Yang Chengyu, Liu Yang, Wang Ziyan, Lin Minmin, Liu Chao
Department of Biomedical Engineering, College of Engineering, Southern University of Science and Technology, Shenzhen, China.
Guangdong Provincial Key Laboratory of Advanced Biomaterials, Southern University of Science and Technology, Shenzhen, China.
FASEB J. 2022 Oct;36(10):e22530. doi: 10.1096/fj.202200339RRR.
Despite the best treatment, approximately 10% of fractures still face undesirable repair and result in delayed unions or non-unions. Dynamic mechanical stimulation promotes bone formation, when applied at the correct time frame, with optimal loading magnitude, frequency, and repetition. Controlled mechanical loading significantly increases osteogenic cells during the matrix deposition phase of bone repair. In the bone defect, the blood vessel network guides the initial bone formation activities. A unique blood vessel subtype (Type H) exists in bone, which expresses high levels of CD31 and endomucin, and functions to couple angiogenesis and osteogenesis. However, how this form of controlled mechanical loading regulates the Type H vessels and promotes bone formation is still not clear. Sphingosine 1-phosphate (S1P) participates in the bone anabolic process and is a key regulator of the blood vessel. Its receptor, sphingosine 1-phosphate receptor 1 (S1Pr1), is a mechanosensitive protein that regulates vascular integrity. Therefore, we hypothesis that controlled anabolic mechanical loading promotes bone repair by acting on Type H vessels. To study the effect of S1Pr1 on loading induced-bone repair, we utilized a stabilized tibial defect model, which allows for the application of anabolic mechanical loading. Mechanical loading upregulated S1Pr1 within the entire defect, with up to 80% expressed in blood vessels, as observed by deep tissue imaging. Additionally, S1Pr1 antagonism by W146 inhibited the anabolic effects of mechanical loading. We showed that mechanical loading or activating S1Pr1 could induce YAP nuclear translocation, a key regulator in the cell's mechanical response, in endothelial cells (ECs) in vitro. Inhibition of S1Pr1 in endothelial cells by siRNA reduced loading-induced YAP nuclear translocation and expressions of angiogenic genes. In vivo, YAP nuclear translocation in Type H vessels was up-regulated after mechanical loading but was inhibited by antagonizing S1Pr1. S1Pr1 agonist, FTY720, increased bone volume and Type H vessel volume, similar to that of mechanical stimulation. In conclusion, controlled anabolic mechanical loading enhanced bone formation mainly through Type H vessels in a S1Pr1-dependent manner.
尽管采用了最佳治疗方法，但仍有大约10%的骨折面临不理想的修复情况，并导致延迟愈合或不愈合。动态机械刺激在正确的时间框架内，以最佳的加载幅度、频率和重复次数应用时，可促进骨形成。在骨修复的基质沉积阶段，控制性机械加载可显著增加成骨细胞。在骨缺损中，血管网络引导着最初的骨形成活动。骨中存在一种独特的血管亚型（H型），其表达高水平的CD31和内粘蛋白，并具有耦合血管生成和成骨的功能。然而，这种形式的控制性机械加载如何调节H型血管并促进骨形成仍不清楚。鞘氨醇-1-磷酸（S1P）参与骨合成代谢过程，是血管的关键调节因子。其受体鞘氨醇-1-磷酸受体1（S1Pr1）是一种机械敏感蛋白，可调节血管完整性。因此，我们假设控制性合成代谢机械加载通过作用于H型血管促进骨修复。为了研究S1Pr1对加载诱导的骨修复的影响，我们使用了稳定的胫骨缺损模型，该模型允许应用合成代谢机械加载。通过深层组织成像观察到，机械加载使整个缺损内的S1Pr1上调，其中高达80%在血管中表达。此外，W146对S1Pr1的拮抗作用抑制了机械加载的合成代谢作用。我们发现，机械加载或激活S1Pr1可在体外诱导内皮细胞（ECs）中YAP核转位，YAP是细胞机械反应中的关键调节因子。通过siRNA抑制内皮细胞中的S1Pr1可减少加载诱导的YAP核转位和血管生成基因的表达。在体内，机械加载后H型血管中的YAP核转位上调，但通过拮抗S1Pr1受到抑制。S1Pr1激动剂FTY720增加了骨体积和H型血管体积，类似于机械刺激的效果。总之，控制性合成代谢机械加载主要通过依赖S1Pr1的H型血管增强骨形成。
