線粒體氧化應(yīng)激與心肌重構(gòu)研究進(jìn)展

賈春澍,范志民,陳曉亮,任立群*

(1.吉林大學(xué)藥學(xué)院實(shí)驗(yàn)藥理與毒理學(xué)教研室,吉林長(zhǎng)春130021;2.吉林大學(xué)白求恩第一醫(yī)院乳腺外科;3.吉林大學(xué)中日聯(lián)誼醫(yī)院泌尿外科)

心力衰竭是工業(yè)化國(guó)家致死的首要原因[1]。這也是一個(gè)日益嚴(yán)重的公共衛(wèi)生問題,主要是由于人口老齡化和老人心力衰竭患病率升高。大量的基礎(chǔ)、臨床和人口科學(xué)研究促進(jìn)了心力衰竭的現(xiàn)代治療,但左心室(left ventricular,LV)衰竭發(fā)生和發(fā)展最根本的機(jī)制仍未完全闡明?；钚匝醮?Reactive oxygen species,R OS)如超氧負(fù)離子(·O2-)和羥自由基(-OH)可導(dǎo)致膜磷脂、蛋白和DNA氧化[2],并與一系列病理狀態(tài)有關(guān),如缺血再灌注損傷[3],神經(jīng)變形性疾病[4]及衰老[5]。在生理狀態(tài)下,活性氧簇的毒性效應(yīng)可以被超氧化物歧化酶(superoxide dismutase,SOD)、谷胱甘肽過氧化物酶(glutathione peroxidase,GSHPx)、過氧化氫酶及其他非酶抗氧化劑清除。但是,當(dāng)ROS的產(chǎn)生超過抗氧化劑的防御能力時(shí),氧化應(yīng)激即對(duì)生物組織產(chǎn)生功能和結(jié)構(gòu)上的破壞效應(yīng)。ROS隨即導(dǎo)致心肌收縮力下降及結(jié)構(gòu)損傷。氧化應(yīng)激在心肌衰竭發(fā)展過程中的LV重構(gòu)的病理生理機(jī)制中所起的作用日益受到重視?，F(xiàn)有的證據(jù)表明,ROS的突出作用是作為一個(gè)信號(hào)分子對(duì)激素、生長(zhǎng)和凝血因子、細(xì)胞因子和氧分壓改變的作用做出反應(yīng)[6]。在低氧狀態(tài)下,高水平的線粒體ROS能夠誘導(dǎo)低氧誘導(dǎo)因子(hypoxiainducible factor,HIF-1α)的激活。HIFs是細(xì)胞對(duì)低氧適應(yīng)性反應(yīng)的主要因子。線粒體ROS與低氧狀態(tài)下HIF-1α的表達(dá)密切相關(guān),多種蛋白激酶參與ROS與HIF-1α表達(dá)之間的信號(hào)轉(zhuǎn)導(dǎo)[7],其具體機(jī)制仍待闡明。另外,也有研究認(rèn)為抗氧化劑加重心力衰竭[8]。

1 心力衰竭過程中的線粒體氧化應(yīng)激

目前的實(shí)驗(yàn)及臨床證明ROS的產(chǎn)生促進(jìn)心力衰竭[9-12]。脂質(zhì)過氧化物水平和 8-iso-前列腺素 F2α(8-isoprostaglandin F2a,8-iso-PGF2a)是ROS產(chǎn)生的主要生物學(xué)標(biāo)志物。心力衰竭患者的血清和心包液中這兩項(xiàng)指標(biāo)明顯升高并與其嚴(yán)重程度相關(guān)[9,12]。Belch等[9]報(bào)道丙二醛水平與LV射血分?jǐn)?shù)呈現(xiàn)明顯負(fù)相關(guān)(r=-0.35)。Mallat等[12]應(yīng)用NYHA分類和超聲心動(dòng)圖評(píng)價(jià)心肌衰竭的嚴(yán)重度,證明其與心包液中8-iso-PGF2a含量相關(guān):有癥狀的心力衰竭患者(NYHA II和III)心包液中8-iso-PGF2a含量明顯高于無癥狀(NYHA I)心力衰竭患者,并與病情嚴(yán)重程度相關(guān)(P=0.000 3)。另外,心包液中8-iso-PGF2a與LV舒張末期及收縮末期直徑呈正相關(guān)(P=0.008,P=0.026,respectively)[12]。心臟中R OS的細(xì)胞來源包括心肌細(xì)胞,上皮細(xì)胞和中性粒細(xì)胞。心肌細(xì)胞ROS產(chǎn)生的亞細(xì)胞定位包括線粒體電子傳遞,NAD(P)H氧化酶,和黃嘌呤脫氫酶/黃嘌呤氧化酶。心臟是攝氧率最高的器官,基礎(chǔ)代謝狀態(tài)下每分鐘每克體重消耗約0.1 ml O2[13]。為滿足氧化代謝ATP合成的需要,整個(gè)機(jī)體中心肌細(xì)胞具最高的線粒體體積密度。線粒體通過單電子經(jīng)呼吸鏈傳遞至氧分子產(chǎn)生ROS。在生理狀態(tài)下,線粒體呼吸鏈傳遞過程產(chǎn)生微量ROS,肌細(xì)胞的內(nèi)源性清除機(jī)制隨即發(fā)揮清除作用。

