Intraepithelial and interstitial deposition of pathological prion protein in kidneys of scrapie-affected sheep

Prions have been documented in extra-neuronal and extra-lymphatic tissues of humans and various ruminants affected by Transmissible Spongiform Encephalopathy (TSE). The presence of prion infectivity detected in cervid and ovine blood tempted us to reason that kidney, the organ filtrating blood derived proteins, may accumulate disease associated PrPSc. We collected and screened kidneys of experimentally, naturally scrapie-affected and control sheep for renal deposition of PrPScfrom distinct, geographically separated flocks. By performing Western blot, PET blot analysis and immunohistochemistry we found intraepithelial (cortex, medulla and papilla) and occasional interstitial (papilla) deposition of PrPScin kidneys of scrapie-affected sheep. Interestingly, glomerula lacked detectable signals indicative of PrPSc. PrPScwas also detected in kidneys of subclinical sheep, but to significantly lower degree. Depending on the stage of the disease the incidence of PrPScin kidney varied from approximately 27% (subclinical) to 73.6% (clinical) in naturally scrapie-affected sheep. Kidneys from flocks without scrapie outbreak were devoid of PrPSc. Here we demonstrate unexpectedly frequent deposition of high levels of PrPScin ovine kidneys of various flocks. Renal deposition of PrPScis likely to be a pre-requisite enabling prionuria, a possible co-factor of horizontal prion-transmission in sheep.