Upregulation of the Genes Encoding Lysosomal Hydrolases, a Perforin-Like Protein, and Peroxidases in the Brains of Mice Affected with an Experimental Prion Disease

Abstract

In an attempt to identify the molecules involved in the pathogenesis of prion diseases, we performed cDNA subtraction on the brain tissues of mice affected with an experimental prion disease and the unaffected control. The genes identified as being upregulated in the prion-affected brain tissue included those encoding a series of lysosomal hydrolases (lysozyme M and both isoforms of ␤-N-acetylhexosaminidase), a perforin-like protein (macrophage proliferation-specific gene-1 [MPS-1]), and an oxygen radical scavenger (peroxiredoxin). Dramatic increases in the expression level occurred at between 12 and 16 weeks after intracerebral inoculation of the prion, coinciding with the onset of spongiform degeneration. The proteinase K-resistant prion protein (PrP Sc ) became detectable by immunoblotting well before 12 weeks, suggesting a causal relationship between this and the gene activation. Immunohistochemistry paired with in situ hybridization on sections of the affected brain tissue revealed that expression of the peroxiredoxin gene was detectable only in astrocytes and was noted throughout the affected brain tissue. On the other hand, the genes for the lysosomal hydrolases and MPS-1 were overexpressed exclusively by microglia, which colocalized with the spongiform morphological changes. A crucial role for microglia in the spongiform degeneration by their production of neurotoxic substances, and possibly via the aberrant activation of the lysosomal system, would have to be considered.

Identification of Upregulated Genes in Scrapie-Infected Brain Tissue

“…High LAPTm5 expression levels are associated with an increased lysosomal activity of microglial cells in the vicinity of spongiform histological changes (37). This observation further substantiates the possible involvement of an aberrant activation of the microglial lysosomal system in neurodegeneration (26). 2Ј,5Ј-Oligo(A) synthetase is most likely expressed by glial as well as neuronal cells (2).…”

Unique inflammatory RNA profiles of microglia in Creutzfeldt–Jakob disease

“…The most potently induced transcript in CJD microglia was that of lysozyme M, an important bacteriolytic enzyme expressed in activated macrophages. Lysozyme M has previously been identified as an up-regulated gene in CJD brain (16) and Sindbis virus infections of the nervous system (17). In CJD infection, this up-regulation likely reflects a general increase in lysosomal proteolytic activity, because it was accompanied by the induction of several lysosomal proteases, with concomitant downregulation of protease inhibitors (Fig.…”

Identification of Genes Involved in the Host Response to Neurovirulent Alphavirus Infection

“…Although some of these genes such as the proteasomal components are involved in antigen processing, the upregulated expression of genes involved in lysosomal, ubiquitin-mediated, and other forms of proteolysis could have additional, as yet undefined effects on the pathogenesis of CNS viral infections. For example, a role for upregulation of the gene encoding lysosomal M (the protein degradation gene with the greatest increase in expression in dsTE12H-infected brains) has been postulated to play a role in microglia-induced neurotoxic injury and the generation of spongiform changes in the brains of mice affected with an experimental prion disease (32). We also observed decreases in expression of several host genes encoding proteins that localize to synaptic nerve terminals and are involved in synaptic function (e.g., endophilin, ␣-SNAP, ankyrin G, complexin II, and heat shock cognate protein 70), although these decreases were modest and it is difficult to speculate on their biological significance.…”