Low-Dose Ionizing γ-Radiation Promotes Proliferation of Human Mesenchymal Stem Cells and Maintains Their Stem Cell Characteristics

ABSTRACT

Mesenchymal stem cells (MSCs), which are multipotent and have self-renewal ability, support the regeneration of damaged normal tissue. A number of external stimuli promote migration of MSCs into peripheral blood and support their participation inwound healing. In an attempt to harness the potential beneficial effects of such external stimuli, we exposed human MSCs (hMSCs) to one such stimulus-low-dose ionizing radiation (LDIR)-and examined their biological properties. To this end, we evaluated differences in proliferation, cell cycle, DNA damage, expression of surface markers (CD29, CD34, CD90, and CD105), and differentiation potential ofhMSCs before and after irradiation with γ-rays generated using a ¹³⁷ CSirradiator.At doses less than 50 mGy, LDIR had no significant effect on the viability or apoptosis of hMSCs. Interestingly, 10 mGyofLDIR increased hMSC viability by 8% (p<0.001) comparedwith non-irradiatedhMSCs.At doses less than 50 mGy, LDIR did not induceDNA damage, including DNA strand breaks, or cause cellular senescence or cell-cycle arrest. Surface marker expression and in vitro differentiation potential of hMSCs were maintained after two exposures to LDIR at 10 mGy per dose. In conclusion, a two-dose exposure to LDIR at 10 mGy per dose not only facilitates proliferation of hMSCs, it alsomaintains the stem cell characteristics of hMSCswithout affecting their viability.These results provide evidence for the potential ofLDIRas an external stimulus for in vitro expansion of hMSCs and application in tissue engineering and regenerative medicine.