UTILIZATION OF MILITARY-RELEVANT MUSCLE INJURY MODELS TO IDENTIFY PHARMACOLOGICAL TREATMENT STRATEGIES

This study was designed to characterize critical molecules involved in skeletal muscle response to ischemia-reperfusion (I/R) and blunt trauma injury in order to identify strategies for pharmacological intervention. For I/R injury, a tourniquet was applied to rat hind limbs for 3 h. Extensor digitorum longus (EDL) muscles from the healthy and I/R leg were harvested 2 h post-reperfusion for analysis. For the blunt trauma model, mice were anesthetized, the tibialis anterior (TA) muscle was exposed, and injury was induced by applying a steel probe (cooled to -20 C) to the belly of the TA muscle. Muscle samples were collected from the healthy and injured leg 3, 10, 24, 48, and 72 h post-injury. Quantitative Real Time Polymerase Chain Reaction (qRT-PCR), immunoblotting, and immunohistochemistry were used to quantify/localize analytes of interest. I/R resulted in a significant (p<0.05) upregulation of MT (4.7- fold) and MMP-9 (2.6- fold) mRNA, with no change in MMP-2. Blunt trauma/freeze injury resulted in an upregulation of mRNA expression at 3h, 10h, 24h, 48h, and 72h, respectively for MT (2.15-, 3.43-, 4.23-, 3.50-, 1.2 (n.s.)- fold), MMP-2 (1.25-(n.s), 1.28-(n.s), 1.07-(n.s), 1.84- and 1.86-fold), and MMP-3 (4.70-, 67.68-, 40.04-, 24.29, and 14.0-fold). Protein levels of MT and MMP-2 also increased several-fold post-injury with a decrease in the active form of MMP-3. We conclude that MT production is related to injury-induced oxidative-stress, which affects extracellular matrix integrity, explaining our observed increase in the MMPs. Thus, oxidative- mediated extracellular matrix disruption is a potential mechanism for skeletal muscle proteolysis post-injury.