title: Alpha-smooth muscle actin is crucial for focal adhesion maturation in myofibroblasts.
abstract: Cultured myofibroblasts are characterized by stress fibers, containing alpha-smooth muscle actin (alpha-SMA) and by supermature focal adhesions (FAs), which are larger than FAs of alpha-SMA-negative fibroblasts. We have investigated the role of alpha-SMA for myofibroblast adhesion and FA maturation. Inverted centrifugation reveals two phases of initial myofibroblast attachment: during the first 2 h of plating microfilament bundles contain essentially cytoplasmic actin and myofibroblast adhesion is similar to that of alpha-SMA-negative fibroblasts. Then, myofibroblasts incorporate alpha-SMA in stress fibers, develop mature FAs and their adhesion capacity is significantly increased. When alpha-SMA expression is induced in 5 d culture by TGFbeta or low serum levels, fibroblast adhesion is further increased correlating with a "supermaturation" of FAs. Treatment of myofibroblasts with alpha-SMA fusion peptide (SMA-FP), which inhibits alpha-SMA-mediated contractile activity, reduces their adhesion to the level of alpha-SMA negative fibroblasts. With the use of flexible micropatterned substrates and EGFP-constructs we show that SMA-FP application leads to a decrease of myofibroblast contraction, shortly followed by disassembly of paxillin- and beta3 integrin-containing FAs; alpha5 integrin distribution is not affected. FRAP of beta3 integrin-EGFP demonstrates an increase of FA protein turnover following SMA-FP treatment. We conclude that the formation and stability of supermature FAs depends on a high alpha-SMA-mediated contractile activity of myofibroblast stress fibers.
authors.affiliation: Department of Pathology, Centre Medical Universitaire, University of Geneva, Switzerland. boris.hinz@epfl.ch
authors.forename: Boris
authors.initials: B
authors.lastname: Hinz
authors.forename: Vera
authors.initials: V
authors.lastname: Dugina
authors.forename: Christoph
authors.initials: C
authors.lastname: Ballestrem
authors.forename: Bernhard
authors.initials: B
authors.lastname: Wehrle-Haller
authors.forename: Christine
authors.initials: C
authors.lastname: Chaponnier
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D022001:Focal Adhesions / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D051381:Rats
chemical_list: D000199:Actins