Abnormal cytokine response and autoantigen production in IgA-producing subpopulations in IgA nephropathy

摘要

Abstract IgA nephropathy (IgAN) is the most common primary glomerulonephritis. It leads to end-stage kidney disease (ESKD) in 40-50% of patients. IgAN patients often exhibit macroscopic hematuria, commonly associated with upper-respiratory tract infections. This exacerbation of kidney injury seen during episodes of mucosal infection and inflammation suggests a connection between the two. In biopsies of IgAN patients, the defining characteristic of this disease is the deposits of polymeric IgA1, typically with IgG and complement C3 co- deposits. Analysis of the deposited IgA1 revealed enrichment for galactose-deficient IgA1 (Gd-IgA1) compared to circulatory IgA1. In addition, the co-deposited IgG is specific for Gd-IgA1. This appears to be immune complex deposition, which is also found in circulation of patients. Serum levels of Gd-IgA1 and anti-Gd-IgA1- IgG autoantibodies are elevated in IgAN patients, associate with disease progression, and can be found complexed in circulation. This circulatory autoantigen (Gd-IgA1) is typically found in the polymeric form, which is unique to the mucosal region. This suggests that a subset of IgA1-producing cells could be migrating from mucosal regions, or there is abnormal IgA1-producing cells formed elsewhere. Initial observations that mucosal infections associated with transient hematuria in IgAN patients led to the thesis that pro-inflammatory stimulation could increase circulatory Gd-IgA1-containing immune complexes, causing renal injury. We recently published that IL-6 stimulation in EBV-immortalized IgA1-producing cells from IgAN patients, but not controls, preferentially increased Gd-IgA1 production due to an enhanced and prolonged STAT3 activation. In addition, preliminary data in our lab from single-cell transcriptome profiling using immortalized IgA-producing cells from IgAN patients and healthy controls revealed multiple populations of IgA1-producing cells that have differential responses to cytokine stimulation. These observations led to our hypothesis that enhanced Gd- IgA1 production is a result of abnormal cytokine response in a subset of IgA1-producing cells. In Aim 1, we will test the hypothesis that cytokine exposure has differential effects on subsets of IgA1-producing cells in EBV- immortalized IgA1-producing cells from IgAN patients vs. healthy and disease controls. In Aim 2, we will test the hypothesis that subsets of IgA1-producing cells that have differential responses to cytokine stimulation are preferentially producing Gd-IgA1. The combination of these two aims will help identify the specific IgA1- producing cell subsets that contribute to autoantigen production. These studies will enable testing of novel research hypotheses and yield new preliminary data towards a competitive R01 proposal.