Prion protein in sheep urine.

The misfolded form of cellular prion protein (PrP(C)) is the main component of the infectious agent of transmissible spongiform encephalopathies and the validated biomarker for these diseases. The expression of PrP(C) is highest in the central nervous system and has been found in peripheral tissues. Soluble PrP(C) has been detected in cerebrospinal fluid, urine, serum, milk, and seminal plasma. In this study, attempts were made to characterize prion protein in urine samples from normal and scrapie-infected sheep. Urine samples from scrapie-infected sheep and age-matched healthy sheep were collected and analyzed by Western blot following concentration. A protease K-sensitive protein band with a molecular weight of approximately 27-30 kDa was visualized after immunoblotting with anti-PrP monoclonal antibodies to a C-terminal part of PrP(C), but not after immunoblotting with monoclonal antibodies to an N-terminal epitope of PrP(C) or with secondary antibodies only. The amount of PrP(C) in the urine of 49 animals (control group: n = 16; naturally scrapie-infected group: n = 33) was estimated by comparison with known amounts of ovine recombinant PrP in the immunoblot. Background concentration of PrP(C) in urine was found to be 0-0.16 ng/ml (adjusted to the initial nonconcentrated volume of the urine samples). Seven out of 33 naturally scrapie-infected animals had an elevated level (0.3-4.7 ng/ml) of PrP(C) in urine. The origin of PrP(C) in urine and the reason for the increased level of PrP(C) in scrapie-infected sheep urine has yet to be explored.