Identification of a novel macrophage phenotype that develops in response to atherogenic phospholipids via Nrf2

Regulation of macrophage immunometabolism in atherosclerosis

After activation, cells of the myeloid lineage undergo robust metabolic transitions, as well as discrete epigenetic changes, that can dictate both ongoing and future inflammatory responses. In atherosclerosis, in which macrophages play central roles in the initiation, growth, and ultimately rupture of arterial plaques, altered metabolism is a key feature that dictates macrophage function and subsequent disease progression. This Review explores how factors central to the plaque microenvironment (for example, altered cholesterol metabolism, oxidative stress, hypoxia, apoptotic and necrotic cells, and hyperglycemia) shape the metabolic rewiring of macrophages in atherosclerosis as well as how these metabolic shifts in turn alter macrophage immune-effector and tissue-reparative functions. Finally, this overview offers insight into the challenges and opportunities of harnessing metabolism to modulate aberrant macrophage responses in disease.

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.

Deficiency of Dab2 (Disabled Homolog 2) in Myeloid Cells Exacerbates Inflammation in Liver and Atherosclerotic Plaques in LDLR (Low-Density Lipoprotein Receptor)-Null Mice-Brief Report

OBJECTIVE

Inflammatory macrophages promote the development of atherosclerosis. We have identified the adaptor protein Dab2 (disabled homolog 2) as a regulator of phenotypic polarization in macrophages. The absence of Dab2 in myeloid cells promotes an inflammatory phenotype, but the impact of myeloid Dab2 deficiency on atherosclerosis has not been shown.

APPROACH AND RESULTS

To determine the role of myeloid Dab2 in atherosclerosis, Ldlr-/- mice were reconstituted with either Dab2-positive or Dab2-deficient bone marrow and fed a western diet. Consistent with our previous finding that Dab2 inhibits NFκB (nuclear factor κ-light-chain-enhancer of activated B cells) signaling in macrophages, Ldlr-/- mice reconstituted with Dab2-deficient bone marrow had increased systemic inflammation as evidenced by increased serum IL-6 (interleukin-6) levels and increased inflammatory cytokine expression levels in liver. Serum lipid levels were significantly lower in Ldlr-/- mice reconstituted with Dab2-deficient bone marrow, and further examination of livers from these mice revealed drastically increased inflammatory tissue damage and massive infiltration of immune cells. Surprisingly, the atherosclerotic lesion burden in Ldlr-/- mice reconstituted with Dab2-deficient bone marrow was decreased compared with Ldlr-/- mice reconstituted with wild-type bone marrow. Further analysis of aortic root sections revealed increased macrophage content and evidence of increased apoptosis in lesions from Ldlr-/- mice reconstituted with Dab2-deficient bone marrow but no difference in collagen or α-smooth muscle actin content.

CONCLUSIONS

Dab2 deficiency in myeloid cells promotes inflammation in livers and atherosclerotic plaques in a mouse model of atherosclerosis. Nevertheless, decreased serum lipids as a result of massive inflammatory liver damage may preclude an appreciable increase in atherosclerotic lesion burden in mice reconstituted with Dab2-deficient bone marrow.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

Connexins: Synthesis, Post-Translational Modifications, and Trafficking in Health and Disease

Connexins are tetraspan transmembrane proteins that form gap junctions and facilitate direct intercellular communication, a critical feature for the development, function, and homeostasis of tissues and organs. In addition, a growing number of gap junction-independent functions are being ascribed to these proteins. The connexin gene family is under extensive regulation at the transcriptional and post-transcriptional level, and undergoes numerous modifications at the protein level, including phosphorylation, which ultimately affects their trafficking, stability, and function. Here, we summarize these key regulatory events, with emphasis on how these affect connexin multifunctionality in health and disease.

The Ethanolamine Permease EutH Promotes Vacuole Adaptation of Salmonella enterica and Listeria monocytogenes during Macrophage Infection

Ethanolamine is a ubiquitous and essential molecule within a host. Significantly, bacterial pathogens exploit ethanolamine during infection to promote growth and regulate virulence. The ethanolamine permease EutH is dispensable for growth in vitro under standard conditions, whereas EutH is required for ethanolamine utilization at low pH. These findings suggested a model in which EutH facilitates diffusion of ethanolamine into the bacterial cell in acidic environments. To date, the ecological significance of this model has not been thoroughly investigated, and the importance of EutH to bacterial growth under physiologically relevant conditions is not known. During infection, immune cells internalize invading bacteria within an acidic, nutrient-depleted vacuole called the phagosome. Here, we investigated the hypothesis that EutH promotes bacterial survival following phagocytosis. Our findings indicate that EutH is important for survival and replication of the facultative intracellular pathogens Salmonella enterica serovar Typhimurium and Listeria monocytogenes during prolonged or transient exposure to the phagosome, respectively. Furthermore, in agreement with EutH being important in the acidic environment, neutralization of the vacuole abolished the requirement for EutH. Significantly, consistent with a role for EutH in promoting intramacrophage survival, EutH was not required during S Typhimurium local intestinal infection but specifically conferred an advantage upon dissemination to peripheral organs. These findings reveal a physiologically relevant and conserved role for EutH in spatiotemporal niche adaptation during infection.

Immune consequences of penfluridol treatment associated with inhibition of glioblastoma tumor growth

Glioblastoma is the most common and lethal brain tumor associated with only 12% median survival rate of patients. Despite the development of advanced surgical, radiation or use of combinations of anti-cancer drugs, treatment for glioblastoma patients is still a challenge. The major contributing factor in glioblastoma progression and resistive nature is its ability to evade the immune surveillance. Hence, modulating the immune system in glioblastoma tumors could be an important strategy for anticancer therapeutics. Penfluridol, an antipsychotic drug has been shown to have anti-cancer properties in our recently published studies. The present study evaluates the immune response of penfluridol in glioblastoma tumors. Our results demonstrated that penfluridol treatment significantly suppressed glioblastoma tumor growth. Our current results demonstrated about 72% suppression of myeloid derived suppressor cells (MDSCs) with penfluridol treatment in mouse bearing U87MG glioblastoma tumors. MDSCs are known to increase regulatory T cells (Treg), which are immunosuppressive in nature and suppresses M1 macrophages that are tumor suppressive in nature. Our results also showed suppression of regulatory T cells as well as elevation of M1 macrophages with penfluridol treatment by 58% and 57% respectively. Decrease in CCL4 as well as IFNγ with penfluridol treatment was also observed indicating decrease in overall tumor inflammation. This is the first report demonstrating immune modulations by penfluridol treatment associated with glioblastoma tumor growth suppression prompting further investigation to establish penfluridol as a treatment option for glioblastoma patients.

Innate and adaptive immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disorder of the large and medium-size arteries characterized by the subendothelial accumulation of cholesterol, immune cells, and extracellular matrix. At the early onset of atherogenesis, endothelial dysfunction takes place. Atherogenesis is further triggered by the accumulation of cholesterol-carrying low-density lipoproteins, which acquire properties of damage-associated molecular patterns and thereby trigger an inflammatory response. Following activation of the innate immune response, mainly governed by monocytes and macrophages, the adaptive immune response is started which further promotes atherosclerotic plaque formation. In this review, an overview is given describing the role of damage-associated molecular patterns, NLRP3 inflammasome activation, and innate and adaptive immune cells in the atherogenesis process.

Macrophage-Targeted Therapeutics for Metabolic Disease

Macrophages are cells of the innate immune system that are resident in all tissues, including metabolic organs such as the liver and adipose tissue (AT). Because of their phenotypic flexibility, they play beneficial roles in tissue homeostasis, but they also contribute to the progression of metabolic disease. Thus, they are ideal therapeutic targets for diseases such as insulin resistance (IR), nonalcoholic fatty liver disease (NAFLD), and atherosclerosis. Recently, discoveries in the area of drug delivery have facilitated phenotype-specific targeting of macrophages. In this review we discuss advances in potential therapeutics for metabolic diseases via macrophage-specific delivery. We highlight micro- and nanoparticles, liposomes, and oligopeptide complexes, and how they can be used to alter macrophage phenotype for a more metabolically favorable tissue environment.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in "distant" pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

Transfusion-related immunomodulation: a reappraisal

PURPOSE OF REVIEW

This review summarizes current and prior observations regarding transfusion-related immunomodulation (TRIM) and puts these ideas into a modern immunological context, incorporating concepts from innate, adaptive, and nutritional immunity. We propose that TRIM research focus on determining whether there are specific, well-defined immunosuppressive effects from transfusing 'pure' red blood cells (RBCs) themselves, along with the by-products produced by the stored RBCs as a result of the 'storage lesion.' Macrophages are a key cell type involved in physiological and pathological RBC clearance and iron recycling. The plasticity and diversity of macrophages makes these cells potential mediators of immune suppression that could constitute TRIM.

RECENT FINDINGS

Recent reports identified the capacity of macrophages and monocytes to exhibit 'memory.' Exposure to various stimuli, such as engulfment of apoptotic cells and interactions with ß-glucan and lipopolysaccharide, were found to induce epigenetic, metabolic, and functional changes in certain myeloid cells, particularly macrophages and monocytes.

SUMMARY

Macrophages may mediate the immunosuppressive aspects of TRIM that arise as a result of transfused RBCs and their storage lesion induced by-products.

Sulforaphane Inhibits Lipopolysaccharide-Induced Inflammation, Cytotoxicity, Oxidative Stress, and miR-155 Expression and Switches to Mox Phenotype through Activating Extracellular Signal-Regulated Kinase 1/2-Nuclear Factor Erythroid 2-Related Factor 2/Antioxidant Response Element Pathway in Murine Microglial Cells

Sulforaphane (SFN) is a natural product with cytoprotective, anti-inflammatory, and antioxidant effects. In this study, we evaluated the mechanisms of its effects on lipopolysaccharide (LPS)-induced cell death, inflammation, oxidative stress, and polarization in murine microglia. We found that SFN protects N9 microglial cells upon LPS-induced cell death and suppresses LPS-induced levels of secreted pro-inflammatory cytokines, tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6. SFN is also a potent inducer of redox sensitive transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), which is responsible for the transcription of antioxidant, cytoprotective, and anti-inflammatory genes. SFN induced translocation of Nrf2 to the nucleus via extracellular signal-regulated kinase 1/2 (ERK1/2) pathway activation. siRNA-mediated knockdown study showed that the effects of SFN on LPS-induced reactive oxygen species, reactive nitrogen species, and pro-inflammatory cytokine production and cell death are partly Nrf2 dependent. Mox phenotype is a novel microglial phenotype that has roles in oxidative stress responses. Our results suggested that SFN induced the Mox phenotype in murine microglia through Nrf2 pathway. SFN also alleviated LPS-induced expression of inflammatory microRNA, miR-155. Finally, SFN inhibits microglia-mediated neurotoxicity as demonstrated by conditioned medium and co-culture experiments. In conclusion, SFN exerts protective effects on microglia and modulates the microglial activation state.

Macrophage Polarization in Chronic Inflammatory Diseases: Killers or Builders?

Macrophages are key cellular components of the innate immunity, acting as the main player in the first-line defence against the pathogens and modulating homeostatic and inflammatory responses. Plasticity is a major feature of macrophages resulting in extreme heterogeneity both in normal and in pathological conditions. Macrophages are not homogenous, and they are generally categorized into two broad but distinct subsets as either classically activated (M1) or alternatively activated (M2). However, macrophages represent a continuum of highly plastic effector cells, resembling a spectrum of diverse phenotype states. Induction of specific macrophage functions is closely related to the surrounding environment that acts as a relevant orchestrator of macrophage functions. This phenomenon, termed polarization, results from cell/cell, cell/molecule interaction, governing macrophage functionality within the hosting tissues. Here, we summarized relevant cellular and molecular mechanisms driving macrophage polarization in “distant” pathological conditions, such as cancer, type 2 diabetes, atherosclerosis, and periodontitis that share macrophage-driven inflammation as a key feature, playing their dual role as killers (M1-like) and/or builders (M2-like). We also dissect the physio/pathological consequences related to macrophage polarization within selected chronic inflammatory diseases, placing polarized macrophages as a relevant hallmark, putative biomarkers, and possible target for prevention/therapy.

New Insights into the Immunobiology of Mononuclear Phagocytic Cells and Their Relevance to the Pathogenesis of Cardiovascular Diseases

Macrophages are the primary immune cells that reside within the myocardium, suggesting that these mononuclear phagocytes are essential in the orchestration of cardiac immunity and homeostasis. Independent of the nature of the injury, the heart triggers leukocyte activation and recruitment. However, inflammation is harmful to this vital terminally differentiated organ with extremely poor regenerative capacity. As such, cardiac tissue has evolved particular strategies to increase the stress tolerance and minimize the impact of inflammation. In this sense, growing evidences show that mononuclear phagocytic cells are particularly dynamic during cardiac inflammation or infection and would actively participate in tissue repair and functional recovery. They respond to soluble mediators such as metabolites or cytokines, which play central roles in the timing of the intrinsic cardiac stress response. During myocardial infarction two distinct phases of monocyte influx have been identified. Upon infarction, the heart modulates its chemokine expression profile that sequentially and actively recruits inflammatory monocytes, first, and healing monocytes, later. In the same way, a sudden switch from inflammatory macrophages (with microbicidal effectors) toward anti-inflammatory macrophages occurs within the myocardium very shortly after infection with Trypanosoma cruzi, the causal agent of Chagas cardiomyopathy. While in sterile injury, healing response is necessary to stop tissue damage; during an intracellular infection, the anti-inflammatory milieu in infected hearts would promote microbial persistence. The balance of mononuclear phagocytic cells seems to be also dynamic in atherosclerosis influencing plaque initiation and fate. This review summarizes the participation of mononuclear phagocyte system in cardiovascular diseases, keeping in mind that the immune system evolved to promote the reestablishment of tissue homeostasis following infection/injury, and that the effects of different mediators could modulate the magnitude and quality of the immune response. The knowledge of the effects triggered by diverse mediators would serve to identify new therapeutic targets in different cardiovascular pathologies.

Macrophages sensing oxidized DAMPs reprogram their metabolism to support redox homeostasis and inflammation through a TLR2-Syk-ceramide dependent mechanism

OBJECTIVE

Macrophages control tissue homeostasis and inflammation by sensing and responding to environmental cues. However, the metabolic adaptation of macrophages to oxidative tissue damage and its translation into inflammatory mechanisms remains enigmatic.

