Maintenance of Macrophage Redox Status by ChREBP Limits Inflammation and Apoptosis and Protects against Advanced Atherosclerotic Lesion Formation

Dysregulated cellular metabolism in atherosclerosis: mediators and therapeutic opportunities

Accumulating evidence over the past decades has revealed an intricate relationship between dysregulation of cellular metabolism and the progression of atherosclerotic cardiovascular disease. However, an integrated understanding of dysregulated cellular metabolism in atherosclerotic cardiovascular disease and its potential value as a therapeutic target is missing. In this Review, we (1) summarize recent advances concerning the role of metabolic dysregulation during atherosclerosis progression in lesional cells, including endothelial cells, vascular smooth muscle cells, macrophages and T cells; (2) explore the complexity of metabolic cross-talk between these lesional cells; (3) highlight emerging technologies that promise to illuminate unknown aspects of metabolism in atherosclerosis; and (4) suggest strategies for targeting these underexplored metabolic alterations to mitigate atherosclerosis progression and stabilize rupture-prone atheromas with a potential new generation of cardiovascular therapeutics.

Interferon-gamma ameliorates experimental autoimmune encephalomyelitis by inducing homeostatic adaptation of microglia

Compelling evidence has shown that interferon (IFN)-γ has dual effects in multiple sclerosis and in its animal model of experimental autoimmune encephalomyelitis (EAE), with results supporting both a pathogenic and beneficial function. However, the mechanisms whereby IFN-γ may promote neuroprotection in EAE and its effects on central nervous system (CNS)-resident cells have remained an enigma for more than 30 years. In this study, the impact of IFN-γ at the peak of EAE, its effects on CNS infiltrating myeloid cells (MC) and microglia (MG), and the underlying cellular and molecular mechanisms were investigated. IFN-γ administration resulted in disease amelioration and attenuation of neuroinflammation associated with significantly lower frequencies of CNS CD11b⁺ myeloid cells and less infiltration of inflammatory cells and demyelination. A significant reduction in activated MG and enhanced resting MG was determined by flow cytometry and immunohistrochemistry. Primary MC/MG cultures obtained from the spinal cord of IFN-γ-treated EAE mice that were ex vivo re-stimulated with a low dose (1 ng/ml) of IFN-γ and neuroantigen, promoted a significantly higher induction of CD4⁺ regulatory T (Treg) cells associated with increased transforming growth factor (TGF)-β secretion. Additionally, IFN-γ-treated primary MC/MG cultures produced significantly lower nitrite in response to LPS challenge than control MC/MG. IFN-γ-treated EAE mice had a significantly higher frequency of CX3CR1^high MC/MG and expressed lower levels of program death ligand 1 (PD-L1) than PBS-treated mice. Most CX3CR1^highPD-L1^lowCD11b⁺Ly6G^- cells expressed MG markers (Tmem119, Sall2, and P2ry12), indicating that they represented an enriched MG subset (CX3CR1^highPD-L1^low MG). Amelioration of clinical symptoms and induction of CX3CR1^highPD-L1^low MG by IFN-γ were dependent on STAT-1. RNA-seq analyses revealed that in vivo treatment with IFN-γ promoted the induction of homeostatic CX3CR1^highPD-L1^low MG, upregulating the expression of genes associated with tolerogenic and anti-inflammatory roles and down-regulating pro-inflammatory genes. These analyses highlight the master role that IFN-γ plays in regulating microglial activity and provide new insights into the cellular and molecular mechanisms involved in the therapeutic activity of IFN-γ in EAE.

The role of ChREBP in carbohydrate sensing and NAFLD development

Excessive sugar consumption and defective glucose sensing by hepatocytes contribute to the development of metabolic diseases including type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). Hepatic metabolism of carbohydrates into lipids is largely dependent on the carbohydrate-responsive element binding protein (ChREBP), a transcription factor that senses intracellular carbohydrates and activates many different target genes, through the activation of de novo lipogenesis (DNL). This process is crucial for the storage of energy as triglycerides in hepatocytes. Furthermore, ChREBP and its downstream targets represent promising targets for the development of therapies for the treatment of NAFLD and T2DM. Although lipogenic inhibitors (for example, inhibitors of fatty acid synthase, acetyl-CoA carboxylase or ATP citrate lyase) are currently under investigation, targeting lipogenesis remains a topic of discussion for NAFLD treatment. In this Review, we discuss mechanisms that regulate ChREBP activity in a tissue-specific manner and their respective roles in controlling DNL and beyond. We also provide in-depth discussion of the roles of ChREBP in the onset and progression of NAFLD and consider emerging targets for NAFLD therapeutics.

