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Abstract: FR-PO692

The Serine Protease HTRA1 Mouse Model: A Gateway to Identify the Cellular Origin of New Antigens

Session Information

Category: Glomerular Diseases

  • 1401 Glomerular Diseases: From Inflammation to Fibrosis

Authors

  • Al-Rabadi, Laith, University of Utah Health, Salt Lake City, Utah, United States
  • Campsen, Jeff, University of Utah Health, Salt Lake City, Utah, United States
  • Caza, Tiffany, Arkana Laboratories, Little Rock, Arkansas, United States
  • Endlich, Nicole, Nipoka, Greifswald, Greifswald, Germany
  • Huang, Yufeng, University of Utah Health, Salt Lake City, Utah, United States
  • Oka, Chio, Nara Sentan Kagaku Gijutsu Daigakuin Daigaku, Ikoma, Nara, Japan
  • Haecker, Hans, University of Utah Health, Salt Lake City, Utah, United States
  • Beck, Laurence H., Boston Medical Center, Boston, Massachusetts, United States
Background

While initial membranous nephropathy (MN) autoantigens like PLA2R were found to be transmembrane podocyte proteins, more recently identified antigens are secreted proteins or not clearly derived from podocytes. Whether immune complexes in these cases assemble in situ or are deposited after forming in the circulation remains unclear.

Methods

WT and HTRA1 KO mice were immunized with full-length human HTRA1. Immunofluorescence, confocal microscopy and RNAscope were used to identify the origin of autoantigen in HTRA1-associated MN.

Results

As shown in Figure 1, MN pathology with mouse HTRA1-mouse IgG immune complexes in a membranous loop pattern and more significant proteinuria was observed in WT, but not HTRA1 KO, mice that were previously immunized with recombinant human HTRA1, despite the presence of circulating anti-human HTRA1 in both animals. This finding suggested that mouse HTRA1 autoantibodies were formed against a shared epitope between human and mouse proteins, leading to in situ immune complex formation at the GBM. Furthermore, RNAscope (Figure 2) demonstrated podocytes to be the cellular source of HTRA1.

Conclusion

The presence of HTRA1-mIgG deposits in actively immunized WT but not KO mice, along with increased podocyte expression of HTRA1 by podocytes, argues against deposition of circulating immune complexes and instead argues for a podocyte origin of this secreted autoantigen and formation of in situ immune deposits. We will further confirm this hypothesis using a podocyte-specific HTRA1 KO.