Scar Formation: Cellular Mechanisms

Abstract Fibroblasts are key players in the maintenance of skin homeostasis and in orchestrating physiological tissue repair. Fibroblasts secrete and are embedded in a sophisticated extracellular matrix, and a complex and interactive dialogue exists between fibroblasts and their microenvironment. In addition to the secretion of the extracellular matrix, fibroblasts and myofibroblasts secrete extracellular matrix remodeling enzymes, matrix metalloproteinases and their inhibitors, and tissue inhibitors of metalloproteinases and are thus able to remodel the extracellular matrix. Myofibroblasts and their microenvironment form a network that evolves during tissue repair. This network has reciprocal actions affecting cell differentiation, cell proliferation, cell quiescence, or apoptosis and has actions on growth factor bioavailability by binding, sequestration, and activation. Mechanical forces also play a role in regulating the myofibroblast phenotype as cells are subjected to mechanical stress and mechanical signaling is activated. Innervation is also involved in both skin repair processes and differentiation of myofibroblasts. In pathological situations, for example, in excessive scarring, the dialogue between myofibroblasts and their microenvironment can be altered or disrupted, leading to defects in tissue repair or to pathological scarring, such as that seen in hypertrophic scars. Better understanding of the intimate dialogue between myofibroblasts and their local microenvironment is needed and will be important in aiding the identification of new therapeutic targets and discovery of new drugs to treat or prevent aberrant tissue repair and scarring.