The Effect Of MicroRNA-34a On Ionizing Radiation-induced DNA Damage Repair In Murine Hematopoietic Stem Cells

With the wide application of nuclear energy and nuclear technology,the threat of ionizing radiation damage is more and more serious.The hematopoietic system is one of the most sensitive tissues to ionizing radiation in the human body.Ionizing radiation-caused damage in hematopoietic system can lead to anemia(red blood cell depletion),hemorrhage(platelet depletion),infection(bone marrow and lymphoid immune effector cell depletion)and even death.Hematopoietic stem cells(HSCs)are a group of self-renewing primitive pluripotent cells,which are also the key to maintain the lifelong hematopoietic function in the body.Therefore,more and more attention has been paid to the research on the injury mechanism and prevention of hematopoietic stem cells induced by ionizing radiation.It has been reported that non-coding single chain microRNA(miRNA)is widely involved in the hematopoietic regulation process and plays an important role in the radiation toxicity,and can even be used as a biomarker for dose estimation and prognosis after accidental radiation exposure.Tumor suppressor microRNA-34a(miR-34a)is one of the early miRNA concerned in radiobiological studies,which is involved in the regulation of various tissue and cell activities after irradiation.Studies have confirmed that miR-34 a is not only an important hematopoietic regulator,but also participates in the regulation of multiline differentiation including neural stem cells,embryonic stem cells and pluripotent stem cells.However,whether miR-34 a is involved in the regulation of hematopoietic stem cell development and its association with the injury of hematopoietic stem cells caused by ionizing radiation have not been reported.In this study,we selected C57BL/6 mice and miR-34 a knockout mice as the research objects.Firstly,we detected the expression level of miR-34 a in various hematopoietic cells by flow cytometry and q-PCR.Subsequently,we analyzed the effect of miR-34 a knockout on the proportion and quiescence of hematopoietic stem cells,as well as peripheral blood counts,in mice under homeostasis.On this basis,we measured the expression level of miR-34 a in irradiated hematopoietic stem cells by q-PCR,and then analyzed the effect of miR-34 a knockout on the number and DNA damage repair in hematopoietic stem cells from mice after irradiation by flow cytometry and immunofluorescence staining,respectively.After that,the effect of miR-34 a knockout on the function of hematopoietic stem cells after radiation was investigated by transplantation.The underlying mechanism of miR-34 a regulates irradiated hematopoietic stem cells was explored.Finally,miR-34 a agomir was applied to enhance the expression level of miR-34 a in irradiated mouse hematopoietic stem cells,and its protective effect on irradiated hematopoietic stem cells was analyzed.The main research results and conclusions are as follows:1.miR-34 a is expressed in all hematopoietic cells in mouse bone marrow,while there is no significant difference in its expression among these cells.2.miR-34 a deficiency has no significant effect on the number,cell cycle and apoptosis of mouse hematopoietic stem cells under steady state conditions.3.miR-34 a knockout has no significant effect on peripheral blood counts in mice.4.Ionizing radiation can induce the expression of miR-34 a in mouse hematopoietic stem cells in a dose-dependent manner.5.miR-34 a deficiency leads to more severe increased apoptosis and decreased hematopoietic stem cells induced by irradiation.6.Ionizing radiation can cause more seriously decreased DNA damage repair and reconstruction function in hematopoietic stem cell from miR-34 a knockout mice,and these effects may be independent of p53.7.Tail vein injection of miR-34 a agomir can increase the expression level of miR-34 a in hematopoietic stem cells,which can protect hematopoietic stem cells from ionizing radiation-caused damage.In summary,this reveal for the first time that miR-34 a plays a critical role in regulation of hematopoietic stem cells in the context of radiation,although its deficiency does not affect homeostatic hematopoiesis.Meanwhile,it was found that treatment of mice with miR-34 a agomir can promote the survival and functional recovery of hematopoietic stem cells after radiation,which provides a new insight for protecting hematopoietic stem cells from radiation damage.