The Role of B Cells and B Cell Toll-like Receptors in Glucose Intolerance

描述(申请人提供)：2型糖尿病(T2D)与慢性炎症有关，慢性炎症主要源于免疫系统细胞。这些细胞被T2D患者体内环境长期激活，包括血浆游离脂肪酸(FFAs)和内毒素水平升高。FFA和内毒素都是Toll样受体(TLRs)的配体，两者通常在TLR结合时激活促炎细胞因子的产生。这些细胞因子可能在以T2D和其他代谢综合征为特征的慢性全身性炎症中发挥重要作用。多项研究表明，通过阻断TLR功能来控制肥胖小鼠的炎症可以降低胰岛素抵抗的发生率，这是T2D的一个特征。虽然许多细胞类型是炎性细胞因子的来源，但免疫细胞细胞因子是胰岛素抵抗所必需的。综上所述，这些分析表明，TLR激活的免疫系统细胞炎症是促进T2D和其他代谢性疾病的关键过程。虽然单核细胞通常被认为是产生致炎细胞因子的最重要的免疫细胞类型，但B细胞也能产生大量的细胞因子。我们对T2D患者B细胞的新数据表明，B细胞TLR2和TLR4的激活通常会导致促炎细胞因子的产生。然而，TLR4配体减少了TLR2介导的肿瘤坏死因子-1的产生。这种抗炎作用可能被T2D患者的B细胞完全不能分泌IL-10所平衡，IL-10是一种关键的抗炎细胞因子。在T2D患者中发现TLR4阳性的B细胞百分比升高，以及这些B细胞对TLR配体的混合性炎症反应，导致假设B细胞和B细胞TLRs通过调节炎症从而调节胰岛素抵抗和糖耐量而在T2D中发挥重要作用。由于T2D患者的全身内毒素血症和游离脂肪酸升高提供了无数的TLR配体，我们的初步数据预测B细胞TLRs在体内通过细胞因子调节影响T2D。尽管对人类B细胞TLR功能的更多研究可能具有重要的机制和临床意义，但这一系列研究的下一个关键步骤是明确证明B细胞和B细胞TLRs在T2D炎症和发病机制中发挥作用。这些研究将在饮食诱导肥胖的T2D小鼠模型中进行，该模型利用现有的基因改变小鼠。该项目将测试1.缺乏B细胞；2.TLR仅对B细胞起作用；3.B细胞特异性TLR失活对体内高脂肪饮食的炎症和代谢结果的影响。这些研究将确定B细胞在代谢失衡中的作用，并预测使用已批准的B细胞消融疗法作为代谢综合征和T2D的新治疗方法的可能疗效。 与公共卫生相关：2型糖尿病(T2D)正以世界范围内的流行率增加，这种疾病的治疗手段有限。炎症在T2D的病因和并发症中起重要作用。由免疫细胞细胞因子产生的炎症在胰岛素抵抗中起着被证明的作用，这是T2D的关键特征之一。髓系细胞因子在T2D中的作用相对较好。我们在T2D患者中的新研究表明，B细胞可能是T2D中细胞因子的另一个主要来源。然而，从本质上讲，我们的人类受试者研究不能明确地将B细胞与疾病的发病机制联系起来。该项目建议使用模型生物来测试B细胞及其表面受体在T2D中的作用。重要的是，这项工作将确定现有的B细胞消融疗法是否可以用作T2D的根本性新疗法。

DESCRIPTION (provided by applicant): Type 2 diabetes (T2D) is associated with chronic inflammation that predominantly originates from immune system cells. These cells are chronically activated by the in vivo milieu of T2D patients, which includes elevated plasma levels of free fatty acids (FFAs) and endotoxin. Both of FFAs and endotoxin are ligands for toll-like receptors (TLRs), and both generally activate pro-inflammatory cytokine production upon TLR engagement. These cytokines likely play important roles in the chronic systemic inflammation characterizing T2D and other metabolic syndromes. Multiple studies show that controlling inflammation in obese mice by blocking TLR function decreases the incidence of insulin resistance, a hallmark of T2D. Although many cell types are sources of inflammatory cytokines, immune cell cytokines are required for insulin resistance. Taken together, these analyses indicate that TLR-activated inflammation from immune system cells is a key process that promotes T2D and other metabolic diseases. Although monocytes are generally considered the most important immune cell type for pro-inflammatory cytokine production, B cells also produce significant levels of cytokines. Our new data on B cells from T2D patients demonstrate that B cell TLR2 and TLR4 activation generally results in production of pro-inflammatory cytokines. However, TLR4 ligand decreases TLR2- mediated production of TNF-1. This anti-inflammatory effect may be balanced by the complete inability of B cells from T2D patients to secrete IL-10, a critical anti-inflammatory cytokine. The discoveries of an elevated percentage of TLR4-positive B cells in T2D patients and the mixed inflammatory responses of these B cells to TLR ligands lead to the hypothesis that B cells and B cell TLRs play important roles in T2D by regulating inflammation thus insulin resistance and glucose tolerance. Because the general endotoxemia and elevated free fatty acids in T2D patients provide innumerable TLR ligands, our preliminary data predict that B cell TLRs influence T2D through cytokine regulation in vivo. Although additional studies on human B cell TLR function are likely to be mechanistically and clinically important, the next critical step in this line of investigation is to unequivocally demonstrate B cells and B cell TLRs play roles in T2D inflammation and pathogenesis. These studies will be undertaken in a diet-induced obesity mouse model of T2D that takes advantage of available genetically altered mice. This project will test the effects of 1. the absence of B cells; 2. TLR function only on B cells; and 3. B cell-specific TLR inactivation on inflammatory and metabolic outcomes of high fat diet in vivo. These studies will define the role of B cells in metabolic imbalance, and predict the likely efficacy of using approved B cell ablation therapies as new treatments for metabolic syndrome and T2D. PUBLIC HEALTH RELEVANCE: Type 2 diabetes (T2D) is increasing at epidemic rates world-wide, and the treatment arsenal for this disease is limited. Inflammation plays an important role in the etiology and complications of T2D. Inflammation stemming from immune cell cytokine production plays a demonstrated role in insulin resistance, one of the key features of T2D. The role of myeloid cell cytokines in T2D is relatively well understood. Our new work in T2D patients demonstrates that B cells may be another major source of cytokines in T2D. However, our human subjects research, by its nature, cannot definitively link B cells to disease pathogenesis. The project proposes to test the role of B cells and their surface receptors in T2D using model organisms. Importantly, this work will determine whether existing B cell ablation therapies can be used as fundamentally new treatments for T2D.