Bovine PrP expression levels in transgenic mice influence transmission characteristics of atypical bovine spongiform encephalopathy

Until recently, transmissible spongiform encephalopathy (TSE) disease in cattle was thought to be caused by a single agent strain, bovine spongiform encephalopathy (BSE) (classical BSE or BSE-C). However, due to the initiation of a large-scale surveillance programme throughout Europe, two atypical BSE strains, bovine amyloidotic spongiform encephalopathy (BASE, also named BSE-L) and BSE-H have since been discovered. These atypical BSE isolates have been previously transmitted to a range of transgenic mouse models overexpressing PrP from different species at different levels, on a variety of genetic backgrounds. To control for genetic background and expression level in the analysis of these isolates, we performed here a comprehensive comparison of the neuropathological and molecular properties of all three BSE agents (BASE, BSE-C and BSE-H) upon transmission into the same gene-targeted transgenic mouse line expressing the bovine prion protein (Bov6) and a wild-type control of the same genetic background. Significantly, upon challenge with these BSE agents, we found that BASE did not produce shorter survival times in these mice compared with BSE-C, contrary to previous studies using overexpressing bovine transgenic mice. Amyloid plaques were only present in mice challenged with atypical BSE and neuropathological features, including intensity of PrP deposition in the brain and severity of vacuolar degeneration were less pronounced in BASE compared with BSE-C-challenged mice

Variable tau accumulation in murine models with abnormal prion protein deposits

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177The conversion of cellular prion protein (PrP) into a misfolded isoform is central to the development of prion diseases. However, the heterogeneous phenotypes observed in prion disease may be linked with the presence of other misfolded proteins in the brain. While hyperphosphorylated tau (p.tau) is characteristic of Alzheimer's disease (AD), p.tau is also observed in human prion diseases. To explore this association in the absence of potential effects due to aging, drug treatment, agonal stage and postmortem delay we analyzed p.tau and PrP immunopositivity in mouse models. Analyses were performed on mice inoculated with prion agents, and mice with PrP amyloid in the absence of prion disease. We observed that p.tau was consistently present in animals with prion infectivity (models that transmit disease upon serial passage). In contrast, p.tau was very rarely observed or absent in mice with PrP amyloid plaques in the absence of prion replication. These data indicate that the formation of p.tau is not linked to deposition of misfolded PrP, but suggest that the interaction between replication of infectivity and host factors regulate the formation of p.tau and may contribute to the heterogeneous phenotype of prion diseases.https://doi.org/10.1016/j.jns.2017.10.040383pubpubDecember 201

Experimental Bovine Spongiform Encephalopathy in Squirrel Monkeys:The Same Complex Proteinopathy Appearing after Very Different Incubation Times

Incubation periods in humans infected with transmissible spongiform encephalopathy (TSE) agents can exceed 50 years. In humans infected with bovine spongiform encephalopathy (BSE) agents, the effects of a “species barrier,” often observed when TSE infections are transmitted from one species to another, would be expected to increase incubation periods compared with transmissions of same infectious agents within the same species. As part of a long-term study investigating the susceptibility to BSE of cell cultures used to produce vaccines, we inoculated squirrel monkeys (Saimiri sp., here designated SQ) with serial dilutions of a bovine brain suspension containing the BSE agent and monitored them for as long as ten years. Previously, we showed that SQ infected with the original “classical” BSE agent (SQ-BSE) developed a neurological disease resembling that seen in humans with variant CJD (vCJD). Here, we report the final characterization of the SQ-BSE model. We observed an unexpectedly marked difference in incubation times between two animals inoculated with the same dilution and volume of the same C-BSE bovine brain extract on the same day. SQ-BSE developed, in addition to spongiform changes and astrogliosis typical of TSEs, a complex proteinopathy with severe accumulations of protease-resistant prion protein (PrP(TSE)), hyperphosphorylated tau (p-tau), ubiquitin, and α-synuclein, but without any amyloid plaques or β-amyloid protein (Aβ) typical of Alzheimer’s disease. These results suggest that PrP(TSE) enhanced the accumulation of several key proteins characteristically seen in human neurodegenerative diseases. The marked variation in incubation periods in the same experimental TSE should be taken into account when modeling the epidemiology of human TSEs

