Klotho: a novel phosphaturic substance acting as an autocrine enzyme in the renal proximal tubule

FASEB J. 2010 Sep;24(9):3438-50. doi: 10.1096/fj.10-154765. Epub 2010 May 13.

Abstract

Klotho has profound effects on phosphate metabolism, but the mechanisms of how Klotho affects phosphate homeostasis is unknown. We detected Klotho in the proximal tubule cell, brush border, and urinary lumen, where phosphate homeostasis resides. Increasing Klotho in the kidney and urine chronically by transgenic overexpression or acutely by intravenous infusion caused hypophosphatemia, phosphaturia from decreased proximal phosphate reabsorption, and decreased activity and protein of the principal renal phosphate transporter NaPi-2a. The phosphaturic effect was present in FGF23-null mice, indicating a direct action distinct from Klotho's known role as a coreceptor for FGF23. Direct inhibition of NaPi-2a by Klotho was confirmed in cultured cells and in cell-free membrane vesicles characterized by acute inhibition of transport activity followed by decreased cell surface protein. Transport inhibition can be mimicked by recombinant beta-glucuronidase and is associated with proteolytic degradation and reduced surface NaPi-2a. The inhibitory effect of Klotho on NaPi-2a was blocked by beta-glucuronidase inhibitor but not by protease inhibitor. Klotho is a novel phosphaturic substance that acts as an enzyme in the proximal tubule urinary lumen by modifying glycans, which cause decreased transporter activity, followed by proteolytic degradation and possibly internalization of NaPi-2a from the apical membrane.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Glucuronidase / antagonists & inhibitors
  • Glucuronidase / genetics
  • Glucuronidase / metabolism*
  • Glucuronidase / pharmacology
  • Glycoproteins / pharmacology
  • Homeostasis / drug effects
  • Homeostasis / genetics
  • Hypophosphatemia, Familial / chemically induced
  • Immunoblotting
  • Immunohistochemistry
  • Kidney Tubules / enzymology*
  • Mice
  • Mice, Transgenic
  • Microscopy, Fluorescence
  • Microscopy, Immunoelectron
  • Microvilli / metabolism
  • Phosphates / metabolism
  • Protease Inhibitors / pharmacology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sodium-Phosphate Cotransporter Proteins, Type IIa / genetics
  • Sodium-Phosphate Cotransporter Proteins, Type IIa / metabolism

Substances

  • Glycoproteins
  • Phosphates
  • Protease Inhibitors
  • Sodium-Phosphate Cotransporter Proteins, Type IIa
  • beta-glucuronidase inhibitor
  • Glucuronidase
  • klotho protein