Porter Ryan M, Huckle William R, Goldstein Aaron S
Department of Chemical Engineering, Virginia Polytechnic Institute, Blacksburg, Virginia 24061-0211, USA.
J Cell Biochem. 2003 Sep 1;90(1):13-22. doi: 10.1002/jcb.10592.
Dexamethasone is capable of directing osteoblastic differentiation of bone marrow stromal cells (BMSCs) in vitro, but its effects are not lineage-specific, and sustained exposure has been shown to down-regulate collagen synthesis and induce maturation of an adipocyte subpopulation within BMSC cultures. Such side effects might be reduced if dexamethasone is applied in a regimented manner, but the discrete steps in osteoblastic maturation that are stimulated by dexamethasone are not known. To examine this, dexamethasone was added to medium to initiate differentiation of rat BMSCs cultures and then removed after a varying number of days. Cell layers were analyzed for cell number, rate of collagen synthesis, expression of osteocalcin (OC), bone sialoprotein (BSP) and lipoprotein lipase (LpL), and matrix mineralization. Withdrawal of dexamethasone at 3 and 10 days was found to enhance cell number relative to continuous exposure, but did not affect to decrease collagen synthesis slightly. Late markers of osteoblastic differentiation, BSP expression and matrix mineralization, were also sensitive to dexamethasone and increased systematically with exposure while LpL systematically decreased. These results indicate that dexamethasone acts at both early and late stages to direct proliferative osteoprogenitor cells toward terminal maturation.
地塞米松能够在体外诱导骨髓基质细胞（BMSC）向成骨细胞分化，但其作用并非具有谱系特异性，并且已有研究表明持续暴露会下调胶原蛋白合成，并诱导BMSC培养物中脂肪细胞亚群的成熟。如果以规范的方式应用地塞米松，这种副作用可能会减少，但地塞米松刺激成骨细胞成熟的具体步骤尚不清楚。为了对此进行研究，将地塞米松添加到培养基中以启动大鼠BMSC培养物的分化，然后在不同天数后去除。分析细胞层的细胞数量、胶原蛋白合成速率、骨钙素（OC）、骨唾液蛋白（BSP）和脂蛋白脂肪酶（LpL）的表达以及基质矿化情况。结果发现，与持续暴露相比，在第3天和第10天撤去地塞米松可增加细胞数量，但对胶原蛋白合成略有减少的影响不大。成骨细胞分化的晚期标志物，即BSP表达和基质矿化，对地塞米松也很敏感，并且随着暴露时间的延长而系统性增加，而LpL则系统性降低。这些结果表明，地塞米松在早期和晚期均发挥作用，引导增殖性骨祖细胞向终末成熟分化。
