KLF4 and Myeloid Cell Biology

描述（申请人提供）：代谢综合征（MetS）是一系列生物化学和物理紊乱，困扰着全球近20-25%的个体。越来越多的人认识到，慢性炎症不仅是MetS发展的统一基础机制，而且是动脉粥样硬化血栓形成性心血管疾病（这些个体发病率和死亡率的主要来源）的后续发展的统一基础机制。最近的研究强调了单核细胞/巨噬细胞谱系的细胞在MetS的发展及其后果如动脉粥样硬化血栓形成中的重要作用。单核细胞/巨噬细胞谱系的细胞表现出显著的可塑性，这使得它们能够调节其表型并有效地响应环境信号并改变其表型。为了简单起见，已经开发了将炎性巨噬细胞分类为M1并且将抗炎性巨噬细胞分类为M2巨噬细胞的模型系统。这两个亚群的平衡被认为是严重影响生理和病理炎症反应，但其形态和功能的分子决定因素仍然知之甚少。Kruppel样因子（KLF）是一种锌指转录因子，参与包括造血生物学在内的多种生物学过程。虽然我们小组和其他人以前的研究涉及KLF 4在骨髓细胞生物学，在体内的生理相关性尚未阐明。基于我们的初步研究，KLF 4表达在M2群体中被鉴定，并且在M1巨噬细胞中强烈降低-在体内人类炎症范例中重现的观察结果。获得和丧失功能的研究表明，KLF 4促进M2遗传程序并抑制M1靶基因。骨髓特异性KLF 4缺失的小鼠表现出特征性的M1表型，其杀菌活性增强就是证明。此外，响应于高脂肪饮食（HFD），这些动物发展出与MetS一致的许多特征，包括肥胖、血脂异常、胰岛素抗性和促动脉粥样硬化/促血栓形成状态。这些观察结果为中心假设提供了基础，即KLF 4是控制巨噬细胞亚群特异性和功能的上游分子开关。为了更好地理解KLF 4在巨噬细胞极化和功能中的确切作用，提出了三个目标。在目标1中，我们将描述髓系细胞中KLF 4表达的上游调控机制。在目标2中，我们将确定KLF 4调节M1/M2表型能力的分子基础。在目标3中，研究将确定髓样KLF 4表达改变对胰岛素抵抗和动脉粥样硬化血栓形成的影响。总之，这些研究将阐明KLF 4介导的M2表型极化的分子基础，以及KLF 4充足和不足对胰岛素抵抗和动脉粥样硬化血栓形成的功能后果。

DESCRIPTION (provided by applicant): The metabolic syndrome (MetS) is a constellation of biochemical and physical derangements that afflicts nearly 20-25% of individuals worldwide. It is increasingly appreciated that chronic inflammation is a unifying underlying mechanism not only for the development of MetS but also for the subsequent development of atherothrombotic cardiovascular disease - the primary source of morbidity and mortality in these individuals. Recent studies highlight an essential role for cells of the monocyte/macrophage lineage in the development of MetS and its consequences such as atherothrombosis. Cells of the monocyte/macrophages lineage exhibit remarkable plasticity that allows them to modulate their phenotype and efficiently respond to environmental signals and change their phenotype. For purposes of simplicity, a model system that classifies inflammatory macrophages as M1 and anti-inflammatory macrophages as M2 macrophages has been developed. The balance of these two subsets is thought to critically influence the physiologic and pathologic inflammatory response yet the molecular determinants of their speciation and function remain poorly understood. Kruppel-like factors (KLFs) are zinc-finger transcription factors implicated in a wide spectrum of biological processes including hematopoietic biology. Although previous studies by our group and others implicated KLF4 in myeloid cell biology, the in vivo physiological relevance has not been elucidated. Based on our preliminary studies, KLF4 expression is identified with the M2 population and strongly reduced in M1 macrophages - observations that are recapitulated in human inflammatory paradigms in vivo. Gain and loss-of-function studies reveal that KLF4 promotes an M2 genetic program and inhibits M1 target genes. Mice bearing myeloid-specific deletion of KLF4 exhibit a characteristic M1 phenotype as evidenced by enhanced bactericidal activity. Further, in response to a high fat diet (HFD), these animals develop numerous features consistent with MetS including obesity, dyslipidemia, insulin resistance, and a pro-atherogenic/pro-thrombotic state. These observations provide the foundation for the central hypothesis that KLF4 is an upstream molecular switch governing macrophage subset specification and function. To better understand the precise role of KLF4 in macrophage polarization and function, three aims are proposed. In Aim 1, we will delineate the upstream mechanisms governing KLF4 expression in myeloid cells. In Aim 2, we will determine the molecular basis for KLF4's ability to regulate the M1/M2 phenotype. In Aim 3, studies will determine the effect of altered myeloid KLF4 expression on insulin resistance and atherothrombosis. Collectively, these studies will elucidate the molecular basis for KLF4-mediated polarization towards the M2 phenotype and the functional consequences of KLF4 sufficiency and deficiency on insulin resistance and atherothrombosis.