Leptin-induced IL-6 production is mediated by leptin receptor, insulin receptor substrate-1, phosphatidylinositol 3-kinase, Akt, NF-κB, and p300 pathway in microglia

Leptin, the adipocyte-secreted hormone that centrally regulates weight control, is known to function as an immunomodulatory regulator. We investigated the signaling pathway involved in IL-6 production caused by leptin in microglia. Microglia expressed the long (OBRI) and short (OBRs) isoforms of the leptin receptor. Leptin caused concentration- and time-dependent increases in IL-6 production. Leptin-mediated IL-6 production was attenuated by OBRI receptor antisense oligonucleotide, PI3K inhibitor (Ly294002 and wortmannin), Akt inhibitor (IL-6-hydroxymethyl-chiro-inositol-2-((R)-2-O-methyl 3-O-octadecylcarbonate)), NF-kappa B inhibitor (pyrrolidine dithiocarbamate), I kappa B protease inhibitor (L-1-tosylamido-2phenylenylethyl chloromethyl ketone), I kappa B alpha phosphorylation inhibitor (Bay 117082), or NF-kappa B inhibitor peptide. Transfection with insulin receptor substrate (IRS)-1 small- interference RNA or the dominant-negative mutant of p85 and Akt also inhibited the potentiating action of leptin. Stimulation of microglia with leptin activated I kappa B kinase alpha/I kappa B kinase 171 I kappa B alpha phosphorylation, I kappa B alpha degradation, p65 phosphorylation at Ser(276), p65 and p50 translocation from the cytosol to the nucleus, and kappa B-luciferase activity. Leptin-mediated an increase of I kappa B kinase alpha/kappa B kinase beta activity, kappa B-luciferase activity, and p65 and p50 binding to the NF-kappa B element was inhibited by wortmannin, Akt inhibitor, and IRS-1 smallinterference RNA. The binding of p65 and p50 to the NF-kappa B elements, as well as the recruitment of p300 and the enhancement of histone H3 and H4 acetylation on the IL-6 promoter was enhanced by leptin. Our results suggest that leptin increased IL-6 production in microglia via the leptin receptor/IRS-1/PI3K/Akt/NF-kappa B and p300 signaling pathway.