Adenosine 5′-Monophosphate-Activated Protein Kinase Regulates IL-10-Mediated Anti-Inflammatory Signaling Pathways in Macrophages

AMP-activated protein kinase (AMPK) is a conserved serine/threonine kinase with a critical function in the regulation of metabolic pathways in eukaryotic cells. Recently, AMPK has been shown to play an additional role as a regulator of inflammatory activity in leukocytes. Treatment of macrophages with chemical AMPK activators, or forced expression of a constitutively active form of AMPK, results in polarization to an anti-inflammatory phenotype. In addition, we reported previously that stimulation of macrophages with anti-inflammatory cytokines such as IL-10, IL-4, and TGF-beta results in rapid activation of AMPK, suggesting that AMPK contributes to the suppressive function of these cytokines. In this study, we investigated the role of AMPK in IL-10-induced gene expression and anti-inflammatory function. IL-10-stimulated wild-type macrophages displayed rapid activation of PI3K and its downstream targets Akt and mammalian target of rapamycin complex (mTORC1), an effect that was not seen in macrophages generated from AMPK alpha 1-deficient mice. AMPK activation was not impacted by treatment with either the PI3K inhibitor LY294002 or the JAK inhibitor CP-690550, suggesting that IL-10-mediated activation of AMPK is independent of PI3K and JAK activity. IL-10 induced phosphorylation of both Tyr(705) and Ser(727) residues of STAT3 in an AMPK alpha 1-dependent manner, and these phosphorylation events were blocked by inhibition of Ca2+/calmodulin-dependent protein kinase kinase beta, an upstream activator of AMPK, and by the mTORC1 inhibitor rapamycin, respectively. The impaired STAT3 phosphorylation in response to IL-10 observed in AMPK alpha 1-deficient macrophages was accompanied by reduced suppressor of cytokine signaling 3 expression and an inadequacy of IL-10 to suppress LPS-induced proinflammatory cytokine production. Overall, our data demonstrate that AMPK alpha 1 is required for IL-10 activation of the PI3K/Akt/mTORC1 and STAT3-mediated anti-inflammatory pathways regulating macrophage functional polarization.