Urinary Sodium Wasting and Disrupted Collecting Duct Function in Mice with dRTA-Causing SLC4A1 Mutations

Abstract

Distal renal tubular acidosis (dRTA) results in metabolic acidosis due to impaired urinary acidification and can also result in an unexplained urinary sodium-wasting phenotype. Here, we report the generation and characterization of a novel dRTA mutant mouse line, Ae1 L919X knockin (KI). Homozygous L919X KI mice exhibit typical dRTA features including a reduced ability to acidify urine in response to an acid load. This renal acidification defect was associated with a reduced number of Ae1-positive type A intercalated cells. To assess whether these mice exhibit urinary sodium-wasting as seen in some dRTA patients, homozygous KI L919X 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 -10b, suggesting a compensatory paracellular pathway in the loop of Henle. Consistent with data from human patients, L919X KI mice displayed a milder phenotype than R607H KI mice. Our findings reveal that both mouse strains are appropriate models for dRTA with a urinary salt-wasting phenotype and a compensatory up-regulation of the paracellular pathway in the ascending limb of the loop of Henle.