LDL delivery of microbial small RNAs drives atherosclerosis through macrophage TLR8

Macrophages present a spectrum of phenotypes that mediate both the pathogenesis and resolution of atherosclerotic lesions. Inflammatory macrophage phenotypes are pro-atherogenic, but the stimulatory factors that promote these phenotypes remain incompletely defined. Here we demonstrate that microbial small RNAs (msRNA) are enriched on low-density lipoprotein (LDL) and drive pro-inflammatory macrophage polarization and cytokine secretion via activation of the RNA sensor toll-like receptor 8 (TLR8). Removal of msRNA cargo during LDL re-constitution yields particles that readily promote sterol loading but fail to stimulate inflammatory activation. Competitive antagonism of TLR8 with non-targeting locked nucleic acids was found to prevent native LDL-induced macrophage polarization in vitro, and re-organize lesion macrophage phenotypes in vivo, as determined by single-cell RNA sequencing. Critically, this was associated with reduced disease burden in distinct mouse models of atherosclerosis. These results identify LDL-msRNA as instigators of atherosclerosis-associated inflammation and support alternative functions of LDL beyond cholesterol transport.

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

Vitamin D boosts immune response of macrophages through a regulatory network of microRNAs and mRNAs

Vitamin D is associated with the stimulation of innate immunity, inflammation, and host defense against pathogens. Macrophages express receptors of Vitamin D, regulating transcription of genes related to immune processes. However, the transcriptional and post-transcriptional strategies controlling gene expression in differentiated macrophages, and how they are influenced by Vitamin D are not well understood. We studied whether Vitamin D enhances immune response by regulating the expression of microRNAs and mRNAs. Analysis of the transcriptome showed differences in expression of 199 genes, of which 68% were up-regulated, revealing the cell state of monocyte-derived macrophages differentiated with Vitamin D (D3-MDMs) as compared to monocyte-derived macrophages (MDMs). The differentially expressed genes appear to be associated with pathophysiological processes, including inflammatory responses, and cellular stress. Transcriptional motifs in promoter regions of up- or down-regulated genes showed enrichment of VDR motifs, suggesting possible roles of transcriptional activator or repressor in gene expression. Further, microRNA-Seq analysis indicated that there were 17 differentially expressed miRNAs, of which, 7 were up-regulated and 10 down-regulated, suggesting that Vitamin D plays a critical role in the regulation of miRNA expression during macrophages differentiation. The miR-6501-3p, miR-1273h-5p, miR-665, miR-1972, miR-1183, miR-619-5p were down-regulated in D3-MDMs compared to MDMs. The integrative analysis of miRNA and mRNA expression profiles predict that miR-1972, miR-1273h-5p, and miR-665 regulate genes PDCD1LG2, IL-1B, and CD274, which are related to the inflammatory response. Results suggest an essential role of Vitamin D in macrophage differentiation that modulates host response against pathogens, inflammation, and cellular stress.

Intron retention is a stress response in sensor genes and is restored by Japanese herbal medicines: A basis for future clinical applications

Intron retention (IR) is a regulatory mechanism that can retard protein production by acting at the level of mRNA processing. We recently demonstrated that IR occurs at the pre-symptomatic state during the aging process of a mouse model of aging, providing a promising biomarker for that state, and can be restored to the normal state by juzentaihoto (JTT), a Japanese herbal medicine (Kampo) (Okada et al. 2021). Here we characterized the genes that accumulate retained introns, examined the biological significance of increased IR in these genes for the host, and determined whether drugs other than JTT can have this effect. By analyzing RNA-sequencing data generated from the hippocampus of the 19-week-old SAMP8 mouse, a model for studying age-related depression and Alzheimer's disease, we showed that genes with increased IR are generally involved in multiple metabolic pathways and have pivotal roles in sensing homeostasis. We thus propose that IR is a stress response and works to fine-tune the expression of many downstream target genes, leading to lower levels of their translation under stress conditions. Interestingly, Kampo medicines, as well as other organic compounds, restored splicing of a specific set of retained introns in these sensor genes in accordance with the physiological recovery conditions of the host, which corresponds with the recovery of transcripts represented by differentially expressed genes. Thus, analysis of IR genes may have broad applicability in evaluating the pre-symptomatic state based on the extent of IR of selective sensor genes, opening a promising early diagnosis of any diseases and a strategy for evaluating efficacies of several drugs based on the extent of IR restoration of these sensor genes.

Long Noncoding RNA MIAT Controls Advanced Atherosclerotic Lesion Formation and Plaque Destabilization

Supplemental Digital Content is available in the text.

