THE NONSYNAPTIC EXPRESSION OF TRANSFORMING-GROWTH-FACTOR-BETA-2 IS NEURALLY REGULATED AND VARIES BETWEEN SKELETAL-MUSCLE FIBER TYPES

In adult skeletal muscles, transforming growth factor-beta 2 is restri cted to the postsynaptic domain of the neuromuscular junction. The var ious putative functions of this transforming growth factor-beta 2 pred ict different patterns of transforming growth factor-beta 2 expression in denervated muscles. We therefore denervated rat tibialis anterior, extensor digitorum longus and soleus muscles and examined the express ion of transforming growth factor-beta 2 using semi-quantitative rever se-trascription polymerase chain reaction and immunohistochemistry. De nervation up-regulated transforming growth factor-beta 2 expression ex trasynaptically with little or no effect on synaptic expression. The u p-regulation was detectable by one day, had become significant by thre e days and remained elevated for at least two weeks. This proves that the transforming growth factor-beta 2 associated with the neuromuscula r junction is not under neural control and is consistent with transfor ming growth factor-beta 2 being a trophic factor for motoneurons. This pattern of transforming growth factor-beta 2 expression is similar to that described for other proteins associated with the neuromuscular j unction, notably the acetylcholine receptor subunit genes. However, in contrast to the acetylcholine receptor subunit genes, the extent of u p-regulation of transforming growth factor-beta 2 Varied between fibre types, with the glycolytic IIB fibres being less affected than other fibre types. (C) 1998 IBRO. Published by Elsevier Science Ltd.