Etanercept, a Widely Used Inhibitor of Tumor Necrosis Factor-a (TNF- a), Prevents Retinal Ganglion Cell Loss in a Rat Model of Glaucoma Miin Roh1,2, Yan Zhang 1 , Yusuke Murakami1, Aristomenis Thanos1, Sung Chul Lee2, Demetrios G. Vavvas1, Larry I. Benowitz3*, Joan W. Miller1* 1 Angiogenesis Laboratory and Retina Service, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, United States of America, 2 Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea, 3 Laboratories for Neuroscience Research in Neurosurgery and F. M. Kirby Neurobiology Center, Children’s Hospital, Departments of Surgery and Ophthalmology and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts, United States of America Abstract Background: Visual loss in glaucoma is associated with pathological changes in retinal ganglion cell (RGC) axons and a slow decline in the RGC population. Age and elevated intraocular pressure (IOP) are the main risk factors for glaucomatous loss of vision. Several studies have implicated the proinflammatory cytokine tumor necrosis factor- a (TNF-a) as a link between elevated IOP and RGC death, but the cellular source of TNF-a and its causative role in RGC death remain uncertain. Here, using a rat model of glaucoma, we investigated the source of elevated TNF- a and examined whether Etanercept, a TNF-a blocker that is in common clinical use for other indications, is protective against RGC death. Methodology/Principal Findings: Episcleral vein cauterization (EVC) caused intraocular pressure (IOP) to be elevated for at least 28 days. IOP elevation resulted in a dramatic increase in TNF-a levels within a few days, axonal degeneration, and a 38% loss of RGCs by 4 weeks. Immunostaining coupled with confocal microscopy showed that OHT induced robust induction of TNF-a in Iba-1-positive microglia around the optic nerve head (ONH). Despite persistent elevation of IOP, Etanercept reduced microglial activation, TNF-a levels, axon degeneration in the optic nerve, and the loss of RGCs. Conclusions/Significance: Ocular hypertension (OHT) triggers an inflammatory response characterized by the appearance of activated microglia around the ONH that express TNF-a. Blocking TNF-a activity with a clinically approved agent inhibits this microglial response and prevents axonal degeneration and loss of RGCs. These findings suggest a new treatment strategy for glaucoma using TNF- a antagonists or suppressors of inflammation. Citation: Roh M, Zhang Y, Murakami Y, Thanos A, Lee SC, et al. (2012) Etanercept, a Widely Used Inhibitor of Tumor Necrosis Factor-a (TNF- a), Prevents Retinal Ganglion Cell Loss in a Rat Model of Glaucoma. PLoS ONE 7(7): e40065. doi:10.1371/journal.pone.0040065 Editor: Steven Barnes, Dalhousie University, Canada Received April 18, 2012; Accepted May 31, 2012; Published July 3, 2012 Copyright: 2012 Roh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the Neovascular Research Fund (JM, MR), the Bacardi Fund (DV), the Research to Prevent Blindness Foundation (DV), the Lions Eye Research Fund (DV), the Onassis Foundation (DV), a Fight For Sight Grant-in-Aid (DV), the Harvard Ophthalmology Department (DV), and National Eye Institute grants EY014104 (JM) and EY05690 (LB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exists. * E-mail: larry.benowitz@childrens.harvard.edu (LB); joan_miller@meei.harvard.edu (JM) Introduction Retinal ganglion cell (RGC) death and subsequent visual field defects that progress to blindness are the underlying pathophys- iology of glaucoma [1]. Age is the leading risk factor, with elevated intraocular pressure (IOP) being the only risk factor that can be modified [2–4]. Lowering IOP with surgery or drugs reduces the rate of optic nerve head (ONH) damage and progressive visual field loss by almost half, firmly establishing IOP reduction as an effective treatment for glaucoma. Proposed mechanisms linking RGC loss to elevated IOP include a compressive effect on the cribriform plates of the lamina cribrosa [5], pressure-induced tissue ischemia [6,7], and local cellular response mechanisms [8]. Considerable evidence suggests that the damage begins within the optic nerve due to structural changes within the lamina cribrosa [9], leading to cellular changes that influence RGC viability [10]. Histopathological studies of the glaucomatous ONH reveal astrocyte and microglial activation accompanying neural damage [11,12]. Activated microglia display an altered morphol- ogy, producing cytotoxic and degenerative factors [13,14]. TNF-a is a proinflammatory cytokine that is secreted in response to infection and trauma, and can lead to apoptosis in susceptible cells through the activation of caspases [15] or indirectly via activation of microglia [16]. TNF-a and its receptor have been detected in the ONH of glaucoma patients [12,17,18] and in a rat model of glaucoma [19], suggesting that TNF-a may be an important factor in the neurodegenerative process of glaucoma. Using a mouse model of glaucoma, we previously found that TNF-a mediates the cytotoxic effect of ocular hypertension (OHT) on RGCs through a mechanism that involves microglial activation and loss of oligodendrocytes [20]. However, those studies left open several questions, including the cellular source of PLoS ONE | www.plosone.org 1 July 2012 | Volume 7 | Issue 7 | e40065