Transmissible spongiform encephalopathies arise as a consequence of infection of the central nervous system by prions, where neurons and glial cells are regarded as primary targets. Neuronal loss and gliosis, associated with the accumulation of misfolded prion protein (PrP), are hallmarks of prion diseases; yet the mechanisms underlying such disorders remain unclear. Here we introduced a cell system based on primary cerebellar cultures established from transgenic mice expressing ovine PrP and then exposed to sheep scrapie agent. Upon exposure to low doses of infectious agent, such cultures, unlike cultures originating from PrP null mice, were found to accumulate de novo abnormal PrP and infectivity, as assessed by mouse bioassay. Importantly, using astrocyte and neuron͞astrocyte cocultures, both cell types were found capable of sustaining efficient prion propagation independently, leading to the production of proteinase K-resistant PrP of the same electrophoretic profile as in diseased brain. Moreover, contrasting with data obtained in chronically infected cell lines, late-occurring apoptosis was consistently demonstrated in the infected neuronal cultures. Our results provide evidence that primary cultured neural cells, including postmitotic neurons, are permissive to prion replication, thus establishing an approach to study the mechanisms involved in prion-triggered neurodegeneration at a cellular level.T ransmissible spongiform encephalopathies (TSE), which include Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy in cattle, and scrapie in sheep, are fatal neurodegenerative disorders caused by prions, a class of unconventional agents that targets the CNS in mammals. A hallmark of prion diseases is the accumulation of abnormal prion protein (PrP Sc ), a misfolded form of the cellular PrP (PrP c ). Transmissibility is believed to stem from the ability of the prion isoform to promote the conformational transition from PrP c to PrP Sc . Biologically distinct prion strains can propagate in a same host, presumably through the perpetuation of different specific PrP Sc conformers (1-3).Although it seems clear that neuronal dysfunction must lie at the root of the clinical disorders observed in these diseases, it is still obscure what triggers neurodegeneration and what role nonneuronal cells may play in this process. There is ample evidence to support a primary role of the neurons in prion propagation and neuropathogenesis into the CNS. Intra-or perineuronal PrP Sc deposition, spongiform vacuolation involving cell soma and processes, and neuronal loss are typical histopathological changes observed in TSE-affected brain tissues (4, 5). Transgenic mice with PrP expression specifically targeted to neurons have been obtained that turned out to be fully susceptible to prion disease (6). More recently, it was shown that an acute neuron-targeted depletion of PrP in the brain of mice with ongoing infection is able to prevent neuronal loss and progression to disease and even to reverse early spongiform chang...

Mammalian prions exist as multiple strains which produce characteristic and highly reproducible phenotypes in defined hosts. How this strain diversity is encoded by a protein-only agent remains one of the most interesting and challenging questions in biology with wide relevance to understanding other diseases involving the aggregation or polymerisation of misfolded host proteins. Progress in understanding mammalian prion strains has however been severely limited by the complexity and variability of the methods used for their isolation from infected tissue and no high resolution structures have yet been reported. Using high-throughput cell-based prion bioassay to re-examine prion purification from first principles we now report the isolation of prion strains to exceptional levels of purity from small quantities of infected brain and demonstrate faithful retention of biological and biochemical strain properties. The method’s effectiveness and simplicity should facilitate its wide application and expedite structural studies of prions.

Disease-related PrPSc [pathogenic PrP (prion protein)] is classically distinguished from its normal cellular precursor, PrPC(cellular PrP) by its detergent insolubility and partial resistance to proteolysis. Although molecular diagnosis of prion disease has historically relied upon detection of protease-resistant fragments of PrPSc using PK (proteinase K), it is now apparent that a substantial fraction of disease-related PrP is destroyed by this protease. Recently, thermolysin has been identified as a complementary tool to PK, permitting isolation of PrPSc in its full-length form. In the present study, we show that thermolysin can degrade PrPC while preserving both PK-sensitive and PK-resistant isoforms of disease-related PrP in both rodent and human prion strains. For mouse RML (Rocky Mountain Laboratory) prions, the majority of PK-sensitive disease-related PrP isoforms do not appear to contribute significantly to infectivity. In vCJD (variant Creutzfeldt–Jakob disease), the human counterpart of BSE (bovine spongiform encephalopathy), up to 90% of total PrP present in the brain resists degradation with thermolysin, whereas only ∼15% of this material resists digestion by PK. Detection of PK-sensitive isoforms of disease-related PrP using thermolysin should be useful for improving diagnostic sensitivity in human prion diseases.