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Kidney Week

Abstract: PO1208

Polycystin 2 Mediates Endoplasmic Reticulum K+-Ca2+ Exchange to Protect Against Polycystic Kidney Disease

Session Information

Category: Genetic Diseases of the Kidneys

  • 1001 Genetic Diseases of the Kidneys: Cystic

Authors

  • Padhy, Biswajit, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States
  • Xie, Jian, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States
  • Huang, Chou-Long, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States

Group or Team Name

  • Huang Lab
Background

Prevailing view is that PKD is a ciliopathy. Yet, PC2 is most abundantly expressed in ER. Early studies showed that PC2 is involved in agonist-induced ER Ca2+ release. Decrease in ER Ca2+ release in PC2-deficient cells is believed to contribute to cAMP overproduction and cystogenesis. Recent patch-clamp recordings reveal that PC2 channel is ~40X more selective to K+ than Ca2+, raising the question regarding how PC2 mediates ER Ca2+ release and role of ER-localized PC2 in PKD pathogenesis. To avoid potential polarization impeding ion fluxes, Ca2+ release from ER lumen to cytosol requires coupled counter cation exchange and/or parallel anion movement.

Methods

ER Ca2+ release is assayed by fura2 fluorimetry stimulated by ATP. PC2-deficient morphant zebrafish and doxycycline-inducible adult-onset PC2-deficient mice are used for in vivo PKD model.

Results

ATP-stimulated ER Ca2+ release is blunted in PC2-null epithelial cells in which re-expression of WT, but not LOF, PC2 restores ER Ca2+ release. TricB (trimeric intracellular cation-B) is an ER resident K+ channel mediates K+-Ca2+ exchange for IP3R-mediated Ca2+ release. Expressing WT, but not LOF mutant, TricB rescues ER Ca2+ release in PC2-null cells. Vice versa, TricB-null cells have defective ER Ca2+ release, which is rescued by expression of recombinant WT PC2. Zebrafish injected with PC2 antisense morpholino develops dorsal curvature. Co-injecting WT, but not LOF mutant, PC2 RNA rescues phenotypes in PC2-deficient morphant fish. Co-injecting WT, but not LOF, TricB RNA rescues defects in PC2-morphant fish. ER targeting of ROMK K+ channel normally expresses on the cell surface rescues Ca2+ release defect and PC2-morphant phenotypes. PC2L1, a PC2 related channel normally expresses on cell membrane and cilia, does not rescue PC2-deficient morphant fish. Transgenic expression of TricB in adult-onset kidney-specific Pkd2-inactivated mice ameliorates cystogenesis. Double deletion of TricB and Pkd2 in mice reveal synergistic genetic interactions.

Conclusion

Our results provide compelling support for the notion that ER resident PC2 plays an important role in anti-cystogenesis of PKD. The mechanism of action is likely through mediating cytosol-to-ER lumen K+ flux to facilitate Ca2+ release via IP3R.

Funding

  • NIDDK Support