核因子-kB信号通路与自噬在动脉粥样硬化发生发展中的相互调节作用

2019-10-18 07:10:11 心脑血管病防治 2019年4期

赵嫦清 王志明 杨丽霞

[摘 要] 动脉粥样硬化(atherosclerosis,AS)是一种复杂的慢性血管炎症疾病,由多种AS相关细胞与其表达的促炎因子相互作用促进其发生发展。核因子-kB(NF-kB)信号通路是由多种细胞因子介导的经典信号通路,不仅参与炎症反应,也调控细胞损伤、氧化应激、细胞凋亡等过程。而自噬是细胞稳态的溶酶体降解过程,在一定范围内的自噬激活可调节炎症反应。AS多伴有炎症反应并与自噬密切相关,NF-kB的激活可介导自噬,而自噬的过度激活抑制NF-kB活性。本研究主要对NF-kB与自噬在AS中的相互关系做一综述。

[关键词] 动脉粥样硬化;炎症反应;核因子-kB;自噬;斑块稳定性

中图分类号:R543? 文献标识码:A? 文章编号:1009-816X(2019)04-0355-03

动脉粥样硬化(atherosclerosis,AS)是一种复杂的慢性血管炎症疾病,具有经典的炎症变性、渗出及增生等特点。炎症反应贯穿动脉粥样硬化病变的各个阶段,可能是多种致动脉粥样硬化机制的共同环节和通路。其整个过程涉及到炎症因子的刺激、血管内皮细胞(ECs)损伤、平滑肌细胞(VSMCs)增殖迁移及巨噬细胞浸润等[1]。而核因子-kB(NF-kB)信号通路及自噬均参与AS发生、发展的多个过程。

1 NF-kB信号通路与AS

NF-kB是一类广泛存在于真核细胞胞质中,与一种抑制蛋白(IkB)结合存在,当应激和损伤状态时肿瘤坏死因子(TNF-α)、脂多糖(LPS)等促炎因子能与细胞膜TNF受体结合,最先激活IKKα和IKKβ,导致NF-kB与IkB解离,NF-kB得以活化,活化的NF-kB进入细胞核,作用于相应基因的启动子,作为调节炎症反应、氧化应激和免疫的主要核转录因子[2]。NF-kB信号通路是一种炎症通路,在动脉粥样硬化部位和斑块中可发现活化的NF-kB,而在正常血管中很少检测到其表达[3]。郑学忠等[4]的研究显示,NF-kB信号通路在AS中参与氧化应激、炎症反应、ECs损伤、VSMCs的增殖、巨噬细胞浸润等。炎症细胞向血管壁的浸润需先与内皮细胞粘附,此过程涉及大量粘附分子的产生,进一步引起内皮细胞的损伤,大量研究显示该过程均有NF-kB信号通路激活。DebRoy等[5]在LPS介导的ECs中发现,基质相互作用分子(STIM1)能调节ECs外钙离子内流,使ECs的通透性增加。LPS诱导后可致STIM1表达增加,而抑制NF-kB通路后,STIM1的表达则明显降低,并证明了NF-kB信号通路的激活可促使NF-kB与STIM1启动子的结合,从而增加STIM1的表达而引起ECs的损伤。Shen等[6]的研究中表明,Ang Ⅱ通过AT1受体激活NF-kB信号通路而诱导VSMC表型由静止型转化为增殖型。既往研究亦证实NF-kB的激活可促使ECs、VSMCs、巨噬细胞的浸润[7]。

2 自噬与AS

自噬即细胞的自我吞噬,是细胞稳态的溶酶体降解途径。自噬作为炎症的负调节剂,可通过清除受损的细胞器和抑制促炎复合物的形成,减缓炎症反应。很多学者认为自噬的受损和缺乏而激活炎性体是加剧动脉粥样硬化进程的原因之一[8]。既往的实验研究发现,自噬核心基因的消融加剧了鼠动脉粥样硬化;然而自噬同样调节炎症反应、ECs损伤、VSMC增殖迁移和巨噬细胞浸润。

