The regulation and function of phosphate in the human body.
Inorganic phosphate (Pi) is required for cellular function and skeletal mineralization. Serum Pi level is maintained within a narrow range through a complex interplay between intestinal absorption, exchange with intracellular and bone storage pools, and renal tubular reabsorption. Pi is abundant in the diet, and intestinal absorption of Pi is efficient and minimally regulated. The kidney is a major regulator of Pi homeostasis and can increase or decrease its Pi reabsorptive capacity to accommodate Pi need. The crucial regulated step in Pi homeostasis is the transport of Pi across the renal proximal tubule. Type II sodium-dependent phosphate (Na/Pi) cotransporter (NPT2) is the major molecule in the renal proximal tubule and is regulated by hormones and nonhormonal factors. Recent studies of inherited and acquired hypophosphatemia which exhibit similar biochemical and clinical features, have led to the identification of novel genes, phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and fibroblast growth factor-23 (FGF-23), that play a role in the regulation of Pi homeostasis. The PHEX gene encodes an endopeptidase, predominantly expressed in bone and teeth but not in kidney. FGF-23 may be a substrate of this endopeptidase and inhibit renal Pi reabsorption. In a survey in the United States and in Japan, the amount of phosphorus from food is gradually increasing. It is thought that excess amounts of phosphorus intake for long periods are a strong factor in bone impairment and ageing. The restriction of phosphorus intake seems to be important under low calcium intake to keep QOL on high level.
Takeda
Eiji
E
Department of Clinical Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima, Japan. takeda@nutr.med.tokushima-u.ac.jp
Taketani
Yutaka
Y
Sawada
Naoki
N
Sato
Tadatoshi
T
Yamamoto
Hironori
H
D000375:Aging / Q000502:physiology*; D002874:Chromosome Mapping; D002877:Chromosomes, Human; D041321:Chromosomes, Human, X; D000089703:Fibroblast Growth Factor-23; D006801:Humans; D007015:Hypophosphatemia, Familial / Q000235:genetics; D010710:Phosphates / Q000032:analysis / Q000378:metabolism*; D011788:Quality of Life; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D027981:Symporters / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
C000717427:FGF23 protein, human; D010710:Phosphates; C493548:SLC17A2 protein, human; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D027981:Symporters; D000089703:Fibroblast Growth Factor-23