IL-33 attenuates cardiac remodeling following myocardial infarction via inhibition of the p38 MAPK and NF-κB pathways

Interleukin-33/sST2: Dynamic assessment in patients with acute coronary syndrome

PURPOSE

Interleukin (IL)-33 and its soluble receptor ST2 (sST2) play a crucial role in the immune response. sST2 has been approved by the Food and Drug Administration as a prognostic biomarker of mortality in chronic heart failure patients, however, the role of IL-33 and sST2 in atherosclerotic cardiovascular disease remains unclear. The aim of this study was to measure serum level of IL-33 and sST2 of patients at the onset of acute coronary syndrome (ACS) and 3 months after primary percutaneous revascularization.

PATIENTS AND METHODS

Forty patients were divided into ST segment elevation myocardial infarction (STEMI) group, non-ST segment elevation myocardial infarction (NSTEMI) and unstable angina (UA) group. IL-33 and sST2 level were measured with ELISA. Additionally, IL-33 expression in peripheral blood mononuclear cells (PBMCs), was evaluated.

RESULTS

All ACS patients had a significantly lower level of sST2 3 months after ACS as compared to the baseline (p ​< ​0.039). The STEMI patients had higher serum levels of IL-33 at the moment of ACS as compared to 3 months after the event, with an average decrease of 17.87 ​pg/ml (p ​< ​0.007). Conversely, sST2 serum levels were still high after 3 months following an ACS in STEMI patients. ROC curve demonstrated that increased IL-33 serum level could be STEMI predictor.

CONCLUSIONS

The assessment of the baseline and dynamics of changes in IL-33 and sST2 concentrations in patients with ACS may be important for the diagnostic process and may help in understanding of how the immune mechanisms work at the moment of an ACS event.

Modulation of IL-33/ST2 signaling as a potential new therapeutic target for cardiovascular diseases

IL-33 belongs to the IL-1 family of cytokines, which function as inducers of Th2 cytokine production by binding with ST2L and IL-1RAcP. This, in turn, activates various signaling pathways, including the mitogen-activated protein kinase (MAPK), the inhibitor of Kappa-B kinase (IKK) pathway, and the phospholipase D-sphingosine kinase pathway. IL-33 has demonstrated protective effects against various cardiovascular diseases (CVDs) by inducing Th2 cytokines and promoting alternative activating M2 polarization. However, the soluble decoy form of ST2 (sST2) mitigates the biological effects of IL-33, exacerbating CVDs. Furthermore, IL-33 also plays a significant role in the development of asthma, arthritis, atopic dermatitis, and anaphylaxis through the activation of Th2 cells and mast cells. In this review, we aim to demonstrate the protective role of IL-33 against CVDs from 2005 to the present and explore the potential of serum soluble ST2 (sST2) as a diagnostic biomarker for CVDs. Therefore, IL-33 holds promise as a potential therapeutic target for the treatment of CVDs.

POU Class 2 Associating Factor 1 Exerts a Protective Effect on the Respiratory Syncytial Virus-Induced Acute Bronchiolitis by the NF-κB Pathway

Background

Respiratory syncytial virus (RSV) is the main pathogen causing acute bronchiolitis, which is common in infants and young children. A previous study revealed the possible involvement of POU class 2 associating factor 1 (POU2AF1) in RSV-triggered acute bronchiolitis. We attempted to clarify the specific action mechanism of POU2AF1 underlying RSV-triggered inflammation.

Methods

RT-qPCR measured POU2AF1 levels in RSV-infected children, mice, and airway epithelial cell lines (HBECs). HE staining showed histopathological features in the lung tissue of RSV-infected mice. ELISA examined the contents of proinflammatory cytokines in RSV-infected mice. Western blotting evaluated the protein abundance of proinflammatory cytokines in RSV-infected HBECs and assessed NF-κB pathway-associated protein expression in RSV-infected mice and RSV-treated HBECs.

Results

POU2AF1 presented depletion in RSV-infected children, mice, and HBECs. RSV-infected triggered lung injury and inflammatory cell infiltration in the mouse lung tissue, while POU2AF1 overexpression rescued these changes. RSV-infected induced inflammatory impairment in HBECs, whereas POU2AF1 reversed this effect. POU2AF1 suppressed the upregulated NF-κB pathway-associated protein expression in mice and HBECs under RSV infection.

Conclusion

POU2AF1 exerts a protective impact on RSV-induced acute bronchiolitis in vitro and in vivo through the NF-κB pathway. Our research may provide a novel direction for better therapy of RSV-triggered acute bronchiolitis.

Interleukin-33 Mediates Cardiomyopathy After Acute Kidney Injury by Signaling to Cardiomyocytes

BACKGROUND

Acute kidney injury (AKI) is a short-term life-threatening condition that, if survived, can lead to renal insufficiency and development of chronic kidney disease. The pathogenesis of AKI and chronic kidney disease involves direct effects on the heart and the development of hypertrophy and cardiomyopathy.

METHODS

We used mouse models of ischemia/reperfusion AKI and unilateral ureteral obstruction to investigate the role of IL-33 (interleukin-33) and its receptor-encoding gene Il1rl1 (also called ST2L [suppression of tumorigenicity 2]) in cardiac remodeling after AKI. Mice with cell type-specific genetic disruption of the IL-33/ST2L axis were used, and IL-33 monoclonal antibody, adeno-associated virus encoding IL-33 or ST2L, and recombinant IL-33, as well.

RESULTS

Mice deficient in Il33 were refractory to cardiomyopathy associated with 2 models of kidney injury. Treatment of mice with monoclonal IL-33 antibody also protected the heart after AKI. Moreover, overexpression of IL-33 or injection of recombinant IL-33 induced cardiac hypertrophy or cardiomyopathy, but not in mice lacking Il1rl1. AKI-induced cardiomyopathy was also reduced in mice with cardiac myocyte-specific deletion of Il1rl1 but not in endothelial cell- or fibroblast-specific deletion of Il1rl1. Last, overexpression of the ST2L receptor in cardiac myocytes recapitulated induction of cardiac hypertrophy.

CONCLUSIONS

These results indicate that IL-33 released from the kidney during AKI underlies cardiorenal syndrome by directly signaling to cardiac myocytes, suggesting that antagonism of IL-33/ST2 axis would be cardioprotective in patients with kidney disease.

