Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China.
FASEB J. 2023 Sep;37(9):e23147. doi: 10.1096/fj.202300977R.
Long-term spaceflight can result in bone loss and osteoblast dysfunction. Frizzled-9 (Fzd9) is a Wnt receptor of the frizzled family that is vital for osteoblast differentiation and bone formation. In the present study, we elucidated whether Fzd9 plays a role in osteoblast dysfunction induced by simulated microgravity (SMG). After 1-7 days of SMG, osteogenic markers such as alkaline phosphatase (ALP), osteopontin (OPN), and Runt-related transcription factor 2 (RUNX2) were decreased, accompanied by a decrease in Fzd9 expression. Furthermore, Fzd9 expression decreased in the rat femur after 3 weeks of hindlimb unloading. In contrast, Fzd9 overexpression counteracted the decrease in ALP, OPN, and RUNX2 induced by SMG in osteoblasts. Moreover, SMG regulated phosphorylated glycogen synthase kinase-3β (pGSK3β) and β-catenin expression or sublocalization. However, Fzd9 overexpression did not affect pGSK3β and β-catenin expression or sublocalization induced by SMG. In addition, Fzd9 overexpression regulated protein kinase B also known as Akt and extracellular signal-regulated kinase (ERK) phosphorylation and induced F-actin polymerization to form the actin cap, press the nuclei, and increase nuclear pore size, thereby promoting the nuclear translocation of Yes-associated protein (YAP). Our study findings provide mechanistic insights into the role of Fzd9 in triggering actin polymerization and activating YAP to rescue SMG-induced osteoblast dysfunction and suggest that Fzd9 is a potential target to restore osteoblast function in individuals with bone diseases and after spaceflight.
长期的太空飞行会导致骨质流失和成骨细胞功能障碍。卷曲蛋白 9（Fzd9）是卷曲家族的 Wnt 受体，对成骨细胞分化和骨形成至关重要。在本研究中，我们阐明了 Fzd9 是否在模拟微重力（SMG）诱导的成骨细胞功能障碍中发挥作用。在 SMG 作用 1-7 天后，碱性磷酸酶（ALP）、骨桥蛋白（OPN）和 runt 相关转录因子 2（RUNX2）等成骨标志物的表达降低，同时 Fzd9 的表达也降低。此外，在大鼠股骨 3 周后进行后肢去负荷，Fzd9 的表达减少。相比之下，Fzd9 的过表达可逆转 SMG 诱导的成骨细胞中 ALP、OPN 和 RUNX2 的减少。此外，SMG 调节磷酸化糖原合酶激酶 3β（pGSK3β）和β-连环蛋白的表达或亚细胞定位。然而，Fzd9 的过表达不影响 SMG 诱导的 pGSK3β 和β-连环蛋白的表达或亚细胞定位。此外，Fzd9 的过表达调节蛋白激酶 B 也称为 Akt 和细胞外信号调节激酶（ERK）的磷酸化，并诱导 F-肌动蛋白聚合形成肌动蛋白帽，挤压细胞核，并增加核孔大小，从而促进 Yes 相关蛋白（YAP）的核转位。我们的研究结果为 Fzd9 在触发肌动蛋白聚合和激活 YAP 以挽救 SMG 诱导的成骨细胞功能障碍中的作用提供了机制见解，并表明 Fzd9 是恢复患有骨病和太空飞行后个体成骨细胞功能的潜在靶点。
