In those cell types, FGF23 expression is stimulated by the calcitriol (via the vitamin D receptor [VDR] signaling pathway) and hyperphosphatemia (via the sensing of extracellular phosphate levels mediated by type III sodium-dependent phosphate transporter [PiT2]) [9,13] and FGFR1c [14]. Here, FGF23 is linked to hyperphosphatemia.