Institute of Orthopedic Research and Biomechanics, University Medical Center Ulm, Helmholtzstraße 14, 89081 Ulm, Germany.
Institute of Orthopedic Research and Biomechanics, University Medical Center Ulm, Helmholtzstraße 14, 89081 Ulm, Germany.
Bone. 2023 Jul;172:116781. doi: 10.1016/j.bone.2023.116781. Epub 2023 Apr 25.
External mechanostimulation applied by whole-body low-magnitude high-frequency vibration (LMHFV) was demonstrated to cause no or negative effects on fracture healing in estrogen-competent rodents, while in ovariectomized (OVX), estrogen-deficient rodents bone formation after fracture was improved. Using mice with an osteoblast-specific deletion of the estrogen receptor α (ERα), we demonstrated that ERα signaling in osteoblasts is required for both the anabolic and catabolic effects of LMHFV during bone fracture healing in OVX and non-OVX mice, respectively. Because the vibration effects mediated by ERα were strictly dependent on the estrogen status, we hypothesized different roles of ligand-dependent and -independent ERα signaling. To investigate this assumption in the present study, we used mice with a deletion of the C-terminal activation function (AF) domain-2 of the ERα receptor, which mediated ligand-dependent ERα signaling (ERαAF-2). OVX and non-OVX ERαAF-2 animals were subjected to femur osteotomy followed by vibration treatment. We revealed that estrogen-competent mice lacking the AF-2 domain were protected from LMHFV-induced impaired bone regeneration, while the anabolic effects of vibration in OVX mice were not affected by the AF-2 knockout. RNA sequencing further showed that genes involved in Hippo/Yap1-Taz and Wnt signaling were significantly downregulated upon LMHFV in the presence of estrogen in vitro. In conclusion, we demonstrated that the AF-2 domain is crucial for the negative effects of vibration during bone fracture healing in estrogen-competent mice suggesting that the osteoanabolic effects of vibration are rather mediated by ligand-independent ERα signaling.
全身低频高幅机械刺激（LMHFV）的外部机械刺激被证明对雌激素功能正常的啮齿动物骨折愈合没有或产生负面影响，而在去卵巢（OVX）、雌激素缺乏的啮齿动物中，骨折后骨形成得到改善。使用成骨细胞中雌激素受体 α（ERα）特异性缺失的小鼠，我们证明 ERα 在成骨细胞中的信号传导对于 LMHFV 在 OVX 和非 OVX 小鼠骨折愈合过程中的合成代谢和分解代谢作用分别是必需的。由于 ERα 介导的振动作用严格依赖于雌激素状态，我们假设配体依赖性和非依赖性 ERα 信号传导有不同的作用。为了在本研究中研究这一假设，我们使用了 ERα 受体 C 端激活功能（AF）域-2 缺失的小鼠，该缺失介导了配体依赖性 ERα 信号传导（ERαAF-2）。对 OVX 和非 OVX ERαAF-2 动物进行股骨切开术，然后进行振动治疗。我们发现，缺乏 AF-2 结构域的雌激素功能正常的小鼠对 LMHFV 引起的骨再生受损具有保护作用，而振动对 OVX 小鼠的合成代谢作用不受 AF-2 敲除的影响。RNA 测序进一步表明，在体外雌激素存在的情况下，与 Hippo/Yap1-Taz 和 Wnt 信号相关的基因在 LMHFV 作用下显著下调。总之，我们证明了 AF-2 结构域对于雌激素功能正常的小鼠骨折愈合过程中振动的负性作用是至关重要的，这表明振动的成骨作用是通过配体非依赖性 ERα 信号传导介导的。
