Influence of Interleukin-1 Beta Induction and Mitogen-activated Protein Kinase Phosphorylation on Optic Nerve Ligation-induced Matrix Metalloproteinase-9 Activation in the Retina

Ischemic damage to the retina is a multifaceted process that results in irreversible loss of ganglion cells and blinding disease. Although the mechanisms underlying ischemia-induced ganglion cell death in the retina are not clearly understood, we have recently reported that retinal damage induced by ligation of the optic nerve results in increased matrix metalloproteinase-9 (MMP-9) synthesis and promotes ganglion cell loss. In this study, we have investigated the roles of IL-1beta and mitogen activated protein kinases in MMP-9 induction in the retina. Optic nerve ligation led to a transient increase in IL-1beta and MMP-9 levels and phosphorylation of p42/p44 mitogen activated protein kinases (extracellular signal-regulated kinases, ERK1 and ERK2) in the retina. We found no significant increase in phosphorylation of p38 MAP kinase or c-jun N-terminal kinases indicating that ERK1/2 plays a major role in MMP-9 induction. Intravitreal injection of IL-1 receptor antagonist (IL-1Ra) or MAP kinase inhibitor U0126 significantly decreased both ERK1/2 phosphorylation and MMP-9 induction suggesting that interruption of this cascade might attenuate retinal damage. In support of this, intravitreal injection of IL-1Ra and U0126 offered significant protection against optic nerve-induced retinal damage. These results suggest that optic nerve ligation-induced IL-1beta promotes retinal damage by increasing MMP-9 synthesis in the retina.