Keloid formation is a wound healing response, which fails to resolve and leads to formation of a raised collagen mass extending beyond the original wound margins. Keloids are typically excluded from palms and soles. Therefore we compared keloid and palmar fibroblasts in vitro using fibroblasts from nonaffected individuals as controls. Collagen I, a-smooth muscle actin and thrombospondin-1 were found at higher levels in keloid than in palmar fibroblasts. These differences were ameliorated by addition of TGFb1. The potential for resolution of the wound healing response was estimated analyzing apoptosis during serum starvation. Annexin V and TUNEL assays showed that palmar fibroblasts underwent faster apoptosis, than did the keloid fibroblasts, and started detaching. Addition of TGFb1 counteracted this effect. The weak expression of the myofibroblast phenotype and the advanced apoptosis of palmar fibroblasts suggest mechanisms for the exclusion of keloids from palmar sites.

BackgroundWounds in the nonglabrous skin of keloid-prone individuals tend to cause large disordered accumulations of collagen which extend beyond the original margins of the wound. In addition to abnormalities in keloid fibroblasts, comparison of dermal fibroblasts derived from nonwounded glabrous or nonglabrous skin revealed differences that may account for the observed location of keloids.MethodsFibroblast apoptosis and the cellular content of α-smooth-muscle actin, TGFβ1 receptorII and ED-A fibronectin were estimated by FACS analysis. The effects of TGFβ1 and serum were examined.ResultsIn monolayer cultures non-glabrous fibroblasts were slower growing, had higher granularity and accumulated more α-smooth-muscle actin than fibroblasts from glabrous tissues. Keloid fibroblasts had the highest level of α-smooth-muscle actin in parallel with their expression level of ED-A fibronectin. TGFβ1 positively regulated α-smooth-muscle actin expression in all fibroblast cultures, although its effects on apoptosis in fibroblasts from glabrous and non-glabrous tissues were found to differ. The presence of collagen I in the ECM resulted in reduction of α-smooth-muscle actin. A considerable percentage of the apoptotic fibroblasts in attached gels were α-smooth-muscle actin positive. The extent of apoptosis correlated positively with increased cell and matrix relaxation. TGFβ1 was unable to overcome this apoptotic effect of matrix relaxation.ConclusionThe presence of myofibroblasts and the apoptosis level can be regulated by both TGFβ1 and by the extracellular matrix. However, reduction of tension in the matrix is the critical determinant. This predicts that the tension in the wound bed determines the type of scar at different body sites.

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