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IL-10 regulates macrophage activation through activation of SHIP Ghanipour, Ali

Abstract

IL-10 is a potent anti-inflammatory and immunosuppressive cytokine, which regulates macrophages by activation of the STAT3 pathway. However, several lines of evidence suggest that IL-10 can inhibit macrophage activation independent of STAT3 through currently unknown mechanisms and pathways. Here for the first time, we show that in murine macrophages, IL-10 activates Src Homology 2 Domain-containing Inositol 5'-Phosphatase (SHIP), a molecule with reported anti-inflammatory effects. Activation of SHIP by IL-10 is required for inhibition of Tumor necrosis factor alpha (TNFα) in macrophages. Additional experiments revealed that IL-10 activation of SHIP acted at the post-transcriptional level and inhibited translation of TNFα . Using a novel small molecule activator of SHIP, AQX-016A, we further confirmed that activation of SHIP alone could inhibit TNFα translation. IL-10 activation of SHIP results in the inhibition of the LPS induced increase in the PI3K product, PIP3, at the membrane. However, conflicting data as to the role of PI3K in regulation of TNFα have been presented. Our studies show that PI3K inhibition downregulates TNFα production in peritoneal and several other macrophage lines, and upregulates it bone marrow derived macrophages (BMDM). Interestingly, this difference is due to the increased amount of autocrine negative regulators produced in BMDM, removal of which exposes the positive role PI3K plays in regulation of TNFα. Therefore, our studies confirm that PI3K activity positively regulates TNFα production in macrophages and that inhibition of TNFα by IL-10 or AQX-016A through activation of SHIP is likely due to SHIP'S ability to antagonize this pathway. The importance of this pathway is further highlighted as IL-10 inhibition of LPS-induced septic shock in mice lacking one allele of SHIP is significantly attenuated. Furthermore, activation of SHIP by AQX-016A inhibits TNFα production in septic mice. We also found that IL-10 inhibited LPS induced p38 activity in a cell-dependent manner. However in all cells tested, IL-10 activated p38 rapidly. We identified several IL-10 induced genes including CRIM1, a transmembrane protein with no previous report of involvement in the immune system. We found that IL-10 induction of CRIM1 was partly dependent on the activity of p38. However, expression of CRIM1 does not seem to be involved in the anti-inflammatory effects of IL-10.

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