ClC5

ClC-5 is a member of the CLC family of chloride channels and transporters. In humans, it is encoded by the CLCN5 gene. The protein is expressed predominantly in the kidney, especially in proximal tubule cells, with additional expression in other epithelia and the brain.

ClC-5 localizes to endosomes and lysosomes within renal proximal tubule cells, where it associates with endocytic receptors such as megalin and cubilin. Its activity supports receptor-mediated endocytosis of low-molecular-weight proteins that are filtered by the glomerulus and subsequently reabsorbed in the proximal tubule.

Functional overview: ClC-5 functions as a chloride/proton exchanger (antiporter) in endosomal membranes. By providing chloride conductance, it operates with the vacuolar-type H+-ATPase to acidify endosomes and maintain ion balance, which is necessary for cargo processing and the release of ligands from receptors during endocytosis.

Clinical significance: Mutations in CLCN5 cause Dent disease type 1, an X-linked recessive proximal tubulopathy. Hallmarks include low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and varying degrees of renal impairment. The disease reflects impaired endocytic reclamation of filtered proteins due to defective endosomal ion homeostasis.

Genetics and structure: CLCN5 encodes a multi-pass transmembrane protein of the CLC family. Pathogenic variants disrupt endosomal Cl-/H+ exchange, contributing to disease pathophysiology and the associated renal phenotype.