Heterogeneity of human macrophages in culture and in atherosclerotic plaques

Reprogramming and targeting of cholesterol metabolism in tumor-associated macrophages

Cholesterol, as a major component of cell membranes, is closely related to the metabolic regulation of cells and organisms; tumor-associated macrophages play an important push role in tumor progression. We know that tumor-associated macrophages are polarized from macrophages, and the abnormalities of cholesterol metabolism that may be induced during their polarization are worth discussing. This manuscript focuses on metabolic abnormalities in tumor-associated macrophages, and first provides a basic summary of the regulatory mechanisms of abnormal macrophage polarization. Subsequently, it comprehensively describes the features of abnormal glucose, lipid and cholesterol metabolism in TAMs as well as the different regulatory pathways. Then, the paper also discusses the link between abnormal cholesterol metabolism in TAMs and tumors, chronic diseases and aging. Finally, the paper summarizes cancer therapeutic strategies targeting cholesterol metabolism that are already in clinical trials, as well as nanomaterials capable of targeting cholesterol metabolism that are in the research stage, in the hope of providing value for the design of targeting materials. Overall, elucidating metabolic abnormalities in tumor-associated macrophages, particularly cholesterol metabolism, could provide assistance in tumor therapy and the design of targeted drugs.

The Role of mtDNA Mutations in Atherosclerosis: The Influence of Mitochondrial Dysfunction on Macrophage Polarization

Atherosclerosis is a complex inflammatory process associated with high-mortality cardiovascular diseases. Today, there is a growing body of evidence linking atherosclerosis to mutations of mitochondrial DNA (mtDNA). But the mechanism of this link is insufficiently studied. Atherosclerosis progression involves different cell types and macrophages are one of the most important. Due to their high plasticity, macrophages can demonstrate pro-inflammatory and pro-atherogenic (macrophage type M1) or anti-inflammatory and anti-atherogenic (macrophage type M2) effects. These two cell types, formed as a result of external stimuli, differ significantly in their metabolic profile, which suggests the central role of mitochondria in the implementation of the macrophage polarization route. According to this, we assume that mtDNA mutations causing mitochondrial disturbances can play the role of an internal trigger, leading to the formation of macrophage M1 or M2. This review provides a comparative analysis of the characteristics of mitochondrial function in different types of macrophages and their possible associations with mtDNA mutations linked with inflammation-based pathologies including atherosclerosis.

Macrophage membrane-camouflaged biomimetic nanoparticles for rheumatoid arthritis treatment via modulating macrophage polarization

Rheumatoid arthritis (RA) is a debilitating autoimmune disease characterized by chronic joint inflammation and cartilage damage. Current therapeutic strategies often result in side effects, necessitating the development of targeted and safer treatment options. This study introduces a novel nanotherapeutic system, 2-APB@DGP-MM, which utilizes macrophage membrane (MM)-encapsulated nanoparticles (NPs) for the targeted delivery of 2-Aminoethyl diphenylborinate (2-APB) to inflamed joints more effectively. The NPs are designed with a matrix metalloproteinase (MMP)-cleavable peptide, allowing for MMP-responsive drug release within RA microenvironment. Comprehensive in vitro and in vivo assays confirmed the successful synthesis and loading of 2-APB into the DSPE-GPLGVRGC-PEG (DGP) NPs, as well as their ability to repolarize macrophages from a pro-inflammatory M1 to an anti-inflammatory M2 phenotype. The NPs demonstrated high biocompatibility, low cytotoxicity, and enhanced cellular uptake. In a collagen-induced arthritis (CIA) mouse model, intra-articular injection of 2-APB@DGP-MM significantly reduced synovial inflammation and cartilage destruction. Histological analysis corroborated these findings, demonstrating marked improvements in joint structure and delayed disease progression. Above all, the 2-APB@DGP-MM nanotherapeutic system offers a promising and safe approach for RA treatment by modulating macrophage polarization and delivering effective agents to inflamed joints.

Dynamic alterations in M2 macrophage subtypes enhance flap expansion efficiency and tissue regeneration

Dilatation of soft skin tissue is a common surgical procedure in plastic surgery. M2 macrophages play a critical role in reducing inflammation, promoting epithelial and vascular endothelial cell proliferation, enhancing collagen synthesis in fibroblasts, and orchestrating extracellular matrix remodelling by promoting angiogenesis, epithelialisation, and fibrosis. Macrophages improve flap survival by promoting microangiogenesis and collagen remodelling. However, the role of macrophages in flap expansion has not yet been investigated. Improving the expansion efficiency of dilatation flaps and promoting flap vascularisation are the pressing problems in the fields of plastic and reconstruction surgery. In the present study, we used a mouse model to assess the effects of macrophage activation on skin expansion, thickness, ultrastructure, intradermal angiogenesis, and collagen and cytokine levels. Our findings revealed dynamic changes in the macrophage content and subtypes within the expansion flaps. The enrichment of M2 macrophages significantly enhanced the efficiency of flap expansion, vascularisation, and collagen synthesis. Our findings underline the pivotal role of M2 macrophages in tissue regeneration at the molecular and biochemical levels. These findings provide a basis for improving flap expansion efficiency using M2 macrophages.

Disable 2, A Versatile Tissue Matrix Multifunctional Scaffold Protein with Multifaceted Signaling: Unveiling Role in Breast Cancer for Therapeutic Revolution

The Disabled-2 (DAB2) protein, found in 80-90% of various tumors, including breast cancer, has been identified as a potential tumor suppressor protein. On the contrary, some hypothesis suggests that DAB2 is associated with the modulation of the Ras/MAPK pathway by endocytosing the Grb/Sos1 signaling complex, which produces oncogenes and chemoresistance to anticancer drugs, leading to increased tumor growth and metastasis. DAB2 has multiple functions in several disorders and is typically under-regulated in several cancers, making it a potential target for treatment of cancer therapy. The primary function of DAB2 is the modulation of transforming growth factor- β (TGF-β) mediated endocytosis, which is involved in several mechanisms of cancer development, including tumor suppression through promoting apoptosis and suppressing cell proliferation. In this review, we will discuss in detail the mechanisms through which DAB2 leads to breast cancer and various advancements in employing DAB2 in the treatment of breast cancer. Additionally, we outlined its role in other diseases. We propose that upregulating DAB2 could be a novel approach to the therapeutics of breast cancer.

Mechanistic insight: Linking cardiovascular complications of inflammatory bowel disease

Cardiovascular diseases (CVD) are the leading cause of mortality worldwide despite an aggressive reduction of traditional cardiovascular risk factors. Underlying inflammatory conditions such as inflammatory bowel disease (IBD) increase the risk of developing CVD. A broad understanding of the underlying pathophysiological processes between IBD and CVD is required to treat and prevent cardiovascular events in patients with IBD. This review highlights the commonality between IBD and CVD, including dysregulated immune response, genetics, environmental risk factors, altered gut microbiome, stress, endothelial dysfunction and abnormalities, to shed light on an essential area of modern medicine.

Multilevel Heterogeneity of Colorectal Cancer Liver Metastasis

Colorectal cancer liver metastasis (CRLM) is a highly heterogeneous disease. Therapies that target both primary foci and liver metastasis are severely lacking. Therefore, understanding the features of metastatic tumor cells in the liver is valuable for the overall control of CRLM patients. In this review, we summarize the heterogeneity exhibited in CRLM from five aspects (gene, transcriptome, protein, metabolism, and immunity). In addition to genetic heterogeneity, the other four aspects exhibit significant heterogeneity. Compared to primary CRC, the dysregulation of epithelial-mesenchymal transition (EMT)-related proteins, the enhanced metabolic activity, and the increased infiltration of immunosuppressive cells are detected in CRLM. Preclinical evidence shows that targeting the EMT process or enhancing cellular metabolism may represent a novel approach to increasing the therapeutic efficacy of CRLM.

