Turnover of Adipose Tissue Macrophages

描述(由申请人提供)： 巨噬细胞逐渐聚集到脂肪组织(AT)是饮食诱导肥胖的一个标志，被认为是AT和外周组织胰岛素抵抗发展的关键。由于AT巨噬细胞(ATM)聚集的重要性，该领域的大多数研究人员几乎都专注于调节AT巨噬细胞聚集的分子机制。然而，AT是体内最具可塑性的组织之一，具有在正负能量平衡期间急剧膨胀和收缩的能力。因此，自动取款机的积累很可能是一个动态事件，反映了自动取款机的招募、保留和移除之间的平衡。这导致人们认为，在AT扩张过程中巨噬细胞的加速积累实际上可能主要反映了ATM移除的缺陷，而不仅仅是反映了招募的增加。在这一应用中，令人振奋的新的初步数据表明，ATM细胞死亡可能是一个重要的生理机制，调节ATM周转，并有助于AT的动态平衡在减肥期间。首先，Western印迹分析表明，肥胖小鼠的AT巨噬细胞丰富的SVF中的凋亡标记物低于瘦小鼠。第二，免疫荧光染色显示肥胖者与瘦肉者相比，TUNELpos；F4/80pos(凋亡巨噬细胞)减少。瘦型ATM较高水平的细胞凋亡提示，ATM细胞死亡可能是瘦型AT的一种生理调节过程，在肥胖过程中受损。为了支持ATM周转受到调节这一概念，我们的数据显示，ATM细胞在减肥期间“恢复”。这些新的观察结果使我们考虑了这样一种可能性，即细胞凋亡对ATM的周转和清除是必要的，以维持健康的AT。因此，在这一应用中要检验的假设是：细胞凋亡有助于维持AT中巨噬细胞数量的动态平衡。这一假设隐含的是，在体重增加期间ATM周转率的下降与新巨噬细胞募集的增加同时发生，并可能有助于肥胖期间AT内巨噬细胞的滞留。这一假设令人震惊，因为它关注的是招募无关的机制，导致肥胖症患者ATM的增加。我们的研究将解决目前对免疫系统对体重增加和减轻过程中产生的代谢压力做出反应的机制的理解中的一个关键空白。我们的假设将在以下目标中得到验证：具体目标1：确定ATM细胞凋亡的时间和空间调节。我们假设ATM细胞凋亡在正能量平衡过程中受损，在负能量平衡过程中恢复。特定目的2：确定嗜酸性粒细胞是否调节ATM细胞的凋亡。我们假设，嗜酸性粒细胞调节ATM的凋亡和周转。具体目标3：确定ATM细胞凋亡受损的生理后果。我们假设，抑制巨噬细胞凋亡将导致ATM含量增加以及局部和全身性IR。

DESCRIPTION (provided by applicant): The progressive recruitment of macrophages to adipose tissue (AT) is a hallmark of diet-induced obesity and is thought to be key for the development of insulin resistance both in AT and peripheral tissues. Because of the importance of AT macrophage (ATM) accumulation most investigators in the field have focused almost exclusively on the molecular mechanisms mediating their recruitment. However, AT is one of the most plastic tissues in the body, with the capacity to expand and contract dramatically during positive and negative energy balance. It was therefore reasoned that ATM accumulation is likely to be a dynamic event reflecting a balance of ATM recruitment, retention, and removal. This led to the consideration that the accelerated accumulation of macrophages in AT during its expansion might in fact primarily reflect a defect in ATM removal rather than simply reflecting increased recruitment. In this application exciting new preliminary data is presented showing that ATM cell death may be an important physiological mechanism mediating ATM turnover and contributing to AT homeostasis during weight loss. First, Western blot analysis shows that apoptosis markers are lower in macrophage-enriched SVFs of AT from obese compared to lean mice. Second, immunofluorescence staining demonstrates decreased TUNELpos;F4/80pos (apoptotic macrophages) in obese compared to lean AT. The higher levels of apoptosis in lean ATMs suggest that ATM cell death may be a physiologically regulated process in lean AT that becomes impaired during obesity. In support of the concept that ATM turnover is regulated, our data demonstrate that ATM apoptosis is "restored" during weight loss. These novel observations have led us to consider the possibility that apoptosis is essential to ATM turnover and removal to maintain healthy AT. Thus, the hypothesis to be tested in this application is: apoptosis contributes to the homeostatic maintenance of macrophage numbers in AT. Implicit within this hypothesis is that a decrease in ATM turnover during weight gain occurs in parallel with increased recruitment of new macrophages and may contribute to the retention of macrophages within AT during obesity. This hypothesis is striking in that it focuses on recruitment-independent mechanisms for ATM accrual in obesity. Our studies will address a critical void in the current understanding of mechanisms by which the immune system responds to the metabolic stresses incurred during weight gain and loss. Our hypothesis will be tested in the following aims: Specific Aim 1: To determine the temporal and spatial regulation of ATM apoptosis. We hypothesize that ATM apoptosis is impaired during positive energy balance and restored during negative energy balance. Specific Aim 2: To determine whether eosinophils regulate ATM apoptosis. We hypothesize that eosinophils regulate the apoptosis and turnover of ATMs. Specific Aim 3: To determine the physiological consequences of impaired ATM apoptosis. We hypothesize that inhibition of macrophage apoptosis will result in increased ATM content as well as local and systemic IR.