棕色脂肪外泌体诱导白色脂肪棕色化的关键机制及仿生学研究

白色脂肪棕色化是肥胖相关代谢性疾病防治的新希望。探讨脂肪棕色化的内源性机制，有望为安全高效诱导白色脂肪棕色化提供线索。课题组前期研究发现寒冷暴露后棕色脂肪来源外泌体能够诱导白色脂肪棕色化；进一步机制研究提示同源盒基因Lhx8是棕色脂肪功能维系的重要基因，寒冷暴露可能通过RNA结合蛋白HuR将Lhx8 mRNA选择性装载入外泌体，并传递给白色脂肪，进而诱导棕色化。本项目拟结合外泌体及基因干预手段，通过细胞和小鼠模型明确棕色脂肪外泌体及其装载的Lhx8在寒冷刺激诱导白色脂肪棕色化中的重要作用；在此基础上，结合免疫共沉淀及荧光素酶报告系统等方法，阐明寒冷刺激下RNA结合蛋白HuR选择性加载Lhx8入外泌体，以及Lhx8在受体细胞转录激活线粒体合成关键基因进而诱导脂肪棕色化的分子机制；最后创建能够负载Lhx8 mRNA的工程化外泌体，并探讨其诱导脂肪棕色化的效能，期望为肥胖治疗提供新的思路和策略。

White adipose tissue and brown adipose tissue function differently in metabolism. Browning of the white fat is recognized as the novel target for the therapy of obesity and obesity associated metabolic syndrome. Exploring the endogenous mechanisms how browning of white adipose tissue occurs, would certainly shed light on developing strategies for browning induction and thus obesity therapy. Previously, we have found that cold exposure stimulate the exosome secretion, which in turn induces browning of the white fat. Preliminary mechanism study revealed that the homeobox gene Lhx8 is essential for the maintenance of brown fat. Bioinformatics analysis and preliminary study suggest that the exosomal Lhx8 might promote mitochondria biogenesis through transcriptional regulation of PGC1α and TFAM. Moreover, RNA binding protein HuR might be involved in the sorting of Lhx8 into exosomes under cold stimulus. In the proposed project, we would like to: (1) Confirm the contribution of brown fat derived exosomes and the exosomal Lhx8 in the browning of white adipose tissue during cold exposure by cold exposure animal model and cell culture experiments. (2) Decode the mechanism whether and how HuR involved in the sorting of Lhx8 into the exosomes by HuR knockdown/overexpression, RNA-IP, and reporter assay. (3) Reveal the mechanism how Lhx8 promotes mitochondria biogenesis by focusing on the transcriptional regulation of PGC1α and TFAM. We will identify the cis-elements for Lhx8 on the promoters of PGC1α and TFAM by ChIP and luciferase reporter assay. (4) Engineer exosomes to deliver Lhx8 efficiently to the adipose tissue and observe the effects of the engineered exosomes in white fat browning and obesity treatment by injection of the exosomes in the obese mice. The proposed project would possibly find a novel mechanism how browning of white adipose tissue occurs and establish a promising strategy to induce brown fat tissue by engineered exosomes.