IL-33/ST2 immunobiology in coronary artery disease: A systematic review and meta-analysis

The IL-33/ST2 axis is reported to be controversially associated with coronary artery disease (CAD). A systematic review of the association between the IL-33/ST2 axis and CAD revealed that IL-33/ST2 plays a protective role in CAD and serum sST2 and IL-33 levels are increased in patients with cardiovascular disease. Therefore, the association of IL-33/ST2 single nucleotide polymorphisms (SNPs) with CAD prevalence, prognosis, and risk factors was assessed by performing a meta-analysis. Through a literature search of relevant articles in various databases using the relevant keywords, seven studies were included in the analysis. The meta-analysis showed that the IL-33/ST2 axis was associated with increased CAD risk [pooled odds ratio (OR) = 1.17, 95% confidence interval (CI): 1.13–1.20]. Gene subgroup analysis showed a close association of IL1RL1 (OR = 1.25, 95% CI: 1.20–1.30; I² = 85.9%; p = 0.000) and IL1RAcP (OR = 1.42, 95% CI: 1.26–1.60; I² = 27.1%; p = 0.203) with increased CAD risk. However, the association for the IL-33 gene was not statistically significant. SNPs rs7044343 (T), rs10435816 (G), rs11792633 (C) in IL-33 gene were associated with a protective effect in CAD. However, rs7025417 (T) in IL-33, rs11685424 (G) in IL1RL1, rs950880 (A) in sST2, and rs4624606 (A) in IL1RAcP were related to increased CAD risk. Overall, polymorphisms in IL-33/ST2 axis components were associated with increased CAD risk. These results may help identify key features of IL-33/ST2 immunobiology in CAD along with potential treatment strategies to lower disease burden.

Protective effect of nicorandil against myocardial ischemia/reperfusion injury mediated via IL33/ST2 signaling pathway

Myocardial ischemia-reperfusion injury (MI/RI), a complication of myocardial injury, is associated with high rates of mortality and disability. We aimed to explore the effect of nicorandil™ against MI/RI and investigated the underlying molecular mechanisms. In this in vitro study, hypoxia/reoxygenation (H/R) processing of H9c2 cells significantly suppressed the expressions of IL33 and ST2, reduced cell viability, increased production of reactive oxygen species, downregulated protein expression of Bcl-2, upregulated protein expressions of Bax, cleaved caspase3, and cleaved PARP, increased intracellular calcium overload, and induced cell apoptosis. Nicorandil processing reduced H/R-induced H9c2 cell damage. Nicorandil processing ameliorated the H/R-induced inhibition of the IL33 and ST2 expression in H9c2 cells. 5-Hydroxydecanoate blocked the effects of nicorandil on H9c2 cell viability, ROS production, and apoptosis and inhibited both IL33 and ST2. Similarly, the protective effect of nicorandil was restrained after inhibition of the IL33/ST2 pathway. Our findings suggest that the protective effect of nicorandil against H/R-induced H9c2 cell apoptosis was mediated through IL33/ST2 signaling pathway.

Prognostic Value of β1 Adrenergic Receptor Autoantibody and Soluble Suppression of Tumorigenicity-2 in Patients With Acutely Decompensated Heart Failure

Background

Both β1 adrenergic receptor autoantibody (β1-AA) and soluble suppression of tumorigenicity-2 (sST2) take a role in the pathological remodeling of heart failure. However, limited studies investigated the correlation between the expression of β1-AA and sST2 in patients with acutely decompensated heart failure (ADHF).

Objective

To explore the correlation between β1-AA and sST2, and evaluate their prognostic value in patients with ADHF.

Methods

Patients who were admitted for ADHF were included. The N-terminal pro-brain natriuretic peptide (NT-proBNP), sST2, and β1-AA in blood samples were tested at hospital admission and then followed up for assessing the outcomes. Pearson correlation analysis was used to explore the correlation between β1-AA and sST2. The effects of β1-AA, sST2, or the combination of them on the all-cause mortality of patients with ADHF were assessed by Multivariate Cox regression analysis.

Results

There were 96 patients with ADHF and 96 control populations enrolled. The β1-AA was significantly higher in ADHF than in the control group (0.321 ± 0.06 vs. 0.229 ± 0.04, P = 0.000). Pearson correlation analysis showed that β1-AA was positively correlated with sST2 (r = 0.593), NT-proBNP (r = 0.557), Procalcitonin (r = 0.176), and left ventricular end-diastolic diameter (r = 0.315), but negatively correlated with triglycerides (r = −0.323), and left ventricular ejection fraction (r = −0.430) (all P < 0.05) in ADHF. Patients with ADHF, complicated with both high β1-AA and sST2, showed the highest all-cause mortality during an average of 25.5 months of follow-up. Multivariate Cox regression showed the combination of both high β1-AA and sST2 independently correlated with the all-cause mortality after adjustment for other risk factors (hazard ratio 3.348, 95% CI 1.440 to 7.784, P = 0.005). After adding with β1-AA and sST2, the area under the curves for the prognostic all-cause mortality could increase from 0.642 to 0.748 (P = 0.011).

Conclusion

The β1-AA is positively correlated with sST2 in patients with ADHF. Elevated plasma β1-AA and sST2 level in patients with ADHF are associated with poorer prognoses.

Curcumin, novel application in reversing myocardial fibrosis in the treatment for atrial fibrillation from the perspective of transcriptomics in rat model

In order to explore the possible mechanism of curcumin in the treatment of AF, we focused on the myocardial fibrosis in the pathogenesis of atrial fibrillation to explore whether curcumin could play a role in the treatment of AF by reducing myocardial fibrosis.Rats were given daily gavage of saline (control and AF groups) or curcumin (4 mL/kg, concentration: 50 mg/mL, curcumin groups) during days 4-28. The rat model of AF was induced by Ach - CaCl₂, and evaluate the therapeutic effect of curcumin on the duration of AF rhythm, the degree of myocardial fibrosis and the secretion of inflammatory factors in serum. RNA-seq to explore the possible mechanism of curcumin alleviating myocardial fibrosis of AF. curcumin significantly inhibits the duration of AF and reduces the degree of left atrial fibrosis. ELISA results showed curcumin could significantly reduce the secretion of IL-17A, IL-1β, IL -6 and TGF-β1. Bioinformatics analyses revealed that the IL-17 signaling pathway are involved in the therapeutic mechanism of curcumin. Furthermore, The genes encoding Col1a1, Fasn, Pck1, Bmp10, IL33 and Figf were pivotal and possible key genes for the therapeutic mechanisms of curcumin.Curcumin can reduce the degree of left atrial fibrosis of AF and the secretion of inflammatory factors. The therapeutic effect of curcumin on AF was attributed to its effect on the IL-17 signaling pathway. Besides, COL1A1, FASN, PCK1, BMP10, IL33 and FIGF were the pivotal genes associated with mechanisms of action of curcumin on AF.

