Background. Excessive or insufficient intake of methionine (Met) causes neuronal dysfunction, neurodegeneration, cerebrovascular dysfunction, vascular leakage, and short-term memory loss, which result in the occurrence of Alzheimer’s disease- (AD-) like symptoms. Objective. To determine the relationship between high methionine diets (HMD) induced AD-like symptoms and 5-methylcytosine (5-mC) level. Methods. C57BL/6J mice were randomly divided into two groups: the control group (Maintain diets) and the model group (2% HMD). Mice were fed with 2% HMD for 9 weeks. Animals were weighed and food intake was recorded weekly. Open field test, nesting ability test, Y maze test, new object recognition test, and Morris water maze test were used to detect the motor, learning, and memory ability. Hematoxylin-eosin (HE) staining was used to observe the damage of cells in hippocampus and cortex. Immunofluorescence (IF) staining was used to detect the expression and distribution of amyloid-β 1-40 (Aβ_1-40), amyloid-β 1-42 (Aβ_1-42), and 5-methylcytosine (5-mC) in hippocampus and cortex. Western blotting (WB) was used to determine the expression of Aβ and DNA methyltransferases- (DNMTs-) related proteins in the cortex. Enzyme-linked immunosorbent assay (ELISA) was performed to detect homocysteine (Hcy) level (ELISA). Results. Feeding of HMD decreased the body weight and food intake of mice. Behavioral testing revealed that HMD caused learning, memory, and motor ability impairment in the mice. HE staining results showed that HMD feeding caused damage of hippocampal and cortical neurons, along with disordered cell arrangement, and loss of neurons. Furthermore, HMD increased the contents of Aβ_1-40, Aβ_1-42, and 5-mC in the hippocampus and cortex. WB results showed that HMD increased the expression of Aβ production-related proteins, such as amyloid precursor protein (APP) and beta-secretase 1 (BACE1), and decreased the expression of Aβ metabolism-related protein in the cortex, including insulin-degrading enzyme (IDE) and neprilysin (NEP). Additionally, the decreased expression of DNA methyltransferase1 (DNMT1) was observed in HMD-treated mice, but there was no significant change of DNMT3a level. ELISA results showed that HMD increased the levels of Hcy in serum. Conclusion. Our result suggested that the HMD can cause neurotoxicity, leading to AD-like symptoms in mice, which may be related to 5-mC elevated.

中文翻译：

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高蛋氨酸饮食诱发的阿尔茨海默病样症状伴随着大脑中 5-甲基胞嘧啶水平升高

背景。蛋氨酸（Met）摄入过多或不足会导致神经元功能障碍、神经变性、脑血管功能障碍、血管渗漏和短期记忆丧失，从而导致出现阿尔茨海默病（AD-）样症状。客观。确定高蛋氨酸饮食 (HMD) 诱导的 AD 样症状与 5-甲基胞嘧啶 (5-mC) 水平之间的关系。方法。C57BL/6J小鼠随机分为两组：对照组（维持饮食）和模型组（2% HMD）。用 2% HMD 喂养小鼠 9 周。每周对动物称重并记录食物摄入量。采用旷场试验、筑巢能力试验、Y迷宫试验、新物体识别试验、Morris水迷宫试验检测运动、学习、记忆能力。苏木精-伊红（HE）染色用于观察海马和皮层细胞的损伤情况。免疫荧光(IF)染色检测淀粉样蛋白-β1-40 ( A β _1-40 )、淀粉样蛋白-β 1-42 (A β _1-42)，以及海马和皮质中的 5-甲基胞嘧啶 (5-mC)。Western印迹（WB）用于确定皮质中Aβ和DNA甲基转移酶（DNMTs-）相关蛋白的表达。进行酶联免疫吸附试验（ELISA）以检测同型半胱氨酸（Hcy）水平（ELISA）。结果。喂食 HMD 降低了小鼠的体重和食物摄入量。行为测试显示，HMD 导致小鼠学习、记忆和运动能力受损。HE染色结果显示，HMD喂养导致海马和皮层神经元受损，细胞排列紊乱，神经元丢失。此外，HMD增加了A β _1-40、A β _{1-42的含量}，以及海马和皮质中的 5-mC。WB 结果显示，HMD 增加了 A β产生相关蛋白，如淀粉样前体蛋白 (APP) 和 β-分泌酶 1 (BACE1) 的表达，并降低了皮质中 A β代谢相关蛋白的表达，包括胰岛素-降解酶（IDE）和脑啡肽酶（NEP）。此外，在 HMD 处理的小鼠中观察到 DNA 甲基转移酶 1 (DNMT1) 的表达降低，但 DNMT3a 水平没有显着变化。ELISA结果显示HMD增加了血清中Hcy的水平。结论。我们的结果表明，HMD 可引起神经毒性，导致小鼠出现 AD 样症状，这可能与 5-mC 升高有关。