Long noncoding RNAs (lncRNAs) are important regulators of biological processes involved in vascular tissue homeostasis and disease development. The present study assessed the functional contribution of the lncRNA myocardial infarction-associated transcript (MIAT) to atherosclerosis and carotid artery disease.

The role of SIRT2 in vascular-related and heart-related diseases: A review

At present, cardiovascular disease is one of the important factors of human death, and there are many kinds of proteins involved. Sirtuins family proteins are involved in various physiological and pathological activities of the human body. Among them, there are more and more studies on the relationship between sirtuin2 (SIRT2) protein and cardiovascular diseases. SIRT2 can effectively inhibit pathological cardiac hypertrophy. The effect of SIRT2 on ischaemia‐reperfusion injury has different effects under different conditions. SIRT2 can reduce the level of reactive oxygen species (ROS), which may help to reduce the severity of diabetic cardiomyopathy. SIRT2 can affect a variety of cardiovascular diseases, energy metabolism and the ageing of cardiomyocytes, thereby affecting heart failure. SIRT2 also plays an important role in vascular disease. For endothelial cell damage used by oxidative stress, the role of SIRT2 is bidirectional, which is related to the degree of oxidative stress stimulation. When the degree of stimulation is small, SIRT2 plays a protective role, and when the degree of stimulation increases to a certain level, SIRT2 plays a negative role. In addition, SIRT2 is also involved in the remodelling of blood vessels and the repair of skin damage.

Walnut Supplementation Restores the SIRT1-FoxO3a-MnSOD/Catalase Axis in the Heart, Promotes an Anti-Inflammatory Fatty Acid Profile in Plasma, and Lowers Blood Pressure on Fructose-Rich Diet

The benefits of walnut (Juglans regia) consumption for metabolic health are known, but the molecular background underlying their putative antioxidant and anti-inflammatory/immunomodulatory effects is underexplored. We assessed that walnut supplementation (6 weeks) reverted unfavorable changes of the SIRT1/FoxO3a/MnSOD/catalase axis in the heart induced by fructose-rich diet (FRD). Intriguingly, Nox4 was increased by both FRD and walnut supplementation. FRD increased the cytosolic fraction and decreased the nuclear fraction of the uniquely elucidated ChREBP in the heart. The ChREBP nuclear fraction was decreased in control rats subjected to walnuts. In addition, walnut consumption was associated with a reduction in systolic BP in FRD and a decrease in fatty acid AA/EPA and AA/DHA ratios in plasma. In summary, the protective effect of walnut supplementation was detected in male rats following the fructose-induced decrease in antioxidative/anti-inflammatory capacity of cardiac tissue and increase in plasma predictors of low-grade inflammation. The current results provide a novel insight into the relationship between nutrients, cellular energy homeostasis, and the modulators of inflammatory/immune response in metabolic syndrome, emphasizing the heart and highlighting a track for translation into nutrition and dietary therapeutic approaches against metabolic disease.

Metabolic Consequences of Efferocytosis and its Impact on Atherosclerosis

Billions of cells undergo apoptosis daily and are swiftly removed by macrophages through an evolutionarily conserved program termed "efferocytosis". Consequently, macromolecules within an apoptotic cell significantly burden a phagocyte with nutrients, such as lipids, oligonucleotides, and amino acids. In response to this nutrient overload, metabolic reprogramming must occur for the process of efferocytosis to remain non-phlogistic and to execute successive rounds of efferocytosis. The inability to undergo metabolic reprogramming after efferocytosis drives inflammation and impairs its resolution, often promoting many chronic inflammatory diseases. This is particularly evident for atherosclerosis, as metabolic reprogramming alters macrophage function in every stage of atherosclerosis, from the early formation of benign lesions to the progression of clinically relevant atheromas and during atherosclerosis regression upon aggressive lipid-lowering. This Review focuses on the metabolic pathways utilized upon apoptotic cell ingestion, the consequences of these metabolic pathways in macrophage function thereafter, and the role of metabolic reprogramming during atherosclerosis. Due to the growing interest in this new field, I introduce a new term, "efferotabolism", as a means to define the process by which macrophages break down, metabolize, and respond to AC-derived macromolecules. Understanding these aspects of efferotabolism will shed light on novel strategies to combat atherosclerosis and compromised inflammation resolution.

