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Polycystin 2 Mediates Endoplasmic Reticulum K+-Ca2+ Exchange to Protect Against Polycystic Kidney Disease: PO1208
Abstract   Peer reviewed

Polycystin 2 Mediates Endoplasmic Reticulum K+-Ca2+ Exchange to Protect Against Polycystic Kidney Disease: PO1208

Biswajit Padhy, Jian Xie, Chou-Long Huang and Huang Lab
Journal of the American Society of Nephrology, Vol.32(10S), pp.393-393
10/2021
DOI: 10.1681/ASN.20213210S1393d

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Abstract

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. Conclusions: 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.

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