秦碧媛,曾春芳
(四川省德陽市人民醫(yī)院呼吸內(nèi)科,四川 德陽 618000)
慢性阻塞性肺疾病(COPD)是發(fā)病率、致死率均高的慢性氣道炎癥疾?。?~3],每年導(dǎo)致數(shù)百萬人死亡[4]。眾所周知,該疾病是環(huán)境及基因共同作用導(dǎo)致,吸煙為首要的危險(xiǎn)因素[5],早期僅為生物化學(xué)和細(xì)胞水平事件,無明顯癥狀,診斷困難,嚴(yán)重威脅人類健康。急性加重期的死亡率增加2.5%[6],反復(fù)急性加重將降低患者的長期生存率[7,8],因而,尋找能早期診斷COPD,早期發(fā)現(xiàn)COPD急性加重的生物標(biāo)記物成為研究熱點(diǎn)?,F(xiàn)今,蛋白組學(xué)已經(jīng)廣泛運(yùn)用到生物標(biāo)記物的研究中[9~11],新近研究發(fā)現(xiàn),熱休克蛋白-27(heat shock protein-27,HSP-27)及親環(huán)蛋白(cyclophilin,CyP)在早期COPD患者中表達(dá)升高,具有一定特異性,可早期診斷,干預(yù),改善預(yù)后?,F(xiàn)就上述兩種生物標(biāo)記物在COPD中的研究進(jìn)展做一綜述。
HSP是細(xì)胞在一些應(yīng)激條件下,如熱休克,葡萄糖饑餓,或受到病原菌感染時(shí)高效表達(dá)的一族蛋白。作為一種分子伴侶,它不僅在應(yīng)激條件下高效表達(dá),在生理情況下,也參與重要細(xì)胞生理活動(dòng),如蛋白質(zhì)轉(zhuǎn)位,折疊和裝配,協(xié)助變性的蛋白重新折疊,或者將無法恢復(fù)的蛋白質(zhì)轉(zhuǎn)移給蛋白質(zhì)降解系統(tǒng),使之降解,從而避免進(jìn)一步傷害,因此HSP對(duì)細(xì)胞具有保護(hù)作用。除此之外,在受到感染和發(fā)生自身免疫疾病時(shí),HSP可作為一重要抗原被免疫系統(tǒng)識(shí)別,因此在醫(yī)學(xué)方面的作用也日益收到重視。熱休克蛋白按分子量可分為 HPS60,HPS70,HSP90,HPS110及 SHPS家族(低分子量熱休克蛋白)[12],HSP-27是低分子量HSP(sHSP)家族中重要的一員。當(dāng)細(xì)胞受到脅迫,如熱和氧化應(yīng)激等,熱休克轉(zhuǎn)錄因子與熱休克蛋白調(diào)節(jié)元件結(jié)合激活HSP-27基因,使HSP-27表達(dá)增加并且被磷酸化,磷酸化的HSP-27是一種具有保護(hù)細(xì)胞功能的活性形式,作為分子伴侶,促進(jìn)蛋白質(zhì)正確折疊,維持和保護(hù)蛋白質(zhì)構(gòu)象[13],阻止其變性,聚集和沉淀;保護(hù)細(xì)胞免受自由基,熱,缺血等各種應(yīng)激損失,有抗氧化[14~16],抗細(xì)胞凋亡,抗免疫損傷等作用。應(yīng)激時(shí),HSP-27被誘導(dǎo)短暫升高,當(dāng)應(yīng)激事件終止時(shí),HSP-27可立即下調(diào)至正常水平,它只在細(xì)胞保護(hù)需求增加時(shí)表達(dá)增加。已有大量研究發(fā)現(xiàn)血漿HSP-27在炎性疾病中表達(dá)增加,包括急性冠脈綜合征及慢性移植腎腎?。?7,18]。相較而言,該蛋白表達(dá)與 COPD 發(fā)生、發(fā)展、加重之間的關(guān)系正開始成為研究熱點(diǎn)。借助某些試驗(yàn)結(jié)果,我們認(rèn)為該生物標(biāo)記物有助于人類早期發(fā)現(xiàn)及評(píng)估病情嚴(yán)重程度:①可早期篩查及發(fā)現(xiàn)COPD:煙草與COPD的發(fā)生發(fā)展息息相關(guān),煙草中含有4700化學(xué)物質(zhì),其中含有的極高濃度的自由基和氧化劑,它們通過氧化應(yīng)激和炎癥機(jī)制,促進(jìn)了COPD 的形成和發(fā)展[19,20]。