Abstract
Stem cells contained within the dental mesenchymal stromal cell (MSC) population are crucial for tissue homeostasis. Assuring their genomic stability is therefore essential. Exposure of stem cells to ionizing radiation (IR) is potentially detrimental for normal tissue homeostasis. Although it has been established that exposure to high doses of ionizing radiation (IR) has severe adverse effects on MSCs, knowledge about the impact of low doses of IR is lacking. Here we investigated the effect of low doses of X-irradiation with medical imaging beam settings (<0.1 Gray; 900 mGray per hour), in vitro, on pediatric dental mesenchymal stromal cells containing dental pulp stem cells from deciduous teeth, dental follicle progenitor cells and stem cells from the apical papilla. DNA double strand break (DSB) formation and repair kinetics were monitored by immunocytochemistry of γH2AX and 53BP1 as well as cell cycle progression by flow cytometry and cellular senescence by senescence-associated β-galactosidase assay and ELISA. Increased DNA DSB repair foci, after exposure to low doses of X-rays, were measured as early as 30 min post-irradiation. The number of DSBs returned to baseline levels 24 h after irradiation. Cell cycle analysis revealed marginal effects of IR on cell cycle progression, although a slight G2/M phase arrest was seen in dental pulp stromal cells from deciduous teeth 72 h after irradiation. Despite this cell cycle arrest, no radiation-induced senescence was observed. In conclusion, low X-ray IR doses (< 0.1 Gray; 900 mGray per hour), were able to induce significant increases in the number of DNA DSBs repair foci, but cell cycle progression seems to be minimally affected. This highlights the need for more detailed and extensive studies on the effects of exposure to low IR doses on different mesenchymal stromal cells.
Highlights
Stem cells contained within the dental mesenchymal stromal cell (MSCs) population are of paramount importance for tissue homeostasis which are potentially important targets of ionizing radiation (IR) exposure
The aim of this study is to investigate the effects of low dose X-ray exposure with medical imaging beam settings (< 100 mGy; 900 mGy/h) on stem cells from human exfoliated deciduous teeth (SHEDs), dental follicle stem cells (DFSCs), and SCAPs extracted from pediatric patients
DNA double strand break (DSB) formation and repair kinetics were monitored in dental mesenchymal stromal cells (SHED, DFSC, and SCAP), that were isolated from pediatric donors, by microscopic analysis of co-localized γH2AX and 53BP1 foci (N = 3)
Summary
Stem cells contained within the dental mesenchymal stromal cell (MSCs) population are of paramount importance for tissue homeostasis which are potentially important targets of ionizing radiation (IR) exposure. They can accumulate genotoxic damage following IR exposure, which is either repaired efficiently, or they can accumulate irreversible damage. The International Society for Cellular Therapy has prompt to define the isolation of mesenchymal stem cells as non-clonal cultures of stromal cells containing stem cells with different multipotent properties, committed progenitors, and differentiated cells [9,10,11] An overview of these cells and their potential use in dentistry is given by Bansal and Jain [12]
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