Low-Dose Ionizing Radiation Affects Mesenchymal Stem Cells via Extracellular Oxidized Cell-Free DNA: A Possible Mediator of Bystander Effect and Adaptive Response.

V A Sergeeva,E M Malinovskaya,E S Ershova,O A Dolgikh,S V Kostyuk,A V Ermakov,S V Stukalov,L V Kameneva,S I Kutsev,N N Veiko,V L Izhevskaya,V P Veiko,A A Kalyanov,M S Konkova

doi:10.1155/2017/9515809

Abstract

We have hypothesized that the adaptive response to low doses of ionizing radiation (IR) is mediated by oxidized cell-free DNA (cfDNA) fragments. Here, we summarize our experimental evidence for this model. Studies involving measurements of ROS, expression of the NOX (superoxide radical production), induction of apoptosis and DNA double-strand breaks, antiapoptotic gene expression and cell cycle inhibition confirm this hypothesis. We have demonstrated that treatment of mesenchymal stem cells (MSCs) with low doses of IR (10 cGy) leads to cell death of part of cell population and release of oxidized cfDNA. cfDNA has the ability to penetrate into the cytoplasm of other cells. Oxidized cfDNA, like low doses of IR, induces oxidative stress, ROS production, ROS-induced oxidative modifications of nuclear DNA, DNA breaks, arrest of the cell cycle, activation of DNA reparation and antioxidant response, and inhibition of apoptosis. The MSCs pretreated with low dose of irradiation or oxidized cfDNA were equally effective in induction of adaptive response to challenge further dose of radiation. Our studies suggest that oxidized cfDNA is a signaling molecule in the stress signaling that mediates radiation-induced bystander effects and that it is an important component of the development of radioadaptive responses to low doses of IR.

Highlights

Human beings are constantly exposed to background sources of ionizing radiation (IR) both of natural and artificial origin [1]
We first demonstrated that treatment of mesenchymal stem cells (MSCs) with low-dose ionizing radiation (LDIR) (10 cGy) increases the level of 8-oxodG in cell-free DNA (cfDNA) obtained from the culture medium 2–2.5-fold
We constructed a plasmid containing a DNA fragment that contains a (G)n repeat that is easy to oxidize, which penetrates into the cytoplasm of MSCs when they are irradiated as shown by fluorescence microscopy

Summary

Introduction

Human beings are constantly exposed to background sources of IR both of natural (terrestrial and cosmic) and artificial origin (nuclear energy, nuclear accidents, radiation for medical purposes) [1]. The biological effects of low-dose ionizing radiation (LDIR) exposure are still not adequately understood. There are many published reports available, the understanding of fundamental biological processes and signaling pathways involved in the response to LDIR in human cells is still inconsistent and not fully conclusive [2]. NOX4 mRNA in treated cells compared to control (three biological replicates). Gate R encircles the fraction of MSCs with elevated values of FL1-NOX4 (flow cytometry). (c) Distribution of cells treated with 10 cGy radiation according to the FL1-NOX4 signal strength (flow cytometry). LDIR or addition of cfDNAox and cfDNAoxR fragments to the medium elevates the level of cells with multiple DNA breaks 3–5-fold within 20 min (Figures 6(c) and 6(d)), but after 2 h, this level decreases and only cells containing very few breaks are present (Figure 6(d)). Unoxidized gDNA and cfDNA fragments do not induce DNA breaks during the first 2 h of incubation

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