吉林大学学报(医学版)  2016, Vol. 42 Issue (02): 250-254

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陈国兵, 吴谨准, 连珠兰, 占珠琴, 白海涛
CHEN Guobing, WU Jinzhun, LIAN Zhulan, ZHAN Zhuqin, BAI Haitao
脂多糖对大鼠肺损伤及肺组织中AQP1和AQP5表达的影响
Effects of lipopolysaccharide on lung injury and expressions of AQP1 and AQP5 in lung tissue of rats
吉林大学学报(医学版), 2016, 42(02): 250-254
Journal of Jilin University (Medicine Edition), 2016, 42(02): 250-254
10.13481/j.1671-587x.20160212

文章历史

收稿日期: 2015-05-30
脂多糖对大鼠肺损伤及肺组织中AQP1和AQP5表达的影响
陈国兵, 吴谨准, 连珠兰, 占珠琴, 白海涛    
厦门大学附属第一医院儿科PICU, 福建厦门 361003
摘要: 目的: 探讨大鼠经静脉注射脂多糖(LPS)对急性肺损伤(ALI)及肺组织中水通道蛋白1(AQP1)和水通道蛋白5(AQP5)表达的影响,阐明其作用机制。方法: SPF级2月龄雄性Wistar大鼠48只随机分为对照组和LPS组(n=24),分别经尾静脉注射生理盐水和LPS,每组分别于注射后2、6、12和24 h时间点采集标本,每个时间点6只。HE染色观察肺组织病理学变化;测定大鼠肺湿/干质量(W/D)比、肺渗透指数;ELISA法检测血清肿瘤坏死因子α(TNF-α)和巨噬细胞炎性蛋白1α(MIP-1α)水平;采用Western blotting、免疫组织化学和Real-Time PCR方法检测大鼠肺组织中AQP1和AQP5蛋白及mRNA表达水平。结果: 与对照组比较,LPS组大鼠血清TNF-α和MIP-1α水平在注射LPS后2、6和12h时间点均明显升高(P<0.05),至24h时逐渐恢复正常。HE染色,注射LPS后2h大鼠肺组织出现水肿和炎性细胞浸润,以12h时间点最明显;LPS组各时间点大鼠肺W/D比、肺渗透指数均较对照组明显升高(P<0.05),12h时间点最明显。与对照组比较,LPS组各时间点大鼠肺组织中AQP1和AQP5 mRNA及蛋白表达水平均明显下降(P<0.01),以12h时间点下降最明显。结论: LPS可导致大鼠ALI和肺组织中AQP1及AQP5表达水平下调,并参与了肺水肿的形成。
关键词: 脂多糖    肺损伤    水通道蛋白1    水通道蛋白5    
Effects of lipopolysaccharide on lung injury and expressions of AQP1 and AQP5 in lung tissue of rats
CHEN Guobing, WU Jinzhun, LIAN Zhulan, ZHAN Zhuqin, BAI Haitao    
Department of Pediatrics, First Affiliated Hospital, Xiamen University, Xiamen 361003, China
Abstract: Objective: To investigate the effects of lipopolysaccharide (LPS) on the acute lung injury (ALI) and expressions of aquaporin 1 (AQP1) and aquaporin 5 (AQP5) in lung tissue of the rats. Methods: Forty-eight SPF grade male Wistar rats were randomly divided into control group and LPS group (n=24).The rats in LPS group were intravenously injected with LPS to induce ALI models, and the rats in control group were injected with saline.The rats were sacrificed at 2, 6, 12 and 24 h, and the samples were collected after the successful modeling.The pathological changes of lung tissue were observed with HE staining; the lung wet/dry weight (W/D) ratio and lung permeability index were detected; ELISA was used to detect the levels of TNF-α and MIP-1α.The expression levels of AQP1 and AQP5 protein and mRNA were measured by Western blotting, immunohistochemistry and Real-Time PCR methods.Results: Compared with control group, the TNF-α and MIP-1α levels in LPS group were significantly elevated at 2, 6 and 12 h (P<0.05), and at 24 h they were gradually reduced to the normal level.The HE staining results showed the alveolar and interstitial edema at 2 h after LPS injection, obviously in 12 h.The lung W/D ratios and pulmonary permeability indexes at different time points in LPS group were significantly higher than those in control group (P<0.05), and they reached the peak at 12 h.The expression levels of AQP1 and AQP5 mRNA and protein in lung tissue of the rats at different time points in LPS group were significantly lower than those in control group (P<0.01).Conclusion: LPS can induce ALI in the rats and down-regulate the expressions of AQP1 and AQP5; LPS is involved in the formation of pulmonary edema.
Key words: lipopolysaccharide    lung injury    aquaporins 1    aquaporins 5    

