Quantitative analysis of the secretion of the MCP family of chemokines by muscle cells.

The plasticity of skeletal muscle allows the body to adapt to various physiological demands such as growth, exercise and tissue regeneration and repair. The secreted factors from muscle exert their action via auto-, para-, and endocrine mechanisms, thereby influencing the maintenance of total body homeostasis. In addition, the regulation of muscle proliferation, differentiation, and regeneration is often perturbed by inflammatory processes and is dependent on the pattern of expression of pro-inflammatory stimuli. Studies examining the cross talk between factors released by muscle and cytokines secreted by other tissues are still very limited. In order to comprehensively characterize the low abundant low molecular weight secreted proteins during the course of muscle differentiation we used a mass spectrometry-based proteomics strategy. The application of the triple encoding Stable Isotope Labeling by Amino acids in Cell culture (SILAC) method for quantitative analysis resulted in the identification and generation of quantitative profiles of 59 growth factors and cytokines, including 9 classical chemokines. The members of the CC chemokine family of proteins such as monocyte chemotactic proteins 1, 2, and 3 (MCP-1/CCL2, MCP-2/CCL8, and MCP-3/CCL7) showed a distinct pattern of secretion during differentiation. Further analysis using combinatorial RNA and protein approaches demonstrated that the MCPs are regulated via both post-transcriptional and post-translational mechanisms. Analyses of the autocrine function of all three MCPs reveal similar activation of downstream effectors in muscle cells. Finally, we show that the expression of the MCPs in skeletal muscle is also regulated by pro-inflammatory stimuli, indicating a much broader cross talk and interaction between inflammatory-dependent systems than previously anticipated.