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GPI-anchor signal sequence influences PrPC sorting, shedding and signalling, and impacts on different pathomechanistic aspects of prion disease in mice. PLoS Pathog 2019; 15:e1007520. [PMID: 30608982 PMCID: PMC6334958 DOI: 10.1371/journal.ppat.1007520] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 01/16/2019] [Accepted: 12/11/2018] [Indexed: 12/31/2022] Open
Abstract
The cellular prion protein (PrPC) is a cell surface glycoprotein attached to the membrane by a glycosylphosphatidylinositol (GPI)-anchor and plays a critical role in transmissible, neurodegenerative and fatal prion diseases. Alterations in membrane attachment influence PrPC-associated signaling, and the development of prion disease, yet our knowledge of the role of the GPI-anchor in localization, processing, and function of PrPCin vivo is limited We exchanged the PrPC GPI-anchor signal sequence of for that of Thy-1 (PrPCGPIThy-1) in cells and mice. We show that this modifies the GPI-anchor composition, which then lacks sialic acid, and that PrPCGPIThy-1 is preferentially localized in axons and is less prone to proteolytic shedding when compared to PrPC. Interestingly, after prion infection, mice expressing PrPCGPIThy-1 show a significant delay to terminal disease, a decrease of microglia/astrocyte activation, and altered MAPK signaling when compared to wild-type mice. Our results are the first to demonstrate in vivo, that the GPI-anchor signal sequence plays a fundamental role in the GPI-anchor composition, dictating the subcellular localization of a given protein and, in the case of PrPC, influencing the development of prion disease. The prion protein (PrPC) is a glycoprotein attached to the neuronal surface via a GPI-anchor. When misfolded to PrPSc, it leads to fatal neurodegenerative diseases which propagates from host to host. PrPSc is the principal component of the infectious agent of prion diseases, the “prion”. Misfolding occurs at the plasma membrane, and when PrPC lacks the GPI-anchor, neuropathology and incubation time of prion disease are strongly modified. Moreover, the composition of the PrPC GPI-anchor impacts on the conversion process. To study the role of the GPI-anchor in the pathophysiology of prion diseases in vivo, we have generated transgenic mice where the PrPC GPI-signal sequence (GPI-SS) is replaced for the one of Thy-1, a neuronal protein with a distinct GPI-anchor and membrane localization. We found that the resulting protein, PrPCGPIThy-1, shows a different GPI-anchor composition, increased axonal localization, and reduced enzymatic shedding. After prion infection, disease progression is significantly delayed, and the neuropathology and cellular signaling are changed. The present work demonstrates that the GPI-SS per se determines the GPI-anchor composition and localization of a given protein and it stresses the importance of PrPC membrane anchorage in prion disease.
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Bate C, Williams A. Monomeric amyloid-β reduced amyloid-β oligomer-induced synapse damage in neuronal cultures. Neurobiol Dis 2017; 111:48-58. [PMID: 29272738 DOI: 10.1016/j.nbd.2017.12.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Revised: 11/12/2017] [Accepted: 12/12/2017] [Indexed: 12/25/2022] Open
Abstract
Alzheimer's disease is a progressive neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) in the brain. Aβ oligomers are believed to cause synapse damage resulting in the memory deficits that are characteristic of this disease. Since the loss of synaptic proteins in the brain correlates closely with the degree of dementia in Alzheimer's disease, the process of Aβ-induced synapse damage was investigated in cultured neurons by measuring the loss of synaptic proteins. Soluble Aβ oligomers, derived from Alzheimer's-affected brains, caused the loss of cysteine string protein and synaptophysin from neurons. When applied to synaptosomes Aβ oligomers increased cholesterol concentrations and caused aberrant activation of cytoplasmic phospholipase A2 (cPLA2). In contrast, Aβ monomer preparations did not affect cholesterol concentrations or activate synaptic cPLA2, nor did they damage synapses. The Aβ oligomer-induced aggregation of cellular prion proteins (PrPC) at synapses triggered the activation of cPLA2 that leads to synapse degeneration. Critically, Aβ monomer preparations did not cause the aggregation of PrPC; rather they reduced the Aβ oligomer-induced aggregation of PrPC. The presence of Aβ monomer preparations also inhibited the Aβ oligomer-induced increase in cholesterol concentrations and activation of cPLA2 in synaptosomes and protected neurons against the Aβ oligomer-induced synapse damage. These results support the hypothesis that Aβ monomers are neuroprotective. We hypothesise that synapse damage may result from a pathological Aβ monomer:oligomer ratio rather than the total concentrations of Aβ within the brain.
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Affiliation(s)
- Clive Bate
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA, UK.
| | - Alun Williams
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK.
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Bate C. Breaking the Cycle, Cholesterol Cycling, and Synapse Damage in Response to Amyloid-β. J Exp Neurosci 2017; 11:1179069517733096. [PMID: 29238218 PMCID: PMC5721958 DOI: 10.1177/1179069517733096] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Accepted: 09/01/2017] [Indexed: 01/04/2023] Open
Abstract
Soluble amyloid-β (Aβ) oligomers, a key driver of pathogenesis in Alzheimer disease, bind to cellular prion proteins (PrPC) expressed on synaptosomes resulting in increased cholesterol concentrations, movement of cytoplasmic phospholipase A2 (cPLA2) to lipid rafts and activation of cPLA2. The formation of Aβ-PrPC-cPLA2 complexes was controlled by the cholesterol ester cycle. Thus, Aβ activated cholesterol ester hydrolases which released cholesterol from stores of cholesterol esters; the increased cholesterol concentrations stabilised Aβ-PrPC-cPLA2 complexes. Conversely, cholesterol esterification reduced cholesterol concentrations causing the dispersal of Aβ-PrPC-cPLA2. In cultured neurons, the cholesterol ester cycle regulated Aβ-induced synapse damage; inhibition of cholesterol ester hydrolases protected neurons, whereas inhibition of cholesterol esterification increased the Aβ-induced synapse damage. Here, I speculate that a failure to deactivate signalling pathways can lead to pathology. Consequently, the esterification of cholesterol is a key factor in the dispersal of Aβ-induced signalling platforms and synapse degeneration.
