PrPC Governs Susceptibility to Prion Strains in Bank Vole, While Other Host Factors Modulate Strain Features

Abstract

Bank vole is a rodent species that shows differential susceptibility to the experimental transmission of different prion strains. In this work, the transmission features of a panel of diverse prions with distinct origins were assayed both in bank vole expressing methionine at codon 109 (Bv109M) and in transgenic mice expressing physiological levels of bank vole PrP^C (the BvPrP-Tg407 mouse line). This work is the first systematic comparison of the transmission features of a collection of prion isolates, representing a panel of diverse prion strains, in a transgenic-mouse model and in its natural counterpart. The results showed very similar transmission properties in both the natural species and the transgenic-mouse model, demonstrating the key role of the PrP amino acid sequence in prion transmission susceptibility. However, differences in the PrP^Sc types propagated by Bv109M and BvPrP-Tg407 suggest that host factors other than PrP^C modulate prion strain features.

Importance: The differential susceptibility of bank voles to prion strains can be modeled in transgenic mice, suggesting that this selective susceptibility is controlled by the vole PrP sequence alone rather than by other species-specific factors. Differences in the phenotypes observed after prion transmissions in bank voles and in the transgenic mice suggest that host factors other than the PrP^C sequence may affect the selection of the substrain replicating in the animal model.

FIG 1

Brain PrP^C expression in a homozygous BvPrP-Tg407 mouse line in comparison to Bv109M brain detected with the 2A11 MAb. The immunoblots illustrate a representative set of three independent experiments, and the diagrams represent the mean quantification using the Image Lab program after capture with ChemiDoc XRS+ under nonsaturating conditions. The data from the Bv109M brain were considered 1 relative unit. Molecular masses (in kDa) are shown on the right of the blot.

FIG 2

Western blot analysis of brain PrP^res from Bv109M or from BvPrP-Tg407 (Tg407) mice detected with Sha31 (A) or 12B2 (B) MAb. Animals were infected with the different Bv109M-adapted prions as indicated at the top. Similar quantities of PrP^res (according to the Sha31 MAb) were loaded in each lane for better comparison. The same quantities of PrP^res were loaded in both panels. Molecular masses (in kDa) are shown at the left of the blots.

FIG 3

Glycoform analysis of PrP^res from Bv109M and BvPrP-Tg407 (Tg407) inoculated with SS7/vole (A), SS3/vole (B), 139A/vole (C), or Ca-BSE/vole (D). PrP^res was detected by Western blotting using the Sha31 MAb as for Fig. 2. The data shown are the means of at least four measurements in two or more different Western blots using the Image Lab program after capture with ChemiDoc XRS+ under nonsaturating conditions. The error bars indicate SD.

FIG 4

Conformational stability and solubility assay of different prion strains in BvPrP-Tg407 and Bv109M. Shown are dose-response curves of conformational stability of brain PrP^Sc from BvPrP-Tg407 (Tg407) and Bv109M inoculated with SS-7/vole (A), SS-3/vole (B), Ca-BSE-1/vole (C), and 139 A/vole (D). The curves were obtained by plotting the fraction of PrP^Sc remaining in the pellet as a function of the GdnHCl concentration and best fitted using a four-parameter logistic equation. Individual curves were combined within each strain group. The [GdnHCl]_1/2 values of SS-7/vole, SS-3/vole, Ca-BSE-1/vole, and 139/vole were 2.04 M, 1.88 M, 1.82 M, and 1.64 M, respectively, in Bv109M and 2.16 M, 1.83 M, 1.80 M, and 1.53 M in BvPrP-Tg407. The error bars indicate SD.

FIG 5

Western blot analysis of brain PrP^res from either Bv109M or BvPrP-Tg407 (Tg407) mice infected with prion isolates from different species detected with Sha31 (A) or 12B2 (B) MAb: cattle (Ca-BSE H and Ca-BSE), sheep (Sh-BSE, SS-10, and SS-N799-97), or human (sCJD and vCJD). PrP^res of brain from Bv109M infected with Ca-BSE was from the second passage in Bv109M. Similar quantities of PrP^res (according to the Sha31 MAb) were loaded in each lane for better comparison. The same quantities of PrP^res were loaded in both panels. Molecular masses (in kDa) are shown at the left of the blots.

FIG 6

Kaplan-Meier survival curves of Bv109M inoculated on second passages with brains of sheep-BSE- or vCJD-infected Bv109M with 18 kDa (solid lines) or 17 kDa (dashed lines) PrP^res. The original inoculum used for each group is indicated at the top of each panel, except for panel A, which compiles all groups of Bv109M-inoculated animals included in panels B, C, and D. P was calculated by the log-rank (Mantel-Cox) test.