Knowledge gaps to understanding cardiac macrophage polarization following myocardial infarction

Crosstalk between macrophages and cardiac cells after myocardial infarction

Cardiovascular diseases, such as myocardial infarction (MI), are a leading cause of death worldwide. Acute MI (AMI) inflicts massive injury to the coronary microcirculation, causing large-scale cardiomyocyte death due to ischemia and hypoxia. Inflammatory cells such as monocytes and macrophages migrate to the damaged area to clear away dead cells post-MI. Macrophages are pleiotropic cells of the innate immune system, which play an essential role in the initial inflammatory response that occurs following MI, inducing subsequent damage and facilitating recovery. Besides their recognized role within the immune response, macrophages participate in crosstalk with other cells (including cardiomyocytes, fibroblasts, immune cells, and vascular endothelial cells) to coordinate post-MI processes within cardiac tissue. Macrophage-secreted exosomes have recently attracted increasing attention, which has led to a more elaborate understanding of macrophage function. Currently, the functional roles of macrophages in the microenvironment of the infarcted heart, particularly with regard to their interaction with surrounding cells, remain unclear. Understanding the specific mechanisms that mediate this crosstalk is essential in treating MI. In this review, we discuss the origin of macrophages, changes in their distribution post-MI, phenotypic and functional plasticity, as well as the specific signaling pathways involved, with a focus on the crosstalk with other cells in the heart. Thus, we provide a new perspective on the treatment of MI. Further in-depth research is required to elucidate the mechanisms underlying crosstalk between macrophages and other cells within cardiac tissue for the identification of potential therapeutic targets. Video Abstract.

Dysregulated lncRNAs are involved in the progress of myocardial infarction by constructing regulatory networks

Long noncoding RNAs (lncRNAs) mediate important epigenetic regulation in a wide range of biological processes. However, the effect of all dysregulated lncRNAs in myocardial infarction (MI) is not clear. Whole transcriptome sequencing analysis was used to characterize the dynamic changes in lncRNA and mRNA expression. A gene network was constructed, and genes were classified into different modules using WGCNA. In addition, for all dysregulated lncRNAs, gene ontology analysis and cis-regulatory analysis were applied. The results demonstrated that a large number of the differentially co-expressed genes were primarily linked to the immune system process, inflammatory response, and innate immune response. The functional pathway analysis of the MEblue module included immune system process and apoptosis, and MEbrown included the T-cell receptor signal pathway by WGCNA. In addition, through cis-acting analysis of lncRNA regulation, the cis-regulated mRNAs were mainly enriched in immune system processes, innate immune responses, and VEGF signal pathways. We found that lncRNA regulation of mRNAs plays an important role in immune and inflammatory pathways. Our study provides a foundation to further understand the role and potential mechanism of dysregulated lncRNAs in the regulation of MI, in which many of them could be potential targets for MI.

Macrophage polarization in hypoxia and ischemia/reperfusion: Insights into the role of energetic metabolism

Macrophages, the key cells of innate immunity, possess wide phenotypical and functional heterogeneity. In vitro studies showed that microenvironment signals could induce the so-called polarization of macrophages into two phenotypes: classically activated macrophages (M1) or alternatively activated macrophages (M2). Functionally, they are considered as proinflammatory and anti-inflammatory/pro-regenerative, respectively. However, in vivo studies into macrophage states revealed a continuum of phenotypes from M1 to M2 state instead of the clearly distinguished extreme phenotypes. An important role in determining the type of polarization of macrophages is played by energy metabolism, including the activity of oxidative phosphorylation. In this regard, hypoxia and ischemia that affect cellular energetics can modulate macrophage polarization. Here, we overview the data on macrophage polarization during metabolic shift-associated pathologies including ischemia and ischemia/reperfusion in various organs and discuss the role of energy metabolism potentially triggering the macrophage polarization.

Fibroblasts orchestrate cellular crosstalk in the heart through the ECM

Cell communication is needed for organ function and stress responses, especially in the heart. Cardiac fibroblasts, cardiomyocytes, immune cells, and endothelial cells comprise the major cell types in ventricular myocardium that together coordinate all functional processes. Critical to this cellular network is the non-cellular extracellular matrix (ECM) that provides structure and harbors growth factors and other signaling proteins that affect cell behavior. The ECM is not only produced and modified by cells within the myocardium, largely cardiac fibroblasts, it also acts as an avenue for communication among all myocardial cells. In this Review, we discuss how the development of therapeutics to combat cardiac diseases, specifically fibrosis, relies on a deeper understanding of how the cardiac ECM is intertwined with signaling processes that underlie cellular activation and behavior.

Organized Chaos: Deciphering Immune Cell Heterogeneity's Role in Inflammation in the Heart

During homeostasis, immune cells perform daily housekeeping functions to maintain heart health by acting as sentinels for tissue damage and foreign particles. Resident immune cells compose 5% of the cellular population in healthy human ventricular tissue. In response to injury, there is an increase in inflammation within the heart due to the influx of immune cells. Some of the most common immune cells recruited to the heart are macrophages, dendritic cells, neutrophils, and T-cells. In this review, we will discuss what is known about cardiac immune cell heterogeneity during homeostasis, how these cell populations change in response to a pathology such as myocardial infarction or pressure overload, and what stimuli are regulating these processes. In addition, we will summarize technologies used to evaluate cell heterogeneity in models of cardiovascular disease.