NF-κB p65 regulates hepatic lipogenesis by promoting nuclear entry of ChREBP in response to a high carbohydrate diet

Overconsumption of sucrose and other sugars has been associated with nonalcoholic fatty liver disease (NAFLD). Reports suggest hepatic de novo lipogenesis (DNL) as an important contributor to and regulator of carbohydrate-induced hepatic lipid accumulation in NAFLD. The mechanisms responsible for the increase in hepatic DNL due to overconsumption of carbohydrate diet are less than clear; however, literatures suggest high carbohydrate diet to activate the lipogenic transcription factor carbohydrate response element-binding protein (ChREBP), which further transcribes genes involved in DNL. Here, we provide an evidence of an unknown link between nuclear factor kappa-light chain enhancer of activated B cells (NF-κB) activation and increased DNL. Our data indicates high carbohydrate diet to enforce nuclear shuttling of hepatic NF-κB p65 and repress transcript levels of sorcin, a cytosolic interacting partner of ChREBP. Reduced sorcin levels, further prompted ChREBP nuclear translocation, leading to enhanced DNL and intrahepatic lipid accumulation both in vivo and in vitro. We further report that pharmacological inhibition of NF-κB abrogated high carbohydrate diet-mediated sorcin repression and thereby prevented ChREBP nuclear translocation and this, in turn, attenuated hepatic lipid accumulation both in in vitro and in vivo. Additionally, sorcin knockdown blunted the lipid-lowering ability of the NF-κB inhibitor in vitro. Together, these data suggest a heretofore unknown role for NF-κB in regulating ChREBP nuclear localization and activation, in response to high carbohydrate diet, for further explorations in lines of NAFLD therapeutics.

Upregulation of Mlxipl induced by cJun in the spinal dorsal horn after peripheral nerve injury counteracts mechanical allodynia by inhibiting neuroinflammation

Mlxipl regulates glucose metabolism, lipogenesis and tumorigenesis and has a wide-ranging impact on human health and disease. However, the role of Mlxipl in neuropathic pain remains unknown. In this study, we found that Mlxipl was increased in the ipsilateral L4-L6 spinal dorsal horn after Spared Nerve Injury surgery. Knockdown of Mlxipl in the ipsilateral L4-L6 spinal dorsal horn by intraspinal microinjection aggravated Spared Nerve Injury-induced mechanical allodynia and inflammation in the spinal dorsal horn, on the contrary, overexpression of Mlxipl inhibited mechanical allodynia and inflammation. Subsequently, the rat Mlxipl promoter was analyzed using bioinformatics methods to predict the upstream transcription factor cJun. Luciferase assays and ChIP-qPCR confirmed that cJun bound to the promoter of Mlxipl and enhanced its expression. Finally, we demonstrated that Mlxipl inhibited the inflammatory responses of lipopolysaccharide-induced microglia and that Mlxipl was regulated by the transcription factor cJun. These findings suggested that cJun-induced Mlxipl upregulation in the spinal dorsal horn after peripheral nerve injury provided a protective mechanism for the development and progression of neuropathic pain by inhibiting microglial-derived neuroinflammation. Targeting Mlxipl in the spinal dorsal horn might represent an effective strategy for the treatment of neuropathic pain.

Metabolic Reprogramming of Macrophages in Atherosclerosis: Is It All about Cholesterol?

Hypercholesterolemia contributes to the chronic inflammatory response during the progression of atherosclerosis, in part by favoring cholesterol loading in macrophages and other immune cells. However, macrophages encounter a substantial amount of other lipids and nutrients after ingesting atherogenic lipoprotein particles or clearing apoptotic cells, increasing their metabolic load and impacting their behavior during atherosclerosis plaque progression. This review examines whether and how fatty acids and glucose shape the cellular metabolic reprogramming of macrophages in atherosclerosis to modulate the onset phase of inflammation and the later resolution stage, in which the balance is tipped toward tissue repair.

Intracellular and Intercellular Aspects of Macrophage Immunometabolism in Atherosclerosis

Macrophage immunometabolism, the changes in intracellular metabolic pathways that alter the function of these highly plastic cells, has been the subject of intense interest in the past few years, in part because macrophage immunometabolism plays important roles in atherosclerosis and other inflammatory diseases. In this review article, part of the Compendium on Atherosclerosis, we introduce the concepts of (1) intracellular immunometabolism-the canonical pathways of intrinsic cell activation leading to changes in intracellular metabolism, which in turn alter cellular function; and (2) intercellular immunometabolism-conditions in which intermediates of cellular metabolism are transferred from one cell to another, thereby altering the function of the recipient cell. The recent discovery that the metabolite cargo of dead and dying cells ingested through efferocytosis by macrophages can alter metabolic pathways and downstream function of the efferocyte is markedly changing the way we think about macrophage immunometabolism. Metabolic transitions of macrophages contribute to their functions in all stages of atherosclerosis, from lesion initiation to formation of advanced lesions characterized by necrotic cores, to lesion regression following aggressive lipid lowering. This review article discusses recent advances in our understanding of these different aspects of macrophage immunometabolism in atherosclerosis. With the increasing understanding of the roles of macrophage immunometabolism in atherosclerosis, new exciting concepts and potential targets for intervention are emerging.

