title: The phosphatonins and the regulation of phosphate transport and vitamin D metabolism.
abstract: Phosphate homeostasis is preserved during variations in phosphate intake by short-term intrinsic renal and intestinal adaptations in transport processes, and by more long-term hormonal mechanisms, which regulate the efficiency of phosphate transport in the kidney and intestine. Recently, several phosphaturic peptides such as fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein-4 (sFRP-4), extracellular phosphoglycoprotein (MEPE) and fibroblast growth factor 7 (FGF-7) have been shown to play a pathogenic role in several hypophosphatemic disorders such as tumor-induced osteomalacia (TIO), autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemic rickets (XLH), the McCune-Albright syndrome (MAS) and fibrous dysplasia (FD). These proteins induce phosphaturia and hypophosphatemia in vivo, and inhibit sodium-dependent renal phosphate transport in cultured renal epithelial cells. Interestingly, despite the induction of hypophosphatemia by FGF-23 and sFRP-4 in vivo, serum 1, 25-dihydroxyvitamin D (1alpha,25(OH)(2)D) concentrations are decreased or remain inappropriately normal, suggesting an inhibitory effect of these proteins on 25-hydroxyvitamin D 1alpha-hydroxylase activity. In FGF-23 knockout mice, 25-hydroxyvitamin D 1alpha-hydroxylase expression is increased and elevated serum 1alpha,25(OH)(2)D levels cause significant hypercalcemia and hyperphosphatemia. MEPE, however, increases circulating 1alpha,25(OH)(2)D. Circulating or local concentrations of these peptides/proteins may regulate 25-hydroxyvitamin D 1alpha-hydroxylase activity in renal tissues under physiologic circumstances.
authors.affiliation: Nephrology and Hypertension Research, Department of Medicine, Biochemistry and Molecular Biology, Mayo Clinic, MS 1-120, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Stacy
authors.initials: S
authors.lastname: Sommer
authors.forename: Theresa
authors.initials: T
authors.lastname: Berndt
authors.forename: Theodore
authors.initials: T
authors.lastname: Craig
authors.forename: Rajiv
authors.initials: R
authors.lastname: Kumar
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000378:metabolism*; D001692:Biological Transport; D004032:Diet; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D007668:Kidney / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D001685:Biological Factors; C000717427:FGF23 protein, human; C000717428:Fgf23 protein, mouse; D010710:Phosphates; D011518:Proto-Oncogene Proteins; D014807:Vitamin D; D010758:Phosphorus; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23