The mechanics of epithelial tissues

人体的许多空洞和自由表面(如肠道、肺、血管)由仅有几个细胞厚的组织构成。这些上皮组织将人体的内部环境与外部环境隔开。作为正常功能的一部分，上皮组织不断地暴露在巨大的机械变形中：肺泡在呼吸过程中变形，肠上皮抵抗肠道的蠕动运动，血管内皮细胞暴露在血流中的脉动流体剪应力下。在疾病中，当突变或病原体影响细胞骨架(细胞骨架)或相互连接细胞的连接导致脆弱组织在日常功能中撕裂时，上皮细胞的机械功能尤其明显(例如大疱性表皮、葡萄球菌水泡)。上皮组织内的细胞通过细胞间连接彼此紧密相连：一些连接形成屏障，限制溶质通过组织，而另一些连接则整合相邻细胞的细胞骨架，形成能够承受机械应力的强大多细胞组织。尽管它们具有明确的机械作用，但目前人们对上皮组织的力学机制以及构成组织的细胞和组成细胞的蛋白质的机械特性如何产生的了解甚少。这主要是由于缺乏特定的实验技术来测量组织的内在力学性质，同时监测细胞和亚细胞的运动。我们开发了一种新的工具，通过拉伸培养的上皮细胞来量化上皮组织的力学性能。在组织变形期间，可以测量施加的机械张力，并可以在亚细胞、细胞和组织长度尺度上同时对组织进行成像，从而可以作为施加的力的函数来准确地监测亚细胞组件的结构、细胞的形状及其最终的重组。为了补充这个实验工具，我们开发了一个新的上皮组织计算模型，可以作为解释和改进我们的实验的一种手段。现在，我们建议使用我们的新技术来了解哪些蛋白质在设定上皮组织的机械特性方面起到了作用。为此，我们将专注于三个目标：1)开发一种系统的方法来描述组织的力学特性2)发现是什么蛋白质决定组织的力学特性3)将我们的发现合并到组织的计算模型中。目标1旨在创建一种系统的方法来收集所有必要的信息来全面描述正常组织的力学特性。在目标2中，我们将询问特定蛋白质的缺失如何影响组织的力学特性。为了回答这个问题，我们将降低组成组织的细胞中选定基因的表达水平，并测量这如何影响组织的机制。我们还将研究基因枯竭如何改变组织的组织和组成它的细胞。我们将特别关注脆性上皮临床研究中确定的蛋白质，因为它们与患者和潜在的姑息治疗直接相关。在目标3中，我们将使用目标2的结果来使用计算和统计方法来确定什么细胞结构对于设定组织力学是最重要的。此外，这一分析和来自目标2的实验将直接支持专门为研究大变形的组织力学而定制的模型的发展，并用于完善我们对细胞内蛋白质表达的变化如何导致上皮片失效的理解，例如在临床病例中。拟议的研究将极大地提高我们对上皮组织的机制以及病理如何影响组织强度的理解。

Many of the cavities and free surfaces of the human body (e.g. gut, lungs, blood vessels) are lined by tissues just a few cells thick. These epithelial tissues separate the body's internal environment from the external environment. As part of their normal function, epithelial tissues are continuously exposed to large mechanical deformations: lung alveoli deform during respiration, intestinal epithelia resist peristaltic movements in the gut, and endothelia are exposed to pulsatile fluid shear stresses in blood flow. The mechanical function of epithelia is particularly apparent in disease when mutations or pathogens affecting the cell skeleton (cytoskeleton) or junctions linking cells to one another result in fragile tissues that tear during routine function (e.g. epidermis bullosa, staphylococcus blistering). Cells within epithelial tissues are tightly connected to one another by intercellular junctions: some junctions form a barrier restricting the passage of solutes across the tissue whilst others integrate the cytoskeletons of neighbouring cells to form a strong multicellular tissue that can withstand mechanical stresses. Despite their clear mechanical role, little is currently known about the mechanics of epithelial tissues and how this derives from the mechanical properties of the cells that make up the tissue and the proteins that make up the cells. This is primarily due to the lack of specific experimental techniques to measure the intrinsic mechanical properties of tissues while monitoring cellular and subcellular traits.We have developed a novel tool to quantify the mechanics of epithelial tissues by stretching cultured epithelia. During tissue deformation, the applied mechanical tension can be measured and the tissues can be simultaneously imaged at subcellular, cellular and tissue length scales, such that the architecture of the sub-cellular components, the shape of the cells and their eventual reorganisation can be accurately monitored as a function of the imposed force. To complement this experimental tool, we have developed a novel computational model of epithelial tissues that can serve as a means to interpret and refine our experiments.We now propose to use our new techniques to understand what proteins play a role in setting the mechanical properties of epithelial tissues. To do this, we will focus on three aims:1) Develop a systematic methodology for characterizing the mechanics of tissues2) Discover what proteins set tissue mechanical properties3) Incorporate our findings into a computational model of tissues.Aim1 is geared at creating a systematic methodology for collecting all of the necessary information to fully characterise the mechanics of normal tissues.In aim 2, we will ask how the absence of a given protein affects the mechanics of a tissue. To answer this question, we will reduce the level of expression of a chosen gene in the cells that make up the tissue and measure how this affects the mechanics of the tissue. We will also examine how gene depletion changes the organization of the tissue and the cells that compose it. We will pay particular attention to proteins identified in clinical studies of fragile epithelia, as they have direct relevance to patients and potential palliative therapies.In aim 3, we will use computational and statistical approaches to identify what cellular structures are the most important for setting tissue mechanics using the results of aim 2. Moreover, this analysis and the experiments from aim 2 will directly support the development of a model specifically tailored to study tissue mechanics at large deformation and used to refine our understanding of how changes in protein expression within cells can lead to failure of epithelial sheets, as in clinical cases.In summary, the proposed investigations will greatly enhance our understanding of the mechanics of epithelial tissues and how pathologies can affect tissue strength.