Transcript Phenotypic diversity in acquired human prion diseases

Overview
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Nature of the infectious particle in TSE
TSE strains
Role of PrPC in disease
Potential therapeutic targets
Implications for other neurodegenerative
diseases
Prion Diseases: Transmissible
Spongiform Encephalopathies
• Fatal neurodegenerative diseases in man and
mammals
• Transmissible under natural and
experimental conditions
• Lengthy incubation period with no
conventional host response
• Characteristic neuropathology with
spongiform change in grey matter
• Associated with conversion of PrPC to PrPSc
Prion diseases of humans and
animals
• Scrapie in sheep and
goats
• Transmissible mink
encephalopathy
• Chronic wasting
disease in deer & elk
• Bovine spongiform
encephalopathy
• Feline spongiform
encephalopathy
• Kuru
• Creutzfeldt-Jakob
disease
• Gerstmann-StrausslerScheinker disease
• Fatal familial
insomnia
• Variant CreutzfeldtJakob disease
Protein-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;95:13363-83
Role of
C
PrP
in TSE
• PrPC is required for disease propagation and
neuropathology
• PrPC with GPI anchor to cell membrane
transduces or potentiates the neurotoxicity of TSE
infection
• Tg PrP null mice do not propagate TSE infectivity
• Tg mice expressing only anchorless PrPC can
propagate TSE infectivity, but with greatly
reduced neuropathology and clinical effects
Infectious particle in prion
diseases
• Nonfibrillar particles between 300-600 kDa
(mass equivalent to ~14-28 PrP molecules)
• Other molecular constituents?
• Cofactors for infectivity – sulphated GAG
or nucleic acids?
PrPres Isotype by Western blot
Treatment with
proteinase K results
in N-terminal
truncation of PrPres
Distinct isotypes of
PrPres characterize
different forms of CJD
Isotypes differ in
extent of truncation
and degree of
glycosylation site
occupancy
Multiple conformations of
Sc
PrP ?
• “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?
PRNP codon 129 genotype
frequencies
MM
MV
VV
Normal
population
37%
51%
12%
Sporadic CJD
71%
15%
14%
vCJD
100%
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Idiopathic human prion diseases
Prion
disease
Sporadic CJD
(Myoclonic,
Heidenhain
variants)
Sporadic CJD
(Ataxic
variant)
Sporadic CJD
(Kuru-plaque
variant)
Sporadic CJD
(Sporadic
fatal
insomnia)
Sporadic CJD
(Cortical
variant)
Sporadic CJD
PRNP
mutation
None
PRNP
codon 129
MM, MV
PrPres Histological
isotype correlate
Type 1
None
VV
Type 2A
None
MV
Type 2A
None
MM
None
MM
None
VV
Type 2A
Type 2A
(Basic
glycans)
Type 1
Synaptic and coarse
granular PrP staining in
cortex.
Plaque-like, focal and
perineuronal PrP
staining.
Amyloid plaques in the
cerebellum.
Reference
Parchi et al 1999
Parchi et al 1999
Parchi et al 1999
Thalamic atrophy.
PrP staining faint and
variable.
Parchi et al 1999
Pan et al 2001
Cortical perivacuolar
PrP staining.
Parchi et al 1999
Pan et al 2001
Faint synaptic PrP
staining.
Parchi et al 1999
Do 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 PrPres
Soto et al, 2005
Cellular co-factors & conversion:
mammalian RNA
Mammalian brain
extracts
contain RNA that
stimulate the
conversion of PrPC to
PrPSc in a modified
PMCA reaction
(Deleault et al, Nature
2003;425:717-720)
res
PrP
Conservation of
isotype
following transmission to mice
PrPres (kDa)
Inoculum
Host
Host PRNP
None
Human
FFI(D178, M129)
19
FFI
Mouse
Tg(MHu2M)
19
FFI Tg(MHu2M)
Mouse
Tg(MHu2M)
19
None
Human
fCJD(E200K)
21
fCJD
Mouse
Tg(MHu2M)
21
fCJD Tg(MHu2M)
Mouse
Tg(MHu2M)
21
Telling et al 1996
Conservation of targeting
following transmission to mice
FFI transmitted to
Tg(MHu2M)Prnp0/0 mice
Thalamic pathology
fCJDE200K transmitted to
Tg(MHu2M)Prnp0/0 mice
Cortical pathology
Telling et al 1996
Aspects 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 129
• Presence or absence of bound divalent cations
(Cu2+)
• Extent of of asparagine-linked glycosylation site
occupancy
• Composition and complexity of attached glycans
Pathogenic mechanism
• If 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 PrPC
– The acquisition of a toxic function by PrPSc
– Production of toxic intermediate or by-product
Neurodegenerative mechanism
Hope 2000
Problems with anti-TSE therapy
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Which compound(s) to use?
What route of delivery to use?
Is peripheral treatment required?
How long to treat?
Approaches to treatment of TSE
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Prevention of PrPC conversion
Dissolution of PrPSc aggregates
Enhanced PrPSc clearance
Neuronal rescue?
Strategies to prevent PrPC
conversion
• Inhibition of expression by RNA
interference
• Binding to site(s) for physiological ligands,
resulting in PrPC clustering and
internalisation from cell surface
Compounds with in vivo antiTSE activity
Class/compound
Example
Sulphonated dyes
Sulphated glycans
Cyclic tetrapyrroles
Polyene antibiotics
Quinolenes
Metal chelators
Tetracyclines
Congo red
pentosan polysulphate
porphyrins
amphotericin B
quinacrine
penicillamine
doxycyline
Detection of PrPSc in the peripheral tissues in CJD
sCJD
vCJD
CNS
PNS
Optic nerve
Retina
Olfactory epithelium
CNS
PNS
Optic nerve
Retina
Wadsworth et al, (2001),
Lancet, 358, pp171-80
Head et al, (2004), American
Journal of Pathology, 164,
pp143-53
Appendix
Lymph node
Peyers’ patches
Tonsil
Spleen
Thymus
Probable pattern of tissue infectivity in vCJD
INFECTIVITY
CNS
Infectivity
(perhaps
1,000
times
higher
than LRS)
LRS
Infectivity
TIME
Onset of
symptoms
Neurodegenerative 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 deposits
• Proteinaceous, fibrillar, and rich in b-pleated sheet
secondary structure
• “Fatal attractions” between abnormally folded forms of
specific normal cellular proteins resulting in specific
neurodegenerative diseases
• A common feature of Alzheimer disease, Parkinson
disease, Huntington disease, amyotrophic lateral sclerosis
and prion diseases
Neurodegenerative diseases associated
with abnormal protein conformations
(toxic gain of function)
Disease
Gene product
Alzheimer’s disease
Creutzfeldt-Jakob disease
Parkinson’s disease
Huntingdon’s disease
Machado-Joseph disease
(SCA 3)
APP and Ab
PrPc and PrPSc
a synuclein
Huntingtin
Ataxin 3
Neuronal 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 length
• Functional plasticity
• Environment subject to control by many other
structures, including astrocytes and the
blood-brain barrier
Review
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Nature of the infectious particle in TSE
TSE strains
Role of PrPC in disease
Potential therapeutic targets
Implications for other neurodegenerative
diseases