Lec 1 PRIONS

Recognize proteins can be infectious, Understand pathophysiology of transmissible spongioform encephalopathies, To learn different forms of prion mediated diseases

What are Transmissible Spongiform Encephalopathies (TSEs)?

• type of disease

• death rate

• Cure

• Neurodegenerative disease

• always fatal

• no available therapies

Why are Transmissible Spongiform Encephalopathies (TSEs) Transmissible?

b/c they can be transmitted experimentally by inoculation

ex.

in an experiment, brain tissue from an animal with a TSE is injected into a healthy lab animal. If the healthy animal later develops the disease, that shows the disease is transmissible by inoculation.

Why are Transmissible Spongiform Encephalopathies (TSEs) Spongiforms?

b/c microscopic vacuoles in brain tissue are feature that help identify the disease

Why are Transmissible Spongiform Encephalopathies (TSEs) Encephalopathies?

b/c they are disease (-pathy) of the brain (-encephalo)

What causes TSEs?

Prions

• infectious agents

What is Scrapie?

• when was it found (how old is it?)

• what is the type of disease and who is it impacting?

• what does this disease cause

• transmission?

• transmissible to humans?

• Oldest known TSE

• neurodivergent disease of sheep and goats

• animals compulsively scrape off their fleece

• transmitted from ewes to offspring (not well understood)

• not transmissible to humans

What are the 5 different TSE diseases

Scrapie

Bovine Spongioform Encephalopathy (BSE)

Creutzfeldt Jakob Disease (CJD)

Kuru

Chronic Wasting Disease (CWD)

Define the prion theory

• What were TSEs initially considered to be caused by?

• What did S. Pruisner propose?

• TSEs were considered to be caused by an unidentified slow virus

• S. Pruisner proposed that TCE disease were caused by MISFOLDED PROTEINS rather than bacteria or viruses

• 
  

What was the dogma about transmissible infections, and how did the prion theory challenge it?

DOGMA: that transmissible infections required nucleic acid

PRION THEORY: Suggested that proteins ONLY is what caused TSEs

What happened to S.Pruisner when he proposed the prion theory?

• lost his funding

• denied tenure

(article) Why does the prion theory propose that the scrapie agent is a protein-based infectious particle rather than one that relies on nucleic acids?

Sensitivity to proteases shows it contains a protein required for infectivity

• while five procedures that modify nucleic acids failed to inactivate it.

What 2 words is Prion composed of?

Protein + Infection

What are prions and where can they be found in the body?

• who has them?

What they are: A form of host protein that does NOT contain nucleic acid

Who has them: Everyone has prions (natural)

Found where: found predominantly on the surface of neurons

What is PrPC?

What does it stand for?

• the natural protein in everyones bodies; NOT INFECTIOUS

• The Cellular (C) Prion Protein

Why is PrPC a highly conserved protein in mammals?

• its amino acid seq. has changed very little over evolution

What is the function of PrPC?

normal function is not well understood

• thought to be involved in synaptic function

What is PrPSc?

What does it stand for?

• the smallest known infectious agent

• A modified form of PrPC

• Stands for Scrapie (Sc) Prion Protein

Why does PrPSc not trigger an immune response?

• Body recognizes it as a self protein

• PrPSc shares the exact same primary amino acid sequence as the normal, PrPC

How do PrPSc appear in the body?

• PrPC is converted into PrPSc

• this happens through an irreversible conformation change

What is the difference between PrPC vs PrPSc?

the difference is the structure of both proteins

otherwise are the same protein

Describe the structure of PrPC

• alpha helices or beta sheets?

• soluble / insoluble

• degraded or resistant to proteins

• aggregates or doesn’t aggregate

• Rich is alpha helices

• Soluble

• Degraded by proteases

• Doesn’t aggregate

Describe PrPSc

• Rich in beta helices

• insoluble

• resistant to proteases

• aggregates

What is one of the reasons why PrPSc is very hard to find a cure?

• It is extremely resistant to autoclaving, disinfectants, radiation etc..

How does PrPSc lead to cell death, according to the model?

