recently through the use of new transgenic tools employed in the powerful Drosophila system, which have allowed unprecedented temporal control and single neuron imaging resolution. These recent studies reveal that activity-dependent mechanisms are indeed required to refine circuit maps in Drosophila during precise, restricted windows of late-phase development. Such mechanisms of circuit refinement may be key to understanding a number of human neurological diseases, including developmental disorders such as Fragile X syndrome (FXS) and autism, which are hypothesized to result from defects in synaptic connectivity and activity-dependent circuit function. This review focuses on our current understanding of activity-dependent synaptic connectivity in Drosophila, primarily through analyzing the role of the fragile X mental retardation protein (FMRP) in the Drosophila FXS disease model. The particular emphasis of this review is on the expanding array of new genetically-encoded tools that are allowing cellular events and molecular players to be dissected with ever greater precision and detail.
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Affiliation(s)
- Charles R Tessier
- Department of Biological Sciences, Vanderbilt University Nashville, TN, USA
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65
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Gazi M, Shyamala BV, Bhat KM. A neurodegenerative disease affecting synaptic connections in Drosophila mutant for the tumor suppressor morphogen Patched. Dev Biol 2009; 334:311-23. [PMID: 19635474 DOI: 10.1016/j.ydbio.2009.07.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 06/24/2009] [Accepted: 07/17/2009] [Indexed: 11/27/2022]
Abstract
The tumor suppressor morphogen, Patched (Ptc), has an extensive homology to the Niemann-Pick-C 1 (NPC1) protein. The NPC disease is a paediatric, progressive and fatal neurodegenerative disorder thought to be due to an abnormal accumulation of cholesterol in neurons. Here, we report that patched mutant adults develop a progressive neurodegenerative disease and their brain contains membranous and lamellar inclusions. There is also a significant reduction in the number of synaptic terminals in the brain of the mutant adults. Interestingly, feeding cholesterol to wild type flies generates inclusions in the brain, but does not cause the disease. However, feeding cholesterol to mutant flies increases synaptic connections and suppresses the disease. Our results suggest that sequestration of cholesterol in the mutant brain in the form of membranous material and inclusions affects available pool of cholesterol for cellular functions. This, in turn, negatively affects the synaptic number and contributes to the disease-state. Consistent with this, in ptc mutants there is a reduction in the pool of cholesterol esters, and cholesterol-mediated suppression of the disease accompanies an increase in cholesterol esters. We further show that Ptc does not function directly in this process since gain of function for Hedgehog also induces the same disease with a reduction in the level of cholesterol esters. We believe that loss of function for ptc causes neurodegeneration via two distinct ways: de-repression of genes that interfere with lipid trafficking, and de-repression of genes outside of the lipid trafficking; the functions of both classes of genes ultimately converge on synaptic connections.
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Affiliation(s)
- Michal Gazi
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX 77555, USA
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66
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Lessing D, Bonini NM. Maintaining the brain: insight into human neurodegeneration from Drosophila melanogaster mutants. Nat Rev Genet 2009; 10:359-70. [PMID: 19434080 PMCID: PMC2820605 DOI: 10.1038/nrg2563] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The fruitfly Drosophila melanogaster has enabled significant advances in neurodegenerative disease research, notably in the identification of genes that are required to maintain the structural integrity of the brain, defined by recessive mutations that cause adult onset neurodegeneration. Here, we survey these genes in the fly and classify them according to five key cell biological processes. Over half of these genes have counterparts in mice or humans that are also associated with neurodegeneration. Fly genetics continues to be instrumental in the analysis of degenerative disease, with notable recent advances in our understanding of several inherited disorders, Parkinson's disease, and the central role of mitochondria in neuronal maintenance.
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Affiliation(s)
- Derek Lessing
- Howard Hughes Medical Institute, University of Pennsylvania, Philadelphia, PA 19104
| | - Nancy M. Bonini
- Howard Hughes Medical Institute, University of Pennsylvania, Philadelphia, PA 19104
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104
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67
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Ruivo R, Anne C, Sagné C, Gasnier B. Molecular and cellular basis of lysosomal transmembrane protein dysfunction. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:636-49. [DOI: 10.1016/j.bbamcr.2008.12.008] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 12/10/2008] [Accepted: 12/11/2008] [Indexed: 02/04/2023]
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68
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Karten B, Peake KB, Vance JE. Mechanisms and consequences of impaired lipid trafficking in Niemann-Pick type C1-deficient mammalian cells. Biochim Biophys Acta Mol Cell Biol Lipids 2009; 1791:659-70. [PMID: 19416638 DOI: 10.1016/j.bbalip.2009.01.025] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2008] [Accepted: 01/20/2009] [Indexed: 11/18/2022]
Abstract
Niemann-Pick C disease is a fatal progressive neurodegenerative disorder caused in 95% of cases by mutations in the NPC1 gene; the remaining 5% of cases result from mutations in the NPC2 gene. The major biochemical manifestation of NPC1 deficiency is an abnormal sequestration of lipids, including cholesterol and glycosphingolipids, in late endosomes/lysosomes (LE/L) of all cells. In this review, we summarize the current knowledge of the NPC1 protein in mammalian cells with particular focus on how defects in NPC1 alter lipid trafficking and neuronal functions. NPC1 is a protein of LE/L and is predicted to contain thirteen transmembrane domains, five of which constitute a sterol-sensing domain. The precise function of NPC1, and the mechanism by which NPC1 and NPC2 (both cholesterol binding proteins) act together to promote the movement of cholesterol and other lipids out of the LE/L, have not yet been established. Recent evidence suggests that the sequestration of cholesterol in LE/L of cells of the brain (neurons and glial cells) contributes to the widespread death and dysfunction of neurons in the brain. Potential therapies include treatments that promote the removal of cholesterol and glycosphingolipids from LE/L. Currently, the most promising approach for extending life-span and improving the quality of life for NPC patients is a combination of several treatments each of which individually modestly slows disease progression.
