Week 1 Prion Flashcards
Background and History to Spongiform Encephalopathies- Prion Diseases
What are prion diseases?
What is the neuropathologpy of prion diseases?
What aggregates? what are they resistant to?
Prion diseases are a group of fatal neurodegenerative disorders
Neuropathology; spongiform degeneration of the central nervous system. Protein aggregates and amyloid plaques are seen, which are resistant to proteolytic degradation.
Prion disease can be:
Name the three forms of disease and examples for each
Sporadic
Make 85% of cases
Often called:
•Creutzfeldt-Jakob Disease (CJD)
Familial (heritable)
Examples:
•GSS (Gertsmann-Straussler-Scheinker)
• Familial CJD
• Fatal Familial Insomnia (FFI)
Infectious:
•Transmissible Spongiform Encephalopathies,
TSE’s
•Iatrogenic CJD (iCJD)
Infectious: Transmissible Spongiform Encephalopathies
(TSE’s)
Describe the Kuru tribe link to prion disease
Kuru the trembling
Tribes people in New Guinea performed cannibalism (ate the brain of relatives)
Incubation of 5 to 30 years therefore they did not see the link - until western intervention
Once the cannibalism stopped, Kuru cases TSE dropped:
What is
Latrogenic CJD (iCJD)?
What about sterilisation of surgical instruments?
Infection by surgical instruments
–Injection of human growth hormone (90 deaths)
•Incubation between 3 and 20 years
–
–Cornea and other grafts (60 deaths)
•Incubation 1 to 14 years
–
–Surgical instruments
•Problems with sterilisation
Prion material is not a virus or bacteria, it is therefore it will not be removed by biolling it
Human TSE
Do different TSE’s e.g sCJD and kuru have different pathologies? what is distinct?
What other disease shows similar symptoms to TSE
In humans different TSE – different pathology, distinct patterns of plaque protein deposition is different, the symptoms and progress is different.
Interestingly TSE shows similar symptoms to Alzheimer’s disease.
Packing of fibres can generate cross shape in plaques
TSE’s in Mammals
Scrapie is found in _____
How long has it existed?
Is it heritable or infectious?
Can it be transmitted to humans?
Another example of TSE found in mammals?
- Scrapie in sheep
- Scrapie in sheep existed for centuries, through out the world.
- Scrapie has a transmissible and inheritable component to the Spongiform Encephalopathies. Scrapie is infectious but certain breeds are more prone to the diseases.
- Not transmitted to humans
- Also Chronic Wasting Disease (CWD) in Deer (Canada)
Bovine spongiform encephalopathy
1992 height of crisis - how many cows were killed per week?
What was the cause of BSE?
What did BSE spread to?
(Mad cow disease)
At height of BSE Crisis 1992: 1,000 cows per week reported with BSE
•160,000 cattle have died from BSE
•Estimated 1 million have been infected
•Mean incubation of 5 years, while cattle are slaughtered at 2-3 years
•
•Caused by a change in rendering process in Britain in the late 1970’s
•
•Initial infection form meat and bone meal (MBM) of sheep. Further infection from MBM from cows
•£5.5 Billion Cost of Cattle slaughter
•
•Also BSE spread in Mink, Mule, Deer, Cats from MBM infected beef
Politics of BSE
Sunday Times, May 1990. Leading food scientist calls for slaughter of 6 million cows. The UK government does not agree with him. He is accused of ‘scare-mongering’.
Daily Mirror, March1996 MAD COW CAN KILL YOU. Government to admit it today. We have already eaten 1,000,000 mad cows.
Times June 1996 Scientists find direct evidence for BSE link. A French group injected macaque monkeys with BSE the pathology that was produced in their brain was very similar to that found with patients that have died recently with vCJD.
OCT 1996 The European Union has banned imports of British beef. McDonald’s has pulled British Big Macs from its menu.
1999 European Union confirmed that it will lift its ban on British beef on August 1, 1999. However, exports are fraction of pre 1996 level
New variant CJD (vCJD)
What is the cause of vCJD?
New variant CJD (vCJD)
vCJD has been linked to ingestion of beef contaminated with bovine spongiform encephalopathy (BSE)
Only observed in UK and France in teenagers and young adults;~170 deaths probably linked to infected beef and the mad cow epidemic. Initial fears suggested a possible million deaths.
Summary;
Summary;
Prion diseases can be: Inheritable, Infectious or Sporadic
In Humans: CJD, fCJD, Kuru, vCJD
BSE caused by change in rendering process
Oct 1996 Beef Ban
vCJD 170 deaths -in future
Search for the infectious agent
What were prion disease thought to be? Why?
However what contradicted this?
Prion disease not a virus
Scrapie, Kuru, and CJD were initially thought to be a “Slow Virus”
- *Similiar to virus becasue:**
1. Infection of the host initiates the production of millions of similar infectious particles
- There is a Species Barrier
•However, unusually..
–No immune response
–Strong resistance to Heat treatment
Scrapie - and example of a prion disease
Affect after treatment with increasing UV dose?
DNA and RNA sensitive to UV radiation - what did this suggest about replication of scrapie (prion disase)?
Resistant to UV and ionising radiation
DNA and RNA very sensitive to UV radiation
“Does the agent of scrapie replicate without nucleic acid” Published in Nature 1967
Until 1982, this was largely ignored, as it was believed only a virus or bacterium can cause infectious diseases.
This is because the central dogma of DNA biology would be contradicted; it did not make sense that there was NO nucleic acid in Scrapie
Although some similarities it was concluded that Scrapie was not caused by a virus
–No immune response
–Not effected by heat treatment,
–UV ionisation has no effect
Protein only hypothesis
When was this propsed? Who by?
How did they do this?
In 1982, Stan Prusiners’, Lab isolated refined fractions of brain material that was infectious when injected into hamsters.
Used fractionation: polyethylene-glycol precipitation, nuclease digestion, and density gradient centrifugation
He looked at this isolated infectious material did not contain any virus or bacteria. It almost exclusively contained protein. No DNA, RNA, or nucleic acid present.
What was the proteinaceous infectious particle called?
What affect did procedures that modified virus have on prion particle?
What about protein digestion?
The infectious material was called Prion particle.
•Procedures that modified virus had no effect on the infectivity of the Prion particle. While protein-digestion produced a reduction in scrapie infectivity
•
•The Prion particles were found to be derived from a single protein, the Prion Protein.
What are the two isoforms of the Prion Protein?
Cellular PrP-C; this is the form found in healthy brains
Scrapie PrP-Sc; if infected or have developed a sporadic CJD you will have the second form, now Scrapie rather than referring to sheep is the term used to describe the infected form.
Structure of the Cellular Prion Protein
What does CD spec show?
What does NMR show?
Structure of the Cellular Prion Protein
Structural Data on Cellular PrP
Circular Dichroism (CD) Spectroscopy
Strong negative CD bands at 222 nm and 208 nm indicate a predominately-helical protein
42 % a-helix
3 % b-sheet
55 % other- including random
NMR
NMR can tell you structure on a per residue basis, NMR chem shifts indicate two structurally distinct domains, 23-126 unstructured, then we get positive deviations in chemical shifts in blocks that show three alpha-helix’s.