Macrophage polarization and metabolism in atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of fatty deposits in the inner walls of vessels. These plaques restrict blood flow and lead to complications such as heart attack or stroke. The development of atherosclerosis is influenced by a variety of factors, including age, genetics, lifestyle, and underlying health conditions such as high blood pressure or diabetes. Atherosclerotic plaques in stable form are characterized by slow growth, which leads to luminal stenosis, with low embolic potential or in unstable form, which contributes to high risk for thrombotic and embolic complications with rapid clinical onset. In this complex scenario of atherosclerosis, macrophages participate in the whole process, including the initiation, growth and eventually rupture and wound healing stages of artery plaque formation. Macrophages in plaques exhibit high heterogeneity and plasticity, which affect the evolving plaque microenvironment, e.g., leading to excessive lipid accumulation, cytokine hyperactivation, hypoxia, apoptosis and necroptosis. The metabolic and functional transitions of plaque macrophages in response to plaque microenvironmental factors not only influence ongoing and imminent inflammatory responses within the lesions but also directly dictate atherosclerotic progression or regression. In this review, we discuss the origin of macrophages within plaques, their phenotypic diversity, metabolic shifts, and fate and the roles they play in the dynamic progression of atherosclerosis. It also describes how macrophages interact with other plaque cells, particularly T cells. Ultimately, targeting pathways involved in macrophage polarization may lead to innovative and promising approaches for precision medicine. Further insights into the landscape and biological features of macrophages within atherosclerotic plaques may offer valuable information for optimizing future clinical treatment for atherosclerosis by targeting macrophages.

DHX9 Strengthens Atherosclerosis Progression By Promoting Inflammation in Macrophages

Atherosclerosis (AS) is the main cause of cerebrovascular diseases, and macrophages play important roles in atherosclerosis. DExH-Box helicase 9 (DHX9), as a member of DExD/H-box RNA helicase superfamily II, is identified as an autoantigen in the sera of systemic lupus erythematosus patients to trigger inflammation. The aim of this study was to investigate whether DHX9 is involved in AS development, especially in macrophages-mediated-inflammatory responses. We find that DHX9 expression is significantly increased in oxLDL or interferon-γ-treated macrophages and peripheral blood mononuclear cells (PBMCs) from patients with coronary artery disease (CAD). Knockdown of DHX9 inhibits lipid uptake and pro-inflammatory factors expression in macrophages, and ameliorates TNF-α-mediated monocyte adhesion capacity. Furthermore, we find that oxLDL stimulation promotes DHX9 interaction with p65 in macrophages, and further enhances the transcriptional activity of DHX9-p65-RNA Polymerase II complex to produce inflammatory factors. Moreover, using ApoE -/- mice fed with western diet to establish AS model, we find that knockdown of DHX9 mediated by adeno-associated virus-Sh-DHX9 through tail vein injection evidently alleviates AS progression in vivo. Finally, we also find that knockdown of DHX9 inhibits p65 activation, inflammatory factors expression, and the transcriptional activity of p65-RNA Polymerase II complex in PBMCs from patients with CAD. Overall, these results indicate that DHX9 promotes AS progression by enhancing inflammation in macrophages, and suggest DHX9 as a potential target for developing therapeutic drug.

Polysaccharides of Plantago asiatica enhance antitumor activity via regulating macrophages to M1-like phenotype

Monocyte-derived macrophages can be polarized into antitumor M1 phenotype, which inhibited the growth of tumors, and immune-suppressive M2 phenotype, which promoted the development and metastasis of tumors. Plantain polysaccharide (PLP), extracted from the Plantago asiatica, has shown its various biological activities. However, the ability of PLP involved in immune regulation was still obscure. Accordingly, we aimed to investigate whether PLP could polarize macrophages and further inhibit 4T1 tumor cells in vivo and in vitro. In this research, in vitro results showed that PLP displayed the potential in polarizing RAW264.7 macrophages into M1 phenotype and indirect inhibiting migratory effect on 4T1 cells. Furthermore, the phagocytosis and the release of reactive oxygen species (ROS) of macrophages were enhanced. In vivo anti-tumor results demonstrated that PLP could effectively inhibit the growth of 4T1 breast tumors by promoting accumulation of macrophages and T cells in the spleen and lymph node. In conclusion, these findings indicated that PLP inhibited the proliferation and progression of breast tumors by accumulating CD4⁺, CD8⁺ T cells and M1-like macrophages in lymph node and spleen, and therefore provided an experimental basis for PLP as a potential antitumor adjunctive therapy in preclinical and clinical trials.

Gene Expression Profiling of Peripheral Blood Mononuclear Cells in Type 2 Diabetes: An Exploratory Study

Background and Objectives: Visceral obesity is associated with chronic low-grade inflammation that predisposes to metabolic syndrome. Indeed, infiltration of adipose tissue with immune-inflammatory cells, including 'classical' inflammatory M1 and anti-inflammatory 'alternative' M2 macrophages, causes the release of a variety of bioactive molecules, resulting in the metabolic complications of obesity. This study examined the relative expression of macrophage phenotypic surface markers, cholesterol efflux proteins, scavenger receptors, and adenosine receptors in human circulating peripheral blood mononuclear cells (PBMCs), isolated from patients with type 2 diabetes mellitus (T2DM), with the aim to phenotypically characterize and identify biomarkers for these ill-defined cells. Materials and Methodology: PBMCs were isolated from four groups of adults: Normal-weight non-diabetic, obese non-diabetic, newly diagnosed with T2DM, and T2DM on metformin. The mRNA expression levels of macrophage phenotypic surface markers (interleukin-12 (IL-12), C-X-C motif chemokine ligand 10 (CXCL10), C-C motif chemokine ligand 17 (CCL17), and C-C motif receptor 7 (CCR7)), cholesterol efflux proteins (ATP-binding cassette transporter-1 (ABCA1), ATP binding cassette subfamily G member 1 (ABCG1), and sterol 27-hydroxylase (CYP27A)), scavenger receptors (scavenger receptor-A (SR-A), C-X-C motif ligand 16 (CXCL16), and lectin-like oxidized LDL receptor-1 (LOX-1)), and adenosine receptors (adenosine A2A receptor (A2AR) and adenosine A3 receptor (A3R)) were measured using qRT-PCR. Results: In PBMCs from T2DM patients, the expression of IL-12, CCR7, ABCA1, and SR-A1 was increased, whereas the expression of CXCL10, CCL17, ABCG1,27-hydroxylase, LOX-1, A2AR and A3R was decreased. On the other hand, treatment with the antidiabetic drug, metformin, reduced the expression of IL-12 and increased the expression of 27-hydroxylase, LOX-1, CXCL16 and A2AR. Conclusions: PBMCs in the circulation of patients with T2DM express phenotypic markers that are different from those typically present in adipose tissue M1 and M2 macrophages and could be representative of metabolically activated macrophages (MMe)-like cells. Our findings suggest that metformin alters phenotypic markers of MMe-like cells in circulation.

Unexpected Role of MPO-Oxidized LDLs in Atherosclerosis: In between Inflammation and Its Resolution

Inflammation and its resolution are the result of the balance between pro-inflammatory and pro-resolving factors, such as specialized pro-resolving mediators (SPMs). This balance is crucial for plaque evolution in atherosclerosis, a chronic inflammatory disease. Myeloperoxidase (MPO) has been related to oxidative stress and atherosclerosis, and MPO-oxidized low-density lipoproteins (Mox-LDLs) have specific characteristics and effects. They participate in foam cell formation and cause specific reactions when interacting with macrophages and endothelial cells. They also increase the production of intracellular reactive oxygen species (ROS) in macrophages and the resulting antioxidant response. Mox-LDLs also drive macrophage polarization. Mox-LDLs are known to be pro-inflammatory particles. However, in the presence of Mox-LDLs, endothelial cells produce resolvin D1 (RvD1), a SPM. SPMs are involved in the resolution of inflammation by stimulating efferocytosis and by reducing the adhesion and recruitment of neutrophils and monocytes. RvD1 also induces the synthesis of other SPMs. In vitro, Mox-LDLs have a dual effect by promoting RvD1 release and inducing a more anti-inflammatory phenotype macrophage, thereby having a mixed effect on inflammation. In this review, we discuss the interrelationship between MPO, Mox-LDLs, and resolvins, highlighting a new perception of the role of Mox-LDLs in atherosclerosis.