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Affiliation(s)
- Barbara Karten
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada
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69
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Jeibmann A, Paulus W. Drosophila melanogaster as a model organism of brain diseases. Int J Mol Sci 2009; 10:407-440. [PMID: 19333415 PMCID: PMC2660653 DOI: 10.3390/ijms10020407] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2008] [Revised: 01/16/2009] [Accepted: 01/20/2009] [Indexed: 01/29/2023] Open
Abstract
Drosophila melanogaster has been utilized to model human brain diseases. In most of these invertebrate transgenic models, some aspects of human disease are reproduced. Although investigation of rodent models has been of significant impact, invertebrate models offer a wide variety of experimental tools that can potentially address some of the outstanding questions underlying neurological disease. This review considers what has been gleaned from invertebrate models of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, metabolic diseases such as Leigh disease, Niemann-Pick disease and ceroid lipofuscinoses, tumor syndromes such as neurofibromatosis and tuberous sclerosis, epilepsy as well as CNS injury. It is to be expected that genetic tools in Drosophila will reveal new pathways and interactions, which hopefully will result in molecular based therapy approaches.
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Affiliation(s)
- Astrid Jeibmann
- Author to whom correspondence should be addressed; E-Mail:
; Tel. +49-251 83 57549; Fax: +49-251 83 56971
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70
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Venkatachalam K, Long AA, Elsaesser R, Nikolaeva D, Broadie K, Montell C. Motor deficit in a Drosophila model of mucolipidosis type IV due to defective clearance of apoptotic cells. Cell 2008; 135:838-51. [PMID: 19041749 DOI: 10.1016/j.cell.2008.09.041] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 07/25/2008] [Accepted: 09/17/2008] [Indexed: 11/27/2022]
Abstract
Disruption of the Transient Receptor Potential (TRP) mucolipin 1 (TRPML1) channel results in the neurodegenerative disorder mucolipidosis type IV (MLIV), a lysosomal storage disease with severe motor impairments. The mechanisms underlying MLIV are poorly understood and there is no treatment. Here, we report a Drosophila MLIV model, which recapitulates the key disease features, including abnormal intracellular accumulation of macromolecules, motor defects, and neurodegeneration. The basis for the buildup of macromolecules was defective autophagy, which resulted in oxidative stress and impaired synaptic transmission. Late-apoptotic cells accumulated in trpml mutant brains, suggesting diminished cell clearance. The accumulation of late-apoptotic cells and motor deficits were suppressed by expression of trpml(+) in neurons, glia, or hematopoietic cells. We conclude that the neurodegeneration and motor defects result primarily from decreased clearance of apoptotic cells. Since hematopoietic cells in humans are involved in clearance of apoptotic cells, our results raise the possibility that bone marrow transplantation may limit the progression of MLIV.
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Affiliation(s)
- Kartik Venkatachalam
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Cho KI, Yi H, Yeh A, Tserentsoodol N, Cuadrado L, Searle K, Hao Y, Ferreira PA. Haploinsufficiency of RanBP2 is neuroprotective against light-elicited and age-dependent degeneration of photoreceptor neurons. Cell Death Differ 2008; 16:287-97. [PMID: 18949001 DOI: 10.1038/cdd.2008.153] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Prolonged light exposure is a determinant factor in inducing neurodegeneration of photoreceptors by apoptosis. Yet, the molecular bases of the pathways and components triggering this cell death event are elusive. Here, we reveal a prominent age-dependent increase in the susceptibility of photoreceptor neurons to undergo apoptosis under light in a mouse model. This is accompanied by light-induced subcellular changes of photoreceptors, such as dilation of the disks at the tip of the outer segments, prominent vesiculation of nascent disks, and autophagy of mitochondria into large multilamellar bodies. Notably, haploinsufficiency of Ran-binding protein-2 (RanBP2) suppresses apoptosis and most facets of membrane dysgenesis observed with age upon light-elicited stress. RanBP2 haploinsufficiency promotes decreased levels of free fatty acids in the retina independent of light exposure and turns the mice refractory to weight gain on a high-fat diet, whereas light promotes an increase in hydrogen peroxide regardless of the genotype. These studies demonstrate the presence of age-dependent and RanBP2-mediated pathways modulating membrane biogenesis of the outer segments and light-elicited neurodegeneration of photoreceptors. Furthermore, the findings support a mechanism whereby the RanBP2-dependent production of free fatty acids, metabolites thereof or the modulation of a cofactor dependent on any of these, promote apoptosis of photoreceptors in concert with the light-stimulated production of reactive oxygen species.
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Affiliation(s)
- K-in Cho
- Department of Ophthalmology, Duke University Medical Center, Durham, NC, USA
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