Department of Orthopaedics, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
Department of Orthopaedic Surgery, The Third Hospital of Hebei Medical University, Shijiazhuang, 050051, China.
Signal Transduct Target Ther. 2023 Jul 5;8(1):260. doi: 10.1038/s41392-023-01457-w.
Traumatic brain injury (TBI) accelerates fracture healing, but the underlying mechanism remains largely unknown. Accumulating evidence indicates that the central nervous system (CNS) plays a pivotal role in regulating immune system and skeletal homeostasis. However, the impact of CNS injury on hematopoiesis commitment was overlooked. Here, we found that the dramatically elevated sympathetic tone accompanied with TBI-accelerated fracture healing; chemical sympathectomy blocks TBI-induced fracture healing. TBI-induced hypersensitivity of adrenergic signaling promotes the proliferation of bone marrow hematopoietic stem cells (HSCs) and swiftly skews HSCs toward anti-inflammation myeloid cells within 14 days, which favor fracture healing. Knockout of β3- or β2-adrenergic receptor (AR) eliminate TBI-mediated anti-inflammation macrophage expansion and TBI-accelerated fracture healing. RNA sequencing of bone marrow cells revealed that Adrb2 and Adrb3 maintain proliferation and commitment of immune cells. Importantly, flow cytometry confirmed that deletion of β2-AR inhibits M2 polarization of macrophages at 7th day and 14th day; and TBI-induced HSCs proliferation was impaired in β3-AR knockout mice. Moreover, β3- and β2-AR agonists synergistically promote infiltration of M2 macrophages in callus and accelerate bone healing process. Thus, we conclude that TBI accelerates bone formation during early stage of fracture healing process by shaping the anti-inflammation environment in the bone marrow. These results implicate that the adrenergic signals could serve as potential targets for fracture management.
创伤性脑损伤(TBI)可加速骨折愈合,但其中的潜在机制仍很大程度上未知。越来越多的证据表明,中枢神经系统(CNS)在调节免疫系统和骨骼内稳态方面发挥着关键作用。然而,CNS 损伤对造血细胞的影响却被忽视了。在这里,我们发现,TBI 伴随的交感神经张力显著升高,并且加速了骨折愈合;化学性交感神经切除术阻断了 TBI 诱导的骨折愈合。TBI 诱导的肾上腺素能信号敏感性促进了骨髓造血干细胞(HSCs)的增殖,并在 14 天内迅速将 HSCs 向抗炎性髓系细胞倾斜,有利于骨折愈合。敲除β3-或β2-肾上腺素能受体(AR)消除了 TBI 介导的抗炎性巨噬细胞扩增和 TBI 加速的骨折愈合。骨髓细胞的 RNA 测序显示,Adrb2 和 Adrb3 维持免疫细胞的增殖和分化。重要的是,流式细胞术证实,β2-AR 的缺失抑制了第 7 天和第 14 天巨噬细胞的 M2 极化;并且在β3-AR 敲除小鼠中,TBI 诱导的 HSCs 增殖受损。此外,β3-和β2-AR 激动剂协同促进 M2 巨噬细胞在骨痂中的浸润,并加速骨愈合过程。因此,我们得出结论,TBI 通过在骨髓中形成抗炎环境,在骨折愈合的早期阶段加速骨形成。这些结果表明,肾上腺素能信号可以作为骨折管理的潜在靶点。
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