Background

Scar tissue formation at the tendon-bone interface caused by excessive inflammation leads to insufficient healing strength, while the phagocytic clearance of dying cells (efferocytosis) has profound consequences on macrophage polarisation and the inflammatory response. Modulating the inflammatory microenvironment may have satisfactory curative effects in patients with anterior cruciate ligament reconstruction (ACLR).

Methods

Bone marrow-derived macrophages (BMDMs) and polymorphonuclear leukocytes (PMNs) were harvested from bone marrow. The effects of milk fat globulin protein E8 (MFG-E8) on macrophage polarisation were compared with those of M1 and M2 macrophages induced by conventional methods. The BMDMs and apoptotic PMNs co-culture system was used to assess the efficiency of efferocytosis. The biological functions of MFG-E8 in tendon-bone healing by regulating macrophage efferocytosis and polarisation were further investigated using a rat ACLR model.

Results

BMDMs and PMNs were successfully isolated. Compared to conventional induction methods, MFG-E8 alone did not significantly induce macrophage M1 or M2 polarisation, but it could partially reverse the expression of inducible nitric oxide synthase (iNOS) in M1 macrophages. In vitro studies revealed that appropriate dosing of MFG-E8 could significantly promote the efficiency of macrophage efferocytosis and subsequently increase M2 polarisation. More importantly, significantly increased peri-tunnel new bone formation, tighter connected interface and better mechanical properties were observed after ACLR when treated with MFG-E8 in vivo. We further demonstrated that MFG-E8 remarkably facilitated the clearance of apoptotic cells and increased the number of M2 macrophages at the interface between the tendon graft and bone tunnel in the early postoperative stage.

Conclusion

MFG-E8 promoted tendon-bone healing histologically and biomechanically, probably by the regulation of inflammatory processes via macrophage efferocytosis and M2 polarisation.

The translational potential of this article: Regulation of macrophage efferocytosis and M2 polarization by MFG-E8 is expected to be a therapeutic strategy for promoting tendon-bone healing in patients undergoing ACLR.

中文翻译：

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MFG-E8通过调节前交叉韧带重建后巨噬细胞的细胞增多和M2极化来促进腱骨愈合

背景

过度炎症引起的肌腱-骨界面瘢痕组织形成导致愈合强度不足，而垂死细胞的吞噬清除（胞吐作用）对巨噬细胞极化和炎症反应具有深远的影响。调节炎症微环境可能对前交叉韧带重建（ACLR）患者有满意的疗效。

方法

从骨髓中收获骨髓来源的巨噬细胞 (BMDM) 和多形核白细胞 (PMN)。比较了乳脂球蛋白E8（MFG-E8）对巨噬细胞极化的影响与常规方法诱导的M1和M2巨噬细胞的差异。BMDMs 和凋亡 PMNs 共培养系统用于评估 efferocytosis 的效率。使用大鼠 ACLR 模型进一步研究了 MFG-E8 通过调节巨噬细胞 efferocytosis 和极化在腱骨愈合中的生物学功能。

结果

BMDMs 和 PMNs 被成功分离。与传统的诱导方法相比，单独的 MFG-E8 不会显着诱导巨噬细胞 M1 或 M2 极化，但它可以部分逆转 M1 巨噬细胞中诱导型一氧化氮合酶 (iNOS) 的表达。体外研究表明，MFG-E8 的适当剂量可以显着促进巨噬细胞胞吐作用的效率，并随后增加 M2 极化。更重要的是，在体内用 MFG-E8 处理 ACLR 后，观察到显着增加的隧道周围新骨形成、更紧密的连接界面和更好的机械性能。

结论

MFG-E8 在组织学和生物力学上促进肌腱-骨愈合，可能是通过巨噬细胞胞吐作用和 M2 极化调节炎症过程。

本文的转化潜力：MFG-E8 调节巨噬细胞胞吐作用和 M2 极化有望成为促进 ACLR 患者腱骨愈合的治疗策略。