During atherosclerotic plaque formation, smooth muscle cells (SMCs) accumulate in the intima and undergo a transition from a contractile to a synthetic phenotype, influencing disease progression. In a co-culture model between S100A4-stimulated human aortic SMCs and human monocytes, we demonstrated that monocytes up-regulated markers typical of anti-inflammatory M2 macrophages and adjusted metabolism of cholesterol. In vivo, we identified S100A4-expressing SMCs in the mouse aortic media prior their accumulation in the intima. Characterization of medial SMCs by means of single-cell RNA sequencing revealed heterogeneity among S100A4-expressing medial SMCs. We investigated the impact of blood-derived monocytes and extracellular S100A4 on the atherosclerosis progression in vivo. Unexpectedly, monocyte depletion led to larger atherosclerotic lesions compared to control animals, while S100A4 neutralization had no visible impact on the lesion area. Our findings shed light on the role of S100A4 in the crosstalk between SMCs and monocytes in atherosclerosis.