Claudin-3: Physiological Role in Renal Cortical Collecting Duct

Background: In the kidney, ion and fluid transport across epithelia can occur via the transcellular or paracellular pathways. Tight junctions play a key role in mediating paracellular ion reabsorption in the kidney. The renal collecting duct (CD) is the place of fine tuning of Na+ reabsorption and it is mainly regulated by aldosterone. Aldosterone classically regulates Na+ transport through the transcellular pathway. We hypothesized that aldosterone modulates also the paracellular pathway. Paracellular ion permeability is mainly dependent on tight junction permeability. Claudin-3 is one of the main tight junction proteins expressed along the CD. Methods: We used cultured mouse CD principal cells (mCCD) and mouse models to study the effects of aldosterone on claudin-3. Overexpression and silencing of claudin-3 were used to assess the paracellular permeability of claudin-3. WT and claudin-3 knockout male mice were fed for 7 days with either low (0.01 %), normal (0.18 % ) or high sodium (1.25 %) diet. One group of mice fed a low sodium diet received 0.35 mg/100g body wt/day of spironolactone for 7 days. Results: We showed that aldosterone increased protein levels of claudin-3 in cultured CD principal cells. Overexpression of claudin-3 was associated with a reduction in paracellular permeability to sodium and chloride, whereas silencing of claudin-3 was associated with the opposite effect. We also showed that a low-salt diet, which stimulated aldosterone secretion, was associated with increased claudin-3 abundance in the mouse kidney. Reciprocally, mice treated with spironolactone, a mineralocorticoid receptor antagonist, displayed decreased claudin-3 expression. Importantly, claudin-3 knockout mice displayed increased γ-ENaC and claudin-4 protein abundance under low-salt diet compared to WT mice. Conclusion: Our results show that aldosterone modulates the expression of claudin-3 and that claudin-3 acts as paracellular NaCl barrier. We also show a specific adaptation of clausin-3 deficient mice to low-salt diet. Claudin-3 may then play an important role in preventing the backflow of reabsorbed NaCl.