图1 LGG对麻醉手术老年小鼠海马区小胶质活化的影响
Published:20 March 2024,
Received:07 November 2023,
Accepted:21 February 2024
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To investigate the effects of Lactobacillus rhamnosus GG (LGG)on microglia and Tau phosphorylation in the hippocampus of aged mice induced by anesthesia and surgery.
A total of thirty 18-month-old C57BL/6J mice were randomly divided into three groups: control group, anesthesia surgery group, and anesthesia surgery + LGG group (10 mice/group). The aged mice were oral administered by NS or LGG 109 CFU 150 μL once a day for 20 days. Then anesthesia surgery group and anesthesia surgery +LGG group received anesthesia with isoflurane and exploratory laparotomy. The activation status of microglia in the hippocampus was detected by immunofluorescence staining 12 hours after surgery. IL-6 concentration changes was detected by ELISA. The expression changes of Tau protein phosphorylation site (Tau-pS202/pT205) and total Tau protein was detected by western blot.
The microglia in the hippocampus of the control group were in a resting state, and the concentration of inflammatory factor IL-6 was (82.08 ± 12.07) pg/mL in control group. Compared to the control group, the anesthesia surgery group showed microglial cell Microglia were activated, the concentration of inflammatory factors IL-6 increased significantly to (123.7±5.72) pg/mL (P=0.000), and the expression of phosphorylated Tau-pS202/pT205 increased the hippocampus (P=0.002). Compared to the anesthesia surgery group, the activated microglia were inhibited, the concentration of IL-6 decreased to (96.68±9.59) pg/mL (P=0.008), and the expression of phosphorylated Tau-pS202/pT205 reduced significantly in the AS+LGG group (P=0.002). While there were no significant changes in total Tau protein among 3 groups.
Preoperative administration of probiotic LGG can alleviate the activation of microglia, increased secretion of inflammatory factors, and increased Tau protein phosphorylation levels in the hippocampus of elderly mice caused by anesthesia surgery.
术后谵妄(postoperative delirium, POD)是高龄患者最常见的术后神经系统并发症。但因其发生发展机制复杂,探索新的防治POD的方法仍然是目前迫切需要解决的临床课题。肠道菌群是人体肠道的正常微生物,参与营养、能量代谢、免疫、炎症、肿瘤等多种病理生理过程。越来越多的证据显示肠道菌群可通过肠脑轴参与阿尔兹海默症(Alzheimer’s disease, AD)、术后认知功能障碍(postoperative cognitive dysfunction, POCD)、POD等中枢神经退行性疾病的发生发展[
SPF 级2月龄C57BL/6小鼠,购自中山大学实验动物中心,许可证号为 SCXK(粤)2021-0029。饲养于中山大学东校区SPF级动物实验室,5只/笼。室内温度 20 ℃~24 ℃,相对湿度35%~45%,室内光线12 h明暗交替,经饲养培育至18月龄。所有对动物处置的实验过程符合中山大学实验室动物伦理学要求(伦理编号:AP20220219)。所有小鼠没有意外死亡或按照动物伦理委员会的要求实施安乐死的情况。
