Iron deficiency drives an autosomal dominant hypophosphatemic rickets (ADHR) phenotype in fibroblast growth factor-23 (Fgf23) knock-in mice.

Abstract

Autosomal dominant hypophosphatemic rickets (ADHR) is unique among the disorders involving Fibroblast growth factor 23 (FGF23) because individuals with R176Q/W and R179Q/W mutations in the FGF23 (176)RXXR(179)/S(180) proteolytic cleavage motif can cycle from unaffected status to delayed onset of disease. This onset may occur in physiological states associated with iron deficiency, including puberty and pregnancy. To test the role of iron status in development of the ADHR phenotype, WT and R176Q-Fgf23 knock-in (ADHR) mice were placed on control or low-iron diets. Both the WT and ADHR mice receiving low-iron diet had significantly elevated bone Fgf23 mRNA. WT mice on a low-iron diet maintained normal serum intact Fgf23 and phosphate metabolism, with elevated serum C-terminal Fgf23 fragments. In contrast, the ADHR mice on the low-iron diet had elevated intact and C-terminal Fgf23 with hypophosphatemic osteomalacia. We used in vitro iron chelation to isolate the effects of iron deficiency on Fgf23 expression. We found that iron chelation in vitro resulted in a significant increase in Fgf23 mRNA that was dependent upon Mapk. Thus, unlike other syndromes of elevated FGF23, our findings support the concept that late-onset ADHR is the product of gene-environment interactions whereby the combined presence of an Fgf23-stabilizing mutation and iron deficiency can lead to ADHR.

• Authors: Emily G Farrow, Xijie Yu, Lelia J Summers, Siobhan I Davis, James C Fleet, Matthew R Allen, Alexander G Robling, Keith R Stayrook, Victoria Jideonwo, Martin J Magers, Holly J Garringer, Ruben Vidal, Rebecca J Chan, Charles B Goodwin, Siu L Hui, Munro Peacock, Kenneth E White
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 108 Issue 46 Pg. E1146-55 (Nov 15 2011) ISSN: 1091-6490 [Electronic] United States
• PMID: 22006328 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Fgf23 protein, mouse
• Fibroblast Growth Factors
• Fibroblast Growth Factor-23
• Glucuronidase
• Klotho Proteins

Topics

• Anemia, Iron-Deficiency (complications)
• Animals
• Familial Hypophosphatemic Rickets (genetics, physiopathology)
• Female
• Fibroblast Growth Factor-23
• Fibroblast Growth Factors (genetics)
• Gene-Environment Interaction
• Glucuronidase (metabolism)
• Hypophosphatemia (genetics)
• Iron Deficiencies
• Klotho Proteins
• MAP Kinase Signaling System
• Male
• Mice
• Mice, Transgenic
• Osteocytes (cytology)
• Osteomalacia (genetics)
• Phenotype
• Protein Structure, Tertiary
• Rats