上皮间充质转化机制在胆道闭锁纤维化中研究

上皮间充质转化机制在胆道闭锁纤维化中的研究ABSTRACT就BA的病因学的最新研究进展作一综述。

INTRODUCTION胆道闭锁（biliary atresia, BA）是新生儿时期原因不明的一类胆汁淤积性疾病，出生一个月后逐渐出现体重增长缓慢、皮肤黄染、无胆色粪和肝脏肿大等典型的胆道梗阻表现。

患者肝脏病理特点为不同程度的炎症浸润伴有毛细胆管增生，胆汁淤积及间充质组织增多。

如果在2-3个月时早期诊断，可以通过Kasai术重建胆汁引流系统，成功率可达80% (1–3). 尽管目前手术成功率较高，在胆道重建术(Kasai术)后患儿的肝脏病变也将持续进展，主要表现为不同程度的毛细胆管炎症、纤维化并进行性加重，最终导致肝硬化。

数据统计, 术后2年70–80% 患者需要肝脏移植, 因此，目前BA是儿童期肝移植的最常见原因，50%以上的儿童肝移植原发病变为胆道闭锁[5, 6]. 就胆道闭锁疾病的发病机制而言，现在更倾向于解释为，是由多种因素的综合作用而导致的胆管系统的进行性病变(1,7)。

需要强调的是胆道闭锁并不是单纯的肝外胆管纤维化梗阻性疾病，与之伴随的肝内胆道系统进行性的病变决定着患者的预后和最终结果。

所以Kasai术的成功后，接踵而来的便是如何提高自体肝存活率的问题；因此需要对胆道闭锁中自体肝纤维化的病因及发病机制进行深入的探讨。

对大量历史文献阅读后，提出肝内中小型胆管上皮细胞发生了上皮间充质转化，并最终导致肝内胆管增生和纤维化的假设。

Without a better understanding of the etiology and pathogenesis发病机制of this intrahepatic 胆管硬化sclerosing cholangitic process in BA, little progress can be expected in improving the nontransplantation outcome of patients. Therefore, there has been a renewed interest in recent years in understanding the underlying pathogenetic mechanisms of BA.It is now apparent that BA is a phenotype resulting from several pathogenic processes that culminate in obstruction of the biliary tree(1,7). The majority (80%) of cases of BA in Western countries are of the perinatal or acquired form. These most commonly involving abdominal situs, and has been dubbed the embryonic or fetal form.Defective morphogenesis, caused by mutations in genes regulating biliary development, has been proposed in these cases. In otherwise normal infants are presumably born with a patent biliary system which undergoes progressive inflammation and fibro-obliteration initiated by a perinatal insult. Although the etiology of this form is not completely understood, proposed precipitating factors include infectious, toxic, vascular, and immune mediators. The second form of BA is associated with other congenital anomalies, most this review, we will examine recent data supporting the proposed viral and immunologic pathogenesis of the perinatal form of BA, and the potential role for defective genetic regulation of bile duct development in the embryonic form.From significant histologic evidence, theBECs forming small- and medium-sized bile ducts undergoingEMT may account for prominent bile ductularproliferation and directly contribute to fibrogenesis in BA..GENERAL CHARACTERISTICS OF EMT上皮-间充质转化是指上皮细胞通过特定程序转化为具有间质表型细胞的生物学过程。

在胚胎发育、慢性炎症、组织重建、癌症转移和多种纤维化疾病中发挥了重要作用，其主要的特征有细胞黏附分子(如E-钙黏蛋白)表达的减少、细胞角蛋白细胞骨架转化为波形蛋白（Vimentin）为主的细胞骨架及形态上具有间充质细胞的特征等。

通过EMT，上皮细胞失去了细胞极性，失去与基底膜的连接等上皮表型，获得了较高的迁移与侵袭、抗凋亡和降解细胞外基质的能力等间质表型。

EMT是上皮细胞来源的恶性肿瘤细胞获得迁移和侵袭能力的重要生物学过程。

阐明调控恶性肿瘤细胞发生EMT过程的分子机制，明确其在恶性肿瘤的发生、发展、转移中的病理意义，并探索基于EMT关键分子的诊断方法及靶向EMT关键分子的治疗手段是肿瘤转移中EMT机制研究的关键科学问题。

上皮-间质表型转变(Epi恤elial-Mescnchymad Transition，EMT)是指上皮细胞获得了成纤维细胞样表型．出现间叶细胞表面标志物，如纤维母细胞特异蛋白．1(fibroblast specific protein 1，FSPI，又称为S100A4)、纤维连接蛋白(fibronectin)、波形蛋白(vimentin)等；增加or-smooth muscIe actin(a-SMA)、转化生长园子一B(transforming growth factor-J3，TGF-p)、基质金属蛋白酶．2和9(matrix mctalloproteinases 2 and 9，MMP-2／9)、I型／lII型胶原表达。

同时上皮标志物表达下调或丢失，如细胞角蛋白(oytokeratin)，上皮钙粘素(E-cadherin)，oJpl．r-连环蛋白(“[3／y-catcnin)、紧密连接蛋白(zonula cccludcn 1．ZO．1)等。

细胞功能变化特点是上皮细胞损失极性和细胞．细胞问通讯，获得迁移和侵袭细胞学行为[16]。

EMT和间质-上皮转变(MET)是胚胎发育时期的生理现象[17]。

在早期胚胎发育过程中，外胚层的原始上皮细胞经过EMT形成原亚顶极胚层(仃opobla嘶c germ layers)中的原始间充质细胞．在中胚层期这些间充质细胞在白血病抑制因子(LIF)和骨形态形成蛋白-7(BoneMorphogenicprotein7，BMP-7，亦称为成骨蛋白)等因子的作用下经历MET生成次级上皮(Secondary epithelium)，形成新的上皮组织。