Inhibition of NF-κB/IL-33/ST2 Axis Ameliorates Acute Bronchiolitis Induced by Respiratory Syncytial Virus

Background/Aim

Bronchiolitis is a common acute lower respiratory tract infectious disease in infants. Respiratory syncytial virus (RSV) infection is one of the main causes. Bronchiolitis can lead to a significant increase in the incidence of asthma in young children, but the mechanism of bronchiolitis transforming into asthma is still unclear. The study was aimed at investigating the role of NF-κB/IL-33/ST2 axis on RSV-induced acute bronchiolitis.

Methods

A total of 40 infants diagnosed with acute bronchiolitis infected by RSV, and 20 normal infants were included in this study. BALB/c mice (6-8 weeks old, 20 ± 1.1 g) were used as study models. Enzyme-linked immunosorbent assay (ELISA), quantitative real time PCR, western blot analysis, immunohistochemical staining, and flow cytometry analysis were performed to examine relevant indicators.

Results

IL-33 level was significantly elevated, and Th1/Th2 ratio is imbalance after in infants with acute bronchiolitis. In vivo study, we found that NF-κB/IL-33/ST2 axis is mediated the Th2 cytokine levels and BAL cell number induced by RSV. Acute bronchiolitis induced by RSV in a mouse model is attenuated after inhibition of NF-κB/IL-33/ST2 pathway. Moreover, we also confirmed that macrophages are important sources of IL-33 and are regulated by NF-κB pathway in RSV-induced mice.

Conclusion

We confirmed that inhibition of NF-κB/IL-33/ST2 axis could attenuate acute bronchiolitis by RSV infected. Our findings not only demonstrate the potential role of IL-33 antibody in attenuating RSV-induced lung damage but also provide a new insight into better prevention of RSV-induced asthma by mediating NF-κB/IL-33/ST2 axis.

Downregulation of IFIT3 relieves the inflammatory response and myocardial fibrosis of mice with myocardial infarction and improves their cardiac function

Myocardial infarction (MI) is a common cardiovascular disease with high morbidity and mortality. In this study, we explored the role of interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) in MI. MI was induced by ligation of the left anterior descending coronary artery. Lentivirus-mediated RNA interference of IFIT3 expression was performed by tail vein injection 72 h before MI modeling. Cardiac injury indexes and inflammatory response were examined 3 days after MI. Cardiac function indexes, infarct size, and cardiac fibrosis were assessed 4 weeks after MI. IFIT3 expression was upregulated in myocardial tissues at both 3 days and 4 weeks after MI. Knockdown of IFIT3 significantly relieved the myocardial injury, as evidenced by the decrease in serum levels of cTnI and CK-MB. In addition, IFIT3 knockdown significantly reduced the number of CD68⁺ macrophages and the levels of interleukin-1β, interleukin-6, and tumor necrosis factor-α, indicating that the inflammatory response was relieved. Moreover, IFIT3 silencing also significantly improved cardiac function and reduced infarct size, myocardial fibrosis, and collagen content in mice with MI. Mechanically, the present study showed that the activation of the mitogen-activated protein kinase (MAPK) pathway was observed in myocardial tissues of MI mice, which was blocked by IFIT3 knockdown, as indicated by the decreased phosphorylation of JNK, p-38, and ERK. Collectively, our results revealed the role of IFIT3 in the inflammatory response and myocardial fibrosis after MI, indicating that IFIT3 might be a potential target for MI treatment.

Group 2 innate lymphoid cells contribute to IL-33-mediated alleviation of cardiac fibrosis

Rationale: The major cause of heart failure is myocardium death consequent to detrimental cardiac remodeling and fibrosis following myocardial infarction. The cardiac protective cytokine interleukin (IL)-33, which signals by ST2 receptor binding, is associated with group 2 innate lymphoid cell (ILC2) activation and regulates tissue homeostasis and repair following tissue injury in various tissues. However, the distribution and role of IL-33-responsive ILC2s in cardiac fibrosis remain unclear. In this study, we elucidated the roles of IL-33-responsive cardiac-resident ILC2s and IL-33-mediated immunomodulatory functions in cardiac fibrosis.

Methods: We examined the distribution of cardiac ILC2s by using flow cytometry. The roles of IL-33-mediated ILC2 expansion in cardiac fibrosis was evaluated in the mouse model of catecholamine-induced cardiac fibrosis. ILC-deficient Rag2^‒/‒IL2Rγc^‒/‒ mice were implemented to determine the contribution of endogenous ILC in the progression of cardiac fibrosis. Histopathological assessments, speckle tracking echocardiography, and transcriptome profile analysis were performed to determine the effects of IL-33-mediated cardiac protective functions.

Results: We identified the resident cardiac ILC2s, which share similar cell surface marker and transcriptional factor expression characteristics as peripheral blood and lung tissue ILC2s. IL-33 treatment induced ILC2 expansion via ST2. In vivo, ILC-deficient Rag2^‒/‒IL2Rγc^‒/‒ mice developed exacerbated cardiac fibrosis following catecholamine-induced stress cardiac injury. IL-33 treatment expanded cardiac ILC2s and revealed protective effects against cardiac tissue damage with reduced cardiomyocyte death, immune cell infiltration, tissue fibrosis, and improved myocardial function. Transcriptome analysis revealed that IL-33 attenuated extracellular matrix synthesis- and fibroblast activation-associated gene expressions. IL13-knockout or epidermal growth factor receptor (EGFR) inhibition abolished IL-33-mediated cardiac protective function, confirming IL-13 and EGFR signaling as crucial for IL-33-mediated cardioprotective responses. Moreover, ILC2-produced BMP-7 served as a novel anti-fibrotic factor to inhibit TGF-β1-induced cardiac fibroblast activation.

Conclusion: Our findings indicate the presence of IL-33-responsive ILC2s in cardiac tissue and that IL-33-mediated ILC2 expansion affords optimal cardioprotective function via ILC2-derived factors. IL-33-mediated immunomodulation is thus a promising strategy to promote tissue repair and alleviate cardiac fibrosis following acute cardiac injury.

