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Mabbott NA. How do PrP Sc Prions Spread between Host Species, and within Hosts? Pathogens 2017; 6:pathogens6040060. [PMID: 29186791 PMCID: PMC5750584 DOI: 10.3390/pathogens6040060] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 11/16/2017] [Accepted: 11/21/2017] [Indexed: 12/22/2022] Open
Abstract
Prion diseases are sub-acute neurodegenerative diseases that affect humans and some domestic and free-ranging animals. Infectious prion agents are considered to comprise solely of abnormally folded isoforms of the cellular prion protein known as PrPSc. Pathology during prion disease is restricted to the central nervous system where it causes extensive neurodegeneration and ultimately leads to the death of the host. The first half of this review provides a thorough account of our understanding of the various ways in which PrPSc prions may spread between individuals within a population, both horizontally and vertically. Many natural prion diseases are acquired peripherally, such as by oral exposure, lesions to skin or mucous membranes, and possibly also via the nasal cavity. Following peripheral exposure, some prions accumulate to high levels within the secondary lymphoid organs as they make their journey from the site of infection to the brain, a process termed neuroinvasion. The replication of PrPSc prions within secondary lymphoid organs is important for their efficient spread to the brain. The second half of this review describes the key tissues, cells and molecules which are involved in the propagation of PrPSc prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. This section also considers how additional factors such as inflammation and aging might influence prion disease susceptibility.
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Affiliation(s)
- Neil A Mabbott
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Easter Bush, Midlothian EH25 9RG, UK
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Mabbott NA. Immunology of Prion Protein and Prions. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2017; 150:203-240. [PMID: 28838662 DOI: 10.1016/bs.pmbts.2017.06.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Many natural prion diseases are acquired peripherally, such as following the oral consumption of contaminated food or pasture. After peripheral exposure many prion isolates initially accumulate to high levels within the host's secondary lymphoid tissues. The replication of prions within these tissues is essential for their efficient spread to the brain where they ultimately cause neurodegeneration. This chapter describes our current understanding of the critical tissues, cells, and molecules which the prions exploit to mediate their efficient propagation from the site of exposure (such as the intestine) to the brain. Interactions between the immune system and prions are not only restricted to the secondary lymphoid tissues. Therefore, an account of how the activation status of the microglial in the brain can also influence progression of prion disease pathogenesis is provided. Prion disease susceptibility may also be influenced by additional factors such as chronic inflammation, coinfection with other pathogens, and aging. Finally, the potential for immunotherapy to provide a means of safe and effective prophylactic or therapeutic intervention in these currently untreatable diseases is considered.
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Affiliation(s)
- Neil A Mabbott
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom.
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Jeffrey M, McGovern G, Barron R, Baumann F. Membrane pathology and microglial activation of mice expressing membrane anchored or membrane released forms of Aβ and mutated human Alzheimer's precursor protein (APP). Neuropathol Appl Neurobiol 2014; 41:458-70. [PMID: 25131655 DOI: 10.1111/nan.12173] [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] [Received: 05/21/2014] [Accepted: 07/23/2014] [Indexed: 12/29/2022]
Abstract
AIMS Alzheimer's disease and the transmissible spongiform encephalopathies or prion diseases accumulate misfolded and aggregated forms of neuronal cell membrane proteins. Distinctive membrane lesions caused by the accumulation of disease-associated prion protein (PrP(d)) are found in prion disease but morphological changes of membranes are not associated with Aβ in Alzheimer's disease. Membrane changes occur in all prion diseases where PrP(d) is attached to cell membranes by a glycosyl-phosphoinositol (GPI) anchor but are absent from transgenic mice expressing anchorless PrP(d). Here we investigate whether GPI membrane attached Aβ may also cause prion-like membrane lesions. METHODS We used immunogold electron microscopy to determine the localization and pathology of Aβ accumulation in groups of transgenic mice expressing anchored or unanchored forms of Aβ or mutated human Alzheimer's precursor protein. RESULTS GPI attached Aβ did not replicate the membrane lesions of PrP(d). However, as with PrP(d) in prion disease, Aβ peptides derived from each transgenic mouse line initially accumulated on morphologically normal neurite membranes, elicited rapid glial recognition and neurite Aβ was transferred to attenuated microglial and astrocytic processes. CONCLUSIONS GPI attachment of misfolded membrane proteins is insufficient to cause prion-like membrane lesions. Prion disease and murine Aβ amyloidosis both accumulate misfolded monomeric or oligomeric membrane proteins that are recognized by glial processes and acquire such misfolded proteins prior to their accumulation in the extracellular space. In contrast to prion disease where glial cells efficiently endocytose PrP(d) to endolysosomes, activated microglial cells in murine Aβ amyloidosis are not as efficient phagocytes.
