Persistence in degenerating sciatic nerve of substances having a trophic influence upon cultured muscle

Abstract

Citrate-soluble proteins were extracted from normal and degenerating chicken sciatic nerves and added to chick embryonic skeletal muscle cultures to determine the trophic influences of the soluble proteins upon muscle cells. The soluble protein from normal or degenerating nerves was equally effective in promoting the protein synthesis, maturation, and long-term maintenance of muscle cells. Normal or degenerating nerve protein stimulated [ 14C]leucine incorporation into muscle cell protein and enhanced the morphologic maturation of muscle cells in culture. Furthermore, matured, cross-striated myotubes survived longer in the presence of normal or degenerating nerve protein than in control cultures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis on thin-layer gels revealed similar electrophoretic patterns for normal and degenerating nerve proteins. Electrophoretic gels also revealed the presence in these extracts of a protein with MW R 84,000 which migrated in a manner identical to a neurotrophic protein which was recently purified from chicken sciatic nerves. The present results indicate that neural proteins having trophic influences upon muscle in vitro persist in degenerating sciatic nerve. We therefore conclude that the in vivo changes in muscle after denervation are not due to the depletion of trophic substances following nerve transection.