Cell type-specific influences on HHT pathogenesis

描述(申请人提供)：在遗传性出血性毛细血管扩张症(HHT)中，多器官的动静脉畸形(AVM)和毛细血管扩张是导致反复自发性出血的主要病理病变，可危及生命并导致长期残疾。一种流行的观点认为，HHT是由基因单倍性不足引起的 HHT1中的Endoglin(ENG，转化生长因子/骨形态发生蛋白的辅助受体)或HHT2中的ALK1(ACVLR1，转化生长因子/骨形态发生蛋白的1型受体)等致病基因之一的体细胞内皮细胞。然而，我们和其他人的研究表明，体细胞EC中的基因单倍体不足不足以解释AVM的发生发展和HHT表型的变化。相反，我们的数据支持以下假设：AVM的发生和发展是几个因素相互作用的结果：(1)内皮细胞中ENG或ALK1的纯合子功能丧失；(2)来自造血干细胞(HSC)的EC和巨噬细胞的贡献；以及(3)HHT单核细胞和巨噬细胞的促炎表型。我们已经开发了几个小鼠模型，这些模型在多个器官中具有动静脉动静脉畸形，复制了人类HHT的表型。我们将使用这些模型和多伦多大学圣迈克尔医院HHT中心提供的HHT患者的血液样本来验证这些假说。在目标1中，我们将使用HHT1和HHT2小鼠模型和一种新的肺器官模型来确定AVM形成所需的Eng或Alk1缺失EC的数量是否因器官不同而不同，并与病变严重程度呈正相关。在目标2中，我们将使用HSC移植实验来确定HSC来源的Alk1或Eng零的内皮细胞和巨噬细胞在AVM的启动和发展中的作用。在目标3中，我们将使用小鼠模型和HHT患者的单核细胞来研究HHT单核细胞和巨噬细胞如何促进AVM的进展。该项目将是对AVM形成和发展过程中涉及的细胞类型的第一次系统研究。我们特定目标的实现将导致我们对HHT患者动静脉动静脉畸形形成方式的理解发生范式转变。我们提出的研究结果将使我们对HHT中AVM发病的基本机制有更全面的了解，并使我们处于更好的位置来设计特定的治疗方法。该项目中正在测试的机制的验证可以导致潜在的治疗方法，这些疗法可以在临床前试验中进行测试。这将是该领域的一个重大进步，因为目前HH患者的治疗选择非常有限。

DESCRIPTION (provided by applicant): In hereditary hemorrhagic telangiectasia (HHT), arteriovenous malformations (AVMs) in multiple organs and telangiectasia are the major pathological lesions causing recurrent spontaneous hemorrhage that can be life- threatening and leads to long-term disability. A prevailing view is that HHT is caused by haploinsufficiency in somatic endothelial cells (ECs) of one of its causative genes, such as endoglin (ENG, an accessory receptor of TGFß/BMP) in HHT1 or ALK1 (ACVLR1, a type 1 receptor of TGFß/BMP) in HHT2. However, studies by us and others suggest that gene haploinsufficiency in somatic EC alone is inadequate to explain AVM development and progression and the variations in HHT phenotypes. Instead, our data support the hypotheses that AVM development and progression result from an interplay of several factors: (1) a dose-dependent homozygous loss-of-function of ENG or ALK1 in ECs; (2) contribution of EC and macrophage derived from hematopoietic stem cells (HSC); and (3) pro-inflammatory phenotype of HHT monocytes and macrophages. We have developed several mouse models that have AVMs in multiple organs, replicating the human HHT phenotype. We will use these models and blood specimens from HHT patients provided by HHT Center in St. Michael's hospital of University of Toronto to test these hypotheses. In Aim 1 we will use HHT1 and HHT2 mouse models and a novel lung organoid model to determine if the quantity of Eng- or Alk1-null EC required for AVM formation is different among organs and is positive correlate with lesion severity. In Aim 2, we will use HSC transplantation experiments to determine the roles of HSC-derived Alk1- or Eng-null ECs and macrophages in AVM initiation and progression. In Aim 3, we will use both mouse models and blood monocytes from HHT patients to investigate how HHT monocytes and macrophages promote AVM progression. This project will be the first systematic investigation of the cell types involved in AVM formation and progression. The accomplishment of our specific aims will lead to a paradigm shift on our understanding of how AVMs form in HHT patients. The results of our proposed studies will lead to a fuller knowledge of the basic mechanisms of AVM pathogenesis in HHT, and put us in a much better position to design specific therapies. Validation of the mechanisms being tested in this project can lead to potential therapies that can be tested in pre-clinical trials. This would be a significant advance for the field since therapeutic options for HH patients are currently very limited.