Microbiota Regulation of Pro-atherogenic Phagocytes − Separating Metabolic and Inflammatory Mechanisms

A significant hallmark of the chronic inflammatory disease, atherosclerosis, is the accumulation of pro-inflammatory M1-like macrophages (macs) and dendritic cells (DCs) in coronary arteries that respond to pro-atherogenic stimuli and fail to digest lipids that contribute to the formation of foam cells in atherosclerotic plaques. Mechanisms that reduce Mac/DC inflammation, increase lipid degradation, and prevent foam cell formation are likely to decrease progression of atherosclerosis. Mechanisms that regulate autophagy in macs and DCs will likely reveal targets for the prevention of atherosclerosis. Mouse models of high-fat diets demonstrate a link between microbiota composition and the development of obesity, diabetes, and atherosclerosis through several mechanisms best demonstrated by the microbiota-dependent production of TMAO that promotes atherosclerosis. We have identified a tryptophan-derived microbiota metabolite, indole, that has novel immunomodulatory properties. This strong association between obesity, inflammation, and the microbiota has led us to the hypothesis that microbiota-derived metabolites in the GI tract might regulate dietary saturated fat-induced inflammation. To test this hypothesis, we generated bone marrow-derived macrophages (BMDMs) and dendritic cells (BMDCs) and tested the effects of indole on these cells in the context of saturated fatty acid-induced inflammation. We investigated pro-inflammatory cytokine production, M1 macrophage development, and metabolic flux. Here, we demonstrate that indole reduces saturated fatty acid-derived inflammation in BMDCs and BMDMs and regulates metabolic programming of phagocytes by inducing autophagy on a level similar to rapamycin.