201
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Sitara D, Razzaque MS, St-Arnaud R, Huang W, Taguchi T, Erben RG, Lanske B. Genetic ablation of vitamin D activation pathway reverses biochemical and skeletal anomalies in Fgf-23-null animals. THE AMERICAN JOURNAL OF PATHOLOGY 2006; 169:2161-70. [PMID: 17148678 PMCID: PMC1762489 DOI: 10.2353/ajpath.2006.060329] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/06/2006] [Indexed: 12/30/2022]
Abstract
Fibroblast growth factor-23 (FGF-23) is one of the circulating phosphaturic factors associated with renal phosphate wasting. Fgf-23-/- animals show extremely high serum levels of phosphate and 1,25-dihydroxyvitamin D3, along with abnormal bone mineralization and soft tissue calcifications. To determine the role of vitamin D in mediating altered phosphate homeostasis and skeletogenesis in the Fgf-23-/- mice, we generated mice lacking both the Fgf-23 and 1alpha-hydroxylase genes (Fgf-23-/-/1alpha(OH)ase-/-). In the current study, we have identified the cellular source of Fgf-23 in adult mice. In addition, loss of vitamin D activities from Fgf-23-/- mice reverses the severe hyperphosphatemia to hypophosphatemia, attributable to increased urinary phosphate wasting in Fgf-23-/-/1alpha(OH)ase-/- mice, possibly as a consequence of decreased expression of NaPi2a. Ablation of vitamin D from Fgf-23-/- mice resulted in further reduction of total bone mineral content and bone mineral density and reversed ectopic calcification of skeleton and soft tissues, suggesting that abnormal mineral ion homeostasis and impaired skeletogenesis in Fgf-23-/- mice are mediated through enhanced vitamin D activities. In conclusion, using genetic manipulation studies, we have provided evidence for an in vivo inverse correlation between Fgf-23 and vitamin D activities and for the severe skeletal and soft tissue abnormalities of Fgf-23-/- mice being mediated through vitamin D.
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Affiliation(s)
- Despina Sitara
- Department of Developmental Biology, Harvard School of Dental Medicine, REB 303, 188 Longwood Ave., Boston, MA 02115, USA, and The Genetics Unit, Shriners Hospital, Montreal, Quebec, Canada
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202
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Hesse M, Fröhlich LF, Zeitz U, Lanske B, Erben RG. Ablation of vitamin D signaling rescues bone, mineral, and glucose homeostasis in Fgf-23 deficient mice. Matrix Biol 2006; 26:75-84. [PMID: 17123805 DOI: 10.1016/j.matbio.2006.10.003] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Revised: 10/05/2006] [Accepted: 10/06/2006] [Indexed: 12/27/2022]
Abstract
To explore further the role of the vitamin D axis for fibroblast growth factor-23 (FGF23) signaling, we mated Fgf-23 deficient (Fgf-23(-/-)) mice and vitamin D receptor (VDR) mutant mice with a non-functioning VDR. To prevent secondary hyperparathyroidism in VDR and compound mutant mice, all mice were kept on a rescue diet enriched with calcium, phosphorus, and lactose. Consistent with previous findings, Fgf-23(-/-) animals showed hypercalcemia, hyperphosphatemia, growth retardation, ectopic calcifications, severe osteoidosis, skin atrophy, and renal dysfunction. In addition, here we describe that Fgf-23(-/-) mice are hypoglycemic, and have profoundly increased peripheral insulin sensitivity and improved subcutaneous glucose tolerance, but normal renal expression of the aging suppressor gene Klotho. Although VDR and double mutants on the rescue diet still had moderately elevated parathyroid hormone serum levels and lower bone mineral density compared to wild-type mice, double mutant mice were normocalcemic and normophosphatemic, and had normal body weight, normal renal function, and no ectopic calcifications. Ablation of vitamin D signaling in compound mutants also normalized subcutaneous glucose tolerance tests and insulin secretory response. In conclusion, our results indicate that the alterations in mineral and carbohydrate metabolism present in Fgf-23(-/-) mice require an intact vitamin D signaling pathway.
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Affiliation(s)
- Martina Hesse
- Institute of Pathophysiology, Department of Natural Sciences, University of Veterinary Medicine, Veterinaerplatz 1, 1210 Vienna, Austria
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203
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Bhan I, Shah A, Holmes J, Isakova T, Gutierrez O, Burnett SM, Jüppner H, Wolf M. Post-transplant hypophosphatemia: Tertiary 'Hyper-Phosphatoninism'? Kidney Int 2006; 70:1486-94. [PMID: 16941023 DOI: 10.1038/sj.ki.5001788] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hypophosphatemia is a common complication of kidney transplantation. Tertiary hyperparathyroidism has long been thought to be the etiology, but hypophosphatemia can occur despite low parathyroid hormone (PTH) levels and can persist after high PTH levels normalize. Furthermore, even in the setting of normal allograft function, hypophosphatemia, and hyperparathyroidism, calcitriol levels remain inappropriately low following transplantation, suggesting that mechanisms other than PTH contribute. Fibroblast growth factor-23 (FGF-23) induces phosphaturia, inhibits calcitriol synthesis, and accumulates in chronic kidney disease. We performed a prospective, longitudinal study of 27 living donor transplant recipients to test the hypotheses that excessive FGF-23 accounts for hypophosphatemia and decreased calcitriol levels following kidney transplantation. Hypophosphatemia <2.5 mg/dl developed in 85% of subjects, including one who had previously undergone parathyroidectomy; 37% developed phosphate < or =1.5 mg/dl. The mean pre-transplant FGF-23 level was 1,218+/-542 RU/ml. Within the first week following transplantation, mean levels decreased to 557+/-579 RU/ml, which were still above normal. FGF-23 was independently associated with serum phosphate (P < 0.01), urinary excretion of phosphate (P < 0.01), and calcitriol levels (P < 0.01); PTH was not independently associated with any of these parameters. We calculated area under the curve for FGF-23 and PTH between the pre- and first post-transplant levels as a summary measure of early exposure to these phosphaturic hormones. An area under the FGF-23 curve greater than the median was associated with a relative risk of developing hypophosphatemia < or =1.5 mg/dl of 5.3 (P = 0.02) compared with lower levels. Increased area under the PTH curve was not associated with greater risk of hypophosphatemia. Excessive FGF-23 exposure in the early post-transplant period appears to be more strongly associated with post-transplant hypophosphatemia than PTH.
