Received November 8, 2004
Revised January 5, 2005
Accepted after revision April 12, 2005

¹ Tel Aviv University
² University of Florida

^* To whom correspondence should be addressed. E-mail: elie{at}post.tau.ac.il.

	Abstract

Metalloproteinases (MMPs) are a proteolytic enzymes that function in the extracellular matrix to degrade connective tissues. While it is clear that exercise-induced injury in skeletal muscle promotes increased expression of MMP, the relationship between exercise intensity and expression of MMP in muscles is unknown. These experiments tested the hypothesis that exercise-induced expression of matrix metalloproteinases (MMP-2 and MMP-9) is dose-dependent such that high intensity endurance exercise increases MMP expression whereas low intensity endurance exercise will not promote MMP expression in skeletal muscles. Female rats (4 months old) completed two weeks of treadmill running at either low (18 m/min; ~50% VO2 max) and high intensity (32 m/min; ~70%VO2 max) speeds (up to 50 min/day). Non-running, sedentary animals served as controls. Muscle mRNA and protein levels of matrix metalloproteinases (MMP-2 and MMP-9) were assessed in gastrocnemius (Gast), Quadriceps, and Soleus (Sol) muscles by reverse transcriptase-polymerase chain reaction and western blotting, respectively. Results reveal that exercise did not alter the expression of MMP-9 in any of the muscles investigated. In contrast, high intensity exercise increased both mRNA and protein levels of MMP-2 in skeletal muscles containing a high percentage of fast type II fibers (i.e., Gast and superficial quadriceps). These results support the hypothesis that high intensity exercise is required to promote the expression of MMP-2 in skeletal muscles and that the influence of exercise on MMP-2 expression is dominant in muscles containing a high percentage of fast fibers.

Key Words: Ageing, Antioxidant, Muscle