title: Dietary and serum phosphorus regulate fibroblast growth factor 23 expression and 1,25-dihydroxyvitamin D metabolism in mice.
abstract: Fibroblast growth factor-23 (FGF-23) is a novel circulating peptide that regulates phosphorus (Pi) and vitamin D metabolism, but the mechanisms by which circulating FGF-23 itself is regulated are unknown. To determine whether the serum FGF-23 concentration is regulated by dietary intake of Pi, we fed wild-type (WT), Npt2a gene-ablated (Npt2a(-/-)), and Hyp mice diets containing varying Pi contents (0.02-1.65%). In WT mice, increases in dietary Pi intake from 0.02-1.65% induced a 7-fold increase in serum FGF-23 and a 3-fold increase in serum Pi concentrations. Across the range of dietary Pi, serum FGF-23 concentrations varied directly with serum Pi concentrations (r(2) = 0.72; P < 0.001). In Npt2a(-/-) mice, serum FGF-23 concentrations were significantly lower than in WT mice, and these differences could be accounted for by the lower serum Pi levels in Npt2a(-/-) mice. The serum concentrations of FGF-23 in Hyp mice were 5- to 25-fold higher than values in WT mice, and the values varied with dietary Pi intake. Fgf-23 mRNA abundance in calvaria was significantly higher in Hyp mice than in WT mice on the 1% Pi diet; in both groups of mice, fgf-23 mRNA abundance in calvarial bone was suppressed by 85% on the low (0.02%) Pi diet. In WT mice fed the low (0.02%) Pi diet, renal mitochondrial 1alpha-hydroxylase activity and renal 1alpha-hydroxylase (P450c1alpha) mRNA abundance were significantly higher than in mice fed the higher Pi diets and varied inversely with serum FGF-23 concentrations (r(2) = 0.86 and r(2) = 0.64; P < 0.001, respectively). The present data demonstrate that dietary Pi regulates the serum FGF-23 concentration in mice, and such regulation is independent of phex function. The data suggest that genotype-dependent and dietary Pi-induced changes in the serum FGF-23 concentration reflect changes in fgf-23 gene expression in bone.
authors.affiliation: Department of Pediatrics, University of California, San Francisco, 94143-0748, USA.
authors.forename: Farzana
authors.initials: F
authors.lastname: Perwad
authors.forename: Nasreen
authors.initials: N
authors.lastname: Azam
authors.forename: Martin Y H
authors.initials: MY
authors.lastname: Zhang
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Yamashita
authors.forename: Harriet S
authors.initials: HS
authors.lastname: Tenenhouse
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Portale
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D007015:Hypophosphatemia, Familial / Q000097:blood; D007668:Kidney / Q000201:enzymology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009994:Osmolar Concentration; D010758:Phosphorus / Q000097:blood*; D016226:Phosphorus, Dietary / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa / Q000172:deficiency; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism; D065668:Vitamin D3 24-Hydroxylase
chemical_list: C000717428:Fgf23 protein, mouse; D016226:Phosphorus, Dietary; D012333:RNA, Messenger; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D014807:Vitamin D; D010758:Phosphorus; D005346:Fibroblast Growth Factors; C097949:1,25-dihydroxyvitamin D; D000089703:Fibroblast Growth Factor-23; D013250:Steroid Hydroxylases; C406322:vitamin D 1-alpha hydroxylase; D065668:Vitamin D3 24-Hydroxylase