Presence of glioma stroma mesenchymal stem cells in a murine orthotopic glioma model

Purpose: High-grade gliomas are closely related to the mesenchymal phenotype which might be explained by unorthodox differentiation of glioma cancer stem cells (gCSCs). We reasoned that other non-neural stem cells, especially mesenchymal stem cells (MSCs), might play a role in expresssing mesenchymal phenotype of high-grade gliomas. Thus we hypothesized that cells resembling MSCs exist in glioma specimens. Methods: We created a mouse (m) orthotopic glioma model using human gCSCs. Single-cell suspensions were isolated from glioma specimens and cultured according to the methods for mMSCs or gliomaspheres. These cells were analyzed by fluorescence-activated cell sorting (FACS) for surface markers associated with mMSCs or gCSCs. Glioma stroma (GS)-MSCs were exposed to mesenchymal differentiation conditions. To decide the location of GS-MSCs, sections of orthotopic glioma models were analyzed by immunofluorescent labeling. Results: GS-MSCs were isolated which were morphologically similar to mMSCs. FACS analysis showed that the GS-MSCs had similar surface markers to mMSCs (stem cell antigen-1 [Sca-1] ⁺, CD9 ⁺, CD45 ^-, CD11b ^-, CD31 ^-, and nerve/glial antigen 2 [NG2] ^-). GS-MSCs were capable of mesenchymal differentiation. Immunofluorescent labeling indicated that GS-MSCs are located around blood vessels, are distinct from endothelial cells, and have features that partially overlap with vascular pericytes. Conclusions: Our results indicate that cells similar to mMSCs exist in glioma specimens. The GS-MSCs might be located around vessels, which suggests that GS-MSCs may provide the mesenchymal elements of the vascular niche. GS-MSCs may represent non-neural stem cells that act as an important source of mesenchymal elements, particularly during the growth of gliomas.