Mitochondrial Metabolic Reprogramming by CD36 Signaling Drives Macrophage Inflammatory Responses

Transfection of miR-31* boosts oxidative phosphorylation metabolism in the mitochondria and enhances recombinant protein production in Chinese hamster ovary cells

MicroRNAs are increasingly being used to enhance relevant pathways of interest during CHO cell line development and to optimise biopharmaceutical production processes. Previous studies have demonstrated that genetic manipulation of microRNAs has led to the development of highly productive phenotypes by increasing cell density through modifying the cell cycle, extending the culture lifespan by delaying apoptotic mechanisms, or improving the energetic flux by targeting mitochondrial metabolism. Re-programming mitochondrial metabolism has arisen as a potential area of interest due to the potential to decrease the Warburg effect and increase cell specific productivity with significant impact on the manufacture of recombinant therapeutic proteins. In this study, we have demonstrated a role for miR-31* to enhance specific productivity in CHO cells by boosting oxidative phosphorylation in the mitochondria. A detailed analysis of the mitochondrial metabolism revealed that miR-31* transfection increases basal oxygen consumption and spare respiratory capacity that leads to an increase in ATP production. Additionally, a proteomic analysis unveiled a number of potential targets involved in fatty acid metabolism and the TCA cycle, both implicated in mitochondrial metabolism. This data demonstrates a potential role for miR-31* to reprogramme the mitochondrial energetic metabolism and increase recombinant protein production in CHO cells.

CD36 Senses Dietary Lipids and Regulates Lipids Homeostasis in the Intestine

Dietary lipids absorbed in the intestine are closely related to the development of metabolic syndrome. CD36 is a multi-functional scavenger receptor with multiple ligands, which plays important roles in developing hyperlipidemia, insulin resistance, and metabolic syndrome. In the intestine, CD36 is abundant on the brush border membrane of the enterocytes mainly localized in proximal intestine. This review recapitulates the update and current advances on the importance of intestinal CD36 in sensing dietary lipids and regulating intestinal lipids uptake, synthesis and transport, and regulating intestinal hormones secretion. However, further studies are still needed to demonstrate the complex interactions between intestinal CD36 and dietary lipids, as well as its importance in diet associated metabolic syndrome.

Experimental study on alleviating atherosclerosis through intervention of mitochondrial calcium transport and calcium-induced membrane permeability transition

To investigate the effort of mitochondrial calcium transport and calcium-induced membrane permeability transition in alleviating atherosclerosis. The experimental mice were divided into three groups: the control group (C57BL/6 mice with normal diet), the atherosclerosis group (apolipoprotein E-deficient (ApoE-/-) mice with high-fat diet) and the mitochondrial targeting agent group (ApoE-/- mouse with high-fat diet). The mean fluorescence intensity of Ca²⁺ in the atherosclerosis group is significantly higher than control group and mitochondrial targeting agent group. But the mean fluorescence intensity of Ca²⁺-ATPase is lower than other groups. The macrophage recruitment (F4/80 positive area) and the expression of tumor necrosis factor alpha, interleukin-6, pyrin domain containing protein 3, intercellular cell adhesion molecule-1, p38 mitogen-activated protein kinase and Jun kinase 1/2 phosphorylation in the atherosclerosis group are higher that other groups. Treatment with mitochondrial targeting agents reduced the levels of elevated cyt C and cleaved caspase-3 in atherosclerotic mice (p<0.05). Mitochondrial targeting agents interfere with mitochondrial calcium transport and calcium-induced membrane permeability transition, inhibit MAPK/JNK pathway activation, inhibit foam cell formation and alleviate the process of atherosclerosis.

