Neutrophil Expansion And Netosis Are Essential For Adverse Left Ventricular Remodeling And Dysfunction In Chronic Ischemic Heart Failure

Chronic inflammation contributes significantly to disease progression in heart failure (HF) with the expansion and adverse activation of macrophages, dendritic cells, and T cells in the failing heart. Neutrophils play a well-known role in the initial acute immune response to myocardial infarction (MI), however, whether and how they contribute to inflammation and adverse LV function and remodeling in chronic ischemic HF is unknown. We tested the hypothesis that activated neutrophils are required for tissue remodeling and disease progression in HF in mice studied 4 and 8 weeks after MI during established ischemic HF (vs sham). CD11b + Ly6G + neutrophils were expanded in peripheral blood (PB), heart, spleen and bone marrow 8 w post-MI. Neutrophils in the failing heart were localized to the MI border zone and augmented in remote zone myocardium by immunofluorescent staining. CXCL1 and CXCL5 expression was increased in the failing heart, consistent with chemotactic signals for myocardial neutrophil recruitment. Plasma from HF mice elicited greater chemotaxis in naïve neutrophils (vs naïve plasma) by time-lapse video microscopy. Further, PB neutrophils from HF mice exhibited significantly increased neutrophil extracellular trap (NET) production, with concomitant increase in plasma NETs (histone-DNA complexes) in HF mice. The direct pathological impact of NETs was demonstrated by intramyocardial injection of isolated NETs into naïve hearts mimicking HF with decreased EF, LV dilation, and fibrosis. Finally, the in vivo role of neutrophils in chronic HF (4 and 8 w post-MI) was determined via depletion studies using genetic (Ly6G-diptheria toxin receptor mice) and antibody (1A8) based approaches. Neutrophil depletion significantly improved LV EF and reduced end systolic and diastolic volumes. 1A8 treated HF mice also exhibited reduced remote zone fibrosis. The necessity of NETosis in HF development was confirmed using neutrophil and myeloid – specific PAD4 deletion where the decline in LV EF and increase in volumes in HF were attenuated. In conclusion , neutrophil expansion and NETosis are important contributors to chronic inflammation in HF and play an obligatory role in the development of LV dysfunction and remodeling in ischemic cardiomyopathy.