Transgenic mice expressing fibroblast growth factor 23 under the control of the alpha1(I) collagen promoter exhibit growth retardation, osteomalacia, and disturbed phosphate homeostasis.
Mutations in the fibroblast growth factor 23 gene, FGF23, cause autosomal dominant hypophosphatemic rickets (ADHR). The gene product, FGF-23, is produced by tumors from patients with oncogenic osteomalacia (OOM), circulates at increased levels in most patients with X-linked hypophosphatemia (XLH) and is phosphaturic when injected into rats or mice, suggesting involvement in the regulation of phosphate (Pi) homeostasis. To better define the precise role of FGF-23 in maintaining Pi balance and bone mineralization, we generated transgenic mice that express wild-type human FGF-23, under the control of the alpha1(I) collagen promoter, in cells of the osteoblastic lineage. At 8 wk of age, transgenic mice were smaller (body weight = 17.5 +/- 0.57 vs. 24.3 +/- 0.37 g), exhibited decreased serum Pi concentrations (1.91 +/- 0.27 vs. 2.75 +/- 0.22 mmol/liter) and increased urinary Pi excretion when compared with wild-type littermates. The serum concentrations of human FGF-23 (undetectable in wild-type mice) was markedly elevated in transgenic mice (>7800 reference units/ml). Serum PTH levels were increased in transgenic mice (231 +/- 62 vs. 139 +/- 44 pg/ml), whereas differences in calcium and 1,25-dihydroxyvitamin D were not apparent. Expression of Npt2a, the major renal Na(+)/Pi cotransporter, as well as Npt1 and Npt2c mRNAs, was significantly decreased in the kidneys of transgenic mice. Histology of tibiae displayed a disorganized and widened growth plate and peripheral quantitative computerized tomography analysis revealed reduced bone mineral density in transgenic mice. The data indicate that FGF-23 induces phenotypic changes in mice resembling those of patients with ADHR, OOM, and XLH and that FGF-23 is an important determinant of Pi homeostasis and bone mineralization.
Department of Surgical Sciences, University Hospital, SE-751 85 Uppsala, Sweden.
Tobias
T
Larsson
Richard
R
Marsell
Ernestina
E
Schipani
Claes
C
Ohlsson
Osten
O
Ljunggren
Harriet S
HS
Tenenhouse
Harald
H
Jüppner
Kenneth B
KB
Jonsson
D000818:Animals; D001842:Bone and Bones / Q000473:pathology / Q000502:physiology; D002113:Calcification, Physiologic; D002118:Calcium / Q000097:blood / Q000652:urine; D024042:Collagen Type I / Q000235:genetics*; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000235:genetics* / Q000378:metabolism*; D006130:Growth Disorders / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D010018:Osteomalacia / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D010280:Parathyroid Glands / Q000473:pathology / Q000502:physiology; D010641:Phenotype; D010710:Phosphates / Q000097:blood* / Q000652:urine; D011401:Promoter Regions, Genetic; D014807:Vitamin D / Q000378:metabolism
D024042:Collagen Type I; C000717427:FGF23 protein, human; C000717428:Fgf23 protein, mouse; D010710:Phosphates; D014807:Vitamin D; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002118:Calcium