IL-33 induces type-2-cytokine phenotype but exacerbates cardiac remodeling post-myocardial infarction with eosinophil recruitment, worsened systolic dysfunction, and ventricular wall rupture

Myocardial infarction (MI) is the leading cause of mortality worldwide. Interleukin (IL)-33 (IL-33) is a cytokine present in most cardiac cells and is secreted on necrosis where it acts as a functional ligand for the ST2 receptor. Although IL-33/ST2 axis is protective against various forms of cardiovascular diseases, some studies suggest potential detrimental roles for IL-33 signaling. The aim of the present study was to examine the effect of IL-33 administration on cardiac function post-MI in mice. MI was induced by coronary artery ligation. Mice were treated with IL-33 (1 μg/day) or vehicle for 4 and 7 days. Functional and molecular changes of the left ventricle (LV) were assessed. Single cell suspensions were obtained from bone marrow, heart, spleen, and peripheral blood to assess the immune cells using flow cytometry at 1, 3, and 7 days post-MI in IL-33 or vehicle-treated animals. The results of the present study suggest that IL-33 is effective in activating a type 2 cytokine milieu in the damaged heart, consistent with reduced early inflammatory and pro-fibrotic response. However, IL-33 administration was associated with worsened cardiac function and adverse cardiac remodeling in the MI mouse model. IL-33 administration increased infarct size, LV hypertrophy, cardiomyocyte death, and overall mortality rate due to cardiac rupture. Moreover, IL-33-treated MI mice displayed a significant myocardial eosinophil infiltration at 7 days post-MI when compared with vehicle-treated MI mice. The present study reveals that although IL-33 administration is associated with a reparative phenotype following MI, it worsens cardiac remodeling and promotes heart failure.

Innate Immunity Effector Cells as Inflammatory Drivers of Cardiac Fibrosis

Despite relevant advances made in therapies for cardiovascular diseases (CVDs), they still represent the first cause of death worldwide. Cardiac fibrosis and excessive extracellular matrix (ECM) remodeling are common end-organ features in diseased hearts, leading to tissue stiffness, impaired myocardial functional, and progression to heart failure. Although fibrosis has been largely recognized to accompany and complicate various CVDs, events and mechanisms driving and governing fibrosis are still not entirely elucidated, and clinical interventions targeting cardiac fibrosis are not yet available. Immune cell types, both from innate and adaptive immunity, are involved not just in the classical response to pathogens, but they take an active part in “sterile” inflammation, in response to ischemia and other forms of injury. In this context, different cell types infiltrate the injured heart and release distinct pro-inflammatory cytokines that initiate the fibrotic response by triggering myofibroblast activation. The complex interplay between immune cells, fibroblasts, and other non-immune/host-derived cells is now considered as the major driving force of cardiac fibrosis. Here, we review and discuss the contribution of inflammatory cells of innate immunity, including neutrophils, macrophages, natural killer cells, eosinophils and mast cells, in modulating the myocardial microenvironment, by orchestrating the fibrogenic process in response to tissue injury. A better understanding of the time frame, sequences of events during immune cells infiltration, and their action in the injured inflammatory heart environment, may provide a rationale to design new and more efficacious therapeutic interventions to reduce cardiac fibrosis.

A Unique Population of Regulatory T Cells in Heart Potentiates Cardiac Protection From Myocardial Infarction

BACKGROUND

Regulatory T cells (Tregs), traditionally recognized as potent suppressors of immune response, are increasingly attracting attention because of a second major function: residing in parenchymal tissues and maintaining local homeostasis. However, the existence, unique phenotype, and function of so-called tissue Tregs in the heart remain unclear.

METHODS

In mouse models of myocardial infarction (MI), myocardial ischemia/reperfusion injury, or cardiac cryoinjury, the dynamic accumulation of Tregs in the injured myocardium was monitored. The bulk RNA sequencing was performed to analyze the transcriptomic characteristics of Tregs from the injured myocardium after MI or ischemia/reperfusion injury. Photoconversion, parabiosis, single-cell T-cell receptor sequencing, and adoptive transfer were applied to determine the source of heart Tregs. The involvement of the interleukin-33/suppression of tumorigenicity 2 axis and Sparc (secreted acidic cysteine-rich glycoprotein), a molecule upregulated in heart Tregs, was further evaluated in functional assays.

RESULTS

We showed that Tregs were highly enriched in the myocardium of MI, ischemia/reperfusion injury, and cryoinjury mice. Transcriptomic data revealed that Tregs isolated from the injured hearts had plenty of differentially expressed transcripts in comparison with their lymphoid counterparts, including heart-draining lymphoid nodes, with a phenotype of promoting infarct repair, indicating a unique characteristic. The heart Tregs were accumulated mainly because of recruitment from the circulating Treg pool, whereas local proliferation also contributed to their expansion. Moreover, a remarkable case of repeatedly detected T-cell receptor of heart Tregs, more than that of spleen Tregs, suggests a model of clonal expansion. Besides, Helios^highNrp-1^high phenotype proved the mainly thymic origin of heart Tregs, with a small contribution of phenotypic conversion of conventional CD4⁺ T cells, proved by the analysis of T-cell receptor repertoires and conventional CD4⁺ T cells adoptive transfer experiments. The interleukin-33/suppression of tumorigenicity 2 axis was essential for sustaining heart Treg populations. Last, we demonstrated that Sparc, which was highly expressed by heart Tregs, acted as a critical factor to protect the heart against MI by increasing collagen content and boosting maturation in the infarct zone.

CONCLUSIONS

We identified and characterized a phenotypically and functionally unique population of heart Tregs that may lay the foundation to harness Tregs for cardioprotection in MI and other cardiac diseases.

Role of long noncoding RNA MEG3/miR-378/GRB2 axis in neuronal autophagy and neurological functional impairment in ischemic stroke

Autophagy has been shown to maintain neural system homeostasis during stroke. However, the molecular mechanisms underlying neuronal autophagy in ischemic stroke remain poorly understood. This study aims to investigate the regulatory mechanisms of the pathway consisting of MEG3 (maternally expressed gene 3), microRNA-378 (miR-378), and GRB2 (growth factor receptor-bound protein 2) in neuronal autophagy and neurological functional impairment in ischemic stroke. A mouse model of the middle cerebral artery occluded-induced ischemic stroke and an in vitro model of oxygen-glucose deprivation-induced neuronal injury were developed. To understand the role of the MEG3/miR-378/GRB2 axis in the neuronal regulation, the expression of proteins associated with autophagy in neurons was measured by Western blotting analysis, and neuron death was evaluated using a lactate dehydrogenase leakage rate test. First, it was found that the GRB2 gene, up-regulated in middle cerebral artery occluded-operated mice and oxygen-glucose deprivation-exposed neurons, was a target gene of miR-378. Next, miR-378 inhibited neuronal loss and neurological functional impairment in mice, as well as neuronal autophagy and neuronal death by silencing of GRB2. Confirmatory in vitro experiments showed that MEG3 could specifically bind to miR-378 and subsequently up-regulate the expression of GRB2, which in turn suppressed the activation of Akt/mTOR pathway. Taken together, these findings suggested that miR-378 might protect against neuronal autophagy and neurological functional impairment and proposed that a MEG3/miR-378/GRB2 regulatory axis contributed to better understanding of the pathophysiology of ischemic stroke.

