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Animal cornea is an avascular transparent tissue that is suitable for research on wound healing-related scarring and neovascularization. Here we show that loss of tumor necrosis factor α (TNFα) potentiates the undesirable, pathogenic response of wound healing in an alkali-burned cornea in mice. Excessive invasion of macrophages and subsequent formation of a vascularized scar tissue were much more marked in TNFα-null knockout (KO) mice than in wild-type mice. Such an unfavorable outcome in KO mice was abolished by Smad7gene introduction, indicating the involvement of transforming growth factor β or activin/Smad signaling. Bone marrow transplantation from wild-type mice normalized healing of the KO mice, suggesting the involvement of bone marrow-derived inflammatory cells in this phenomenon. Co-culture experiments showed that loss of TNFα in macrophages, but not in fibroblasts, augmented the fibroblast activation as determined by detection of α-smooth muscle actin, the hallmark of myofibroblast generation, mRNA expression of collagen Iα2 and connective tissue growth factor, and detection of collagen protein. TNFα in macrophages may be required to suppress undesirable excessive inflammation and scarring, both of which are promoted by transforming growth factor β, and for restoration of tissue architecture in a healing alkali-burned cornea in mice.

We evaluated the therapeutic efficacy of topical administration of SN50, an inhibitor of nuclear factor-κB, in a corneal alkali burn model in mice. An alkali burn was produced with 1 N NaOH in the cornea of C57BL/6 mice under general anesthesia. SN50 (10 μg/μl) or vehicle was topically administered daily for up to 12 days. The eyes were processed for histological or immunohistochemical examination after bromodeoxyuridine labeling or for semiquantification of cytokine mRNA. Topical SN50 suppressed nuclear factor-κB activation in local cells and reduced the incidence of epithelial defects/ulceration in healing corneas. Myofibroblast generation, macrophage invasion, activity of matrix metalloproteinases, basement membrane destruction, and expression of cytokines were all decreased in treated corneas compared with controls. To elucidate the role of tumor necrosis factor (TNF)-α in epithelial cell proliferation, we performed organ culture of mouse eyes with TNF-α, SN50, or an inhibitor of c-Jun N-terminal kinase (JNK) and examined cell proliferation in healing corneal epithelium in TNF-α−/−mice treated with SN50. An acceleration of epithelial cell proliferation by SN50 treatment was found to depend on TNF-α/JNK signaling. In conclusion, topical application of SN50 is effective in treating corneal alkali burns in mice.

Damage to the cornea from chemical burns is a serious clinical problem that often leads to permanent visual impairment. Because transforming growth factor (TGF)-β has been implicated in the response to corneal injury, we evaluated the effects of altered TGF-β signaling in a corneal alkali burn model using mice treated topically with an adenovirus (Ad) expressing inhibitory Smad7 and mice with a targeted deletion of the TGF-β/activin signaling mediator Smad3. Expression of exogenous Smad7 in burned corneal tissue resulted in reduced activation of Smad signaling and nuclear factor-κB signaling via RelA/p65. Resurfacing of the burned cornea by conjunctival epithelium and its differentiation to cornea-like epithelium were both accelerated in Smad7-Ad-treated corneas with suppressed stromal ulceration, opacification, and neovascularization 20 days after injury. Introduction of the Smad7 gene suppressed invasion of monocytes/macrophages and expression of monocyte/macrophage chemotactic protein-1, TGF-β1, TGF-β2, vascular endothelial growth factor, matrix metalloproteinase-9, and tissue inhibitors of metalloproteinase-2 and abolished the generation of myofibroblasts. Although acceleration of healing of the burned cornea was also observed in mice lacking Smad3, the effects on epithelial and stromal healing were less pronounced than those in corneas treated with Smad7. Together these data suggest that overexpression of Smad7 may have effects beyond those of simply blocking Smad3/TGF-β signaling and may represent an effective new strategy for treatment of ocular burns.