Inhibition of AMPK through Lyn-Syk-Akt enhances FcεRI signal pathways for allergic response

AMPK was shown to negatively regulate Fc epsilon RI activation, and Fc epsilon R-mediated Fyn activation can counteract the LKB1/AMPK axis in mast cells. However, the relationship between the major Src family kinase Lyn and AMPK remains poorly defined. Here, we investigate the molecular mechanism for AMPK inhibition by Fc epsilon RI-Lyn signaling in rat RBL-2H3 cells. We found that Fc epsilon RI activation could rapidly inhibit AMPK activation through increased AMPK phosphorylation at the inhibitory Ser485/491 residues without a change at the activating Th172 residue, and this was accompanied by a reduction of ACC phosphorylation. Using specific inhibitors and gene silencing, we found that such AMPK inhibition involved a signaling cascade through Lyn-Syk-Akt. When AMPK was activated by AICAR, A769662 and metformin, Fc epsilon RI-mediated Syk, ERK, JNK and p38 activation, and TNF alpha release were all inhibited. Consistently, AMPK inhibition by compound C increased Fc epsilon RI-mediated Lyn activation. Moreover, AMPK activation dominantly impaired IgE-induced recruitment of signal proteins to the Fc epsilon RI by blocking the formation of Fc epsilon RI beta-Lyn-Syk, Fc epsilon RI gamma-Lyn-Syk, and AMPK-Fc epsilon RI beta complexes. In vitro kinase assay further revealed the ability of AMPK alpha 2 to phosphorylate Fc epsilon RI beta in the complex. In vivo, AMPK activation by metformin could readily reduce vascular permeability and ear swelling in a mouse model of passive cutaneous anaphylaxis mediated by IgE. In summary, our findings demonstrate that IgE-mediated Fc epsilon RI activation results in AMPK inhibition through activation of Lyn-Syk-Akt pathway, and as such Fc epsilon RI receptor can efficiently propagate Lyn-mediated allergic signaling and response. These results provide important insights into the use of AMPK activators for the treatment of allergic diseases.