1 / 15

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

avon
Télécharger la présentation

The Strain Problem

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related