Distinct transmissibility features of TSE sources derived from ruminant prion diseases by the oral route in a transgenic mouse model (TgOvPrP4) overexpressing the ovine prion protein

Abstract

Transmissible spongiform encephalopathies (TSEs) are a group of fatal neurodegenerative diseases associated with a misfolded form of host-encoded prion protein (PrP). Some of them, such as classical bovine spongiform encephalopathy in cattle (BSE), transmissible mink encephalopathy (TME), kuru and variant Creutzfeldt-Jakob disease in humans, are acquired by the oral route exposure to infected tissues. We investigated the possible transmission by the oral route of a panel of strains derived from ruminant prion diseases in a transgenic mouse model (TgOvPrP4) overexpressing the ovine prion protein (A136R154Q171) under the control of the neuron-specific enolase promoter. Sources derived from Nor98, CH1641 or 87V scrapie sources, as well as sources derived from L-type BSE or cattle-passaged TME, failed to transmit by the oral route, whereas those derived from classical BSE and classical scrapie were successfully transmitted. Apart from a possible effect of passage history of the TSE agent in the inocula, this implied the occurrence of subtle molecular changes in the protease-resistant prion protein (PrPres) following oral transmission that can raises concerns about our ability to correctly identify sheep that might be orally infected by the BSE agent in the field. Our results provide proof of principle that transgenic mouse models can be used to examine the transmissibility of TSE agents by the oral route, providing novel insights regarding the pathogenesis of prion diseases.

Figure 1. Survival periods and PrPres detection of individual TgOvPrP4 mice challenged by oral versus intra-cerebral route.

▵: intra-cerebral, O: oral. Empty circles or triangles correspond to PrPres negative mice whereas full circles or full triangles represent PrPres positive mice.

Figure 2. Western blot of brain PrPres in TgOvPrP4 mice infected with classical scrapie or BSE.

Mice were challenged by oral (lane 5–8) or the intra-cerebral route (lanes 1–4). A) Western blot detection of PrPres by Sha 31 antibody of different sources derived from classical BSE in cattle (lanes 1, 5), classical BSE in sheep (lanes 2, 6), C506M3 scrapie strain (lanes 3, 7) and natural classical scrapie isolate (lanes 4, 8). The equivalent tissue quantities loaded per lane are indicated at the bottom of each lane. Bars to the left indicate the 29.0 and 20.1 kDa marker positions. B) Differences of the unglycosylated PrPres apparent molecular masses compared to that in mice infected with source derived from ovine BSE by the same inoculation route (means +/− SD of 5 repeated assays). The raw apparent molecular mass of unglycosylated PrPres is indicated for the ovine BSE infected mouse. C) Tern-plot representation of the proportions of diglycosylated (H), monoglycosylated (M) and unglycosylated (L) bands of PrPres for different sources derived from classical BSE in cattle (□), classical BSE in sheep (▵), C506M3 scrapie strain (X) and natural classical scrapie isolate (+) (blue: intra-cerebral, red: oral). The means for all repetitions (n = 5) are plotted.

Figure 3. Western profiles in TgOvPrP4 mice infected with source derived from a natural scrapie isolate.

PrPres detected, using SAF84 antibody, from four individual TgOvPrP4 mice infected with a natural scrapie isolate , at the second passage by the intra-cerebral route (lanes 1–4). PrPres of TgOvPrP4 mice infected with the C506M3 and CH1641 experimental scrapie sources were used as controls. A) The apparent molecular mass measured for the unglycosylated PrPres band in this representative Western blot is indicated at the bottom of each lane. Bars to the left indicate the 29.0 and 20.1 kDa marker positions. B) PrPres was analysed after PNGase deglycosylation. Bars to the left indicate the 20.1 and 14.3 kDa marker positions.

Figure 4. Western blot of spleen PrPres in TgOvPrP4 mice infected with classical scrapie or BSE.

Mice were challenged by oral (lane 5–8) or the intra-cerebral route (lanes 1–4). A) Western blot detection of PrPres by Sha 31 antibody of different sources derived from classical BSE in cattle (lanes 1, 5), classical BSE in sheep (lanes 2, 6), C506M3 scrapie strain (lanes 3, 7) and natural classical scrapie isolate (lanes 4, 8). The equivalent tissue quantities loaded per lane are indicated at the bottom of each lane. Bars to the left indicate the 29.0 and 20.1 kDa marker positions. B) Differences of the unglycosylated PrPres apparent molecular masses compared to that in mice infected with source derived from ovine BSE by the same inoculation route (means +/− SD of 5 repeated assays). The raw apparent molecular mass of unglycosylated PrPres is indicated for the ovine BSE infected mouse. C) Tern-plot representation of the proportions of diglycosylated (H), monoglycosylated (M) and unglycosylated (L) bands of PrPres for different sources derived from classical BSE in cattle (□), classical BSE in sheep (▵), C506M3 scrapie strain (X) and natural classical scrapie isolate (+) (blue: intra-cerebral, red: oral). The means for all repetitions (n = 5) are plotted.