As musculoskeletal (MSK) disorders continue to increase globally, there is an increased need for novel, in vitro models to efficiently study human bone physiology in the context of both healthy and diseased conditions. For these models, the inclusion of innate immune cells is critical. Specifically, signaling factors generated from macrophages play key roles in the pathogenesis of many MSK processes and diseases, including fracture, osteoarthritis, infection etc. In this study, we aim to engineer three-dimensional (3D) and macrophage-encapsulated bone tissues in vitro, to model cell behavior, signaling, and other biological activities in vivo, in comparison to current two-dimensional models. We first investigated and optimized 3D culture conditions for macrophages, and then co-cultured macrophages with mesenchymal stem cells (MSCs), which were induced to undergo osteogenic differentiation to examine the effect of macrophage on new bone formation. Seeded within a 3D hydrogel scaffold fabricated from photocrosslinked methacrylated gelatin, macrophages maintained high viability and were polarized toward an M1 or M2 phenotype. In co-cultures of macrophages and human MSCs, MSCs displayed immunomodulatory activities by suppressing M1 and enhancing M2 macrophage phenotypes. Lastly, addition of macrophages, regardless of polarization state, increased MSC osteogenic differentiation, compared with MSCs alone, with proinflammatory M1 macrophages enhancing new bone formation most effectively. In summary, this study illustrates the important roles that macrophage signaling and inflammation play in bone tissue formation.

中文翻译：

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三维体外骨模型中巨噬细胞对间充质干细胞成骨的影响。


随着肌肉骨骼 (MSK) 疾病在全球范围内持续增加，人们越来越需要新型体外模型来有效研究健康和患病条件下的人体骨骼生理学。对于这些模型，包含先天免疫细胞至关重要。具体来说，巨噬细胞产生的信号因子在许多 MSK 过程和疾病的发病机制中发挥着关键作用，包括骨折、骨关节炎、感染等。在这项研究中，我们的目标是在体外设计三维 (3D) 和巨噬细胞封装的骨组织，与当前的二维模型相比，对体内细胞行为、信号传导和其他生物活动进行建模。我们首先研究并优化了巨噬细胞的3D培养条件，然后将巨噬细胞与间充质干细胞（MSC）共培养，诱导其进行成骨分化，以检查巨噬细胞对新骨形成的影响。巨噬细胞接种在由光交联甲基丙烯酸明胶制成的 3D 水凝胶支架内，保持高活力并极化为 M1 或 M2 表型。在巨噬细胞和人 MSC 的共培养中，MSC 通过抑制 M1 和增强 M2 巨噬细胞表型而表现出免疫调节活性。最后，与单独的 MSC 相比，添加巨噬细胞，无论极化状态如何，都会增加 MSC 成骨分化，其中促炎性 M1 巨噬细胞最有效地促进新骨形成。总之，这项研究说明了巨噬细胞信号传导和炎症在骨组织形成中发挥的重要作用。