Calmodulin-dependent signalling pathways are activated and mediate the acute inflammatory response of injured skeletal muscle.

There is a close relationship between skeletal muscle physiology and Ca²⁺ /CaM signalling. Despite the effects of Ca²⁺ /CaM signalling on immune and inflammatory responses have been extensively explored, few studies have investigated the role of CaM pathway activation on the post-injury muscle inflammatory response. In this study, we investigated the role of CaM-dependent signalling in muscle inflammation in cardiotoxin induced myoinjuries in mice. The CaMKII, CaMKIV and NFAT pathways are likely to be simultaneously activated in muscle cells and in infiltrating lymphocytes and to regulate the immune behaviours of myofibres in an inflammatory environment, and these pathways ultimately affect the outcome of muscle inflammation.

Calcium/calmodulin (Ca²⁺ /CaM) signalling is essential for immune and inflammatory responses in tissues. However, whether Ca²⁺ /CaM signalling interferes with muscle inflammation is unclear. Here we investigated roles of CaM-dependent signalling in muscle inflammation in mice that had acute myoinjuries in the tibialis anterior muscle induced by intramuscular cardiotoxin (CTX) injections and received intraperitoneal injections of either CaM inhibitor calmidazolium chloride (CCL) or CaM agonist calcium-like peptide 1 (CALP1). Multiple inflammatory parameters, including muscle autoantigens and toll-like receptors (TLRs), mononuclear cell infiltration, cytokines and chemokines associated with peripheral muscle inflammation, were examined after the injury and treatment. CALP1 treatment enhanced intramuscular infiltration of monocytes/macrophages into the damaged tibialis anterior (TA) muscle and up-regulated mRNA and protein levels of muscle autoantigens (Mi-2, HARS, and Ku70) and Toll-like receptor 3 (TLR3), and mRNA levels of TNF-α, IL-6, MCP1, MCP3 and MIP-1α in damaged muscle. In contrast, CCL treatment decreased the intramuscular cell infiltration and mRNA levels of the inflammatory mediators. After CALP1 treatment, a substantial up-regulation in CaM-dependent kinase II (CaMKII), CaM kinase IV (CaMKIV) and nuclear factor of activated T cells (NFAT) activity was detected in CD45⁺ cells isolated from the damaged muscle. More pro-inflammatory F4/80⁺ Ly-6C⁺ cells were detected in CD45-gated cells after CALP1 treatment than in those after CCL treatment or no treatment. Consistently, in IFN-γ-stimulated cultured myoblasts and myotubes, CALP1 treatment up-regulated activities of CaMKII, CaMKIV and NFAT and levels of class I/II major histocompatibility complexes (MHC-I/II) and TLR3. Our findings demonstrated that CaM-dependent signalling pathways mediate injury-induced acute muscle inflammatory response. This article is protected by copyright. All rights reserved.