Extracellular Matrix and Myofibrils During Unloading and Reloading of Skeletal Muscle

Abstract

The aim of the study was to elucidate the effect of unloading and reloading on the collagen expression and synthesis rate of myofibrillar proteins in fast-twitch (FT) muscle in relation to changes in muscle strength and motor activity. Northern blot analysis was used for testing the specificity of cDNA probes and protein synthesis rate was measured according to incorporation of radioactive leucine into different protein fractions. Unloading depresses collagen type I and III (p<0.001), type IV (p<0.05) and reloading enhances collagen expression in fast-twitch skeletal muscle in comparison with unloading. Enhanced expression of matrix metalloproteinase-2 continued during the first week of reloading (p<0.01) and tissue inhibitor of metalloproteinase-2 during reloading (p<0.05). Changes in collagen expression in FT muscle are in good agreement with changes in myofibrillar protein synthesis during unloading and reloading. In conclusion alterations in extracellular matrix and myofibrillar apparatus in FT skeletal muscle are related to changes in muscle strength and motor activity, are significant in exercise training and determination of recovery periods in the training process as well as in athletes' rehabilitation.

Neuromuscular Electrical Stimulation Induces Beneficial Adaptations in the Extracellular Matrix of Quadriceps Muscle After Anterior Cruciate Ligament Transection of Rats

“…6 Type IV collagen is the major component in the basement membranes and plays a critical role in the cellular arrangement, structural support, protection, and maintenance of muscular functional integrity. 9,10 Skeletal muscle atrophy is associated with an increase in connective tissue (CT) accumulation. 9,10 Skeletal muscle atrophy is associated with an increase in connective tissue (CT) accumulation.…”

“…7Y10 The ECM is important not only for the maintenance of tensile strength and elasticity in skeletal muscle tissues but also for the assembly of neuromuscular and myotendinous junctions and for the regeneration of myofibers after injury, skeletal muscle atrophy, or excessive exercise. 9,10 Thus, ECM balance needs to adapt continually to changing environmental demands inherent to muscle atrophy, and it would result in structural and functional deterioration of skeletal muscle fibers. If this accumulation is not minimized, it can lead to interstitial skeletal muscle fibrosis and harmful effects to muscular elasticity.…”

“…9,10 This fact could be associated with maladaptive modifications of quadriceps ECM remodeling, which could involve MMP-2 in net degradation of type IV collagen during the first 2 wks after ACL injury. Clinically, skeletal muscle atrophy is associated with an increase in CT accumulation, which leads to interstitial skeletal muscle fibrosis and harmful effects to muscular elasticity.…”

The skeletal muscle secretome: an emerging player in muscle–bone crosstalk

“…23,24 Insulin treatment of rat myotubes increases secretion of MMP-2, and serum levels of MMP-2 are elevated in diabetic patients suffering from hyperinsulinemia. 46 MMP-2 expression increases with exercise 47 and with re-loading following hindlimb suspension, 48 and decreases with injury, 49 but is elevated in skeletal muscle following disuse. 50 These data show that MMP-2, like SPARC, has an important role in muscle tissue remodeling during various repair events.…”

The emerging role of skeletal muscle extracellular matrix remodelling in obesity and exercise

“…1). Functions of skeletal muscle ECM include muscle maintenance, myogenesis, regeneration and reinnervation (13), adaptations to training (14)(15)(16)(17) and atrophy after periods of disuse (18).…”