益生菌LGG(Mommy’s Bliss Pharmaceuticals, USA),AT-8抗体 (1: 500, MN1020, Invitrogen)用于检测Tau蛋白丝氨酸202 (Tau-pS202)和苏氨酸205(Tau-pT205)磷酸化。total-Tau 抗体 (1:1 000,ab254256, Abcam, Cambridge, MA), β-actin 抗体 (1: 5 000, Sigma, St. Louis, MO),IBa-1抗体(1:1 000,019-1917,FUJIFILM Wako,Japan),小鼠 IL-6 Immunoassay kit (M6000B, R&D Systems, Minneapolis, MN)。
酶标仪(ELX800,Bio-Tek);pH计(InLab413,Mettler Toledo);电子天平(AB204-S,Mettler Toledo);荧光倒置显微镜(NIKON,Japan);Power/PAC BASIC电泳仪(Bio-rad,USA);低速离心机(TDL80-213,上海安亭科学仪器厂);超声波细胞粉碎仪(Sonycs,南京新辰生物科技公司)。
1.4.1 实验动物分组
18月龄老年小鼠30只随机分为3组:对照组(生理盐水灌胃),麻醉手术组(麻醉手术+生理盐水灌胃)、麻醉手术+LGG组(麻醉手术+LGG灌胃),10只/组。对照组小鼠150 μL生理盐水灌胃,每日 1 次,连续 20 d。麻醉手术组小鼠接受相同剂量和时间的生理盐水灌胃,然后接受体积分数1.4%异氟醚2 h麻醉+剖腹探查手术。麻醉手术+LGG组小鼠 LGG 109 CFU 用 150 μL生理盐水重悬灌胃,每日 1 次,连续 20 d,然后接受体积分数1.4%异氟醚 2 h麻醉+剖腹探查手术。
1.4.2 动物剖腹探查手术模型
参照本课题组之前的方法建立手术模型[
1.4.3 免疫荧光染色
每组小鼠随机取4只麻醉、仰卧位固定,用剪刀剪开剑突下皮肤,然后打开胸腔,暴露心脏,将灌注针从心尖部位,插入升主动脉,剪开左心耳,依次快速灌注生理盐水 100 mL、40 g/L多聚甲醛100 mL,取出脑组织,多聚甲醛后固定24 h,质量分数10%~30%蔗糖的磷酸缓冲液中梯度脱水。把脑组织放在冰冻切片机上,速冻后切片,厚度调整为15 μm,逐片收集,将脑片平铺贴在载玻片上。0.3%过氧化氢处理 10 min,体积分数0.3%Triton X-100破膜,质量分数2%BSA室温封闭 lh, IBa-1 一抗(0.5 μg/mL)4 ℃摇床孵育过夜,PBS 洗 3 次,每次5 min。荧光二抗(1:2 000)避光室温孵育 2 h,PBS洗 3 次,每次5 min。Hoechst33342染液染细胞核,37 °C孵育 10 min,PBS洗 3 次。加入抗荧光衰减封片剂后封片,荧光显微镜下观察采集图像。
1.4.4 新鲜海马组织提取蛋白
每组剩余的6只小鼠麻醉后断头处死,取出双侧大脑组织,用预冷PBS液冲洗,用镊子在预冷的冰盘上快速分离海马组织后将其放入EP管中,加入含有蛋白酶抑制剂的细胞裂解液,用超声将海马组织匀浆。离心 20 min,2 000~3 000 r/min(r = 5 cm)。仔细收集上清,- 80 ℃冰箱保存用于后续ELISA和western blot检测。
1.4.5 ELISA检测海马炎症因子IL-6浓度
提取好的海马蛋白BCA法进行蛋白定量。彻底混匀将要使用的试剂,设立空白孔和标准品对照孔,在样品孔中依次加入 100 μL 标准品和样品,每孔加入50 μL稀释好的生物素标记的检测因子的抗体,封闭,向每孔加入100 μL稀释好的链霉亲和素标记的HRP,再封闭,37 ℃孵育0.5~1 h,洗涤3次,加入底物溶液显色,在不透光的铝盒中孵育,每孔加入100 μL 终止液终止反应,30 min内在酶标仪上以 450 nm 测OD值,根据标准曲线计算浓度。
1.4.6 蛋白印记法检测海马区Tau-pS202/pT205、Total-Tau蛋白表达变化
提取好的海马蛋白BCA法进行蛋白定量。取蛋白 30 g 与上样缓冲液混匀98 °C 加热5 min 变性,离心后上样,80~100 V电泳分离。然后100 V、90 min电转移至硝酸纤维素膜,含5 g/L脱脂奶粉的TBST室温封闭1 h,加入一抗孵育 4 °C 过夜用,1∶5 000 二抗室温孵育45 min,ECL显影液显影后于凝胶成像系统采集图像。用 Image J 软件分析蛋白条带灰度值,以Tau-pS202/pT205/β-actin 、total Tau/β-actin灰度值比值进行统计分析。
采用SPSS 26.0软件进行统计分析。符合正态分布的计量资料以均数±标准差(ˉX ± S)表示,不符合正态分布的计量资料以中位数(四分位数间距)表示。行方差齐性检验后,采用单因素方差分析进行组间比较。进一步两两比较用LSD法。 P<0.05为差异有统计学意义。
免疫荧光染色结果显示,对照组海马区小胶质细胞胞体较小,突起细长。麻醉手术组小胶质细胞活化增殖,胞体变大,突起粗短。麻醉手术+LGG组较麻醉手术组活化增殖,胞体稍增大,部分突起仍细长(
图1 LGG对麻醉手术老年小鼠海马区小胶质活化的影响
Fig. 1 Effects of LGG on activation of microglia in the hippocampus of elderly mice undergoing anesthesia and surgery
A-C: control group; D-F: anesthesia surgery group; G-I: anesthesia surgery + LGG group. A, D, G: Bar=100 μm; B, C, E, F,H, I:Bar=50 μm. The red fluorescence represents the IBA-1 labeled microglia, the blue fluorescence represents the H33258 labeled nucleus, and the white arrow indicates the cell body of the microglia.
