Duchêne, Johan

Abstract Myocardial infarction (MI) triggers a systemic neutrophil response, yet the roles of distinct neutrophil subsets in cardiac remodeling remain unclear. Studying this requires murine models that accurately mirror human neutrophil dynamics. Here, we show that a minimally invasive intact-chest MI model is more pathophysiologically relevant than the standard open-chest approach for investigating post-MI immune responses. In the open-chest model, surgical trauma disrupts bone marrow homeostasis, releases large numbers of immature neutrophils, and masks MI-specific immune mechanisms. In contrast, the intact-chest model preserves bone marrow integrity and induces only a modest rise in circulating immature neutrophils, closely reflecting MI patient profiles. We further demonstrate that accumulation of immature neutrophils in the infarcted heart exacerbates cardiac dysfunction. Beyond neutrophils, the overall cardiac immune landscape differs markedly between both models. Collectively, our findings establish the intact-chest model as superior for studying post-MI inflammation and reveal immature neutrophils as mediators of adverse cardiac remodeling.

Background: Amino acid metabolism is crucial for inflammatory processes during atherogenesis. The endogenous amino acid homoarginine is a robust biomarker for cardiovascular outcome and mortality with high levels being protective. However, the underlying mechanisms remain elusive. We investigated the effect of homoarginine supplementation on atherosclerotic plaque development with a particular focus on inflammation. Methods: Female ApoE-deficient mice were supplemented with homoarginine (14 mg/L) in drinking water starting 2 weeks before and continuing throughout a 6-week period of Western-type diet feeding. Control mice received normal drinking water. Immunohistochemistry and flow cytometry were used for plaque- and immunological phenotyping. T cells were characterized using mass spectrometry–based proteomics, by functional in vitro approaches, for example, proliferation and migration/chemotaxis assays as well as by super-resolution microscopy. Results: Homoarginine supplementation led to a 2-fold increase in circulating homoarginine concentrations. Homoarginine-treated mice exhibited reduced atherosclerosis in the aortic root and brachiocephalic trunk. A substantial decrease in CD3 + T cells in the atherosclerotic lesions suggested a T-cell–related effect of homoarginine supplementation, which was mainly attributed to CD4 + T cells. Macrophages, dendritic cells, and B cells were not affected. CD4 + T-cell proteomics and subsequent pathway analysis together with in vitro studies demonstrated that homoarginine profoundly modulated the spatial organization of the T-cell actin cytoskeleton and increased filopodia formation via inhibition of Myh9 (myosin heavy chain 9). Further mechanistic studies revealed an inhibition of T-cell proliferation as well as a striking impairment of the migratory capacities of T cells in response to relevant chemokines by homoarginine, all of which likely contribute to its atheroprotective effects. Conclusions: Our study unravels a novel mechanism by which the amino acid homoarginine reduces atherosclerosis, establishing that homoarginine modulates the T-cell cytoskeleton and thereby mitigates T-cell functions important during atherogenesis. These findings provide a molecular explanation for the beneficial effects of homoarginine in atherosclerotic cardiovascular disease.