PDF(Pubmed)
Abstract：
Apoptosis is crucial for tissue homeostasis and organ development. In bone, apoptosis is recognized to be a main fate of osteoblasts, yet the relevance of this process remains underexplored. Using our murine model with inducible Caspase 9, the enzyme that initiates intrinsic apoptosis, we triggered apoptosis in a proportion of mature osteocalcin (OCN+) osteoblasts and investigated the impact on postnatal bone development. Osteoblast apoptosis stimulated efferocytosis by osteal macrophages. A five-week stimulation of OCN+ osteoblast apoptosis in 3-week-old male and female mice significantly enhanced vertebral bone formation while increasing osteoblast precursors. A similar treatment regimen to stimulate osterix+ cell apoptosis had no impact on bone volume or density. The vertebral bone accrual following stimulation of OCN+ osteoblast apoptosis did not translate in improved mechanical strength due to disruption of the lacunocanalicular network. The observed bone phenotype was not influenced by changes in osteoclasts but was associated with stimulation of macrophage efferocytosis and vasculature formation. Phenotyping of efferocytic macrophages revealed a unique transcriptomic signature and expression of factors including VEGFA. To examine whether macrophages participated in the osteoblast precursor increase following osteoblast apoptosis, macrophage depletion models were employed. Depletion of macrophages via clodronate-liposomes and the CD169-diphtheria toxin receptor mouse model resulted in marked reduction in leptin receptor+ and osterix+ osteoblast precursors. Collectively, this work demonstrates the significance of osteoblast turnover via apoptosis and efferocytosis in postnatal bone formation. Importantly, it exposes the potential of targeting this mechanism to promote bone anabolism in the clinical setting.
摘要：
细胞凋亡对于组织稳态和器官发育至关重要。在骨头里，凋亡被认为是成骨细胞的主要命运，然而，这一过程的相关性仍未得到充分探索。使用我们的小鼠模型与诱导型半胱天冬酶9，启动内在凋亡的酶，我们在一定比例的成熟骨钙蛋白（OCN）成骨细胞中触发了凋亡，并研究了其对出生后骨发育的影响。成骨细胞凋亡刺激骨巨噬细胞的有效细胞增殖。在3周龄的雄性和雌性小鼠中，对OCN成骨细胞凋亡进行五周的刺激可显着增强椎骨骨形成，同时增加成骨细胞前体。刺激osterix细胞凋亡的类似治疗方案对骨体积或密度没有影响。由于腔隙网络的破坏，刺激OCN成骨细胞凋亡后的椎骨积累并未转化为机械强度的改善。观察到的骨表型不受破骨细胞变化的影响，但与刺激巨噬细胞红细胞增多和血管形成有关。脱细胞巨噬细胞的表型分析揭示了独特的转录组特征和包括VEGFA在内的因子的表达。为了检查巨噬细胞是否参与成骨细胞凋亡后成骨细胞前体的增加，采用巨噬细胞耗竭模型。通过clodronate-脂质体和CD169-白喉毒素受体小鼠模型消耗巨噬细胞，导致瘦素受体和osterix成骨细胞前体的显着减少。总的来说，这项工作证明了通过细胞凋亡和细胞增生进行的成骨细胞更新在出生后骨形成中的意义。重要的是,它揭示了在临床环境中靶向该机制促进骨合成代谢的潜力。
