Cellular prion protein status in sheep: tissue-specific biochemical signatures

Abstract

Expression of the cellular prion protein PrPC is sine qua none for the development of transmissible spongiform encephalopathy and thus for the accumulation of the illness-associated conformer PrPSc. Therefore, the tissue distribution of PrPC at the protein level in both quantitative and qualitative terms was investigated. PrPC was quantified using a two-site enzyme immunometric assay which was calibrated with purified ovine recombinant prion protein (rPrP). The most PrPC-rich tissue was the brain, followed by the lungs, skeletal muscle, heart, uterus, thymus and tongue, which contained between 20- and 50-fold less PrPC than the brain. The PrPC content of these tissues seems to be comparable between sheep. Other organs, however, showed different, but low, levels of the protein depending on the animal examined. This was also the case for tissues from the gastrointestinal tract. The tissue containing the lowest concentration of PrPC was shown to be the liver, where PrPC was found to be between 564- and 16000-fold less abundant than in the brain. PrPC was concentrated from crude cellular extracts by immunoprecipitation using several monoclonal and polyclonal anti-ovine PrP antibodies. Interestingly, it was observed that the isoform profile of PrPC was tissue-specific. The most atypical electrophoretic profile of PrPC was found in the skeletal muscle, where two polypeptides of 32 and 35 kDa were detected.