Mechanisms and factors involved in development of hypertrophic scars

Fibroblasts in granulation tissue (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle cells, such as the presence of microfilament bundles and the expression of alpha-smooth muscle actin. The mechanisms leading to the development of such myofibroblastic features remain unclear. Both in vivo and in vitro investigations suggest the participation of growth factors, cytokines, and extracellular matrix in the regulation of alpha-smooth muscle actin expression. During normal wound healing, myofibroblasts disappear when the wound is fully re-epithelialized. In contrast, the expression of alpha-smooth muscle actin is a permanent feature of myofibroblasts present in fibrocontractive diseases. In hypertrophic scars, the presence of these cells may represent an important element in the pathogenesis of retraction. Different therapeutic modalities available for the treatment of hypertrophic scars cause a decrease in the number of alpha-smooth muscle actin expressing myofibroblasts. Further studies regarding the expression of cytoskeleton markers in fibroblastic cells are needed to understand the mechanisms of scarring and fibrosis.