Heterogenous mitochondrial ultrastructure and metabolism of human glioblastoma cells: differences between stem-like and differentiated cancer cells in response to chemotherapy

Background Glioblastoma stem-like cells (GSCs) contribute to the resistance of glioblastoma (GBM) tumors to standard therapies. The cellular and molecular background of the resistance of GSCs to the chemotherapeutic agent temozolomide is not yet fully understood, in particular in the context of cellular metabolism and the role of mitochondria. The aim of this study was to perform a detailed ultrastructural characterization of the mitochondria of GSCs prior and post temozolomide exposure and to compare it to differentiated GBM cells. Methods Patient-derived and established GSC and GBM differentiated cell lines were used for the study. The ultrastructure of the mitochondria of the examined cell lines was assessed by transmission electron microscopy. The microscopic analysis was complemented and compared by an analysis of cell metabolism using cell viability assay and extracellular flux analysis using Seahorse assay. Results We found that the metabolic profile of GSCs is quiescent and aerobic. Their elongated mitochondria with highly organized cristae is indicating increased biogenesis and mitochondrial fusion and corresponds to a more OXPHOS-dependent metabolism. The metabolism of GSCs is dependent on OXPHOS and there are no changes in defective mitochondria fraction after the treatment with temozolomide. In contrast, differentiated GBM cells with fragmented mitochondria, which have less organized cristae, are more energetic and glycolytic. Temozolomide treatment induced significant ultrastructural mitochondrial damage in differentiated GBM cells and had less effect on mitochondria in GSCs, suggesting that mitochondria play an important role in the resistance of GSCs to temozolomide treatment. Conclusions We demonstrated differences in mitochondrial ultrastructure and cellular metabolism between GSCs and differentiated GBM cells in response to temozolomide. This study provides a basis for further studies addressing the chemotherapy resistance of GSCs and the effects of different treatment regimens on the mitochondrial structure and function of GSCs. Graphical Abstract