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Affiliation(s)
- Martin Jeffrey
- Animal Health and Veterinary Laboratories Agency, Lasswade Laboratory, Penicuik, Midlothian, UK
| | - Gillian McGovern
- Animal Health and Veterinary Laboratories Agency, Lasswade Laboratory, Penicuik, Midlothian, UK
| | - Rona Barron
- Neurobiology Division, Roslin Institute & R(D)SVS, University of Edinburgh, Roslin, Midlothian, UK
| | - Frank Baumann
- Department of Cellular Neurology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.,German Centre for Neurodegenerative Diseases (DZNE), Tübingen, Germany
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Close interactions between sympathetic neural fibres and follicular dendritic cells network are not altered in Peyer's patches and spleen of C57BL/6 mice during the preclinical stage of 139A scrapie infection. J Neuroimmunol 2014; 272:1-9. [PMID: 24841625 DOI: 10.1016/j.jneuroim.2014.04.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 03/31/2014] [Accepted: 04/08/2014] [Indexed: 11/21/2022]
Abstract
During preclinical stage of prion diseases, secondary lymphoid organs seem to play an important role in prion amplification prior the invasion of the associated peripheral nervous system. In mice, it was shown that the relative positioning of follicular dendritic cells (FDC) and sympathetic nervous system (SNS) affects the velocity of neuroinvasion following scrapie inoculation. In this study, we checked if scrapie infection, by oral or intraperitoneal route, could influence this neuroimmune interface between FDC and tyrosine hydroxylase (TH) positive neural fibres within Peyer's patches (PP) and spleen of the C57BL/6 mouse strain. We concluded that, in vivo, scrapie 139A and ME7 strains do not modify FDC-SNS neuroimmune interface. However, age seems to alter this neuroimmune interface and thus could influence the neuroinvasion in prion pathogenesis.
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Cho IS, Spinner DS, Kascsak RJ, Meeker HC, Kim BS, Park SY, Schuller-Levis G, Park E. Altered lymphocyte proliferation and innate immune function in scrapie 139A- and ME7-infected mice. Viral Immunol 2013; 26:192-200. [PMID: 23656168 DOI: 10.1089/vim.2012.0091] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Lymphoid organs play an important role in prion disease development and progression. While the role of lymphoid organs and changes in immune-related genes have been extensively investigated in scrapie-infected animals, innate immunity has not. Previous studies examined lymphocyte function in scrapie-infected C3H/HeJ mice, which exhibit defects in lipopolysaccharide (LPS) response now known to result from a mutation in Toll-like receptor (TLR) 4. We examined immune function in scrapie-infected CD1 mice, which are LPS responders. Lymphocyte proliferation from CD1 mice infected with either 139A or ME7 scrapie was measured in response to concanavalin (Con) A or LPS at 1 and 3 months after infection. Following LPS exposure, mice infected 3 months with ME7, but not 139A, demonstrated significantly decreased lymphocyte proliferation compared to controls. After Con A exposure, lymphocyte proliferation in scrapie-infected mice did not differ from controls. Gender-specific comparison of lymphocyte proliferation showed significant decreases in mitogenic responses in females infected 3 months with either 139A or ME7, compared to controls. Males infected for 3 months with ME7, but not 139A, showed significantly decreased proliferation after lymphocyte exposure to LPS, but not Con A. Neither gender showed changes in lymphocyte proliferation after 1 month of scrapie infection. Innate immune activation of peritoneal macrophages was determined via production of nitric oxide (NO), IL-6, and TNF-α after exposure to TLR ligands. TNF-α and IL-6 production were reduced in macrophages from females infected with either scrapie strain for 3 months, while NO production after TLR agonist plus IFN-γ exposure was decreased in both females and males infected for 3 months with 139A, compared to ME7. These data demonstrated altered innate immunity, suggesting hormonal and/or other gender-specific regulation may contribute to gender differences in some immune functions. Our data demonstrate lymphocyte proliferation and innate immune functioning in scrapie-infected mice deteriorate with disease progression.