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Affiliation(s)
- I Bhan
- Renal Unit, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA
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204
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Abstract
BACKGROUND The study of a distinct group of renal phosphate wasting disorders with bone disease which comprise X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets (ADHR) and tumour-induced osteomalacia (TIO) gave rise to the identification of different hormone-like peptides, also known as phosphatonins. These factors are responsible for the major disease features that characterize XLH, ADHR and TIO. Recent reports on one of these phosphatonins, fibroblast growth factor-23 (FGF-23), point to a general role of this factor in mineral ion metabolism. OBJECTIVES The main focus regards recent evidence implicating FGF-23 in normal and disordered mineral homeostasis with special emphasis on chronic kidney disease. The interactions of FGF-23 with phosphate, parathyroid hormone and vitamin D are discussed in detail. SUMMARY The FGF-23 has been shown to increase urinary phosphate excretion, inhibit bone mineralization and suppress 1,25-dihydroxy vitamin D(3)[1,25(OH)(2)D(3)], the main characteristics that XLH, ADHR and TIO have in common. Apart from its role in these phosphate wasting disorders serum FGF-23 is elevated in hypoparathyroidism and humoral hypercalcaemia of malignancy and responds to altered dietary phosphate and calcium supply in healthy subjects. The FGF-23 is also variably elevated in chronic kidney disease and associated secondary hyperparathyroidism where it correlates positively with serum phosphate and parathyroid hormone and negatively with 1,25(OH)(2)D(3). Such relationships, along with data from experimental studies, raise the question of whether FGF-23 contributes to the pathophysiology of chronic kidney disease.
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Affiliation(s)
- B Bielesz
- Institute of Physiology, Zurich, Switzerland.
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205
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Antoniucci DM, Yamashita T, Portale AA. Dietary phosphorus regulates serum fibroblast growth factor-23 concentrations in healthy men. J Clin Endocrinol Metab 2006; 91:3144-9. [PMID: 16735491 DOI: 10.1210/jc.2006-0021] [Citation(s) in RCA: 312] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
CONTEXT Fibroblast growth factor 23 (FGF-23) is important in the regulation of phosphorus and vitamin D metabolism. States of excess circulating FGF-23 are associated with renal phosphate wasting and inappropriately low serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] concentrations. Conversely, states of absent or biologically inactive circulating FGF-23 are associated with increased serum phosphorus and 1,25(OH)(2)D concentrations. Restriction of the dietary intake of phosphorus increases renal phosphate reabsorption and 1,25(OH)(2)D production, whereas the opposite occurs when dietary phosphorus is supplemented. OBJECTIVE We sought to determine whether serum FGF-23 concentration is regulated by dietary phosphorus and thereby mediates the physiological response of serum 1,25(OH)(2)D to changes in dietary phosphorus. DESIGN, SETTING, AND PARTICIPANTS We studied 13 healthy men as inpatients during a 4-wk dietary phosphorus intervention study. INTERVENTION Subjects consumed a constant diet that provided 500 mg of phosphorus per day, which was supplemented to achieve three phosphorus intakes, each of 9 d: 1) control = 1500 mg/d; 2) supplemented = 2300 mg/d; 3) restricted = 625 mg/d. Intakes of calcium, sodium, potassium, magnesium, and energy were constant. MAIN OUTCOME MEASURE Serum FGF-23, 1,25(OH)(2)D, phosphorus, and calcium concentrations were measured. RESULTS Serum FGF-23 concentrations decreased significantly from 30.7 +/- 8.7 pg/ml during phosphorus supplementation to 19.6 +/- 7.0 pg/ml during phosphorus restriction. Serum 1,25(OH)(2)D concentrations increased significantly from 29 +/- 10 pg/ml (75 +/- 26 pmol/liter) during phosphorus supplementation to 40 +/- 16 pg/ml (104 +/- 42 pmol/liter) during phosphorus restriction (P < 0.001). Serum 1,25(OH)(2)D concentrations varied inversely with those of serum FGF-23 (r = -0.67, P < 0.001). CONCLUSIONS We conclude that in healthy men, changes in dietary phosphorus within the physiological range of intakes regulate serum FGF-23 concentrations and suggest that dietary phosphorus regulation of 1,25(OH)(2)D production is mediated, at least in part, by changes in circulating FGF-23.
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Affiliation(s)
- Diana M Antoniucci
- University of California-San Francisco, 533 Parnassus Avenue, San Francisco, CA 94143-0748, USA
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206
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Stewart I, Roddie C, Gill A, Clarkson A, Mirams M, Coyle L, Ward C, Clifton-Bligh P, Robinson BG, Mason RS, Clifton-Bligh RJ. Elevated serum FGF23 concentrations in plasma cell dyscrasias. Bone 2006; 39:369-76. [PMID: 16644301 DOI: 10.1016/j.bone.2006.01.163] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Accepted: 01/30/2006] [Indexed: 02/01/2023]
Abstract
Fibroblast growth factor 23 (FGF23) is now recognized as a key regulator of phosphate metabolism. Numerous reports have found elevated serum FGF23 concentrations in oncogenic osteomalacia associated with mesenchymal tumors. Hypophosphatemic osteomalacia more rarely occurs in non-mesenchymal tumors. We identified elevated serum FGF23 levels in one patient with chronic lymphatic leukemia (CLL) and hypophosphatemia, prompting us to examine FGF23 concentrations in other patients with B-cell neoplasms. FGF23 levels were elevated in several patients with myeloma and monoclonal gammopathy of undetermined significance (MGUS), and were significantly associated with serum paraprotein and beta-2 microglobulin concentrations in these patients. Hypophosphatemia was not observed even in those patients with elevated FGF23, and a weak positive correlation was noted between serum FGF23 and phosphate concentrations. Malignant plasma cells in bone marrow trephines from patients with myeloma showed cytoplasmic expression of FGF23, similar to the cytoplasmic localization of FGF23 already described in mesenchymal tumors associated with oncogenic osteomalacia. Our findings contribute to an expanding literature regarding abnormal FGF/FGF receptor-signaling in myeloma. The absence of hypophosphatemia in these cases suggests either that FGF23 produced by clonal B-cells lacks systemic bioactivity or that other factors contribute to maintain serum phosphate. We suggest that the relationship between FGF23 and skeletal disease associated with plasma cell dyscrasias deserves further study.
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Affiliation(s)
- Inge Stewart
- Cancer Genetics Department, Kolling Institute of Medical Research, Royal North Shore Hospital, St Leonards, NSW 2065, Australia
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207
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Abstract
Inactivating mutations of the PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) endopeptidase, the disease-causing gene in X-linked hypophosphatemia (XLH), results in increased circulating levels of fibroblastic growth factor-23 (FGF23), a bone-derived phosphaturic factor. To determine the causal role of FGF23 in XLH, we generated a combined Fgf23-deficient enhanced green fluorescent protein (eGFP) reporter and Phex-deficient Hyp mouse model (Fgf23(+/-)/Hyp). eGFP expression was expressed in osteocytes embedded in bone that exhibited marked upregulation of eGFP in response to Phex deficiency and in CD31-positive cells in bone marrow venules that expressed low eGFP levels independently of Phex. In bone marrow stromal cells (BMSCs) derived from Fgf23(-/-)/Hyp mice, eGFP expression was also selectively increased in osteocyte-like cells within mineralization nodules and detected in low levels in CD31-positive cells. Surprisingly, eGFP expression was not increased in cell surface osteoblasts, indicating that Phex deficiency is necessary but not sufficient for increased Fgf23 expression in the osteoblast lineage. Additional factors, associated with either osteocyte differentiation and/or extracellular matrix, are necessary for Phex deficiency to stimulate Fgf23 gene transcription in bone. Regardless, the deletion of Fgf23 from Hyp mice reversed the hypophosphatemia, abnormal 1,25(OH)(2)D(3) levels, rickets, and osteomalacia associated with Phex deficiency. These results suggest that Fgf23 acts downstream of Phex to cause both the renal and bone phenotypes in Hyp mice.
