Regulation of Type 1 Inflammation in Diet-induced Obesity

肥胖与炎症有关，特别是脂肪组织(AT)，它与肥胖相关的疾病有关，包括胰岛素抵抗和2型糖尿病。AT炎症主要表现为“1型炎症(T1i)”增加，伴随着CD4T辅助1细胞(Th1)、CD8细胞毒性T效应记忆/效应细胞(“Tc1”)和M1样巨噬细胞的增加，但嗜酸性粒细胞、Th2和M2样巨噬细胞减少。然而，T1i，特别是Th1/Tc1在肥胖中的转录机制还没有完全确定。在我们的初步研究中，免疫细胞对T1i极化的关键转录因子STAT1被升高和磷酸化，这表明在高脂饮食(HFD，高饱和脂肪)小鼠的AT和AT T细胞中，早期和持续的激活。值得注意的是，去除小鼠T细胞(包括CD4T细胞和CD8T细胞)中的STAT1降低了ATTh1/Tc1，增加了嗜酸性粒细胞，并防止了高脂诱导的肥胖，增强了白色AT褐变，增加了能量消耗，改善了胰岛素抵抗。体外研究表明，Th1抑制脂肪细胞的褐变。因此，我们形成了我们的中心假设：在HFD诱导的肥胖中，AT T细胞极化为Th1/Tc1，抑制白色AT褐变，反向调节AT代谢功能，促进肥胖和胰岛素抵抗；机制上，STAT1在AT T细胞中上调并持续激活，并介导Th1/Tc1。去除或抑制T细胞中的STAT1可抑制AT Th1/Tc1极化，使嗜酸性粒细胞增多，但M1样巨噬细胞减少，导致AT褐变的“去抑制”和能量消耗增加，从而减少肥胖和改善胰岛素抵抗。提出了三个目标：目标1将研究在HFD诱导的肥胖中STAT1是如何在AT T细胞中调节的；目标2将研究T细胞STAT1如何在肥胖的AT炎症和代谢功能中起作用，包括STAT1在CD4和CD8 T细胞中的作用以及T细胞对脂肪细胞褐化和代谢的调节；目标3将确定抑制STAT1通路或诱导去除T细胞中的STAT1是否逆转肥胖患者的AT炎症和代谢功能障碍。将使用来自小鼠和人的T细胞的组织培养以及小鼠模型，包括细胞特异性组成性或诱导性STAT1消融的小鼠，使用JAK/STAT1信号的药物抑制剂治疗的小鼠，以及过继转移免疫细胞或嗜酸性粒细胞耗竭的小鼠。将使用流式细胞术、免疫染色、Luminex技术、纳米线系统、定量PCR、RNA-Seq、全身和组织特异性代谢功能分析以及其他必要的技术。我们的方法将确定一种新的机制，调节AT T细胞T1i在肥胖中的作用，并研究调控途径在肥胖相关的炎症和代谢功能中的作用，以及针对这一途径预防和治疗肥胖及相关的炎症和代谢疾病的可能性。

Obesity is associated with inflammation, particularly in adipose tissue (AT), which has been implicated in obesity-linked diseases including insulin resistance and type 2 diabetes. AT inflammation is evidenced mainly by increases in “type 1 inflammation (T1I),” with elevated CD4+ T helper 1 cells (Th1), CD8+ cytotoxic T effector memory/effector cells (“Tc1”), and M1-like macrophages, but decreases in eosinophils, Th2, and M2-like macrophages. However, the transcriptional mechanisms for T1I, Th1/Tc1 in particular, in obesity have not been fully defined. In our pilot study, STAT1, a key transcription factor for immune cell polarization to T1I, was elevated and phosphorylated, indicating activation, in AT and AT T cells early and persistently in mice on high-fat diet (HFD, high in saturated fat). Strikingly, ablation of STAT1 in T cells (which include CD4+ and CD8+ T cells) in mice (tSTAT1-ko) reduced AT Th1/Tc1, raised eosinophils, and protected against HFD-induced obesity, with enhanced white AT browning, increased energy expenditure, and improved insulin resistance. In vitro study showed that Th1 repress adipocyte browning. Thus, we formed our central hypotheses that in obesity induced by HFD, AT T cells polarize into Th1/Tc1, which repress white AT browning, adversely regulate AT metabolic functions, and accelerate adiposity and insulin resistance; mechanistically, STAT1 is upregulated and activated early and persistently in AT T cells and mediates Th1/Tc1. Ablation or inhibition of STAT1 in T cells suppresses AT Th1/Tc1 polarization, with increased eosinophils but reduced M1-like macrophages, leading to “derepression” of AT browning and enhanced energy expenditure, thereby reducing adiposity and improving insulin resistance. Three aims are proposed: aim 1 will examine how STAT1 is regulated in AT T cells in HFD-induced obesity; aim 2 will examine how T cell STAT1 contributes to AT inflammation and metabolic functions in obesity including the roles of STAT1 in CD4+ vs CD8+ T cells and T cell regulation of adipocyte browning and metabolism; aim 3 will determine whether inhibition of the STAT1 pathway or inducible ablation of STAT1 in T cells reverses AT inflammation and metabolic dysfunctions in established obesity. Tissue culture with T cells from mice and humans and mouse models including mice with cell-specific constitutive or inducible ablation of STAT1, mice treated with pharmacological inhibitors of Jak/STAT1 signaling, and mice with adoptive transfer of immune cells or eosinophil depletion will be used. Flow cytometry, immunostaining, Luminex technology, NanoString system, quantitative PCR, RNA-seq, whole-body and tissue-specific metabolic function assays, and other necessary techniques will be employed. Our approach will identify a novel mechanism that regulates AT T cell T1I in obesity and examine the role of the regulatory pathway in obesity-linked inflammation and metabolic functions and the potential of targeting this pathway to prevent and treat obesity and related inflammation and metabolic disease.