Chronic Benzene Exposure Aggravates Pressure Overload-Induced Cardiac Dysfunction

Benzene is a ubiquitous environmental pollutant abundant in household products, petrochemicals and cigarette smoke. Benzene is a well-known carcinogen in humans and experimental animals; however, little is known about the cardiovascular toxicity of benzene. Recent population-based studies indicate that benzene exposure is associated with an increased risk for heart failure. Nonetheless, it is unclear whether benzene exposure is sufficient to induce and/or exacerbate heart failure. We examined the effects of benzene (50 ppm, 6 h/day, 5 days/week, 6 weeks) or HEPA-filtered air exposure on transverse aortic constriction (TAC)-induced pressure overload in male C57BL/6J mice. Our data show that benzene exposure had no effect on cardiac function in the Sham group; however, it significantly compromised cardiac function as depicted by a significant decrease in fractional shortening and ejection fraction, as compared with TAC/Air-exposed mice. RNA-seq analysis of the cardiac tissue from the TAC/benzene-exposed mice showed a significant increase in several genes associated with adhesion molecules, cell-cell adhesion, inflammation, and stress response. In particular, neutrophils were implicated in our unbiased analyses. Indeed, immunofluorescence studies showed that TAC/benzene exposure promotes infiltration of CD11b+/S100A8+/myeloperoxidase+-positive neutrophils in the hearts by 3-fold. In vitro, the benzene metabolites, hydroquinone and catechol, induced the expression of P-selectin in cardiac microvascular endothelial cells by 5-fold and increased the adhesion of neutrophils to these endothelial cells by 1.5-2.0-fold. Benzene metabolite-induced adhesion of neutrophils to the endothelial cells was attenuated by anti-P-selectin antibody. Together, these data suggest that benzene exacerbates heart failure by promoting endothelial activation and neutrophil recruitment.

Sphingosine-1-phosphate interactions in the spleen and heart reflect extent of cardiac repair in mice and failing human hearts

Sphingosine-1-phosphate (S1P) is a bioactive mediator in inflammation. Dysregulated S1P is demonstrated as a cause of heart failure (HF). However, the time-dependent and integrative role of S1P interaction with receptors in HF is unclear after myocardial infarction (MI). In this study, the sphingolipid mediators were quantified in ischemic human hearts. We also measured the time kinetics of these mediators post-MI in murine spleen and heart as an integrative approach to understand the interaction of S1P and respective S1P receptors in the transition of acute (AHF) to chronic HF (CHF). Risk-free 8-12 wk male C57BL/6 mice were subjected to MI surgery, and MI was confirmed by echocardiography and histology. Mass spectrometry was used to quantify sphingolipids in plasma, infarcted heart, spleen of mice, and ischemic and healthy human heart. The physiological cardiac repair was observed in mice with a notable increase of S1P quantity (pmol/g) in the heart and spleen significantly reduced in patients with ischemic HF. The circulating murine S1P levels were increased during AHF and CHF despite lowered substrate in CHF. The S1PR1 receptor expression was observed to coincide with the respective S1P quantity in mice and human hearts. Furthermore, selective S1P1 agonist limited inflammatory markers CCL2 and TNF-α and accelerated reparative markers ARG-1 and YM-1 in macrophages in the presence of Kdo2-Lipid A (KLA; potent inflammatory stimulant). This report demonstrated the importance of S1P/S1PR1 signaling in physiological inflammation during cardiac repair in mice. Alteration in these axes may serve as the signs of pathological remodeling in patients with ischemia.NEW & NOTEWORTHY Previous studies indicate that sphingosine-1-phosphate (S1P) has some role in cardiovascular disease. This study adds quantitative and integrative systems-based approaches that are necessary for discovery and bedside translation. Here, we quantitated sphinganine, sphingosine, sphingosine-1-phosphate (S1P) in mice and human cardiac pathobiology. Interorgan S1P quantity and respective systems-based receptor activation suggest cardiac repair after myocardial infarction. Thus, S1P serves as a therapeutic target for cardiac protection in clinical translation.

Heart Failure Syndrome With Preserved Ejection Fraction Is a Metabolic Cluster of Non-resolving Inflammation in Obesity

Heart failure with preserved ejection fraction (HFpEF) is an emerging disease with signs of nonresolving inflammation, endothelial dysfunction, and multiorgan defects. Moreover, based on the clinical signs and symptoms and the rise of the obesity epidemic, the number of patients developing HFpEF is increasing. From recent molecular and cellular studies, it becomes evident that HFpEF is not a single and homogenous disease but a cluster of heterogeneous pathophysiology with aging at the base of the pyramid. Obesity superimposed on aging drives the number of inflammatory pathways that intersect with metabolic dysfunction and suboptimal inflammation. Here, we compiled information on obesity-directed macrophage dysfunction that coincide with metabolic defects. Obesity-associated proinflammatory stimuli facilitates heart and interorgan inflammation in HFpEF. Furthermore, diversified mechanisms that drive heart failure urge the need of studying pervasive and unresolved inflammation in animal models to understand HFpEF. A broad and system-based approach will help to study major translational aspects of HFpEF, since no single animal model recapitulates all signs of differential HFpEF stages in the clinical setting. Here, we covered experimental models that target HFpEF and emphasized the advances observed with formyl peptide 2 (FPR2) receptor, a prime sensor that is important in inflammation-resolution signaling. Dysfunction of FPR2 led to the development of spontaneous obesity, impaired macrophage function, and triggered kidney fibrosis, providing evidence of multiorgan defects in HFpEF in an obesogenic aging experimental model.

