Dietary vitamin D deprivation suppresses fibroblast growth factor 23 signals by reducing serum phosphorus levels in laying hens.

The present study was carried out to evaluate the effect of dietary supplemental vitamin D on fibroblast growth factor 23 (FGF23) signals as well as phosphorus homeostasis and metabolism in laying hens. Fourteen 40-week-old Hy-Line Brown layers were randomly assigned into 2 treatments: 1) vitamin D restriction group ( 7) fed 0 IU/kg vitamin D diet, and 2) regular vitamin D group ( 7) fed 1,600 IU/kg vitamin D diet. The study lasted for 21 d. Serum parameters, phosphorus and calcium excretion status, and tissue expressions of type II sodium-phosphate co-transporters (NPt2), FGF23 signals and vitamin D metabolic regulators were determined. Hens fed the vitamin D restricted diet had decreased serum phosphorus levels (by 31.3%,  = 0.028) when compared to those fed regular vitamin D diet. In response to the decreased serum phosphorus, the vitamin D restricted laying hens exhibited: 1) suppressed kidney expressions of 25-hydroxyvitamin D 1-α-hydroxylase (, by 52.8%,  = 0.036) and 1,25-dihydroxyvitamin D 24-hydroxylase (, by 99.4%,  = 0.032); 2) suppressed serum levels of FGF23 (by 14.6%,  = 0.048) and increased serum alkaline phosphatase level (by 414.1%,  = 0.012); 3) decreased calvaria mRNA expressions of fibroblast growth factor receptors (, by 85.2%,  = 0.003, , by 89.4%,  = 0.014, , by 88.8%,  = 0.017, , by 89.6%,  = 0.030); 4) decreased kidney mRNA expressions of (by 65.5%,  = 0.021), (by 66.0%,  = 0.050) and (by 68.8%,  = 0.038); 5) decreased kidney protein expression of type 2a sodium-phosphorus co-transporters (by 54.3%,  = 0.039); and 6) increased percent excreta calcium (by 26.9%,  = 0.002). In conclusion, the deprivation of dietary vitamin D decreased FGF23 signals in laying hens by reducing serum FGF23 level and suppressing calvaria and kidney mRNA expressions of FGF23 receptors.