Role of estrogen receptor signaling in low-magnitude high-frequency vibration-induced effects on bone fracture healing

由于其骨合成代谢作用，低强度高频全身振动（LMHFV）被认为是一种无创、经济、安全的治疗骨质疏松症患者增加骨量和改善骨质量的方法。我们对LMHFV对骨折愈合的影响知之甚少。实验研究报告了相互矛盾的结果。研究表明，LMHFV支持雌激素缺乏的啮齿动物的骨再生，而在雌激素充足的动物中，没有观察到任何影响或负面影响。这表明雌激素在骨修复机械刺激中的主要作用，并暗示LMHFV可能仅在有限的目标人群中有益。然而，潜在的分子机制仍然知之甚少。在本提案的前期工作中，我们使用ER α和ER β敲除小鼠研究了雌激素受体（ER）信号在lmhfv诱导的骨折愈合效应中的作用。我们的结果表明，内质网α -信号的关键作用，而不是内质网β -信号。然而，该项目仍需解决的问题是，LMHFV的作用是由配体依赖性还是非配体依赖性内质网α信号传导引起的，以及骨折愈伤组织中的哪种细胞类型是机械刺激的目标。为了回答第一个问题，我们将使用ER α - af1 -0和ER α - af2 -0小鼠进行骨折愈合研究，因为AF-1结构域负责配体依赖性和非依赖性信号传导，而AF-2仅发挥配体依赖性信号传导。为了确定相关的细胞类型，我们将使用细胞特异性ER α敲除小鼠。其他的体内和体外实验将进行，以确定LMHFV期间内质网α信号传导的分子靶点，以及内质网α信号传导是否与其他途径，如Wnt/ β -连环蛋白信号传导，在机械转导过程中相互作用。该项目的研究结果可能对建立基于lmhfv的骨折患者治疗方案具有临床意义。

Due to its osteoanabolic effects, low-magnitude high-frequency whole-body vibration (LMHFV) is supposed to provide a non-invasive, cost-effective and safe treatment to increase bone mass and improve bone quality in osteoporotic patients. Much less is known about the effects of LMHFV on bone fracture healing. Experimental studies reported contradictory results. It has been shown that LMHFV supports bone regeneration in estrogen-deficient rodents, whereas, in estrogen-competent animals, no or negative effects were observed. This indicates a major role for estrogen in mechanostimulation of bone repair and implies that LMHFV might only be beneficial in confined target populations. However, the underlying molecular mechanisms remain poorly understood. In preliminary work for this proposal, we studied the role of estrogen receptor (ER) signaling in LMHFV-induced effects on fracture healing using ER alpha- and ER beta-knockout mice. Our results suggest a critical role of ER alpha-, but not of ER beta-signaling. However, remaining open questions which should be addressed by the proposed project are, if ligand-dependent or ligand-independent ER alpha-signaling is responsible for the effects of LMHFV and which cell types in the fracture callus are the targets for mechanostimulation. To answer the first question, we will use ER alpha-AF1-0 and ER alpha-AF2-0 mice for fracture healing studies, since the AF-1 domain is responsible for ligand-dependent and -independent signaling, whereas AF-2 exerts only ligand-dependent signaling. To identify the involved cell types, we will use cell-specific ER alpha-knockout mice. Additional in vivo and in vitro experiments will be performed to identify molecular targets of ER alpha signaling during LMHFV and if ER alpha- signaling interact with other pathways, such as Wnt/beta-catenin-signaling, during mechanotransduction. The results of the proposed project might be clinically relevant to establish LMHFV-based treatment options for fracture patients.