A C. elegans model for functional analysis of ADPKD variants in cilia, extracellular vesicles, and sensory signaling
Interpreting the pathogenic significance of missense variants in human disease gene candidates remains a major challenge in precision medicine. Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic cause of kidney failure and caused by mutations in the PKD1 or PKD2 genes that encode polycystin-1 and polycystin-2. Here, we establish C. elegans as a platform for the functional classification of PC2 variants by characterizing PKD-2C180S, the C. elegans ortholog of the likely pathogenic human variant PC2C331S. Using CRISPR/Cas9 endogenous genome editing combined with dual-color fluorescent reporters and super-resolution imaging, we show that PKD-2C180S severely reduces protein stability, abolishes ciliary and extracellular vesicle (EV) localization, and eliminates sensory function comparable to a pkd-2 null allele. In heterozygous animals, PKD-2C180S is recessive and exerts no dominant-negative effect on wild-type PKD-2 trafficking, protein levels, or function, establishing that PKD-2 is haplosufficient in this model. PKD-2C180S also abolishes ciliary and EV localization of the PC1 homolog LOV-1 and reduces LOV-1 cell body levels comparable to pkd-2 null animals, consistent with PC2 functioning as a molecular chaperone for PC1 stability and trafficking. Genetic epistasis experiments show that PKD-2C180S protein levels are unaffected in lov-1 mutants, indicating that the PKD-2C180S mutation acts prior to complex assembly. Quantitative analysis reveals that LOV-1*PKD-2 complexes are more stable at the ciliary membrane and more efficiently packaged into EVs than PKD-2 lacking LOV-1. Together, this work demonstrates that PC2C331S may act recessively via loss of polycystin complex function and establishes a C. elegans pipeline for the mechanistic classification of ADPKD-associated variants.