张荟 蒋沁 姚进
血红素加氧酶-1与角膜病、青光眼、白内障及视网膜疾病的关系△
张荟 蒋沁 姚进
血红素加氧酶-1;角膜病;青光眼;白内障;视网膜病;抗氧化;细胞保护
血红素加氧酶-1(heme oxygenase-1,HO-1)是体内最重要的内源性抗氧化酶之一。它可以催化血红素分解为一氧化碳、铁离子和胆绿素,HO-1及其产物具有抗氧化、抗炎和抗凋亡等功能。越来越多的研究显示,诱导HO-1表达上调可以保护角膜、小梁网、晶状体及视网膜等眼部组织免受氧化损伤,成为治疗相关眼科疾病的潜在靶点。本文就HO-1在眼科疾病中的最新研究进展作一综述。
[眼科新进展,2014,34(4):385-388]
氧化应激是多种眼科疾病发生发展的重要机制。机体通过本身的内源性抗氧化系统抵抗氧化损伤,血红素加氧酶-1(heme oxygenase-1,HO-1)就是其中分布最广泛的一种抗氧化酶。HO-1与其他抗氧化酶不同,它能将血红素分解成等摩尔的胆绿素、铁离子和CO[1],而这些终末产物同时也具有抗氧化活性,发挥强大的细胞保护作用[2-3]。近年来,HO-1的抗氧化、抗炎、抗凋亡等作用引起越来越多的关注。深入了解其与眼科疾病的关系,将为调控HO-1治疗眼科疾病提供理论基础。本文就HO-1在眼科疾病中的最新研究进展作一综述。
HO有三种亚型,即HO-1、HO-2和HO-3。研究最多的是HO-1同工酶。人体中HO-1相对分子质量为32 800,由288个氨基酸组成。HO-1又称热休克蛋白32,能被过氧化氢、紫外线、重金属(如钴、铬等)、低氧和细胞因子等多种因素诱导并显著表达。因此,HO-1也称诱导型HO。HO-2是在正常生理条件下起作用的结构型HO,在体内稳定表达,不受外界因素干扰。HO-3降解血红素的能力极低,其确切功能还有待进一步研究。
HO-1比任何酶都易被多种刺激所诱导,其表达主要是在转录水平上进行调节。HO-1启动子上有两个增强子区,即El和E2。多个应激反应元件位于El和E2之间,使HO-1具有强诱导性[4]。应激反应元件包括核因子-E2相关因子2(nuclear factor-E2 related factor2,Nrf2)、转录因子活化蛋白1、核转录因子κB、缺氧诱导因子-1等。其中几个重要的信号通路介导外部刺激对HO-1的诱导反应。丝裂原活化蛋白激酶(MAPK)家族(p38、ERK和JUK)直接或间接参与HO-1的上调。PI3K/Akt、JAK-STAT、TLR、IL-10及蛋白激酶A、C、G等也参与HO-1基因的调控。人群中HO-1的表达水平是千变万化的,这是因为HO-1基因的启动子具有高度多态性,包含不同重复数量GT二核苷酸序列[5]。研究发现,在GT短序列(GT≤23)的内皮细胞中,HO-1基因转录和表达的水平更高,细胞保护作用更强[6]。
HO-1抗氧化、抗炎、抗凋亡作用与其催化产物CO、游离铁和胆绿素密切相关。内源性CO主要来自HO的催化反应,是体内重要的细胞信号分子,调节体内多种生理和病理过程。CO以自分泌或旁分泌方式与胞浆内可溶性鸟苷酸环化酶(sGC)结合,催化三磷酸鸟苷(GTP)生成环鸟苷酸(cGMP),刺激依赖cGMP的蛋白激酶、磷酸二酯酶或调节离子通道。大量研究表明CO介导了HO-1 的主要抗炎抗氧化功能[7-8]。游离铁能迅速诱导铁蛋白合成并与之结合,促进游离铁的螯合,使细胞内铁含量减少,因此铁蛋白具有抗氧化的作用。最近的研究证明,HO-1的细胞保护作用与铁蛋白的表达升高有关[9]。胆绿素是机体重要的内源性强效抗氧化剂。实验证明,在各种病理生理活动中胆绿素具有很强的细胞保护作用[10-12]。
HO-1是机体重要的抗氧化酶,在眼内广泛分布。Abraham等[13]1987年首次在人角膜上皮细胞中发现HO的活性。以后的研究进一步发现HO也分布在眼内其他组织。HO-2作为组成型HO,在视网膜上的不同分布取决于动物的物种。HO-2只在猴视网膜神经节细胞(retinal ganglion cell,RGC)的胞体中分布,而不存在于内丛状层、内核层和外核层[14]。HO-2分布在龟视网膜光感受器、无长突细胞、双极细胞和神经节细胞内。在大鼠中,HO-2分布在内层视网膜的神经节细胞和无长突细胞中[15]。与HO-2不同,HO-1是诱导型HO,体内、体外实验证明,在诱导因素的作用下,视网膜色素上皮(retinal pigment epithelium,RPE)细胞[16]、RGC[17]、光感受器细胞[18]、Müller细胞[19]、晶状体上皮细胞(human lens epithelial cells,LECs)[20]和小梁网细胞[21]等均有HO-1的表达。HO-3在眼内的分布仍未知。
