Effects of Osteocalcin and Osteopontin on Damage Morphology and Bone Fragility

描述（由申请人提供）：虽然较低的骨量与骨脆弱性增加有关，但在上一个资助周期进行的研究表明，微损伤形成的模式和程度影响骨的抗骨折性或“韧性”。年轻供者骨韧性较好，微损伤表现为弥漫性损伤。相比之下，老年供者的骨头主要形成线状微裂缝，这些微裂缝合并导致骨折。损伤形态和韧性之间这种独特联系的基础尚不清楚。我们的初步研究首次表明，骨的弥漫性损伤以熔融矿化聚集体之间的扩张带的形式开始。扩张带骨钙素（OC）和骨桥蛋白（OPN）染色阳性。与对照组相比，弥漫性损伤区OC和OPN的含量更高，OC缺失或骨基质磷酸化会降低韧性。由于OPN和OC随组织和供体年龄的变化而变化，并且彼此之间以及与形成扩张带和弥漫性损伤的骨矿物质密切相关，因此这些非胶原基质蛋白的修饰和丢失可能决定了损伤形态和骨骨折的倾向。因此，该项目的总体目标是研究OC和OPN在与年龄相关的骨脆性中的作用。来自人类尸体、衰老小鼠和转基因（敲除-/-和杂合子）小鼠的骨骼，包括OC-/-、OC、OPN-/- OPN、OPN-OC-/-和OPN-OC及其对照，将进行机械和免疫组织化学评估，以研究：（H1）：骨中OC和/或OPN的缺失或修饰是否会增加骨的脆弱性，以及骨在弥漫性损伤时形成线性微裂纹的倾向；（H2）与年龄相关的骨脆性增加与OC和/或OPN的改变和丢失有关，它们与弥漫性损伤和线状微裂纹的共定位不同。由于OC和OPN水平可以通过激素和机械负荷来控制，因此它们与损伤形成和骨易碎性之间的直接关系的证据将导致预测骨折的新模式的发展，以及改善骨质量和降低骨折风险的策略。

DESCRIPTION (provided by applicant): Although lower bone mass is associated with increased bone fragility, studies conducted during the last grant cycle demonstrated that the mode and magnitude of microdamage formation affects bone's resistance to fracture or 'toughness'. Bones from younger donors are superior in toughness and form diffuse damage as the prominent morphology of microdamage. In contrast, bones from older donors predominantly form linear microcracks that coalesce to cause fracture. The basis of this unique association between damage morphology and toughness is not known. Our preliminary studies show for the first time that diffuse damage in bone initiates in the form of dilatational bands between the fused mineralized aggregates. Dilatational bands stain positive for osteocalcin (OC) and osteopontin (OPN). OC and OPN are present in higher amounts in diffuse damage areas than in controls and the deletion of OC or phosphorylation of bone matrix decreases toughness. Because OPN and OC vary with tissue and donor age, and are intimately associated with each other and with bone mineral where dilatational bands and diffuse damage form, the modification and loss of these non-collagenous matrix proteins may determine the damage morphology and bone's propensity to fracture. Thus the overall goal of this project is to investigate the role of OC and OPN in age-related bone fragility. Bones from human cadavers, aging mouse and transgenic (knock-outs-/- & hetrozygotes) mice including OC-/-, OC, OPN-/- OPN, OPN-OC-/- and OPN-OC and their controls will be subjected to mechanical and immunohistochemical evaluations to investigate whether: (H1): The deletion or modification of OC and or OPN in bone increases bone fragility and bone's propensity to form linear microcracks over diffuse damage; (H2) The age-related increase in bone fragility is associated with the modification and loss of OC and/or OPN that co-localize differently with diffuse damage and linear microcracks. Since OC and OPN levels can be manipulated through hormones and mechanical loading, the evidence of their new direct relationship to damage formation and bone fragility will lead to the development of novel modalities for predicting fracture, as well as strategies for improving bone quality and reducing the fracture risk.