摘要
研究表明突触损伤与认知功能障碍密切相关,狐猴酪氨酸激酶1(LMTK1)是影响突触生长的关键性激酶。二氢麦角胺(DHE)是一种生物活性较高的麦角生物碱衍生物,它对认知、记忆处理和运动控制具有一定的调节作用。本研究旨在探讨DHE对阿尔茨海默病(AD)模型动物突触形态和可塑性及认知功能的影响。4月龄SAMR1小鼠作为对照(n = 12),4月龄SAMP8小鼠被随机分为3组(每组12只):AD组、DHE低剂量组以及高剂量组,连续8周每日腹腔注射DHE注射液或生理盐水。采用免疫荧光、高尔基染色、电生理、Morris水迷宫以及Western blot实验研究DHE对AD模型小鼠突触形态、突触可塑性、认知功能以及LMTK1下游TBC1D9B磷酸化水平的影响。构建沉默和过表达LMTK1的C17.2细胞,运用免疫荧光实验研究DHE对LMTK1沉默和过表达后神经细胞突触长度的影响。免疫荧光实验结果显示SAMP8小鼠给予DHE后,突触后标记物PSD95显著增加,这提示DHE可以增加AD小鼠海马体突触密度;高尔基染色实验结果表明,AD模型小鼠海马内突触发生萎缩,而高剂量组DHE显著改善了突触萎缩;电生理实验结果表明,与正常小鼠相比,AD模型小鼠长时程增强(LTP)水平明显降低(P < 0.000 1),而DHE给药后LTP显著改善;Morris水迷宫实验结果进一步表明,DHE可以改善AD小鼠的认知障碍;Western blot实验结果表明,AD小鼠海马内P-LMTK1水平显著增加,DHE给药后,其下游效应蛋白P-TBC1D9B水平显著降低;体外细胞免疫荧光实验结果表明,DHE显著改善了过表达LMTK1的神经细胞的突触萎缩,而当LMTK1沉默后,其改善作用消失。本研究提示DHE可能通过作用于LMTK1改善AD状态下的突触萎缩及认知功能障碍。
阿尔茨海默病(Alzheimer’s disease,AD)是一种神经退行性疾病,主要表现为患者的认知功能受损,但其发病机制目前尚不清
越来越多的证据表明,突触功能损伤或突触缺失与AD患者认知受损显著相
CCK8试剂(上海翌圣生物科技有限公司);Western blot及免疫染色相关试剂、嘌呤霉素(江苏碧云天生物科技有限公司);多克隆抗体PSD95、高尔基染液(武汉赛维尔生物科技有限公司);Alexa Fluo
倒置荧光显微镜 (日本Olympus公司);水迷宫装置(北京众实迪创公司);ANY-maze动物行为学采集分析软件(英国Global Biotech公司);病理切片机(上海徕卡仪器公司);包埋机(武汉俊杰电子有限公司);PANNORAMIC 259全景切片扫描仪(匈牙利3dhistech公司);Synerg
AD模型小鼠SAMP8和对照小鼠SAMR1,适应性饲养1个月,4月龄时,将SAMP8小鼠随机分为3组(每组12只),包括疾病组(SAMP8)、SAMP8+1 mg/kg DHE组,以及SAMP8+2 mg/kg DHE组。相同月龄的SAMR1小鼠(n = 12)作为正常空白对照组(blank-SAMR1)。小鼠腹腔注射给药,每天1次,连续给药8周后,进行后续实验。DHE的给药剂量和周期参照文献[
给药完成后,每组随机挑选3只,处死,取海马,进行Western blot实验(抗P-LMTK1,1∶2 500,抗P-TBC1D9B,1∶800),用凝胶图像系统记录结果。通过Image J软件分析结果。
每组剩余9只小鼠进行水迷宫实验。实验流程参照文献[
水迷宫实验结束后的小鼠,每组随机挑选3只麻醉取脑,于ACSF中利用振动切片机切片放入28 ℃ ACSF中进行孵育。转移至记录槽内,2 mL/min进行灌流。刺激脑片海马Schaffer侧枝,在CA1辐射层树突记录得到兴奋性突触后电位(EPSP)。双钨丝电极刺激脉冲(0.1 ms)每隔15 秒进行1次,强度为0.5 mA。使用Axoclamp 2B amplifier在20 kHz采样,10 kHz过滤后输出。使用Digitdata 1200进行数字信号转换。基线条件:每分钟4次,波宽0.1 ms,持续记录10 min。使用一个高频刺激(high frequency stimulation,HFS,100 Hz)产生长时程增强(long-term potentiation,LTP),并在HFS后持续记录40 min。采用pCLAMP 10.0分别测量EPSP起点和终点与负峰得差值,计算其平均值。LTP诱导成功标志是HFS后EPSP的均值不小于基线的120%。
“2.4”项中剩余的6只小鼠处死后,取半脑,固定、包埋、切片、脱蜡至水及抗原修复后。进行封闭、一抗孵育(抗PSD95,1∶200)、二抗孵育(Alexa Fluo
将“2.5”项下剩余的半脑组织块经固定、切块、染色后,于80%的冰醋酸中过夜浸没,组织变软后置于30%蔗糖溶液中切片,晾干后进行显影定影。用Image-Pro Plus 6.0分别测量每张400倍图片中心完整神经元上的第2或3树突分支30 ~ 90 μm长度范围内树突棘的个数,测量长度及计数该长度内树突棘数量,以每10微米树突棘个数作为其密度 = 树突棘数量/树突长度 × 10。使用Image J 1.51K分析软件中Neuron J插件绘制每张400倍图片中心神经元胞体结构图,使用Shollanaly插件,以胞体为中心做间距为10 μm的10个同心圆,计数树突与同心圆的交点数,并计算出10个交点数之和。
在96孔板中以每孔2 × 1
dcas9-SAM转录激活系统过表达LMTK1由吉满生物科技设计合成。C17.2细胞以每毫升1.5 × 1
siRNA靶向LMTK1的重组慢病毒(LMTK1-siRNA:5′-GCUCAGUGCAGCUCCUCAA-dTdT-3′)和对照慢病毒(Ctrl-siRNA:5′-UUCUCCGAACGUGUCACGUdTd-3′)合成于上海汉恒生物科技有限公司。沉默细胞株的构建步骤参考上述过表达细胞株的构建。感染后用8 μg/mL嘌呤霉素筛选48 h。进行Western blot实验验证转染效率,兔源LMTK1、兔源β-tubulin抗体及兔源二抗稀释比分别为1∶1 000、1∶4 000、1∶4 000。
取对数生长期的C17.2细胞,以每孔40个细胞接种于96孔板,37 ℃、5%CO2培养4 h,加入分化培养基,继续培养5 d,每48小时更换新的分化培养基。第5天,加药,继续培养24 h。固定、通透、封闭后,每孔加入兔源beta-Ⅲ Tubulin抗体(1∶50)约50 μL, 4 ℃孵育过夜。PBST洗涤后,加入Alexa Fluo
突触后密度蛋白95(postsynaptic density 95,PSD95)是突触后密度区树突棘的主要支架蛋白,可反映突触的密度和数量,被认为是突触后可塑性的生物标志

