The propagation of hamster-adapted scrapie PrPSc can be enhanced by reduced pyridine nucleotide in vitro

Establishment of a Special Platform for the Research of Prion and the Diagnosis of Human Prion Disease - China's Studies

The studies of prions and prion disease usually need many special platforms and techniques that differ from those for classical microbes. Search of new biomarkers and establishment of new methods for the diagnosis of human prion diseases are priorities in the field of prion study.

Protein Misfolding Cyclic Amplification Cross-Species Products of Mouse-Adapted Scrapie Strain 139A and Hamster-Adapted Scrapie Strain 263K with Brain and Muscle Tissues of Opposite Animals Generate Infectious Prions

Transmission of prions between mammalian species is limited by a "species barrier," a biological effect involving an increase in incubation period to decrease the percentage of animals succumbing to disease. In this study, we used protein misfolding cyclic amplification (PMCA) technique, which accelerates the conversion of prion proteins in vitro. Direct interspecies PMCA involving 144 cycles confirmed that both mouse-adapted scrapie strain 139A and hamster-adapted 263K could use brain homogenates of opposite species to form proteinase K (PK)-resistant PrP proteins (PrP^res). Newly formed interspecies prions could stably propagate themselves in subsequent serial PMCA passages. The two types of PMCA-generated cross-species PrP^res changed their glycosylation profiles, which was similar to that observed during interspecies infection by the mouse agent 139A in vivo. These profiles were distinct from individual seeded PrP^Sc and possessed properties of new hosts. Comparative analysis with respect to PK resistance showed no significant diversity between PMCA-PrP^res and native PrP^Sc or between brain and muscle PrP^res. However, PrP^res from the relatively early cycles of serial PMCA showed lower PK resistance than those from later cycles. Inoculation of these PMCA products amplified with homogeneous or heterogeneous brain tissues (cross-species products) induced experimental transmissible spongiform encephalopathies. These results suggested that PMCA can help prion strains to overcome species barrier and to propagate efficiently both in vitro and in vivo.

Insect cell-derived cofactors become fully functional after proteinase K and heat treatment for high-fidelity amplification of glycosylphosphatidylinositol-anchored recombinant scrapie and BSE prion proteins

The central event in prion infection is the conformational conversion of host-encoded cellular prion protein (PrP(C)) into the pathogenic isoform (PrP(Sc)). Diverse mammalian species possess the cofactors required for in vitro replication of PrP(Sc) by protein-misfolding cyclic amplification (PMCA), but lower organisms, such as bacteria, yeasts, and insects, reportedly lack the essential cofactors. Various cellular components, such as RNA, lipids, and other identified cofactor molecules, are commonly distributed in both eukaryotes and prokaryotes, but the reasons for the absence of cofactor activity in lower organisms remain to be elucidated. Previously, we reported that brain-derived factors were necessary for the in vitro replication of glycosylphosphatidylinositol-anchored baculovirus-derived recombinant PrP (Bac-PrP). Here, we demonstrate that following protease digestion and heat treatment, insect cell lysates had the functional cofactor activity required for Bac-PrP replication by PMCA. Mammalian PrP(Sc) seeds and Bac-PrP(Sc) generated by PMCA using Bac-PrP and insect cell-derived cofactors showed similar pathogenicity and produced very similar lesions in the brains of inoculated mice. These results suggested that the essential cofactors required for the high-fidelity replication of mammalian PrP(Sc) were present in the insect cells but that the cofactor activity was masked or inhibited in the native state. We suggest that not only RNA, but also DNA, are the key components of PMCA, although other cellular factors were necessary for the expression of the cofactor activity of nucleic acids. PMCA using only insect cell-derived substances (iPMCA) was highly useful for the ultrasensitive detection of PrP(Sc) of some prion strains.

Cyclic amplification of prion protein misfolding

Protein misfolding cyclic amplification (PMCA) is a technique that takes advantage of the nucleation-dependent prion replication process to accelerate the conversion of PrP(C) into PrP(Sc) in the test tube. PMCA uses ultrasound waves to fragment the PrP(Sc) polymers, increasing the amount of seeds present in the infected sample without affecting their ability to act as conversion nuclei. Over the past 5 years, PMCA has become an invaluable technique to study diverse aspects of prions. The PMCA technology has been used by several groups to understand the molecular mechanism of prion replication, the cellular factors involved in prion propagation, the intriguing phenomena of prion strains and species barriers, to detect PrP(Sc) in tissues and biological fluids, and to screen for inhibitors against prion replication. In this chapter, we describe a detailed protocol of the PMCA technique, highlighting some of the important technical aspects to obtain a successful and reproducible application of the technology.

Acute exposure to prion infection induces transient oxidative stress progressing to be cumulatively deleterious with chronic propagation in vitro

Neuronal loss is a pathological feature of prion diseases for which increased reactive oxygen species (ROS) and consequent oxidative stress is one proposed mechanism. The processes underlying ROS production in prion disease and the precise relationship to misfolding of the prion protein remain obscure. Using cell culture models of prion infection we found that cells demonstrate a rapid, prion protein (PrP) dependent, increase in intracellular ROS following exposure to infectious inoculum. ROS production correlated with internalisation and increased intracellular protease resistant PrP (PrP(Res)). The ROS increase was predominantly lysosomal in origin but not sustained, with cells adapting within 48 hours. Overall ROS levels remained normal in the chronically prion infected cell population; however a subpopulation characterised by loss of membrane phosphatidylserine asymmetry exhibited highly peroxidised intracellular aggregates that localised with PrP and intense caspase activation. These apoptotic cells showed increased ROS closely correlating with increased PrP(Res). Our findings demonstrate that a PrP-dependent, transient, increase in intracellular ROS is characteristic of acute cellular prion infection, while chronic phases of prion infection in vitro are associated with a significant subpopulation manifesting apoptosis accompanying heightened oxidative stress and increased PrP(Res) burden. Such observations strengthen the direct links between heightened ROS and ongoing prion propagation with eventual cellular demise.

Redox control of prion and disease pathogenesis

Imbalance of brain metal homeostasis and associated oxidative stress by redox-active metals like iron and copper is an important trigger of neurotoxicity in several neurodegenerative conditions, including prion disorders. Whereas some reports attribute this to end-stage disease, others provide evidence for specific mechanisms leading to brain metal dyshomeostasis during disease progression. In prion disorders, imbalance of brain-iron homeostasis is observed before end-stage disease and worsens with disease progression, implicating iron-induced oxidative stress in disease pathogenesis. This is an unexpected observation, because the underlying cause of brain pathology in all prion disorders is PrP-scrapie (PrP(Sc)), a beta-sheet-rich conformation of a normal glycoprotein, the prion protein (PrP(C)). Whether brain-iron dyshomeostasis occurs because of gain of toxic function by PrP(Sc) or loss of normal function of PrP(C) remains unclear. In this review, we summarize available evidence suggesting the involvement of oxidative stress in prion-disease pathogenesis. Subsequently, we review the biology of PrP(C) to highlight its possible role in maintaining brain metal homeostasis during health and the contribution of PrP(Sc) in inducing brain metal imbalance with disease progression. Finally, we discuss possible therapeutic avenues directed at restoring brain metal homeostasis and alleviating metal-induced oxidative stress in prion disorders.