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Lozada Ortiz J, Betancor M, Pérez Lázaro S, Bolea R, Badiola JJ, Otero A. Endoplasmic reticulum stress and ubiquitin-proteasome system impairment in natural scrapie. Front Mol Neurosci 2023; 16:1175364. [PMID: 37152434 PMCID: PMC10160437 DOI: 10.3389/fnmol.2023.1175364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 04/06/2023] [Indexed: 05/09/2023] Open
Abstract
Chronic accumulation of misfolded proteins such as PrPSc can alter the endoplasmic reticulum homeostasis triggering the unfolded protein response (UPR). In this pathogenic event, the molecular chaperones play an important role. Several reports in humans and animals have suggested that neurodegeneration is related to endoplasmic reticulum stress in diseases caused by the accumulation of misfolded proteins. In this study, we investigated the expression of three endoplasmic reticulum stress markers: PERK (protein kinase R-like endoplasmic reticulum kinase), BiP (binding immunoglobulin protein), and PDI (Protein Disulfide Isomerase). In addition, we evaluated the accumulation of ubiquitin as a marker for protein degradation mediated by the proteasome. These proteins were studied in brain tissues of sheep affected by scrapie in clinical and preclinical stages of the disease. Results were compared with those observed in healthy controls. Scrapie-infected sheep showed significant higher levels of PERK, BiP/Grp78 and PDI than healthy animals. As we observed before in models of spontaneous prion disease, PDI was the most altered ER stress marker between scrapie-infected and healthy sheep. Significantly increased intraneuronal and neuropil ubiquitinated deposits were observed in certain brain areas in scrapie-affected animals compared to controls. Our results suggest that the neuropathological and neuroinflammatory phenomena that develop in prion diseases cause endoplasmic reticulum stress in brain cells triggering the UPR. In addition, the significantly higher accumulation of ubiquitin aggregates in scrapie-affected animals suggests an impairment of the ubiquitin-proteasome system in natural scrapie. Therefore, these proteins may contribute as biomarkers and/or therapeutic targets for prion diseases.
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Thellung S, Corsaro A, Dellacasagrande I, Nizzari M, Zambito M, Florio T. Proteostasis unbalance in prion diseases: Mechanisms of neurodegeneration and therapeutic targets. Front Neurosci 2022; 16:966019. [PMID: 36148145 PMCID: PMC9485628 DOI: 10.3389/fnins.2022.966019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 08/05/2022] [Indexed: 01/18/2023] Open
Abstract
Transmissible spongiform encephalopathies (TSEs), or prion diseases, are progressive neurodegenerative disorders of the central nervous system that affect humans and animals as sporadic, inherited, and infectious forms. Similarly to Alzheimer's disease and other neurodegenerative disorders, any attempt to reduce TSEs' lethality or increase the life expectancy of affected individuals has been unsuccessful. Typically, the onset of symptoms anticipates the fatal outcome of less than 1 year, although it is believed to be the consequence of a decades-long process of neuronal death. The duration of the symptoms-free period represents by itself a major obstacle to carry out effective neuroprotective therapies. Prions, the infectious entities of TSEs, are composed of a protease-resistant protein named prion protein scrapie (PrPSc) from the prototypical TSE form that afflicts ovines. PrPSc misfolding from its physiological counterpart, cellular prion protein (PrPC), is the unifying pathogenic trait of all TSEs. PrPSc is resistant to intracellular turnover and undergoes amyloid-like fibrillation passing through the formation of soluble dimers and oligomers, which are likely the effective neurotoxic entities. The failure of PrPSc removal is a key pathogenic event that defines TSEs as proteopathies, likewise other neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's disease, characterized by alteration of proteostasis. Under physiological conditions, protein quality control, led by the ubiquitin-proteasome system, and macroautophagy clears cytoplasm from improperly folded, redundant, or aggregation-prone proteins. There is evidence that both of these crucial homeostatic pathways are impaired during the development of TSEs, although it is still unclear whether proteostasis alteration facilitates prion protein misfolding or, rather, PrPSc protease resistance hampers cytoplasmic protein quality control. This review is aimed to critically analyze the most recent advancements in the cause-effect correlation between PrPC misfolding and proteostasis alterations and to discuss the possibility that pharmacological restoring of ubiquitin-proteasomal competence and stimulation of autophagy could reduce the intracellular burden of PrPSc and ameliorate the severity of prion-associated neurodegeneration.
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Affiliation(s)
- Stefano Thellung
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
| | - Alessandro Corsaro
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
| | - Irene Dellacasagrande
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
| | - Mario Nizzari
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
| | - Martina Zambito
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
| | - Tullio Florio
- Section of Pharmacology, Department of Internal Medicine (DiMI), University of Genova, Genova, Italy
- IRCCS Ospedale Policlinico San Martino, Genova, Italy
- *Correspondence: Tullio Florio
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Restelli E, Capone V, Pozzoli M, Ortolan D, Quaglio E, Corbelli A, Fiordaliso F, Beznoussenko GV, Artuso V, Roiter I, Sallese M, Chiesa R. Activation of Src family kinase ameliorates secretory trafficking in mutant prion protein cells. J Biol Chem 2021; 296:100490. [PMID: 33662396 PMCID: PMC8059059 DOI: 10.1016/j.jbc.2021.100490] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Revised: 02/04/2021] [Accepted: 02/26/2021] [Indexed: 11/25/2022] Open
Abstract
Fatal familial insomnia (FFI), genetic Creutzfeldt-Jakob disease (gCJD), and Gerstmann-Sträussler-Scheinker (GSS) syndrome are neurodegenerative disorders linked to prion protein (PrP) mutations. The pathogenic mechanisms are not known, but increasing evidence points to mutant PrP misfolding and retention in the secretory pathway. We previously found that the D178N/M129 mutation associated with FFI accumulates in the Golgi of neuronal cells, impairing post-Golgi trafficking. In this study we further characterized the trafficking defect induced by the FFI mutation and tested the 178N/V129 variant linked to gCJD and a nine-octapeptide repeat insertion associated with GSS. We used transfected HeLa cells, embryonic fibroblasts and primary neurons from transgenic mice, and fibroblasts from carriers of the FFI mutation. In all these cell types, the mutant PrPs showed abnormal intracellular localizations, accumulating in the endoplasmic reticulum (ER) and Golgi. To test the efficiency of the membrane trafficking system, we monitored the intracellular transport of the temperature-sensitive vesicular stomatite virus glycoprotein (VSV-G), a well-established cargo reporter, and of endogenous procollagen I (PC-I). We observed marked alterations in secretory trafficking, with VSV-G accumulating mainly in the Golgi complex and PC-I in the ER and Golgi. A redacted version of mutant PrP with reduced propensity to misfold did not impair VSV-G trafficking, nor did artificial ER or Golgi retention of wild-type PrP; this indicates that both misfolding and intracellular retention were required to induce the transport defect. Pharmacological activation of Src family kinase (SFK) improved intracellular transport, suggesting that mutant PrP impairs secretory trafficking through corruption of SFK-mediated signaling.