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Affiliation(s)
- Clive Bate
- Department of Pathology and Pathogen Biology, The Royal Veterinary College, Hatfield,UK
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Bate C, Nolan W, Williams A. Does the tail wag the dog? How the structure of a glycosylphosphatidylinositol anchor affects prion formation. Prion 2017; 10:127-30. [PMID: 26901126 DOI: 10.1080/19336896.2016.1148237] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
There is increasing interest in the role of the glycosylphosphatidylinositol (GPI) anchor attached to the cellular prion protein (PrP(C)). Since GPI anchors can alter protein targeting, trafficking and cell signaling, our recent study examined how the structure of the GPI anchor affected prion formation. PrP(C) containing a GPI anchor from which the sialic acid had been removed (desialylated PrP(C)) was not converted to PrP(Sc) in prion-infected neuronal cell lines and in scrapie-infected primary cortical neurons. In uninfected neurons desialylated PrP(C) was associated with greater concentrations of gangliosides and cholesterol than PrP(C). In addition, the targeting of desialylated PrP(C) to lipid rafts showed greater resistance to cholesterol depletion than PrP(C). The presence of desialylated PrP(C) caused the dissociation of cytoplasmic phospholipase A2 (cPLA2) from PrP-containing lipid rafts, reduced the activation of cPLA2 and inhibited PrP(Sc) production. We conclude that the sialic acid moiety of the GPI attached to PrP(C) modifies local membrane microenvironments that are important in PrP-mediated cell signaling and PrP(Sc) formation.
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Affiliation(s)
- Clive Bate
- a Department of Pathology and Pathogen Biology , Royal Veterinary College , North Mymms, Herts , UK
| | - William Nolan
- a Department of Pathology and Pathogen Biology , Royal Veterinary College , North Mymms, Herts , UK
| | - Alun Williams
- b Department of Veterinary Medicine , University of Cambridge , Cambridge , UK
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Sialylated glycosylphosphatidylinositols suppress the production of toxic amyloid-β oligomers. Biochem J 2017; 474:3045-3058. [PMID: 28729427 DOI: 10.1042/bcj20170239] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 07/07/2017] [Accepted: 07/19/2017] [Indexed: 01/30/2023]
Abstract
The production of amyloid-β (Aβ) is a key factor driving pathogenesis in Alzheimer's disease (AD). Increasing concentrations of soluble Aβ oligomers within the brain lead to synapse degeneration and the progressive dementia characteristic of AD. Since Aβ exists in both disease-relevant (toxic) and non-toxic forms, the factors that affected the release of toxic Aβ were studied in a cell model. 7PA2 cells expressing the human amyloid precursor protein released Aβ oligomers that caused synapse damage when incubated with cultured neurones. These Aβ oligomers had similar potency to soluble Aβ oligomers derived from the brains of Alzheimer's patients. Although the conditioned media from 7PA2 cells treated with the cellular prion protein (PrPC) contained Aβ, it did not cause synapse damage. The loss of toxicity was associated with a reduction in Aβ oligomers and an increase in Aβ monomers. The suppression of toxic Aβ release was dependent on the glycosylphosphatidylinositol (GPI) anchor attached to PrPC, and treatment of cells with specific GPIs alone reduced the production of toxic Aβ. The efficacy of GPIs was structure-dependent and the presence of sialic acid was critical. The conditioned medium from GPI-treated cells protected neurones against Aβ oligomer-induced synapse damage; neuroprotection was mediated by Aβ monomers. These studies support the hypothesis that the ratio of Aβ monomers to Aβ oligomers is a critical factor that regulates synapse damage.
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West E, Osborne C, Bate C. The cholesterol ester cycle regulates signalling complexes and synapse damage caused by amyloid-β. J Cell Sci 2017; 130:3050-3059. [PMID: 28760925 DOI: 10.1242/jcs.205484] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 07/26/2017] [Indexed: 02/01/2023] Open
Abstract
Cholesterol is required for the formation and function of some signalling platforms. In synaptosomes, amyloid-β (Aβ) oligomers, the causative agent in Alzheimer's disease, bind to cellular prion proteins (PrPC) resulting in increased cholesterol concentrations, translocation of cytoplasmic phospholipase A2 (cPLA2, also known as PLA2G4A) to lipid rafts, and activation of cPLA2 The formation of Aβ-PrPC complexes is controlled by the cholesterol ester cycle. In this study, Aβ activated cholesterol ester hydrolases, which released cholesterol from stores of cholesterol esters and stabilised Aβ-PrPC complexes, resulting in activated cPLA2 Conversely, cholesterol esterification reduced cholesterol concentrations causing the dispersal of Aβ-PrPC complexes. In cultured neurons, the cholesterol ester cycle regulated Aβ-induced synapse damage; cholesterol ester hydrolase inhibitors protected neurons, while inhibition of cholesterol esterification significantly increased Aβ-induced synapse damage. An understanding of the molecular mechanisms involved in the dispersal of signalling complexes is important as failure to deactivate signalling pathways can lead to pathology. This study demonstrates that esterification of cholesterol is a key factor in the dispersal of Aβ-induced signalling platforms involved in the activation of cPLA2 and synapse degeneration.
