Antisense inhibition of syndecan-3 expression during skeletal muscle differentiation accelerates myogenesis through a basic fibroblast growth factor-dependent mechanism

Syndecan-3 is a member of a family of transmembrane proteoglycans that poss es highly homologous cytoplasmic and transmembrane domains and function as extracellular matrix receptors and low-affinity receptors for signaling mol ecules such as basic fibroblasts growth factor (FGF-2). Syndecan-3 is trans iently expressed in developing limb bud and absent in adult skeletal muscle . In this study we investigated the expression of syndecan-3 and its role o n FGF-2-dependent inhibition of myogenesis, Syndecan-3 expression was down- regulated during skeletal muscle differentiation of C2C12 myoblasts, as det ermined by Northern blot analyses and immunoprecipitation. To probe the fun ction of syndecan-3 during myogenesis, C2C12 myoblasts were stably transfec ted with a plasmid coding for antisense syndecan-3 mRNA The resulting inhib ition of syndecan-3 expression caused accelerated skeletal muscle different iation, as determined by expression of creatine kinase and myosin and myobl ast fusion. Expression of a master transcription factor for muscle differen tiation, myogenin, was also accelerated in antisense syndecan-3-transfected myoblasts compared with control transfected and wild type cells. Reduced e xpression of syndecan-3 resulted in a 13-fold decrease in sensitivity to FG F-S-dependent inhibition of myogenin expression. Addition of heparin partia lly reversed this effect. These results demonstrate that syndecan-3 express ion is down-regulated during differentiation and the level of expression of membrane-bound heparan sulfate on myoblast surface is critical for fine mo dulation of responsiveness to FGF-2. These findings strongly suggest a role for syndecan-3 in regulation of skeletal muscle terminal differentiation.