Insulin-Attenuated Inflammatory Response of Dendritic Cells in Diabetes by Regulating RAGE-PKC<i>β</i>1-IRS1-NF-<i>κ</i>B Signal Pathway: A Study on the Anti-Inflammatory Mechanism of Insulin in Diabetes

Abstract

Background . Diabetes is associated with chronic inflammation, and dendritic cells (DCs) have proinflammatory effect in diabetes. The anti-inflammatory effect of insulin on diabetes is not entirely clear. The study aims to examine insulin-induced effects on the inflammatory response in DCs. Methods . Twenty-one C57BL/6 mice were divided into 3 groups. Streptozotocin was injected into the diabetic mice model. The bone marrow-derived DCs (BMDCs) were obtained from C57BL/6 mice. CD83, CD86, and type II major histocompatibility complex (MHC-II) of BMDCs were measured by flow cytometry. The fluctuations in the RNA levels of cytokines and chemokines were analyzed by quantitative RT-PCR. The concentrations of IFN- γ and TNF- α were calculated using ELISA kits, and the proteins were detected using western blot. Results . In CD11c + DCs derived from the spleens with hyperglycemia, the expression of CD83 and CD86 in diabetic mice was significantly upregulated, coupled with a higher secretion level of cytokines and chemokines, and increased phosphorylation of NF- κ B and I κ B. Insulin therapy was found to have a reversal effect on the inflammatory response and immune maturation in DCs. In AGEs-BSA-stimulated BMDCs, insulin repressed the immune maturation and downregulated the expression of RAGE, phospho-PKC β 1, and serine phospho-IRS1 in an adose-dependent manner. Such effects can be abolished by PMA, but not IR-neutralizing antibody. AGEs-BSA-induced BMDCs immune maturation was inhibited by the neutralizing antibody of RAGE, the PKC β 1 inhibitor, or the IRS1 siRNA. Conclusions . Insulin has the capability of attenuating the inflammatory response of DCs in diabetes, partly through the downregulation of RAGE expression followed by the inhibition of PKC β 1 phosphorylation and IRS1 serine phosphorylation, resulting in the inactivation of IR binding-independent NF- κ B. This might partly explain the antiatherogenic effect of insulin on diabetes.