The effect of myeloperoxidase-oxidized LDL on THP-1 macrophage polarization and repolarization

Macrophages (Mφs) play a crucial role in the development of atherosclerosis by engulfing modified LDL particles and forming foam cells, the hallmark of atherosclerosis. Many studies suggest that myeloperoxidase-oxidized LDL (Mox-LDL) is an important pathophysiological model for LDL modification in vivo. Classically (M1) and alternatively activated (M2) Mφs are both implicated in the process of atherogenesis. Mφs are highly plastic cells whereby they undergo repolarization from M1 to M2 and vice versa. Since little is known about the effects of Mox-LDL on Mφ polarization and repolarization, our study aimed at evaluating the in vitro effects of Mox-LDL at this level through making use of the well-established model of human THP-1-derived Mφs. Resting M0-Mφs were polarized toward M1- and M2-Mφs, then M0-, M1- and M2-Mφs were all treated with physiological concentrations of Mox-LDL to assess the effect of Mox-LDL treatment on Mφ polarization and repolarization. Treatment of M0-Mφs with a physiological concentration of Mox-LDL had no significant effects at the level of their polarization. However, treatment of M1-Mφs with Mox-LDL resulted in a significant reduction in their IL-10 cytokine secretion. Our results point to a potential role of Mox-LDL in increasing the pro-inflammatory state in Mφs through reducing the release of the anti-inflammatory cytokine, IL-10.

Lipid-Laden Macrophages and Inflammation in Atherosclerosis and Cancer: An Integrative View

Atherosclerotic arterial plaques and malignant solid tumors contain macrophages, which participate in anaerobic metabolism, acidosis, and inflammatory processes inherent in the development of either disease. The tissue-resident macrophage populations originate from precursor cells derived from the yolk sac and from circulating bone marrow-derived monocytes. In the tissues, they differentiate into varying functional phenotypes in response to local microenvironmental stimulation. Broadly categorized, the macrophages are activated to polarize into proinflammatory M1 and anti-inflammatory M2 phenotypes; yet, noticeable plasticity allows them to dynamically shift between several distinct functional subtypes. In atherosclerosis, low-density lipoprotein (LDL)-derived cholesterol accumulates within macrophages as cytoplasmic lipid droplets thereby generating macrophage foam cells, which are involved in all steps of atherosclerosis. The conversion of macrophages into foam cells may suppress the expression of given proinflammatory genes and thereby initiate their transcriptional reprogramming toward an anti-inflammatory phenotype. In this particular sense, foam cell formation can be considered anti-atherogenic. The tumor-associated macrophages (TAMs) may become polarized into anti-tumoral M1 and pro-tumoral M2 phenotypes. Mechanistically, the TAMs can regulate the survival and proliferation of the surrounding cancer cells and participate in various aspects of tumor formation, progression, and metastasis. The TAMs may accumulate lipids, but their type and their specific roles in tumorigenesis are still poorly understood. Here, we discuss how the phenotypic and functional plasticity of macrophages allows their multifunctional response to the distinct microenvironments in developing atherosclerotic lesions and in developing malignant tumors. We also discuss how the inflammatory reactions of the macrophages may influence the development of atherosclerotic plaques and malignant tumors, and highlight the potential therapeutic effects of targeting lipid-laden macrophages in either disease.

A Src-H3 acetylation signaling axis integrates macrophage mechanosensation with inflammatory response

Macrophages are mechanosensitive cells that can exquisitely fine-tune their function in response to their microenvironment. While macrophage polarization results in concomitant changes in cell morphology and epigenetic reprogramming, how biophysically-induced signaling cascades contribute to gene regulatory programs that drive polarization remains unknown. We reveal a cytoskeleton-dependent Src-H3 acetylation (H3Ac) axis responsible for inflammation-associated histone hyperacetylation. Inflammatory stimuli caused increases in traction forces, Src activity and H3Ac marks in macrophages, accompanied by reduced cell elongation and motility. These effects were curtailed following disruption of H3Ac-signaling through either micropattern-induced cell elongation or inhibition of H3Ac readers (BRD proteins) directly. Src activation relieves the suppression of p300 histone acetyltransferase (HAT) activity by PKCδ. Furthermore, while inhibition of Src reduced p300 HAT activity and H3Ac marks globally, local H3Ac levels within the Src promoter were increased, suggesting H3Ac regulates Src levels through feedback. Together, our study reveals an adhesome-to-epigenome regulatory nexus underlying macrophage mechanosensation, where Src modulates H3Ac-associated epigenetic signaling as a means of tuning inflammatory gene activity and macrophage fate decisions in response to microenvironmental cues.

Leukocyte Trafficking via Lymphatic Vessels in Atherosclerosis

In recent years, lymphatic vessels have received increasing attention and our understanding of their development and functional roles in health and diseases has greatly improved. It has become clear that lymphatic vessels are critically involved in acute and chronic inflammation and its resolution by supporting the transport of immune cells, fluid, and macromolecules. As we will discuss in this review, the involvement of lymphatic vessels has been uncovered in atherosclerosis, a chronic inflammatory disease of medium- and large-sized arteries causing deadly cardiovascular complications worldwide. The progression of atherosclerosis is associated with morphological and functional alterations in lymphatic vessels draining the diseased artery. These defects in the lymphatic vasculature impact the inflammatory response in atherosclerosis by affecting immune cell trafficking, lymphoid neogenesis, and clearance of macromolecules in the arterial wall. Based on these new findings, we propose that targeting lymphatic function could be considered in conjunction with existing drugs as a treatment option for atherosclerosis.

The response of macrophages and their osteogenic potential modulated by micro/nano-structured Ti surfaces

Current understanding on the interactions between micro/nano-structured Ti surfaces and macrophages is still limited. In this work, TiO₂ nano-structures were introduced onto acid-etched Ti surfaces by alkali-heat treatment, ion exchange and subsequent heat treatment. By adjusting the concentration of NaOH during alkali-heat treatment, nano-flakes, nano-flakes mixed with nano-wires or nano-wires could formed on acid-etched Ti surfaces. The micro- and micro/nano-structured Ti surfaces possessed similar surface chemical and phase compositions. In vitro results indicate that the morphology of macrophages was highly dependent on the morphological features of nano-structures. Nano-flakes and nano-wires were favorable to induce the formation of lamellipodia and filopodia, respectively. Compared to micro-structured Ti surface, micro/nano-structured Ti surfaces polarized macrophages to their M2 phenotype and enhanced the gene expressions of osteogenic growth factors in macrophages. The M2 polarized macrophages promoted the maturation of osteoblasts. Compared to that with nano-flakes or nano-wires, the surface with mixed features of nano-flakes and nano-wires exhibited stronger anti-inflammatory and osteo-immunomodulatory effects. The findings presented in the current work suggest that introducing micro/nano-topographies onto Ti-based implant surfaces is a promising strategy to modulate the inflammatory response and mediate osteogenesis.

