Abstract 571: Atherogenic Macrophages Transfer microRNA-containing Exosomes to Naïve Cells and Promote Macrophage Migration

Abstract

Atherosclerosis, a maladaptive inflammatory disease, is driven by the interplay between excess cholesterol accumulation in the vessel wall and the immune system. Macrophages are fundamental to the propagation of atherosclerosis due to their capacity to engulf modified lipoproteins and induce a pro-inflammatory state. Macrophages and other immune cells can secrete miRNAs in exosomes as a form of extracellular communication during inflammation and infection. miRNAs are small noncoding RNAs that post-transcriptionally regulate gene expression by degradation or translational inhibition of target mRNAs and can repress gene expression in recipient cells when transferred via exosomes or other vesicles. Here, we hypothesize that atherogenic macrophages secrete miRNAs in exosomes to mediate cell-cell communication, which regulates the atherogenic response. Results: We examined the miRNA expression profile of exosomes from control and cholesterol-loaded (oxLDL-treated) mouse macrophages. Among the 88 differentially expressed miRNAs, 68 were down-regulated whereas 20 were up-regulated in exosomes isolated from cholesterol-loaded macrophages relative to control. The enrichment of several miRNAs such as miR-146a, miR-128, miR-185 and miR-503 in exosomes from atherogenic macrophages was confirmed by qPCR. Bioinformatic pathway analysis suggests that atherogenic exosomal miRNAs regulate cell migration and adhesion pathways via targeting the 3’UTR of migration/adhesion genes (i.e. integrin α3, VE-cadherin, CXCR4). Interestingly, live cell imaging demonstrated that fluorescent-labeled exosomes secreted from control or oxLDL-loaded macrophages were internalized by naïve macrophages and exogenous miRNA (from C.elegans) can transfer from normal/atherogenic macrophage exosomes to naïve cells. Further, naïve macrophages treated with extracellular components from atherogenic but not control macrophages promoted the migration of naïve cells towards a chemokine stimulus (1.5-fold increase in migration relative to control). Thus, miRNAs secreted from atherogenic macrophages may promote atherosclerosis by regulating macrophage migration in the vessel wall and we are now testing the function of these exo-miRNAs in vitro and in vivo.