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Abstract: PO1404

Mesangial-Cell Activation by Circulating Immune Complexes Consisting of Galactose-Deficient IgA1 and IgG Autoantibodies from Patients with IgA Nephropathy

Session Information

Category: Glomerular Diseases

  • 1201 Glomerular Diseases: Fibrosis and Extracellular Matrix

Authors

  • Huang, Zhi qiang, The University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Zhang, Xianwen, Long Hua Hospital, Shanghai, Shanghai, China
  • Hall, Stacy D., The University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Wang, Lin, Long Hua Hospital, Shanghai, Shanghai, China
  • Chen, Yiping, Long Hua Hospital, Shanghai, Shanghai, China
  • Julian, Bruce A., The University of Alabama at Birmingham, Birmingham, Alabama, United States
  • Novak, Jan, The University of Alabama at Birmingham, Birmingham, Alabama, United States
Background

We and others have shown that immune complexes from the circulation of patients with IgA nephropathy (IgAN) that contain galactose-deficient IgA1 (Gd-IgA1) can induce proliferation of mesangial cells (MC) in culture. Here, we assessed cellular responses and signal transduction in MC after stimulation with CIC.

Methods

Quiescent primary human MC were stimulated for 15 min at 37°C, with or without inhibitors, with circulating immune complexes (CIC) isolated from sera of patients with IgAN. Cell lysates were analyzed directly, or after immunoprecipitation (IP) with antibodies specific for integrin β1 or PDGFR-β, by SDS-PAGE/immunoblotting for IgA, IgG, phospho-ERK1/2, phospho-PEGFR-β, talin, and Axl.

Results

Cell lysates from MC stimulated with CIC and the corresponding IP products of integrin β1 contained IgA and IgG. Amounts of IgA and IgG were significantly reduced by an inhibitor of integrin α1β1 (obtustatin), but not by an inhibitor of integrin α5β1 (RGD), and partially inhibited by a tyrosine-kinase inhibitor (dasatinib). CIC induced phosphorylation of ERK1/2 that was inhibited by obtustatin, RGD, dasatinib, and a Chinese herbal medicine, ShenPing decoction (SP) that has been used to treat IgAN patients in China. Dasatinib and SP inhibited CIC-induced phosphorylation of PDGFR-β and Axl. In IP products of integrin β1 from CIC-activated MC, cytoskeleton-associated protein talin, known to activate ERK1/2, was associated with integrin β1. SP blocked binding of talin to integrin β1. In IP products of PDGFR-β, CIC induced association of integrin β1 with PDGFR-β, a process that may subsequently induce activation of MAP kinases. Dasatinib and SP inhibited this association.

Conclusion

Integrin α1β1 mediated activation of MC by IgA-IgG CIC; CIC activated multiple protein-tyrosine kinases in MC, leading to MAP kinase activation and cellular proliferation. Some of the inhibitors in this study may provide information about the mechanism of MC activation by the pathogenic CIC and, thus, inform development of future disease-specific therapeutic approaches.

Funding

  • NIDDK Support