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M. Valapala, J. K. Vishwanatha; Role of Annexin A2 in Glutamate-Induced ECM Changes and Retinal Ganglion Cell Death. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3701.
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Glutamate excitotoxicity has been implicated as one of the factors contributing to the pathogenesis of glaucoma. Hyperstimualtion of glutamate receptors as a result of excessive accumulation of glutamate leads to elevated intracellular levels of calcium. The downstream events leading to RGC damage after excitotoxic injury are poorly understood. Recent evidence suggests 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 and associated matrix metalloproteinases. Pathological proteolysis of the ECM results in detachment induced apoptosis of RGCs. Annexin A2 is a calcium-dependent phospholipid binding protein which 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 proteolytic center and its associated proteases in glutamate induced changes in the ECM and subsequent loss of RGCs.Methods &
Here we characterize the expression of annexin A2 in rat retinal sections, primary RGCs and in a differentiated and undifferentiated transformed cell line; RGC-5. Live cell calcium imaging and time lapse confocal microscopy were performed to demonstrate glutamate-mediated calcium influx in RGC-5 cells. Treatment with a calcium ionophore, A23187 increases the phospholipid binding affinity of annexin A2. We also show that annexin A2 translocates from the cytosol to the extracytoplasmic membrane in both differentiated and undifferentiated RGC-5 cells upon glutamate induced exictotoxicity. Furthermore, this translocation is independent of new protein synthesis and is regulated by intracellular levels of calcium.
These results suggest that elevated levels of extracellular annexin A2 acts as a facilitator in glutamate induced changes in the ECM and subsequent retinal ganglion cell death. (This study was supported in part by grants from the National Center for Minority Health and Health Disparities, National Institutes of Health (P20 MD001633), and Alcon Research, Inc.)
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