title: High dexamethasone concentration prevents stimulatory effects of TNF-alpha and LPS on IL-6 secretion from the precursors of human muscle regeneration.
abstract: A frequent finding in patients surviving critical illness myopathy is chronic muscle dysfunction. Its pathogenesis is mostly unknown; one explanation could be that muscle regeneration, which normally follows myopathy, is insufficient in these patients because of a high glucocorticoid level in their blood. Glucocorticoids can prevent stimulatory effects of proinflammatory factors on the interleukin (IL)-6 secretion, diminishing in this way the autocrine and paracrine IL-6 actions known to stimulate proliferation at the earliest, myoblast stage of muscle formation. To test this hypothesis, we compared the effects of major proinflammatory agents [tumor necrosis factor (TNF)-alpha and endotoxin lipopolysaccharide (LPS)] on the IL-6 secretion from the muscle precursors and then studied the influence of dexamethasone (Dex) on these effects. Mononuclear myoblasts, which still proliferate, were compared with myotubes in which this capacity is already lost. For correct interpretation of results, cultures were examined for putative apoptosis and necrosis. We found that constitutive secretion of IL-6 did not differ significantly between myoblasts and myotubes; however, the TNF-alpha- and LPS-stimulated IL-6 release was more pronounced (P < 0.001) in myoblasts. Dex, applied at the 0.1-100 nM concentration range, prevented constitutive and TNF-alpha- and LPS-stimulated IL-6 release at both developmental stages but only at high concentration (P < 0.01). Although there are still missing links to it, our results support the concept that high concentrations of glucocorticoids, met in critically ill patients, prevent TNF-alpha- and LPS-stimulated IL-6 secretion. This results in reduced IL-6-mediated myoblast proliferation, leading to the reduced final mass of the regenerated muscle.
authors.affiliation: Laboratory for Molecular Neurobiology, Institute of Pathophysiology, School of Medicine, University of Ljubljana, Zaloska 4, 1000 Ljubljana, Slovenia.
authors.forename: Oja
authors.initials: O
authors.lastname: Prelovsek
authors.forename: Tomaz
authors.initials: T
authors.lastname: Mars
authors.forename: Marko
authors.initials: M
authors.lastname: Jevsek
authors.forename: Matej
authors.initials: M
authors.lastname: Podbregar
authors.forename: Zoran
authors.initials: Z
authors.lastname: Grubic
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003907:Dexamethasone / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D042381:Granulocyte Precursor Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000008:administration & dosage*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D032448:Myoblasts, Skeletal / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D012038:Regeneration / Q000187:drug effects / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage*
chemical_list: D004338:Drug Combinations; D015850:Interleukin-6; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D003907:Dexamethasone