Macrophage extracellular traps promote maladaptive cardiac remodelling and heart failure via PAD4-dependent mechanisms
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Abstract
Aims
The activation of inflammatory cells, particularly macrophages, plays a pivotal role in the pathogenesis of cardiac remodelling and heart failure. Emerging evidence indicates that extracellular traps released from inflammatory immune cells contribute to the progression of various pathologies. However, the clinical relevance and mechanistic role of macrophage extracellular traps (METs) in heart failure remain to be elucidated.
Methods and Results
Endomyocardial biopsy specimens from 69 patients with heart failure were analysed by fluorescent immunostaining to identify and quantify METs. The numbers of METs per myocardial tissue area in patients with heart failure showed a negative correlation with left ventricular (LV) ejection fraction and a positive correlation with LV end-diastolic diameter. Patients with higher MET counts had significantly lower event-free survival from the composite cardiac events. In a murine model of pressure overload by transverse aortic constriction (TAC), METs were most abundantly observed at 3 days post-TAC and remained detectable throughout the 4-week observation period. In vitro, time-dependent MET formation was induced by an intrinsic trigger of mitochondrial DNA in bone marrow-derived macrophages from wild-type (WT) mice, but not in peptidyl arginine deiminase 4 (PAD4)-deficient macrophages, indicating that PAD4 activity is indispensable for MET formation. The recipient mice transplanted with bone marrow cells from PAD4 knockout mice showed more preserved cardiac function, reduced myocardial fibrosis, and improved survival in response to TAC, compared to those transplanted with WT mice. Ex vivo analyses demonstrated that conditioned medium containing METs from WT macrophages induced fibroblast-to-myofibroblast transition via Toll-like receptor 4 signalling.
Conclusions
PAD4-dependent MET formation from bone marrow-derived macrophages represents a novel driver of cardiac remodelling. Targeting MET formation may offer a potential therapeutic strategy for heart failure.
Translational Perspective
Macrophage extracellular traps (METs) are abundant in myocardial tissue from patients with heart failure with reduced ejection fraction and are associated with adverse left ventricular remodelling and worse clinical outcomes. These findings support myocardial MET burden as a potential tissue biomarker to improve risk stratification in heart failure patients. In mice, pressure overload induces MET formation, and hematopoietic PAD4 deficiency suppresses myocardial METs, attenuates fibrosis, preserves cardiac function, and improves survival. Mechanistically, mitochondrial DNA-enriched cardiomyocyte-derived exophers trigger PAD4-dependent METs, which activate cardiac fibroblasts through TLR4 signalling. Suppressing METs represents a potential therapeutic strategy to attenuate the progression of heart failure.
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Taken together, these findings12suggest that higher myocardial MET burden is associated with adverse outcomes in13patients with HFrEF
Was analysis of inflammatory cascades performed to infer degree to which METs were activating downstream inflammatory processes?
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