Becerra J, Andrades J A, Ertl D C, Sorgente N, Nimni M E
Division of Surgical Research, Children's Hospital Los Angeles, University of Southern California, USA.
J Bone Miner Res. 1996 Nov;11(11):1703-14. doi: 10.1002/jbmr.5650111114.
Bone maintenance requires a continuous source of osteoblasts throughout life. Its remodeling and regeneration during fracture repair is ensured by osteoprogenitor stem cells which are part of the stroma of the bone marrow (BM). Many investigators have reported that in cultured BM stromal cells there is a cell population that will differentiate along an osteogenic lineage if stimulated by the addition of osteogenic inducers, such as dexamethasone (dex), beta-glycerophosphate (beta-GP), transforming growth factor beta-1 (TGF-beta 1) and bone morphogenetic protein-2 (BMP-2). Here we report the effects of demineralized bone matrix (DBM) on the osteogenic differentiation of BM stromal cells in vitro, using morphological criteria, alkaline phosphatase (AP) activity, and calcium accumulation. DBM and DBM-conditioned medium (DBMcm) enhanced bone formation in the presence of dex and beta-GP, whereas DBM particles caused changes in the cell phenotype. Temporal expression of total and skeletal AP by BM stromal cells from 4-week-old rats showed a biphasic pattern enhanced by DBM and suggesting the presence of two cell populations. In one population, AP synthesis reaches a maximum during the first week in culture, following which cells either die or loose their ability to synthesize AP. A second, less abundant population begins to proliferate and synthesize AP during the second and third weeks. The synthesis of AP, which often decreases by the third week, can be maintained at high levels only if DBM is added to the cultures. BM stromal cells isolated from 24- and 48-week-old rats showed a decrease or loss of this biphasic AP expression pattern compared with cells isolated from 4-week-old rats. The addition of DBM to cultures derived from 24- and 48-week-old rats stimulated mostly the second cell population to synthesize AP, suggesting that DBM contains a factor(s) that acts on a specific bone marrow cell population by increasing the proliferation of active cells or inducing the differentiation of dormant cells.
骨骼的维持在一生中都需要持续的成骨细胞来源。骨折修复过程中的重塑和再生由作为骨髓（BM）基质一部分的骨祖干细胞来确保。许多研究人员报告称，在培养的BM基质细胞中，存在一个细胞群体，如果添加成骨诱导剂，如地塞米松（dex）、β-甘油磷酸酯（β-GP）、转化生长因子β-1（TGF-β1）和骨形态发生蛋白-2（BMP-2），该细胞群体将沿着成骨谱系分化。在此，我们使用形态学标准、碱性磷酸酶（AP）活性和钙积累来报告脱矿骨基质（DBM）对体外BM基质细胞成骨分化的影响。DBM和DBM条件培养基（DBMcm）在存在dex和β-GP的情况下增强了骨形成，而DBM颗粒导致细胞表型发生变化。4周龄大鼠的BM基质细胞中总AP和骨特异性AP的时间表达呈现双相模式，DBM增强了这种模式，表明存在两个细胞群体。在一个群体中，AP合成在培养的第一周达到最大值，之后细胞要么死亡，要么失去合成AP的能力。第二个数量较少的群体在第二周和第三周开始增殖并合成AP。AP的合成通常在第三周会下降，只有在向培养物中添加DBM时才能维持在高水平。与从4周龄大鼠分离的细胞相比，从24周龄和48周龄大鼠分离的BM基质细胞显示出这种双相AP表达模式的减少或丧失。向来自24周龄和48周龄大鼠的培养物中添加DBM主要刺激第二个细胞群体合成AP，这表明DBM含有一种因子，该因子通过增加活性细胞的增殖或诱导休眠细胞的分化作用于特定的骨髓细胞群体。
