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 (PrPSc) 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 PrPSc, extended the scrapie incubation period, and markedly reduced total RNA concentrations. These results prompted us to investigate whether RNA molecules are cofactors for PrPSc propagation. RNase A treatment of partially purified PrP and of 263K scrapie brain homogenates was sufficient to increase the sensitivity of PrPSc to proteinase K degradation. This is the first evidence that suggests that RNA molecules are a component of PrPSc. Treatment with RNase A alone and PrP 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 PrPSc and that oxidized molecules can be important in scrapie agent replication and prion infectivity.