Insulin regulates macrophage activation through activin A.
Strict control of serum glucose with insulin has been associated with a reduction in the development of multiple organ dysfunction syndrome potentially through alterations in macrophage activation. Although the mechanism responsible for this effect remains poorly elucidated, recent work has suggested that this may occur through the PI3K/AKT pathway. As a result, we set out to investigate the role and means of activation of this pathway by insulin on endotoxin-mediated activation of tissue-fixed macrophages.


METHODS
THP-1 cells were stimulated with endotoxin with or without 24 h of insulin pretreatment. Cellular protein was extracted and analyzed by immunoblot for factors essential to Toll-like receptor 4 signaling. Supernatants were analyzed by enzyme-linked immunosorbent assay for TNF-alpha and IL-8 production. In addition, potential effect of the transforming growth factor superfamily was analyzed through selective inhibition of either the transforming growth factor beta or activin A receptors.


RESULTS
Endotoxin exposure resulted in the activation of extracellular signal-regulated kinase 1/2, p38 and Jun kinase, the degradation of IkappaB, the activation of nuclear factor kappaB, and the production of TNF-alpha and IL-8. Insulin pretreatment delayed endotoxin-mediated extracellular signal-regulated kinase 1/2, p38 and Jun kinase, the degradation of IkappaB, the activation of nuclear factor kappaB, and the production of TNF-alpha and IL-8. Insulin alone was associated with an increase in cytoplasmic SH2-containing inositol 5'-phosphatase (SHIP) but a decrease in lipid raft bound SHIP. The changes induced by insulin on SHIP and endotoxin-mediated signaling were reversed by activin A blockade.


CONCLUSIONS
Insulin results in regulation of macrophage activity in response to endotoxin through the release of activin A and subsequent production of SHIP. This increase in cytoplasmic SHIP results in attenuated endotoxin-mediated intracellular signaling and inflammatory mediator production.
Cuschieri
Joseph
J
Department of Surgery, University of Washington, Seattle, Washington, USA. jcuschie@u.washington.edu
Bulger
Eileen
E
Grinsell
Rebecca
R
Garcia
Iris
I
Maier
Ronald V
RV
D028341:Activins / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D016207:Cytokines / Q000378:metabolism; D004731:Endotoxins / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D000072181:Inositol Polyphosphate 5-Phosphatases; D007328:Insulin / Q000494:pharmacology*; D016209:Interleukin-8 / Q000378:metabolism; D008262:Macrophage Activation / Q000187:drug effects*; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D016207:Cytokines; D004731:Endotoxins; D020672:I-kappa B Proteins; D007328:Insulin; D016209:Interleukin-8; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C422405:activin A; D028341:Activins; D000072000:NF-KappaB Inhibitor alpha; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases