MOLECULAR BIOLOGY OF THE INTERRELATIONSHIP BETWEEN BONE CELLS IN THE LOW CALCIUM ENVIRONMENT

采用低钙饮食喂养大鼠，研究了低钙环境下骨基质蛋白基因表达的变化。30日龄雄性Wistar大鼠，平均体重70-85 g，分别饲喂正常钙饲料（0.5%Ca，0.35%P，对照组）和低钙饲料（0.05%Ca，0.35%P，低钙组）。在第6天在乙醚麻醉下处死大鼠。取出骨组织并进一步处理用于原位杂交和北方印迹分析。接触显微放射摄影显示松质骨干骺端有明显的骨吸收。骨表面出现大量破骨细胞。此外，成骨细胞呈多层结构，高尔基体区明显，占骨表面较大面积。原位杂交结果显示成骨细胞中骨桥蛋白和I型胶原基因在多层次表达。这一观察结果表明，在低钙状态下骨形成活性升高。北方印迹法未能显示对照组和低钙组大鼠基因表达的差异。这种差异可能是由于松质骨和皮质骨对低钙应力的反应不同。目前的结果表明，尽管由于低钙环境导致严重的骨吸收，但在松质骨中骨形成受到刺激。这反映了高骨转换率，这是由钙缺乏期间钙稳态的反应引发的。

Gene expressions of bone matrix proteins during low calcium environment was studied using a rat fed with a low calcium diet. Thirty days old male Wistar rats, mean body weight 70-85 g, were fed either normal calcium diet (0.5% Ca, 0.35% P, controls) or low Ca diet (0.05% Ca, 0.35% P, low Ca group). Rats were sacrificed under ether anesthesia at day 6. Bone tissues were removed and further processed for in situ hybridization and northern blot analysis. Contact microradiography showed a remarkable bone resorption in the metaphysis of trabecular bone. Many osteoclasts appeared on the bone surface. In addition, multi layrs of osteoblasts, which have the prominent Golgi-area, occupied the larger area of bone surface. In situ hybridization showed the high levels of osteopontin and collagen type I genes in the osteoblast in multi layrs. This observation indicated that bone formation activity was elevated during the low calcium state. Northern blot, however, failed to show the difference in gene expression between the control and low calcium rats. This discrepancy may be due to the different response to the low calcium stress between the cancellous and the cortical bone. The present result demonstrates that despite the severe bone resorption due to the low calcium environment, the bone formation was stimulated in the cancellous bone. This is a reflection of high rate of bone turn over, which was initiated by the response of calcium homeostasis during the calcium deficiency.