Decoding the Molecular and Cellular Mechanisms of Mutant KRAS-driven Brain Arteriovenous Malformations

总结 脑动静脉畸形（bAVM）是由动脉和静脉之间的异常连接组成 缺乏毛细血管网的组织结果，来自供血动脉的高压血液直接分流 注入静脉这些血管病变变得扩张和高度重塑，导致一个扩大的缠结。 容易破裂的血管事实上，bAVM是儿童出血性卒中的主要原因 和年轻人。目前所有bAVM的治疗方式，包括手术、栓塞或放射治疗， 存在显著的残疾或死亡风险，约20%的bAVM患者无法使用这些选项，原因是 过度风险。由于这些并发症，具有较低发病率的替代医学策略，如 迫切需要靶向药物治疗。但是，我们首先需要清楚地了解 bAVM发展和维持的生物学基础。大多数bAVM偶发， 有家族病史使用全外显子组测序，我们最近发现了体细胞，激活 KRAS基因中的突变，其编码参与信号转导的GT3。所识别的 突变局限于内皮，并导致KRAS被锁定在GTP结合的“ON”状态。值得注意的是， 我们已经建立了突变KRAS内皮特异性表达的小鼠和斑马鱼模型， 揭示了这些遗传损伤足以导致疾病。我们继续展示， 通过对培养细胞的转录谱分析和对表达突变KRAS的斑马鱼的体内研究， 许多KRAS诱导的分子和细胞变化需要MEK/ERK活性。还有很多东西要学 关于散发性bAVM的病因和我们的细胞培养，小鼠和斑马鱼模型将使我们能够 定义参与启动和维持的分子，细胞和形态学变化 bAVM。我们将利用我们在bAVM动物模型、成像、细胞生物学、信号传导和单细胞 RNA测序，以获得前所未有的深入了解bAVM疾病的过程。此信息将 用于设计药物干预措施以改善患者结局。我们的建议将：1） 确定可以重塑血管的KRAS突变内皮细胞的阈值，2）识别血管床 3）确定KRAS突变如何影响血流动力学 信号传导和bAVM进展，4）揭示细胞自主和非细胞自主机制， 突变型KRAS，以及4）在我们的研究中确定bAVM维持对KRAS和MEK激活的需求。 临床前模型。总之，这些研究将扩大我们对bAVM发病机制的理解， 评估KRAS/MEK通路的抑制是否可能是人类追求的可行治疗靶点 bAVM患者。

SUMMARY Brain arteriovenous malformations (bAVMs) are composed of abnormal connections between arteries and veins that lack an intervening capillary network. As a result, high-pressure blood from feeding arteries shunts directly into veins. These vascular lesions become distended and highly remodeled, resulting in a tangle of enlarged blood vessels that are prone to rupture. Indeed, bAVMs are a leading cause of hemorrhagic stroke in children and young adults. All current treatment modalities for bAVMs, including surgery, embolization or radiation carry a significant risk of disability or death, and these options are not available for ~20% of bAVM patients due to excessive risk. Because of these complications, alternative medical strategies with lower morbidities such as targeted pharmacological therapies are desperately needed. However, we first need a clear understanding of the biology underlying bAVM development and maintenance. The majority of bAVMs occur sporadically without a family history of the disease. Using whole exome sequencing, we recently identified somatic, activating mutations in the KRAS gene, which encodes a GTPase that is involved in signal transduction. The identified mutations were confined to the endothelium and result in KRAS being locked in a GTP-bound ‘ON’ state. Notably, we have established mouse and zebrafish models of endothelial-specific expression of mutant KRAS, which have revealed the sufficiency for these genetic lesions to drive disease. We have gone on to demonstrate, through transcriptional profiling of cultured cells and in vivo studies in zebrafish expressing mutant KRAS, that many KRAS-induced molecular and cellular changes require MEK/ERK activity. Much remains to be learned regarding the etiology of sporadic bAVMs and our cell culture, mouse and zebrafish models will enable us to define the molecular, cellular and morphological changes that are involved in the initiation and maintenance of bAVMs. We will utilize our expertise in animal models of bAVMs, imaging, cell biology, signaling and single-cell RNA sequencing, to gain unprecedented insight into the bAVM disease process. This information will be leveraged for the design of pharmacological interventions to improve patient outcomes. Our proposal will: 1) define the threshold of KRAS mutant endothelial cells that can remodel vessels, 2) identify the vascular bed(s) that are susceptible to active KRAS expression, 3) determine how KRAS mutations impact hemodynamic signaling and bAVM progression, 4) uncover the cell-autonomous and non-cell autonomous mechanisms of mutant KRAS, and 4) determine the requirement for KRAS and MEK activation for bAVM maintenance in our pre-clinical models. Together, these studies will expand our understanding of bAVM pathogenesis and will assess whether inhibition of the KRAS/MEK pathway may be a viable therapeutic target to pursue in human patients with bAVM.