Department of Internal Medicine III and Institute for Clinical Immunology, University of Erlangen-Nuremberg, Erlangen, Germany.
Ann Rheum Dis. 2013 May;72(5):761-8. doi: 10.1136/annrheumdis-2012-201671. Epub 2012 Sep 12.
Autophagy is a homeostatic process to recycle dispensable and damaged cell organelles. Dysregulation of autophagic pathways has recently been implicated in the pathogenesis of various diseases. Here, we investigated the role of autophagy during joint destruction in arthritis.
Autophagy in osteoclasts was analysed in vitro and ex vivo by transmission electron microscopy, Western blotting and immunohistochemistry for Beclin1 and Atg7. Small molecule inhibitors, LysMCre-mediated knockout of Atg7 and lentiviral overexpression of Beclin1 were used to modulate autophagy in vitro and in vivo. Osteoclast differentiation markers were quantified by real-time PCR. The extent of bone and cartilage destruction was analysed in human tumour necrosis factor α transgenic (hTNFα tg) mice after adoptive transfer with myeloid specific Atg7-deficient bone marrow.
Autophagy was activated in osteoclasts of human rheumatoid arthritis (RA) showing increased expression of Beclin1 and Atg7. TNFα potently induced the expression of autophagy-related genes and activated autophagy in vitro and in vivo. Activation of autophagy by overexpression of Beclin1-induced osteoclastogenesis and enhanced the resorptive capacity of cultured osteoclasts, whereas pharmacologic or genetic inactivation of autophagy prevented osteoclast differentiation. Arthritic hTNFα tg mice transplanted with Atg7(fl/fl)×LysMCre(+) bone marrow cells (BMC) showed reduced numbers of osteoclasts and were protected from TNFα-induced bone erosion, proteoglycan loss and chondrocyte death.
These findings demonstrate that autophagy is activated in RA in a TNFα-dependent manner and regulates osteoclast differentiation and bone resorption. We thus provide evidence for a central role of autophagy in joint destruction in RA.
自噬是一种回收不必要和受损细胞器的稳态过程。自噬途径的失调最近与各种疾病的发病机制有关。在这里，我们研究了自噬在关节炎关节破坏中的作用。
通过透射电子显微镜、Western blot 和 Beclin1 和 Atg7 的免疫组织化学分析体外和体外破骨细胞中的自噬。使用小分子抑制剂、LysM Cre 介导的 Atg7 敲除和 Beclin1 的慢病毒过表达来调节体外和体内的自噬。通过实时 PCR 定量破骨细胞分化标志物。在接受髓样特异性 Atg7 缺陷骨髓过继转移后，分析人肿瘤坏死因子α转基因（hTNFα tg）小鼠中的骨和软骨破坏程度。
类风湿关节炎（RA）患者的破骨细胞中自噬被激活，Beclin1 和 Atg7 的表达增加。TNFα 强烈诱导自噬相关基因的表达，并在体外和体内激活自噬。通过过表达 Beclin1 激活自噬诱导破骨细胞生成，并增强培养破骨细胞的吸收能力，而药理学或遗传失活自噬可防止破骨细胞分化。接受 Atg7(fl/fl)×LysMCre(+)骨髓细胞（BMC）移植的关节炎 hTNFα tg 小鼠中破骨细胞数量减少，并免受 TNFα 诱导的骨侵蚀、蛋白聚糖丢失和软骨细胞死亡的保护。
这些发现表明，自噬在 RA 中以 TNFα 依赖性方式被激活，并调节破骨细胞分化和骨吸收。因此，我们为自噬在 RA 关节破坏中的中心作用提供了证据。