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Affiliation(s)
- Elena Restelli
- Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Vanessa Capone
- Department of Innovative Technologies in Medicine & Dentistry, University G. D'Annunzio, Chieti, Italy; Center for Advanced Studies and Technology (CAST), University G. D'Annunzio, Chieti, Italy
| | - Manuela Pozzoli
- Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Davide Ortolan
- Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Elena Quaglio
- Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Alessandro Corbelli
- Bio-Imaging Unit, Department of Cardiovascular Medicine, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Fabio Fiordaliso
- Bio-Imaging Unit, Department of Cardiovascular Medicine, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | | | | | - Ignazio Roiter
- ULSS 2 Marca Trevigiana, Ca' Foncello Hospital, Treviso, Italy
| | - Michele Sallese
- Department of Innovative Technologies in Medicine & Dentistry, University G. D'Annunzio, Chieti, Italy; Center for Advanced Studies and Technology (CAST), University G. D'Annunzio, Chieti, Italy
| | - Roberto Chiesa
- Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy.
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Otero A, Betancor M, Eraña H, Fernández Borges N, Lucas JJ, Badiola JJ, Castilla J, Bolea R. Prion-Associated Neurodegeneration Causes Both Endoplasmic Reticulum Stress and Proteasome Impairment in a Murine Model of Spontaneous Disease. Int J Mol Sci 2021; 22:ijms22010465. [PMID: 33466523 PMCID: PMC7796520 DOI: 10.3390/ijms22010465] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 12/30/2020] [Accepted: 12/31/2020] [Indexed: 01/08/2023] Open
Abstract
Prion diseases are a group of neurodegenerative disorders that can be spontaneous, familial or acquired by infection. The conversion of the prion protein PrPC to its abnormal and misfolded isoform PrPSc is the main event in the pathogenesis of prion diseases of all origins. In spontaneous prion diseases, the mechanisms that trigger the formation of PrPSc in the central nervous system remain unknown. Several reports have demonstrated that the accumulation of PrPSc can induce endoplasmic reticulum (ER) stress and proteasome impairment from the early stages of the prion disease. Both mechanisms lead to an increment of PrP aggregates in the secretory pathway, which could explain the pathogenesis of spontaneous prion diseases. Here, we investigate the role of ER stress and proteasome impairment during prion disorders in a murine model of spontaneous prion disease (TgVole) co-expressing the UbG76V-GFP reporter, which allows measuring the proteasome activity in vivo. Spontaneously prion-affected mice showed a significantly higher accumulation of the PKR-like ER kinase (PERK), the ER chaperone binding immunoglobulin protein (BiP/Grp78), the ER protein disulfide isomerase (PDI) and the UbG76V-GFP reporter than age-matched controls in certain brain areas. The upregulation of PERK, BiP, PDI and ubiquitin was detected from the preclinical stage of the disease, indicating that ER stress and proteasome impairment begin at early stages of the spontaneous disease. Strong correlations were found between the deposition of these markers and neuropathological markers of prion disease in both preclinical and clinical mice. Our results suggest that both ER stress and proteasome impairment occur during the pathogenesis of spontaneous prion diseases.
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Affiliation(s)
- Alicia Otero
- Centro de Encefalopatías y Enfermedades Transmisibles Emergentes, Universidad de Zaragoza IA2 IIS Aragón, 50013 Zaragoza, Spain; (A.O.); (M.B.); (J.J.B.)
| | - Marina Betancor
- Centro de Encefalopatías y Enfermedades Transmisibles Emergentes, Universidad de Zaragoza IA2 IIS Aragón, 50013 Zaragoza, Spain; (A.O.); (M.B.); (J.J.B.)
| | - Hasier Eraña
- ATLAS Molecular Pharma S.L., Parque tecnológico de Bizkaia, 48160 Derio, Spain;
- Center for Cooperative Research in Biosciences (CIC bioGUNE) Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, 48160 Derio, Spain; (N.F.B.); (J.C.)
| | - Natalia Fernández Borges
- Center for Cooperative Research in Biosciences (CIC bioGUNE) Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, 48160 Derio, Spain; (N.F.B.); (J.C.)
| | - José J. Lucas
- Centro de Biología Molecular ‘Severo Ochoa’ (CBMSO) CSIC/UAM, 28049 Madrid, Spain;
- Networking Research Center on Neurodegenerative Diseases (CIBERNED), Instituto de Salud Carlos III, 28031 Madrid, Spain
| | - Juan José Badiola
- Centro de Encefalopatías y Enfermedades Transmisibles Emergentes, Universidad de Zaragoza IA2 IIS Aragón, 50013 Zaragoza, Spain; (A.O.); (M.B.); (J.J.B.)
| | - Joaquín Castilla
- Center for Cooperative Research in Biosciences (CIC bioGUNE) Basque Research and Technology Alliance (BRTA), Bizkaia Technology Park, 48160 Derio, Spain; (N.F.B.); (J.C.)
- IKERBasque Basque Foundation for Science, 48009 Bilbao, Spain
| | - Rosa Bolea
- Centro de Encefalopatías y Enfermedades Transmisibles Emergentes, Universidad de Zaragoza IA2 IIS Aragón, 50013 Zaragoza, Spain; (A.O.); (M.B.); (J.J.B.)
- Correspondence:
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Bouybayoune I, Comerio L, Pasetto L, Bertani I, Bonetto V, Chiesa R. Cyclophillin A deficiency accelerates RML-induced prion disease. Neurobiol Dis 2019; 130:104498. [PMID: 31181281 DOI: 10.1016/j.nbd.2019.104498] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 05/14/2019] [Accepted: 06/05/2019] [Indexed: 01/17/2023] Open
Abstract
Prion diseases typically involve brain deposition of abnormally folded prion protein, which is associated with activated glia and increased cytokine production. Cyclophilin A (CypA) is a ubiquitous protein with peptidyl prolyl cis-trans isomerase activity, which regulates protein folding, and can be secreted by cells in response to inflammatory stimuli. On the basis of in vitro studies, CypA was proposed to mediate glial activation during prion infection. To investigate the role of CypA in vivo, we inoculated CypA+/+, CypA+/- and CypA-/- mice with the RML prion strain, and recorded the time to onset of neurological signs and to terminal disease, and the astrocyte and microglia response at presymptomatic and symptomatic stages. Time to onset of disease and survival were significantly shorter in CypA-deficient mice than CypA-expressing controls. CypA-deficient mice had significantly greater microglial activation in the presymptomatic stage, and analysis of anti- and pro-inflammatory microglial markers indicated a shift towards a pro-inflammatory phenotype. There was no difference in astrocyte activation. This suggests that CypA contributes to dampening the pro-inflammatory microglial response during the early stage of RML-induced prion disease.
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Affiliation(s)
- Ihssane Bouybayoune
- Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy
| | - Liliana Comerio
- Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy
| | - Laura Pasetto
- Department of Biochemistry and Molecular Pharmacology, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy
| | - Ilaria Bertani
- Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy
| | - Valentina Bonetto
- Department of Biochemistry and Molecular Pharmacology, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy
| | - Roberto Chiesa
- Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, 20156 Milano, Italy.
