Updates on renal phosphate transport.

Objective: The kidneys control systemic phosphate balance by regulating phosphate transporters mediating the reabsorption of inorganic phosphate (Pi). At least three different Na + -driven Pi cotransporters are located in the brush border membrane (BBM) of proximal tubule cells, NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3) and PiT-2 (SLC20A2). This review will discuss novel aspects of their regulation, pharmacology, and genetics.

Results: Renal NaPi transporters are not only acutely regulated by the phosphaturic hormones parathyroid hormone (PTH) and Fibroblast Growth Factor 23 (FGF23) but possibly also by further mechanisms. A role of inositol hexakisphosphate (IP6) kinases has been found and their deletion from kidneys causes hypophosphatemia, hyperphosphaturia, and bone demineralization. Inhibitors of NaPis elicit phosphaturia and may reduce levels of PTH and FGF23 in chronic kidney disease (CKD) models. The relevance of renal NaPi transporters is highlighted by loss-of-function mutations in SLC34 transporters and analysis of patients provides new insights into diseases caused by variants. Major manifestations include nephrocalcinosis and -lithiasis, rickets, and variants may predispose to an accelerated decline in kidney function.

Conclusions: Renal Pi transporters are regulated, may provide novel drug targets for prevention or treatment of hyperphosphatemia, and contribute to the genetic risk to develop kidney stones and CKD.