Characterization of the role of O-GlcNAcylation in osteoclastogenesis

在生理条件下，通过破骨细胞诱导的骨吸收和成骨细胞触发的骨形成之间的平衡来维持骨量。然而，在炎性关节炎如类风湿性关节炎（RA）中，破骨细胞分化的增加使这种平衡发生扭曲，导致进行性骨丢失。O-GlcNAc化是一种翻译后修饰，其中单个O-连接的β-D-N-乙酰葡糖胺（O-GlcNAc）残基与靶蛋白的丝氨酸或苏氨酸残基连接。虽然O-GlcNAc化是最常见的蛋白质修饰之一，但其在骨稳态中的作用尚未得到系统研究。在我们的初步结果中，我们证明了O-GlcNAc化的动态变化是破骨细胞生成所必需的。在破骨细胞生成的早期阶段，增加的O-GlcNAc化促进破骨细胞分化，而其下调是破骨细胞成熟所必需的。肿瘤坏死因子α（TNFα）促进O-GlcNAc化的动态调节，以促进炎性关节炎中的破骨细胞生成。O-GlcNAc转移酶（OGT）或O-GlcNAc酶（OGA）的靶向药物或遗传抑制分别在分化的早期阶段和后期成熟期间阻止破骨细胞分化，并改善实验性关节炎中的局部和全身骨丢失。本课题旨在进一步研究O-GlcNAc化在破骨细胞生成中的作用。具体而言，我们计划表征O-GlcNAc化调节破骨细胞生成的分子机制，研究O-GlcNAc化在循环破骨细胞前体中作为生物标志物的效用，研究O-GlcNAc化在非炎性骨丢失中对破骨细胞生成的作用，并探索O-GlcNAc化在高血糖诱导的破骨细胞生成加速中的作用。

Bone mass is maintained by the balance between osteoclast-induced bone resorption and osteo-blast-triggered bone formation in physiological conditions. In inflammatory arthritis such as rheumatoid arthritis (RA), however, increased osteoclast differentiation skews this balance resulting in progressive bone loss. O-GlcNAcylation is a posttranslational modification with attachment of a single O-linked β-D-N-acetylglucosamine (O-GlcNAc) residue to serine or threonine residues of target proteins. Although O-GlcNAcylation is one of the most common protein modifications, its role in bone homeostasis has not been systematically investigated. In our preliminary results, we demonstrate that dynamic changes in O-GlcNAcylation are required for osteoclastogenesis. Increased O-GlcNAcylation promotes osteoclast differentiation during early stages of osteoclastogenesis, whereas its downregulation is required for osteoclast maturation. Tumor necrosis factor α (TNFα) fosters the dynamic regulation of O-GlcNAcylation to promote osteoclastogenesis in inflammatory arthritis. Targeted pharmaceutical or genetic inhibition of O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA) arrests osteoclast differentiation during early stages of differentiation and during later maturation, respectively, and ameliorates local and systemic bone loss in experimental arthritis. With the current project application, we aim to investigate further the role of O-GlcNAcylation in osteoclastogenesis. Specifically, we plan to characterize the molecular mechanisms by which O-GlcNAcylation regulates osteoclastogenesis, to study the utility of O-GlcNAcylation in circulating osteoclast precursors as biomarkers, to investigate the role of O-GlcNAcylation on osteoclastogenesis in non-inflammatory bone loss and to explore the role of O-GlcNAcylation in hyperglycemia-induced acceleration of osteoclastogenesis.