使用ELISA检测3组海马区脑组织IL-6浓度,结果显示对照组为82.08±12.07 pg/mL,麻醉手术组为123.7±5.72 pg/mL,麻醉手术+LGG组为96.68±9.59 pg/mL。单因素方差分析,3组之间IL-6浓度变化差异有统计学意义(F=19.81,P=0.001;
图2 LGG对麻醉手术老年小鼠海马区炎症因子IL-6浓度的影响
Fig. 2 Effects of LGG on the concentration of inflammatory factor IL-6 in the hippocampus of elderly mice undergoing anesthesia surgery
*: P=0.000, **: P=0.008.
Western blotting结果显示,3组海马区Tau-pS202/pT205表达水平差异有统计学差异(F=13.46,P=0.001)。麻醉手术组Tau-pS202/pT205相对表达量均值较对照组升高0.191(P=0.002),95%置信区间为(-0.304,-0.078 1)。麻醉手术+LGG组均值比麻醉手术组下降0.188(P=0.002),95%置信区间为(0.076 15,0.301 6)。而3组total Tau蛋白相对表达量差异无统计学意义(F=0.147,P=0.866;
图3 LGG对麻醉手术老年小鼠海马区 Tau-pS202/pT205和total Tau蛋白表达的影响
Fig. 3 Effects of LGG on Tau-pS202/pT205 and total Tau protein expression in the hippocampus of elderly mice undergoing anesthesia surgery
A: Tau-pS202/pT205 and total Tau protein expression; B: Tau-pS202/pT205, *: P=0.002, **: P=0.002; C: total Tau, all P>0.05.
POD的发生发展机制非常复杂,涉及年龄、手术、合并的基础疾病等。POD通常发生在接受心脏、骨外科、剖腹探查等大手术后,高龄是其独立危险因素。虽然近年来医疗水平有了较大提高,但是POD的发生率仍居高不下,因此其临床防治的策略仍然是目前研究的热点。
受不同的刺激反应调控,小胶质细胞激活后迅速增殖并向两个方向分化:促炎的M1表型或抑炎的M2表型。与成年小鼠相比,老年小鼠的小胶质细胞胞体较大,突起粗短,且M1小胶质细胞和M2小胶质细胞均比成年小鼠增加。手术后以M1小胶质细胞增加为主[
Tau蛋白有很多的磷酸化位点,目前认为Tau蛋白 Ser202、Thr205、Thr212、Ser214、Thr217 和 Ser396/404等多个位点过度磷酸化均参与认知功能障碍[
LGG 是最著名的鼠李糖乳杆菌,属于乳杆菌属、鼠李糖乳杆菌种。LGG 具有耐酸、耐胆汁盐、耐多种抗生素等生物学特点。LGG在耐胃酸和胆汁方面的性能非常突出,可以活体进入人体肠道。LGG 可以定殖在人体内长达两周之久,起到调节肠道菌群、预防和治疗腹泻、和提高机体免疫力等作用[
总之,本研究发现老年小鼠术前服用益生菌鼠李糖乳杆菌可减轻麻醉手术导致的海马区小胶质细胞激活、炎症因子分泌增加、以及Tau蛋白磷酸化水平增加。这是益生菌改善老年小鼠POD行为的重要机制之一。
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