Mechanisms of microvascular wound repair II. Injury induces transformation of endothelial cells into myofibroblasts and the synthesis of matrix proteins.

Under normal growth conditions, in vitro dermal microvascular endothelial cells (HDMEC) retain an epithelioid morphology and do not synthesize matrix proteins found increased in scar tissue. When injured by a standard scratch, cells at the wound edge and within the culture transform into spindle-shaped, myofibroblast-like cells. To determine if the transformed cells synthesize matrix proteins, expression of type I collagen and alpha smooth muscle actin (alpha-SMA) was investigated by immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Twelve hours following injury, a major upregulation in expression of alpha-SMA and type I collagen was observed both in cells proximal and distal to the wound edge. Cells with the typical morphology of myofibroblasts and displaying intracellular alpha-SMA positive fibrils were observed in HDMEC throughout the culture. In contrast, type IV collagen, a basement membrane protein, was not detected in migrating cells. Following completion of wound repair (24-36 h), type I collagen was no longer expressed and type IV collagen synthesis increased to prewound levels. Quantitative RT-PCR confirmed the changes in gene expression for both type I collagen and alpha-SMA at each time point during repair. These results demonstrate that normal skin microvascular endothelial cells retain an ability to transform into myofibroblast-like cells when injured and to synthesize matrix proteins not expressed in noninjured cells. The synthesis of matrix proteins by injured endothelial cells suggests a direct role for the endothelium in the pathology of scar formation.