No abstract

Chronic inflammation contributes significantly to disease progression in heart failure (HF), and is characterized by expansion of activated macrophages, dendritic cells, and T cells in the failing heart. Neutrophils play a well-known role as the initial drivers of inflammatory response to myocardial infarction (MI), thereby providing the platform for the subsequent recruitment of macrophages and T cells. However, whether and how neutrophils contribute to inflammation and adverse LV remodeling in chronic HF are unknown. We tested the hypothesis that activated neutrophils are required for tissue remodeling and disease progression in HF. Male C57Bl/6 mice were studied 4 and 8 weeks after left coronary artery ligation during established ischemic HF (sham-operated controls). As assessed by flow cytometry, CD11b + Ly6G + neutrophils were expanded in the peripheral blood (4 w post-MI), and in the bone marrow, spleen, and heart at 8 w post-MI. Immunostaining revealed that in the failing heart, neutrophils were primarily localized to the MI border zone, but also augmented in remote zone myocardium. CXCL1 and CXCL5 chemokine expression was increased in the failing heart, consistent with chemotactic signals for myocardial neutrophil recruitment. Isolated naïve neutrophils also exhibited increased chemotaxis in response to plasma from HF mice (versus plasma from naïve mice), as assessed by time-lapse video microscopy. Moreover, blood neutrophils isolated from HF mice exhibited significantly increased neutrophil extracellular trap (NET) production as compared to control neutrophils, whereas plasma NETs (histone-DNA complexes) were increased in HF mice. Finally, the in vivo role of neutrophils in chronic HF (8 w post-MI) was determined via depletion studies using genetic (Ly6G-diptheria toxin receptor mice) and antibody (1A8) based approaches. In both models, 2 and 4 w of neutrophil depletion, respectively, significantly improved LV systolic function and reduced end systolic volume. 1A8 treated HF mice also exhibited reduced remote zone fibrosis. We conclude: neutrophil expansion and activation are important components of the chronic inflammatory response in HF, and play an obligatory role in the progression of LV remodeling in ischemic cardiomyopathy.

No abstract