Mitochondrial Mutations and Genetic Factors Determining NAFLD Risk

NAFLD (non-alcoholic fatty liver disease) is a widespread liver disease that is often linked with other life-threatening ailments (metabolic syndrome, insulin resistance, diabetes, cardiovascular disease, atherosclerosis, obesity, and others) and canprogress to more severe forms, such as NASH (non-alcoholic steatohepatitis), cirrhosis, and HCC (hepatocellular carcinoma). In this review, we summarized and analyzed data about single nucleotide polymorphism sites, identified in genes related to NAFLD development and progression. Additionally, the causative role of mitochondrial mutations and mitophagy malfunctions in NAFLD is discussed. The role of mitochondria-related metabolites of the urea cycle as a new non-invasive NAFLD biomarker is discussed. While mitochondria DNA mutations and SNPs (single nucleotide polymorphisms) canbe used as effective diagnostic markers and target for treatments, age and ethnic specificity should be taken into account.

Macrophage Metabolic Signaling during Ischemic Injury and Cardiac Repair

Macrophages are instrumental for the repair of organs that become injured due to ischemia, yet their potential for healing is sensitive to the availability of metabolites from the surrounding milieu. This sensitivity extends beyond anabolic and catabolic reactions, as metabolites are also leveraged to control production of secreted factors that direct intercellular crosstalk. In response to limiting extracellular oxygen, acute-phase macrophages activate hypoxia-inducible transcription factors that repurpose cellular metabolism. Subsequent repair-phase macrophages secrete cytokines to activate stromal cells, the latter which contribute to matrix deposition and scarring. As we now appreciate, these distinct functions are calibrated by directing flux of carbons and cofactors into specific metabolic shunts. This occurs through glycolysis, the pentose phosphate shunt, the tricarboxylic acid cycle, oxidative phosphorylation, nicotinamide adenine dinucleotides, lipids, amino acids, and through lesser understood pathways. The integration of metabolism with macrophage function is particularly important during injury to the ischemic heart, as glucose and lipid imbalance lead to inefficient repair and permanent loss of non-regenerative muscle. Here we review macrophage metabolic signaling under ischemic stress with implications for cardiac repair.

ZBTB20 Positively Regulates Oxidative Stress, Mitochondrial Fission, and Inflammatory Responses of ox-LDL-Induced Macrophages in Atherosclerosis

Atherosclerosis (AS) is one of the most serious and common cardiovascular diseases affecting human health. AS is featured by the accumulation of plaques in vessel walls. The pathophysiology of AS is relevant in the low-density lipoprotein (LDL) uptake by macrophages, as well as the conversion of macrophages to foam cells. However, the mechanisms about how macrophages regulate AS have not been fully elucidated. In this study, we aimed to illuminate the roles of ZBTB20 and to excavate the underlying regulative mechanisms of ZBTB20 in AS. The microarray analysis revealed that ZBTB20 was a hub gene in the oxidative stress and inflammatory responses induced by oxidized LDL (ox-LDL) in AS. Correspondingly, our validation studies showed that ZBTB20 increased in either the human atherosclerotic lesion or the ox-LDL-stimulated macrophages. Moreover, the knockdown of ZBTB20 decreased M1 polarization, suppressed the proinflammatory factors, inhibited mitochondrial fission, and reduced the oxidative stress level of macrophages induced by ox-LDL. The mechanistic studies revealed that the ZBTB20 knockdown suppressed NF-κB/MAPK activation and attenuated the mitochondrial fission possibly via regulating the nucleus translocation of NRF2, a pivotal transcription factor on redox homeostasis. Our in vivo studies showed that the sh-ZBTB20 adenovirus injection could reduce the progression of AS in apolipoprotein E-deficient (ApoE^−/−) mice. All in all, these results suggested that ZBTB20 positively regulated the oxidative stress level, mitochondrial fission, and inflammatory responses of macrophages induced by ox-LDL, and the knockdown of ZBTB20 could attenuate the development of AS in ApoE^−/− mice.

