Expression of Toll-like receptor 4 in retina following optic nerve crush in rat

Background: Toll-like receptor 4 (TLR4) is an immune related receptor. It plays an important role in inducing inflammation response. The inflammatory response secondary to optic nerve crush will results in serious retinal damage. It is worthy of studying the expression and effect of TLR4 in retina after optic nerve crush. Objective: This experimental study was to explore the role of TLR4 in the loss of retinal ganglion cells (RGCs) after optic nerve crush. Methods: Twenty-four SPF adult health Sprague-Dawley (SD) rats were used in the study and radomized into two groups based to the experimental time. The optical nerve crush models were established by crushing the optical nerve in the right eyes of the rats, and the left normal eyes served as controls. The rats were sacrificed by over anesthesia and retinas were isolated 3 days and 7 days after operation. Expression of TLR4 in the retinas was detected using immunofluorescence method. Reverse trancription PCR (RT-PCR) and Western blot were applied respectively for the detection of TLR4 mRNA and protein in the retinas. The apoptosis of RGCs was evaluated using TUNEL staining. The use and care of experimental animals followed the "Guide for the Care and Use of Laboratory Animals" of NIH. This study was approved by the Institutional Animal Care and Use Committee at the Zhongshan Ophthalmic Center. Results: The expression of TLR4 in rat retinas presented with green fluorescence mainly in the inner layer of retinas. The fluorescence was enhanced in the model 3 days group and the model 7 days group compared with the corresponding control groups. The relative expressing values of TLR4 mRNA in the retinas were 2.92 ± 0.06 and 3.92 ± 0.12 in the model 3 days and 7 days groups, respectively, which were significantly higher than 2.87 ± 0.12 and 3.44 ± 0.17 in the control 3 days and 7 days group (t_3d=-12.888, P < 0.001; t_7d=-4.669, P=0.010). In the model 3 days group and model 7 days group, the grey values of TLR4 protein were 1.14 ± 0.05 and 1.49 ± 0.03, and those in the control 3 days and 7 days groups were 0.99 ± 0.09 and 1.38 ± 0.07, showing significant differences between them (t_3d=-11.324, P < 0.001; t_7d=-5.638, P=0.005). Apoptotic RGCs were obviously increased in the optic nerve damage group in comparison with the control group. Conclusions: The TLR4 is over-expressed in the inner layer of retina after optic nerve crush, which suggestes that TLR4 is probably involved in the loss of RGCs after optic nerve crush.