Disrupting polycystin-2 EF hand Ca2+ affinity does not alter channel function or contribute to polycystic kidney disease

Abstract

Approximately 15% of autosomal dominant polycystic kidney disease (ADPKD) is caused by variants in PKD2PKD2 encodes polycystin-2, which forms an ion channel in primary cilia and endoplasmic reticulum (ER) membranes of renal collecting duct cells. Elevated internal Ca²⁺ modulates polycystin-2 voltage-dependent gating and subsequent desensitization - two biophysical regulatory mechanisms that control its function at physiological membrane potentials. Here, we refute the hypothesis that Ca²⁺ occupancy of the polycystin-2 intracellular EF hand is responsible for these forms of channel regulation, and, if disrupted, results in ADPKD. We identify and introduce mutations that attenuate Ca²⁺-EF hand affinity but find channel function is unaltered in the primary cilia and ER membranes. We generated two new mouse strains that harbor distinct mutations that abolish Ca²⁺-EF hand association but do not result in a PKD phenotype. Our findings suggest that additional Ca²⁺-binding sites within polycystin-2 or Ca²⁺-dependent modifiers are responsible for regulating channel activity.

Keywords: ADPKD; Biophysics; Ca2+ regulation; Ion channels; Polycystin; Primary cilia.