Yang Cui-cui, Kuai Xue-xian, Gao Wen-bin, Yu Jian-chun, Wang Qi, Li Lin, Zhang Lan
Department of Pharmacology, Xuanwu Hospital of Capital Medical University; Beijing Institute for Brain disorder; Beijing Engineering Research Center for Nerve System Drugs; Key Laboratory for Neurodegenerative Diseases of Ministry of Education, Beijing, China.
First Teaching Hospital of Tianjin University of Traditional Chinese Medicine, Tianjin, China.
J Alzheimers Dis. 2016;51(1):33-44. doi: 10.3233/JAD-150728.
An accumulation of hyperphosphorylated tau in the brain is a hallmark of Alzheimer's disease (AD). Deficits in protein phosphatase 2A (PP2A) are associated with tau hyperphosphorylation in AD.
To investigate the effects of morroniside (MOR), isolated from Cornus officinalis, on tau hyperphosphorylation and its underlying mechanisms related to PP2A.
SK-N-SH cells were pretreated with 50-200 μM MOR for 24 h followed by 20 nM okadaic acid (OA) for 6 h. PP2Ac siRNA was transfected into HEK293 cells to determine the direct interaction of MOR with PP2A. Western blotting was used to measure the expression of proteins and enzymes. PP2A activity was measured by molybdenum blue spectrophotometry.
Pretreatment with MOR improved the cellular morphological damage and inhibited tau hyperphosphorylation in SK-N-SH cells induced by OA, a PP2A inhibitor. Moreover, MOR increased PP2A activity, concurrent with a decrease in the expression of demethylated PP2A at Leu309 and phosphorylated PP2A at Tyr307. MOR decreased protein phosphatase methylesterase 1 (PME-1) expression and the ratio of PME-1/leucine carboxyl methyltransferase 1 (LCMT-1). Furthermore, MOR treatment decreased the phosphorylation of Src at Tyr416, which regulates the phosphorylation of PP2A. MOR had no effect on PP2Ac expression and tau hyperphosphorylation in PP2Ac siRNA-transfected cells.
MOR attenuated OA-induced tau hyperphosphorylation via PP2A activation, and its mechanism might be related to the regulation of PP2Ac post-translational modification and upstream enzymes such as Src and PME-1.
大脑中过度磷酸化tau蛋白的积累是阿尔茨海默病（AD）的一个标志。蛋白磷酸酶2A（PP2A）缺陷与AD中的tau蛋白过度磷酸化有关。
研究从山茱萸中分离出的莫诺苷（MOR）对tau蛋白过度磷酸化的影响及其与PP2A相关的潜在机制。
用50 - 200μM的MOR预处理SK-N-SH细胞24小时，随后用20 nM冈田酸（OA）处理6小时。将PP2Ac小干扰RNA转染到HEK293细胞中，以确定MOR与PP2A的直接相互作用。采用蛋白质免疫印迹法检测蛋白质和酶的表达。通过钼酸蓝分光光度法测量PP2A活性。
用MOR预处理可改善细胞形态损伤，并抑制由PP2A抑制剂OA诱导的SK-N-SH细胞中tau蛋白过度磷酸化。此外，MOR增加了PP2A活性，同时降低了亮氨酸309处去甲基化PP2A和酪氨酸307处磷酸化PP2A的表达。MOR降低了蛋白磷酸酶甲基酯酶1（PME-1）的表达以及PME-1/亮氨酸羧基甲基转移酶1（LCMT-1）的比例。此外，MOR处理降低了酪氨酸416处Src的磷酸化，Src可调节PP2A的磷酸化。MOR对PP2Ac小干扰RNA转染细胞中的PP2Ac表达和tau蛋白过度磷酸化没有影响。
MOR通过激活PP2A减轻OA诱导的tau蛋白过度磷酸化，其机制可能与PP2Ac翻译后修饰以及Src和PME-1等上游酶的调节有关。
