FGF23 cleavage by furin in osteocytes contributes to a time dependent secretion of FGF23 cleaved peptides. (A) Cortical bone Fgf23 mRNA, serum (B) cFGF23, (C) iFGF23, (D) i/cFGF23, (E) IP/WB of circulating FGF23 peptides, and cortical bone mRNA expression of (F) Galnt3, (G) Fam20c and (H) Furin in 6-week-old WT mice up to 6 hours after administration of a single dose of 250 ng/g IL-1β. Supernatant (I) cFGF23, (J) iFGF23 and (K) i/cFGF23 in 24 hours cultures of bone explants from Fgf23^KO mice treated with recombinant murine iFGF23 (10 ng/mL) and IL-1β (10 ng/mL) and furin inhibitor (0 or 15 μg/mL). Serum (L) cFGF23, (M) iFGF23, (N) i/cFGF23, (O) bone Fgf23 mRNA, (P) serum phosphate, and (Q) 1,25OH₂D in 6-week-old WT and Furin^Dmp1-cKO mice 6 hours after administration of a single dose of 250 ng/g IL-1β. n ≥ 3 per group, P < .05 vs (∗) Ctr, (a) Fgf23^KO + FGF23, (b) Fgf23^KO + FGF23 + IL-1β, (c) WT Ctr, (d) Furin^Dmp1-cKO Ctr, (e) WT IL-1β.