Jayash Soher Nagi, Duff Thomas, Tanveer Qaisar, Promruk Worachet, Farquharson Colin
The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Midlothian EH25 9RG, Scotland, UK.
Bone Rep. 2025 Jul 30;26:101863. doi: 10.1016/j.bonr.2025.101863. eCollection 2025 Sep.
The provision of inorganic phosphate (P) for biomineralisation is under systemic and local control. Locally, osteoblast production of phosphatases such as tissue-nonspecific alkaline phosphatase (TNAP) and PHOSPHO1 is required for normal skeletal mineralisation and osteoblasts may sense extracellular P concentrations to control local phosphatase activity and thereby "fine-tune" P production and delivery for biomineralisation. This has been poorly explored and this study examined the ability of osteoblasts to sense and respond to extracellular P to control the local expression of TNAP and PHOSPHO1. Extracellular P downregulated the expression of PHOSPHO1 and TNAP by human primary osteoblasts at both mRNA and protein levels. Increasing P concentrations also reduced the mRNA expression of the type III Na- P co-transporters, PiT-1 and PiT-2 and selectively enhanced ERK1/2 phosphorylation. Inhibition of PiT-1 and PiT-2 by Foscarnet or MEK1/2 by UO126 abolished the downregulation of and expression by extracellular Pi. Moreover, extracellular P phosphorylated fibroblast growth factor receptor (FGFR) substrate 2α (FRS2α) and this activation was abolished by Foscarnet. Also, blocking FGFR signalling inhibited the phosphorylation of ERK1/2 and prevented the decrease in and expression by extracellular P. Similar results were observed in cultured murine calvaria. Osteoblast matrix mineralisation by extracellular P was dependent upon type III Na- P co-transporters and FGFR signalling. In conclusion, these results suggest an interplay between FGFR and P transporters is required for osteoblasts to sense and respond to extracellular P. This understanding advances our knowledge of the molecular control of physiological bone mineralisation by osteoblasts.
生物矿化所需无机磷酸盐（P）的供应受全身和局部控制。在局部，成骨细胞产生的磷酸酶，如组织非特异性碱性磷酸酶（TNAP）和PHOSPHO1，是正常骨骼矿化所必需的，成骨细胞可能感知细胞外P浓度以控制局部磷酸酶活性，从而“微调”生物矿化的P产生和递送。这方面的研究较少，本研究检测了成骨细胞感知和响应细胞外P以控制TNAP和PHOSPHO1局部表达的能力。细胞外P在mRNA和蛋白质水平下调人原代成骨细胞中PHOSPHO1和TNAP的表达。增加P浓度也降低了III型钠 - 磷共转运体PiT - 1和PiT - 2的mRNA表达，并选择性增强ERK1/2磷酸化。膦甲酸抑制PiT - 1和PiT - 2或UO126抑制MEK1/2可消除细胞外Pi对 和 表达的下调作用。此外，细胞外P使成纤维细胞生长因子受体（FGFR）底物2α（FRS2α）磷酸化，而膦甲酸可消除这种激活作用。同样，阻断FGFR信号传导可抑制ERK1/2的磷酸化，并防止细胞外P导致的 和 表达降低。在培养的小鼠颅骨中也观察到类似结果。细胞外P介导的成骨细胞基质矿化依赖于III型钠 - 磷共转运体和FGFR信号传导。总之，这些结果表明FGFR与P转运体之间的相互作用是成骨细胞感知和响应细胞外P所必需的。这一认识推进了我们对成骨细胞生理性骨矿化分子控制的了解。
