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Background Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by mutations in PKD1 and PKD2 , which encode PC1 and PC2, respectively. PC1 and PC2 assemble a cation channel complex enriched in primary cilium, a sensory organelle associated with various developmental diseases including PKD. Accumulating evidence supports the necessity of functional PC complex in cilia to prevent cystogenesis in the kidney, indicating that improving their ciliary levels may ameliorate defects underlying PKD pathogenesis. Yet, molecular mechanisms underlying the ciliary targeting and homeostasis of the PC complex are not fully understood. Methods Indirect immunofluorescence microscopy was utilized to monitor ciliary levels of PC1 and PC2 in renal epithelial cells. Electrophysiology analysis in oocytes was employed to determine the channel activity of the PC complex. Cystogenesis in the kidney was measured using in vitro 3D-Matrigel cell models and ex vivo mouse embryonic kidney models. Results Suppressing INPP5E or activating PIPKIγ raised ciliary levels of the PC complex in both normal renal epithelial cells and cells carrying ADPKD mutations that interrupt the trafficking of PCs into cilia, including GANAB inactivation and the trafficking PKD1 mutation, p.Arg3277Cys (RC). PC1 RC formed a complex with PC2 and exhibited normal channel activity in vitro . An INPP5E inhibitor that increases PC1 and PC2 in cilia, suppressed in vitro forskolin-induced cystogenesis of IMCD3 cells in 3D Matrigel and ex vivo cyst formation in embryonic Pkd1 RC/RC mouse kidneys. Conclusions Our results demonstrated that increasing the ciliary level of PCs, by manipulating a ciliary phosphoinositide signaling axis, enhanced the functionality of PCs and suppressed cystogenesis of renal epithelial cells in vitro .
Chen et al. (Tue,) studied this question.