Ligands of peroxisome proliferator-activated receptor-alpha promote glutamate transporter-1 endocytosis in astrocytes

Astrocytes, a stellate-shape glial population in the central nervous system (CNS), maintain glutamate homeostasis in adult CNS by undergoing glutamate uptake at the synapse through their glutamate transporter-1 (GLT-1). Peroxisome proliferator-activated receptor-a (PPAR alpha) can be activated by endogenous saturated fatty acids to regulate astrocytic lipid metabolism and functions. However, it is unclear if PPARa can exert the regulatory action on GLT-1 expression in astrocytes. This study showed that treatment with palmitic acid (PA) and the other two PPARa agonists (GW 7647 and WY 14,643) caused no change in the morphology of astrocytes, whereas membranous GLT-1 protein levels in astrocytes were significantly decreased by PA and PPARa agonists. Through lentivirus-mediated overexpression of GLT-1 tagged with red fluorescent protein (GLT-I-RFP), we also observed that GLT-1-RFP puncta in the processes of astrocytes were inhibited by the PPARa agonists. This reduction was prevented by the addition of the PPARa antagonist, GW6471. GLT-1-RFP was co -localized to the early endosome marker-EEA1 in astrocytes treated with the PPARa agonists. Moreover, PPARa-induced inhibition in membranous GLT-1 expression was abolished by the addition of dynamin inhibitor (dynasore). Furthermore, the co-treatment of astrocytes with PPARa agonists and dynasore, or with PPARa agonists and protein kinase C (PKC) inhibitor bis-indolylmaleimide 1 (BIS1), prevented the endocytosis of GLT-1-RFP. Based on the results, we conclude that the PPARa agonists increased GLT-1 endocytosis in astrocytes possibly through the PKC signaling pathway. In addition, our findings provide important information of PPARa involvement in the downregulation of astrocytic glutamate uptake via the promoted GLT-1 endocytosis. (C) 2017 Elsevier Ltd. All rights reserved.