The mechanics of epithelial tissues

人体的许多空腔和游离表面（如肠、肺、血管）由只有几个细胞厚的组织排列。这些上皮组织将身体的内部环境与外部环境分开。作为其正常功能的一部分，上皮组织持续暴露于较大的机械变形：肺泡在呼吸过程中变形，肠上皮抵抗肠道蠕动运动，内皮暴露于血液流动中的脉动流体剪切应力。在疾病中，当突变或病原体影响细胞骨架（细胞骨架）或连接细胞的连接导致脆弱的组织在正常功能中撕裂（如大疱表皮、葡萄球菌起泡）时，上皮的机械功能特别明显。上皮组织内的细胞通过细胞间连接紧密相连：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邻近细胞的细胞骨架，形成强大的多细胞组织，可以承受机械应力。尽管上皮组织具有明确的机械作用，但目前人们对上皮组织的力学机制知之甚少，也不知道这是如何从组成组织的细胞和组成细胞的蛋白质的力学特性中得出的。这主要是由于缺乏特定的实验技术来测量组织的内在机械特性，同时监测细胞和亚细胞特性。我们开发了一种新的工具，通过拉伸培养上皮来量化上皮组织的力学。在组织变形过程中，施加的机械张力可以被测量，组织可以同时在亚细胞、细胞和组织长度尺度上成像，这样亚细胞成分的结构、细胞的形状和它们最终的重组可以作为施加的力的函数被精确地监测。为了补充这个实验工具，我们开发了一种新的上皮组织计算模型，可以作为解释和完善我们实验的手段。我们现在建议使用我们的新技术来了解哪些蛋白质在设置上皮组织的机械特性中起作用。为此，我们将集中在三个目标上：1)发展一种系统的方法来描述组织的力学特性；2)发现哪些蛋白质决定组织的力学特性；3)将我们的发现纳入组织的计算模型。Aim1旨在创建一种系统的方法来收集所有必要的信息，以充分表征正常组织的力学特性。在目标2中，我们将询问缺乏特定蛋白质如何影响组织的力学。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，并测量这对组织机制的影响。我们还将研究基因消耗如何改变组织和组成它的细胞的组织。我们将特别关注脆弱上皮临床研究中发现的蛋白质，因为它们与患者和潜在的姑息治疗直接相关。在目标3中，我们将使用计算和统计方法来确定哪些细胞结构对于使用目标2的结果设置组织力学最重要。此外，该分析和aim 2中的实验将直接支持专门用于研究大变形组织力学的模型的开发，并用于完善我们对细胞内蛋白质表达变化如何导致上皮片失败的理解，如在临床病例中。总之，提出的调查将大大提高我们对上皮组织的机制和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.