低氧致炎與低氧性肺動脈高壓

夏世金 吳俊珍 胡明冬

低氧致炎與低氧性肺動脈高壓

Hypoxia-induced inflammation and hypoxic pulmonary hypertension

夏世金1吳俊珍1胡明冬2

低氧； 肺動脈高壓； 炎癥

低氧性肺動脈高壓(hypoxic pulmonary hypertension, HPH)對人的長期嚴(yán)重危害依然未得到很好解決，是一治療極為棘手、高致死率和高致殘率的病理生理綜合征，被認(rèn)為是“假惡性”腫瘤[1]。低氧性肺血管結(jié)構(gòu)重建(hypoxic pulmonary vascular structural remodeling, HPVSR)和低氧性肺血管收縮(hypoxic pulmonary vasoconstriction, HPV)是HPH形成的兩大基本病理生理特征[2]。肺血管內(nèi)皮細(xì)胞(pulmonary vascular endothelial cell, PVEC)、肺血管平滑肌細(xì)胞(pulmonary vascular smooth muscle cell, PVSMC)和肺成纖維細(xì)胞是構(gòu)成肺血管壁的主要細(xì)胞，這些細(xì)胞結(jié)構(gòu)和功能的異常變化是導(dǎo)致HPVSR和HPV的主要原因。目前，對HPH的機制：①HPH機制復(fù)雜，尚未完全闡明；②有關(guān)HPH機制理論可歸納為低氧性肺血管結(jié)構(gòu)重建學(xué)說、低氧性肺血管收縮學(xué)說、低氧性肺血栓學(xué)說、低氧性細(xì)胞增殖學(xué)說、低氧性細(xì)胞凋亡學(xué)說和低氧性炎癥學(xué)說等。在HPH治療方面: HPH治療策略有降低肺動脈壓力、抑制血管異常增生、減輕肺血管肥厚及其結(jié)構(gòu)重建和抗炎等。近年來，以前未被足夠重視的低氧性炎癥機制和抗炎治療策略在HPH研究中越來越受到高度關(guān)注，并可望成為研究的重點和熱點。

一、低氧性炎癥是HPH發(fā)生的主要原因之一

研究表明，低氧能誘發(fā)炎癥，可稱之為低氧性炎癥。低氧是HPH的獨立危險因素[2]。臨床研究顯示,肺動脈高壓(pulmonary artery hypertension, PAH)患者肺血管叢狀病變周圍存在T細(xì)胞、B細(xì)胞、巨噬細(xì)胞及樹突狀細(xì)胞等炎癥細(xì)胞浸潤[3]。PAH患者血清白細(xì)胞介素-1(interleukin-1, IL-1)、IL-6 、腫瘤壞死因子-α(tumor necrosis factor-α, TNF-α)、C反應(yīng)蛋白(C-reactive protein, CRP)和單核細(xì)胞趨化因子1(monocyte chemotactic factor-1, MCP-1)等水平明顯升高[4]，且肺動脈叢狀病變處趨化因子CX3CLl和CCL5表達顯著升高，誘導(dǎo)縮血管物質(zhì)血管內(nèi)皮生長因子(vascular endothelial growth factor, VEGF)、內(nèi)皮素-l(endothelin, ET-1)、血小板衍化生長因子(platelet -derived growth factor, PDGF)等高表達[5]。炎性細(xì)胞及其分泌的炎性細(xì)胞因子、趨化因子、黏附分子等可導(dǎo)致PVEC損傷和PVSMC的增殖，從而參與HPV 和HPVSR進程[3]。這些研究結(jié)果提示炎癥是PAH形成的重要因素[3]。

