mTOR and VEGFR2 pathways in HHT pathogenesis

项目摘要/摘要(说明) 遗传性出血性毛细血管扩张症(HHT)是一种常染色体显性遗传病，其特征是 全身性和潜在威胁生命的血管异常称为动静脉畸形 (Avms)。HHT突变主要发现在ALK1和ENG基因中，并导致BMP9/10功能丧失- 内皮细胞中的ALK1-ENG信号转导。最近的证据表明，HHT的发病机制和AVM 肿瘤的发生需要内皮细胞mTOR和VEGFR2通路的异常过度激活。整体而言 该计划的目标是表征mTOR和VEGFR2过度激活的精确机制 ALK1-ENG功能丧失，并确定这些机制的靶向是否具有疾病修饰作用 HHT细胞和小鼠模型的特性和治疗潜力。使用全转录组审问， 我们的初步研究表明，mTOR和VEGFR2的联合药理抑制 在纠正病理性基因表达特征方面显示出显著的协同和有效性 BMP9/10-免疫阻断(BMP9/101b)小鼠HHT模型。引人注目的是，双重mTOR-VEGFR2抑制被阻断 BMP9/10Ib中视网膜、肝脏、肺和粘膜的血管病理和动静脉畸形以避免出血和贫血 老鼠。从机制上讲，我们的初步数据显示，在ALK1-ENG抑制的下游， 血管生成素-2/Tie2受体信号转导是mTOR-VEGFR2激活和AVM的重要触发因素 HHT小鼠的发育。因此，我们的数据支持HHT发病机制的工作模型 有缺陷的ANG2-mTOR-VEGFR2通路，针对这些机械缺陷的干预可能 在HHT中提供治疗益处。基于这些结果，我们在目标1中建议评估内皮细胞 MTOR和VEGFR2是独立激活的，以及它们是否都是AVM开发所必需的 HHT小鼠。为此，单独针对mTOR和mTOR的药物和基因缺失方法 VEGFR2将用于两种HHT小鼠模型：BMP9/10Ib小鼠和新产生的敲门(KI)小鼠 表达HHT引起的ALK1突变的小鼠。在目标2中，我们将描述mTOR的精确机制 在HHT小鼠体内和体外原代内皮细胞中，通过ANG2/Tie2信号过度激活VEGFR2， 包括在HHT患者的血液中生长的内皮细胞。最后，在目标3中，我们将确定Tie2是否下调 阻断HHT小鼠的血管病理。

PROJECT SUMMARY/ABSTRACT (DESCRIPTION) Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disorder characterized by the development of systemic and potentially life-threatening vascular anomalies called arteriovenous malformations (AVMs). HHT mutations are mostly found in the ALK1 and ENG genes and lead to a loss-of-function of BMP9/10- ALK1-ENG signaling in endothelial cells (ECs). Recent evidence suggests that HHT pathogenesis and AVM development require the aberrant overactivation of the endothelial mTOR and VEGFR2 pathways. The overall goal of this program is to characterize the precise mechanisms of mTOR and VEGFR2 overactivations upon ALK1-ENG loss-of-function, and determine whether targeting of these mechanisms has disease-modifying properties and therapeutic potential in cell and mouse models of HHT. Using whole-transcriptome interrogation, our preliminary investigation has shown that combined pharmacological inhibition of mTOR and VEGFR2 demonstrated a remarkable synergy and efficacy in correcting a pathological gene expression signature in the BMP9/10-immunoblocked (BMP9/10ib) mouse model of HHT. Strikingly, dual mTOR-VEGFR2 inhibition blocked vascular pathology and AVMs in the retina, liver, lungs, and mucosa to avert bleeding and anemia in BMP9/10ib mice. Mechanistically, our preliminary data revealed that, downstream of ALK1-ENG inhibition, changes in angiopoietin-2 (ANG2)/Tie2 receptor signaling were important triggers for mTOR-VEGFR2 activation and AVM development in HHT mice. Therefore, our data support the working model that HHT pathogenesis is caused by defective ANG2-mTOR-VEGFR2 pathways, and that interventions targeting these mechanistic defects might provide therapeutic benefit in HHT. Based on these results, we propose in Aim 1 to assess whether endothelial mTOR and VEGFR2 are independently activated and whether they are both required for AVM development in HHT mice. To this end, pharmacological and gene deletion approaches independently targeting mTOR and VEGFR2 will be employed in two HHT mouse models: the BMP9/10ib mice and a newly generated knockin (KI) mouse expressing a HHT-causing ALK1 mutation. In Aim 2, we will delineate the precise mechanism of mTOR and VEGFR2 overactivation by ANG2/Tie2 signaling, both in vivo in HHT mice and in vitro in primary ECs, including in HHT patient blood outgrowth ECs. Lastly in Aim 3, we will determine whether Tie2 derepression blocks vascular pathology in HHT mice.