RAP1 protects from obesity, diabetes and metabolic syndrome through its extra telomeric role regulating gene expression (young mouse white fat)

RAP1 is one of the components of shelterin, the capping complex at chromosome ends or telomeres. Unlike other shelterins, however, RAP1 is not essential for preventing telomere fusions. RAP1 also binds along chromosome arms, where it is proposed to regulate gene expression. To investigate the non-telomeric roles of RAP1 in vivo, we generated a RAP1 whole-body knock-out mouse model. Unexpectedly, these mice presented an early onset of obesity, which was particularly severe in females and was aggravated under a high-fat diet. Rap1-deficient mice showed abnormal accumulation of fat in abdominal depots and developed signs of type II diabetes and metabolic syndrome, including hepatic steatosis and high fasting plasma levels of insulin, glucose, cholesterol, and alanine transaminase. Gene expression analyses of the liver and visceral white fat from Rap1-deficient mice before the onset of obesity indicated deregulation of key metabolic transcriptional programs including fatty acid metabolism, PPARa signalling and glucose metabolism. Transcriptome and Western blotting analyses in liver further identified Ppara and Pgc1a and their target genes as the key metabolic pathways affected by Rap1 deletion. Finally, we show here that RAP1 binds to Ppara and Pgc1a loci and modulates their transcription. These findings underscore an unprecedented role for a telomere-binding protein in the regulation of metabolism. 2 condition experiment: WT versus Rap1 knockout. Tissue: white gonadal fat. 4 biological replicates per genotype. Mice were 10 weeks old.RAP1是端粒帽复合物（shelterin）的组分之一，该复合物覆盖于染色体末端即端粒之上。然而与其他端粒帽复合物蛋白不同，RAP1并非预防端粒融合所必需的组分。RAP1还可结合于染色体臂区域，据推测其可调控基因表达。为探究RAP1在体内的非端粒依赖性功能，我们构建了全身性RAP1敲除小鼠模型。出乎意料的是，该模型小鼠过早出现肥胖表型，该表型在雌性小鼠中尤为显著，且在高脂饮食喂养下会进一步加重。RAP1敲除小鼠表现出腹部脂肪库的异常蓄积，并出现Ⅱ型糖尿病与代谢综合征的相关体征，包括肝脂肪变性、空腹血浆胰岛素、葡萄糖、胆固醇及丙氨酸转氨酶水平升高。在肥胖表型出现前，对RAP1敲除小鼠的肝脏及内脏白色脂肪组织进行基因表达分析，结果显示关键代谢转录程序出现失调，涵盖脂肪酸代谢、过氧化物酶体增殖物激活受体α（PPARα）信号通路与葡萄糖代谢等过程。对肝脏组织开展的转录组学与蛋白质印迹（Western blotting）分析进一步证实，Ppara、Pgc1a及其靶基因所在的关键代谢通路是RAP1敲除所影响的核心通路。最后，本研究证实RAP1可结合至Ppara与Pgc1a的基因座并调控其转录。上述发现首次揭示了端粒结合蛋白在代谢调控中的全新功能。本实验设置两组对照：野生型（WT）与RAP1敲除型。检测组织为性腺白色脂肪组织。每种基因型设置4个生物学重复。实验小鼠均为10周龄。