4.1HO-1与角膜病角膜病是我国主要的致盲性眼病之一。由于角膜的特殊解剖位置,其易于受到创伤和感染等外界刺激因素的影响;同时由于角膜本身没有血管,机体循环内的抗氧化分子难以到达角膜上皮,因此角膜自身的抗氧化防御系统显得尤为重要。Braunstein等[22]用人角膜上皮细胞系(human corneal epithelial cell line, HCE-T)研究发现,给予HO-1诱导剂(氯化锌、氯化亚锡和血红素)可减少眼部刺激(包括过氧化氢、异丙醇、氢氧化钠和三氯乙酸)的细胞毒作用;相反,给予HO-1抑制剂锌原卟啉(ZnPP)能增强刺激物对细胞活性的影响。Patil等[23]在角膜炎动物模型的研究中发现,用氯化亚锡诱导HO-1的表达,可加快角膜炎小鼠的伤口愈合,角膜基质细胞浸润减轻,促炎性脂质介质和细胞因子的产生也显著减少。Bellner等[24]用HO-2缺失的小鼠和野生型小鼠制作角膜机械损伤模型,他们发现HO-2缺失的小鼠角膜炎症和新生血管更明显,同时其角膜损伤处HO-1的诱导表达减少,用胆绿素预处理能减弱HO-2缺失小鼠的炎症和新生血管反应。Bellner等[25]进一步研究发现,胆绿素还能挽救HO-2缺失小鼠角膜损伤后久治不愈的慢性炎症。Halilovic等[26]用体外角膜损伤模型研究发现,角膜擦伤后HO-1及其活性短暂性升高。用胆绿素或CORM-A1(CO供体)能加速伤口的愈合。这些体内、体外的研究结果表明,HO-1在控制角膜炎症反应中起到至关重要的作用。
4.2HO-1与青光眼青光眼是一种进行性视神经病变,是以特征性的视野缺损为特点的眼科疾病。目前认为,氧化应激在青光眼的发生发展中起重要作用,RGC及其轴突进行性死亡是视野缺损的最终原因。由此,保护RGC在青光眼治疗中尤为重要。最近有实验证明,钴原卟啉(CoPP)诱导大鼠RGC高表达HO-1,通过减少p53、 caspase-3、核转录因子-κB、iNOS和MCP-1介导的巨噬细胞浸润,从而对急性青光眼导致的视网膜缺血再灌注损伤起保护作用[27]。Koriyama等[28]研究发现,α-硫辛酸通过Keap1/Nrf2信号通路诱导HO-1的表达,保护RGC免受氧化应激损伤。病理性眼压升高是青光眼的主要危险因素之一。Privitera等[29]发现应用HO-1的诱导剂——氯高铁血红素可以降低兔眼压,从而减少高眼压对RGC的损伤。此外,CO作为HO-1的主要产物之一,大量研究证明CO也是眼压的重要调节分子[30]。这些研究结果表明,HO-1/CO作为眼压的调节因子,为青光眼的治疗提供了新的靶点。
4.3HO-1与白内障白内障是晶状体部分或完全的混浊,它是世界上可逆性致盲性眼病的主要病因。年龄相关性白内障的发病机制是复杂的,尚未得到充分的阐明。一般认为,氧化应激在白内障的发生和发展中起十分重要的作用[31-32]。HO-1是反映细胞氧化应激水平的敏感可靠的指标,且具有抗氧化损伤的作用。Abraham等[33]发现,将人HO-1基因转染到兔玻璃体内,在晶状体内检测到HO-1 mRNA的表达。最近有研究证明,白藜芦醇通过增加HO-1、超氧化物歧化酶-1和过氧化物酶对人LECs氧化损伤起保护作用[20],褪黑激素通过PI3K/Akt信号通路诱导HO-1、Nrf2、过氧化氢酶和丙二醛的表达,保护LECs免受过氧化氢导致的细胞凋亡[34]。但HO-1与白内障的关系还需进一步研究。
4.4HO-1与年龄相关性黄斑变性年龄相关性黄斑变性(age-related macular degeneration,AMD)是发达国家老龄人中视力丧失的首要病因。随着我国人口老龄化趋势的加剧,AMD的患病率有不断增高的趋势。AMD的发病机制虽然不完全清楚,但氧化应激在AMD的发生发展中起重要作用。HO-1被认为是一种抗氧化损伤的细胞防御因子。Frank等[35]研究发现,人RPE中HO-1和HO-2抗原水平随年龄增加而降低,其中新生血管性AMD患者相对于正常对照组降低更明显。Miyamura等[36]也观察到在正常人RPE中,HO-1 mRNA和HO-1蛋白的表达随年龄增长而下降。HO-1在人RPE中的表达随着年龄的增加而减少。提示HO-1的表达减少可能参与了AMD的发生发展过程。最近体外实验证明,姜黄素诱导人RPE中HO-1的表达,减少ROS的产生,从而缓解人RPE氧化应激损伤[37]。再者,有研究指出黄酮类化合物通过Nrf2通路上调HO-1的表达,阻断细胞内活性氧的累积,保护RPE和RGC氧化应激诱导的损伤[16,38]。最新研究发现,虾青素激活PI3K/Akt通路,上调Nrf2介导的HO-1、苯醌氧化还原酶1等的表达,可减轻RPE氧化应激损伤[39]。
4.5HO-1与糖尿病视网膜病变糖尿病视网膜病变(diabetic retinopathy,DR)是最常见的糖尿病微血管并发症之一,是成年人群致盲的主要原因之一。大量研究证明,氧化应激是DR发生发展中的关键因素。流行病学研究发现,血糖控制不佳、抗氧化酶mRNA的低表达与DR的发生发展密切相关[40]。Castilho等[41]研究发现,采用电穿孔基因转染技术将pcDNA3-HO-1质粒转入视网膜血管内皮细胞,HO-1的表达和活性增加,HO-1在氧化或氧化应激条件下对血管内皮细胞起保护作用。da Silva等[42]发现糖尿病患者视网膜中的HO-1 mRNA表达是降低的。与糖尿病患者结果不同,链脲佐菌素(streptozotoein,STZ)诱导的糖尿病大鼠6周后视网膜HO-1表达增加[43]。提示糖尿病大鼠早期,视网膜HO-1的表达增加可能是应激性增加,在病程的进展中HO-1可能会有一个时间依赖性的变化。这与细胞实验研究相一致,在血管内皮细胞中葡萄糖对HO-1的诱导依赖于葡萄糖的自身水平,葡萄糖轻度增高,HO-1的表达和活性增加,以抗氧化应激和细胞凋亡,而葡萄糖增加过多,活性氧大量生成,阻断HO-1的上调,最终导致细胞的高死亡率[44]。进一步研究发现,氯高铁血红素诱导HO-1表达上调可减轻糖尿病大鼠RGC的病理损害[45]。以上结果均显示了HO-1治疗DR的可喜前景。
