One of key functions of skeletal muscle is its secretory activity. Skeletal muscle produces and releases cytokines, which have been named myokines. Myokines are released in response to muscle contractions and exert autocrine, paracrine or endocrine effects. The first identified and most researched myokine is interleukin-6 (IL-6). The IL-6 family of cytokines is defined by its common signaling through the membrane bound receptor glycoprotein 130. IL-6 cytokines have an important role in autocrine and/or paracrine regulation of metabolism in skeletal muscle as well as in in regulation of various biological processes in other tissues and organs through their receptors. They are also implicated in the pathophysiology of various metabolic, liver and gastrointestinal disorders, which makes them interesting pharmaceutical targets and thus a focus of attention in recent research. The systemic effects of IL-6 cytokines are well known, but their mechanisms of action and their production in skeletal muscle are still not fully elucidated, which will be crucial for the development of treatments of various pathophysiological states. All IL-6 cytokines, except for IL-31, signal through at least one gp130 β-receptor subunit and induce common intracellular signaling pathways. Gp130 receptors function either as a homodimer or a heterodimer, comprised of one gp130 beta-receptor subunit in combination with one of the other three β-receptors. It is still not very well known which signaling pathways are activated during skeletal muscle cell differentiation. To shed further light on this topic, we aimed to determine the expression pattern of selected receptors of IL-6 family cytokines at different stages of differentiation. For the experimental model we used cultured primary human skeletal muscle cells. Cells were differentiated into myotubes for seven days and expression of target genes was analyzed using quantitative real-time PCR at three stages of differentiation. We demonstrated that the expression of selected receptors for the IL-6 family cytokines; gp130, OSMR, LIFR, CNTFR and IL27RA was constant during differentiation of cultured skeletal muscle cells.
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