Immunometabolism in Cancer and Inflammation

肿瘤微环境代表了一个复杂的多细胞环境，其中各种细胞类型竞争其功能所需的资源。肿瘤细胞促进宿主血管的扩张，以维持其快速增殖所需的足够的营养水平。同时，肿瘤细胞抑制宿主防御机制来阻止排斥反应。肿瘤介导的免疫抑制的许多机制已经被描述，以及一些目标代谢途径。例如，高度糖酵解的肿瘤会消耗微环境中的葡萄糖，抑制T细胞的增殖和激活。由此产生的来自肿瘤的乳酸升高可以转录重编程肿瘤相关巨噬细胞，使其成为促进肿瘤生长和进展的免疫抑制细胞。考虑到这些类型的相互作用，我们认为肿瘤是一个独特的代谢环境，或生态位，在其中肿瘤细胞和免疫细胞竞争资源并适应彼此的存在。许多癌症的侵袭性反映了肿瘤在这个生态位中发挥主导作用的能力，抑制了试图促进肿瘤扩张、血管化和传播的免疫反应。该项目的重点是了解细胞代谢过程中刺激诱导的改变，以及它们在使免疫细胞满足与激活相关的增强代谢需求方面发挥的关键作用。因此，我们的工作包括对控制免疫细胞功能的代谢网络的精确解剖，以及对疾病代谢基础的研究。我们在这一领域的工作已经为我们揭示炎症细胞和肿瘤之间的实质性代谢相互作用提供了令人兴奋的可能性，并可能在治疗上加以利用。在该项目的一个方面，我们发现骨髓细胞上表达的触发受体(TREM)-1的可溶性版本是肾癌的生物标志物。我们的发现有助于TREM受体家族在包括癌症在内的多种炎症性疾病中发挥作用。我们的工作还定义了丙酮酸激酶肌-2 （PKM2）在自然杀伤细胞（NK）和CD4+ T细胞代谢控制中的典型作用。作为糖酵解的倒数第二酶，PKM将磷酸烯醇丙酮酸和ADP转化为ATP和丙酮酸，ATP和丙酮酸要么发酵成乳酸，要么输入线粒体氧化。我们的工作已经确定PKM2是NK细胞和T细胞功能的中心代谢调节因子。在NK细胞中，PKM2的缺失控制细胞ROS水平并抑制Myc信号传导，而在CD4+ T细胞中，PKM2控制丙酮酸氧化，其缺失导致大量氧化性细胞死亡。这些发现强调了PKM2作为丙酮酸利用调节因子的典型功能，并有助于将该代谢途径指定为NK和CD4+ T细胞功能的中心调节因子。我们早期对腹膜生态位的独特性及其在巨噬细胞功能中的作用的研究，以及我们对中性粒细胞在癌症中的代谢适应的定义，极大地完善了我们对代谢适应在特定生态位（如腹膜腔）中促进癌症进展的理解。我们在这个项目中的工作已经确定了腹腔癌症导致巨噬细胞中免疫应答基因1 （Irg1）的表达上调和衣康酸的积累。我们发现Irg-1促进肿瘤部分是通过提高脂质利用。我们发现来自晚期癌症患者腹水的髓系细胞表达Irg1，并确定Irg-1是一个有吸引力的治疗靶点，因为去除Irg-1的表达可显著降低小鼠腹膜肿瘤负荷。我们扩展了Irg-1在肿瘤中的作用，进一步分析了衣康酸在巨噬细胞生理和脂质代谢中的作用。我们发现，在高脂饮食（HFD）喂养期间，肝脏巨噬细胞产生衣康酸，诱导肝细胞对脂质利用的增加，从而更好地控制脂质肥胖。人类非酒精性脂肪性肝炎（NASH）患者的肝脏显示Irg-1表达增加，衣康酸水平升高。通过葡萄糖和胰岛素耐量的恶化，Irg1-/-小鼠喂养HFD加重了肝脏肥胖和更明显的代谢紊乱。从机制上讲，通过通量分析，衣康酸暴露增加了肝细胞的氧化磷酸化，13C标记显示棕榈酸酯的利用率更高。我们提出衣康酸活化衣康酰辅酶a抑制底物水平磷酸化，降低ATP水平导致脂质利用代偿性增加。我们正在进行的工作旨在扩展我们对itaconate生理学的研究，并利用肿瘤相关巨噬细胞发育模型来定义肿瘤中巨噬细胞功能的其他调节因子。除了对癌症的直接研究外，我们还确定了一氧化氮（NO）在巨噬细胞激活过程中代谢重编程中的作用。我们发现这些细胞的一些代谢特征完全是由于NO的产生。NO对这些细胞代谢适应的深远影响包括控制几个关键代谢物，包括衣康酸盐、柠檬酸盐、α -酮戊二酸盐和琥珀酸盐。我们之前已经发现，自体NO是必要的，足以驱动与“糖酵解承诺”相关的氧化磷酸化的下降。利用无偏倚代谢组学、表达分析、代谢通量分析、13C碳示踪实验和酶学，我们广泛地定义了NO在巨噬细胞代谢重编程中的作用。我们在这个项目上的工作证明了先天免疫细胞的强大能力，不仅可以调整它们的代谢组合，还可以通过改变代谢生态位的组成来潜在地发挥代谢作用。正在进行的工作将更深入地探索NO和衣康酸在各种生理系统中的代谢作用，深入研究TME的肿瘤免疫串扰，并确定衣康酸产生的新来源和生物学。总之，这些发现将白细胞代谢酶定义为真正的治疗靶点，并证明了在与癌症相关的独特生理利基背景下理解免疫代谢的重要性。

The tumor microenvironment represents a complex multicellular milieu where various cell types compete for the resources necessary for their function(s). Tumor cells promote the expansion of host vasculature to maintain sufficient levels of the nutrients required for their rapid proliferation. At the same time, tumor cells subjugate host defense mechanisms to thwart rejection. Many mechanisms of tumor-mediated immunosuppression have been described, and several target metabolic pathways. For example, highly glycolytic tumors deplete glucose in the microenvironment, suppressing T cell proliferation and activation. The resulting elevated lactate from the tumor can transcriptionally reprogram tumor-associated macrophages into immunosuppressive cells promoting tumor growth and progression. Taking these types of interactions into consideration, we view the tumor as a unique metabolic environment, or niche, within which the tumor cells and immune cells compete for resources and adapt to each other's presence. The aggressive nature of many cancers reflects the ability of tumors to exert a dominant role in this niche, subjugating the attempted immune response to facilitate tumor expansion, vascularization, and dissemination. This project is focused on understanding stimulation-induced alterations in cellular metabolic processes and the critical role that they play in enabling immune cells to meet the enhanced metabolic demands associated with activation. Thus, our work involves precise dissection of metabolic networks that govern immune cell function, as well as the investigation of the metabolic foundations of disease. Our work in this area has already provided us with exciting possibilities for unraveling, and possibly therapeutically exploiting, the substantial metabolic interactions between inflammatory cells and the tumor. In one aspect of this project, we found that a soluble version of Triggering Receptors Expressed on Myeloid cells (TREM)-1 is a biomarker in renal cancer. Our findings contribute to the role that the TREM family of receptors play in a variety of inflammatory diseases including cancer. Our work also defines the canonical role of pyruvate kinase muscle-2 (PKM2) in the metabolic control of Natural Killer (NK) cells and CD4+ T cells. As the penultimate enzyme of