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Updated: Jun 13, 2025
Implementing Patch Clamp and Live Fluorescence Microscopy to Monitor Functional Properties of Freshly Isolated PKD Epithelium
Published on: September 1, 2015
Pathogenic variants in the polycystin pore helix cause distinct forms of channel dysfunction
Orhi Esarte Palomero1, Eduardo Guadarrama1, Paul G DeCaen1,2
1Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60061.
Abstract:
PKD2 is a member of the polycystin subfamily of transient receptor potential (TRP) ion channel subunits which traffic and function in primary cilia organelle membranes. Millions of individuals carry pathogenic genetic variants in PKD2 that cause a life-threatening condition called autosomal dominant polycystic kidney disease (ADPKD). Although ADPKD is a common monogenetic disorder, there is no drug cure or available therapeutics which address the underlying channel dysregulation. Furthermore, the structural and mechanistic impacts of most disease-causing variants are uncharacterized. Using direct cilia electrophysiology, cryogenic electron microscopy (cryo-EM), and superresolution imaging, we have found mechanistic differences in channel dysregulation caused by three germline missense variants located in PKD2's pore helix 1. Variant C632R reduces protein thermal stability, resulting in impaired channel assembly and abolishes primary cilia trafficking. In contrast, variants F629S and R638C retain native cilia trafficking but exhibit gating defects. Cryo-EM structures (2.7 to 2.8 Å resolution) indicate loss of critical pore helix interactions which precipitate allosteric collapse of the channels inner gate. Results demonstrate how ADPKD-causing mutations cause mechanistically divergent and ranging impacts on PKD2 function, despite their shared structural proximity. These unexpected findings highlight the need for structural and biophysical characterization of polycystin variants, which will guide rational drug development of ADPKD therapeutics.
Insights
Autosomal dominant polycystic kidney disease (ADPKD) arises from PKD2 gene variants. This study reveals distinct molecular mechanisms underlying PKD2 channel dysfunction, paving the way for targeted ADPKD therapies.
Area of Science:
- Molecular Biology
- Biophysics
- Genetics
Background:
- Autosomal dominant polycystic kidney disease (ADPKD) is a common, life-threatening genetic disorder caused by pathogenic variants in the PKD2 gene.
- PKD2 encodes a subunit of the polycystin subfamily of transient receptor potential (TRP) ion channels, crucial for primary cilia function.
- Current ADPKD treatments lack cures and do not address the root cause of channel dysregulation; the structural and mechanistic impacts of most disease-causing variants remain unknown.
Purpose of the Study:
- To investigate the mechanistic differences in PKD2 channel dysfunction caused by specific disease-associated missense variants.
- To elucidate the structural and biophysical consequences of these variants on PKD2 protein stability, assembly, trafficking, and gating.
- To provide insights for the rational development of targeted therapeutics for ADPKD.
Main Methods:
- Direct cilia electrophysiology to assess channel function in its native environment.
- Cryo-electron microscopy (cryo-EM) to determine high-resolution structures of PKD2 variants.
- Superresolution imaging to visualize protein localization and trafficking within primary cilia.
Main Results:
- Three missense variants (C632R, F629S, R638C) in the PKD2 pore helix were analyzed.
- Variant C632R reduced protein stability, impaired assembly, and abolished cilia trafficking.
- Variants F629S and R638C maintained cilia trafficking but exhibited distinct gating defects, with cryo-EM structures revealing allosteric collapse of the channel's inner gate due to disrupted pore helix interactions.
Conclusions:
- Disease-causing mutations in PKD2 can lead to mechanistically divergent impacts on channel function, even those located in close structural proximity.
- These findings underscore the necessity of detailed structural and biophysical characterization of polycystin variants.
- Understanding variant-specific mechanisms is critical for guiding the development of effective, targeted drug therapies for ADPKD.
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