Exploring The Hematopoietic Support Capability Of Mouse Fetal Liver Stromal Cells In Vivo

Background and purpose:Mammalian fetal liver(FL)hematopoietic stage is the period during which the hematopoietic stem cells(HSCs)mature and rapidly expand.The hematopoietic microenvironment composed of FL stromal cells plays an important role in this process.At present,researchers have focused on inducing different types of cells into HSCs using FL stromal cells in vitro,while their hematopoietic-supporting capability in vivo is yet to be further explored.The purpose of this study was to reveal the differences of different types of FL stromal cells and to explore their hematopoietic support capability in vivo.Method and content:In this study,FL and bone marrow(BM)stromal cells of C57BL/6 mice were obtained by adherent culture in vitro,and cultured stromal cells were identified using five surface markers:CD29,CD44,CD106,CD45,and Sca-1.Thereafter,2.3*10⁵ FL stromal cells and 1.7*10⁴ mouse bone marrow LK(Lin-c^-Kit⁺)cells were co-transplanted into the recipient mice which were irradiated with 9.0 Gy ⁶⁰Co?-rays by means of bone marrow injection.Meanwhile,the LK group and the co-injection group of LK and mouse embryonic fibroblast(MEF)were used as controls.By observing the survival rate of the recipients,detecting the changes of various blood parameters and the chimeric rate of the exogenous blood cells,we could evaluate the status of hematopoietic reconstitution,and then analyzing the hematopoietic support ability of FL stromal cells in vivo.Results and conclusion:During our culture,we found two different stromal cells morphology:spindle-like and fibroblast-like cells in both FL and BM.The surface markers of spindle-like cells were expressed as CD106^-CD45⁺CD29⁺CD44⁺,while the expression of fibroblast-like cells were CD106⁺CD45^-CD29⁺CD44⁺.The results of transplantation experiments showed that the survival rate of LK and FL stromal cells co-injection group within two months was 100%,while some recipients of LK group and MEF co-injection group died within one to two weeks after radiation and the two-month survival rates of them were 80%.The blood parameters of recipient mice of the three groups recovered to normal within 1.5 months to 2 months,but platelet levels in the LK and FL stromal cells co-injection group were higher than other groups in the first 2 week after transplantation.The levels of red blood cells and hemoglobin in the second week were significantly higher than those in the LK group.After 9 weeks of transplantation,the chimeric rate in peripheral blood of recipient mice was 70%-80%,and about 90%in bone marrow.The experiment results showed that the fetal liver and bone marrow stromal cells contain two types of cells from the morphology:spindle-like and fibroblast-like cells,and the two types of cells have different surface marker expression patterns.What's more,engraftment of LK cells in bone marrow could reconstruct the hematopoietic system effectively and FL stromal cells may promote the recovery of platelets and red blood cells in the early stage of the reconstitution,thereby keeping the recipients from death caused by hematopoietic failure.