Innate and Adaptive Immune Mechanisms in Arthritis

描述（由申请人提供）：类风湿关节炎由宿主免疫失调引起。自从我们最初克隆小鼠巨噬细胞迁移抑制因子（MIF）以来，我们一直专注于这种介质在类风湿关节炎发病机制中的作用。我们发现抗MIF在实验性关节炎中具有保护作用，我们报道了MIF能够克服糖皮质激素免疫抑制，诱导ERK1/2 MAP激酶的持续激活，并通过抑制激活诱导的细胞凋亡来促进炎症。我们发现了高表达的MIF等位基因及其与类风湿关节炎严重程度的关联，证实了MIF在人类疾病中的重要性；这些数据在最近的一项大型多中心研究中得到证实，并扩展到青少年特发性关节炎。在目前的资助期内，我们通过创建MIF完全缺失和细胞系特异性缺失的遗传模型（MIF- ko, MIF flox）来阐明MIF的功能，并且我们开发了一种“敲入”小鼠，编码突变的MIF，解决了关于该蛋白神秘的变异体酶活性的问题。我们还确定MIF信号转导需要两种蛋白质的复合物：CD74和CD44，前者结合MIF，后者通过激活Src家族酪氨酸激酶启动信号传导。在这个竞争性更新中，我们将重点关注最近阐明的MIF受体的功能。我们的具体目标是：1；定义MIF受体复合物（CD74/CD44）在适应性免疫反应中的作用我们的工作假设是通过MIF受体的信号传导维持活化T淋巴细胞的存活并调节适应性免疫反应。2. 确定MIF信号受体、CD44和CD44变异亚型在类风湿关节炎免疫病理中的功能重要性。CD44剪接变异体在T细胞中的表达与运输反应增强有关；在基质细胞中，随着侵袭性表型的增加。我们的工作假设是，MIF诱导CD44的选择性剪接，这调节了MIF依赖性反应，并有助于类风湿关节炎的免疫发病机制。3. 鉴定MIF结合受体（CD74）的高效小分子拮抗剂。结构-功能研究表明，MIF的n端区域与MIF受体的CD74组分结合。我们将评估合理设计与MIF n端区域结合的小分子，以抑制MIF与CD74的相互作用并改善实验诱导的关节炎。获得的信息将具有广泛的应用，因为它将提供MIF受体复合物（CD74/CD44）如何参与类风湿性关节炎免疫病理的机制见解。这些研究的转化影响在于，对MIF受体作用的更精确定义将加速小分子MIF抑制剂的开发。这些抑制剂可能在那些具有高表达MIF等位基因和表现出MIF依赖性炎症性疾病的患者中显示出最大的疗效。公共卫生相关性：宿主免疫反应在类风湿关节炎的发病机制中起关键作用。免疫细胞因子巨噬细胞迁移抑制因子（MIF）编码于一个功能多态性基因位点，并与类风湿关节炎的严重程度相关。本提案的目的是显示MIF细胞表面受体如何调节免疫反应，以及受体的不同结构形式如何促进免疫病理。我们还将测试一类新的合理设计的小分子，以阻止MIF与其受体的相互作用。如果成功，这一信息将导致加速开发用于治疗类风湿性关节炎的MIF抑制剂。

DESCRIPTION (provided by applicant): Rheumatoid arthritis results from a dysregulation in host immunity. Since our initial cloning of murine macrophage migration inhibitory factor (MIF), we have focused on the role of this mediator in the pathogenesis of rheumatoid arthritis. We showed that anti-MIF is protective in experimental arthritis and we reported on MIF's ability to override glucocorticoid immunosuppression, induce sustained activation of ERK1/2 MAP kinases, and promote inflammation by inhibiting activation-induced apoptosis. The importance of MIF in human disease was validated by our discovery of high-expression MIF alleles and their association with rheumatoid arthritis severity; these data were confirmed recently in a larger multi- center study and extended to juvenile idiopathic arthritis. In the currently funded period, we elucidated MIF function by creating genetic models for the complete and cell-lineage specific deletion of MIF (MIF-KO, mif flox), and we developed a "knock-in" mouse encoding a mutant MIF that resolved questions about the protein's enigmatic tautomerase activity. We also established that MIF signal transduction requires a complex of two proteins: CD74, which binds MIF, and CD44, which initiates signaling by activating Src family tyrosine kinases. In this competitive renewal, we will focus on the function of the recently elucidated MIF receptor. Our Specific Aims are: 1. Define the Role of the MIF Receptor Complex (CD74/CD44) in the Adaptive Immune Response. Our working hypothesis is that signaling through the MIF receptor sustains the survival of activated T lymphocytes and regulates the adaptive immune response. 2. Define the Functional Importance of the MIF Signaling Receptor, CD44, and of CD44 Variant Isoforms in the Immunopathology of Rheumatoid Arthritis. The expression of CD44 splice variants in T cells is associated with an enhanced trafficking response; and in stromal cells, with an increase in invasive phenotype. Our working hypothesis is that MIF induces the alternative splicing of CD44, which regulates MIF-dependent responses and contributes to the immunopathogenesis of rheumatoid arthritis. 3. Identify High-potency, Small Molecule Antagonists of the MIF Binding Receptor (CD74). Structure-function studies indicate that MIF's N-terminal region binds to the CD74 component of the MIF receptor. We will evaluate small molecules that were rationally designed to bind to the MIF N-terminal region for their ability to inhibit MIF interaction with CD74 and ameliorate experimentally-induced arthritis. The information to be gained will have broad application because it will provide mechanistic insight into how the MIF receptor complex (CD74/CD44) contributes to the immunopathology of rheumatoid arthritis. The translational impact of these studies is that a more precise definition of MIF-receptor action will accelerate the development of small molecule MIF inhibitors. Such inhibitors may show greatest efficacy in those patients with high-expression MIF alleles and who manifest an MIF-dependent form of inflammatory disease. PUBLIC HEALTH RELEVANCE: The host immune response plays a critical role in the pathogenesis of rheumatoid arthritis. The immune cytokine, macrophage migration inhibitory factor (MIF), is encoded in a functionally polymorphic genetic locus and is associated with the severity of rheumatoid arthritis. The goal of this proposal is to show how the MIF cell surface receptor regulates the immune response and how different structural forms of the receptor promote immunopathology. We also will test a new class of rationally designed small molecules for their ability to block MIF interaction with its receptor. If successful, this information will lead to the accelerated development of MIF inhibitors for the treatment of rheumatoid arthritis.