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Saito A, Imaizumi K. The broad spectrum of signaling pathways regulated by unfolded protein response in neuronal homeostasis. Neurochem Int 2018; 119:26-34. [DOI: 10.1016/j.neuint.2017.06.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 06/19/2017] [Accepted: 06/26/2017] [Indexed: 02/08/2023]
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Chiesa R, Restelli E, Comerio L, Del Gallo F, Imeri L. Transgenic mice recapitulate the phenotypic heterogeneity of genetic prion diseases without developing prion infectivity: Role of intracellular PrP retention in neurotoxicity. Prion 2017; 10:93-102. [PMID: 26864450 PMCID: PMC4981194 DOI: 10.1080/19336896.2016.1139276] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI). The reason for this variability is not known. It has been suggested that prion strains with unique self-replicating and neurotoxic properties emerge spontaneously in individuals carrying PrP mutations, dictating the phenotypic expression of disease. We generated transgenic mice expressing the FFI mutation, and found that they developed a fatal neurological illness highly reminiscent of FFI, and different from those of similarly generated mice modeling genetic CJD and GSS. Thus transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs expressed in these mice are misfolded but unable to self-replicate. They accumulate in different compartments of the neuronal secretory pathway, impairing the membrane delivery of ion channels essential for neuronal function. Our results indicate that conversion of mutant PrP into an infectious isoform is not required for pathogenesis, and suggest that the phenotypic variability may be due to different effects of mutant PrP on intracellular transport.
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Affiliation(s)
- Roberto Chiesa
- a Laboratory of Prion Neurobiology, Department of Neuroscience, IRCCS - "Mario Negri" Institute for Pharmacological Research , Milan , Italy
| | - Elena Restelli
- a Laboratory of Prion Neurobiology, Department of Neuroscience, IRCCS - "Mario Negri" Institute for Pharmacological Research , Milan , Italy
| | - Liliana Comerio
- a Laboratory of Prion Neurobiology, Department of Neuroscience, IRCCS - "Mario Negri" Institute for Pharmacological Research , Milan , Italy
| | - Federico Del Gallo
- b Department of Health Sciences , University of Milan Medical School , Milan , Italy
| | - Luca Imeri
- b Department of Health Sciences , University of Milan Medical School , Milan , Italy
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Puig B, Altmeppen HC, Glatzel M. Misfolding leads the way to unraveling signaling pathways in the pathophysiology of prion diseases. Prion 2017; 10:434-443. [PMID: 27870599 DOI: 10.1080/19336896.2016.1244593] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
A misfolded version of the prion protein represents an essential component in the pathophysiology of fatal neurodegenerative prion diseases, which affect humans and animals alike. They may be of sporadic origin, acquired through exogenous introduction of infectious misfolded prion protein, or caused by genetic alterations in the prion protein coding gene. We have recently described a novel pathway linking retention of mutant prion protein in the early secretory pathway to activation p38-MAPK and a neurodegenerative phenotype in transgenic mice. Here we review the consequences that mutations in prion protein have on intracellular transport and stress responses focusing on protein quality control. We also discuss the neurotoxic signaling elicited by the accumulation of mutant prion protein in the endoplasmic reticulum and the Golgi apparatus. Improved knowledge about these processes will help us to better understand complex pathogenesis of prion diseases, a prerequisite for therapeutic strategies.
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Affiliation(s)
- Berta Puig
- a Institute of Neuropathology, University Medical Center Hamburg-Eppendorf , Hamburg , Germany
| | - Hermann C Altmeppen
- a Institute of Neuropathology, University Medical Center Hamburg-Eppendorf , Hamburg , Germany
| | - Markus Glatzel
- a Institute of Neuropathology, University Medical Center Hamburg-Eppendorf , Hamburg , Germany
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Fang S, Wang R, Liu H, Zhuang W, Wang Z, Zhang J, Pei L, Liu Y, Su Y. The retention of prion protein in the endoplasmic reticulum prevents N2A cells from proteasome inhibition-induced cytotoxicity. Biochem Biophys Res Commun 2017; 491:500-507. [PMID: 28669732 DOI: 10.1016/j.bbrc.2017.06.176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 06/28/2017] [Indexed: 11/27/2022]
Abstract
Prion disease is a fatal neurodegenerative disease that may result from the conversion of normal cellular prion protein (PrPC) to the pathogenic scrapie PrP isoform (PrPSc), however, how proliferation of prion leads to neuronal apoptosis is still not clear. In this study, to explore the role of the endoplasmic reticulum (ER) in prion diseases, we engineered the KDEL ER-retention motif to the C-terminus of PrPC and studied its effect on N2A cell toxicity. The KDEL retention signal led to the accumulation of PrP in the ER, and KDEL signal could effectively deplete PrP from the cell surface and trap PrP in the ER/Cis-Golgi compartment. PrPC molecules were delayed in their transit along the early pathway of the secretory compartment, however, they did not aggregate, and were not resistant to Proteinase K (PK) or become detergent-insoluble. Moreover, we found that the ER was not the site where PrP became detergent-insoluble and acquired PK resistance. In addition, an MTT assay indicated cells expressing PrPC/N2A were sensitive to proteasome inhibition, but not N2A cells expressing PrPKDEL. Our findings suggest that the ER is not a compartment in which wild type PrPC is able to initiate aggregation, protease resistance or other scapie-like properties of PrP.
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Affiliation(s)
- Shuping Fang
- Novomab Biopharmaceuticals Inc, Nanjing 210042, China
| | - Ruixue Wang
- China Pharmaceutical University, Nanjing 210009, China
| | - Honghao Liu
- Novomab Biopharmaceuticals Inc, Nanjing 210042, China
| | | | - Zhen Wang
- Novomab Biopharmaceuticals Inc, Nanjing 210042, China
| | - Jianjun Zhang
- China Pharmaceutical University, Nanjing 210009, China
| | - Lili Pei
- Novomab Biopharmaceuticals Inc, Nanjing 210042, China
| | - Yumei Liu
- China Pharmaceutical University, Nanjing 210009, China
| | - Yunpeng Su
- Novomab Biopharmaceuticals Inc, Nanjing 210042, China; Department of Pharmacology, Binzhou Medical University, Yantai 256603, Shandong, China.