METHODS

Here we identify the critical regulatory pathways that are induced by endogenous oxidation-derived DAMPs (oxidized phospholipids, OxPL) in vitro, leading to formation of a unique redox-regulatory metabolic phenotype (Mox), which is strikingly different from conventional classical or alternative macrophage activation.

RESULTS

Unexpectedly, metabolomic analyses demonstrated that Mox heavily rely on glucose metabolism and the pentose phosphate pathway (PPP) to support GSH production and Nrf2-dependent antioxidant gene expression. While the metabolic adaptation of macrophages to OxPL involved transient suppression of aerobic glycolysis, it also led to upregulation of inflammatory gene expression. In contrast to classically activated (M1) macrophages, Hif1α mediated expression of OxPL-induced Glut1 and VEGF but was dispensable for Il1β expression. Mechanistically, we show that OxPL suppress mitochondrial respiration via TLR2-dependent ceramide production, redirecting TCA metabolites to GSH synthesis. Finally, we identify spleen tyrosine kinase (Syk) as a critical downstream signaling mediator that translates OxPL-induced effects into ceramide production and inflammatory gene regulation.

CONCLUSIONS

Together, these data demonstrate the metabolic and bioenergetic requirements that enable macrophages to translate tissue oxidation status into either antioxidant or inflammatory responses via sensing OxPL. Targeting dysregulated redox homeostasis in macrophages could therefore lead to novel therapies to treat chronic inflammation.

Anti-inflammatory Nanomedicine for Cardiovascular Disease

Coronary artery disease, in the development of which inflammation mediated by innate immune cells plays a critical role, is one of the leading causes of death worldwide. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are a widely used lipid-lowering drug that has lipid-independent vasculoprotective effects, such as improvement of endothelial dysfunction, antioxidant properties, and inhibitory effects on inflammation. Despite recent advances in lipid-lowering therapy, clinical trials of statins suggest that anti-inflammatory therapy beyond lipid-lowering therapy is indispensible to further reduce cardiovascular events. One possible therapeutic option to the residual risk is to directly intervene in the inflammatory process by utilizing a nanotechnology-based drug delivery system (nano-DDS). Various nano-sized materials are currently developed as DDS, including micelles, liposomes, polymeric nanoparticles, dendrimers, carbon nanotubes, and metallic nanoparticles. The application of nano-DDS to coronary artery disease is a feasible strategy since the inflammatory milieu enhances incorporation of nano-sized materials into mononuclear phagocytic system and permeability of target lesions, which confers nano-DDS on “passive-targeting” property. Recently, we have developed a polymeric nanoparticle-incorporating statin to maximize its anti-inflammatory property. This statin nanoparticle has been tested in various disease models, including plaque destabilization and rupture, myocardial ischemia-reperfusion injury, and ventricular remodeling after acute myocardial infarction, and its clinical application is in progress. In this review, we present current development of DDS and future perspective on the application of anti-inflammatory nanomedicine to treat life-threatening cardiovascular diseases.

Nrf2, the Master Regulator of Anti-Oxidative Responses

Tight regulation of inflammation is very important to guarantee a balanced immune response without developing chronic inflammation. One of the major mediators of the resolution of inflammation is the transcription factor: the nuclear factor erythroid 2-like 2 (Nrf2). Stabilized following oxidative stress, Nrf2 induces the expression of antioxidants as well as cytoprotective genes, which provoke an anti-inflammatory expression profile, and is crucial for the initiation of healing. In view of this fundamental modulatory role, it is clear that both hyper- or hypoactivation of Nrf2 contribute to the onset of chronic diseases. Understanding the tight regulation of Nrf2 expression/activation and its interaction with signaling pathways, known to affect inflammatory processes, will facilitate development of therapeutic approaches to prevent Nrf2 dysregulation and ameliorate chronic inflammatory diseases. We discuss in this review the principle mechanisms of Nrf2 regulation with a focus on inflammation and autophagy, extending the role of dysregulated Nrf2 to chronic diseases and tumor development.

Contribution of Adipose Tissue to Development of Cancer

Solid tumor growth and metastasis require the interaction of tumor cells with the surrounding tissue, leading to a view of tumors as tissue-level phenomena rather than exclusively cell-intrinsic anomalies. Due to the ubiquitous nature of adipose tissue, many types of solid tumors grow in proximate or direct contact with adipocytes and adipose-associated stromal and vascular components, such as fibroblasts and other connective tissue cells, stem and progenitor cells, endothelial cells, innate and adaptive immune cells, and extracellular signaling and matrix components. Excess adiposity in obesity both increases risk of cancer development and negatively influences prognosis in several cancer types, in part due to interaction with adipose tissue cell populations. Herein, we review the cellular and noncellular constituents of the adipose "organ," and discuss the mechanisms by which these varied microenvironmental components contribute to tumor development, with special emphasis on obesity. Due to the prevalence of breast and prostate cancers in the United States, their close anatomical proximity to adipose tissue depots, and their complex epidemiologic associations with obesity, we particularly highlight research addressing the contribution of adipose tissue to the initiation and progression of these cancer types. Obesity dramatically modifies the adipose tissue microenvironment in numerous ways, including induction of fibrosis and angiogenesis, increased stem cell abundance, and expansion of proinflammatory immune cells. As many of these changes also resemble shifts observed within the tumor microenvironment, proximity to adipose tissue may present a hospitable environment to developing tumors, providing a critical link between adiposity and tumorigenesis. © 2018 American Physiological Society. Compr Physiol 8:237-282, 2018.

Pathophysiological relevance of macrophage subsets in atherogenesis

Macrophages are highly heterogeneous and plastic cells. They were shown to play a critical role in all stages of atherogenesis, from the initiation to the necrotic core formation and plaque rupture. Lesional macrophages primarily derive from blood monocyte, but local macrophage proliferation as well as differentiation from smooth muscle cells have also been described. Within atherosclerotic plaques, macrophages rapidly respond to changes in the microenvironment, shifting between pro- (M1) or anti-inflammatory (M2) functional phenotypes. Furthermore, different stimuli have been associated with differentiation of newly discovered M2 subtypes: IL-4/IL-13 (M2a), immunecomplex (M2b), IL-10/glucocorticoids (M2c), and adenosine receptor agonist (M2d). More recently, additional intraplaque macrophage phenotypes were also recognized in response to CXCL4 (M4), oxidized phospholipids (Mox), haemoglobin/haptoglobin complexes (HAmac/M(Hb)), and heme (Mhem). Such macrophage polarization was described as a progression among multiple phenotypes, which reflect the activity of different transcriptional factors and the cross-talk between intracellular signalling. Finally, the distribution of macrophage subsets within different plaque areas was markedly associated with cardiovascular (CV) vulnerability. The aim of this review is to update the current knowledge on the role of macrophage subsets in atherogenesis. In addition, the molecular mechanisms underlying macrophage phenotypic shift will be summarised and discussed. Finally, the role of intraplaque macrophages as predictors of CV events and the therapeutic potential of these cells will be discussed.