Changes in the number of mast cells, expression of fibroblast growth factor-2 and extent of interstitial fibrosis in established and advanced hypertensive heart disease

INTRODUCTION

An increasing number of studies have shed light on the role of cardiac mast cells in the pathogenesis of hypertension-induced myocardial remodeling. Mast cells promote fibroblast activation, myofibroblast differentiation and subsequent collagen accumulation through the action of tryptase, chymase, histamine and fibroblast growth factor-2. The aim of the present study was to report on the changes in the number of mast cells as evaluated through toluidine blue, tryptase and c-kit staining, to assess the extent of interstitial fibrosis and correlate it with the changes in the number of mast cells and to analyze the immunohistochemical expression of fibroblast growth factor-2 in two groups of spontaneously hypertensive rats indicative of established and advanced hypertensive heart disease. A novel aspect of our work was the analysis of all parameters in the right ventricle.

MATERIAL AND METHODS

For the present study, we used 6- and 12-month-old spontaneously hypertensive rats. A light microscopic study was conducted on sections stained with hematoxylin and eosin and toluidine blue. For the immunohistochemical study we used monoclonal antibodies against mast cell tryptase and fibroblast growth factor-2 and a polyclonal antibody against c-kit. The expression of fibroblast growth factor-2 was assessed semi-quantitatively through ImageJ. The number of mast cells was evaluated on toluidine blue-, tryptase- and c-kit-stained sections and a comparative statistical analysis with the Mann-Whitney test was conducted between the two age groups. A separate statistical analysis between results obtained through immunostaining for tryptase and for c-kit was conducted in each age group with the Wilcoxon signed-rank test. The extent of fibrosis was assessed quantitatively on slides stained with Mallory's trichrome stain as a percentage of the whole tissue and compared between the two age groups. Spearman's correlation was used to test whether a correlation exists between the number of mast cells and the percentage of interstitial fibrosis.

RESULTS

Mast cells with typical cytoplasmic granules were visualized in the interstitial tissue and in the perivascular zone in both age groups. In both ventricles, their number increased significantly in 12-month-old animals as evaluated through all three staining methods. Moreover, immunostaining for tryptase and for c-kit yielded comparable results. The immunoreactivity of fibroblast growth factor-2 increased in both ventricles in older animals. Expression of this protein was particularly intensive in the cytoplasm of connective tissue cells with the characteristic features of mast cells mainly found in the areas of fibrotic alterations in 12-month-old spontaneously hypertensive rats. In both ventricles, interstitial fibrosis was more extensive throughout the myocardium of older animals and was positively correlated with the changes in the number of mast cells in both age groups.

CONCLUSION

The present study reported for the first time that the increase in the number of mast cells, observed as hypertension-induced myocardial changes progress, is statistically significant and confirmed that this process takes place in both ventricles. This increase is accompanied by a higher expression of fibroblast growth factor-2 and is more strongly correlated with the more pronounced interstitial fibrosis in older animals, further supporting the role of mast cells in the structural changes taking place in the myocardium in response to systemic hypertension.

Interleukin-1 and the Inflammasome as Therapeutic Targets in Cardiovascular Disease

The intracellular sensing protein termed NLRP3 (for NACHT, LRR, and PYD domains-containing protein 3) forms a macromolecular structure called the NLRP3 inflammasome. The NLRP3 inflammasome plays a major role in inflammation, particularly in the production of IL (interleukin)-1β. IL-1β is the most studied of the IL-1 family of cytokines, including 11 members, among which are IL-1α and IL-18. Here, we summarize preclinical and clinical findings supporting the key pathogenetic role of the NLRP3 inflammasome and IL-1 cytokines in the formation, progression, and complications of atherosclerosis, in ischemic (acute myocardial infarction), and nonischemic injury to the myocardium (myocarditis) and the progression to heart failure. We also review the clinically available IL-1 inhibitors, although not currently approved for cardiovascular indications, and discuss other IL-1 inhibitors, not currently approved, as well as oral NLRP3 inflammasome inhibitors currently in clinical development. Canakinumab, IL-1β antibody, prevented the recurrence of ischemic events in patients with prior acute myocardial infarction in a large phase III clinical trial, including 10 061 patients world-wide. Phase II clinical trials show promising data with anakinra, recombinant IL-1 receptor antagonist, in patients with ST-segment-elevation acute myocardial infarction or heart failure with reduced ejection fraction. Anakinra also improved outcomes in patients with pericarditis, and it is now considered standard of care as second-line treatment for patients with recurrent/refractory pericarditis. Rilonacept, a soluble IL-1 receptor chimeric fusion protein neutralizing IL-1α and IL-1β, has also shown promising results in a phase II study in recurrent/refractory pericarditis. In conclusion, there is overwhelming evidence linking the NLRP3 inflammasome and the IL-1 cytokines with the pathogenesis of cardiovascular diseases. The future will likely include targeted inhibitors to block the IL-1 isoforms, and possibly oral NLRP3 inflammasome inhibitors, across a wide spectrum of cardiovascular diseases.

Novel Mechanisms of Exercise-Induced Cardioprotective Factors in Myocardial Infarction

Exercise training has been reported to ameliorate heart dysfunction in both humans and animals after myocardial infarction (MI). Exercise-induced cardioprotective factors have been implicated in mediating cardiac repair under pathological conditions. These protective factors secreted by or enriched in the heart could exert cardioprotective functions in an autocrine or paracrine manner. Extracellular vesicles, especially exosomes, contain key molecules and play an essential role in cell-to-cell communication via delivery of various factors, which may be a novel target to study the mechanism of exercise-induced benefits, besides traditional signaling pathways. This review is designed to demonstrate the function and underlying protective mechanism of exercise-induced cardioprotective factors in MI, with an aim to offer more potential therapeutic targets for MI.

