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Transmissible Spongiform Encephalopathies (TSEs) a.k.a. Prion Diseases. Transmissible  can be spread Spongiform  resembling a sponge Encephalopathies  disorders/diseases of the brain. Characteristics of TSEs.

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Transmissible Spongiform Encephalopathies (TSEs)

a.k.a.Prion Diseases

Transmissible  can be spread

Spongiform  resembling a sponge

Encephalopathies disorders/diseases of the brain


Characteristics of tses
Characteristics of TSEs

  • Cause insomnia, weight loss, ataxia (loss of coordination), memory loss, dementia, death

  • Incubation time ranges from 1-60 years

  • Transmissible

  • Invariably fatal

Spongiform lesions in the brain


Examples of TSE Diseases

Animals

  • Humans

  • Scrapie (sheep & goat)

  • Bovine spongiform encephalopathy (BSE, a.k.a. Mad Cow)

  • Chronic wasting disease (CWD;deer & elk)

  • Kuru

  • Creutzfeldt-Jakob disease (CJD)


Kuru: A TRANSMISSIBLE encephalopathy

Spongiform lesions

Spongiform lesions

Gajdusek and Alpers (1965)


What is the causative agent of TSEs?

  • Agent could resist ionizing and UV radiation

     NOT a nucleic acid-based agent (not a virus)

  • What about Protein?

  • Infectious agent purified by Stanley Prusiner in 1982

  • identified as PrP, or prion protein (Nobel Prize, 1997)

  • Agent could pass through 0.2 m filter

     NOT a bacterium (bacteria are usually 0.5-5 m)


The Prion Hypothesis of TSEs

The infectious agent is a misfolded protein (PrP, or prion) that propagates in the absence of nucleic acid by transmission of its altered and pathogenic conformation to the normal host version of the protein.

Direct experimental evidence in support of this hypothesis has been difficult to obtain


Prion terminology

  • Prion proteins (PrP) are encoded by the host genome

  • PrPC(C for cellular) is the normal cellular form of prions

  • PrPSc(Sc for scrapie) is the misfolded form

  • PrPC can adopt the alternatively folded form, PrPSc, which causes disease


Structural Characteristics of PrPC and PrPSc

  • The amino acid sequences of PrPC and PrPScare identical, but the proteins differ in their three-dimensional conformation

  • PrPC – rich in -helixes and little β-sheet

  • PrPSc – less rich in -helixes and much more β-sheet structure

PrPC

PrPSc


Prion conformational conversion

  • PrPSc acts as a template on which PrPC is refolded into the infectious disease-causing PrPSc form

PrPC

PrPSc


PMCA: protein misfolding

cyclic amplification

+

PrPC

PrPSc

  • Mix small quantities of PrPSc with excess of PrPC

  • PrPSc aggregates during incubation

  • Sonication breaks PrPSc aggregates into small pieces; this acts to multiply the number of “converting units”

  • Repeat to get detectable levels of PrPSc

sonicate

incubate

Serially repeat

Adapted from Trends in Neuroscience, 2002 Aug;25(8):390-4.



Figure 1A.

Multiple rounds of PMCA using recombinant PrP in the presence of synthetic anionic phospholipid (POPG) and RNA results in a PK-resistant band appearing after 17 rounds.


Figure 1B.

The PMCA product generated in Figure 1A is highly resistant to PK (a defining feature of misfolded, infectious prion proteins).


Figure 1C.

The PK-resistant species is found in the pellet (not supernatant) after centrifugation, and results in a 15KDa PK-resistant band at the C-terminus (insolubility, aggregation, and PK-resistant core at C-terminus are defining features of misfolded, infectious prion protein).


Figure 1D.

PMCA seeded with rPrP-res produced PK-resistant PrP bands in normal mouse brain homogenate whereas unseeded PMCA did not.


Figure 1E.

Infection of a mouse neuronal cell line with rPRP-res generated in PMCA results in a PK-resistant PrP band (Numbers indicate cell passages after infection).


What is the overall purpose of showing the series of experiments in Figure 1?

  • To demonstrate that PMCA of bacterially-expressed PrP using RNA and POPG generated a PrP protein with all the characteristics of a PrPSc

    • PK-resistant C-terminal core

    • insolubility

    • tendency to aggregate

    • ability to propagate a PK-resistant conformation to endogenous PrPC


Table 1. experiments in Figure 1?

Intracerebral inoculation of rPrP-res generated by PMCA with POPG and RNA invariably caused disease in mice, demonstrating that the misfolded protein produced from recombinant PrP is infectious and pathogenic.


Do the results of this paper support or contradict the “ experiments in Figure 1?Prion Hypothesis”? Why?

While the efficient in vitro production of PrP-res required the addition of cofactors, the fundamental principle of the Prion Hypothesis is supported by this data, in that the disease is transmitted by a misfolded protein.


