title: Fibroblast growth factor 23 impairs phosphorus and vitamin D metabolism in vivo and suppresses 25-hydroxyvitamin D-1alpha-hydroxylase expression in vitro.
abstract: Fibroblast growth factor-23 (FGF-23) is critical to the pathogenesis of a distinct group of renal phosphate wasting disorders: tumor-induced osteomalacia, X-linked hypophosphatemia, and autosomal dominant and autosomal recessive hypophosphatemic rickets. Excess circulating FGF-23 is responsible for their major phenotypic features which include hypophosphatemia due to renal phosphate wasting and inappropriately low serum 1,25(OH)2D concentrations. To characterize the effects of FGF-23 on renal sodium-phosphate (Na/P(i)) cotransport and vitamin D metabolism, we administered FGF-23(R176Q) to normal mice. A single injection (0.33 microg/g body wt) induced significant hypophosphatemia, 20 and 29% decreases (P < 0.001) in brush-border membrane (BBM) Na/Pi cotransport at 5 and 17 h after injection, respectively, and comparable decreases in the abundance of type IIa Na/P(i) cotransporter protein in BBM. Multiple injections (6, 12, and 24 mug/day for 4 days) induced dose-dependent decreases (38, 63, and 75%, respectively) in renal abundance of 1alpha-hydroxylase mRNA (P < 0.05). To determine whether FGF-23(R176Q) exerts a direct action on 1alpha-hydroxylase gene expression, we examined its effects in cultured human (HKC-8) and mouse (MCT) renal proximal tubule cells. FGF-23(R176Q) (1 to 10 ng/ml) induced a dose-dependent decrease in 1alpha-hydroxylase mRNA with a maximum suppression of 37% (P < 0.05). Suppression was detectable after 6 h of exposure and maximal after 21 h. In MCT cells, FGF-23(R176Q) suppressed 1alpha-hydroxylase mRNA and activated the ERK1/2 signaling pathway. The MAPK inhibitor PD98059 effectively abolished FGF-23-induced suppression of 1alpha-hydroxylase mRNA by blocking signal transduction via ERK1/2. These novel findings provide evidence that FGF-23 directly regulates renal 1alpha-hydroxylase gene expression via activation of the ERK1/2 signaling pathway.
authors: Pediatrics, University of California San Francisco, San Francisco, California, USA.
authors: Farzana
authors: F
authors: Perwad
authors: Martin Y H
authors: MY
authors: Zhang
authors: Harriet S
authors: HS
authors: Tenenhouse
authors: Anthony A
authors: AA
authors: Portale
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000037:antagonists & inhibitors* / Q000235:genetics; D000818:Animals; D001120:Arginine; D002460:Cell Line; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000494:pharmacology*; D005966:Glucuronidase / Q000235:genetics; D005973:Glutamine; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D000090265:Klotho Proteins; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008871:Microvilli / Q000378:metabolism; D010758:Phosphorus / Q000097:blood / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000494:pharmacology; D013250:Steroid Hydroxylases / Q000235:genetics; D014807:Vitamin D / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: C000717427:FGF23 protein, human; C000717428:Fgf23 protein, mouse; D020033:Protein Isoforms; D012333:RNA, Messenger; D017468:Receptors, Fibroblast Growth Factor; D011994:Recombinant Proteins; D005973:Glutamine; D014807:Vitamin D; D010758:Phosphorus; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D001120:Arginine; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D048049:Extracellular Signal-Regulated MAP Kinases; D005966:Glucuronidase; D000090265:Klotho Proteins