應(yīng)用電子自旋共振(electron spin resonance,ESR)光譜學(xué),5,5’二甲基-1-吡咯啉-N-氧化物(DMPO)作為捕捉物,在正常的亞線粒體結(jié)構(gòu)抑制電子傳遞鏈的復(fù)合體I和復(fù)合體 Ш導(dǎo)致大量·O2-的產(chǎn)生[14]。在NADH作用下,衰竭心臟的線粒體較正常心臟產(chǎn)生更多的·O2-,說明線粒體電子傳遞鏈?zhǔn)恰2-的主要來源。進(jìn)一步來說,線粒體功能衰竭伴隨著復(fù)合酶活力的降低。因此,線粒體是衰竭心臟ROS的主要來源,同時(shí)也證明線粒體衰竭和氧化應(yīng)激[15]的病理生理關(guān)聯(lián)。

2 線粒體DNA損傷,功能衰竭和氧化應(yīng)激

線粒體具其單獨(dú)的基因組,即mtDNA,一個(gè)閉合環(huán)狀雙鏈DNA分子,約16.5 KB。mtDNA有兩個(gè)啟動(dòng)子,輕鏈(LSP)和重鏈啟動(dòng)子(HSP)。線粒體功能受mtDNA的調(diào)控,同時(shí)mtDNA轉(zhuǎn)錄和/或復(fù)制因子也對(duì)其產(chǎn)生影響[16]。這就提出了mtDNA損傷和線粒體基因轉(zhuǎn)錄或復(fù)制的異常與心力衰竭相關(guān)的可能。實(shí)際上,很多證據(jù)表明心力衰竭與mtDNA在質(zhì)和量上的缺陷相關(guān)[17-20]。線粒體功能和mtDNA拷貝數(shù)的下降在心肌缺血后心力衰竭的發(fā)展中發(fā)揮著重要作用[17,21]。

ROS能夠在其形成或靠近形成部位損傷線粒體大分子。因此,除了產(chǎn)生 R OS,線粒體本身也能被ROS損傷,mtDNA是主要的靶點(diǎn)。原因如下,首先,線粒體基因組無組蛋白參與組裝,即缺少了對(duì)抗ROS損傷的一道屏障。第二,mtDNA的DNA修復(fù)能力有限。第三,線粒體內(nèi)形成大量的·O2-,并且不能通過線粒體膜,因此,ROS損傷大部分局限在線粒體內(nèi)。實(shí)際上,mtDNA聚集了大量DNA氧化產(chǎn)物,8-羥基,明顯高于核DNA[22]。與核編碼基因不同,線粒體編碼基因表達(dá)調(diào)控主要依賴于mtDNA的拷貝數(shù)[23]。因此,線粒體損傷主要表現(xiàn)在mtDNA的損傷,即線粒體RNA(mtRNA)轉(zhuǎn)錄子,蛋白合成和線粒體功能的下降[24,25]。衰竭心臟中線粒體結(jié)構(gòu)損傷和功能衰竭與ROS升高水平有關(guān),主要表現(xiàn)為線粒體脂質(zhì)過氧化物水平升高,mtDNA拷貝數(shù)下降,mtRNA轉(zhuǎn)錄子數(shù)目下降,及低復(fù)合酶活力導(dǎo)致的氧化能力下降[21]。更重要的是,衰竭心臟的Ⅰ,Ⅲ,和Ⅳ復(fù)合酶活力下降,而單純由核DNA編碼的復(fù)合酶Ⅱ和檸檬酸合成酶活力無下降表現(xiàn)。慢性的ROS產(chǎn)生增高與線粒體損傷和功能衰竭有關(guān),即形成線粒體功能下降的惡性循環(huán),大量的ROS產(chǎn)生引起細(xì)胞損傷。mtDNA損傷通過上述機(jī)制參與心肌重構(gòu)和心力衰竭的發(fā)生和發(fā)展。

