Single-Cell Immune Microenvironment Atlas of Human Myocardial Infarction Focusing on Myeloid Cells and Functional Differentiation of Macrophage Subtypes

Background: Myocardial infarction (MI) is characterized by extensive immune activation and dynamic remodeling of the cardiac microenvironment, in which myeloid cells play critical roles in regulating inflammation and tissue repair. However, the cellular heterogeneity, developmental trajectories, and intercellular communication networks of myeloid cell subtypes during MI remain incompletely understood. Methods: Single-cell RNA sequencing (scRNA-seq) data from MI tissues were integrated to construct a comprehensive immune atlas. Cell clustering, differential expression, cell cycle, and functional enrichment analyses were performed to characterize cellular composition and biological functions. CytoTRACE, Monocle2, and Slingshot were applied to investigate macrophage differentiation trajectories, whereas transcriptional regulatory network analysis and CellChat were used to identify regulatory modules and intercellular communication pathways. Results: A total of 44,574 high-quality cells comprising 24 cell types were identified, which revealed prominent myeloid cell accumulation and enhanced immune activation in infarcted tissues. Macrophages were enriched in infarcted regions and exhibited increased proliferative activity and immune-related pathway activation. Four transcriptionally distinct macrophage subtypes were identified (C0 GPNMB + , C1 S100A4 + , C2 IL1B + , and C3 EGR1 + ), among which C 1 S100A4 + macrophages predominated, displayed the strongest proliferative ability, and expressed high levels of inflammatory mediators, including IL1B, CCL3, and CXCL8. Trajectory and regulatory analyses revealed dynamic macrophage differentiation and subtype-specific transcriptional programs. Cell-cell communication analysis identified C1 S100A4 + macrophages as a central signaling hub interacting with endothelial cells, fibroblasts, and immune cells through CXCL, MHC-II, and TNF pathways, thereby suggesting their critical role in post-MI inflammatory remodeling. Conclusion: This study provided a comprehensive single-cell immune atlas of MI and systematically elucidated the heterogeneity, developmental dynamics, transcriptional regulation, metabolic reprogramming, and intercellular communication of macrophage subtypes. C1 S100A4 + macrophages were identified as a key inflammatory population orchestrating immune remodeling after MI. Our findings provide insights into the cellular mechanisms underlying cardiac injury that may offer potential therapeutic targets for precision immunomodulation in MI.