Atg13介导线粒体自噬新途径调控RA滑膜成纤维细胞凋亡的机制

The rate of complete remission of rheumatoid arthritis (RA) with current available therapy is less effective. Resistance to apoptosis of rheumatoid arthritis synovial fibroblasts (RASFs) attributes to RA progression and low response to treatment. RASFs can survive in an environment enriched with oxygen radicals and cytokines even mitochondrial dysfunction emerging, suggesting a survival mechanism is involved. In our previous study, with methotrexate (MTX) treatment, an association of autophagy activation and resistance to apoptosis had been displayed in RASFs. Autophagy-related protein 13 (Atg13), a critical component in initiation complex of mitophagy, displayed phosphorylated modification during RASFs activation, when screening all those autophagy related proteins. In addition, the levels of Atg13 and p38 MAPK, upstream regulator of Atg13, declined with MTX therapy in RA synovial tissue. Based on literature and ours' findings, we hypothesized that resistance to apoptosis of RASFs was regulated by mitophagy via p38 MAPK-Atg13 phosphorylation. In current study, we sought to identify the relationship between Atg13-induced mitophagy and resistance to apoptosis in RASFs. Firstly, the combination of p38 MAPK and Atg13 will be confirmed by coimmunoprecipitation, the exact site(s) of Atg13 phosphorylation will be explored in RASFs by in vivo kinase assay, in vitro kinase assay and site-directed mutation analysis. Secondly, we sought to reveal mitophagy activation and apoptosis suppression via p38 MAPK-Atg13 phosphorylation in RASFs and NOD/SCID mouse model. In addition, the effect of Atg13 phosphorylation site(s) polymorphism as well as efficacy of MTX treatment will be explored. With this study, the critical function of Atg13 in mitophagy and resistance to apoptosis in RASFs can be revealed, which will enrich the mechanism of resistance to apoptosis of RASFs.

类风湿关节炎滑膜成纤维细胞（RASFs）凋亡抵抗是疾病持续进展及治疗应答不佳的中心环节。RASFs生存于富含氧自由基的内环境中，存在线粒体损伤但因某种机制清除损伤线粒体抑制凋亡。我们前期发现甲氨蝶呤（MTX）作用下的自噬增强与RASFs凋亡抑制相关，线粒体自噬关键蛋白Atg13被磷酸化修饰，Atg13及上游p38 MAPK在MTX治疗后下调。我们推测MTX作用下p38 MAPK下调Atg13磷酸化介导线粒体自噬抑制RASFs凋亡。本课题拟：①在分子和细胞水平明确RASFs中p38 MAPK磷酸化Atg13，筛选磷酸化特异性位点；②在细胞、动物模型中，以CRISPR/Cas9对RASFs进行靶向编辑，验证p38 MAPK-Atg13磷酸化介导线粒体自噬抑制RASFs凋亡；③RA患者中验证Atg13特异性磷酸化位点多态性预测RA疗效。丰富RASFs凋亡抵抗的机制，有助于对治疗应答不佳的理解。

类风湿性关节炎（RA）是常见的慢性自身免疫炎症性疾病，以多发破坏性的关节炎为主要特征，现有改变病情的抗风湿药物（DMARDs）可在一定程度上减缓关节破坏，但仍有40%的患者对治疗无应答。RA治疗无应答的机制仍不明确，滑膜成纤维样细胞（RA-FLSs）的活化调控增强是近期关注的机制之一。RA-FLSs可产生大量炎性因子，并具有一定的肿瘤细胞特征，表现为对药物不敏感、异常增殖、凋亡抵抗。改善RA-FLSs凋亡抵抗可能提高治疗应答。但目前RA-FLSs凋亡抵抗的机制仍不清楚，据此，本课题探讨RA中最重要的炎症因子IL-1β与RA-FLSs凋亡的关系；明确IL-1β影响RA-FLSs凋亡抵抗的分子机制；在RA患者中讨论炎症相关因子HMGB1的基因多态性与传统DMARDs治疗应答的关系；为难治性RA新治疗靶点的探索，RA个体化治疗提供数据。. 通过本项目的实施发现RA滑膜中高表达IL-1β，细胞学试验提示随着IL-β浓度升高，RA-FLSs凋亡下降，自噬上调；IL-1β通过AKT/mTOR/Atg13通路调节自噬，下调Atg13后自噬抑制，凋亡增加；IL-1β与HMGB1表达正相关，HMGB1基因rs2249825位点的G基因型与传统DMARDs治疗无应答相关。. 在本课题支持下确定了IL-1β通过AKT/mTOR/Atg13通路调节自噬影响RA-FLSs的凋亡，阐明了RA中炎症与滑膜增生的关系，丰富了RA-FLSs凋亡抵抗的机制。为RA新治疗靶点的研究提供数据。此外，炎症相关的HMGB1基因rs2249825位点的与传统DMARDs治疗无应答相关，为RA个体化治疗提供数据。