Adiponectin Promotes Endotoxin Tolerance in Macrophages by Inducing IRAK-M Expression

High levels of plasma adiponectin are associated with low levels of inflammatory markers and cardioprotection. The mechanism via which adiponectin exerts its anti-inflammatory effect is yet unknown. In the present study, we demonstrate that globular adiponectin (gAd) induces the expression of the inactive isoform of IL-1R-associated kinases (IRAK), IRAK-M. Homologous deletion of IRAK-M in IRAK-M−/− mice abolished the tolerogenic properties of gAd because pretreatment of IRAK-M−/− macrophages with gAd did not suppress LPS-induced proinflammatory cytokine production. GAd activated the MAPKs MEK1/2 and ERK1/2 in macrophages via their upstream regulator Tpl2. Activation of ERK1/2 via Tpl2 appeared necessary for the induction of IRAK-M because gAd did not induce IRAK-M in Tpl2−/− macrophages or in macrophages pretreated with the MEK1/2 inhibitor UO126. In addition, activation of PI3K and Akt1 also appeared necessary for the induction of IRAK-M by gAd, because treatment of Akt1−/− macrophages or pretreatment of macrophages with the PI3K inhibitor wortmannin abolished gAd-induced IRAK-M expression. Analysis of IRAK-M expression in human peripheral blood cells confirmed that serum adiponectin was negatively associated with IRAK-M and responsiveness to LPS. In conclusion, our data demonstrate that IRAK-M is a major mediator of gAd-induced endotoxin tolerance in primary macrophages, expression of which depends on the activation of Tpl2/ERK and PI3K/Akt1 signaling pathways.