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Galina Dvoriantchikova, Andrea Rachelle Santos, Xenia Dvoriantchikova, Dmitry V Ivanov; The Role Of Myd88 And Trif Signaling-Mediated Inflammation In Ischemia-Reperfusion-Induced Retinal Damage. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1893.
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Toll-like receptors have been demonstrated to play an important role in ischemia-reperfusion (IR)-induced innate immune response in the central nerve system (CNS). At the same time, the role of two toll-like receptor signaling cascades, Myd88- and Trif-dependent, in IR injury was poorly understood. We performed this study to clarify the role of these pathways in IR induced inflammation and neuronal damage.
Myd88- and Trif-deficient animals and C57BL/6J mice as the wild type control were obtained from the Jackson Laboratory. Retinal IR injury was induced by unilateral elevation of intraocular pressure for 45 minutes by direct corneal cannulation. The changes in expression of toll-like receptor family members, Myd88, Trif, as well as pro-inflammatory genes 6 hours postreperfusion were assessed by quantitative RT-PCR. Ganglion cell layer (GCL) neurons, astrocytes and microglial cells were identified in flat-mounted retinas by immunohistochemistry using cell type specific markers NeuN, Gfap and Cd11b respectively. Cell death was evaluated by the direct counting of neurons in the GCL of flat-mounted retinas seven days postreperfusion.
We found that while expression levels of Tlr1, Tlr2 and Myd88 were increased in ischemic retinas, transcription levels of Tlr3, Tlr4 and Tlr9 were reduced in ischemic retinas after 6 hours. At the same time, we found no significant differences in the level of Tlr7 and Trif expression between ischemic and sham-operated retinas. The mice that lacked Trif showed significantly reduced expression of pro-inflammatory genes 6 hours after reperfusion and significantly increased survival of GCL neurons 7 days after IR. At the same time, while Myd88 deficient animals had an even lower level of inflammation in ischemic tissue compared to the mice that lacked Trif, the levels of damage in ischemic tissue of Myd88 deficient animals varied considerably.
Our findings suggest that while Trif signaling promotes neurotoxic inflammation in ischemic tissue, Myd88 signaling cascade may play a more complex role in IR injury. Thus, the design of effective therapy for patients suffering from IR injury should be based on a clear delineation of the beneficial and detrimental effects of toll-like receptor signaling mediated inflammation in ischemic tissue.
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