Novel reprogramming of neutrophils modulates inflammation resolution during atherosclerosis

TICAM2-related pathway mediates neutrophil exhaustion

Pathogenic inflammation and immune suppression are the cardinal features that underlie the pathogenesis of severe systemic inflammatory syndrome and sepsis. Neutrophil exhaustion may play a key role during the establishment of pathogenic inflammation and immune suppression through elevated expression of inflammatory adhesion molecules such as ICAM1 and CD11b as well as immune-suppressors such as PD-L1. However, the mechanism of neutrophil exhaustion is not well understood. We demonstrated that murine primary neutrophils cultured in vitro with the prolonged lipopolysaccharides (LPS) stimulation can effectively develop an exhaustive phenotype resembling human septic neutrophils with elevated expression of ICAM1, CD11b, PD-L1 as well as enhanced swarming and aggregation. Mechanistically, we observed that TICAM2 is involved in the generation of neutrophil exhaustion, as TICAM2 deficient neutrophils have the decreased expression of ICAM1, CD11b, PD-L1, and the reduced aggregation following the prolonged LPS challenge as compared to wild type (WT) neutrophils. LPS drives neutrophil exhaustion through TICAM2 mediated activation of Src family kinases (SFK) and STAT1, as the application of SFK inhibitor Dasatinib blocks neutrophil exhaustion triggered by the prolonged LPS challenge. Functionally, TICAM2 deficient mice were protected from developing severe systemic inflammation and multi-organ injury following the chemical-induced mucosal damage. Together, our data defined a key role of TICAM2 in facilitating neutrophil exhaustion and that targeting TICAM2 may be a potential approach to treating the severe systemic inflammation.

Innate Priming of Neutrophils Potentiates Systemic Multiorgan Injury

Excessive inflammatory reactions mediated by first-responder cells such as neutrophils contribute to the severity of multiorgan failure associated with systemic injury and infection. Systemic subclinical endotoxemia due to mucosal leakage may aggravate neutrophil activation and tissue injury. However, mechanisms responsible for neutrophil inflammatory polarization are not well understood. In this study, we demonstrate that subclinical low-dose endotoxemia can potently polarize neutrophils into an inflammatory state in vivo and in vitro, as reflected in elevated expression of adhesion molecules such as ICAM-1 and CD29, and reduced expression of suppressor molecule CD244. When subjected to a controlled administration of gut-damaging chemical dextran sulfate sodium, mice conditioned with subclinical dose LPS exhibit significantly elevated infiltration of neutrophils into organs such as liver, colon, and spleen, associated with severe multiorgan damage as measured by biochemical as well as histological assays. Subclinical dose LPS is sufficient to induce potent activation of SRC kinase as well as downstream activation of STAT1/STAT5 in neutrophils, contributing to the inflammatory neutrophil polarization. We also demonstrate that the administration of 4-phenylbutyric acid, an agent known to relieve cell stress and enhance peroxisome function, can reduce the activation of SRC kinase and enhance the expression of suppressor molecule CD244 in neutrophils. We show that i.v. injection of 4-phenylbutyric acid conditioned neutrophils can effectively reduce the severity of multiorgan damage in mice challenged with dextran sulfate sodium. Collectively, our data, to our knowledge, reveal novel inflammatory polarization of neutrophils by subclinical endotoxemia conducive for aggravated multiorgan damage as well as potential therapeutic intervention.

Neutrophil Phenotypes in Coronary Artery Disease

Clinical evidence indicates that innate immune cells may contribute to acute coronary syndrome (ACS). Our prospective study aimed at investigating the association of neutrophil phenotypes with ACS. 108 patients were categorized into chronic stable coronary artery disease (n = 37), unstable angina (UA) (n = 19), Non-ST-Elevation Myocardial Infarction (NSTEMI) (n = 25), and ST-Elevation Myocardial Infarction (STEMI) (n = 27). At the time of inclusion, blood neutrophil subpopulations were analysed by flow cytometry. Differential blood cell count and plasma levels of neutrophilic soluble markers were recorded at admission and, for half of patients, at six-month follow-up. STEMI and NSTEMI patients displayed higher neutrophil count and neutrophil-to-lymphocyte ratio than stable and UA patients (p < 0.0001), which normalized at six-month post-MI. Atypical low-density neutrophils were detected in the blood of the four patient groups. STEMI patients were characterized by elevated percentages of band cells compared to the other patients (p = 0.019). Multivariable logistic regression analysis revealed that plasma levels of total myeloperoxidase was associated with STEMI compared to stable (OR: 1.434; 95% CI: 1.119–1.837; P < 0.0001), UA (1.47; 1.146–1.886; p = 0.002), and NSTEMI (1.213; 1.1–1.134; p = 0.0001) patients, while increased neutrophil side scatter (SSC) signal intensity was associated with NSTEMI compared to stable patients (3.828; 1.033–14.184; p = 0.045). Hence, changes in neutrophil phenotype are concomitant to ACS.

