Radiation exposure of peripheral mononuclear blood cells alters the composition and function of their extracellular vesicles

Normal tissue toxicity is a dose-limiting factor in radiation therapy. One component of normal tissue that is continuously exposed during therapeutic irradiation is the circulating population of peripheral blood mononuclear cells (PBMC). PBMCs are highly sensitive to ionizing radiation (IR), however little is known about how ionizing radiation (IR) affects the PBMC response on a systemic level. Therefore it was the aim of this study to investigate whether IR was capable to induce changes in the composition and function of extracellular vesicles (EVs) secreted from PBMCs after radiation exposure to different doses.Whole blood samples from healthy donors were irradiated with 0 Gy, 0.1 Gy, 2 Gy or 6 Gy X-rays and PBMC-secreted EVs were isolated 72 hours later. Proteome and miRNome analysis of EVs showed a dose-dependent increase in the number of significantly deregulated proteins and microRNAs. For both, proteome and microRNA data, principal component analysis showed a dose-dependent separation of control and exposed groups. Integrated pathway analysis of the radiation-regulated EV proteins and microRNAs consistently predicted an association of deregulated molecules with apoptosis, cell death and survival. Functional studies identified endothelial cells as an efficient EV recipient system, in which irradiation of recipient cells further increased the uptake. Furthermore we detected an apoptosis suppressive effect of EVs from irradiated PBMCs in endothelial recipient cells. In summary, our study demonstrates that IR modifies the communication between PBMCs and endothelial cells. We identified EVs from irradiated PBMC donors as transmitters of protective signals to irradiated endothelial cells. Thus our data may lead to the discovery of biomarker candidates for radiation dosimetry and even more importantly, they suggest EVs as a novel systemic communication pathway between irradiated and non-irradiated normal, non-cancer tissues.