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Review
. 2014 Nov;37(11):1121-6.
doi: 10.1007/s40618-014-0158-6. Epub 2014 Sep 7.

Alpha Klotho and phosphate homeostasis

Affiliations
Review

VSports手机版 - Alpha Klotho and phosphate homeostasis

A Bian et al. J Endocrinol Invest. 2014 Nov.

Abstract

The Klotho family consists of three single-pass transmembrane proteins—αKlotho, βKlotho and γKlotho. Each of them combines with fibroblast growth factor (FGF) receptors (FGFRs) to form receptor complexes for various FGF’s. αKlotho is a co-receptor for physiological FGF23 signaling and appears essential for FGF23-mediated regulation of mineral metabolism VSports手机版. αKlotho protein also plays a FGF23-independent role in phosphate homeostasis. Animal experimental studies and clinical observations have demonstrated that αKlotho deficiency leads to severe hyperphosphatemia; moderate elevation of αKlotho reduces serum phosphate and extremely high αKlotho induces hypophosphatemia and high-FGF23. αKlotho maintains circulating phosphate in a narrow range by modulating intestinal phosphate absorption, urinary phosphate excretion by the kidney, and phosphate distribution into bone rather than soft tissue in concerted interaction with other calciophosphotropic hormones such as PTH, FGF23, and 1,25-(OH)2 vitamin D. The role of αKlotho in maintenance of phosphate homeostasis is mediated by direct suppression of Na-dependent phosphate cotransporters in target organs. Therefore, αKlotho manipulation may be a novel strategy for genetic and acquired phosphate disorders and for medical conditions with αKlotho deficiency such as chronic kidney disease in future. .

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Figures

Figure 1
Figure 1. αKlotho inhibits Na-dependent phosphate co-transporters
Phosphate absorption from food is regulated by NaPi-2b and PiT-1 in small intestine, and phosphate reabsorption from urine by NaPi-2a, 2c and PiT-2 in renal proximal tubules. Gut and kidney are the two major organs to modulate phosphate excretion based on dietary intake and phosphate concentration in extracellular fluid, which is also maintained by phosphate trafficking across bone controlled by NaPi-2a and PiT-1 in osteoblast. Membrane αKlotho can regulate urinary phosphate excretion through FGF23 signaling pathway. In addition, soluble αKlotho can also exert phosphaturic action via a FGF23-independent manner to directly modulate NaPi-2a activity. The role of αKlotho in modulation of bone formation is known but αKlotho protein is not expressed in bone; soluble αKlotho is therefore considered an alternative candidate. How soluble αKlotho affects NaPi transport activity in the bone has not been addressed, although αKlotho has been shown to suppress NaPi-2a expression and activity in proximal tubules and PiT-1 expression and activity in vascular smooth muscle cells. Therefore, it is still premature to conclude that αKlotho can directly affect bone development and mineralization.

References

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