Phenotypic Modulation of Macrophages and Vascular Smooth Muscle Cells in Atherosclerosis-Nitro-Redox Interconnections

Monocytes/macrophages and vascular smooth muscle cells (vSMCs) are the main cell types implicated in atherosclerosis development, and unlike other mature cell types, both retain a remarkable plasticity. In mature vessels, differentiated vSMCs control the vascular tone and the blood pressure. In response to vascular injury and modifications of the local environment (inflammation, oxidative stress), vSMCs switch from a contractile to a secretory phenotype and also display macrophagic markers expression and a macrophagic behaviour. Endothelial dysfunction promotes adhesion to the endothelium of monocytes, which infiltrate the sub-endothelium and differentiate into macrophages. The latter become polarised into M1 (pro-inflammatory), M2 (anti-inflammatory) or Mox macrophages (oxidative stress phenotype). Both monocyte-derived macrophages and macrophage-like vSMCs are able to internalise and accumulate oxLDL, leading to formation of “foam cells” within atherosclerotic plaques. Variations in the levels of nitric oxide (NO) can affect several of the molecular pathways implicated in the described phenomena. Elucidation of the underlying mechanisms could help to identify novel specific therapeutic targets, but to date much remains to be explored. The present article is an overview of the different factors and signalling pathways implicated in plaque formation and of the effects of NO on the molecular steps of the phenotypic switch of macrophages and vSMCs.

Histopathological and Immune Prognostic Factors in Colo-Rectal Liver Metastases

Prognostic studies are increasingly providing new tools to stratify colo-rectal liver metastasis patients into clinical subgroups, with remarkable implications in terms of clinical management and therapeutic choice. Here, the strengths and hurdles of current prognostic tools in colo-rectal liver metastasis are discussed. Alongside more classic histopathological parameters, which capture features related to the tumor component, such as tumor invasion, tumor growth pattern and regression score, we will discuss immune mediators, which are starting to be considered important features. Their objective quantification has shown significant results in prognostication studies, with most of the work focused on adaptive immune cells, namely T cells. As for macrophages, they are only starting to be appreciated and we will present recent advances in evaluation of macrophage morphological features. Deeper knowledge acquired by multiparametric analyses is rapidly uncovering the variety of immune players that should be assessed. The future projection is to implement deep-learning histopathological tools and to integrate histopathological and immune metrics in multiparametric scores, with the ultimate objective to achieve a deeper resolution of the tumor features and their relevance for colo-rectal liver metastasis.

Cholesterol loading suppresses the atheroinflammatory gene polarization of human macrophages induced by colony stimulating factors

In atherosclerotic lesions, blood-derived monocytes differentiate into distinct macrophage subpopulations, and further into cholesterol-filled foam cells under a complex milieu of cytokines, which also contains macrophage-colony stimulating factor (M-CSF) and granulocyte-macrophage-colony stimulating factor (GM-CSF). Here we generated human macrophages in the presence of either M-CSF or GM-CSF to obtain M-MØ and GM-MØ, respectively. The macrophages were converted into cholesterol-loaded foam cells by incubating them with acetyl-LDL, and their atheroinflammatory gene expression profiles were then assessed. Compared with GM-MØ, the M-MØ expressed higher levels of CD36, SRA1, and ACAT1, and also exhibited a greater ability to take up acetyl-LDL, esterify cholesterol, and become converted to foam cells. M-MØ foam cells expressed higher levels of ABCA1 and ABCG1, and, correspondingly, exhibited higher rates of cholesterol efflux to apoA-I and HDL2. Cholesterol loading of M-MØ strongly suppressed the high baseline expression of CCL2, whereas in GM-MØ the low baseline expression CCL2 remained unchanged during cholesterol loading. The expression of TNFA, IL1B, and CXCL8 were reduced in LPS-activated macrophage foam cells of either subtype. In summary, cholesterol loading converged the CSF-dependent expression of key genes related to intracellular cholesterol balance and inflammation. These findings suggest that transformation of CSF-polarized macrophages into foam cells may reduce their atheroinflammatory potential in atherogenesis.

The neurorepellent, Slit2, prevents macrophage lipid loading by inhibiting CD36-dependent binding and internalization of oxidized low-density lipoprotein

Atherosclerosis is characterized by retention of modified lipoproteins, especially oxidized low density lipoprotein (oxLDL) within the sub-endothelial space of affected blood vessels. Recruited monocyte-derived and tissue-resident macrophages subsequently ingest oxLDL by binding and internalizing oxLDL via scavenger receptors, particularly CD36. The secreted neurorepellent, Slit2, acting through its transmembrane receptor, Roundabout-1 (Robo-1), was previously shown to inhibit recruitment of monocytes into nascent atherosclerotic lesions. The effects of Slit2 on oxLDL uptake by macrophages have not been explored. We report here that Slit2 inhibits uptake of oxLDL by human and murine macrophages, and the resulting formation of foam cells, in a Rac1-dependent and CD36-dependent manner. Exposure of macrophages to Slit2 prevented binding of oxLDL to the surface of cells. Using super-resolution microscopy, we observed that exposure of macrophages to Slit2 induced profound cytoskeletal remodeling with formation of a thick ring of cortical actin within which clusters of CD36 could not aggregate, thereby attenuating binding of oxLDL to the surface of cells. By inhibiting recruitment of monocytes into early atherosclerotic lesions, and the subsequent binding and internalization of oxLDL by macrophages, Slit2 could represent a potent new tool to combat individual steps that collectively result in progression of atherosclerosis.

A versatile and customizable low-cost 3D-printed open standard for microscopic imaging

Modern microscopes used for biological imaging often present themselves as black boxes whose precise operating principle remains unknown, and whose optical resolution and price seem to be in inverse proportion to each other. With UC2 (You. See. Too.) we present a low-cost, 3D-printed, open-source, modular microscopy toolbox and demonstrate its versatility by realizing a complete microscope development cycle from concept to experimental phase. The self-contained incubator-enclosed brightfield microscope monitors monocyte to macrophage cell differentiation for seven days at cellular resolution level (e.g. 2 μm). Furthermore, by including very few additional components, the geometry is transferred into a 400 Euro light sheet fluorescence microscope for volumetric observations of a transgenic Zebrafish expressing green fluorescent protein (GFP). With this, we aim to establish an open standard in optics to facilitate interfacing with various complementary platforms. By making the content and comprehensive documentation publicly available, the systems presented here lend themselves to easy and straightforward replications, modifications, and extensions.

Open standard microscopy is urgently needed to give low-cost solutions to researchers and to overcome the reproducibility crisis in science. Here the authors present a 3D-printed, open-source modular microscopy toolbox UC2 (You. See. Too.) for a few hundred Euros.

Macrophage morphology correlates with single-cell diversity and prognosis in colorectal liver metastasis

It has long been known that in vitro polarized macrophages differ in morphology. Stemming from a conventional immunohistology observation, we set out to test the hypothesis that morphology of tumor-associated macrophages (TAMs) in colorectal liver metastasis (CLM) represents a correlate of functional diversity with prognostic significance. Density and morphological metrics of TAMs were measured and correlated with clinicopathological variables. While density of TAMs did not correlate with survival of CLM patients, the cell area identified small (S-TAM) and large (L-TAM) macrophages that were associated with 5-yr disease-free survival rates of 27.8% and 0.2%, respectively (P < 0.0001). RNA sequencing of morphologically distinct macrophages identified LXR/RXR as the most enriched pathway in large macrophages, with up-regulation of genes involved in cholesterol metabolism, scavenger receptors, MERTK, and complement. In single-cell analysis of mononuclear phagocytes from CLM tissues, S-TAM and L-TAM signatures were differentially enriched in individual clusters. These results suggest that morphometric characterization can serve as a simple readout of TAM diversity with strong prognostic significance.

Human monocyte-derived macrophages: Pathogenetic role in plaque rupture associated to systemic inflammation

BACKGROUND

Macrophages play a key role in coronary plaque destabilization. In-vitro human monocyte-derived macrophages (MDMs) are used to study macrophages infiltrating tissue. Optical coherence tomography (OCT) provides an in-vivo insight of the coronary arteries. We compared the MDMs morpho-phenotype and culprit plaque features at OCT in acute coronary syndrome (ACS) patients according to the underlying plaque pathobiology.

