Dietary vitamin D_(3) 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_(3) 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_(3) restriction group(n=7)fed 0 IU/kg vitamin D_(3) diet,and 2)regular vitamin D_(3) group(n=7)fed 1,600 IU/kg vitamin D_(3) 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_(3) metabolic regulators were determined.Hens fed the vitamin D_(3) restricted diet had decreased serum phosphorus levels(by 31.3%,P=0.028)when compared to those fed regular vitamin D_(3) diet.In response to the decreased serum phosphorus,the vitamin D_(3) restricted laying hens exhibited:1)suppressed kidney expressions of 25-hydroxyvitamin D 1-a-hydroxylase(CYP27B1,by 52.8%,P=0.036)and 1,25-dihydroxyvitamin D 24-hydroxylase(CYP24A1,by 99.4%,P=0.032);2)suppressed serum levels of FGF23(by 14.6%,P=0.048)and increased serum alkaline phosphatase level(by 414.1%,P=0.012);3)decreased calvaria mRNA expressions of fibroblast growth factor receptors(FGFR1,by 85.2%,P=0.003,FGFR2,by 89.4%,P=0.014,FGFR3,by 88.8%,P=0.017,FGFR4,by 89.6%,P=0.030);4)decreased kidney mRNA expressions of FGFR1(by 65.5%,P=0.021),FGFR4(by 66.0%,P=0.050)and KLOTHO(by 68.8%,P=0.038);5)decreased kidney protein expression of type 2a sodium-phosphorus co-transporters(by 54.3%,P=0.039);and 6)increased percent excreta calcium(by 26.9%,P=0.002).In conclusion,the deprivation of dietary vitamin D_(3) decreased FGF23 signals in laying hens by reducing serum FGF23 level and suppressing calvaria and kidney mRNA expressions of FGF23 receptors.