3 NF-kB信号通路与自噬

在动脉粥样硬化中,NF-kB信号通路作为一种炎症通路,与自噬之间存在正负反馈调节,共同调节斑块稳定性。

3.1 NF-kB信号通路正向调节自噬水平:NF-kB可以正向调节AS中自噬水平。在一项关于小鼠纹状体细胞的研究中发现,p53是NF-kB的靶基因,NF-kB的核转位上调p53的表达,抑制NF-kB核转位可下调p53的表达[9]。最近的研究发现,p53上调表达能通过激活其下游基因(DRAM)从而激活自噬,进一步说明NF-kB的激活上调自噬水平。同时在神经元中也发现,激活谷氨酸受体可诱发IkBα的降解而激活NF-kB,引发神经元自噬。近年Xie等[10]在野百合碱诱导的大鼠肺动脉高压(PAH)模型中也发现,NF-kB可诱导自噬激活引起高脂血癥介导的心脏重塑,而抑制NF-kB或自噬可防止右心室收缩压(RVSP)、右心室肥厚指数(RVHI)的增加和肺动脉重塑,这些结果表明抑制NF-κB或自噬可阻止PAH的发展。总之,NF-kB信号通路在心血管中正向调节自噬水平,减缓AS进展。

3.1.1 NF-kB信号通路激活自噬减轻炎症反应:近年Xia等[11]发现,PM2.5在小鼠主动脉内皮细胞中可通过FHL2(四个半LIM结构域2)激活NF-kB信号通路,从而激活自噬,导致白介素-6(IL-6)等炎症因子的表达降低。同时也有研究发现,TG2作为TGM2基因编码的80kDa酶,与癌细胞密切相关,其过量表达可激活NF-kB信号通路,引起IL-6/STAT3表达增加,从而激活自噬,抑制IL-2、4等炎症因子的表达。当抑制TG2或者NF-kB后,IL-6/STAT3的表达明显降低,炎症因子表达明显升高[12]。进一步证实NF-kB/IL-6/STAT3/自噬通路的存在。

3.1.2 NF-kB信号通路激活自噬减轻内皮细胞损伤:NF-kB信号通路正向调节自噬水平,对ECs也产生一定的影响。Peng等[13]在ApoE-小鼠中发现,甲基胞嘧啶双加氧酶2(TET2)的过表达可通过降低自噬标志Beclin 1启动子的甲基化水平,增加ECs自噬通量,下调炎症反应。而抑制TET2的表达导致内皮型一氧化氮合酶(eNOS)水平的上调和内皮素-1水平的下调,导致ECs损伤,增加AS的发生[14]。在Guo等[15]的研究中,自噬可诱导eNOS表达,减少人体中的氧化应激,减轻内皮损伤,减缓AS进程。

3.1.3 NF-kB信号通路激活自噬减少VSMCs的增殖迁移:VSMCs在AS中也同样参与自噬过程。VSMCs可分泌多种细胞因子,减轻炎症反应,其大量增殖迁移可加剧AS进程[16]。Grootaer等[17]在VSMCs中发现,脂质过氧化产物4-羟基壬烯醛(4-HNE)可通过单磷酸腺苷活化蛋白激酶(AMPK)和雷帕霉素靶蛋白(mTOR)独立机制增强自噬,使VSMCs免受4-HNE诱导的细胞死亡,减少其增殖迁移。Wu等[18]的研究同样发现,上调自噬和激活AMPK/mTOR信号通路可减少ROS的产生而抑制VSMCs的增殖迁移。

