Combination of insulin-like growth factor (IGF)-I and IGF-binding protein-1 promotes fibroblast-embedded collagen gel contraction

Wound contraction is an important event that minimizes the wound defect during the healing process. Involvement of insulin-like growth factor (IGF)-I and IGF-binding protein (IGFBP)-1 in wound contraction was studied using an in vitro model. Human dermal fibroblasts (1 x 10(5) cells/ml) were incorporated into a porcine type I collagen (0.21% final) in serum-free medium. The fibroblast-embedded collagen gels in a 12-well plate were floated from the well, and various reagents were then added to the assay medium. The surface area of the gel was calculated by measuring the diameters of the collagen gel. IGF-I at high doses (30 and 100 ng/ml) revealed 6.8% (P < 0.01) and 7.7% (P < 0.001) gel contraction, respectively, and des (1-3) IGF-I at 10 ng/ml produced a 4.5% gel contraction (P < 0.01). Meanwhile, IGFBP-I did not induce any significant contraction throughout the tested concentrations (0.1-100 ng/ml). A combination of IGF-I and IGFBP-1 at 1 ng/ml of each reagent, a concentration at which gel contraction was not observed when each of the reagents was tested individually, produced a 14% gel contraction (P < 0.001), whereas combinations of des (1-3) IGF-I with IGFBP-1 at the same concentrations did not promote gel contraction. The increased IGFBP-I doses in combination with 1 ng/ml IGF-I tended to enhance the gel contraction. IGF-I- and IGFBP-1-induced gel contraction was prominent during the initial 12-h incubation period. When anti-IGF-I, anti-IGFBP-1, or anti-IGF-I receptor antibody was added to the assay medium before the addition of IGF-I and IGFBP-1, the IGF-I- and IGFBP-1-induced gel contraction was significantly suppressed (P < 0.001). Endothelin-1, a vasoconstrictor peptide that is known to promote fibroblast-embedded collagen gel contraction, appeared to be partially involved in the IGF-I- and IGFBP-1-induced gel contraction, because the addition of an endothelin receptor antagonist (Bosentan or BE-18257B at 1 mu g/ml) moderately suppressed the IGF-I- and IGFBP-1-induced gel contraction (P < 0.01). On the other hand, when IGF-I and IGFBP-1 were applied with endothelin-1 (1 nM), an enhanced gel contraction (29.4%) was observed that was significantly greater than that induced by either individually (P < 0.001). These results clearly indicate that the combination of IGF-I and IGFBP-1 promotes fibroblast contraction in collagen gel, and that this phenomenon is caused by IGFBP-1's strong potentiation of the IGF-I-induced gel contraction.