| Description: |
Fibroblast growth factors (FGFs) [, ]are a family of multifunctional proteins, often referred to as 'promiscuous growth factors' due to their diverse actions on multiple cell types [, ]. FGFs are mitogens, which stimulate growth or differentiation of cells of mesodermal or neuroectodermal origin. The function of FGFs in developmental processes include mesoderm induction, anterior-posterior patterning, limb development, and neural induction and development. In mature tissues, they are involved in diverse processes including keratinocyte organisation and wound healing [, , , , , ]. FGF involvement is critical during normal development of both vertebrates and invertebrates, and irregularities in their function leads to a range of developmental defects [, , , ]. Fibroblast growth factors are heparin-binding proteins and interactions with cell-surface-associated heparan sulfate proteoglycans have been shown to be essential for FGF signal transduction. FGFs have internal pseudo-threefold symmetry (β-trefoil topology) []. There are currently over 20 different FGF family members that have been identified in mammals, all of which are structurally related signaling molecules [, ]. They exert their effects through four distinct membrane fibroblast growth factor receptors (FGFRs), FGFR1 to FGFR4 [], which belong to the tyrosine kinase superfamily. Upon binding to FGF, the receptors dimerize and their intracellular tyrosine kinase domains become active [].This entry represents fibroblast growth factor 23 (FGF23), which is secreted by osteoblasts and osteoclasts []. FGF23 acts on kidneys, where it decreases the expression of NPT2, a sodium-phosphate cotransporter in the proximal tubule []. FGF23 is responsible for phosphate metabolism, decreasing the reabsorption and increasing excretion of phosphate []. FGF23 is involved in the pathogenesis of three hypophosphatemic disorders; oncogenic osteomalacia (OOM), X-linked hypophosphatemia (XLH) and autosomal dominant hypophosphatemic rickets (ADHR). These conditions are characterised by hypophosphatemia, decreased renal phosphate reabsorption, normal or low serum calcitriol concentrations and defective skeletal mineralisation [, , ]. |
