Loss of Tumor Necrosis Factor α Potentiates Transforming Growth Factor β-mediated Pathogenic Tissue Response during Wound Healing

Abstract

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 ␣ (TNF␣) 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 TNF␣-null knockout (KO) mice than in wild-type mice. Such an unfavorable outcome in KO mice was abolished by Smad7 gene introduction, indicating the involvement of transforming growth factor ␤ or activin/Smad signaling. Bone marrow transplantation from wild-type mice normalized healing of the KO mice, suggesting the involvement of bone marrowderived inflammatory cells in this phenomenon. Coculture experiments showed that loss of TNF␣ in macrophages, but not in fibroblasts, augmented the fibroblast activation as determined by detection of ␣-smooth muscle actin, the hallmark of myofibroblast generation, mRNA expression of collagen I␣2 and connective tissue growth factor, and detection of collagen protein. TNF␣ in macrophages may be required to suppress undesirable excessive inflammation and scarring, both of which are promoted by transforming growth factor ␤, and for restoration of tissue architecture in a healing alkali-burned cornea in mice.

Transforming Growth Factor β1-mediated Activation of the Smooth Muscle α-Actin Gene in Human Pulmonary Myofibroblasts Is Inhibited by Tumor Necrosis Factor-α via Mitogen-activated Protein Kinase Kinase 1-dependent Induction of the Egr-1 Transcriptional Repressor

“…Secretion of the proinflammatory cytokine TNF-␣ also is elevated after tissue injury to assist in neovasculogenesis but persists during formation of the provisional matrix when it may help balance TGF␤1-mediated matrix biosynthesis in myofibroblasts and prevent progression to hypertrophic scarring (Verrecchia and Mauviel, 2004). The process of matrix equilibration seems quite important in tissue homeostasis since TGF␤1-mediated fibrosis after corneal injury is much more severe in TNF-␣ null mice that lack robust inflammatory responses compared with wild-type mice (Saika et al, 2006). Several pulmonary fibroproliferative diseases seem to involve dysfunctional signal transduction interplay between profibrotic TGF␤1 activated by alveolar phagocytic cells and proinflammatory TNF-␣ released by polarized T cells.…”

“…Although comparatively little is known about mechanisms of myofibroblast attenuation, one approach under study is based on the ability of proinflammatory cytokines such as interferon (IFN) ␥ and TNF-␣ to antagonize profibrotic TGF␤1 signaling (Verrecchia and Mauviel, 2004;Breitkopf et al, 2006;Dooley et al, 2006). TNF-␣ is a 17.5-kDa polypeptide produced by activated macrophages as well as injured stromal and epithelial cells (Verrecchia and Mauviel, 2004;Saika et al, 2006). TNF-␣ mediates host immune responses to microbial infection, tissue injury, and inflammation and has been implicated in etiology of chronic diseases such as rheumatoid arthritis, osteoarthritis, viral myocarditis, and heart failure (Tracey and Cerami, 1993).…”

Significance of lipid mediators in corneal injury and repair

“…tissue repair; however, myofi broblasts in culture, despite their expression of PAF-R, are also resistant to apoptosis, and after 24 h of treating isolated myofi broblasts with PAF, only 12% of the cells tested TUNEL positive ( 118 ). A recent study using TNF ␣ knockout mice in which corneas were alkali burnt also shows an increase in myofi broblasts, compared with wild-type mice ( 119 ). TNF ␣ modulates human corneal fi broblast apoptosis through inhibition of NF-B ( 120 ); in addition, myofi broblasts express TNF ␣ -R1, a major signaling receptor for TNF ␣ .…”

Impaired cornea wound healing in a tenascin C-deficient mouse model

“…Another set of cultures was incubated for 48 h with or without exogenous TGFb1 at 1.0 ng/ml and was processed for western blotting for aSMA protein as previously reported. 17,18 Statistical Analysis In HE histology, the numbers of the eyes with or without closure (or being occupied with newly formed granulation tissue) of the incision were determined and were statistically analyzed by using Fisher's exact test with significance as Po0.05. Data obtained from real-time RT-PCR were shown as means±s.d.…”

“…17,18 Ten dishes were prepared for each culture condition. Another set of cultures was incubated for 48 h with or without exogenous TGFb1 at 1.0 ng/ml and was processed for western blotting for aSMA protein as previously reported.…”