Figure 1 Effect of dihydroergotamine (DHE) on the expression of postsynaptic dense 95 in hippocampus of Alzheimer’s disease (AD) mouse ()
A: Representative immunofluorescence images of presynaptic marker PSD-95 (green, FITC, magnification, × 8.7). Nuclei was stained in blue (DAPI); B: Average area density of PSD-95 SAMR1: Senescence-accelerated mouse resistant 1; SAMP8: Senescence-accelerated prone mouse strain
树突棘是兴奋性突触的主要突触后元素,是记忆和认知的关键结构。高尔基染色结果(

Figure 2 Effect of DHE on the density of dendritic spines and number of branches in hippocampus of AD mouse ()
A: Typical electron micrographs of dendritic spines from the hippocampus by the method of Golgi-Cox staining (magnification, × 9; scale bar: 400 µm); B: Average dendritic spine density; C: Average number of spine branche
长时程增强(long-term potentiation,LTP)是突触可塑性的特定表现形

Figure 3 DHE improved impaired hippocampal long-term potentiation (LTP) in AD mice ()
A: Normalized field excitatory post synaptic potentials (fEPSP) amplitude to field stimulation before and after high frequency stimulation (HFS); B: Average fEPSP of mice after HFS
为了探究DHE对AD模型小鼠认知功能的改善作用,进行了Morris水迷宫实验评估小鼠的学习记忆能力。第1天的可视化平台实验中,观察到各组小鼠的逃生潜伏期和游泳速度没有显著性差异(P > 0.05),表明各组小鼠的视力和运动能力没有差别(

Figure 4 Effect of DHE on learning and spatial memory performance of AD mice in the morris water maze task ()
A: Escape latency and swimming speed of four groups during the visible platform trail; B:Escape latency of four groups in the acquisition training trail; C: Percentage of time spent in the platform quadrant and platform crossover time in the probe trail; D:Escape latency of four groups in the reversal trail
利用Western blot实验探究SAMR1和SAMP8小鼠海马体中LMTK1磷酸化水平的变化以及DHE对其下游TBC1D9B磷酸化蛋白(P-TBC)表达的影响。结果如

Figure 5 Effect of DHE on expression of P-LMTK1 and P-TBC in hippocampus ()
A: Relative expression of P-LMTK1; B: Relative expression of P-TBC
为研究DHE对C17.2细胞的毒性作用,进行了CCK8实验。2 μmol/L的DHE给药达到72 h时,对C17.2细胞无显著毒性作用,细胞存活率为92%。
利用基因转录激活技术CRISPR-SAM系统构建LMTK1过表达的C17.2细胞株,研究DHE对LMTK1过表达的神经祖细胞突触长度的影响。利用RT-qPCR测定3种稳转株的基因过表达效率,如

Figure 6 Effects of DHE on synaptic length after LMTK1 over-expression ()
A: Relative expression of LMTK1 in control and three kinds of SAM gRNA cell (n = 3). B: Immunofluorescence photos of C17.2 cells (n = 10); C: Mean length of synapse in C17.2 cells (n = 10)
为了验证DHE是否通过抑制LMTK1的活性发挥神经突触的改善作用。本研究通过对神经细胞C17.2进行si-LMTK1干扰,建立LMTK1基因沉默的细胞株。

Figure 7 Relative expression of LMTK1 in control, negative control and S-LMTK1 groups ()
*P < 0.05

Figure 8 Effects of DHE on synaptic length after LMTK1 silencing ()
A: Immunofluorescence photos of C17.2 cells; B: Mean length of synapse in C17.2 cells
越来越多的证据表明AD早期阶段就会发生突触结构和功能损
突触的形态和功能与认知功能密切相关,胞内体转运途径是神经突触生长的关键过程。胞内体转运途径主要包含3个步骤:首先将形成突触所需的物质“打包”成早期核内体,然后早期核内体将这些物质转运至突触并将其“打包”成循环核内体;最后循环核内体将蛋白插入到细胞膜中形成突触,早期核内体将需要降解的蛋白“打包”成晚期核内
本研究发现DHE可以显著增加AD模型小鼠海马区突触密度并改善突触萎缩和认知功能,其改善作用可能是通过靶向突触生长的关键调控激酶LMTK1。这提示增加突触密度是未来改善AD患者认知功能的一种新策略。

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