Open AccessInorganic phosphate homeostasis and the role of dietary phosphorus
Author(s) -
Takeda Eiji,
Yamamoto Hironori,
Nashiki Kunitaka,
Sato Tadatoshi,
Arai Hidekazu,
Taketani Yutaka
Publication year - 2004
Publication title -
journal of cellular and molecular medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.44
H-Index - 130
eISSN - 1582-4934
pISSN - 1582-1838
DOI - 10.1111/j.1582-4934.2004.tb00274.x
Subject(s) - phex , hypophosphatemic rickets , osteomalacia , hypophosphatemia , endocrinology , reabsorption , medicine , homeostasis , chemistry , rickets , kidney , renal physiology , distal convoluted tubule , fibroblast growth factor 23 , biochemistry , biology , parathyroid hormone , vitamin d and neurology , calcium
Abstract 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. 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 Pi, parathyroid hormone and by 1,25‐dihydroxyvitamin D. Recent studies of inherited and acquired hypophosphatemia [X‐linked hypophosphatemic rickets/osteomalacia (XLH), autosomal dominant hypophosphatemic rickets/osteomalacia (ADHR) and tumor‐induced rickets/osteomalacia (TIO)], which exhibit similar biochemical and clinical features, have led to the identification of novel genes, PHEX and FGF23, that play a role in the regulation of Pi homeostasis. The PHEX gene, which is mutated in XLH, encodes an endopeptidase, predominantly expressed in bone and teeth, but not in kidney. FGF‐23 may be a substrate of this endopeptidase and may therefore accumulate in patients with XLH. In the case of ADHR mutations in the furin cleavage site, which prevent the processing of FGF‐23 into fragments, lead to the accumulation of a “stable” circulating form of the peptide which also inhibits renal Pi reabsorption. In the case of TIO, ectopic overproduction of FGF‐23 overwhelms its processing and degradation by PHEX, leading to the accumulation of FGF‐23 in the circulation and inhibition of renal Pi reabsorption. Mice homozygous for severely hypomorphic alleles of the Klotho gene exhibit a syndrome resembling human aging, including atherosclerosis, osteoporosis, emphysema, and infertility. The KLOTHO locus is associated with human survival, defined as postnatal life expectancy, and longevity, defined as life expectancy after 75. In considering the relationship of klotho expression to the dietary Pi level, the klotho protein seemed to be negatively controlled by dietary Pi.