| Metabolic and immune responses are the most basic and important survival requirements in multicellular organisms. Recent studies have shown a close link between metabolism and inflammation. Identifying the molecular mechanisms linking metabolism and immunity is critical for the design of therapeutic treatments for metabolic and inflammatory diseases. AMP-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase that regulates energy homeostasis and metabolic stress. When the cellular AMP/ATP ratio is high, AMPK is activated, switching off ATP-consuming anabolic pathways and switching on ATP-producing catabolic pathways. The goal of this dissertation was to investigate the role of AMPK in macrophage inflammatory activity.;Herein, we demonstrate a role of AMP-activated protein kinase (AMPK) as a potent counter-regulator of inflammatory signaling pathways in macrophages. Stimulation of macrophages with anti-inflammatory cytokines (i.e., IL-4, IL-10 and TGFbeta) resulted in the rapid phosphorylation/activation of AMPK, whereas stimulation of macrophages with a proinflammatory stimulus (LPS) resulted in AMPK dephosphorylation/inactivation. Inhibition of AMPKalpha expression by RNA interference dramatically increased the mRNA levels of LPS-induced TNFalpha, IL-6 and cyclooxygenase-2 (COX-2). Likewise, expression of a dominant negative AMPKalpha1 in macrophages enhanced TNFalpha and IL-6 protein synthesis in response to LPS stimulation, while diminishing the production of IL-10. In contrast, transfection of macrophages with a constitutively active form of AMPKalpha1 resulted in decreased LPS-induced TNFalpha and IL-6 production, and heightened production of IL-10. In addition, we found that AMPK negatively regulated LPS-induced IkappaB-alpha degradation and positively regulated Akt activation, possibly through PTEN inhibition, accompanied by inhibition of GSK3beta and activation of CREB. Furthermore, we provided evidence that IL-10 activated AMPK through the LKB1 complex, an upstream kinase of AMPK. Overall, our results demonstrate that AMPK directs signaling pathways in macrophages in a manner that suppresses proinflammatory responses and promotes macrophage polarization to an anti-inflammatory functional phenotype. Our work reveals AMPK as a molecular link between metabolism and immunity. Therefore, AMPK may constitute a therapeutic target for a broad range of metabolic and inflammatory diseases. |
