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Abstract: SA-OR048

Discovery of Novel Podocyte Endoplasmic Reticulum Calcium Stabilizers to treat Nephrotic Syndrome

Session Information

Category: Glomerular Diseases

  • 1204 Podocyte Biology

Authors

  • Park, Sun-Ji, Washington University in St. Louis, St Louis, Missouri, United States
  • Kim, Yeawon, Washington University in St. Louis, St Louis, Missouri, United States
  • Yang, Shyh-Ming, National Center for Advancing Translational Sciences (NCATS), NIH, Rockville, Maryland, United States
  • Henderson, Mark J., National Center for Advancing Translational Sciences (NCATS), NIH, Rockville, Maryland, United States
  • Yang, Wei, Washington University in St. Louis, St Louis, Missouri, United States
  • Lindahl, Maria, University of Helsinki, Helsinki, Finland
  • Urano, Fumihiko, Washington University in St. Louis, St Louis, Missouri, United States
  • Chen, Ying Maggie, Washington University in St. Louis, St Louis, Missouri, United States
Background

Podocyte injury is the hallmark of primary nephrotic syndrome (NS), a leading cause of chronic kidney disease affecting approximately 500 million people worldwide. Despite the importance of podocyte endoplasmic reticulum (ER) stress in the pathogenesis of NS, currently no treatment targets the podocyte ER. For the first time, we have developed a new class of drugs-podocyte ER calcium channel stabilizers, to treat NS.

Methods

We have developed a podocyte ER stress-induced monogenic NS mouse model with an engineered human C321R mutation in laminin β2, which is synthesized and secreted by podocytes. Western blot and RNA sequencing of isolated mouse glomeruli or cultured primary podocytes were utilized to determine accelerated ER calcium efflux-mediated pro-apoptotic pathway. Moreover, a Gaussia luciferase-based assay utilizing secreted ER calcium-monitoring proteins (SERCaMPs) was performed to monitor ER calcium depletion in primary podocytes and to screen for novel ER calcium stabilizers. Lastly, our mouse model was exploited to test the therapeutic effect of an identified drug.

Results

We have identified a novel therapeutic target, podocyte ER type 2 ryanodine receptor/calcium release channel (RyR2). It was phosphorylated at Ser2808 under ER stress, resulting in podocyte ER calcium leak and cytosolic calcium elevation. The altered intracellular calcium homeostasis led to activation of calcium-dependent cytosolic protease calpain 2 and cleavage of its important downstream substrates, including the apoptotic molecule procaspase 12 and podocyte cytoskeletal protein talin 1. More importantly, we have identified a chemical compound K201 and a novel biotherapeutic protein mesencephalic astrocyte-derived neurotrophic factor (MANF), which can reduce RyR2 phosphorylation and inhibit pro-apoptotic calpain 2-caspase 12 signaling in podocytes undergoing ER stress. Most excitingly, K201 treatment attenuated proteinuria and improved kidney function in our podocyte ER stress-induced NS mouse model.

Conclusion

Podocyte RyR2 remodeling contributes to ER stress-induced podocyte injury. Podocyte ER calcium channel stabilizers, including K201 and MANF, could be emerging therapies for the treatment of podocyte ER stress-induced NS.

Funding

  • NIDDK Support