Analysis of the shear stress-induced transcriptional program during vasculardevelopment

血管系统由内皮管的分支网络组成，是发育过程中形成的第一个器官系统。它对氧气和营养物质在身体各个部位的分配很重要。血管系统的初始形成是由遗传因素控制的，并且已经确定了几种影响内皮细胞迁移和增殖的信号通路。在后期，生理反馈机制，如血流的变化，从而产生剪切应力，强烈影响内皮生物学。例如，剪切应力有助于适当的血管重塑，从而改善血液流动模式。此外，一些疾病状况与剪切应力的变化有关。动脉粥样硬化斑块的形成优先发生在血管分支点，其血流模式受到干扰。异常血流进一步发生在动静脉畸形区域。在这种情况下，大动脉和静脉之间的直接连接绕过了正常的毛细血管床，导致组织灌注受损。因此，调节血管发育和体内平衡的几个关键过程是由内皮细胞对剪切应力的反应控制的。尽管这种调节很重要，但我们对内皮细胞感知和反应剪切应力的机制的理解非常有限。我们的目的是回答有关内皮细胞对剪切应力的反应的两个基本问题。我们将研究剪切应力诱导的转录程序是如何调控的。为了做到这一点，我们将使用染色质免疫沉淀和测序（ChIP-Seq）鉴定内皮细胞中剪切应力控制的增强元件，并将它们与它们调节的基因联系起来。然后，我们将确定与这些增强因子结合的转录因子，并阐明它们在血管重塑过程中的功能。我们将进一步明确删除血流响应增强元件，并询问其对基因表达和内皮生物学的影响。总之，这些研究将为内皮细胞对剪切应力反应的调节提供重要的见解。在第二个目标中，我们将研究斑马鱼内啡肽突变体的表型，这些突变体呈现动静脉畸形。内啡肽是转化生长因子β (tgf - β)途径的一员，与人类遗传性出血性毛细血管扩张症（HHT）有关，HHT也以动静脉畸形为特征。我们可以证明血流强烈影响内啡肽突变鱼的动静脉畸形。我们将研究内啡肽如何决定内皮细胞对剪切应力的适当反应，从而有助于我们对HHT病因的理解。

The vasculature, consisting of a ramified network of endothelial tubes, is the first organ system to form during development. It is important for the distribution of oxygen and nutrients to all parts of the body. The initial formation of the vasculature is governed by hard-wired genetic factors and several signaling pathways influencing the migration and proliferation of endothelial cells have been identified. At later stages, physiological feedback mechanisms, such as changes in blood flow, and thus shear stress, strongly influence endothelial biology. For instance, shear stress contributes to proper blood vessel remodeling, thereby improving blood flow patterns. In addition, several disease conditions are associated with changes in shear stress. Atherosclerotic plaque formation preferentially occurs at blood vessel branch points, which exhibit disturbed flow patterns. Aberrant blood flow furthermore occurs in regions of arterio-venous malformations. In this setting, a direct connection between a large artery and a vein bypasses the normal capillary bed, leading to impaired tissue perfusion. Therefore, several key processes regulating vascular development and homeostasis are controlled by endothelial cell responses to shear stress. Despite the importance of this regulation, our understanding of the mechanisms by which endothelial cells perceive and react to shear stress is only very limited. We aim at answering two fundamental questions pertaining to endothelial cell responses to shear stress. We will investigate how the shear stress induced transcriptional program is regulated. In order to do so, we will identify shear stress controlled enhancer elements in endothelial cells using Chromatin Immunoprecipitation followed by sequencing (ChIP-Seq) and associate them with the genes they regulate. We will then identify the transcription factors binding to these enhancer elements and elucidate their functions during vascular remodeling. We will furthermore specifically delete flow responsive enhancer elements and interrogate the effect on gene expression and endothelial biology. Together, these studies will provide major insights into the regulation of endothelial cell responses to shear stress. In a second aim, we will investigate the phenotype of zebrafish endoglin mutants, which present with arterio-venous malformations. Endoglin is a member of the transforming growth factor beta (TGF-beta) pathway and associated with the human genetic disorder hereditary hemorrhagic telangiectasia (HHT), which is also characterized by arterio-venous malformations. We could show that blood flow strongly influenced arterio-venous malformations in endoglin mutant fish. We will investigate how endoglin determines proper endothelial cell responses to shear stress and thereby contribute to our understanding of HHT aetiology.