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Nuclear isoforms of fibroblast growth factor 2 are novel inducers of hypophosphatemia via modulation of FGF23 and KLOTHO.

ABSTRACT: FGF2 transgenic mice were developed in which type I collagen regulatory sequences drive the nuclear high molecular weight FGF2 isoforms in osteoblasts (TgHMW). The phenotype of TgHMW mice included dwarfism, decreased bone mineral density (BMD), osteomalacia, and decreased serum phosphate (P(i)). When TgHMW mice were fed a high P(i) diet, BMD was increased, and dwarfism was partially reversed. The TgHMW phenotype was similar to mice overexpressing FGF23. Serum FGF23 was increased in TgHMW mice. Fgf23 mRNA in bones and fibroblast growth factor receptors 1c and 3c and Klotho mRNAs in kidneys were increased in TgHMW mice, whereas the renal Na(+)/P(i) co-transporter Npt2a mRNA was decreased. Immunohistochemistry and Western blot analyses of TgHMW kidneys showed increased KLOTHO and decreased NPT2a protein. The results suggest that overexpression of HMW FGF2 increases FGF23/FGFR/KLOTHO signaling to down-regulate NPT2a, causing P(i) wasting, osteomalacia, and decreased BMD. We assessed whether HMW FGF2 expression was altered in the Hyp mouse, a mouse homolog of the human disease X-linked hypophosphatemic rickets/osteomalacia. Fgf2 mRNA was increased in bones, and Western blots showed increased FGF2 protein in nuclear fractions from osteoblasts of Hyp mice. In addition, immunohistochemistry demonstrated co-localization of FGF23 and HMW FGF2 protein in osteoblasts and osteocytes from Hyp mice. This study reveals a novel mechanism of regulation of the FGF23-P(i) homeostatic axis.

SUBMITTER: Xiao L

PROVIDER: S-EPMC2807337 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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Nuclear isoforms of fibroblast growth factor 2 are novel inducers of hypophosphatemia via modulation of FGF23 and KLOTHO.

Xiao Liping L Naganawa Takahiro T Lorenzo Joseph J Carpenter Thomas O TO Coffin J Douglas JD Hurley Marja M MM

The Journal of biological chemistry 20091120 4

FGF2 transgenic mice were developed in which type I collagen regulatory sequences drive the nuclear high molecular weight FGF2 isoforms in osteoblasts (TgHMW). The phenotype of TgHMW mice included dwarfism, decreased bone mineral density (BMD), osteomalacia, and decreased serum phosphate (P(i)). When TgHMW mice were fed a high P(i) diet, BMD was increased, and dwarfism was partially reversed. The TgHMW phenotype was similar to mice overexpressing FGF23. Serum FGF23 was increased in TgHMW mice. F ...[more]

PMID: 19933269

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Project description:Fibroblast growth factor 23 (FGF23) is responsible for phosphate wasting and the phenotypic changes observed in human diseases such as X-linked hypophosphatemia (XLH). Targeted overexpression of nuclear high-molecular weight fibroblast growth factor 2 isoforms (HMW isoforms) in osteoblasts resulted in a transgenic mouse with phenotypic changes similar to XLH, including increased FGF23, hypophosphatemia, and rickets/osteomalacia. The goal of this study was to assess whether HMW isoforms also reduced mineralized bone formation via phosphate-independent effects in bone marrow stromal cells (BMSCs) by modulating FGF23/FGF receptor (FGFR)/extracellular signal-regulated kinase (ERK) signaling. To determine if decreased bone formation in BMSC cultures from HMW transgenic mice could be rescued by blocking this pathway, an FGF23 neutralizing antibody, the FGFR tyrosine kinase inhibitor SU5402 and the mitogen-activated protein kinase (MAPK) inhibitor PD98059 were used. FGF23 levels in the conditioned medium of HMW BMSC cultures were dramatically increased compared to BMSC from control (Vector) mice. Mineralized nodule formation was significantly decreased in HMW BMSC cultures compared with control cultures. The decreased nodule formation in HMW cultures was partially rescued by the FGF23 neutralizing antibody, SU5402 and PD98059. mRNA levels for the osteoblast-related genes, osteocalcin, Runt-related transcription factor 2 (Runx2), and osterix, and the osteocyte-related gene dentin matrix acidic phosphoprotein 1 (Dmp1) were significantly decreased in HMW cultures compared with control cultures, and the decreases were partially rescued by SU5402 or PD98059 treatment. Matrix-gla-protein (Mgp) mRNA was significantly higher in HMW cultures compared with control cultures, reduced by SU5402, but further increased by PD98059. Our results suggest that phosphate-independent effects of HMW isoforms in vitro may be directly mediated in part via FGF23 and that HMW isoforms signal via FGF23/FGFR/MAPK to inhibit bone formation in vitro.

Project description:Fibroblast growth factor 23 (FGF23) is a hormone mainly secreted by bone cells. Its most prominent effects are the regulation of renal phosphate reabsorption and calcitriol (active vitamin D, 1,25(OH)2D3) formation, effects dependent on its co-receptor αKlotho. Besides these actions, further paracrine and endocrine effects exist. The production of FGF23 is regulated by 1,25(OH)2D3, parathyroid hormone, dietary phosphate intake, iron status, as well as inflammation. Glucocorticoids are hormones with anti-inflammatory properties and are, therefore, widely used for acute and chronic inflammatory diseases, autoimmune disorders, and malignancies. The present study explored whether glucocorticoids influence the production of FGF23 in vitro as well as in mice. Fgf23 transcription was analyzed by semi-quantitative real-time PCR. Serum concentrations of FGF23 and 1,25(OH)2D3 were measured by ELISA. Urinary phosphate and Ca2+ excretion were determined in metabolic cages. As a result, in UMR106 rat osteoblast-like cells and in MC3T3-E1 cells, both, dexamethasone and prednisolone, downregulated Fgf23 transcription and FGF23 protein synthesis. Dexamethasone increased Dmp1 and Phex (encoding FGF23-regulating genes) as well as Nfkbia (encoding NFκB inhibitor IκBα) transcription in UMR106 cells. In mice, a single injection of dexamethasone or prednisolone was followed by a significant decrease of serum C-terminal and intact FGF23 concentration and bone Fgf23 mRNA expression within 12 h. These effects were paralleled by increased renal phosphate excretion and enhanced 1,25(OH)2D3 formation. We conclude that a single glucocorticoid treatment strongly downregulates the FGF23 plasma concentration. KEY MESSAGES: Glucocorticoids dexamethasone and prednisolone suppress the formation of bone-derived hormone fibroblast growth factor 23 (FGF23) in vitro. The effect is accompanied by an upregulation of Dmp1, Phex, and IκBα, negative regulators of FGF23, in UMR106 osteoblast-like cells. Glucocorticoid receptor antagonist RU-486 attenuates the effect of dexamethasone on FGF23, Dmp1, and Phex. In mice, a single glucocorticoid dose suppresses FGF23 and enhances 1,25(OH)2D3 (active vitamin D).

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Nuclear isoforms of fibroblast growth factor 2 are novel inducers of hypophosphatemia via modulation of FGF23 and KLOTHO.

Publications

Nuclear isoforms of fibroblast growth factor 2 are novel inducers of hypophosphatemia via modulation of FGF23 and KLOTHO.

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