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Halliday M, Radford H, Zents KAM, Molloy C, Moreno JA, Verity NC, Smith E, Ortori CA, Barrett DA, Bushell M, Mallucci GR. Repurposed drugs targeting eIF2α-P-mediated translational repression prevent neurodegeneration in mice. Brain 2017; 140:1768-1783. [PMID: 28430857 PMCID: PMC5445255 DOI: 10.1093/brain/awx074] [Citation(s) in RCA: 198] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Revised: 12/21/2016] [Accepted: 01/31/2017] [Indexed: 01/06/2023] Open
Abstract
See Mercado and Hetz (doi:10.1093/brain/awx107) for a scientific commentary on this article.Signalling through the PERK/eIF2α-P branch of the unfolded protein response plays a critical role in controlling protein synthesis rates in cells. This pathway is overactivated in brains of patients with Alzheimer’s disease and related disorders and has recently emerged as a promising therapeutic target for these currently untreatable conditions. Thus, in mouse models of neurodegenerative disease, prolonged overactivation of PERK/eIF2α-P signalling causes sustained attenuation of protein synthesis, leading to memory impairment and neuronal loss. Re-establishing translation rates by inhibition of eIF2α-P activity, genetically or pharmacologically, restores memory and prevents neurodegeneration and extends survival. However, the experimental compounds used preclinically are unsuitable for use in humans, due to associated toxicity or poor pharmacokinetic properties. To discover compounds that have anti-eIF2α-P activity suitable for clinical use, we performed phenotypic screens on a NINDS small molecule library of 1040 drugs. We identified two compounds, trazodone hydrochloride and dibenzoylmethane, which reversed eIF2α-P-mediated translational attenuation in vitro and in vivo. Both drugs were markedly neuroprotective in two mouse models of neurodegeneration, using clinically relevant doses over a prolonged period of time, without systemic toxicity. Thus, in prion-diseased mice, both trazodone and dibenzoylmethane treatment restored memory deficits, abrogated development of neurological signs, prevented neurodegeneration and significantly prolonged survival. In tauopathy-frontotemporal dementia mice, both drugs were neuroprotective, rescued memory deficits and reduced hippocampal atrophy. Further, trazodone reduced p-tau burden. These compounds therefore represent potential new disease-modifying treatments for dementia. Trazodone in particular, a licensed drug, should now be tested in clinical trials in patients.
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Affiliation(s)
- Mark Halliday
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Helois Radford
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Karlijn A M Zents
- Department of Clinical Neurosciences, University of Cambridge, Cambridge Biomedical Campus, Cambridge, CB2 0AH, UK
| | - Collin Molloy
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Julie A Moreno
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Nicholas C Verity
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Ewan Smith
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Catharine A Ortori
- Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, UK
| | - David A Barrett
- Centre for Analytical Bioscience, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, UK
| | - Martin Bushell
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Giovanna R Mallucci
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
- Department of Clinical Neurosciences, University of Cambridge, Cambridge Biomedical Campus, Cambridge, CB2 0AH, UK
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Wiersma VI, van Hecke W, Scheper W, van Osch MAJ, Hermsen WJM, Rozemuller AJM, Hoozemans JJM. Activation of the unfolded protein response and granulovacuolar degeneration are not common features of human prion pathology. Acta Neuropathol Commun 2016; 4:113. [PMID: 27793194 PMCID: PMC5086055 DOI: 10.1186/s40478-016-0383-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 10/18/2016] [Indexed: 11/29/2022] Open
Abstract
Human prion diseases are fatal neurodegenerative disorders with a genetic, sporadic or infectiously acquired aetiology. Neuropathologically, human prion diseases are characterized by deposition of misfolded prion protein and neuronal loss. In post-mortem brain tissue from patients with other neurodegenerative diseases characterized by protein misfolding, including Alzheimer’s disease (AD) and frontotemporal lobar degeneration with tau pathology (FTLD-tau), increased activation of the unfolded protein response (UPR) has been observed. The UPR is a cellular stress response that copes with the presence of misfolded proteins. Recent studies have indicated that UPR activation is also involved in experimental models of prion disease and have suggested intervention in the UPR as a therapeutic strategy. On the other hand, it was previously shown that the active form of the UPR stress sensor dsRNA-activated protein kinase-like ER kinase (PERK) is not increased in post-mortem brain tissue samples from human prion disease cases. In the present study, we assessed the active form of another UPR stress sensor, inositol-requiring enzyme 1α (IRE1α), in human post-mortem frontal cortex of a large cohort of sporadic, inherited and acquired prion disease patients (n = 47) and non-neurological controls. Immunoreactivity for phosphorylated IRE1α was not increased in prion disease cases compared with non-neurological controls. In addition, immunoreactivity for phosphorylated PERK was unaltered in human prion disease cases included in the current cohort. Moreover, no difference in the extent of granulovacuolar degeneration, a pathological feature associated with the presence of UPR activation markers, was detected. Our data indicate that, in contrast to AD and primary tauopathies, activation of the UPR is not a common feature of human prion pathology.
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Abstract
Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disorders characterised by long incubation period, short clinical duration, and transmissibility to susceptible species. Neuronal loss, spongiform changes, gliosis and the accumulation in the brain of the misfolded version of a membrane-bound cellular prion protein (PrP(C)), termed PrP(TSE), are diagnostic markers of these diseases. Compelling evidence links protein misfolding and its accumulation with neurodegenerative changes. Accordingly, several mechanisms of prion-mediated neurotoxicity have been proposed. In this paper, we provide an overview of the recent knowledge on the mechanisms of neuropathogenesis, the neurotoxic PrP species and the possible therapeutic approaches to treat these devastating disorders.
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Peters SL, Déry MA, LeBlanc AC. Familial prion protein mutants inhibit Hrd1-mediated retrotranslocation of misfolded proteins by depleting misfolded protein sensor BiP. Hum Mol Genet 2016; 25:976-88. [PMID: 26740554 DOI: 10.1093/hmg/ddv630] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 12/29/2015] [Indexed: 01/09/2023] Open
Abstract
Similar to many proteins trafficking through the secretory pathway, cellular prion protein (PrP) partly retrotranslocates from the endoplasmic reticulum to the cytosol through the endoplasmic reticulum-associated degradation (ERAD) pathway in an attempt to alleviate accumulation of cellular misfolded PrP. Surprisingly, familial PrP mutants fail to retrotranslocate and simultaneously block normal cellular PrP retrotranslocation. That impairments in retrotranslocation of misfolded proteins could lead to global disruptions in cellular homeostasis prompted further investigations into PrP mutant retrotranslocation defects. A gain- and loss-of-function approach identified human E3 ubiquitin ligase, Hrd1, as a critical regulator of PrP retrotranslocation in mammalian cells. Expression of familial human PrP mutants, V210I(129V) and M232R(129V), not only abolished PrP retrotranslocation, but also that of Hrd1-dependent ERAD substrates, transthyretin TTR(D18G) and α1-anti-trypsin A1AT(NHK). Mutant PrP expression decreased binding immunoglobulin protein (BiP) levels by 50% and attenuated ER stress-induced BiP by increasing BiP turnover 6-fold. Overexpression of BiP with PrP mutants rescued retrotranslocation of PrP, TTR(D18G) and A1AT(NHK). PrP mutants-induced cell death was also rescued by co-expression of BiP. These results show that PrP mutants highjack the Hrd1-dependent ERAD pathway, an action that would result in misfolded protein accumulation especially in terminally differentiated neurons. This could explain the age-dependent neuronal degeneration in familial prion diseases.