Carbohydrate response element binding protein (ChREBP) correlates with colon cancer progression and contributes to cell proliferation

Cancers are characterized by reprogrammed glucose metabolisms to fuel cell growth and proliferation. Carbohydrate response element binding protein (ChREBP) is a glucose-mediated transcription factor that strongly regulates glycolytic and lipogenic pathways. It has been shown to associate with metabolic diseases, such as obesity, diabetes and non-alcoholic fatty liver diseases. However, how it associates with cancers has not been well understood. In this study, ChREBP expression was assessed by immunohistochemistry in colon tissue arrays containing normal colon tissue and cancer tissue at different clinical stages. Tissue mRNA levels of ChREBP were also measured in a cohort of colon cancer patients. We found that ChREBP mRNA and protein expression were significantly increased in colon cancer tissue compared to healthy colon (p < 0.001), and their expression was positively correlated to colon malignancy (for mRNA, p = 0.002; for protein p < 0.001). Expression of lipogenic genes (ELOVL6 and SCD1) in colon cancer was also positively associated with colon malignancy (for both genes, p < 0.001). In vitro, ChREBP knockdown with siRNA transfection inhibited cell proliferation and induced cell cycle arrest without changes in apoptosis in colon cancer cell lines (HT29, DLD1 and SW480). Glycolytic and lipogenic pathways were inhibited but the p53 pathway was activated after ChREBP knockdown. Taken together, ChREBP expression is associated with colon malignancy and it might contribute to cell proliferation via promoting anabolic pathways and inhibiting p53. In addition, ChREBP might represent a novel clinical useful biomarker to evaluate the malignancy of colon cancer.

miR-221 Alleviates the Ox-LDL-Induced Macrophage Inflammatory Response via the Inhibition of DNMT3b-Mediated NCoR Promoter Methylation

Atherosclerosis (AS) is a chronic inflammatory disease, and macrophages play a key role in all phases of AS. Recent studies have shown that miR-221 is a biomarker for AS and stroke; however, the role and mechanism of miR-221 in AS are unclear. Herein, we found that miR-221 and NCoR levels were decreased in ox-LDL-treated THP-1-derived macrophages. In contrast, DNMT3b, IL-6, and TNF-α expression levels were increased under these conditions. Upregulation of miR-221 or NCoR could partially inhibit ox-LDL-induced IL-6 and TNF-α expression. Further studies showed that DNMT3b was a target of miR-221. DNMT3b inhibition also suppressed IL-6 and TNF-α expression and increased NCoR expression in the presence of ox-LDL. Moreover, DNMT3b was involved in ox-LDL-induced DNA methylation in the promoter region of NCoR. These findings suggest that miR-221 suppresses ox-LDL-induced inflammatory responses via suppressing DNMT3b-mediated DNA methylation in the promoter region of NCoR. These results provide a rationale for using intracellular miR-211 as a possible antiatherosclerotic target.

Metabolomic fingerprint of coronary blood in STEMI patients depends on the ischemic time and inflammatory state

In this study we investigated whether the metabolomic analysis could identify a specific fingerprint of coronary blood collected during primary PCI in STEMI patients. Fifteen samples was subjected to metabolomic analysis. Subsequently, the study population was divided into two groups according to the peripheral blood neutrophil-to-lymphocyte ratio (NLR), a marker of the systemic inflammatory response. Regression analysis was then applied separately to the two NLR groups. A partial least square (PLS) regression identified the most significant involved metabolites and the PLS-class analysis revealed a significant correlation between the metabolic profile and the total ischemic time only in patients with an NLR > 5.77.

Lysosomal Cholesterol Hydrolysis Couples Efferocytosis to Anti-Inflammatory Oxysterol Production

RATIONALE

Macrophages face a substantial amount of cholesterol after the ingestion of apoptotic cells, and the LIPA (lysosomal acid lipase) has a major role in hydrolyzing cholesteryl esters in the endocytic compartment.

OBJECTIVE

Here, we directly investigated the role of LIPA-mediated clearance of apoptotic cells both in vitro and in vivo.

