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M. K. Ko, N. A. Rao; TLR4-Dependent, TNF- Mediated Oxidative Stress/Mitochondrial DNA Damage of Photoreceptor as an Innate Immune Response. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2492.
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© ARVO (1962-2015); The Authors (2016-present)
Our previous studies showed oxidative stress in the photoreceptor mitochondria during the early phase of experimental autoimmune uveitis even before the infiltration of inflammatory cells. Moreover, complete Freund's adjuvant (CFA) alone, injected subcutaneously, induced the innate immune response of TLR4 expression in the retina. Herein, we investigated whether TLR4 activation causes retinal photoreceptor oxidative stress as an innate immune response.
To screen the differential gene regulation profiles in oxidative stress and apoptosis, we used PCR super-array in the retina of B10.RIII mice injected with CFA compared to control groups on day 5 post-injection (p.i). CFA-mediated TLR4 activation, oxidative stress, mitochondrial DNA (mtDNA) damage, and apoptosis were determined in MyD88, TLR4, TNF-α, and caspase 7 knockout (KO) mice using quantitative real-time PCR (qPCR), ELISA, Western blot analysis, and immunohistochemistry.
Oxidative stress-related and apoptosis genes were up-regulated in retinas of CFA-injected mice compared to controls on day 5 p.i without any inflammatory cell infiltration in retina and uvea. mtDNA damage and oxidative stress, confirmed by qPCR and 8-OHdG immunostaining, were shown especially in inner segments of photoreceptors of CFA-injected B10.RIII; however, there was no damage in MyD88 KO mice. Along with up-regulation of oxidative stress related genes, TLR4-mediated TNF-α expression, shown in the retina and serum, was co-localized with TNFR1 and 8-OHdG; however, CFA-mediated iNOS was significantly reduced in TNF-α KO mice. There were CFA-mediated induction of caspase 7 and caspase 8 and further activation of caspase 3 was attenuated by caspase 8 inhibitor in vivo and significantly blocked in caspase 7 KO mice.
TLR4-mediated innate immune response, mainly via TNF-α, resulted in oxidative stress and apoptotic phenomenon in the photoreceptor, in which depended on MyD88-mediated pathway but not depended in adaptive immunity. Among up-regulated apoptotic genes, caspase 7 may be a major executioner in the induction of mitochondrial pathway-mediated apoptosis.
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