Absence of spontaneous disease and comparative prion susceptibility of transgenic mice expressing mutant human prion proteins.

Approximately 15 % of human prion disease is associated with autosomal-dominant pathogenic mutations in the prion protein (PrP) gene. Previous attempts to model these diseases in mice have expressed human PrP mutations in murine PrP, but this may have different structural consequences. Here, we describe transgenic mice expressing human PrP with P102L or E200K mutations and methionine (M) at the polymorphic residue 129. Although no spontaneous disease developed in aged animals, these mice were readily susceptible to prion infection from patients with the homotypic pathogenic mutation. However, while variant Creutzfeldt-Jakob disease (CJD) prions transmitted infection efficiently to both lines of mice, markedly different susceptibilities to classical (sporadic and iatrogenic) CJD prions were observed. Prions from E200K and classical CJD M129 homozygous patients, transmitted disease with equivalent efficiencies and short incubation periods in human PrP 200K, 129M transgenic mice. However, mismatch at residue 129 between inoculum and host dramatically increased the incubation period. In human PrP 102L, 129M transgenic mice, short disease incubation periods were only observed with transmissions of prions from P102L patients, whereas classical CJD prions showed prolonged and variable incubation periods irrespective of the codon 129 genotype. Analysis of disease-related PrP (PrP(Sc)) showed marked alteration in the PrP(Sc) glycoform ratio propagated after transmission of classical CJD prions, consistent with the PrP point mutations directly influencing PrP(Sc) assembly. These data indicate that P102L or E200K mutations of human PrP have differing effects on prion propagation that depend upon prion strain type and can be significantly influenced by mismatch at the polymorphic residue 129.

Dissociation of pathological and molecular phenotype of variant Creutzfeldt-Jakob disease in transgenic human prion protein 129 heterozygous mice.

All neuropathologically confirmed cases of variant Creutzfeldt-Jakob disease (vCJD), characterized by abundant florid plaques and type 4 disease-related prion protein (PrP(Sc)) in the brain, have been homozygous for methionine at polymorphic residue 129 of PRNP. The distinctive neuropathological and molecular phenotype of vCJD can be faithfully recapitulated in Prnp-null transgenic mice homozygous for human PrP M129 but not V129, where a distinct prion strain is propagated. Here we model susceptibility of 129MV heterozygotes, the most common PRNP genotype, in transgenic mice and show that, remarkably, propagation of type 4 PrP(Sc) was not associated with characteristic vCJD neuropathology. Depending on the source of the inoculum these mice can develop four distinct disease phenotypes after challenge with bovine spongiform encephalopathy (BSE) prions or vCJD (human-passaged BSE) prions. vCJD-challenged mice had higher attack rates of prion infection than BSE-challenged recipients. These data argue that human PRNP 129 heterozygotes will be more susceptible to infection with vCJD prions than to cattle BSE prions and may present with a neuropathological phenotype distinct from vCJD.

Phenotypic heterogeneity in inherited prion disease (P102L) is associated with differential propagation of protease-resistant wild-type and mutant prion protein.

Inherited prion diseases are caused by PRNP coding mutations and display marked phenotypic heterogeneity within families segregating the same pathogenic mutation. A proline-to-leucine substitution at prion protein (PrP) residue 102 (P102L), classically associated with the Gerstmann-Sträussler-Scheinker (GSS) phenotype, also shows marked clinical and pathological heterogeneity, including patients with a Creutzfeldt-Jakob disease (CJD) phenotype. To date, this heterogeneity has been attributed to temporal and spatial variance in the propagation of distinct protease-resistant (PrP(Sc)) isoforms of mutant PrP. Here, using a monoclonal antibody that recognizes wild-type PrP, but not PrP 102L, we reveal a spectrum of involvement of wild-type PrP(Sc) in P102L individuals. PrP(Sc) isoforms derived from wild-type and mutant PrP are distinct both from each other and from those seen in sporadic and acquired CJD. Such differential propagation of disease-related isoforms of wild-type PrP and PrP 102L provides a molecular mechanism for generation of the multiple clinicopathological phenotypes seen in inherited prion disease.

Human prion protein with valine 129 prevents expression of variant CJD phenotype.

Variant Creutzfeldt-Jakob disease (vCJD) is a unique and highly distinctive clinicopathological and molecular phenotype of human prion disease associated with infection with bovine spongiform encephalopathy (BSE)-like prions. Here, we found that generation of this phenotype in transgenic mice required expression of human prion protein (PrP) with methionine 129. Expression of human PrP with valine 129 resulted in a distinct phenotype and, remarkably, persistence of a barrier to transmission of BSE-derived prions on subpassage. Polymorphic residue 129 of human PrP dictated propagation of distinct prion strains after BSE prion infection. Thus, primary and secondary human infection with BSE-derived prions may result in sporadic CJD-like or novel phenotypes in addition to vCJD, depending on the genotype of the prion source and the recipient.

Pathogenic human prion protein rescues PrP null phenotype in transgenic mice.

Infectious prion diseases may be acquired, sporadic or inherited in their aetiology. Inherited prion diseases are caused by coding mutations in the prion protein (PrP) gene. We investigated whether one of the commonest of these mutations, E200K, results in a functionally inactive prion protein by expressing human PrP 200K in transgenic mice homozygous for murine PrP null alleles. We examined the intrinsic properties of hippocampal CA1 pyramidal cells in these mice by measuring the resting potential, time constants and amplitude of the slow after-hyperpolarisation (AHP). These mice show rescue of the reduced slow AHP electrophysiological phenotype found in PrP null mice. Using the AHP as a marker for PrP function, we conclude that this pathogenic PrP mutation, does not significantly affect the normal neuronal function of PrP.

BSE prions propagate as either variant CJD-like or sporadic CJD-like prion strains in transgenic mice expressing human prion protein.

Variant Creutzfeldt-Jakob disease (vCJD) has been recognized to date only in individuals homozygous for methionine at PRNP codon 129. Here we show that transgenic mice expressing human PrP methionine 129, inoculated with either bovine spongiform encephalopathy (BSE) or variant CJD prions, may develop the neuropathological and molecular phenotype of vCJD, consistent with these diseases being caused by the same prion strain. Surprisingly, however, BSE transmission to these transgenic mice, in addition to producing a vCJD-like phenotype, can also result in a distinct molecular phenotype that is indistinguishable from that of sporadic CJD with PrP(Sc) type 2. These data suggest that more than one BSE-derived prion strain might infect humans; it is therefore possible that some patients with a phenotype consistent with sporadic CJD may have a disease arising from BSE exposure.