Temporal neutrophil polarization following myocardial infarction

TLDR

The study aimed to characterize temporal neutrophil polarization and activation mechanisms following myocardial infarction. In vitro, neutrophils polarized to a proinflammatory N1 phenotype by lipopolysaccharide and interferon‑γ or to an anti‑inflammatory N2 phenotype by interleukin‑4, while in vivo damage‑associated molecular patterns activated toll‑like receptor‑4 to drive N1 polarization. Neutrophils isolated from the infarcted left ventricle displayed a proinflammatory N1 phenotype at day 1 and an anti‑inflammatory N2 phenotype by days 5–7, with N1 remaining >80% yet increasing N2 over time; N1 abundance correlated with infarct wall thinning via matrix metalloproteinases‑12 and ‑25, transforming growth factor‑β1 suppressed proinflammatory production, and this work is the first to identify N1 and N2 neutrophils in the infarct region and link N1 polarization to DAMP‑mediated TLR4 activation.

Abstract

Although macrophage phenotypes have been well studied in the myocardial infarction (MI) setting, this study investigated temporal neutrophil polarization and activation mechanisms. Neutrophils isolated from the infarcted left ventricle (LV) of mice showed high expression of proinflammatory markers at Day 1 and anti-inflammatory markers at Days 5 and 7 post-MI, indicating distinct neutrophil phenotypes along the post-MI time continuum. Flow cytometry analysis revealed that although proinflammatory N1 neutrophils were always predominant (>80% of total neutrophils at each time point), the percentage of N2 neutrophils increased post-MI from 2.4 ± 0.6% at Day 1 to 18.1 ± 3.0% at Day 7. In vitro, peripheral blood neutrophils were polarized to proinflammatory N1 by lipopolysaccharide and interferon-γ or anti-inflammatory N2 by interleukin-4, indicating high plasticity potential. The in vivo post-MI relevant LV damage-associated molecular patterns (DAMPs) polarized neutrophils to a proinflammatory N1 phenotype by activating toll-like receptor-4. Transforming growth factor-β1 inhibited proinflammatory production in neutrophils. N1 neutrophils positively correlated with infarct wall thinning at Day 7 post-MI, possibly due to high production of matrix metalloproteinases-12 and -25. This study is the first to identify the existence of N1 and N2 neutrophils in the infarct region and reveals that N1 polarization could be mediated by DAMPs.