Regulation of Phosphate Transporters and Novel Regulator of Phosphate Metabolism

Abstract

Phosphorus is essential for all living organisms. It plays an important role in maintaining biological functions, such as energy metabolism, cell membrane formation, and bone mineralization. Various factors in the intestine, kidneys, and bones regulate the homeostasis of the inorganic phosphate (Pi) concentration in the body. X-linked hypophosphatemia (XLH), the most common form of hereditary hypophosphatemic rickets, is characterized by an impaired mineralization of the bone matrix, hypertrophic chondrocytes with hypophosphatemia, and active vitamin D resistance in childhood. Phosphate-regulating gene with homologies to endopeptidases on the X chromosome was recognized as the responsible gene for XLH. XLH is classified as fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets. The enhanced FGF23 stimulates renal phosphate wasting by downregulating sodium-dependent Pi cotransporters, NaPi2a and NaPi2c proteins, in the proximal tubules. Recently, transmembrane protein (Tmem) 174 has been identified as a novel regulator of phosphate transporters. This review introduces the role of Tmem174 in the Pi homeostasis in the body.

XPR1: a regulator of cellular phosphate homeostasis rather than a Pi exporter

“…Bones store much of total body Pi which can be mobilized in states of low Pi and Ca 2+ levels, crucially regulated by parathyroid hormone (PTH) and—indirectly—by 1,25(OH) 2 vitamin D 3 . Endocrine signalling also affects transcellular Pi absorption in the intestine and controls renal excretion to maintain body Pi homeostasis [ 16 , 17 ]. In the kidney, Pi is freely filtered in the glomerulus followed by transcellular re-uptake from the primary urine in the proximal tubule.…”