Taylor Goldbeck

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Professor and Head of
Neuropathology at Yale-
Department of Surgery and
Faculty of Neurosciences and
Virology
Focuses on dementia was emphasis on TSEs
“We think it is most likely the host PrP is a required receptor for TSE viruses, and that viral
PrP-membrane interactions ultimately cause a pathological
PrP response. Ongoing experiments are designed to test this viral hypothesis”

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Prion strain- defined as “infectious isolates that, when transmitted to identical hosts, exhibit distinct prion-disease phenotypes”
Prion strain diversity first seen in goats
PrP-c and PrP-sc can be unglycosylated, monoglycosylated or diglycosylated.
Aguzzi, A., Heikenwalder, M., Polymenidou, M. (2007). Insights into prion strains and neurotoxicity. Nature . 8:552-561

Aguzzi et al. (2007). Insights into prion strains and neurotoxicity. Nature.
8): 552-561

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PrP-res
◦ Part of response, not the cause
◦ Host protein
“(i) The variety of unique and mutable agent strains, a property of nuclei acid not protein”
◦ Initial thoughts on this point?

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Manuelidis et al (1997)
Argue:
◦ Several strains, same PrP amino acid sequence
◦ Different phenotypes
 Due to PrP protein or hidden virus?
Experiment
◦ Change a CJD strain into a strain that produced plaques and cerebellar lesions
 Evaluated host recognition by responses of microglia and astrocytes
 Used inbred mice, guinea pigs, and rats.
 2/6 rats showed a response after first passage
Manueldis, L., Fritch, W., Xi, Y. (1997). Evolution of a strain of CJD that Induces
BSE-Like Plaques. Science . 277(5322): 94-98.

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If you were pro protein-only hypothesis, how would you explain the reactive microglia and astrocytes?
Authors state “Species barrier and host responses (reactive microglia, astrocytes, and development of new strain that can produce plaques/lesions from a strain that couldn’t before) to the foreign agent are too complex to just be explained by the host’s PrP sequence”
◦ If you were pro protein-only hypothesis, how would you respond to this?

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“TSE strains maintain their identity despite various changes in prion protein. This fact strongly implicates a relatively stable but mutable viral genome” (from Yale bio page)
Wanted to see whether PrP-res itself encoded intrinsic infectivity characteristics
Slow SY strain and fast virulent FU CJD strain infect GT1 cells into various cell lines
◦ Kept phenotypes through passage but remained indistinguishable by PrP-res banding or glycosylation patterns
 FU had different PrP-res patterns in different cell lines
 Still had same incubation time and clinical features
◦ Amount of PrP-res was not quantitatively related to infectivity
“It is the biology of these agents: their evolution spread, cell specificity, latency, virus-like interference capabilities and occusional mutation which continues to indicate a viral causative agent”
◦ Arjona et al. (2004). Two Creutzfeldt-Jakob disease agents reproduce prion protein-independent identities in cell cultures. PNAS . 101(23): 8768-8773

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Authors argue “These findings (two strains that have different phenotypes but same PrPres banding or glycosylation patterns) are problematic for the prion hypothesis where abnormal PrP folding or glycosylation, and hense PrP-res band patterns, are postulated to encode each agent strain”
◦ If you were pro- protein-only hypothesis, how would you respond?

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Methods: Exposed cells to various dilutions of prion samples, let the cells propagate, determined the proportion of PrP-sc containing cells by ELISA
◦ Strain 22L transferred from brain to PK1 cells
◦ In the presence of swainsonine, 22L-infected PK1 cells led to drug-resistant variants
◦ 22L prions transferred to R33 cell population
◦ R33 incompetent/swa-sensitive cells return to brain
Mahal et at. (2010). Transfer of a prion strain to different hosts leads to emergence of strain variants. PNAS . 107(52): 22653-22658

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Showed prions can adapt to survive in a new host environment
◦ When transferring from one cell line to another, prion properties chance
“Darwinian Evolution without DNA”
◦ Prions can develop mutations  drug resistance
◦ Fold in different ways  new strains
◦ Transferred to a new host  which strain ‘wins’?
Your thoughts
◦ If you were Manulidis, how would you respond to this paper?

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Back to PrP glycosylation
◦ Study by Cancellotti et al., (2013) showed that the passage of mice that expressed a PrP that either partially or completely lacked N-glycan affected the phenotypic characteristics of at least one TSE strain
Back to species barrier
◦ Quasispecies hypothesis
 Several PrP-sc conformations in infectious innoculum. One best suited for new host is selected for
 Problem- there isn’t a lot of evidence that a large number of conformations exists in an innoculum
 Another problem?
Explaining the relationship between PrP-res and infectivity
Poggiolini, I., Saverloni, D., Parchi, P. (2013). Prion Protein Misfolding, Strains, and Neurotoxicity:
An Update from Studies on Mammalian Prions.
Nature medicine . 563-567
International Journal of Cellular Biology . 1-24
Soto, C and Castilla, J. (2004). The controversial protein-only hypothesis of prion propagation.