A data-driven computational model enables integrative and mechanistic characterization of dynamic macrophage polarization

Macrophages are highly plastic immune cells that dynamically integrate microenvironmental signals to shape their own functional phenotypes, a process known as polarization. Here we develop a large-scale mechanistic computational model that for the first time enables a systems-level characterization, from quantitative, temporal, dose-dependent, and single-cell perspectives, of macrophage polarization driven by a complex multi-pathway signaling network. The model was extensively calibrated and validated against literature and focused on in-house experimental data. Using the model, we generated dynamic phenotype maps in response to numerous combinations of polarizing signals; we also probed into an in silico population of model-based macrophages to examine the impact of polarization continuum at the single-cell level. Additionally, we analyzed the model under an in vitro condition of peripheral arterial disease to evaluate strategies that can potentially induce therapeutic macrophage repolarization. Our model is a key step toward the future development of a network-centric, comprehensive "virtual macrophage" simulation platform.

Network Analysis Reveals a Distinct Axis of Macrophage Activation in Response to Conflicting Inflammatory Cues

Macrophages are subject to a wide range of cytokine and pathogen signals in vivo, which contribute to differential activation and modulation of inflammation. Understanding the response to multiple, often-conflicting cues that macrophages experience requires a network perspective. In this study, we integrate data from literature curation and mRNA expression profiles obtained from wild type C57/BL6J mice macrophages to develop a large-scale computational model of the macrophage signaling network. In response to stimulation across all pairs of nine cytokine inputs, the model predicted activation along the classic M1-M2 polarization axis but also a second axis of macrophage activation that distinguishes unstimulated macrophages from a mixed phenotype induced by conflicting cues. Along this second axis, combinations of conflicting stimuli, IL-4 with LPS, IFN-γ, IFN-β, or TNF-α, produced mutual inhibition of several signaling pathways, e.g., NF-κB and STAT6, but also mutual activation of the PI3K signaling module. In response to combined IFN-γ and IL-4, the model predicted genes whose expression was mutually inhibited, e.g., iNOS or Nos2 and Arg1, or mutually enhanced, e.g., Il4rα and Socs1, validated by independent experimental data. Knockdown simulations further predicted network mechanisms underlying functional cross-talk, such as mutual STAT3/STAT6-mediated enhancement of Il4rα expression. In summary, the computational model predicts that network cross-talk mediates a broadened spectrum of macrophage activation in response to mixed pro- and anti-inflammatory cytokine cues, making it useful for modeling in vivo scenarios.

Liposomal delivery of azithromycin enhances its immunotherapeutic efficacy and reduces toxicity in myocardial infarction

A growing body of evidence shows that altering the inflammatory response by alternative macrophage polarization is protective against complications related to acute myocardial infarction (MI). We have previously shown that oral azithromycin (AZM), initiated prior to MI, reduces inflammation and its negative sequelae on the myocardium. Here, we investigated the immunomodulatory role of a liposomal AZM formulation (L-AZM) in a clinically relevant model to enhance its therapeutic potency and avoid off-target effects. L-AZM (40 or 10 mg/kg, IV) was administered immediately post-MI and compared to free AZM (F-AZM). L-AZM reduced cardiac toxicity and associated mortality by 50% in mice. We observed a significant shift favoring reparatory/anti-inflammatory macrophages with L-AZM formulation. L-AZM use resulted in a remarkable decrease in cardiac inflammatory neutrophils and the infiltration of inflammatory monocytes. Immune cell modulation was associated with the downregulation of pro-inflammatory genes and the upregulation of anti-inflammatory genes. The immunomodulatory effects of L-AZM were associated with a reduction in cardiac cell death and scar size as well as enhanced angiogenesis. Overall, L-AZM use enhanced cardiac recovery and survival after MI. Importantly, L-AZM was protective from F-AZM cardiac off-target effects. We demonstrate that the liposomal formulation of AZM enhances the drug’s efficacy and safety in an animal model of acute myocardial injury. This is the first study to establish the immunomodulatory properties of liposomal AZM formulations. Our findings strongly support clinical trials using L-AZM as a novel and clinically relevant therapeutic target to improve cardiac recovery and reduce heart failure post-MI in humans.

A long noncoding RNA regulates inflammation resolution by mouse macrophages through fatty acid oxidation activation

Proper resolution of inflammation is vital for repair and restoration of homeostasis after tissue damage, and its dysregulation underlies various noncommunicable diseases, such as cardiovascular and metabolic diseases. Macrophages play diverse roles throughout initial inflammation, its resolution, and tissue repair. Differential metabolic reprogramming is reportedly required for induction and support of the various macrophage activation states. Here we show that a long noncoding RNA (lncRNA), lncFAO, contributes to inflammation resolution and tissue repair in mice by promoting fatty acid oxidation (FAO) in macrophages. lncFAO is induced late after lipopolysaccharide (LPS) stimulation of cultured macrophages and in Ly6C^hi monocyte-derived macrophages in damaged tissue during the resolution and reparative phases. We found that lncFAO directly interacts with the HADHB subunit of mitochondrial trifunctional protein and activates FAO. lncFAO deletion impairs resolution of inflammation related to endotoxic shock and delays resolution of inflammation and tissue repair in a skin wound. These results demonstrate that by tuning mitochondrial metabolism, lncFAO acts as a node of immunometabolic control in macrophages during the resolution and repair phases of inflammation.

Regulation of Myocardial Extracellular Matrix Dynamic Changes in Myocardial Infarction and Postinfarct Remodeling

The article represents literature review dedicated to molecular and cellular mechanisms underlying clinical manifestations and outcomes of acute myocardial infarction. Extracellular matrix adaptive changes are described in detail as one of the most important factors contributing to healing of damaged myocardium and post-infarction cardiac remodeling. Extracellular matrix is reviewed as dynamic constantly remodeling structure that plays a pivotal role in myocardial repair. The role of matrix metalloproteinases and their tissue inhibitors in fragmentation and degradation of extracellular matrix as well as in myocardium healing is discussed. This review provides current information about fibroblasts activity, the role of growth factors, particularly transforming growth factor β and cardiotrophin-1, colony-stimulating factors, adipokines and gastrointestinal hormones, various matricellular proteins. In conclusion considering the fact that dynamic transformation of extracellular matrix after myocardial ischemic damage plays a pivotal role in myocardial infarction outcomes and prognosis, we suggest a high importance of further investigation of mechanisms underlying extracellular matrix remodeling and cell-matrix interactions in cardiovascular diseases.

