Journal
FASEB JOURNAL
Volume 29, Issue 7, Pages 2894-2904Publisher
FEDERATION AMER SOC EXP BIOL
DOI: 10.1096/fj.14-266668
Keywords
eccentric exercise; satellite cell; repeated-bout effect; muscle damage
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This study determined the contribution of extracellular matrix (ECM) remodeling to the protective adaptation of human skeletal muscle known as the repeated-bout effect (RBE). Muscle biopsies were obtained 3 hours, 2 days, and 27 days following an initial bout (B1) of lengthening contractions (LCs) and 2 days following a repeated bout (B2) in 2 separate studies. Biopsies from the nonexercised legs served as controls. In the first study, global transcriptomic analysis indicated widespread changes in ECM structural, deadhesive, and signaling transcripts, 3 hours following LC. To determine if ECM remodeling is involved in the RBE, we conducted a second study by use of a repeated-bout paradigm. TNC immunoreactivity increased 10.8-fold following B1, was attenuated following B2, and positively correlated with LC-induced strength loss (r(2) = 0.45; P = 0.009). Expression of collagen I, III, and IV (COL1A1, COL3A1, COL4A1) transcripts was unchanged early but increased 5.7 +/- 2.5-, 3.2 +/- 0.9-, and 2.1 +/- 0.4-fold (P < 0.05), respectively, 27 days post-B1 and were unaffected by B2. Likewise, TGF-beta signaling demonstrated a delayed response following LC. Satellite cell content increased 80% (P < 0.05) 2 days post-B1 (P < 0.05), remained elevated 27 days post-B1, and was unaffected by B2. Collectively, the data suggest sequential ECM remodeling characterized by early deadhesion and delayed reconstructive activity that appear to contribute to the RBE.
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