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Affiliation(s)
- Shiguang Liu
- The Kidney Institute, The University of Kansas Medical Center, Kansas City, KS 66160, USA.
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208
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Razzaque MS, Lanske B. Hypervitaminosis D and premature aging: lessons learned from Fgf23 and Klotho mutant mice. Trends Mol Med 2006; 12:298-305. [PMID: 16731043 DOI: 10.1016/j.molmed.2006.05.002] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 04/18/2006] [Accepted: 05/16/2006] [Indexed: 02/07/2023]
Abstract
The essential role of low levels of vitamin D during aging is well documented. However, possible effects of high levels of vitamin D on the aging process are not yet clear. Recent in vivo genetic-manipulation studies have shown increased serum level of vitamin D and altered mineral-ion homeostasis in mice that lack either fibroblast growth factor 23 (Fgf23) or klotho (Kl) genes. These mice develop identical phenotypes consistent with premature aging. Elimination or reduction of vitamin-D activity from Fgf23 and Kl mutant mice, either by dietary restriction or genetic manipulation could rescue premature aging-like features and ectopic calcifications, resulting in prolonged survival of both mutants. Such in vivo experimental studies indicated that excessive vitamin-D activity and altered mineral-ion homeostasis could accelerate the aging process.
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Affiliation(s)
- Mohammed S Razzaque
- Department of Developmental Biology, Harvard School of Dental Medicine, Research and Educational Building, 190 Longwood Avenue, Boston, MA 02115, USA.
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209
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Abstract
klotho mutant mice were originally described as a short-lived mouse model with premature aging-like disorders. The klotho gene responsible for these phenotypes encodes a type I membrane protein with a considerable similarity to beta-glycosidase. klotho is predominantly expressed in tissues functioning in the regulation of calcium homeostasis. Suggested functions of Klotho are (i) a fundamental regulator of calcium homeostasis, namely, a cofactor for the fibroblast growth factor (FGF) receptor 1c in FGF23 signaling and a regulator of parathyroid hormone secretion; (ii) a hormone that interferes with the intracellular signaling of insulin and insulin-like growth factor-1; and (iii) a beta-glucuronidase that activates the transient receptor potential ion channel TRPV5 by trimming its sugar moiety. How can we reconcile these pleiotropic functions of Klotho? Is there any common mechanism? Further in vivo studies, and biochemical as well as physiological analyses, are required for a better understanding of the molecular aspects of Klotho.
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Affiliation(s)
- Yo-ichi Nabeshima
- Department of Pathology and Tumor Biology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
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210
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White KE, Larsson TE, Econs MJ. The roles of specific genes implicated as circulating factors involved in normal and disordered phosphate homeostasis: frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor 23. Endocr Rev 2006; 27:221-41. [PMID: 16467171 DOI: 10.1210/er.2005-0019] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Normal serum phosphate (Pi) concentrations are relatively tightly controlled by endocrine mediators of Pi balance. Recent data involving several disorders of Pi homeostasis have shed new light on the regulation of serum Pi balance. It has been hypothesized that circulating phosphaturic factors, or phosphatonins, exist that, when present at high serum concentrations, directly act on the kidney to induce renal Pi wasting. This review will focus upon recently discovered factors that are overexpressed in tumors associated with tumor-induced osteomalacia and have reported activity consistent with effecting Pi balance in vivo. Currently, the best-characterized group of phosphatonin-like polypeptides includes secreted frizzled related protein-4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor-23. Our understanding of these factors will, in the short term, aid us in understanding normal Pi balance and, in the future, help to design novel therapeutic strategies for disorders of Pi handling.
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Affiliation(s)
- Kenneth E White
- Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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211
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Liu S, Tang W, Zhou J, Stubbs JR, Luo Q, Pi M, Quarles LD. Fibroblast growth factor 23 is a counter-regulatory phosphaturic hormone for vitamin D. J Am Soc Nephrol 2006; 17:1305-15. [PMID: 16597685 DOI: 10.1681/asn.2005111185] [Citation(s) in RCA: 478] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The regulation of the phosphaturic factor fibroblast growth factor 23 (FGF23) is not well understood. It was found that administration of 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) to mice rapidly increased serum FGF23 concentrations from a basal level of 90.6 +/- 8.1 to 213.8 +/- 14.6 pg/ml at 8 h (mean +/- SEM; P < 0.01) and resulted in a four-fold increase in FGF23 transcripts in bone, the predominate site of FGF23 expression. In the Hyp-mouse homologue of X-linked hypophosphatemic rickets, administration of 1,25(OH)(2)D(3) further increased circulating FGF23 levels. In Gcm2 null mice, low 1,25(OH)(2)D(3) levels were associated with a three-fold reduction in FGF23 levels that were increased by administration of 1,25(OH)(2)D(3). In osteoblast cell cultures, 1,25(OH)(2)D(3) but not calcium, phosphate, or parathyroid hormone stimulated FGF23 mRNA levels and resulted in a dose-dependent increase in FGF23 promoter activity. Overexpression of a dominant negative vitamin D receptor inhibited 1,25(OH)(2)D(3) stimulation of FGF23 promoter activity, and mutagenesis of the FGF23 promoter identified a vitamin D-responsive element (-1180 GGAACTcagTAACCT -1156) that is responsible for the vitamin D effects. These data suggest that 1,25(OH)(2)D(3) is an important regulator of FGF23 production by osteoblasts in bone. The physiologic role of FGF23 may be to act as a counterregulatory phosphaturic hormone to maintain phosphate homeostasis in response to vitamin D.
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Affiliation(s)
- Shiguang Liu
- Department of Internal Medicine and the Kidney Institute, University of Kansas Medical Center, 3901 Rainbow Boulevard, Room 6020 WHE, MS 3018, Kansas City, KS 66160, USA.
