Phosphatonins: novel insights and clinical perspectives

Phosphate plays a vital role in several biological processes including energy and nucleic acid metabolism, cell signaling and bone mineralization. Several endocrine factors coordinately act on the intestine, kidney and bone to maintain their physiological homeostasis. A number of peptides, collectively known as phosphatonins, have recently been identified as regulators of phosphate metabolism in physiological and pathological conditions. These factors--fibroblast growth factors (FGF) 23 and 7, secreted frizzled related protein 4 (sFRP-4), and matrix extracellular phosphoglycoprotein (MEPE)--primarily regulate tubular phosphate reabsorption by acting on the transmembrane expression of SLC34 sodium-phosphate cotransporters. FGF- 23, FGF-7 and sFRP-4 also inhibit the biosynthesis of 1,25(OH)2D3, leading to decreased intestinal phosphate absorption. In this review, we discuss the biological properties of these peptides, their physiological roles, and the alterations in their concentrations in various hypophosphatemic and hyperphosphatemic clinical disorders.