The IL-6/GP130 signaling pathway in myeloid cells modulates the inflammatory response during sepsis

Abstract

Background and Aim: Ascites and its bacterial infection (SBP) is a frequent and dangerous complication in patients suffering from liver cirrhosis. After bacterial peritonitis, the mobilization of the regulatory myeloid cells is a major requirement to prevent sepsis. Current research on inflammatory pathways has shown that GP130 in hepatocytes is essential in the modulation of inflammation. Therefore, we investigated the contribution of the GP130 pathway for the skewing of macrophage towards the regulatory M2 phenotype in a model of peritonitis. Methods: Depletion of GP130 in hematopoietic cell-deficient mice was achieved by bone marrow transplantation (BMC) using MxCre GP130loxp/loxp GFP (cre- BMC-WT; cre+ BMC-KO) as donors into WT as recipients. Subsequently, the recipients underwent cecal ligation and puncture (CLP) – a model of bacterial peritonitis. Additionally, bone marrow derived macrophages (BMDM) generated from BMC-WT and BMC-KO mice were stimulated with LPS, LPS/IFNγ, IL-4, IL-10/IL-4 or medium. Results: Clinical signs of sepsis such as lethargy, piloerection, tremors and respiratory distress associated with a significant decrease in survival and increased organ damage – liver, kidney and spleen – were more severely manifested in BMC-KO mice after CLP. Moreover, BMC-KO mice exhibited a pronounced pro-inflammatory response assessed by the expression of iNOS and IL-12. Concomitantly, TNFα, IL-12 and IL-6 levels in the peritoneal lavage fluid were significantly elevated in the BMC-KO mice. Next, we sought to determine the general role of GP130 in macrophage polarization. Thus, we generated BMDM from BMC-WT and BMC-KO mice and stimulated them with LPS, LPS/IFNγ, IL-4 or medium. Our data clearly showed (a) reduced expression of Arginase I and MMR after IL-4 stimulation and; (b) defective IL-6 response after stimulation with LPS/IFNγ. The anti-inflammatory phenotype, associated with a reduction of IL-4Rα, was rescued by the exogenous addition of IL-10 in vivo and in vitro. Conclusion: These data identify IL-6/GP130 signaling pathway as a critical component in myeloid lineage of immune cells for host survival and control of inflammation and infection during bacterial peritonitis. The IL-6/GP130 signaling cascade is required for the maintenance of the cytokine responses by regulating the activation of M1 macrophages during bacterial peritonitis and sepsis.