Department of Biological Sciences, National University of Singapore, Singapore 117543.
Development. 2012 Jan;139(1):141-50. doi: 10.1242/dev.071035. Epub 2011 Nov 17.
Osteoclasts are macrophage-related bone resorbing cells of hematopoietic origin. Factors that regulate osteoclastogenesis are of great interest for investigating the pathology and treatment of bone diseases such as osteoporosis. In mammals, receptor activator of NF-κB ligand (Rankl) is a regulator of osteoclast formation and activation: its misexpression causes osteoclast stimulation and osteoporotic bone loss. Here, we report an osteoporotic phenotype that is induced by overexpression of Rankl in the medaka model. We generated transgenic medaka lines that express GFP under control of the cathepsin K promoter in osteoclasts starting at 12 days post-fertilization (dpf), or Rankl together with CFP under control of a bi-directional heat-shock promoter. Using long-term confocal time-lapse imaging of double and triple transgenic larvae, we monitored in vivo formation and activation of osteoclasts, as well as their interaction with osteoblasts. Upon Rankl induction, GFP-positive osteoclasts are first observed in the intervertebral regions and then quickly migrate to the surface of mineralized neural and haemal arches, as well as to the centra of the vertebral bodies. These osteoclasts are TRAP (tartrate-resistant acid phosphatase) and cathepsin K positive, mononuclear and highly mobile with dynamically extending protrusions. They are exclusively found in tight contact with mineralized matrix. Rankl-induced osteoclast formation resulted in severe degradation of the mineralized matrix in vertebral bodies and arches. In conclusion, our in vivo imaging approach confirms a conserved role of Rankl in osteoclastogenesis in teleost fish and provides new insight into the cellular interactions during bone resorption in an animal model that is useful for genetic and chemical screening.
破骨细胞是来源于造血系统的巨噬细胞相关的骨吸收细胞。调节破骨细胞生成的因素对于研究骨质疏松症等骨骼疾病的病理学和治疗方法具有重要意义。在哺乳动物中，核因子-κB 受体激活剂配体（Rankl）是破骨细胞形成和激活的调节剂：其异常表达会导致破骨细胞刺激和骨质疏松性骨丢失。在这里，我们报告了一种在斑马鱼模型中由 Rankl 过表达引起的骨质疏松表型。我们生成了转基因斑马鱼系，这些鱼在受精后 12 天（dpf）开始，GFP 在组织蛋白酶 K 启动子的控制下在破骨细胞中表达，或者 Rankl 与 CFP 在双向热休克启动子的控制下表达。使用双转基因和三转基因幼虫的长期共聚焦延时成像，我们监测了体内破骨细胞的形成和激活，以及它们与成骨细胞的相互作用。在 Rankl 诱导后，首先在椎骨区域观察到 GFP 阳性的破骨细胞，然后这些破骨细胞迅速迁移到矿化的神经和血弓的表面，以及椎体的中心。这些破骨细胞 TRAP（耐酒石酸酸性磷酸酶）和组织蛋白酶 K 阳性，单核，高度移动，具有动态延伸的突起。它们仅与矿化基质紧密接触。Rankl 诱导的破骨细胞形成导致椎体和弓状骨的矿化基质严重降解。总之，我们的体内成像方法证实了 Rankl 在硬骨鱼类破骨细胞生成中的保守作用，并为骨骼吸收过程中的细胞相互作用提供了新的见解，这种动物模型可用于遗传和化学筛选。
