Systems-Mechanobiology of Endothelial Gap Dynamics

脉管系统是一个复杂的系统，对高级生物体的功能至关重要。它由大血管组成，这些血管分支成越来越小的血管。在最小的尺度上，微血管系统由小动脉、小静脉和毛细血管组成。在这里，氧气和营养物质在血管和组织之间交换。此外，免疫细胞或癌细胞可以通过血管内的间隙转移到周围组织中。对于免疫系统来说，这是一项至关重要的功能，因为免疫细胞需要到达感染部位。然而，高水平的迁移也可能导致慢性炎症，癌细胞在转移过程中会迁移血管。因此，血管间隙的严格调节在体内平衡过程中至关重要，而间隙的失调可能导致疾病。我们初步的数学建模/体外实验工作表明，内皮细胞（排列在血管上的细胞）的细胞内力量平衡调节着细胞间间隙的形成。我们发现这些间隙最常发生在三个内皮细胞之间的顶点点，并且可能在没有迁移细胞的情况下自主出现。这一发现补充了早期的研究，发现了由迁移细胞释放的炎症信号在内皮细胞调节中的关键作用。我们进一步表明，迁移细胞可能通过向间隙迁移来利用这些自主形成的间隙，在那里它们穿过内皮。因此，研究内皮的动态性质以及由此形成的间隙，对于理解免疫和癌症转移的重要生理过程至关重要。在体内，微血管的动力学受到许多其他生物物理特性的影响，这些特性在大多数体外检测中不存在。值得注意的是，血管中的血流，内皮细胞与周围细胞外基质的相互作用，以及微血管复杂的几何和拓扑结构，都被发现分别影响内皮动力学。在体内，这些特性同时存在。系统生物学模型通常用于研究细胞在多种刺激下的决策。然而，目前的系统生物学模型侧重于研究多种分子刺激，如炎症细胞因子，但不能捕获生物物理刺激。因此，迫切需要将多种生物物理刺激的作用纳入系统生物学模型。在这个项目中，我们正在开发一种综合建模/实验方法，将多种生理生物物理特性结合到数学模型和体外分析中。我们的方法将推进模型和实验迭代在一起，以获得前所未有的洞察内皮微血管的动态性质。其结果将是一个多功能的数学建模平台，用于研究微血管动态稳态，并将为内皮动力学对疾病的贡献奠定基础。此外，我们将推进我们最近开发的工程体外试验，可以在复杂的细胞外基质中产生稳定的，灌注的3D微血管，因此非常适合验证我们的数学建模预测。结合建模/实验系统将用于测试几种特定的生物学假设，这些假设是关于内皮动力学和间隙形成的主要贡献者的复杂作用。

The vasculature is a complex system, critical to the functioning of higher-level organisms. It is composed of large vessels that branch into smaller and smaller vessels. On the smallest scale, the microvasculature consists of arterioles, venules and capillaries. Here, oxygen and nutrients are exchanged between the vessels and the tissue. Also, immune or cancer cells can transmigrate through gaps within the blood vessels into the surrounding tissues. For the immune system, this is a critical function, as immune cells need to reach sites of infection. However, high levels of transmigration may also contribute to chronic inflammation, and cancer cells transmigrate the blood vessels during metastasis. Therefore, a tight regulation of the blood vessel gaps is critical during homeostasis, and de-regulation of gaps may contribute to diseases.Our preliminary mathematical modelling/in vitro experimental work revealed that a balance of intracellular forces in the endothelial cells, the cells that line the blood vessels, regulates the formation of gaps in between the cells. We found that these gaps occur most frequently at the vertex points between three endothelial cells, and may appear autonomously, in absence of transmigrating cells. This finding complemented earlier studies that uncovered a critical role of inflammatory signals, released by transmigrating cells, in the regulation of endothelial cells. We further showed that transmigrating cells may exploit these autonomously forming gaps by migrating towards the gaps, where they cross the endothelium. Therefore, studying the dynamic nature of the endothelium, and the resulting formation of gaps, is critical to understand the physiologically important processes of immune and cancer transmigration.In vivo, the dynamics of the microvasculature is influenced by several further biophysical properties not present in most in vitro assays. Notably, blood flow in the vessels, interactions of endothelial cells with the surrounding extracellular matrix, and the complex geometry and topology of the microvasculature, have all been found to influence endothelial dynamics individually. In vivo these properties exist simultaneously. Systems biology models are typically employed to study cellular decision making in response to multiple stimuli. However, current systems biology models are focused on the study of multiple molecular stimuli, e.g. inflammatory cytokines, but cannot capture biophysical stimuli. Therefore, there is an urgent need to incorporate the effect of multiple biophysical stimuli into systems biology models.In this project, we are developing an integrative modelling/experimental approach that incorporates multiple physiological biophysical properties into both mathematical models and in vitro assays. Our approach will advance models and experiments iteratively together to gain unprecedented insights into the dynamic nature of the endothelial microvasculature. The outcome will be a versatile mathematical modelling platform to study the dynamics of the microvasculature in homeostasis, and will underpin future work on the contribution of endothelial dynamics to diseases. Moreover, we will advance our recently developed engineered in vitro assays that can generate stable, perfused 3D microvasculature in complex extracellular matrices, and that is therefore ideally suited to validate our mathematical modelling predictions. The combined modelling/experimental system will be used to test several specific biological hypotheses on the complex role of major contributors to endothelial dynamics and gap formation.