歐陽卿等[21]通過對(duì)比研究發(fā)現(xiàn),COPD組肺組織中氧化應(yīng)激相關(guān)酶類較對(duì)照組表達(dá)水平普遍增高,提示吸煙COPD患者肺組織氧化應(yīng)激可能強(qiáng)于非COPD吸煙者,再次印證氧化應(yīng)激是COPD的重要機(jī)制。Kelsen等[22]報(bào)道吸煙者肺組織中HSP-27表達(dá)上調(diào),Hacker等[23]發(fā)現(xiàn),相對(duì)于無 COPD的吸煙者,COPD患者血清HSP-27濃度更高;Ruicheng等[24]發(fā)現(xiàn),HSP-27 在吸煙者肺組織中的表達(dá)上調(diào),尤其是吸煙伴COPD患者;Jan Ankersmit等[25]針對(duì)94名健康的男性和女性吸煙者,研究其高解析度CT掃描、肺功能測(cè)試及血液樣本,發(fā)現(xiàn)HSP-27的水平與CT掃描發(fā)現(xiàn)的肺損傷具有顯著相關(guān)性。認(rèn)為血液中高水平的HSP-27能預(yù)示慢性阻塞性肺病早期階段的肺損害,而此時(shí)肺功能中肺容積的變化可能還在正常范圍,因而認(rèn)為HSP-27的蛋白質(zhì)有可能成為COPD早期檢測(cè)的新的血液生物標(biāo)志物,有助于該疾病早期發(fā)現(xiàn),早期干預(yù),改善疾病的預(yù)后。②評(píng)估COPD的嚴(yán)重程度:HSP-27具有抗凋亡作用[26],該作用使其成為內(nèi)在的免疫調(diào)節(jié)劑有可能控制COPD的過度炎癥介質(zhì)反應(yīng)。我們已知,HSP-27隨著細(xì)胞保護(hù)需求增加時(shí)表達(dá)增加[27],COPD是慢性炎癥性疾病,故而在穩(wěn)定期及急性加重期其HSP-27都高于正常人群,而急性加重期,HSP-27升高更為明顯,這將有助于我們臨床中鑒別患者癥狀加重是急性加重,還是本身肺功能差,甚至是急性左心衰導(dǎo)致。Hacker等[23]研究發(fā)現(xiàn),血清HSP-27水平將隨著的COPD嚴(yán)重性而進(jìn)行性升高,這可能與后期COPD患者肺組織及其他組織釋放更多HSP-27入血有關(guān)系,我們現(xiàn)在知道,COPD是全身炎癥性疾病,但其全身性炎癥反應(yīng)是肺局部炎癥反應(yīng)的“溢出”,還是由于致炎因素(如煙草)在氣道和全身合并發(fā)生,尚存爭(zhēng)議。該實(shí)驗(yàn)也許能為“溢出理論”提供某些依據(jù)。從HSP-27在穩(wěn)定期及急性加重期表達(dá)差異,現(xiàn)在我們認(rèn)為血清HSP-27有可能作為COPD新標(biāo)記物,判斷疾病的嚴(yán)重程度,是否存在急性加重,在指導(dǎo)治療上有重要作用。但因?yàn)檠錒SP-27在許多具有不良的預(yù)后的慢性疾病中表達(dá)升高,如惡性腫瘤[28~30],白血病[27]、腎功能損傷和和心血管疾病等,因此作為一種用于新的生物標(biāo)記物,還需深入研究,確定它的臨界值,以提高臨床應(yīng)用的靈敏性、特異性。
CyP是發(fā)現(xiàn)于1984年的一族胞漿蛋白,因其能與免疫抑制劑環(huán)孢霉素A(cyclosporinA,CsA)結(jié)合而得名,CyP家族在整個(gè)蛋白質(zhì)組中僅占據(jù)一部分,但廣泛存在,非常保守,具有多功能的特性使CyP在整個(gè)細(xì)胞生命期內(nèi)扮演著至關(guān)重要的角色。
現(xiàn)有研究發(fā)現(xiàn)CyP家族具有多種生物學(xué)活性,包括通過催化含脯氨酸的寡肽底物順反異構(gòu)作用的肽脯氨酰順反異構(gòu)酶(peptidyl-prolylcis-trans isomerases,PPIase)而幫助蛋白質(zhì)折疊和組裝;起到分子伴侶的作用,在應(yīng)激反應(yīng)中參與調(diào)節(jié)信號(hào)轉(zhuǎn)導(dǎo)途徑[31],并影響 RNA的剪接過程,參與蛋白質(zhì)翻譯[32],細(xì)胞周期調(diào)節(jié)及調(diào)控細(xì)胞應(yīng)激反應(yīng)有重要作用[33],其作用涉及抑制T細(xì)胞活化信號(hào)的傳導(dǎo)、肽基脯氨酸順反異構(gòu)酶活性、伴侶分子活性、人類類固醇激素受體的活化調(diào)節(jié)等。人類的CyP可分為幾個(gè)亞家族,目前陸續(xù)已經(jīng)大約有130種CyP同源異構(gòu)體被發(fā)現(xiàn)和克隆。