Health disparities: Intracellular consequences of social determinants of health

Health disparities exist dependent on socioeconomic status, living conditions, race/ethnicity, diet, and exposures to environmental pollutants. Herein, the various exposures contributing to a person's exposome are collectively considered social determinants of health (SDOH), and the SDOH-exposome impacts health more than health care. This review discusses the extent of evidence of the physiologic consequences of these exposures at the intracellular level. We consider how the SDOH-exposome, which captures how individuals live, work and age, induces cell processes that modulate a conceptual "redox rheostat." Like an electrical resistor, the SDOH-exposome, along with genetic predisposition and age, regulate reductive and oxidative (redox) stress circuits and thereby stimulate inflammation. Regardless of the source of the SDOH-exposome that induces chronic inflammation and immunosenescence, the outcome influences cardiometabolic diseases, cancers, infections, sepsis, neurodegeneration and autoimmune diseases. The endogenous redox rheostat is connected with regulatory molecules such as NAD⁺/NADH and SIRT1 that drive redox pathways. In addition to these intracellular and mitochondrial processes, we discuss how the SDOH-exposome can influence the balance between metabolism and regulation of immune responsiveness involving the two main molecular drivers of inflammation, the NLRP3 inflammasome and NF-κB induction. Mitochondrial and inflammasome activities play key roles in mediating defenses against pathogens and controlling inflammation before diverse cell death pathways are induced. Specifically, pyroptosis, cell death by inflammation, is intimately associated with common disease outcomes that are influenced by the SDOH-exposome. Redox influences on immunometabolism including protein cysteines and ion fluxes are discussed regarding health outcomes. In summary, this review presents a translational research perspective, with evidence from in vitro and in vivo models as well as clinical and epidemiological studies, to outline the intracellular consequences of the SDOH-exposome that drive health disparities in patients and populations. The relevance of this conceptual and theoretical model considering the SARS-CoV-2 pandemic are highlighted. Finally, the case of asthma is presented as a chronic condition that is modified by adverse SDOH exposures and is manifested through the dysregulation of immune cell redox regulatory processes we highlight in this review.

Novel insights: Dynamic foam cells derived from the macrophage in atherosclerosis

Atherosclerosis can be regarded as a chronic disease derived from the interaction between disordered lipoproteins and an unsuitable immune response. The evolution of foam cells is not only a significant pathological change in the early stage of atherosclerosis but also a key stage in the occurrence and development of atherosclerosis. The formation of foam cells is mainly caused by the imbalance among lipids uptake, lipids treatment, and reverse cholesterol transport. Although a large number of studies have summarized the source of foam cells and the mechanism of foam cells formation, we propose a new idea about foam cells in atherosclerosis. Rather than an isolated microenvironment, the macrophage multiple lipid uptake pathways, lipid internalization, lysosome, mitochondria, endoplasmic reticulum, neutral cholesterol ester hydrolase (NCEH), acyl-coenzyme A-cholesterol acyltransferase (ACAT), and reverse cholesterol transport are mutually influential, and form a dynamic process under multi-factor regulation. The macrophage takes on different uptake lipid statuses depending on multiple uptake pathways and intracellular lipids, lipid metabolites versus pro-inflammatory factors. Except for NCEH and ACAT, the lipid internalization of macrophages also depends on multicellular organelles including the lysosome, mitochondria, and endoplasmic reticulum, which are associated with each other. A dynamic balance between esterification and hydrolysis of cholesterol for macrophages is essential for physiology and pathology. Therefore, we propose that the foam cell in the process of atherosclerosis may be dynamic under multi-factor regulation, and collate this study to provide a holistic and dynamic idea of the foam cell.

Origins and diversity of macrophages in health and disease

Macrophages are the first immune cells in the developing embryo and have a central role in organ development, homeostasis, immunity and repair. Over the last century, our understanding of these cells has evolved from being thought of as simple phagocytic cells to master regulators involved in governing a myriad of cellular processes. A better appreciation of macrophage biology has been matched with a clearer understanding of their diverse origins and the flexibility of their metabolic and transcriptional machinery. The understanding of the classical mononuclear phagocyte system in its original form has now been expanded to include the embryonic origin of tissue‐resident macrophages. A better knowledge of the intrinsic similarities and differences between macrophages of embryonic or monocyte origin has highlighted the importance of ontogeny in macrophage dysfunction in disease. In this review, we provide an update on origin and classification of tissue macrophages, the mechanisms of macrophage specialisation and their role in health and disease. The importance of the macrophage niche in providing trophic factors and a specialised environment for macrophage differentiation and specialisation is also discussed.

