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Abstract: FR-OR03

Vitamin D Receptor Regulates Furin-Mediated FGF23 Cleavage

Session Information

Category: Bone and Mineral Metabolism

  • 401 Bone and Mineral Metabolism: Basic

Authors

  • Simic, Petra, Massachusetts General Hospital, Boston, Massachusetts, United States
  • Bastepe, Isinsu, Massachusetts General Hospital, Boston, Massachusetts, United States
  • Zhou, Wen, Massachusetts General Hospital, Boston, Massachusetts, United States
  • Ay, Birol, Massachusetts General Hospital, Boston, Massachusetts, United States
  • Rhee, Eugene P., Massachusetts General Hospital, Boston, Massachusetts, United States
  • Bastepe, Murat, Massachusetts General Hospital, Boston, Massachusetts, United States
Background

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that decreases serum phosphate. The full-length protein, intact FGF23 (iFGF23), is cleaved by furin protease at an Arg-XX-Arg site into inactive N-terminal (aa 25-179) and C-terminal (aa 180-251) fragments. Several studies have proposed a putative role of vitamin D in the regulation of furin in the context of infections. Therefore, we investigated the effect of vitamin D (1,25(OH)2 D) and vitamin D receptor (VDR) on furin-mediated cleavage of FGF23.

Methods

In Vdr knock out (Vdr-/-) mice, we first quantitated the relative abundance of FGF23 and its fragments in circulation, utilizing ELISA assays that specifically detect only iFGF23, or a combination of iFGF23 and C-terminal cleavage fragments (cFGF23). We further evaluated gene expression and protein levels of furin in bone marrow and plasma and furin activity in plasma. We administered a furin inhibitor, decanoyl-RVKR-CMK, i.p. to test if furin mediates cleavage in Vdr-/- animals. Conversely, we administered recombinant furin protein to wild type mice to test if its effect on FGF23 cleavage can be blocked by 1,25(OH)2 D administration. All experiments were repeated in vitro in the osteocyte-like Ocy454 cells in which Vdr was knocked out using CRISPR/Cas9.

Results

Mice lacking VDR had a 25-fold increase in FGF23 cleavage, judged by the cFGF23-to-iFGF23 ratio, and elevated furin gene expression, protein levels and activity compared to wild type (WT) littermates. Inhibition of furin activity by decanoyl-RVKR-CMK fully blocked increased FGF23 cleavage in Vdr-/- animals, and decreased cFGF23 to levels comparable to WT mice. This effect was recapitulated in a cell-autonomous manner in Vdr deficient Ocy454 cells. Moreover, 1,25(OH)2 D injection increased total FGF23 without an increase in FGF23 cleavage, with cFGF23/iFGF23 ratio being comparable to vehicle injected animals. When administered with furin recombinant protein, 1,25(OH)2 D fully blocked furin’s effect on increased FGF23 cleavage.

Conclusion

In summary, 1,25(OH)2 D and VDR suppress furin-induced FGF23 cleavage, providing a mechanism by which vitamin D signaling can augment biologically active FGF23 levels.

Funding

  • NIDDK Support