TRAIL expressing monocyte/macrophages reduce inflammation and attenuate atherosclerosis

Circulating TRAIL is reduced in cardiovascular disease patients and TRAIL deletion in mice exacerbates disease. The source of TRAIL and protective mechanism(s) are unclear. Monocyte TRAIL mRNA was reduced from coronary artery disease patients, strikingly associating with reduced plasma TRAIL. A strong inverse correlation between plasma TRAIL and IL-18 was observed, with IL-18 repressing monocyte TRAIL mRNA. In mice, two sources were investigated using bone-marrow (BM) transplants; TRAIL expressed only in BM (BM-TRAIL) or everywhere except BM (parenchymal-TRAIL), vs. whole-body TRAIL ablation (null-TRAIL). BM-TRAIL attenuated macrophage content and atherosclerosis. BM-derived macrophages with TRAIL deletion were more inflammatory, with impaired migration and reduced expression of cholesterol efflux, efferocytosis and nitric oxide-controlling genes. TRAIL expression also reduced islet macrophage content, but only parenchymal-TRAIL islets had improved function. Recombinant TRAIL administration stimulated insulin expression and islet mass. We propose TRAIL maintains monocyte/macrophage homeostasis and limits the progression of atherosclerosis and islet dysfunction. Gene expression of aortic tissue from wildtype C57Bl6/J mice (n=3) were compared to Trail-/- knockout mice (n=3) to identify overall effect of TRAIL knockout. Trail knockout mice were sourced from Amgen.