人類親環(huán)蛋白A(CyPA)是由165個(gè)氨基酸組成,分子量為18 kDa的胞漿蛋白,存在于細(xì)胞質(zhì)基質(zhì)中,被首個(gè)認(rèn)為是抗免疫反應(yīng)藥物的胞漿結(jié)合蛋白,通過催化脯氨酰肽鍵的順反異構(gòu)化來調(diào)節(jié)大量蛋白的活性[34~37],研究顯示,CyPA 在缺氧,氧化應(yīng)激及炎癥的誘導(dǎo)下在多個(gè)組織中表達(dá)增加[38~40],參與蛋白質(zhì)折疊、裝配與運(yùn)輸,參與免疫抑制,還可介導(dǎo)膽固醇轉(zhuǎn)運(yùn),發(fā)揮前炎性因子的功能,并且在信號(hào)轉(zhuǎn)導(dǎo)中具有重要作用。從而認(rèn)為CypA在炎癥、腫瘤中扮演著重要作用,而氧化應(yīng)激、炎癥正是COPD發(fā)病機(jī)制中的中心環(huán)節(jié),故COPD與CyPA的關(guān)系逐漸引起科研人員重視。Ruicheng等[24]研究發(fā)現(xiàn),CyPA在COPD患者肺組織中表達(dá)增加,尤其是吸煙的COPD患者中更為明顯,同時(shí)發(fā)現(xiàn),無論有無COPD,吸煙者的吸煙指數(shù)對(duì)CyPA的表達(dá)沒有明顯影響。眾所周知,煙草通過氧化應(yīng)激及炎癥機(jī)制促進(jìn)了COPD的發(fā)生發(fā)展,因而,吸煙者肺組織的CyPA表達(dá)增加,與氧化應(yīng)激有密切關(guān)系,炎癥也起到一定作用。而CyPA的表達(dá)在吸煙的COPD患者高于非吸煙者的COPD患者,則說明缺氧和炎癥更多參與到了COPD的形成發(fā)展中。但鑒于CypA與COPD關(guān)系的研究仍較少,它的表達(dá)與急性加重是否存在聯(lián)系,與全身炎癥的關(guān)系如何,尚未闡明,但初步的實(shí)驗(yàn)已經(jīng)提示該標(biāo)記物在研究中的廣闊前景。
人類親環(huán)蛋白B(CyPB)由208個(gè)氨基酸組成,因自身N末端特定信號(hào)序列被引導(dǎo)定位至內(nèi)質(zhì)網(wǎng)或線粒體中的蛋白。CyPB與CyPA的同源性很高,其核心序列幾乎相同,與CyPA有64%的同源性,CyPB可與淋巴細(xì)胞結(jié)合[41],調(diào)節(jié)環(huán)孢霉素介導(dǎo)的免疫抑制。Soo-Taek等[42]通過對(duì)穩(wěn)定期COPD患者及急性加重期COPD患者的痰液進(jìn)行包括CyP B在內(nèi)的數(shù)種生物標(biāo)記物檢測(cè)后,發(fā)現(xiàn)該生物標(biāo)記物在穩(wěn)定期表達(dá)不明顯而在急性加重期患者的痰液中表達(dá)升高。目前其在COPD急性加重期患者中升高的機(jī)理尚不明確,有可能CyPB參與了該疾病的形成和發(fā)展,也有可能是疾病的產(chǎn)物之一,同理于與炎性反應(yīng)標(biāo)記物CRP[43],CyPB有望成為COPD急性加重的生物標(biāo)記物之一。
HSP-27與CyP具有氧化應(yīng)激保護(hù),調(diào)控炎癥的發(fā)生、細(xì)胞凋亡,抗免疫損傷等作用,近年研究逐漸深入和廣泛,有望成為早期診斷及鑒別是否急性加重的簡(jiǎn)便靈敏的指標(biāo),但它們具體的作用機(jī)制,調(diào)節(jié)和影響因素尚不明了,是否能將該生物標(biāo)記物作為標(biāo)靶進(jìn)行干預(yù)進(jìn)而改善疾病的進(jìn)程更缺乏實(shí)驗(yàn)依據(jù),研究前景非常廣泛,亟待更多的實(shí)驗(yàn)闡明。
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