Background A keloid is a specific skin lesion that expands beyond the boundaries of the original injury as it heals. Histologically, it is characterized by the excessive accumulation of collagen. However, the reasons for the expansion and the invasive nature of keloids remain unknown.

Objectives We evaluated collagen degradation and migration by cultured keloid fibroblasts based on the assumption that these variables were of functional relevance to the expanding and invasive nature of keloid lesions.

Methods Collagen production was investigated by the detection of type 1 collagen (procollagen type 1C peptide: P1P). Matrix metalloproteinase (MMP)‐1 (interstitial collagenase) and MMP‐2 (gelatinase‐A), were investigated as elements of the collagen degradation system. Enzyme immunoassays were performed to measure the production of P1P, MMP‐1, MMP‐2, and tissue inhibitor of metalloproteinase (TIMP)‐1. To assess the production of MMP‐2 its gelatinolytic activity was measured by zymography using gelatin‐containing gels. The participation of transforming growth factor‐β1 (TGF‐β1) in the production and degradation of collagen was also investigated. Finally, the migratory activity of keloid fibroblasts was evaluated using a colony dispersion assay.

Results The production of type 1 collagen, MMP‐1, MMP‐2, and TIMP‐1 by keloid fibroblasts was 3‐fold, 6‐fold, 2·4‐fold, and 2‐fold greater than that of normal dermal fibroblasts, respectively. Production of P1P was increased when TGF‐β1 was added to cultures of keloid fibroblasts, while it was decreased when anti‐TGF‐β1 antibody was added to the cultures. In contrast, the production of MMP‐1 was decreased by the addition of TGF‐β1 to cultured keloid fibroblasts, while it was increased when anti‐TGF‐β1 antibody was added to the cultures. The production of MMP‐2 increased after treatment with TGF‐β1, but did not change significantly when anti‐TGF‐β1 antibody was added to the cultures. Production of TIMP‐1 did not change significantly when either TGF‐β1 or anti‐TGF‐β1 antibody was added to the cultures. Keloid fibroblasts showed a 2·5‐fold increase of migratory activity compared with normal dermal fibroblasts, while the migratory activity of these fibroblasts was reduced to the control level by treatment with a broad‐spectrum MMP inhibitor (GM 6001).

Conclusions Cultured keloid fibroblasts showed increased production of collagen and MMPs, and TGF‐β1 played a role in this regulation of production. In addition, increased production of MMPs had a role in the high migratory activity of cultured keloid fibroblasts.