Increased mRNA expression of tissue inhibitors of metalloproteinase-1 and -2 in Duchenne muscular dystrophy

In dystrophinopathies, disease severity is generally related to the extent of muscle fibrosis. To determine whether a decrease in matrix degradation contributes to the severe fibrosis seen in Duchenne muscular dystrophy (DMD), we quantified RNA transcript numbers for the fibrolytic matrix metalloproteinases (MMP)-1 and -2 and their natural tissue inhibitors (TIMP)-1 and -2 in DMD muscle as well as in pathological and normal controls. In addition, we investigated gelatinase (MMP-2) enzyme activity by zymography. We found an up-regulation of TIMP-1, TIMP-2 and MMP-2 RNA in DMD muscle. Zymography revealed an increase in MMP-2 activity in DMD muscle homogenates, which was absent in pathological and normal controls. Therefore, besides enhanced fibrogenesis, a disturbance of matrix degradation may play a significant role in muscle fibrosis in DMD. TIMP-1 should be investigated further as a promising target for pharmacological intervention to prevent muscle fibrosis in DMD.