Acute skeletal muscle injury: CCL2 expression by both monocytes and injured muscle is required for repair
ABSTRACT CC chemokine ligand 2 (CCL2), a ligand of CC chemokine receptor 2 (CCR2), is essential to mount an adequate inflammatory response to repair acute skeletal muscle injury. We studied the mechanisms by which CCL2 regulates muscle inflammation and regeneration. Mobilization of monocytes/macrophages (MOs/MPs) but not lymphocytes or neutrophils was impaired from bone marrow to blood and from blood to injured muscles in Ccl2(-/-) mice. This was accompanied by poor phagocytosis, reduced up-regulation of insulin-like growth factor-1 (IGF-1), and impaired muscle regeneration. Bone marrow transfer from wild-type mice to irradiated Ccr2(-/-) but not Ccl2(-/-) mice restored muscle inflammation. Intravenously injected CCL2-deficient bone marrow monocytes could not enter wild-type injured muscles as well as wild-type bone marrow monocytes. Intravenously injected wild-type bone marrow monocytes could not enter CCL2-deficient injured muscles as well as wild-type injured muscles. CCL2 stimulated IGF-1 expression by wild-type but not CCR2-deficient intramuscular macrophages. A single intramuscular injection of IGF-1, but not PBS, markedly improved muscle regeneration in Ccl2(-/-) mice. We conclude that CCL2 is a major ligand of CCR2 to recruit MOs/MPs into injured muscles to conduct phagocytosis and produce IGF-1 for injury repair. CCL2 needs to be expressed by bone marrow cells, circulating monocytes, and injured muscle tissue cells to recruit MOs/MPs into injured muscles. CCL2/CCR2 signaling also up-regulates IGF-1 expression by intramuscular macrophages to promote acute skeletal muscle injury repair.
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ABSTRACT: Excessive inflammatory response may delay the regeneration and damage the normal muscle fibers upon myoinjury. It would be important to be able to attenuate the inflammatory response and decrease inflammatory cells infiltration in order to improve muscle regeneration formation, resulting in better muscle functional recovery after myoinjury. This study was undertaken to explore the role of Nitric oxide (NO) during skeletal muscle inflammatory process, using a mouse model of Notexin induced myoinjury. Intramuscular injection (tibialis anterior, TA) of Notexin was performed for preparing mice myoinjury. NO synthase inhibitor (L-NAME) or NO donor (SNP) was intraperitoneally injected into model mice. On day 4 and 7 post-injury, expression of muscle-autoantigens and toll-like receptors (TLRs) was evaluated from muscle tissue by qRT-PCR and Western Blot; the intramuscular infiltration of monocytes/macrophage (CD11b(+) or F4/80(+) cells), CD8(+) T cell (CD3ε(+)CD8α(+)), apoptotic cell (CD11b(+)caspase3(+)), and MHC-I molecule H-2K(b)-expressing myofibers in damaged muscle were assessed by imunoflourecence analysis; the mRNAs expression of cytokines and chemokines associated with the preferential biological role during the muscle damage-induced inflammation response, were assessed by qRT-PCR. We detected the reduced monocytes/macrophages infiltration, and increased apoptotic cells in the damaged muscle treated with SNP comparing to untreatment. As well, SNP treatment down-regulated mRNA and protein levels of muscle autoantigens, TLR3, and mRNA levels of TNF-α, IL-6, MCP-1, MCP-3, and MIP-1α in damaged muscle. On the contrary, L-NAME induced more severe intramuscular infiltration of inflammatory cells, and mRNA level elevation of the above inflammatory mediators. Notably, we observed an increased number of MHC-I (H2-K(b)) positive new myofibers, and of the infiltrated CD8(+) T cells in damaged muscle at the day 7 after L-NAME treatment. The result herein shows that, NO can act as an endogenous anti-inflammatory molecule during the ongoing muscle inflammation. Our finding may provide new insight to optimize NO-based therapies for improving muscle regeneration after myoinjury.International journal of biological sciences 01/2015; 11(2):156-67. DOI:10.7150/ijbs.10283 · 4.37 Impact Factor
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ABSTRACT: Toll-like receptor 4 (TLR4) recognizes specific structural motifs associated with microbial pathogens and also responds to certain endogenous host molecules associated with tissue damage. In Duchenne muscular dystrophy (DMD), inflammation plays an important role in determining the ultimate fate of dystrophic muscle fibers. In this study, we used TLR4-deficient dystrophic mdx mice to assess the role of TLR4 in the pathogenesis of DMD. TLR4 expression was increased and showed enhanced activation following agonist stimulation in mdx diaphragm muscle. Genetic ablation of TLR4 led to significantly increased muscle force generation in dystrophic diaphragm muscle, which was associated with improved histopathology including decreased fibrosis, as well as reduced pro-inflammatory gene expression and macrophage infiltration. TLR4 ablation in mdx mice also altered the phenotype of muscle macrophages by inducing a shift toward a more anti-inflammatory (iNOS(neg) CD206(pos)) profile. In vitro experiments confirmed that lack of TLR4 is sufficient to influence macrophage activation status in response to classical polarizing stimuli such as IFN-gamma and IL-4. Finally, treatment of dystrophic mice with glycyrrhizin, an inhibitor of the endogenous TLR4 ligand, high mobility group box (HMGB1), also pointed to involvement of the HMGB1-TLR4 axis in promoting dystrophic diaphragm pathology. Taken together, our findings reveal TLR4 and the innate immune system as important players in the pathophysiology of DMD. Accordingly, targeting either TLR4 or its endogenous ligands may provide a new therapeutic strategy to slow disease progression. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: email@example.com.Human Molecular Genetics 12/2014; DOI:10.1093/hmg/ddu735 · 6.68 Impact Factor
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ABSTRACT: Regular exercise reduces the risk for numerous chronic diseases. Exercise not only impacts the contracting skeletal muscle but also elicits systemic changes. The exact mechanisms driving the more systemic changes have yet to be resolved, but exercise factors are thought to be an important missing link. Exercise factors are proteins that are released from skeletal muscle into the circulation during exercise. They represent a subclass of myokines, which are classified as proteins secreted from skeletal muscle serving a signaling role. Here, we provide an overview of the current literature on myokines. Many studies have focused on the identification of new myokines using a variety of approaches. These studies have generated an extensive list of myokines, but so far, the functional relevance of many of these novel myokines remains unclear. Few of these myokines represent putative exercise factors. Currently, IL-6, secreted protein acidic and rich in cysteine, angiopoietin-like 4, chemokine (C-X3-C motif) ligand 1, and chemokine (C-C motif) ligand 2 have the highest potential to serve as exercise factors because for all these factors, there is clear evidence that plasma levels increase during exercise. In our view, the future focus should be on characterizing the functional role of myokines in the acute and chronic response to exercise and explore their potential as a target for metabolic diseases.-Catoire, M., and Kersten, S. The search for exercise factors in humans. © FASEB.The FASEB Journal 01/2015; DOI:10.1096/fj.14-263699 · 5.48 Impact Factor