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Affiliation(s)
- Ewan West
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts, AL9 7TA, UK
| | - Craig Osborne
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts, AL9 7TA, UK
| | - Clive Bate
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts, AL9 7TA, UK
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Sarnataro D, Pepe A, Zurzolo C. Cell Biology of Prion Protein. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2017; 150:57-82. [PMID: 28838675 DOI: 10.1016/bs.pmbts.2017.06.018] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cellular prion protein (PrPC) is a mammalian glycoprotein which is usually found anchored to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. The precise function of PrPC remains elusive but may depend upon its cellular localization. PrPC misfolds to a pathogenic isoform PrPSc, the causative agent of neurodegenerative prion diseases. Nonetheless some forms of prion disease develop in the apparent absence of infectious PrPSc, suggesting that molecular species of PrP distinct from PrPSc may represent the primary neurotoxic culprits. Indeed, in some inherited cases of human prion disease, the predominant form of PrP detectable in the brain is not PrPSc but rather CtmPrP, a transmembrane form of the protein. The relationship between the neurodegeneration occurring in prion diseases involving PrPSc and that associated with CtmPrP remains unclear. However, the different membrane topology of the PrP mutants, as well as the presence of the GPI anchor, could influence both the function and the intracellular localization and trafficking of the protein, all being potentially very important in the pathophysiological mechanism that ultimately causes the disease. Here, we review the latest findings on the fundamental aspects of prions biology, from the PrPC biosynthesis, function, and structure up to its intracellular traffic and analyze the possible roles of the different topological isoforms of the protein, as well as the GPI anchor, in the pathogenesis of the disease.
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Affiliation(s)
- Daniela Sarnataro
- University of Naples "Federico II", Naples, Italy; Ceinge-Biotecnologie avanzate, s.c.a r.l., Naples, Italy.
| | - Anna Pepe
- University of Naples "Federico II", Naples, Italy; Unité de Trafic Membranaire et Pathogenese, Institut Pasteur, Paris, France
| | - Chiara Zurzolo
- University of Naples "Federico II", Naples, Italy; Unité de Trafic Membranaire et Pathogenese, Institut Pasteur, Paris, France
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PrP Knockout Cells Expressing Transmembrane PrP Resist Prion Infection. J Virol 2017; 91:JVI.01686-16. [PMID: 27847358 DOI: 10.1128/jvi.01686-16] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 11/01/2016] [Indexed: 11/20/2022] Open
Abstract
Glycosylphosphatidylinositol (GPI) anchoring of the prion protein (PrPC) influences PrPC misfolding into the disease-associated isoform, PrPres, as well as prion propagation and infectivity. GPI proteins are found in cholesterol- and sphingolipid-rich membrane regions called rafts. Exchanging the GPI anchor for a nonraft transmembrane sequence redirects PrPC away from rafts. Previous studies showed that nonraft transmembrane PrPC variants resist conversion to PrPres when transfected into scrapie-infected N2a neuroblastoma cells, likely due to segregation of transmembrane PrPC and GPI-anchored PrPres in distinct membrane environments. Thus, it remained unclear whether transmembrane PrPC might convert to PrPres if seeded by an exogenous source of PrPres not associated with host cell rafts and without the potential influence of endogenous expression of GPI-anchored PrPC To further explore these questions, constructs containing either a C-terminal wild-type GPI anchor signal sequence or a nonraft transmembrane sequence containing a flexible linker were expressed in a cell line derived from PrP knockout hippocampal neurons, NpL2. NpL2 cells have physiological similarities to primary neurons, representing a novel and advantageous model for studying transmissible spongiform encephalopathy (TSE) infection. Cells were infected with inocula from multiple prion strains and in different biochemical states (i.e., membrane bound as in brain microsomes from wild-type mice or purified GPI-anchorless amyloid fibrils). Only GPI-anchored PrPC supported persistent PrPres propagation. Our data provide strong evidence that in cell culture GPI anchor-directed membrane association of PrPC is required for persistent PrPres propagation, implicating raft microdomains as a location for conversion. IMPORTANCE Mechanisms of prion propagation, and what makes them transmissible, are poorly understood. Glycosylphosphatidylinositol (GPI) membrane anchoring of the prion protein (PrPC) directs it to specific regions of cell membranes called rafts. In order to test the importance of the raft environment on prion propagation, we developed a novel model for prion infection where cells expressing either GPI-anchored PrPC or transmembrane-anchored PrPC, which partitions it to a different location, were treated with infectious, misfolded forms of the prion protein, PrPres We show that only GPI-anchored PrPC was able to convert to PrPres and able to serially propagate. The results strongly suggest that GPI anchoring and the localization of PrPC to rafts are crucial to the ability of PrPC to propagate as a prion.
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Katorcha E, Srivastava S, Klimova N, Baskakov IV. Sialylation of Glycosylphosphatidylinositol (GPI) Anchors of Mammalian Prions Is Regulated in a Host-, Tissue-, and Cell-specific Manner. J Biol Chem 2016; 291:17009-19. [PMID: 27317661 PMCID: PMC5016106 DOI: 10.1074/jbc.m116.732040] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 06/09/2016] [Indexed: 01/08/2023] Open
Abstract
Prions or PrP(Sc) are proteinaceous infectious agents that consist of misfolded, self-replicating states of the prion protein or PrP(C) PrP(C) is posttranslationally modified with N-linked glycans and a sialylated glycosylphosphatidylinositol (GPI) anchor. Conformational conversion of PrP(C) gives rise to glycosylated and GPI-anchored PrP(Sc) The question of the sialylation status of GPIs within PrP(Sc) has been controversial. Previous studies that examined scrapie brains reported that both sialo- and asialo-GPIs were present in PrP(Sc), with the majority being asialo-GPIs. In contrast, recent work that employed cultured cells claimed that only PrP(C) with sialylo-GPIs could be recruited into PrP(Sc), whereas PrP(C) with asialo-GPIs inhibited conversion. To resolve this controversy, we analyzed the sialylation status of GPIs within PrP(Sc) generated in the brain, spleen, or cultured N2a or C2C12 myotube cells. We found that recruiting PrP(C) with both sialo- and asialo-GPIs is a common feature of PrP(Sc) The mixtures of sialo- and asialo-GPIs were observed in PrP(Sc) universally regardless of prion strain as well as host, tissue, or type of cells that produced PrP(Sc) Remarkably, the proportion of sialo- versus asialo-GPIs was found to be controlled by host, tissue, and cell type but not prion strain. In summary, this study found no strain-specific preferences for selecting PrP(C) with sialo- versus asialo-GPIs. Instead, this work suggests that the sialylation status of GPIs within PrP(Sc) is regulated in a cell-, tissue-, or host-specific manner and is likely to be determined by the specifics of GPI biosynthesis.