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Affiliation(s)
- In Soo Cho
- Animal, Plant and Fisheries Quarantine and Inspection Agency, Anyang, Gyunggi-do, Republic of Korea
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Membrane toxicity of abnormal prion protein in adrenal chromaffin cells of scrapie infected sheep. PLoS One 2013; 8:e58620. [PMID: 23469286 PMCID: PMC3587603 DOI: 10.1371/journal.pone.0058620] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Accepted: 02/05/2013] [Indexed: 11/19/2022] Open
Abstract
Transmissible spongiform encephalopathies (TSEs) or prion diseases are associated with accumulations of disease specific PrP (PrP(d)) in the central nervous system (CNS) and often the lymphoreticular system (LRS). Accumulations have additionally been recorded in other tissues including the peripheral nervous system and adrenal gland. Here we investigate the effect of sheep scrapie on the morphology and the accumulation of PrP(d) in the adrenal medulla of scrapie affected sheep using light and electron microscopy. Using immunogold electron microscopy, non-fibrillar forms of PrP(d) were shown to accumulate mainly in association with chromaffin cells, occasional nerve endings and macrophages. PrP(d) accumulation was associated with distinctive membrane changes of chromaffin cells including increased electron density, abnormal linearity and invaginations. Internalisation of PrP(d) from the chromaffin cell plasma membrane occurred in association with granule recycling following hormone exocytosis. PrP(d) accumulation and internalisation from membranes is similarly associated with perturbations of membrane structure and trafficking in CNS neurons and tingible body macrophages of the LRS. These data suggest that a major toxic effect of PrP(d) is at the level of plasma membranes. However, the precise nature of PrP(d)-membrane toxicity is tissue and cell specific suggesting that the normal protein may act as a multi-functional scaffolding molecule. We further suggest that the co-localisation of PrP(d) with exocytic granules of the hormone trafficking system may provide an additional source of infectivity in blood.
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Chianini F, Sisó S, Ricci E, Eaton SL, Finlayson J, Pang Y, Hamilton S, Steele P, Reid HW, Cantile C, Sales J, Jeffrey M, Dagleish MP, González L. Pathogenesis of scrapie in ARQ/ARQ sheep after subcutaneous infection: effect of lymphadenectomy and immune cell subset changes in relation to prion protein accumulation. Vet Immunol Immunopathol 2013; 152:348-58. [PMID: 23398720 DOI: 10.1016/j.vetimm.2013.01.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Revised: 01/07/2013] [Accepted: 01/10/2013] [Indexed: 12/19/2022]
Abstract
It is well established that the infectious agent of scrapie can replicate in the lymphoreticular system (LRS). However, the effects of removal of LRS target tissues on the pathogenesis of the infection and the accumulation of disease-associated prion protein (PrP(d)) in LRS tissues on specific immune cell subsets are poorly understood aspects. To address these questions 16 ARQ/ARQ sheep were subcutaneously inoculated in the drainage area of the prefemoral lymph node with brain homogenate derived from Suffolk sheep naturally infected with scrapie. Fourteen sheep were then subjected to either early (14-17 days post-inoculation [dpi]) or late (175-201 dpi) lymphadenectomy and culled at preclinical or clinical stages of infection. Neither late nor even early lymphadenectomy prevented infection or had any effect on the accumulation of PrP(d) in the LRS or CNS suggesting a rapid organic dissemination of the infectious agent after inoculation. Lymph nodes from eight scrapie inoculated sheep selected on the basis of the amount of PrP(d) in their LRS tissues (negative, low or high) were examined for six different immune cell markers. The PrP(d) negative lymph nodes from two sheep with no evidence of scrapie infection showed lower numbers of cluster of determination (CD) 21 positive cells than PrP(d) positive nodes, irrespective of their location (hind leg or head). However, quantitative differences in the expression of this marker were not detected when comparing lymph nodes with low and high levels of PrP(d) accumulation, suggesting that proliferation of CD21 positive cells is related to scrapie infection, but not directly linked to the magnitude of PrP(d) accumulation. An additional observation of the study was that sheep that were methionin-threonine at codon 112 of the prion protein gene showed lower attack rates than methionine homozygotes (67% and 100%, respectively) and also generally lower levels of PrP(d) accumulation in the LRS and brain and increased survival times, suggesting an influence of such polymorphism in the susceptibility to scrapie.
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Affiliation(s)
- F Chianini
- Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Scotland, UK.