METHODS AND RESULTS

We show that LIPA inhibition causes a defective efferocytic response because of impaired generation of 25-hydroxycholesterol and 27-hydroxycholesterol. Reduced synthesis of 25-hydroxycholesterol after LIPA inhibition contributed to defective mitochondria-associated membrane leading to mitochondrial oxidative stress-induced NLRP3 (NOD-like receptor family, pyrin domain containing) inflammasome activation and caspase-1-dependent Rac1 (Ras-related C3 botulinum toxin substrate 1) degradation. A secondary event consisting of failure to appropriately activate liver X receptor-mediated pathways led to mitigation of cholesterol efflux and apoptotic cell clearance. In mice, LIPA inhibition caused defective clearance of apoptotic lymphocytes and stressed erythrocytes by hepatic and splenic macrophages, culminating in splenomegaly and splenic iron accumulation under hypercholesterolemia.

CONCLUSIONS

Our findings position lysosomal cholesterol hydrolysis as a critical process that prevents metabolic inflammation by enabling efficient macrophage apoptotic cell clearance.

Metabolic adaptation of macrophages in chronic diseases

In response to physiological and pathological stimuli, macrophages are able to adapt and shape their phenotype, giving rise to a broad range of functional activation that is unique in different organs and different pathologies. The plasticity of macrophages is accomplished not only by di stinct signalling pathways and transcriptional profiles but also by specific engagement of preferential metabolic pathways. In the last decade, macrophage metabolism became the object of multiple studies showing that, by altering nutrient availability or by blocking specific metabolic pathway it is possible to skew macrophage phenotype and alter their effector functions. This field of research opens new therapeutic windows for the cure of several disease. Here we will give an overview of the current knowledge of macrophage metabolism in cancer, atherosclerosis and obesity and how this knowledge could be translated in therapeutic opportunities.

SIRT2 decreases atherosclerotic plaque formation in low-density lipoprotein receptor-deficient mice by modulating macrophage polarization

Compelling evidence has demonstrated that the M1 macrophage phenotype is central to atherosclerotic lesion development. SIRT2, an NAD⁺-dependent sirtuin deacetylase, is involved in modulating macrophage polarization. However, the role of SIRT2 in atherosclerotic progression remains unknown. Female LDL receptor knockout (LDLr^-/-) mice were randomly divided into four groups for treatment with saline, empty lentivirus, lentivirus-SIRT2, or shRNA-SIRT2 for 4 weeks. Thereafter, the mice were fed an atherogenic high-fat diet (HFD) for another 8 weeks. Atherosclerotic plaques were assessed in the aortic sinus by morphometry, immunohistochemistry and immunofluorescence analyses. Aortic levels of macrophage polarization markers were analysed by Western blot and immunofluorescence analyses. We found that lentivirus-SIRT2-treated LDLr^-/- mice had decreased plaque areas in the aortic sinus and developed a more stable plaque phenotype, as shown by decreased macrophage infiltration and apoptosis. In addition, treatment with lentivirus-SIRT2 significantly reduced the expression of iNOS (inducible nitric oxide synthase) and increased the levels of ARG-1 (arginase-1) in atheromas. These findings suggest that SIRT2 inhibited atherosclerotic plaque progression and enhanced plaque stability in LDLr^-/- mice by inhibiting macrophage polarization towards the M1 phenotype.

The regulation and role of carbohydrate response element-binding protein in metabolic homeostasis and disease

The transcription factor carbohydrate response element-binding protein (ChREBP) is a member of the basic helix-loop-helix leucine zipper transcription factor family. Under high-glucose conditions, it has a role in regulating the expression of key genes involved in various pathways, including glycolysis, gluconeogenesis and lipogenesis. It does this by forming a tetrameric complex made up of two ChREBP/Mlx heterodimers, which enables it to bind to the carbohydrate response element (ChoRE) in the promoter region of its target genes to regulate transcription. Because ChREBP plays a key role in glucose signalling and metabolism, and aberrations in glucose homeostasis are often present in metabolic diseases, this transcription factor presents itself as an enticing target with respect to further understanding metabolic disease mechanisms and potentially uncovering new therapeutic targets.

Atherosclerosis and Cancer; A Resemblance with Far-reaching Implications

Atherosclerosis and cancer are chronic diseases considered two of the main causes of death all over the world. Taking into account that both diseases are multifactorial, they share not only several important molecular pathways but also many ethiological and mechanistical processes from the very early stages of development up to the advanced forms in both pathologies. Factors involved in their progression comprise genetic alterations, inflammatory processes, uncontrolled cell proliferation and oxidative stress, as the most important ones. The fact that external effectors such as an infective process or a chemical insult have been proposed to initiate the transformation of cells in the artery wall and the process of atherogenesis, emphasizes many similarities with the progression of the neoplastic process in cancer. Deregulation of cell proliferation and therefore cell cycle progression, changes in the synthesis of important transcription factors as well as adhesion molecules, an alteration in the control of angiogenesis and the molecular similarities that follow chronic inflammation, are just a few of the processes that become part of the phenomena that closely correlates atherosclerosis and cancer. The aim of the present study is therefore, to provide new evidence as well as to discuss new approaches that might promote the identification of closer molecular ties between these two pathologies that would permit the recognition of atherosclerosis as a pathological process with a very close resemblance to the way a neoplastic process develops, that might eventually lead to novel ways of treatment.