One microenvironment does not fit all: heterogeneity beyond cancer cells

Human cancers exhibit formidable molecular heterogeneity, to a large extent accounting for the incomplete and transitory efficacy of current anti-cancer therapies. However, neoplastic cells alone do not manifest the disease, but conscript a battery of non-tumor cells to enable and sustain hallmark capabilities of cancer. Escaping immunosurveillance is one of such capabilities. Tumors evolve immunosuppressive microenvironment to subvert anti-tumor immunity. In this review, we will focus on tumor-associated myeloid cells, which constitute an essential part of the immune microenvironment and reciprocally interact with cancer cells to establish malignancy toward metastasis. The diversity and plasticity of these cells constitute another layer of heterogeneity, beyond the heterogeneity of cancer cells themselves. We envision that immune microenvironment co-evolves with the genetic heterogeneity of tumor. Addressing the question of how genetically distinct tumors shape and are shaped by unique immune microenvironment will provide an attractive rationale to develop novel immunotherapeutic modalities. Here, we discuss the complex nature of tumor microenvironment, with an emphasis on the cellular and functional heterogeneity among tumor-associated myeloid cells as well as immune environment heterogeneity in the context of a full spectrum of human breast cancers.

Myeloid P2Y2 receptor promotes acute inflammation but is dispensable for chronic high-fat diet-induced metabolic dysfunction

The purinergic receptor P2Y2 binds ATP to control chemotaxis of myeloid cells, and global P2Y2 receptor knockout mice are protected in models of acute inflammation. Chronic inflammation mediated by macrophages and other immune cells in adipose tissue contributes to the development of insulin resistance. Here, we investigate whether mice lacking P2Y2 receptors on myeloid cells are protected against acute and chronic inflammation. Wild-type mice were transplanted with either wild-type or P2Y2 receptor null bone marrow and treated with a sublethal dose of endotoxin as a model of acute inflammation, or fed a high-fat diet to induce obesity and insulin resistance as a model of chronic inflammation. P2Y2^-/- chimeric mice were protected against acute inflammation. However, high-fat diet feeding induced comparable inflammation and insulin resistance in both WT and P2Y2^-/- chimeric mice. Of note, confocal microscopy revealed significantly fewer crown-like structures, assemblies of macrophages around adipocytes, in P2Y2^-/- chimeric mice compared to WT chimeric mice. We conclude that P2Y2 receptors on myeloid cells are important in mediating acute inflammation but are dispensable for the development of whole body insulin resistance in diet-induced obese mice.

Functional diversity of macrophages in vascular biology and disease

Atherosclerosis is a multifactorial chronic inflammatory disease and is largely responsible for cardiovascular disease, the most common cause of global mortality. The hallmark of atherogenesis is immune activation following lipid accumulation in the arterial wall. In particular, macrophages play a non-redundant role in both the progression and regression of inflammation in the atherosclerotic lesion. Macrophages are remarkably heterogeneous phagocytes that perform versatile functions in health and disease. Their functional diversity in vascular biology is only partially mapped. Targeting macrophages is often highlighted as a therapeutic approach for cancer, metabolic and inflammatory diseases. Future strategies for therapeutic intervention in atherosclerosis may benefit from attempts to reduce local proliferation of pro-inflammatory macrophage subsets or enhance resolution of inflammation. Thus, characterisation of macrophage subsets during atherosclerosis would empower clinical interventions. Therefore, it would be of fundamental importance to understand how pathological factors modulate macrophage activity in order to exploit their use in the treatment of atherosclerosis and other diseases.

Heterogeneity of atherosclerotic plaque macrophage origin, phenotype and functions: Implications for treatment

Macrophages are key players in atherosclerotic lesions, regulating the local inflammatory milieu and plaque stability by the secretion of many inflammatory molecules, growth factors and cytokines. Monocytes have long been considered to be the main source of plaque macrophages. However, recent findings provide evidence for proliferation of local macrophages or transdifferentiation from other vascular cells as alternative sources. Recent years of research focused on the further identification and characterisation of macrophage phenotypes and functions. In this review we describe the advances in our understanding of monocyte and macrophage heterogeneity and its implications for specific therapeutic interventions, aiming to reduce the ever growing significant risk of cardiovascular events without any detrimental side effects on the patient's immune response.

Pleiotropic effects of oxidized phospholipids

Oxidized phospholipids (OxPLs) are increasingly recognized to play a role in a variety of normal and pathological states. OxPLs were implicated in regulation of inflammation, thrombosis, angiogenesis, endothelial barrier function, immune tolerance and other important processes. Rapidly accumulating evidence suggests that OxPLs are biomarkers of atherosclerosis and other pathologies. In addition, successful application of experimental drugs based on structural scaffold of OxPLs in animal models of inflammation was recently reported. This review briefly summarizes current knowledge on generation, methods of quantification and biological activities of OxPLs. Furthermore, receptor and cellular mechanisms of these effects are discussed. The goal of the review is to give a broad overview of this class of lipid mediators inducing pleiotropic biological effects.

The effect of oxidized phospholipids on phenotypic polarization and function of macrophages

Oxidized phospholipids are products of lipid oxidation that are found on oxidized low-density lipoproteins and apoptotic cell membranes. These biologically active lipids were shown to affect a variety of cell types and attributed pro-as well as anti-inflammatory effects. In particular, macrophages exposed to oxidized phospholipids drastically change their gene expression pattern and function. These 'Mox,'macrophages were identified in atherosclerotic lesions, however, it remains unclear how lipid oxidation products are sensed by macrophages and how they influence their biological function. Here, we review recent developments in the field that provide insight into the structure, recognition, and downstream signaling of oxidized phospholipids in macrophages.

Macrophage complexity in human atherosclerosis: opportunities for treatment?

PURPOSE OF REVIEW

The pivotal role of macrophages in experimental atherosclerosis is firmly established, but their contribution to human disease is less well defined. In this review we have outlined the current insights on macrophage phenotypes and their presumed precursors, monocytes, in clinical atherosclerosis, and their association with disease progression. Moreover, we will assess major clinical modifiers of macrophage-mediated plaque inflammation and define the outstanding questions for further study.

RECENT FINDINGS

Our survey indicates that macrophage accumulation and status in human plaques are linked with lesion progression and destabilization as well as with symptomatic coronary artery disease. Likewise, levels of their precursors, circulating monocytes were repeatedly seen to associate with atherosclerosis and to predict clinical outcome. Furthermore, the presence and phenotype of both macrophages and monocytes appears to be responsive to the traditional risk factors of atherosclerosis, including hypercholesterolemia, hypertension, and type 2 diabetes, and to treatment thereof, with clear repercussions on disease development.

SUMMARY

Although plaque macrophages and their precursor cells do represent attractive targets for treating cardiovascular diseases, this therapeutic avenue requires much deeper understanding of the complexity of macrophage biology in human atherosclerosis than available at present.

CXCL4-induced macrophages in human atherosclerosis

Atherosclerosis is considered an inflammatory disease of the arterial wall. Monocytes and monocyte-derived cells (most often termed macrophages) play an essential role in the formation of atherosclerotic lesions, as they take up lipids leading to subsequent foam cell formation accompanied by release of pro-inflammatory cytokines. Similarly, platelets have been discovered to represent an important cell type mediating inflammatory and immune processes in atherogenesis, mainly by secreting chemokines, which are stored in the platelets' alpha granules, upon platelet activation. Therefore, the interaction between monocyte-derived cells and platelets is of exceptional importance. In this review, we specifically focus on the chemokine (platelet factor-4, PF4) and its effects on monocytes and monocyte-derived cells. By formation of heterodimers dimers and -oligomers with CCL5, CXCL4 induces binding of monocytes cells to endothelial cell and thereby promotes diapedesis of monocytes into the subendothelial space. CXCL4 also affects the differentiation of monocytes as it induces a specific macrophage phenotype, which we suggested to term "M4". For example, CXCL4-induced macrophages irreversibly lose the hemoglobin-haptoglobin scavenger receptor CD163. The combination of CD68, S100A8, and MMP7 turned out to reliably identify M4 macrophages both in vitro and in vivo within atherosclerotic lesions. In human atherosclerotic plaques, M4 macrophages are predominantly present in the adventitia and the intima and their prevalence is associated with plaque instability suggesting that they are a marker of pro-inflammatory activity. Overall, CXCL4-induced M4 macrophages may represent a target for diagnostic and therapeutic interventions in human atherosclerotic disease.

