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Cain MD, Salimi H, Diamond MS, Klein RS. Mechanisms of Pathogen Invasion into the Central Nervous System. Neuron 2020; 103:771-783. [PMID: 31487528 DOI: 10.1016/j.neuron.2019.07.015] [Citation(s) in RCA: 56] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2019] [Revised: 06/09/2019] [Accepted: 07/12/2019] [Indexed: 12/16/2022]
Abstract
CNS infections continue to rise in incidence in conjunction with increases in immunocompromised populations or conditions that contribute to the emergence of pathogens, such as global travel, climate change, and human encroachment on animal territories. The severity and complexity of these diseases is impacted by the diversity of etiologic agents and their routes of neuroinvasion. In this review, we present historical, clinical, and molecular concepts regarding the mechanisms of pathogen invasion of the CNS. We also discuss the structural components of CNS compartments that influence pathogen entry and recent discoveries of the pathways exploited by pathogens to facilitate CNS infections. Advances in our understanding of the CNS invasion mechanisms of different neurotropic pathogens may enable the development of strategies to control their entry and deliver drugs to mitigate established infections.
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Affiliation(s)
- Matthew D Cain
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Hamid Salimi
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Michael S Diamond
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110, USA; The Andrew M. and Jane M. Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Robyn S Klein
- Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA.
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2
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Skuja S, Zieda A, Ravina K, Chapenko S, Roga S, Teteris O, Groma V, Murovska M. Structural and Ultrastructural Alterations in Human Olfactory Pathways and Possible Associations with Herpesvirus 6 Infection. PLoS One 2017; 12:e0170071. [PMID: 28072884 PMCID: PMC5224992 DOI: 10.1371/journal.pone.0170071] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2016] [Accepted: 12/28/2016] [Indexed: 12/11/2022] Open
Abstract
Structural and ultrastructural alterations in human olfactory pathways and putative associations with human herpesvirus 6 (HHV-6) infection were studied. The olfactory bulb/tract samples from 20 subjects with an unspecified encephalopathy determined by pathomorphological examination of the brain autopsy, 17 healthy age-matched and 16 younger controls were used. HHV-6 DNA was detected in 60, 29, and 19% of cases in these groups, respectively. In the whole encephalopathy group, significantly more HHV-6 positive neurons and oligodendrocytes were found in the gray matter, whereas, significantly more HHV-6 positive astrocytes, oligodendrocytes, microglia/macrophages and endothelial cells were found in the white matter. Additionally, significantly more HHV-6 positive astrocytes and, in particular, oligodendrocytes were found in the white matter when compared to the gray matter. Furthermore, when only HHV-6 PCR+ encephalopathy cases were studied, we observed similar but stronger associations between HHV-6 positive oligodendrocytes and CD68 positive cells in the white matter. Cellular alterations were additionally evidenced by anti-S100 immunostaining, demonstrating a significantly higher number of S100 positive cells in the gray matter of the whole encephalopathy group when compared to the young controls, and in the white matter when compared to both control groups. In spite the decreased S100 expression in the PCR+ encephalopathy group when compared to PCR- cases and controls, groups demonstrated significantly higher number of S100 positive cells in the white compared to the gray matter. Ultrastructural changes confirming the damage of myelin included irregularity of membranes and ballooning of paranodal loops. This study shows that among the cellular targets of the nervous system, HHV-6 most severely affects oligodendrocytes and the myelin made by them.
