The Effect of A2A Receptor Antagonist on Microglial Activation in Experimental Glaucoma

PURPOSE. We investigated the effect of A(2A) receptor (A(2A)R) antagonist on microglial activation and retinal ganglion cell (RGC) survival under chronic ocular hypertension (COH), and explored the relationship between microglial activation and RGC survival by means of in vitro and in vivo experiments. METHODS. An animal model of COH was induced in one eye of male Sprague-Dawley (SD) rats by ligation of three episcleral veins. The survival of RGCs and the activation of microglia under COH without or with intravitreous injection of A(2A)R antagonist ZM241385 were assessed by fluorescent labeling, real time PCR and Western blot. ELISA was used to measure the secretion of inflammatory mediators by microglia when glutamate and/or ZM241385 was added into the culture system. RESULTS. Compared to the baseline, RGC density 2 weeks after COH induction decreased at the central (2436 +/- 143 cells/mm(2) pre-and 2130 +/- 148 cells/mm(2) post-COH induction) and peripheral (2219 +/- 140 cells/mm(2) pre-and 1953 +/- 142 cells/mm(2) post-COH induction) retina. The microglia changed their ramified morphology to an amoeboid form with increase in TNF-alpha and IL-1 beta expression after COH. These changes, however, were ameliorated with intravitreous ZM241385 (RGC density only dropped to 2287 +/- 135 cells/mm(2)). The upregulation of those proinflammatory cytokines secreted by microglia in vitro under high concentration of glutamate was downregulated when ZM241385 was added into the culture system. CONCLUSIONS. A2AR antagonist ZM241385 could reduce the activation of microglia and downregulate the proinflammatory cytokines expression under the conditions of COH and high concentration of glutamate, which may be one of the mechanisms that protected RGCs in experimental glaucoma.