• PrPSc converts PrPC on the cell surface into more PrPSc, which is taken in by endocytosis and accumulates in endosomes

• It keeps accumulating as the endosome contents are transferred to lysosomes, and the result is cell death.

A mouse with its prion protein gene removed is injected in the CNS with infectious prion protein from a sheep brain lesion. What happens to the mouse and why?

The mouse does not develop disease.

It has no PrPC for PrPSc to convert, so PrPSc cannot accumulate and cause cell death.

Where is the highest concentration of PrPc?

• in the brain

What causes the neurons in the brain to die due to prions?

• the accumulation of prions cause neurons to die

What are amyloid plaques (a feature of TSE disease)

• misfolded protein that clump together in tissue in the brain

What are symptoms of TSE disease

• takes long time for symptoms to appear

• Personality changes

• lack of coord.

• involuntary jerking

What are three important characteristics of Prion diseases?

• PrPSc can be infectious

• prnp can induce TSEs and be heritable

• Normal prnp can be mutated → sporadic

note: prions are proteins encoded by genes, therefore inheritable

What are the modes of transmission from prions? What is the most efficient and least eff.?

Intracerebral (IC) - Most

Intravenous (IV)

Intraperitoneal (IP)

Subcutaneous

Intragastric (Oral) - Least

What is Bovine Spongiform Encephalopathy (BSE)?
What is its history

• mad cow disease

• Britans started feeding cows the remains of other cows. One of those cows had sporadic disease. The caused contaminated beef in the food chain

What is the development of BSE?

• can take 5 years or longer

What is Variant Creutzfeldt Jakob Disease (vCJD)?

• transmission of mad cow disease to humans via consumption of cow brain or spinal cord

When comparing the second graph to the first, why did we only have 25 cases at the peak of the epidemic? (first graph is BSC cases and second is vCJD cases)

• b/c oral consumption of prions is inefficient

Why did the Canadian Blood services have screening question regarding the mad cow disease?

To prevent mad cow disease from spreading they had a screening question asking if any canadians had lived in the UK during a certain period

Ban was lifted in 2023

What would happen in Canada if a Canadian beef cow had BSE?

• the entire herd would be eliminated

What ban was placed to help prevent BSE

• feeding of rendered protein products from ruminants

What is CJD? (Classic Creutzfeldt - Jakob Disease)

What are the three major categories?

• also a prion disease that has 3 major categories

1. Sporadic → no known environmental source (85% of cases)

2. Hereditary (familial) → genetic mutation passed on (15% of cases)

3. Latrogenic: from a medical procedure due to contaminated equipment (<1%)

Is classic CJD contagious through casual contact?

No

What is Kuru?

• how did it come about?

• what does kuru mean?

The Fore people of Papua New Guinea practices ritual cannibalism during funerals

• means “to shake” — b/c body tremors are symptoms of the disease

What is the incubation period of kuru?

anywhere from 5-20 years to develop the disease

What could the original source of Kuru be?

• likely consumption of a sporadic CJD individual

Which mutation allowed the people of Papua New Guinea to be resistant to CDJ?

• PrPC had a M129V mutation that allowed resistance to CDJ

• was found in those exposed to kuru and survived the epidemic of Papua New Guinea

• took 50 yrs to develop this resistance

What is Chronic Wasting Disease (CWD)? What is its mode of transmission?

TSE of deer

• mode of transmission is unknown

What does the diagram show?

• shows how PrPSc clump together into long amyloid fibrils

• then shows how the fibrils are injected into mouse brain

• Over time, the red prion deposits spread through the brain and the mouse dies

What happened to the lab tech. handling brain sections from transgenic mice expressing the human prion gene?

• The lab tech accidently had their skin punctured with forceps that were used to handle the samples

• the patient then died 9 years later with clear evidence of vCJD

What is Alzheimers disease?

• build up of beta amyloid and Tau in the brain

What is the relation of Alzheimers disease w/ TSE?

Alzheimer is NOT a prion disease

• they are both dementing disorders that involve the misfolding of proteins and causing aggregates