Prion protein interacts with bace1 and differentially regulates its activity towards wild type and swedish mutant amyloid precursor protein

In Alzheimer disease amyloid-β (Aβ) peptides derived from the amyloid precursor protein (APP) accumulate in the brain. Cleavage of APP by the β-secretase BACE1 is the rate-limiting step in the production of Aβ. We have reported previously that the cellular prion protein (PrP(C)) inhibited the action of BACE1 toward human wild type APP (APP(WT)) in cellular models and that the levels of endogenous murine Aβ were significantly increased in PrP(C)-null mouse brain. Here we investigated the molecular and cellular mechanisms underlying this observation. PrP(C) interacted directly with the prodomain of the immature Golgi-localized form of BACE1. This interaction decreased BACE1 at the cell surface and in endosomes where it preferentially cleaves APP(WT) but increased it in the Golgi where it preferentially cleaves APP with the Swedish mutation (APP(Swe)). In transgenic mice expressing human APP with the Swedish and Indiana familial mutations (APP(Swe,Ind)), PrP(C) deletion had no influence on APP proteolytic processing, Aβ plaque deposition, or levels of soluble Aβ or Aβ oligomers. In cells, although PrP(C) inhibited the action of BACE1 on APP(WT), it did not inhibit BACE1 activity toward APP(Swe). The differential subcellular location of the BACE1 cleavage of APP(Swe) relative to APP(WT) provides an explanation for the failure of PrP(C) deletion to affect Aβ accumulation in APP(Swe,Ind) mice. Thus, although PrP(C) exerts no control on cleavage of APP(Swe) by BACE1, it has a profound influence on the cleavage of APP(WT), suggesting that PrP(C) may be a key protective player against sporadic Alzheimer disease

Insights into Mechanisms of Chronic Neurodegeneration

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177Chronic neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and prion diseases are characterised by the accumulation of abnormal conformers of a host encoded protein in the central nervous system. The process leading to neurodegeneration is still poorly defined and thus development of early intervention strategies is challenging. Unique amongst these diseases are Transmissible Spongiform Encephalopathies (TSEs) or prion diseases, which have the ability to transmit between individuals. The infectious nature of these diseases has permitted in vivo and in vitro modelling of the time course of the disease process in a highly reproducible manner, thus early events can be defined. Recent evidence has demonstrated that the cell-to-cell spread of protein aggregates by a “prion-like mechanism” is common among the protein misfolding diseases. Thus, the TSE models may provide insights into disease mechanisms and testable hypotheses for disease intervention, applicable to a number of these chronic neurodegenerative diseases.https://doi.org/10.3390/ijms1701008217pubpub

Allelic Origin of Protease-Sensitive and Protease-Resistant Prion Protein Isoforms in Gerstmann-Sträussler-Scheinker Disease with the P102L Mutation

