Department of Oral and Maxillofacial Surgery, School & Hospital of Stomatology, Tongji University, Shanghai, China.
Shanghai Engineering Research Center of Tooth Restoration and Regeneration, Shanghai, China.
J Cell Physiol. 2019 Nov;234(11):21182-21192. doi: 10.1002/jcp.28721. Epub 2019 Apr 29.
Osteocytes, entrapped within the mineralized bone matrix, has been found to have numerous functions such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. Due to a specialized morphology and surrounding structure, osteocytes are more tolerant to hypoxia during osteoporosis, fracture, osteoarthritis, and orthodontic-orthognathic combination therapy. Hypoxia-inducible factor-1α (HIF-1α) is one of the master regulators of hypoxia reactions, playing an important role in bone modeling, remodeling, and homeostasis. This study aimed to investigate the pivotal functional role of HIF-1α in osteocytes initiating of bone remodeling under hypoxia. In the present study, the osteoclasts formation induced by RAW264.7 was significantly promoted in conditioned media (CM) from osteocytic MLO-Y4 exposed to hypoxia in vitro. Therefore, hypoxic MLO-Y4 cells simulated by 100 μmol/L CoCl or 2% O stably expressed HIF-1α proteins and upregulated the expression of receptor activator of nuclear factor-κB ligand (RANKL) at both the messenger RNA (mRNA) and protein level. Furthermore, with the Knockdown of HIF-1α, the expression of RANKL mRNA and protein decreased after transient transfection. In addition, the phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription (STAT3) was also correlated with HIF-1α and RANKL levels under hypoxia. Then AG490, a JAK2 inhibitor, inhibited p-JAK2, p-STAT3 and RANKL expression. It was possible that AG490 disturbed the contact of HIF-1α and RANKL by JAK2/STAT3 pathway, influencing osteoclastogenesis. Our findings suggested that HIF-1α promoted the expression of RANKL by activating JAK2/STAT3 pathway in MLO-Y4 cells, and enhanced osteocyte-mediated osteoclastic differentiation in vitro.
骨细胞被困在矿化的骨基质中，被发现具有许多功能，例如通过调节破骨细胞和成骨细胞的活性来充当骨重塑的协调者，并且还作为内分泌细胞发挥作用。由于其特殊的形态和周围结构，骨细胞在骨质疏松症、骨折、骨关节炎和正畸正颌联合治疗期间对缺氧更耐受。缺氧诱导因子-1α（HIF-1α）是缺氧反应的主要调节因子之一，在骨建模、重塑和动态平衡中发挥重要作用。本研究旨在探讨 HIF-1α 在骨细胞启动缺氧下骨重塑中的关键功能作用。在本研究中，体外缺氧条件下，暴露于缺氧的 MLO-Y4 成骨细胞条件培养基（CM）显著促进 RAW264.7 诱导的破骨细胞形成。因此，用 100μmol/L CoCl 或 2% O 模拟的缺氧 MLO-Y4 细胞稳定表达 HIF-1α 蛋白，并在上、下 mRNA 和蛋白水平上调核因子-κB 配体受体激活剂（RANKL）的表达。此外，随着 HIF-1α 的敲低，瞬时转染后 RANKL mRNA 和蛋白的表达减少。此外，在缺氧下，Janus 激酶 2（JAK2）和信号转导和转录激活因子 3（STAT3）的磷酸化也与 HIF-1α 和 RANKL 水平相关。然后，JAK2 抑制剂 AG490 抑制了 p-JAK2、p-STAT3 和 RANKL 的表达。AG490 可能通过 JAK2/STAT3 通路干扰 HIF-1α 和 RANKL 的接触，影响破骨细胞生成。我们的研究结果表明，HIF-1α 通过激活 MLO-Y4 细胞中的 JAK2/STAT3 通路促进 RANKL 的表达，并增强体外骨细胞介导的破骨细胞分化。
