Daculsi G, Pilet P, Cottrel M, Guicheux G
Centre de Recherche sur les matériaux d'intérêt biologique, INSERM E 99-03, Faculté de Chirurgie Dentaire, Nantes, France.
J Biomed Mater Res. 1999 Nov;47(2):228-33. doi: 10.1002/(sici)1097-4636(199911)47:2<228::aid-jbm13>3.0.co;2-z.
The role of adhesion molecules like osteopontin and bone sialoprotein, both containing the Arg-Gly-Asp sequence have been shown to have a role in mineral formation, whereas fibronectin (FN), another adhesive protein, was never studied during the mineralization processes. The formation and maturation of biological apatite crystals are under matrix control, and one of the roles of specific crystal proteins is to control the nucleation and growth of biological apatite during the mineralization process (promotion or inhibition). In the case of calcium phosphate ceramic used as a bone substitute, a dissolution-precipitation process occurs after implantation before the bone ingrowth and bone mineralization. The early precipitation consists of common biological apatite crystals. These crystals are the result of secondary nucleation and a heteroepitaxic growth process on synthetic residual crystals. In in vivo studies, hydroxyapatite crystals were implanted subcutaneously into mice for 1 or 2 weeks. Fibronectin immunogold labeling of the newly formed crystals on surfaces of high-resolution transmission electron microscopy sections of retrieved implants revealed the close association of these precipitated crystals with FN. In in vitro experiments using a solution of human FN incubated in the presence of calcium phosphate crystals, we obtained apatite crystal precipitation. The fibronectin network observed in high-resolution transmission electron microscopy showed numerous clusters of very small particles (1 nm in diameter and 2 nm in length), whereas the same experiment realized as control on albumin revealed no crystal precipitation. These results demonstrate for the first time the role of FN in early biological crystal nucleation. This process could have important biological significance in accounting for ectopic calcification, primary nucleation in calcified tissue, and bone ingrowth on calcium phosphate ceramics.
骨桥蛋白和骨唾液蛋白等黏附分子都含有精氨酸-甘氨酸-天冬氨酸序列，它们在矿物质形成中发挥作用，而另一种黏附蛋白纤连蛋白（FN）在矿化过程中从未被研究过。生物磷灰石晶体的形成和成熟受基质控制，特定晶体蛋白的作用之一是在矿化过程中控制生物磷灰石的成核和生长（促进或抑制）。在用作骨替代物的磷酸钙陶瓷的情况下，植入后在骨长入和骨矿化之前会发生溶解-沉淀过程。早期沉淀由常见的生物磷灰石晶体组成。这些晶体是二次成核以及在合成残余晶体上的异质外延生长过程的结果。在体内研究中，将羟基磷灰石晶体皮下植入小鼠体内1或2周。对取出的植入物的高分辨率透射电子显微镜切片表面上新形成的晶体进行纤连蛋白免疫金标记，结果显示这些沉淀晶体与FN密切相关。在使用人FN溶液在磷酸钙晶体存在下孵育的体外实验中，我们获得了磷灰石晶体沉淀。在高分辨率透射电子显微镜下观察到的纤连蛋白网络显示有许多非常小的颗粒簇（直径1纳米，长度2纳米），而以白蛋白作为对照进行的相同实验未显示晶体沉淀。这些结果首次证明了FN在早期生物晶体成核中的作用。这一过程在解释异位钙化、钙化组织中的初级成核以及磷酸钙陶瓷上的骨长入方面可能具有重要的生物学意义。
