Kidney Week

Abstract: SA-OR13

Channel Function of Polycystin-2 in Endoplasmic Reticulum Protects Against Polycystic Kidney Disease

Session Information

• Genetics, Development, and Therapies
  November 05, 2022 | Location: W308, Orange County Convention Center‚ West Building
  Abstract Time: 04:48 PM - 04:57 PM

Category: Genetic Diseases of the Kidneys

• 1101 Genetic Diseases of the Kidneys: Cystic

Authors

• Padhy, Biswajit, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Biswajit Padhy, PhD

• Xie, Jian, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Jian Xie,

• Wang, Runping, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Runping Wang,

• Lin, Fang, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Fang Lin,

• Huang, Chou-Long, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Chou-Long Huang,

Group or Team Name

• Huang Lab

Background

Autosomal dominant polycystic kidney disease (ADPKD) is among the most common monogenic inherited disease in humans leading to end-stage renal disease. Mutations in PKD2 gene that encodes PC2 protein are responsible for ~15% of the ADPKD cases. The prevailing view is that altered Ca²⁺ influx by mutated PC2 in the primary cilia is the cause for ADPKD pathogenesis. Yet, most of PC2 is localized to endoplasmic reticulum (ER) and more permeable to K⁺ than Ca²⁺. In the cilia-centric view, ER-localized PC2 mainly facilitates ciliary targeting of PC1-PC2 complexes.

Methods

The trimeric intracellular channel-B (TricB), aka TMEM38B, is an ER resident K⁺ channel that mediates K⁺-Ca²⁺ counterion exchange for inositol trisphosphate-mediated Ca²⁺ release. Using TricB as experimental tool, we explored the function of ER-localized PC2 and its role in ADPKD pathogenesis by using cultured cells, zebrafish, and mouse models.

Results

ATP-induced ER Ca²⁺ release was defective in PC2-null renal epithelial cells, which was reversed by exogenous expression of TricB. Likewise, exogenous PC2 reversed ER Ca²⁺ release defect in TricB-null HEK293 cells. Microinjection of wildtype but not non-functional TricB mRNA into PC2-morphant zebrafish embryos ameliorated pronephric cysts. Similarly, ER targeting of ROMK K⁺ channel normally expresses on the plasma membrane suppressed the cystic phenotypes. R6G mutant of PC2 that fails to localize to cilia was still capable of reversing ER Ca²⁺ release defect in PC2-null cultured cells and PC2-deficient zebrafish phenotypes. Transgenic expression of TricB reversed cystic phenotypes in conditional Pkd2-inactivated mice. TricB deletion enhanced cystogenesis in Pkd2-heterozygous kidneys.

Conclusion

ER-localized PC2 plays an important role in the pathogenesis of ADPKD. It acts as a K⁺ channel to facilitate K⁺-Ca²⁺ counterion exchange for inositol trisphosphate-mediated Ca²⁺ release. The results challenge the current cilia-centric dogma providing insights for understanding ADPKD pathogenesis and proof-of-principle for pharmacotherapy by TricB activators.

Funding

• NIDDK Support