Neutrophil Depletion Attenuates Muscle Injury following Exhaustive Exercise.

PURPOSE: The infiltration of macrophages in skeletal muscle during exhaustive exercise promotes inflammation, myofiber lesion, and muscle injury. Although neutrophils upregulate macrophage infiltration in skeletal muscles during exercise, the role of neutrophils in promoting muscle injury following exhaustive exercise remains unclear. In this study, we investigated the effects of pre-exercise neutrophil depletion with anti-neutrophil antibody treatment on muscle injury, inflammation, and macrophage infiltration following exhaustive exercise. METHODS: Male C57BL/6J mice were randomly assigned to four groups, namely, Sedentary with control antibody (n = 10), Sedentary with anti-neutrophil antibody (n = 10), Exhaustive exercise with control antibody (n = 10), and Exhaustive exercise with anti-neutrophil antibody (n = 10). The mice were given intraperitoneal injection of the anti-neutrophil antibody (anti-Ly-6G, clone 1A8) or the control antibody (anti-Ly-6G, clone 2A3), and remained inactive or performed exhaustive exercise on a treadmill 48 h after the injection. Twenty-four hours after the exhaustive exercise, the gastrocnemius muscles were removed for histological and PCR analyses. Infiltration of neutrophils and macrophages was evaluated with Ly-6G and F4/80 immunohistochemistry staining procedures. Muscle fiber injury was detected based on the number of IgG staining fiber. The mRNA expression levels of proinflammatory cytokines and chemokines were evaluated with real time-RT-PCR. RESULTS: Exhaustive exercise increased neutrophil infiltration into the gastrocnemius muscle substantially by 3.1-fold and caused muscle injury, but these effects were markedly suppressed by pre-exercise treatment with anti-neutrophil antibody (neutrophil infiltration, 0.42-fold and muscle injury, 0.18-fold). Treatment with anti-neutrophil antibody also decreased macrophage infiltration (0.44-fold) and mRNA expression of TNF-[alpha] (0.55-fold) and IL-6 (0.51-fold) in the skeletal muscle after exhaustive exercise. CONCLUSION: These results suggest that neutrophils contribute to exacerbating muscle injury by regulating inflammation through the induction of macrophage infiltration. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially. (C) 2016 American College of Sports Medicine

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