Exogenous CXCL4 infusion inhibits macrophage phagocytosis by limiting CD36 signalling to enhance post-myocardial infarction cardiac dilation and mortality

Aims

Macrophage phagocytosis of dead cells is a prerequisite for inflammation resolution. Because CXCL4 induces macrophage phagocytosis in vitro, we examined the impact of exogenous CXCL4 infusion on cardiac wound healing and macrophage phagocytosis following myocardial infarction (MI).

Methods and results

CXCL4 expression significantly increased in the infarct region beginning at Day 3 post-MI, and macrophages were the predominant source. Adult male C57BL/6J mice were subjected to coronary artery occlusion, and MI mice were randomly infused with recombinant mouse CXCL4 or saline beginning at 24 h post-MI by mini-pump infusion. Compared with saline controls, CXCL4 infusion dramatically reduced 7 day post-MI survival [10% (3/30) for CXCL4 vs. 47% (7/15) for saline, P < 0.05] as a result of acute congestive heart failure. By echocardiography, CXCL4 significantly increased left ventricular (LV) volumes and dimensions at Day 5 post-MI (all P < 0.05), despite similar infarct areas compared with saline controls. While macrophage numbers were similar at Day 5 post-MI, CXCL4 infusion increased Ccr4 and Itgb4 and decreased Adamts8 gene levels in the infarct region, all of which linked to CXCL4-mediated cardiac dilation. Isolated Day 5 post-MI macrophages exhibited comparable levels of M1 and M4 markers between saline and CXCL4 groups. Interestingly, by both ex vivo and in vitro phagocytosis assays, CXCL4 reduced macrophage phagocytic capacity, which was connected to decreased levels of the phagocytosis receptor CD36. In vitro, a CD36 neutralizing antibody (CD36Ab) significantly inhibited macrophage phagocytic capacity. The combination of CXCL4 and CD36Ab did not have an additive effect, indicating that CXCL4 regulated phagocytosis through CD36 signalling. CXCL4 infusion significantly elevated infarct matrix metalloproteinase (MMP)-9 levels at Day 5 post-MI, and MMP-9 can cleave CD36 as a down-regulation mechanism.

Conclusion

CXCL4 infusion impaired macrophage phagocytic capacity by reducing CD36 levels through MMP-9 dependent and independent signalling, leading to higher mortality and LV dilation.

M1-like macrophage-derived exosomes suppress angiogenesis and exacerbate cardiac dysfunction in a myocardial infarction microenvironment

The roles and the underlying mechanisms of M1-type macrophages in angiogenesis and postmyocardial infarction (MI) cardiac repair have remained unclear. In this study, we investigated the role of M1-like macrophage-derived exosomes in a MI microenvironment. We found that the proinflammatory M1-like-type macrophages released an extensive array of proinflammatory exosomes (M1-Exos) after MI. M1-Exos exerted an anti-angiogenic effect and accelerated MI injury. They also exhibited highly expressed proinflammatory miRNAs, such as miR-155. miR-155 was transferred to endothelial cells (ECs), leading to the inhibition of angiogenesis and cardiac dysfunction by downregulating its novel target genes, including Rac family small GTPase 1 (RAC1), p21 (RAC1)-activated kinase 2 (PAK2), Sirtuin 1 (Sirt1), and protein kinase AMP-activated catalytic subunit alpha 2 (AMPKα2). M1-Exos depressed Sirt1/AMPKα2-endothelial nitric oxide synthase and RAC1-PAK2 signaling pathways by simultaneously targeting the five molecule nodes (genes), reduced the angiogenic ability of ECs, aggravated myocardial injury, and restrained cardiac healing. The elucidation of this mechanism provides novel insights into the functional significance of M1 macrophages and their derived exosomes on angiogenesis and cardiac repair. This mechanism can be used as a novel potential therapeutic approach for the prevention and treatment of MI.

Understanding the mechanisms that determine extracellular matrix remodeling in the infarcted myocardium

Myocardial Infarction (MI) initiates a series of wound healing events that begins with up-regulation of an inflammatory response and culminates in scar formation. The extracellular matrix (ECM) is intricately involved in all stages from initial break down of existing ECM to synthesis of new ECM to form the scar. This review will summarize our current knowledge on the processes involved in ECM remodeling after MI and identify the gaps that still need to be filled.

Spatiotemporal Dynamics of Immune Cells in Early Left Ventricular Remodeling After Acute Myocardial Infarction in Mice

Myocardial infarction remains a leading cause of morbidity and death. Insufficient delivery of oxygen to the myocardium sets into play a complicated process of repair that involves the temporal recruitment of different immune cells so as to remove debris and necrotic cells expeditiously and to form effective scar tissue. Clearly defined and overlapping phases have been identified in the process, which transitions from an overall proinflammatory to anti-inflammatory phenotype with time. Variations in the strength of the phases as well as in the co-ordination among them have profound consequences. Too strong of an inflammatory phase can result in left ventricular wall thinning and eventual rupture, whereas too strong of an anti-inflammatory phase can lead to cardiac stiffening, arrhythmias, or ventricular aneurisms. In both cases, heart failure is an intermediate consequence with death being the likely outcome. Here, we summarize the role of key immune cells in the repair process of the heart after left ventricular myocardial infarction, along with the associated cytokines and chemokines. A better understanding of the immune response ought to lead hopefully to improved therapies that exploit the natural repair process for mending the infarcted heart.

