The peroxisome proliferator activated receptor gamma agonist pioglitazone increases functional expression of the glutamate transporter excitatory amino acid transporter 2 (EAAT2) in human glioblastoma cells

// Jared Ching 1, 2 , Stephanie Amiridis 1, 2 , Stanley S. Stylli 1, 4 , Andrew R. Bjorksten 3 , Nicole Kountouri 1 , Thomas Zheng 2 , Lucy Paradiso 1 , Rodney B. Luwor 1 , Andrew P. Morokoff 1, 4 , Terence J. O’Brien 2 , Andrew H. Kaye 1, 4 1 Department of Surgery, The University of Melbourne, The Royal Melbourne Hospital, Victoria, Australia 2 Department of Medicine, The University of Melbourne, The Royal Melbourne Hospital, Victoria, Australia 3 Department of Anaesthesia and Pain Management, The Royal Melbourne Hospital, Victoria, Australia 4 Department of Neurosurgery, The Royal Melbourne Hospital, Victoria, Australia Correspondence to: Andrew H. Kaye, e-mail: a.kaye@unimelb.edu.au Keywords: glutamate, pioglitazone, PPAR gamma, glioblastoma multiforme, EAAT2 Received: March 19, 2015      Accepted: May 21, 2015      Published: June 03, 2015 ABSTRACT Glioma cells release glutamate through expression of system x c - , which exchanges intracellular glutamate for extracellular cysteine. Lack of the excitatory amino acid transporter 2 (EAAT2) expression maintains high extracellular glutamate levels in the glioma microenvironment, causing excitotoxicity to surrounding parenchyma. Not only does this contribute to the survival and proliferation of glioma cells, but is involved in the pathophysiology of tumour-associated epilepsy (TAE). We investigated the role of the peroxisome proliferator activated receptor gamma (PPARγ) agonist pioglitazone in modulating EAAT2 expression in glioma cells. We found that EAAT2 expression was increased in a dose dependent manner in both U87MG and U251MG glioma cells. Extracellular glutamate levels were reduced with the addition of pioglitazone, where statistical significance was reached in both U87MG and U251MG cells at a concentration of ≥ 30 μM pioglitazone ( p < 0.05). The PPARγ antagonist GW9662 inhibited the effect of pioglitazone on extracellular glutamate levels, indicating PPARγ dependence. In addition, pioglitazone significantly reduced cell viability of U87MG and U251MG cells at ≥ 30 μM and 100 μM ( p < 0.05) respectively. GW9662 also significantly reduced viability of U87MG and U251MG cells with 10 μM and 30 μM ( p < 0.05) respectively. The effect on viability was partially dependent on PPARγ activation in U87MG cells but not U251MG cells, whereby PPARγ blockade with GW9662 had a synergistic effect. We conclude that PPARγ agonists may be therapeutically beneficial in the treatment of gliomas and furthermore suggest a novel role for these agents in the treatment of tumour associated seizures through the reduction in extracellular glutamate.