In vivo genetic evidence for klotho-dependent, fibroblast growth factor 23 (Fgf23) -mediated regulation of systemic phosphate homeostasis.
A major breakthrough in systemic phosphate homeostasis regulation was achieved by the demonstration of strikingly similar physical, morphological, and biochemical phenotypes of fibroblast growth factor 23 (Fgf23) and klotho ablated mice, which led to identification of klotho as an Fgf23 signaling cofactor. Here, we generated Fgf23 and klotho double-knockout (Fgf23(-/-)/klotho(-/-)) mice to test the hypothesis whether Fgf23 has a klotho-independent function. Fgf23(-/-)/klotho(-/-) mice are viable and have high serum phosphate levels, similar to Fgf23(-/-) and klotho(-/-) single-knockout mice. In addition, the Fgf23(-/-)/klotho(-/-) mice have increased renal expression of the sodium/phosphate cotransporter NaP(i)2a and of 1- alpha-hydroxylase concomitant with increased serum levels of 1,25-dihydroxyvitamin-D, as also observed in the Fgf23(-/-) and klotho(-/-) mice. Moreover, Fgf23(-/-)/klotho(-/-) mice show soft tissue and vascular calcification, severe muscle wasting, hypogonadism, pulmonary emphysema, distention of intestinal wall, and skin atrophy, all of which are also seen in Fgf23(-/-) and klotho(-/-) mice. Notably, injection of bioactive FGF23 protein into Fgf23(-/-)/klotho(-/-) and klotho(-/-) mice does not lower serum phosphate, whereas in wild-type and Fgf23(-/-) mice, it reduces serum phosphate. Together, these results provide compelling evidence that Fgf23 does not have a klotho-independent role in the regulation of systemic phosphate and vitamin D homeostasis.
Nakatani
Teruyo
T
Department of Developmental Biology, Harvard School of Dental Medicine, 188 Longwood Ave., Boston, MA 02115, USA.
Sarraj
Bara
B
Ohnishi
Mutsuko
M
Densmore
Michael J
MJ
Taguchi
Takashi
T
Goetz
Regina
R
Mohammadi
Moosa
M
Lanske
Beate
B
Razzaque
M Shawkat
MS
D000818:Animals; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005966:Glucuronidase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D007668:Kidney / Q000378:metabolism; D000090265:Klotho Proteins; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism*; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa / Q000378:metabolism; D015996:Survival Rate; D016482:Urinalysis
C000717428:Fgf23 protein, mouse; D010710:Phosphates; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D005966:Glucuronidase; D000090265:Klotho Proteins