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Shravan K Chintala; Toll-like receptor 3 (TLR3) promotes IOP-mediated degeneration of retinal ganglion cells in a mouse model of glaucoma. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2544.
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© ARVO (1962-2015); The Authors (2016-present)
Elevated intraocular pressure (IOP) has been suggested to promote the degeneration of retinal ganglion cells (RGCs) through oxidative stress in Primary Open-Angle Glaucoma (POAG). However, the signaling mechanisms underlying oxidative stress-mediated RGC degeneration remain unclear. This study investigated the role of an oxidative stress-response protein, Toll-like receptor 3 (TLR3), in the degeneration of RGCs in a mouse model of POAG.
IOP was elevated in C57BL/6 and Tlr3 knockout mice by injecting fluorescent- polystyrene microbeads into the anterior chamber. Once a week, until four weeks, IOP levels were measured by using Tono-Pen XL. At various time periods after injecting microbeads, relative levels of TLR3 in retinal proteins extracted from wild-type and Tlr3 knockout mice was determined by western blot analysis. Localization of TLR3 protein in the retina was determined by immunohistochemistry. Degeneration of RGCs was assessed by immunohistochemistry by using an antibody against brain-specific home box/POU domain protein 3a (Brn3a). Degeneration of axons in the retina was determined by using an antibody against neuronal class III beta-tubulin (Tuj1), and the degeneration of axons in the optic nerve was assessed by transmission electron microscopy (TEM).
At the end of four weeks, microbead-injected eyes developed elevated IOP ranging from 24-26 mm Hg when compared to saline-injected control eyes (12-14 mm Hg). Elevated IOP up-regulated TLR3, as well as its downstream target protein c-Jun-N-terminal kinase-3 (JNK3), specifically in RGCs and promoted ~54% degeneration of RGCs when compared to control retinas. At the end of four weeks, elevated IOP promoted significant degeneration of axons in both the retina and the optic nerve. Injection of microbeads into Tlr3 knockout mouse eyes also led to an increase in IOP similar to the levels observed in microbead-injected wild-type mouse eyes. However, neither TLR3 nor JNK3 protein levels were increased in the retinas from Tlr3 knockout mice and elevated IOP resulted in only ~28% degeneration of RGCs.
The results presented in this study provide evidence that elevated IOP promotes the degeneration of RGCs by up-regulating the protein levels of TLR3 and JNK3 in RGCs. These findings suggest the inhibition of TLR3 as well as JNK3 protein levels may lead to neuroprotection in glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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