Exploring the Role of Egr2 in the Alternative Activation of Macrophages

描述（由申请人提供）：过敏原、致病菌和病毒诱导和加重哮喘的机制尚不清楚。虽然哮喘可以控制，但许多患者对标准治疗没有反应，并可能出现严重的并发症。因此，迫切需要创新的策略来开发新的治疗靶点。根据我们自己和其他人的数据，巨噬细胞对哮喘的病理生理有贡献，这一点越来越清楚。巨噬细胞分化为多种功能表型，具有明显不同的特征。LPS/IFN处理巨噬细胞？经历经典激活，表达高水平的iNOS，并建立强大的促炎反应来杀死细胞内细菌。另一方面，il -4处理的巨噬细胞经历另一种激活。这些细胞被称为选择性活化巨噬细胞（AAM），表达高水平的精氨酸酶I和YM1/2，并建立了一种对组织修复和对蠕虫寄生虫的免疫反应很重要的表型。我们发现AAM与过敏性哮喘的严重程度有直接关系。AAM也允许细胞内细菌生长。因此，了解AAM分化受调控的机制具有重要意义。我们已经证明il -4诱导的AAM分化依赖于STAT6。然而，我们不清楚巨噬细胞向AAM型的分化是如何在STAT6下游被控制的，这代表了知识上的空白。我们发现，即使在其他细胞因子存在的情况下，IL-4也主导着巨噬细胞向替代状态的分化。此外，利用基因表达阵列和新型Egr2- egfp报告小鼠，我们发现IL-4在诱导AAM特征基因之前，以stat6依赖的方式快速有效地诱导转录因子Egr2的表达。基于这些结果，我们提出IL-4通过诱导Egr2的表达从而控制巨噬细胞表型来驱动AAM的分化和功能。因此，在本R21中，我们将开发新的小鼠模型来跟踪Egr2阳性巨噬细胞，并确定Egr2对体外和体内AAM分化的影响。本探索性研究的具体目的是：1)确定Egr2在体外促进AAM分化中是否必要和充分；2)开发新的小鼠品系来评估Egr2在体内AAM分化中的作用；3)确定Egr2在体内AAM分化中是否必要。这些研究新颖，高风险/高影响，因为它们将确定STAT6下游的一个基因，该基因负责巨噬细胞的选择性分化。Egr2作为控制AAM分化的转录因子的特性将有很高的评价

DESCRIPTION (provided by applicant): Allergens and pathogenic bacteria and viruses induce and exacerbate asthma by mechanisms that are not yet understood. While asthma can be controlled, many patients do not respond to standard treatments and can develop serious complications. Consequently, there is an urgent need for innovative strategies to develop novel therapeutic targets. Based on our own data and others, it is becoming clear that macrophages contribute to the pathophysiology of asthma. Macrophages differentiate into several functional phenotypes with markedly distinct characteristics. Macrophages treated with LPS/IFN? undergo classical activation, express high levels of iNOS, and establish a strong proinflammatory response to kill intracellular bacteria. On the other hand, IL-4-treated macrophages undergo an alternative activation. These cells, termed alternatively activated macrophages (AAM), express high levels of arginase I and YM1/2, and establish a phenotype that is important for tissue repair and immune responses to helminthic parasites. We have found that AAM directly contribute to the severity of allergic asthma. AAM are also permissive for growth of intracellular bacteria. Thus, understanding the mechanism by which AAM differentiation is regulated is significant. We have shown that IL-4-induced AAM differentiation is dependent on STAT6. However, we do not understand how the differentiation of macrophages to the AAM type is controlled downstream of STAT6, representing a gap in knowledge. We found that IL-4 dominantly controlled the differentiation of macrophages to the alternative state, even in the presence of other cytokines. Furthermore, using gene expression arrays and a novel Egr2-EGFP reporter mouse, we found that IL-4 rapidly and potently induced the expression of the transcription factor Egr2 in a STAT6-dependent manner, preceding the induction of AAM signature genes. Based on these results, we propose that IL-4 drives AAM differentiation and function by inducing the expression of Egr2 thereby controlling macrophage phenotype. Therefore, in this R21 we will develop new mouse models to track Egr2 positive macrophages and determine the impact of Egr2 on AAM differentiation in vitro and in vivo. The specific aims designed for this exploratory study are 1) to determine whether Egr2 is necessary and sufficient to promote AAM differentiation in vitro, 2) to develop novel mouse lines to assess the role of Egr2 in AAM differentiation in vivo, and 3) to determine whether Egr2 is necessary for AAM differentiation in vivo. These studies are novel, and high risk/high impact because they will define a gene downstream of STAT6 that is responsible for alternative macrophage differentiation. The characterization of Egr2 as a transcription factor that controls AAM differentiation will have high impact in the field of Type II inflammation as it may lead to the development of Egr2 as a new therapeutic target for asthma and infection. PUBLIC HEALTH RELEVANCE: The prevalence of asthma has dramatically increased in the United States over the past 30 years and has reached epidemic proportions. Current asthma therapies are not effective for all patients. Certain types of macrophages can make asthma symptoms worse. Our research project will analyze whether the transcription factor Egr2 controls the differentiation of macrophages to the alternative type in response to the cytokine IL-4. Our proposed studies may identify new targets for the treatment of asthma.