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The Strain Problem

The Strain Problem. Taylor Goldbeck. Laura Manuelidis - Who is she?. Professor and Head of Neuropathology at Yale- Department of Surgery and Faculty of Neurosciences and Virology Focuses on dementia was emphasis on TSEs

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The Strain Problem

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  1. The Strain Problem Taylor Goldbeck

  2. Laura Manuelidis- Who is she? • 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”

  3. How do viral strains occur?

  4. Prion Strains • 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

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

  6. High CJD Infectivity Remains After Prion Protein is Destroyed • 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?

  7. Evidence for Viral Genome • 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.

  8. Your Thoughts- • 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?

  9. Evidence for Viral Genome • “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

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

  11. Evidence for prion protein-only hypothesis • 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

  12. “The fact that they behave like viruses doesn’t mean they’re anything like a virus”- Weissman (coauthor) • 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?

  13. Other evidence for prion protein-only hypothesis • Back to PrPglycosylation • 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. International Journal of Cellular Biology. 1-24 Soto, C and Castilla, J. (2004). The controversial protein-only hypothesis of prion propagation. Nature medicine. 563-567

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