Increased proliferation in keloid fibroblasts wounded in vitro.

A keloid is a pathological overgrowth of scar expanding beyond the boundaries of the initiating skin wound. Ultimately, this expansive scar is a result of excess collagen synthesized by fibroblasts within the wound. The processes that lead to this collagen excess remain unknown. An in vitro wound model was developed to test the hypothesis that fibroblasts isolated from keloid tissue and wounded in vitro might proliferate more rapidly that similarly wounded normal dermal fibroblasts. Keloid fibroblasts (KF) and normal human dermal fibroblasts (NDF) were grown to confluence and quiescence in flexible-bottomed culture plates. Wounds were created in a standardized fashion using a specially designed jig. The jig utilized a 25 gauge needle to reproducibly ablate 16-20% of cells from confluent cell sheets. Wounded and nonwounded cells were labeled with 3H-thymidine at 24, 48, 72 and 96 hr postwounding to measure DNA synthesis. Wounded KF and NDF demonstrated increased 3H-thymidine incorporation compared to nonwounded control cultures, and wounded KF demonstrated significantly higher levels of 3H-thymidine incorporation than wounded NDF both 24 and 48 hr after wounding. A similar trend was seen in cell counts. The wounded KF also showed a statistically greater labeling index quantitated by autoradiography than did wounded NDF. The increased commitment to DNA synthesis in response to wounding in vitro in keloid fibroblasts correlates with pathology seen in vivo. Keloid fibroblasts may have a lower inherent threshold for S phase entry than do normal fibroblasts contributing to the increased proliferation of keloid fibroblasts in response to wounding in vitro.