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212
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Bergwitz C, Roslin NM, Tieder M, Loredo-Osti JC, Bastepe M, Abu-Zahra H, Frappier D, Burkett K, Carpenter TO, Anderson D, Garabedian M, Sermet I, Fujiwara TM, Morgan K, Tenenhouse HS, Juppner H. SLC34A3 mutations in patients with hereditary hypophosphatemic rickets with hypercalciuria predict a key role for the sodium-phosphate cotransporter NaPi-IIc in maintaining phosphate homeostasis. Am J Hum Genet 2006; 78:179-92. [PMID: 16358214 PMCID: PMC1380228 DOI: 10.1086/499409] [Citation(s) in RCA: 297] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Accepted: 11/07/2005] [Indexed: 12/22/2022] Open
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare disorder of autosomal recessive inheritance that was first described in a large consanguineous Bedouin kindred. HHRH is characterized by the presence of hypophosphatemia secondary to renal phosphate wasting, radiographic and/or histological evidence of rickets, limb deformities, muscle weakness, and bone pain. HHRH is distinct from other forms of hypophosphatemic rickets in that affected individuals present with hypercalciuria due to increased serum 1,25-dihydroxyvitamin D levels and increased intestinal calcium absorption. We performed a genomewide linkage scan combined with homozygosity mapping, using genomic DNA from a large consanguineous Bedouin kindred that included 10 patients who received the diagnosis of HHRH. The disease mapped to a 1.6-Mbp region on chromosome 9q34, which contains SLC34A3, the gene encoding the renal sodium-phosphate cotransporter NaP(i)-IIc. Nucleotide sequence analysis revealed a homozygous single-nucleotide deletion (c.228delC) in this candidate gene in all individuals affected by HHRH. This mutation is predicted to truncate the NaP(i)-IIc protein in the first membrane-spanning domain and thus likely results in a complete loss of function of this protein in individuals homozygous for c.228delC. In addition, compound heterozygous missense and deletion mutations were found in three additional unrelated HHRH kindreds, which supports the conclusion that this disease is caused by SLC34A3 mutations affecting both alleles. Individuals of the investigated kindreds who were heterozygous for a SLC34A3 mutation frequently showed hypercalciuria, often in association with mild hypophosphatemia and/or elevations in 1,25-dihydroxyvitamin D levels. We conclude that NaP(i)-IIc has a key role in the regulation of phosphate homeostasis.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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213
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Razzaque MS, Sitara D, Taguchi T, St-Arnaud R, Lanske B. Premature aging-like phenotype in fibroblast growth factor 23 null mice is a vitamin D-mediated process. FASEB J 2006; 20:720-2. [PMID: 16436465 PMCID: PMC2899884 DOI: 10.1096/fj.05-5432fje] [Citation(s) in RCA: 251] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Fibroblast growth factor 23 null mice (Fgf-23-/-) have a short lifespan and show numerous biochemical and morphological features consistent with premature aging-like phenotypes, including kyphosis, severe muscle wasting, hypogonadism, osteopenia, emphysema, uncoordinated movement, T cell dysregulation, and atrophy of the intestinal villi, skin, thymus, and spleen. Furthermore, increased vitamin D activities in homozygous mutants are associated with severe atherosclerosis and widespread soft tissue calcifications; ablation of vitamin D activity from Fgf-23-/- mice, by genetically deleting the 1alpha(OH)ase gene, eliminates atherosclerosis and ectopic calcifications and significantly rescues premature aging-like features of Fgf-23-/- mice, resulting in prolonged survival of Fgf-23-/-/1alpha(OH)ase-/- double mutants. Our results indicate a novel role of Fgf-23 in developing premature aging-like features through regulating vitamin D homeostasis. Finally, our data support a new model of interactions among Fgf-23, vitamin D, and klotho, a gene described as being associated with premature aging process.
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Affiliation(s)
- Mohammed S. Razzaque
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts
| | - Despina Sitara
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts
| | - Takashi Taguchi
- Department of Pathology, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan
| | | | - Beate Lanske
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts
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214
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Abstract
Fibroblast growth factor 23 (FGF23) is a circulating factor that plays critical roles in phosphate and vitamin D metabolism, as evidenced by the fact that FGF23 missense mutations cause autosomal dominant hypophosphatemic rickets (ADHR). Autosomal dominant hypophosphatemic rickets is characterized by hypophosphatemia with inappropriately normal 1,25-dihydroxyvitamin D concentrations, as well as bone pain, fracture and rickets. This phenotype parallels that of patients with tumor induced osteomalacia (TIO), X-linked hypophosphatemic rickets (XLH), and fibrous dysplasia (FD), in whom elevated serum FGF23 levels are often observed. The fibroblast growth factor receptors (FGFR1-4) play key roles in skeletal development, as well as in normal metabolic processes. Several FGFR isoforms that potentially mediate the activity of FGF23 have been implicated. In the short term, these findings will lead to further understanding of FGF23 function, and potentially in the long term, to targeted therapies in disorders of hypo- and hyperphosphatemia that involve FGF23.
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Affiliation(s)
- Xijie Yu
- Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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215
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Berndt TJ, Schiavi S, Kumar R. "Phosphatonins" and the regulation of phosphorus homeostasis. Am J Physiol Renal Physiol 2005; 289:F1170-82. [PMID: 16275744 DOI: 10.1152/ajprenal.00072.2005] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phosphate ions are critical for normal bone mineralization, and phosphate plays a vital role in a number of other biological processes such as signal transduction, nucleotide metabolism, and enzyme regulation. The study of rare disorders associated with renal phosphate wasting has resulted in the discovery of a number of proteins [fibroblast growth factor 23 (FGF-23), secreted frizzled related protein 4 (sFRP-4), matrix extracellular phosphoglycoprotein, and FGF 7 (FGF-7)] that decrease renal sodium-dependent phosphate transport in vivo and in vitro. The "phosphatonins," FGF-23 and sFRP-4, also inhibit the synthesis of 1alpha,25-dihydroxyvitamin D, leading to decreased intestinal phosphate absorption and further reduction in phosphate retention by the organism. In this review, we discuss the biological properties of these proteins, alterations in their concentrations in various clinical disorders, and their possible physiological role.
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Affiliation(s)
- Theresa J Berndt
- Division of Nephrology and Hypertension, Department of Medicine, Mayo Clinic Rochester, Mayo College of Medicine, MN 55905, USA
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216
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Abstract
PURPOSE OF REVIEW We summarize the most recent findings on the proteins that interact with sodium/inorganic phosphate (Na/Pi) cotransporters, the factors that regulate Pi homeostasis and their role in pathology. RECENT FINDINGS Studies in animal models and cell lines identified proteins mandatory to correct trafficking of the kidney-specific Na/Pi cotransporter NPT2a and its control by the parathyroid hormone. Expression of the intestinal cotransporter NPT2b is controlled by calcitriol, the ubiquitin ligase Nedd-4 and the serum glucocorticoid inducible kinase. Recent data confirm that fibroblast growth factor 23 plays a central role in the control of Pi homeostasis. Mice disrupted for or overexpressing this gene exhibit significant alteration of Pi transport and calcitriol metabolism. In humans, fibroblast growth factor 23 mutations are responsible for autosomal hypophosphataemic rickets or tumoral calcinosis. This gene also seems to be involved in hyperparathyroidism in patients with chronic kidney disease. Several new phosphaturic factors have been identified. Moderate increases in serum Pi concentration may have deleterious effects on lifespan in humans with chronic kidney disease. Disruption of the Klotho gene in mice is associated with hyperphosphataemia and decreased lifespan. Polymorphisms in this gene, in humans and in mice, influence vascular calcification and survival. SUMMARY Pi homeostasis depends on the activity of Na/Pi cotransporters in intestine and kidney. Na/Pi transporter activity is regulated by cellular and endocrine factors, among which fibroblast growth factor 23 plays a central role. Adequate control of Pi homeostasis is crucial, as a moderate increase in serum Pi concentration and polymorphisms in genes involved in Pi metabolism may influence the aging process and lifespan.
