Role of fibronectin in the inhibitory effect of TGF-beta on choline acetyltransferase activity in co-cultures of spinal cord neurons and myotubes.

We have recently shown that the enhanced expression of choline acetyltransferase (ChAT) activity in co-cultures of spinal cord motoneurons and muscle cells was blocked by transforming growth factor-beta (TGF-beta) (Dev. Brain Res., 57, 129-137, 1990). This study was performed to investigate the role of fibronectin in this effect. TGF-beta increased fibronectin level about 2-fold in extracellular matrix of spinal cord cells and skeletal myotubes in culture. Addition of a synthetic polypeptide that competitively inhibits fibronectin binding to its cell surface receptor recovered the TGF-beta-induced suppression of ChAT activity in co-cultures. The polypeptide did not affect ChAT activity in cultures of spinal cord cells alone or in co-cultures without TGF-beta. These results indicate that TGF-beta inhibits the stimulation of ChAT activity in spinal cord neurons in co-culture through a change in the composition and/or amount of fibronectin in the extracellular matrix at neuromuscular contacts.