A G Protein-coupled, IP3/protein Kinase C Pathway Controlling the Synthesis of Phosphaturic Hormone FGF23

Dysregulated actions of bone-derived phosphaturic hormone fibroblast growth factor 23 (FGF23) result in several inherited diseases, such as X-linked hypophosphatemia (XLH), and contribute substantially to the mortality in kidney failure. Mechanisms governing FGF23 production are poorly defined. We herein found that ablation of the Gq/11α-like, extralarge Gα subunit (XLαs), a product of GNAS, exhibits FGF23 deficiency and hyperphosphatemia in early postnatal mice (XLKO). FGF23 elevation in response to parathyroid hormone, a stimulator of FGF23 production via cAMP, was intact in XLKO mice, while skeletal levels of protein kinase C isoforms α and δ (PKCα and PKCδ) were diminished. XLαs ablation in osteocyte-like Ocy454 cells suppressed the levels of FGF23 mRNA, inositol 1,4,5-trisphosphate (IP3), and PKCα/PKCδ proteins. PKC activation in vivo via injecting phorbol myristate acetate (PMA) or by constitutively active Gqα-Q209L in osteocytes and osteoblasts promoted FGF23 production. Molecular studies showed that the PKC activation-induced FGF23 elevation was dependent on MAPK signaling. The baseline PKC activity was elevated in bones of Hyp mice, a model of XLH. XLαs ablation significantly, but modestly, reduced serum FGF23 and elevated serum phosphate in Hyp mice. These findings reveal a potentially hitherto-unknown mechanism of FGF23 synthesis involving a G protein-coupled IP3/PKC pathway, which may be targeted to fine-tune FGF23 levels.