Metformin Can Alleviate the Symptom of Patient with Diabetic Nephropathy Through Reducing the Serum Level of Hcy and IL-33

Background

Interleukin-33 (IL-33) and homocysteine (Hcy) were found to be up-regulated in patients with diabetic nephropathy (DN), and the present study aimed to investigate whether metformin (MT) can influence the serum levels of IL-33 and Hcy in patients with DN.

Methods

Sixty patients with type 2 diabetes mellitus (DM) were divided into DM group (albumin: Alb <20 mg/L), DN group (Alb >20mg/L), and DN+ MT treatment group, with 20 cases in each group. Patients in each group were treated with insulin for 3 months, and patients in DN+MT group was treated with insulin+MT for 3 months. The serum levels of IL-33, urinary microalbumin excretion rate (UAE), body mass index (BMI), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), creatinine (Cr), cystatin C (CysC) and Hcy were measured before and after medication. Twenty normal subjects were involved as control.

Results

BMI, Hcy and TC were reduced and HDL-C was increased of patients had been treated with metformin and insulin. UAE, Cr, Ccr and CysC had no differences before and after treatment. The serum level of IL-33 significantly up-regulated in patients with DN, and MT treatment significantly decreased the serum level of IL-33 in patients with DN.

Conclusion

Metformin could alleviate the symptom of patient with DN through decreasing the serum level of IL-33 and Hcy.

The interleukin-33-mediated inhibition of expression of two key genes implicated in atherosclerosis in human macrophages requires MAP kinase, phosphoinositide 3-kinase and nuclear factor-κB signaling pathways

Atherosclerosis, a chronic inflammatory disorder of the walls of arteries, causes more deaths worldwide than any other disease. Cytokines, which are present at high levels in atherosclerotic plaques, play important roles in regulating the initiation and the progression of the disease. Previous studies using animal and cell culture model systems revealed protective, anti-atherogenic effects of the cytokine interleukin-33 (IL-33). The action of this cytokine involves both the induction and suppression of expression of many genes. Unfortunately, the signaling pathways that are responsible for the inhibition of gene expression by this cytokine are poorly understood. Further studies are required given the important roles of genes whose expression is inhibited by IL-33 in key cellular processes associated with atherosclerosis such as monocyte recruitment, foam cell formation and lipoprotein metabolism. We have investigated here the roles of various known IL-33 activated signaling pathways in such inhibitory actions using RNA interference-mediated knockdown assays and monocyte chemotactic protein-1 and intercellular adhesion molecule-1 as model genes. Key roles were identified for extracellular signal-regulated kinase-1/2, p38α kinase, c-Jun N-terminal kinase-1/2, phosphoinositide 3-kinase-γ, and p50 and p65 nuclear factor-κB in such inhibitory action of IL-33. These studies provide new insights on the signaling pathways through which IL-33 inhibits the macrophage expression of key atherosclerosis-associated genes.

Inflammation in myocardial injury: mesenchymal stem cells as potential immunomodulators

Ischemic heart disease is a growing worldwide epidemic. Improvements in medical and surgical therapies have reduced early mortality after acute myocardial infarction and increased the number of patients living with chronic heart failure. The irreversible loss of functional cardiomyocytes puts these patients at significant risk of ongoing morbidity and mortality after their index event. Recent evidence suggests that inflammation is a key mediator of postinfarction adverse remodeling in the heart. In this review, we discuss the cardioprotective and deleterious effects of inflammation and its mediators during acute myocardial infarction. We also explore the role of mesenchymal stem cell therapy to limit secondary injury and promote myocardial healing after myocardial infarction.

Yin-Yang 1 transcription factor modulates ST2 expression during adverse cardiac remodeling post-myocardial infarction

BACKGROUND

The cardioprotective effects of metformin remain poorly defined. Interleukin (IL)-33/ST2L signaling is a novel cardioprotective pathway, which is antagonized by the soluble isoform sST2. No data exist about the regulation of ST2 expression. This study aimed to evaluate the pathophysiological implication of Yin-Yang 1 (Yy1) transcription factor in cardiac remodeling and the expression of the soluble ST2 isoform.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in Wistar rats randomly receiving metformin or saline solution by permanent ligation of the left anterior coronary artery. In addition, a model of cardiomyocyte "biochemical strain" was used. Metformin administration improved post-MI cardiac remodeling, an effect that was associated with increased IL-33 and reduced sST2 levels in the myocardium. The anti-remodeling effects of metformin were also associated with a decrease in the transcription factor Yy1 intranuclear level and lower levels of phosphorylated HDAC4 within the cytoplasmic space. These effects were also observed in a cardiomyocyte biochemical strain model, where Yy1 silencing or HDAC4 inhibition blocked sST2 production in cardiomyocytes. Metformin blocked the HDAC4 phosphorylation induced by MI, preventing its export from the nucleus to the cytosol. The presence of dephosphorylated HDAC4 in the nucleus acted as a co-repressor of Yy1, repressing sST2 expression.

CONCLUSION

The transcription factor Yy1 regulates sST2 expression, and repression of Yy1 by metformin results in lower levels of sST2 that are associated with favorable myocardial remodeling. The manipulation of YY1 or its co-repressor HDAC4 emerge as new targets to modulate ST2/IL33 signaling and prevent adverse cardiac remodeling.

Mast Cells in Cardiac Fibrosis: New Insights Suggest Opportunities for Intervention

Mast cells (MC) are innate immune cells present in virtually all body tissues with key roles in allergic disease and host defense. MCs recognize damage-associated molecular patterns (DAMPs) through expression of multiple receptors including Toll-like receptors and the IL-33 receptor ST2. MCs can be activated to degranulate and release pre-formed mediators, to synthesize and secrete cytokines and chemokines without degranulation, and/or to produce lipid mediators. MC numbers are generally increased at sites of fibrosis. They are potent, resident, effector cells producing mediators that regulate the fibrotic process. The nature of the secretory products produced by MCs depend on micro-environmental signals and can be both pro- and anti-fibrotic. MCs have been repeatedly implicated in the pathogenesis of cardiac fibrosis and in angiogenic responses in hypoxic tissues, but these findings are controversial. Several rodent studies have indicated a protective role for MCs. MC-deficient mice have been reported to have poorer outcomes after coronary artery ligation and increased cardiac function upon MC reconstitution. In contrast, MCs have also been implicated as key drivers of fibrosis. MC stabilization during a hypertensive rat model and an atrial fibrillation mouse model rescued associated fibrosis. Discrepancies in the literature could be related to problems with mouse models of MC deficiency. To further complicate the issue, mice generally have a much lower density of MCs in their cardiac tissue than humans, and as such comparing MC deficient and MC containing mouse models is not necessarily reflective of the role of MCs in human disease. In this review, we will evaluate the literature regarding the role of MCs in cardiac fibrosis with an emphasis on what is known about MC biology, in this context. MCs have been well-studied in allergic disease and multiple pharmacological tools are available to regulate their function. We will identify potential opportunities to manipulate human MC function and the impact of their mediators with a view to preventing or reducing harmful fibrosis. Important therapeutic opportunities could arise from increased understanding of the impact of such potent, resident immune cells, with the ability to profoundly alter long term fibrotic processes.

