Gronowicz G A, McCarthy M B
Department of Orthopedics, University of Connecticut Health Center, Farmington 06032.
Endocrinology. 1995 Feb;136(2):598-608. doi: 10.1210/endo.136.2.7530648.
Prolonged glucocorticoid treatment causes osteoporosis in vivo and inhibits bone formation in vitro. We have previously shown that glucocorticoids inhibit calcification and alter osteoblast organization in a mineralizing bone organ culture system. In this study, the effect of glucocorticoids on osteoblast adhesion to bone matrix proteins and integrin expression was examined in primary rat osteoblasts and a transformed rat osteosarcoma-derived cell line ROS 17/2.8. After 24 h of treatment with corticosterone, these cells displayed a concentration-dependent decrease in adhesion to type I collagen and fibronectin. Adhesion was significantly decreased as early as 4 h after glucocorticoid administration. With 100 nM corticosterone treatment for 24 h, inhibition of the adhesion of ROS 17/2.8 cells and primary osteoblasts to fibronectin was 75 +/- 10% and 50 +/- 8%, and inhibition of adhesion to collagen was 31 +/- 10% and 65 +/- 5%, respectively. This effect was specific for osteoblasts, because glucocorticoids did not change the adhesion of fibroblasts. However, glucocorticoids did inhibit the adhesion of all cell types to rat osteonectin. To determine whether the change in osteoblast attachment to collagen and fibronectin was due to an alteration in integrin levels, the plasma membranes of these cells were labeled with [125I]lactoperoxidase, solubilized, and immunoprecipitated with an antibody to beta 1. A 24-h treatment with 100 nM corticosterone caused 80 +/- 2% and 64 +/- 9% decreases in beta 1 levels in primary osteoblasts and ROS 17/2.8 cells, respectively. These results were confirmed with immunofluorescence microscopy, which showed a glucocorticoid-induced decrease in beta 1 staining. Treatment of primary rat osteoblasts and ROS 17/2.8 cells for 72 h with corticosterone also decreased beta 1-integrin messenger RNA levels in a dose-dependent manner. We have demonstrated that the inhibition of integrin expression by glucocorticoids is involved in the decrease in osteoblast adhesion to bone extracellular matrix proteins. These data suggest that integrin modulation may influence osteoblast function and bone formation and, thus, contribute to glucocorticoid-induced osteoporosis.
长期使用糖皮质激素治疗会在体内导致骨质疏松，并在体外抑制骨形成。我们之前已经表明，糖皮质激素在矿化骨器官培养系统中会抑制钙化并改变成骨细胞的组织结构。在本研究中，我们在原代大鼠成骨细胞和一种转化的大鼠骨肉瘤衍生细胞系ROS 17/2.8中检测了糖皮质激素对成骨细胞黏附于骨基质蛋白及整合素表达的影响。用皮质酮处理24小时后，这些细胞对I型胶原和纤连蛋白的黏附呈现出浓度依赖性降低。早在给予糖皮质激素后4小时，黏附就显著降低。用100 nM皮质酮处理24小时后，ROS 17/2.8细胞和原代成骨细胞对纤连蛋白黏附的抑制率分别为75±10%和50±8%，对胶原黏附的抑制率分别为31±10%和65±5%。这种效应是成骨细胞特有的，因为糖皮质激素不会改变成纤维细胞的黏附。然而，糖皮质激素确实会抑制所有细胞类型对大鼠骨连接素的黏附。为了确定成骨细胞对胶原和纤连蛋白黏附的变化是否是由于整合素水平的改变，这些细胞的质膜用[125I]乳过氧化物酶标记，溶解后用抗β1抗体进行免疫沉淀。用100 nM皮质酮处理24小时导致原代成骨细胞和ROS 17/2.8细胞中β1水平分别降低80±2%和64±9%。这些结果通过免疫荧光显微镜得到证实，其显示糖皮质激素诱导β1染色减少。用皮质酮处理原代大鼠成骨细胞和ROS 17/2.8细胞72小时也会以剂量依赖性方式降低β1整合素信使核糖核酸水平。我们已经证明，糖皮质激素对整合素表达的抑制与成骨细胞对骨细胞外基质蛋白黏附的降低有关。这些数据表明，整合素调节可能会影响成骨细胞功能和骨形成，从而导致糖皮质激素诱导的骨质疏松。