A mechanistic integrative computational model of macrophage polarization: Implications in human pathophysiology

Macrophages respond to signals in the microenvironment by changing their functional phenotypes, a process known as polarization. Depending on the context, they acquire different patterns of transcriptional activation, cytokine expression and cellular metabolism which collectively constitute a continuous spectrum of phenotypes, of which the two extremes are denoted as classical (M1) and alternative (M2) activation. To quantitatively decode the underlying principles governing macrophage phenotypic polarization and thereby harness its therapeutic potential in human diseases, a systems-level approach is needed given the multitude of signaling pathways and intracellular regulation involved. Here we develop the first mechanism-based, multi-pathway computational model that describes the integrated signal transduction and macrophage programming under M1 (IFN-γ), M2 (IL-4) and cell stress (hypoxia) stimulation. Our model was calibrated extensively against experimental data, and we mechanistically elucidated several signature feedbacks behind the M1-M2 antagonism and investigated the dynamical shaping of macrophage phenotypes within the M1-M2 spectrum. Model sensitivity analysis also revealed key molecular nodes and interactions as targets with potential therapeutic values for the pathophysiology of peripheral arterial disease and cancer. Through simulations that dynamically capture the signal integration and phenotypic marker expression in the differential macrophage polarization responses, our model provides an important computational basis toward a more quantitative and network-centric understanding of the complex physiology and versatile functions of macrophages in human diseases.

Reparative macrophage transplantation for myocardial repair: a refinement of bone marrow mononuclear cell-based therapy

Reparative macrophages play an important role in cardiac repair post-myocardial infarction (MI). Bone marrow mononuclear cells (BM-MNCs) have been investigated as a donor for cell therapy but with limited clinical success. These cells, however, may be utilized as a source for reparative macrophages. This translational study aimed to establish a robust in vitro protocol to produce functional reparative macrophages from BM-MNCs and to establish pre-clinical evidence of the efficacy of reparative macrophage transplantation for the treatment of MI. Mouse BM-MNCs were treated with M-CSF plus IL-4, IL-10, TGF-β1 or combinations of these in vitro. The concomitant administration of M-CSF and IL-4 produced the highest rate and largest number of CD11b+F4/80+CD206+ reparative macrophages. Expression and secretion of tissue repair-related factors including IGF-1, TGF-β1, VEGF and IL1-ra were remarkably enhanced in reparative macrophages compared to BM-MNCs. These cells were transplanted in a mouse MI model, resulting in evident improvement in cardiac function recovery, compared to BM-MNC transplantation. Histological studies showed that reparative macrophage transplantation enhanced myocardial tissue repair including augmented microvascular formation, reduced cardiomyocyte hypertrophy and attenuated interstitial fibrosis. Moreover, survival of reparative macrophages in the heart post-transplantation was increased compared to BM-MNCs. Reparative macrophage transplantation also increased host-derived reparative macrophages in part through TGF-β secretion. In conclusion, concomitant M-CSF + IL-4 treatment effectively produced reparative macrophages from BM-MNCs in vitro. Transplantation of produced reparative macrophage achieved a superior therapeutic efficacy, compared to BM-MNC transplantation, through the enhanced quantity and quality of donor cell engraftment. Further development of this advanced cell-based therapy is warranted.

CD8+ T-cells negatively regulate inflammation post-myocardial infarction

The adaptive immune response is key for cardiac wound healing post-myocardial infarction (MI) despite low T-cell numbers. We hypothesized that CD8⁺ T-cells regulate the inflammatory response, leading to decreased survival and cardiac function post-MI. We performed permanent occlusion of the left anterior descending coronary artery on C57BL/6J and CD8a^tm1mak mice (deficient in functional CD8⁺ T-cells). CD8a^tm1mak mice had increased survival at 7 days post-MI compared with that of the wild-type (WT) and improved cardiac physiology at day 7 post-MI. Despite having less mortality, 100% of the CD8a^tm1mak group died because of cardiac rupture compared with only 33% of the WT. Picrosirius red staining and collagen immunoblotting indicated an acceleration of fibrosis in the infarct area as well as remote area in the CD8a^tm1mak mice; however, this increase was due to elevated soluble collagen implicating poor scar formation. Plasma and tissue inflammation were exacerbated as indicated by higher levels of Cxcl1, Ccl11, matrix metalloproteinase (MMP)-2, and MMP-9. Immunohistochemistry and flow cytometry indicated that the CD8a^tm1mak group had augmented numbers of neutrophils and macrophages at post-MI day 3 and increased mast cell markers at post-MI day 7. Cleavage of tyrosine-protein kinase MER was increased in the CD8a^tm1mak mice, resulting in delayed removal of necrotic tissue. In conclusion, despite having improved cardiac physiology and overall survival, CD8a^tm1mak mice had increased innate inflammation and poor scar formation, leading to higher incidence of cardiac rupture. Our data suggest that the role of CD8⁺ T-cells in post-MI recovery may be both beneficial and detrimental to cardiac remodeling and is mediated via a cell-specific mechanism.NEW & NOTEWORTHY We identified new mechanisms implicating CD8⁺ T-cells as regulators of the post-myocardial infarction (MI) wound healing process. Mice without functional CD8⁺ T-cells had improved cardiac physiology and less mortality 7 days post MI compared with wild-type animals. Despite having better overall survival, animals lacking functional CD8⁺ T-cells had delayed removal of necrotic tissue, leading to poor scar formation and increased cardiac rupture, suggesting that CD8⁺ T-cells play a dual role in the cardiac remodeling process.