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Affiliation(s)
- Sandra Skuja
- Institute of Anatomy and Anthropology, Riga Stradins University, Riga, Latvia
- * E-mail:
| | - Anete Zieda
- Institute of Anatomy and Anthropology, Riga Stradins University, Riga, Latvia
| | - Kristine Ravina
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, California, United States of America
| | - Svetlana Chapenko
- A. Kirchenstein Institute of Microbiology and Virology, Riga Stradins University, Riga, Latvia
| | - Silvija Roga
- Department of Pathology, Riga 1st Hospital, Riga, Latvia
| | - Ojars Teteris
- Latvian State Centre for Forensic Medical Examination, Riga, Latvia
| | - Valerija Groma
- Institute of Anatomy and Anthropology, Riga Stradins University, Riga, Latvia
| | - Modra Murovska
- A. Kirchenstein Institute of Microbiology and Virology, Riga Stradins University, Riga, Latvia
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3
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Too IHK, Yeo H, Sessions OM, Yan B, Libau EA, Howe JLC, Lim ZQ, Suku-Maran S, Ong WY, Chua KB, Wong BS, Chow VTK, Alonso S. Enterovirus 71 infection of motor neuron-like NSC-34 cells undergoes a non-lytic exit pathway. Sci Rep 2016; 6:36983. [PMID: 27849036 PMCID: PMC5111112 DOI: 10.1038/srep36983] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 10/20/2016] [Indexed: 01/08/2023] Open
Abstract
Enterovirus 71 (EV71) causing Hand, Foot and Mouth Disease, is regarded as the most important neurotropic virus worldwide. EV71 is believed to replicate in muscles and infect motor neurons to reach the central nervous system (CNS). To further investigate the mechanisms involved, we have employed the motor neuron cell line NSC-34. NSC-34 cells were permissive to EV71 and virus production yields were strain-dependent with differential efficacy at the entry, replication and egress steps. Furthermore, unlike all the other cell lines previously reported, EV71-infected NSC-34 cells neither displayed cytopathic effect nor underwent apoptosis. Instead, autophagy was markedly up-regulated and virus-containing autophagic vacuoles were isolated from the culture supernatant, providing the first experimental evidence that EV71 can adopt a non-lytic exit pathway. Finally, the ability of EV71 to infect productively NSC-34 cells correlated with its ability to invade the CNS in vivo, supporting the relevance of NSC-34 cells to study the intrinsic neurovirulence of EV71 strains.
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Affiliation(s)
- Issac Horng Khit Too
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Immunology Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Huimin Yeo
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Immunology Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - October Michael Sessions
- Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, 8 College Road, 169857, Singapore
| | - Benedict Yan
- Department of Laboratory Medicine, 5 Lower Kent Ridge Road, National University Hospital, 119074, Singapore
| | - Eshele Anak Libau
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Immunology Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Josephine L C Howe
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore
| | - Ze Qin Lim
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Immunology Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Shalini Suku-Maran
- Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Neurobiology and Ageing Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Wei-Yi Ong
- Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Neurobiology and Ageing Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Kaw Bing Chua
- Temasek Life Sciences Laboratory, 5 A Engineering Drive 1, National University of Singapore, 117411, Singapore
| | - Boon Seng Wong
- Neurobiology and Ageing Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore.,Department of Physiology, Yong Loo Lin School of Medicine, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
| | - Vincent T K Chow
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore
| | - Sylvie Alonso
- Department of Microbiology &Immunology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore.,Immunology Programme, Life Sciences Institute, CeLS building, 28 Medical Drive, National University of Singapore, 117456, Singapore
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4
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Méndez F, de Garay T, Rodríguez D, Rodríguez JF. Infectious bursal disease virus VP5 polypeptide: a phosphoinositide-binding protein required for efficient cell-to-cell virus dissemination. PLoS One 2015; 10:e0123470. [PMID: 25886023 PMCID: PMC4401730 DOI: 10.1371/journal.pone.0123470] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Accepted: 02/18/2015] [Indexed: 11/19/2022] Open
Abstract
Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is a major avian pathogen responsible for an immunosuppressive disease affecting juvenile chickens. The IBDV genome is formed by two dsRNA segments. The largest one harbors two partially overlapping open reading frames encoding a non-structural polypeptide, known as VP5, and a large polyprotein, respectively. VP5 is non-essential for virus replication. However, it plays a major role in IBDV pathogenesis. VP5 accumulates at the plasma membrane (PM) of IBDV-infected cells. We have analyzed the mechanism underlying the VP5 PM targeting. Updated topological prediction algorithm servers fail to identify a transmembrane domain within the VP5 sequence. However, the VP5 polycationic C-terminal region, harboring three closely spaced patches formed by two or three consecutive basic amino acid residues (lysine or arginine), might account for its PM tropism. We have found that mutations, either C-terminal VP5 deletions or replacement of basic amino acids by alanine residues, that reduce the electropositive charge of the VP5 C-terminus abolish PM targeting. Lipid overlay assays performed with an affinity-purified Flag-tagged VP5 (FVP5) protein version show that this polypeptide binds several phosphoinositides (PIP), exhibiting a clear preference for monophosphate species. Experiments performed with FVP5 mutant proteins lacking the polycationic domain demonstrate that this region is essential for PIP binding. Data gathered with IBDV mutants expressing C-terminal deleted VP5 polypeptides generated by reverse genetics demonstrate that the VP5-PIP binding domain is required both for its PM targeting in infected cells, and for efficient virus dissemination. Data presented here lead us to hypothesize that IBDV might use a non-lytic VP5-dependent cell-to-cell spreading mechanism.
