title: Prothymosin-alpha preconditioning activates TLR4-TRIF signaling to induce protection of ischemic retina.
abstract: Prothymosin-alpha protects the brain and retina from ischemic damage. Although prothymosin-alpha contributes to toll-like receptor (TLR4)-mediated immnunopotentiation against viral infection, the beneficial effects of prothymosin-alpha-TLR4 signaling in protecting against ischemia remain to be elucidated. In this study, intravitreal administration of prothymosin-alpha 48 h before induction of retinal ischemia prevented retinal cellular damage as evaluated by histology, and retinal functional deficits as evaluated by electroretinography. Prothymosin-alpha preconditioning completely prevented the ischemia-induced loss of ganglion cells with partial survival of bipolar and photoreceptor cells, but not amacrine cells, in immunohistochemistry experiments. Prothymosin-alpha treatment in the absence of ischemia caused mild activation, proliferation, and migration of retinal microglia, whereas the ischemia-induced microglial activation was inhibited by prothymosin-alpha preconditioning. All these preventive effects of prothymosin-alpha preconditioning were abolished in TLR4 knock-out mice and by pre-treatments with anti-TLR4 antibodies or minocycline, a microglial inhibitor. Prothymosin-alpha preconditioning inhibited the retinal ischemia-induced up-regulation of TLR4-related injury genes, and increased expression of TLR4-related protective genes. Furthermore, the prothymosin-alpha preconditioning-induced prevention of retinal ischemic damage was abolished in TIR-domain-containing adapter-inducing interferon-β knock-out mice, but not in myeloid differentiation primary response gene 88 knock-out mice. Taken together, the results of this study suggest that prothymosin-alpha preconditioning selectively drives TLR4-TIR-domain-containing adapter-inducing interferon-β signaling and microglia in the prevention of retinal ischemic damage. We propose the following mechanism for prothymosin-alpha (ProTα) preconditioning-induced retinal prevention against ischemia: ProTα preconditioning-induced prevention of retinal ischemic damage is mediated by selective activation of the TIR-domain-containing adapter-inducing interferon-β (TRIF)- interferon regulatory factor 3 (IRF3) pathway downstream of toll-like receptor 4 (TLR4) in microglia, resulting in up-regulation of TRIF-IRF3-dependent protective genes and down-regulation of myeloid differentiation primary response gene 88 (MyD88)-Nuclear factor (NF)κB-dependent injury genes. Detailed investigations would be helpful to test the efficacy of ProTα as a therapeutic agent for the prevention of ischemic disorders.
authors.affiliation: Department of Pharmacology and Therapeutic Innovation, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Sebok Kumar
authors.initials: SK
authors.lastname: Halder
authors.affiliation: Department of Pharmacology and Therapeutic Innovation, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Hayato
authors.initials: H
authors.lastname: Matsunaga
authors.affiliation: Laboratory of Vaccine Science, Immunology Frontier Research Center, Osaka University, Osaka, Japan.
authors.forename: Ken J
authors.initials: KJ
authors.lastname: Ishii
authors.affiliation: Department of Pharmacology and Therapeutic Innovation, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D007511:Ischemia / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology; D011498:Protein Precursors / Q000494:pharmacology*; D012164:Retinal Diseases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013947:Thymosin / Q000031:analogs & derivatives* / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D008070:Lipopolysaccharides; D011498:Protein Precursors; D013947:Thymosin; D051197:Toll-Like Receptor 4; C476286:Ticam1 protein, mouse; C493487:Tlr4 protein, mouse; C040782:prothymosin alpha
keywords: TLR4; TRIF; ischemia; microglia; neuroprotection; prothymosin-alpha