阿尔茨海默病中P38MAPK信号通路的研究进展.doc

阿尔茨海默病中p38MAPK信号通路的研究进展【摘要】随着人类步入老龄化社会, 阿尔茨海默病(Alzheimers disease, AD)的发病率不断增加, 但其发病机制仍不明确。近年来研究发现p38MAPK信号通路既参与了AD中A沉积所致的小胶质细胞和星形胶质细胞的活化，又与Tau蛋白的异常磷酸化密切相关。本文将对以上内容进行综述。【关键词】p38MAPK信号通路；阿尔茨海默病；-淀粉样肽；tau蛋白Progress of p38MAPK signal way in Alzheimers DiseaseWang Di; Zhou Yan (clinical medicine of seven years in Grade 09,Capital Medical University ; Basic Medical College, Capital Medical University)【ABSTRACT】In modern aging society, the incidence of Alzheimers disease (AD) has been increasing significantly. However, the pathogenesis of AD has not ever been elucidated. Recent study reported that the p38MAPK signal way is significantly related to both the activation of microglia as well as astrocytes and phosphorylation of Tau protein. Here we provide a review on the mechanism of p38MAPK talked above.【KEY WORDS】p38MAPK; Alzheimers disease; Amyloid-beta peptide; Tau protein 阿尔茨海默病(Alzheimers Disease, AD)是一种常见于老年人的中枢神经系统退行性变疾病,以进行性认知功能障碍、精神行为异常及生活能力减退等为主要表现,是痴呆病中最常见的类型。其特征性病理学改变为脑神经细胞外出现淀粉样蛋白(Amyloid-beta peptide,A)聚集形成的老年斑,脑神经细胞内tau蛋白异常聚集形成的神经原纤维缠结,脑皮质细胞有不同程度的减少以及星形胶质细胞的增生及肥大, 并且脑内有大量的A的沉积。其中A肽可引起炎症反应而致神经元丧失和认知功能障碍Tyler A. Kokjohn, Gregory D. Van Vickle, Chera L. Maarouf, et al. Chemical characterization of pro-inflammatory amyloid-beta peptides in human atherosclerotic lesions and plateletsJ. Biochimica et Biophysica Acta, 2011, 1812: 15081514.。AD患者尸检发现脑内p38活性升高Swatton JE, Sellers LA, Faull RL, et al. Increased MAP kinase activity in Alzheimers and Down syndrome but not in schizophrenia human brainJEur J Neurosci,2004,19: 2711-2719 ，提示AD的病理变化与p38 MAPK信号通路密切相关。阐明AD中的信号转导过程有助于为其治疗提供新的思路。本文将对p38 MAPK信号通路及其在AD中的作用作一综述。1 p38MAPK信号通路1.1 p38MAPK信号通路的组成p38MAPK是哺乳动物应激与炎症激活的丝裂原活化蛋白激酶（MAPK）家族的重要组成成分。p38 MAPK通过磷酸化三级酶促级联反应把细胞外信号向细胞内传递，其中包括要三个关键激酶: MAPK、MAPKK、MAPKKK。细胞受到刺激后首先使MAPKKK激活，转而激活MAPKK，再由MAPKK对MAPK双位点磷酸化。虽然分子量为38KD的p38MAPK有4种同源异构体，分别为p38(1/2)、p38(1/2)、p38、p38,但所有的亚型都是在Thr180和Tyr182双重磷酸化 Ashwell JD. The many paths to p38 mitogen-activated protein kinase activation in the immune systemJ . Nat Rev Immunol, 2006,6:532-540.。1.2 p38MAPK信号通路的功能p38 MAPK信号通路与其它信号通路共同介导细胞应激诱发的基因表达和酶活性的改变。p38 MAPK通路参与神经细胞的存活、分化和发育过程，但多数情况下，p38MAPK被认为主要在促炎途径和促凋亡途径中行使功能。并且这两个功能与AD的发病密切相关。1.2.1 炎性反应在体内和体外，p38既可被多种促炎细胞因子活化，启动后续的细胞炎性反应，还参与介导其它胞外信号引起的炎性细胞因子或炎性产物的表达和释放。促炎的p38路径在细胞受到应激的早期发挥保护作用，但其进一步活化致使炎性细胞因子持续高水平表达，最终导致组织细胞损伤和功能障碍。Crittenden等体外实验发现 Crittenden PL, Filipov NMManganeseinduced potentiation of in vitro proinflammatory cytokine production by activated microglial cells is associated with persistent activation of p38 MAPKJ. Toxicol In Vitro,2008,22:18-27，锰通过激活小胶质细胞导致致炎细胞因子增多，这与p38MAPK持续性激活有关。其中，p38在炎性反应中起关键作用，成为治疗的新靶点Schindler JF, Monahan JB, Smith WG. p38 pathway kinases as anti-inflammatory drugJ.J Dent Res , 2007 ,86:800-811.。1.2.2 调控细胞凋亡Saulsbury等实验发现Saulsbury MD, Heyliger SO, Wang K, et alCharacterization of chlorpyrifos-induced apoptosis in placental cellsJ .Toxicology,2008,244:98-110，在毒死蜱诱导胎盘细胞凋亡过程中，激活p38 MAPK可以保护胎盘细胞免受其损伤。研究发现p38MAPK可能通过以下途径调控细胞凋亡：(1)激活c-jun和c-fos；(2)诱导bax转位；(3)介导Caspases的活化；(4)上调TNF表达；(5)增强c-myc表达；(6)磷酸化p53；(7)参与Fas/FasL介导的凋亡。2 p38MAPK信号通路与A介导的炎性反应在AD患者脑中,A肽可激活胶质细胞引起炎症反应而致神经元丧失和认知功能障碍。1997年，McDonald等首次在原代大鼠胶质细胞中发现A能活化p38MAPK途径McDonald DR, Bamberger ME, Combs CK, et al. BetaAmyloid fibrils activate parallel mitogenactivated protein kinase pathways in microglia and THP1 monocytes J.J Neurosci,1998,18:44514460。