Relationship between extracellular matrix, contractile apparatus, muscle mass and strength in case of glucocorticoid myopathy.

The purpose of this study was to evaluate the effect of dexamethasone on the contractile apparatus and extracellular matrix (ECM) components of slow-twitch (ST) soleus (Sol) and fast-twitch (FT) extensor digitorum longus (EDL) muscle. The specific aim was to assess the development of glucocorticoid-induced myopathy on the level of contractile apparatus and ECM, paying attention to the expression of fibrillar forming collagen types I and III and nonfibrillar type IV collagen expression in extracellular compartment of muscle. Degradation of myofibrillar proteins increased from 2.62+/-0.28 to 5.58+/-0.49% per day during glucocorticoids excess. Both fibril- and network-forming collagen-specific mRNA levels decreased at the same time in both types of skeletal muscle. Specific mRNA level for MMP-2 did not change significantly during dexamethasone administration. Hindlimb grip strength simultaneously decreased. The effect of excessive glucocorticoids on the extracellular compartment did not differ significantly in skeletal muscles with different twitch characteristics.