The Role of PPAR Gamma in Fat-Resident Regulatory T Cells and Glucose Homeostasis

描述(申请人提供)：胰岛素抵抗和2型糖尿病通常伴随着肥胖，并与肥胖有关，因为肥胖状态下发生的低级别慢性脂肪组织炎症。最近，适应性免疫系统的细胞被证明参与了脂肪组织炎症的调节。具体地说，调节性T细胞(Tregs)是具有免疫抑制功能的T淋巴细胞的一个亚群，在瘦小但不肥胖的小鼠的脂肪组织中丰富。这些脂肪滞留的Tregs(FTregs)可能在抑制炎症和防止内脏脂肪中的胰岛素抵抗方面起到作用。它们在小鼠内脏脂肪中的丰度与内脏脂肪中的炎症水平以及胰岛素抵抗呈负相关。最近的一项研究表明，与从小鼠的脾或淋巴结分离的Tregs相比，fTregs具有不同的基因表达特征。特别是，在fTregs中特异上调的基因之一是过氧化物酶体增殖物激活受体伽马(PPAR！)，它是脂肪形成和生物代谢的关键调节因子。此外，初步研究表明，当PPAR！在老鼠的Tregs中被专门删除，Tregs不再富含内脏脂肪。因此，假设fTregs的脂肪特异性适应依赖于PPAR的表达和转录活性！在这些牢房里。这一建议试图表征上游诱导PPAR！及其在fTregs中的下游转录靶标所涉及的关键分子机制。此外，对于作为PPAR！激动剂的一类重要的抗糖尿病药物--噻唑烷二酮(TZDS)的治疗作用机制，将使用我们实验室建立的小鼠模型来研究PPAR！“在fTregs中的必要性。首先，假设PPAR的独特表达！在fTregs中是由于内脏脂肪组织中独特的脂肪因子/细胞因子环境所致。PPAR涉及的上游信号通路！FTregs的诱导将通过体外功能丧失实验进行剖析。第二，假设一旦表达，PPAR！以一种独特的方式重塑fTregs的转录签名，并启用fTreg特有的功能，包括维持内脏脂肪中Treg的丰富，并潜在地保护胰岛素抵抗。因此，将使用芯片序列和微阵列表达技术来定位PPAR！在fTregs中使用cstrome并识别关键PPAR！可能介导fTreg功能的下游靶点。第三，假设PPAR的表达！在fTregs中是TZDS在代谢应激下充分发挥其治疗和胰岛素敏化潜力的关键。带有Treg特异性PPAR的小鼠！将产生缺失，并喂饲含或不含TZD的高脂饮食。TZD的防护能力 这些小鼠的胰岛素抵抗和代谢综合征的进展情况将与野生型小鼠进行比较。综上所述，这些研究将系统地描述PPAR的作用！并阐明了fTregs在肥胖相关2型糖尿病发病机制中的作用。 公共卫生相关性：肥胖相关的2型糖尿病是一种日益严重的全球流行病，临床干预措施不足以预防由2型糖尿病常见的衰弱后遗症引起的过早发病率和死亡率，这些后遗症包括视网膜病变、神经病变、血管疾病、心脏病和肾脏疾病。我们的研究试图在分子水平上表征一种新发现的细胞群体，即脂肪驻留调节 T细胞，这可能在抵抗胰岛素抵抗和2型糖尿病方面起到保护作用。这项研究可能为肥胖相关的2型糖尿病患者提供一种新的基于细胞的治疗方法奠定基础。

DESCRIPTION (provided by applicant): Insulin resistance and type-2 diabetes often accompany obesity and have been linked to obesity by the low- grade chronic inflammation of adipose tissue that occurs in the obese state. Recently, cells of the adaptive immune system have been shown to be involved in the regulation of adipose tissue inflammation. Specifically, regulatory T cells (Tregs), a subset of T lymphocytes with an immunosuppressive function, are enriched in adipose tissue of lean, but not obese, mice. These fat-resident Tregs (fTregs) may have a role in suppressing inflammation and preventing insulin resistance in the visceral fat. Their abundance in the visceral fat of mice inversely correlates with the level of inflammation in the visceral fat as well as insulin resistance. A recent study showed that fTregs have a different gene expression signature compared to Tregs isolated from the spleen or lymph nodes in mice. In particular, one of the genes specifically upregulated in fTregs is peroxisome proliferator-activated receptor gamma (PPAR!), a key regulator of adipogenesis and organismal metabolism. In addition, preliminary studies have shown that when PPAR! is specifically deleted in Tregs in mice, Tregs are no longer enriched in the visceral fat. It is thus hypothesized that th fat-specific adaptation of fTregs is dependent upon the expression and transcriptional activity of PPAR! in these cells. This proposal seeks to characterize the key molecular mechanisms involved in the upstream induction of PPAR!"and its downstream transcriptional targets in fTregs. Furthermore, the necessity of PPAR!"in fTregs for the therapeutic mechanism of action of thiazolidinediones (TZDs), an important anti-diabetic class of drugs that are PPAR!"agonists, will be investigated using a mouse model generated in our lab. First, it is hypothesized that the unique expression of PPAR! in fTregs is due to a distinct adipokine/cytokine milieu within visceral adipose tissue. The upstream signaling pathways involved in PPAR! induction in fTregs will be dissected using in vitro loss-of-function experiments. Second, it is hypothesized that, once expressed, PPAR! acts in a unique way to reshape the transcriptional signature of fTregs and to enable fTreg-specific function, including maintenance of Treg enrichment in visceral fat and potentially protection against insulin resistance. Thus, ChIP-Seq and microarray expression technologies will be used to map the PPAR! cistrome in fTregs and identify key PPAR! downstream targets that could potentially mediate fTreg function. Third, it is hypothesized that expression of PPAR! in fTregs is critical for TZDs to exert their full therapeutic, insulin-sensitizing potential in mice under metabolic stress. Mice with a Treg-specific PPAR! deletion will be generated and fed high fat diet with or without TZD. The ability of TZDs to protect against progression of insulin resistance and metabolic syndrome in these mice will be compared to their wild-type counterparts. Taken together, these studies will systematically characterize the role of PPAR! in fTregs and illuminate the role of fTregs in the pathogenesis of obesity-related type-2 diabetes. PUBLIC HEALTH RELEVANCE: Obesity-related type-2 diabetes is a growing global epidemic with clinical interventions that are insufficient to prevent premature morbidity and mortality arising from the common debilitating sequelae of type-2 diabetes including retinopathy, neuropathy, vascular disease, heart disease, and kidney disease. Our research seeks to characterize, on a molecular level, a newly discovered population of cells, fat-resident regulatory T cells, that could possibly play a role in protection against insulin resistance and type-2 diabetes. This research could lay the groundwork for a novel cell-based therapy for patients suffering from obesity-related type-2 diabetes.