alpha-cleavage of PrPC by Aspirin suppresses prion infection

Abstract

Background: The conversion of the cellular prion protein, PrPC, into its pathogenic form, PrPSc, is the hallmark of prion diseases. In physiological conditions, PrPC can be cleaved at α-site, which generates the C1 and N1 fragments, and disrupts a region critical for conversion into PrPSc. Plasmin is known as an enzyme that cleaves PrPC at α-site; however, the function of plasmin in prion propagation remains elusive. In the current study, the role of plasmin and Aspirin, known to stimulate plasmin activity, in α-cleavage of PrPC and prion suppression was investigated.

Material and Methods: The effect of plasmin and Aspirin was evaluated using an in vitro assay, which mimics the aggregation process of prion protein into amyloids. In the cell-based model, ScN2a cells were incubated with Aspirin and endogenous plasmin activity was measured. The generation of C1 and N1 fragments were also detected by immunoblotting. The elimination of PrPSc by Aspirin was investigated in ScN2a. Finally, the ability of Aspirin to interfere with the susceptibility of N2a to prions was determined using standard scrapie cell assay.

Results: Aspirin promoted plasmin activity by inducing α-cleavage of PrP, resulting in the inhibition of PrP aggregation in vitro. Moreover, the endogenous plasmin activity in the ScN2a was significantly enhanced by the action of Aspirin. The generation of C1 fragment was increased in the membrane fraction of the cells incubated with Aspirin, indicating that Aspirin activated α- cleavage of PrPC. In addition, Aspirin significantly reduced the level of PrPSc in cells permanently infected with prions. Finally, Aspirin significantly decreased the number of N2a cells infected with prions.

Conclusions: Aspirin promoting plasmin-mediated α-cleavage of PrPC suppressed PrPSc propagation.