探討神經醯胺對CaMKII相關訊息傳遞路徑和學習記憶的影響

Abstract

神經醯胺是一種由鞘胺醇鹼骨架和不同碳鏈長度的脂肪酸組成的神經脂質，在許多生理過程中扮演非常重要的角色，例如調控訊號傳遞路徑。在過去的研究中，我們發現在野生型小鼠離乳後給予神經醯胺能增進成年後的記憶行為，利用初級培養的神經細胞也發現神經醯胺可增加CaMKII的磷酸化，CaMKII是一個與學習與記憶相關的蛋白質。本研究即探討神經醯胺在細胞層級的作用機制，以及利用阿茲海默症模式小鼠J20做為動物模式，探討在其離乳後給予神經醯胺是否可改善記憶缺失。結果顯示初級培養神經細胞給予神經醯胺刺激後，會使CaMKII磷酸化，且活化轉錄因子CREB以及活化Erk。而以目前的研究參數進行的實驗則發現神經醯胺並不會使神經細胞中鈣離子濃度產生變化。另外在更下游與表觀遺傳相關修飾的研究則發現給予神經醯胺可以使H3K4甲基化成H3K4 me3，並提高Egr1的表現量。將神經醯胺以皮下注射給予阿茲海默症模式小鼠J20，對小鼠的一些基本參數如體重、葡萄糖耐受性、發炎指標GOT、GPT以及組織切片觀察，發現給予神經醯胺並不影響上述生理參數。在動物行為方面，神經醯胺並不改善小鼠的焦慮行為，但可觀察到透過莫氏水迷津所檢測之短期空間記憶有顯著的進步。綜合以上，神經醯胺能使神經細胞中和記憶相關的蛋白質活化，且改善阿茲海默症模式小鼠J20的短期空間記憶，表示早期給予神經醯胺可能有助於學習與記憶的能力。

Ceramides are composed of sphingosine base and fatty acids with different carbon chain lengths. It plays important roles in a variety of physiological processes including regulation of signal transduction pathways. In the previous study, we demonstrated that ceramides given at early lives of mice can improve learning and memory behavior in adulthood. We also found that these effects correlated with the increase of phosphorylation of CaMKII, a signal molecule has been shown to be related to learning and memory. In this study, we intend to explore the mechanism of ceramides on signaling in primary neurons. We also test if ceramides given after weaning can alleviate the memory impairment in Alzheimer’s disease animal model J20 mice. The results show that phosphorylation of CaMKII T286 were upregulated after ceramides treatment in primary glutamatergic neurons. The ceramides also increase the phosphorylation of CREB and Erk as well as the methylation of H3K4 and the expression of Egr1. In the animal experiments, the body weight, glucose tolerance test, GOT (glutamic oxaloacetic transaminase), GPT (glutamic pyruvic transaminase), and tissue histology were not different in the J20 mice versus wild type after any treatment. In the animal behavior test, it was found that ceramides have no effect on the J20 mice in terms of open field test and elevated plus maze. However, ceramides given after wean on J20 mice could significantly improve the memory behavior in the Morris water maze test. Taken together, ceramides can increase CaMKII/CREB and Erk pathway and this might be relevant to memory related function in neurons. Moreover, ceramides given at early stage of J20 mice could improve their memory in adulthood. Therefore, ceramides given at early lifetime might have beneficial effect on short-term memory.