The apoptosis of mature osteocytes is the main factor causing damage to the microstructure of cortical bone in glucocorticoid-induced osteoporosis (GIOP). Our previous research found damaged areas and empty osteocytes lacunae in the tibial cortical bone of GIOP mice. However, the specific mechanism has not been clarified. Recently, a study showed that the quality of the cortical bone significantly increased by knocking out Notum, a gene encoding α/β hydrolase. However, it is not clear whether Notum affects cortical bone remodeling by participating in glucocorticoids (GCs)-induced apoptosis of osteocytes. The present study aimed to explore the correlation between Notum, osteocytes apoptosis, and cortical bone quality in GIOP. Prednisolone acetate was intragastrically administered to mice for two weeks. Histochemical staining was applied to evaluate changes in GIOP and Notum expression. Osteocytes were stimulated with prednisolone, and cell viability was assessed via CCK8. Hoechst 33342/PI staining, flow cytometry, RT-PCR, and western blot were used to detect osteocytes apoptosis, siRNA transfection efficiency, and expressions of pathway related factors. The results showed that the number of empty osteocytes lacunae increased in GIOP mice. TUNEL-stained apoptotic osteocytes and Notum immuno-positive osteocytes were also observed. Furthermore, prednisolone was found to promote Notum expression and osteocytes apoptosis in vitro. Knocking down Notum via siRNA partially restored osteocytes apoptosis and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/glycogen synthase kinase-3β (GSK3β)/β-catenin pathway. These findings showed GCs-induced osteocytes apoptosis by promoting Notum expression and inhibiting PI3K/AKT/GSK3β/β-catenin pathway. Thus, Notum might be a potential therapeutic target for the treatment of GIOP.

成熟骨细胞的凋亡是导致糖皮质激素性骨质疏松症（GIOP）皮质骨微结构受损的主要因素。我们之前的研究在 GIOP 小鼠的胫骨皮质骨中发现了受损区域和空洞的骨细胞。但具体机制尚未明确。最近，一项研究表明，通过敲除 Notum（一种编码 α/β 水解酶的基因）可以显着提高皮质骨的质量。然而，尚不清楚 Notum 是否通过参与糖皮质激素 (GCs) 诱导的骨细胞凋亡来影响皮质骨重塑。本研究旨在探讨 GIOP 中 Notum、骨细胞凋亡和皮质骨质量之间的相关性。将醋酸泼尼松龙灌胃给予小鼠两周。应用组织化学染色来评估 GIOP 和 Notum 表达的变化。用泼尼松龙刺激骨细胞，并通过 CCK8 评估细胞活力。Hoechst 33342/PI染色、流式细胞仪、RT-PCR和western blot检测骨细胞凋亡、siRNA转染效率和通路相关因子的表达。结果表明，GIOP小鼠的空骨细胞腔隙数量增加。还观察到 TUNEL 染色的凋亡性骨细胞和 Notum 免疫阳性骨细胞。此外，发现泼尼松龙在体外促进 Notum 表达和骨细胞凋亡。通过 siRNA 敲低 Notum 可部分恢复骨细胞凋亡和磷酸肌醇 3-激酶 (PI3K)/蛋白激酶 B (AKT)/糖原合酶激酶-3β (GSK3β)/β-连环蛋白通路。这些发现表明 GCs 通过促进 Notum 表达和抑制 PI3K/AKT/GSK3β/β-catenin 通路诱导骨细胞凋亡。因此，Notum 可能是治疗 GIOP 的潜在治疗靶点。