Alpha-smooth muscle actin is crucial for focal adhesion maturation in myofibroblasts.
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.
Hinz
Boris
B
Department of Pathology, Centre Medical Universitaire, University of Geneva, Switzerland. boris.hinz@epfl.ch
Dugina
Vera
V
Ballestrem
Christoph
C
Wehrle-Haller
Bernhard
B
Chaponnier
Christine
C
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
D000199:Actins