Neutrophil-induced skeletal muscle damage: a calculated and controlled response following hindlimb unloading and reloading.
Neutrophils phagocyte necrotic debris and release cytokines, enzymes, and oxidative factors. In the present study, we investigated the contribution of neutrophils to muscle injury, dysfunction, and recovery using an unloading and reloading model. Mice were submitted to 10 days of hindlimb unloading and were transiently depleted in neutrophils with anti-Ly6G/Ly6C antibody prior to reloading. Leukocyte accumulation and muscle function were assessed immunohistologically and functionally in vitro. In addition, soleus muscles submitted to unloading and reloading were incubated in vitro with LPS (100 microg/ml) to determine whether exogenous stimulus would activate neutrophil response and produce extensive muscle damage. Contractile properties were recorded every hour for 6 h, and muscles were subsequently incubated in procion orange to assess muscle damage. Neutrophil depletion affected neither the loss in muscle force nor the time of recovery in atrophied and reloaded soleus muscles. However, atrophied and reloaded soleus muscles that contained high concentration of neutrophils experienced a 20% greater loss in force than atrophied and reloaded soleus muscles depleted in neutrophils following in vitro incubation with LPS. Procion orange dye also confirmed that neutrophils induced a 2.5-fold increase in muscle membrane damage in the presence of LPS. These results show that neutrophil infiltration during modified mechanical loading is highly regulated and efficiently eliminated, with no significant muscle fiber injury unless the activation state of neutrophils is modified by the presence of LPS.
Dumont
Nicolas
N
Centre Hospitalier Universitaire de Québec-Centre de Recherche du Centre Hospitalier de l'Université Laval, 2705 Boulevard Laurier, T-R-93, Quebec City, QC, Canada G1V 4G2.
Bouchard
Patrice
P
Frenette
Jérôme
J
D000818:Animals; D019417:Hindlimb Suspension; D007249:Inflammation / Q000473:pathology* / Q000503:physiopathology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology; D009133:Muscular Atrophy / Q000473:pathology* / Q000503:physiopathology; D020556:Neutrophil Infiltration / Q000187:drug effects; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology / Q000473:pathology*; D009195:Peroxidase / Q000378:metabolism; D020127:Recovery of Function; D013997:Time Factors
D008070:Lipopolysaccharides; D009195:Peroxidase