Myeloid-specific Triacylglycerol Storage in Inflammation and Metabolic Disease

描述（由申请人提供）：巨噬细胞和树突状细胞（骨髓细胞；MC）充当免疫哨兵，在组织中巡逻以识别和消除外来入侵者。不幸的是，这些细胞也可以通过炎症激活对慢性饮食诱导的肥胖 (DIO) 做出反应，在胰岛素反应性组织中积累，形成与 2 型糖尿病的发展有关的“无菌”炎症级联反应。新出现的数据支持这样的概念，即这种反应是由脂肪或肝细胞释放的脂质引发的，这些脂质是脂肪细胞或肝细胞释放的脂质。 被常驻 MC 吸收，调节其功能以激发组织中的炎症序列。我的 NIDDK 赞助的临床医生科学家职业发展奖 (K08) 探讨了 MC 如何对抗促炎脂质，特别是饱和脂肪酸 (FA) 的重要生物医学问题。我假设 MC 可以通过将细胞内 FA 储存为三酰甘油 (TG) 来减少细胞内 FA 上升带来的毒性，防止它们流入破坏性的细胞区室和通路。我利用遗传学来操纵小鼠 MC 中的 TG 储存能力，以调节 FA 诱导的组织炎症并改善代谢疾病。我发现，酰基 CoA：二酰基甘油酰基转移酶 1 (DGAT1)（一种参与 TG 合成的酶 (aP2-Dgat1)）表达增加的 MC 具有增加的 TG 储存能力和对 FA 诱导的炎症的抵抗力 (4)。值得注意的是，移植 aP2-Dgat1 骨髓的小鼠的饮食引起的炎症和脂肪组织中的 MC 浸润较少，并且免受饮食引起的胰岛素抵抗 (4)。该提案旨在扩大我当前的 K08 对描述 MC 在 DIO 进展为糖尿病中的作用的影响，并通过两种方式实现：A. 到目前为止，我们的工作重点是 DGAT1。然而，DGAT1 是两种已知的哺乳动物 DGAT 酶之一（另一种是 DGAT2），它们的联合作用基本上解释了大多数细胞类型中形成的所有 TG。因此，确定 TG 储存本身限制 MC 中饱和 FA 毒性作用的程度需要针对两种 DGAT 酶的工具，以便研究 TG 储存能力已被完全废除的 MC。我们建议将不能储存TG的转基因造血祖细胞移植到受辐射的小鼠体内，产生MC完全缺乏TG储存能力的小鼠。我们将测试这些小鼠对长期高脂肪饮食的反应。 B. 到目前为止，我们一直关注白色脂肪组织中控制炎症和胰岛素抵抗的过程。然而，MC 与其他几种对糖尿病发展很重要的组织中的实质细胞共存，我们希望探索 MC TG 储存如何在这些情况下调节炎症。我们建议通过确定 MC 特异性 TG 储存在脂肪肝疾病进展为肝脏炎症和胰岛素抵抗中的作用，在肝脏中实现这一目标。

DESCRIPTION (provided by applicant): Macrophages and dendritic cells (myeloid cells; MCs) function as immunologic sentinels, patrolling tissues to recognize and eliminate foreign invaders. Unfortunately, these cells can also respond to chronic diet-induced obesity (DIO) with inflammatory activation, accumulating in insulin-responsive tissues in a "sterile" inflammatory cascade implicated in the development of diabetes type 2. Emerging data support the concept that this response is instigated by lipids released from, for example, fat or liver cells, that are taken up by resident MCs, modulating their function to incite an inflammatory sequence in the tissue. My NIDDK-sponsored Clinician-Scientist Career Development Award (K08) explores the important biomedical question of how MCs contend with pro-inflammatory lipids, in particular saturated fatty acids (FAs). I have hypothesized that MCs can reduce toxicity from a rising tide of intracellular FAs by storing them as triacylglycerol (TG), preventing their flux into damaging cellular compartments and pathways. I have used genetics to manipulate TG storage capacity in murine MCs in order to modulate FA-induced inflammation in tissues and ameliorate metabolic diseases. I showed that MCs with increased expression of acyl CoA: diacylglycerol acyltransferase 1 (DGAT1), an enzyme involved in TG synthesis (aP2-Dgat1), have increased TG storage capacity and resistance to FA-induced inflammation (4). Remarkably, mice transplanted with aP2-Dgat1 bone marrow have less diet-induced inflammation and MC infiltration in fat tissue, and are protected from diet-induced insulin resistance (4). This proposl seeks to extend the impact of my current K08 on delineating the role of MCs in the progression of DIO to diabetes, and does so in two ways: A. Until now, our work has focused on DGAT1. However, DGAT1 is one of two known mammalian DGAT enzymes (DGAT2 is the other), and their combined action accounts for essentially all the TG formed in most cell types. Therefore, determining the degree to which TG storage per se limits the toxic effects of saturated FAs in MCs requires tools that target both DGAT enzymes, allowing the study of MCs in which TG storage capacity has been abolished altogether. We propose to transplant genetically modified hematopoietic progenitors that cannot store TG into irradiated mice, producing mice with MCs lacking TG storage capacity altogether. We will test the response of these mice to a chronically high-fat diet. B. Until now, we have focused on processes governing inflammation and insulin resistance in white adipose tissue. However, MCs coexist with parenchymal cells in several other tissues important to the development of diabetes, and we would like to explore how MC TG storage modulates inflammation in each of these contexts. We propose here to do so in the liver, by determining the role of MC-specific TG storage in the progression of fatty liver disease to liver inflammation and insulin resistance.