Abstract

The effective removal of apoptotic cells (ACs) by macrophages, termed “efferocytosis”, is essential for resolving inflammation and promoting tissue repair. Accordingly, impaired efferocytosis underlies chronic diseases, such as atherosclerosis, and underscores the need to restore this process. Pro-resolving macrophages execute successive rounds of efferocytosis and produce the pro-resolving polyamine putrescine, which is critically regulated by its rate-limiting enzyme ornithine decarboxylase (ODC1). Despite valuable insights, critical gaps remain in our understanding of how putrescine biosynthesis is regulated during inflammation resolution. Therefore, we sought to explore the mechanisms underlying the signaling pathways governing ODC1 gene expression, putrescine biosynthesis, and their role in inflammation resolution and atherosclerosis regression. We found that ODC1 expression in lesional macrophages decreased during atherosclerosis progression ( Ldlr -/- mice fed a high-fat, Western-type diet (HFD) for 16 weeks), whereas ODC1 expression substantially increased during atherosclerosis regression ( Ldlr -/- mice fed an HFD for 16 weeks then treated with a virus that restores hepatic LDLR and switched to normal chow for 5 more weeks). Consistently, early-stage human atherosclerotic plaques (Type 1-2) showed high levels of ODC1 in CD68 + macrophages, yet lesional macrophages in advanced-stage human atheromas (Type 3-5) showed low levels of ODC1. In vitro studies in humans and mice indicated that engulfment of ACs enhanced ODC1 expression, which was unaffected by AC binding or its degradation. However, blocking actin polymerization prevented ODC1 upregulation by apoptotic cells whereas stimulating its polymerization enhanced ODC1 expression. Furthermore, uptake of inert beads similarly increased ODC1 expression, relying on a novel pathway involving integrin αV-mediated Stat3 activation and Myc-dependent Odc1 transcription. These newly identified mechanisms illuminate previously unknown mechanisms driving inflammation resolution and reveal new avenues for developing targeted therapies in atherosclerotic cardiovascular disease.