Mon4 as a novel monocyte subset with distinct profile and predictor of poor outcomes in individuals with myocardial infarction

Recently, a new monocyte subset known as Mon4, characterized by distinct gene expressions, has been identified but remains poorly characterized. In this study, our objective was to comprehensively characterise Mon4 in healthy individuals and explore its correlation with major adverse cardiovascular events (MACE) in patients with ST-elevation myocardial infarction (STEMI). Our study enrolled 20 healthy individuals and 245 STEMI patients who underwent primary percutaneous coronary intervention (PCI). We analysed monocyte subsets using flow cytometry and collected bone marrow samples from 11 healthy individuals. Cardiac function assessments were performed in STEMI patients through echocardiography within 3 days post-PCI. Mon4 displayed significant differences compared to Mon1, Mon2, and Mon3 in various parameters among healthy individuals, underscoring its distinct profile. In STEMI patients, above-median Mon4 counts were associated with a increased risk of MACE (hazard ratio [HR] 3.11, 95% confidence interval [CI] 1.55-6.24, p = 0.01) and heart failure (HR 3.25, 95% CI 1.14-9.24, p = 0.03) after adjusting for other predictive factors. This study highlights the unique characteristics of Mon4 and its clinical significance. The distinctive gene signature of Mon4, coupled with its association with MACE and heart failure, suggests its potential utility as a biomarker for risk assessment in MI patients. Further investigations are warranted to explore the therapeutic potential of targeting Mon4 in reducing cardiovascular complications following MACE.