Turnover of Adipose Tissue Macrophages

描述（由申请人提供）： 巨噬细胞向脂肪组织（AT）的进行性募集是饮食诱导的肥胖的标志，并且被认为是AT和外周组织中胰岛素抵抗发展的关键。由于AT巨噬细胞（ATM）积累的重要性，该领域的大多数研究人员几乎只关注介导其募集的分子机制。然而，AT是身体中最具可塑性的组织之一，在正负能量平衡期间能够急剧膨胀和收缩。因此，有理由认为，ATM积累可能是一个动态事件，反映了ATM招募、保留和移除的平衡。这导致了这样的考虑，即在AT扩张期间，巨噬细胞在AT中的加速积累实际上可能主要反映了ATM去除的缺陷，而不是简单地反映了募集的增加。在这个应用程序中，令人兴奋的新的初步数据显示，ATM细胞死亡可能是一个重要的生理机制介导的ATM营业额，并有助于在减肥过程中的AT稳态。首先，蛋白质印迹分析显示，与瘦小鼠相比，肥胖小鼠AT的巨噬细胞富集的SVFs中的凋亡标记物较低。第二，免疫荧光染色显示与瘦AT相比，肥胖者中TUNEL阳性细胞F4/80阳性细胞（凋亡巨噬细胞）减少。在瘦型AT中较高水平的细胞凋亡表明，ATM细胞死亡可能是瘦型AT中的生理调节过程，其在肥胖期间受损。为了支持ATM营业额受到调节的概念，我们的数据表明，ATM细胞凋亡在减肥过程中被“恢复”。这些新的观察结果使我们考虑细胞凋亡对ATM周转和清除以维持健康AT至关重要的可能性。因此，在本申请中待测试的假设是：细胞凋亡有助于AT中巨噬细胞数量的稳态维持。这一假设中隐含的是，体重增加期间ATM周转率降低与新巨噬细胞募集增加平行发生，并可能有助于肥胖期间AT内巨噬细胞的保留。这一假设是惊人的，因为它集中在招募独立的机制，ATM积累肥胖。我们的研究将解决目前对免疫系统对体重增加和减轻期间发生的代谢应激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进行测试：具体目标1：确定ATM凋亡的时间和空间调节。我们推测ATM凋亡在正能量平衡时受损，在负能量平衡时恢复。具体目标2：确定嗜酸性粒细胞是否调节ATM凋亡。我们假设嗜酸性粒细胞调节ATM的凋亡和营业额。具体目标3：确定受损的ATM细胞凋亡的生理后果。我们推测抑制巨噬细胞凋亡将导致ATM含量增加以及局部和全身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.