The role of stem cell factor and c-KIT in keloid pathogenesis: do tyrosine kinase inhibitors have a potential therapeutic role?

Summary Background  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. Objectives  To examine the role of the SCF/c-KIT system in keloid pathogenesis. Methods  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. Results  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. Conclusion  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.