Bones and Immunology Laboratory, Mater Research Institute-The University of Queensland, Translational Research Institute, Woolloongabba, Queensland, 4102, Australia.
Gold Coast University Hospital, Southport, Queensland, 4215, Australia; The University of Queensland, Faculty of Medicine, Herston, Queensland, 4092, Australia; Griffith University, School of Medicine, Southport, Queensland, 4215, Australia.
Biomaterials. 2019 Mar;196:51-66. doi: 10.1016/j.biomaterials.2017.10.033. Epub 2017 Oct 22.
Osteal macrophages (osteomacs) contribute to bone homeostasis and regeneration. To further distinguish their functions from osteoclasts, which share many markers and growth factor requirements, we developed a rapid, enzyme-free osteomac enrichment protocol that permitted characterization of minimally manipulated osteomacs by flow cytometry. Osteomacs differ from osteoclasts in expression of Siglec1 (CD169). This distinction was confirmed using the CD169-diphtheria toxin (DT) receptor (DTR) knock-in model. DT treatment of naïve CD169-DTR mice resulted in selective and striking loss of osteomacs, whilst osteoclasts and trabecular bone area were unaffected. Consistent with a previously-reported trophic interaction, osteomac loss was accompanied by a concomitant and proportionately striking reduction in osteoblasts. The impact of CD169 macrophage depletion was assessed in two models of bone injury that heal via either intramembranous (tibial injury) or endochondral (internally-plated femoral fracture model) ossification. In both models, CD169 macrophage, including osteomac depletion compromised bone repair. Importantly, DT treatment in CD169-DTR mice did not affect osteoclast frequency in either model. In the femoral fracture model, the magnitude of callus formation correlated with the number of F4/80 macrophages that persisted within the callus. Overall these observations provide compelling support that CD169 osteomacs, independent of osteoclasts, provide vital pro-anabolic support to osteoblasts during both bone homeostasis and repair.
破骨细胞前体细胞（骨细胞）有助于骨稳态和再生。为了进一步区分其与破骨细胞的功能，破骨细胞具有许多共同的标志物和生长因子需求，我们开发了一种快速、无酶的骨细胞富集方案，允许通过流式细胞术对最小程度处理的骨细胞进行特征分析。骨细胞在 Siglec1（CD169）的表达上与破骨细胞不同。使用 CD169-白喉毒素（DT）受体（DTR）敲入模型证实了这一区别。DT 处理幼稚的 CD169-DTR 小鼠导致骨细胞的选择性和显著丢失，而破骨细胞和小梁骨面积不受影响。与先前报道的营养相互作用一致，骨细胞丢失伴随着成骨细胞的同时和相应的显著减少。在两种通过膜内（胫骨损伤）或软骨内（内部板状股骨骨折模型）成骨愈合的骨损伤模型中评估了 CD169 巨噬细胞耗竭的影响。在这两种模型中，CD169 巨噬细胞（包括骨细胞）耗竭都损害了骨修复。重要的是，在 CD169-DTR 小鼠中，DT 处理不会影响两种模型中的破骨细胞频率。在股骨骨折模型中，骨痂形成的程度与骨痂内持续存在的 F4/80 巨噬细胞数量相关。总体而言，这些观察结果有力地支持了 CD169 骨细胞，独立于破骨细胞，在骨稳态和修复过程中为成骨细胞提供重要的促合成代谢支持。