Regulation of Type 2 Immunity in Myocardial Infarction

Type 2 immunity participates in the pathogeneses of helminth infection and allergic diseases. Emerging evidence indicates that the components of type 2 immunity are also involved in maintaining metabolic hemostasis and facilitating the healing process after tissue injury. Numerous preclinical studies have suggested regulation of type 2 immunity-related cytokines, such as interleukin-4, -13, and -33, and cell types, such as M2 macrophages, mast cells, and eosinophils, affects cardiac functions after myocardial infarction (MI), providing new insights into the importance of immune modulation in the infarcted heart. This review provides an overview of the functions of these cytokines and cells in the setting of MI as well as their potential to predict the severity and prognosis of MI.

Long-term interleukin-33 treatment delays disease onset and alleviates astrocytic activation in a transgenic mouse model of amyotrophic lateral sclerosis

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Th2-type cytokine IL-33 delayed the disease onset of female SOD1-G93 A transgenic ALS mice.

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IL-33 decreased the proportion of T cells in the spleens and lymph nodes of female mice.

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IL-33 decreased astrocytic activation in the spinal cord of female mice.

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Male mice were unresponsive to the treatment.

Inflammation is a prominent feature of the neuropathology of amyotrophic lateral sclerosis (ALS). Emerging evidence suggests that inflammatory cascades contributing to the disease progression are not restricted to the central nervous system (CNS) but also occur peripherally. Indeed, alterations in T cell responses and their secreted cytokines have been detected in ALS patients and in animal models of ALS. One key cytokine responsible for the shift in T cell responses is interleukin-33 (IL-33), which stimulates innate type 2 immune cells to produce a large amount of Th2 cytokines that are possibly beneficial in the recovery processes of CNS injuries. Since the levels of IL-33 have been shown to be decreased in patients affected with ALS, we sought to determine whether a long-term recombinant IL-33 treatment of a transgenic mouse model of ALS expressing G93A-superoxide dismutase 1 (SOD1-G93A) alters the disease progression and ameliorates the ALS-like disease pathology. SOD1-G93A mice were treated with intraperitoneal injections of IL-33 and effects on disease onset and inflammatory status were determined. Spinal cord (SC) neurons, astrocytes and T-cells were exposed to IL-33 to evaluate the cell specific responses to IL-33. Treatment of SOD1-G93A mice with IL-33 delayed the disease onset in female mice, decreased the proportion of CD4+ and CD8 + T cell populations in the spleen and lymph nodes, and alleviated astrocytic activation in the ventral horn of the lumbar SC. Male SOD1-G93A mice were unresponsive to the treatment. In vitro studies showed that IL-33 is most likely not acting directly on neurons and astrocytes, but rather conveying its effects through peripheral T-cells. Our results suggest that strategies directed to the peripheral immune system may have therapeutic potential in ALS. The effect of gender dimorphisms to the treatment efficacy needs to be taken into consideration when designing new therapeutic strategies for CNS diseases.

MicroRNA-26b relieves inflammatory response and myocardial remodeling of mice with myocardial infarction by suppression of MAPK pathway through binding to PTGS2

BACKGROUND

Myocardial infarction (MI) is a common cardiovascular disease caused by myocardial ischemia. Also, microRNA (miRNA) participates in the pathophysiology of many cardiovascular diseases, which can affect stem cell transplantation in the treatment of MI. In this study, our aim is to explore effect of miR-26b on inflammatory response and myocardial remodeling through the MAPK pathway by targeting PTGS2 in mice with MI.

METHODS

Microarray data analysis was conducted to screen MI-related differentially expressed gens (DEGs). Relationship between miR-26b and PTGS2 was testified. Cardiac function, inflammatory reaction, infarct size, and myocardial fibrosis were observed. The miR-26b expression and mRNA and protein levels of, PTGS2, ERK, JNK and p38 and Bcl-2/Bax were examined. The effect of miR-26b on cell apoptosis was also analyzed.

RESULTS

MiR-26b was predicted to target PTGS2 further to mediate the MAPK pathway, thus affecting MI. MiR-26b negatively targeted PTGS2. MI mice showed decreased cardiac function, as well as increased inflammatory reaction, myocardial injury, area of fibrosis and myocardial cell apoptosis. After injection of miR-26b agomir or NS-398 (PTGS2 inhibitor), inflammatory response of MI mice was attenuated and myocardial remodeling induced by MI was alleviated.

CONCLUSION

These findings indicate that miR-26b inhibits PTGS2 to activate the MAPK pathway, so as to reduce inflammatory response and improve myocardial remodeling in mice with MI.

Paeoniflorin improves pressure overload-induced cardiac remodeling by modulating the MAPK signaling pathway in spontaneously hypertensive rats

Paeoniflorin (PF) is a main bioactive component of the root of Paeonia lactiflora Pal, and previous investigations suggest that it may impact cardiac remodeling in spontaneous hypertensive rats (SHR) via the MAPK signaling pathway. Thus, the purpose of this investigation was to examine the impacts of paeoniflorin cardiac function in SHR rats. Cardiac function and blood pressure were observed using echocardiography and non-invasive tail pressure gauge. Heart histopathology was assessed by histological staining and transmission electron microscopy. Genomic sequencing was performed and signaling pathway enrichment analyzed the function of differentially expressed genes(DEGs). Biochemical kits were used to analyze the serum level of proinflammatory cytokines including TNF-α, IL-6 and MCP-1. qRT-PCR proved the mRNA expression of Ngfr, Grin2b, and Ntf4. MAPK pathways were determined via western blot. Paeoniflorin decreased blood pressure and increased hemodynamic indexes. 131 DEGs were identified (SHR vs. PF), and mainly enriched on the MAPK signaling pathway. Paeoniflorin reduced IL-6, MCP-1, Ngfr, Grin2b, and Ntf4, and also decreased p-JNK, p-Erk1/2, and p-p38 proteins compared with the SHR group. Paeoniflorin attenuated cardiac hypertrophy, cardiac fibrosis, and inflammation, and subsequently improved LV function. In conclusion, the cardioprotective role of paeoniflorin was associated with the inhibition of MAPK signaling pathway.

