Lecture 13 (Prion Diseases)

What do modern cows eat?

In modern industrial cattle-farming, various commercial feeds are used, which may contain ingredients including antibiotics, hormones, pesticides and protein supplements.

What is the central dogma of molecular biology?

Information flow : DNA ->RNA ->Protein

What was proposed as an explanation to the cause of Bovine spongiform encephalopathy (Creutzfeldt-Jakob disease)?

Prions were proposed as an explanation to the disease

What are Prions Resistant to?

Proteases, Heat, Radiation, and formalin treatment, infectivity can be reduced by these treatments

What does PRIONS stand for?

Proteinaceous Infectious Particles that lack Nucleic acid

How is MCD diagnosed?

- Examination of brain biopsies - Immunofluorescence test on tonsilar biopsies / Western blot

What are transmissible spongiform encephalopathies (TSE)(Human form)

- Kuru - Creutzfeldt-Jakob disease (CJD) - Gerstmann-Straussler-Scheinker syndrome - Alpers syndrome

How do you effectively decontaminate an area from Prions?

- Protein hydrolysis - Reduction or destruction of protein tertiary structure. - Bleach, caustic soda, and strong acidic detergents

What are the visibile end results of MCD post-mortem?

- noninflammatory lesions - vacuoles - amyloid protein deposits - astrogliosis.

What changes to cow meal may have caused Mad Cow Disease?

-A change to the rendering process in the early 1980s may have resulted in a large increase of the infectious agents in the cattle feed. --A change in British laws that allowed a lower temperature sterilization of the protein meal

What is a key feature of Mad Cow Disease in cows? And which location has been most affected?

-A feature of the disease is the inability of the infected animal to stand. -UK = worse affected = 180K cattle infected = 4.4 million slaughtered

Prion Diseases

-All such agents have been discovered to propagate by transmitting a mis-folded protein state -The protein itself does not self-replicate and the process is dependent on the presence of the polypeptide in the host organism -All known prion diseases affect the structure of the brain or other neural tissue and all are currently untreatable and are always fatal

Where is Kuru more prevalent?

-Kuru was 8-9 times more prevalent in women and children than in men -Men of the village took the choice cuts, the women and children would eat the rest of the body including the brain, where the prion particles were particularly concentrated

Kuru Origins

-Kuru was first noted in the Fore tribe of the Eastern Highlands Province of Papua New Guinea as Australian administrators explored the area in 1957 -believe disease spread easily and rapidly due to endocannibalistic funeral practices, in which relatives consumed the deceased to return the :life force" of the deceased to his hamlet

What are current controls of transmissible encephalopathies (TSE)?

-No treatments available -Stop cannibalism -Eliminate animal products from livestock feed -Neurosurgical tools disinfected in 5% hypochlorite or 1 M NaOH & autoclaved at 15 psi for 1 hr

3 important Prion Facts

-No virion structure or genome -Elicits no immune response -Extremely resistant to inactivation by heat, disinfectants & radiation

What are transmissible spongiform encephalopathies (TSE)(Animal form)

-Scrapie (sheep & goats) -Bovine spongiform encephalopathy (BSE) -Chronic wasting disease (mule, deer, and elk) -Transmissible Mink encephalopathy

What is the disease progression of MCD?

1) A long incubation period (several years) which has given rise to the term "slow infection." 2) Loss of muscle coordination which leads to a difficulty in walking, indicating a functional disorder of the cerebellum. 3) Dementia characterized initially by loss of memory, diminished intellect and poor judgement. 4) Progressive insomnia characterized by a marked reduction or loss of the slow-wave and rapid-eye-movement phases.

What is a proposed mechansims for Prion Propagation?

1) Endogenous PrPc interacts with PrPsc 2)Conversion of PrPc to PrPsc (elongation, conformational change) 3) accumlation of PrPc Or: -Spontaneous generation of PrPsc -Conversion of mutant PrPc to PrPsc -Inoculation of PrPsc

What are the WHO reccomendations for cleaning surgical equipment

1) Immerse in 1M NaOH or 5% sodium hypochlorite for 1 hour 2) Remove and rinse in water 3) Then transfer to an open pan and heat in a gravity displacement (121C) or in a porous-load (134C) autoclave for 1 hour 4) Clean 5) Then perform routine sterilization processes

What are the 4 features of a TSE

1) spongiform change 2) neuronal loss 3) astrocytosis 4) amyloid plaque formation

What are the 3 forms of transmission by TSEs

1)Genetic 2)Sporadic 3)Infectious - these are through ingestion of infected foodstuffs and iatrogenic means (blood transfusion)

What is the progression of Mad Cow Disease

1)Infection 2)Incubation Period (1-30 years) 3) Prodrome(3.5 months) 5)Dementia/Myoclonic stage (4 months) 6) Death

What are the Symptoms of Mad Cow Disease?

