CaMK Ⅱ/HDAC4途径参与雷帕霉素对学习记忆的调节作用

CaMK Ⅱ/HDAC4 Pathway Involved in the Regulation of Rapamycin on Learning and Memory

雷帕霉素(rapamycin,Rap)在多种生物中有抗衰老和增强学习记忆的作用。HDAC4是Ⅱα类组蛋白去乙酰化酶(classⅡαhistone deacetylases),参与神经细胞的记忆形成及其他的功能。然而,二者在功能上的联系及雷帕霉素在学习记忆中的作用机制尚未见报告。本研究证明,HDAC4作为雷帕霉素信号途径的下游底物,雷帕霉素可通过依赖钙-钙调蛋白的蛋白激酶Ⅱ(Ca MKⅡ)/HDAC4途径调控学习记忆。小鼠水迷宫实验显示,雷帕霉素能有效改善D-半乳糖(D-galactose,Dgal)所致的学习记忆障碍,增强D-半乳糖诱导衰老小鼠和普通小鼠的学习记忆能力。已知Ca MKⅡ可修饰HDAC4的246位丝氨酸磷酸化。蛋白质印迹检测显示,雷帕霉素作用后的小脑海马细胞HDAC4(Ser246)和Ca MKⅡ(Thr286)磷酸化水平降低,而总蛋白水平无明显变化。D-半乳糖诱导衰老小鼠脑海马细胞HDAC4(Ser246)和Ca MKⅡ(Thr286)磷酸化水平较对照组无明显变化。本实验结果结合以往的研究揭示,雷帕霉素通过抑制其靶蛋白(mammalian target of rapamycin,m TOR)而减少Ca MKⅡ磷酸化水平,低磷酸化的Ca MKⅡ失去活性不能催化HDAC4磷酸化,HDAC4的磷酸化水平影响其定位和功能。本研究证明,Ca MKⅡ/HDAC4为雷帕霉素调控学习记忆的一个可能途径,而HDAC4调控学习记忆的机制还需要进一步研究。

Rapamycin has been shown to increase the lifespan of organisms and promote learning and memory processes. HDAC4 is a class Ⅱ α histone deacetylase involved in the establishment of memory and other functions of neuronal cells. However,the role of HDAC4 in association with the mechanism of rapamycin on learning and memory processes remained unknown. Mice water maze experiment showed that rapamycin rescued the aging-related learning and memory impairment caused by D-galactose. We examined the phosphorylation of Ca MKⅡ on threonine 286 and HDAC4 phosphorylation at serine 246 in hippocampal neuronal cells by Western blotting. Decreased phosphorylation was found with rapamycin treatments,but no significant changes in D-galactose-induced aging mice. As rapamycin could inhibit the m TOR（ mammalian target of rapamycin） kinase for Ca MKⅡphosphorylation,the subsequent reduction of HDAC4 phosphorylaiton was hypothesized to affect its localization and function. This study suggested thatHDAC4 cold be a downstream substrate of rapamycin signaling. Rapamycin could regulate learning and memory through calcium / calmodulin-dependent protein kinases（ Ca MKⅡ） / HDAC4 pathway.