Modulating neutrophil phenotype via mesenchymal stromal cell paracrine signals; insights from human and mouse experiments

Neutrophils play a central role in the inflammatory and reparative processes following myocardial infarction (MI), and can switch between pro-inflammatory (N1) and reparatory (N2) states, influencing disease outcomes. Mesenchymal stromal cells (MSC), known for their immunomodulatory effects, may hold the key to controlling neutrophil behaviour. In this study, we explored how MSC influence neutrophil states both in vitro and in vivo in an MI mouse model. We developed a reliable system to study neutrophils by differentiating HL-60 cells into neutrophil-like cells (dHL-60). These cells were polarized into N1 and N2 types, showing distinct protein markers and cytokine signatures. When exposed to MSC, pro-inflammatory N1 cells reduced their production of inflammatory signals (TNFa, MCP-1), while N2 cells increased their reparatory signals (IL-10, TGM2). In mice with MI, MSC reduced the number of neutrophils migrating to damaged heart tissue and altered their transcriptomic signatures. Surprisingly, MSC enhanced inflammatory pathways in heart neutrophils while dampening their ability to support tissue repair. These findings underscore the complex role of MSC in modulating neutrophil responses, demonstrating a nuanced impact on inflammatory and reparative pathways in the cardiac microenvironment. While the results highlight MSC' potential to influence immune cell behaviour, they also reveal context-specific effects that warrant further investigation to fully elucidate their therapeutic implications in cardiovascular disease. Overall design: Gene expression profiling analysis of RNA-seq data from cardiac and blood neutrophils isolated from C57Bl/6J mice with and without MSC treatment, after induced myocardial infarction. Samples were collected 3 days after LCA ligation.