Neutrophil-induced skeletal muscle damage: a calculated and controlled response following hindlimb unloading and reloading

Abstract

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.

Chemokine CXCL16 Regulates Neutrophil and Macrophage Infiltration into Injured Muscle, Promoting Muscle Regeneration

“…Therefore, an underlying mechanism for CXCL16-induced improvement in regeneration could be related to reduced infiltration of neutrophils because neutrophil can induce cytotoxic reactive oxygen species-mediated damage to myofibers. 3,5,6 In addition to establishing a critical role of CXCL16 in recruiting different inflammatory cells into injured muscle, our results indicate that CXCL16 influences the variation in the pattern of cytokine/chemokine expressed in injured muscles. This is of interest because Pelosi et al 17 recently reported that muscle overexpression insulin-like growth factor-1 enhances regeneration through a mechanism associated with decreased expression of MIP-1␣ and MIP-1␤.…”

“…An increase in neutrophil infiltration is relevant because Dumont et al 3 reported that blocking the infiltration of neutrophils into injured muscles improves processes of regeneration. Therefore, an underlying mechanism for CXCL16-induced improvement in regeneration could be related to reduced infiltration of neutrophils because neutrophil can induce cytotoxic reactive oxygen species-mediated damage to myofibers.…”

Time course of diaphragm function recovery after controlled mechanical ventilation in rats

“…These data are in agreement with those of Van Gammeren et al (42), obtained after 2 h of reloading. By contrast, hindlimb reloading following unloading was shown to be characterized by an infiltration of neutrophils followed by macrophages (7,11). In this context, macrophages are believed to promote muscle membrane repair and regeneration of muscle fibers (8,41), while the exact role of neutrophils remains to be determined.…”

Inflammation et régénération musculaire

“…Ainsi, dans un modèle de dommage modéré, produit par la remise en charge de muscles atrophiés, les neutrophiles ne présentent pas d'effet néfaste sur le regain de la force musculaire. Cependant, dans ce même modèle, l'ajout d'un agent bactérien active les neutrophiles qui induisent alors des dommages secondaires au tissu musculaire [14]. Récemment, un effet favorable sur la régéné-ration musculaire d'un autre type de granulocytes, les éosinophiles, a été montré via leur capacité à produire de l'IL-4 [15].…”