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Affiliation(s)
- Dominique Prié
- Inserm U 426 et Institut Fédératif de Recherche 02, Faculty of Medicine, Xavier Bichat, Paris, France.
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217
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Abstract
Until recently, the action of two hormones - parathyroid hormone (PTH) and calcitriol - on three target tissues - bone, kidney, and gut - has been thought to regulate the closely linked homeostasis of calcium and phosphates. In this system, an increase in the plasma concentration of one ion often leads to a reciprocal change in the concentration of the other and PTH stimulates 1 alpha-hydroxylase activity and calcitriol synthesis in renal proximal tubular cells. A second phosphate regulation system was recently identified. It involves one or more phosphaturic hormones, called "phosphatonins", that is, circulating factors with potent phosphaturic activity. The key phosphatonin appears to be a fibroblast growth factor, known as FGF23. It is now established that FGF23 regulates not only phosphate homeostasis, but also vitamin D metabolism. In contrast to PTH, however, FGF23 inhibits rather than stimulates 1 alpha-hydroxylase activity and calcitriol synthesis.
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Affiliation(s)
- C Silve
- Inserm U 683, Faculté de médecine Xavier Bichat, 75018 Paris.
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218
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Yu X, Ibrahimi OA, Goetz R, Zhang F, Davis SI, Garringer HJ, Linhardt RJ, Ornitz DM, Mohammadi M, White KE. Analysis of the biochemical mechanisms for the endocrine actions of fibroblast growth factor-23. Endocrinology 2005; 146:4647-56. [PMID: 16081635 PMCID: PMC4140631 DOI: 10.1210/en.2005-0670] [Citation(s) in RCA: 183] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Fibroblast growth factor (FGF)-23 has emerged as an endocrine regulator of phosphate and of vitamin D metabolism. It is produced in bone and, unlike other FGFs, circulates in the bloodstream to ultimately regulate phosphate handling and vitamin D production in the kidney. Presently, it is unknown which of the seven principal FGF receptors (FGFRs) transmits FGF23 biological activity. Furthermore, the molecular basis for the endocrine mode of FGF23 action is unclear. Herein, we performed surface plasmon resonance and mitogenesis experiments to comprehensively characterize receptor binding specificity. Our data demonstrate that FGF23 binds and activates the c splice isoforms of FGFR1-3, as well as FGFR4, but not the b splice isoforms of FGFR1-3. Interestingly, highly sulfated and longer glycosaminoglycan (GAG) species were capable of promoting FGF23 mitogenic activity. We also show that FGF23 induces tyrosine phosphorylation and inhibits sodium-phosphate cotransporter Npt2a mRNA expression using opossum kidney cells, a model kidney proximal tubule cell line. Removal of cell surface GAGs abolishes the effects of FGF23, and exogenous highly sulfated GAG is capable of restoring FGF23 activity, suggesting that proximal tubule cells naturally express GAGs that are permissive for FGF23 action. We propose that FGF23 signals through multiple FGFRs and that the unique endocrine actions of FGF23 involve escape from FGF23-producing cells and circulation to the kidney, where highly sulfated GAGs most likely act as cofactors for FGF23 activity. Our biochemical findings provide important insights into the molecular mechanisms by which dysregulated FGF23 signaling leads to disorders of hyper- and hypophosphatemia.
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Affiliation(s)
- Xijie Yu
- Department of Medical & Molecular Genetics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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219
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Collins MT, Lindsay JR, Jain A, Kelly MH, Cutler CM, Weinstein LS, Liu J, Fedarko NS, Winer KK. Fibroblast growth factor-23 is regulated by 1alpha,25-dihydroxyvitamin D. J Bone Miner Res 2005; 20:1944-50. [PMID: 16234967 DOI: 10.1359/jbmr.050718] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2005] [Revised: 06/08/2005] [Accepted: 07/13/2005] [Indexed: 12/20/2022]
Abstract
UNLABELLED Serum FGF-23 regulation was studied in patients with hypoparathyroidism or pseudohypoparathyroidism treated with calcitriol. Serum FGF-23 levels changed in parallel in response to changes in serum 1,25-D, suggesting that FGF-23 may be regulated by 1,25-D. In addition, the phosphaturic effect of FGF-23 may be diminished in the absence of PTH action on the kidney. INTRODUCTION Fibroblast growth factor (FGF)-23 is a recently described hormone that has been shown to be involved in the regulation of phosphate and vitamin D metabolism. The physiologic role of FGF-23 in mineral metabolism and how serum FGF-23 levels are regulated have yet to be elucidated. Three patients with mineral metabolism defects that allowed for the investigation of the regulation of FGF-23 were studied. MATERIALS AND METHODS Patient 1 had postsurgical hypoparathyroidism and Munchausen's syndrome and consumed a pharmacologic dose of calcitriol. Patient 2 had postsurgical hypoparathyroidism and fibrous dysplasia of bone. She was treated with increasing doses of calcitriol followed by synthetic PTH(1-34). Patient 3 had pseudohypoparathyroidism type 1B and tertiary hyperparathyroidism. She underwent parathyroidectomy, which was followed by the development of hungry bone syndrome and hypocalcemia, requiring treatment with calcitriol. Serum FGF-23 and serum and urine levels of mineral metabolites were measured in all three patients. RESULTS Patient 1 had an acute and marked increase in serum FGF-23 (70 to 670 RU/ml; normal range, 18-108 RU/ml) within 24 h in response to high-dose calcitriol administration. Patient 2 showed stepwise increases in serum FGF-23 from 117 to 824 RU/ml in response to increasing serum levels of 1alpha,25-dihydroxyvitamin D (1,25-D). Finally, before parathyroidectomy, while hypercalcemic, euphosphatemic, with low levels of 1,25-D (10 pg/ml; normal range, 22-67 pg/ml), and with very high serum PTH (863.7 pg/ml; normal range, 6.0-40.0 pg/ml), patient 3 had high serum FGF-23 levels (217 RU/ml). After surgery, while hypocalcemic, euphosphatemic, and with high serum levels of serum 1,25-D (140 pg/ml), FGF-23 levels were higher than preoperative levels (305 RU/ml). It seemed that the phosphaturic effect of FGF-23 was diminished in the absence of PTH or a PTH effect. CONCLUSIONS Serum FGF-23 may be regulated by serum 1,25-D, and its phosphaturic effect may be less in the absence of PTH.
