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Background Keloid scarring is a dermal fibroproliferative disorder characterized by increased fibroblast proliferation and excessive production of collagen and extracellular matrix (ECM) components. To date, the role of cytokines in keloid pathogenesis has not been completely unravelled. Interleukin (IL)-18 is a pro-inflammatory cytokine that plays important roles in wound healing, fibrogenesis and carcinogenesis. Objectives Our aim was to study the role of the IL-18 system in keloid pathogenesis. Materials and methods Expression and localization of IL-18 and its receptor (IL-18R) were investigated in normal skin and keloid tissues using Western blot and immunohistochemistry. We further studied the expression of the IL-18 system in normal and keloid-derived cell lines in a coculture model. Results Results from Western blot and immunohistochemistry revealed that IL-18, IL-18Rα and IL-18Rβ expression was elevated in keloid tissue compared with normal skin tissue. Studies on the expression of IL-18 and its antagonist, IL-18 binding protein (IL-18BP), using a coculture model demonstrated severe IL-18/IL-18BP imbalance in keloid keratinocyte/keloid fibroblast (KK/KF) cocultures with significant elevation of bioactive IL-18 whereas IL-18BP levels remained the same. This overproduction of bioactive IL-18 in keloid cocultures could be due to increased caspase-1 and decreased caspase-3 expression in keloid tissue, as well as decreased soluble IL-10 levels observed in keloid cocultures. The important inductive effects of IL-18 on KFs were further underscored by the observation that exposure of KF to IL-18 resulted in increased collagen and ECM component synthesis, and increased secretion of profibrotic cytokines such as IL-6 and IL-8. Finally, the addition of phosphatidylinositol 3-kinase (PI3K), mitogen activation protein kinase (MAPK), specificity protein 1 (Sp1) and mammalian target of rapamycin (mTOR) inhibitors inhibited IL-18 secretion in keloid cocultures. Conclusions The present study has proven that the IL-18 system plays an important role in keloid pathogenesis via epithelial-mesenchymal interactions. It also suggests a therapeutic potential of PI3K, MAPK, Sp1 and mTOR inhibitors in the treatment of keloid scarring. [ABSTRACT FROM AUTHOR]

Keloids are fibroproliferative disorders characterized by increased deposition of extracellular matrix components. Stem cell factor (SCF) and its receptor c-KIT are expressed in a wide variety of cells and have also been demonstrated to be important modulators of the wound healing process. To examine the role of the SCF/c-KIT system in keloid pathogenesis. Immunohistochemical staining and Western blot analyses were used to examine localization and expression of SCF and c-KIT in keloid and normal skin tissue. This was followed by the detection of SCF and c-KIT expression in fibroblasts cultured in vitro and fibroblasts exposed to serum. To investigate the effect of epithelial-mesenchymal interactions, a two-chamber system was employed in which keratinocytes on membrane inserts were cocultured with the fibroblasts. SCF and c-KIT expression levels in all cell extracts and conditioned media were assayed by Western blotting. In another set of experiments, the effect of imatinib (Glivec, Gleevec; Novartis Pharma AG, Basel, Switzerland) on keloid fibroblasts was examined. SCF and c-KIT were upregulated in keloid scar tissue and in cultured fibroblasts stimulated with serum, highlighting their importance in the initial phase of wound healing. We further demonstrated that epithelial-mesenchymal interactions, mimicked by coculture of keratinocytes and fibroblasts in vitro, not only stimulated secretion of the soluble form of SCF in keloid cocultures but also brought about shedding of the extracellular domain of c-KIT perhaps by upregulation of tumour necrosis factor-α converting enzyme which was also upregulated in keloid scars in vivo and keloid cocultures in vitro. In addition keloid cocultures expressed increased levels of phosphorylated c-KIT highlighting an activation of the SCF/c-KIT system. Finally, we demonstrated that imatinib, a tyrosine kinase inhibitor, may be a possible therapeutic agent for keloids. These data indicate that the SCF/c-KIT system plays an important role in scar pathogenesis, and underscore the role of imatinib as a key therapeutic agent in keloid scars. [ABSTRACT FROM AUTHOR]