Abstract
Diagnostic imaging delivering low doses of radiation often accompany human mesenchymal stem cells (MSCs)-based therapies. However, effects of low dose radiation on MSCs are poorly characterized. Here we examine patterns of phosphorylated histone H2AX (γH2AX) and phospho-S1981 ATM (pATM) foci formation in human gingiva-derived MSCs exposed to X-rays in time-course and dose-response experiments. Both γH2AX and pATM foci accumulated linearly with dose early after irradiation (5-60 min), with a maximum induction observed at 30-60 min (37 ± 3 and 32 ± 3 foci/cell/Gy for γH2AX and pATM, respectively). The number of γH2AX foci produced by intermediate doses (160 and 250 mGy) significantly decreased (40-60%) between 60 and 240 min post-irradiation, indicating rejoining of DNA double-strand breaks. In contrast, γH2AX foci produced by low doses (20-80 mGy) did not change after 60 min. The number of pATM foci between 60 and 240 min decreased down to control values in a dose-independent manner. Similar kinetics was observed for pATM foci co-localized with γH2AX foci. Collectively, our results suggest differential DNA double-strand break signaling and processing in response to low vs. intermediate doses of X-rays in human MSCs. Furthermore, mechanisms governing the prolonged persistence of γH2AX foci in these cells appear to be ATM-independent.
Highlights
Multipotent mesenchymal stromal cells (MSCs) are the most studied and characterized type of stem cells currently used in regenerative medicine [1, 2]
Our first set of experiments aimed at detailed characterization of dose-responses for γH2AX and phospho-S1981 ataxia telangiectasia mutated (ATM) (pATM) foci in MSCs exposed to X-ray doses of 20, 40, 80, 160 and 250 mGy
For the highest dose of 250 mGy, we found the maximum number of γH2AX foci at 60 min post-irradiation, followed by a 60% decrease in the following 3 h (Figure 3A)
Summary
Multipotent mesenchymal stromal cells (MSCs) are the most studied and characterized type of stem cells currently used in regenerative medicine [1, 2]. MSCs are described in the literature as substrate-dependent fibroblast-like cells with clonogenic properties and ability to self-renew [3, 4]. These cells express a specific set of surface markers, most of which are common with fibroblasts [5, 6]. Along with the orthodox differentiation, gingival MSCs are arguably able to undergo the non-orthodox differentiation into the neuronal lineage [17, 18] since they originate from the neural crest cells [17]. Up to 90% of the cells in primary cultures of gingival-derived MSCs are characterized by typical stem-cell markers and 40–70% express pluripotency genes Oct, Sox and Nanog [19] and active telomerase [20]
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