Cytokines are produced locally by myocytes in rat skeletal muscle during endotoxemia

Abstract

Cytokines act as chemical mediators during the inflammatory process. Measurements of cytokine levels in tissue have previously been performed in homogenized tissue, but the true concentrations in native interstitial fluid (ISF), i.e., the compartment where cytokines exert their biologically active role, have remained unknown. The role of skeletal muscle myocytes as a source for cytokines during endotoxemia was explored by collecting muscle ISF using a wick method, and the levels of 14 cytokines in ISF and plasma were related to the corresponding changes in mRNA levels to reveal any potential discrepancies between gene expression and protein release of cytokines to ISF. The majority of investigated cytokines were elevated in muscle ISF during endotoxemia, and an analysis of cytokine mRNA levels revealed consistency between gene expression and protein release. The elevated cytokine level in ISF, in addition to elevated gene expression in muscle, indicated a significant local production and release of several proinflammatory cytokines and chemokines within skeletal muscle tissue during endotoxemia. Immunohistochemistry revealed that myocytes constituted a significant source of IL-1beta and TNF-alpha production during endotoxemia, whereas the contribution from inflammatory cells i.e., leukocytes, was found to be less significant. Muscle cells apparently constitute an important source of several different cytokines during endotoxemia, governing the level in the muscle microenvironment, and are likely to contribute significantly to cytokine levels in plasma.