Parathyroid hormone controls paracellular Ca transport in the thick ascending limb by regulating the tight-junction protein Claudin14.

Renal Ca reabsorption is essential for maintaining systemic Ca homeostasis and is tightly regulated through the parathyroid hormone (PTH)/PTHrP receptor (PTH1R) signaling pathway. We investigated the role of PTH1R in the kidney by generating a mouse model with targeted deletion of PTH1R in the thick ascending limb of Henle (TAL) and in distal convoluted tubules (DCTs): Mutant mice exhibited hypercalciuria and had lower serum calcium and markedly increased serum PTH levels. Unexpectedly, proteins involved in transcellular Ca reabsorption in DCTs were not decreased. However, claudin14 (Cldn14), an inhibitory factor of the paracellular Ca transport in the TAL, was significantly increased. Analyses by flow cytometry as well as the use of knock-in reporter mice confirmed increased Cldn14 expression and promoter activity in the TAL of mice. Moreover, PTH treatment of HEK293 cells stably transfected with CLDN14-GFP, together with PTH1R, induced cytosolic translocation of CLDN14 from the tight junction. Furthermore, mice with high serum PTH levels, regardless of high or low serum calcium, demonstrated that PTH/PTH1R signaling exerts a suppressive effect on Cldn14. We therefore conclude that PTH1R signaling directly and indirectly regulates the paracellular Ca transport pathway by modulating Cldn14 expression in the TAL. Finally, systemic deletion of Cldn14 completely rescued the hypercalciuric and lower serum calcium phenotype in mice, emphasizing the importance of PTH in inhibiting Cldn14. Consequently, suppressing CLDN14 could provide a potential treatment to correct urinary Ca loss, particularly in patients with hypoparathyroidism.