Laboratoire du Métabolisme osseux, Centre de recherche BioMed, Département des Sciences Biologiques, Université du Québec à Montréal, Canada.
Calcif Tissue Int. 2011 Mar;88(3):246-53. doi: 10.1007/s00223-010-9455-z. Epub 2011 Jan 5.
Adequate bone formation is assured by the coordinated proliferation, migration, differentiation, and secretory functions of osteoblasts. Epidemiological studies have linked insufficient dietary magnesium (Mg) intake to osteoporosis. Here, we investigated the role of melastatin-like transient receptor potential 7 (TRPM7), a calcium (Ca) and Mg channel, in osteoblastic differentiation of the murine MC3T3 cell line. Osteoblastic differentiation was monitored by alkaline phosphatase activity, osteocalcin gene expression, and extracellular matrix mineralization. Gene expression of TRPM7 increased with osteoblastic differentiation, suggesting the importance of intracellular Ca/Mg homeostasis to cell differentiation. Alteration of intracellular Ca/Mg homeostasis by culture conditions with low extracellular Ca or Mg significantly reduced the osteoblastic differentiation markers alkaline phosphatase activity and osteocalcin gene expression. In accordance, matrix mineralization was reduced under low extracellular Ca or Mg levels. Nevertheless, expression of collagen type I, the predominant matrix protein, was increased in low-Mg culture conditions, indicating that dysfunction of matrix protein production cannot account for the reduced mineralization. Silencing TRPM7 expression during the differentiation period also reduced osteoblastic differentiation and the extent of matrix mineralization. Gene expression of osteoblastic transcription factor Runx2 was reduced by conditions of culture under low extracellular Ca or Mg levels, as well as by TRPM7 silencing. Our results indicate that intracellular Ca and Mg homeostasis ensured by TRPM7 expression is important for the osteoblastic differentiation of MC3T3 cells. Thus, Mg deficiency, a common condition among the population, may be associated with altered osteoblastic differentiation leading to inadequate bone formation and the development of osteoporosis.
成骨细胞的增殖、迁移、分化和分泌功能的协调保证了足够的骨形成。流行病学研究将镁（Mg）摄入不足与骨质疏松联系起来。在这里，我们研究了钙（Ca）和 Mg 通道 melastatin 样瞬时受体电位 7（TRPM7）在小鼠 MC3T3 细胞系成骨分化中的作用。碱性磷酸酶活性、骨钙素基因表达和细胞外基质矿化来监测成骨细胞分化。TRPM7 的基因表达随着成骨细胞分化而增加，表明细胞分化对细胞内 Ca/Mg 稳态的重要性。培养条件下改变细胞内 Ca/Mg 稳态，即低细胞外 Ca 或 Mg，显著降低碱性磷酸酶活性和骨钙素基因表达等成骨分化标志物。相应地，在低细胞外 Ca 或 Mg 水平下基质矿化减少。然而，在低 Mg 培养条件下，主要基质蛋白 I 型胶原的表达增加，表明基质蛋白产生的功能障碍不能解释矿化减少的原因。在分化期沉默 TRPM7 表达也降低了成骨分化和基质矿化的程度。低细胞外 Ca 或 Mg 水平以及 TRPM7 沉默降低了成骨转录因子 Runx2 的基因表达。我们的结果表明，TRPM7 表达保证的细胞内 Ca 和 Mg 稳态对 MC3T3 细胞的成骨分化很重要。因此，人群中常见的镁缺乏可能与成骨细胞分化改变有关，导致骨形成不足和骨质疏松症的发展。
