DIFFERENTIAL EXPRESSION OF TENASCIN AFTER DENERVATION, DAMAGE OR PARALYSIS OF MOUSE SOLEUS MUSCLE

The expression of the extracellular matrix molecule tenascin was studied by immunocytochemistry and Western blotting in soleus muscles of adult mice after nerve damage (denervation), muscle injury (induced by enforced running or freezing) and functional block of synaptic transmission (botulinum toxin). Enhanced expression of tenascin in the extracellular spaces around focally damaged muscle fibres was found already 10 h after onset of running on a motor-driven treadmill which causes muscle injury in soleus muscle. Tenascin expression reached a peak at 23 days post-exercise, after which it declined gradually and became undetectable by two weeks after injury. Similarly, cryo-damage of soleus muscles in situ led to upregulation of tenascin. Chronic muscle denervation after sciatic nerve transection caused a persistent (studied up to 31 days) expression of tenascin at denervated endplates and in intramuscular nerve branches but not in other tissue compartments. Local application of botulinum toxin Type A, which results in muscle inactivity but not in tissue degeneration, however, did not induce tenascin expression 12 h to 12 days post-injection. Expression of tenascin after denervation and muscle damage, but its absence after paralysis, were verified by SDS-PAGE and Western blot analysis. Independent of the type of injury (muscle, nerve or both) the known major isoforms of mouse tenascin, as judged by M, comparison, were re-expressed, with no preponderance of individual M, forms. These results show that tenascin expression in adult muscles is induced by both axon and muscle fibre damage but not by muscle inactivity. In contrast, NCAM, in accordance with previous observations, showed enhanced expression both as a result of inactivity and in association with tissue repair.