Keloid Fibroblasts Resist Ceramide-Induced Apoptosis by Overexpression of Insulin-Like Growth Factor I Receptor

Abstract

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

The effect of tranilast on fibroblast activation protein α (FAP-α) expression in normal and keloid fibroblasts in vitro

“…However, in keloid fibroblasts characterized by a chronic pathological phenotype, FAP-α is resistant to this agent. Different responsiveness of genes in normal and keloid fibroblasts to antifibrotic and proapoptotic factors was observed previously [22,23]. Resistance to many kinds of therapies is also observed in other activated fibroblasts (e.g.…”

“…Z kolei w fibroblastach keloidowych, które odznaczają się przewlekle patologicznym fenotypem, FAP-α wykazuje odporność na działanie tego leku. We wcześniejszych badaniach obserwowano różnice w odpowiedzi prawidłowych i keloidowych fibroblastów na czynniki przeciwfibrotyczne i proapoptotyczne [22,23]. Oporność na wiele rodzajów leczenia stwierdza się także w innych aktywowanych fibroblastach (np.…”

Hypertrophic Scarring and Keloids: Pathomechanisms and Current and Emerging Treatment Strategies

“…Central to the formation of hypertrophic scar and keloid scar tissue is an alteration of the fibroblast phenotype (36,37). Indeed, when compared with normal fibroblasts, keloid fibroblasts show increased numbers of growth-factor receptors and respond more briskly to growth factors like PDGF and TGF-β, which may upregulate these abnormal cells from the beginning of wound healing (38,39). Using Affymetrix-chip analysis to identify pathways critical to keloid pathogenesis, Smith and colleagues found increased expression of several IGFbinding and IGF-binding-related proteins and decreased expression of a subset of Wnt-pathway inhibitors and multiple IL-1-inducible genes, providing preliminary evidence for epigenetic silencing of a subset of genes in the altered program of keloid fibroblasts (40).…”

Normal and Pathologic Soft Tissue Remodeling: Role of the Myofibroblast, with Special Emphasis on Liver and Kidney Fibrosis

“…This latter proposition, however, lacks conclusive evidence to date. Recent papers have shown data supporting the possibility that there is increased survival of fibroblasts from keloid scars in response to signals that would normally induce apoptosis (Chodon et al, 2000;Ishihara et al, 2000), while other studies suggest a possible imbalance between proliferation and apoptosis in keloids and hypertrophic scars but without clear evidence of decreased levels of apoptosis (Akasawa et al, 2001;Luo et al, 2001). The expression of genes that are protective against apoptosis, such as Bcl-2, has been shown to be increased in keloids and hypertrophic scars, suggesting a mechanism through which an imbalance between proliferation and apoptosis may be achieved (Teofoli et al, 1999).…”