Elucidating the role of GCN2 in the pathogenesis of pulmonary vascular disease

肺动脉高压是一个术语，描述了一组疾病，它们具有以下共同特征：进出肺部的血管中的血压水平升高，如果不及时治疗，会导致心力衰竭，最终导致死亡。肺动脉高压主要有两种类型。在第一种类型中，阻塞位于供血肺部的动脉水平（“肺动脉高压”），而在第二种类型中，阻塞发生在引流肺部的静脉水平或以下（“肺静脉高压”）。最近，人们发现了一种新的遗传性疾病，可引起一种罕见的肺动脉高压，即肺动脉静脉闭塞性疾病（PVOD），它兼具动脉和静脉的特征。这个问题是由一种叫做GCN2的蛋白质基因突变引起的。GCN2蛋白在一种被称为综合应激反应的反应中至关重要，这种反应通常在蛋白质缺乏的时期被激活。此前没有证据表明这种蛋白质的问题会影响心脏或肺部循环；所以这是一个全新的研究领域。此前，遗传性肺动脉高压与另一种产生骨形态发生蛋白受体II型（BMPR2）蛋白质的基因的问题有关。有这种问题的患者缺乏BMPR2。发现这一遗传问题导致了治疗肺动脉高压的新方法，如增加BMPR2水平或激活剩余的BMPR2。这些药物目前正在老鼠身上进行试验。我们希望GCN2的发现将推动同样的过程，特别是在肺静脉闭塞性疾病和一般的肺动脉高压中。目前，对于PVOD或肺静脉高压，除了移植之外，没有其他特定的治疗方法，很少有患者有资格接受移植。我打算研究GCN2缺乏究竟是如何影响心脏和肺部的。为此，我们将使用几种疾病模型，如缺乏GCN2基因的果蝇和小鼠，以及移植时捐献的GCN2突变患者的血液样本和肺血管细胞。我们将首先将完全缺乏该基因的小鼠与正常小鼠进行比较，看看gcn2缺陷小鼠是否会发生肺动脉高压。如果没有，我们将观察这些小鼠与缺乏BMPR2的小鼠杂交是否会“发现”这种疾病。到目前为止，我们已经发现gcn2缺陷小鼠出现轻度肺动脉高压，并且通过添加BMPR-2缺陷进一步加剧。我们的下一步是观察GCN2是否是一种保护因子，以及替换或激活GCN2是否会对小鼠的肺动脉高压起到保护作用。我们还从果蝇研究中得知，GCN2和BMPR2通路重叠。例如，激活GCN2通路可以减少苍蝇翅膀和苍蝇细胞对BMPR2刺激的反应。我将检查从人类肺血管中提取的细胞是否也如此。如果BMPR2位于GCN2相关通路的下游，那么激活BMPR2可能是治疗与GCN2缺乏相关的肺动脉高压的另一种方法。一旦我们了解GCN2缺乏如何导致小鼠肺动脉高压的发展，我们将在使用肺动脉高压患者捐献的血液和组织样本的实验中验证这些理论是否得到支持。最终，我们的目标是为gcn2相关的肺动脉高压开发新的治疗方法，并在患者的临床试验中进行测试。

Pulmonary hypertension is a term that describes a group of diseases which have in common the following feature: increased blood pressure levels in the blood vessels leading into and out of the lungs, which leads to heart failure and finally death, if left untreated. There are two main types of pulmonary hypertension. In the first type, the obstruction is at the level of the arteries feeding the lungs ('pulmonary arterial hypertension') and in the second type the obstruction occurs either at or below the level of the veins draining the lungs ('pulmonary venous hypertension'). Recently there has been a discovery of a new inherited problem which can cause a rare form of pulmonary hypertension, pulmonary veno-occlusive disease (PVOD), which combines both arterial and venous features. This problem consists of mutations in the gene for a protein called general control nonderepressible 2, or GCN2. The GCN2 protein is crucially important in a reaction known as the integrated stress response, which is usually activated in periods of protein starvation. There has been no previous hint that problems with this protein can affect the heart or lung circulation; so this is a completely new area of research. Inherited pulmonary arterial hypertension has previously been linked with problems in another gene which creates a protein known as bone morphogenetic protein receptor type II (BMPR2). Patients with this problem have a deficiency of BMPR2. Finding this genetic problem has led to new ways to treat pulmonary arterial hypertension such as increasing BMPR2 levels or by activating the remaining BMPR2. These are currently being tested in mice. It is our hope that the discovery of GCN2 will drive the same process for pulmonary veno-occlusive disease specifically and pulmonary hypertension in general. Currently there is no specific treatment for either PVOD or pulmonary venous hypertension other than a transplant, which very few patients are eligible for. I plan to examine how exactly GCN2 deficiency affects the heart and lungs. To do this, we will use several models of the disease, such as fruit flies and mice lacking the GCN2 gene, and blood samples and lung blood vessel cells by patients with GCN2 mutations donated at the time of transplant. We will initially compare mice that are completely lacking this gene with normal mice and see whether GCN2-deficient mice develop pulmonary hypertension. If they don't, we will see whether crossing these mice with mice lacking BMPR2 will 'uncover' the disease. So far we have discovered that GCN2-deficient mice develop mild pulmonary hypertension and this is further exacerbated by adding in BMPR-2 deficiency. Our next steps are to see whether GCN2 is a protective factor and if replacing and or activating GCN2 will be protective against pulmonary hypertension in miceWe also know from the fly studies that the GCN2 and BMPR2 pathways overlap. For example, activating the GCN2 pathway reduces the reaction to stimulation of BMPR2 in fly wings and in fly cells. I will examine if this is also true in cells taken from human lung blood vessels. If BMPR2 is downstream of GCN2-related pathways then perhaps activating BMPR2 will be an alternative way of treating pulmonary hypertension associated with GCN2 deficiency. Once we understand how GCN2 deficiency leads to development of pulmonary hypertension in mice, we will check if these theories are supported in experiments using blood and tissue samples donated by pulmonary hypertension patients. Eventually we aim to develop new treatments for GCN2-associated pulmonary hypertension and to test them in clinical trials in patients.