Assessing the susceptibility of transgenic mice overexpressing deer prion protein to bovine spongiform encephalopathy

Abstract

Several transgenic mouse models have been developed which facilitate the transmission of chronic wasting disease (CWD) of cervids and allow prion strain discrimination. The present study was designed to assess the susceptibility of the prototypic mouse line, Tg(CerPrP)1536(+/-), to bovine spongiform encephalopathy (BSE) prions, which have the ability to overcome species barriers. Tg(CerPrP)1536(+/-) mice challenged with red deer-adapted BSE resulted in 90% to 100% attack rates, and BSE from cattle failed to transmit, indicating agent adaptation in the deer.

FIG 1

Susceptibility of Tg(CerPrP)1536^+/− mice to BSE and cervid-adapted BSE. (A) Survival curves of Tg(CerPrP)1536^+/− mice inoculated with bovine BBP12/92 and cervid D1 and D2 isolates. Mice with confirmed clinical TSE status affect the profile of the curve, and they are indicated as downward-oriented steps. TSE-negative mice are indicated by upward-oriented marks. Downward-oriented marks indicate TSE-confirmed mice which died prior to the development of clinical signs. The last two categories of subjects were treated as intercurrent deaths and do not alter the profile of the curve. (B) Lesion profiles of cervid-adapted BSE isolates D1 and D2 in Tg(CerPrP)1536^+/− mice. IC, intracerebral challenge; IC&IP, combined intracerebral and intraperitoneal challenge. Lesion profiles depicting means and standard errors of the means (SEMs) of the results from experiments performed with at least five clinically positive mice per brain area are shown. Gray matter areas were scored as follows: G1, dorsal medulla nuclei, including cochlear nuclei; G2, granular layer of the cerebellar cortex adjacent to the fourth ventricle; G3, superior colliculus; G4, hypothalamus; G5, thalamus; G6, hippocampus; G7, septal nuclei of the paraterminal body; G8, cerebral cortex (at the level of G4 and G5); and G9, cerebral cortex (at the level of G7). White matter areas were scored as follows: W1, cerebellar white matter; W2, mesencephalic tegmentum; and W3, the cerebral peduncles.

FIG 2

Immunohistochemical staining of PrP^Sc in the central nervous system (CNS) of a diseased Tg(CerPrP)1536^+/− mouse. (A) PrP^Sc-specific deposits in the hippocampal and dorsal thalamic areas of a mouse challenged with cervid-adapted BSE. (B) Lack of PrP^Sc-specific deposits in Tg(CerPrP)1536^+/− mice challenged with the BBP12/92 BSE inoculum. Bars, 500 μm.

FIG 3

Western blot of Tg(CerPrP)1536^+/− mice challenged with cervid-passaged BSE and cattle-derived BSE. BBP 12/92, bovine BSE brain pool; D1 inoculum and D2 inoculum, 10% brain homogenates of diseased European red deer challenged with BBP12/92; D1 and D2, mice challenged with D1 inoculum and D2 inoculum, respectively; IC, intracerebral challenge; IC&IP, combined intracerebral and intraperitoneal challenge; BBP12/92 inoculum, a 10% homogenate of BBP12/92 which was used to inoculate European red deer that were used as deer BSE sources in the current study; BBP12/92 IC or IC&IP, mice were inoculated with BBP12/92 inoculum IC or IC&IP, respectively. Samples were diluted to give optimal band definition. The equivalent values for wet weight tissue loaded per lane were as follows: BBP12/92, 0.05 mg; D1 inoculum, 0.19 mg; D1 IC, 0.06 mg; D1 IC/IP, 0.19 mg; D2 inoculum, 0.19 mg; D2 IC, 0.06 mg; D2 IC/IP, 0.075 mg; BBP12/92 inoculum, 0.19 mg; BBP12/92 IC and BPP12/92 IC/IP, 3.75 mg. Note that equal amounts of tissue (0.19 mg per lane) were loaded for all inocula.