羊栖菜岩藻聚糖硫酸酯靶向激活Nrf2-Keap1-ARE信号通路改善胰岛素抵抗的结构基础及机制研究

Sargassum fusiforme (Harv.) Setchel, a kind of brown algae widely distributed in China, Korea, and Japan, has been applied as a therapeutic for thousands of years. It is well known as a longevity vegetable in Eastern Asia with important economic value and medicinal application, because it is a rich source of health-promoting products. It contains a significant proportion of fucoidan, which has been demonstrated to possess a number of biological activities, including antitumor and antioxidant activities, immunomodulatory activities. SFPS, the fucoidan from Sargassum fusiforme, has the effects of alleviating insulin resistance and relieving glucose and lipid metabolism disorders in type 2 diabetes, but its structural basis and structure-activity relationship are not clear yet. .Accumulated evidence shows that SFPS can activate Nrf2-Keap1-ARE signaling pathway, promote the expression of antioxidant enzymes and phase Ⅱ detoxification enzymes against oxidative stress injury, and then prolongs the lifespan of fruit fly and mice, suggesting that the SFPS may alleviate insulin resistance and relieve type 2 diabetes via Nrf2-Keap1-ARE signaling pathway. In this study, SFPS will be degraded into oligosaccharides and screen active fraction with interfering activity against obesity-induced IR by bioactivity-guide isolation. We will further analyze the fine structure to clarify the structure-activity relationship, and then investigate the intrinsic correlation mechanism that how the Nrf2-Keap1-ARE signal axis to maintain the steady state of oxidative stress in vivo and alleviating the progress of insulin resistance and type 2 diabetes. The present study not only explores the structure-activity relationship and the mechanism of SFPS in alleviating type 2 diabetes, but also provides new strategy of screening for novel carbohydrate lead compounds and the development of functional products for the prevention and treatment of type 2 diabetes, as well as high value-added development of Sargassum fusiforme.

羊栖菜是近岸养殖的大型经济褐藻，被誉为“长寿菜”，岩藻聚糖硫酸酯SFPS是其重要活性成分。SFPS具有改善胰岛素抵和缓解2型糖尿病糖脂代谢紊乱的作用，但其结构基础和构效关系尚不清晰。课题组前期研究表明，SFPS通过激活Nrf2-Keap1-ARE信号通路抵抗氧化应激损伤，延长果蝇和小鼠的寿命，提示SFPS可能通过Nrf2-Keap1-ARE信号通路发挥改善胰岛素抵和治疗2型糖尿病的作用。本研究将对SFPS进行可控性降解，靶向筛选具有干预胰岛素抵抗的活性寡糖片段，通过精细结构的解析和化学修饰探讨构效关系，深入揭示其调控Nrf2-Keap1-ARE信号通路维护体内氧化应激稳态与干预胰岛素抵抗、缓解2型糖尿病作用的内在关联机制。本研究不仅对SFPS改善2型糖尿病的构效关系和作用机制进行科学探究，也为新型糖类先导化合物的筛选和防治2型糖尿病的功能产品研发，以及羊栖菜资源的高附加值开发提供科学依据。

羊栖菜（Sargassum fusiforme）是浙江省特色大型经济褐藻，被誉为“长寿菜”，温州市洞头区是我国羊栖菜的主产区。羊栖菜富含多种活性物质，其中岩藻聚糖硫酸酯（S. fusiforme fucoidan, SFF）是其重要活性成分之一。已有大量研究报道SFF具有减肥降脂、改善胰岛素抵和缓解2型糖尿病糖脂代谢紊乱的良好功效，但其精细的作用机制尚不清晰。本研究建立了经济高效的羊栖菜岩藻聚糖硫酸酯SFF提取工艺，并优化可控性降解工艺；解析羊栖菜岩藻聚糖硫酸酯理化性质及精细结构表征。同时发现SFF可以通过重塑高脂膳食（HFD）扰乱的肠道菌群，显着提高牛磺熊去氧胆酸（TUDCA，一种结合胆汁酸）水平并抑制结肠中的法尼醇X受体（FXR）信号传导。SFF给药降低了HFD小鼠血清和结肠组织中的神经酰胺水平，并降低SPT和CerS基因的表达，这些基因编码对由 FXR 信号调节的神经酰胺的生物合成至关重要的酶。Pearson相关性分析表明，TUDCA 水平与肠道细菌梭菌呈正相关，这在伪无菌小鼠中得到了进一步验证。 综上所述，研究结果表明，SFF 通过重塑肠道菌群来增加 TUDCA 水平，而天然 FXR 拮抗剂 TUDCA 抑制 FXR/SHP 信号通路，减少结肠来源的神经酰胺生物合成，从而改善饮食诱导肥胖的胰岛素抵抗 (DIO) 小鼠。 此外，TUDCA通过胆汁酸的肝肠循环，重吸收回到肝脏，在肝脏中通过拮抗KEAP1与Nrf2的结合，从而释放Nrf2入核，激活Nrf2信号通路，通过上调多种抗氧化酶的表达，重塑体内ROS与抗氧化水平的动态平衡，提高周围组织靶细胞对胰岛素的敏感性，从而干预肥胖引起的胰岛素抵抗和2型糖尿病的发生、发展。