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Marruchella G, Ligios C, Di Guardo G. Age, scrapie status, PrP genotype and follicular dendritic cells in ovine ileal Peyer’s patches. Res Vet Sci 2012; 93:853-6. [DOI: 10.1016/j.rvsc.2011.09.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2011] [Revised: 08/23/2011] [Accepted: 09/07/2011] [Indexed: 10/17/2022]
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Mabbott NA. Prion pathogenesis and secondary lymphoid organs (SLO): tracking the SLO spread of prions to the brain. Prion 2012; 6:322-33. [PMID: 22895090 PMCID: PMC3609058 DOI: 10.4161/pri.20676] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Prion diseases are subacute neurodegenerative diseases that affect humans and a range of domestic and free-ranging animal species. These diseases are characterized by the accumulation of PrPSc, an abnormally folded isoform of the cellular prion protein (PrPC), in affected tissues. The pathology during prion disease appears to occur almost exclusively within the central nervous system. The extensive neurodegeneration which occurs ultimately leads to the death of the host. An intriguing feature of the prion diseases, when compared with other protein-misfolding diseases, is their transmissibility. Following peripheral exposure, some prion diseases accumulate to high levels within lymphoid tissues. The replication of prions within lymphoid tissue has been shown to be important for the efficient spread of disease to the brain. This article describes recent progress in our understanding of the cellular mechanisms that influence the propagation of prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. A thorough understanding of these events will lead to the identification of important targets for therapeutic intervention, or alternatively, reveal additional processes that influence disease susceptibility to peripherally-acquired prion diseases.
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Affiliation(s)
- Neil A Mabbott
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, Midlothian, UK.
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McCulloch L, Brown KL, Bradford BM, Hopkins J, Bailey M, Rajewsky K, Manson JC, Mabbott NA. Follicular dendritic cell-specific prion protein (PrP) expression alone is sufficient to sustain prion infection in the spleen. PLoS Pathog 2011; 7:e1002402. [PMID: 22144895 PMCID: PMC3228802 DOI: 10.1371/journal.ppat.1002402] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 10/11/2011] [Indexed: 11/20/2022] Open
Abstract
Prion diseases are characterised by the accumulation of PrPSc, an abnormally folded isoform of the cellular prion protein (PrPC), in affected tissues. Following peripheral exposure high levels of prion-specific PrPSc accumulate first upon follicular dendritic cells (FDC) in lymphoid tissues before spreading to the CNS. Expression of PrPC is mandatory for cells to sustain prion infection and FDC appear to express high levels. However, whether FDC actively replicate prions or simply acquire them from other infected cells is uncertain. In the attempts to-date to establish the role of FDC in prion pathogenesis it was not possible to dissociate the Prnp expression of FDC from that of the nervous system and all other non-haematopoietic lineages. This is important as FDC may simply acquire prions after synthesis by other infected cells. To establish the role of FDC in prion pathogenesis transgenic mice were created in which PrPC expression was specifically “switched on” or “off” only on FDC. We show that PrPC-expression only on FDC is sufficient to sustain prion replication in the spleen. Furthermore, prion replication is blocked in the spleen when PrPC-expression is specifically ablated only on FDC. These data definitively demonstrate that FDC are the essential sites of prion replication in lymphoid tissues. The demonstration that Prnp-ablation only on FDC blocked splenic prion accumulation without apparent consequences for FDC status represents a novel opportunity to prevent neuroinvasion by modulation of PrPC expression on FDC. Prion diseases are infectious neurological disorders and are considered to be caused by an abnormally folded infectious protein termed PrPSc. Soon after infection prions accumulate first upon follicular dendritic cells (FDC) in lymphoid tissues before spreading to the brain where they cause damage to nerve cells. Cells must express the normal cellular prion protein PrPC to become infected with prions. However, whether FDC are infected with prions or simply acquire them from other infected cells is unknown. To establish the role of FDC in prion disease PrPC expression was specifically “switched on” or “off” only on FDC. We show that PrPC-expressing FDC alone are sufficient to sustain prion replication in the spleen. Furthermore, prion replication is blocked in the spleen when PrPC-expression is switched off only on FDC. These data definitively demonstrate that FDC are the essential sites of prion replication in lymphoid tissues.
