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PRIONS –an update
Dr Nitin Gupta
Department of Microbiology
AIIMS, New Delhi
Contents
• History
• Introduction
• PrPC and PrPSc
• Replication in Prions
• Pathogenesis
• Animal Prion Diseases
• Human Prion Diseases
• Disinfection & Sterilization
• Therapeutics
• Prevention
Daniel Carleton Gajdusek
• Kuru by ritualistic consumption
• successfully transmitted to primates
• Suggested viral causation
• got Nobel prize for his work in 1976
Gajdusek, D. Carleton et al. Science155(3759): 212–214.
Stanley B. Prusiner
• purified the hypothetical infectious protein
• named it Prion (Proteinaceous Infectious particles)
won the Nobel Prize in Physiology or Medicine in 1997
Prions
• proteinaceous infectious particle
• resistant to inactivation by procedures that modify nucleic acids – UV &ionizing radiation
– Dry heat
– Formaldehyde & glutaraldehyde
– DNAse & RNAse
– Digestion with proteinase K
• prion protein designated as - PrP
Annu. Rev. Microbiol. 2013. 67:543–64
Misfolded Proteins
Annu. Rev. Microbiol. 2013. 67:543–64
PrPC
• PrPC (for Common or Cellular) or PrPsen (protease sensitive)
• normal monomeric properly folded protein
• mainly alpha-helical structure
• found on outer surface of neurons
• attached by a glycosylphosphatidyl-inositol (GPI) anchor to
CM(differentiates from other misfolded proteins)
Málaga-Trillo E et al. March 2009. PLoS Biology 7 (3): e55.
Abbott A (2010). Nature
cell-cell adhesion
and intracellular
signaling
cell-cell communication
myelination in
Schwann cells
maintenance of long-term
memory
Proposed
functions of
PrPc
PrPSc
• PrPSc (for Scrapie) or PrPres (protease resistant)
• abnormal and oligomeric form
• amino acid sequences are identical to that of PrPC
• it has a higher proportion of β-sheet structure
Annu. Rev. Microbiol. 2013. 67:543–64
Os pub health res persp 2013 4(1), 57-66
Replication in Prions
• Prion induces PrPC into PrPSc
• PrPSc acts as template to guide the misfolding
conformational alteration is not immunogenic
• There are two models for Prion replication
Aguzzi A (2008).PNAS, 105(1): 11–2
Heterodimer model of replication
Fibril model of prion replication
Human Transmission
Nature reviews, Dec 2013, vol13
Pathogenesis
Archives of Medical Research 36 (2005) 622–627
Infection and peripheral replication
Neuroinvasion Neurodegeneration
Nature reviews, Dec 2013, vol13
Nature reviews, Dec 2013, vol13
Animal Prion
Diseases
Scrapie Bovine Spongiform
Encephalopathy (
BSE)
Chronic Wasting
Disease (CWD)
Transmissible
mink
encephalopathy
Feline
spongiform
encephalopathy
Ungulate
spongiform
encephalopathy
compulsively scrape off their fleeces due to intense itching
Transmission occurs through birth fluid or faeces
Not infectious to humans
animals become ataxic and wasted
Lichens reduce no. of prions in soil
Massive outbreaks in 1980s and 90s
Due to contaminated cattle feed
transmitted to man as vCJD in 1996
Bovine Spongiform Encephalopathy
Lancet.2005.Volume 366, Issue 9488
Lancet.2005.Volume 366, Issue 9488
Chronic Wasting Disease
Human prion
diseases
Creutzfeldt-Jakob
Disease (CJD)
Variant Creutzfeldt-
Jakob Disease(vCJD)
Gerstmann-Straussler-
Scheinker Syndrome Kuru
Proteinase sensitive
neuronopathy(new
entity described in
2008)
Fatal Familial
Insomnia
Genetics in Prion disease
Gene coding normal protein in humans (”PRNP”)
located on the short arm of chromosome 20.
• Patients with the D178N mutation and
homozygous for valine at codon129 develop CJD,
homozygous for methionine at 129 have FFI
Kuru
• Literal meaning ‘Shivering’ or
‘Trembling
• Mainly affected women and young
children
• Presents with Ataxia, Unsteady gait,
Cerebellar disorders
• Associated with ritual
cannibalism(stopped in 1950s)
Fatal familial insomnia
• rare fatal disorder identified in Italian families.
• MC gene mutation detected at D178N.
