Description
FGF23 is a protein of ∼30 kDa that is proteolytically processed to generate smaller NH2-terminal (18 kDa) and COOH-terminal (12 kDa) fragments. The NH2- terminal fragment of FGF23 contains the FGF receptor (FGFR) -binding domain. In vivo studies using synthetic peptides have indicated that neither of the processed NH2-terminal or COOH- terminal fragments of FGF23 can influence serum phosphate levels. FGF23 can decrease the activity of NaPi-2a and NaPi-2c cotransporters to reduce renal phosphate reabsorption and thereby can increase urinary phosphate excretion. Similarly, FGF23 can suppress the expression of 1-α-hydroxylase to reduce the production of the active vitamin D metabolite 1,25 (OH) 2D. Moreover, FGF23 can also induce 24- hydroxylase, which degrades 1,25 (OH) 2D