Fibroblast growth factor 23 (FGF23) increases
phosphorus excretion and decreases
calcitriol (1,25(
OH)2D) levels. FGF23 increases from early stages of
renal failure. We evaluated whether strict control of
phosphorus intake in
renal failure prevents the increase in FGF23 and to what extent
inflammation impairs regulation of FGF23. The study was performed in 5/6 nephrectomized (Nx) Wistar rats fed diets containing 0.2-1.2%
phosphorus for 3 or 15 days. FGF23 levels significantly increased in all Nx groups in the short-term (3-day) experiment. However, at 15 days, FGF23 increased in all Nx rats except in those fed 0.2%
phosphorus. In a second experiment, Nx rats fed low
phosphorus diets (0.2 and 0.4%) for 15 days received daily intraperitoneal
lipopolysaccharide (LPS)
injections to induce
inflammation. In these rats, FGF23 increased despite the low
phosphorus diets. Thus, higher FGF23 levels were needed to maintain
phosphaturia and normal serum
phosphorus values. Renal Klotho expression was preserved in Nx rats on a 0.2%
phosphorus diet, reduced on a 0.4%
phosphorus diet, and markedly reduced in Nx rats receiving LPS. In ex vivo experiments, high
phosphorus and LPS increased nuclear β-
catenin and p65-NFκB and decreased Klotho. Inhibition of
inflammation and Wnt signaling activation resulted in decreased FGF23 levels and increased renal Klotho. In conclusion, strict control of
phosphorus intake prevented the increase in FGF23 in
renal failure, whereas
inflammation independently increased FGF23 values. Decreased Klotho may explain the renal resistance to FGF23 in
inflammation. These effects are likely mediated by the activation of NFkB and Wnt/β-
catenin signaling.