Abstract

Extracellular Vesicle-Mediated Transfer of Functional RNA Between Tissues

Stefan Momma, Group Leader, University Hospital Frankfurt

Extracellular vesicles (EVs) emerge as important carriers for intercellular communication and they have been implicated in many biological processes. However, due to their small size and the difficulties of manipulating them, the data on EV biology has thus far been based mainly on in vitro or indirect in vivo evidence, or on experiments involving ex vivo manipulations. Furthermore, it is difficult to establish the exact cells of origin as well as individual cellular targets for in vivo experiments. Thus, the extent and pathogenic role of EV signalling in vivo, particularly with regard to the transfer of functional RNA, remains poorly understood. Using the Cre-Lox system we can overcome some of the major shortcomings in this field by establishing a method to trace the functional transfer of RNA by EVs in vivo. We could show that expression of Cre recombinase in transgenic mice as well as in tumour cells leads to the release of EVs containing Cre mRNA, but no measurable amounts of protein. In mice with a Cre reporter background, this leads to an irreversible induction of marker gene expression in cells receiving Cre EVs. In this way we could identify the direct transfer of functional RNA from blood to neurons in the brain as a novel route of communication between the immune system and the brain. Furthermore, this process is greatly enhanced by systemic inflammation. Additionally, we could show that the principal target cells of tumour-derived EVs in the tumour microenvironment are immune cells, particularly cells of the immature myeloid lineage (MDSCs) that can suppress the immune response. Thus we present a novel method to investigate the extent and function of EV mediated signalling in vivo.