Involvement Of Bone Marrow-derived Cells In Tissue Repairing Of Combined Radiation And Wound Injury

Nuclear war,nuclear accidents,terrorist attacks and radiotherapy after surgery frequently cause accompany with radiation exposure combined with traumatic tissue injury,which is nominated combined radiation and wound injury(CRWI).CRWI has two unique characteristics and is totally different from simple injury,such as simple mechanical trauma or simple radiation injury.One characteristic is radiation injury always plays a leading role in the occurrence and development of CRWI.The other one is the synergistic effects of CRWI.Different injuries in CRWI could interact with each other then induce damage at the molecular,cellular,tissue,and organ levels that are unique and more profound than either injury alone.The same radiation when combined with injury is more likely to increase mortality and risk of multiple organ failure,and cause complicate systemic reactions,which can enhance acute radiation effects and delay wound healing.Till now,there is no ideal treatment method for CRWI.The successful application of stem cell transplantation in regenerative medicine and tissue engineering has opened up a new window for the treatment of CRWI.Bone marrow contains many types of stem cells,including hematopoietic stem cells(HSCs)and mesenchymal stem cells(MSCs).HSCs can alleviate the early hematopoietic failure caused by radiation.MSCs,which have been implicated in the differentiation and repair of injured tissues and the secretion of cytokines,play a very important role in the healing of damaged tissues.It has been proven that different types of bone marrow-derived cells(BMDCs)including MSCs,HSCs and monocytes /macrophages are involved in tissue and organ repair after radiation injury.Researchers have used BMDCs to treat acute radiation sickness,and obtained effective therapeutic results.However,there are few studies on the roles and mechanisms of BMDCs involved in CRWI repairing.Therefore,the function of BMDCs in CRWI treatment has not been well characterized.In this research,we study the therapeutic effects of exogenous BMDCs in CRWI.By investigating the distribution and different phenotypes of the engrafted BMDCs in animal CRWI model,we provide new clues for the treatment of CRWI.The main contents and results of this study are summarized as below:1.We established a CRWI model using C57BL/6J mice and administrated BMDCs from enhanced green fluorescent protein(EGFP)-transgenic mouse to C57BL/6J one to examine the therapeutic effect of BMDCs in CRWI mice.Peripheral blood EGFP+ cell chimerism was respectively 54.5+7%,91.6+4.5% and 90.9+3.1% in 7 days,15 days and 30 days after transplantation.BMDCs transplantation significantly alleviate CRWI damaged effects,such as peripheral blood cells decrease,multiple organ pathological damage and body weight loss,and promoted cell proliferation in granulation tissue,angiogenesis and collagen deposition and maturation in CRWI wound,and accelerated the speed of wound healing.2.The distribution characteristics of engrafted BMDCs in CRWI tissues were further studied.We divided groups of CRWI,simple radiation,simple wound and untreated control to compare the chimerism of BMDCs in different injury models.Firstly,by utilizing in vivo flow cytometry(IVFC),we found that BMDCs had long-term stability of the existence and proliferation in peripheral blood.At 18 days after transplantation of BMDCs,donor cells could not be detected in the peripheral blood of the recipients without radiation damage.Secondly,obvious engraftment was detected in bone marrow,liver,lung,intestine,skin and other parts 7 days after CRWI.The cell colonization further increased at 15 day.A large number of colonized BMDCs also were detected at 30 days.Instead,chimerism were rarely detected in non-radiation injury ones at 15 days and 30 days.In addition,BMDCs had a dominant distribution in the intestinal and skin wounds after CRWI or radiation injury.And the colonization of BMDCs in CRWI group was more than that of simple radiation injury group.Based on this,we further examined the surface marker using intestine and skin slides,and analyzed the function of various cell subsets related to the process of injury repair.We found that CD45+ hematopoietic cells and vimentin+ stromal cells were the main types of colonlized BMDCs in the intestine and skin.And few of them were ?-smooth muscle actin(?-SMA)positive cells and CD68+ macrophages.It suggested that hemotopoietic cells and stromal cells of BMDCs might play an important role in intestinal and cutaneous tissue repair,but exogenous a-SMA+ cells and macrophages may not.Conclusions: we successfully transplanted BMDCs to CRWI mice to establish chimeric model.Systemic transplantation of BMDCs,which had therapeutic effects on CRWI mice,and it promoted hematopoietic recovery and local wound healing,and reduced the pathological damage of various tissues and organs.Long-term stable chimerism and coloniation of BMDCs in peripheral blood and multiple organs of CRWI mice were detected.It was also found that the colonization of cells had dominant distribution in the intestine and cutaneous wounds.The analysis of cell surface markers further reveal that CD45+ and vimentin+ cells played an important role in intestinal and cutaneous tissue repair,and a-SMA+ cells and macrophages not.These data provided a further understanding of the BMDCs' role involved in CRWI tissue repair,also provided a basis for the treatment of BMDCs to CRWI.