Prions of ruminants show distinct splenotropisms in an ovine transgenic mouse model

Abstract

Background: Transmissible agents involved in prion diseases differ in their capacities to target different regions of the central nervous system and lymphoid tissues, which are also host-dependent.

Methodology/principal findings: Protease-resistant prion protein (PrP(res)) was analysed by Western blot in the spleen of transgenic mice (TgOvPrP4) that express the ovine prion protein under the control of the neuron-specific enolase promoter, after infection by intra-cerebral route with a variety of transmissible spongiform encephalopathies (TSEs) from cattle and small ruminants. Splenic PrP(res) was consistently detected in classical BSE and in most natural scrapie sources, the electrophoretic pattern showing similar features to that of cerebral PrP(res). However splenic PrP(res) was not detected in L-type BSE and TME-in-cattle, or in the CH1641 experimental scrapie isolate, indicating that some TSE strains showed reduced splenotropism in the ovine transgenic mice. In contrast with CH1641, PrP(res) was also consistently detected in the spleen of mice infected with six natural "CH1641-like" scrapie isolates, but then showed clearly different molecular features from those identified in the brains (unglycosylated PrP(res) at approximately 18 kDa with removal of the 12B2 epitope) of ovine transgenic mice or of sheep. These features included different cleavage of the main PrP(res) cleavage product (unglycosylated PrP(res) at approximately 19 kDa with preservation of the 12B2 epitope) and absence of the additional C-terminally cleaved PrP(res) product (unglycosylated form at approximately 14 kDa) that was detected in the brain.

Conclusion/significance: Studies in a transgenic mouse model expressing the sheep prion protein revealed different capacities of ruminant prions to propagate in the spleen. They showed unexpected features in "CH1641-like" ovine scrapie suggesting that such isolates contain mixed conformers with distinct capacities to propagate in the brain or lymphoid tissues of these mice.

Figure 1. Western blot analysis of PrP^res in the spleen and brain of TgOvPrP4 mice.

PrP^res from the spleen (lanes S) and brain (lanes B) was extracted from TgOvPrP4 mice infected with classical scrapie or bovine TSEs. PrP^res was detected using Sha31 (panels B and C) or 12B2 (panel A) antibody. Note that the equivalent tissue quantities loaded per lane, indicated by figures at the bottom of each panel (in tenths of mg), were much higher from the spleens than from the brain in L-type BSE (50×) and TME-in-cattle (200×). Bars to the left indicate the 29.0 and 20.1 kDa marker positions.

Figure 2. Western blot analysis of “CH1641-like” scrapie isolates in TgOvPrP4 mice.

PrP^res in the spleen (lanes S in panels A and B, panel D) and brain (lanes B in panels A and B, panel C) were compared in TgOvPrP4 mice infected with natural “CH1641-like” and experimental CH1641 scrapie isolates. PrP^res was detected using Sha31 (panel A), 12B2 (panel B) or SAF84 (panels C and D) antibody. Note that the equivalent tissue quantities loaded per lane, indicated by figures at the bottom of each panel (in tenths of mg), were much higher from the spleen than from the brain in CH1641 (30×). The arrow indicates the position of the monoglycosylated band of the C-terminal PrP^res product and the head arrows indicate the 22–25 kDa band. Bars to the left indicate the 29.0 and 20.1 kDa marker positions in panels A and B, as well as the 14.3 kDa marker position in panels C and D.