Therapeutic Targeting of Neutrophil Extracellular Traps in Atherogenic Inflammation.

Neutrophils and neutrophil extracellular traps (NETs) have a robust relationship with atherothrombotic disease risk, which led to the idea that interfering with the release of NETs therapeutically would ameliorate atherosclerosis. In human studies, acute coronary events and the pro-thrombotic state cause markedly elevated levels of circulating deoxyribonucleic acid (DNA) and chromatin, suggesting that DNase I might produce cardiovascular benefit. DNase I reproduced the phenotype of peptidylarginine deiminase 4 (PAD4) deficiency and showed a significant benefit for atherothrombotic disease in experimental mouse models. However, the mechanisms of benefit remain unclear. Insights into the mechanisms underlying NET release and atherogenic inflammation have come from transgenic mouse studies. In particular, the importance of neutrophil NET formation in promoting atherothrombotic disease has been shown and linked to profound pro-inflammatory and pro-thrombotic effects, complement activation and endothelial dysfunction. Recent studies have shown that myeloid deficiency of PAD4 leads to diminished NET formation, which in turn protects against atherosclerosis burden, propagation of its thrombotic complications and notably macrophage inflammation in plaques. In addition, oxidative stress and neutrophil cholesterol accumulation have emerged as important factors driving NET release, likely involving mitochondrial reactive oxidants and neutrophil inflammasome activation. Further elucidation of the mechanisms linking hyperlipidaemia to the release of NETs may lead to the development of new therapeutics specifically targeting atherogenic inflammation, with likely benefit for cardiovascular diseases.

Van Avondt K ，Maegdefessel L ，Soehnlein O 《-》

Plasma high density lipoproteins: Therapeutic targeting and links to atherogenic inflammation.

Plasma HDL levels have an inverse relationship to coronary artery disease (CAD) risk, which led to the idea that increasing HDL levels therapeutically would ameliorate atherosclerosis. Human genetic deficiency of CETP caused markedly elevated HDL and moderately reduced non-HDL cholesterol levels, suggesting that CETP inhibitors might produce cardiovascular benefit. The CETP inhibitor anacetrapib reproduced the phenotype of homozygous CETP deficiency and showed a highly significant benefit for CAD in the REVEAL trial. However, the magnitude of this effect was moderate, and the mechanism of benefit remains unclear. Insights into the mechanisms underlying macrophage cholesterol efflux and reverse cholesterol transport have come from monogenic human disorders and transgenic mouse studies. In particular, the importance of the ATP binding cassette transporters ABCA1 and ABCG1 in promoting cholesterol efflux from myeloid and other hematopoietic cells has been shown and linked to aberrant myelopoiesis and macrophage inflammation. Recent studies have shown that myeloid deficiency of ABCA1 and ABCG1 leads to macrophage and neutrophil inflammasome activation, which in turn promotes atherosclerotic plaque development and notably the formation of neutrophil extracellular traps (NETs) in plaques. In addition, clonal hematopoiesis has emerged as an important CAD risk factor, likely involving macrophage inflammation and inflammasome activation. Further elucidation of the mechanisms linking plaque accumulation of cholesterol and oxidized lipids to myeloid cell inflammation may lead to the development of new therapeutics specifically targeting atherogenic inflammation, with likely benefit for CAD.

Tall AR 《-》

Myeloid-Specific Deletion of Peptidylarginine Deiminase 4 Mitigates Atherosclerosis.

Liu Y ，Carmona-Rivera C ，Moore E ，Seto NL ，Knight JS ，Pryor M ，Yang ZH ，Hemmers S ，Remaley AT ，Mowen KA ，Kaplan MJ ... -  《Frontiers in Immunology》

Hypercholesterolemia Impairs Clearance of Neutrophil Extracellular Traps and Promotes Inflammation and Atherosclerotic Plaque Progression.

Dhawan UK ，Bhattacharya P ，Narayanan S ，Manickam V ，Aggarwal A ，Subramanian M ... -  《-》

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

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.

Eghbalzadeh K ，Georgi L ，Louis T ，Zhao H ，Keser U ，Weber C ，Mollenhauer M ，Conforti A ，Wahlers T ，Paunel-Görgülü A ... -  《Frontiers in Immunology》