Presentation on theme: "Overview Nature of the infectious particle in TSE TSE strains"— Presentation transcript:
1Overview Nature of the infectious particle in TSE TSE strains Role of PrPC in diseasePotential therapeutic targetsImplications for other neurodegenerative diseases
2Prion Diseases: Transmissible Spongiform Encephalopathies Fatal neurodegenerative diseases in man and mammalsTransmissible under natural and experimental conditionsLengthy incubation period with no conventional host responseCharacteristic neuropathology with spongiform change in grey matterAssociated with conversion of PrPC to PrPSc
3Prion diseases of humans and animals Scrapie in sheep and goatsTransmissible mink encephalopathyChronic wasting disease in deer & elkBovine spongiform encephalopathyFeline spongiform encephalopathyKuruCreutzfeldt-Jakob diseaseGerstmann-Straussler-Scheinker diseaseFatal familial insomniaVariant Creutzfeldt-Jakob disease
4Protein-only version of the prion hypothesis “Prions are transmissible particles that are devoid of nucleic acid and seem to be composed entirely of a modified protein (PrPSc).”“The normal, cellular PrP (PrPC) is converted into PrPSc through a post-translational process during which it acquires a high beta-sheet content.”Prusiner SB, Proc Natl Acad Sci USA 1998;95:
6Role of PrPC in TSEPrPC is required for disease propagation and neuropathologyPrPC with GPI anchor to cell membrane transduces or potentiates the neurotoxicity of TSE infectionTg PrP null mice do not propagate TSE infectivityTg mice expressing only anchorless PrPC can propagate TSE infectivity, but with greatly reduced neuropathology and clinical effects
7Infectious particle in prion diseases Nonfibrillar particles between kDa (mass equivalent to ~14-28 PrP molecules)Other molecular constituents?Cofactors for infectivity – sulphated GAG or nucleic acids?
8PrPres Isotype by Western blot Treatment with proteinase K results in N-terminal truncation of PrPresDistinct isotypes of PrPres characterize different forms of CJDIsotypes differ in extent of truncation and degree of glycosylation site occupancy
9Multiple conformations of PrPSc? “In contrast to pathogens carrying a nucleic acid genome, prions appear to encipher strain-specific properties in the tertiary structure of PrPSc.” (Prusiner)Is there evidence for heritable structural diversity in different prion diseases?
12Do different PrPres types replicate with fidelity in vitro? When human PrPC is converted to PrPres in a PMCA reaction the product has both the conformation and the glycosylation ratio of the in-put PrPresSoto et al, 2005
13Cellular co-factors & conversion: mammalian RNA Mammalian brain extractscontain RNA that stimulate the conversion of PrPC to PrPSc in a modified PMCA reaction(Deleault et al, Nature 2003;425: )
14Conservation of PrPres isotype following transmission to mice Telling et al 1996
15Conservation of targeting following transmission to mice FFI transmitted to Tg(MHu2M)Prnp0/0 miceThalamic pathologyfCJDE200K transmitted to Tg(MHu2M)Prnp0/0 miceCortical pathologyTelling et al 1996
16Aspects of PrPSc structure that might encipher strain properties Extent of structural re-arrangement (conversion to b-sheet) at the N-terminus.Presence of methionine or valine at codon 129Presence or absence of bound divalent cations (Cu2+)Extent of of asparagine-linked glycosylation site occupancyComposition and complexity of attached glycans
17Pathogenic mechanismIf we accept the centrality of of the conversion of PrPC to PrPSc in the pathogenic process, then there are in principle three possible alternatives:The loss of an essential function of PrPCThe acquisition of a toxic function by PrPScProduction of toxic intermediate or by-product
24Detection of PrPSc in the peripheral tissues in CJD vCJDCNSPNSOptic nerveRetinaAppendixLymph node Peyers’ patchesTonsilSpleenThymussCJDCNSPNSOptic nerveRetinaOlfactory epitheliumWadsworth et al, (2001), Lancet, 358, pp171-80Head et al, (2004), American Journal of Pathology, 164, pp143-53In certain prion diseases PrPSc accumulation has been shown to occur not on in the CNS, but also peripheral tissueUnderstanding the peripheral pathogenesis of the different forms of CJD is important for the differential diagnosis of these diseases and provides us with information for assessing the potential risk of iatrogenic spreadvCJD is known to differ from other human prion diseases in the greater extent to which PrPSc can be detected in the peripheral tissuesIn contrast, PrPSc is largely confined to the Central Nervous System in sporadic CJDThese two patterns have been thought to be due to the different routes of infection in variant and sCJD.In the case of vCJD the infection works its way in from the periphery, whereas in sCJD, the disease occurs within the central nervous system and migrates out by centrifugal spread.
26Neurodegenerative disease and aberrant protein deposition Classical neuropathology identifies abnormal histological structures which are diagnostic for particular conditions.Nuclear and cytoplasmic inclusion bodies and extracellular amyloid depositsProteinaceous, fibrillar, and rich in b-pleated sheet secondary structure“Fatal attractions” between abnormally folded forms of specific normal cellular proteins resulting in specific neurodegenerative diseasesA common feature of Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis and prion diseases
27Neurodegenerative diseases associated with abnormal protein conformations (toxic gain of function) Disease Gene productAlzheimer’s disease APP and AbCreutzfeldt-Jakob disease PrPc and PrPScParkinson’s disease a synucleinHuntingdon’s disease HuntingtinMachado-Joseph disease Ataxin 3(SCA 3)
28Neuronal vulnerability to “toxic gain of function” Neurones are post-mitotic cells which cannot be replaced (liable to damage by increasing DNA mutations?)Unique metabolic demands - some neurones have to maintain an axon over 1m in lengthFunctional plasticityEnvironment subject to control by many other structures, including astrocytes and the blood-brain barrier
29Review Nature of the infectious particle in TSE TSE strains Role of PrPC in diseasePotential therapeutic targetsImplications for other neurodegenerative diseases