N-3 PUFAs induce inflammatory tolerance by formation of KEAP1-containing SQSTM1/p62-bodies and activation of NFE2L2

Inflammation is crucial in the defense against infections but must be tightly controlled to limit detrimental hyperactivation. Our diet influences inflammatory processes and omega-3 polyunsaturated fatty acids (n-3 PUFAs) have known anti-inflammatory effects. The balance of pro- and anti-inflammatory processes is coordinated by macrophages and macroautophagy/autophagy has recently emerged as a cellular process that dampens inflammation. Here we report that the n-3 PUFA docosahexaenoic acid (DHA) transiently induces cytosolic speckles of the autophagic receptor SQSTM1/p62 (sequestosome 1) (described as SQSTM1/p62-bodies) in macrophages. We suggest that the formation of SQSTM1/p62-bodies represents a fast mechanism of NFE2L2/Nrf2 (nuclear factor, erythroid 2 like 2) activation by recruitment of KEAP1 (kelch like ECH associated protein 1). Further, the autophagy receptor TAX1BP1 (Tax1 binding protein 1) and ubiquitin-editing enzyme TNFAIP3/A20 (TNF α induced protein 3) could be identified in DHA-induced SQSTM1/p62-bodies. Simultaneously, DHA strongly dampened the induction of pro-inflammatory genes including CXCL10 (C-X-C motif chemokine ligand 10) and we suggest that formation of SQSTM1/p62-bodies and activation of NFE2L2 leads to tolerance towards selective inflammatory stimuli. Finally, reduced CXCL10 levels were related to the improved clinical outcome in n-3 PUFA-supplemented heart-transplant patients and we propose CXCL10 as a robust marker for the clinical benefits mobilized by n-3 PUFA supplementation.

Oxidized Low-Density Lipoprotein Loading of Macrophages Downregulates TLR-Induced Proinflammatory Responses in a Gene-Specific and Temporal Manner through Transcriptional Control

Hypercholesterolemia is a key risk factor for atherosclerosis and leads to the uptake of native and oxidized low-density lipoprotein (oxLDL) by macrophages (Mϕs) and foam cell formation. Inflammatory processes accompany Mϕ foam cell formation in the artery wall, yet the relationship between Mϕ lipid loading and their response to inflammatory stimuli remains elusive. We investigated proinflammatory gene expression in thioglycollate-elicited peritoneal Mϕs, bone marrow-derived Mϕs and dendritic cells, and RAW264.7 cells. Loading with oxLDL did not induce peritoneal Mϕ apoptosis or modulate basal-level expression of proinflammatory genes. Upon stimulation of TLR4, the rapid induction of IFN-β was inhibited in cells loaded with oxLDL, whereas the induction of other proinflammatory genes by TLR4 (LPS), TLR3 (polyriboinosinic-polyribocytidylic acid), TLR2 (Pam₃CSK₄), and TLR9 (CpG) remained comparable within the first 2 h. Subsequently, the expression of a subset of proinflammatory genes (e.g., IL-1β, IL-6, CCL5) was reduced in oxLDL-loaded cells at the level of transcription. This phenomenon was partially dependent on NF erythroid 2-related factor 2 (NRF2) but not on nuclear liver X receptors α and β (LXRα,β), peroxisome proliferator-activated receptor-γ (PPARγ), and activating transcription factor 3 (ATF3). LPS-induced NF-κB reporter activity and intracellular signaling by NF-κB and MAPK pathways were comparable in oxLDL-loaded Mϕs, yet the binding of p65/RelA (the prototypic NF-κB family member) was reduced at IL-6 and CCL5 promoters. This study revealed that oxLDL loading of Mϕs negatively regulates transcription at late stages of TLR-induced proinflammatory gene expression and implicates epigenetic mechanisms such as histone deacetylase activity.

An interaction map of circulating metabolites, immune gene networks, and their genetic regulation

BACKGROUND

Immunometabolism plays a central role in many cardiometabolic diseases. However, a robust map of immune-related gene networks in circulating human cells, their interactions with metabolites, and their genetic control is still lacking. Here, we integrate blood transcriptomic, metabolomic, and genomic profiles from two population-based cohorts (total N = 2168), including a subset of individuals with matched multi-omic data at 7-year follow-up.

RESULTS

We identify topologically replicable gene networks enriched for diverse immune functions including cytotoxicity, viral response, B cell, platelet, neutrophil, and mast cell/basophil activity. These immune gene modules show complex patterns of association with 158 circulating metabolites, including lipoprotein subclasses, lipids, fatty acids, amino acids, small molecules, and CRP. Genome-wide scans for module expression quantitative trait loci (mQTLs) reveal five modules with mQTLs that have both cis and trans effects. The strongest mQTL is in ARHGEF3 (rs1354034) and affects a module enriched for platelet function, independent of platelet counts. Modules of mast cell/basophil and neutrophil function show temporally stable metabolite associations over 7-year follow-up, providing evidence that these modules and their constituent gene products may play central roles in metabolic inflammation. Furthermore, the strongest mQTL in ARHGEF3 also displays clear temporal stability, supporting widespread trans effects at this locus.

CONCLUSIONS

This study provides a detailed map of natural variation at the blood immunometabolic interface and its genetic basis, and may facilitate subsequent studies to explain inter-individual variation in cardiometabolic disease.

Similarities in the Metabolic Reprogramming of Immune System and Endothelium

Cellular metabolism has been known for its role in bioenergetics. In recent years, much light has been shed on the reprogrammable cellular metabolism underlying many vital cellular processes, such as cell activation, proliferation, and differentiation. Metabolic reprogramming in immune and endothelial cells (ECs) is being studied extensively. These cell compartments are implicated in inflammation and pathogenesis of many diseases but their similarities in metabolic reprogramming have not been analyzed in detail. One of the most notable metabolic reprogramming is the Warburg-like effect, famously described as one of the hallmarks of cancer cells. Immune cells and ECs can display this phenotype that is characterized by a metabolic switch favoring glycolysis over oxidative phosphorylation (OXPHOS) in aerobic conditions. Though energy-inefficient, aerobic glycolysis confers many benefits to the respiring cells ranging from higher rate of adenosine triphosphate production to maintaining redox homeostasis. Chemical and biological regulators either promote or perturb this effect. In this review, nitric oxide, hypoxia-inducible factor, and adenosine monophosphate-activated protein kinase have been discussed for their common involvement in metabolic reprogramming of both systems. From in vitro and animal studies, various discrepancies exist regarding the effects of those regulators on metabolic switch. However, it is generally accepted that glycolysis favors inflammatory reactions while OXPHOS favors anti-inflammatory processes. The reasons for such observation are currently subject of intense studies and not completely understood. Finally, metabolic reprogramming in immune cells and ECs does not limit to the physiological state in health but can also be observed in pathological states, such as atherosclerosis and cancer. These new insights provide us with a better understanding of the similarities in metabolic reprogramming across a number of cell types, which could pave the way for future research and possible metabolic-based therapeutics.