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Affiliation(s)
- Michael T Collins
- Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892-4320, USA.
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220
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Larsson T, Davis SI, Garringer HJ, Mooney SD, Draman MS, Cullen MJ, White KE. Fibroblast growth factor-23 mutants causing familial tumoral calcinosis are differentially processed. Endocrinology 2005; 146:3883-91. [PMID: 15961556 DOI: 10.1210/en.2005-0431] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Familial tumoral calcinosis (TC, OMIM 211900) is a heritable disorder characterized by hyperphosphatemia, normal or elevated serum 1,25-dihydroxyvitamin D, and often severe ectopic calcifications. Two recessive mutations in fibroblast growth factor-23 (FGF23), serine 71/glycine (S71G) and serine 129/phenylalanine (S129F), were identified as causing TC. Herein, we undertook comprehensive biochemical analyses of an extended TC family carrying the S71G FGF23 mutation, which revealed that heterozygous (serine/glycine, S/G) individuals had elevated serum FGF23 C-terminal fragments compared with wild-type (serine/serine, S/S) family members (P < 0.025). To understand the differential processing of FGF23 in TC patients, we transiently expressed S71G as well as S129F FGF23. FGF23 ELISA in tandem with Western analyses revealed increased proteolytic cleavage of mutant FGF23 and a limited secretion of intact protein. Furthermore, S71G and S129F FGF23 carrying mutations that disrupt the furin-like protease RXXR motif in FGF23 rescued the secretion of the intact protein, and both TC mutant proteins harboring the R176Q mutation revealed no altered sensitivity to trypsin compared with the native (R176Q)FGF23. Finally, S71G, but not S129F mutant FGF23, is rescued by temperature. In summary, FGF23 mutations causing TC lead to increased intracellular proteolysis of FGF23, most likely by furin-like proteases, due to conformational changes of the mutant protein. The destabilizing nature of these mutations provides new insight into the pathophysiology of TC and exemplifies the physiological importance of FGF23 in phosphate and vitamin D metabolism.
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Affiliation(s)
- Tobias Larsson
- Department of Medical and Molecular Genetics, 975 West Walnut Street, IB130, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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221
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Inoue Y, Segawa H, Kaneko I, Yamanaka S, Kusano K, Kawakami E, Furutani J, Ito M, Kuwahata M, Saito H, Fukushima N, Kato S, Kanayama HO, Miyamoto KI. Role of the vitamin D receptor in FGF23 action on phosphate metabolism. Biochem J 2005; 390:325-31. [PMID: 15885032 PMCID: PMC1184586 DOI: 10.1042/bj20041799] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2004] [Revised: 04/25/2005] [Accepted: 05/10/2005] [Indexed: 11/17/2022]
Abstract
FGF23 (fibroblast growth factor 23) is a novel phosphaturic factor that influences vitamin D metabolism and renal re-absorption of Pi. The goal of the present study was to characterize the role of the VDR (vitamin D receptor) in FGF23 action using VDR(-/-) (VDR null) mice. Injection of FGF23M (naked DNA encoding the R179Q mutant of human FGF23) into VDR(-/-) and wildtype VDR(+/+) mice resulted in an elevation in serum FGF23 levels, but had no effect on serum calcium or parathyroid hormone levels. In contrast, injection of FGF23M resulted in significant decreases in serum Pi levels, renal Na/Pi co-transport activity and type II transporter protein levels in both groups when compared with controls injected with mock vector or with FGFWT (naked DNA encoding wild-type human FGF23). Injection of FGF23M resulted in a decrease in 25-hydroxyvitamin D 1a-hydroxylase mRNA levels in VDR(-/-) and VDR(+/+) mice, while 25-hydroxyvitamin D 24-hydroxylase mRNA levels were significantly increased in FGF23M-treated animals compared with mock vector control- or FGF23WT-treated animals. The degree of 24-hydroxylase induction by FGF23M was dependent on the VDR, since FGF23M significantly reduced the levels of serum 1,25(OH)2D3 [1,25-hydroxyvitamin D3] in VDR(+/+) mice, but not in VDR(-/-) mice. We conclude that FGF23 reduces renal Pi transport and 25-hydroxyvitamin D 1a-hydroxylase levels by a mechanism that is independent of the VDR. In contrast, the induction of 25-hydroxyvitamin D 24-hydroxylase and the reduction of serum 1,25(OH)2D3 levels induced by FGF23 are dependent on the VDR.
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Key Words
- fibroblast growth factor 23
- kidney
- phosphate transport
- vitamin d receptor
- adhr, autosomal dominant hypophosphataemic rickets
- bbmv, brush-border membrane vesicle
- fgf, fibroblast growth factor
- fgf23m, naked dna encoding the r179q mutant of human fgf23
- fgf23wt, naked dna encoding wild-type human fgf23
- gapdh, glyceraldehyde-3-phosphate dehydrogenase
- 1α(oh)ase, 25-hydroxyvitamin d3 1α-hydroxylase
- 24(oh)ase, 25-hydroxyvitamin d 24-hydroxylase
- 1,25(oh)2d3, 1,25-dihydroxyvitamin d3
- pth, parathyroid hormone
- rt-pcr, reverse transcription–pcr
- vdr, vitamin d receptor
- xlh, x-linked hypophosphataemia
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Affiliation(s)
- Yoshio Inoue
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
- †Department of Urology, The University of Tokushima School of Medicine, 3-18-15, Kuramoto-Cho, Tokushima 770-8503, Japan
| | - Hiroko Segawa
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Ichiro Kaneko
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Setsuko Yamanaka
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | | | - Eri Kawakami
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Junya Furutani
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Mikiko Ito
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Masashi Kuwahata
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
| | - Hitoshi Saito
- ‡Chugai Pharmaceutical Co. Ltd., Gotenba 412-8513, Japan
| | | | - Shigeaki Kato
- §Institute of Molecular and Cellular Biosciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan
| | - Hiro-omi Kanayama
- †Department of Urology, The University of Tokushima School of Medicine, 3-18-15, Kuramoto-Cho, Tokushima 770-8503, Japan
| | - Ken-ichi Miyamoto
- *Department of Molecular Nutrition, Institute of Health Bioscience, The University of Tokushima Graduate School, Kuramoto-cho 3, Tokushima 770-8503, Japan
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222
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Abstract
Fibroblast growth factor (FGF) 23 shares a fundamentally common structure with the members of the FGF family and has a unique sequence extension at the C-terminus. The molecular behavior of FGF23 as a systemic factor can be justified by the altered conformation of the beta-trefoil structure similar to that suspected in FGF19. On the other hand, the biological activity of FGF23 is quite distinct from those of other FGFs and requires the C-terminal unique extended structure. Two types of enzyme-linked immunosorbent assays (ELISA) have been developed to detect the intact mature form of FGF23 and its C-terminal portion. The former ELISA method enables the detection of rodent FGF23 and human FGF23. Studies on experimental animal models and laboratory examinations of physiologic and disordered conditions using these assays are contributing toward elucidating the physiology and pathophysiology of FGF23.