Mitochondria orchestrate macrophage effector functions in atherosclerosis

Macrophages are pivotal in the initiation and development of atherosclerotic cardiovascular diseases. Recent studies have reinforced the importance of mitochondria in metabolic and signaling pathways to maintain macrophage effector functions. In this review, we discuss the past and emerging roles of macrophage mitochondria metabolic diversity in atherosclerosis and the potential avenue as biomarker. Beyond metabolic functions, mitochondria are also a signaling platform integrating epigenetic, redox, efferocytic and apoptotic regulations, which are exquisitely linked to their dynamics. Indeed, mitochondria functions depend on their density and shape perpetually controlled by mitochondria fusion/fission and biogenesis/mitophagy balances. Mitochondria can also communicate with other organelles such as the endoplasmic reticulum through mitochondria-associated membrane (MAM) or be secreted for paracrine actions. All these functions are perturbed in macrophages from mouse or human atherosclerotic plaques. A better understanding and integration of how these metabolic and signaling processes are integrated and dictate macrophage effector functions in atherosclerosis may ultimately help the development of novel therapeutic approaches.

The role of CD36 in cardiovascular disease

CD36, also known as the scavenger receptor B2, is a multifunctional receptor widely expressed in various organs. CD36 plays a crucial role in the uptake of long-chain fatty acids, the main metabolic substrate in myocardial tissue. The maturation and transportation of CD36 is regulated by post-translational modifications, including phosphorylation, ubiquitination, glycosylation, and palmitoylation. CD36 is decreased in pathological cardiac hypertrophy caused by ischaemia-reperfusion and pressure overload, and increased in diabetic cardiomyopathy and atherosclerosis. Deficiency of CD36 alleviates diabetic cardiomyopathy and atherosclerosis, while overexpression of CD36 eliminates ischaemia-reperfusion damage, together suggesting that CD36 is closely associated with the progression of cardiovascular diseases and may be a new therapeutic target. This review summarizes the regulation and post-translational modifications of CD36 and evaluates its role in cardiovascular diseases and its potential as a therapeutic target.

Metabolic Reprogramming is a Hallmark of Metabolism Itself

The reprogramming of metabolism has been identified as one of the hallmarks of cancer. It is becoming more and more frequent to connect other diseases with metabolic reprogramming. This article aims to argue that metabolic reprogramming is not driven by disease but instead is the main hallmark of metabolism, based on its dynamic behavior that allows it to continuously adapt to changes in the internal and external conditions.

Metabolic Reprogramming in Immune Response and Tissue Inflammation

Innate and adaptive immunity participate in and regulate numerous human diseases. Increasing evidence implies that metabolic reprogramming mediates immune cell functional changes during immune responses. In this review, we present and discuss our current understanding of metabolic regulation in different immune cells and their subsets in response to pathological stimuli. An interactive biochemical and molecular model was established to characterize metabolic reprogramming and their functional implication in anti-inflammatory, immune resolution, and proinflammatory responses. We summarize 2 major features of metabolic reprogramming in inflammatory stages in innate and adaptive immune cells: (1) energy production and biosynthesis reprogramming, including increased glycolysis and decreased oxidative phosphorylation, to secure faster ATP production and biosynthesis for defense response and damage repair and (2) epigenetic reprogramming, including enhanced histone acetylation and suppressed DNA methylation, due to altered accessibility of acetyl/methyl group donor and metabolite-modulated enzymatic activity. Finally, we discuss current strategies of metabolic and epigenetic therapy in cardiovascular disease and recommend cell-specific metabolic and gene-targeted site-specific epigenetic alterations for future therapies.