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Affiliation(s)
- Sarah L Peters
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Ch. Cote Ste-Catherine, Montreal, QC H3T 1E2, Canada and Department of Neurology and Neurosurgery, McGill University, 3775 University Street, Montreal, QC H2A 2B4, Canada
| | - Marc-André Déry
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Ch. Cote Ste-Catherine, Montreal, QC H3T 1E2, Canada and Department of Neurology and Neurosurgery, McGill University, 3775 University Street, Montreal, QC H2A 2B4, Canada
| | - Andrea C LeBlanc
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Ch. Cote Ste-Catherine, Montreal, QC H3T 1E2, Canada and Department of Neurology and Neurosurgery, McGill University, 3775 University Street, Montreal, QC H2A 2B4, Canada
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Torres M, Matamala JM, Duran-Aniotz C, Cornejo VH, Foley A, Hetz C. ER stress signaling and neurodegeneration: At the intersection between Alzheimer's disease and Prion-related disorders. Virus Res 2015; 207:69-75. [DOI: 10.1016/j.virusres.2014.12.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 10/28/2014] [Accepted: 12/10/2014] [Indexed: 01/23/2023]
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15
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Torres M, Medinas DB, Matamala JM, Woehlbier U, Cornejo VH, Solda T, Andreu C, Rozas P, Matus S, Muñoz N, Vergara C, Cartier L, Soto C, Molinari M, Hetz C. The Protein-disulfide Isomerase ERp57 Regulates the Steady-state Levels of the Prion Protein. J Biol Chem 2015; 290:23631-45. [PMID: 26170458 DOI: 10.1074/jbc.m114.635565] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Indexed: 12/19/2022] Open
Abstract
Although the accumulation of a misfolded and protease-resistant form of the prion protein (PrP) is a key event in prion pathogenesis, the cellular factors involved in its folding and quality control are poorly understood. PrP is a glycosylated and disulfide-bonded protein synthesized at the endoplasmic reticulum (ER). The ER foldase ERp57 (also known as Grp58) is highly expressed in the brain of sporadic and infectious forms of prion-related disorders. ERp57 is a disulfide isomerase involved in the folding of a subset of glycoproteins in the ER as part of the calnexin/calreticulin cycle. Here, we show that levels of ERp57 increase mainly in neurons of Creutzfeldt-Jacob patients. Using gain- and loss-of-function approaches in cell culture, we demonstrate that ERp57 expression controls the maturation and total levels of wild-type PrP and mutant forms associated with human disease. In addition, we found that PrP physically interacts with ERp57, and also with the closest family member PDIA1, but not ERp72. Furthermore, we generated a conditional knock-out mouse for ERp57 in the nervous system and detected a reduction in the steady-state levels of the mono- and nonglycosylated forms of PrP in the brain. In contrast, ERp57 transgenic mice showed increased levels of endogenous PrP. Unexpectedly, ERp57 expression did not affect the susceptibility of cells to ER stress in vitro and in vivo. This study identifies ERp57 as a new modulator of PrP levels and may help with understanding the consequences of ERp57 up-regulation observed in human disease.
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Affiliation(s)
- Mauricio Torres
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - Danilo B Medinas
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - José Manuel Matamala
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Department of Neurological Sciences, Faculty of Medicine, University of Chile, Santiago 7500691, Chile
| | - Ute Woehlbier
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - Víctor Hugo Cornejo
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - Tatiana Solda
- the Institute for Research in Biomedicine, Bellinzona CH6500, Switzerland
| | - Catherine Andreu
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - Pablo Rozas
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile
| | - Soledad Matus
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Neurounion Biomedical Foundation, CENPAR, Santiago 7630614, Chile
| | - Natalia Muñoz
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Neurounion Biomedical Foundation, CENPAR, Santiago 7630614, Chile
| | - Carmen Vergara
- the Department of Neurological Sciences, Faculty of Medicine, University of Chile, Santiago 7500691, Chile
| | - Luis Cartier
- the Department of Neurological Sciences, Faculty of Medicine, University of Chile, Santiago 7500691, Chile
| | - Claudio Soto
- the Department of Neurology, University of Texas Medical School, Houston, Texas 77030, and
| | - Maurizio Molinari
- the Institute for Research in Biomedicine, Bellinzona CH6500, Switzerland, the Università della Svizzera Italiana, Lugano CH6900, Switzerland, the Ecole Polytechnique Fédérale de Lausanne, School of Life Sciences, Lausanne CH1015, Switzerland
| | - Claudio Hetz
- From the Biomedical Neuroscience Institute, Faculty of Medicine, University of Chile, Santiago 8380453, Chile, the Program of Cellular and Molecular Biology, Institute of Biomedical Sciences, Center for Molecular Studies of the Cell, University of Chile, Santiago 8380453, Chile, the Harvard School of Public Health, Boston, Massachusetts 02115
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16
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Affiliation(s)
- Roberto Chiesa
- Department of Neuroscience, IRCCS–Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy
- * E-mail:
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17
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Bouybayoune I, Mantovani S, Del Gallo F, Bertani I, Restelli E, Comerio L, Tapella L, Baracchi F, Fernández-Borges N, Mangieri M, Bisighini C, Beznoussenko GV, Paladini A, Balducci C, Micotti E, Forloni G, Castilla J, Fiordaliso F, Tagliavini F, Imeri L, Chiesa R. Transgenic fatal familial insomnia mice indicate prion infectivity-independent mechanisms of pathogenesis and phenotypic expression of disease. PLoS Pathog 2015; 11:e1004796. [PMID: 25880443 PMCID: PMC4400166 DOI: 10.1371/journal.ppat.1004796] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 03/09/2015] [Indexed: 11/18/2022] Open
Abstract
Fatal familial insomnia (FFI) and a genetic form of Creutzfeldt-Jakob disease (CJD178) are clinically different prion disorders linked to the D178N prion protein (PrP) mutation. The disease phenotype is determined by the 129 M/V polymorphism on the mutant allele, which is thought to influence D178N PrP misfolding, leading to the formation of distinctive prion strains with specific neurotoxic properties. However, the mechanism by which misfolded variants of mutant PrP cause different diseases is not known. We generated transgenic (Tg) mice expressing the mouse PrP homolog of the FFI mutation. These mice synthesize a misfolded form of mutant PrP in their brains and develop a neurological illness with severe sleep disruption, highly reminiscent of FFI and different from that of analogously generated Tg(CJD) mice modeling CJD178. No prion infectivity was detectable in Tg(FFI) and Tg(CJD) brains by bioassay or protein misfolding cyclic amplification, indicating that mutant PrP has disease-encoding properties that do not depend on its ability to propagate its misfolded conformation. Tg(FFI) and Tg(CJD) neurons have different patterns of intracellular PrP accumulation associated with distinct morphological abnormalities of the endoplasmic reticulum and Golgi, suggesting that mutation-specific alterations of secretory transport may contribute to the disease phenotype. Genetic prion diseases are degenerative brain disorders caused by mutations in the gene encoding the prion protein (PrP). Different PrP mutations cause different diseases, including Creutzfeldt-Jakob disease (CJD) and fatal familial insomnia (FFI). The reason for this variability is not known, but assembly of the mutant PrPs into distinct aggregates that spread in the brain by promoting PrP aggregation may contribute to the disease phenotype. We previously generated transgenic mice modeling genetic CJD, clinically identified by dementia and motor abnormalities. We have now generated transgenic mice carrying the PrP mutation associated with FFI, and found that they develop severe sleep abnormalities and other key features of the human disorder. Thus, transgenic mice recapitulate the phenotypic differences seen in humans. The mutant PrPs in FFI and CJD mice are aggregated but unable to promote PrP aggregation. They accumulate in different intracellular compartments and cause distinct morphological abnormalities of transport organelles. These results indicate that mutant PrP has disease-encoding properties that are independent of its ability to self-propagate, and suggest that the phenotypic heterogeneity may be due to different effects of aggregated PrP on intracellular transport. Our study provides new insights into the mechanisms of selective neuronal dysfunction due to protein aggregation.
