DataSheet1_Traffic Patterns of the Migrating Endothelium: How Force Transmission Regulates Vascular Malformation and Functional Shunting During Angiogenic Remodelling.pdf

Angiogenesis occurs in distinct phases: initial spouting is followed by remodelling in which endothelial cells (ECs) composing blood vessels rearrange by migrating against the direction of flow. Abnormal remodelling can result in vascular malformation. Such is the case in mutation of the Alk1 receptor within the mouse retina which disrupts flow-migration coupling, creating mixed populations of ECs polarised with/against flow which aggregate into arteriovenous malformations (AVMs). The lack of live imaging options in vivo means that the collective EC dynamics that drive AVM and the consequences of mixed populations of polarity remain a mystery. Therefore, our goal is to present a novel agent-based model to provide theoretical insight into EC force transmission and collective dynamics during angiogenic remodelling. Force transmission between neighbouring agents consists of extrusive forces which maintain spacing and cohesive forces which maintain the collective. We performed migration simulations within uniformly polarised populations (against flow) and mixed polarity (with/against flow). Within uniformly polarised populations, extrusive forces stabilised the plexus by facilitating EC intercalation which ensures that cells remained evenly distributed. Excess cohesion disrupts intercalation, resulting in aggregations of cells and functional shunting. Excess cohesion between ECs prevents them from resolving diameter balances within the plexus, leading to prolonged flow reversals which exert a critical behaviour change within the system as they switch the direction of cell migration and traffic patterns at bifurcations. Introducing mixtures of cell polarity dramatically changed the role of extrusive forces within the system. At low extrusion, opposing ECs were able to move past each other; however, at high extrusion the pushing between cells resulted in migration speeds close to zero, forming traffic jams and disrupting migration. In our study, we produced vascular malformations and functional shunting with either excess cohesion between ECs or mixtures of cell polarity. At the centre of both these mechanisms are cell-cell adherens junctions, which are involved in flow sensing/polarity and must remodelling dynamically to allow rearrangements of cells during vascular patterning. Thus, our findings implicate junctional dysfunction as a new target in the treatment and prevention of vascular disease and AVMs.

血管生成（Angiogenesis）具有明确的不同阶段：初始出芽阶段结束后，随即进入血管重塑阶段，在此阶段中构成血管的内皮细胞（endothelial cells, ECs）会逆着血流方向迁移并发生重排。异常的血管重塑可引发血管畸形（vascular malformation）。以小鼠视网膜内的Alk1受体（Alk1 receptor）突变为例，该突变会破坏血流-迁移耦合机制，产生同时具有正向/逆向血流极化表型的内皮细胞混合种群，这些细胞最终聚集形成动静脉畸形（arteriovenous malformations, AVMs）。
目前体内活体成像技术的缺失，使得驱动动静脉畸形发生的内皮细胞集体动力学特征，以及混合极化细胞种群所带来的后续效应仍未被阐明。因此，本研究旨在提出一种全新的基于智能体的模型（agent-based model），以从理论层面解析血管生成重塑过程中内皮细胞的力传递与集体动力学行为。
相邻智能体间的力传递包含两类：一类是维持细胞间距的外挤作用力（extrusive forces），另一类是维持细胞集体结构的黏附作用力（cohesive forces）。我们分别在均匀极化（逆血流方向）的细胞种群与混合极化（正向/逆向血流方向）的细胞种群中开展了迁移模拟实验。
在均匀极化的细胞种群中，外挤作用力通过促进内皮细胞的相互嵌入（intercalation）稳定了血管丛，确保细胞分布均匀。过量的黏附作用力则会破坏细胞间的嵌入过程，引发细胞聚集与功能性分流（functional shunting）。内皮细胞间过强的黏附会阻碍血管丛内的管径平衡调节，导致血流持续逆转；而血流逆转会改变系统内的关键行为模式，使细胞迁移方向与分叉处的流动模式发生切换。
引入细胞极化混合种群后，外挤作用力在系统中的作用发生了显著变化。在低外挤作用力条件下，极化方向相反的内皮细胞可相互穿行；但当外挤作用力过高时，细胞间的推挤作用会使迁移速率趋近于零，形成交通拥堵并破坏正常迁移过程。
本研究表明，无论是内皮细胞间黏附作用力过强，还是存在细胞极化混合种群，均可引发血管畸形与功能性分流。这两种致病机制的核心均为细胞间黏着连接（adherens junctions）——该结构参与血流感知与细胞极化过程，且需要发生动态重塑以允许血管模式形成过程中的细胞重排。因此，本研究结果提示，连接蛋白功能异常可作为血管疾病与动静脉畸形治疗及预防的全新靶点。