Differential expression of urokinase‐type plasminogen activator and plasminogen activator inhibitor‐1 in early and late gestational mouse skin and skin wounds

Early gestation fetal mouse skin heals without scars. Plasminogen activator inhibitor-1 (PAI-1) has been associated with postnatal organ fibrosis. We hypothesized that the relative balance between urokinase-type plasminogen activator (uPA) and PAI-1 expression in favor of uPA prevents scarring in early fetal skin wounds, whereas a change in favor of PAI-1 in late gestation results in wound scarring. To evaluate uPA and PAI-1 expression, 1-mm skin wounds were made in E14.5 and E18 mice and harvested 24, 48, or 96 hours postwounding. Aprotinin (2 mg/ml)-coated beads were injected into selected E14.5 wounds. Normal skin and skin wounds were evaluated for uPA, PAI-1, and collagen expression. We showed that in normal skin uPA level is higher in E14.5 than in E18 mice, while PAI-1 is lower in E14.5 than in E18 mice. After wounding, E14.5 wounds show a moderate increase in uPA and a minimal increase in PAI-1. E18 wounds show a transient increase in uPA but a significant, sustained increase in PAI-1. Addition of aprotinin to E14.5 wounds causes an increase in collagen deposition. We conclude that the differential expression of uPA and PAI-1 in the skin of early vs. late gestation mice may contribute to the degree of scar formation seen after cutaneous injury.