Reduction of prion infectivity and levels of scrapie prion protein by lithium aluminum hydride: Implications for RNA in prion diseases

Previous studies indicate that RNA may be required for proteinase-resistant prion protein (PrP) amplification and for infectious prion formation in vitro, suggesting that RNA molecules may function as cellular cofactors for abnormal PrP (PrP^Sc) formation and become part of the structure of the infectious agent. To address this question, we used chemicals that can cleave phosphodiester bonds of RNA and assessed their effects on the infectious agent. Lithium aluminum hydride, a reducing agent that can induce reductive cleavage of oxidized molecules such as carbonyls, carboxyl acids, esters, and phosphodiester bonds, did not affect cellular PrP degradation; however, it destroyed PrP^Sc, extended the scrapie incubation period, and markedly reduced total RNA concentrations. These results prompted us to investigate whether RNA molecules are cofactors for PrP propagation. RNase A treatment of partially purified PrP^Sc and of 263K scrapie brain homogenates was sufficient to increase the sensitivity of PrP^Sc to proteinase K degradation. This is the first evidence that suggests that RNA molecules are a component of PrP^Sc. Treatment with RNase A alone and PrP^Sc degradation by RNase A plus proteinase K in vitro, however, did not result in loss of scrapie infectivity compared with the effects of lithium aluminum hydride. Together, these data suggest that RNA molecules may be important for maintaining the structure of PrP^Sc and that oxidized molecules can be important in scrapie agent replication and prion infectivity.