Neutrophil Adaptations upon Recruitment to the Lung: New Concepts and Implications for Homeostasis and Disease

Neutrophils have a prominent role in all human immune responses against any type of pathogen or stimulus. The lungs are a major neutrophil reservoir and neutrophilic inflammation is a primary response to both infectious and non-infectious challenges. While neutrophils are well known for their essential role in clearance of bacteria, they are also equipped with specific mechanisms to counter viruses and fungi. When these defense mechanisms become aberrantly activated in the absence of infection, this commonly results in debilitating chronic lung inflammation. Clearance of bacteria by phagocytosis is the hallmark role of neutrophils and has been studied extensively. New studies on neutrophil biology have revealed that this leukocyte subset is highly adaptable and fulfills diverse roles. Of special interest is how these adaptations can impact the outcome of an immune response in the lungs due to their potent capacity for clearing infection and causing damage to host tissue. The adaptability of neutrophils and their propensity to influence the outcome of immune responses implicates them as a much-needed target of future immunomodulatory therapies. This review highlights the recent advances elucidating the mechanisms of neutrophilic inflammation, with a focus on the lung environment due to the immense and growing public health burden of chronic lung diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), and acute lung inflammatory diseases such as transfusion-related acute lung injury (TRALI).

New Approaches to Target Inflammation in Heart Failure: Harnessing Insights from Studies of Immune Cell Diversity

Despite mounting evidence implicating inflammation in cardiovascular diseases, attempts at clinical translation have shown mixed results. Recent preclinical studies have reenergized this field and provided new insights into how to favorably modulate cardiac macrophage function in the context of acute myocardial injury and chronic disease. In this review, we discuss the origins and roles of cardiac macrophage populations in the steady-state and diseased heart, focusing on the human heart and mouse models of ischemia, hypertensive heart disease, and aortic stenosis. Specific attention is given to delineating the roles of tissue-resident and recruited monocyte-derived macrophage subsets. We also highlight emerging concepts of monocyte plasticity and heterogeneity among monocyte-derived macrophages, describe possible mechanisms by which infiltrating monocytes acquire unique macrophage fates, and discuss the putative impact of these populations on cardiac remodeling. Finally, we discuss strategies to target inflammatory macrophage populations.

Nutraceutical Extract from Dulse (Palmaria palmata L.) Inhibits Primary Human Neutrophil Activation

Palmaria palmata L. (Palmariaceae), commonly known as “dulse”, is a red alga that grows on the northern coasts of the Atlantic and Pacific oceans, and is widely used as source of fiber and protein. Dulse is reported to contain anti-inflammatory and antioxidant compounds, albeit no study has investigated these effects in primary human neutrophils. Implication strategies to diminish neutrophil activation have the potential to prevent pathological states. We evaluated the ability of a phenolic dulse extract (DULEXT) to modulate the lipopolysaccharide (LPS)-mediated activation of primary human neutrophils. Intracellular reactive oxygen species (ROS) were measured by fluorescence analysis and nitric oxide (NO) production using the Griess reaction. Inflammatory enzymes and cytokines were detected by ELISA and RT-qPCR. The results show that DULEXT diminished the neutrophil activation related to the down-regulation of TLR4 mRNA expression, deceased gene expression and the LPS-induced release of the chemoattractant mediator IL-8 and the pro-inflammatory cytokines IL-1β, IL-6 and TNF-α. ROS, NO, and myeloperoxidase (MPO) were also depressed. The data indicated that DULEXT has the potential to disrupt the activation of human primary neutrophils and the derived inflammatory and prooxidant conditions, and suggest a new role for Palmaria palmata L. in the regulation of the pathogenesis of health disorders in which neutrophils play a key role, including atherosclerosis.

