Marinovich Ryan, Soenjaya Yohannes, Wallace Gregory Q, Zuskov Andre, Dunkman Andrew, Foster Brian L, Ao Min, Bartman Kevin, Lam Vida, Rizkalla Amin, Beier Frank, Somerman Martha J, Holdsworth David W, Soslowsky Louis J, Lagugné-Labarthet François, Goldberg Harvey A
Department of Biochemistry, University of Western Ontario, London, ON, Canada.
Biomedical Engineering Program, University of Western Ontario, London, ON, Canada.
Matrix Biol. 2016 May-Jul;52-54:325-338. doi: 10.1016/j.matbio.2016.01.016. Epub 2016 Jan 28.
Tendons/ligaments insert into bone via a transitional structure, the enthesis, which is susceptible to injury and difficult to repair. Fibrocartilaginous entheses contain fibrocartilage in their transitional zone, part of which is mineralized. Mineral-associated proteins within this zone have not been adequately characterized. Members of the Small Integrin Binding Ligand N-linked Glycoprotein (SIBLING) family are acidic phosphoproteins expressed in mineralized tissues. Here we show that two SIBLING proteins, bone sialoprotein (BSP) and osteopontin (OPN), are present in the mouse enthesis. Histological analyses indicate that the calcified zone of the quadriceps tendon enthesis is longer in Bsp(-/-) mice, however no difference is apparent in the supraspinatus tendon enthesis. In an analysis of mineral content within the calcified zone, micro-CT and Raman spectroscopy reveal that the mineral content in the calcified fibrocartilage of the quadriceps tendon enthesis are similar between wild type and Bsp(-/-) mice. Mechanical testing of the patellar tendon shows that while the tendons fail under similar loads, the Bsp(-/-) patellar tendon is 7.5% larger in cross sectional area than wild type tendons, resulting in a 16.5% reduction in failure stress. However, Picrosirius Red staining shows no difference in collagen organization. Data collected here indicate that BSP is present in the calcified fibrocartilage of murine entheses and suggest that BSP plays a regulatory role in this structure, influencing the growth of the calcified fibrocartilage in addition to the weakening of the tendon mechanical properties. Based on the phenotype of the Bsp(-/-) mouse enthesis, and the known in vitro functional properties of the protein, BSP may be a useful therapeutic molecule in the reattachment of tendons and ligaments to bone.
肌腱/韧带通过一种过渡性结构——附着点插入骨骼，附着点易受损伤且难以修复。纤维软骨性附着点在其过渡区含有纤维软骨，其中一部分发生了矿化。该区域内与矿物质相关的蛋白质尚未得到充分表征。小整合素结合配体N-连接糖蛋白（SIBLING）家族成员是在矿化组织中表达的酸性磷酸蛋白。在此我们表明，两种SIBLING蛋白，骨唾液蛋白（BSP）和骨桥蛋白（OPN），存在于小鼠附着点中。组织学分析表明，股四头肌肌腱附着点的钙化区在Bsp(-/-)小鼠中更长，然而在冈上肌肌腱附着点中没有明显差异。在对钙化区内矿物质含量的分析中，显微CT和拉曼光谱显示，野生型和Bsp(-/-)小鼠股四头肌肌腱附着点钙化纤维软骨中的矿物质含量相似。髌腱的力学测试表明，虽然肌腱在相似负荷下失效，但Bsp(-/-)髌腱的横截面积比野生型肌腱大7.5%，导致失效应力降低16.5%。然而，天狼星红染色显示胶原组织没有差异。此处收集的数据表明，BSP存在于小鼠附着点的钙化纤维软骨中，并表明BSP在该结构中起调节作用，除了削弱肌腱力学性能外，还影响钙化纤维软骨的生长。基于Bsp(-/-)小鼠附着点的表型以及该蛋白已知的体外功能特性，BSP可能是肌腱和韧带重新附着于骨骼的一种有用治疗分子。