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Affiliation(s)
- Takeyoshi Yamashita
- Pharmaceutical Research Laboratories, Pharmaceutical Division, Kirin Brewery Co., Ltd, Takasaki, Gunma, Japan.
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223
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Imel EA, Econs MJ. Fibroblast Growth Factor 23: Roles in Health and Disease: Figure 1. J Am Soc Nephrol 2005; 16:2565-75. [PMID: 16033853 DOI: 10.1681/asn.2005050573] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Affiliation(s)
- Erik A Imel
- Department of Medicine, Division of Endocrinology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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224
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Razzaque MS, St-Arnaud R, Taguchi T, Lanske B. FGF-23, vitamin D and calcification: the unholy triad. Nephrol Dial Transplant 2005; 20:2032-5. [PMID: 16030043 DOI: 10.1093/ndt/gfh991] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- Mohammed S Razzaque
- Department of Oral and Developmental Biology, Research and Educational Building, Room 312, Harvard School of Dental of Medicine, 190 Longwood Ave, Boston, MA 02115, USA.
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225
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Shimada T, Yamazaki Y, Takahashi M, Hasegawa H, Urakawa I, Oshima T, Ono K, Kakitani M, Tomizuka K, Fujita T, Fukumoto S, Yamashita T. Vitamin D receptor-independent FGF23 actions in regulating phosphate and vitamin D metabolism. Am J Physiol Renal Physiol 2005; 289:F1088-95. [PMID: 15998839 DOI: 10.1152/ajprenal.00474.2004] [Citation(s) in RCA: 252] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
FGF23 suppresses both serum phosphate and 1,25-dihydroxyvitamin D [1,25D] levels in vivo. Because 1,25D itself is a potent regulator of phosphate metabolism, it has remained unclear whether FGF23-induced changes in phosphate metabolism were caused by a 1,25D-independent mechanism. To address this issue, we intravenously administered recombinant FGF23 to vitamin D receptor (VDR) null (KO) mice as a rapid bolus injection and evaluated the early effects of FGF23. Administration of recombinant FGF23 further decreased the serum phosphate level in VDR KO mice, accompanied by a reduction in renal sodium-phosphate cotransporter type IIa (NaPi2a) protein abundance and a reduced renal 25-hydroxyvitamin D-1alpha-hydroxylase (1alphaOHase) mRNA level. Thus FGF23-induced changes in NaPi2a and 1alphaOHase expression are independent of the 1,25D/VDR system. However, 24-hydroxylase (24OHase) mRNA expression remained undetectable by the treatment with FGF23. We also analyzed the regulatory mechanism for FGF23 expression. The serum FGF23 level was almost undetectable in VDR KO mice, whereas dietary calcium supplementation significantly increased circulatory levels of FGF23 and its mRNA abundance in bone. This finding indicates that calcium is another determinant of FGF23 production that occurs independently of the VDR-mediated mechanism. In contrast, dietary phosphate supplementation failed to induce FGF23 expression in the absence of VDR, whereas marked elevation in circulatory FGF23 was observed in wild-type mice fed with a high-phosphate diet. Taken together, FGF23 works, at least in part, in a VDR-independent manner, and FGF23 production is also regulated by multiple mechanisms involving VDR-independent pathways.
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Affiliation(s)
- Takashi Shimada
- Pharmaceutical Research Laboratories, Kirin Brewery Co., Ltd., Takasaki, Gunma 370-1295, Japan
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226
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Fukagawa M, Nii-Kono T, Kazama JJ. Role of fibroblast growth factor 23 in health and in chronic kidney disease. Curr Opin Nephrol Hypertens 2005; 14:325-9. [PMID: 15930999 DOI: 10.1097/01.mnh.0000172717.49476.80] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
PURPOSE OF REVIEW This review summarizes the molecular properties and biological roles of a new phosphaturic factor, fibroblast growth factor 23 (FGF23). Significant roles of FGF23 are discussed, especially in terms of its effects on the kidney, the main target organ. RECENT FINDINGS FGF 23 is a recently discovered phosphaturic factor. Several animal experiments including overexpression or ablation of the FGF23 gene have recently revealed the significant effects of this factor on phosphate excretion and on vitamin D synthesis in the kidney. Although FGF23 was originally identified as a factor responsible for several hypophosphatemic disorders, recent data indicate its role in the physiological regulation of phosphate homeostasis. In chronic kidney disease, FGF23 plays a crucial role in the pathogenesis of secondary hyperparathyroidism. Effects of FGF23 on other organs including bone and intestine remain to be elucidated. SUMMARY FGF23 is a physiological regulator of phosphate homeostasis. Excessive activity of FGF23 with normal renal function results in hypophosphatemia, low 1,25-dihydroxyvitamin D levels, and rickets/osteomalacia. By contrast, excessive FGF23 activity suppresses 1,25-dihydroxyvitamin D synthesis, but may not be sufficient to excrete the phosphate load appropriately with deteriorating renal function, both of which contribute to the development of hyperparathyroidism.
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Affiliation(s)
- Masafumi Fukagawa
- Division of Nephrology & Dialysis Center, Kobe University School of Medicine, Kobe, Japan.
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227
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Erben RG, Mayer D, Weber K, Jonsson K, Jüppner H, Lanske B. Overexpression of human PHEX under the human beta-actin promoter does not fully rescue the Hyp mouse phenotype. J Bone Miner Res 2005; 20:1149-60. [PMID: 15940367 DOI: 10.1359/jbmr.050212] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2004] [Revised: 01/29/2005] [Accepted: 02/18/2005] [Indexed: 12/13/2022]
Abstract
UNLABELLED XLH in humans and the Hyp phenotype in mice are caused by inactivating Phex mutations. Overexpression of human PHEX under the human beta-actin promoter in Hyp mice rescued the bone phenotype almost completely, but did not affect phosphate homeostasis, suggesting that different, possibly independent, pathophysiological mechanisms contribute to hyperphosphaturia and bone abnormalities in XLH. INTRODUCTION Mutations in PHEX, a phosphate-regulating gene with homologies to endopeptidases on the X chromosome, are responsible for X-linked hypophosphatemia (XLH) in humans, and its mouse homologs, Hyp, Phex(Hyp-2J), Phex(Hyp-Duk), Gy, and Ska1. PHEX is thought to inactivate a phosphaturic factor, which may be fibroblast growth factor 23 (FGF)-23. Consistent with this hypothesis, FGF-23 levels were shown to be elevated in most patients with XLH and in Hyp mice. The aim of this study was, therefore, to examine whether transgenic overexpression of PHEX under the human beta-actin promoter would rescue the Hyp phenotype. MATERIALS AND METHODS We tested this hypothesis by generating two mouse lines expressing human PHEX under the control of a human beta-actin promoter (PHEX-tg). With the exception of brain, RT-PCR analyses showed transgene expression in all tissues examined. PHEX protein, however, was only detected in bone, muscle, lung, skin, and heart. To assess the role of the mutant PHEX, we crossed female heterozygous Hyp mice with male heterozygous PHEX-tg mice to obtain wildtype (WT), PHEX-tg, Hyp, and Hyp/PHEX-tg offspring, which were examined at 3 months of age. RESULTS PHEX-tg mice exhibited normal bone and mineral ion homeostasis. Hyp mice showed the known phenotype with reduced body weight, hypophosphatemia, hyperphosphaturia, and rickets. Hyp/PHEX-tg mice had almost normal body weight relative to WT controls, showed a dramatic improvement in femoral BMD, almost normal growth plate width, and, despite remaining disturbances in bone mineralization, almost normal bone architecture and pronounced improvements of osteoidosis and of halo formation compared with Hyp mice. However, Hyp and Hyp/PHEX-tg mice had comparable reductions in tubular reabsorption of phosphate and were hypophosphatemic relative to WT controls. CONCLUSION Our data suggest that different, possibly independent, pathophysiological mechanisms contribute to renal phosphate wasting and bone abnormalities in Hyp and XLH.