Inhibition of MicroRNA-9-5p Protects Against Cardiac Remodeling Following Myocardial Infarction in Mice

Follistatin-like 1 (Fstl1) protects cardiomyocytes from a broad spectrum of pathologic injuries including myocardial infarction (MI). It is worthy of note that although cardiac Fstl1 is elevated in post-MI microenvironment, its cardioprotective role is still restricted to a limited extent considering the frequency and severity of adverse cardiac remodeling following MI. We therefore propose that intrinsic Fstl1-suppressing microRNA (miRNA) may exist in the heart and its neutralization may further facilitate post-MI recovery. Here, miR-9-5p is predicted as one of the potential Fstl1-targeting miRNAs whose expression is decreased in ischemic myocardium and reversely correlated with Fstl1. Luciferase activity assay further validated Fstl1 as a direct target of miR-9-5p. In addition, forced expression of miR-9-5p in H9c2 cells is concurrent with diminished expression of Fstl1 and vice versa. Importantly, transfection of miR-9-5p mimics in hypoxic H9c2 cells exacerbates cardiac cell death, lactate dehydrogenase release, reactive oxygen species accumulation, and malonyldialdehyde concentration. More importantly, in vivo silencing of miR-9-5p by a specific antagomir in a murine acute MI model effectively preserves post-MI heart function with attenuated fibrosis and inflammatory response. Further studies demonstrated that antagomir treatment stabilizes Fstl1 expression as well as blocks cardiac cell death and reactive oxygen species generation in both ischemia-challenged hearts and hypoxia-treated cardiomyoblasts. Finally, cytoprotection against hypoxic challenge by miR-9-5p inhibitor is partially reversed by knockdown of Fstl1, indicating a novel role of miR-9-5p/Fstl1 axis in survival defense against hypoxic challenge. In summary, these findings identified miR-9-5p as a mediator of hypoxic injury in cardiomyoblasts and miR-9-5p suppression prevents cardiac remodeling after acute MI, providing a potential strategy for early treatment against MI.

Glycoproteomic Profiling Provides Candidate Myocardial Infarction Predictors of Later Progression to Heart Failure

We hypothesized that identifying plasma glycoproteins that predict the development of heart failure following myocardial infarction (MI) could help to stratify subjects at risk. Plasma collected at visit 2 (2005-2008) from an MI subset of Jackson Heart Study participants underwent glycoproteomics and was grouped by the outcome: (1) heart failure hospitalization after visit 2 (n = 15) and (2) without hospitalization by 2012 (n = 45). Proteins were mapped for biological processes and functional pathways using Ingenuity Pathway Analysis and linked to clinical characteristics. A total of 198 glycopeptides corresponding to 88 proteins were identified (data available via ProteomeXchange with identifier PXD009870). Of these, 14 glycopeptides were significantly different between MI and MI + HF groups and corresponded to apolipoprotein (Apo) F, transthyretin, Apo C-IV, prostaglandin-D2 synthase, complement C9, and CD59 (p < 0.05 for all). All proteins were elevated in the MI + HF group, except CD59, which was lower. Four canonical pathways were upregulated in the MI + HF group (p < 0.05 for all): acute phase response, liver X receptor/retinoid X receptor, and macrophage reactive oxygen species generation. The coagulation pathway was significantly downregulated in the MI + HF group (p < 0.05). Even after adjustment for age and sex, Apo F was associated with the increased risk for heart failure (OR = 21.84; 95% CI 3.20-149.14). In conclusion, glycoproteomic profiling provided candidate early MI predictors of later progression to heart failure.

Macrophages and Cardiovascular Health

Research during the last decade has generated numerous insights on the presence, phenotype, and function of myeloid cells in cardiovascular organs. Newer tools with improved detection sensitivities revealed sizable populations of tissue-resident macrophages in all major healthy tissues. The heart and blood vessels contain robust numbers of these cells; for instance, 8% of noncardiomyocytes in the heart are macrophages. This number and the cell's phenotype change dramatically in disease conditions. While steady-state macrophages are mostly monocyte independent, macrophages residing in the inflamed vascular wall and the diseased heart derive from hematopoietic organs. In this review, we will highlight signals that regulate macrophage supply and function, imaging applications that can detect changes in cell numbers and phenotype, and opportunities to modulate cardiovascular inflammation by targeting macrophage biology. We strive to provide a systems-wide picture, i.e., to focus not only on cardiovascular organs but also on tissues involved in regulating cell supply and phenotype, as well as comorbidities that promote cardiovascular disease. We will summarize current developments at the intersection of immunology, detection technology, and cardiovascular health.

Specialized Pro-resolving Mediators Directs Cardiac Healing and Repair with Activation of Inflammation and Resolution Program in Heart Failure

After myocardial infarction, splenic leukocytes direct biosynthesis of specialized pro-resolving mediators (SPMs) that are essential for the resolution of inflammation and tissue repair. In a laboratory environment, after coronary ligation of healthy risk free rodents (young adult mice) leukocytes biosynthesize SPMs with induced activity of lipoxygenases and cyclooxygenases, which facilitate cardiac repair. Activated monocytes/macrophages drive the biosynthesis of SPMs following experimental myocardial infarction in mice during the acute heart failure. In the presented review, we provided the recent updates on SPMs (resolvins, lipoxins and maresins) in cardiac repair that may serve as novel therapeutics for future heart failure therapy/management. We incorporated the underlying causes of non-resolving inflammation following cardiac injury if superimposed with obesity, hypertension, diabetes, disrupted circadian rhythm, co-medication (painkillers or oncological therapeutics), and/or aging that may delay or impair the biosynthesis of SPMs, intensifying pathological remodeling in heart failure.