動物實驗表明，在HPH大鼠PVSMC中，促炎細(xì)胞因子巨噬細(xì)胞移動抑制因子 (migration inhibitory factor, MIF)表達升高，進而增強肺動脈血管收縮，參與HPH發(fā)生[6]。PVSMC中的Rho/Rho-kinase (ROCK) 信號通路在PAH的發(fā)病機制中發(fā)揮著重要作用。Rho-kinase 有2個亞型，ROCK1 和 ROCK2，在不同細(xì)胞中發(fā)揮不同的作用，ROCK1主要在循環(huán)炎癥細(xì)胞，ROCK2主要在脈管系統(tǒng)中起作用[7]。在低氧培養(yǎng)的PVEC和HPH動物模型中可誘導(dǎo)出brahma-related gene 1 (Brg1) 和 brahma (Brm) 。Brg1/Brm過表達增強，同時其消耗減少，導(dǎo)致細(xì)胞黏附分子(cell adhesion molecule, CAM)的過量轉(zhuǎn)錄[8]。低氧時PVEC中15-脂氧合酶(15-lipoxygenase)出現(xiàn)高表達，后者可提高NK-κB的活性[9]。慢性HPH中，NALP3 炎癥小體激活，導(dǎo)致促炎癥細(xì)胞因子分泌，尤其是IL-1β，引起中性粒細(xì)胞炎癥，激活的炎癥細(xì)胞進一步招募更多的炎癥細(xì)胞并釋放大量的炎癥因子引起炎癥的瀑布反應(yīng)，損傷血管內(nèi)皮細(xì)胞[10]。

研究發(fā)現(xiàn)，低氧誘導(dǎo)因子-1(hypoxia-inducible factor 1, HIF-1)是介導(dǎo)低氧性炎癥的信號通路。低氧使巨噬細(xì)胞和中性粒細(xì)胞中HIF-1 激活。HIF-1可上調(diào)VEGF及其受體表達,使局部血管通透性增強，導(dǎo)致更多的免疫細(xì)胞到達炎癥部位，引起PVEC的炎癥性損傷[11]。低氧時HIF-1α過度表達可增強NF-κB p65核定位與轉(zhuǎn)錄活性，導(dǎo)致上皮細(xì)胞釋放大量的趨化因子和細(xì)胞因子(TNF-α等)[12]。而TNF-α可誘導(dǎo)成纖維細(xì)胞大量表達NF-κB[13]，低氧時小鼠PVSMC中NF-κB表達增強，促進HIF-1α轉(zhuǎn)錄[14]。低氧所誘導(dǎo)細(xì)胞產(chǎn)生和釋放的炎癥細(xì)胞因子可強化NF-κB通路，增加HIF表達，反過來又加劇細(xì)胞低氧[15]。上述研究提示HIF-1與NF-κB會話信號通路(cross talk)可能在調(diào)控HPH炎癥發(fā)生中處于重要地位[16]，是維系低氧與炎癥惡性循環(huán)的紐帶，可望成為有效干預(yù)HPH的理想靶標(biāo)，值得深入研究。此外，環(huán)磷酸腺苷應(yīng)答元件結(jié)合蛋白(CAMP response element binding protein, CREB)是一種重要的核轉(zhuǎn)錄因子，參與炎癥細(xì)胞因子(如IL-6等)等基因的轉(zhuǎn)錄，與NF-κB存在“cross talk”關(guān)系[17]，與低氧損傷及HPH密切相關(guān)[18]，近年來受到極大的關(guān)注，可能在HPH炎癥中發(fā)揮重要作用。

二、炎癥性低氧是HPH發(fā)展的一個重要因素

在HPH中，炎癥反應(yīng)可導(dǎo)致肺組織的氧供需失衡，肺組織細(xì)胞代謝需氧量劇增，肺微循環(huán)血栓等阻斷氧的供給。炎癥是肺組織對損害因子的一種防御反應(yīng)，但侵入肺部的炎性細(xì)胞耗氧量增加，炎癥部位形成低氧環(huán)境，加重低氧程度[12]。低氧可誘發(fā)炎癥，炎癥又可加重低氧，于是2012年著名雜志刊文提出“inflammatory hypoxia，炎癥性低氧”新概念[19]。

動物實驗表明,早期發(fā)現(xiàn)炎癥細(xì)胞因子受體拮抗劑對PAH大鼠模型有一定的效果[20-21]，近期發(fā)現(xiàn)間質(zhì)干細(xì)胞移植能逆轉(zhuǎn)HPH[12]。但HPH的抗炎研究主要集中于動物模型，而抗炎藥物對HPH早期有效，可是存在有免疫抑制問題[22]，臨床應(yīng)用已受到嚴(yán)格的限制。因此，尋求安全有效的HPH抗炎策略已成為當(dāng)務(wù)之急。

