Abstract 102: MicroRNA-33 Inhibition Reprograms Monocyte/macrophage Dynamics in Atherosclerosis to Promote Plaque Regression

Abstract

The inhibition of microRNA (miR)-33 promotes regression of atherosclerosis by increasing plasma HDL and reverse cholesterol transport levels, and reducing plaque inflammation. We sought to understand how anti-miR-33 treatment impacts monocyte and macrophage dynamics in the plaque to promote inflammation resolution. Ldlr -/- mice were fed a western diet for 14 weeks to establish plaques, after which mice were switched to chow diet to halt atherosclerosis progression and treated with anti-miR-33 or control anti-miR oligonucleotides for 4 weeks. As we reported previously, anti-miR-33 treatment increased plasma levels of HDL cholesterol by 30%, and concurrently reduced plaque size (-25%) and macrophage content (-30%), compared to control anti- miR treatment. Analysis of monocyte kinetic processes revealed that anti-miR-33 treatment normalized hypercholesterolemia associated monocytosis and reduced common myeloid progenitor (CMP) cells in the splenic reservoir. Interestingly, despite a 40% reduction in circulating monocytes, monocyte tracking assays revealed an increase in Ly6C hi monocyte recruitment into plaques of anti-miR-33 treated mice. These findings are consistent with our recent study showing that Ly6C hi monocytes are required for atherosclerosis regression and are a source of tissue reparative M2 macrophages. Indeed, we find that M2 macrophages, as well as atheroprotective regulatory T cells are enriched in plaques of anti-miR-33 treated mice. Finally, although the proliferation of macrophages in plaques did not change, we observed a 40% increase in the number of apoptotic cells in anti- miR33 treated mice, and an increase in macrophage efferocytosis (clearance of apoptotic cells) - markers that are consistent with resolution of inflammation. Collectively, our results provide insight into the mechanisms underlying anti-miR- 33’s atheroprotective actions, which now include reprogramming of monocyte/ macrophage dynamics to resolve inflammation in the plaque.