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Affiliation(s)
- Elizaveta Katorcha
- From the Center for Biomedical Engineering and Technology and the Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Saurabh Srivastava
- From the Center for Biomedical Engineering and Technology and the Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Nina Klimova
- From the Center for Biomedical Engineering and Technology and the Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Ilia V Baskakov
- From the Center for Biomedical Engineering and Technology and the Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
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Baskakov IV, Katorcha E. Multifaceted Role of Sialylation in Prion Diseases. Front Neurosci 2016; 10:358. [PMID: 27551257 PMCID: PMC4976111 DOI: 10.3389/fnins.2016.00358] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 07/18/2016] [Indexed: 11/13/2022] Open
Abstract
Mammalian prion or PrP(Sc) is a proteinaceous infectious agent that consists of a misfolded, self-replicating state of a sialoglycoprotein called the prion protein, or PrP(C). Sialylation of the prion protein N-linked glycans was discovered more than 30 years ago, yet the role of sialylation in prion pathogenesis remains poorly understood. Recent years have witnessed extraordinary growth in interest in sialylation and established a critical role for sialic acids in host invasion and host-pathogen interactions. This review article summarizes current knowledge on the role of sialylation of the prion protein in prion diseases. First, we discuss the correlation between sialylation of PrP(Sc) glycans and prion infectivity and describe the factors that control sialylation of PrP(Sc). Second, we explain how glycan sialylation contributes to the prion replication barrier, defines strain-specific glycoform ratios, and imposes constraints for PrP(Sc) structure. Third, several topics, including a possible role for sialylation in animal-to-human prion transmission, prion lymphotropism, toxicity, strain interference, and normal function of PrP(C), are critically reviewed. Finally, a metabolic hypothesis on the role of sialylation in the etiology of sporadic prion diseases is proposed.
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Affiliation(s)
- Ilia V. Baskakov
- Department of Anatomy and Neurobiology, Center for Biomedical Engineering and Technology, University of Maryland School of MedicineBaltimore, MD, USA
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Bate C, Nolan W, McHale-Owen H, Williams A. Sialic Acid within the Glycosylphosphatidylinositol Anchor Targets the Cellular Prion Protein to Synapses. J Biol Chem 2016; 291:17093-101. [PMID: 27325697 DOI: 10.1074/jbc.m116.731117] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Indexed: 11/06/2022] Open
Abstract
Although the cellular prion protein (PrP(C)) is concentrated at synapses, the factors that target PrP(C) to synapses are not understood. Here we demonstrate that exogenous PrP(C) was rapidly targeted to synapses in recipient neurons derived from Prnp knock-out((0/0)) mice. The targeting of PrP(C) to synapses was dependent upon both neuronal cholesterol concentrations and the lipid and glycan composition of its glycosylphosphatidylinositol (GPI) anchor. Thus, the removal of either an acyl chain or sialic acid from the GPI anchor reduced the targeting of PrP(C) to synapses. Isolated GPIs (derived from PrP(C)) were also targeted to synapses, as was IgG conjugated to these GPIs. The removal of sialic acid from GPIs prevented the targeting of either the isolated GPIs or the IgG-GPI conjugate to synapses. Competition studies showed that pretreatment with sialylated GPIs prevented the targeting of PrP(C) to synapses. These results are consistent with the hypothesis that the sialylated GPI anchor attached to PrP(C) acts as a synapse homing signal.
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Affiliation(s)
- Clive Bate
- From the Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA and
| | - William Nolan
- From the Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA and
| | - Harriet McHale-Owen
- From the Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA and
| | - Alun Williams
- the Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, United Kingdom
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Bate C, Nolan W, Williams A. Glycosylphosphatidylinositols: More than just an anchor? Commun Integr Biol 2016; 9:e1149671. [PMID: 27195066 PMCID: PMC4857774 DOI: 10.1080/19420889.2016.1149671] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 01/29/2016] [Indexed: 11/02/2022] Open
Abstract
There is increasing interest in the role of glycosylphosphatidylinositol (GPI) anchors that attach some proteins to cell membranes. Far from being biologically inert, GPIs influence the targeting, intracellular trafficking and function of the attached protein. Our recent paper demonstrated the role of sialic acid on the GPI of the cellular prion protein (PrP(C)). The "prion diseases" arise following the conversion of PrP(C) to a disease-associated isoform called PrP(Sc) or "prion". Our paper showed that desialylated PrP(C) inhibited PrP(Sc) formation. Aggregated PrP(Sc) creates a signaling platform in the cell membrane incorporating and activating cytoplasmic phospholipase A2 (cPLA2), an enzyme that regulates PrP(C) trafficking and hence PrP(Sc) formation. The presence of desialylated PrP(C) caused the dissociation of cPLA2 from PrP-containing platforms, reduced the activation of cPLA2 and inhibited PrP(Sc) production. We concluded that sialic acid contained within the GPI attached to PrP(C) modifies local membrane microenvironments that are important in PrP-mediated cell signaling and PrP(Sc) formation.
