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Abstract: FR-PO913

Proteasomal Dysfunction Enhances the Glomerular Accumulation of the Membranous Nephropathy Antigen THSD7A Following Autoantibody Binding

Session Information

Category: Glomerular Diseases

  • 1204 Podocyte Biology

Authors

  • Sachs, Wiebke, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Herwig, Johanna, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Neitzel, Karen, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Skuza, Sinah, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Wedekind, Uta, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Tomas, Nicola M., University Medical Center Hamburg-Eppendorf, Hamburg, Germany
  • Meyer-Schwesinger, Catherine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

Group or Team Name

  • AG Meyer-Schwesinger
Background

Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in Caucasian adults. In MN, podocyte membrane antigens such as the thrombospondin domain-like containing 7A (THSD7A) serve as targets to immunity. Diagnostic for MN is an enhanced antigen reactivity and antigen/antibody deposition in the subepithelial podocyte space and podocyte cytoplasm, for which the underlying mechanisms are unknown. The aim of this project is to investigate the mode of THSD7A degradation under homeostatic conditions and upon autoantibody binding, and whether alterations of THSD7A degradation relate to the pathological glomerular THSD7A accumulation in MN.

Methods

THSD7A half-life and homeostatic THSD7A degradation pathways were investigated in kidney slice cultures, cultured podocytes, and naïve Balb/C mice treated with either vehicle, proteasomal or lysosomal inhibitors. Furthermore, mice with genetic lysosomal dysfunction were used. To assess the involvement of protein turnover for the subepithelial accumulation of THSD7A following autoantibody binding, cultured podocytes were treated with rabbit anti-THSD7A IgG, and the model of rabbit anti-THSD7A MN was induced in Balb/C mice in the absence or presence of proteasomal or lysosomal inhibitors. Cells and mice were analyzed by Western blot, qPCR and high-resolution confocal microscopy.

Results

Under homeostatic conditions THSD7A has a long half-life in vitro and in vivo, and its protein content is regulated by the lysosomal system in naïve cultured podocytes and mice. Upon autoantibody binding, THSD7A is cross-linked at the plasma membrane and internalized through the endosomal system into multivesicular bodies. Internalized autoantibody-THSD7A complexes are degraded by both the lysosomal and proteasomal system. Impairment of the proteasomal system results in the (for MN typical) glomerular deposition of THSD7A in the subepithelial space and podocyte cytoplasm.

Conclusion

Homeostatic THSD7A levels are regulated by lysosomal degradation. Upon autoantibody binding, pathological glomerular THSD7A accumulation additionally strongly depends on the proteasomal system.