Compelling transgenetic evidence for transmission of bovine spongiform encephalopathy prions to humans

Abstract

There is growing concern that bovine spongiform encephalopathy (BSE) may have passed from cattle to humans. We report here that transgenic (Tg) mice expressing bovine (Bo) prion protein (PrP) serially propagate BSE prions and that there is no species barrier for transmission from cattle to Tg(BoPrP) mice. These same mice were also highly susceptible to a new variant of Creutzfeldt-Jakob disease (nvCJD) and natural sheep scrapie. The incubation times (approximately 250 days), neuropathology, and disease-causing PrP isoforms in Tg(BoPrP)Prnp(0/0) mice inoculated with nvCJD and BSE brain extracts were indistinguishable and differed dramatically from those seen in these mice injected with natural scrapie prions. Our findings provide the most compelling evidence to date that prions from cattle with BSE have infected humans and caused fatal neurodegeneration.

Figure 1

Vacuolation histograms in Tg(BoPrP)Prnp^0/0 mice inoculated with BSE, nvCJD, and scrapie prions. The BSE and nvCJD histograms are very similar and both are different from scrapie (Sc). Mean and standard deviations are shown. NC, neocortex; Hp, hippocampus; Th, thalamus; Hb, habenula; Hy, hypothalamus; Cd, caudate nucleus; BF, basal forebrain; BS, pontine and midbrain tegmentum; PG, periaqueductal gray. N = the number of animals analyzed.

Figure 2

Amyloid plaques in Tg(BoPrP)Prnp^0/0 mice inoculated with BSE and nvCJD prions. Subcallosal PrP-immunopositive amyloid plaques (C and E) and coarse nonamyloid PrP deposits (D and F) are characteristic of BSE (C and D) and nvCJD (E and F) and not of scrapie (A and B). Staining was performed as described in Materials and Methods. (Bar in F = 25 μm.)

Figure 3

Regional distribution of PrP^Sc in the brains of Tg(BoPrP) mice inoculated with BSE prions. The neuroanatomic distribution of protease-resistant PrP^Sc was virtually identical in Tg(BoPrP)Prnp^0/0 mice inoculated with BSE (C and D) and nvCJD (E and F) prions but different from that found in mice inoculated with sheep scrapie (Sc) prions (A and B). The distribution of PrP^Sc correlates well with the vacuolation scores in Fig. 1. A, C, and E are coronal sections of the cerebral hemispheres at the level of the thalamus and hippocampus. B, D, and F are coronal sections through the pons and cerebellum. Am, amygdala; GC, granule cell layer of cerebellar cortex; Hb, habenula; Hp, hippocampus; Hy, hypothalamus; IC, internal capsule; NC, neocortex; N7, facial nerve; Py, pyramidal tract; S5, spinal tract of trigeminal nerve; Th, thalamus; ZI, zona incerta.

Figure 4

Characterization of PrP^Sc fragments by immunoblot. Western blots of PrP in brains from Tg mice inoculated with BSE, nvCJD, and sporadic CJD (sCJD) prions. Lane 1, undigested PG31/90 BSE brain. Lane 2, PG31/90 BSE brain control. Lanes 3 and 4, Tg(BoPrP)4125/Prnp^0/0 mice clinically ill after inoculation with BSE inocula PG31/90 and GJ248/85, respectively. Lanes 5 and 6, Tg(BoPrP)4125/Prnp^0/0 mice clinically ill after inoculation with PG31/90 and GJ248/85, respectively, after a single serial passage in Tg(BoPrP)4125/Prnp^0/0 mice. Lanes 7 and 8, Tg(BoPrP)4125/Prnp^0/0 mice clinically ill after inoculation with prions from nvCJD patient RU96/02. Lane 9, sCJD, patient RG. Lane 10, nvCJD patient RU96/02. A is an exposure selected to clearly show differences in the PrP glycoform ratios. B is a longer exposure of lanes 7–10, selected to make the lower molecular weight unglycosylated fragment more evident.