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Affiliation(s)
- Clive Bate
- Department of Pathology and Pathogen Biology, Royal Veterinary College , North Mymms, Hertfordshire, UK
| | - William Nolan
- Department of Pathology and Pathogen Biology, Royal Veterinary College , North Mymms, Hertfordshire, UK
| | - Alun Williams
- Department of Veterinary Medicine, University of Cambridge , Cambridge, UK
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Glimepiride protects neurons against amyloid-β-induced synapse damage. Neuropharmacology 2016; 101:225-36. [DOI: 10.1016/j.neuropharm.2015.09.030] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Revised: 08/04/2015] [Accepted: 09/28/2015] [Indexed: 12/30/2022]
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Bate C, Nolan W, Williams A. Sialic Acid on the Glycosylphosphatidylinositol Anchor Regulates PrP-mediated Cell Signaling and Prion Formation. J Biol Chem 2015; 291:160-70. [PMID: 26553874 DOI: 10.1074/jbc.m115.672394] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Indexed: 01/24/2023] Open
Abstract
The prion diseases occur following the conversion of the cellular prion protein (PrP(C)) into disease-related isoforms (PrP(Sc)). In this study, the role of the glycosylphosphatidylinositol (GPI) anchor attached to PrP(C) in prion formation was examined using a cell painting technique. PrP(Sc) formation in two prion-infected neuronal cell lines (ScGT1 and ScN2a cells) and in scrapie-infected primary cortical neurons was increased following the introduction of PrP(C). In contrast, PrP(C) containing a GPI anchor from which the sialic acid had been removed (desialylated PrP(C)) was not converted to PrP(Sc). Furthermore, the presence of desialylated PrP(C) inhibited the production of PrP(Sc) within prion-infected cortical neurons and ScGT1 and ScN2a cells. The membrane rafts surrounding desialylated PrP(C) contained greater amounts of sialylated gangliosides and cholesterol than membrane rafts surrounding PrP(C). Desialylated PrP(C) was less sensitive to cholesterol depletion than PrP(C) and was not released from cells by treatment with glimepiride. The presence of desialylated PrP(C) in neurons caused the dissociation of cytoplasmic phospholipase A2 from PrP-containing membrane rafts and reduced the activation of cytoplasmic phospholipase A2. These findings show that the sialic acid moiety of the GPI attached to PrP(C) modifies local membrane microenvironments that are important in PrP-mediated cell signaling and PrP(Sc) formation. These results suggest that pharmacological modification of GPI glycosylation might constitute a novel therapeutic approach to prion diseases.
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Affiliation(s)
- Clive Bate
- From the Department of Pathology and Pathogen Biology, Royal Veterinary College, North Mymms, Hertfordshire AL9 7TA, United Kingdom and
| | - William Nolan
- From the Department of Pathology and Pathogen Biology, Royal Veterinary College, North Mymms, Hertfordshire AL9 7TA, United Kingdom and
| | - Alun Williams
- the Department of Veterinary Medicine, University of Cambridge, Cambridge CB3 OES, United Kingdom
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West E, Osborne C, Nolan W, Bate C. Monoacylated Cellular Prion Proteins Reduce Amyloid-β-Induced Activation of Cytoplasmic Phospholipase A2 and Synapse Damage. BIOLOGY 2015; 4:367-82. [PMID: 26043272 PMCID: PMC4498305 DOI: 10.3390/biology4020367] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Revised: 05/21/2015] [Accepted: 05/25/2015] [Indexed: 12/30/2022]
Abstract
Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) and the loss of synapses. Aggregation of the cellular prion protein (PrPC) by Aβ oligomers induced synapse damage in cultured neurons. PrPC is attached to membranes via a glycosylphosphatidylinositol (GPI) anchor, the composition of which affects protein targeting and cell signaling. Monoacylated PrPC incorporated into neurons bound “natural Aβ”, sequestering Aβ outside lipid rafts and preventing its accumulation at synapses. The presence of monoacylated PrPC reduced the Aβ-induced activation of cytoplasmic phospholipase A2 (cPLA2) and Aβ-induced synapse damage. This protective effect was stimulus specific, as treated neurons remained sensitive to α-synuclein, a protein associated with synapse damage in Parkinson’s disease. In synaptosomes, the aggregation of PrPC by Aβ oligomers triggered the formation of a signaling complex containing the cPLA2.a process, disrupted by monoacylated PrPC. We propose that monoacylated PrPC acts as a molecular sponge, binding Aβ oligomers at the neuronal perikarya without activating cPLA2 or triggering synapse damage.
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Affiliation(s)
- Ewan West
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL97TA, UK.
| | - Craig Osborne
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL97TA, UK.
| | - William Nolan
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL97TA, UK.
| | - Clive Bate
- Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL97TA, UK.
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Puig B, Altmeppen H, Glatzel M. The GPI-anchoring of PrP: implications in sorting and pathogenesis. Prion 2015; 8:11-8. [PMID: 24509692 DOI: 10.4161/pri.27892] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The cellular prion protein (PrP(C)) is an N-glycosylated GPI-anchored protein usually present in lipid rafts with numerous putative functions. When it changes its conformation to a pathological isoform (then referred to as PrP(Sc)), it is an essential part of the prion, the agent causing fatal and transmissible neurodegenerative prion diseases. There is growing evidence that toxicity and neuronal damage on the one hand and propagation/infectivity on the other hand are two distinct processes of the disease and that the GPI-anchor attachment of PrP(C) and PrP(Sc) plays an important role in protein localization and in neurotoxicity. Here we review how the signal sequence of the GPI-anchor matters in PrP(C) localization, how an altered cellular localization of PrP(C) or differences in GPI-anchor composition can affect prion infection, and we discuss through which mechanisms changes on the anchorage of PrP(C) can modify the disease process.
