The Role of Transmethylation Reactions in Autoimmunity

描述(由申请者提供)：该项目侧重于确定转甲基化在与系统自身免疫相关的先天和获得性免疫反应中的作用。这是一个新的免疫学研究领域，基于我们和其他人最近的研究，表明抑制反甲基化会影响正常的免疫和自身免疫反应。我们假设，转甲基化对炎症和免疫反应至关重要，阻断这一翻译后过程可能会削弱全身自身免疫。为了支持这一点，我们在已发表的和初步的研究中明确地证明，抑制S-腺苷-L-同型半胱氨酸水解酶(SAHase)是参与转甲基化的主要酶，通过减少参与TCR信号转导的几个关键蛋白的磷酸化/激活而导致免疫抑制。值得注意的是，这种效应在CD4中被注意到，但在CD8T细胞中没有，并且与Vav1精氨酸甲基化减少相关。我们还发现，通过抑制转甲基化，不同TLR配体的刺激作用以及由此产生的炎性细胞因子显著减少。更重要的是，用可逆SAHase抑制剂治疗器官特异性自身免疫小鼠模型(EAE)和狼疮小鼠模型(MRL-Faslpr和BXSB)显著降低了疾病的发生率、严重程度和进展。在这里，我们建议进行机制研究，以进一步确定蛋白质甲基化影响正常和自身免疫反应的特异性和途径，具有以下三个特定目的：1)确定T细胞中存在哪些蛋白精氨酸甲基转移酶(PRMT)，确定在CD4T细胞中甲基化Vav1的特异性PRMT(S)，并确定特定PRMT在T细胞、B细胞和巨噬细胞功能中的作用；2)确定转甲基化抑制干扰TLR依赖和TLR非依赖性的由核酸及其复合体诱导的炎症介质的分子通路，被认为参与了狼疮的发病；以及3)描述在狼疮模型的疾病进展过程中由于转甲基化抑制而发生的细胞和功能变化。这些研究将显著提高我们对翻译后修饰如何影响正常和异常免疫反应的了解，并有可能确定治疗自身免疫性疾病的新靶点。 公共卫生相关性：翻译后修饰，如转甲基化，极大地扩展了蛋白质的功能谱系，并对免疫细胞功能产生关键影响。我们的初步研究表明，反甲基化是T细胞、B细胞和巨噬细胞充分激活所必需的，更重要的是，它对于器官特异性和系统性自身免疫性疾病的进展是必要的。在这一应用中，我们建议进一步确定转甲基化促进免疫细胞激活和狼疮样系统自身免疫的机制。这项工作有可能为这种疾病和其他自身免疫性疾病确定新的治疗靶点。

DESCRIPTION (provided by applicant): This project focuses on defining the role of transmethylation in the innate and adaptive immune responses relevant to systemic autoimmunity. This is a new area of immunological research that is based on recent studies by us and others showing that inhibition of transmethylation affects normal immune and autoimmune responses. We hypothesize that transmethylation is critical for inflammation and immune responses and that blockade of this post-translational process can curtail systemic autoimmunity. In support of this, we have specifically documented in published and preliminary studies that inhibition of S-adenosyl-L-homocysteine hydrolase (SAHase), a major enzyme involved in transmethylation, leads to immunosuppression by reducing phosphorylation/activation of several key proteins involved in TCR signaling. Strikingly, this effect was noted in CD4, but not CD8 T cells, and correlated with reduced arginine methylation of Vav1. We also documented that stimulation by diverse TLR ligands and the consequent production of inflammatory cytokines was significantly reduced by inhibition of transmethylation. More importantly, treatment of an organ-specific autoimmune mouse model (EAE) and lupus mouse models (MRL-Faslpr and BXSB) with a reversible SAHase inhibitor markedly reduced the incidence, severity, and progression of disease. Here, we propose to perform mechanistic studies to further define the specificity and pathways by which protein methylation affects normal and autoimmune responses with the following three specific aims: 1) determine what PRMT (protein arginine methyltransferase) members are present in T cells, identify the specific PRMT(s) that methylates Vav1 in CD4 T cells, and determine the role of specific PRMTs in T cell, B cell, and macrophage function; 2) define the molecular pathways by which transmethylation inhibition interferes with TLR-dependent and TLR-independent induction of inflammatory mediators by nucleic acids and complexes thereof, thought to be involved in lupus pathogenesis; and 3) characterize the cellular and functional changes that occur due to transmethylation inhibition during disease progression in lupus models. These studies should significantly advance our knowledge of how post-translational modifications affect normal and abnormal immune responses, and have the potential for identifying novel targets for the treatment of autoimmune diseases. PUBLIC HEALTH RELEVANCE: Post-translational modifications such as transmethylation greatly expand the functional repertoire of proteins and have critical effects on immune cell function. Our preliminary studies indicate that transmethylation is required for the full activation of T cells, B cells and macrophages and, importantly, is necessary for the progression of both organ-specific and systemic autoimmune diseases. In this application, we propose to further define the mechanisms by which transmethylation promotes immune cell activation and lupus-like systemic autoimmunity. This work has the potential of identifying novel therapeutic targets for this and other autoimmune diseases.