急性肺损伤(acute lung injury,ALI)是由严重感染和创伤等多种病理因素所致的弥漫性肺损伤性疾病,脂多糖(lipopolysaccharide,LPS)引起的脓毒症是造成ALI最常见的原因[1]。ALI主要病理基础是炎性细胞浸润和渗出性肺水肿导致急性呼吸衰竭,其发病机制尚未完全阐明[2]。水通道蛋白(aquaporins,AQPs)对水具有特异性转运功能,具有低抗肺水肿形成的作用[3, 4],研究[5, 6]表明:生理和病理情况下AQPs在肺泡细胞的水平衡调节上有重要作用。以往有关ALI的研究多集中于促进肺水肿的有害因素方面,如炎性介质、细胞因子等对肺血管内皮和肺上皮细胞的损伤作用[7],而有关对机体内调节肺水平衡的水通道蛋白1(AQP1)和水通道蛋白5(AQP5)的研究较少。本研究探讨大鼠经静脉注射LPS对ALI及肺组织中AQP1和AQP5表达的影响及其意义。

1 材料与方法 1.1 动物和主要试剂

SPF级2月龄Wistar大鼠48只,雄性,平均体质量(285.7±15.0)g,购自上海斯莱克实验动物有限公司,动物许可证号:SCXK沪2003-0003。LPS (美国Sigma公司),肿瘤坏死因子α(tumor necrosis factor α,TNF-α)和巨噬细胞炎性蛋白1α(macrophage inflammatory protein-1α,MIP-1α)检测试剂盒(上海鑫乐生物公司),ECL化学发光试剂盒(美国Pierce公司),苏木素(福州迈新生物公司),Trizol和cDNA合成试剂盒和RT-qPCR试剂盒(日本Takara公司),RNA提取试剂盒和BCA蛋白质定量试剂盒(北京天根生化公司),PCR引物(美国Invitrogen公司),SDS和PVDF转印膜(美国PALL公司),兔抗大鼠AQP1抗体(美国Santa Cruz公司),兔抗小鼠AQP5抗体、兔抗大鼠β-Actin抗体和山羊抗兔多克隆二抗(美国Abcam公司)。

1.2 动物分组和模型制备

48只大鼠随机分为对照组和LPS组,各组分为2、6、12和24h 4个时间点,每个时间点6只。LPS组大鼠经尾静脉注射LPS (5 mg·kg-1,浓度 5 g ·L-1),对照组大鼠注射等量生理盐水。观察LPS组大鼠呼吸频率、精神状态,当大鼠出现呼吸频率加快、躁动不安、紫绀时采取部分大鼠肺组织行HE染色、测定肺湿/干质量(wet/dry weight,W/D)比,检测血清TNF-α和MIP-1α水平,出现异常时提示大鼠ALI模型制备成功。

1.3 血清炎性因子和ALI相关指标测定 1.3.1 ELISA法检测大鼠血清TNF-α和MIP-1α水平

大鼠腹腔注射3.5%的水合氯醛(10 mL·kg-1)麻醉,腹主动脉采血5mL注入生化管,3500 r·min-1 离心10 min,取上清液,按操作步骤进行TNF-α和MIP-1α水平测定。

1.3.2 HE染色病理学观察

取右上小块肺组织经10%甲醛固定24h,常规石蜡包埋,5μm切片,苏木素-伊红(HE)染色,光镜下观察大鼠肺组织病理学表现。

1.3.3 W/D比值测定

取右肺组织50~100mg,吸水纸吸干,立即称质量记作肺湿质量。然后置于80℃烤箱,48h后(质量不再减轻)称质量记为肺干质量,计算W/D比值,以此了解肺组织含水量。

1.3.4 支气管肺泡灌洗液(BALF)中蛋白水平和肺渗透指数测定

采用BCA蛋白质定量试剂盒,用多功能酶标仪于562nm处检测其吸光度(A)值,绘出蛋白质标准曲线,根据A值计算血浆及BALF中蛋白水平,进而计算肺渗透指数。肺渗透指数=BALF蛋白水平 /血浆蛋白水平。