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Affiliation(s)
- Laura McCulloch
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
| | - Karen L. Brown
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
| | - Barry M. Bradford
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
| | - John Hopkins
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
| | - Mick Bailey
- Division of Veterinary Pathology, Infection and Immunity, School of Clinical Veterinary Science, University of Bristol, Avon, United Kingdom
| | - Klaus Rajewsky
- Program in Cellular and Molecular Medicine, Children's Hospital, and Immune Disease Institute, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jean C. Manson
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
| | - Neil A. Mabbott
- The Roslin Institute & Royal (Dick) School of Veterinary Sciences, University of Edinburgh, Midlothian, United Kingdom
- * E-mail:
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Jeffrey M, McGovern G, Sisó S, González L. Cellular and sub-cellular pathology of animal prion diseases: relationship between morphological changes, accumulation of abnormal prion protein and clinical disease. Acta Neuropathol 2011; 121:113-34. [PMID: 20532540 DOI: 10.1007/s00401-010-0700-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Revised: 05/04/2010] [Accepted: 05/19/2010] [Indexed: 11/24/2022]
Abstract
The transmissible spongiform encephalopathies (TSEs) or prion diseases of animals are characterised by CNS spongiform change, gliosis and the accumulation of disease-associated forms of prion protein (PrP(d)). Particularly in ruminant prion diseases, a wide range of morphological types of PrP(d) depositions are found in association with neurons and glia. When light microscopic patterns of PrP(d) accumulations are correlated with sub-cellular structure, intracellular PrP(d) co-localises with lysosomes while non-intracellular PrP(d) accumulation co-localises with cell membranes and the extracellular space. Intracellular lysosomal PrP(d) is N-terminally truncated, but the site at which the PrP(d) molecule is cleaved depends on strain and cell type. Different PrP(d) cleavage sites are found for different cells infected with the same agent indicating that not all PrP(d) conformers code for different prion strains. Non-intracellular PrP(d) is full-length and is mainly found on plasma-lemmas of neuronal perikarya and dendrites and glia where it may be associated with scrapie-specific membrane pathology. These membrane changes appear to involve a redirection of the predominant axonal trafficking of normal cellular PrP and an altered endocytosis of PrP(d). PrP(d) is poorly excised from membranes, probably due to increased stabilisation on the membrane of PrP(d) complexed with other membrane ligands. PrP(d) on plasma-lemmas may also be transferred to other cells or released to the extracellular space. It is widely assumed that PrP(d) accumulations cause neurodegenerative changes that lead to clinical disease. However, when different animal prion diseases are considered, neurological deficits do not correlate well with any morphological type of PrP(d) accumulation or perturbation of PrP(d) trafficking. Non-PrP(d)-associated neurodegenerative changes in TSEs include vacuolation, tubulovesicular bodies and terminal axonal degeneration. The last of these correlates well with early neurological disease in mice, but such changes are absent from large animal prion disease. Thus, the proximate cause of clinical disease in animal prion disease is uncertain, but may not involve PrP(d).
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Affiliation(s)
- Martin Jeffrey
- Veterinary Laboratories Agency, Lasswade Laboratory, Pentlands Science Park, Bush Loan, Penicuik, Midlothian, EH26 0PZ, UK.
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Characterization of the role of dendritic cells in prion transfer to primary neurons. Biochem J 2010; 431:189-98. [PMID: 20670217 DOI: 10.1042/bj20100698] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
TSEs (transmissible spongiform encephalopathies) are neurodegenerative diseases caused by pathogenic isoforms (PrPSc) of the host-encoded PrPc (cellular prion protein). After consumption of contaminated food, PrPSc deposits rapidly accumulate in lymphoid tissues before invasion of the CNS (central nervous system). However, the mechanisms of prion spreading from the periphery to the nervous system are still unclear. In the present study, we investigated the role of DCs (dendritic cells) in the spreading of prion infection to neuronal cells. First, we determined that BMDCs (bone-marrow-derived DCs) rapidly uptake PrPSc after exposure to infected brain homogenate. Next, we observed a progressive catabolism of the internalized prion aggregates. Similar experiments performed with BMDCs isolated from KO (knockout) mice or mice overexpressing PrP (tga20) indicate that both PrPSc uptake and catabolism are independent of PrPc expression in these cells. Finally, using co-cultures of prion-loaded BMDCs and cerebellar neurons, we characterized the transfer of the prion protein and the resulting infection of the neuronal cultures. Interestingly, the transfer of PrPSc was triggered by direct cell-cell contact. As a consequence, BMDCs retained the prion protein when cultured alone, and no transfer to the recipient neurons was observed when a filter separated the two cultures or when neurons were exposed to the BMDC-conditioned medium. Additionally, fixed BMDCs also failed to transfer prion infectivity to neurons, suggesting an active transport of prion aggregates, in accordance with a role of TNTs (tunnelling nanotubes) observed in the co-cultures.
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