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, i nvasiveness beyond the original boundary of the insult, and recurrence of l esions. The exact etiology is unknown, however. Our hypothesis is that kelo ids are acquired as a result of an abnormal or prolonged wound healing proc ess, with persistent proliferation and extracellular matrix production of f ibroblasts that should otherwise discontinue in normal wound healing. In th is study, we examined the response of keloid fibroblasts to proapoptotic si gnaling. Cell-permeable ceramide, N-acetyl-D-sphingosine, induced apoptosis of dermal fibroblasts in a dose- and time-dependent manner, which was dete cted by phase contrast microscopy, fluorescent microscopy, the TUNEL method , flow cytometric analysis, and WST-1 assay. In contrast, keloid fibroblast s resisted apoptosis induced by N-acetyl-D-sphingosine (percent survival wi th 40 mM ceramide treatment for 12 h, normal versus keloid: 9.6% +/- 6.6% v s 66.8% +/- 5.5%). Western blotting analysis showed insulin-like growth fac tor I receptor overexpression in keloid ftbroblasts, but not in normal fibr oblasts. Exogenously added insulin-like growth factor I enhanced the resist ance of keloid fibroblasts to ceramide-induced apoptosis. Wortmannin, a pho sphatidylinositol 3 kinase inhibitor, suppressed the antiapoptotic action o f insulin-like growth factor I in keloid fibroblasts. Our results suggest t hat keloid fibroblasts overexpressing insulin-like growth factor I receptor are resistant to apoptosis, thus allowing persistent proliferation and pro duction of excessive extracellular matrix.