Kannan Rahasudha, Koh Amy J, Kent Robert N, Bhutada Kaira, Wasi Fatima, Wagner Leon, Kozloff Kenneth, Baker Brendon M, Roca Hernan, McCauley Laurie K
Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
J Cell Mol Med. 2024 Dec;28(24):e70300. doi: 10.1111/jcmm.70300.
Macrophage efferocytosis (clearance of apoptotic cells) is crucial for tissue homeostasis and wound repair, where macrophages secrete factors that promote resolution of inflammation and regenerative signalling. This study examined the role of efferocytic macrophage-associated CCL2 secretion, its influence on mesenchymal stem/progenitor cell (MSPC) chemotaxis, and in vivo cell recruitment using Ccr2 (KO) mice with disrupted CCL2 receptor signalling in two regenerative models: ossicle implants and ulnar stress fractures. Single cell RNA sequencing and PCR validation indicated that efferocytosis of various apoptotic cells at bone injury sites (osteoblasts, pre-osteoblasts, MSPC) upregulated CCL2. CCL2 gradients enhanced MSPC migration through type I collagen matrices. In vivo, MSPC (LepR) infiltration was significantly reduced while macrophage (F4/80) infiltration increased in KO ossicle implants versus WT. In ulnar stress fractures, micro-CT revealed increased mineralized callus incidence in CCR2 KO male mice 5 days post injury (dpi) versus WT. By 7-dpi callus fractional bone volume, trabecular thickness, and bone mineral density were increased versus WT. Immunohistochemistry of mice 5-dpi confirmed an increase in callus area (including soft tissue); however, the percent of osteoprogenitors (%Osx) within the callus was not different. These findings suggest that CCL2 differentially impacts MSPC recruitment depending on bone wound healing model.
巨噬细胞的胞葬作用（凋亡细胞清除）对于组织稳态和伤口修复至关重要，在此过程中巨噬细胞分泌促进炎症消退和再生信号传导的因子。本研究使用在两种再生模型（听小骨植入和尺骨应力性骨折）中CCL2受体信号传导中断的Ccr2（基因敲除）小鼠，研究了与胞葬作用相关的巨噬细胞分泌CCL2的作用、其对间充质干/祖细胞（MSPC）趋化性的影响以及体内细胞募集情况。单细胞RNA测序和PCR验证表明，骨损伤部位（成骨细胞、前成骨细胞、MSPC）各种凋亡细胞的胞葬作用上调了CCL2。CCL2梯度增强了MSPC通过I型胶原基质的迁移。在体内，与野生型相比，基因敲除小鼠听小骨植入物中MSPC（LepR）浸润显著减少，而巨噬细胞（F4/80）浸润增加。在尺骨应力性骨折中，显微CT显示，与野生型相比，CCR2基因敲除雄性小鼠在损伤后5天（dpi）矿化骨痂发生率增加。到7 dpi时，与野生型相比，骨痂的骨体积分数、小梁厚度和骨密度增加。对5 dpi小鼠的免疫组织化学分析证实骨痂面积（包括软组织）增加；然而，骨痂内骨祖细胞（%Osx）的百分比没有差异。这些发现表明，CCL2根据骨伤口愈合模型对MSPC募集有不同影响。
