Prions

Question 1

what are classical pathogens?

Answer 1

-organisms/particles with nucleic acid genomes

Question 2

what are prions?

Answer 2

-misfolded proteins that can become infectious
-can withstand very high heat
-lack nucleic acid

Question 3

what is the protein-only prion theory? (NO)

Answer 3

-developed by Stanley Prusiner’s
-claims that the infectious misfolded protein is the cause of disease spread by converting normal proteins into the same misfolded form without any involvement from DNA or RNA

Question 4

what is the common form of the prion protein?

Answer 4

-PrPsc is the prion form of PrPc
-PrPc is a normal protein found in the brain on the surface of neurons

Question 5

what are the human and animal diseases caused by prions?

Answer 5

-scrapie (sheep, first one described)
-BSE (cattle)
-chronic wasting disease (elk + deer)
-Kuru (humans, cannibalism)
-Creutzfeldt-Jakob disease (humans, spontaneous and non-spontaneous variants)

Question 6

what is a characteristic of the diseases caused by prions?

Answer 6

-very slow diseases with 1-35 years between infection and symptoms

Question 7

what is the difference between normal Cruetzfeldt-Jakob disease and the variant Cruetzfeldt-Jakob disease?

Answer 7

-normal Cruetzfeldt-Jakob disease is spontaneous and tends to be in older adults
-variant Cruetzfeldt-Jakob disease is from eating contaminated beef and tends to be in younger adults

Question 8

what is the purpose of the PrPc protein?

Answer 8

-prevents neuron apoptosis (cannot be regenerated, very important)
-aids in neuron communication

Question 9

what are the characteristics of PrPc?

Answer 9

-host encoded glycoprotein
-uninfective
-alpha helical conformation with linker sequences
-susceptible to proteases (degrade after 3-6 hours)
-not heat resistant (heat sensitive)

Question 10

what are the characteristics of PrPsc?

Answer 10

-infective
-Beta sheet structure instead of alpha helices
-protease resistant because of its configuration
-accumulate within the cell once it becomes too much for the surface (form vacuoles (holes))
-heat resistant

Question 11

how does PrPc become PrPsc?

Answer 11

-normal cells express PrPc at the cell membrane as linear proteins
-PrPsc exists freely as a result of a spontaneous process and releases from the membrane, it can interact with PrPc, which releases it from the cell membrane and converts PrPc to PrPsc
-cells produce more PrPc and the cycle repeats
-PrPsc accumulates as plaques and is then internalized by the cells

Question 12

how do prion diseases develop by mutation? (NO)

Answer 12

-mutations in codon 129 of PrPc in chromosome 20
-leads to CJD (cerebrum is the target), Gertsmann-Straissler-Scheinker syndrome (cerebellum is the target), and fatal familial insomnia (thalamus is the target)
-less common

Question 13

how do prion diseases develop more commonly? (NO)

Answer 13

-exposure to an infective agent such as contaminated food, medical products (blood, transplants, latrogenic), or surgical instruments (strong binding to metal surfaces)
-can also have mother to fetus transmission (not a lot of evidence supporting)

Question 14

how do the prions shed in the body? (NO)

Answer 14

-shed through skin, feces, milk, urine, nasal secretions, saliva, and placenta

Question 15

how do prion diseases cross between species?

Answer 15

-Scrapie in sheeps and goats get transmitted to all other animals except humans
-humans get it from cattle

Question 16

what is the diagnosis and treatment for prion diseases? (NO)

Answer 16

-very difficult because there is no culturing or serology (study of serum and other bodily fluids to find antibodies)
-no inflammation seen in tissues
-tonsillar tissues can be a good source of PrPsc (go through a PMCA to study mechanisms and presence of prions when mixed with copious amounts of PrPc)
-no treatment currently, but experimental studies are being done with rodents with polyanionic and tricyclic compounds

Question 17

what is PMCA? (NO)

Answer 17

-protein misfolding cyclic amplification (protein based assay)
-like a PCR
-uses blood or tonsil tissue
-take the PrPsc from tonsils and combine it with PrPc from animal or human brain tissue (can be contaminated and give a false positive)
-go through sonication and incubation (40-100 cycles)

Question 18

what is new method of testing blood or tonsil tissue? (NO)

Answer 18

-RT-QuIC (real time-quacking-induced conversion)
-preferred by clinicians
-uses artificial PrPc so there is no contamination
-shaking and incubation is done and results come in 3 days