Abstract
INTRODUCTION: Glioblastoma multiforme (GBM) cells release glutamate through expression of system xc−, which exchanges intracellular glutamate for extracellular cysteine. Lack of glutamate uptake through low excitatory amino acid transporter 2 (EAAT2) expression permits high extracellular glutamate levels, causing damaging excitotoxicty to surrounding parenchyma and epileptogenesis at the peritumoural edge. PPARγ agonists upregulate EAAT2 expression and prevent glutamate mediated excitotoxicity in stroke models. We investigated PPARγ agonists in GBM glutamate regulation. METHOD: Glioma cell lines U87MG and U251, and Glioma stem cells (GSCs) isolated from freshly resected tumour specimens were exposed to increasing concentrations of Pioglitazone. Effects on cell viability, protein expression and extracellular glutamate levels were evaluated with an ATP assay, Western Blotting and HPLC respectively. RESULTS: EAAT2 expression was upregulated in a dose and time dependent manner in both U87MG and U251 cells. Glutamate levels were reduced with the addition of pioglitazone, where statistical significance was reached in U251 cells at a concentration of 30 µM pioglitazone (n = 3, p < 0.05). Pioglitazone significantly reduced the cell viability of U87MG and U251 cells at concentrations of ≥ 30 µM (n = 4, p < 0.05) and 100 µM (n = 6, p < 0.05) respectively. Photomicrographs revealed morphological changes in the glioma cell lines and inability of the GSCs to form neurospheres with increasing pioglitazone concentrations. CONCLUSION: This study provides preliminary evidence of PPARγ-mediated regulation of EAAT2 expression in human glioblastoma cells and suggests a novel treatment strategy for glioma associated seizures.