A kidney stone-associated CLDN4 variant impairs tight junction stability and paracellular ion permeability

Claudin-4 (CLDN4) is a tight junction protein that contributes to epithelial barrier function and regulation of paracellular ion permeability in the distal nephron. Although CLDN4 dysfunction has been linked to tubular transport abnormalities, its role in calcium handling and kidney stone disease remains unclear. We examined the molecular and functional effects of a kidney stone-associated CLDN4 variant, P74L, using doxycycline-inducible epithelial cell models expressing human wild-type (WT) or P74L CLDN4. Compared with WT CLDN4, the P74L variant displayed reduced protein stability, impaired junctional incorporation, and decreased surface expression. In contrast with WT CLDN4, whose overexpression increased transepithelial electrical resistance and restricted paracellular sodium, chloride, and calcium permeability, P74L CLDN4 failed to confer these effects. Expression of P74L CLDN4 was associated with reduced CLDN3 and CLDN7 protein abundance without significant changes in CLDN8 or transcriptional regulation of other distal ion transport genes. Together, these findings identify CLDN4 P74L as a loss-of-function variant that compromises epithelial barrier function and fails to restrict paracellular calcium permeability, possibly leading to altered calcium handling relevant to nephrolithiasis.