Increased vascular endothelial growth factor may account for elevated level of plasminogen activator inhibitor-1 via activating ERK1/2 in keloid fibroblasts

Keloids are characterized as an "overexuberant" healing response in which disequilibrium between production and catabolism of extracellular matrix (ECM) occurs. Previous studies from our laboratory and others demonstrate an intrinsically higher level of plasminogen activator inhibitor-1 (PAI-1) expression in keloid tissues and cultured fibroblasts compared with normal bordering skin. These findings support the concept that an altered balance of activator and inhibitor activities in the plasminogen system, in particular, an overexpression of PAI-1, may partly contribute to keloid formation and tissue fibrosis. Vascular endothelial growth factor (VEGF) has been implicated as a critical factor in regulating angiogenesis and inflammation under both physiological and pathological conditions. This study was designed to assess whether VEGF plays a role in keloid fibrosis. We report that VEGF was expressed at higher levels in keloid tissues and their derived fibroblasts compared with their associated normal skin. We have further demonstrated that VEGF stimulated the expression of PAI-1, but not urokinase plasminogen activator (uPA), in keloid fibroblasts at both mRNA and protein levels, in a dose- and time-dependent manner. However, treatment of normal skin fibroblasts with VEGF exerted little effects on PAI-1 gene expression. Additionally, we have characterized for the first time that the extracellular signal-regulated kinase (ERK)1/2 signaling pathway is mainly involved in VEGF-induced PAI-1 expression and have demonstrated its potential as a target molecule for modulation of scar fibrosis. These findings suggest that VEGF may play an important role in keloid formation by altering ECM homeostasis toward a state of impaired degradation and excessive accumulation.