Gerstmann-Sträussler-Scheinker (GSS) disease is a dominantly inherited prion disease associated with point mutations in the Prion Protein gene. The most frequent mutation associated with GSS involves a proline-to-leucine substitution at residue 102 of the prion protein, and is characterized by marked variability at clinical, pathological and molecular levels. Previous investigations of GSS P102L have shown that disease-associated pathological prion protein, or PrPSc, consists of two main conformers, which under exogenous proteolysis generates a core fragment of 21 kDa and an internal fragment of 8 kDa. Both conformers are detected in subjects with spongiform degeneration, whereas only the 8 kDa fragment is recovered in cases lacking spongiosis. Several studies have reported an exclusive derivation of protease-resistant PrPSc isoforms from the mutated allele; however, more recently, the propagation of protease-resistant wild-type PrPSc has been described. Here we analyze the molecular and pathological phenotype of six GSS P102L cases characterized by the presence of 21 and 8 kDa PrP fragments and two subjects with only the 8 kDa PrP fragment. Using sensitive protein separation techniques and Western blots with antibodies differentially recognizing wild-type and mutant PrP we observed a range of PrPSc allelic conformers, either resistant or sensitive to protease treatment in all investigated subjects. Additionally, tissue deposition of protease-sensitive wild-type PrPSc molecules was seen by conventional PrP immunohistochemistry and paraffin-embedded tissue blot. Our findings enlarge the spectrum of conformational allelic PrPSc quasispecies propagating in GSS P102L thus providing a molecular support to the spectrum of disease phenotypes, and, in addition, impact the diagnostic role of PrP immunohistochemistry in prion diseases

Variable tau accumulation in murine models with abnormal prion protein deposits

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177The conversion of cellular prion protein (PrP) into a misfolded isoform is central to the development of prion diseases. However, the heterogeneous phenotypes observed in prion disease may be linked with the presence of other misfolded proteins in the brain. While hyperphosphorylated tau (p.tau) is characteristic of Alzheimer's disease (AD), p.tau is also observed in human prion diseases. To explore this association in the absence of potential effects due to aging, drug treatment, agonal stage and postmortem delay we analyzed p.tau and PrP immunopositivity in mouse models. Analyses were performed on mice inoculated with prion agents, and mice with PrP amyloid in the absence of prion disease. We observed that p.tau was consistently present in animals with prion infectivity (models that transmit disease upon serial passage). In contrast, p.tau was very rarely observed or absent in mice with PrP amyloid plaques in the absence of prion replication. These data indicate that the formation of p.tau is not linked to deposition of misfolded PrP, but suggest that the interaction between replication of infectivity and host factors regulate the formation of p.tau and may contribute to the heterogeneous phenotype of prion diseases.https://doi.org/10.1016/j.jns.2017.10.040383pubpubDecember 201

Insights into mechanisms of chronic neurodegeneration

Chronic neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and prion diseases are characterised by the accumulation of abnormal conformers of a host encoded protein in the central nervous system. The process leading to neurodegeneration is still poorly defined and thus development of early intervention strategies is challenging. Unique amongst these diseases are Transmissible Spongiform Encephalopathies (TSEs) or prion diseases, which have the ability to transmit between individuals. The infectious nature of these diseases has permitted in vivo and in vitro modelling of the time course of the disease process in a highly reproducible manner, thus early events can be defined. Recent evidence has demonstrated that the cell-to-cell spread of protein aggregates by a “prion-like mechanism” is common among the protein misfolding diseases. Thus, the TSE models may provide insights into disease mechanisms and testable hypotheses for disease intervention, applicable to a number of these chronic neurodegenerative diseases

Ablation of prion protein in wild type human amyloid precursor protein (APP) transgenic mice does not alter the proteolysis of APP, levels of amyloid-β or pathologic phenotype

The cellular prion protein (PrPC) has been proposed to play an important role in the pathogenesis of Alzheimer's disease. In cellular models PrPC inhibited the action of the β-secretase BACE1 on wild type amyloid precursor protein resulting in a reduction in amyloid-β (Aβ) peptides. Here we have assessed the effect of genetic ablation of PrPC in transgenic mice expressing human wild type amyloid precursor protein (line I5). Deletion of PrPC had no effect on the α- and β-secretase proteolysis of the amyloid precursor protein (APP) nor on the amount of Aβ38, Aβ40 or Aβ42 in the brains of the mice. In addition, ablation of PrPC did not alter Aβ deposition or histopathology phenotype in this transgenic model. Thus using this transgenic model we could not provide evidence to support the hypothesis that PrPC regulates Aβ production