Klotho in the kidney distal convolution regulates urinary Klotho excretion and kidney calcium reabsorption, but not phosphate homeostasis

INTRODUCTION: Klotho acts as a coreceptor for the phosphaturic hormone fibroblast growth factor-23 (FGF-23) and exists in both a membrane-bound and a soluble form (sKlotho) found in blood and urine. Klotho protein is moderately expressed in kidney proximal tubule and more abundant in the distal convolution (DC), which includes the distal convoluted tubule (DCT) and connecting tubule (CNT). However, the function of Klotho in the DC, particularly its role in sKlotho release and regulation of mineral metabolism, remains unclear. METHODS: scRNA-seq was performed on isolated mouse DC cells. Four novel gene-modified mouse models were generated with Klotho deleted in the entire DC, the late DCT/CNT, the DCT only, and pan-tubular. RESULTS: mice exhibited profound hypercalciuria and reduced bone density. On the other hand, pan-tubular Klotho deficiency in mice led to severe phosphate imbalance and loss of both serum/urine sKlotho. CONCLUSIONS: DC-derived Klotho regulates urinary sKlotho levels and controls calcium ion reabsorption, while Klotho in proximal tubule maintains phosphate homeostasis and likely regulates circulating sKlotho levels.