Inhibition of STAT3 Signaling Reduces IgA1 Autoantigen Production in IgA Nephropathy

Abstract

IntroductionIgA nephropathy is a chronic renal disease characterized by mesangial immunodeposits that contain autoantigen, which is aberrantly glycosylated IgA1 with some hinge-region O-glycans deficient in galactose. Macroscopic hematuria during an upper respiratory tract infection is common among patients with IgA nephropathy, which suggests a connection between inflammation and disease activity. Interleukin-6 (IL-6) is an inflammatory cytokine involved in IgA immune response. We previously showed that IL-6 selectively increases production of galactose-deficient IgA1 in IgA1-secreting cells from patients with IgA nephropathy.MethodsWe characterized IL-6 signaling pathways involved in the overproduction of galactose-deficient IgA1. To understand molecular mechanisms, IL-6 signaling was analyzed by kinomic activity profiling and Western blotting, followed by confirmation assays using siRNA knock-down and small-molecule inhibitors.ResultsSTAT3 was differentially activated by IL-6 in IgA1-secreting cells from patients with IgA nephropathy compared with those from healthy control subjects. Specifically, IL-6 induced enhanced and prolonged phosphorylation of STAT3 in the cells from patients with IgA nephropathy, which resulted in overproduction of galactose-deficient IgA1. This IL-6−mediated overproduction of galactose-deficient IgA1 could be blocked by small molecule inhibitors of JAK/STAT signaling.DiscussionOur results revealed that IL-6−induced aberrant activation of STAT3-mediated overproduction of galactose-deficient IgA1. STAT3 signaling pathway may thus represent a new target for disease-specific therapy of IgA nephropathy.

Leukemia Inhibitory Factor Signaling Enhances Production of Galactose-Deficient IgA1 in IgA Nephropathy

“…IL-6 canonical signaling utilizes the JAK/STAT3 pathway [49][50][51], a critical interface between autoimmunity and immune deficiency. Recently, we determined that abnormal IL-6-induced signaling through IL-6 receptor-gp130 and JAK2/STAT3 pathway was associated with elevated synthesis of Gd-IgA1 by IgA1-producing cells from patients with IgAN but not HC [26]. Loss of STAT3 signaling disrupts the mucosal barrier in disease such as Crohn's disease, resulting in epithelial expression of the IL-6-like cytokine Upd3, leading to activation of JAK/STAT signaling, differentiation of cells that form the progenitor cells niche, and abnormal proliferation of progenitor cells [52].…”

“…The Gd-IgA1 concentration was expressed in units (U) defined as the ratio of OD determined for the individual sample and the OD for a standard Gd-IgA1 (Ale) myeloma protein. Specifically, 100 U was defined as the OD of 100 ng of the standard Gd-IgA1 protein [26].…”

“…ON-TAR-GETplus Non-targeting SMARTpool siRNAs served as a control. Cells were inoculated at density 5 × 10 5 /mL 24 h before siRNAs were added, following our previously published protocol [26]. Before transfection, the cells were harvested by centrifugation for 10 min at 300 g and resuspended at room temperature in Nucleofector Solution C (Lonza, Basel, Switzerland) at density of 2.5 × 10 6 cells per 100 μL for each transfection.…”

“…We have previously shown that IL-6 induces an abnormal signaling in IgA1-producing cells from patients with IgAN. This process involves enhanced and extended signaling through the JAK/STAT3 pathway, leading to elevated production of Gd-IgA1 [26]. In this study, we assessed the effect of LIF and OSM on IgA and Gd-IgA1 production by IgA1-secreting cell lines and determined the signaling mechanisms responsible for LIF-mediated enhancement of Gd-IgA1 production.…”

Glucocorticoids Reduce Aberrant O-Glycosylation of IgA1 in IgA Nephropathy Patients

“…Such mechanisms could contribute to the etiology of synpharyngitic hematuria. Recently, it was reported that modulation of IL-6-triggered intracellular signaling by STAT3 could alleviate Gal deficiency of IgA1 [16]. …”