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Affiliation(s)
- Ihssane Bouybayoune
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Susanna Mantovani
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Federico Del Gallo
- Department of Health Sciences, University of Milan Medical School, Milan, Italy
| | - Ilaria Bertani
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Elena Restelli
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Liliana Comerio
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Laura Tapella
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Francesca Baracchi
- Department of Health Sciences, University of Milan Medical School, Milan, Italy
| | | | - Michela Mangieri
- Division of Neuropathology and Neurology, IRCCS Foundation “Carlo Besta” National Neurological Institute, Milan, Italy
| | - Cinzia Bisighini
- Bio-Imaging Unit, Department of Cardiovascular Research, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | | | - Alessandra Paladini
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Claudia Balducci
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Edoardo Micotti
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Gianluigi Forloni
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Joaquín Castilla
- CIC bioGUNE, Parque Tecnológico de Bizkaia, Derio, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - Fabio Fiordaliso
- Bio-Imaging Unit, Department of Cardiovascular Research, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
| | - Fabrizio Tagliavini
- Division of Neuropathology and Neurology, IRCCS Foundation “Carlo Besta” National Neurological Institute, Milan, Italy
| | - Luca Imeri
- Department of Health Sciences, University of Milan Medical School, Milan, Italy
| | - Roberto Chiesa
- Department of Neuroscience, IRCCS—“Mario Negri” Institute for Pharmacological Research, Milan, Italy
- * E-mail:
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18
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Abstract
SIGNIFICANCE Impairment of the ubiquitin-proteasome system (UPS) has been implicated in the pathogenesis of a wide variety of neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's diseases. The most significant risk factor for the development of these disorders is aging, which is associated with a progressive decline in UPS activity and the accumulation of oxidatively modified proteins. To date, no therapies have been developed that can specifically up-regulate this system. RECENT ADVANCES In the neurodegenerative brain, dysfunction of the UPS has been associated with the deposition of ubiquitinated protein aggregates and widespread disruption of the proteostasis network. Recent research has identified further evidence of impairment in substrate ubiquitination and proteasomal degradation, which could contribute to the loss of cellular proteostasis in neurodegenerative disease. Novel strategies for activation of the UPS by genetic manipulation and treatment with synthetic compounds have also recently been identified. CRITICAL ISSUES Here, we discuss the specific roles of the UPS in the healthy central nervous system and establish how dysfunctional components can contribute to neurotoxicity in the context of disease. FUTURE DIRECTIONS Knowledge of the UPS components that are specifically or preferentially involved in neurodegenerative disease will be critical in the development of targeted therapies which aim at limiting the accumulation of misfolded proteins without gross disturbance of this major proteolytic pathway.
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Affiliation(s)
- Chris McKinnon
- Department of Neurodegenerative Disease, University College London Institute of Neurology , London, United Kingdom
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19
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Prion-induced and spontaneous formation of transmissible toxicity in PrP transgenic Drosophila. Biochem J 2014; 463:31-40. [PMID: 25000212 DOI: 10.1042/bj20140129] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Prion diseases are fatal transmissible neurodegenerative diseases of various mammalian species. Central to these conditions is the conversion of the normal host prion protein PrP(C) into the abnormal prion conformer PrP(Sc). Mature PrP(C) is attached to the plasma membrane by a glycosylphosphatidylinositol anchor, whereas during biosynthesis and metabolism cytosolic and secreted forms of the protein may arise. The role of topological PrP(C) variants in the mechanism of prion formation and prion-induced neurotoxicity during prion disease remains undefined. In the present study we investigated whether Drosophila transgenic for ovine PrP targeted to the plasma membrane, to the cytosol or for secretion, could produce transmissible toxicity following exposure to exogenous ovine prions. Although all three topological variants of PrP were efficiently expressed in Drosophila, cytosolic PrP was conformationally distinct and required denaturation before recognition by immunobiochemical methods. Adult Drosophila transgenic for pan neuronally expressed ovine PrP targeted to the plasma membrane, to the cytosol or for secretion exhibited a decreased locomotor activity after exposure at the larval stage to ovine prions. Proteinase K-resistant PrP(Sc) was detected by protein misfolding cyclic amplification in prion-exposed Drosophila transgenic for membrane-targeted PrP. Significantly, head homogenate from all three variants of prion-exposed PrP transgenic Drosophila induced a decreased locomotor activity when transmitted to PrP recipient flies. Drosophila transgenic for PrP targeted for secretion exhibited a spontaneous locomotor defect in the absence of prion exposure that was transmissible in PrP transgenic flies. Our data are consistent with the formation of transmissible prions in PrP transgenic Drosophila.
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20
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Moreno JA, Halliday M, Molloy C, Radford H, Verity N, Axten JM, Ortori CA, Willis AE, Fischer PM, Barrett DA, Mallucci GR. Oral treatment targeting the unfolded protein response prevents neurodegeneration and clinical disease in prion-infected mice. Sci Transl Med 2014; 5:206ra138. [PMID: 24107777 DOI: 10.1126/scitranslmed.3006767] [Citation(s) in RCA: 426] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
During prion disease, an increase in misfolded prion protein (PrP) generated by prion replication leads to sustained overactivation of the branch of the unfolded protein response (UPR) that controls the initiation of protein synthesis. This results in persistent repression of translation, resulting in the loss of critical proteins that leads to synaptic failure and neuronal death. We have previously reported that localized genetic manipulation of this pathway rescues shutdown of translation and prevents neurodegeneration in a mouse model of prion disease, suggesting that pharmacological inhibition of this pathway might be of therapeutic benefit. We show that oral treatment with a specific inhibitor of the kinase PERK (protein kinase RNA-like endoplasmic reticulum kinase), a key mediator of this UPR pathway, prevented UPR-mediated translational repression and abrogated development of clinical prion disease in mice, with neuroprotection observed throughout the mouse brain. This was the case for animals treated both at the preclinical stage and also later in disease when behavioral signs had emerged. Critically, the compound acts downstream and independently of the primary pathogenic process of prion replication and is effective despite continuing accumulation of misfolded PrP. These data suggest that PERK, and other members of this pathway, may be new therapeutic targets for developing drugs against prion disease or other neurodegenerative diseases where the UPR has been implicated.
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Affiliation(s)
- Julie A Moreno
- MRC Toxicology Unit, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
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21
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Synaptic dysfunction in prion diseases: a trafficking problem? Int J Cell Biol 2013; 2013:543803. [PMID: 24369467 PMCID: PMC3863542 DOI: 10.1155/2013/543803] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 10/08/2013] [Indexed: 11/26/2022] Open
Abstract
Synaptic dysfunction is an important cause of neurological symptoms in prion diseases, a class of clinically heterogeneous neurodegenerative disorders caused by misfolding of the cellular prion protein (PrPC). Experimental data suggest that accumulation of misfolded PrPC in the endoplasmic reticulum (ER) may be crucial in synaptic failure, possibly because of the activation of the translational repression pathway of the unfolded protein response. Here, we report that this pathway is not operative in mouse models of genetic prion disease, consistent with our previous observation that ER stress is not involved. Building on our recent finding that ER retention of mutant PrPC impairs the secretory trafficking of calcium channels essential for synaptic function, we propose a model of pathogenicity in which intracellular retention of misfolded PrPC results in loss of function or gain of toxicity of PrPC-interacting proteins. This neurotoxic modality may also explain the phenotypic heterogeneity of prion diseases.