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Subcellular distribution of the prion protein in sickness and in health. Virus Res 2015; 207:136-45. [PMID: 25683509 DOI: 10.1016/j.virusres.2015.02.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Revised: 02/03/2015] [Accepted: 02/03/2015] [Indexed: 11/22/2022]
Abstract
The cellular prion protein (PrP(C)) is an ubiquitously expressed glycoprotein that is most abundant in the central nervous system. It is thought to play a role in many cellular processes, including neuroprotection, but may also contribute to Alzheimer's disease and some cancers. However, it is best known for its central role in the prion diseases, such as Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE), and scrapie. These protein misfolding diseases can be sporadic, acquired, or genetic and are caused by refolding of endogenous PrP(C) into a beta sheet-rich, pathogenic form, PrP(Sc). Once prions are present in the central nervous system, they increase and spread during a long incubation period that is followed by a relatively short clinical disease phase, ending in death. PrP molecules can be broadly categorized as either 'good' (cellular) PrP(C) or 'bad' (scrapie prion-type) PrP(Sc), but both populations are heterogeneous and different forms of PrP(C) may influence various cellular activities. Both PrP(C) and PrP(Sc) are localized predominantly at the cell surface, with the C-terminus attached to the plasma membrane via a glycosyl-phosphatidylinositol (GPI) anchor and both can exist in cleaved forms. PrP(C) also has cytosolic and transmembrane forms, and PrP(Sc) is known to exist in a variety of conformations and aggregation states. Here, we discuss the roles of different PrP isoforms in sickness and in health, and show the subcellular distributions of several forms of PrP that are particularly relevant for PrP(C) to PrP(Sc) conversion and prion-induced pathology in the hippocampus.
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Sialylation of prion protein controls the rate of prion amplification, the cross-species barrier, the ratio of PrPSc glycoform and prion infectivity. PLoS Pathog 2014; 10:e1004366. [PMID: 25211026 PMCID: PMC4161476 DOI: 10.1371/journal.ppat.1004366] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 07/28/2014] [Indexed: 12/15/2022] Open
Abstract
The central event underlying prion diseases involves conformational change of the cellular form of the prion protein (PrPC) into the disease-associated, transmissible form (PrPSc). PrPC is a sialoglycoprotein that contains two conserved N-glycosylation sites. Among the key parameters that control prion replication identified over the years are amino acid sequence of host PrPC and the strain-specific structure of PrPSc. The current work highlights the previously unappreciated role of sialylation of PrPC glycans in prion pathogenesis, including its role in controlling prion replication rate, infectivity, cross-species barrier and PrPSc glycoform ratio. The current study demonstrates that undersialylated PrPC is selected during prion amplification in Protein Misfolding Cyclic Amplification (PMCAb) at the expense of oversialylated PrPC. As a result, PMCAb-derived PrPSc was less sialylated than brain-derived PrPSc. A decrease in PrPSc sialylation correlated with a drop in infectivity of PMCAb-derived material. Nevertheless, enzymatic de-sialylation of PrPC using sialidase was found to increase the rate of PrPSc amplification in PMCAb from 10- to 10,000-fold in a strain-dependent manner. Moreover, de-sialylation of PrPC reduced or eliminated a species barrier of for prion amplification in PMCAb. These results suggest that the negative charge of sialic acid controls the energy barrier of homologous and heterologous prion replication. Surprisingly, the sialylation status of PrPC was also found to control PrPSc glycoform ratio. A decrease in PrPC sialylation levels resulted in a higher percentage of the diglycosylated glycoform in PrPSc. 2D analysis of charge distribution revealed that the sialylation status of brain-derived PrPC differed from that of spleen-derived PrPC. Knocking out lysosomal sialidase Neu1 did not change the sialylation status of brain-derived PrPC, suggesting that Neu1 is not responsible for desialylation of PrPC. The current work highlights previously unappreciated role of PrPC sialylation in prion diseases and opens multiple new research directions, including development of new therapeutic approaches. The central event underlying prion diseases involves conformational change of the cellular form of the prion protein (PrPC) into disease-associated, transmissible form (PrPSc). The amino acid sequence of PrPC and strain-specific structure of PrPSc are among the key parameters that control prion replication and transmission. The current study showed that PrPC posttranslational modification, specifically sialylation of N-linked glycans, plays a key role in regulating prion replication rate, infectivity, cross-species barrier and PrPSc glycoform ratio. A decrease in PrPC sialylation level increased the rate of prion replication in a strain-specific manner and reduced or eliminated a species barrier when prion replication was seeded by heterologous seeds. At the same time, a decrease in sialylation correlated with a drop in infectivity of PrPSc material produced in vitro. The current study also demonstrated that the PrPSc glycoform ratio, which is an important feature used for strain typing, is not only controlled by prion strain or host but also the sialylation status of PrPC. This study opens multiple new directions in prion research, including development of new therapeutic approaches.
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Tavares E, Macedo JA, Paulo PM, Tavares C, Lopes C, Melo EP. Live-cell FRET imaging reveals clustering of the prion protein at the cell surface induced by infectious prions. Biochim Biophys Acta Mol Basis Dis 2014; 1842:981-91. [DOI: 10.1016/j.bbadis.2014.02.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 01/14/2014] [Accepted: 02/04/2014] [Indexed: 01/16/2023]
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Hirsch TZ, Hernandez-Rapp J, Martin-Lannerée S, Launay JM, Mouillet-Richard S. PrP(C) signalling in neurons: from basics to clinical challenges. Biochimie 2014; 104:2-11. [PMID: 24952348 DOI: 10.1016/j.biochi.2014.06.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Accepted: 06/10/2014] [Indexed: 01/05/2023]
Abstract
The cellular prion protein PrP(C) was identified over twenty-five years ago as the normal counterpart of the scrapie prion protein PrP(Sc), itself the main if not the sole component of the infectious agent at the root of Transmissible Spongiform Encephalopathies (TSEs). PrP(C) is a ubiquitous cell surface protein, abundantly expressed in neurons, which constitute the targets of PrP(Sc)-mediated toxicity. Converging evidence have highlighted that neuronal, GPI-anchored PrP(C) is absolutely required for prion-induced neuropathogenesis, which warrants investigating into the normal function exerted by PrP(C) in a neuronal context. It is now well-established that PrP(C) can serve as a cell signalling molecule, able to mobilize transduction cascades in response to interactions with partners. This function endows PrP(C) with the capacity to participate in multiple neuronal processes, ranging from survival to synaptic plasticity. A diverse array of data have allowed to shed light on how this function is corrupted by PrP(Sc). Recently, amyloid Aβ oligomers, whose accumulation is associated with Alzheimer's disease (AD), were shown to similarly instigate toxic events by deviating PrP(C)-mediated signalling. Here, we provide an overview of the various signal transduction cascades ascribed to PrP(C) in neurons, summarize how their subversion by PrP(Sc) or Aβ oligomers contributes to TSE or AD neuropathogenesis and discuss the ensuing clinical implications.
