Department of Biomedical Engineering, Fu Foundation School of Engineering and Applied Science, Columbia University, New York, New York, USA.
Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Cells Tissues Organs. 2024;213(3):235-244. doi: 10.1159/000531098. Epub 2023 May 22.
The primary cilium is a solitary, sensory organelle with many roles in bone development, maintenance, and function. In the osteogenic cell lineage, including skeletal stem cells, osteoblasts, and osteocytes, the primary cilium plays a vital role in the regulation of bone formation, and this has made it a promising pharmaceutical target to maintain bone health. While the role of the primary cilium in the osteogenic cell lineage has been increasingly characterized, little is known about the potential impact of targeting the cilium in relation to osteoclasts, a hematopoietic cell responsible for bone resorption. The objective of this study was to determine whether osteoclasts have a primary cilium and to investigate whether or not the primary cilium of macrophages, osteoclast precursors, serves a functional role in osteoclast formation. Using immunocytochemistry, we showed the macrophages have a primary cilium, while osteoclasts lack this organelle. Furthermore, we increased macrophage primary cilia incidence and length using fenoldopam mesylate and found that cells undergoing such treatment showed a significant decrease in the expression of osteoclast markers tartrate-resistant acid phosphatase, cathepsin K, and c-Fos, as well as decreased osteoclast formation. This work is the first to show that macrophage primary cilia resorption may be a necessary step for osteoclast differentiation. Since primary cilia and preosteoclasts are responsive to fluid flow, we applied fluid flow at magnitudes present in the bone marrow to differentiating cells and found that osteoclastic gene expression by macrophages was not affected by fluid flow mechanical stimulation, suggesting that the role of the primary cilium in osteoclastogenesis is not a mechanosensory one. The primary cilium has been suggested to play a role in bone formation, and our findings indicate that it may also present a means to regulate bone resorption, presenting a dual benefit of developing ciliary-targeted pharmaceuticals for bone disease.
初级纤毛是一种单一的感觉细胞器，在骨骼发育、维持和功能中具有多种作用。在成骨细胞谱系中，包括骨骼干细胞、成骨细胞和骨细胞，初级纤毛在调节骨形成中起着至关重要的作用，这使其成为维持骨骼健康的有前途的药物靶点。虽然初级纤毛在成骨细胞谱系中的作用已经越来越被描述，但对于靶向纤毛与破骨细胞（一种负责骨吸收的造血细胞）的潜在影响知之甚少。本研究的目的是确定破骨细胞是否具有初级纤毛，并研究巨噬细胞（破骨细胞前体）的初级纤毛是否在破骨细胞形成中发挥功能作用。通过免疫细胞化学，我们表明巨噬细胞具有初级纤毛，而破骨细胞缺乏该细胞器。此外，我们使用甲磺酸酚妥拉明增加巨噬细胞初级纤毛的发生率和长度，发现接受这种处理的细胞中破骨细胞标志物抗酒石酸酸性磷酸酶、组织蛋白酶 K 和 c-Fos 的表达显著降低，并且破骨细胞形成减少。这项工作首次表明，巨噬细胞初级纤毛吸收可能是破骨细胞分化的必要步骤。由于初级纤毛和前成骨细胞对流体流动有反应，我们在分化细胞中施加了骨髓中存在的大小的流体流动，并发现巨噬细胞的破骨细胞基因表达不受流体流动机械刺激的影响，这表明初级纤毛在破骨细胞发生中的作用不是机械感觉作用。初级纤毛被认为在骨形成中发挥作用，我们的发现表明它也可能提供一种调节骨吸收的方法，为开发针对纤毛的骨疾病药物提供了双重益处。
