Charles A. Dinarello - US grants

PROJECT SUMMARY Inflammation is an immune response protecting us from infection and injury. However, unchecked or improperly activated inflammation can result in chronic diseases such as arthritis, cardiovascular diseases and insulin resistance. Insulin resistance is a metabolic condition in which tissues no longer respond to insulin. A major function of insulin is to lower blood glucose levels by promoting glucose uptake into peripheral tissues including skeletal muscles and adipocytes. Insulin-stimulated glucose uptake is mediated by GLUT4, a facilitative glucose transporter enriched in insulin-responsive tissues. Under basal conditions, GLUT4 is sequestered in intracellular storage vesicles. Upon insulin stimulation, GLUT4 is relocated from intracellular vesicles to the cell surface where it facilitates the uptake of excess blood glucose into the cells for disposal. Defects in GLUT4 exocytosis disrupt blood glucose balance and are a hallmark of insulin resistance. Commonly associated with obesity, insulin resistance is a characteristic feature of type 2 diabetes (T2D). Laboratory and clinical studies have established that inflammation plays a central role in the pathogenesis of insulin resistance. In particular, the two proinflammatory cytokines interleukin 1? (IL-1?) and tumor necrosis factor alpha (TNF?) directly interfere with insulin responses in adipocytes, hepatocytes and skeletal muscles. While the connection of proinflammatory cytokines to insulin resistance is well established, the molecular mechanisms of cytokine-induced insulin resistance remains poorly understood. The major goal of this exploratory project is to help bridge this gap by globally identifying mediators of cytokine-induced insulin resistance, using insulin-dependent GLUT4 exocytosis as a model system. In this work, we will first determine whether and how GLUT4 trafficking regulators are impaired by IL-1? and TNF?. We will also perform new unbiased genome-wide genetic screens to identify suppressors of cytokine-induced impairment in GLUT4 exocytosis. These exploratory studies will pave the path for a full understanding of cytokine-associated insulin resistance and will likely identify novel therapeutic targets for treating insulin resistance and T2D. This work will also serve as a springboard to understanding other functions of proinflammatory cytokines in the immune system.

Project Summary/Abstract Interleukin-37 (IL-37), a member of the IL-1 family, has been a neglected cytokine mostly because there is no mouse homologue for IL-37. However, we expressed human IL-37 in mice, which revealed that IL-37 broadly suppresses innate inflammation and acquire immunity and that recombinant human IL-37 accomplishes the same in wild type mice. Similar to IL-1? and IL-33, IL-37 is a dual function cytokine in that IL-37 translocates to the nucleus but also binds its cell surface receptor complex. The present application focuses on the mechanism for these properties. The translocation of IL-37 to the nucleus depends on caspase-1 cleavage followed by the carboxyl domain binding to chromatin. To determine to what extent nuclear IL-37 contributes to suppression of innate and acquire immunity, we have generated a new strain of mice that lacks the ability for IL-37 to translocate to the nucleus by to mutating the caspase-1 recognition site on IL-37 without altering the activity of caspase-1 in the same cell. In order to establish an independent role for nuclear IL-37, the cell surface receptors for IL-37 (IL-18 Receptor ??chain) will be prevented using a blocking antibody in short-term models. In both short and long-term models, we will use mice deficient in IL-1R8, the IL-37 co-receptor. The second Aim of this proposal directly addresses the binding of IL-37 to the IL-18 Binding Protein (IL-18BP) and investigates whether administration of IL-18BP reduces the protection afforded by endogenous IL-37. We have generated a transgenic mouse expressing human IL-18BP to determine whether administration of recombinant human IL-37 is less effective in mice expressing human IL-18BP. Since recombinant human IL-37 possesses several properties to suppress innate and acquired immunity, the translational component of the proposal is the development of IL-37 as a therapeutic. As with several members of the IL-1 family, the N- and C-terminal for optimal biologic activity is unknown. We have produced a recombinant form of IL-37 fused to the Fc domain of human IgG1 (IL-37Fc fusion protein) and demonstrated its efficacy. We will now determine the N- and C-termini of IL-37 for an optimal form of recombinant IL-37 to limit of innate inflammation. Once this has been established, an improved IL-37Fc fusion protein will also be produced and tested in preclinical models. The overall goal of these studies is to advance the biology and clinical significance of IL-37 as well as to exploit its anti- inflammatory properties as a therapeutic.