1.4 大鼠肺组织中AQP1和AQP5 蛋白及mRNA表达水平 1.4.1 Real-Time PCR检测大鼠肺组织中AQP1和AQP5 mRNA表达水平

取大鼠肺组织50mg,采用TRizol法抽提总RNA,检测其浓度和纯度。以β-actin为内参,进行AQP1和AQP5 Real-Time PCR检测。AQP1(280 bp)上游引物序列:5'-TCACTTGGCCGAAATGACCTG-3',下游引物序列:5'-GTCCCACCCAGAAAATCCAGT-3';AQP5(151 bp)上游引物序列:5'-TCCAGGACCACACCAGAAAG-3',下游引物序列:5'-ATAAAATAGCACTCCGTGAGCC-3';β-actin(81 bp)上游引物序列:5'- ACTGCCGCATCCTCTTCCTC-3',下游引物序列:5'-GAACCGCTCATTGCCGATAGTG-3'。Real-Time PCR反应条件:95℃预变性30 s,95℃、5 s,58℃、20 s,72℃、20 s,共40个循环。AQP1和AQP5基因表达采用荧光定量PCR仪上的配套软件进行半定量分析。

1.4.2 Western blotting法检测AQP1及AQP5蛋白表达水平

取大鼠同一部位肺组织样品约50mg,依次清洗、匀浆和裂解,常规提取组织蛋白,测定组织总蛋白浓度,取30μg蛋白质样品,加入等体积的2×SDS-PAGE样品缓冲液,沸水煮5min,进行SDS-PAGE蛋白电泳。其后转移至PVDF膜,按免疫印迹说明步骤操作,ECL发光、显影后用凝胶成像系统检测蛋白条带A值,以AQPs与β-actin蛋白的A值比值表示蛋白表达水平。

1.4.3 免疫组织化学法检测大鼠肺组织中AQP1和AQP5蛋白

采用链霉亲和素-过氧化物酶复合物 (SABC)方法。5 μm切片脱蜡至水,3%过氧化氢(H2O2)灭活内源性过氧化物酶5~10 min,热修复抗原,血清封闭20 min,滴加AQPs一抗,4℃过夜,加山羊抗兔IgG(二抗),37℃、20 min,滴加SABC,37℃、20 min,每一次20min后均在磷酸盐缓冲液(PBS)中漂洗3次。二氨基联苯胺(DAB)显色,封片,电子显微镜观察、照相。染色结果判定:肺组织出现棕黄或棕褐色颗粒为阳性。

1.5 统计学分析

采用SPSS 19.0软件包进行统计学分析。样本均来自正态分布总体,血清炎性因子及ALI相关指标以x±s表示,组间比较采用独立样本t检验,组内比较采用单因素方差分析。以P<0.05为差异有统计学意义。

2 结 果 2.1 各组大鼠血清炎性因子水平

与对照组比较,在LPS注射后2、6和12h时间点LPS组大鼠血清TNF-α和MIP-1α水平均明显升高(P<0.05或P<0.01),至24h时间点逐渐恢复正常。见表 1

表1 对照组和LPS组大鼠血清TNF-α和MIP-1α水平、肺W/D比、BALF中蛋白水平及肺渗透指数 Tab.1 Levels of serum TNF-α and MIP-1α,lung W/D ratios,protein levels in BALF and lung permeability indexes of rats in control group and LPS group
(n=6,x±s)
GroupTNF-αMIP-1αW/D ratio Protein in BALFPermeability index(×10-3)
*P<0.05,** P<0.01 compared with control group.
Control
LPS 2 h
        6 h
      z12 h
      24 h
70.26±2.62
78.66±6.64*
79.59±3.56**
79.69±5.96**
71.48±6.19
115±9
143±8*
157±7**
127±11*
115±16
4.22±0.35
5.32±0.71*
5.37±0.78*
5.72±0.88**
5.02±0.77*
0.36±0.05
0.53±0.06*
0.55±0.11*
0.58±0.09**
0.50±0.03*
3.50±0.23
5.56±0.35**
5.81±0.62*
5.95±0.23**
5.05±0.12*
2.2 各组大鼠ALI相关指标的变化

病理切片显示:LPS组2 h时间点大鼠出现肺泡和间质水肿及炎性细胞浸润,以6和12 h最为明显,至24h有所好转;对照组大鼠支气管、肺泡和血管结构正常。见图 1(插页三)。LPS组大鼠肺W/D比值、BALF中蛋白水平和肺渗透指数均高于对照组(P<0.05),12h时间点最明显。见表 1

A: Control group; B: LPS group (2 h). 图1 2组大鼠肺组织HE染色结果(×200) Fig.1 Results of HE staining of lung tissue of rats in two groups with immune cell(×200)
2.3 各组大鼠肺组织中AQP1和AQP5 mRNA及蛋白表达

