LET-767参与胰岛素信号通路调控脂代谢的分子机理研究

Insulin/IGF-1 signaling pathway plays critical roles regulating energy metabolism, and is associated with many metabolic diseases such as diabetes, insulin resistance, etc. It is highly conserved among model organisms from C. elegans, Drosophila, to mammals. However, it still remains unknown whether new factors involve in this pathway to regulate lipid metabolism. Previously, we performed comparative lipid droplet proteomics between the insulin receptor daf-2 mutant and the wild type N2, and found that the expression of LET-767, a homologue of mammalian 17β-HSD3/12, was upregulated in daf-2 mutant worms compared with N2 worms. Furthermore, we discovered that LET-767 inhibits the nuclear translocation of FOXO/DAF-16, a well-known downstream target of insulin/IGF-1 signals. Here, we proposed four research directions to characterize the role of LET-767 in the regulation of lipid metabolism via insulin/IGF-1 signaling pathway. First of all, how LET-767 regulates the nuclear translocation of FOXO/DAF-16. Secondly, what are the mechanisms of FOXO/DAF-16 regulating the transcription expression of ATGL-1. Thirdly, how LET-767 affects the biosynthesis of fatty acids and lipid accumulation. Lastly, what are the functions and mechanisms of LET-767 LD localization? In summary, this proposal will allow us to understand the roles of LET-767 in insulin/IGF-1 signaling pathway to regulate lipid metabolism, as well as new insights into the pathogenesis of obesity and diabetes.

胰岛素/IGF-1信号通路是重要的调控能量代谢的信号通路，与糖尿病、胰岛素抵抗等多种代谢性疾病有关。该信号通路非常保守，从低等的模式生物秀丽线虫、果蝇、到哺乳动物如老鼠、人中都存在。前期工作中，我们利用秀丽线虫，通过脂滴蛋白质组学，发现线虫中17β-HSD3/12同源蛋白LET-767受胰岛素信号负调控，抑制FOXO/DAF-16入核调控脂代谢，这是我们新发现的一条负调控信号通路。在此基础上，我们提出以下四个方面研究内容：1）LET-767调控FOXO/DAF-16入核的分子机制；2）FOXO/DAF-16转录调控ATGL表达的分子机制；3）LET-767调控脂肪酸合成的机制；4）LET-767在脂滴上的功能及机制。这些研究不仅加深我们对胰岛素信号通路调控脂代谢机制，了解肥胖症和糖尿病的发病机理，而且新发掘到的一些影响脂代谢的基因可能作为未来治疗靶标。

脂滴（lipid droplets，LDs）是一种从原核生物细菌到真核生物酵母、哺乳动物中都非常保守的细胞器。胰岛素/IGF-1信号通路是重要的调控能量代谢的信号通路，与糖尿病、胰岛素抵抗等多种代谢性疾病有关。该信号通路非常保守，从低等的模式生物秀丽线虫、果蝇、到哺乳动物如老鼠、人中都存在。. 本研究提取纯化野生型和daf-2突变体线虫的脂滴，分析二者脂滴蛋白的差异，共找到167个脂滴相关蛋白发生显著性变化。通过RNAi筛选，找到类固醇脱氢酶LET-767，抑制let-767能够降低daf-2突变体脂肪含量，缩短daf-2突变体寿命。LET-767主要表达在内质网和脂滴上，在daf-2突变体中，LET-767不仅总蛋白表达量增加，并且在脂滴上表达增加。抑制let-767，甘油三酯水解酶1（adipose triglyceride lipase 1，ATGL-1）的表达量增加，脂肪分解加速，从而降低daf-2和age-1的脂肪含量。ATGL-1过表达能够恢复daf-2的突变体寿命至野生型水平。let-767调节ATGL-1表达依赖于转录因子DAF-16/FoxO；同时let-767 干扰促进DAF-16转录因子的入核。这些研究结果表明，LET-767是一个新的脂滴蛋白，功能上LET-767拮抗ATGL-1平衡线虫脂代谢稳态和寿命。