Cheng S L, Zhang S F, Avioli L V
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Cell Biochem. 1996 May;61(2):182-93. doi: 10.1002/(sici)1097-4644(19960501)61:2<182::aid-jcb3>3.0.co;2-q.
Glucocorticoids have been shown to induce the differentiation of bone marrow stromal osteoprogenitor cells into osteoblasts and the mineralization of the matrix. Since the expression of bone matrix proteins is closely related to the differentiation status of osteoblasts and because matrix proteins may play important roles in the mineralization process, we investigated the effects of dexamethasone (Dex) on the expression of bone matrix proteins in cultured normal human bone marrow stromal cells (HBMSC). Treatment of HBMSC with Dex for 23 days resulted in a significant increase in alkaline phosphatase activity with maximum values attained on day 20 at which time the cell matrix was mineralized. Northern blot analysis revealed an increase in the steady-state mRNA level of alkaline phosphatase over 4 weeks of Dex exposure period. The observed increase in the alkaline phosphatase mRNA was effective at a Dex concentration as low as 10(-10) M with maximum values achieved at 10(-8)M. In contrast, Dex decreased the steady-state mRNA levels of both bone sialoprotein (BSP) and osteopontin (OPN) over a 4 week observation period when compared to the corresponding control values. The relative BSP and OPN mRNA levels among the Dex treated cultures, however, showed a steady increase after more than 1 week exposure. The expression of osteocalcin mRNA which was decreased after 1 day Dex exposure was undetectable 4 days later. Neither control nor Dex-treated HBMSC secreted osteocalcin into the conditioned media in the absence of 1 ,25(OH)(2)D(3) during a 25-day observation period. The accumulated data indicate that Dex has profound and varied effects on the expression of matrix proteins produced by human bone marrow stromal cells. With the induced increment in alkaline phosphatase correlating with the mineralization effects of Dex, the observed concomitant decrease in osteopontin and bone sialoprotein mRNA levels and the associated decline of osteocalcin are consistent with the hypothesis that the regulation of the expression of these highly negatively charged proteins is essential in order to maximize the Dex-induced mineralization process conditioned by normal human bone marrow stromal osteoprogenitor cells.
糖皮质激素已被证明可诱导骨髓基质骨祖细胞分化为成骨细胞，并促进基质矿化。由于骨基质蛋白的表达与成骨细胞的分化状态密切相关，且基质蛋白可能在矿化过程中发挥重要作用，因此我们研究了地塞米松（Dex）对培养的正常人骨髓基质细胞（HBMSC）中骨基质蛋白表达的影响。用Dex处理HBMSC 23天导致碱性磷酸酶活性显著增加，在第20天达到最大值，此时细胞基质发生矿化。Northern印迹分析显示，在Dex暴露的4周内，碱性磷酸酶的稳态mRNA水平增加。观察到的碱性磷酸酶mRNA增加在低至10^(-10) M的Dex浓度下有效，在10^(-8) M时达到最大值。相比之下，与相应的对照值相比，在4周的观察期内，Dex降低了骨唾液蛋白（BSP）和骨桥蛋白（OPN）的稳态mRNA水平。然而，在Dex处理的培养物中，相对BSP和OPN mRNA水平在暴露超过1周后呈稳定增加。Dex暴露1天后降低的骨钙素mRNA表达在4天后无法检测到。在25天的观察期内，在没有1,25(OH)2D3的情况下，对照和Dex处理的HBMSC均未将骨钙素分泌到条件培养基中。积累的数据表明，Dex对人骨髓基质细胞产生的基质蛋白表达具有深远且多样的影响。随着诱导的碱性磷酸酶增加与Dex的矿化作用相关，观察到的骨桥蛋白和骨唾液蛋白mRNA水平的同时降低以及骨钙素的相关下降与以下假设一致，即调节这些高度带负电荷的蛋白质的表达对于最大化由正常人骨髓基质骨祖细胞介导
