Training differentially regulates elastin level and proteolysis in skeletal and heart muscles and aorta in healthy rats

Exercise induces changes in muscle fibers and the extracellular matrix that may depend on elastin content and the activity of proteolytic enzymes. We investigated the influence of endurance training on the gene expression and protein content and/or activity of elastin, elastase, cathepsin K, and plasmin in skeletal and heart muscles and in the aorta. Healthy rats were randomly divided into untrained (n=10) and trained (n=10; 6 weeks of endurance training with increasing load) groups. Gene expression was evaluated via qRT-PCR. Elastin content was measured via enzyme-linked immunosorbent assay and enzyme activity was measured fluorometrically. Elastin content was significantly higher in skeletal (P=0.0014) and heart muscle (P=0.000022) from trained rats versus untrained rats, but not in the aorta. Although mRNA levels in skeletal muscle did not differ between groups, the activities of elastase (P=0.0434), cathepsin K (P=0.0343) and plasmin (P=0.000046) were higher in trained rats. The levels of cathepsin K (P=0.0288) and plasminogen (P=0.0005) mRNA were higher in heart muscle from trained rats, but enzyme activity was not. Enzyme activity in the aorta did not differ between groups. Increased elastin content in muscles may result in better adaption to exercise, as may remodeling of the extracellular matrix in skeletal muscle.