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Affiliation(s)
- Fernando Méndez
- Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología-CSIC, Cantoblanco, 28049, Madrid, Spain
| | - Tomás de Garay
- Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología-CSIC, Cantoblanco, 28049, Madrid, Spain
| | - Dolores Rodríguez
- Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología-CSIC, Cantoblanco, 28049, Madrid, Spain
| | - José F. Rodríguez
- Department of Molecular and Cellular Biology, Centro Nacional de Biotecnología-CSIC, Cantoblanco, 28049, Madrid, Spain
- * E-mail:
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5
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Taylor MP, Enquist LW. Axonal spread of neuroinvasive viral infections. Trends Microbiol 2015; 23:283-8. [PMID: 25639651 DOI: 10.1016/j.tim.2015.01.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Revised: 12/31/2014] [Accepted: 01/07/2015] [Indexed: 02/05/2023]
Abstract
Neuroinvasive viral infections invade the nervous system, often eliciting serious disease and death. Members of four viral families are both neuroinvasive and capable of transmitting progeny virions or virion components within the long neuronal extensions known as axons. Axons provide physical structures that enable viral infection to spread within the host while avoiding extracellular immune responses. Technological advances in the analysis of in vivo neural circuits, neuronal culturing, and live imaging of fluorescent fusion proteins have enabled an unprecedented view into the steps of virion assembly, transport, and egress involved in axonal spread. In this review we summarize the literature supporting anterograde (axon to cell) spread of viral infection, describe the various strategies of virion transport, and discuss the effects of spread on populations of neuroinvasive viruses.
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Affiliation(s)
- Matthew P Taylor
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59718, USA.
| | - Lynn W Enquist
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA; Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA
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Sanz-Moreno A, Fuhrmann D, Zankel A, Reingruber H, Kern L, Meijer D, Niemann A, Elsässer HP. Late onset neuropathy with spontaneous clinical remission in mice lacking the POZ domain of the transcription factor Myc-interacting zinc finger protein 1 (Miz1) in Schwann cells. J Biol Chem 2014; 290:727-43. [PMID: 25416780 DOI: 10.1074/jbc.m114.605931] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The transcription factor Miz1 (Myc-interacting zinc finger 1) is a known regulator of the cell cycle but also has cell cycle-independent functions. Here we analyzed the role of Miz1 in the peripheral nervous system, using an early embryonic conditional knock-out model in which the Miz1 POZ domain is ablated in Schwann cells. Although the development of myelinated nerve fibers was not impaired, Miz1ΔPOZ mice acquired behavioral signs of a peripheral neuropathy at the age of 3 months. At this time, ultrastructural analysis of the sciatic nerve showed de- and dysmyelination of fibers, with massive outfoldings and a focal infiltration of macrophages. Although the expression of genes encoding structural myelin proteins, such as periaxin, myelin basic protein, and myelin protein zero, was decreased, genes associated with a negative regulation of myelination, including c-Jun, Sox2, and Id2, were up-regulated in Miz1ΔPOZ mice compared with controls. In animals older than 4 months, the motor disabilities vanished, and the ultrastructure of the sciatic nerve exhibited numerous tomacula and remyelinated fibers, as indicated by thinner myelin. No second acute attack was observed up to the age of 1 year. Thus, the deletion of the Miz1 POZ domain in Schwann cells induces an acute neuropathy with a subsequent regeneration in which there is ongoing balancing between de- and remyelination. Miz1ΔPOZ mice are impaired in the maintenance of myelinated fibers and are a promising model for studying remyelination in adult peripheral nerves.
