Mechanism of tropism of umbilical cord mesenchymal stem cells to glioma stem cells

Abstract

Objective To study the tropism of umbilical cord mesenchymal stem cells (UCMSCs) to glioma stem cells and their mechanism. Methods The isolated humanized UCMSCs were cultured and identified. The glioma stem cells were induced to remain at the resting, proliferation or differentiation states by soft or hard agar combined with stemness maintenance factors (epidermal growth factor [EGF] and basic fibroblast growth factor [bFGF]): soft agar+ EGF+ bFGF group, hard agar+EGF+bFGF group, and hard agar group; clone spheres of the stem cells were cultured for 7 d, and then, the growth curve of clone spheres diameters was drawn; flow cytometry was used to detect the cell cycle of the stem cells 72 h after culture; CD133, Ki67 and GFAP expressions in the clone spheres of stem cells in the three groups were observed by immunofluorescent staining; the tropism aptitude of UCMSCs to glioma stem cells at different states was detected by Transwell dual chamber culture system; the protein expression levels of stem cell factor (SCF), stromal-derived factor (SDF)-1 and vascular endothelial growth factor (VEGF) in glioma stem cells were monitored by enzyme immunoassay (ELISA); Western blotting was used to measure the protein expression levels of c-Kit, C-X-C chemokine receptor type 4 (CXCR-4) and VEGF receptor in UCMSCs. Results The diameters of clone spheres in the hard agar+EGF+bFGF group and hard agar group were significantly larger than those in the soft agar+EGF+bFGF group on the second and 7th d of culture (P<0.05); cell cycle analysis indicated that glioma stem cells in the soft agar+EGF+bFGF group, hard agar+EGF+bFGF group, and hard agar group were successfully remained at the resting, proliferation or differentiation states; high CD133 expression ([95.79±5.31] %) was noted in the cells of soft agar+EGF+bFGF group, high Ki67 and GFAP expressions ([89.39±7.45 and 63.49±16.54] %) were noted in the cells of hard agar+EGF+ bFGF group, and high GFAP expression ([97.36±3.48] %) was noted in the cells of hard agar group; Transwell assay indicated that the migration percentage of cells from the hard agar+EGF+bFGF group was significantly higher than that in the soft agar+EGF+bFGF group, hard agar group and two control groups (P<0.05). higher protein expression levels of SCF, SDF-1 and VEGF in the hard agar+ EGF+ bFGF group were noted as compared with those in the soft agar+EGF+bFGF group and hard agar group (P<0.05). UCMSCs were induced to express significantly higher levels of c-Kit, CXCR4 and VEGF receptor in the hard agar+EGF+bFGF group as compared with those in the soft agar+EGF+bFGF group and hard agar group (P<0.05). Conclusion SCF/c-Kit, SDF-1/CXCR4 and VEGF/VEGFR axis expression defects might be the potential mechanism of the migration defect of UCMSCs to glioma stem cells at the resting state. Key words: Glioma; Tumor stem cell; Mesenchymal stem cell; Tropism