Effects of increased matrix metalloproteinase-9 expression on skeletal muscle fibrosis in prolonged alcoholic myopathies of rats

This study evaluated the effects of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) on injured gastrocnemius, soleus and plantaris muscles, induced by alcohol in rats. A total of 60 male Sprague-Dawley rats (2.5 months old, 200±20 g) were divided into 6 groups: i) untreated skeletal muscle and analyzed 2 weeks later (A1 group, 5 rats); ii) untreated skeletal muscle and analyzed 6 weeks later (A2 group, 5 rats); iii) untreated skeletal muscle and analyzed 12 weeks later (A3 group, 5 rats); iv) injured skeletal muscle and analyzed 2 weeks later (B1 group, 15 rats); v) injured skeletal muscle and analyzed 6 weeks later (B2 group, 15 rats); and vi) injured skeletal muscle and analyzed 12 weeks later (B3 group, 15 rats). The injured and uninjured muscles were observed by light microscopy and polarization microscopy. The MMP activity was evaluated through zymography, and messenger RNA (mRNA) of MMP-9 and of MMP-2 were assessed by RT-PCR. The expression of MMP-9 was assessed by Western blot analysis. The plantaris and gastrocnemius muscles in the rats subjected to alcohol ingestion were found to have a high expression of MMP-9, but not of MMP-2. Picrosirius red staining was used to assess whether increased fibrosis in the skeletal muscle was associated with alcohol exposure in rats. The study indicated that alcohol may be involved in the skeletal muscle interstitial fibrosis in our model of alcohol‑exposed rats through increased MMP-9 expression, and that this increased expression may aggravate the development of prolonged alcohol muscle injury.