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Affiliation(s)
- Adrián Sanz-Moreno
- From the Department of Cytobiology and Cytopathobiology, Philipps University of Marburg, Robert-Koch-Strasse 6, 35033 Marburg, Germany
| | - David Fuhrmann
- From the Department of Cytobiology and Cytopathobiology, Philipps University of Marburg, Robert-Koch-Strasse 6, 35033 Marburg, Germany
| | - Armin Zankel
- Graz University of Technology, 8010 Graz, Austria
| | | | - Lara Kern
- From the Department of Cytobiology and Cytopathobiology, Philipps University of Marburg, Robert-Koch-Strasse 6, 35033 Marburg, Germany
| | - Dies Meijer
- Erasmus Medical Center, 3015GE Rotterdam, Netherlands, and
| | | | - Hans-Peter Elsässer
- From the Department of Cytobiology and Cytopathobiology, Philipps University of Marburg, Robert-Koch-Strasse 6, 35033 Marburg, Germany,
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7
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Abstract
The cell-to-cell spread of cytoplasmic constituents such as nonenveloped viruses and aggregated proteins is usually thought to require cell lysis. However, mechanisms of unconventional secretion have been described that bypass the secretory pathway for the extracellular delivery of cytoplasmic molecules. Components of the autophagy pathway, an intracellular recycling process, have been shown to play a role in the unconventional secretion of cytoplasmic signaling proteins. Poliovirus is a lytic virus, although a few examples of apparently nonlytic spread have been documented. Real demonstration of nonlytic spread for poliovirus or any other cytoplasmic constituent thought to exit cells via unconventional secretion requires demonstration that a small amount of cell lysis in the cellular population is not responsible for the release of cytosolic material. Here, we use quantitative time-lapse microscopy to show the spread of infectious cytoplasmic material between cells in the absence of lysis. siRNA-mediated depletion of autophagy protein LC3 reduced nonlytic intercellular viral transfer. Conversely, pharmacological stimulation of the autophagy pathway caused more rapid viral spread in tissue culture and greater pathogenicity in mice. Thus, the unconventional secretion of infectious material in the absence of cell lysis is enabled by components of the autophagy pathway. It is likely that other nonenveloped viruses also use this pathway for nonlytic intercellular spread to affect pathogenesis in infected hosts.
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Abstract
Virus infections usually begin in peripheral tissues and can invade the mammalian nervous system (NS), spreading into the peripheral (PNS) and more rarely the central (CNS) nervous systems. The CNS is protected from most virus infections by effective immune responses and multilayer barriers. However, some viruses enter the NS with high efficiency via the bloodstream or by directly infecting nerves that innervate peripheral tissues, resulting in debilitating direct and immune-mediated pathology. Most viruses in the NS are opportunistic or accidental pathogens, but a few, most notably the alpha herpesviruses and rabies virus, have evolved to enter the NS efficiently and exploit neuronal cell biology. Remarkably, the alpha herpesviruses can establish quiescent infections in the PNS, with rare but often fatal CNS pathology. Here we review how viruses gain access to and spread in the well-protected CNS, with particular emphasis on alpha herpesviruses, which establish and maintain persistent NS infections.
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Affiliation(s)
- Orkide O Koyuncu
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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Das Sarma J. Microglia-mediated neuroinflammation is an amplifier of virus-induced neuropathology. J Neurovirol 2013; 20:122-36. [PMID: 23979705 DOI: 10.1007/s13365-013-0188-4] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 06/14/2013] [Accepted: 07/03/2013] [Indexed: 02/07/2023]
Abstract
Microglia, the major resident immune cells in the central nervous system (CNS) are considered as the key cellular mediators of neuroinflammatory processes. In the past few years, microglial research has become a main focus in cellular neuroimmunology and neuroinflammation. Chronic/remitting neurological disease such as multiple sclerosis (MS) has long been considered an inflammatory autoimmune disease with the infiltration of peripheral myelin-specific T cells into the CNS. With the rapid advancement in the field of microglia and astrocytic neurobiology, the term neuroinflammation progressively started to denote chronic CNS cell-specific inflammation in MS. The direct glial responses in MS are different from conventional peripheral immune responses. This review attempts to summarize current findings of neuroinflammatory responses within the CNS by direct infection of neural cells by mouse hepatitis virus (MHV) and the mechanisms by which glial cell responses ultimately contribute to the neuropathology on demyelination. Microglia can be persistently infected by MHV. Microglial activation and phagocytosis are recognized to be critically important in the pathogenesis of demyelination. Emerging evidence for the pathogenic role of microglia and the activation of inflammatory pathways in these cells in MHV infection supports the concept that microglia induced neuroinflammation is an amplifier of virus-induced neuropathology.
