FADD负性调控细胞自噬：脂质导致肾小管损伤的新机制

Obesity and dyslipidemia are the major risk factors for the development of chronic kidney disease (CKD), but the mechanism remains unclear. As a key adaptor protein transmitting apoptotic signals mediated by the death receptors, FADD also functions in many non-apoptotic pathological and physiological processes. Data from our preliminary study and online database revealed that the expression of FADD was significantly up-regulated in kidneys of CKD patients, obese animals, and renal tubular epithelial cell (RTEC) treated with the oxidized lipid of oxLDL. Furthermore, we found that overexpression of FADD inhibited the autophagy of RTECs and worsened cell apoptosis. In contrast, silencing FADD promoted cell apoptosis in line with enhanced autophagy in RTECs, suggesting that FADD was involved in lipid-induced tubular injury possibly through regulation of autophagy. Further preliminary study and some known concept indicated that FADD could directly regulate autophagy gene ATG5. Additionally, preliminary data and bioinformatics analysis suggested that transcription factor Oct-1 could be a key regulator of FADD in lipid-induced renal tubular injury. Therefore, we hypothesized that Oct-1-regulated FADD might mediate lipid-induced renal tubular injury via suppressing ATG5 and autophagy. In the present proposal, employing the models of animal, cell and molecule, we will fully investigate the functions of FADD in lipid-induced kidney injury, providing new targets for the treatment of lipid disorder-related kidney injury.

肥胖及脂代谢紊乱是CKD的重要危险因素，但脂质导致肾损伤的机制仍不清楚。FADD在死亡受体介导的细胞凋亡中十分重要，同时也具有众多非凋亡的生物学功能。前期工作发现在脂质处理的肾小管上皮细胞（RTEC）及肥胖小鼠和CKD患者肾组织，FADD表达上调。过表达FADD抑制了RTEC自噬并加剧了脂质诱导的细胞凋亡；而沉默FADD则上调了ATG5，提示FADD可能通过抑制ATG5介导的自噬参与了脂质引起的RTEC损伤。此外，生物信息学分析显示转录因子Oct-1与FADD启动子区有四个结合位点，脂质处理也增加了Oct-1表达，而过表达Oct-1则上调了FADD。因而推测：脂质可能通过Oct-1上调FADD表达，后者通过下调ATG5而抑制自噬，加剧了肾小管细胞损伤，促进了CKD的发生。本课题将在动物、细胞和分子水平探讨FADD在脂质引起的肾小管损伤中的作用及机制，为临床治疗脂代谢相关的肾损伤提供新靶点。

急性肾损伤、糖尿病、肥胖、脂代谢紊乱、高尿酸血症等代谢因素在慢性肾脏病发生和进展中的作用被越来越多的研究所证实。FADD即Fas相关死亡结构域蛋白，在Fas等死亡相关受体介导的细胞凋亡过程中发挥关键的信号转导作用，是细胞凋亡途径中关键的接头蛋白，在肾脏中的表达主要位于肾小管，但FADD与肾脏疾病的关系尚无深入的研究报道。本研究探索了FADD在肾脏病发生过程中的作用和相关机制。首先我们通过构建脂质诱导的肾小管上皮细胞损伤模型，研究了FADD在脂质诱导肾小管上皮细胞中的作用和机制。我们的实验结果显示，氧化低密度脂蛋白处理肾小管上皮细胞，导致FADD表达上调，抑制了细胞自噬促进了细胞凋亡，下调FADD的表达能够改善氧化低密度脂蛋白诱导的细胞凋亡，但是敲除FADD则会加剧细胞凋亡。其次，我们研究了FADD在顺铂诱导的急性肾损伤中的作用和机制，通过给小鼠注射20mg/kg顺铂成功构建小鼠AKI模型，实验结果显示，FADD在顺铂诱导的小鼠AKI肾组织以及小鼠肾小管上皮细胞中表达均显著上调。小鼠体内过表达FADD则显著抑制了顺铂诱导的AKI，体外培养的肾小管上皮细胞中过表达FADD也显著抑制顺铂诱导的细胞凋亡，而敲除FADD之后却加剧了顺铂诱导的细胞凋亡。进一步的，转录组学结果显示，FADD敲除加剧了细胞坏死的发生，免疫共沉淀实验也显示，FADD缺失上调了顺铂诱导的坏死复合物的形成，而坏死抑制剂以及过表达FADD都能显著抑制细胞坏死的发生，我们的实验结果显示FADD可能作为一种细胞内天然的细胞坏死抑制剂。. 此外，我们也进行了AKI防治相关药物的探索研究，我们的研究发现，缺氧诱导因子脯氨酰羟化酶活性抑制剂FG-4592改善顺铂诱导AKI，具备临床治疗AKI的潜能。