Glioblastoma (GB) is the most common and most aggressive brain tumour in humans. Glioblastoma stem cells (GMC) are responsible for resistance to radiotherapy and chemotherapy, the maintenance and spread of the tumour, and its recurrence. Mesenchymal stem cells (MMC) are also present in the tumour microenvironment, which, through interactions with glioblastoma cells, promote GB development and increase the self-renewal capacity of GMC and their invasion. It has not been studied so far how MMC affect GMC growth and invasion. We determined the influence of cellular interactions between GMC and MMC on the growth and invasion of glioblastoma cells in a 3D model of spheroids in vitro and in the brains of zebrafish embryos (Danio rerio). We showed that MMC affected the morphology of GMC in the spheroids of co-culture. Using confocal microscopy, we also showed differences in morphology between GMC in monoculture and co-culture with MMC in vivo. We demonstrated that the presence of MMC increased GMC growth in in vitro and in vivo tumour models. MMCs were more invasive than GMCs, but in co-culture GMCs reduced MMC invasion in vitro. In contrast, GMC invasion was significantly higher in the in vivo model compared to injected MMCs. The reason for the differences in invasion in different models used is in the microenvironment, which is more complex in the brains of zebrafish. We showed that MMCs are important in the tumour microenvironment as they promote GMC growth.
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