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22
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Crosstalk between Endoplasmic Reticulum Stress and Protein Misfolding in Neurodegenerative Diseases. ACTA ACUST UNITED AC 2013. [DOI: 10.1155/2013/256404] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Under physiological conditions, the endoplasmic reticulum (ER) is a central subcellular compartment for protein quality control in the secretory pathway that prevents protein misfolding and aggregation. Instrumental in protein quality control in the ER is the unfolded protein response (UPR), which is activated upon ER stress to reestablish homeostasis through a sophisticated transcriptionally and translationally regulated signaling network. However, this response can lead to apoptosis if the stress cannot be alleviated. The presence of abnormal protein aggregates containing specific misfolded proteins is recognized as the basis of numerous human conformational disorders, including neurodegenerative diseases. Here, I will highlight the overwhelming evidence that the presence of specific aberrant proteins in Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), prion diseases, and Amyotrophic Lateral Sclerosis (ALS) is intimately associated with perturbations in the ER protein quality control machinery that become incompetent to restore protein homeostasis and shift adaptive programs toward the induction of apoptotic signaling to eliminate irreversibly damaged neurons. Increasing our understanding about the deadly crosstalk between ER dysfunction and protein misfolding in these neurodegenerative diseases may stimulate the development of novel therapeutic strategies able to support neuronal survival and ameliorate disease progression.
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Roussel BD, Kruppa AJ, Miranda E, Crowther DC, Lomas DA, Marciniak SJ. Endoplasmic reticulum dysfunction in neurological disease. Lancet Neurol 2013; 12:105-18. [PMID: 23237905 DOI: 10.1016/s1474-4422(12)70238-7] [Citation(s) in RCA: 340] [Impact Index Per Article: 30.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Endoplasmic reticulum (ER) dysfunction might have an important part to play in a range of neurological disorders, including cerebral ischaemia, sleep apnoea, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, the prion diseases, and familial encephalopathy with neuroserpin inclusion bodies. Protein misfolding in the ER initiates the well studied unfolded protein response in energy-starved neurons during stroke, which is relevant to the toxic effects of reperfusion. The toxic peptide amyloid β induces ER stress in Alzheimer's disease, which leads to activation of similar pathways, whereas the accumulation of polymeric neuroserpin in the neuronal ER triggers a poorly understood ER-overload response. In other neurological disorders, such as Parkinson's and Huntington's diseases, ER dysfunction is well recognised but the mechanisms by which it contributes to pathogenesis remain unclear. By targeting components of these signalling responses, amelioration of their toxic effects and so the treatment of a range of neurodegenerative disorders might become possible.
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Affiliation(s)
- Benoit D Roussel
- Department of Medicine, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK
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24
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Cohen E, Avrahami D, Frid K, Canello T, Levy Lahad E, Zeligson S, Perlberg S, Chapman J, Cohen OS, Kahana E, Lavon I, Gabizon R. Snord 3A: a molecular marker and modulator of prion disease progression. PLoS One 2013; 8:e54433. [PMID: 23349890 PMCID: PMC3549992 DOI: 10.1371/journal.pone.0054433] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Accepted: 12/11/2012] [Indexed: 01/06/2023] Open
Abstract
Since preventive treatments for prion disease require early identification of subjects at risk, we searched for surrogate peripheral markers characterizing the asymptomatic phases of such conditions. To this effect, we subjected blood mRNA from E200K PrP CJD patients and corresponding family members to global arrays and found that the expression of Snord3A, a non-coding RNA transcript, was elevated several times in CJD patients as compared to controls, while asymptomatic carriers presented intermediate Snord3A levels. In the brains of TgMHu2ME199K mice, a mouse model mimicking for E200K CJD, Snord 3A levels were elevated in an age and disease severity dependent manner, as was the case for brains of these mice in which disease was exacerbated by copper administration. Snord3A expression was also elevated in scrapie infected mice, but not in PrP0/0 mice, indicating that while the expression levels of this transcript may reflect diverse prion etiologies, they are not related to the loss of PrPC’s function. Elevation of Snord3A was consistent with the activation of ATF6, representing one of the arms of the unfolded protein response system. Indeed, SnoRNAs were associated with reduced resistance to oxidative stress, and with ER stress in general, factors playing a significant role in this and other neurodegenerative conditions. We hypothesize that in addition to its function as a disease marker, Snord3A may play an important role in the mechanism of prion disease manifestation and progression.
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Affiliation(s)
- Eran Cohen
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
| | - Dana Avrahami
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
| | - Kati Frid
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
| | - Tamar Canello
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
| | - Ephrat Levy Lahad
- Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem, Israel
- Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Sharon Zeligson
- Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem, Israel
- Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Shira Perlberg
- Medical Genetics Institute, Shaare Zedek Medical Center, Jerusalem, Israel
- Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Joab Chapman
- Department of Neurology, Sheba Medical Center, Sackler Faculty, Tel Aviv University, Israel
| | - Oren S. Cohen
- Department of Neurology, Sheba Medical Center, Sackler Faculty, Tel Aviv University, Israel
| | - Esther Kahana
- Department of Neurology, Barzilai Medical Center, Ashkelon, Israel
| | - Iris Lavon
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
| | - Ruth Gabizon
- Department of Neurology, Hadassah Medical Center, The Agnes Ginges Center of Human Neurogenetics, Jerusalem, Israel
- * E-mail:
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25
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Abstract
Prion diseases comprise a family of fatal neurodegenerative disorders caused by the conformational re-arrangement of a normal host-encoded protein, PrP (C) , to an abnormal infectious isoform termed PrP (Sc) . Currently, the precise cellular mechanism(s) underlying prion disease pathogenesis remain unclear. Evidence suggests a role for the ubiquitin proteasome system (UPS), a protein degradation pathway that is critical for maintaining cellular proteostasis. Dysfunction of the UPS has been implicated in various neurodegenerative diseases. However, the mechanisms of this impairment remain unknown in many cases, and evidence that disease-associated misfolded proteins are able to directly inhibit the function of the proteasome has been lacking. Recently, we have shown data describing a mechanism of proteasome impairment by the direct interaction of β-sheet-rich PrP to reduce gate opening and inhibit substrate entry. This novel mechanism may provide a model for how other misfolded, disease-associated proteins might interact with the proteasome to disrupt its function. Targeting the UPS to restore proteostasis in neurodegenerative disorders in which misfolded proteins accumulate offers a possible target for therapeutic intervention.
