Distraction osteogenesis (DO) is a well-established surgical technique for treating bone defect and limb lengthening. The major drawback of DO is the long treatment period as the external fixator has to be kept in place until consolidation is completed. Calcitonin gene-related peptide (CGRP) has been reported to promote angiogenesis by affecting endothelial progenitor cells (EPCs) in limb ischemia and wound healing. Thus, the goal of this study was to evaluate the angiogenic effect of exogenous CGRP on bone regeneration in a rat DO model. Exogenous CGRP was directly injected into the bone defect after each cycle of distraction in vivo. Microcomputed tomography, biomechanical test, and histological analysis were performed to assess the new bone formation. Angiography and immunofluorescence were performed to assess the formation of blood vessels. CD31⁺CD144⁺ EPCs in the bone defect were quantified with flow cytometry. In in vitro study, bone marrow stem cells (BMSCs) were used to investigate the effect of CGRP on EPCs production during endothelial differentiation. Our results showed that CGRP significantly promoted bone regeneration and vessel formation after consolidation. CGRP significantly increased the fraction of CD31⁺CD144⁺EPCs and the capillary density in the bone defect at the end of distraction phase. CGRP increased EPC population in the endothelial differentiation of BMSCs in vitro by activating PI3K/AKT signaling pathway. Furthermore, differentiated EPCs rapidly assembled into tube-like structures and promoted osteogenic differentiation of BMSCs. In conclusion, CGRP increased EPC population and promoted blood vessel formation and bone regeneration at the defect region in a DO model.

中文翻译：

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降钙素基因相关肽通过增加血管生成来增强牵引成骨。

牵引成骨 (DO) 是一种成熟的手术技术，用于治疗骨缺损和肢体延长。DO 的主要缺点是治疗时间长，因为外固定器必须保持在原位，直到巩固完成。据报道，降钙素基因相关肽 (CGRP) 通过影响肢体缺血和伤口愈合中的内皮祖细胞 (EPC) 来促进血管生成。因此，本研究的目的是评估外源性 CGRP 对大鼠 DO 模型中骨再生的血管生成作用。在体内每个牵张周期后将外源性CGRP直接注射到骨缺损处. 进行微计算机断层扫描、生物力学测试和组织学分析以评估新骨形成。进行血管造影和免疫荧光以评估血管的形成。用流式细胞术对骨缺损中的CD31 ⁺ CD144 ^{+ EPCs 进行量化。}在体外研究中，骨髓干细胞 (BMSCs) 用于研究 CGRP 在内皮分化过程中对 EPCs 产生的影响。我们的研究结果表明，CGRP 显着促进骨再生和巩固后血管形成。CGRP 显着增加了 CD31 ⁺ CD144 ^+的分数牵张期结束时骨缺损中的 EPC 和毛细血管密度。CGRP通过激活PI3K/AKT信号通路增加体外BMSCs内皮分化中的EPC群体。此外，分化的EPCs迅速组装成管状结构，促进了BMSCs的成骨分化。总之，CGRP 在 DO 模型中增加了 EPC 数量并促进了缺损区域的血管形成和骨再生。