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Propagation of RML prions in mice expressing PrP devoid of GPI anchor leads to formation of a novel, stable prion strain.

Mahal SP, Jablonski J, Suponitsky-Kroyter I, Oelschlegel AM, Herva ME, Oldstone M, Weissmann C - PLoS Pathog. (2012)

Bottom Line: PrP(C), a host protein which in prion-infected animals is converted to PrP(Sc), is linked to the cell membrane by a GPI anchor.We found that RML and ME7, but not 22L prions propagated in tgGPI⁻ brain developed novel cell tropisms, as determined by the Cell Panel Assay (CPA).Surprisingly, the levels of proteinase K-resistant PrP(Sc) (PrP(res)) in RML- or ME7-infected tgGPI⁻ brain were 25-50 times higher than in wild-type brain.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectology, Scripps Florida, Jupiter, Florida, United States of America.

ABSTRACT
PrP(C), a host protein which in prion-infected animals is converted to PrP(Sc), is linked to the cell membrane by a GPI anchor. Mice expressing PrP(C) without GPI anchor (tgGPI⁻ mice), are susceptible to prion infection but accumulate anchorless PrP(Sc) extra-, rather than intracellularly. We investigated whether tgGPI⁻ mice could faithfully propagate prion strains despite the deviant structure and location of anchorless PrP(Sc). We found that RML and ME7, but not 22L prions propagated in tgGPI⁻ brain developed novel cell tropisms, as determined by the Cell Panel Assay (CPA). Surprisingly, the levels of proteinase K-resistant PrP(Sc) (PrP(res)) in RML- or ME7-infected tgGPI⁻ brain were 25-50 times higher than in wild-type brain. When returned to wild-type brain, ME7 prions recovered their original properties, however RML prions had given rise to a novel prion strain, designated SFL, which remained unchanged even after three passages in wild-type mice. Because both RML PrP(Sc) and SFL PrP(Sc) are stably propagated in wild-type mice we propose that the two conformations are separated by a high activation energy barrier which is abrogated in tgGPI⁻ mice.

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Conjectural free energy profile.(A) The RML quasi-species in wild-type brain are confined to a set of wells separated from those of the SFL quasi-species by a high activation energy barrier. (B) In tgGPI− brain the transition to the “SFLGPI-” set of conformations is enabled by a lower activation energy barrier. (C) SFLGPI- prions introduced into wild-type brain can now occupy, and are trapped in, the set of “SFL wells” which was not accessible to RML prions in (A).
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ppat-1002746-g005: Conjectural free energy profile.(A) The RML quasi-species in wild-type brain are confined to a set of wells separated from those of the SFL quasi-species by a high activation energy barrier. (B) In tgGPI− brain the transition to the “SFLGPI-” set of conformations is enabled by a lower activation energy barrier. (C) SFLGPI- prions introduced into wild-type brain can now occupy, and are trapped in, the set of “SFL wells” which was not accessible to RML prions in (A).

Mentions: In all these cases the changes were reversed when the prions were propagated in the original environment; assuming that properties of prions are encoded by the precise conformation of the cognate PrPSc, we concluded that the conformational states underlying adaptation to the cellular environment are separated by low activation energy barriers which allowed reversible conformational switches leading to “strain variants” or “sub-strains” [75]. In contrast to these earlier results with 22L prions, we now report that when RML prions from wild-type brain were propagated in brain producing anchorless PrP, a GPI−-PrPSc conformer adapted to that environment evolved, and when this was transferred to wild-type mice, a novel conformation of wild-type PrPSc, which we designated SFL, distinct from that of the original RML, was stably maintained. Because SFL does not revert to RML, it must be either better adapted to propagation in wild-type brain, prevented from reverting by a high activation energy barrier or both (Figure 5). Of note, methods commonly used to distinguish strains, such as incubation period, western blotting or conformational stability assays could not differentiate between RML and SFL, whereas this was readily achieved with the Extended Cell Panel Assay (ECPA) [77]. ME7 also acquired distinct properties when propagated in tgGPI− brain, however it reverted to what appears to be its original form when passaged through wild-type brain. Strain switching has been observed previously in transfer between animal species, when 139A prions were transferred from mouse to hamster and back to mouse [78]; in that case, a different amino acid sequence in the intermediate host may have led to the adoption of a more favorable conformation, which was preserved when the prions were returned to the original host. Mutated PrPSc could be formed if accretion of GPI−-PrPC to wild-type seed entailed adoption of a conformation slightly different from that of the seed, or if wild-type PrPSc contained a variety of mutant seeds –possibly at a low level– to one or some of which the resident GPI−PrPC preferentially accreted, adopting its conformation [76].


