[Macrophages depletion impairs skeletal muscle regeneration by regulating inflammation and oxidative stress levels].

The objective of this study was to explore the roles of macrophages in the regeneration of injured skeletal muscle and the mechanisms involved. Mice were randomly divided into the following groups: muscle contusion (S), muscle contusion control (S), macrophages depleted (T) and macrophages depleted control (T) groups. Muscle contusion model was created by high-energy blunt injury. Macrophages depletion model was constructed by injection of clodronate-liposomes. Their gastrocnemius muscles were harvested at the time points of 1, 3, 7 and 14 d post-injury. The changes in skeletal muscle morphology were assessed by hematoxylin-eosin (HE) staining and Masson's trichrome staining. The mRNA and protein levels of inflammatory cytokines, chemokines and oxidative stress factors were analyzed by real-time polymerase chain reaction (RCR) and Western blotting, respectively. HE staining results showed that a small amount of regenerating myofibers were observed in the S group (14 d post-injury), whereas a large number of regenerating muscle fibers were observed in the T group. Quantitative analyses showed that the sizes of regenerating myofibers were significantly smaller in the T group as compared with the S group at 14 d post-injury (P < 0.05). At the same time, Masson staining results showed that macrophage depletion significantly increased the area of fibrosis as compared with the S group at 14 d post-injury (P < 0.01). The expression levels of inflammatory cytokines, chemokines, and oxidative stress factors were increased significantly after muscle injury. Moreover, macrophage depletion increased the expressions of inflammatory cytokines, chemokines and oxidative stress factors as compared with the S group during the later stage of injury (7-14 d post-injury). These results suggest that macrophages depletion can aggravate fibrosis and impair muscle regeneration, and inflammatory cytokines, chemokines and oxidative stress factors may be involved in this process.