Objective To induce the differentiation of bone marrow mesenchymal stem cells(BM-MSCs) into hematopoietic cells using the fetal liver stromal cell-conditioned medium(FLSC-CM), and investigate the effects of hematopoietic cells differentiated by BM-MSCs on the hematopoietic function of mice with bone marrow suppression induced by cyclophosphamide(CTX).

Methods A total of twenty-four Balb/c mice were randomly divided into the blank control group and three CTX injection dosage groups(40 mg/kg, 60 mg/kg, and 80 mg/kg).The continuous intraperitoneal injection for 8 days was carried out.The optimal CTX dose for short-term modeling was determined through the detection of red blood cell and white blood cell levels and spleen index.The BM-MSCs were obtained from the bone marrow of SD rats by the whole bone marrow method combined with differential adhesion method.Balb/c mice at 12.5-14.5 days of gestation were selected.Fetal liver tissues were taken to culture fetal liver stromal cells and prepare FLSC-CM.BM-MSCs were induced to differentiate into hematopoietic cells in vitro, and divided into the BM-MSCs group, IL-6+SCF+BM-MSCs group and FLSC-CM+BM-MSCs group.The induced cells were collected, and injected into the model mice via the tail vein.The hematopoietic function of mice was evaluated by measuring the levels of red blood cells and white blood cell, spleen index, granulocyte-macrophage colony-forming units(CFU-GM) and bone marrow pathological morphology.

Results The mouse model of bone marrow suppression caused by CTX was constructed.Compared with the control group, the red blood cells in each experimental group significantly decreased on the sixth and ninth days (P < 0.01).Among them, the 80 mg/kg group continued to significantly decrease from the third to the ninth day(P < 0.01).The white blood cell count decreased significantly in all experimental groups from day 1 to day 3(P < 0.01).On the sixth and ninth days, the increasing of white blood cell count in the 40 mg/kg and 60 mg/kg groups were higher than that in the control group, and the difference was more significant in the 60 mg/kg group(P < 0.05 to P < 0.01).Although the white blood cell count in the 80 mg/kg group increased, it was still lower than that in the control group, and the difference was not statistically significant(P>0.05).Eight days after inducing BM-MSCs to differentiate into hematopoietic cells in vitro, it was observed under the microscope that the floating cells in the FLSC-CM+BM-MSCs group were more than those in the other two groups.On the sixth day after transplantation-induced cell, the levels of red blood cell and white blood cell in the peripheral blood of each group from high to low were the FLSC-CM+BM-MSCs group, IL-6+SCF+BM-MSCs group and BM-MSCs group.Among them, the white blood cell level in the FLSC-CM+BM-MSCs group significantly increased on the sixth day(P < 0.01).The sequence of CFU-GM colony formation from high to low was consistent with the level of peripheral blood cells.Compared with the BM-MSCs group, there were statistically significant differences in the FLSC-CM+BM-MSCs group and IL-6+SCF+BM-MSCs group(P < 0.05).The order of spleen index from high to low was reversed, but the difference was not statistically significant(P>0.05).Bone marrow sections showed that compared with the other two groups, the number of nucleated cells in the FLSC-CM+BM-MSCs group increased significantly.

Conclusions The dosage of 80 mg/kg CTX is more suitable for establishing a short-term mouse model of bone marrow suppression, and the cells differentiated from BM-MSCs induced by FLSC-CM can improve the hematopoietic function of mice with bone marrow suppression caused by CTX.