In X‐linked hypophosphatemia (XLH) and in its murine homologue, the
Hyp mouse, increased circulating concentrations of fibroblast growth factor 23 (FGF‐23) are critical to the pathogenesis of disordered metabolism of phosphate (P
i) and 1,25‐dihydroxyvitamin D [1,25(OH)
2D]. In this study, we hypothesized that in
Hyp mice, FGF‐23‐mediated suppression of renal 1,25(OH)
2D production and P
i reabsorption depends on activation of mitogen‐activated protein kinase (MAPK) signaling. Wild‐type and
Hyp mice were administered either vehicle or the MEK inhibitor PD0325901 (12.5 mg/kg) orally daily for 4 days. At baseline, the renal abundance of
early growth response 1 (
egr1) mRNA was approximately 2‐fold greater in
Hyp mice than in wild‐type mice. Treatment with PD0325901 greatly suppressed
egr1 mRNA abundance in both wild‐type and
Hyp mice. In
Hyp mice, PD0325901 induced an 8‐fold increase in renal
1α‐hydroxylase mRNA expression and a 4‐fold increase in serum 1,25(OH)
2D concentrations compared with vehicle‐treated
Hyp mice. Serum P
i levels in
Hyp mice increased significantly after treatment with PD0325901, and the increase was associated with increased renal
Npt2a mRNA abundance and brush‐border membrane Npt2a protein expression. These findings provide evidence that in
Hyp mice, MAPK signaling is constitutively activated in the kidney and support the hypothesis that the FGF‐23‐mediated suppression of renal 1,25(OH)
2D production and P
i reabsorption depends on activation of MAPK signaling via MEK/ERK1/2. These findings demonstrate the physiologic importance of MAPK signaling in the actions of FGF‐23 in regulating renal 1,25(OH)
2D and P
i metabolism. © 2011 American Society for Bone and Mineral Research
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