INSERM, UMR 756, 92296 Châtenay-Malabry, France.
Cell Microbiol. 2011 Nov;13(11):1683-702. doi: 10.1111/j.1462-5822.2011.01647.x. Epub 2011 Aug 24.
Gardia intestinalis, the aetiological agent of giardiasis, one of the most common intestinal diseases in both developing and developed countries, induces a loss of epithelial barrier function and functional injuries of the enterocyte by mechanisms that remain unknown. Three possible mechanisms have been proposed: (i) Giardia may directly alter the epithelial barrier after a close interaction between the trophozoite and polarized intestinal cells, (ii) intestinal functions may be altered by factors secreted by Giardia including an 'enterotoxin', proteinases and lectins, and (iii) based on mouse studies, a mechanism involving the intervention of activated T lymphocytes. We used fully differentiated cultured human intestinal Caco-2/TC7 cells forming a monolayer and expressing several polarized functions of enterocytes of small intestine to investigate the mechanisms by which G. intestinalis induces structural and functional alterations in the host intestinal epithelium. We first report that adhesion of G. intestinalis at the brush border of enterocyte-like cells involves the lipid raft membrane microdomains of the trophozoite. We report an adhesion-dependent disorganization of the apical F-actin cytoskeleton that, in turn, results in a dramatic loss of distribution of functional brush border-associated proteins, including sucrase-isomaltase (SI), dipeptidylpeptidase IV (DPP IV) and fructose transporter, GLUT5, and a decrease in sucrose enzyme activity in G. intestinalis-infected enterocyte-like cells. We observed that the G. intestinalis trophozoite promotes an adhesion-dependent decrease in transepithelial electrical resistance (TER) accompanied by a rearrangement of functional tight junction (TJ)-associated occludin, and delocalization of claudin-1. Finally, we found that whereas the occludin rearrangement induced by G. intestinalis was related to apical F-actin disorganization, the delocalization of claudin-1 was not.
肠道寄生原虫贾第虫是引起贾第虫病的病原体，这种疾病是在发展中国家和发达国家中都很常见的一种肠道疾病。贾第虫通过尚未明确的机制引起上皮屏障功能丧失和肠细胞功能损伤。目前提出了三种可能的机制：（i） 滋养体与极化肠细胞密切相互作用后，贾第虫可能直接改变上皮屏障；（ii） 贾第虫分泌的因子（包括“肠毒素”、蛋白酶和凝集素）可能改变肠道功能；（iii） 基于小鼠研究，一种涉及激活的 T 淋巴细胞干预的机制。我们使用完全分化的培养人肠道 Caco-2/TC7 细胞形成单层，并表达小肠肠细胞的几种极化功能，来研究贾第虫诱导宿主肠道上皮结构和功能改变的机制。我们首先报告，贾第虫滋养体在肠细胞样细胞的刷状缘上的黏附涉及滋养体的脂筏膜微区。我们报告了黏附依赖性的顶端 F-肌动蛋白细胞骨架的解聚，这反过来又导致功能性刷状缘相关蛋白（包括蔗糖酶-异麦芽糖酶（SI）、二肽基肽酶 IV（DPP IV）和果糖转运体 GLUT5）的分布显著丢失，以及感染的肠细胞样细胞中蔗糖酶活性降低。我们观察到，贾第虫滋养体促进黏附依赖性的跨上皮电阻（TER）降低，同时功能性紧密连接（TJ）相关闭合蛋白发生重排，claudin-1 发生定位改变。最后，我们发现贾第虫诱导的闭合蛋白重排与顶端 F-肌动蛋白解聚有关，而 claudin-1 的定位改变则不是。
