Effect of Nutritional Factors on Macrophage Accumulation in Adipose Tissue

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Dietary factors play an important role in generating inflammatory signals that can lead to macrophage accumulation in adipose tissue. They do so by stimulating the expression in adipocytes of monocyte chemotactic factors, including monocyte chemoattractant protein-1 (MCP-1) and serum amyloid A3 (SAA3), the form of SAA produced by adipocytes. These nutritional factors include glucose excess, certain saturated fatty acids and dietary cholesterol (or oxysterols that result from cholesterol oxidation in foods). Conversely, fish oils appear to have the opposite effect and may protect against macrophage accumulation in visceral fat. In this grant we plan to test the overall hypothesis that nutritional factors that result in the generation of reactive oxygen species or other inflammatory stimuli will activate NF¿B-dependent chemotactic pathways in adipocytes, leading to the generation of chemotactic factors, macrophage accumulation, insulin resistance and systemic inflammation. To this end we propose three specific aims: (1) To evaluate mechanisms by which nutrients regulate the expression of monocyte chemotactic factors by adipocytes in vitro; (2) To investigate several potential mechanism that might account for these effects, including the roles of the toll-like receptor 4 (TLR4), n-3 polyunsaturated fatty acids, a protein called FLAP (which generates a powerful lipid chemotactic factor) and SAA3, on the accumulation of macrophages in visceral adipose tissue in vivo; and (3) To assess potential mechanisms by which dietary cholesterol and dietary oxysterols lead to macrophage accumulation in adipose tissue. Collectively these studies will provide critical information regarding the role of nutrients and nutrient excess in macrophage accumulation in adipose tissue, and will lead to therapeutic insights into how to reduce adipose tissue inflammation and its downstream consequences.