炎症反应中，中性粒细胞是第一种穿过血管内皮细胞进入组织并到达炎症部 位的细胞类型。它是帮助器官启动和维持免疫反应的关键角色，通过向树突状细 胞、单核细胞和 T 细胞发出信号来形成整体免疫应答。本课题组前期研究发现中 性粒细胞迁移过程中，通过头部前伸和尾部收缩可以在内皮细胞或细胞外基质上 快速迁移，并在迁移过程中遗留下大量富含整合素的膜结构（曳尾结构）。但是， 目前尚不清楚曳尾的形成机制与细胞迁移之间的定量关系、以及在这一过程中起 关键作用的调控因素。 本文以中性粒细胞迁移过程中曳尾结构形成的力学-化学-生物学耦合机制 为切入点，构建了一个包含化学信号通路、分子力学、细胞力学、细胞变形和运 动的跨尺度全细胞迁移模型。对中性粒细胞在不同基质上的趋化迁移进行了数值 模拟，研究了中性粒细胞迁移过程中曳尾结构的形成机制、以及不同生物、物理、 化学环境改变下的动态响应规律，并分析了中性粒细胞在黏附性与非黏附性基底 上迁移行为的差异性。主要工作包括以下三个方面： 1）模型建立：在多层级力学-化学耦合模型与细胞迁移的马达-离合器模型基 础上，建立跨尺度全细胞迁移模型。对细胞在黏附性基底上的迁移速度、曳尾数 量进行分析，结果表明：细胞接收到趋化信号之后，利用信号转导的平衡-抑制机 制快速地对接收到的胞外信号加以处理，Rac、RhoA 通过拮抗作用分别在细胞 首、尾产生极化分布，同时两者调控下游的细胞骨架效应器微丝相关蛋白 Arp2/3、 肌球蛋白 myosin，并通过它们影响整合素的局部浓度，从而对细胞迁移速度与曳 尾生成进行调控。模拟结果与实验结果基本一致。 2）参数分析：基于跨尺度全细胞迁移模型，考察了胞外参数（基底刚度 Ksub、 趋化梯度 C）与胞内参数（上下位点分子键的解离速率 koff’与 koff、下位点分子键 结合速率 kon、微丝空载速度 vu、马达最大拉力 Fm、整合素密度 nc）等多种因素 对细胞迁移状态的影响。结果发现：细胞迁移速度与基底刚度 Ksub、微丝空载速 度 vu 呈现双向依赖关系；曳尾形成的数量随着基底刚度 Ksub、整合素-配体分子 键的结合率 kon、微丝空载速度 vu、马达最大拉力 Fm、整合素-配体分子键上位点 的解离率 koff’和整合素密度 nc 的增加而单调增加，而随着趋化梯度 C 和整合素配体分子键的解离率 koff 的增加而减少。 3）模型应用：在现有模型基础上，通过将下位点分子键结合速率 kon 减小至 0 从而模拟了非黏附性基底上细胞迁移过程。考察了非黏附性基底上细胞迁移速 度的变化，结果表明：随着基底与细胞之间分子键连接的消失，细胞的迁移速度 更加平滑，不再呈现出波动的周期性特点，平均迁移速度也相较黏附性基底上细 胞的迁移有较大提高。上述工作有助于深入理解迁移细胞在复杂生理刺激条件下的动态响应规律， 并为阐明中性粒细胞迁移的力学-化学-生物学耦合机制和探究调节中性粒细胞 迁移过程中影响曳尾形成的关键因素提供了一种解释。

Neutrophils are the first cells to transmigrate the vascular endothelium and enter into the tissues, arriving at the site of inflammation during the inflammatory cascade. They play a crucial role in initiating and sustaining the immune responses of the organism by signaling to dendritic cells, monocytes, and T cells. Our previous work has shown that neutrophils utilize anterior protrusion and posterior contraction to rapidly migrate onto the endothelium or extracellular matrix. During migration, these cells tend to leave behind membranous trails enriched with integrins that are ripped down from the cell body. However, it remains unclear how these trails are formed, how this trail formation is quantitatively correlated with cell migration dynamics, and what the key regulatory factors are involved in this process. This work focused on elucidating the mechanical-chemical-biological coupling mechanism formed by the trailing structure during neutrophil migration. A multiscale whole-cell migration model was developed to incorporate chemical signaling pathways, molecular mechanics, cell mechanics, cell deformation, and cell movement. Numerical simulations were conducted to investigate the chemotactic migration of neutrophils on different substrates, and to study the trail formation mechanism during neutrophil migration, as well as the dynamics of cellular trails under different biological, physical, and chemical environments. Moreover, the migrating behaviors of neutrophils on the adherent and non-adherent substrates were elaborated. These findings provide insights into the responses of trail formation under complex physiological stimuli, and the mechanical-chemical-biological coupling mechanism of neutrophils. Major outcomes were summarized as follows: 1) Model development: A multiscale whole-cell migration model was established based on both the multi-layered mechanochemical model and the motor-clutch model of cell migration. The model was used to analyze the migrating speed and number of trails on the adhesive substrate. Numerical simulations showed that, after receiving chemotactic signals, cells quickly process these extracellular signals by utilizing the balance-inhibition mechanism of signal transduction. With antagonistic action, Rac and RhoA respectively are polarized at the rear and head of cells, regulating the relevant downstream cytoskeletal effectors Arp2-3 and myosin, which further affects the local concentration of integrin and regulates cell migration and trail generation. These simulations were found to be in agreement with those experimental results. 2) Parameter analysis: Using the multiscale whole cell migration model, the effects of extracellular factors (substrate hardness Ksub, chemokine concentration C) and intracellular factors (off-rate of the upper and lower sites of molecular bonds koff’ and koff, on-rate of integrin-ligand bonds kon, motor unloaded velocity vu of microwires, motor stall force Fm, and clutch number nc) on cell migration were investigated. Results showed that the cell migrating speed is dependent on both substrate stiffness Ksub and motor unloaded velocity vu. The number of trails formed increases monotonically with increasing substrate hardness Ksub, on-rate of integrin-ligand bonds kon, motor unloaded velocity vu, motor stall force Fm, off-rate of the lower sites integrin-ligand molecular bonds koff’, and clutch number nc, but decreases with increasing chemokine concentration C and off-rate koff of the upper sites integrin-ligand molecular bonds. 3) Model application: Cell migration on a non-adhesive substrate was simulated by reducing the on-rate of integrin-ligand bonds kon to zero, based on the above model. The changes in cell migrating speed on the non-adhesive substrate were investigated, and the results showed that the disappearance of molecular bonds between the substrate and the cell presented the smoother cell migration without visible periodic fluctuations. Additionally, the average migrating speed was significantly higher than that of adhesive migration. In summary, this work furthers the understandings of dynamic responses of those migrating cells under complicated physiological stimuli, and deciphers the mechanicalchemical-biological coupling of neutrophil migration and the key factors that influences the trail formation in neutrophil migration.