Deciphering Macrophage Phenotypes upon Lipid Uptake and Atherosclerosis

In the progression of atherosclerosis, macrophages are the key immune cells for foam cell formation. During hyperlipidemic condition, phagocytic cells such as monocytes and macrophages uptake oxidized low-density lipoproteins (oxLDLs) accumulated in subintimal space, and lipid droplets are accumulated in their cytosols. In this review, we discussed the characteristics and phenotypic changes of macrophages in atherosclerosis and the effect of cytosolic lipid accumulation on macrophage phenotype. Due to macrophage plasticity, the inflammatory phenotypes triggered by oxLDL can be re-programmed by cytosolic lipid accumulation, showing downregulation of NF-κB activation followed by activation of anti-inflammatory genes, leading to tissue repair and homeostasis. We also discuss about various in vivo and in vitro models for atherosclerosis research and next generation sequencing technologies for foam cell gene expression profiling. Analysis of the phenotypic changes of macrophages during the progression of atherosclerosis with adequate approach may lead to exact understandings of the cellular mechanisms and hint therapeutic targets for the treatment of atherosclerosis.

Vascular Endothelial Cells and Innate Immunity

In addition to the roles of endothelial cells (ECs) in physiological processes, ECs actively participate in both innate and adaptive immune responses. We previously reported that, in comparison to macrophages, a prototypic innate immune cell type, ECs have many innate immune functions that macrophages carry out, including cytokine secretion, phagocytic function, antigen presentation, pathogen-associated molecular patterns-, and danger-associated molecular patterns-sensing, proinflammatory, immune-enhancing, anti-inflammatory, immunosuppression, migration, heterogeneity, and plasticity. In this highlight, we introduce recent advances published in both ATVB and many other journals: (1) several significant characters classify ECs as novel immune cells not only in infections and allograft transplantation but also in metabolic diseases; (2) several new receptor systems including conditional danger-associated molecular pattern receptors, nonpattern receptors, and homeostasis associated molecular patterns receptors contribute to innate immune functions of ECs; (3) immunometabolism and innate immune memory determine the innate immune functions of ECs; (4) a great induction of the immune checkpoint receptors in ECs during inflammations suggests the immune tolerogenic functions of ECs; and (5) association of immune checkpoint inhibitors with cardiovascular adverse events and cardio-oncology indicates the potential contributions of ECs as innate immune cells.

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.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

Obesity, Hypertension, and Cardiac Dysfunction: Novel Roles of Immunometabolism in Macrophage Activation and Inflammation

Obesity and hypertension, which often coexist, are major risk factors for heart failure and are characterized by chronic, low-grade inflammation, which promotes adverse cardiac remodeling. While macrophages play a key role in cardiac remodeling, dysregulation of macrophage polarization between the proinflammatory M1 and anti-inflammatory M2 phenotypes promotes excessive inflammation and cardiac injury. Metabolic shifting between glycolysis and mitochondrial oxidative phosphorylation has been implicated in macrophage polarization. M1 macrophages primarily rely on glycolysis, whereas M2 macrophages rely on the tricarboxylic acid cycle and oxidative phosphorylation; thus, factors that affect macrophage metabolism may disrupt M1/M2 homeostasis and exacerbate inflammation. The mechanisms by which obesity and hypertension may synergistically induce macrophage metabolic dysfunction, particularly during cardiac remodeling, are not fully understood. We propose that obesity and hypertension induce M1 macrophage polarization via mechanisms that directly target macrophage metabolism, including changes in circulating glucose and fatty acid substrates, lipotoxicity, and tissue hypoxia. We discuss canonical and novel proinflammatory roles of macrophages during obesity-hypertension-induced cardiac injury, including diastolic dysfunction and impaired calcium handling. Finally, we discuss the current status of potential therapies to target macrophage metabolism during heart failure, including antidiabetic therapies, anti-inflammatory therapies, and novel immunometabolic agents.