Role of Annexin A2 in Glutamate‐induced Extracellular matrix (ECM) Changes and Retinal Ganglion Cell Death

Abstract

Glutamate excitotoxicity mediated increase in intracellular Ca2+ levels has been implicated in the pathogenesis of glaucoma. The downstream events leading to RGC damage after excitotoxic injury are poorly understood. It is suggested that retinal ganglion cells (RGCs) respond to excitotoxic injury by activating protease‐mediated remodeling of the extracellular matrix (ECM) through the plasminogen activator (PA)‐plasminogen (PG) system which results in detachment induced apoptosis of RGCs. Annexin A2 is a Ca2+ and phospholipid binding protein, it serves as a proteolytic center at the cell surface by recruiting matrix remodeling proteases and their substrates. Our goal is to determine the role of the annexin A2 and its associated proteases in glutamate excitotoxicity. Here we characterize the expression of annexin A2 in rat retinal sections, primary RGCs and in a transformed cell line; RGC‐5. Live cell Ca2+ imaging and time lapse confocal microscopy demonstrate glutamate‐mediated Ca2+ influx in RGC‐5 cells. A23187, a Ca2+ ionophore increases the phospholipid binding affinity of annexin A2. We demonstrate that annexin A2 translocates to the membrane of RGC‐5 cells upon glutamate treatment in a process that is independent of new protein synthesis and regulated by Ca2+.These results suggest that annexin A2 acts as a facilitator in glutamate induced changes in the ECM and subsequent RGC death.(Supported in part by grants from the National Center for Minority Health and Health Disparities, NIH (P20 MD001633), and Alcon Research, Inc.)