各组大鼠AQP1蛋白在肺间质出现阳性表达,AQP5蛋白在肺泡上皮细胞的顶膜面表达。见图 2(插页三)。与对照组比较,LPS组大鼠肺组织中AQP1和AQP5蛋白及mRNA表达水平明显下降(P<0.01),且随时间的延长逐渐下调,12h时间点表达水平最少,至24h时间点其表达水平有所升高。见图 3~5

图2 AQP1(A)和AQP5(B)蛋白在大鼠肺组织中的表达(免疫组织化学,×400) Fig.2 Expressions of AQP1(A) and AQP5 (B) protein in lung tissue of rats ( Immunohistochemistry, ×400)
Lane 1-4:Control group at 2,6,12 and 24h;Lane 5-8:LPS group at 2,6,12 and 24h. 图3 Western blotting法检测大鼠肺组织中AQP1和AQP5蛋白表达 Fig.3 Expressions of AQP1 and AQP5 proteins in lung tissue of rats detected by Western blotting method
A:AQP1;*P<0.05,** P<0.01 vs control group;P<0.05 vs 12 h in LPS group.B:AQP5; *P<0.01 vs control group;P<0.01 vs 6 h in LPS group; #P<0.05 vs 2 h in LPS group. 图4 2组大鼠肺组织中AQP1和AQP5蛋白表达水平 Fig.4 Expression levels of AQP1 and AQP5 proteins in lung tissue of rats in two groups
A:AQP1;*P<0.01 vs control group;P<0.05,△△P<0.01 vs 2 h;#P<0.01vs 6 h in LPS group; P<0.05 vs 12 h in LPS group;B:AQP5; *P<0.01 vs control group; P<0.01 vs 6h in LPS group; #P<0.01 vs 2 h in LPS group; P<0.01 vs 12 h in LPS group. 图5 2组大鼠肺组织中AQP1和AQP5 mRNA表达水平 Fig.5 Expression levels of AQP1 and AQP5 mRNA in lung tissue of rats in two groups
3 讨 论

革兰阴性细菌感染产生内毒素,其主要成分LPS是引起脓毒症最常见的毒素[8],脓毒症后大量细胞因子释放,如TNF-α、MIP-1α和IL-6等,引起炎症级联效应[9],导致ALI。ALI以中性粒细胞聚集、肺泡上皮的完整性破坏为特点,导致肺泡-毛细血管基底膜受损,肺微血管通透性增高,引起肺泡和间质渗出性肺水肿[10, 11]。本实验中大鼠静脉注射LPS后出现烦躁、紫绀、呼吸加快;血清炎性因子TNF-α和MIP-1α水平明显升高;病理学显示肺泡上皮细胞出现肿胀、间质水肿,肺W/D比、BALF中蛋白水平和肺渗透指数均较对照组明显升高,说明大鼠注射LPS后导致ALI,随着时间的延长,肺组织损伤逐渐加重,12 h达高峰,24 h时血清炎性因子水平相对下降,肺损伤指标也逐渐改善。

ALI是一个组织弥散性肺泡炎和损伤后修复重建的复杂病理生理过程,其早期特征性改变是肺泡炎性水肿,继之出现肺间质增生和肺纤维化,最终导致呼吸功能的完全丧失[12, 13]。AQPs是一种对水具有特异性转运功能的细胞膜通道蛋白,在膜中以四聚体形式存在,每一单体形成一个功能性水通道,具有抵抗肺水肿形成的作用[14],目前在哺乳动物肺组织中有6种AQPs(AQP1、AQP3、AQP4、AQP5、AQP8和AQP9)表达并参与肺液体转运[15],研究[16, 17]表明:AQP1和AQP5参与了肺泡炎性水肿的形成,而AQP3和AQP4在肺水肿过程中无表达变化。本实验结果显示:AQP1在肺间质出现阳性表达,主要分布在肺血管内皮细胞和肺间质细胞膜,AQP5在肺泡上皮细胞顶膜和黏膜下腺泡细胞膜有表达。LPS组AQP1和AQP5蛋白及mRNA表达水平随时间的延长逐渐下调,与肺组织损伤相关指标的变化存在明显负相关关系,肺损伤越重,AQP1和AQP5表达水平越低。上述结果提示LPS造成的ALI和肺泡炎性水肿可能与炎性因子攻击导致肺组织AQP1和AQP5表达水平下调、进而降低了AQPs对水肿液体的清除能力有关。

ALI的发病机制尚未完全阐明,其病理基础为肺泡炎性水肿。如果能在肺损伤初期对肺组织水平衡进行干预,就有可能阻断ALI的发生、发展进程。AQPs在肺水转运以及水肿液清除方面的研究可能是未来的发展方向。

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