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Affiliation(s)
- Reinhold G Erben
- Institute of Physiology, Physiological Chemistry and Animal Nutrition, Ludwig Maximilians University, Munich, Germany
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228
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Gutierrez O, Isakova T, Rhee E, Shah A, Holmes J, Collerone G, Jüppner H, Wolf M. Fibroblast growth factor-23 mitigates hyperphosphatemia but accentuates calcitriol deficiency in chronic kidney disease. J Am Soc Nephrol 2005; 16:2205-15. [PMID: 15917335 DOI: 10.1681/asn.2005010052] [Citation(s) in RCA: 693] [Impact Index Per Article: 36.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Hyperphosphatemia, calcitriol deficiency, and secondary hyperparathyroidism (SHPT) are common complications of chronic kidney disease (CKD). Fibroblast growth factor-23 (FGF-23) is a novel phosphaturic hormone that also inhibits renal 1alpha-hydroxylase activity and thus may be involved in the pathogenesis of SHPT. Several hypotheses were tested: that FGF-23 increases as renal function declines; is linearly associated with serum phosphate levels; is associated with increased phosphaturia independent of parathyroid hormone (PTH); and is associated with decreased calcitriol levels independent of renal function, hyperphosphatemia, and vitamin D stores. FGF-23, PTH, 25(OH)D3, calcitriol, calcium, phosphate, and urinary fractional excretion of phosphate (Fe(PO4)) were measured in 80 CKD patients. Multiple linear regression was used to test the hypotheses. FGF-23 and PTH were inversely associated with estimated GFR (eGFR), whereas calcitriol levels were linearly associated with eGFR. Hyperphosphatemia and hypocalcemia were present in only 12 and 6% of patients, respectively, all of whose eGFR was <30. Increased Fe(PO4) was associated with decreased eGFR, and both increased FGF-23 and PTH were independently associated with increased Fe(PO4). Increased FGF-23 and decreased 25(OH)D3 were independent predictors of decreased calcitriol, but the effects on calcitriol levels of renal function itself and hyperphosphatemia were completely extinguished by adjusting for FGF-23. It is concluded that FGF-23 levels increase early in CKD before the development of serum mineral abnormalities and are independently associated with serum phosphate, Fe(PO4), and calcitriol deficiency. Increased FGF-23 may contribute to maintaining normal serum phosphate levels in the face of advancing CKD but may worsen calcitriol deficiency and thus may be a central factor in the early pathogenesis of SHPT.
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Affiliation(s)
- Orlando Gutierrez
- Department of Medicine Internal Medicine Residency Training Program, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA
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229
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Sitara D, Razzaque MS, Hesse M, Yoganathan S, Taguchi T, Erben RG, Jüppner H, Lanske B. Homozygous ablation of fibroblast growth factor-23 results in hyperphosphatemia and impaired skeletogenesis, and reverses hypophosphatemia in Phex-deficient mice. Matrix Biol 2005; 23:421-32. [PMID: 15579309 PMCID: PMC2894977 DOI: 10.1016/j.matbio.2004.09.007] [Citation(s) in RCA: 363] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2004] [Revised: 09/24/2004] [Accepted: 09/24/2004] [Indexed: 11/16/2022]
Abstract
Fibroblast growth factor-23 (FGF-23), a recently identified molecule that is mutated in patients with autosomal dominant hypophosphatemic rickets (ADHR), appears to be involved in the regulation of phosphate homeostasis. Although increased levels of circulating FGF-23 were detected in patients with different phosphate-wasting disorders such as oncogenic osteomalacia (OOM) and X-linked hypophosphatemia (XLH), it is not yet clear whether FGF-23 is directly responsible for the abnormal regulation of mineral ion homeostasis and consequently bone development. To address some of these unresolved questions, we generated a mouse model, in which the entire Fgf-23 gene was replaced with the lacZ gene. Fgf-23 null (Fgf-23-/-) mice showed signs of growth retardation by day 17, developed severe hyperphosphatemia with elevated serum 1,25(OH)2D3 levels, and died by 13 weeks of age. Hyperphosphatemia in Fgf-23-/- mice was accompanied by skeletal abnormalities, as demonstrated by histological, molecular, and various other morphometric analyses. Fgf-23-/-) mice had increased total-body bone mineral content (BMC) but decreased bone mineral density (BMD) of the limbs. Overall, Fgf-23-/- mice exhibited increased mineralization, but also accumulation of unmineralized osteoid leading to marked limb deformities. Moreover, Fgf-23-/- mice showed excessive mineralization in soft tissues, including heart and kidney. To further expand our understanding regarding the role of Fgf-23 in phosphate homeostasis and skeletal mineralization, we crossed Fgf-23-/- animals with Hyp mice, the murine equivalent of XLH. Interestingly, Hyp males lacking both Fgf-23 alleles were indistinguishable from Fgf-23/-/ mice, both in terms of serum phosphate levels and skeletal changes, suggesting that Fgf-23 is upstream of the phosphate regulating gene with homologies to endopeptidases on the X chromosome (Phex) and that the increased plasma Fgf-23 levels in Hyp mice (and in XLH patients) may be at least partially responsible for the phosphate imbalance in this disorder.
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Affiliation(s)
- Despina Sitara
- Department of Oral and Developmental Biology, The Forsyth Institute, Harvard School of Dental Medicine, 140 The Fenway, Boston, MA, 02115, USA
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230
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Jonsson KB. The role of fibroblast growth factor 23 in renal disease. Nephrol Dial Transplant 2005; 20:479-82. [PMID: 15735238 DOI: 10.1093/ndt/gfh701] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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