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Affiliation(s)
- Jayasri Das Sarma
- Department of Biological Sciences, Indian Institute of Science Education and Research, Kolkata, India,
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Sato F, Tanaka H, Hasanovic F, Tsunoda I. Theiler's virus infection: Pathophysiology of demyelination and neurodegeneration. ACTA ACUST UNITED AC 2011; 18:31-41. [PMID: 20537875 DOI: 10.1016/j.pathophys.2010.04.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 02/28/2010] [Accepted: 04/08/2010] [Indexed: 02/08/2023]
Abstract
Multiple sclerosis (MS) has been suggested to be an autoimmune demyelinating disease of the central nervous system (CNS), whose primary target is either myelin itself, or myelin-forming cells, the oligodendrocytes. Although axonal damage occurs in MS, it is regarded as a secondary event to the myelin damage. Here, the lesion develops from the myelin (outside) to the axons (inside) "Outside-In model". The Outside-In model has been supported by an autoimmune model for MS, experimental autoimmune (allergic) encephalomyelitis (EAE). However, recently, (1) EAE-like disease has also been shown to be induced by immune responses against axons, and (2) immune responses against axons and neurons as well as neurodegeneration independent of inflammatory demyelination have been reported in MS, which can not be explained by the Outside-In model. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a viral model for MS. In TMEV infection, axonal injury precedes demyelination, where the lesion develops from the axons (inside) to the myelin (outside) "Inside-Out model". The initial axonal damage could result in the release of neuroantigens, inducing autoimmune responses against myelin antigens, which potentially attack the myelin from outside the nerve fiber. Thus, the Inside-Out and Outside-In models can make a "vicious" immunological cycle or initiate an immune cascade.
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Affiliation(s)
- Fumitaka Sato
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, School of Medicine in Shreveport, Shreveport, LA 71130, USA
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Abstract
Viral infections are a major cause of human disease. Although most viruses replicate in peripheral tissues, some have developed unique strategies to move into the nervous system, where they establish acute or persistent infections. Viral infections in the central nervous system (CNS) can alter homeostasis, induce neurological dysfunction and result in serious, potentially life-threatening inflammatory diseases. This Review focuses on the strategies used by neurotropic viruses to cross the barrier systems of the CNS and on how the immune system detects and responds to viral infections in the CNS. A special emphasis is placed on immune surveillance of persistent and latent viral infections and on recent insights gained from imaging both protective and pathogenic antiviral immune responses.
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12
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A mechanism of virus-induced demyelination. Interdiscip Perspect Infect Dis 2010; 2010:109239. [PMID: 20652053 PMCID: PMC2905936 DOI: 10.1155/2010/109239] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Accepted: 03/20/2010] [Indexed: 11/17/2022] Open
Abstract
Myelin forms an insulating sheath surrounding axons in the central and peripheral nervous systems and is essential for rapid propagation of neuronal action potentials. Demyelination is an acquired disorder in which normally formed myelin degenerates, exposing axons to the extracellular environment. The result is dysfunction of normal neuron-to-neuron communication and in many cases, varying degrees of axonal degeneration. Numerous central nervous system demyelinating disorders exist, including multiple sclerosis. Although demyelination is the major manifestation of most of the demyelinating diseases, recent studies have clearly documented concomitant axonal loss to varying degrees resulting in long-term disability. Axonal injury may occur secondary to myelin damage (outside-in model) or myelin damage may occur secondary to axonal injury (inside-out model). Viral induced demyelination models, has provided unique imminent into the cellular mechanisms of myelin destruction. They illustrate mechanisms of viral persistence, including latent infections, virus reactivation and viral-induced tissue damage. These studies have also provided excellent paradigms to study the interactions between the immune system and the central nervous system (CNS). In this review we will discuss potential cellular and molecular mechanism of central nervous system axonal loss and demyelination in a viral induced mouse model of multiple sclerosis.