Carbon monoxide-releasing molecule, CORM-3, modulates alveolar macrophage M1/M2 phenotype in vitro

Alveolar macrophages are key contributors to both the promotion and resolution of inflammation in the lung and are categorized into pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. The change in M1/M2 balance has been reported in various pulmonary diseases and is a target for therapeutic intervention. The aim of this study was to assess the modulation of M1/M2 phenotype in alveolar macrophages by water-soluble carbon monoxide-releasing molecule-3 (CORM-3). Rat alveolar macrophages (AM) (NR8383) in culture were stimulated with LPS (5 ng/ml)/IFN-γ (10 U/ml) or IL-4 (10 ng/ml)/IL-13 (10 ng/ml) to induce M1 and M2 phenotypes, respectively. Expression of M1 phenotype markers, iNOS and TNF-α, and M2 phenotype markers, CD206 and Ym-1, was assessed by western blotting after 1, 3, 6, or 24 h in the absence or presence of CORM-3 (0.15 mM) treatment. Inactive CORM-3 (iCORM-3) was used as a control. Treatment of naïve (unstimulated) AM with CORM-3 promoted progression of the M2 phenotype as evidenced by the increased expression of CD206 (at 1 h; 1.8-fold) and Ym-1 (at 3 h; 1.9-fold), respectively. Surprisingly, CORM-3 treatment also upregulated the expression of iNOS protein as assessed 6 h following stimulation of AM with CORM-3 (2.6-fold). On the contrary, CORM-3 effectively reduced LPS/IFN-γ-induced expression of iNOS protein (0.6-fold); however, it had no effect on TNF-α expression. Finally, CORM-3 acutely (1-3 h) upregulated CD206 (1.4-fold) and Ym-1 (1.6-fold) levels in IL-4-/IL-13-treated (M2-stimulus) macrophages. These findings indicate that CORM-3 modulates macrophage M1 and M2 phenotypes in vitro with respect to continuous suppression of iNOS expression in M1-polarized macrophages and transient (early-phase) upregulation of CD206 and Ym-1 proteins in M2-polarized macrophages.

An agent-based model of leukocyte transendothelial migration during atherogenesis

A vast amount of work has been dedicated to the effects of hemodynamics and cytokines on leukocyte adhesion and trans-endothelial migration (TEM) and subsequent accumulation of leukocyte-derived foam cells in the artery wall. However, a comprehensive mechanobiological model to capture these spatiotemporal events and predict the growth and remodeling of an atherosclerotic artery is still lacking. Here, we present a multiscale model of leukocyte TEM and plaque evolution in the left anterior descending (LAD) coronary artery. The approach integrates cellular behaviors via agent-based modeling (ABM) and hemodynamic effects via computational fluid dynamics (CFD). In this computational framework, the ABM implements the diffusion kinetics of key biological proteins, namely Low Density Lipoprotein (LDL), Tissue Necrosis Factor alpha (TNF-α), Interlukin-10 (IL-10) and Interlukin-1 beta (IL-1β), to predict chemotactic driven leukocyte migration into and within the artery wall. The ABM also considers wall shear stress (WSS) dependent leukocyte TEM and compensatory arterial remodeling obeying Glagov's phenomenon. Interestingly, using fully developed steady blood flow does not result in a representative number of leukocyte TEM as compared to pulsatile flow, whereas passing WSS at peak systole of the pulsatile flow waveform does. Moreover, using the model, we have found leukocyte TEM increases monotonically with decreases in luminal volume. At critical plaque shapes the WSS changes rapidly resulting in sudden increases in leukocyte TEM suggesting lumen volumes that will give rise to rapid plaque growth rates if left untreated. Overall this multi-scale and multi-physics approach appropriately captures and integrates the spatiotemporal events occurring at the cellular level in order to predict leukocyte transmigration and plaque evolution.

Harnessing macrophage plasticity for tissue regeneration

Macrophages are versatile and plastic effector cells of the immune system, and contribute to diverse immune functions including pathogen or apoptotic cell removal, inflammatory activation and resolution, and tissue healing. Macrophages function as signaling regulators and amplifiers, and influencing their activity is a powerful approach for controlling inflammation or inducing a wound-healing response in regenerative medicine. This review discusses biomaterials-based approaches for altering macrophage activity, approaches for targeting drugs to macrophages, and approaches for delivering macrophages themselves as a therapeutic intervention.

Identification of the histone lysine demethylase KDM4A/JMJD2A as a novel epigenetic target in M1 macrophage polarization induced by oxidized LDL

Oxidized low density lipoprotein (oxLDL) induces macrophage activation, an event essential for atherosclerosis. Emerging evidence supports that epigenetic regulation plays important roles in macrophage activation and function. However, it remains unclear which epigenetic modulator is responsible for oxLDL-induced macrophage activation. Here, we identify for the first time KDM4A (JMJD2A) as an epigenetic modifying enzyme that controls oxLDL-induced pro-inflammatory M1 polarization of macrophages. OxLDL triggered M1 polarization of murine and human macrophages, characterized by expression of iNOS and robust production of inflammatory cytokines (e.g., TNF-α, MCP-1, IL-1β). In contrast, protein level of the M2 marker Arg1 was clearly decreased after treated with oxLDL. Notably, exposure to oxLDL resulted in markedly increased expression of KDM4A in macrophages. Functionally, shRNA knockdown of KDM4A significantly impaired M1 polarization and expression of inflammatory cytokines induced by oxLDL, accompanied by increased expression of Arg1 and VEGF. However, inhibition of KDM4A by shRNA or the pan-selective KDM inhibitor JIB-04 did not affect oxLDL-mediated activation of the NF-κB and hypoxia inducible factor (HIF) pathways, and vice versa. In addition, JIB-04 induced apoptosis of macrophages in a dose-dependent manner, an event attenuated by oxLDL. Together, these findings argue that KDM4A might represent a novel epigenetic modulator that acts to direct oxLDL-induced M1 polarization of macrophages, while its up-regulation is independent of NF-κB and HIF activation, two signals critical for pro-inflammatory activation of macrophages. They also suggest that KDM4A might serve as a potential target for epigenetic therapy in prevention and treatment of inflammatory diseases such as atherosclerosis.

