Essential and separable roles for Syndecan-3 and Syndecan-4 in skeletal muscle development and regeneration

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Abstract
Syndecan-3 and syndecan-4 function as coreceptors for tyrosine kinases and in cell adhesion. Syndecan-3-/- mice exhibit a novel form of muscular dystrophy characterized by impaired locomotion, fibrosis, and hyperplasia of myonuclei and satellite cells. Explanted syndecan-3-/- satellite cells mislocalize MyoD, differentiate aberrantly, and exhibit a general increase in overall tyrosine phosphorylation. Following induced regeneration, the hyperplastic phenotype is recapitulated. While there are fewer apparent defects in syndecan-4-/- muscle, explanted satellite cells are deficient in activation, proliferation, MyoD expression, myotube fusion, and differentiation. Further, syndecan-4-/- satellite cells fail to reconstitute damaged muscle, suggesting a unique requirement for syndecan-4 in satellite cell function.