Role of ER-Mitochondria interface in the regulation of Glioma Stem Cells

Abstract

Abstract Purpose: Glioblastoma (GBM) treatment is extremely challenging due to the high complexity of the tumor, being one of the tumors in which a subpopulation of highly resistant cancer initiating cells (GICs) has been clearly identified. Thus, understanding the differences between GICs and tumor bulk cells is therefore essential to move to less conventional but more efficient approaches. Methods: fluorimetry was used to measure glucose uptake, mitochondrial calcium, intracellular oxidants and mitochondrial membrane potential. Spectrophotometry was used to monitor lactate dehydrogenase activity. Self-renewal was determined by the limiting dilution assay and cell death by trypan blue exclusion assays. Protein expression was determined by western blot while gene expression was determined by real-time PCR. Results: We found that, unlike their differentiated progeny, GICs survival and stemness depend on mitochondrial metabolism. GICs present higher glucose uptake and mitochondrial membrane potential and less LDH activity, being more sensitive to mitochondrial inhibition than their differentiated counterparts. Calcium flux seems to play an essential role in the maintenance of this distinct metabolic phenotype with a decrease in the expression of VDAC and Grp75, two of the main proteins in the transfer of calcium from endoplasmic reticulum (ER) to the mitochondria. Disruption of ER homeostasis using ER stress inducers or inhibition of ER-mitochondrial contact sites using the Grp75 inhibitor MKT-707 resulted in GICs cytotoxicity and loss of stemness. Moreover, MKT-077 also potentiates the effect of temozolomide, current treatment for glioblastoma. Conclusions: our data indicates that ER-mitochondrial homeostasis is essential for regulation of GICs metabolism, survival and stemness.