Integrin and dystrophin associated adhesion protein complexes during regeneration of shearing-type muscle injury

In shearing injury both the myofibres and connective tissue framework are b reached and the muscle-tendon continuity is disrupted. During regeneration the firm myofibre to extracellular matrix (ECM) adhesion must be re-establi shed. We have analysed the expression of selected molecules implementing th is adhesion in regenerating myofibres 2-56 days after transection of rat so leus muscle using quantitative immunohistochemistry and Northern blotting. beta 1 integrin mRNA level and alpha 7 integrin and vinculin immunoreactivi ties were transiently increased in both the intact and regenerating parts o f the transected myofibres by day 5-7 with normalization by day 10-14. Afte r day 14, alpha 7 integrin and vinculin accumulated at the tips of the rege nerating myofibres, indicating formation of new mini-myotendinous junctions (mMTJ). Immunoreactivities for dystrophin and associated proteins as well as merosin appeared in regenerating myotubes by day 3-4 reaching control le vels by day 56. Our results suggest that integrin and dystrophin associated molecules are complementary in myofibre-ECM adhesion. During regeneration, ruptured myofibres temporarily reinforce their integrin mediated lateral a dhesion until mMTJs are formed. Thereby the load on the newly formed scar a nd the risk of rerupture are I educed. Dystrophin associated molecules appe ar later and replace integrin on the lateral aspects, while both complexes are abundant at the mMTJs. These molecular events correspond to our previou s results on tensile strength. (C) 2000 Elsevier Science B.V. All lights re served.