Propagation of RML prions in mice expressing PrP devoid of GPI anchor leads to formation of a novel, stable prion strain.

Mahal SP, Jablonski J, Suponitsky-Kroyter I, Oelschlegel AM, Herva ME, Oldstone M, Weissmann C - PLoS Pathog. (2012)

Conjectural free energy profile.(A) The RML quasi-species in wild-type brain are confined to a set of wells separated from those of the SFL quasi-species by a high activation energy barrier. (B) In tgGPI− brain the transition to the “SFLGPI-” set of conformations is enabled by a lower activation energy barrier. (C) SFLGPI- prions introduced into wild-type brain can now occupy, and are trapped in, the set of “SFL wells” which was not accessible to RML prions in (A).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369955&req=5

ppat-1002746-g005: Conjectural free energy profile.(A) The RML quasi-species in wild-type brain are confined to a set of wells separated from those of the SFL quasi-species by a high activation energy barrier. (B) In tgGPI− brain the transition to the “SFLGPI-” set of conformations is enabled by a lower activation energy barrier. (C) SFLGPI- prions introduced into wild-type brain can now occupy, and are trapped in, the set of “SFL wells” which was not accessible to RML prions in (A).
Mentions: In all these cases the changes were reversed when the prions were propagated in the original environment; assuming that properties of prions are encoded by the precise conformation of the cognate PrPSc, we concluded that the conformational states underlying adaptation to the cellular environment are separated by low activation energy barriers which allowed reversible conformational switches leading to “strain variants” or “sub-strains” [75]. In contrast to these earlier results with 22L prions, we now report that when RML prions from wild-type brain were propagated in brain producing anchorless PrP, a GPI−-PrPSc conformer adapted to that environment evolved, and when this was transferred to wild-type mice, a novel conformation of wild-type PrPSc, which we designated SFL, distinct from that of the original RML, was stably maintained. Because SFL does not revert to RML, it must be either better adapted to propagation in wild-type brain, prevented from reverting by a high activation energy barrier or both (Figure 5). Of note, methods commonly used to distinguish strains, such as incubation period, western blotting or conformational stability assays could not differentiate between RML and SFL, whereas this was readily achieved with the Extended Cell Panel Assay (ECPA) [77]. ME7 also acquired distinct properties when propagated in tgGPI− brain, however it reverted to what appears to be its original form when passaged through wild-type brain. Strain switching has been observed previously in transfer between animal species, when 139A prions were transferred from mouse to hamster and back to mouse [78]; in that case, a different amino acid sequence in the intermediate host may have led to the adoption of a more favorable conformation, which was preserved when the prions were returned to the original host. Mutated PrPSc could be formed if accretion of GPI−-PrPC to wild-type seed entailed adoption of a conformation slightly different from that of the seed, or if wild-type PrPSc contained a variety of mutant seeds –possibly at a low level– to one or some of which the resident GPI−PrPC preferentially accreted, adopting its conformation [76].

Bottom Line: PrP(C), a host protein which in prion-infected animals is converted to PrP(Sc), is linked to the cell membrane by a GPI anchor.We found that RML and ME7, but not 22L prions propagated in tgGPI⁻ brain developed novel cell tropisms, as determined by the Cell Panel Assay (CPA).Surprisingly, the levels of proteinase K-resistant PrP(Sc) (PrP(res)) in RML- or ME7-infected tgGPI⁻ brain were 25-50 times higher than in wild-type brain.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectology, Scripps Florida, Jupiter, Florida, United States of America.

ABSTRACT
PrP(C), a host protein which in prion-infected animals is converted to PrP(Sc), is linked to the cell membrane by a GPI anchor. Mice expressing PrP(C) without GPI anchor (tgGPI⁻ mice), are susceptible to prion infection but accumulate anchorless PrP(Sc) extra-, rather than intracellularly. We investigated whether tgGPI⁻ mice could faithfully propagate prion strains despite the deviant structure and location of anchorless PrP(Sc). We found that RML and ME7, but not 22L prions propagated in tgGPI⁻ brain developed novel cell tropisms, as determined by the Cell Panel Assay (CPA). Surprisingly, the levels of proteinase K-resistant PrP(Sc) (PrP(res)) in RML- or ME7-infected tgGPI⁻ brain were 25-50 times higher than in wild-type brain. When returned to wild-type brain, ME7 prions recovered their original properties, however RML prions had given rise to a novel prion strain, designated SFL, which remained unchanged even after three passages in wild-type mice. Because both RML PrP(Sc) and SFL PrP(Sc) are stably propagated in wild-type mice we propose that the two conformations are separated by a high activation energy barrier which is abrogated in tgGPI⁻ mice.

Show MeSH
Related in: MedlinePlus