The Rescue Mechanism Of Recombination Human Bone Morphogenetic Protein-2 For Acute Hematopoietic Injury In Mice Exposed To γ-ray

Aim: Adult mammalian bone marrow contains two types of stem cells:haematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) that arethe key composition in hematopoietic microenvironment. The proliferation anddifferentiation of hematopoiesis depend on hematopoietic microenvironment.Interaction of hematopoietic cytokines and cells in hematopoieticmicroenvironment generates various signals, which supports the proliferationanddifferentiationofhematopoieticcells.Itiswellknownthatexposureto?-raynot only causes acute bone marrow suppression but also leads to long-termresidual hematopoieticinjury.Thelatteris duetodamageofhematopoietic stemcells (HSCs) self-renewal. Our previous studies have shown that recombinationhuman bone morphogenetic protein-2 (rhBMP-2) can rescue acutehematopoietic damage of mice exposed to ?-ray, which is concerned withpromotion of rhBMP-2 in the proliferation of HSCs. In order to further confirmthe mechanism of rhBMP-2's rescuing acute hematopoietic injury in mice exposed toγ-ray, we carried out this experiment to demonstrate that theproliferation and differentiation of MSCs regulated by rhBMP-2 plays a crucialroleinrescuinghematopoieticinjuryinmiceexposedto?-ray.Methods: (1) The XTT method was used to detect the effect of rhBMP-2on the proliferation of MSCs cultured in vitro. (2) The real-time quantitativePCR was used to detect the effect of rhBMP-2 on the hematopoietic cytokinesmRNAexpressionsofMSCsculturedinvitro.(3)TheELISAwasusedtodetectthe effect of rhBMP-2 on the hematopoietic cytokines protein level of MSCscultured in vitro. (4) MSCs from Green Fluorescent Protein (GFP) transgenicmice were marked with Hoechst33342 before transplanted into BALB/c mice.Immunofluorescent staining and flow cytometry were employed to detect thedifferentiationofMSCsinvivoaftertransplantationfor6weeks.Results: (1) rhBMP-2 significantly promoted MSCs proliferation in doseranging from 10 ng/ml - 1×105 ng/ml in a dose-dependent manner. However,this proliferation effect turned down with further increased dose of rhBMP-2 to1×106 ng /ml. (2) rhBMP-2 significantly promoted hematopoietic cytokinesmRNA expression such as IL-7, IL-11, G-CSF, M-CSF, and SCF. (3) Theprotein levels of hematopoietic cytokines such as IL-6, IL-7, IL-11, and M-CSFin the supernatant of cultured MSCs with rhBMP-2 were higher than those ofculturedMSCs without rhBMP-2.(4)MSCs couldhometotheradiation-injuredhematopoietic tissues and differentiate to hematopoietic cells when the micewere exposed toγ-ray. The effect of MSCs was enhanced byrhBMP-2, whichacceleratedthehematopoieticrestoration.Conclusion: Normal hematopoiesis depends on interaction ofhematopoietic cells and hematopoietic microenvironment. Hematopoieticmicroenvironment can support and regulate establishment, proliferation, differentiation, development and maturity of hematopoietic cells. In conclusion,MSCs play an important role in hematopoietic restoration. The effect ofrhBMP-2 promotes the proliferation and differentiation of mesenchymal stemcells, which not only improved the haematopoietic microenvironment, but alsoand accelerated the production of haematopoietic cells in mice exposed to ?-ray,which may be important mechanism of rhBMP-2 rescuing the hematopoieticinjuryofmice.