Inhibition by transforming growth factor β of choline acetyltransferase stimulation in a co-culture of spinal cord and muscle cells from mice

Abstract

Choline acetyltransferase (CAT) activity increased 11-fold in co-cultures of spinal cord and muscle cells from fetal mice relative to cultures of spinal cord cells alone. The addition of transforming growth factor-β (TGF-β) to the medium at 30 pM throughout the culture period inhibited the increase of CAT activity in the co-cultures, but did not affect the activity in cultures of spinal cord cells alone. TGF-β did not inhibit glutamic acid decarboxylase activity in the co-cultures. Other growth factors such as epidermal growth factor, fibroblast growth factor and β-NGF had little or no effect on CAT activity. TGF-β markedly inhibited the fusion of myoblasts to myotubes and the expression of marker enzymes for muscle differentiation. When TGF-β was included during muscle culture and removed before inoculation with spinal cord cells, myoblasts did not subsequently form myotubes. CAT activity in the spinal cord cells, however, markedly increased in co-cultures with the undifferentiated myoblasts. When TGF-β was added to the co-cultures after myotube formation was complete, the increase in CAT activity was inhibited according to the length of TGF-β treatment. These results suggest that TGF-β inhibits the muscle-induced stimulation of CAT activity by inhibiting the production, secretion and/or action of trophic factors from muscle.