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Affiliation(s)
- Théo Z Hirsch
- INSERM UMR-S1124, 75006 Paris, France; Université Paris Descartes, Sorbonne Paris Cité, UMR-S1124, 75006 Paris, France
| | - Julia Hernandez-Rapp
- INSERM UMR-S1124, 75006 Paris, France; Université Paris Descartes, Sorbonne Paris Cité, UMR-S1124, 75006 Paris, France; Université Paris Sud 11, ED419 Biosigne, 91400 Orsay, France
| | - Séverine Martin-Lannerée
- INSERM UMR-S1124, 75006 Paris, France; Université Paris Descartes, Sorbonne Paris Cité, UMR-S1124, 75006 Paris, France
| | - Jean-Marie Launay
- AP-HP Service de Biochimie, Fondation FondaMental, INSERM U942 Hôpital Lariboisière, 75010 Paris, France; Pharma Research Department, F. Hoffmann-La-Roche Ltd., CH-4070 Basel, Switzerland
| | - Sophie Mouillet-Richard
- INSERM UMR-S1124, 75006 Paris, France; Université Paris Descartes, Sorbonne Paris Cité, UMR-S1124, 75006 Paris, France.
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Walsh KP, Minamide LS, Kane SJ, Shaw AE, Brown DR, Pulford B, Zabel MD, Lambeth JD, Kuhn TB, Bamburg JR. Amyloid-β and proinflammatory cytokines utilize a prion protein-dependent pathway to activate NADPH oxidase and induce cofilin-actin rods in hippocampal neurons. PLoS One 2014; 9:e95995. [PMID: 24760020 PMCID: PMC3997518 DOI: 10.1371/journal.pone.0095995] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 04/02/2014] [Indexed: 11/18/2022] Open
Abstract
Neurites of neurons under acute or chronic stress form bundles of filaments (rods) containing 1∶1 cofilin∶actin, which impair transport and synaptic function. Rods contain disulfide cross-linked cofilin and are induced by treatments resulting in oxidative stress. Rods form rapidly (5-30 min) in >80% of cultured hippocampal or cortical neurons treated with excitotoxic levels of glutamate or energy depleted (hypoxia/ischemia or mitochondrial inhibitors). In contrast, slow rod formation (50% of maximum response in ∼6 h) occurs in a subpopulation (∼20%) of hippocampal neurons upon exposure to soluble human amyloid-β dimer/trimer (Aβd/t) at subnanomolar concentrations. Here we show that proinflammatory cytokines (TNFα, IL-1β, IL-6) also induce rods at the same rate and within the same neuronal population as Aβd/t. Neurons from prion (PrP(C))-null mice form rods in response to glutamate or antimycin A, but not in response to proinflammatory cytokines or Aβd/t. Two pathways inducing rod formation were confirmed by demonstrating that NADPH-oxidase (NOX) activity is required for prion-dependent rod formation, but not for rods induced by glutamate or energy depletion. Surprisingly, overexpression of PrP(C) is by itself sufficient to induce rods in over 40% of hippocampal neurons through the NOX-dependent pathway. Persistence of PrP(C)-dependent rods requires the continuous activity of NOX. Removing inducers or inhibiting NOX activity in cells containing PrP(C)-dependent rods causes rod disappearance with a half-life of about 36 min. Cofilin-actin rods provide a mechanism for synapse loss bridging the amyloid and cytokine hypotheses for Alzheimer disease, and may explain how functionally diverse Aβ-binding membrane proteins induce synaptic dysfunction.
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Affiliation(s)
- Keifer P. Walsh
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
| | - Laurie S. Minamide
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
| | - Sarah J. Kane
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Alisa E. Shaw
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
| | - David R. Brown
- Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom
| | - Bruce Pulford
- Prion Research Center, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America
| | - Mark D. Zabel
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
- Prion Research Center, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America
| | - J. David Lambeth
- Department of Pathology, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Thomas B. Kuhn
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
- Department of Chemistry and Biochemistry, University of Alaska, Fairbanks, Alaska, United States of America
| | - James R. Bamburg
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
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Yi CW, Xu WC, Chen J, Liang Y. Recent progress in prion and prion-like protein aggregation. Acta Biochim Biophys Sin (Shanghai) 2013; 45:520-6. [PMID: 23709368 DOI: 10.1093/abbs/gmt052] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Prion diseases and prion-like protein misfolding diseases involve the accumulation of abnormally aggregated forms of the normal host proteins, such as prion protein and Tau protein. These proteins are special because of their self-duplicating and transmissible characteristics. Such abnormally aggregated proteins mainly formed in neurons, cause the neurons dysfunction, and finally lead to invariably fatal neurodegenerative diseases. Prion diseases appear not only in animals, such as bovine spongiform encephalopathy in cattle and scrapie in sheep, but also in humans, such as Creutzfeldt-Jacob disease, and even the same prion or prion-like proteins can have many different phenotypes. A lot of biological evidence has suggested that the molecular basis for different strains of prions could be hidden in protein conformations, and the misfolded proteins with conformations different from the normal proteins have been proved to be the main cause for protein aggregation. Crowded physiological environments can be imitated in vitro to study how the misfolding of these proteins leads to the diseases in vivo. In this review, we provide an overview of the existing structural information for prion and prion-like proteins, and discuss the post-translational modifications of prion proteins and the difference between prion and other infectious pathogens. We also discuss what makes a misfolded protein become an infectious agent, and show some examples of prion-like protein aggregation, such as Tau protein aggregation and superoxide dismutase 1 aggregation, as well as some cases of prion-like protein aggregation in crowded physiological environments.
