BackgroundChronic wasting disease (CWD) is a prion disease affecting members of the Cervidae family. PrPC primary structures play a key role in CWD susceptibility resulting in extended incubation periods and regulating the propagation of CWD strains. We analyzed the distribution of abnormal prion protein (PrPCWD) aggregates in brain and peripheral organs from orally inoculated white-tailed deer expressing four different PRNP genotypes: Q95G96/Q95G96 (wt/wt), S96/wt, H95/wt and H95/S96 to determine if there are substantial differences in the deposition pattern of PrPCWD between different PRNP genotypes.ResultsAlthough we detected differences in certain brain areas, globally, the different genotypes showed similar PrPCWD deposition patterns in the brain. However, we found that clinically affected deer expressing H95 PrPC, despite having the longest survival periods, presented less PrPCWD immunoreactivity in particular peripheral organs. In addition, no PrPCWD was detected in skeletal muscle of any of the deer.ConclusionsOur data suggest that expression of H95-PrPC limits peripheral accumulation of PrPCWD as detected by immunohistochemistry. Conversely, infected S96/wt and wt/wt deer presented with similar PrPCWD peripheral distribution at terminal stage of disease, suggesting that the S96-PrPC allele, although delaying CWD progression, does not completely limit the peripheral accumulation of the infectious agent.

Prion diseases are a group of neurodegenerative disorders that can be spontaneous, familial or acquired by infection. The conversion of the prion protein PrPC to its abnormal and misfolded isoform PrPSc is the main event in the pathogenesis of prion diseases of all origins. In spontaneous prion diseases, the mechanisms that trigger the formation of PrPSc in the central nervous system remain unknown. Several reports have demonstrated that the accumulation of PrPSc can induce endoplasmic reticulum (ER) stress and proteasome impairment from the early stages of the prion disease. Both mechanisms lead to an increment of PrP aggregates in the secretory pathway, which could explain the pathogenesis of spontaneous prion diseases. Here, we investigate the role of ER stress and proteasome impairment during prion disorders in a murine model of spontaneous prion disease (TgVole) co-expressing the UbG76V-GFP reporter, which allows measuring the proteasome activity in vivo. Spontaneously prion-affected mice showed a significantly higher accumulation of the PKR-like ER kinase (PERK), the ER chaperone binding immunoglobulin protein (BiP/Grp78), the ER protein disulfide isomerase (PDI) and the UbG76V-GFP reporter than age-matched controls in certain brain areas. The upregulation of PERK, BiP, PDI and ubiquitin was detected from the preclinical stage of the disease, indicating that ER stress and proteasome impairment begin at early stages of the spontaneous disease. Strong correlations were found between the deposition of these markers and neuropathological markers of prion disease in both preclinical and clinical mice. Our results suggest that both ER stress and proteasome impairment occur during the pathogenesis of spontaneous prion diseases.

Autophagy is a dynamic cellular mechanism involved in protein and organelle turnover through lysosomal degradation. Autophagy regulation modulates the pathologies associated with many neurodegenerative diseases. Using sheep naturally infected with scrapie as a natural animal model of prion diseases, we investigated the regulation of autophagy in the central nervous system (CNS) during the clinical phase of the disease. We present a gene expression and protein distribution analysis of different autophagy-related markers and investigate their relationship with prion-associated lesions in several areas of the CNS. Gene expression of autophagy markers ATG5 and ATG9 was downregulated in some areas of scrapie brains. In contrast, ATG5 protein accumulates in medulla oblongata and positively correlates with prion deposition and scrapie-related lesions. The accumulation of this protein and p62, a marker of autophagy impairment, suggests that autophagy is decreased in the late phases of the disease. However, the increment of LC3 proteins and the mild expression of p62 in basal ganglia and cerebellum, primarily in Purkinje cells, suggests that autophagy machinery is still intact in less affected areas. We hypothesize that specific cell populations of the CNS may display neuroprotective mechanisms against prion-induced toxicity through the induction of PrPSc clearance by autophagy.