Identifying the molecular and cellular signature of cardiac dilation following myocardial infarction

Establishing molecular and cellular indicators that reflect the extent of dilation of the left ventricle (LV) after myocardial infarction (MI) may improve diagnostic and prognostic capabilities. We queried the Mouse Heart Attack Research Tool (mHART) 1.0 for day 7 post-MI mice (age 3-9 months, untreated males and females) with serial echocardiographic data at days 0, 1, and 7 (n = 51). Mice were classified into two subgroups determined by a median fold change of 1.6 in end-diastolic dimensions (EDD) normalized to pre-MI values; n = 26 fell below (moderate; mean of 1.42 ± 0.01) and n = 25 fell above this cut-off (extreme; mean of 1.79 ± 0.01; p < 0.001 vs. moderate). Plasma proteomic profiling of 34 analytes measured at day 7 post-MI from male mice (n = 12 moderate and 12 extreme) were evaluated as the test dataset, and receiver operating curve (ROC) analysis was used to assess strength of biomarkers. Females (n = 6 moderate and 9 extreme) were used as the validation dataset. Both by t-test and characteristic (ROC) curve analysis, lower macrophage inflammatory protein-1 gamma (MIP-1γ), lymphotactin, and granulocyte chemotactic protein-2 (GCP-2) were identified as plasma indicators for dilation status (p < 0.05 for all). Macrophage numbers were decreased and complement C5, laminin 1, and Ccr8 gene levels were significantly higher in the LV infarcts of the extreme dilation group (p < 0.05 for all). A composite panel including plasma MIP-1γ, lymphotactin, and GCP-2, and LV infarct Ccr8 and macrophage numbers strongly mirrored LV dilation status (AUC = 0.92; p < 0.0001). Using the mHART 1.0 database, we determined that a failure to mount sufficient macrophage-mediated inflammation was indicative of exacerbated LV dilation.

Mapping macrophage polarization over the myocardial infarction time continuum

In response to myocardial infarction (MI), cardiac macrophages regulate inflammation and scar formation. We hypothesized that macrophages undergo polarization state changes over the MI time course and assessed macrophage polarization transcriptomic signatures over the first week of MI. C57BL/6 J male mice (3–6 months old) were subjected to permanent coronary artery ligation to induce MI, and macrophages were isolated from the infarct region at days 1, 3, and 7 post-MI. Day 0, no MI resident cardiac macrophages served as the negative MI control. Whole transcriptome analysis was performed using RNA-sequencing on n = 4 pooled sets for each time. Day 1 macrophages displayed a unique pro-inflammatory, extracellular matrix (ECM)-degrading signature. By flow cytometry, day 0 macrophages were largely F4/80^highLy6C^low resident macrophages, whereas day 1 macrophages were largely F4/80^lowLy6C^high infiltrating monocytes. Day 3 macrophages exhibited increased proliferation and phagocytosis, and expression of genes related to mitochondrial function and oxidative phosphorylation, indicative of metabolic reprogramming. Day 7 macrophages displayed a pro-reparative signature enriched for genes involved in ECM remodeling and scar formation. By triple in situ hybridization, day 7 infarct macrophages in vivo expressed collagen I and periostin mRNA. Our results indicate macrophages show distinct gene expression profiles over the first week of MI, with metabolic reprogramming important for polarization. In addition to serving as indirect mediators of ECM remodeling, macrophages are a direct source of ECM components. Our study is the first to report the detailed changes in the macrophage transcriptome over the first week of MI.

Unified nexus of macrophages and maresins in cardiac reparative mechanisms

Macrophages are immune-sensing "big eater" phagocytic cells responsible for an innate, adaptive, and regenerative response. After myocardial infarction, macrophages predominantly clear the deceased cardiomyocyte apoptotic or necrotic neutrophils to develop a regenerative and reparative program with the activation of the lipoxygenase-mediated maresin (MaR) metabolome at the site of ischemic injury. The specialized proresolving molecule and macrophage mediator in resolving inflammation, MaR-1, produced by human macrophages, has potent defining effects that limit polymorphonuclear neutrophil infiltration, enhance uptake of apoptotic PMNs, regulate inflammation resolution and tissue regeneration, and reduce pain. In addition to proresolving and anti-inflammatory actions, MaR-1 displays potent tissue regenerative effects in stroke and is an antinociceptive. Macrophages actively participate in the biosynthesis of bioactive MaR-2, which exhibits anti-inflammatory, proresolving, and atherosclerotic effects. A new class of macrophage-derived molecules, MaR conjugates in tissue regeneration, is identified that regulates phagocytosis and the repair and regeneration of damaged tissue. The presented review provides a current summary of the effect of MaR in resolution pathophysiology, with relevance to a cardiac repair program.-Jadapalli, J. K., Halade, G. V. Unified nexus of macrophages and maresins in cardiac reparative mechanisms.

Myocardial infarction remodeling that progresses to heart failure: a signaling misunderstanding

After myocardial infarction, remodeling of the left ventricle involves a wound-healing orchestra involving a variety of cell types. In order for wound healing to be optimal, appropriate communication must occur; these cells all need to come in at the right time, be activated at the right time in the right amount, and know when to exit at the right time. When this occurs, a new homeostasis is obtained within the infarct, such that infarct scar size and quality are sufficient to maintain left ventricular size and shape. The ideal scenario does not always occur in reality. Often, miscommunication can occur between infarct and remote spaces, across the temporal wound-healing spectrum, and across organs. When miscommunication occurs, adverse remodeling can progress to heart failure. This review discusses current knowledge gaps and recent development of the roles of inflammation and the extracellular matrix in myocardial infarction remodeling. In particular, the macrophage is one cell type that provides direct and indirect regulation of both the inflammatory and scar-forming responses. We summarize current research efforts focused on identifying biomarker indicators that reflect the status of each component of the wound-healing process to better predict outcomes.

