Role of monocyte/macrophage lectin receptors in obesity-induced inflammation

描述（由申请人提供）：脂肪组织巨噬细胞（ATM）是脂肪组织基质细胞群的关键组成部分。随着肥胖，ATM 的内脏脂肪数量增加，炎症活动也发生质的变化。瘦小鼠的 ATM 由 2 型 ATM 组成，具有低炎症能力，表达 IL-10（一种抗炎细胞因子）。由于饮食引起的肥胖，人群转向以 1 型 ATM 为主的人群，这是一种具有高炎症基因表达的独特 ATM 类型。这些 ATM 亚型之间的平衡非常重要，因为巨噬细胞介导的炎症已被证明是肥胖中胰岛素抵抗的发展所必需的。 PI K08 奖的目标是研究 1 型和 2 型 ATM 之间的平衡如何通过 IL-10 影响脂肪组织和新陈代谢。在这些研究中，我们开发了新技术，使我们能够区分和研究这两种 ATM 类型。颁奖期间的工作表明，1 型和 2 型 ATM 是通过循环单核细胞的不同招募途径产生的。在我们的研究中，我们发现 2 型驻留 ATM 表达 IL-10 和 MGL1（巨噬细胞半乳糖型 c 型凝集素 1），而 1 型 ATM 则不表达。在初步实验中，我们检查了 MGL1 缺陷小鼠，并得出了令人惊讶的发现，它们可以免受饮食引起的肥胖的葡萄糖不耐受和胰岛素抵抗的影响。这种保护作用与以下事实有关：MGL1 在血液中的炎症 7/4hi 单核细胞上表达，并且与对照组相比，肥胖 Mgl1-/- 小鼠中这些单核细胞减少。这些观察结果表明，MGL1 是一种新型受体，可调节炎症单核细胞的水平，类似于 CCR2 和 CX3CR1。该提案的目标是描述 MGL1 如何调节肥胖中的单核细胞功能，以及它如何影响 1 型和 2 型 ATM 之间的平衡。我们将通过解决两个主要目标来阐明 MGL1 在单核细胞中的功能：(1) 评估 MGL1 如何调节单核细胞稳定性和循环中的保留。我们将利用野生型和 Mgl1-/- 小鼠的单核细胞过继转移到瘦和肥胖受体中，以解决维持血液中炎症单核细胞需要 MGL1 的假设。单核细胞-内皮细胞粘附的体外模型将评估 MGL1 介导的细胞-细胞相互作用。 (2) 鉴定肥胖内脏脂肪组织中的MGL1配体。我们将采用亲和纯化方法，利用 MGL1 融合蛋白来鉴定脂肪组织中的 MGL1 配体。总体而言，该提案将扩展 PI K08 奖的新研究方向。 R03 的资金将支持 PI 建立研究项目的独立性。这些研究产生的数据将为更广泛的资助申请奠定基础。 公共卫生相关性：肥胖引起的炎症变化对胰岛素抵抗和糖尿病的发展具有重要影响。许多炎症变化与巨噬细胞和单核细胞的激活有关，这些炎症细胞有助于指导免疫反应。该提案旨在扩大我们对一种新分子的理解，该分子可指导这些肥胖单核细胞的激活。这项研究的结果可能会带来针对 2 型糖尿病的新疗法，旨在阻止肥胖引起的炎症。

DESCRIPTION (provided by applicant): Adipose tissue macrophages (ATMs) are a key component of the adipose tissue stromal cell population. With obesity, ATMs increase in number in visceral fat and also undergo qualitative changes in their inflammatory activity. ATMs in lean mice are comprised of Type 2 ATMs with low inflammatory capacity that express IL-10, an anti-inflammatory cytokine. With diet-induced obesity, the populations shifts to one where Type 1 ATMs predominates, a distinct ATM type with high inflammatory gene expression. The balance between these ATM subtypes is important since macrophage-mediated inflammation has been shown to be required for the develop insulin resistance in obesity. The goal of the PI's K08 award is to examine how the balance between Type 1 and Type 2 ATMs influences adipose tissue and metabolism via IL-10. During these studies, we developed novel techniques that allowed us to distinguish and study the two ATM types. Work during the award showed that Type 1 and Type 2 ATMs are generated by distinct recruitment pathways from circulating monocytes. In our studies, we discovered that Type 2 resident ATMs express both IL-10 and MGL1 (macrophage galactose-type c-type lectin 1) and Type 1 ATMs do not. In preliminary experiments, we examined MGL1 deficient mice and made the surprising finding that they are protected from glucose intolerance and insulin resistance with diet induced obesity. This protection is related to the fact that MGL1 is expressed on inflammatory 7/4hi monocytes in the blood and that these monocytes are decreased in obese Mgl1-/- mice compared to controls. These observations identify MGL1 as a novel receptor that regulates the levels of inflammatory monocytes similar to CCR2 and CX3CR1. The goal of this proposal is to delineate how MGL1 regulates monocyte function in obesity and how this influences the balance between Type 1 and Type 2 ATMs. We will elucidate how MGL1 functions in monocytes by addressing two primary aims: (1) To assess how MGL1 regulates monocyte stability and retention in the circulation. We will utilize adoptive transfer of monocytes from wild type and Mgl1-/- mice into lean and obese recipients to address the hypothesis that MGL1 is required for the maintenance of inflammatory monocytes in the blood. In vitro models of monocyte-endothelial cells adhesion will evaluate MGL1 mediated cell-cell interactions. (2) To identify MGL1 ligands in visceral adipose tissue in obesity. We will use affinity purification approaches to identify MGL1 ligands in adipose tissue using MGL1 fusion proteins. Overall, this proposal will expand upon a new research direction that has extended from the PI's K08 award. Funds from the R03 will support the independence of the PI as he builds his research program. Data generated from these studies will set the stage for a more expansive grant application. PUBLIC HEALTH RELEVANCE: Inflammatory changes in obesity have important consequences on the development of insulin resistance and diabetes. Many of these inflammatory changes relate to the activation of macrophages and monocytes, inflammatory cells that help direct immune responses. This proposal seeks to expand our understanding of a novel molecule that directs the activation of these monocytes with obesity. Results of this study could potentially lead to novel therapies for type 2 diabetes that are directed towards blocking obesity-induced inflammation.