IRAK3 gene silencing prevents cardiac rupture and ventricular remodeling through negative regulation of the NF-κB signaling pathway in a mouse model of acute myocardial infarction

Cardiac rupture and ventricular remodeling are recognized as the severe complications and major risk factors of acute myocardial infarction (AMI). This study aims to evaluate the regulatory roles of interleukin-1 receptor-associated kinase 3 (IRAK3) and nuclear factor-κB (NF-κB) signaling pathway in cardiac rupture and ventricular remodeling. Microarray analysis was performed to screen AMI-related differentially expressed genes and IRAK3 was identified. The models of AMI were established in male C57BL/6 mice to investigate the functional role of IRAK3. Afterwards, lentivirus recombinant plasmid si-IRAK3 was constructed for IRAK3 silencing. Next, cardiac function parameters were measured in response to IRAK3 silencing. The regulatory effects that IRAK3 had on myocardial infarct size and the content of myocardial interstitial collagen were analyzed. The regulation of IRAK3 silencing on the NF-κB signaling pathway was further assayed. The obtained results indicated that highly expressed IRAK3 and activated NF-κB signaling pathway were observed in myocardial tissues of mouse models of AMI, accompanied by increased expression of matrix metalloproteinase (MMP)-2/9 and tissue inhibitor of metalloproteinase 2 (TIMP-2). Notably, IRAK3 gene silencing inhibited the activation of NF-κB signaling pathway. Furthermore, IRAK3 gene silencing led to the decreased thickness of infarct area and collagen content of myocardial interstitium, alleviated diastolic, and systolic dysfunctions, as well as, facilitated cardiac functions in mice with AMI, corresponding to decreased expression of MMP-2/9 expression and increased expression of TIMP-2. Taken together, silencing of IRAK3 inactivates the NF-κB signaling pathway, and thereby impeding the cardiac rupture and ventricular remodeling, which eventually prevents AMI progression.

Conflicting vascular and metabolic impact of the IL-33/sST2 axis

Interleukin 33 (IL-33), which is expressed by several immune cell types, endothelial and epithelial cells, and fibroblasts, is a cytokine of the IL-1 family that acts both intra- and extracellularly to either enhance or resolve the inflammatory response. Intracellular IL-33 acts in the nucleus as a regulator of transcription. Once released from cells by mechanical stress, inflammatory cytokines, or necrosis, extracellular IL-33 is proteolytically processed to act in an autocrine/paracrine manner as an 'alarmin' on neighbouring or various immune cells expressing the ST2 receptor. Thus, IL-33 may serve an important role in tissue preservation and repair in response to injury; however, the actions of IL-33 are dampened by a soluble form of ST2 (sST2) that acts as a decoy receptor and is produced by endothelial and certain immune cells. Accumulating evidence supports the conclusion that sST2 is a biomarker of vascular health with diagnostic and/or prognostic value in various cardiovascular diseases, including coronary artery disease, myocardial infarction, atherosclerosis, giant-cell arteritis, acute aortic dissection, and ischaemic stroke, as well as obesity and diabetes. Although sST2 levels are positively associated with cardiovascular disease severity, the assumption that IL-33 is always beneficial is naïve. It is increasingly appreciated that the pathophysiological importance of IL-33 is highly dependent on cellular and temporal expression. Although IL-33 is atheroprotective and may prevent obesity and type 2 diabetes by regulating lipid metabolism, IL-33 appears to drive endothelial inflammation. Here, we review the current knowledge of the IL-33/ST2/sST2 signalling network and discuss its pathophysiological and translational implications in cardiovascular diseases.

Serum Levels of IL-33 and Correlation with IL-4, IL-17A, and Hypergammaglobulinemia in Patients with Autoimmune Hepatitis

This study investigated the role of IL-33 in the pathogenesis of autoimmune hepatitis (AIH). The levels of IL-33/sST2 and Th1/Th2/Th17-type cytokines were determined by enzyme-linked immunosorbent assay in serum samples obtained from 30 AIH patients and 20 healthy controls (HCs). In addition, a murine model of experimental AIH (EAIH) was established to investigate the role of IL-33 in disease progression. The serum levels of IL-33, sST2, Th17 cytokines (IL-17A), Th1 cytokines (IFN-γ, TNF-α), and Th2 cytokines (IL-4) were significantly elevated in AIH patients compared to HCs. Following immunosuppression therapy, serum levels of IL-33 and sST2 were significantly decreased. Additionally, the serum levels of IL-33 in AIH patients were correlated positively with markers of hypergammaglobulinemia (IgG, IgM, and IgA) and liver injury (γ-GT/ALP). Also, the serum levels of IL-33 in AIH patients were correlated positively with proinflammatory cytokine levels (IL-17A and IL-4). Interestingly, treatment of EAIH mice with a specific IL-33 neutralizing antibody significantly reversed the increasing trend in serum ALT/AST and inhibited the production of the type 2 (IL-4) and type 17 cytokines (IL-17) but not the type 1 cytokine (IFN-γ). Our findings highlight the possible role of the IL-33/sST2 axis in the progression of AIH, opening a new door for developing a novel therapeutic strategy for AIH.

Cardiac macrophage biology in the steady-state heart, the aging heart, and following myocardial infarction

Macrophages play critical roles in homeostatic maintenance of the myocardium under normal conditions and in tissue repair after injury. In the steady-state heart, resident cardiac macrophages remove senescent and dying cells and facilitate electrical conduction. In the aging heart, the shift in macrophage phenotype to a proinflammatory subtype leads to inflammaging. Following myocardial infarction (MI), macrophages recruited to the infarct produce both proinflammatory and anti-inflammatory mediators (cytokines, chemokines, matrix metalloproteinases, and growth factors), phagocytize dead cells, and promote angiogenesis and scar formation. These diverse properties are attributed to distinct macrophage subtypes and polarization status. Infarct macrophages exhibit a proinflammatory M1 phenotype early and become polarized toward an anti-inflammatory M2 phenotype later post-MI. Although this classification system is oversimplified and needs to be refined to accommodate the multiple different macrophage subtypes that have been recently identified, general concepts on macrophage roles are independent of subtype classification. This review summarizes current knowledge about cardiac macrophage origins, roles, and phenotypes in the steady state, with aging, and after MI, as well as highlights outstanding areas of investigation.