Comparison of mRNA expression levels of selected genes in the brain stem of cattle naturally infected with classical and atypical BSE.

Since 2004 cases of atypical bovine spongiform encephalopathy (BSE) in older cattle are recorded on the basis of aberrant glycoprofiles of prion protein resistant to proteolysis (PrP(res)). The nature of those types of PrP(res) is still not fully understood but the epidemiological data indicate that their occurrence is rare. Hitherto, most BSE cases were studied on the basis of the features of pathological form of prion protein (PrP(Sc)) or lesions observed in the gray matter of the brain. Here we propose the gene expression profiling as a method to characterize and distinguish BSE types. Thus, the aim of the study was to compare the activity of some genes which are known to play a role in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Significant differences in the expression level of the selected genes in the brain stem were observed for 7 out of 11 genes tested when the results for BSE affected and healthy control animals were compared. Significant up-regulation of caspase 3, Bax and 14-3-3 protein encoding genes was apparent in the obex of all BSE affected cattle regardless of the prion type. Significant and unique to BSE H-type up-regulation was detected in prion and SOD1 genes, while BSE C-type was characterized by higher Bcl-2 and Fyn gene expression levels in respect to other BSE types and control animals. Different gene expression profiles of bovine brains infected with classical and atypical BSE indicate possible different pathogenesis or origin of the disease.

Coenzyme Q and protein/lipid oxidation in a BSE-infected transgenic mouse model.

Oxidative stress and antioxidants play an important role in neurodegenerative diseases. However, the exact participation of antioxidants in the evolution of prion diseases is still largely unknown. The aim of this study was to assess brain levels of coenzyme Q (CoQ), an endogenous lipophilic antioxidant, and the antioxidant/pro-oxidant status by determining oxidative damage to proteins and lipids after intracerebral bovine spongiform encephalopathy (BSE) infection of transgenic mice expressing bovine prion protein (PrP). Our results indicate that, whereas the ratio between the two CoQ homologues present in mice (CoQ(9) and CoQ(10)) is not altered by prion infection during the course of the disease, significant increases in total CoQ(9) and CoQ(10) were observed in BSE-infected mice 150 days after inoculation. This time point coincided with the first manifestation of PrP(Sc) deposition in nervous tissue. In addition, CoQ(9) and CoQ(10) levels, neuropathological alterations, and PrP(Sc) deposition in nervous tissues underwent further increases as the illness progressed. Lipid and protein oxidation were observed only at the final stage of the disease after clinical signs had appeared. These findings indicate upregulation of CoQ(9)- and CoQ(10)-dependent antioxidant systems in response to the increased oxidative stress induced by prion infection in nervous tissue. However, the induction of these endogenous antioxidant systems seems to be insufficient to prevent the development of the illness.

Slow neurodegeneration and transmissible spongiform encephalopathies/prion diseases. Hypothesis: a cycle involving repeated tyrosine kinase A activation could drive the development of TSEs.

Neurons are specialised non-mitogenic cells. They cannot be replaced after damage, but most survive the lifetime of the individual. This is achieved by a very specialised process of repair and regeneration. During this process, a phase of degeneration in the distal end of the damaged neuron occurs in response to tyrosine kinase activation by nerve growth factor, which results in removal of neuronal detritus from within the cell membrane. As this phase is completed the activity of tyrosine kinase is modulated and the regeneration phase begins. It is postulated that normal prions play a part in the modulation of tyrosine kinase activity; that abnormal prion isoforms may be damaged in the process releasing a few fragments of prion PrP106-126 and that these stimulate release of nerve growth factor, which activates tyrosine kinase once more, setting up the vicious spiral of slow neurodegeneration found in the transmissible spongiform encephalopathies.

Enhanced levels of scrapie responsive gene mRNA in BSE-infected mouse brain.

The expression of the mRNA of nine scrapie responsive genes was analyzed in the brains of FVB/N mice infected with bovine spongiform encephalopathy (BSE). The RNA transcripts of eight genes were overexpressed to a comparable extent in both BSE-infected and scrapie-infected mice, indicating a common series of pathogenic events in the two transmissible spongiform encephalopathies (TSEs). In contrast, the serine proteinase inhibitor spi 2, an analogue of the human alpha-1 antichymotrypsin gene, was overexpressed to a greater extent in the brains of scrapie-infected animals than in animals infected with BSE, reflecting either an agent specific or a mouse strain specific response. The levels of spi 2 mRNA were increased during the course of scrapie prior to the onset of clinical signs of the disease and the increase reached 11 to 45 fold relative to uninfected controls in terminally ill mice. Spi 2, in common with four of the other scrapie responsive genes studied, is known to be associated with pro-inflammatory processes. These observations underline the importance of cell reactivity in TSE. In addition, scrg2 mRNA the level of which is enhanced in TSE-infected mouse brain, was identified as a previously unrecognized long transcript of the murine aldolase C gene. However, the level of the principal aldolase C mRNA is unaffected in TSE. The increased representation of the longer transcript in the late stage of the disease may reflect changes in mRNA processing and/or stability in reactive astrocytes or in damaged Purkinje cells.