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S.T. Hikita, H.R. Jones, K.E. Blaschke, G.S. Ayoub, D.O. Clegg; Attenuation of NMDA–Induced Retinal Ganglion Cell Death in Osteopontin Null Mice . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1271.
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© ARVO (1962-2015); The Authors (2016-present)
Increasing evidence supports a role for inflammation in the progression of glaucoma, a progressive eye disease that is characterized by loss of retinal ganglion cells (RGC). Osteopontin (OPN), a multi–functional, matricellular protein with cytokine and chemoattractant activities, has been implicated in the immune response of various tissues to injury and disease. We have shown previously (ARVO, 2005, #B967) that OPN is a pro–inflammatory molecule in Experimental Autoimmune Uveitis (EAU) and that OPN was expressed by both infiltrating leukocytes and activated microglia. However, little is known about the function of OPN in the glaucomatous retina. Here, we investigate whether OPN exerts a pro–inflammatory effect in the pathogenesis of glaucoma.
N–methyl–D–aspartate (NMDA) was injected into the vitreous space of adult C57BL/6 mice to induce retinal cell death. Next, immunohistochemistry experiments were performed to 1) determine OPN protein localization before and after disease induction, and 2) to identify the cell type(s) expressing OPN protein. Then, ELISA assays were performed to quantify OPN protein amounts in extracts of neural retina and vitreous. To determine whether exogenous OPN could recapitulate immune–related pathologies observed in glaucoma, purified OPN proteins were injected intraocularly in wild type mice and retinal sections were analyzed via immunohistochemistry and TUNEL assay. Finally, OPN null mice were intraocularly injected with NMDA and RGCs were quantified. DBA/2J mice, which spontaneously develop pigmentary glaucoma, were also examined via immunohistochemistry.
Following NMDA treatment, OPN immunoreactivity increased in the retina and localized to a subset of activated isolectin B4–positive microglia. This OPN immunoreactivity was also observed in DBA/2J eyes with increased intraocular pressure. OPN immunoreactivity was present in RGCs prior to and following NMDA treatment. ELISA assays showed increased OPN protein levels in extracts of neural retina and vitreous from NMDA–treated eyes. Intravitreal injection of OPN in resulted in activation of microglia and recruitment of macrophages. Also, TUNEL–positive cells were observed in the RGC layer and throughout the retina. OPN null mice treated with NMDA showed increased RGC survival compared to wild type mice.
Our findings suggest that OPN is involved in the inflammatory mechanisms that may facilitate RGC death in glaucoma.
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