3.1.4 NF-kB信号通路激活自噬抑制巨噬细胞浸润:最近的研究表明,巨噬细胞自噬可通过促进胆固醇外流和抑制炎性体激活来抑制AS的进展[19],巨噬细胞中自噬的缺乏被证明损害胆固醇流出,并可导致IL-1β分泌增加和胆固醇结晶[20]。Wang等[21]在巨噬细胞自噬过程中发现,巨噬细胞可通过miR-384-5p介导的Beclin-1调节AS进展。激活的巨噬细胞抑制mTOR通路来稳定斑块,而巨噬细胞自噬受损刺激其极化为M1型巨噬细胞。已有研究发现,抑制PI3K/Akt/mTOR通路可诱导自噬,减少斑块中巨噬细胞的浸润和炎症因子的表达[22]。可见,自噬可抑制巨噬细胞浸润。

3.2 自噬负向调节NF-kB信号通路:在AS中NF-kB信号通路正向调节自噬水平的同时,自噬也负向调节NF-kB信号通路。自噬抑制NF-kB信号通路可减轻炎症反应、内皮细胞损伤,减弱VSMCs的增殖迁移,减少巨噬细胞浸润。

3.2.1 自噬抑制NF-kB信号通路减轻炎症反应:近年发现,自噬可特异性降解NF-kB信号通路中非经典途径中的关键酶(NIK)和I-kB激酶(IKK)水平,从而减轻炎症反应,减缓AS进程[23]。随后在AS中研究也发现,自噬激活导致NF-kB信号通路上游的促炎介质的自噬体降解,导致促炎基因表达减少,从而减轻炎症反应[24]。

3.2.2 自噬抑制NF-kB信号通路减轻内皮细胞损伤:近年在小鼠肺泡上皮细胞缺氧复氧模型中发现,自噬增强可通过抑制NF-kB信号通路和调节炎症介质的释放来减少肺泡上皮细胞损伤[25]。而在小鼠的肠黏膜上皮细胞中同样也发现,缺氧介导自噬的激活,从而降低NF-kB信号通路的表达,减轻肠黏膜上皮细胞的损伤[26]。可见自噬可通过抑制NF-kB信号通路减轻内皮细胞损伤。

3.2.3 自噬抑制NF-kB信号通路减少VSMCs的增殖迁移:Ramadan等[27]在关于自噬与VSMCs研究中发现,自噬受许多自噬相关基因(ATG)调节,其中ATG7是自噬的必需调节因子,因为它是过氧化物酶体和液泡膜融合所必需的,导致自噬体产生。血管紧张素II(AngII)刺激主动脉内皮细胞后,ATG7合成增加,VSMCs大部分处于静止状态,而SiRNA干扰ATG7后,VSMCs表型由静止型转化成增殖迁移型。也有相继研究发现自噬的激活抑制NF-kB信号通路表达的同时,也抑制VSMCs的增殖[28]。

3.2.4 自噬抑制NF-kB信号通路减少巨噬细胞浸润:在AS中,巨噬细胞的浸润加剧斑块的不稳定性,NF-KB信号通路调节巨噬细胞水平,自噬同样也调节巨噬细胞。M1型巨噬细胞主要分泌IL-1b等促炎因子和细胞因子,NF-kB信号通路的激活可促进M1型巨噬细胞的活化,自噬增强抑制了NF-kB信号通路,而自噬抑制剂(3-MA)作用后增加了M1型巨噬细胞的活化[29]。在一项关于黄曲霉素(AFB1)的研究中發现,AFB1作用于巨噬细胞后,氧自由基和自噬明显增加,M1型巨噬细胞量明显减少[30]。巨噬细胞中通过核苷酸结合寡聚化结构域样受体家族含热蛋白结构域3(NLRP3)炎症小体的激活调节自噬,自噬的激活通过靶向泛素化来抑制IL-1β的分泌和促进前IL-1β的溶酶体降解[31]。雷帕霉素介导的自噬在巨噬细胞中通过减少线粒体活性氧和前IL-1β的释放,IL-1β的减少降低了IL-1β-p38 MAP激酶(MAPK)-NF-kB途径的活性。抑制自噬后,巨噬细胞产生的IL-1β和IL-18明显减少。间接说明雷帕霉素通过抑制NLRP3的正反馈回路炎性体-p38 MAPK-NF-kB途径负向调节巨噬细胞活性[32]。

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