Smooth muscle cell-specific deletion of S100A4 reroutes smooth muscle cell fate and modifies the inflammatory status of murine atherosclerotic lesions

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Swiss National Science Foundation Foundation Centre de Recherches Médicales Carlos and Elsie de Reuter Background aims: S100A4, a small calcium binding protein, plays an important role in vascular smooth muscle cell (SMC) phenotypic switch but its implication in atherosclerotic plaque development and particularly in SMC phenotypic plasticity is not clear yet. By neutralizing S100A4 using a monoclonal antibody, we have previously shown a reduction in overall atherosclerotic burden. However, this strategy did not distinguish the different contribution between SMCs or other S100A4-expressing cells (e.g. macrophages). Methods Herein, we used a lineage tracing mouse model in which we induced a SMC specific deletion of S100A4 (SMC-S100A4Δ/Δ) in an ApoE-/- background. High cholesterol diet was maintained for 12 weeks, after which, SMC-S100A4Δ/Δ and control mice (SMC-S100A4wt/wt) were sacrificed and aortas processed for staining and single cell RNA sequencing (scRNA-seq). Results We showed that S100A4 deletion modulated plaque composition rather than plaque size. ScRNA-seq analysis from SMC-S100A4Δ/Δ and SMC-S100A4wt/wt showed a reduction in macrophages and dendritic cells and an increase in total SMCs, likely participating in fibrous cap stabilization. SMC populations showed a decrease in macrophage-like inflammatory phenotype and an increase in fibroblast-like repair phenotype, as well as retention of specific SMC markers, namely Acta2 and Myh11. Gene expression analysis revealed a reduction in the expression of inflammation markers, fatty acid metabolism, and extracellular matrix-related genes, and an increase in classical SMC markers and maintenance of the contractile phenotype. Conclusion We report an intrinsic function of S100A4 in the establishment of SMC fate within the plaque and, surprisingly, a global impact on the atherosclerotic plaque microenvironnement and inflammation status.