METHODS

Sixty-six patients undergoing coronary angiography and pre-angioplasty OCT of the culprit vessel were allocated to three groups according to mechanism of ACS at OCT and C-reactive protein levels (cut-off: 2 mg/Ll): 1) plaque rupture with systemic inflammation; 2) plaque rupture without systemic inflammation, 3) plaque with intact fibrous cap. A blood sample was collected to obtain MDMs, categorized as having "round" or "spindle" morphology.

RESULTS

Thirty-two patients (48.5%) were assigned to Group 1, 10 (15.2%) to Group 2 and 24 (36.4%) to Group 3. The "round" MDMs were significantly more frequent in Group 1 (39.25 ± 4.98%) than in Group 2 (23.89 ± 3.10%) and Group 3 (23.02 ± 7.89%), p = 0.008. MDMs in Group 1 as compared to Groups 2 and 3 showed lower efferocytosis (8.74 ± 1.38 vs 9.74 ± 2.15 vs 11.41 ± 2.41; p = 0.012), higher tissue factor levels (369.84 ± 101.13 vs 301.89 ± 59.78 vs 231.74 ± 111.47; p = 0.001) and higher heme oxygenase-1 expression (678.78 ± 145.43 vs 419.12 ± 74.44 vs 409.78 ± 64.33; p = 0.008).

CONCLUSIONS

MDMs of ACS patients show morpho-phenotypic heterogeneity with prevalence of pro-thrombotic and pro-oxidative properties in case of plaque rupture and systemic inflammation. Such MDMs subpopulation may take part to the cellular pathways leading to fibrous cap rupture with the subsequent thrombus formation.

Acidic extracellular pH promotes accumulation of free cholesterol in human monocyte-derived macrophages via inhibition of ACAT1 activity

BACKGROUND AND AIMS

In focal areas of advanced human atherosclerotic lesions, the intimal fluid is acidic. An acidic medium impairs the ABCA1-mediated cholesterol efflux from macrophages, so tending to increase their content of free cholesterol, which is then available for esterification by the macrophage enzyme ACAT1. Here we investigated whether low extracellular pH would affect the activity of ACAT1.

METHODS

- Human monocyte-derived macrophages were first incubated with acetyl-LDL at neutral and acidic conditions (pH 7.5, 6.5, and 5.5) to generate foam cells, and then the foam cells were incubated with [³H]oleate-BSA complexes, and the formation of [³H]oleate-labeled cholesteryl esters was measured. ACAT1 activity was also measured in cell-free macrophage extracts.

RESULTS

- In acidic media, ACAT1-dependent cholesteryl [³H]oleate generation became compromised in the developing foam cells and their content of free cholesterol increased. In line with this finding, ACAT1 activity in the soluble cell-free fraction derived from macrophage foam cells peaked at pH 7, and gradually decreased under acidic pH with a rapid drop below pH 6.5. Incubation of macrophages under progressively more acidic conditions (until pH 5.5) lowered the cytosolic pH of macrophages (down to pH 6.0). Such intracellular acidification did not affect macrophage gene expression of ACAT1 or the neutral CEH.

CONCLUSIONS

Exposure of human macrophage foam cells to acidic conditions lowers their intracellular pH with simultaneous decrease in ACAT1 activity. This reduces cholesterol esterification and thus leads to accumulation of potentially toxic levels of free cholesterol, a contributing factor to macrophage foam cell death.

Prognostic significance of tumor-associated macrophages: past, present and future

Tumor tissues are populated by a multitude of macrophages, highly different in functional activity, localization and morphology. A clear contribution to disease progression has been shown in multiple cancer types, holding promise for the development of innovative macrophage-based prognostic tools. Current studies aimed at assessing the prognostic role of macrophages have documented the relevance of the macrophage population as a whole. However, dissecting the diversity of mononuclear phagocytes in tumor tissues has provided important information about the coexistence of distinct populations of macrophages with different prognostic significance. Here we summarize evidence of macrophage prognostic function in human cancer and focus on classical and modern strategies aimed at measuring macrophage features and deciphering their diversity. The wealth of new data generated will reshape our knowledge of macrophage complexity and hopefully foster the forthcoming development of these new metrics into prognostic tools as well as new therapeutic strategies.

Current Research Landscape of Marine-Derived Anti-Atherosclerotic Substances

Atherosclerosis is a chronic disease characterized by lipid accumulation and chronic inflammation of the arterial wall, which is the pathological basis for coronary heart disease, cerebrovascular disease and thromboembolic disease. Currently, there is a lack of low-cost therapeutic agents that effectively slow the progression of atherosclerosis. Therefore, the development of new drugs is urgently needed. The research and development of marine-derived drugs have gained increasing interest from researchers across the world. Many marine organisms provide a rich material basis for the development of atherosclerotic drugs. This review focuses on the latest technological advances in the structures and mechanisms of action of marine-derived anti-atherosclerotic substances and the challenges of the application of these substances including marine polysaccharides, proteins and peptides, polyunsaturated fatty acids and small molecule compounds. Here, we describe the theoretical basis of marine biological resources in the treatment of atherosclerosis.

Classic and new mediators for in vitro modelling of human macrophages

Macrophages are key immune cells in the activation and regulation of immune responses. These cells are present in all tissues under homeostatic conditions and in many disease settings. Macrophages can exhibit a wide range of phenotypes depending on local and systemic cues that drive the differentiation and activation process. Macrophage heterogeneity is also defined by their ontogeny. Tissue macrophages can either derive from circulating blood monocytes or are seeded as tissue-resident macrophages during embryonic development. In humans, the study of in vivo-generated macrophages is often difficult with laborious and cell-changing isolation procedures. Therefore, translatable, reproducible, and robust in vitro models for human macrophages in health and disease are necessary. Most of the methods for studying monocyte-derived macrophages are based on the use of limited factors to differentiate the monocytes into macrophages. Current knowledge shows that the in vivo situation is more complex, and a wide range of molecules in the tissue microenvironment promote and impact on monocyte to macrophage differentiation as well as activation. In this review, macrophage heterogeneity is discussed and the human in vitro models that can be applied for research, especially for monocyte-derived macrophages. We also focus on new molecules (IL-34, platelet factor 4, etc.) used to generate macrophages expressing different phenotypes.

Oral Microbiota and Immune System Crosstalk: A Translational Research

BACKGROUND

Oral pathogens may exert the ability to trigger differently the activation of local macrophage immune responses, for instance Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans induce predominantly pro-inflammatory (M1-like phenotypes) responses, while oral commensal microbiota primarily elicits macrophage functions consistent with the anti-inflammatory (M2-like phenotypes).

METHODS

In healthy individuals vs. periodontal disease patients' blood samples, the differentiation process from monocyte to M1 and M2 was conducted using two typical growth factors, the granulocyte/macrophage colony stimulating factor (GM-CSF) and the macrophage colony stimulating factor (M-CSF).

RESULTS

In contrast with the current literature our outcomes showed a noticeable increase of macrophage polarization from healthy individuals vs. periodontal patients. The biological and clinical significance of these data was discussed.

CONCLUSIONS

Our translational findings showed a significant variance between control versus periodontal disease groups in M1 and M2 marker expression within the second group significantly lower skews differentiation of M2-like macrophages towards an M1-like phenotype. Macrophage polarization in periodontal tissue may be responsible for the development and progression of inflammation-induced periodontal tissue damage, including alveolar bone loss, and modulating macrophage function may be a potential strategy for periodontal disease management.

