Abstract 2078: Integrin α5β1-mediated Interactions With Fibronectin Enhance Tim3 Expression To Drive Efferocytosis By Macrophages

Abstract

Despite significant advances in diagnosing and treating cardiovascular disease, atherosclerosis remains the leading cause of death worldwide. While most atherosclerotic plaques remain asymptomatic, a subset can lead to myocardial infarction, stroke, or sudden death. A plethora of evidence has demonstrated that rupture-prone atheromas contains a large necrotic core owed to defective efferocytosis, the process by which apoptotic cells (ACs) are engulfed and cleared by macrophages. The efficient clearance of apoptotic cells blocks post-apoptotic necrosis and prevents the release of tissue-degrading enzymes, immunogenic epitopes, and proinflammatory mediators. As atherosclerosis advances, substantial remodeling of the extracellular matrix (ECM) occurs whereby transitional ECM proteins, notably fibronectin (FN), deposit into the subendothelial matrix normally dominated by collagen IV and laminins. However, whether macrophage interactions with the ECM alters efferocytosis, inflammation resolution, and atherosclerosis remains unknown. Surprisingly, we discovered that macrophage interactions with FN enhance efferocytosis compared to their interactions with basement membrane proteins. Furthermore, we demonstrate that the primary FN receptor, integrin α5β1, is required for FN-mediated efferocytosis and TIM3 expression, (encoded by Havcr2 ), a known phosphatidylserine receptor that binds to ACs. Moreover, treating mice with established atherosclerosis with the integrin α5β1 antagonistic peptide ATN-161 reduced TIM3 expression in macrophages and expanded necrotic core formation. We also found lesional macrophages from human unstable atheromas displayed significantly lower TIM3 expression compared to macrophages within stable plaques. In a mouse model of atherosclerosis regression, where atherogenic stimuli dissipate, efferocytosis is restored, and FN remains, lesional macrophages showed a substantial increase in TIM3 expression. Thus, while FN is traditionally considered atherogenic in endothelial and smooth muscle cells in the initial stages of atherosclerosis, our data uncovers that macrophage adhesion to FN upregulates TIM3 expression, mediating efferocytosis and promoting features of plaque stability.