• progressive insomnia
• Autonomic disturbance & endocrine disturbances
• Genetic studies-the diagnostic procedure of choice
Gerstmann-Straussler-Scheinker syndrome
• AD, Complete penetrance
• Middle age adults
• Cerebellar ataxia, nystagmus and gait abnormalities
• Demonstartion of PrP mutation( mc-P102L)-best way to
diagnose
CRUETZFELD JACOB DISEASE
Inherited mutation
Mc-missense mutn in codon200
PrPSc accumulation in brain
Familial CJD(15%)
No mutation
Exogenous
Human PrPSc •human pituitary
hormones(MC,13
0)
•dural graft
transplants(110)
•corneal
transplant(3)
•liver transplants
•contaminated
neurosurgical
instruments (6)
Iatrogenic CJD(1%)
Spontaneous mutation
May be age related
Spradic CJD(85%)
Conversion of
PrPc into PrPSc
• Incidence of CJD in world- 1 case/million population
• 1968-1997: 69 cases of CJD from different parts of
India(NIMHANS)
• 1990-1998:10 cases of CJD, GB pant, New Delhi
• 2010-2013:10 cases of CJD from Bangur Institute of
Neurosciences,Kolkata
Variant Creutzfeldt-Jakob disease
• First reported in 1996
• acquired by ingestion of
infected meat products(BSE)
• Transmitted by blood
• No vertical transmission
Os pub health res persp 2013 4(1), 57-66
Classical CJD vs Variant CJD
Characteristic Classic CJD Variant CJD
Median age at death 68 years 28 years
Median duration of illness 4-5 months 13-14 months
Periodic sharp waves on
electroencephalogram
Often present Often absent
"Pulvinar sign" on MRI Not reported Present in >75% of
cases
Presence of "florid plaques" on
neuropathology
Rare or absent Present in large
numbers
Presence of agent in lymphoid
tissue
Not readily
detected
Readily detected
(tonsilar biopsy tissue)
Diagnosis
of CJD
CSF
MRI
EEG Brain
biopsy
Genetic studies
• no cells
• normal glucose
• elevated protein
• CSF 14-3-3 protein
(sCJD)
•most useful
•Increased T2 signal- striatum
(sCJD)
•Increased T2 signal in post
thalamus-Pulvinar sign(vCJD)
•periodic sharp wave
complexes (PSWC)
•high specificity but a low
sensitivity
gold standard
HPE
a) Spongiform changes
b) Neuronal loss
c) Astrocytosis
d) Amyloid plaque
Brain Biopsy
Immunoassays
SANDWICH
ELISA
FORMAT
Clin Dev Immuno,Vol 2013, Article ID 360604,
Os pub health res persp 2013 4(1), 57-66
Distribution of infectivity
High infectivity
(BSL-3)
Brain
• Spinal cord
• Eye
Low infectivity
(BSL-2)
• CSF
• Kidney
• Liver
• Lung
• Lymph nodes/spleen
• Placenta
No infectivity
• Blood
• Tears
• Nasal mucous
• Saliva
• Sweat
• Serous exudate
• Milk
• Semen
• Urine
• Faeces
Sterilization & Disinfection
• infectivity strongly stabilized by drying or fixation with
alcohol, formalin or glutaraldehyde
• Surgical instruments contact high infectivity tissues, single
use recommended
• instruments contaminated by CSF-also single use
• Incineration for all disposable instruments, materials, and
wastes
Sterilization & Disinfection contd..
With Pre treament
Instruments immersed in NaOH or Sodium Hypochlorite
Subjected to Autoclave at 121°C for 30 min to 1hr
Rinsed in water and subjected to routine sterilisation
Without pre treatment
Autoclave at 134°C for 18 minutes
WHO Infection Control Guidelines for Transmissible Spongiform Encephalopathies
THERAPEUTICS
• Universally fatal and incurable
• Pentosan polysulfate by intraventricular infusion slows
disease progression
• Amantadine transiently improves symptoms
• Flupirtine slow cognitive decline
• Astemizole - anti-prion activity
Potential immunotherapy targets
Nature reviews, Dec 2013, vol13
• Innate immunity repeated TLR9 stimulation protective
• Active immunization difficult because tolerance to PrP
Synthetic PrP peptides can be used
• Passive immunisation 1) Abs generated by
immunizing Prnp neg mice with PrP peptides
recombinant PrP
native PrP purified from tissues.
2) PrP-specific monoclonal Ab inhibited prion accumulation in the spleen
Nature reviews, Dec 2013, vol13
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