PGC-1α的特异泛肽化酶 —— RNF34对肝脏糖代谢的调控作用

The transcriptional coactivator PGC-1α is a master regulator of energy metabolism. Previously we have revealed that RNF34 is a bona fide E3 ubiquitin ligase for PGC-1α and negatively regulates brown fat cell metabolism, but whether RNF34 plays a role as an E3 ubiquitin ligase for PGC1-α in liver and the effects of RNF34 on glucose metabolism are still largely unknown. By cell culture studies, we have demonstrated that ectopically over-expressing of wild type RNF34 suppresses PGC-1α target gene and glucose production in liver cells. In vivo, over-expressing RNF34 in mice liver by tail vein injection of the adenovirus causes hypoglycemia upon fasting. Which is very similar with the phenotype of PGC-1α liver-specific knockdown mice, indicating that RNF34 affects glucose metabolism in liver in vivo. We would next investigate the role of endogenous RNF34 in glucose metabolism by liver specific RNF34 knockdown mice and further investigate the signaling pathway that regulates PGC-1α protein degradation by RNF34 in liver. Moreover, we would exam whether diabetes, the pathological conditions that induced by abnormal PGC-1α activity would affect RNF34 expression in liver in mice, which would reveal a physiological relevance of this E3 ligase in glucose metabolism. Our results will clarify the physiological and pathological role of RNF34 in glucose metabolism in liver, which might provide a new therapeutic approach for treatment and prognosis of diabetes.

转录辅激活因子PGC-1α是能量代谢的重要调控因子。此前，我们已证明RNF34是PGC-1α的特异泛肽化酶，通过促进PGC-1α蛋白的降解，负性调节褐色脂肪细胞代谢。但是RNF34是否通过促进PGC-1α降解来影响肝脏糖代谢，还很不清楚。我们发现在肝细胞培养中过表达RNF34降低PGC-1α的靶基因表达和葡萄糖生成；通过尾静脉注射腺病毒在小鼠肝脏中过表达RNF34，使小鼠空腹血糖水平降低。该表现型与肝脏中PGC-1α knockdown小鼠模型极为相似。我们下一步将通过RNF34的肝脏特异knockdown小鼠来进一步研究内源性RNF34在小鼠体内肝脏糖代谢中的作用，并探讨在肝脏中调节RNF34介导的PGC-1α蛋白降解的信号通路。本研究有望揭示RNF34在肝脏糖代谢中的生理和病理作用，这有助于更加深入理解在肝脏中调控PGC-1α功能的分子网络，有望为糖尿病的治疗开辟新的途径。

转录辅激活因子PGC-1α是能量代谢及线粒体生成的重要调控因子。此前，我们已在哺乳细胞水平上证明RNF34是PGC-1α的特异泛肽化酶，通过促进PGC-1α蛋白的降解，负性调节褐色脂肪细胞代谢。但是RNF34在各组织中的生理意义还很不清楚。本研究通过生化实验证明果蝇RNF34也是果蝇PGC-1的泛肽化酶并促进果蝇PGC-1蛋白的降解。肌肉组织特异knockdown dRNF34与对照组相比,果蝇肌肉组织线粒体生成增加，果蝇负趋地性爬行运动速度较对照组加快，运动耐力增加。胰岛素敏感性增强。在高脂饮食状态下肌肉组织特异knockdown dRNF34的果蝇其腹部甘油三酯的含量降低，在肌肉组织中knockdown dRNF34的同时knockdown dPGC-1，使在肌肉组织特异knockdown dRNF34的表现型消失。说明肌肉组织特异knockdown dRNF34的表现型是由dPGC-1所介导的。本研究表明在肌肉组织中抑制RNF34的表达有可能成为治疗肌少症及衰老相关代谢性疾病的新的药物靶点。.另外, 本项目还对神经系统疾病病理机制行了探索。TDP-43和FUS是ALS的两个重要致病基因。本研究发现TDP-43敲除果蝇寿命缺陷可被表达细胞膜骨架关键基因所挽救。提示细胞膜骨架在ALS中起关键作用。糖基化位点对TDP-43的功能起着重要作用。这些研究将揭示一种崭新的ALS病理机制，为ALS诊治提供新思路。.此外,本项目还尝试用独创的方法快速构建首个UAS-ORF转基因果蝇文库。利用该文库进行果蝇挽救筛选等不同筛选，将大大促进包括致病基因在内的基因功能研究，这将有助于快速找到治疗疾病的靶基因。