Temporal spatial expression and function of non-muscle myosin II isoforms IIA and IIB in scar remodeling

Scar contracture is believed to be caused by the cell contractility during the remodeling phase of wound healing. Cell contractility is mediated by non-muscle myosin II (NMMII) and actin, but the temporal-spatial expression profile of NMMII isoforms A and B (IIA and IIB) during the remodeling phase and the role of NMMII in scar fibroblast tissue remodeling are unknown. Human scar tissue immunostained for IIA and IIB showed that both isoforms were highly expressed in scar tissue throughout the remodeling phase of repair and expression levels returned to normal after the remodeling phase. Human scar tissue immunostained for β-, γ- and α-smooth muscle actin showed that all isoforms were consistently expressed throughout the remodeling phase of repair. The β- and γ-smooth muscle actin were widely expressed throughout the dermis, but α-smooth muscle actin was only locally expressed within the dermis. In vitro, fibroblasts explanted from scar tissue were shown to express more IIA than fibroblasts explanted from normal tissue and scar fibroblasts contracted collagen lattices to a greater extent than normal fibroblasts. Blebbistatin was used to demonstrate the function of NMMII in collagen lattice contraction. In normal tissue, fibroblasts are stress-shielded from external tensile stress by the extracellular matrix. After dermal injury and during remodeling, fibroblasts are exposed to a matrix of increased stiffness. The effect of matrix stiffness on IIA and IIB expression was examined. IIA expression was greater in fibroblasts cultured in collagen lattices with increasing stiffness, and in fibroblasts cultured on glass slides compared with polyacrylamide gels with stiffness of 1 kPa. In conclusion, NMMII and actin isoform expression changes coordinately with the remodeling phase of repair, and NMMII is increased as matrix stiffness increases. As NMMII expression increases, so does the fibroblast contractility.