Thrombospondin expression in traumatized skeletal muscle. Correlation of appearance with post-trauma regeneration

Biochemical and immuno-microscopic techniques were used to study temporal involvement of thrombospondin in relation to fibrinogen in muscle regeneration using a rat skeletal muscle-wound model. In undamaged control muscle, no fibrinogen and minimal thrombospondin antigen was found. Following crushing injury, fibrin networks appear immediately, followed by a gradual ordered accumulation of thrombospondin (within a few hours) in the vicinity of the vascular bed and adjacent endomysial connective tissue. Later, thrombospondin becomes associated with connective tissue and basal laminae around muscle fibers throughout the damaged muscle, maximal labelling occurring 3-6 days post-injury. Thrombospondin immunoreactivity decreased thereafter to near normal levels after 7 days post-injury, coincident with the appearance of regenerating muscle fibers. In contrast, little fibrin material remained by five days after injury. Quantitative radioimmunoassay of soluble thrombospondin antigen and radioimmune labelling of thick frozen sections reinforced the qualitative immuno-microscopic observations, with levels peaking at 3-4 days post-trauma, 10-fold over control levels. SDS-PAGE immunoblotting of non-reduced muscle extracts three days after a crush assault shows that the bulk of the thrombospondin incorporated into the injury site exists in a polymerized state (less than or equal to 1000 kD). These results demonstrate that the temporal appearance and disappearance of thrombospondin in the healing of a crushing lesion in muscle is related more closely to the regeneration phase of muscle than to the coagulation phase.