Sweet Sixteenth for ChREBP: Established Roles and Future Goals

With the identification of ChREBP in 2001, our interest in understanding the molecular control of carbohydrate sensing has surged. While ChREBP was initially studied as a master regulator of lipogenesis in liver and fat tissue, it is now clear that ChREBP functions as a central metabolic coordinator in a variety of cell types in response to environmental and hormonal signals, with wide implications in health and disease. Celebrating its sweet sixteenth birthday, we review here the current knowledge about the function and regulation of ChREBP throughout usual and less explored tissues, to recapitulate ChREBP's role as a whole-body glucose sensor.

MondoA/ChREBP: The usual suspects of transcriptional glucose sensing; Implication in pathophysiology

Identification of the Mondo glucose-responsive transcription factors family, including the MondoA and MondoB/ChREBP paralogs, has shed light on the mechanism whereby glucose affects gene transcription. They have clearly emerged, in recent years, as key mediators of glucose sensing by multiple cell types. MondoA and ChREBP have overlapping yet distinct expression profiles, which underlie their downstream targets and separate roles in regulating genes involved in glucose metabolism. MondoA can restrict glucose uptake and influences energy utilization in skeletal muscle, while ChREBP signals energy storage through de novo lipogenesis in liver and white adipose tissue. Because Mondo proteins mediate metabolic adaptations to changing glucose levels, a better understanding of cellular glucose sensing through Mondo proteins will likely uncover new therapeutic opportunities in the context of the imbalanced glucose homeostasis that accompanies metabolic diseases such as type 2 diabetes and cancer. Here, we provide an overview of structural homologies, transcriptional partners as well as the nutrient and hormonal mechanisms underlying Mondo proteins regulation. We next summarize their relative contribution to energy metabolism changes in physiological states and the evolutionary conservation of these pathways. Finally, we discuss their possible targeting in human pathologies.

Macrophages in vascular inflammation and atherosclerosis

Atherosclerosis is characterized by lipid accumulation and chronic inflammation of the arterial wall, and its main complications-myocardial infarction and ischemic stroke-together constitute the first cause of death worldwide. Accumulation of lipid-laden macrophage foam cells in the intima of inflamed arteries has long been recognized as a hallmark of atherosclerosis. However, in recent years, an unexpected complexity in the mechanisms of macrophage accumulation in lesions, in the protective and pathogenic functions performed by macrophages and how they are regulated has been uncovered. Here, we provide an overview of the latest developments regarding the various mechanisms of macrophage accumulation in lesion, the major functional features of lesion macrophages, and how the plaque microenvironment may affect macrophage phenotype. Finally, we discuss how best to apprehend the heterogeneous ontogeny and functionality of atherosclerotic plaque macrophages and argue that moving away from a rigid nomenclature of arbitrarily defined macrophage subsets would be beneficial for research in the field.

Fatty acid metabolism in macrophages: a target in cardio-metabolic diseases

PURPOSE OF REVIEW

Recent studies have highlighted that macrophages dynamically and autonomously handle all the facets of fatty acid (FA) metabolism including FA oxidation and FA synthesis as well as the synthesis of monounsaturated FAs and long chain n-3 and n-6 polyunsaturated FAs.

RECENT FINDINGS

Macrophage M2 polarization is associated with an increase of FA oxidation. However, whether increased FA oxidation simply correlates with or is required for M2 polarization needs to be further evaluated. Macrophage M1 polarization is associated with the activation of FA synthesis, which directly contributes to the inflammatory response and affects cholesterol homeostasis and neutral lipid accumulation. Finally, recent evidences suggest that macrophages are able to autonomously produce signaling monounsaturated FAs, such as palmitoleic acid (C16 : 1 n-7), and long chain n-3 and n-6 polyunsaturated FAs, such as arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid. This pathway is regulated by liver X receptors and has significant consequences on inflammation and on the FA composition of atheroma plaques.

SUMMARY

These studies shed new light on the tight relationship between FA metabolism, macrophage polarization, and M1/M2 macrophage functions. These processes may have major consequences for atherosclerosis pathogenesis as well as other metabolic disorders.

