Prion Diseases

Question 1

what is a gene

Answer 1

a heritable unit

Question 2

what can a prion protein act as

Answer 2

a gene

Question 3

what are TSEs

Answer 3

transmittable spongiform encephalopathy

Question 4

what are the 4 prion diseases in man

Answer 4

• Kuru (infectious)
• Creutzfeldt-Jacob Disease (sporadic, inherited, infectious)
• Fatal Familial Insomnia (inherited)
• Gerstmann-Straussler-Sheinker (inherited)

Question 5

what are prion diseases in other animals

Answer 5

• bovine/feline/mink spongiform encephalopathy
• scrapie

Question 6

what is Kuru disease?

Answer 6

• trembling with fear
• reported in 1957 - last patient in 2008
  fatal neurological disease affected Fore people in highlands of papa new guinea
  spread by cannibalistic funeral practices - ate the brains of affected individuals
  long incubation period but death within 2 years of presentation
  little evidence of dementia

Question 7

what is CJD

Answer 7

sporadic/iatrogenic cases first described in 1922 (80% of all human TSEs)
inherited ~(15%) infectious (5%)
infectious transmission

Question 8

what is the triad of CJD neurological changes

Answer 8

1. spongiform changes
2. neuronal loss
3. gliosis (astro and micro)

selective vulnerability (subset of GABAergic neurons)

Question 9

what do CJD patients get in the brain

Answer 9

‘amyloid’ plaques

Question 10

if CJD is transmitted via infection , how do prions get from digestive system to brain?

Answer 10

GALT - gut associated lymphoid tissue
from intestine through GALT then to peripheral nerves

Question 11

what are peyers patches and why are they relevant in CJD

Answer 11

small patches of lymphatic tissue in ileum
folicular dendritic cells in PP is where prions aggregate
M cells also found in PP and take up particulate matter from intestines

Question 12

how can disease be transmitted genetically AND by infection?

Answer 12

the prion (protein only) hypothesis
Griffiths 1967

Question 13

what is the prion protein only hypothesis?

Answer 13

the long incubation of prion diseases led to ‘slow virus’ concept
the infectious particle DOES NOT HAVE DNA
- there was no virus and no immune response, UV light, X rays and nucleases did not prevent transmission

Question 14

what did crystal analysis show about the infectious particle

Answer 14

any associated DNA would be very small

Question 15

outline the prion protein (PrPc)

Answer 15

highly conserved cell surface protein
expressed in many tissues but high level in neurons
its normal physiological function is unknown (neuronal homeostasis)

Question 16

what are the 2 forms of PrPc

Answer 16

natural PrPc
infectious PrPsc

Question 17

outline PrPc (natural)

Answer 17

highly conserved cell surface protein
high level in neurons
GPI-anchor sialoglycoprotein of 33-35kDa
mostly alpha helical

Question 18

outline PrPsc (infectious)

Answer 18

found as aggregated particles in brain of affected individuals
insoluble in detergents
partially resistant to proteases (VERY hard to break up)
mostly beta-sheet

Question 19

what gene mutation causes prion disease

Answer 19

Prnp1 gene
very polymorphic and many polymorphic variants

Question 20

what is the structural difference between the two proteins

Answer 20

PrPc and PrPsc have identical primary sequence but different secondary structure

Question 21

how does the infectious particle replicate?

Answer 21

by TEMPLATING
PrPsc forms beta sheet
during life inside the cell finds another prion protein that is the normal PrPc, binds and makes it change structure from alpha helical to beta sheet
consequently starts to aggregate
only need one particle to replicate - this happens over and over

Question 22

how can we test the prion protein hypothesis?

Answer 22

using PrP0/PrP0 viable proteins
1990 experiment showed that injecting infectious prion into normal mouse made it die, but if the mouse did not express PrPc and you injected PrPsc, the nothing happened to the mouse
= this shows the infectious particle has a templating function

Question 23

what 3 ways can TSEs arise in

Answer 23

infectious
hereditary
spontaneous

Question 24

there are various strains of PrP - how can we identify them?

Answer 24

they all have the same primary sequence but addition of glycosylation at various sites can cause protease resistance (cut in a different way) which allows for identification

Question 25

what species can be used for prion experiments

Answer 25

yeast
infectious forms Ura2 and Sup35
prion phenotype can be reversed by denaturation and return spontaneously
overproduction of wild type leads to increased prion formation
exists in alpha helical or beta sheet form

Question 26

prion is a term meaning infectious agent made solely of protein but may cause neurodegenerative diseases - what ones?

Answer 26

beta amyloid - alzheimers
alpha-synuclein -parkinsons
Tau - frontotemporal dementia, alzheimers

Question 27

what happens in mice when administered brain homogenates from AD patients

Answer 27

AD is transmitted into mice when they express human APP