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L. Chen, Y. Xia; IKKβ Promotes Corneal Epithelial Cell Wound Healing. Invest. Ophthalmol. Vis. Sci. 2010;51(13):381.
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Immediately after corneal epithelium injury, various inflammatory cytokines and growth factors, including TNF-α, increase their levels at the wounding area. IKKβ is a kinase crucial for the transmission of cytokine signals, such as TNF-α, to the activation of transcription factor NF-ΚB, which in turn regulates gene expression. IKKβ/NF-ΚB pathway is involved in diverse biological processes. We found in previous studies that IKKβ is abundantly expressed in mouse corneal epithelial cells and inhibition of IKKβ activity by a chemical inhibitor delays healing of mouse corneal epithelium debridement, yet the underlining molecular mechanisms need to be clarified.
The telomerase-immortalized human corneal epithelial cells (hTCEpi) and TPCA-1, which is an IKKβ inhibitor, were used as an in vitro system. The hTCEpi cells incubated with various inflammatory cytokines and growth factors, together with TPCA-1 were used to monitor in vitro scrape wound healing and cell growth. The activation status of various signaling pathways was determined by western blot. For in vivo study, a triple transgenic mouse line Krt12rtTA/tet-O-Cre/IkkβFlox was generated, in which the ablation of Ikkβ gene can be induced specifically in the corneal epithelial cells. The corneal epithelial debridement was conducted between control mice and mice with induced Ikkβ ablation in the corneal epithelium. The healing rates were calculated and the eyes were collected at different stages after the wound. Cell proliferation, apoptosis and various signliang pathways were evaluated by Immunohistochemistry.
hTCEpi culture with TNF-α and TPCA-1 do not affect cell growth, but TPCA-1 significantly suppresses scrape wound healing in the presence or absence of TNF-α. Additionally, TPCA-1 blocks TNF-α induced activation of NF-ΚB, p38, and ERK at late stage, but it does not affect TNF-α induced SMAD2, JNK and early ERK activation. Genetic ablation of Ikkβ gene is correlated with delayed healing of corneal epithelial debridement as well as suppressed NF-ΚB and p38 activation in mouse, whereas no difference in cell proliferation or apoptosis was observed.
IKKβ potentiates corneal epithelial cell wound healing both in vitro and in vivo. As IKKβ does not apparently affect cell proliferation or death, it may serve to promote corneal epithelial cell migration. Additionally, TNF-α induces both IKKβ dependent- and independent pathways, providing potential downstream targets of IKKβ that may participate in cell migration.
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