Bovine spongiform encephalopathy (BSE) experiments in Figure 1?

  • “Mad Cow Disease” epidemic (1986-early 2000s)

  • # of infected cattle estimated at > 1 million

  • Spread by cattle being fed “meat and bone meal” produced from infected cattle


The emergence and control of BSE experiments in Figure 1?

Epidemiological studies

First case

Ban on meat and bone in cattle feed

BSE transmission to mice in lab


Human creutzfeldt jakob disease cjd
Human Creutzfeldt-Jakob disease (CJD) experiments in Figure 1?

  • Variant CJD, first reported in 1996

    • <1% of CJD cases

    • Average onset at 28 years of age

    • Distinct pathological and clinicalfeatures

  • CJD is a human TSE

  • Sporadic CJD

    • 85% of CJD cases

    • Average onset at 52 years of age

  • Familial CJD

    • 10-15% of CJD cases

    • Average onset at 60 years of age


  • Relationship of BSE and variant CJD experiments in Figure 1?

    BSE in cattle

    • Association in

      • -Time

      • -Place (UK)

    • >200 human cases

    • Peak has past

    • 4 cases diagnosed in 2010

    vCJD in humans


    What have we learned from the bse and vcjd outbreaks
    What have we learned from the BSE and experiments in Figure 1?vCJD outbreaks?

    • Prion diseases can cross species barriers to infect humans

    • MANY humans exposed, but few infected

    • The majority of individuals who died of vCJD via contaminated beef had a mutation in their native PrP

    • Same mutations are found in sporadic and familial CJD cases

    • PrP mutation likely made cellular PrP more susceptible to misfolding


    Scenario experiments in Figure 1?

    You are a public health official and receive a phone call from a deer hunter in Wisconsin. He will be hunting for deer this season, but has heard some grumblings among friends about Chronic Wasting Disease (a transmissible prion disease) in Wisconsin deer herds.

    He is concerned about the potential risk associated with preparing and eating deer meat and wants to know if he should be concerned and what he can do to reduce the risk.

    Take one minute and write two things that we should consider to assess the potential risk to this person.


    Chronic Wasting Disease (CWD) experiments in Figure 1?

    • A prion disease that affects deer, elk, and moose

    • Highly transmissible within deer and elk populations

    • Identified in 13 states and 2 Canadian provinces

    Confirmed Cases of CWD in the U.S.


    Chronic Wasting Disease (CWD) experiments in Figure 1?

    • Spreads through the deer population by:

    • -animal-to-animal contact (prion shedding into saliva)

    • -contaminated feed and water sources

    • No evidence of CWD transmission to humans has been reported

    • Surveillance has not shown any increase in the incidence of Creutzfeldt-Jakob disease

    • Efficiency of CWD to convert recombinant human PrP into

    • aberrant form is low, but similar to that of BSE and scrapie


    Scenario experiments in Figure 1?

    You are a public health official and receive a phone call from a deer hunter in Wisconsin. He will be hunting for deer this season, but has heard some grumblings among friends about Chronic Wasting Disease (a transmissible prion disease) in Wisconsin deer herds.

    He is concerned about the potential risk associated with preparing and eating deer meat and wants to know if he should be concerned and what he can do to reduce the risk.

    On what information do you base your recommendation?

    What additional information/data would you still like?


    Centers for Disease Control and Prevention (CDC) Recommendation

    “Hunters should consult with their state wildlife agencies to identify areas where CWD occurs and take appropriate precautions when hunting in such areas. Hunters and others should avoid eating meat from deer and elk that look sick or that test positive for CWD. Hunters who harvest deer or elk from known CWD-positive areas may wish to consider having the animal tested for CWD before consuming the meat (information about testing is available from most state wildlife agencies). Persons involved in field-dressing carcasses should wear gloves, bone-out the meat from the animal, and minimize handling of the brain and spinal cord tissues.”


    End. Recommendation


    Extra slides
    Extra slides Recommendation


    CWD in Wisconsin deer Recommendation

    • Surveillance in Wisconsin since 2002

    • 166710 deer tested

    • 1576 positive (≈1%)

    • Prevalence increases

    • with age of deer

    (WI)


    Kuru epidemiology and fore culture
    Kuru Recommendation: Epidemiology and Fore culture

    • Identified in Fore linguistic group of Papua New Guinea in 1954

    • Fore practiced cannibalism as a form of mourning

    • Cessation of cannibalistic rituals led to a decline in disease (last case in 2005)

    Australia


    Kuru Recommendation: A TRANSMISSIBLE encephalopathy

    Spongiform lesions

    Spongiform lesions

    • Gajdusek and Alpers collected brain tissue of deceased 11-year-old Fore girl in mid 1960s

    • Injected into two chimps (1965)

      • One died 2 years later with identical symptoms

      • First proven case of infectious encephalopathy

      • Nobel Prize in Medicine (1976)


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