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1 Kinesiology, The University of Toledo, Toledo, OH, USA
2 Pathology, The Medical College of Ohio, Toledo, OH, USA
* To whom correspondence should be addressed. E-mail: Francis.Pizza{at}utoledo.edu.
The purpose of the study was to: 1) test the hypothesis that skeletal muscle cells (myotubes) after mechanical loading and/or injury are a source of soluble factors that promote neutrophil chemotaxis and superoxide anion (O2.-) production and 2) determine if mechanical loading and/or injury causes myotubes to release cytokines that are known to activate neutrophils (tumor necrosis factor-
(TNF-), interleukin-8 (IL-8), and transforming growth factor-
1 (TGF-1)). Human myotubes were grown in culture and exposed to either a cyclic strain (0, 5, 10, 20, or 30% strain) or a scrape injury protocol. Protocols of 5, 10 and 20% strain did not cause injury whereas, 30% strain and scrape injury caused a modest and a high degree of injury, respectively. Conditioned media from strained myotubes promoted chemotaxis of human blood neutrophils and primed them for O2.- production in a manner that was dependent on a threshold of strain and independent from injury. Neutrophil chemotaxis, but not priming, progressively increased with higher magnitudes of strain. Conditioned media only from scrape injured myotubes increased O2.- production from neutrophils. Concentrations of IL-8 and total TGF-1 in conditioned media were reduced by mechanical loading whereas TNF- and active TGF-1 concentrations were unaffected. In conclusion, skeletal muscle cells after mechanical loading and injury are an important source of soluble factors that differentially influence neutrophil chemotaxis and the stages of neutrophil-derived ROS production. Neutrophil responses elicited by mechanical loading however, did not parallel changes in the release of IL-8, TGF-1, nor TNF- from skeletal muscle cells.
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