然后经过第二轮EIVlT分化彤成各种组织细胞，如脂肪细胞、成骨细胞、肌细胞等。

而成熟组织的次级上皮在应激(如创伤炎症、过氧化应激等)或形成肿瘤时，可出现EMT被重新“激活”的“返祖现象”，形成FSPI+的成纤维细胞，再在TGF．B等作用下形成肌成纤维细胞，导致纤维化发生，或使肿瘤细胞侵袭转移能力增强。

在2007年举行的国际EMT会议和2008年冷泉港（Cold Spring Harbor）实验室会议上，以EMT发生的特定生物学环境为依据将其分为3种亚型1型MET与胚胎植入、发育和器官形成相关的EMT称为1型MET。

其主要生物学功能是通过间充质细胞上皮化（MET）过程产生次级上皮细胞，实现胚胎形成过程中的细胞类型多样化。

2型MET与损伤修复、组织再生和器官纤维化相关的EMT被定义为2型EMT。

其主要生物学作用是通过产生纤维细胞以修复由创伤和炎症反应造成的组织损伤。

生理状态下，当炎症反应缓解后该转化过程即自行停止；然而在炎症反应持续活化的情况下，EMT过程也将持续存在，并最终造成器官纤维化。

3型MET3型MET是指与上皮细胞恶性肿瘤相关的表型转化。

原发性上皮组织肿瘤细胞通过3型EMT形成具有迁移能力的间充质细胞，随血流转移至不同部位，进而通过MET过程形成上皮细胞的肿瘤转移灶。

与1型和2型EMT所形成的完全丧失上皮细胞表型的间充质细胞不同的是，3型EMT形成的转移性肿瘤细胞在获得间充质表型的同时保持一定的上皮细胞的特性。

The ability of cells to alter their phenotypic and morphological characteristics, known as cellular plasticity, is critical in normal embryonic development and adult tissue repair and contributes to the pathogenesis of diseases, such as organ fibrosis and cancer. The epithelial-to-mesenchymal transition (EMT) is a type of cellular plasticity. This tran-sition involves genetic and epigenetic changes as well as alterations in protein expression and post-translational modifications. These changes result in reduced cell-cell adhesion, enhanced cell adhesion to the extracellular matrix, and altered organization of the cytoskele-ton and of cell polarity. Among these modifications, loss of cell polarity represents the nearly invariable, distinguishing feature of EMT that frequently precedes the other traits or might even occur in their absence. EMT transforms cell morphology and physiology, and hence cell identity, from one typical of cells that form a tight barrier, like epithelial and endothelial cells, to one characterized by a highly motile mesenchymal phenotype. Time-resolved proteomic and phosphoproteomic analyses of cells undergoing EMT recently identified thousands of changes in proteins involved in many cellular processes, including cell proliferation and motility, DNA repair, and –unexpectedly – membrane trafficking (1). These results have highlighted a picture of great complexity. First, the EMT transition is not an all-or-none response but rather a gradual process that develops over time. Second, EMT events are highly dynamic and frequently reversible, involving both cell-autonomous and non-autonomous mechanisms. The net results is that EMT generates populations of mixed cells, with partial or full phenotypes, possibly accounting (at least in part) for the physiological as well as pathological cellular heterogeneity of some tissues. Endocytic circuitries have emerged as complex connectivity infrastructures for numerous cellular networks required for the execution ofdifferent biological processes, with a primary role in the control of polarized functions. Thus, they may be relevant for controlling EMT or certain aspects of it. Here, by discussing a few paradigmatic cases, we will outline how endocytosis may be harnessed by the EMT process to promote dynamic changes in cellu-lar identity, and to increase cellular flexibility and adaptation tomicro-environmental cues, ultimately impacting on physiological and pathological processes, first and foremost cancer progression.The epithelial-to-mesenchymal transition (EMT) is a fundamen-tal process in embryonic development and tissue repair.EMTis key also for the progression of diseases, including organ fibrosis and cancer (2–4). The pioneering work in the 1980 of Elizabeth Hay first described an “epithelial-mesenchymal transformation” using a model of chick primitive streak formation (5). Subsequently, the term“transformation” was replaced with “transition,”reflect-ing in part the reversibility of the process and the fact that it is distinct from neoplastic transformation (6, 7). The phenotypic plasticity associated with EMT is revealed by the occurrence of the reverse process, the mesenchymal-epithelial transition (MET), which involves the conversion of mesenchymal cells to epithelial derivatives. Epithelial cells form polarized sheets that are held together by various cell adhesion molecules. Beneath this cell layer, the base-ment membrane anchors epithelial cells to the underlying matrix and maintains apical-basal polarity. Adhesion to both the base-ment membrane and adjacent cells is critical for maintaining the epithelial phenotype (8). During EMT, cells lose these epithelial characteristics, acquir-ing instead an invasive and migratory mesenchymal phenotype, which allows them to leave the tissue parenchyma, undergo mor- phogenetic programs, generate new tissues during development or repair wounded ones, and to enter the blood circulation during cancer metastasis .EMT IN in liver fibrosisLiver fibrosis results from continuous injury to the liver, including viral hepatitis, alcohol abuse, metabolic diseases, autoimmune diseases,and cholestatic liver diseases. In other words, fibrosis is a consequence of the excessive healing response triggered by chronic liver injury. The end stage of liver fibrosis, cirrhosis, is histologically characterized by increased deposition and altered composition of the extracellular matrix (ECM) and the appearance of regenerative nodules再生性小结.肝脏纤维化是由长期肝脏损伤导致，病因繁多：病毒性肝炎、酒精中毒、代谢性疾病、自身免疫疾病和胆汁淤积性疾病等。