Altered balance of proteinase inhibitors in atrophic muscle after denervation

Skeletal muscle denervation leads to an increase of proteolytic activity, w hich is also favoured by reduced levels of alpha (1)antichmotrypsin and nex in H, two serine-proteinase inhibitors normally acting at the neuromuscular junction. In the present experiments we extended our investigation to othe r muscular proteinase inhibitors after denervation. In all muscles examined (soleus, plantaris, extensor digitorum longus) specific immunoreactivity f or alpha (2)macroglobulin (alpha 2M) and alpha (1)proteinase inhibitor (alp ha -1-antitrypsin, ATI) was distributed in peri-endomysial structures as we ll as in small patches inside the fibres. By contrast, inter-a-trypsin inhi bitor (ITI) was mainly localized in the extracellular matrix. These localiz ation patterns did not change substantially in 15-days denervated muscles. Dot-blot analysis revealed a small decrease (about 15%) of alpha 2M in 15-d ays denervated muscles, while ATI and ITI specific activities were substant ially unchanged. RT-PCR allowed us to detect the above protease inhibitor m RNAs in normal muscle homogenates. Denervation atrophy induced by section o f the sciatic nerve resulted in a remarkable reduction of ((2)macroglobulin mRNA (60%) and ITI (30%), but not ATI, as measured by computer-assisted se miquantitative densitometry of electrophoresed RT-PCR bands. The marked dec rease of a2M we have detected in denervated muscle may be responsible, at l east in part, for the proteolytic increase which is known to occur in skele tal muscle during denervation atrophy.