glycolysis, PKM converts phosphoenolpyruvate and ADP into ATP and pyruvate that is either fermented to lactate or imported into the mitochondria for oxidation. Our work has identified PKM2 as a central metabolic regulator of both NK and T cell function. In NK cells, the loss of PKM2 controlled cellular ROS levels and suppressed Myc signaling whereas in CD4+ T cells PKM2 controls pyruvate oxidation, and its absence leads to substantial oxidative cell death. These findings underscore the canonical function of PKM2 as a regulator of pyruvate utilization and contribute to the assignment of this metabolic pathway as a central regulator of NK and CD4+ T cell function. Our earlier work on the uniqueness of the peritoneal niche and its role in macrophage function, followed by our definition of neutrophil metabolic adaptations in cancer, have greatly refined our understanding on the metabolic adaptations that contribute to cancer progression in specific niches such as the peritoneal cavity. Our work in this project has identified cancers of the peritoneal cavity cause the upregulated expression of Immunoresponsive Gene-1 (Irg1) in resident macrophages and accumulation of itaconic acid. We found Irg-1 to promote tumors in part through an enhancement of lipid utilization. We found that myeloid cells from the ascites of advanced cancer patients expressed Irg1 and identify Irg-1 as an attractive therapeutic target, since abrogation of Irg-1 expression significantly reduced peritoneal tumor burden in mice. We have extended our work on Irg-1 in the tumor setting with additional dissection of the role of itaconate in macrophage physiology and lipid metabolism. We find that itaconate produced by macrophages in the liver during feeding with high fat diet (HFD), induces an increase in the lipid utilization of hepatocytes, resulting in better control of lipid adiposity. The livers of human non-alcoholic steatohepatitis (NASH) patients show increased expression of Irg-1 and have elevated levels of itaconate. Irg1-/- mice fed HFD have exacerbated liver adiposity and more pronounced metabolic disorder as revealed by worsened glucose and insulin tolerance. Mechanistically, itaconate exposure increases oxidative phosphorylation in hepatocytes by flux analysis, and 13C labeling shows greater amounts of palmitate utilization. We propose that itaconate activated to itaconyl-CoA suppresses substrate-level phosphorylation, reducing ATP levels leading to compensatory increases in lipid utilization. Our ongoing work seeks to extend our study of itaconate physiology and utilize models of tumor-associated macrophage development to define additional regulators of macrophage function in tumors. In addition to direct studies of cancer, we have defined the role of nitric oxide (NO) in the metabolic reprogramming that occurs during macrophage activation. We found that several of the metabolic characteristics of these cells are solely due to the production of NO. The profound effects of NO on the metabolic adaptations of these cells includes control of several key metabolites including itaconate, citrate, alpha-ketoglutarate, and succinate. We had previously found that autologous NO was necessary and sufficient to drive the decline in oxidative phosphorylation associated with "glycolytic commitment". Using unbiased metabolomics, expression analysis, metabolic flux analysis, 13C carbon tracing experiments, and enzymology, we have extensively defined the role of NO in this metabolic reprogramming of macrophages. Our work on this project demonstrates the powerful ability of innate immune cells to not only adapt their metabolic portfolios but to potentially exert metabolic effects in trans by altering the composition of the metabolic niche. Ongoing work more deeply explores the metabolic effects of NO and itaconate in a variety of physiological systems, delves into the tumor-immune crosstalk of the TME, and defines new sources and biology associated with the production of itaconate. Together, these findings define leukocyte metabolic enzymes as bona fide therapeutic targets and demonstrate the importance of understanding immunometabolism in the context of unique physiological niches relevant to cancer.