Department of Biomedical Engineering, Fourth Military Medical University, Xi'an, China.
State Key Laboratory of Military Stomatology, Department of Orthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, China.
J Cell Physiol. 2019 Jul;234(7):10588-10601. doi: 10.1002/jcp.27734. Epub 2018 Nov 13.
Growing evidence has shown that pulsed electromagnetic fields (PEMF) can modulate bone metabolism in vivo and regulate the activities of osteoblasts and osteoclasts in vitro. Osteocytes, accounting for 95% of bone cells, act as the major mechanosensors in bone for transducing external mechanical signals and producing cytokines to regulate osteoblastic and osteoclastic activities. Targeting osteocytic signaling pathways is becoming an emerging therapeutic strategy for bone diseases. We herein systematically investigated the changes of osteocyte behaviors, functions, and its regulation on osteoclastogenesis in response to PEMF. The osteocyte-like MLO-Y4 cells were exposed to 15 Hz PEMF stimulation with different intensities (0, 5, and 30 Gauss [G]) for 2 hr. We found that the cell apoptosis and cytoskeleton organization of osteocytes were regulated by PEMF with an intensity-dependent manner. Moreover, PEMF exposure with 5 G significantly inhibited apoptosis-related gene expression and also suppressed the gene and protein expression of the receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG) ratio in MLO-Y4 cells. The formation, maturation, and osteoclastic bone-resorption capability of in vitro osteoclasts were significantly suppressed after treated with the conditioned medium from PEMF-exposed (5 G) osteocytes. Our results also revealed that the inhibition of osteoclastic formation, maturation, and bone-resorption capability induced by the conditioned medium from 5 G PEMF-exposed osteocytes was significantly attenuated after abrogating primary cilia in osteocytes using the polaris siRNA transfection. Together, our findings highlight that PEMF with 5 G can inhibit cellular apoptosis, modulate cytoskeletal distribution, and decrease RANKL/OPG expression in osteocytes, and also inhibit osteocyte-mediated osteoclastogenesis, which requires the existence of primary cilia in osteocytes. This study enriches our basic knowledge for further understanding the biological behaviors of osteocytes and is also helpful for providing a more comprehensive mechanistic understanding of the effect of electromagnetic stimulation on bone and relevant skeletal diseases (e.g., bone fracture and osteoporosis).
越来越多的证据表明，脉冲电磁场（PEMF）可以调节体内骨代谢，并调节体外成骨细胞和破骨细胞的活性。成骨细胞占骨细胞的 95%，作为骨中主要的机械感受器，将外部机械信号转导并产生细胞因子，从而调节成骨细胞和破骨细胞的活性。针对成骨细胞信号通路已成为治疗骨疾病的一种新兴治疗策略。本文系统研究了 PEMF 作用下成骨细胞行为、功能及其对破骨细胞形成的调节变化。将类成骨细胞 MLO-Y4 细胞用 15Hz 的 PEMF 以 0、5 和 30 高斯（G）的不同强度刺激 2 小时。结果发现，PEMF 以强度依赖的方式调节成骨细胞的细胞凋亡和细胞骨架组织。此外，5G 的 PEMF 暴露显著抑制了与凋亡相关的基因表达，同时抑制了 MLO-Y4 细胞中核因子κB 受体激活剂配体/骨保护素（RANKL/OPG）比值的基因和蛋白表达。经 PEMF 暴露（5G）成骨细胞条件培养基处理后，体外破骨细胞的形成、成熟和破骨细胞骨吸收能力明显受到抑制。我们的结果还表明，在用极蛋白 siRNA 转染消除成骨细胞中的初级纤毛后，5G PEMF 暴露的成骨细胞条件培养基诱导的破骨细胞形成、成熟和骨吸收能力的抑制作用明显减弱。综上所述，本研究结果表明，5G 的 PEMF 可抑制成骨细胞的细胞凋亡、调节细胞骨架分布和降低 RANKL/OPG 的表达，并抑制成骨细胞介导的破骨细胞形成，这需要成骨细胞中初级纤毛的存在。该研究丰富了我们对成骨细胞生物学行为的基本认识，也有助于更全面地理解电磁场刺激对骨骼及相关骨骼疾病（如骨折和骨质疏松症）的作用机制。
