Fibrin and collagen differentially regulate human dermal microvascular endothelial cell integrins: stabilization of alphav/beta3 mRNA by fibrin1.

Integrin alphavbeta3 is specifically but transiently expressed on the tips of capillary sprouts as they invade the fibrin clot during angiogenesis of cutaneous wound repair. Specific blocking of alphavbeta3 function inhibits granulation tissue formation in cutaneous wounds. The mechanisms of regulation of alphavbeta3 expression on human dermal microvascular endothelial cells, however, have not been fully delineated. As alphavbeta3 was highly expressed on capillary sprouts in 5 d wounds rich in fibrin, but was almost undetectable on blood vessels in 7 d wounds rich in collagen, we hypothesized that the extracellular matrix environment could regulate human dermal micro- vascular endothelial cell alphavbeta3 expression. To address this, human dermal microvascular endothelial cells were cultured on surfaces coated with collagen, fibronectin, and gelatin, and mRNA levels of integrin alphav/beta3 were determined. Compared with human dermal microvascular endothelial cells on collagen, mRNA levels of alphav/beta3 were higher in human dermal microvascular endothelial cells on fibronectin and on gelatin. To simulate the in vivo environment better, human dermal microvascular endothelial cells cultured on collagen were overlaid by fibrin or collagen gels prior to assessment of alphav/beta3 mRNA levels. alphav/beta3 mRNA levels were higher in human dermal microvascular endothelial cells surrounded by a three-dimensional fibrin gel compared with a collagen gel, whether angiogenic factors were present or absent. As modulation of mRNA stability is a potential regulatory mechanism for integrin expression, integrin subunit mRNA stability was assessed. beta3 mRNA decayed much faster than alphav, alpha2, and beta1 mRNA. Three-dimensional fibrin gels enhanced alphav/beta3 mRNA stability compared with collagen gels. We propose that the provisional matrix molecules in the wound clot regulate angiogenesis associated with cutaneous wound repair through their modulation of integrin receptor expression.