Pentraxin 3 recruits complement factor H to protect against oxidative stress-induced complement and inflammasome overactivation

The discovery that genetic abnormalities in complement factor H (FH) are associated with an increased risk for age-related macular degeneration (AMD), the most common cause of blindness among the elderly, raised hope of new treatments for this vision-threatening disease. Nonetheless, over a decade after the identification of this important association, how innate immunity contributes to AMD remains unresolved. Pentraxin 3 (PTX3), an essential component of the innate immunity system that plays a non-redundant role in controlling inflammation, regulates complement by interacting with complement components. Here, we show that PTX3 is induced by oxidative stress, a known cause of AMD, in the retinal pigmented epithelium (RPE). PTX3 deficiency in vitro and in vivo magnified complement activation induced by oxidative stress, leading to increased C3a, FB, and C3d, but not C5b-9 complex formation. Increased C3a levels, resulting from PTX3 deficiency, raised the levels of Il1b mRNA and secretion of activated interleukin (IL)-1β by interacting with C3aR. Importantly, PTX3 deficiency augmented NLRP3 inflammasome activation, resulting in enhanced IL-1β, but not IL-18, production by the RPE. Thus, in the presence of PTX3 deficiency, the complement and inflammasome pathways worked in concert to produce IL-1β in sufficient abundance to, importantly, result in macrophages accumulating in the choroid. These results demonstrate that PTX3 acts as an essential brake for complement and inflammasome activation by regulating the abundance of FH in the RPE, and provide critical insights into the complex interplay between oxidative stress and innate immunity in the early stages of AMD development. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Arteriogenesis in murine adipose tissue is contingent on CD68+ /CD206+ macrophages

OBJECTIVE

The surgical transfer of skin, fat, and/or muscle from a donor site to a recipient site within the same patient is a widely performed procedure in reconstructive surgeries. A surgical pretreatment strategy that is intended to increase perfusion in the flap, termed "flap delay," is a commonly employed technique by plastic surgeons prior to flap transplantation. Here, we explored whether CD68+ /CD206+ macrophages are required for arteriogenesis within the flap by performing gain-of-function and loss-of-function studies in a previously published flap delay murine model.

METHODS AND RESULTS

Local injection of M2-polarized macrophages into the flap resulted in an increase in collateral vessel diameter. Application of a thin biomaterial film loaded with a pharmacological agent (FTY720), which has been previously shown to recruit CD68+ /CD206+ macrophages to remodeling tissue, increased CD68+ /CD206+ cell recruitment and collateral vessel enlargement. Conversely, when local macrophage populations were depleted within the inguinal fat pad via clodronate liposome delivery, we observed fewer CD68+ cells accompanied by diminished collateral vessel enlargement.

CONCLUSIONS

Our study underscores the importance of macrophages during microvascular adaptations that are induced by flap delay. These studies suggest a mechanism for a translatable therapeutic target that may be used to enhance the clinical flap delay procedure.

Biological incorporation of human acellular dermal matrix used in Achilles tendon repair

Human acellular dermal matrices (ADMs) are used successfully in a variety of procedures, including sports medicine related, wound repair, and breast reconstructions, but the mechanism of repair is still not fully understood. An opportunity to explore this mechanism presented itself when a patient experienced a rerupture of the native tendon due to a fall that occurred 2 months after undergoing an Achilles tendon repair using Matracell treated ADM. The ADM was removed and an extensive histology analysis was performed on the tissue. Additionally, a literature review was conducted to determine the mechanism of ADM integration into the tendon structure and explore if differences in this mechanism exist for different types of human ADMS. The histology analysis demonstrated that the healing process during a tendon reconstruction procedure is similar to that of wound healing. Furthermore, the literature review showed that differences exist in the mechanism for integration among various human ADMs and that these differences may be due to variances in the methods and technologies that manufactures use to process human ADMs.

Nuclear Factor (Erythroid-Derived 2)-Like 2 and Thioredoxin-1 in Atherosclerosis and Ischemia/Reperfusion Injury in the Heart

SIGNIFICANCE

Redox signaling is one of the key elements involved in cardiovascular diseases. Two important molecules are the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and the oxidoreductase thioredoxin-1 (Trx-1). Recent Advances: During the previous years, a lot of studies investigated Nrf2 and Trx-1 as protective proteins in cardiovascular disorders. Moreover, post-translational modifications of those molecules were identified that play an important role in the cardiovascular system. This review will summarize changes in the vasculature in atherosclerosis and ischemia reperfusion injury of the heart and the newest findings achieved with Nrf2 and Trx-1 therein. Interestingly, Nrf2 and Trx-1 can act together as well as independently of each other in protection against atherosclerosis and ischemia and reperfusion injury.

CRITICAL ISSUES

In principle, pharmacological activation of a transcription factor-like Nrf2 can be dangerous, since a transcription regulator has multiple targets and the pleiotropic effects of such activation should not be ignored. Moreover, overactivation of Nrf2 as well as long-term treatment with Trx-1 could be deleterious for the cardiovascular system.

FUTURE DIRECTIONS

Therefore, the length of treatment with Nrf2 activators and/or Trx-1 has first to be studied in more detail in cardiovascular disorders. Moreover, a combination of Nrf2 activators and Trx-1 should be investigated and taken into consideration. Antioxid. Redox Signal. 26, 630-644.

Inhibition of Hematopoietic Cell Kinase Activity Suppresses Myeloid Cell-Mediated Colon Cancer Progression

Aberrant activation of the SRC family kinase hematopoietic cell kinase (HCK) triggers hematological malignancies as a tumor cell-intrinsic oncogene. Here we find that high HCK levels correlate with reduced survival of colorectal cancer patients. Likewise, increased Hck activity in mice promotes the growth of endogenous colonic malignancies and of human colorectal cancer cell xenografts. Furthermore, tumor-associated macrophages of the corresponding tumors show a pronounced alternatively activated endotype, which occurs independently of mature lymphocytes or of Stat6-dependent Th2 cytokine signaling. Accordingly, pharmacological inhibition or genetic reduction of Hck activity suppresses alternative activation of tumor-associated macrophages and the growth of colon cancer xenografts. Thus, Hck may serve as a promising therapeutic target for solid malignancies.

The immunology of atherosclerosis

Cardiovascular disease is the leading cause of death worldwide, both in the general population and among patients with chronic kidney disease (CKD). In most cases, the underlying cause of the cardiovascular event is atherosclerosis - a chronic inflammatory disease. CKD accelerates atherosclerosis via augmentation of inflammation, perturbation of lipid metabolism, and other mechanisms. In the artery wall, subendothelial retention of plasma lipoproteins triggers monocyte-derived macrophages and T helper type 1 (T_H1) cells to form atherosclerotic plaques. Inflammation is initiated by innate immune reactions to modified lipoproteins and is perpetuated by T_H1 cells that react to autoantigens from the apolipoprotein B100 protein of LDL. Other T cells are also active in atherosclerotic lesions; regulatory T cells inhibit pathological inflammation, whereas T_H17 cells can promote plaque fibrosis. The slow build-up of atherosclerotic plaques is asymptomatic, but plaque rupture or endothelial erosion can induce thrombus formation, leading to myocardial infarction or ischaemic stroke. Targeting risk factors for atherosclerosis has reduced mortality, but a need exists for novel therapies to stabilize plaques and to treat arterial inflammation. Patients with CKD would likely benefit from such preventive measures.

M1-like monocytes are a major immunological determinant of severity in previously healthy adults with life-threatening influenza

In each influenza season, a distinct group of young, otherwise healthy individuals with no risk factors succumbs to life-threatening infection. To better understand the cause for this, we analyzed a broad range of immune responses in blood from a unique cohort of patients, comprising previously healthy individuals hospitalized with and without respiratory failure during one influenza season, and infected with one specific influenza A strain. This analysis was compared with similarly hospitalized influenza patients with known risk factors (total of n = 60 patients recruited). We found a sustained increase in a specific subset of proinflammatory monocytes, with high TNF-α expression and an M1-like phenotype (independent of viral titers), in these previously healthy patients with severe disease. The relationship between M1-like monocytes and immunopathology was strengthened using murine models of influenza, in which severe infection generated using different models (including the high-pathogenicity H5N1 strain) was also accompanied by high levels of circulating M1-like monocytes. Additionally, a raised M1/M2 macrophage ratio in the lungs was observed. These studies identify a specific subtype of monocytes as a modifiable immunological determinant of disease severity in this subgroup of severely ill, previously healthy patients, offering potential novel therapeutic avenues.

