Fox Transcription factors in lymphatic vessel development

 描述(由申请人提供)：淋巴管系统对于消化系统的脂肪吸收/运输、维持组织液内环境平衡和免疫监测是必不可少的。它还参与许多病理过程，如炎症性疾病和肿瘤转移，以及淋巴水肿，其中淋巴液体从间质组织中排出不足，导致组织肿胀。淋巴水肿最常见的原因是淋巴管生成受损或淋巴瓣缺陷；然而，淋巴管异常和疾病的复杂性质仍然知之甚少。因此，我们的长期目标是了解淋巴管系统的形成和功能的分子和细胞机制。Foxc1和FOXC2是Fox(Forkhead Box)转录因子家族中密切相关的成员，我们的研究小组先前已经证明，小鼠Foxc1和FOXC2在心血管发育中具有许多重要的作用。人类FOXC2基因突变是常染色体显性遗传综合征淋巴水肿-二叉症的原因，该综合征的特征是肢体淋巴引流受阻，静脉瓣膜衰竭，以及额外的一组睫毛生长。最近的研究表明，FOXC2对淋巴瓣的形成也是必不可少的，但FoxC1在淋巴系统中的作用尚未确定。因此，我们最近产生了携带Foxc1和/或FOXC2的淋巴管内皮细胞(LEC)特异性突变的小鼠，这将使我们能够确定Foxc1和FOXC2在导致淋巴管发育的细胞过程中的确切功能。我们的初步研究表明，Foxc1和FOXC2的缺失单独或联合导致淋巴管增生，并伴随着RasGAP基因表达的下降和ERK的过度激活。此外，我们新的全基因组RNA-seq分析表明，Notch1和Dll4等Notch信号基因在从条件化合物LEC-Foxc1和LEC-FOXC2突变体中分离的LEC中显著下调。因此，本应用的目的是研究转录因子Foxc1和FOXC2在淋巴管发育中的作用。我们的中心假设是Foxc1和FOXC2对淋巴细胞命运的决定、淋巴管的生成和淋巴瓣的发育是必不可少的，我们将通过追求以下三个特定目标来检验我们的中心假设并实现这一应用的目标：1)确定Foxc1和FOXC2是否通过与Notch信号通路相互作用而参与淋巴细胞命运的决定。2)明确Foxc1和FOXC2在淋巴管生成过程中调节Ras/ERK通路的机制。3)阐明Foxc1和FOXC2在淋巴瓣发育中的协同和不同作用。总之，我们项目的成果是对Foxc1和FOXC2在淋巴管发育中扮演的关键角色进行了广泛的表征。我们预计我们的发现将对患者护理产生重要的积极影响，因为拟议研究的完成可能会导致预防和治疗淋巴疾病(如淋巴水肿)的新策略的开发和完善。

 DESCRIPTION (provided by applicant): The lymphatic vascular system is essential for lipid absorption/transport from the digestive system, maintenance of tissue fluid homeostasis, and immune surveillance. It is also involved in many pathological processes such as inflammatory disease and tumor metastasis, as well as lymphedema, in which the drainage of lymphatic fluid from the interstitial tissue is insufficient, causing the tissues to swell. Lymphedema is most commonly attributed to impaired lymphangiogenesis or lymphatic-valve deficiency; however, the complex nature of lymphatic vessel abnormalities and disease remain poorly understood. Thus, our long-term goal is to understand the molecular and cellular mechanisms responsible for the formation and function of the lymphatic vascular system. FoxC1 and FoxC2 are closely related members of the Fox (Forkhead box) transcription factor family, and our group has previously shown that murine Foxc1 and Foxc2 have numerous essential roles in cardiovascular development. Mutations in human FOXC2 are responsible for the autosomal dominant syndrome Lymphedema-distichiasis, which is characterized by the obstruction of lymphatic drainage in the limbs, venous valve failure, and the growth of an extra set of eyelashes. Recent studies have shown that Foxc2 is also essential for lymphatic valve formation, but the role of FoxC1 in the lymphatic system has yet to be defined. Thus, we have recently generated mice that carry lymphatic endothelial cell (LEC)-specific mutations for Foxc1, Foxc2, or both, which will enable us to determine the precise functions of Foxc1 and Foxc2 in the cellular processes that lead to the development of lymphatic vessels. Our initial studies indicate that the loss of Foxc1 and Foxc2, alone or in combination, leads to lymphatic hyperplasia and is accompanied by declines in the expression of RasGAP genes and by the hyperactivation of ERK. Furthermore, our new genome-wide RNA-seq analysis indicates that Notch signaling genes such as Notch1 and Dll4 are significantly downregulated in LECs that have been isolated from conditional compound LEC-Foxc1;LEC-Foxc2 mutants. Thus, the objective of this application is to study the role of the transcription factors Foxc1 and Foxc2 in lymphatic vessel development. Our central hypothesis is that Foxc1 and Foxc2 are essential for lymphatic cell fate determination, lymphangiogenesis, and lymphatic valve development, and we will test our central hypothesis and accomplish the objective of this application by pursuing the following three Specific Aims: 1) To determine whether Foxc1 and Foxc2 participate in lymphatic cell fate determination by interacting with the Notch signaling pathway. 2) To define the mechanisms by which Foxc1 and Foxc2 regulate the Ras/ERK pathway during lymphangiogenesis. 3) To elucidate the cooperative and distinct functions of Foxc1 and Foxc2 in lymphatic valve development. In summary, the outcome of our project is an extensive characterization of the critical roles that Foxc1 and Foxc2 play in lymphatic vessel development. We expect our findings to have an important positive impact on patient care, because completion of the proposed studies will likely lead to the development and refinement of novel strategies for preventing and treating lymphatic disorders, such as lymphedema.