Pyrophosphate dysregulation and impaired FGF23/FGFR signaling contributes to impaired matrix mineralization in bone marrow stromal cultures from sickle cell disease mice.

Sickle cell disease (SCD) is characterized by osteopenia and impaired bone mineralization, but the underlying mechanisms remain unclear. Fibroblast growth factor 23 (FGF23), elevated in SCD, regulates phosphate metabolism through FGFRs/klotho and contributes to bone loss. Although FGF23's systemic effects are known, its local actions in SCD bone remain poorly defined. Using bone marrow stromal cells (BMSCs) derived from SCD mice, we previously reported that enhanced local FGF23/FGFR1 signaling and increased osteopontin impair osteoblast mineralization, which is rescued by an FGF23-neutralizing antibody (FGF23Ab). Here, we further investigated downstream signaling and pyrophosphate/phosphate (PPi/Pi)-regulatory mechanisms contributing to mineralization defects. FGF23Ab reduced phospho-FGFR1, restored phospho-FGFR2 and phospho-AKT, and decreased pSTAT3 activation. SCD-BMSCs exhibited increased matrix inhibitors, matrix Gla protein (MGP) and matrix extracellular phosphoglycoprotein (MEPE), and reduced mineralization promoters PHEX and DMP1, which were partially normalized by FGF23Ab. FGF23Ab also corrected elevated PPi-generating enzymes ENPP1 and ANK and restored tissue-nonspecific alkaline phosphatase (TNAP). In contrast, the phosphate importer PiT2 was significantly reduced in SCD BMSCs and was further suppressed with FGF23Ab. These findings indicate that excessive local FGF23 signaling disrupts mineralization by upregulating matrix inhibitors and altering PPi/Pi-regulatory pathways. FGF23 neutralization partially restores mineralization capacity.