Dietary Macronutrient Composition Directs ChREBP Isoform Expression and Glucose Metabolism in Mice

Carbohydrate response element binding protein (ChREBP) is a lipogenic transcription factor that is thought to be involved in the development of hepatic steatosis and insulin resistance. Increased ChREBP expression in liver results in increased hepatic steatosis, and the isoform ChREBPβ in adipose tissue can predict insulin sensitivity in obese humans. As ChREBP is activated by glucose, it was postulated that the composition of diet would regulate ChREBP isoform expression in metabolically relevant tissues.

We compared the effects of diets with high complex carbohydrate, high fat, or a normal chow on ChREBP expression and metabolic parameters in C57BL/6 mice. We found that diets high in fat decrease ChREBP expression in adipose tissue, but isocaloric diets high in carbohydrate have no effect. Interestingly, this decrease in adipose ChREBP was associated with increased inflammatory markers. In the same animals a high carbohydrate diet induced a robust increase in hepatic ChREBPβ expression (≈2-fold; p = 0.0002), but little detectable change in the more abundant ChREBPα transcript. This change was accompanied by increased expression of target genes liver pyruvate kinase (p<0.0001), acetyl-CoA carboxylase (p = 0.0191) and stearoyl-CoA desaturase-1 (p = 0.0045). This increase in ChREBP expression was associated with increased hepatic steatosis, despite no changes in body weight or body fat when compared to chow-fed mice. Unexpectedly, mice fed a high carbohydrate diet displayed enhanced sensitivity to exogenous insulin, despite having mild glucose intolerance and increased liver steatosis.

In summary, we have shown the composition of diet can selectively regulate ChREBP isoform expression in a tissue specific manner. Furthermore, we have shown a high complex carbohydrate diet selectively increases hepatic ChREBPβ expression, which associates with hepatic steatosis but not insulin resistance. In contrast, a high fat diet reduces adipose ChREBP, which associates with inflammation and insulin resistance.

miR-155 Regulated Inflammation Response by the SOCS1-STAT3-PDCD4 Axis in Atherogenesis

Inflammation response plays a critical role in all phases of atherosclerosis (AS). Increased evidence has demonstrated that miR-155 mediates inflammatory mediators in macrophages to promote plaque formation and rupture. However, the precise mechanism of miR-155 remains unclear in AS. Here, we also found that miR-155 and PDCD4 were elevated in the aortic tissue of atherosclerotic mice and ox-LDL treated RAW264.7 cells. Further studies showed that miR-155 not only directly inhibited SOCS1 expression, but also increased the expression of p-STAT and PDCD4, as well as the production of proinflammation mediators IL-6 and TNF-α. Downregulation of miR-155 and PDCD4 and upregulation of SOCS1 obviously decreased the IL-6 and TNF-α expression. In addition, inhibition of miR-155 levels in atherosclerotic mice could notably reduce the IL-6 and TNF-α level in plasma and aortic tissue, accompanied with increased p-STAT3 and PDCD4 and decreased SOCS1. Thus, miR-155 might mediate the inflammation in AS via the SOCS1-STAT3-PDCD4 axis. These results provide a rationale for intervention of intracellular miR-155 as possible antiatherosclerotic targets.

DNMT1-PPARγ pathway in macrophages regulates chronic inflammation and atherosclerosis development in mice

The DNA methyltransferase-mediated proinflammatory activation of macrophages is causally linked to the development of atherosclerosis (AS). However, the role of DNMT1, a DNA methylation maintenance enzyme, in macrophage polarization and AS development remains obscure. Here, we established transgenic mice with macrophage-specific overexpression of DNMT1 (Tg^DNMT1) or PPAR-γ (Tg^PPAR-γ) to investigate their effects on AS progression in ApoE-knockout mice fed an atherogenic diet. Primary macrophages were extracted to study the role of the DNMT1/PPAR-γ pathway in regulating inflammatory cytokine production. We demonstrated that Tg^DNMT1 significantly increased proinflammatory cytokine production in macrophages and plasma, and it accelerated the progression of AS in the atherogenic diet-treated ApoE-knockout mice. Further, we found that the DNA methylation status of the proximal PPAR-γ promoter was regulated by DNMT1 in macrophages. Notably, additional Tg^PPAR-γ or pharmacological activation of PPAR-γ effectively prevented Tg^DNMT1-induced proinflammatory cytokine production in macrophages and AS development in the mouse model. Finally, we demonstrated that elevated DNMT1 was correlated with decreased PPAR-γ, and increased proinflammatory cytokine production in the peripheral blood monocytes isolated from the patients with AS, compared to those of healthy donors. Our findings shed light on a novel strategy for the prevention and therapy of AS.