Seminar

Exploring plasma extracellular vesicles as carriers of infectious prion proteins in blood

Paula Saá, PhD

Extracellular vesicles (EVs) were originally considered to be a cellular mechanism to eliminate unwanted proteins. Recent investigations however, have attributed new roles to these vesicles including intercellular communication and infectious agent dissemination, among others. Little is known about the distribution of prions (the agents implicated in transmissible spongiform encephalopathies, TSEs) in blood. Transfusion of non-leukoreduced red blood cells from asymptomatic donors that subsequently developed variant Creutzfeldt Jacob disease (vCJD), a human form of TSE, resulted in disease transmission to four recipients. Recently, disease-associated prion protein, PrPres, was detected in whole blood of vCJD cases. These findings and the uncertainty about the number of vCJD-infected people question the safety of blood and its derivatives and stress the need of reliable tests for early detection of infected individuals. Cellular prion protein, PrPC, and its misfolded counterpart, PrPres, have been identified in EVs from various TSE cell culture models; and EVs obtained from TSE-infected cell conditioned media have caused clinical disease in mice. Moreover, EVs isolated from blood components contain PrPC. Importantly, this finding raised concerns about the potential spread of PrPres via EVs. In this study we isolated EVs from plasma samples of wild type (wt) and transgenic mice infected with human TSE agents and demonstrated the colocalization of PrPTSE with plasma EVs, obtained from preclinical and clinically sick animals, for the first time. Moreover, we established a new mo-vCJD model, with PrP-overexpressing Tga20 transgenic mice manifesting clinical signs after shorter incubation time than wt mice (104 vs. 140 days). We confirmed presence of PrPres in plasma EV preparations from these animals by PMCA and determined the shortest post-infection period for prionemia detection. The temporal pattern of PrPres in EVs was compared with PrPres occurrence in spleen (potential source of prions in blood) and brain. Our experiments provide an invaluable foundation for the development of new diagnostics and potential targets for TSEs treatment. Further characterization of PrPres-containing microvesicles may lead to the identification of the cellular origin of prion-containing EVs and the site(s) of prion replication in blood. Support The study was partially supported by Fondation Alliance BioSecure, France.