Abstract 205: Macrophage Rac1-IL-1β Signaling Axis Promotes Atherosclerotic Calcification

Abstract

Coronary artery disease caused by atherosclerosis is a major cause of morbidity and mortality worldwide. Calcification of atherosclerotic plaque is a marker of atherosclerotic burden and worsening cardiovascular outcomes. Inflammation plays a role in both atherosclerotic progression and calcification, but the mechanisms of calcification are not entirely well-defined. We sought to understand the role of macrophage Rac1 signaling in the natural progression of atherosclerotic calcification in the context of an experimental model of hyperlipidemia. We developed a tamoxifen-inducible, myeloid specific Rac1 -deletion model ( Csf1r mercremer Rac1 fl/fl ApoE -/- ) to evaluate the impact of macrophage-specific Rac1 on atherosclerotic calcification. After 20 weeks of ad libitum feeding on a cholesterol-supplemented high fat diet, Rac1 -deleted animals demonstrated significantly decreased atherosclerotic calcification compared to wild-type mice, irrespective of modest changes in lipid metabolism as demonstrated by plasma analysis. Mechanistically, Rac1 -deleted bone marrow derived macrophages demonstrated reduced expression of the potent inflammatory cytokine, IL-1β, in response to a cholesterol-based inflammasome activation. Rac1 -deleted macrophages also demonstrated decreased nuclear NF-κB activity and lost binding of NF-κB to its seed site in the IL-1β promoter as evaluated by chromatin immunoprecipitation. We further demonstrated that Rac1 and NF-κB form a complex with each other upon innate inflammatory signaling activation using a proximity ligation assay. We confirmed the important functional role of the Rac1 nuclear localization sequence in the expression of IL-1β, which together with the proximity ligation assay, suggests a role for Rac1 in chaperoning NF-κB to the IL-1β promoter. The interaction between macrophage Rac1 and NF-κB may have implications on numerous inflammatory disease processes, and uncovers a novel signaling contribution of Rac1 as a transcriptional co-factor for IL-1β in the progression of atherosclerosis. Targeted inhibition of Rac1 may have potential as a therapeutic treatment to mitigate progression of vascular calcification.