Compromised Anti-inflammatory Action of Neutrophil Extracellular Traps in PAD4-Deficient Mice Contributes to Aggravated Acute Inflammation After Myocardial Infarction

Abstract

Innate immune responses and rapid recruitment of leukocytes, which regulate inflammation and subsequent healing, play a key role in acute myocardial infarction (MI). Peptidylarginine deiminase 4 (PAD4) is critically involved in chromatin decondensation during the release of Neutrophil Extracellular Traps (NETs) by activated neutrophils. Alternatively, activated macrophages (M2) and accurate collagen deposition determine the repair of the infarcted heart. In this study, we investigated the impact of NETs on macrophage polarization and their role for acute cardiac inflammation and subsequent cardiac healing in a mouse model of acute MI. NETs were found to promote in vitro macrophage polarization toward a reparative phenotype. NETs suppressed pro-inflammatory macrophages (M1) under hypoxia and diminished IL-6 and TNF-α expression. Further on, NETs strongly supported M2b polarization and IL-10 expression. In cardiac fibroblasts, NETs increased TGF-ß expression under hypoxic culture conditions. PAD4−/− mice subjected to permanent ligation of the left anterior descending artery suffered from overwhelming inflammation in the acute phase of MI. Noteworthy, PAD4−/− neutrophils were unable to release NETs upon ex vivo stimulation with ionomycin or PMA, but produced significantly higher amounts of reactive oxygen species (ROS). Increased levels of circulating cell-free DNA, mitochondrial DNA and cardiac troponin were found in PAD4−/− mice in the acute phase of MI when compared to WT mice. Reduced cardiac expression of IL-6, IL-10, and M2 marker genes, as well as increased TNF-α expression, suggested a pro-inflammatory state. PAD4−/− mice displayed significantly increased cardiac MMP-2 expression under baseline conditions. At day 1, post-MI, PAD4−/− mice showed increased end-diastolic volume and increased thinning of the left ventricular wall. Interestingly, improved cardiac function, as demonstrated by significantly increased ejection fraction, was found at day 21. Altogether, our results indicate that NETs support macrophage polarization toward an M2 phenotype, thus displaying anti-inflammatory properties. PAD4 deficiency aggravates acute inflammation and increases tissue damage post-MI, partially due to the lack of NETs.

Peroxiredoxin2 (Prdx2) Reduces Oxidative Stress and Apoptosis of Myocardial Cells Induced by Acute Myocardial Infarction by Inhibiting the TLR4/Nuclear Factor kappa B (NF-κB) Signaling Pathway

“…The physiological level of ROS plays a key role in cell signal transduction and stabilization of the intracellular environment. Some ROS, especially H 2 O 2 , are considered as local signaling molecules [ 18 ]. Therefore, completely quenching the ROS may interrupt the normal signal cascade and have serious adverse consequences.…”

<p>Screening and Identification of Potential Hub Genes in Myocardial Infarction Through Bioinformatics Analysis</p>

“…Il6 is a well-known inflammation-related gene, and many studies regard it as an indicator of inflammation. 43 , 44 We did not discuss it in depth. Ptgs2, also called COX-2, promotes cell proliferation in tumors, accelerates angiogenesis, 45 and reduces inflammation in myocardial infarction.…”

Neutrophil extracellular trap components and myocardial recovery in post-ischemic acute heart failure

“…The crucial role of neutrophils in the conversion of macrophages to a reparative phenotype, as well as the timely development of a fibrotic scar, is evident from studies in mice showing that neutrophil depletion leads to poorer myocardial function and the development of AHF [ 24 ]. Recent data from a murine model of MI indicates that NETs may promote resolution of inflammation [ 25 ] and yet another study showed that NETs likely influence the conversion of monocytes to scar-generating fibrocytes [ 15 ]. Other beneficial effects of neutrophils could mitigate the potential detrimental effects of NETs, complicating interpretation of our results.…”