Macrophage Metabolism of Apoptotic Cell-Derived Arginine Promotes Continual Efferocytosis and Resolution of Injury

Continual efferocytic clearance of apoptotic cells (ACs) by macrophages prevents necrosis and promotes injury resolution. How continual efferocytosis is promoted is not clear. Here, we show that the process is optimized by linking the metabolism of engulfed cargo from initial efferocytic events to subsequent rounds. We found that continual efferocytosis is enhanced by the metabolism of AC-derived arginine and ornithine to putrescine by macrophage arginase 1 (Arg1) and ornithine decarboxylase (ODC). Putrescine augments HuR-mediated stabilization of the mRNA encoding the GTP-exchange factor Dbl, which activates actin-regulating Rac1 to facilitate subsequent rounds of AC internalization. Inhibition of any step along this pathway after first-AC uptake suppresses second-AC internalization, whereas putrescine addition rescues this defect. Mice lacking myeloid Arg1 or ODC have defects in efferocytosis in vivo and in atherosclerosis regression, while treatment with putrescine promotes atherosclerosis resolution. Thus, macrophage metabolism of AC-derived metabolites allows for optimal continual efferocytosis and resolution of injury. [Display omitted] •Macrophages take up arginine and ornithine from apoptotic cells during efferocytosis•Arg1 and ODC convert apoptotic cell-derived arginine and ornithine into putrescine•Putrescine augments subsequent rounds of efferocytosis by increasing Rac1 activation•Lack of Arg1 or ODC blunts continual efferocytosis and resolution of atherosclerosis Macrophages engulf apoptotic cells (ACs) by continual efferocytosis to prevent inflammation and necrosis. Here, Yurdagul et. al. show that this process is linked to the metabolism of AC-derived arginine or ornithine to putrescine, which is required for the optimization of subsequent rounds of efferocytosis and proper resolution of atherosclerosis.