3 線粒體氧化應(yīng)激在心肌重構(gòu)中的作用

氧化應(yīng)激對(duì)心肌細(xì)胞結(jié)構(gòu)和功能有直接的作用,能夠直接激活心肌重構(gòu)和心力衰竭的信號(hào)分子。ROS導(dǎo)致心肌細(xì)胞的表型變化,即離體的心肌細(xì)胞肥大和凋亡[26]。

ROS另一個(gè)作用靶點(diǎn)是金屬基質(zhì)蛋白酶(matrix metalloproteinases,MMPs)。MMPs在正常組織重構(gòu)中發(fā)揮重要的作用,如細(xì)胞遷移,侵襲,增殖和凋亡。并參與多種發(fā)育過程,如血管分枝形態(tài)建成,血管發(fā)生,創(chuàng)傷愈合及細(xì)胞外基質(zhì)降解。MMPs表達(dá)于大量細(xì)胞和組織中并廣泛的降解細(xì)胞外基質(zhì)蛋白[27]。ROS有激活心肌成纖維細(xì)胞MMP的作用[28]。衰竭心肌細(xì)胞MMP活力增高[26,29]。MMP抑制劑具有限制心肌缺血大鼠模型早期LV擴(kuò)張的作用[30]。心肌缺血模型中,MMP-2基因敲除明顯抑制了早期心臟破裂和LV衰竭的發(fā)展,生存率明顯提高[31]。由于 ROS能激活MMP[32],隨即提出了ROS的過多產(chǎn)生過度激活MMPs導(dǎo)致LV重構(gòu)的學(xué)說。持續(xù)的MMP激活可能通過提供一個(gè)異常的細(xì)胞外環(huán)境影響心肌的結(jié)構(gòu)特點(diǎn)。·OH清除劑二甲叉三脲能夠抑制心肌重構(gòu)和心力衰竭相關(guān)的MMP-2激活[33]。這些證據(jù)均表明心肌缺血后的過度氧化應(yīng)激是心肌MMP激活的刺激物,并在心力衰竭發(fā)展過程中發(fā)揮重要作用。

4 氧化應(yīng)激與骨骼肌功能失調(diào)的作用

運(yùn)動(dòng)能力受限是心衰患者的主要癥狀[34],而不依賴于心力衰竭程度[35]。心衰患者運(yùn)動(dòng)能力受限與過度的氧化應(yīng)激有關(guān)[36]。心肌缺血導(dǎo)致的心肌衰竭大鼠骨骼肌ROS含量明顯升高,主要是線粒體產(chǎn)生的·O2-[37]。目前,Kinugawa等[38]闡述了·O2-與運(yùn)動(dòng)能力受限的關(guān)系,·O2-含量升高運(yùn)動(dòng)能力下降,同時(shí)與全身氧耗升高有關(guān)。解偶聯(lián)蛋白(Uncoupling proteins,UCPs)是線粒體內(nèi)膜質(zhì)子運(yùn)載體,能夠降低質(zhì)子線粒體內(nèi)膜電化學(xué)梯度。電化學(xué)梯度的降低導(dǎo)致ATP生物合成的降低。衰竭心肌線粒體表達(dá)UCPs明顯上調(diào)[39]。另外,Echtay等[40]的研究表明線粒體內(nèi)ROS激活UCPs。這些結(jié)果表明ROS能通過上調(diào)UCPs表達(dá)引起能效改變,這可能在心力衰竭發(fā)展過程中骨骼肌的功能失調(diào)發(fā)揮作用。

5 結(jié)語

為改善心力衰竭患者的預(yù)后,我們需要基于心肌重構(gòu)和心力衰竭病理生理過程的深入探尋發(fā)展一種新型的治療方法。線粒體氧化應(yīng)激和mtDNA損傷的調(diào)節(jié)方法的研究可能有助于建立有效治療心力衰竭策略。氧化應(yīng)激不僅涉及心力衰竭,而且與各種心血管疾病包括動(dòng)脈粥樣硬化,高血壓及衰老過程相關(guān)。因此,以調(diào)節(jié)這種不當(dāng)?shù)倪m應(yīng)性的反應(yīng)作為治療策略可能得到廣泛的應(yīng)用。

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