Evidence of p75 Neurotrophin Receptor Involvement in the Central Nervous System Pathogenesis of Classical Scrapie in Sheep and a Transgenic Mouse Model

Neurotrophins constitute a group of growth factor that exerts important functions in the nervous system of vertebrates. They act through two classes of transmembrane receptors: tyrosine-kinase receptors and the p75 neurotrophin receptor (p75(NTR)). The activation of p75(NTR) can favor cell survival or apoptosis depending on diverse factors. Several studies evidenced a link between p75(NTR) and the pathogenesis of prion diseases. In this study, we investigated the distribution of several neurotrophins and their receptors, including p75(NTR), in the brain of naturally scrapie-affected sheep and experimentally infected ovinized transgenic mice and its correlation with other markers of prion disease. No evident changes in infected mice or sheep were observed regarding neurotrophins and their receptors except for the immunohistochemistry against p75(NTR). Infected mice showed higher abundance of p75(NTR) immunostained cells than their non-infected counterparts. The astrocytic labeling correlated with other neuropathological alterations of prion disease. Confocal microscopy demonstrated the co-localization of p75(NTR) and the astrocytic marker GFAP, suggesting an involvement of astrocytes in p75(NTR)-mediated neurodegeneration. In contrast, p75(NTR) staining in sheep lacked astrocytic labeling. However, digital image analyses revealed increased labeling intensities in preclinical sheep compared with non-infected and terminal sheep in several brain nuclei. This suggests that this receptor is overexpressed in early stages of prion-related neurodegeneration in sheep. Our results confirm a role of p75(NTR) in the pathogenesis of classical ovine scrapie in both the natural host and in an experimental transgenic mouse model.