而且，炎症反应被认为是AD的重要病理改变，以小胶质细胞Jian Jiao, Bing Xue, Lei Zhang, et al. Triptolide inhibits amyloid-1-42-induced TNF- and IL-1 production in cultured rat microgliaJJ Neuroimmmunology 2008, 25:32-36. 和星形胶质细胞的活化Soraya L. Valles, Pablo Dolz-Gaiton, Juan Gambini, et al. Estradiol or genistein prevent Alzheimers disease-associated inflammation correlating with an increase PPAR expression in cultured astrocytes J.Brain Research, 2010, 1312: 138-144. 为标志。2.1 p38MAPK信号通路与小胶质细胞的活化Bhat等首次报导在内毒素（LPS）激活的胶质细胞中，p38MAPK对诱导型NO合酶（iNOS）和肿瘤坏死因子-（TNF）基因表达中转录、翻译的调节作用Bhat NR, Zhang P, Lee JC, et al. Extracellular signal-regulated kinase and p38 subgroups of mitogen-activated protein kinases regulate inducible nitric oxide synthase and tumor necrosis factor-alpha gene expression in endotoxin-stimulated primary glial culturesJJ Neurosci, 1998, 18:16331641. 。LPS刺激下p38MAPK介导NO和TNF的合成在小胶质中进一步得到了证实Xing B, Xin T, Hunter R, et al. Pioglitazone inhibition of lipopolysaccharide-induced nitric oxide synthase is associated with altered activity of p38MAP kinase and PI3K/AktJ. J Neuroinflammation, 2008, 5:4. 。在A刺激后，正常组小胶质细胞会释放TNF炎症因子而MK2(MAPK-activated protein kinases2)缺失小鼠则没有释放TNF，而其中MK2直接受p38MAPK的调节，说明A刺激下TNF的释放与p38MAPK信号通路密切相关Culbert AA, Skaper SD, Howlett DR, et al. MAPK-activated protein kinase 2 deficiency in microglia inhibits pro-inflammatory mediator release and resultant neurotoxicityJ. J Biol Chem,2006, 281:23658-23667.。在内毒素（LPS）激活的小鼠BV-2小胶质瘤细胞中，SE1，一种海马分离物，是通过阻断p38等MAPK分子的磷酸化来抑制炎性介质的产生，从而发挥抗炎作用S.W.A. Himaya, BoMi Ryu, Zhong-Ji Qian ,et al. 1-(5-bromo-2-hydroxy-4-methoxyphenyl) ethanone SE1 suppresses pro-inflammatory responses by blocking NF-B and MAPK signaling pathways in activated microgliaJ . Eur J Pharmacology , 2011, 670:608616.。以上研究共同阐述了在A等神经毒性分子的刺激下，小胶质细胞的活化密切依赖p38MAPK信号通路。2.2 p38MAPK信号通路与星形胶质细胞的活化采用免疫组化法和蛋白印迹法分析7个月大的TgCRND8小鼠（表达人类淀粉前体蛋白基因的双突变形式，是AD的理想模型）的海马，发现在老年斑附近以及远方的小胶质细胞、星形胶质细胞和神经元中p38MAPK被显著激活M.G. Giovannini, F. Cerbai, A. Bellucci, et al. Differential activation of mitogen-activated protein kinase signalling pathways in the hippocampus of CRND8 transgenic mouse, a model of Alzheimers diseaseJ. Neurosci, 2008, 153: 618-633. 。AD最早期神经病理学改变之一是A沉积处出现大量活化的星形胶质细胞，使神经递质谷氨酸浓度异常。实验中用A处理培养的小鼠星形胶质细胞时，结果显示A减少了星形胶质细胞对谷氨酸的摄取，从而导致兴奋性神经毒性，并且p38MAPK与其他MAPK通路均参与到上述反应Matos M., Augusto E. ,Oliveira C.R., et al. Amyloid-beta peptide decreases glutamate uptake in cultured astrocytes: involvement of oxidative stress and mitogen-activated protein kinase cascadesJ. Neurosci, 2008, 156:898-910. 。3 p38MAPK信号通路与Tau蛋白异常磷酸化p38在体外可磷酸化tau蛋白，经免疫蛋白试验p38可以磷酸化tau蛋白Thr181、Ser202、Thr205、Ser396和Ser422位点Reynold CH,Nebreda AR,Gibb GM, et al. Reactvating kinasep3 8 phosphorylates tau protein in vitroJ. J Neurochem,1997,69:191198.，而且这些磷酸化位点与AD脑中提取的神经原纤维缠结中tau蛋白的磷酸化位点相一致。免疫细胞化学方法已经确立了磷酸化p38在脑组织细胞及亚细胞中的定位，早期AD病例有高水平的磷酸化p38免疫反应性，免疫反应性最强的地方位于CA2区和连接着CA1区的海马下脚，磷酸化p38的免疫反应性主要位于神经元内早期神经元纤维病变 Sun A,Liu M, Nguyen XV, et al.P38 MAP kinase is activated at early stages in Alzheimers disease brainJ. Exp Neurol,2003,1 83:263268.。Sahara等研究了表达tau蛋白突变基因的转基因小鼠，磷酸化的P38MAPK免疫反应性的小鼠中持续存在神经原纤维缠结，显示p38MAPK与tau蛋白磷酸化关系密切 Sahara N,Vega IE,Ishizawa T, et al. Phosphorylated p38 MAPK specific anti