Division of Growth and Development, Section of Orthodontics, School of Dentistry, University of California, Los Angeles, Los Angeles, CA, USA.
The Affiliated Hospital of Stomatology, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, PR China.
J Bone Miner Res. 2018 Oct;33(10):1813-1825. doi: 10.1002/jbmr.3524. Epub 2018 Jun 29.
Contactin-associated protein-like 4 (Cntnap4) is a member of the neurexin superfamily of transmembrane molecules that have critical functions in neuronal cell communication. Cntnap4 knockout mice display decreased presynaptic gamma-aminobutyric acid (GABA) and increased dopamine release that is associated with severe, highly penetrant, repetitive, and perseverative movements commonly found in human autism spectrum disorder patients. However, no known function of Cntnap4 has been revealed besides the nervous system. Meanwhile, secretory protein neural EGFL-like 1 (Nell-1) is known to exert potent osteogenic effects in multiple small and large animal models without the off-target effects commonly found with bone morphogenetic protein 2. In this study, while searching for a Nell-1-specific cell surface receptor during osteogenesis, we identified and validated a ligand/receptor-like interaction between Nell-1 and Cntnap4 by demonstrating: 1) Nell-1 and Cntnap4 colocalization on the surface of osteogenic-committed cells; 2) high-affinity interaction between Nell-1 and Cntnap4; 3) abrogation of Nell-1-responsive Wnt and MAPK signaling transduction, as well as osteogenic effects, via Cntnap4 knockdown; and 4) replication of calvarial cleidocranial dysplasias-like defects observed in Nell-1-deficient mice in Wnt1-Cre-mediated Cntnap4-knockout transgenic mice. In aggregate, these findings indicate that Cntnap4 plays a critical role in Nell-1-responsive osteogenesis. Further, this is the first functional annotation for Cntnap4 in the musculoskeletal system. Intriguingly, Nell-1 and Cntnap4 also colocalize on the surface of human hippocampal interneurons, implicating Nell-1 as a potential novel ligand for Cntnap4 in the nervous system. This unexpected characterization of the ligand/receptor-like interaction between Nell-1 and Cntnap4 indicates a novel biological functional axis for Nell-1 and Cntnap4 in osteogenesis and, potentially, in neural development and function. © 2018 American Society for Bone and Mineral Research.
神经连接蛋白相关蛋白样 4（Cntnap4）是神经连接蛋白超家族的成员，该超家族的跨膜分子在神经元细胞通讯中具有关键作用。Cntnap4 敲除小鼠表现出 GABA 前突触减少和多巴胺释放增加，这与人类自闭症谱系障碍患者中常见的严重、高度穿透性、重复性和持续运动有关。然而，除了神经系统之外，目前还没有发现 Cntnap4 的已知功能。与此同时，已知分泌蛋白神经 EGFL 样蛋白 1（Nell-1）在多个小动物和大动物模型中具有强大的成骨作用，而没有常见的骨形态发生蛋白 2 的脱靶效应。在这项研究中，当我们在成骨过程中寻找 Nell-1 特异性细胞表面受体时，我们通过证明 Nell-1 和 Cntnap4 之间存在配体/受体样相互作用，鉴定并验证了这一点：1）Nell-1 和 Cntnap4 在成骨细胞表面的共定位；2）Nell-1 和 Cntnap4 之间的高亲和力相互作用；3）通过 Cntnap4 敲低，阻断 Nell-1 反应性 Wnt 和 MAPK 信号转导以及成骨作用；4）在 Wnt1-Cre 介导的 Cntnap4 敲除转基因小鼠中复制 Nell-1 缺陷小鼠中观察到的颅盖 Cleidocranial 发育不良样缺陷。总的来说，这些发现表明 Cntnap4 在 Nell-1 反应性成骨中起关键作用。此外，这是 Cntnap4 在肌肉骨骼系统中的第一个功能注释。有趣的是，Nell-1 和 Cntnap4 也在人类海马中间神经元的表面共定位，这表明 Nell-1 可能是 Cntnap4 在神经系统中的潜在新型配体。Nell-1 和 Cntnap4 之间的这种意想不到的配体/受体样相互作用的特征表明，Nell-1 和 Cntnap4 在成骨过程中具有新的生物学功能轴，并且可能在神经发育和功能中具有新的生物学功能轴。