= Degenerative central nervous system diseases -The diseases are characterized by loss of motor control, dementia, paralysis, wasting and eventually death, typically following pneumonia.

What do Prions affect?

All known prion diseases affect the structure of the brain or other neural tissue and all are currently untreatable and are ALWAYS FATAL

How do Prions propagate?

All prion diseases have been discovered to propagate by transmitting a mis-folded protein state - This protein DOES NOT SELF-REPLICATE and the process is dependent on the presence of the polypeptide in the host organism

What is it called when Humans have Prion Protein Gene Mutation

Creutzfeldt-Jakob disease (genetic CJD) aka genetic CJD for short4

Transmission

Genetic, Sporadic or Infectious -via ingestion of infected foodstuffs and via iatrogenic means (e.g. blood transfusion). -Most TSEs are sporadic and occur in an animal with no prion protein mutation. -Not by casual contact but by infected tissue, body fluids, or contaminated medical instruments

What is the transmission of Mad Cow Diesease

Horizontal transmission, familial (genetic) or sporadic, with no known history of exposure

Creutzfeldt-Jakob disease (genetic CJD)

Humans with prion protein gene mutation

What is the incubation time for Kuru?

Mean incubation period of the disease is 14 years and cases were reported with latencies of 40 years

Prion Replication cycle

PrPc interacts w/PrPsc and has elongation, conformational change, then there is a breakage into multiple new seeds

How do Prions cause neurodegenerative disease?

Prions cause neurodegenerative disease by aggregating extracellularly to form plaques known as amyloid, which disrupt the normal tissue structure

What do prions induce?

Prions induce the fomration of an amyloid fold, in which the protein polymerizes into an aggregate consisting of tightly packed beta sheets

What does a Prion refer to?

Refers to the infectious agent

How are most TSEs transmitted?

Sporadically and can occur in an animal w/no prion protein mutation - not by casual contact but bby infected tissue, body fluids, or contaminated medical instruments

Sterilization of Prions (PrPsc)

Sterilizing Prions is an intensive process that involves the denaturation of the protein to a state where the mol. is no longer able to induce the abnormal folding of normal proteins

What kind of meal was used for cattle prior to and during the Mad Cow Disease Epidemic

The use of meat and bone meal, produced from the ground and cooked left-overs of the slaughtering process as well as from the cadavers of sick and injured animals such as cattle, sheep, or chickens, as a protein supplement in cattle feed was widespread in Europe prior to about 1987

What does Mad Cow Disease Look like in affected tissue sections?

There are microscopic "holes" causing the tissue to develop a "spongy" architecture

Can proteins alone transmit an infectious disease?

Yes, this is a considerable surprise to the scientific community

What can MCD be caused by?

a genetic mutation w/in a gene called Prion Protein Gene

PrP

abbreviation for Prion Protein (may be infectious or non-infectious)

Prodome

an early symptom indicating the onset of a disease or illness

Amyloids

are insoluble fibrous protein aggregates

Amyloid Plaque

are sticky buildup which accumulates outside nerve cells, or neurons

How stable is PrPsc?

extremely stable and accumulates in infected tissue, causing tissue damage and cell death.

What is the history of Kuru?

first studied in the 1950's -isolated Fore tribes in the highlands of New Guinea -called "laughing death" -most likely acquired through ritualistic cannibalism

Is there Renaturation of a Prion?

has not been achieved yet, however partially denatured prions can be renatured to an infective status under certain artificial conditions

Endogenous

having an internal cause or origin

What is a prion?

infectious agent that is composed primarily of protein.

Variant CJD or vCJD

prion diseases can be sporadic, as in sporadic CJD, as well as foodborne. That is, they are contracted when people eat products contaminated with mad cow disease

Why are prions so difficult to sterilize?

prions are resistant to denaturation by chemical and physical agents, making disposal and containment of these particles difficult.

• PrP^C

refers to the endogenous form of prion protein (PrP), which is found in a multitude of tissues --normal form

PrPSc

refers to the misfolded form of PrP, that is responsible for the formation of amyloid plaques and neurodegeneration

What is a Prion defined as?

small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids

What is a PRION disease?

spongiform encephalopathies - this is b/c of the post motem appearance of the brain w/large vacuoles in the cortex and cerebellum. Probably most mammalian species can develop these diseases

Iatrogenic

via blood transfusion

Horizontal transmission

viruses are transmitted among individuals of the same generation