Galectin-3 Identifies a Subset of Macrophages With a Potential Beneficial Role in Atherosclerosis

OBJECTIVE

Galectin-3 (formerly known as Mac-2), encoded by the LGALS3 gene, is proposed to regulate macrophage adhesion, chemotaxis, and apoptosis. We investigated the role of galectin-3 in determining the inflammatory profile of macrophages and composition of atherosclerotic plaques. Approach and Results: We observed increased accumulation of galectin-3-negative macrophages within advanced human, rabbit, and mouse plaques compared with early lesions. Interestingly, statin treatment reduced galectin-3-negative macrophage accrual in advanced plaques within hypercholesterolemic (apolipoprotein E deficient) Apoe-/- mice. Accordingly, compared with Lgals3+/+:Apoe-/- mice, Lgals3-/-:Apoe-/- mice displayed altered plaque composition through increased macrophage:smooth muscle cell ratio, reduced collagen content, and increased necrotic core area, characteristics of advanced plaques in humans. Additionally, macrophages from Lgals3-/- mice exhibited increased invasive capacity in vitro and in vivo. Furthermore, loss of galectin-3 in vitro and in vivo was associated with increased expression of proinflammatory genes including MMP (matrix metalloproteinase)-12, CCL2 (chemokine [C-C motif] ligand 2), PTGS2 (prostaglandin-endoperoxide synthase 2), and IL (interleukin)-6, alongside reduced TGF (transforming growth factor)-β1 expression and consequent SMAD signaling. Moreover, we found that MMP12 cleaves macrophage cell-surface galectin-3 resulting in the appearance of a 22-kDa fragment, whereas plasma levels of galectin-3 were reduced in Mmp12-/-:Apoe-/- mice, highlighting a novel mechanism where MMP12-dependent cleavage of galectin-3 promotes proinflammatory macrophage polarization. Moreover, galectin-3-positive macrophages were more abundant within plaques of Mmp12-/-:Apoe-/- mice compared with Mmp12+/+:Apoe-/- animals.

CONCLUSIONS

This study reveals a prominent protective role for galectin-3 in regulating macrophage polarization and invasive capacity and, therefore, delaying plaque progression.

Reblastatins Inhibit Phenotypic Changes of Monocytes/Macrophages in a Milieu Rich in 27-Hydroxycholesterol

We investigated effects of reblastatins on phenotypic changes in monocytes/macrophages induced by 27-hydroxycholesterol (27OHChol). Treatment of THP-1 monocytic cells with reblastatin derivatives, such as 17-demethoxy-reblastatin (17-DR), 18-dehydroxyl-17-demethoxyreblastatin (WK88-1), 18-hydroxyl-17-demethoxyreblastatin (WK88-2), and 18-hydroxyl-17-demethoxy-4,5-dehydroreblastatin (WK88-3), resulted in blockage of CCL2, CCL3, and CCL4 expression at the transcription and protein levels, which, in turn, impaired migration of monocytes/macrophages and Jurkat T cells expressing CCR5, and almost complete inhibition of transcription of M1 marker cytokines, like CXCL10, CXCL11, and TNF-α. Reblastatins also downregulated surface CD14 as well as soluble CD14 along with inhibition of LPS response and matrix metalloprotease-9 expression. Surface levels of mature dendritic cell (mDC)-specific markers, including CD80, CD83, CD88, CD197, and MHC class I and II molecules, were remarkably down-regulated, and 27OHChol-induced decrease of endocytic activity was recovered following treatment with 17-DR, WK88-1, WK88-2, and WK88-3. However, 15-hydroxyl-17-demethoxyreblastatin (DHQ3) did not affect the molecular or functional changes in monocytic cells induced by 27OHChol. Furthermore, surface levels of CD105, CD137, and CD166 were also down-regulated by 17-DR, WK88-1, WK88-2, and WK88-3, but not by DHQ3. Collectively, results of the current study indicate that, except DHQ3, reblastatins regulate the conversion and differentiation of monocytic cells to an immunostimulatory phenotype and mDCs, respectively, which suggests possible applications of reblastatins for immunomodulation in a milieu rich in oxygenated cholesterol molecules.

Diversity of macrophage phenotypes and responses in atherosclerosis

The presence of macrophages within the plaque is a defining hallmark of atherosclerosis. Macrophages are exposed to various microenvironments such as oxidized lipids and cytokines which effect their phenotypic differentiation and activation. Classically, macrophages have been divided into two groups: M1 and M2 macrophages induced by T-helper 1 and T-helper 2 cytokines, respectively. However, for a decade, greater phenotypic heterogeneity and plasticity of these cells have since been reported in various models. In addition to M1 and M2 macrophage phenotypes, the concept of additional macrophage phenotypes such as M (Hb), Mox, and M4 has emerged. Understanding the mechanisms and functions of distinct phenotype of macrophages can lead to determination of their potential role in atherosclerotic plaque pathogenesis. However, there are still many unresolved controversies regarding their phenotype and function with respect to atherosclerosis. Here, we summarize and focus on the differential subtypes of macrophages in atherosclerotic plaques and their differing functional roles based upon microenvironments such as lipid, intraplaque hemorrhage, and plaque regression.

Electronegative LDL Promotes Inflammation and Triglyceride Accumulation in Macrophages

Electronegative low-density lipoprotein (LDL) (LDL(−)), a modified LDL that is present in blood and exerts atherogenic effects on endothelial cells and monocytes. This study aimed to determine the action of LDL(−) on monocytes differentiated into macrophages. LDL(−) and in vitro-modified LDLs (oxidized, aggregated, and acetylated) were added to macrophages derived from THP1 monocytes over-expressing CD14 (THP1-CD14). Then, cytokine release, cell differentiation, lipid accumulation, and gene expression were measured by ELISA, flow cytometry, thin-layer chromatography, and real-time PCR, respectively. LDL(−) induced more cytokine release in THP1-CD14 macrophages than other modified LDLs. LDL(−) also promoted morphological changes ascribed to differentiated macrophages. The addition of high-density lipoprotein (HDL) and anti-TLR4 counteracted these effects. LDL(−) was highly internalized by macrophages, and it was the major inductor of intracellular lipid accumulation in triglyceride-enriched lipid droplets. In contrast to inflammation, the addition of anti-TLR4 had no effect on lipid accumulation, thus suggesting an uptake pathway alternative to TLR4. In this regard, LDL(−) upregulated the expression of the scavenger receptors CD36 and LOX-1, as well as several genes involved in triglyceride (TG) accumulation. The importance and novelty of the current study is that LDL(−), a physiologically modified LDL, exerted atherogenic effects in macrophages by promoting differentiation, inflammation, and triglyceride-enriched lipid droplets formation in THP1-CD14 macrophages, probably through different receptors.

Sonodynamic therapy in atherosclerosis by curcumin nanosuspensions: Preparation design, efficacy evaluation, and mechanisms analysis

Previous studies have shown that curcumin (Cur) induced by ultrasound has protective effects on atherosclerosis even if low bioavailability of the Cur. The enhancement of bioavailability of the Cur further improved the curative effect of sonodynamic therapy (SDT) on atherosclerosis through nanotechnology. Nanosuspensions as a good drug delivery system had obvious advantages in increasing the solubility and improving the effectiveness of insoluble drugs. The aim of this study was to develop curcumin nanosuspensions (Cur-ns) which used polyvinylpyrrolidone (PVPK30) and sodium dodecyl sulfate (SDS) as stabilizers to improve poor water solubility and bioavailability of the Cur. And then the therapeutic effects of Cur-ns-SDT on atherosclerotic plaques and its possible mechanisms would be investigated and elucidated. Cur-ns with a small particle size has been successfully prepared and the data have confirmed that Cur-ns could be more easily engulfed into RAW264.7 cells than free Cur and accumulated more under the stimulation of the ultrasound. Reactive oxygen species (ROS) inside RAW264.7 cells after SDT led to the decrease of mitochondrial membrane potential (MMP) and the higher expression of cleaved caspase-9/3. The results of in vivo experiments showed that Cur-ns-SDT reduced the level of total cholesterol (TC) and low density lipoprotein (LDL) and promoted the transformation from M1 to M2 macrophages, relieved atherosclerosis syndrome. Therefore, Cur-ns-SDT was a potential treatment of anti-atherosclerosis by enhancing macrophages apoptosis through mitochondrial pathway and inhibiting the progression of plaques by interfering with macrophages polarization.

