Abstract 15471: Neonatal Mesenchymal Stem Cells Rejuvenate Cardiac Myocardium by Regulating Macrophage Polarization Revealed by Single Cell Sequencing After Ischemia-Reperfusion Injury in Rats

Introduction: Stem cells are an emerging therapy for cardiovascular disease. The immune system is modulated by stem cell administration, therefore we sought to characterize the immune environment following stem cell administration. Hypothesis: Neonatal cardiac mesenchymal stem cells (nMSC) improved heart function through an acute sterile immune response characterized by the temporal and regional of macrophages. Methods: nMSC were isolated from healthy neonatal myocardium. Brown Norway rats underwent ischemia-reperfusion injury (IRI) by temporary ligation of left anterior descending artery for 45 minutes. Following closure of the chest cavity, neonatal mesenchymal stem cells (nMSCs), dead nMSCs (dnMSCs), or placebo was administered by intra-coronary injection. At day five heart was collected for single cell suspensions. CD45 positive selection was performed and fed into the Chromium Single Cell Gene Expression workflow (Pleasanton, CA). Single cell sequencing analysis was completed using the Seurat package on RStudio v1.3.1093 (Boston, MA). Echocardiography was completed on post-operative days 7 and 28 for rats not sacrificed for single cell sequencing. Results: Our results demonstrate that nMSC treatment after IRI injury can significantly recover left ventricular ejection fraction. Single-cell sequencing analysis of CD45+ cells identified multiple unique CD68+ clusters. Notably, macrophage cluster 2 primarily consisted of cells from the nMSC treated group, whereas the macrophage cluster 1 was primarily cells from the dnMSC and placebo groups. Gene ontology analysis of macrophage cluster 2 demonstrated that this cluster primarily consisted of macrophages strongly associated with various aspects of the activated immune response, including lymphocyte activation and cytokine production. Conversely, macrophage cluster 1 gene ontology analysis revealed a weaker immune response signature. Conclusions: nMSCs are a promising therapeutic candidate for the treatment of myocardial infarction. The mechanism of this therapy is likely related to macrophage activation that further enhances the immune response in the impacted and at-risk myocardium following IRI injury.