Reinitiation of chondroitin sulphate proteoglycan synthesis in regenerating skeletal muscle

Previous work from this laboratory involved the characterization of a large chondroitin sulphate proteoglycan unique to chick skeletal muscle. This proteoglycan is synthesized by embryonic skeletal muscle both in ovo and in culture but is not synthesized by adult muscle in vivo and myotubes in advanced cultures. Because regenerating skeletal muscle has been found to recapitulate synthesis of embryonic muscle protein isoforms, an analysis was performed to assess whether synthesis of chondroitin sulphate proteoglycans is reinitiated during muscle regeneration. Adult chicken pectoral and leg (gastrocnemius) muscle was injured by excision of a small piece of tissue or by cold injury; in the latter, the basement membrane has been reported to remain intact. At various times after injury, whole animals were exposed to [35S]sulphate and the proteoglycans were isolated by ion-exchange chromatography and analysed. Synthesis of only small proteoglycans, typical of normal adult skeletal muscle, is observed in the contralateral, uninjured muscle. In the regenerating muscle 4 days after injury, there is increased sulphate incorporation and abundant synthesis of chondroitin sulphate proteoglycans. This is observed in both pectoral and leg muscle irrespective of the type of injury, which suggests that the presence of basement membrane does not affect reinitiation of chondroitin sulphate proteoglycan synthesis. By 25 days after injury, synthesis of chondroitin sulphate proteoglycans is still detected but is significantly diminished. These data are consistent with the notion that skeletal muscle regeneration involves a recapitulation of embryonic events and give further credence to the hypothesis that skeletal muscle chondroitin sulphate proteoglycans play a role in some early aspect of myogenesis.