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Affiliation(s)
- Chuan-Wei Yi
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China
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In vivo incorporation of an azide-labeled sugar analog to detect mammalian glycosylphosphatidylinositol molecules isolated from the cell surface. Carbohydr Res 2012; 362:62-9. [PMID: 23085221 DOI: 10.1016/j.carres.2012.09.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 09/11/2012] [Accepted: 09/13/2012] [Indexed: 11/22/2022]
Abstract
N-Acetylgalactosamine (GalNAc) linked to the first mannose of glycosylphosphatidylinositol (GPI) core has been previously reported to be heterogeneously present on some mammalian GPI-anchored proteins. Here we present a method for profiling GalNAc-containing GPI-anchored proteins in mammalian cells by metabolic labeling with tetraacetylated N-azidoacetylgalactosamine (GalNAz) followed by biotinylation of the incorporated sugar analog. We have labeled both endogenous and recombinant GPI-anchored proteins with GalNAz, and demonstrated that the azide-activated sugar gets incorporated into the GPI glycan, likely as an unsubstituted side branch of the core structure. GalNAz was detected only on GPI molecules attached to proteins, and not on GPI precursors, indicating that GalNAc modification takes place after the GPI anchor is transferred to protein. We have highlighted the utility of this cell labeling approach by demonstrating the ability to examine specific GalNAc-containing GPI-anchored proteins isolated non-destructively from separate membrane domains (apical and basolateral) in polarized epithelial cells. This study represents the first demonstration of site-specific in vivo labeling of a GPI moiety with a synthetic sugar analog.
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Last V, Williams A, Werling D. Inhibition of cytosolic Phospholipase A2 prevents prion peptide-induced neuronal damage and co-localisation with Beta III Tubulin. BMC Neurosci 2012; 13:106. [PMID: 22928663 PMCID: PMC3496594 DOI: 10.1186/1471-2202-13-106] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Accepted: 08/21/2012] [Indexed: 11/10/2022] Open
Abstract
Background Activation of phospholipase A2 (PLA2) and the subsequent metabolism of arachidonic acid (AA) to prostaglandins have been shown to play an important role in neuronal death in neurodegenerative disease. Here we report the effects of the prion peptide fragment HuPrP106-126 on the PLA2 cascade in primary cortical neurons and translocation of cPLA2 to neurites. Results Exposure of primary cortical neurons to HuPrP106-126 increased the levels of phosphorylated cPLA2 and caused phosphorylated cPLA2 to relocate from the cell body to the cellular neurite in a PrP-dependent manner, a previously unreported observation. HuPrP106-126 also induced significant AA release, an indicator of cPLA2 activation; this preceded synapse damage and subsequent cellular death. The novel translocation of p-cPLA2 postulated the potential for exposure to HuPrP106-126 to result in a re-arrangement of the cellular cytoskeleton. However p-cPLA2 did not colocalise significantly with F-actin, intermediate filaments, or microtubule-associated proteins. Conversely, p-cPLA2 did significantly colocalise with the cytoskeletal protein beta III tubulin. Pre-treatment with the PLA2 inhibitor, palmitoyl trifluoromethyl ketone (PACOCF3) reduced cPLA2 activation, AA release and damage to the neuronal synapse. Furthermore, PACOCF3 reduced expression of p-cPLA2 in neurites and inhibited colocalisation with beta III tubulin, resulting in protection against PrP-induced cell death. Conclusions Collectively, these findings suggest that cPLA2 plays a vital role in the action of HuPrP106-126 and that the colocalisation of p-cPLA2 with beta III tubulin could be central to the progress of neurodegeneration caused by prion peptides. Further work is needed to define exactly how PLA2 inhibitors protect neurons from peptide-induced toxicity and how this relates to intracellular structural changes occurring in neurodegeneration.
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Affiliation(s)
- Victoria Last
- Department of Pathology and Infectious Diseases, Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA, UK.
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Bate C, Williams A. Clustering of sialylated glycosylphosphatidylinositol anchors mediates PrP-induced activation of cytoplasmic phospholipase A 2 and synapse damage. Prion 2012; 6:350-3. [PMID: 22895089 DOI: 10.4161/pri.21751] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Precisely how the accumulation of PrP (Sc) causes the neuronal degeneration that leads to the clinical symptoms of prion diseases is poorly understood. Our recent paper showed that the clustering of specific glycosylphosphatidylinositol (GPI) anchors attached to PrP proteins triggered synapse damage in cultured neurons. First, we demonstrated that small, soluble PrP (Sc) oligomers caused synapse damage via a GPI-dependent process. Our hypothesis, that the clustering of specific GPIs caused synapse damage, was supported by observations that cross-linkage of PrP (C), either chemically or by monoclonal antibodies, also triggered synapse damage. Synapse damage was preceded by an increase in the cholesterol content of synapses and activation of cytoplasmic phospholipase A 2 (cPLA 2). The presence of a terminal sialic acid moiety, a rare modification of mammalian GPI anchors, was essential in the activation of cPLA 2 and synapse damage induced by cross-linked PrP (C). We conclude that the sialic acid modifies local membrane microenvironments (rafts) surrounding clustered PrP molecules resulting in aberrant activation of cPLA 2 and synapse damage. A recent observation, that toxic amyloid-β assemblies cross-link PrP (C), suggests that synapse damage in prion and Alzheimer diseases is mediated via a common molecular mechanism, and raises the possibility that the pharmacological modification of GPI anchors might constitute a novel therapeutic approach to these diseases.
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Affiliation(s)
- Clive Bate
- Department of Pathology and Infectious Diseases, Royal Veterinary College, Herts, UK.
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