Rendenbach C, Yorgan T A, Heckt T, Otto B, Baldauf C, Jeschke A, Streichert T, David J P, Amling M, Schinke T
Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, 20246, Hamburg, Germany.
Calcif Tissue Int. 2014 May;94(5):474-83. doi: 10.1007/s00223-013-9831-6. Epub 2013 Dec 24.
That phosphate homeostasis is tightly linked to skeletal mineralization is probably best underscored by the fact that the phosphaturic hormone FGF23 is primarily expressed by terminally differentiated osteoblasts/osteocytes and that increased circulating FGF23 levels are causative for different types of hypophosphatemic rickets. In contrast, FGF23 inactivation results in hyperphosphatemia, and unexpectedly this phenotype is associated with severe osteomalacia in Fgf23-deficient mice. In this context it is interesting that different cell types have been shown to respond to extracellular phosphate, thereby raising the concept that phosphate can act as a signaling molecule. To identify phosphate-responsive genes in primary murine osteoblasts we performed genome wide expression analysis with cells maintained in medium containing either 1 or 4 mM sodium phosphate for 6 h. As confirmed by qRT-PCR, this analysis revealed that several known osteoblast differentiation markers (Bglap, Ibsp, and Phex) were unaffected by raising extracellular phosphate levels. In contrast, we found that the expression of Enpp1 and Ank, two genes encoding inhibitors of matrix mineralization, was induced by extracellular phosphate, while the expression of Sost and Dkk1, two genes encoding inhibitors of bone formation, was negatively regulated. The ability of osteoblasts to respond to extracellular phosphate was dependent on their differentiation state, and shRNA-dependent repression of the phosphate transporter Slc20a1 in MC3T3-E1 cells partially abolished their molecular response to phosphate. Taken together, our results provide further evidence for a role of extracellular phosphate as a signaling molecule and raise the possibility that severe hyperphosphatemia can negatively affect skeletal mineralization.
磷酸盐稳态与骨骼矿化紧密相连，这一点或许最能通过以下事实得以强调：排磷激素FGF23主要由终末分化的成骨细胞/骨细胞表达，且循环中FGF23水平升高是导致不同类型低磷性佝偻病的原因。相反，FGF23失活会导致高磷血症，而且出乎意料的是，这种表型与Fgf23基因缺陷小鼠的严重骨软化症相关。在这种情况下，有趣的是已表明不同细胞类型对细胞外磷酸盐有反应，从而提出了磷酸盐可作为信号分子的概念。为了鉴定原代小鼠成骨细胞中的磷酸盐反应基因，我们用在含1 mM或4 mM磷酸钠的培养基中培养6小时的细胞进行了全基因组表达分析。正如qRT-PCR所证实的，该分析显示几个已知的成骨细胞分化标志物（Bglap、Ibsp和Phex）不受细胞外磷酸盐水平升高的影响。相反，我们发现编码基质矿化抑制剂的两个基因Enpp1和Ank的表达受细胞外磷酸盐诱导，而编码骨形成抑制剂的两个基因Sost和Dkk1的表达则受到负调控。成骨细胞对细胞外磷酸盐的反应能力取决于它们的分化状态，并且在MC3T3-E1细胞中通过shRNA依赖性抑制磷酸盐转运体Slc20a1可部分消除它们对磷酸盐的分子反应。综上所述，我们的结果为细胞外磷酸盐作为信号分子的作用提供了进一步证据，并提出了严重高磷血症可能对骨骼矿化产生负面影响的可能性。