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Abstract
Dicer is responsible for the generation of mature micro-RNAs (miRNAs) and loading them into RNA-induced silencing complex (RISC). RISC functions as a probe that targets mRNAs leading to translational suppression and mRNA degradation. Schwann cells (SCs) in the peripheral nervous system undergo remarkable differentiation both in morphology and gene expression patterns throughout lineage progression to myelinating and nonmyelinating phenotypes. Gene expression in SCs is particularly tightly regulated and critical for the organism, as highlighted by the fact that a 50% decrease or an increase to 150% of normal gene expression of some myelin proteins, like PMP22, results in peripheral neuropathies. Here, we selectively deleted Dicer and consequently gene expression regulation by mature miRNAs from Mus musculus SCs. Our results show that in the absence of Dicer, most SCs arrest at the promyelinating stage and fail to start forming myelin. At the molecular level, the promyelinating transcription factor Krox20 and several myelin proteins [including myelin associated glycoprotein (MAG) and PMP22] were strongly reduced in mutant sciatic nerves. In contrast, the myelination inhibitors SOX2, Notch1, and Hes1 were increased, providing an additional potential basis for impaired myelination. A minor fraction of SCs, with some peculiar differences between sensory and motor fibers, overcame the myelination block and formed unusually thin myelin, in line with observed impaired neuregulin and AKT signaling. Surprisingly, we also found signs of axonal degeneration in Dicer mutant mice. Thus, our data indicate that miRNAs critically regulate Schwann cell gene expression that is required for myelination and to maintain axons via axon-glia interactions.
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15
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Bypass suppression of small-plaque phenotypes by a mutation in poliovirus 2A that enhances apoptosis. J Virol 2009; 83:10129-39. [PMID: 19625405 DOI: 10.1128/jvi.00642-09] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rate of protein secretion in host cells is inhibited during infection with several different picornaviruses, with consequences likely to have significant effects on viral growth, spread, and pathogenesis. This Sin(+) (secretion inhibition) phenotype has been documented for poliovirus, foot-and-mouth disease virus, and coxsackievirus B3 and can lead to reduced cell surface expression of major histocompatibility complex class I and tumor necrosis factor receptor as well as reduced extracellular secretion of induced cytokines such as interleukin-6 (IL-6), IL-8, and beta interferon. The inhibition of protein secretion is global, affecting the movement of all tested cargo proteins through the cellular secretion apparatus. To test the physiological significance of the Sin(-) and Sin(+) phenotypes in animal models, Sin(-) mutant viruses are needed that fail to inhibit host protein secretion and also exhibit robust growth properties. To identify such Sin(-) mutant polioviruses, we devised a fluorescence-activated cell sorter-based screen to select virus-infected cells that nevertheless expressed newly synthesized surface proteins. After multiple rounds of selection, candidate Sin(-) mutant viruses were screened for genetic stability, increased secretion of cargo molecules and wild-type translation and growth properties. A newly identified Sin(-) mutant poliovirus that contained coding changes in nonstructural proteins 2A (N32D) and 2C (E253G) was characterized. In this virus, the 2C mutation is responsible for the Sin(-) phenotype and the 2A mutation suppresses a resulting growth defect by increasing the rate of cell death and therefore the rate of viral spread. The 2A-N32D suppressor mutation was not allele specific and, by increasing the rate of cellular apoptosis, affected a completely different pathway than the 2C-E253G Sin(-) mutation. Therefore, the 2A mutation suppresses the 2C-E253G mutant phenotype by a bypass suppression mechanism.
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Abstract
Cellular autophagy, a process that directs cytosolic contents to the endosomal and lysosomal pathways via the formation of double-membraned vesicles, is a crucial aspect of innate immunity to many intracellular pathogens. However, evidence is accumulating that certain RNA viruses, such as poliovirus, subvert this pathway to facilitate viral growth. The autophagosome-like membranes induced during infection with wild-type poliovirus were found to be, unlike cellular autophagosomes, relatively immobile. Their mobility increased upon nocodazole treatment, arguing that vesicular tethering is microtubule dependent. In cells infected with a mutant virus that is defective in its interaction with the host cytoskeleton and secretory pathway, vesicle movement increased, indicating reduced tethering. In all cases, the release of tethering correlated with increased amounts of extracellular virus, which is consistent with the hypothesis that small amounts of cytosol and virus entrapped by double-membraned structures could be released via fusion with the plasma membrane. We propose that this extracellular delivery of cytoplasmic contents be termed autophagosome-mediated exit without lysis (AWOL). This pathway could explain the observed exit, in the apparent absence of cellular lysis, of other cytoplasmic macromolecular complexes, including infectious agents and complexes of aggregated proteins.
