Genes that are expressed differentially in the central nervous system of mice during infection with mouse-adapted scrapie agents were identified in this study. cDNA microarrays were used to examine gene-expression profiles at early, middle (preclinical) and late (clinical) time points after inoculation. A number of genes that showed significant changes in expression during the clinical stage of disease were identified. Of these, 138 were upregulated and 20 were downregulated. A smaller number of genes showed differential expression at the early and middle stages of the disease time course. These genes are interesting, as they may reflect biological processes that are involved in the molecular pathogenesis of the prion agent. At present, little is known about the early events in the disease process that trigger neurodegeneration. Perhaps most interestingly, one group of genes that exhibited decreased expression in all tested stages of the disease was identified in this study. This cluster included four transcripts representing haematopoietic system-related genes, which suggests that the haematopoietic system is involved in the disease process from an early stage.

Detection of the abnormal or the pathogenic form of prion protein (PrP(Sc)) by Western blot (WB) is challenging, especially, for samples derived from cell cultures that contain low levels of PrP(Sc). A variety of PrP(Sc) concentration methods have been reported with various PrP(Sc) recovery efficiencies. Ultracentrifugation is one of the methods used frequently to enrich the pathogenic form of PrP(Sc) prior to WB analyses. The resulting PrP(Sc) pellet is extremely insoluble and often requires sonication to be dissolved, potentially generating aerosols. We modified the common protein-precipitating protocol using trichloroacetic acid to concentrate PrP(Sc) by slow-speed centrifugation, followed by solubilization of the pellets with 6 mol/L urea prior to sodium dodecyl sulphate -- polyacrylamide gel electrophoresis and WB analyses. Comparative studies suggest this simple trichloroacetic acid protocol was more effective in enriching PrP(Sc) presented in cell cultures and brain homogenates than other reported protein-precipitating methods. Furthermore, incorporation of the urea treatment step to dissolve the precipitated PrP(Sc) pellets helped to reduce the infectivity of PrP(Sc).