Du Yu, Gao Xiang, Chen Jianqiang, Chen Xinxin, Liu Hang, He Wenge, Liu Lu, Jiang Yue, He Baicheng, Deng Zhongliang, Liang Chao, Guo Fengjin
Department of Orthopedics, The Second Affiliated Hospital of Chongqing Medical University, Chongqing Medical University, Chongqing, China.
State Key Laboratory of Ultrasound in Medicine and Engineering, School of Basic Medical Sciences, The Second Affiliated Hospital of Chongqing Medical University, Chongqing Medical University, Chongqing, China.
J Orthop Translat. 2024 Nov 25;50:14-29. doi: 10.1016/j.jot.2024.10.004. eCollection 2025 Jan.
O-GlcNAc transferase (OGT) is responsible for attaching O-linked N-acetylglucosamine (O-GlcNAc) to proteins, regulating diverse cellular processes ranging from transcription and translation to signaling and metabolism. This study focuses on the role and mechanisms of OGT in osteogenesis.
We found that OGT is downregulated in osteoporosis by bioinformatics analysis, determined its role in osteogenic differentiation by using OGT inhibitors (or OGA inhibitors) as well as conditional knockout OGT mice in and in , and explored and specific mechanisms by quantitative proteomic analysis and RNA-seq, qRT-PCR, western blotting, immunofluorescence, H&E, ALP, ARS, Masson staining, IHC, micro CT, etc.
we revealed that OGT positively influenced osteogenesis and osteoblast differentiation in as well as ovariectomy (OVX) mice in . Consistently, mice with conditionally depleted OGT exhibited a reduction in bone mass, while O-GlcNAcylation enhancer could partially recover bone mass in ovariectomy (OVX) mice. Mechanistically, quantitative proteomic analysis and high-throughput RNAseq further reveals that HDAC5 is one of the endogenous O-GlcNAcylation substrates, and O-GlcNAcylation of HDAC5 on Thr934 promotes its translocation to lysosomes and subsequent degradation, thus, elevating the O-GlcNAcylation level of HDAC5 leads to its cytoplasmic cleavage, consequently diminished its nuclear entry and enhanced DNA transcription. The OGT-mediated O-GlcNAcylation of HDAC5 modulates the balance between its cytoplasmic proteolysis and nuclear entry, thereby impacting the Notch signaling pathway and DNA epigenetic modifications then playing a role in osteogenesis.
OGT is a regulator that promotes osteoblast differentiation and bone regeneration. Additionally, it highlights the critical function of HDAC5 O-GlcNAcylation in controlling epigenetics. This study offers fresh perspectives on osteogenesis and O-GlcNAcylation, proposing that the OGT-mediated O-GlcNAcylation of HDAC5 could be a promising target for osteoporosis treatment.
On one side, OGT might potentially be used as a new biomarker for clinical diagnosis of osteoporosis (OP) in the future. On the other side, small molecule inhibitors of HDAC5, a glycosylation substrate of OGT, or OGT agonists such as silymarin, could all potentially serve as therapeutic targets for the prevention or treatment of OP in the future.
O-连接的N-乙酰葡糖胺转移酶（OGT）负责将O-连接的N-乙酰葡糖胺（O-GlcNAc）连接到蛋白质上，调节从转录、翻译到信号传导和代谢等多种细胞过程。本研究聚焦于OGT在骨生成中的作用及机制。
我们通过生物信息学分析发现骨质疏松症中OGT表达下调，利用OGT抑制剂（或OGA抑制剂）以及条件性敲除OGT小鼠在体内外确定其在成骨分化中的作用，并通过定量蛋白质组学分析、RNA测序、qRT-PCR、蛋白质免疫印迹、免疫荧光、苏木精-伊红染色、碱性磷酸酶染色、茜素红染色、Masson染色、免疫组化、显微CT等方法探索其具体机制。
我们揭示了OGT在体外以及去卵巢（OVX）小鼠体内对骨生成和成骨细胞分化具有正向影响。一致地，条件性缺失OGT的小鼠骨量减少，而O-GlcNAcylation增强剂可部分恢复去卵巢（OVX）小鼠的骨量。机制上，定量蛋白质组学分析和高通量RNA测序进一步揭示组蛋白去乙酰化酶5（HDAC5）是内源性O-GlcNAcylation底物之一，HDAC5第934位苏氨酸上的O-GlcNAcylation促进其向溶酶体转位并随后降解，因此，提高HDAC5的O-GlcNAcylation水平导致其在细胞质中裂解，从而减少其进入细胞核并增强DNA转录。OGT介导的HDAC5的O-GlcNAcylation调节其细胞质蛋白水解和进入细胞核之间的平衡，从而影响Notch信号通路和DNA表观遗传修饰，进而在骨生成中发挥作用。
OGT是促进成骨细胞分化和骨再生的调节因子。此外，它突出了HDAC5的O-GlcNAcylation在控制表观遗传学中的关键作用。本研究为骨生成和O-GlcNAcylation提供了新的视角，提出OGT介导的HDAC5的O-GlcNAcylation可能是骨质疏松症治疗的一个有前景的靶点。
一方面，OGT未来可能潜在地用作骨质疏松症（OP）临床诊断的新生物标志物。另一方面，HDAC5（OGT的糖基化底物）的小分子抑制剂或水飞蓟素等OGT激动剂未来都可能潜在地用作预防或治疗OP的治疗靶点。
