β谷固醇替代法调节淀粉样前体蛋白代谢的作用及机制

Inhibition of Aβ generation through modulation of APP metabolism is an important therapeutic strategy for AD. It has been demonstrated that the majority of Aβ in the brain is found within cholesterol-enriched regions of membranes known as lipid rafts. Depletion of membrane cholesterol reduces the production of Aβ, but disrupts lipid rafts. β sitosterol, a major component of lipid raft in plant cells, have the structure very similar to that of cholesterol. Our previous studies have shown that β sitosterol inhibits Aβ generation induced by increase in cholesterol in lipid raft, suggesting that β sitosterol can influence the role of cholesterol in APP metabolism. Therefore, we suggest that replacement of membrane cholesterol by β sitosterol may serve as a novel approach to modulate APP metabolism. Preliminary experiments showed that membrane cholesterol could be replaced by β sitosterol, by using 2 hydroxypropyl β cyclodextrin as a carrier. Using APP transgenic cell lines and animal models, this study will test the effect of membrane-incoporated β sitosterol on APP metabolism. To determine the mechanism underlying the effect of membrane-incoporated β sitosterol, this study will also test the activities of APP metabolism-associated enzymes, APP trafficking as well as the distribution of APP and APP metabolism-associated secretase between lipid raft-enriched and non-raft membranes. The results will aid in developing novel therapeutic strategies for AD.

通过调节淀粉样前体蛋白（APP）代谢抑制其代谢产物β淀粉样多肽（Aβ）的生成是治疗Alzheimer病（AD）的一个重要策略。已证实，细胞膜上富含胆固醇的脂筏是Aβ的主要产地。去除脂筏胆固醇可抑制Aβ生成，但破坏了细胞膜的脂筏结构。植物细胞膜脂筏的主要脂质成分β谷固醇与胆固醇结构极为相似。前期研究发现，β谷固醇可抑制脂筏胆固醇增高所诱导的Aβ生成, 提示β谷固醇可影响胆固醇在APP代谢中的作用。由此，我们提出以β谷固醇替代细胞膜胆固醇来调节APP代谢的新方法。预实验显示：以2羟丙基β环糊精为载体可成功将β谷固醇导入细胞膜，并将胆固醇提取出来。本项目拟采用APP转基因的细胞和动物模型来检测β谷固醇替代法对APP代谢的调节作用；并从APP代谢酶活性、APP胞内转运及APP和APP代谢酶在细胞膜上的分布等方面探索β谷固醇替代法调节APP代谢的作用途径。研究结果将为AD的防治开辟新的思路和途径。

通过调节淀粉样前体蛋白（APP）代谢抑制其代谢产物β淀粉样多肽（Aβ）的生成是治疗Alzheimer病（AD）的一个重要策略。本研究采用Western blot、免疫组化、高效液相色谱、水迷宫等手段、小鼠海马神经元细胞系HT22细胞和淀粉样前体蛋白/早老素双转基因动物模型（APP/PS1小鼠）对β谷固醇（BS）替代法调节APP代谢的作用和机制进行了研究，首次发现：（1）以BS替代HT22细胞的细胞膜胆固醇可促进α分泌酶介导的APP代谢，抑制β分泌酶介导的APP代谢，但并不影响细胞膜的稳定性。（2）BS替代法调节APP代谢的机制与细胞膜BS促进APP从细胞膜脂筏向非筏区的转移有关。（3）BS和富含BS的食物橄榄油均可减少APP/PS1鼠脑内β淀粉样蛋白（Aβ）的沉淀，改善APP/PS1鼠的认知功能。（4）BS和富含BS的食物橄榄油改善APP/PS1鼠认知功能的机制与BS在脑组织细胞膜的聚集以及细胞膜BS对APP代谢的调节作用有关。上述结果证实以BS替代细胞膜胆固醇具有调节APP代谢，减少Aβ生成以及改善认知功能的作用，为AD的防治提供了新思路和新途径。