Effect of Dicer-mediated let-7 expression in inflammatory macrophages on atherosclerosis

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Atherosclerosis is a main cause of myocardial infarction and stroke and thus contributes crucially to worldwide mortality. At a cellular level, different types of immune cells, mainly macrophages, accumulate in the arterial wall, where they take up lipoproteins and develop into foam cells. However, macrophages can also polarize into a pro- and anti-inflammatory phenotype, which play key roles in innate immunity. The RNase Dicer produces microRNAs that regulate macrophage polarization. We found that Dicer regulates mitochondrial function in anti-inflammatory macrophages and foam cells by producing miR-10a and let-7, thus reducing atherosclerosis. Moreover, our preliminary results show that Dicer regulates gene expression in inflammatory macrophages, which promotes the removal of dead cells (efferocytosis) and reduces cell death (apoptosis). This proposal aims to study the role of Dicer in inflammatory macrophages in atherosclerosis. We hypothesize that Dicer's production of let-7 miRNAs in inflammatory macrophages reduces atherosclerosis by regulating efferocytosis and apoptosis through mitochondrial proteins and receptors for efferocytosis. This hypothesis will be addressed by three working packages using genetically modified mouse models of atherosclerosis. In the first and second parts, we will investigate the effect of Dicer and let-7 in inflammatory macrophages on efferocytosis using a novel efferocytosis assay. Moreover, we will perform 4D live plaque imaging using confocal microscopy to evaluate the effect of Dicer and let-7 in macrophages on efferocytosis. In addition, we will study how Dicer and let-7 affect mitochondrial dynamics in inflammatory macrophages. In the second part of the proposal, we will also study how let-7 mediates the function of Dicer in inflammatory macrophages by determining functionally relevant binding sites in the Dicer-regulated genes. We will use target site blockers to specifically inhibit the interaction between let-7 and individual potential targets. Thus, we will analyze in the third part the effect of these interactions on efferocytosis, apoptosis, mitochondrial dynamics, and atherosclerosis. The results of this project aim to gain novel insights into the role of inflammatory macrophages in atherosclerosis. Losing miRNAs like let-7 may impair their function and thus promote plaque formation.