Keloid fibroblasts resist ceramide-induced apoptosis by overexpression of insulin-like growth factor I receptor.

Keloids are benign dermal tumors, characterized by overgrowth of lesions, invasiveness beyond the original boundary of the insult, and recurrence of lesions. The exact etiology is unknown, however. Our hypothesis is that keloids are acquired as a result of an abnormal or prolonged wound healing process, with persistent proliferation and extracellular matrix production of fibroblasts that should otherwise discontinue in normal wound healing. In this study, we examined the response of keloid fibroblasts to proapoptotic signaling. Cell-permeable ceramide, N-acetyl-D-sphingosine, induced apoptosis of dermal fibroblasts in a dose- and time-dependent manner, which was detected by phase contrast microscopy, fluorescent microscopy, the TUNEL method, flow cytometric analysis, and WST-1 assay. In contrast, keloid fibroblasts resisted apoptosis induced by N-acetyl-D-sphingosine (percent survival with 40 mM ceramide treatment for 12 h, normal versus keloid: 9.6% +/- 6.6% vs 66.8% +/- 5.5%). Western blotting analysis showed insulin-like growth factor I receptor overexpression in keloid fibroblasts, but not in normal fibroblasts. Exogenously added insulin-like growth factor I enhanced the resistance of keloid fibroblasts to ceramide-induced apoptosis. Wort- mannin, a phosphatidylinositol 3 kinase inhibitor, suppressed the antiapoptotic action of insulin-like growth factor I in keloid fibroblasts. Our results suggest that keloid fibroblasts overexpressing insulin-like growth factor I receptor are resistant to apoptosis, thus allowing persistent proliferation and production of excessive extracellular matrix. J Invest Dermatol 115:1065-1071 2000