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Abstract
The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.
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Affiliation(s)
- W Todd Penberthy
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45237, USA.
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18
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Abstract
Autophagy is a cellular process that creates double-membraned vesicles, engulfs and degrades cytoplasmic material, and generates and recycles nutrients. A recognized participant in the innate immune response to microbial infection, a functional autophagic response can help to control the replication of many viruses. However, for several viruses, there is functional and mechanistic evidence that components of the autophagy pathway act as host factors in viral replicative cycles, viral dissemination, or both. Investigating the mechanisms by which viruses subvert or imitate autophagy, as well as the mechanisms by which they inhibit autophagy, will reveal cell biological tools and processes that will be useful for understanding the many functional ramifications of the double-membraned vesicle formation and cytosolic entrapment unique to the autophagy pathway.
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Tsunoda I. Axonal degeneration as a self-destructive defense mechanism against neurotropic virus infection. Future Virol 2008; 3:579-593. [PMID: 19079794 DOI: 10.2217/17460794.3.6.579] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Theiler's murine encephalomyelitis virus (TMEV) and other neurotropic virus infections result in degeneration of each component of the neuron: apoptosis of the cell body, axonal (Wallerian) degeneration, and dendritic and synaptic pathology. In general, axonal degeneration is detrimental for hosts. However, axonal degeneration can be beneficial in the case of infection with neurotropic viruses that spread in the CNS using axonal transport. C57BL/Wld(S) (Wld(S), Wallerian degeneration slow mutant) mice are protected from axonal degeneration. Wld(S) mice infected with the neurovirulent GDVII strain of TMEV are more resistant to virus infection than wild-type mice, suggesting that axonal preservation contributes to the resistance. By contrast, infection with the less virulent Daniels strain of TMEV results in high levels of virus propagation in the CNS, suggesting that prolonged survival of axons in Wld(S) mice favors virus spread. Thus, axonal degeneration might be a beneficial self-destruct mechanism that limits the spread of neurotropic viruses, in the case of less virulent virus infection. We hypothesize that neurons use 'built-in' self-destruct protection machinery (compartmental neurodegeneration) against neurotropic virus infection, since the CNS is an immunologically privileged site. Early induction of apoptosis in the neuronal cell body limits virus replication. Wallerian degeneration of the axon prevents axonal transport of virus. Dendritic and synaptic degeneration blocks virus transmission at synapses. Thus, the balance between neurodegeneration and virus propagation may be taken into account in the future design of neuroprotective therapy.
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Affiliation(s)
- Ikuo Tsunoda
- Department of Pathology, Division of Cell Biology & Immunology, University of Utah School of Medicine, 30 North 1900 East, MREB, Room 218, Salt Lake City, Utah 84132, USA
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Demyelinating and nondemyelinating strains of mouse hepatitis virus differ in their neural cell tropism. J Virol 2008; 82:5519-26. [PMID: 18385249 DOI: 10.1128/jvi.01488-07] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Some strains of mouse hepatitis virus (MHV) can induce chronic inflammatory demyelination in mice that mimics certain pathological features of multiple sclerosis. We have examined neural cell tropism of demyelinating and nondemyelinating strains of MHV in order to determine whether central nervous system (CNS) cell tropism plays a role in demyelination. Previous studies demonstrated that recombinant MHV strains, isogenic other than for the spike gene, differ in the extent of neurovirulence and the ability to induce demyelination. Here we demonstrate that these strains also differ in their abilities to infect a particular cell type(s) in the brain. Furthermore, there is a correlation between the differential localization of viral antigen in spinal cord gray matter and that in white matter during acute infection and the ability to induce demyelination later on. Viral antigen from demyelinating strains is detected initially in both gray and white matter, with subsequent localization to white matter of the spinal cord, whereas viral antigen localization of nondemyelinating strains is restricted mainly to gray matter. This observation suggests that the localization of viral antigen to white matter during the acute stage of infection is essential for the induction of chronic demyelination. Overall, these observations suggest that isogenic demyelinating and nondemyelinating strains of MHV, differing in the spike protein expressed, infect neurons and glial cells in different proportions and that differential tropism to a particular CNS cell type may play a significant role in mediating the onset and mechanisms of demyelination.
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