Leptin induces IL-8 expression via leptin receptor, IRS-1, PI3K, Akt cascade and promotion of NF-κB/p300 binding in human synovial fibroblasts

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-8 production caused by leptin in both rheumatoid arthritis synovial fibroblasts (RASF) and osteoarthritis synovial fibroblasts (OASF). RASF and OASF expressed the long (OBRI) and short (OBRs) isoforms of the leptin receptor. Leptin caused concentration- and time-dependent increases in IL-8 production. Leptin-mediated IL-8 production was attenuated by OBRI receptor antisense oligonucleotide, JAK2 inhibitor or STAT3 small interference RNA (siRNA). Transfection with insulin receptor substrate (IRS)-1 siRNA or dominant-negative mutant of p85 and Akt or pretreatment with phosphatidylinositol 3-kinase inhibitor (Ly294002 and wortmannin), Akt inhibitor, NF-kappa B inhibitor (PDTC) and NF-kappa B inhibitor peptide also inhibited the potentiating acdon of leptin. Stimulation of RASF with leptin activated I kappa B kinase alpha/beta (IKK alpha/beta), p65 phosphorylation at Ser(276), p65 translocation from the cytosol to the nucleus, and kappa B-luciferase activity. Moreover, pretreatment with p300 inhibitor (curcumin) also blocked IL-8 expression. The binding of p65 to the NF-kappa B elements, as well as the recruitment of p300 and the enhancement of histone H3 acetylation on the IL-8 promoter was enhanced by leptin, which was inhibited by wortmannin, Akt inhibitor or IRS-1 siRNA. These results suggest that leptin increased IL-8 production in synovial fibroblast via the OBR1/JAK2/STAT3 pathway, as well as the activation of IRS1 /PI3K/Akt/NF-kappa B-dependent pathway and the subsequent recruitment of p300. (c) 2008 Elsevier Inc. All rights reserved.