Phenylbutyrate facilitates homeostasis of non-resolving inflammatory macrophages

Non-resolving inflammatory monocytes/macrophages are critically involved in the pathogenesis of chronic inflammatory diseases. However, mechanisms of macrophage polarization are not well understood, thus hindering the development of effective strategies to promote inflammation resolution. In this study, we report that macrophages polarized by subclinical super-low dose LPS preferentially expressed pro-inflammatory mediators such as ccl2 (which encodes the protein monocyte chemo attractant protein-1) with reduced expression of anti-inflammatory/homeostatic mediators such as slc40a1 (which encodes the protein ferroportin-1). We observed significantly elevated levels of the autophagy-associated and pro-inflammatory protein p62 in polarized macrophages, closely correlated with the inflammatory activation of ccl2 gene expression. In contrast, we noted a significant increase of ubiquitinated/inactive nuclear-erythroid-related factor 2 (NRF2), consistent with reduced slc40a1 gene expression in polarized macrophages. Addition of the homeostatic restorative agent phenylbutyrate (4-PBA) effectively reduced cellular levels of p62 as well as ccl2 gene induction by super-low dose LPS. On the other hand, application of 4-PBA also blocked the accumulation of ubiquitinated NRF2 and restored anti-inflammatory slc40a1 gene expression in macrophages. Together, our study provides novel insights with regard to macrophage polarization and reveals 4-PBA as a promising molecule in restoring macrophage homeostasis.

Novel findings in neutrophil biology and their impact on cardiovascular disease

Neutrophils are the most abundant circulating leucocytes in healthy humans. These cells are central players during acute inflammatory responses, although a growing body of evidence supports a crucial role in chronic inflammation and chemokines and cytokines related to it as well. Thus, both humoral and cellular components are involved in the development of plaque formation and atherosclerosis. Accordingly, CANTOS trial using an interleukin-1 beta antibody confirmed that inflammatory cytokines contribute to the occurrence of myocardial infarction and cardiac death independent of changes in lipids. Recent data revealed that neutrophils are a heterogeneous population with different subsets and functional characteristics (i.e. CD177+ cells, OLFM4+ neutrophils, proangiogenic neutrophils, neutrophils undergoing reverse migration, and aged neutrophils). Importantly, neutrophils are able to synthesize de novo proteins. Neutrophil extracellular trap generation and NETosis have been considered as very important weapons in sterile inflammation. Neutrophil-derived microvesicles represent another mechanism by which neutrophils amplify inflammatory processes, being found at high levels both at the site of injury and in the bloodstream. Finally, neutrophil aging can influence their functions also in relation with host age. These recent acquisitions in the field of neutrophil biology might pave the way for new therapeutic targets to prevent or even treat patients experiencing cardiovascular (CV) diseases. Here, we discuss novel findings in neutrophil biology, their impact on CV and cerebrovascular diseases, and the potential implementation of these notions into daily clinical practice.

A transcriptomic model to predict increase in fibrous cap thickness in response to high-dose statin treatment: Validation by serial intracoronary OCT imaging

Background

Fibrous cap thickness (FCT), best measured by intravascular optical coherence tomography (OCT), is the most important determinant of plaque rupture in the coronary arteries. Statin treatment increases FCT and thus reduces the likelihood of acute coronary events. However, substantial statin-related FCT increase occurs in only a subset of patients. Currently, there are no methods to predict which patients will benefit. We use transcriptomic data from a clinical trial of rosuvastatin to predict if a patient's FCT will increase in response to statin therapy.

Methods

FCT was measured using OCT in 69 patients at (1) baseline and (2) after 8–10 weeks of 40  mg rosuvastatin. Peripheral blood mononuclear cells were assayed via microarray. We constructed machine learning models with baseline gene expression data to predict change in FCT. Finally, we ascertained the biological functions of the most predictive transcriptomic markers.

Findings

Machine learning models were able to predict FCT responders using baseline gene expression with high fidelity (Classification AUC = 0.969 and 0.972). The first model (elastic net) using 73 genes had an accuracy of 92.8%, sensitivity of 94.1%, and specificity of 91.4%. The second model (KTSP) using 18 genes has an accuracy of 95.7%, sensitivity of 94.3%, and specificity of 97.1%. We found 58 enriched gene ontology terms, including many involved with immune cell function and cholesterol biometabolism.

Interpretation

In this pilot study, transcriptomic models could predict if FCT increased following 8–10 weeks of rosuvastatin. These findings may have significance for therapy selection and could supplement invasive imaging modalities.