Exploring the Role of Egr2 in the Alternative Activation of Macrophages

描述(申请人提供)：过敏原、致病细菌和病毒通过尚不清楚的机制诱发和加重哮喘。虽然哮喘是可以控制的，但许多患者对标准治疗没有反应，可能会出现严重的并发症。因此，迫切需要创新战略来开发新的治疗靶点。根据我们自己和其他人的数据，巨噬细胞在哮喘的病理生理学中的作用变得越来越明显。巨噬细胞分化为几种具有明显不同特征的功能表型。巨噬细胞经脂多糖/干扰素？经历经典的激活，表达高水平的iNOS，并建立强大的促炎反应来杀灭细胞内的细菌。另一方面，经IL-4处理的巨噬细胞经历了另一种激活。这些细胞被称为交替激活的巨噬细胞(AAM)，表达高水平的精氨酸酶I和YM1/2，并建立了对组织修复和对寄生虫的免疫反应重要的表型。我们发现AAM与过敏性哮喘的严重程度直接相关。AM对胞内细菌的生长也是允许的。因此，了解调节AAM分化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，我们不知道巨噬细胞向AAM类型的分化是如何在STAT6下游受到控制的，这代表着知识的空白。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另一种状态的分化。此外，利用基因表达阵列和一个新的Egr2-EGFP报告小鼠，我们发现IL-4以STAT6依赖的方式快速而有效地诱导转录因子Egr2的表达，在诱导AAM签名基因之前。基于这些结果，我们认为IL-4通过诱导Egr2的表达从而控制巨噬细胞的表型来促进AAM的分化和功能。因此，在R21中，我们将建立新的小鼠模型来追踪Egr2阳性的巨噬细胞，并确定Egr2在体外和体内对AAM分化的影响。本探索性研究的具体目的是：1)确定Egr2是否在体外促进AAM分化所必需的且充分的；2)建立新的小鼠系以评估Egr2在体内AAM分化中的作用；3)确定Egr2在体内是否对AAM分化是必需的。这些研究是新的，高风险/高影响，因为它们将定义STAT6下游负责替代巨噬细胞分化的基因。Egr2作为一个控制AAM分化的转录因子的特性将有很高的 在II型炎症领域的影响，因为它可能导致Egr2作为哮喘和感染的新治疗靶点的发展。

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.