High glucose induces IL-1β expression in human monocytes: mechanistic insights

Abstract

Previously, IL-1β secretion from Type 2 diabetic patients has been shown to be increased compared with controls. In this study, we aimed to delineate the mechanism of IL-1β induction under high-glucose (HG) conditions in human monocytes. THP-1 cells cultured in normal glucose were treated with increasing concentrations of d-glucose (10–25 mM) for 6–72 h. IL-1β and IL-1 receptor antagonist levels were measured by ELISA and Western blots, whereas mRNA was quantitated by RT-PCR. Specific inhibitors and small interfering RNAs of PKC, p38, ERK1/2, NF-κB, and NADPH oxidase were used to determine the mediators in parallel experiments under HG conditions. IL-1β-secreted protein, cellular protein, and mRNA increase under HG conditions is time and dose dependent, with maximum increase at 15 mM (48 h; P < 0.05). IL-1 receptor antagonist release was time and dose dependent, similar to IL-1β expression pattern; however, the molar ratio of IL-1β to IL-1RA was increased. Data from inhibitor and small interfering RNA experiments indicate that IL-1β release under HG is mediated by PKC-α, via phosphorylation of p38 MAPK, and ERK1/2 leading to NF-κB activation, resulting in increased mRNA and protein for IL-1β. At the same time, it appears that NADPH oxidase via p47phox activates NF-κB, resulting in increased IL-1β secretion. Data suggest that, under HG conditions, monocytes release significantly higher amounts of IL-1β through multiple mechanisms, further compounding the disease progression. Targeting signaling pathways mediating IL-1β release could result in the amelioration of inflammation and possibly diabetic vasculopathies.