title: Resistance exercise increases active MMP and β1-integrin protein expression in skeletal muscle.
abstract: Recent studies indicate that matrix metalloproteinases (MMPs) and critical linkage proteins in the extracellular matrix (ECM) regulate skeletal muscle mass, although the effects of resistance training (RT) on protein expression and activity are unclear. Thus, the purpose of the present study was to investigate the effects of RT on MMP activity and expression of ECM-related proteins. Ten male Sprague-Dawley rats were randomly assigned to 1 bout (1B) or 18 bouts (18B) of electrical stimulation. The right gastrocnemius muscle was isometrically contracted via percutaneous electrical stimulation (five sets of 5 sec stimulation × five contractions/set with 5 sec interval between contractions and 3 min rest between sets) once (1B) or every other day for 5 weeks (18B). The left leg served as a control. Activity of MMP-2 and MMP-9, determined via gelatin zymography, was increased (P < 0.05) immediately after 1B. However, MMP activation was not evident following 18B. No changes in collagen IV, laminin α2, α7-integrin, or ILK protein expression were detected immediately following 1B or 18B. However, β1-integrin protein expression was significantly increased (P < 0.05) with 18B. Our results suggest that resistance exercise activates MMPs during the initial phase of RT but this response is attenuated with continuation of RT.
authors.affiliation: Department of Life Sciences, The University of Tokyo, Tokyo, Japan Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan.
authors.forename: Riki
authors.initials: R
authors.lastname: Ogasawara
authors.affiliation: Graduate School of Health and Sport Science, Nippon Sport Science University, Tokyo, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakazato
authors.affiliation: Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Sato
authors.affiliation: Department of Kinesiology and Community Health, Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois.
authors.forename: Marni D
authors.initials: MD
authors.lastname: Boppart
authors.affiliation: Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fujita
keywords: Exercise; gelatinases; integrin; mTOR; muscle hypertrophy