Hindawi Publishing Corporation Journal of Diabetes Research Volume 2013, Article ID 658548, 9 pages http://dx.doi.org/10.1155/2013/658548 Research Article The ERK 1/2 Inhibitor U0126 Attenuates Diabetes-Induced Upregulation of MMP-9 and Biomarkers of Inflammation in the Retina Ghulam Mohammad, Mohammad Mairaj Siddiquei, Mohammad Imtiaz Nawaz, and Ahmed M. Abu El-Asrar Department of Ophthalmology, College of Medicine, King Saud University, P.O. Box 245, Riyadh 11411, Saudi Arabia Correspondence should be addressed to Ghulam Mohammad; gmkbiochembhu@gmail.com Received 21 January 2013; Accepted 25 March 2013 Academic Editor: Mohamed Al-Shabrawey Copyright © 2013 Ghulam Mohammad et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis study was conducted to determine the expression of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in a time-dependent manner and the efect of extracellular-signal-regulated kinases-1/2 (ERK 1/2 ) inhibition on the expressions of MMP-9, TIMP-1, and infammatory biomarkers in the retinas of diabetic rats. Te expression of MMP-9 was quantifed by zymography, and the mRNA level of MMP-9 and TIMP-1 was quantifed by RT-PCR. Te expression of inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-) was examined by Western blot analysis. MMP-9 expression was signifcantly higher in diabetic rat retinas compared to controls at all time points.TIMP-1 expression was nonsignifcantly upregulated at 1week of diabetes and was signifcantly downregulated at 4 and 12 weeks of diabetes. Intravitreal administration of the ERK 1/2 inhibitor U0126 prior to induction of diabetes decreased ERK 1/2 activation, attenuated diabetes-induced upregulation of MMP-9, iNOS, IL-6, and TNF- and upregulated TIMP-1 expression. In MMP-9 knockout mice, diabetes had no efect on retinal iNOS expression and its level remained unchanged. Tese data provide evidence that ERK 1/2 signaling pathway is involved in MMP-9, iNOS, IL-6, and TNF- induction in diabetic retinas and suggest that ERK 1/2 can be a novel therapeutic target in diabetic retinopathy. 1. Introduction Diabetic retinopathy (DR) is the most common microvascu- lar complication of diabetes and remains one of the leading causes of blindness worldwide. DR is characterized by grad- ual progressive alterations in the retinal microvasculature, leading to loss of retinal capillary cells, disruption of vascular barrier, retinal nonperfusion, and preretinal neovasculariza- tion [1–4]. However, the exact molecular mechanisms, which mediate such response, remain largely unknown. In recent years, it has become evident that infammatory mechanisms play an important role in the pathogenesis of DR, and proinfammatory mediators contribute signifcantly to the development and progression of DR [5–13]. Infammation is a multistep process where proteases, growth factors, cytokines, and chemokines are released from retinal cells and interact with each other to promote infammation in the diabetic retinal microenviroment. In the retina, it was shown that diabetes activates induction of proinfammatory mediators such as monocyte chemoattractant protein-1 (MCP-1) [8], interleukin-6 (IL-6) [9], intercellular adhesion molecule- 1 (ICAM-1) [10], inducible nitric oxide synthase (iNOS) [11], tumor necrosis factor-alpha (TNF-)[12], and matrix metalloproteinase-9 (MMP-9) [13]. Recently, much research has focused on MMP-9 because it acts as a potent proin- fammatory, proangiogenic and pro-apoptotic factor, and in diabetes, latent MMP-9 is activated in the retina and facili- tates retinal capillary cell apoptosis, which is a pathological hallmark of DR development [13–17]. Matrix metalloproteinases (MMPs) are a large family of proteinases that remodel extracellular matrix components and play an important role in the regulation of numerous physiological processes including vascular remodeling and angiogenesis. Altered MMPs activities have been implicated