Etanercept, a Widely Used Inhibitor of Tumor Necrosis Factor-α (TNF-α), Prevents Retinal Ganglion Cell Loss in a Rat Model of Glaucoma

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-alpha (TNF-alpha) as a link between elevated IOP and RGC death, but the cellular source of TNF-alpha and its causative role in RGC death remain uncertain. Here, using a rat model of glaucoma, we investigated the source of elevated TNF-alpha and examined whether Etanercept, a TNF-alpha 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-alpha 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-alpha in Iba-1-positive microglia around the optic nerve head (ONH). Despite persistent elevation of IOP, Etanercept reduced microglial activation, TNF-alpha 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-alpha. Blocking TNF-alpha 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-alpha antagonists or suppressors of inflammation.