Biology subjects

Eladari, D.

Publications and source records attributed to Eladari, D..

3 recordsLinked to original sources

bioRxiv2024

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

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.

physiology↗

bioRxiv2024

Renal proximal tubules are sensitive to metabolic acidosis

Patients suffering from distal renal tubular acidosis (dRTA) are sometimes diagnosed with proximal tubule dysfunction with leaks of phosphate, uric acid, amino acids, and low-molecular-weight proteins, also known as Fanconi-like syndrome. The underlying molecular basis is largely elusive. We previously reported on Atp6v0a4 knockout (KO) mice, which exhibit severe metabolic acidosis in combination with proximal tubule dysfunction as evidenced by phosphaturia and proteinuria. Here, we show that Rab7, a key regulator of endo-lysosomal trafficking and lysosomal biogenesis, is strongly diminished in proximal tubules of Atp6v0a4 KO mice, while the number of abnormal Ist1-labelled Lamp1-positive vesicles is increased. This is accompanied by the accumulation of autophagosomes, autolysosomes and autophagic substrates. Importantly, correction of metabolic acidosis with bicarbonate therapy resolves proximal tubule dysfunction and trafficking defects in Atp6v0a4 KO mice. Acid-challenged wildtype mice also show trafficking defects with Rab7-downregulation and an increase in Ist1-labeled Lamp1-positive vesicles and develop proximal tubule damage in the long-term. Similar acidosis-induced alterations also occur in human kidney organoids. Altogether, our data provide insights, why patients suffering from severe dRTA may develop a Fanconi-like syndrome, which may contribute to the progression of chronic kidney failure. Translational StatementPatients with renal acidosis caused by impaired proton secretion in the collecting duct (distal renal tubular acidosis - dRTA) sometimes show unexplained symptoms of proximal tubule dysfunction such as proteinuria and phosphaturia. Here, we show that proximal tubules are particularly sensitive to acidosis as evidenced by impaired trafficking, lysosomal damage and accumulation of autophagic substrates. We also show that early treatment of dRTA by alkali supplementation can prevent proximal tubule dysfunction. Because metabolic acidosis represents a well-known risk factor for the progression of chronic kidney disease (CKD), our findings highlight the potential clinical importance of early alkali supplementation to delay disease progression.

molecular biology↗

bioRxiv2022

Claudin-4, a core component of the tight-junctional complex along the collecting system, is induced in nephrotic syndrome

BackgroundNephrotic syndrome (NS) is characterized by massive sodium chloride retention. Along the kidney tubule, sodium and chloride reabsorption are coupled via a combination of transcellular and paracellular transport pathways. The mechanism of sodium retention in NS has been extensively studied, but the associated chloride transport pathway has not been elucidated. MethodsTo investigate the pathway of chloride retention in NS, we assessed the expression levels of both paracellular and transcellular components of chloride transport in the CD of POD-ATTAC mice and PAN rats, two rodent models of NS. We also used cultured mouse cortical collecting duct cells to see how overexpression or silencing of claudin-4 affect paracellular permeability. Finally, human renal biopsies were used to confirm our in vivo results. ResultsIn control animals, claudin-4 was expressed at low levels in collecting duct (CD). In POD-ATTAC mice and PAN rats, claudin-4 expression was strongly increased in CD beta-intercalated cells (B-IC) and to a lesser extent in CD principal cells and was also induced in connecting tubules. Similarly, we found that claudin-4 was expressed at low levels in normal human kidneys and was dramatically increased in CD cells of nephrotic human kidneys (focal and segmental glomerulosclerosis). In parallel, the expression of pendrin, which exchanges chloride for bicarbonates in B-IC, was decreased in nephrotic compared to control animals. However, the increase in claudin-4 expression observed in NS is likely independent of pendrin abundance. Increased claudin-4 abundance is coupled with increased ENaC-dependent sodium transport. Overexpression or silencing of claudin-4 in mCCDcl1 cells confirmed the preferential permeability of claudin-4 to chloride over sodium. ConclusionsThese results suggest that during NS, transcellular Cl-/HCO - transport decreases while paracellular chloride transport via claudin-4 may increase along the collecting system. Paracellular chloride permeability may constitute a chloride shunt that favors Na+ reabsorption and opposes K+ secretion along the CD in NS. Significance StatementNephrotic syndrome is a common disease characterized by massive proteinuria, hypoalbuminemia and edema due to renal sodium-chloride retention. We demonstrate for the first time an induction of claudin-4 expression indicating a partial shift from transcellular to paracellular chloride transport in the renal collecting system of nephrotic rodents. We confirmed the increased expression of claudin-4 in kidney biopsies of nephrotic patients, highlighting the translational significance of these results. Whether the paracellular pathway may represent a novel target to treat edema in nephrotic syndrome remains to be elucidated.

physiology↗