Ishikawa Y, Wu L N, Genge B R, Mwale F, Wuthier R E
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, USA.
J Bone Miner Res. 1997 Mar;12(3):356-66. doi: 10.1359/jbmr.1997.12.3.356.
Few studies have been directed toward elucidating the action of calcitonin (CT) and parathyroid hormone (PTH) on growth plate chondrocytes, cells directly involved in longitudinal bone growth and provisional calcification. In this study, primary cultures of avian growth plate chondrocytes that calcify without the supplement of beta-glycerophosphate were used to investigate the effects of synthetic human CT and 1-34 bovine PTH on (1) cell division and growth; (2) the deposition of Ca2+ and inorganic phosphate (Pi); (3) the activity of alkaline phosphatase (AP), an enzyme long associated with the mineralization process; (4) the levels of proteoglycans; and (5) the synthesis of collagens. Added continually to preconfluent cultures from day 6 until harvest, CT (1-30 nM) and PTH (0.1-1.0 nM) increased mineral deposition; the maximal increase was seen between days 18-21 at 10 nM CT (175-260%) and 0.5 nM PTH (approximately 170-280%), both p < 0.001. CT had no significant effect on cellular protein, or AP-specific activity, whereas PTH increased cellular protein, DNA, proteoglycan, and collagen content of the cultures in a dosage-dependent manner. AP activity and levels of Type II and X collagens and fibronectin in the culture medium showed a biphasic response to PTH; maximal increases were seen at 0.5 nM between days 15-18. Longer exposure (days 21-27) to PTH at higher levels (5-10 nM) caused a marked decreased in AP activity but a lesser decrease in the collagens. These results indicate that CT and PTH can act directly on chondrocytes to stimulate mineralization, but that PTH specifically stimulated cell division and synthesis of cellular and extracellular proteins by growth plate chondrocytes. The implications of these findings with regard to Ca2+ homeostasis and bone formation are discussed.
很少有研究致力于阐明降钙素（CT）和甲状旁腺激素（PTH）对生长板软骨细胞的作用，这些细胞直接参与纵向骨生长和临时钙化。在本研究中，使用在不添加β-甘油磷酸的情况下钙化的禽生长板软骨细胞原代培养物，来研究合成人CT和1-34牛PTH对以下方面的影响：（1）细胞分裂和生长；（2）Ca2+和无机磷酸盐（Pi）的沉积；（3）碱性磷酸酶（AP）的活性，一种长期与矿化过程相关的酶；（4）蛋白聚糖的水平；以及（5）胶原蛋白的合成。从第6天开始持续添加到融合前培养物中直至收获，CT（1-30 nM）和PTH（0.1-1.0 nM）增加了矿物质沉积；在第18-21天，10 nM CT（175-260%）和0.5 nM PTH（约170-280%）时观察到最大增加，两者p<0.001。CT对细胞蛋白或AP特异性活性没有显著影响，而PTH以剂量依赖的方式增加了培养物中的细胞蛋白、DNA、蛋白聚糖和胶原蛋白含量。培养基中AP活性以及II型和X型胶原蛋白和纤连蛋白的水平对PTH表现出双相反应；在第15-18天，0.5 nM时观察到最大增加。在较高水平（5-10 nM）下较长时间（第21-27天）暴露于PTH导致AP活性显著降低，但胶原蛋白的降低程度较小。这些结果表明，CT和PTH可以直接作用于软骨细胞以刺激矿化，但PTH特异性刺激生长板软骨细胞的细胞分裂以及细胞和细胞外蛋白的合成。讨论了这些发现对Ca2+稳态和骨形成的意义。