综上所述,HO-1在眼部组织氧化应激及其他因素诱导下发挥强效的细胞保护作用。因此,HO-1是治疗AMD、DR等眼科疾病的一个潜在靶点,具有重要的临床意义。
近年来大量实验证明,HO-1诱导剂通过HO-1表达上调参与眼组织的细胞防御,但其是否有不利作用尚需进一步证明。如何以恰当的方式诱导HO-1在眼内适时、适度、安全地表达是目前研究的方向。另外,目前对HO-1的研究大多集中在动物和细胞实验上,在临床应用方面缺乏相应的例证。随着研究方法的推进和临床试验的开展,HO-1在眼科疾病的应用将成为可能,研发的HO-1诱导剂相关药物或HO-1基因疗法有望成为最具潜能的眼科疾病治疗方法。
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date:Nov 6,2013
National Natural Science Foundation of China (No:81271028); Medical Science and Technology Development Program of Nanjing (No:ZKX12047)From theAffiliatedEyeHospitalofNanjingMedicalUniversity,Nanjing210029,JiangsuProvince,China
Research advances in relationship between HO-1 and corneal diseases, glaucoma, cataract,retinal diseases
ZHANG Hui,JIANG Qin,YAO Jin
heme oxygenase-1; corneal diseases; glaucoma; cataract; retinal diseases; antioxidant; cytoprotection
Heme oxygenase -1 (HO-1)is one of the most important endogenous antioxidant enzymes in body. It can catalyze the degradation of heme to carbon monoxide, free iron and biliverdin. HO-1 and its products have antioxidant, anti-inflammatory and anti-apoptosis effects. More and more researches have shown that induction of HO-1 expression can protect cells in cornea, trabecular, lens and retina from oxidative damage, therefore HO-1 has become the potential target for curing disease in such areas. This article reviews the relationship between HO-1 and eye diseases.
张荟,女,1988年3月出生,江苏淮安人,硕士研究生。联系电话:18915160868;E-mail:zhanghui9695@163.com
AboutZHANGHui:Female,born in March,1988.Master degree.Tel:18915160868; E-mail:zhanghui9695@163.com
2013-11-06
国家自然科学基金资助(编号:81271028); 南京市医学科技发展项目(编号:ZKX12047)
210029 江苏省南京市,南京医科大学附属眼科医院
姚进,E-mail:dryaojin@vip.sina.com
张荟,蒋沁,姚进.血红素加氧酶-1与角膜病、青光眼、白内障及视网膜疾病的关系[J].眼科新进展,2014,34(4):385-388.
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10.13389/j.cnki.rao.2014.0107
修回日期:2014-02-12
本文编辑:盛丽娜
Accepteddate:Feb 12,2014
Responsibleauthor:YAO Jin,E-mail:dryaojin@vip.sina.com
[RecAdvOphthalmol,2014,34(4):385-388]