The impact of mechanosensing on dendritic cell biology

生物组织表现出不同的化学和机械特性，这些特性是根据它们的功能量身定做的。一种这样的性质是组织的硬度，以组织弹性模数(E)为单位表示，该单位由组织在机械应力下变形的固有阻力定义。在稳定状态下，树突状细胞(DC)等免疫细胞在体内巡逻，并经历从0.1千帕斯卡(Kpa)到千帕斯卡(Kpa)的广泛组织僵硬。研究涉及组织机械特性改变的疾病，如纤维化和钙化的证据表明，细胞能够感知大型的细胞外物理干扰。然而，在这些疾病模型中，组织机械张力的变化与炎症和组织损伤等复杂的生物变化密切相关，排除了孤立地研究机械力及其对免疫系统的影响。拟议的研究计划的目标是了解细胞外机械力以及其他生物特性(如营养和氧气的可用性)如何影响免疫细胞的动态平衡和功能。我们提出了一项研究计划，旨在1.表征DC中的机械信号转导途径；2.研究免疫细胞在不同张力条件下的功能表现，并结合额外的生理参数，如氧气和营养浓度；3.检测机械应激下免疫细胞内发生的转录和代谢变化。我们将使用由聚二甲基硅氧烷(PDMS)水凝胶涂层平板组成的细胞培养系统来模拟对应于软粘膜和脑(1kPa.)、脂肪组织、脾、淋巴结和肝脏(2-5kPa.)、骨髓(0.3-24.7kPa.)和炎症淋巴器官(50kPa.)的生理张力。在我们的初步研究中，比较了一种生长在刚性和顺应性底物上的骨髓源免疫细胞(骨髓树突状细胞)，发现河马信号分子，带有PDZ结合基序的转录共激活因子(Taz)，是在僵硬张力条件下促进免疫细胞功能的重要介质。因此，我们将研究张力和YAP/Taz信号在免疫细胞分化、功能和代谢调节中的作用。目前尚不清楚体内各种不同的生理机械环境如何调节免疫细胞的发育和动态平衡。拟议的研究计划将为这种以前未被认识到的生物相互作用提供新的见解。鉴于细胞生物学研究的一个基本方面涉及在塑料制品上进行组织培养，其弹性模量在Mpa范围内，比细胞在体内遇到的高出一个数量级，这项研究对体外系统设计回答生物学问题具有重要意义。

Biological tissues display diverse chemical and mechanical properties that are tailored to their functions. One such property is the stiffness of the tissue, expressed in the unit of tissue elastic modulus (E) as defined by its intrinsic resistance to deform under mechanical stress. Under steady state, immune cells such as dendritic cells (DCs) patrol the body and experience a wide spectrum of tissue stiffness, ranging from 0.1 to >64 kilo pascals (kPa). Evidence from studying diseases involving altered tissue mechanical properties, such as fibrosis and calcification, suggests that cells are capable of sensing large extracellular physical disturbances. However, in these disease models, alterations in tissue mechanical tension go hand in hand with complex biological changes such as inflammation and tissue damage, precluding the study of mechanical forces and their impact on the immune system in isolation. The objective of the proposed research program is to understand how extracellular mechanical force, together with additional biological properties such as nutrient and oxygen availability, influences immune cell homeostasis and function. We propose a research program that aims to 1. Characterize the mechanical signal transduction pathways in DCs; 2. Investigate how immune cells behave functionally under differential tension conditions, compounded to additional physiological parameters such as oxygen and nutrient concentrations; 3. Examine the transcriptional and metabolic alterations occurring within immune cells upon mechanical stress. We will employ a cell culturing system consisting of polydimethylsiloxane (PDMS) hydrogel-coated plates to mimic physiological tensions corresponding to soft mucosa and brain (<1kPa), adipose tissue, spleen, lymph nodes and liver (2-5kPa), bone marrow (0.3-24.7kPa), and inflamed lymphoid organs (50kPa). In our preliminary studies, comparison of a type of bone marrow-derived immune cells (bone marrow dendritic cells) grown on stiff vs compliant substrates identified the hippo signaling molecule, transcriptional coactivator with PDZ-binding motif (Taz), as one important mediator promoting immune cell function under stiff tension conditions. We will thus examine the role of tension and Yap/Taz signaling on the regulation of immune cell differentiation, function and metabolism. How diverse, physiological mechanical environments in the body regulate immune cell development and homeostasis is not known. The proposed research program will provide new insights into this previously underrecognized biological interaction. Given that a fundamental aspect of cell biology research involves tissue culturing on plastic wares with elastic modulus in the range of MPa, magnitudes higher than what the cells encounter in the body, this study has important implications on the design of in vitro systems in answering biological questions.