THE FIBRONECTIN DOMAIN ED-A IS CRUCIAL FOR MYOFIBROBLASTIC PHENOTYPE INDUCTION BY TRANSFORMING GROWTH-FACTOR-BETA-1

Transforming growth factor-beta 1 (TGF beta 1), a major promoter of my ofibroblast differentiation, induces alpha-smooth muscle (sn) actin, m odulates the expression of adhesive receptors, and enhances the synthe sis of extracellular matrix (ECM) molecules including ED-A fibronectin (FN), an isoform de novo expressed during wound healing and fibrotic changes. We report here that ED-A FN deposition precedes alpha-SM acti n expression by fibroblasts during granulation tissue evolution in viv o and after TGF beta 1 stimulation in vitro. Moreover, there is a corr elation between in vitro expression of alpha-SM actin and ED-A FN in d ifferent fibroblastic populations. Seeding fibroblasts on ED-A FN does not elicit per se alpha-SM actin expression; however, incubation of f ibroblasts with the anti-ED-A monoclonal antibody IST-9 specifically b locks the TGF beta 1-triggered enhance ment of alpha-SM actin and coll agen type I, but not that of plasminogen activator inhibitor-1 mRNA, I nterestingly, the same inhibiting action is exerted by the soluble rec ombinant domain ED-A, but neither of these inhibitory agents alter FN matrix assembly. Our findings indicate that ED-A-containing polymerize d FN is necessary for the induction of the myofibroblastic phenotype b y TGF beta 1 and identify a hitherto unknown mechanism of cytokine-det ermined gene stimulation based on the generation of an ECM-derived per missive outside in signaling, under the control of the cytokine itself .