Fibroblasts potentiate blood vessel formation partially through secreted factor TIMP-1.

During wound repair, new blood vessels form in response to angiogenic signals emanating from injured tissues. Dermal fibroblasts are known to play an important role in wound healing, and have been linked to angiogenesis; therefore, we sought to understand the mechanisms through which these cells control blood vessel formation. Using a three-dimensional angiogenesis assay we demonstrate that dermal fibroblasts enhance the tube-forming potential of endothelial cells, and this augmentation is partially due to secreted factors present in conditioned media. Interestingly, we identified tissue inhibitor of metalloproteinase-1 (TIMP-1) as a factor uniquely secreted by fibroblasts, and addition of exogenous TIMP-1 increased vessel assembly. The enhancing activity of TIMP-1 was matrix metalloproteinase (MMP)-dependent, since a mutant version of TIMP-1 was unable to promote angiogenesis. Consistent with this, chemical inhibition of MMP-2/9 showed a similar increase in angiogenesis, and addition of exogenous MMP-9 blocked the enhancing effect of TIMP-1. We further demonstrated that TIMP-1 inhibits the production of tumstatin, an anti-angiogenic fragment of collagen IV that is produced by MMP-9 cleavage. Our results support the notion that dermal fibroblasts regulate blood vessel formation through multiple mediators, and provide novel evidence that fibroblast-derived TIMP-1 acts on endothelial cells in a pro-angiogenic capacity.