Abstract 17984: Protective Role of Dicer in Macrophages During Atherogenesis

Abstract

Atherosclerotic lesion development is characterized by the subendothelial accumulation of lipid-laden macrophages. It is known that microRNAs (miRs) are generated by the RNase Dicer and play important roles in macrophage function by negatively regulating post-transcriptional gene expression. Previously, we found that macrophage-derived miR-342-5p enhances atherosclerosis by fostering inflammatory macrophage activation. However, the impact of Dicer-dependent miR expression in macrophages during atherosclerosis is unclear. To study the role of Dicer in macrophages in atherosclerosis, we fed Apoe-/- mice with a myeloid cell-specific deletion of Dicer (LysMCre-Dicerflox) and littermate controls (LysMCre-DicerWT) a high cholesterol diet (HCD) for 3 months. Dicer deletion in myeloid cells was confirmed in bone marrow-derived macrophages isolated from LysMCre-Dicerflox mice by real-time PCR. The lipid deposition in the aortas was increased by 50% in LysMCre-Dicerflox (3.3±0.3%) compared to LysMCre-Dicerwt mice (2.1±0.3%) (p = 0.01, n = 13). The differential blood counts and the serum cholesterol and triglyceride levels were not altered between two groups. We found that 79 miRs, including those highly expressed in macrophages (e.g., miR-146a and miR-223), were down-regulated in LysMCre-Dicerflox aortas compared to controls after 3 months of a HCD (p < 0.05, n = 3) using a miR real-time PCR array. In aortas from LysMCre-Dicerflox mice, 471 genes were up-regulated as determined by whole-genome gene expression profiling using Agilent Mouse Microarrays (p < 0.05, n = 3-4). Genes involved in fatty acid and lipid metabolism were enriched among the up-regulated genes as analyzed by GeneGo MetaCore. Up-regulation of Plg, Ptges2, Eci1, Impa2, Acox2, Thrsp, and the lipid droplet-related genes plin-1, -2, -5 and Cidea was confirmed by real-time PCR. Whereas Plg was predicted to be a target of miR-223 by Targetscan, plin-1, -2, and Ptges2 were identified as potential targets of miR-146a using miRanda. These data indicate a protective role of Dicer during atherogenesis by inhibiting lipid metabolism in lesional macrophages through miRs. Thus, regulation of the lipid metabolism in macrophages might be a critical step in the development of atherosclerosis.