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Kidney Week

Abstract: PO1984

Bag3 as a Potential Mechanoprotector in Podocytes

Session Information

  • Podocyte Biology
    October 22, 2020 | Location: On-Demand
    Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

  • 1204 Podocyte Biology

Authors

  • Plagmann, Ingo, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
  • Rinschen, Markus M., The Scripps Research Institute, La Jolla, United States
  • Heinlein, Karim, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
  • Degenhardt, Jan Christoph, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
  • Unnersjö-Jess, David, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
  • Kohler, Sybille, The University of Edinburgh Centre for Discovery Brain Sciences, Edinburgh, Edinburgh, United Kingdom
  • Schermer, Bernhard, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
  • Benzing, Thomas, Department II of Internal Medicine and Center for Molecular Medicine, University of Cologne, Cologne, Germany
Background

Podocyte loss is a hallmark of glomerular diseases leading to glomerulosclerosis and progresssion of kidney disease. Sitting on the outside of the glomerular tuft podocytes have to withstand extensive mechanical stress due to perfusion and filtration. Hyperfiltration und hyperperfusion e.g. in disease states cause podocyte detachment when overwhelming their mechonoprotective capacity, which start a vicious cycle of mounting strain on the remaining podocytes.
Bag3 is an important mechanoprotector in many mechanical strained tissues and by inducing chaperone-assisted autophagy (CASA) maintains the proteostasis of e.g. Filamin and Synaptopodin – indispensable for podocyte biology. Additionally Bag3 insufficiency renders susceptibility to diabetic nephropathy in a mouse model. These findings point toward Bag3 as a candidate for mechanical stress protection in podocytes.

Methods


Using immunofluorescence, super-resolution-microscopy and mass-spectrometry we examined glomeruli and podocytes for Bag3/CASA expression and characterized the CASA-complex composition in podocytes by immunoprecipitation. The influence of mechanical clues was examined by stiff matrices and cyclic stretch. The role of Bag3 in vivo is being evaluated in different mouse lines (Bag3.P209L mutation, a conditional knockout, fusion-protein).

Results

In the glomerulus the Bag3 and the entire CASA-complex is enriched in podocytes in mass-spectrometry. Bag3 staining localizes to the slit diaphragm protein nephrin in superresolution microscopy. Importantly the co-chaperone Bag3 shows interaction with essential actin-cytoskeleton regulators like RhoA, Arpc2 and Dynamin2 in co-immunoprecipitation. The expression of Bag3 and the CASA-complex in podocytes is regulated by mechanical clues. Knockdown of the Bag3 homologue starvin in drosophila nephrocytes displays a mild filtration disturbance. The dominant-negative Bag3.P209L mutation causes a mild proteinuria in a whole-body overexpression mouse line.

Conclusion


The data further emphasize the role of Bag3 and chaperone-assisted-selective-autophagy in podocyte mechanoprotection and maintenance of podocyte cytoskeleton architecture. Currently undergoing characterization of podocyte specific Bag3 mouse lines and the use of disease models will further help to understand the role of Bag3 at the kidney filtration barrier.

Funding

  • Government Support - Non-U.S.