title: Impairment of insulin signaling in human skeletal muscle cells by co-culture with human adipocytes.
abstract: Adipocyte factors play a major role in the induction of insulin resistance in skeletal muscle. To analyze this cross-talk, we established a system of co-culture of human fat and skeletal muscle cells. Cells of three muscle donors were kept in co-culture with cells of various fat cell donors, and insulin signaling was subsequently analyzed in myocytes. Insulin-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 was completely blocked, with unaltered expression of IRS-1. Troglitazone increased insulin action on IRS-1 phosphorylation, in both the absence and presence of co-culture. Insulin-regulated activation of Akt kinase in the myocytes was significantly reduced after co-culture, with troglitazone restoring insulin action. Addition of tumor necrosis factor (TNF)-alpha (2.5 nmol/l) to myocytes for 48 h reduced IRS-1 expression and inhibited IRS-1 and Akt phosphorylation comparable to the effect of co-culture. Lower doses of TNF-alpha were ineffective. After co-culture, TNF-alpha in the culture medium was below the detection limit of 0.3 pmol/l. A very low level of resistin was detected in the supernatant of myocytes, but not of adipocytes. In conclusion, the release of fat cell factors induces insulin resistance in human skeletal muscle cells; however, TNF-alpha and resistin appear not to be involved in this process.
authors.affiliation: Department of Clinical Biochemistry and Pathobiochemistry, German Diabetes Research Institute, Düsseldorf, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Dietze
authors.forename: Marlis
authors.initials: M
authors.lastname: Koenen
authors.forename: Karin
authors.initials: K
authors.lastname: Röhrig
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Horikoshi
authors.forename: Hans
authors.initials: H
authors.lastname: Hauner
authors.forename: Jürgen
authors.initials: J
authors.lastname: Eckel
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000273:Adipose Tissue / Q000166:cytology / Q000502:physiology; D018929:Cell Culture Techniques / Q000379:methods; D002478:Cells, Cultured; D018920:Coculture Techniques; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
chemical_list: C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt