Prion Diseases: Genetic Polymorphism & Susceptibility Insights

1. PrionsGenetic Polymorphism & Susceptibility Carlos Francisco Mendoza

2. Human Prion Diseases

3. Comparison of PrpC and PrpSc

4. Evidence Supports the Prion Hypothesis

5. Genetic Polymorphism RPSA Polymorphisms have no direct influence on susceptibility to sporadic CJD

8. Susceptibility Post-mortem Immunocytochemistry Showing partial Protease Resistance

10. Disease Transmission and Species Barrier Anne Busch

11. Introduction • Infectious protein agent w/o DNA or RNA • Progressive neurodegenerative diseases: Scrapie, CJD, BSE • In humans : dementia • In other animals : ataxia • Genetic, infectious, sporadic in origin • Involve modified isoform of PrP (mammals) • PrPsc: misfolded • PrPc: normal, constitutively expressed in healthy brain

12. Normal protein → infectious, pathogenic protease resistant protein • Exogenous PrPsc or overproduction of PrpC can cause disease • Brain extracts without pathogenic isoform can be infectious (mice models infected with bovine PrpSC are infectious but PrPSC undetectable) → maybe its not only a protein? • Prpc → prp* & host specific prpsc • Dynamic bistability & threshold properties

13. Conversion of PrPc to PrPsc • α- helix and coil structure -> β-sheet • PrPsc: 30% alphahelix, 45% beta sheet while PrpC is 30% alpha and a little beta (from FITR and CD studies) • PrPsc • 1* structure determined by Prp gene of host • Misfoldedisoform acts as template to convert PrPc into PrPsc within the cell • Faciliated by another protein • Resistant to proteolytic cleavage -> accumulation of extracellular plaques • Only differ in conformation? • One primary structure can lead to multiple conformations?

14. Infectious conversion not yet demonstrated in vivo BUT have shown PrP conversion to a protease resistant isoform, like PrPsc

15. Interspecies transmission Tissue from diseased cattle can infect mice, sheep, pigs, mink after intracerebralinjection Prolonged incubation period upon first passage into new host= species barrier De novo prions reflect host PrP sequence, not PrPsc sequence from donor Incubation time shortens upon subsequent passage into the new host

16. Species barrier • Due to differences in PrP sequence between species • Serial passage (intraspecies): incubation period shortens & pathological properties stabilize • After 3 passages incubation period stable → suggests intermediate conformation in primary infection PrP* which catalyzes formation of host PrPSC, which is autocatalytic

17. Species barrier • Depends on kinetic characteristics of of the conversion reaction of the prion protein

18. Factors contributing to Species Barrier • Difference in Prp sequence from donor to host • Depends on host • Species specificity of protein X: factor binds PrpC and facilitates conversion • Little is known about factor X but it assumed to be a protein

19. 3. Strain of prion • encoded in conformation and together with sequence determines tertiary structure • Infectious material from different sources produces distinct and reproducible patterns of incubation time, proteolytic resistance/cleavage, and distribution within the CNS

20. How can a genetic disease become infectious? • Conformational templating • Mechanism for generation and propagation • System with dynamic bistability and threshold properties

28. References Diego Kaski, Prion Diseases, Medicine 37:11, 2009 Wen-QuanZou, Modeling of human prions and prion diseases in vitro and in vivo, Vol. I, No. 2, 2004 Masato Enari, Scrapie prion protein accumulation by scrapie-infected neuroblastomacells abrogated by exposure to a prion protein antibody, PNAS, 9295-9299, 2001 Rodrigo Morales, The prion strain phenomenon: Molecular basis and unprecedented features, BBA, 681-691, 2007 Jisuk Yun, The first report of RPSA polymorphisms, also called 37/67kDa LRP/LR gene, in sporadic Creutzfeldt-Jakob disease (CJD).

29. Questions