Urinary sodium wasting and disrupted collecting duct function in mice with distal renal tubular acidosis mutations

Distal renal tubular acidosis (dRTA) results in metabolic acidosis owing to impaired urinary acidification and can result in an unexplained urinary sodium-wasting phenotype. We report the generation and characterization of a novel dRTA mutant mouse line, Ae1 L919X knock-in (KI). Homozygous L919X KI mice exhibit typical dRTA features, including reduced ability to acidify urine in response to an acid load. This renal acidification defect was associated with a reduced number of kAE1-positive type A intercalated cells. To assess whether these mice exhibit urinary sodium wasting, homozygous L919X KI mice and the previously described R607H KI mice were fed a salt-depleted acid diet. In line with human patients, both mouse strains exhibited urinary sodium loss. Additionally, we identified increased expression of tight junction proteins claudin 4 and claudin 10b, suggesting a compensatory paracellular pathway. Consistent with data from human patients, L919X KI mice displayed a milder phenotype than that of R607H KI mice. Our findings reveal that both mouse strains are appropriate models for dRTA with a urinary salt-wasting phenotype and compensatory upregulation of the paracellular pathway.