Immune cells in carotid artery plaques: what can we learn from endarterectomy specimens?

INTRODUCTION

Endarterectomy specimens represent a unique opportunity to study atherosclerosis. This review aims to summarize the recent knowledge of atherogenesis from studies characterizing a cellular composition of carotid endarterectomy specimens.

EVIDENCE ACQUISITION

A non-systematic literature review was carried out to summarize recent knowledge regarding ex vivo analysis of carotid artery plaque composition. Upon evaluation of their relevance, and elaborate forward and backward search, 95 articles were included in the review.

EVIDENCE SYNTHESIS

Despite the significant advancement of in vivo imaging techniques, the stroke prediction based on carotid artery plaque morphology is not reliable. Besides analyses of plaque morphology, present studies focus on precise characterization of the different immune cell types and elucidation of their role in plaque development. Plaque content analyses revealed the presence of various immune cells in carotid artery plaques. Presence of different immune cells subpopulations can be connected to some undesirable changes in plaque stability.

CONCLUSIONS

Since the destabilization of the atherosclerotic plaque is a multifactorial process, a combination of various methods should be used to characterize the unstable plaques more accurately. In this context, studies characterizing plaque content from a cellular point of view could elucidate some processes underlying the plaque progression. Together with morphological evaluation, these analyses could enable more precise assessment of plaque stability.

Contrasting effects of membrane enrichment with polyunsaturated fatty acids on phospholipid composition and cholesterol efflux from cholesterol-loaded J774 mouse or primary human macrophages

A high consumption of polyunsaturated fatty acids (PUFAs), particularly n-3 PUFAs, is atheroprotective. PUFAs incorporation into membrane phospholipids alters the functionality of membrane proteins. We studied the consequences of the in vitro supplementation of several PUFAs on the FA profiles and on ABCA1-dependent cholesterol efflux capacities from cholesterol-loaded macrophages. Arachidonic acid (AA, C20:4 n-6) and, to a lesser extent, eicosapentaenoic acid (EPA, C20:5 n-3), dose-dependently impaired cholesterol efflux from cholesterol-loaded J774 mouse macrophages without alterations in ABCA1 expression, whereas docosahexaenoic acid (DHA, C22:6 n-3) had no impact. AA cells exhibited higher proportions of arachidonic acid and adrenic acid (C22:4 n-6), its elongation product. EPA cells exhibited slightly higher proportions of EPA associated with much higher proportions of docosapentaenoic acid (C22:5 n-3), its elongation product and with lower proportions of AA. Conversely, both EPA and DHA and, to a lesser extent, AA decreased cholesterol efflux from cholesterol-loaded primary human macrophages (HMDM). The differences observed in FA profiles after PUFA supplementations were different from those observed for the J774 cells. In conclusion, we are the first to report that AA and EPA, but not DHA, have deleterious effects on the cardioprotective ABCA1 cholesterol efflux pathway from J774 foam cells. Moreover, the membrane incorporation of PUFAs does not have the same impact on cholesterol efflux from murine (J774) or human (HMDM) cholesterol-loaded macrophages. This finding emphasizes the key role of the cellular model in cholesterol efflux studies and may partly explain the heterogeneous literature data on the impact of PUFAs on cholesterol efflux.

Immunobiology of Atherosclerosis: A Complex Net of Interactions

Cardiovascular disease is the leading cause of mortality worldwide, and atherosclerosis the principal factor underlying cardiovascular events. Atherosclerosis is a chronic inflammatory disease characterized by endothelial dysfunction, intimal lipid deposition, smooth muscle cell proliferation, cell apoptosis and necrosis, and local and systemic inflammation, involving key contributions to from innate and adaptive immunity. The balance between proatherogenic inflammatory and atheroprotective anti-inflammatory responses is modulated by a complex network of interactions among vascular components and immune cells, including monocytes, macrophages, dendritic cells, and T, B, and foam cells; these interactions modulate the further progression and stability of the atherosclerotic lesion. In this review, we take a global perspective on existing knowledge about the pathogenesis of immune responses in the atherosclerotic microenvironment and the interplay between the major innate and adaptive immune factors in atherosclerosis. Studies such as this are the basis for the development of new therapies against atherosclerosis.

Integrated DNA methylation and gene expression analysis identifies SLAMF7 as a key regulator of atherosclerosis

Atherosclerosis (AS) is a multifactorial disease. Exploration of DNA methylation in regulating gene transcription in a cell type- and stage-specific manner will shed light on understanding the biological processes associated with plaque stability. We identified 174 up-regulated genes with hypo-methylation in the promoter, and 86 down-regulated genes with hyper-methylation in the promoter, in AS vs. healthy controls. Among them, high expression of signaling lymphocytic activation molecule 7 (SLAM7) was examined in carotid plaque vs. intact tissue, in advanced plaque vs. early atherosclerotic tissue, and SLAMF7 protein expressed significantly higher in the unstable plaques than that in the stable plaques, especially in the CD68-positive macrophages. Depletion of SLAMF7 in plaque-derived macrophages induced a suppressed secretion of proinflammatory cytokines, and inhibited proliferation of vascular smooth muscle cells. These data provide emerging evidence that SLAMF7 could be a target of potential therapeutic intervention in carotid AS.

Biophysical regulation of macrophages in health and disease

Macrophages perform critical functions for homeostasis and immune defense in tissues throughout the body. These innate immune cells are capable of recognizing and clearing dead cells and pathogens, and orchestrating inflammatory and healing processes that occur in response to injury. In addition, macrophages are involved in the progression of many inflammatory diseases including cardiovascular disease, fibrosis, and cancer. Although it has long been known that macrophages respond dynamically to biochemical signals in their microenvironment, the role of biophysical cues has only recently emerged. Furthermore, many diseases that involve macrophages are also characterized by changes to the tissue biophysical environment. This review will discuss current knowledge about the effects of biophysical cues including matrix stiffness, material topography, and applied mechanical forces, on macrophage behavior. We will also describe the role of molecules that are known to be important for mechanotransduction, including adhesion molecules, ion channels, as well as nuclear mediators such as transcription factors, scaffolding proteins, and epigenetic regulators. Together, this review will illustrate a developing role of biophysical cues in macrophage biology, and also speculate upon molecular targets that may potentially be exploited therapeutically to treat disease.

CD14: Biology and role in the pathogenesis of disease

Human monocyte differentiation antigen CD14 is a pattern recognition receptor (PRR) that enhances innate immune responses. CD14 was first identified as a marker of monocytes to signal intracellular responses upon bacterial encounters. Given the absence of an intracellular tail, CD14 was doubted to have the signaling capacities. Later CD14 was confirmed as the TLR co-receptor for the detection of pathogen-associated molecular patterns. However, CD14 has been revealed as a multi-talented receptor. In last decade, CD14 was identified to activate NFAT to regulate the life cycle of myeloid cells in a TLR4-independent manner and to transport inflammatory lipids to induce phagocyte hyperactivation. And its influences on multiple related diseases have been further considered. In this review, we summarize advancements in the basic biology of the CD14 including its structure, binding ligands, signaling pathways, and its roles in the pathogenesis of inflammation, atherosclerosis, tumor and metabolic diseases. We also discuss the therapeutic potential of targeting the CD14 in related diseases.

