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Abstract: SA-PO841

Integrin β1 Mediates Interactions of IgA1-Containing Circulating Immune Complexes from IgA Nephropathy Patients with Cultured Primary Human Mesangial Cells

Session Information

Category: Glomerular Diseases

  • 1401 Glomerular Diseases: From Inflammation to Fibrosis

Authors

  • Huang, Zhi qiang, University of Alabama at Birmingham, Department of Microbiology, Birmingham, Alabama, United States
  • Hall, Stacy D., University of Alabama at Birmingham, Department of Microbiology, Birmingham, Alabama, United States
  • Rizk, Dana V., University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama, United States
  • Julian, Bruce A., University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama, United States
  • Novak, Jan, University of Alabama at Birmingham, Department of Microbiology, Birmingham, Alabama, United States
Background

Biopsy features of IgA nephropathy include proliferation of mesangial cells and glomerular IgA1 that probably originates from deposition of circulating immune complexes (CIC) with variable amounts of IgA1, IgG, complement C3, and other proteins, e.g., fibronectin (FN). C-terminal segment of FN may bind IgA, and serum levels of IgA-FN complexes may have diagnostic value for IgA nephropathy. The mechanism by which CIC induce proliferation of the mesangial cells is not well understood. We explored interactions between CIC, mesangial cells, FN, and FN’s receptors (integrin α1β1 and α5β1).

Methods

Cultured quiescent human mesangial cells were incubated for 15 min at 37°C with CIC from sera of patients with IgA nephropathy, without or with integrin α1β1 inhibitor obtustatin or integrin α5β1 inhibitor RGD. The integrins were immunoprecipitated (IP) from cell lysates using specific antibodies. Cell lysates and IP products were analyzed by SDS-PAGE/immunoblotting with antibodies specific for IgA, IgG, IgM, FN, and selected phosphoproteins. To assess effects of FN on CIC association with mesangial cells, CIC were incubated 15 min at 37°C with the cells and purified FN, with or without obtustatin.

Results

Variable amounts of IgA and IgG were detected in the lysates of cells incubated with CIC. CIC induced phosphorylation of several proteins, including PDGFR-β, Axl, ERK, and integrin β1. Obtustatin reduced the amounts of IgA and IgG in the lysates and decreased CIC-induced phosphorylation of ERK, Axl, integrin β1, and PDGFR-β. IgA, IgG, and FN were detected in the IP with antibodies specific for integrin α1β1 and α5β1. Obtustatin reduced amounts of IgA and IgG in the IP. Addition of FN to the cells with CIC enhanced the amounts of IgA, IgG, and IgM in lysates about 1.2-4.7-fold. Obtustatin decreased the FN-enhanced amounts of IgA, IgG, and IgM in lysates by about 10-25%.

Conclusion

CIC from patients with IgA nephropathy added to cultured mesangial cells induced cellular signaling and variable association of IgA/IgG/IgM in the cell lysates. Addition of FN enhanced the association of IgA/IgG/IgM with the cells. Future studies are needed to define mechanisms of integrin β1 and CIC interactions and a possible role of FN in these processes.

Funding

  • NIDDK Support