Increased iNOS, MMP-2, and HSP-72 in skeletal muscle following high-intensity exercise training

Skeletal muscle adapts to exercise by an upregulation of cellular defenses, such as inducible nitric oxide synthase (iNOS) and matrix metalloproteinase type 2 (MMP-2) and heat shock protein type-72 (HSP-72). The aims of the study were to examine iNOS, MMP-2, and HSP-72 mRNA and protein expression after high-intensity exercise training and to examine whether the expression levels are fiber type dependent. Young Wistar rats were assigned to either 2 or 4 weeks of a high-intensity (32 m/min) running exercise for 40 minutes 5 day per week. A non-running group served as a control. Western blotting and reverse transcriptase-polymerase chain reaction of muscle mRNA and protein levels were assessed in the medial gastrocnemius, quadriceps, soleus, crural, and sternal head of diaphragm muscles. High-intensity exercise training for 4 weeks but not for 2 weeks resulted in a significant increase in both RNA and protein levels of iNOS, MMP-2, and HSP-72 in all muscles examined except the sternal head of diaphragm. High-intensity exercise training is required to promote the expression of iNOS, MMP-2, and HSP-72 in hind limb muscles regardless their muscle fiber type, whereas in the diaphragm the changes are fiber-type dependent.