EC Orthopaedics

The main function of fibroblast growth factor (FGF-23) is to regulate phosphate concentration in plasma suppressing the abundance of phosphate-transporting molecules in the apical membrane of epithelial cells which express FGFR 1, 3, and 4, in the proximal renal tubule, leading to reduced reabsorption of phosphate from the urine.

Under physiological condition FGF-23 is mainly produced by osteoblasts, osteoclasts, and osteocytes as a response to increased Vitamin D (Vit D) concentration in plasma, but also abnormal plasma concentration of phosphate, calcium, parathyroid hormone (PTH), aldosterone or iron deficiency.

Pro-inflammatory cytokines have been shown to stimulate osteoblastic/osteocytic FGF-23 secretion. FGF-23 undergoes some intra-osseous processes that stabilizes the molecule. At a physiological level FGF-target organs are those that express Klotho, like kidney, parathyroids and brain. Under pathological condition immune-cells or cardiomyocytes may also release FGF-23.

The main effect of FGF-23 is to increase kidney phosphate excretion and reduce intestinal phosphate absorption. The excess of FGF-23 along with Vit D deficiency, hypocalcemia, hyperparathyroidism, and hyperphosphatemia, lead to defective bone mineralization and extra-skeletal calcifications. FGF-23 has also been shown to interfere with some markers of bone metabolism and with bone microarchitecture in patients with osteoporosis.

 Keywords: FGF-23; Fibroblast; Phosphate Metabolism; Bone

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