Abstract Body: Neutrophils undergo neutrophil trap formation (NETosis) in states of inflammatory stress. Multiple cardiovascular diseases are associated with NETosis. However, the involvement of NETosis in myocardial injury and the mechanism of NET-induced damage in the heart is unclear. The objective of this study was to determine whether NETosis can independently cause cardiac damage and dysfunction in the context of myocardial ischemia/reperfusion (MI/R) injury, and to examine the direct cytotoxic and indirect mechanisms of NET-induced myocardial injury.

We introduced neutrophils undergoing NETosis and isolated NETs to adult and neonatal cardiomyocyte cultures in vitro, and examined the effect on cardiomyocyte viability. We saw a decrease in live cardiomyocytes with neutrophils independent of NETs. We injected NETs into healthy hearts in vivo, and observed that NETosis causes an acute innate immune infiltration of the myocardium at days 1 and 3 post injection. Transient global longitudinal strain (GLS) deficit was also associated with NET injection, and heart function returned to normal at 4 weeks post-injection. NET injection also resulted in long-term local fibrosis at the site of injection.

We conclude that NETs observed in MI/R injury can have a negative functional impact on the myocardium, and that this effect is mediated by immune infiltration and activation, and permanent tissue fibrosis.