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International audience; Multiple theories exist regarding the origin of bovine spongiform encephalopathy (BSE). An early and prominent theory proposed that BSE was the result of the adaptation of sheep scrapie to cattle. The reports to date indicate that the distribution of the pathological prion protein (PrPSc) in experimental bovine scrapie is largely restricted to the central nervous system (CNS). Here, we describe pathological findings in a calf intracerebrally inoculated with a Spanish classical scrapie isolate. While clinical disease was observed 30 months after inoculation and PrPSc was detected in the CNS, the corresponding phenotype differed from that of BSE. Immunohistochemistry and PMCA also revealed the presence of PrPSc in the peripheral nerves, lymphoid tissues, skeletal muscle and gastrointestinal tract, suggesting centrifugal spread of the scrapie agent from the brain. To the best of our knowledge, this is the first report describing the detection of PrPSc in tissues other than the CNS after experimental transmission of scrapie to cattle.

International audience; AbstractExperimental transmission of the bovine spongiform encephalopathy (BSE) agent has been successfully reported in pigs inoculated via three simultaneous distinct routes (intracerebral, intraperitoneal and intravenous). Sheep derived BSE (Sh-BSE) is transmitted more efficiently than the original cattle-BSE isolate in a transgenic mouse model expressing porcine prion protein. However, the neuropathology and distribution of Sh-BSE in pigs as natural hosts, and susceptibility to this agent, is unknown. In the present study, seven pigs were intracerebrally inoculated with Sh-BSE prions. One pig was euthanized for analysis in the preclinical disease stage. The remaining six pigs developed neurological signs and histopathology revealed severe spongiform changes accompanied by astrogliosis and microgliosis throughout the central nervous system. Intracellular and neuropil-associated pathological prion protein (PrPSc) deposition was consistently observed in different brain sections and corroborated by Western blot. PrPSc was detected by immunohistochemistry and enzyme immunoassay in the following tissues in at least one animal: lymphoid tissues, peripheral nerves, gastrointestinal tract, skeletal muscle, adrenal gland and pancreas. PrPSc deposition was revealed by immunohistochemistry alone in the retina, optic nerve and kidney. These results demonstrate the efficient transmission of Sh-BSE in pigs and show for the first time that in this species propagation of bovine PrPSc in a wide range of peripheral tissues is possible. These results provide important insight into the distribution and detection of prions in non-ruminant animals.

International audience; Bovine spongiform encephalopathy (BSE) can be efficiently transmitted to pigs via intracerebral inoculation. A clear link has been established between the consumption of products of bovine origin contaminated with the BSE agent and the development of variant Creutzfeldt-Jakob disease in humans. Small ruminants can also naturally develop BSE, and sheep-adapted BSE (Sh-BSE) propagates more efficiently than cattle BSE in pigs and in mouse models expressing porcine prion protein. In addition, Sh-BSE shows greater efficiency of transmission to human models than original cow BSE. While infectivity and/or abnormal PrP accumulation have been reported in the central nervous system in BSE-infected pigs, the ability of the agent to replicate in peripheral tissues has not been fully investigated. We previously characterized the presence of prions in a panel of tissues collected at the clinical stage of disease from pigs experimentally infected with Sh-BSE. Western blot revealed low levels of PrPres accumulation in lymphoid tissues, nerves, and skeletal muscles from 4 of the 5 animals analysed. Using protein misfolding cyclic amplification (PMCA), which we found to be 6 log fold more sensitive than direct WB for the detection of pig BSE, we confirmed the presence of the Sh-BSE agent in lymphoid organs, nerves, ileum, and striated muscles from all 5 inoculated pigs. Surprisingly, PrPres positivity was also detected in white blood cells from one pig using this method. The presence of infectivity in lymphoid tissues, striated muscles, and peripheral nerves was confirmed by bioassay in bovine PrP transgenic mice. These results demonstrate the ability of BSE-derived agents to replicate efficiently in various peripheral tissues in pigs. Although no prion transmission has been reported in pigs following oral BSE challenge, our data support the continuation of the Feed Ban measure implemented to prevent entry of the BSE agent into the feed chain.

Background Prion diseases are characterized by the accumulation of the pathogenic PrPSc protein, mainly in the brain and the lymphoreticular system. Although prions multiply/accumulate in the lymph nodes without any detectable pathology, transcriptional changes in this tissue may reflect biological processes that contribute to the molecular pathogenesis of prion diseases. Little is known about the molecular processes that occur in the lymphoreticular system in early and late stages of prion disease. We performed a microarray-based study to identify genes that are differentially expressed at different disease stages in the mesenteric lymph node of sheep naturally infected with scrapie. Oligo DNA microarrays were used to identify gene-expression profiles in the early/middle (preclinical) and late (clinical) stages of the disease. Results In the clinical stage of the disease, we detected 105 genes that were differentially expressed (≥2-fold change in expression). Of these, 43 were upregulated and 62 downregulated as compared with age-matched negative controls. Fewer genes (50) were differentially expressed in the preclinical stage of the disease. Gene Ontology enrichment analysis revealed that the differentially expressed genes were largely associated with the following terms: glycoprotein, extracellular region, disulfide bond, cell cycle and extracellular matrix. Moreover, some of the annotated genes could be grouped into 3 specific signaling pathways: focal adhesion, PPAR signaling and ECM-receptor interaction. We discuss the relationship between the observed gene expression profiles and PrPSc deposition and the potential involvement in the pathogenesis of scrapie of 7 specific differentially expressed genes whose expression levels were confirmed by real time-PCR. Conclusions The present findings identify new genes that may be involved in the pathogenesis of natural scrapie infection in the lymphoreticular system, and confirm previous reports describing scrapie-induced alterations in the expression of genes involved in protein misfolding, angiogenesis and the oxidative stress response. Further studies will be necessary to determine the role of these genes in prion replication, dissemination and in the response of the organism to this disease.

Neuronal loss is one of the characteristics of scrapie neuropathology. Previous analysis of brains from sheep naturally infected with scrapie that were in a terminal stage did not detect a clear induction of apoptosis, although molecular changes were evidenced. As neuronal death could be occurring early in scrapie, we developed a neuropathological and gene expression study of sheep infected with scrapie in a presymptomatic stage. The histopathology, immunolabelling of PrP Sc , Bax and activated caspase-3, and the analysis of the expression of 7 genes involved in the regulation of the mitochondrial pathway of apoptosis were investigated in the following 4 central nervous system areas: medulla oblongata, diencephalon, frontal cortex and cerebellum. Moreover, TUNEL and NeuN immunolabelling was performed in the medulla oblongata. The PrP Sc immunolabelling in the four areas, as well as a neuropil spongiform change, were more evident in the terminal stage than in presymptomatic animals. Cytoplasmic Bax immunostaining was observed in the presymptomatic medulla oblongata. In contrast to symptomatic animals, the immunostaining was not extended to the hypothalamus, indicating the progression of Bax induction during the course of the disease. Although neither caspase-3 immunostaining nor the TUNEL technique detected neurons with apoptosis, NeuN-immunolabelled cell counting determined that presymptomatic animals have already suffered neuronal loss in a lower or equal degree than symptomatic animals. Finally, the gene expression profiles indicated that the mitochondrial pathway of apoptosis was activated with higher intensity in presymptomatic animals than in symptomatic sheep and confirmed the implication of genes such as BAX or AIF in the disease.