Sialylation Controls Prion Fate in Vivo

Prions or PrP^Sc are proteinaceous infectious agents that consist of misfolded, self-replicating states of a sialoglycoprotein called the prion protein or PrP^C The current work tests a new hypothesis that sialylation determines the fate of prions in an organism. To begin, we produced control PrP^Sc from PrP^C using protein misfolding cyclic amplification with beads (PMCAb), and also generated PrP^Sc with reduced sialylation levels using the same method but with partially desialylated PrP^C as a substrate (dsPMCAb). Syrian hamsters were inoculated intraperitoneally with brain-derived PrP^Sc or PrP^Sc produced in PMCAb or dsPMCAb and then monitored for disease. Animals inoculated with brain- or PMCAb-derived PrP^Sc developed prion disease, whereas administration of dsPMCAb-derived PrP^Sc with reduced sialylation did not cause prion disease. Animals inoculated with dsPMCAb-derived material were not subclinical carriers of scrapie, as no PrP^Sc was detected in brains or spleen of these animals by either Western blotting or after amplification by serial PMCAb. In subsequent experiments, trafficking of brain-, PMCAb-, and dsPMCAb-derived PrP^Sc to secondary lymphoid organs was monitored in wild type mice. PrP^Sc sialylation was found to be critical for effective trafficking of PrP^Sc to secondary lymphoid organs. By 6 hours after inoculation, brain- and PMCAb-derived PrP^Sc were found in spleen and lymph nodes, whereas dsPMCAb-derived PrP^Sc was found predominantly in liver. This study demonstrates that the outcome of prion transmission to a wild type host is determined by the sialylation status of the inoculated PrP^Sc Furthermore, this work suggests that the sialylation status of PrP^Sc plays an important role in prion lymphotropism.