In a cohort of influenza patients, previously healthy and young patients who succumbed to life-threatening disease were defined by high levels of circulating M1-like, TNF-α^hi monocytes.

Maxed out macs: physiologic cell clearance as a function of macrophage phagocytic capacity

The phagocytic clearance of host cells is important for eliminating dying cells and for the therapeutic clearance of antibody-targeted cells. As ubiquitous, motile and highly phagocytic immune cells, macrophages are principal players in the phagocytic removal of host cells throughout the body. In recent years, great strides have been made in identifying the molecular mechanisms that control the recognition and phagocytosis of cells by macrophages. However, much less is known about the physical and metabolic constraints that govern the amount of cellular material macrophages can ingest and how these limitations affect the overall efficiency of host cell clearance in health and disease. In this review we will discuss, in the contexts of apoptotic cells and antibody-targeted malignant cells, how physical and metabolic factors associated with the internalization of host cells are relayed to the phagocytic machinery and how these signals can impact the overall efficiency of cell clearance. We also discuss how this information can be leveraged to increase cell clearance for beneficial therapeutic outcomes.

Crucial roles of macrophages in the pathogenesis of autoimmune disease

Macrophages are key players in various immune responses. In addition to functions in innate immunity such as antigen phagocytosis and cytokine production, antigen presentation by macrophage represents a link between innate and acquired immunity. During inflammatory processes, naïve monocytes differentiate into pro-inflammatory M1 and anti-inflammatory M2 macrophages. Resident monocytes/macrophages contribute to immune response that maintains tissue-specific homeostasis. In the target organs of autoimmune diseases, macrophages have dual functions in both the induction and suppression of autoimmune responses, which are mediated by production of various cytokines and chemokines, or by interaction with other immune cells. This review focuses on selected autoimmune diseases, such as systemic lupus erythematosus, multiple sclerosis, rheumatoid arthritis, and Sjögren’s syndrome, to illustrate the key roles of macrophages in the cellular or molecular pathogenesis of autoimmunity. In addition, the contribution of macrophages to each autoimmune disease is compared.

Aorta macrophage inflammatory and epigenetic changes in a murine model of obstructive sleep apnea: Potential role of CD36

Obstructive sleep apnea (OSA) affects 8-10% of the population, is characterized by chronic intermittent hypoxia (CIH), and causally associates with cardiovascular morbidities. In CIH-exposed mice, closely mimicking the chronicity of human OSA, increased accumulation and proliferation of pro-inflammatory metabolic M1-like macrophages highly expressing CD36, emerged in aorta. Transcriptomic and MeDIP-seq approaches identified activation of pro-atherogenic pathways involving a complex interplay of histone modifications in functionally-relevant biological pathways, such as inflammation and oxidative stress in aorta macrophages. Discontinuation of CIH did not elicit significant improvements in aorta wall macrophage phenotype. However, CIH-induced aorta changes were absent in CD36 knockout mice, Our results provide mechanistic insights showing that CIH exposures during sleep in absence of concurrent pro-atherogenic settings (i.e., genetic propensity or dietary manipulation) lead to the recruitment of CD36(+)^high macrophages to the aortic wall and trigger atherogenesis. Furthermore, long-term CIH-induced changes may not be reversible with usual OSA treatment.

PKC-epsilon and TLR4 synergistically regulate resistin-mediated inflammation in human macrophages

BACKGROUND AND AIMS

Resistin has been associated with atherosclerotic inflammation and cardiovascular complications. We and others have previously shown that PKC-epsilon (PKCε) is involved in resistin-induced smooth muscle cell (VSMC) dysfunction at a high pathological concentration. This study aimed to evaluate the role and potential pathways of resistin at a physiological concentration, in atherosclerosis-related inflammation.

METHODS

Plasma from patients with atherosclerosis was analyzed for resistin concentration. Patients were divided into tertiles based on resistin levels and cytokines were compared between tertiles. Macrophages were then treated with resistin in the presence or absence of PKCε inhibitor and/or TLR4 blocking-antibody, and their inflammatory state was evaluated with ELISA, RT-PCR, immunocytochemistry, and Western blot.

RESULTS

We observed significant associations between plasma resistin levels and TNF-α, IL-6, IL-12, MIP-1α, MIP-1β, and CD40L. Our in vitro analyses revealed that resistin activated PKCε via TLR4. This was followed by NF-kB activation and induction of a pro-inflammatory phenotype in macrophages, significantly upregulating CD40, downregulating CD206 and stimulating gene expression and secretion of the inflammatory cytokines, for which we found association in our plasma analysis. Resistin also induced persistent TRAM and CD40L upregulation up to 36 h after resistin treatment. PKCε and TLR4 inhibitors suppressed gene expression to levels similar to control, especially when used in combination.

CONCLUSIONS

Resistin, at a physiological concentration, exacerbates the inflammatory response of macrophages. PKCε is a key upstream mediator in resistin-induced inflammation that may interact synergistically with TLR4 to promote NF-kB activation, while TRAM is an important signal. PKCε and TRAM may represent novel molecular targets for resistin-associated chronic atherosclerotic inflammation.

Identification of a novel series of anti-inflammatory and anti-oxidative phospholipid oxidation products containing the cyclopentenone moiety in vitro and in vivo: Implication in atherosclerosis

Oxidative stress and inflammation are two major contributing factors to atherosclerosis, a leading cause of cardiovascular disease. Oxidation of phospholipids on the surface of low density lipoprotein (LDL) particles generated under oxidative stress has been associated with the progression of atherosclerosis, but the underlying molecular mechanisms remain poorly defined. We identified a novel series of oxidation products containing the cyclopentenone moiety, termed deoxy-A₂/J₂-isoprostanes-phosphocholine, from 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine in vivo using mass spectrometry and by comparison to a chemically synthesized standard. Transcriptomic analysis (RNA-seq) demonstrated that these compounds affected >200 genes in bone marrow-derived macrophages, and genes associated with inflammatory and anti-oxidative responses are among the top 5 differentially expressed. To further investigate the biological relevance of these novel oxidized phospholipids in atherosclerosis, we chemically synthesized a representative compound 1-palmitoyl-2-15-deoxy-δ-12,14-prostaglandin J₂-sn-glycero-3-phosphocholine (15d-PGJ₂-PC) and found that it induced anti-inflammatory and anti-oxidant responses in macrophages through modulation of NF-κB, peroxisome proliferator-activated receptor γ (PPARγ), and Nrf2 pathways; this compound also showed potent anti-inflammatory properties in a mice model of LPS-induced systematic inflammatory response syndrome. Additionally, 15d-PGJ₂-PC inhibited macrophage foam cell formation, suggesting a beneficial role against atherosclerosis. These properties were consistent with decreased levels of these compounds in the plasma of patients with coronary heart disease compared with control subjects. Our findings uncovered a novel molecular mechanism for the negative regulation of inflammation and positive enhancement of anti-oxidative responses in macrophages by these oxidized phospholipids in LDL in the context of atherosclerosis.