Osteogenic and Angiogenic Response to Skeletal Loading

描述（由申请人提供）：骨骼的机械负荷是新骨形成（骨生成）的有力刺激。骨形成在许多情况下（例如，骨的形成（例如骨的发育、骨折愈合）关键地取决于新血管的形成（血管生成），然而血管生成在支持机械负荷诱导的骨生成中的作用尚不清楚。由于衰老和糖尿病引起的血管供应缺陷可能会损害骨骼对机械刺激的反应，从而可能导致骨质疏松性骨折的风险。使用大鼠前肢负荷模型，我们最近量化了骨损伤疲劳负荷后，编织骨形成前血管的快速增加。我们还定量了血管生成基因的上调（例如，VEGF，血管内皮生长因子）和骨诱导基因BMP-2（骨形态发生蛋白-2），意外发现BMP-2首先在血管细胞中表达，然后在骨细胞中表达。在功能上，编织骨的形成与疲劳损伤的水平成比例，并且无论初始损伤的水平如何，加载后两周全骨强度都得到恢复。值得注意的是，血管生成抑制显着降低编织骨疲劳负荷后的反应。一个基本的未知数仍然存在-是什么生物学因素导致编织骨形成后疲劳负荷与板层骨形成后合成代谢负荷？在下一个项目期间，我们将使用前肢压缩的体内负荷模型（在大鼠和小鼠中），因为我们致力于确定机械负荷后导致快速非软骨内骨形成的机械生物学途径的长期目标。在目标1中，我们将比较疲劳负荷与合成代谢负荷的分子、血管和骨形成反应，并确定发育性骨生成（特别是Hedgehog信号）和血管生成在负荷诱导的编织骨和板层骨形成中的作用。在目标2中，我们将确定BMP信号传导（特别是内皮BMP-2）是否是负载诱导的骨生成和血管生成所必需的。总之，这些研究将建立重要的机械生物学因素，介导板层与编织骨形成的不同过程，并阐明血管生成的作用。它们将扩展我们对骨骼应力损伤（疲劳性骨折）的成骨反应的理解，并可能作为未来开发快速骨形成策略以增强弱骨或受损骨的基础。 公共卫生相关性：骨骼部分受机械力调节。该项目的目标是了解机械刺激后控制骨形成的生物学途径。这些信息可能会导致未来的策略，以增加骨量和减少骨骼脆弱性。

DESCRIPTION (provided by applicant): Mechanical loading of the skeleton is a powerful stimulus for new bone formation (osteogenesis). Bone formation in many contexts (e.g., development, fracture healing) depends critically on the formation of new blood vessels (angiogenesis), yet the role of angiogenesis in supporting mechanical loading-induced osteogenesis is not known. Deficits in vascularity due to aging and diabetes may compromise the skeletal response to mechanical stimuli and thus may contribute to osteoporotic fracture risk. Using the rat forelimb loading model, we recently quantified a rapid increase in vascularity after damaging fatigue loading of bone, prior to woven bone formation. We also quantified the upregulation of angiogenic genes (e.g., VEGF, vascular endothelial growth factor) and the osteoinductive gene BMP-2 (bone morphogenetic protein-2) within 1 hr after fatigue loading, with the unexpected finding that BMP-2 expression occurred first in vascular cells then in bone cells. Functionally, woven bone formation occurred in proportion to the level of fatigue damage and whole-bone strength was restored two weeks after loading - regardless of the level of initial damage. Notably, angiogenic inhibition markedly reduced the woven bone response after fatigue loading. A fundamental unknown remains - what are the biological factors that cause woven bone formation after fatigue loading versus lamellar bone formation after anabolic loading? In the next project period we will use the in vivo loading model of forelimb compression (in rats and mice) as we work toward the long term goal of determining the mechano-biological pathways that lead to rapid non-endochondral bone formation after mechanical loading. In Aim 1, we will compare molecular, vascular and bone formation responses to fatigue loading versus anabolic loading, and determine the role of developmental osteogenesis (in particular Hedgehog signaling) and angiogenesis in loading-induced woven and lamellar bone formation. In Aim 2, we will determine if BMP signaling (and in particular endothelial BMP-2) is required for loading-induced osteogenesis and angiogenesis. Taken together, these studies will establish important mechano-biological factors that mediate the distinct processes of lamellar versus woven bone formation and clarify the role of angiogenesis. They will extend our understanding of the osteogenic response to skeletal stress injuries (fatigue fractures) and may serve as a basis for future development of strategies for rapid bone formation to augment weak or damaged bones. PUBLIC HEALTH RELEVANCE: The skeleton is regulated in part by mechanical forces. The goal of this project is to understand the biological pathways that control bone formation following mechanical stimulation. This information may lead to future strategies to increase bone mass and reduce skeletal fragility.