Macrophages are important immune cells involved in the pathogenesis of many inflammatory diseases, including atherosclerosis and are one of the major immune cells in the atherosclerotic lesions. In addition to becoming foam cells upon uptake of modified lipoproteins in the vessel walls, macrophages also mediate the inflammatory responses that are associated with atherosclerotic plaque formation by producing cytokines, chemokines and growth factors. These agents further influence chemoattraction of more monocytes and other immune cells as well as profoundly affect the functions of smooth muscle cells and endothelial cells that are in the vicinity. Therefore, macrophages play an essential role in all stages of atherogenesis including fatty streaks to advanced plaques and eventually to plaque rupture. Thus, understanding the biochemical mechanisms by which macrophage biology (including inflammatory mediator production, and macrophage apoptosis/survival) is regulated is highly critical. Preliminary data demonstrates that macrophage biology is regulated by a serine/threonine kinase, namely, G-protein coupled receptor kinase-2 (GRK2). GRK2 was originally discovered for its role in the phosphorylation of -adrenergic receptor and other GPCRs. Recent studies indicate that there are other cytosolic targets of GRK2. However, the role of GRK2 in macrophages, particularly as it relates to non-GPCRs and cytosolic targets is not well known. Preliminary data demonstrates that tumor necrosis factor- (TNF)-induced NFB signaling, and the consequent inflammatory mediator expression and survival of macrophages are critically regulated by GRK2. Preliminary findings also suggest that GRK2 mediates its effects on NFB signaling via interaction with, and potentially phosphorylation of the inhibitor of NFB signaling namely IB. These results suggest a novel and significant role for this kinase in macrophage biology and therefore in the pathogenesis of atherosclerosis. The objective of this proposal is to further expand on our preliminary findings and examine the mechanisms by which GRK2 regulates macrophage biology and importantly, also test if, loss of GRK2 affects the pathophysiology of atherosclerosis. The overall hypothesis is that GRK2 interaction with and phosphorylation of IB regulates TNF-induced NFB signaling, inflammatory mediator production, and macrophage survival/apoptosis and therefore, plays a crucial role in the pathogenesis of atherosclerosis. To test this hypothesis we will examine the following specific aims: 1. Determine the mechanisms by which GRK-2 regulates TNF-induced NFB pathway in macrophages. 2. Examine the functional relevance of GRK2 in TNF signaling in macrophages. 3. Determine whether loss of GRK2 affects the pathogenesis of atherosclerosis in Apo-E knockout mice. Taken together, our studies should provide important insight into the mechanisms of TNF signaling in macrophages as well as identify potential therapeutic targets in the treatment of chronic inflammatory diseases.
TNF-alpha plays a major role in the development of chronic inflammatory diseases including atherosclerosis. Therefore, understanding the various mechanisms by which TNF-alpha signaling is regulated will help us identify new and novel therapeutic targets to treat atherosclerosis.
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