Biological profile of monocyte-derived macrophages in coronary heart disease patients: implications for plaque morphology

The prevalence of a macrophage phenotype in atherosclerotic plaque may drive its progression and/or instability. Macrophages from coronary plaques are not available, and monocyte-derived macrophages (MDMs) are usually considered as a surrogate. We compared the MDM profile obtained from coronary artery disease (CAD) patients and healthy subjects, and we evaluated the association between CAD MDM profile and in vivo coronary plaque characteristics assessed by optical coherence tomography (OCT). At morphological analysis, MDMs of CAD patients had a higher prevalence of round than spindle cells, whereas in healthy subjects the prevalence of the two morphotypes was similar. Compared to healthy subjects, MDMs of CAD patients had reduced efferocytosis, lower transglutaminase-2, CD206 and CD163 receptor levels, and higher tissue factor (TF) levels. At OCT, patients with a higher prevalence of round MDMs showed more frequently a lipid-rich plaque, a thin-cap fibroatheroma, a greater intra-plaque macrophage accumulation, and a ruptured plaque. The MDM efferocytosis correlated with minimal lumen area, and TF levels in MDMs correlated with the presence of ruptured plaque. MDMs obtained from CAD patients are characterized by a morpho-phenotypic heterogeneity with a prevalence of round cells, showing pro-inflammatory and pro-thrombotic properties. The MDM profile allows identifying CAD patients at high risk.

Identification of Macrophage Genotype and Key Biological Pathways in Circulating Angiogenic Cell Transcriptome

Background

Circulating angiogenic cells (CAC) have been identified as important regulators of vascular biology. However, there is still considerable debate about the genotype and function of CAC.

Methods and Results

Data from publicly available gene expression data sets were used to analyse the transcriptome of in vitro cultured CAC (CAC_iv). Genes and pathways of interest were further evaluated using qPCR comparing CAC_iv versus CD14⁺ monocytic cells. The CAC_iv transcriptome strongly related to tissue macrophages, and more specifically to regulatory M2c macrophages. The cytokine expression profile of CAC_iv was predominantly immune modulatory and resembled the cytokine expression of tumor-associated macrophages (TAM). Pathway analysis revealed previously unrecognized biological processes in CAC_iv, such as riboflavin metabolism and liver X receptor (LXR)/retinoid X receptor (RXR) and farnesoid X receptor (FXR)/retinoid X receptor (RXR) pathways. Analysis of endothelial-specific genes did not show evidence for endothelial transdifferentiation.

Conclusions

CAC_iv are genotypically similar to regulatory M2c macrophages and lack signs of endothelial differentiation.

Nicotinamide Phosphate Transferase (NAMPT) Increases in Plasma in Patients with Acute Coronary Syndromes, and Promotes Macrophages to M2 Polarization

Atherosclerosis is an inflammatory disease; monocytes and macrophages play an important role in the progression of this disease. However, the mechanisms are not fully understood yet. Nicotinamide phosphate transferase (NAMPT) is the rate limiting enzyme in the synthesis of NAD, but extracellular NAMPT shows the characteristics of cytokines/adipokines, suggesting that it may be a link between metabolism and inflammation. In this study, we compared the expression levels of the NAMPT/NAD+/Sirt1 signaling pathway as well as NAMPT, CRP and IL-6 in the peripheral blood mononuclear cell (PBMC), and plasma in patients with acute coronary syndromes and healthy subjects, and analyzed their association with macrophage polarization. The relationship between eNAMPT and iNAMPT and the polarization of macrophages was analyzed by NAD+, NAMPT blocker, and neutralizing antibody treatment. The results showed that the expression of the NAMPT/NAD+/Sirt1 signaling pathway was up-regulated in the peripheral blood of patients with ACS. Inhibition of iNAMPT expression can reduce M1 polarization; however, there was no significant effect on eNAMPT secretion and M2 polarization. Neutralizing eNAMPT by neutralizing antibodies can reduce M2 polarization and decrease the expression levels of IL-10, IL-13, IL-4 and IL-1ra. The addition of NAD+ in the cell culture supernatant had no significant effect on the polarization of M1 but increased the M2 polarization and the expression levels of IL-10 and IL-1ra. Our findings suggested that NAMPT is involved in the pathogenesis of atherosclerosis; the increased expression of eNAMPT in ACS patients may play a protective role by the up regulation of the NAMPT/NAD+/Sirt1 signaling pathway.

Interplay of Autophagy Inducer Rapamycin and Proteasome Inhibitor MG132 in Reduction of Foam Cell Formation and Inflammatory Cytokine Expression

MG132 is a pivotal inhibitor of the ubiquitin-proteasome system (UPS), and rapamycin (RAPA) is an important inducer of autophagy. MG132 and RAPA have been shown to be effective agents that can cure multiple autoimmune diseases by reducing inflammation. Although individual MG132 and RAPA showed protective effects for atherosclerosis (AS), the combined effect of these two drugs and its molecular mechanism are still unclear. In this article we investigate the regulation of oxidative modification of low-density lipoprotein (ox-LDL) stress and foam cell formation in the presence of both proteasome inhibitor MG132 and the autophagy inducer RAPA to uncover the molecular mechanism underlying this process. We established the foam cells model by ox-LDL and an animal model. Then, we tested six experimental groups of MG132, RAPA, and 3MA drugs. As a result, RAPA-induced autophagy reduces accumulation of polyubiquitinated proteins and apoptosis of foam cells. The combination of MG132 with RAPA not only suppressed expression of the inflammatory cytokines and formation of macrophage foam cells, but also significantly affected the NF-κB signaling pathway and the polarization of RAW 264.7 cells. These data suggest that the combination of proteasome inhibitor and autophagy inducer ameliorates the inflammatory response and reduces the formation of macrophage foam cells during development of AS. Our research provides a new way to suppress vascular inflammation and stabilize plaques of late atherosclerosis.

Lipid and Non-lipid Factors Affecting Macrophage Dysfunction and Inflammation in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease and a leading cause of human mortality. The lesional microenvironment contains a complex accumulation of variably oxidized lipids and cytokines. Infiltrating monocytes become polarized in response to these stimuli, resulting in a broad spectrum of macrophage phenotypes. The extent of lipid loading in macrophages influences their phenotype and consequently their inflammatory status. In response to excess atherogenic ligands, many normal cell processes become aberrant following a loss of homeostasis. This can have a direct impact upon the inflammatory response, and conversely inflammation can lead to cell dysfunction. Clear evidence for this exists in the lysosomes, endoplasmic reticulum and mitochondria of atherosclerotic macrophages, the principal lesional cell type. Furthermore, several intrinsic cell processes become dysregulated under lipidotic conditions. Therapeutic strategies aimed at restoring cell function under disease conditions are an ongoing coveted aim. Macrophages play a central role in promoting lesional inflammation, with plaque progression and stability being directly proportional to macrophage abundance. Understanding how mixtures or individual lipid species regulate macrophage biology is therefore a major area of atherosclerosis research. In this review, we will discuss how the myriad of lipid and lipoprotein classes and products used to model atherogenic, proinflammatory immune responses has facilitated a greater understanding of some of the intricacies of chronic inflammation and cell function. Despite this, lipid oxidation produces a complex mixture of products and with no single or standard method of derivatization, there exists some variation in the reported effects of certain oxidized lipids. Likewise, differences in the methods used to generate macrophages in vitro may also lead to variable responses when apparently identical lipid ligands are used. Consequently, the complexity of reported macrophage phenotypes has implications for our understanding of the metabolic pathways, processes and shifts underpinning their activation and inflammatory status. Using oxidized low density lipoproteins and its oxidized cholesteryl esters and phospholipid constituents to stimulate macrophage has been hugely valuable, however there is now an argument that only working with low complexity lipid species can deliver the most useful information to guide therapies aimed at controlling atherosclerosis and cardiovascular complications.