上述研究提示，低氧性炎癥與炎癥性低氧二者共處一體即HPH共同體，且低氧與炎癥存在著惡性循環(huán)關(guān)系，但其機制尚未闡明。就某種意義而言，炎癥既是低氧的“果”，又是加重低氧的“因”，炎癥在HPH發(fā)生中起著關(guān)鍵作用。低氧與炎癥的惡性循環(huán)可能是HPH防治困難的主因之一，而要打破這種惡性循環(huán)的關(guān)鍵環(huán)節(jié)的策略就是抗炎，見圖1。

圖1 低氧導(dǎo)致HPH發(fā)生過程的簡要模擬圖

目前，由于炎癥在HPH發(fā)生發(fā)展的作用與機制尚未闡明，嚴(yán)重制約了抗炎在HPH臨床中的應(yīng)用。因此，積極篩選并明確機體的內(nèi)源性基因，作為干預(yù)HPH的目標(biāo)基因，調(diào)控目標(biāo)基因的內(nèi)源性表達，從而達到安全有效防治HPH之目的是防治HPH的新方向與新策略。

三、表觀遺傳學(xué)是闡明HPH炎癥機制的有效策略

在HPH中炎癥細(xì)胞因子基因表達出現(xiàn)上調(diào)或下調(diào)，那么這些基因的表達變化是一過性的？還是在一定時間內(nèi)維持穩(wěn)定？又能持續(xù)多久？需要從表觀遺傳學(xué)入手解答這些問題。

表觀遺傳學(xué)調(diào)控是一類不涉及遺傳物質(zhì)改變的基因調(diào)節(jié)方式，發(fā)現(xiàn)其幾乎存在于生物調(diào)控的所有環(huán)節(jié)[23]。表觀遺傳學(xué)調(diào)控的一個最常見、最清楚和最重要的機制是DNA甲基化。DNA甲基化可調(diào)控基因表達的開啟、關(guān)閉與水平。甲基化常導(dǎo)致基因表達沉默或降低，去甲基化則使基因表達重新激活。DNA甲基化主要由DNA甲基化轉(zhuǎn)移酶(DNA methyltrasferases, DNMTs)所控制。已鑒定的人類具有催化活性的DNMTs有三種：DNMT1、DNMT3A和DNMT3B[24]。表觀遺傳修飾一旦形成，即使撤除干預(yù)因素，也可長時間保持穩(wěn)定，維持對基因表達水平的調(diào)控，從而參與細(xì)胞和機體形成與環(huán)境相適應(yīng)的穩(wěn)態(tài)。

炎癥細(xì)胞因子DNA甲基化與炎癥相關(guān)疾病密切關(guān)聯(lián)[25]。DNA甲基化在炎癥領(lǐng)域的研究進展較快[26]。TNF-α的DNA甲基化修飾與非腫瘤胃黏膜病變[27]，IL-6的DNA甲基化修飾與口腔癌[28]，IL-10甲基化修飾與乳腺癌密切相關(guān)[29]?？梢酝茰y，低氧作為一種干預(yù)因素，可能會影響炎癥因子基因表達的表觀遺傳修飾調(diào)控。

總之，低氧誘發(fā)炎癥，炎癥又加重低氧，共同參與HPH的發(fā)生和發(fā)展。低氧性炎癥、炎癥性低氧與HPH形成惡性循環(huán)，而抗炎是打破這種惡性循環(huán)的有效策略。抗炎策略的確立依賴于HPH炎癥機制的闡明，而表觀遺傳學(xué)(如DNA甲基化等)為闡明HPH炎癥機制提供了理論依據(jù)和有效方法。

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(本文編輯：王亞南)

夏世金，吳俊珍，胡明冬. 低氧致炎與低氧性肺動脈高壓[J/CD]. 中華肺部疾病雜志： 電子版， 2014， 7(5)： 563-565.

10.3877/cma.j.issn.1674-6902.2014.05.022

國家自然科學(xué)基金(81270115)

1200040 上海，復(fù)旦大學(xué)附屬華東醫(yī)院上海市 老年醫(yī)學(xué)研究所、老年醫(yī)學(xué)科

2400037 重慶，第三軍醫(yī)大學(xué)新橋醫(yī)院全軍 呼吸內(nèi)科研究所

胡明冬， Email: huhanshandd@aliyun.com

R563

A

2014-08-23)