Abstract 583: Targeting of Macrophage Netrin-1 Expression Promotes Plaque Regression and Resolution of Chronic Inflammation in Atherosclerosis

Chronic inflammation in atherosclerosis is driven by the accumulation of cholesterol-laden macrophages in the arterial wall. These pro-inflammatory macrophages persist in this site, and sustain local and systemic inflammation. Recently, we reported that the neuronal guidance protein netrin-1 plays a pivotal role in the retention of macrophages in plaques and the progression of atherosclerosis. To test whether targeting netrin-1 in established atherosclerotic plaques could promote the resolution of chronic inflammation in atherosclerosis and/or induce plaque regression, we developed mice in which macrophage netrin-1 expression could be inducibly deleted by tamoxifen administration (Ntn1 fl/fl CX3CR1 CreER2+ mice). We first induced atherosclerosis in Ntn1 fl/fl CX3CR1 CreER2+ and control Ntn1 fl/fl CX3CR1 CreER2- using a recombinant AAV-vector overexpressing PSCK9 and Western diet feeding. After 20 weeks, 10 mice from each group were sacrificed for baseline plaque measurements, while the remaining mice were switched to chow diet to stop further progression of atherosclerosis and treated with tamoxifen (n=14/group). After 4 weeks, mice were sacrificed to assess the effects of macrophage-specific netrin-1 deletion on plaque size and composition. Analysis of peritoneal macrophages confirmed robust deletion of netrin-1 in tamoxifen treated Ntn1 fl/fl CX3CR1 CreER2+ but not control Ntn1 fl/fl CX3CR1 CreER2- mice. Macrophage-specific deletion of netrin-1 caused a 30% reduction in plaque burden in the aortic arch as measured by en face analysis, compared to control mice. While we observed no change in aortic macrophage content, macrophage-specific netrin-1 deletion was associated with a shift in effector T cell populations in the aorta: we observed a decrease in Th1 cells and an enrichment of Th2 and Treg cells in aortic plaques of Ntn1 fl/fl CX3CR1 CreER2+ compared to control Ntn1 fl/fl CX3CR1 CreER2- . Furthermore, deletion of macrophage netrin-1 expression was associated with a reduction of systemic IL-1β levels. Collectively, these data suggest that targeting macrophage expression of netrin-1 in established atherosclerosis fosters a local pro-resolving and atheroprotective T cell phenotype in plaques and reduces systemic inflammation.