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Affiliation(s)
- Ralph Andre
- Department of Neurodegenerative Disease, University College London Institute of Neurology, Queen Square, London, UK
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26
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Senatore A, Colleoni S, Verderio C, Restelli E, Morini R, Condliffe S, Bertani I, Mantovani S, Canovi M, Micotti E, Forloni G, Dolphin A, Matteoli M, Gobbi M, Chiesa R. Mutant PrP suppresses glutamatergic neurotransmission in cerebellar granule neurons by impairing membrane delivery of VGCC α(2)δ-1 Subunit. Neuron 2012; 74:300-13. [PMID: 22542184 PMCID: PMC3339322 DOI: 10.1016/j.neuron.2012.02.027] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/08/2012] [Indexed: 01/17/2023]
Abstract
How mutant prion protein (PrP) leads to neurological dysfunction in genetic prion diseases is unknown. Tg(PG14) mice synthesize a misfolded mutant PrP which is partially retained in the neuronal endoplasmic reticulum (ER). As these mice age, they develop ataxia and massive degeneration of cerebellar granule neurons (CGNs). Here, we report that motor behavioral deficits in Tg(PG14) mice emerge before neurodegeneration and are associated with defective glutamate exocytosis from granule neurons due to impaired calcium dynamics. We found that mutant PrP interacts with the voltage-gated calcium channel α(2)δ-1 subunit, which promotes the anterograde trafficking of the channel. Owing to ER retention of mutant PrP, α(2)δ-1 accumulates intracellularly, impairing delivery of the channel complex to the cell surface. Thus, mutant PrP disrupts cerebellar glutamatergic neurotransmission by reducing the number of functional channels in CGNs. These results link intracellular PrP retention to synaptic dysfunction, indicating new modalities of neurotoxicity and potential therapeutic strategies.
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Affiliation(s)
- Assunta Senatore
- Dulbecco Telethon Institute, 20156 Milan, Italy, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Simona Colleoni
- Department of Biochemistry and Molecular Pharmacology, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Claudia Verderio
- Department of Medical Pharmacology and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Milan, 20129 Milan, Italy
| | - Elena Restelli
- Dulbecco Telethon Institute, 20156 Milan, Italy, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Raffaella Morini
- Department of Medical Pharmacology and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Milan, 20129 Milan, Italy
| | - Steven B. Condliffe
- Department of Medical Pharmacology and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Milan, 20129 Milan, Italy
| | - Ilaria Bertani
- Dulbecco Telethon Institute, 20156 Milan, Italy, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Susanna Mantovani
- Dulbecco Telethon Institute, 20156 Milan, Italy, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Mara Canovi
- Department of Biochemistry and Molecular Pharmacology, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Edoardo Micotti
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Gianluigi Forloni
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Annette C. Dolphin
- Department of Neuroscience, Physiology and Pharmacology, University College London, WC1E6BT London, UK
| | - Michela Matteoli
- Department of Medical Pharmacology and Consiglio Nazionale delle Ricerche Institute of Neuroscience, University of Milan, 20129 Milan, Italy
- Istituto Clinico Humanitas IRCCS, 20089 Milan, Italy
| | - Marco Gobbi
- Department of Biochemistry and Molecular Pharmacology, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
| | - Roberto Chiesa
- Dulbecco Telethon Institute, 20156 Milan, Italy, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Department of Neuroscience, “Mario Negri” Institute for Pharmacological Research, 20156 Milan, Italy
- Corresponding author
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Wang SB, Shi Q, Xu Y, Xie WL, Zhang J, Tian C, Guo Y, Wang K, Zhang BY, Chen C, Gao C, Dong XP. Protein disulfide isomerase regulates endoplasmic reticulum stress and the apoptotic process during prion infection and PrP mutant-induced cytotoxicity. PLoS One 2012; 7:e38221. [PMID: 22685557 PMCID: PMC3369880 DOI: 10.1371/journal.pone.0038221] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Accepted: 05/01/2012] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Protein disulfide isomerase (PDI), is sorted to be enzymatic chaperone for reconstructing misfolded protein in endoplasmic reticulum lumen. Recently, PDI has been identified as a link between misfolded protein and neuron apoptosis. However, the potential for PDI to be involved in the pathogenesis of prion disease remains unknown. In this study, we propose that PDI may function as a pleiotropic regulator in the cytotoxicity induced by mutated prion proteins and in the pathogenesis of prion diseases. METHODOLOGY/PRINCIPAL FINDINGS To elucidate potential alterations of PDI in prion diseases, the levels of PDI and relevant apoptotic executors in 263K infected hamsters brain tissues were evaluated with the use of Western blots. Abnormal upregulation of PDI, Grp78 and Grp58 was detected. Dynamic assays of PDI alteration identified that the upregulation of PDI started at the early stage and persistently increased till later stage. Obvious increases of PDI and Grp78 levels were also observed in cultured cells transiently expressing PrP mutants, PrP-KDEL or PrP-PG15, accompanied by significant cytotoxicities. Excessive expression of PDI partially eased ER stress and cell apoptosis caused by accumulation of PrP-KDEL, but had less effect on cytotoxicity induced by PrP-PG15. Knockdown of endogenous PDI significantly amended cytotoxicity of PrP-PG15, but had little influence on that of PrP-KDEL. A series of membrane potential assays found that apoptosis induced by misfolded PrP proteins could be regulated by PDI via mitochondrial dysfunction. Moreover, biotin-switch assays demonstrated active S-nitrosylated modifications of PDI (SNO-PDI) both in the brains of scrapie-infected rodents and in the cells with misfolded PrP proteins. CONCLUSION/SIGNIFICANCE Current data in this study highlight that PDI and its relevant executors may function as a pleiotropic regulator in the processes of different misfolded PrP proteins and at different stages during prion infection. SNO-PDI may feed as an accomplice for PDI apoptosis.
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Affiliation(s)
- Shao-Bin Wang
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Qi Shi
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Yin Xu
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Wu-Ling Xie
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Jin Zhang
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Chan Tian
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Yan Guo
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Ke Wang
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Bao-Yun Zhang
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Cao Chen
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Chen Gao
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
| | - Xiao-Ping Dong
- State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, People’s Republic of China
- Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- * E-mail:
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28
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Misfolded PrP impairs the UPS by interaction with the 20S proteasome and inhibition of substrate entry. EMBO J 2011; 30:3065-77. [PMID: 21743439 DOI: 10.1038/emboj.2011.224] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Accepted: 06/16/2011] [Indexed: 01/07/2023] Open
Abstract
Prion diseases are associated with the conversion of cellular prion protein (PrP(C)) to toxic β-sheet isoforms (PrP(Sc)), which are reported to inhibit the ubiquitin-proteasome system (UPS). Accordingly, UPS substrates accumulate in prion-infected mouse brains, suggesting impairment of the 26S proteasome. A direct interaction between its 20S core particle and PrP isoforms was demonstrated by immunoprecipitation. β-PrP aggregates associated with the 20S particle, but did not impede binding of the PA26 complex, suggesting that the aggregates do not bind to its ends. Aggregated β-PrP reduced the 20S proteasome's basal peptidase activity, and the enhanced activity induced by C-terminal peptides from the 19S ATPases or by the 19S regulator itself, including when stimulated by polyubiquitin conjugates. However, the 20S proteasome was not inhibited when the gate in the α-ring was open due to a truncation mutation or by association with PA26/PA28. These PrP aggregates inhibit by stabilising the closed conformation of the substrate entry channel. A similar inhibition of substrate entry into the proteasome may occur in other neurodegenerative diseases where misfolded β-sheet-rich proteins accumulate.
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