Macrophage one-carbon metabolism in atherosclerotic plaque stability - PROJECT SUMMARY/ABSTRACT Atherosclerotic cardiovascular disease (ASCVD), driven by the buildup of fibrofatty plaques in arterial walls, remains the leading cause of death worldwide. Plaque instability, characterized by foam cell apoptosis and impaired efferocytosis, the process by which macrophages clear apoptotic cells, leads to rupture and life- threatening cardiovascular events. In contrast, enhancing efferocytosis by macrophages can promote plaque stability and atherosclerosis regression. Despite significant advances in lipid-lowering therapies, residual ASCVD risk persists, highlighting an urgent need for novel therapeutic targets to stabilize rupture-prone plaques and promote atherosclerosis regression. Recently, we and others identified a critical role for dysregulated amino acid metabolism in ASCVD, consistently demonstrating reduced circulating glycine. Glycine is primarily synthesized from serine by serine hydroxymethyltransferase 2 (SHMT2), which initiates the one-carbon metabolism (1CM) pathway. While 1CM has been extensively studied in cancer, its role in ASCVD is poorly understood, and the impact of macrophage 1CM in atherosclerosis is unknown. Here, we found that macrophage SHMT2 is suppressed as atherosclerosis advances in humans and mice. Using our novel myeloid-specific SHMT2-deficient (Shmt2MKO) mice, we discovered that SHMT2-dependent 1CM in macrophages is crucial for maintaining plaque stability features. Stable-isotope tracing uncovered that SHMT2 loss in macrophages disrupts 1CM leading to inhibition of de novo glutathione synthesis, redox imbalance, and overproduction of serine-derived ceramides. Transcriptomics revealed a suppression of key cytoskeleton remodeling and phagosome regulators, aligned with defective efferocytosis that was rescued by restoring SHMT2. This proposal will address the central hypothesis that impaired SHMT2-dependent 1CM in macrophages drives plaque instability by disrupting efferocytosis through altered redox and ceramide metabolism, while restoring SHMT2 enhances features of plaque stability and atherosclerosis regression. Aim 1 will define the mechanisms by which SHMT2-dependent 1CM drives efferocytosis, elucidate the mechanisms by which macrophage SHMT2 is suppressed by proatherogenic stimuli, and characterize impaired 1CM in human and mouse lesional macrophages using our Shmt2MKO mice, newly generated mice lacking rate-limiting enzymes of glutathione and ceramide synthesis, as well as pharmacological, metabolomics, and novel mass spectrometry imaging approaches. Aim 2 will establish impaired SHMT2- dependent 1CM in macrophages as a driver of plaque instability in atherosclerosis progression and regression, determine redox imbalance, ceramide overproduction, and defective efferocytosis as underlying mechanisms, and evaluate the therapeutic potential of restoring SHMT2 in lesional macrophages using our new mouse models in the Ldlr-/- background, and our validated macrophage-targeting nanoparticle platform. Successful completion of this proposal will define a novel metabolic pathway linking efferocytosis and plaque stability and identify a new target to stabilize rupture-prone atheromas and promote atherosclerosis regression, critical unmet clinical needs.