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.

IL-10 improves cardiac remodeling after myocardial infarction by stimulating M2 macrophage polarization and fibroblast activation

Inflammation resolution is important for scar formation following myocardial infarction (MI) and requires the coordinated actions of macrophages and fibroblasts. In this study, we hypothesized that exogenous interleukin-10 (IL-10), an anti-inflammatory cytokine, promotes post-MI repair through actions on these cardiac cell types. To test this hypothesis, C57BL/6J mice (male, 3- to 6-month old, n = 24/group) were treated with saline or IL-10 (50 μg/kg/day) by osmotic mini-pump infusion starting at day (d) 1 post-MI and sacrificed at d7 post-MI. IL-10 infusion doubled plasma IL-10 concentrations by d7 post-MI. Despite similar infarct areas and mortality rates, IL-10 treatment significantly decreased LV dilation (1.6-fold for end-systolic volume and 1.4-fold for end-diastolic volume) and improved ejection fraction 1.8-fold (both p < 0.05). IL-10 treatment attenuated inflammation at d7 post-MI, evidenced by decreased numbers of Mac-3-positive macrophages in the infarct (p < 0.05). LV macrophages isolated from d7 post-MI mice treated with IL-10 showed significantly elevated gene expression of M2 markers (Arg1, Ym1, and Tgfb1; all p < 0.05). We further performed RNA-seq analysis on post-MI cardiac macrophages and identified 410 significantly different genes (155 increased, 225 decreased by IL-10 treatment). By functional network analysis grouping, the majority of genes (133 out of 410) were part of the cellular assembly and repair functional group. Of these, hyaluronidase 3 (Hyal3) was the most important feature identified by p value. IL-10 treatment decreased Hyal3 by 28%, which reduced hyaluronan degradation and limited collagen deposition (all p < 0.05). In addition, in vivo IL-10 treatment increased fibroblast activation (proliferation, migration, and collagen production), an effect that was both directly and indirectly influenced by macrophage M2 polarization. Combined, our results indicate that in vivo infusion of IL-10 post-MI improves the LV microenvironment to dampen inflammation and facilitate cardiac wound healing.

Macrophage activation and polarization in post-infarction cardiac remodeling

Adverse cardiac remodeling leads to impaired ventricular function and heart failure, remaining a major cause of mortality and morbidity in patients with acute myocardial infarction. It have been shown that, even if all the recommended therapies for ST-segment elevation myocardial infarction are performed, one third of patients undergoes progressive cardiac remodeling that represents morphological basis for following heart failure. The need to extend our knowledge about factors leading to different clinical scenarios of myocardial infarction and following complications has resulted in a research of immuno-inflammatory pathways and molecular activities as the basis for post-infarction remodeling. Recently, macrophages (cells of the innate immune system) have become a subject of scientific interest under both normal and pathological conditions. Macrophages, besides their role in host protection and tissue homeostasis, play an important role in pathophysiological processes induced by myocardial infarction. In this article we summarize data about the function of monocytes and macrophages plasticity in myocardial infarction and outline potential role of these cells as effective targets to control processes of inflammation, cardiac remodeling and healing following acute coronary event.

Methanolic seed extract of Vitis vinifera ameliorates oxidative stress, inflammation and ATPase dysfunction in infarcted and non-infarcted heart of streptozotocin-nicotinamide induced male diabetic rats

BACKGROUND

We hypothesized that consumption of Vitis vinifera seed by diabetics could help to ameliorate myocardial damage. Therefore, in this study, we investigated effects of V. vinifera seed methanolic extract (VVSME) on parameters related to myocardial damage in diabetes with or without myocardial infarction (MI).

METHODS

Streptozotocin-nicotinamide induced diabetic rats received oral VVSME for 28days. MI was induced by intraperitoneal injection of isoproterenol on last two days. Prior to sacrifice, blood was collected and fasting blood glucose (FBG), glycated hemoglobin (HbA1c), lipid profile and insulin levels were measured. Levels of serum cardiac injury marker (troponin-I and CK-MB) were determined and histopathological changes in the heart were observed following harvesting. Levels of oxidative stress (LPO, SOD, CAT, GPx and RAGE), inflammation (NF-κB, TNF-α, IL-1β and IL-6) and cardiac ATPases (Na(+)/K(+)-ATPase and Ca(2+)-ATPase) were determined in heart homogenates. LC-MS was used to identify constituents in the extracts.

RESULTS

Consumption of VVSME by diabetic rats with or without MI improved the metabolic profiles while decreased the cardiac injury marker levels with lesser myocardial damage observed. Additionally, VVSME consumption reduced the levels of LPO, RAGE, TNF-α, Iκκβ, NF-κβ, IL-1β and IL-6 while increased the levels of SOD, CAT, GPx, Na(+)/K(+)-ATPase and Ca(2+)-ATPase in the infarcted and non-infarcted heart of diabetic rats (p<0.05). LC-MS analysis revealed 17 major compounds in VVSME which might be responsible for the observed effects.

CONCLUSIONS

Consumption of VVSME by diabetics helps to ameliorate damage to the infarcted and non-infarcted myocardium by decreasing oxidative stress, inflammation and cardiac ATPases dysfunctions.