CCR2 modulates inflammatory and metabolic effects of high-fat feeding

Therapeutic strategies targeting mechanisms of macrophages in diabetic heart disease

Diabetic heart disease (DHD) is a serious complication in patients with diabetes. Despite numerous studies on the pathogenic mechanisms and therapeutic targets of DHD, effective means of prevention and treatment are still lacking. The pathogenic mechanisms of DHD include cardiac inflammation, insulin resistance, myocardial fibrosis, and oxidative stress. Macrophages, the primary cells of the human innate immune system, contribute significantly to these pathological processes, playing an important role in human disease and health. Therefore, drugs targeting macrophages hold great promise for the treatment of DHD. In this review, we examine how macrophages contribute to the development of DHD and which drugs could potentially be used to target macrophages in the treatment of DHD.

Adipocyte-Specific Hnrnpa1 Knockout Aggravates Obesity-Induced Metabolic Dysfunction via Upregulation of CCL2

Heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) is involved in lipid and glucose metabolism via mRNA processing. However, whether and how HNRNPA1 alters adipocyte function in obesity remain obscure. Here, we found that the obese state downregulated HNRNPA1 expression in white adipose tissue (WAT). The depletion of adipocyte HNRNPA1 promoted markedly increased macrophage infiltration and expression of proinflammatory and fibrosis genes in WAT of obese mice, eventually leading to exacerbated insulin sensitivity, glucose tolerance, and hepatic steatosis. Mechanistically, HNRNPA1 interacted with Ccl2 and regulated its mRNA stability. Intraperitoneal injection of CCL2-CCR2 signaling antagonist improved adipose tissue inflammation and systemic glucose homeostasis. Furthermore, HNRNPA1 expression in human WAT was negatively correlated with BMI, fat percentage, and subcutaneous fat area. Among individuals with 1-year metabolic surgery follow-up, HNRNPA1 expression was positively related to percentage of total weight loss. These findings identify adipocyte HNRNPA1 as a link between adipose tissue inflammation and systemic metabolic homeostasis, which might be a promising therapeutic target for obesity-related disorders.

ARTICLE HIGHLIGHTS

Inflammatory Protein Signatures as Predictive Disease-Specific Markers for Non-Alcoholic Steatohepatitis (NASH)

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic disease worldwide, consisting of a broad spectrum of diseases such as simple steatosis (NAFL), non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatic inflammation plays a key role in the pathophysiology of NAFLD. Inflammatory mediators such as cytokines and chemokines are considered as contributing factors to NAFLD development and progression. In the present study, we aimed to investigate the inflammatory protein signatures as predictive disease-specific markers for non-alcoholic fatty liver disease (NAFLD). This cross-sectional study included healthy control (n = 64), NAFL (n = 109), and NASH (n = 60) human subjects. Serum concentrations of various cytokines and chemokines were evaluated using sensitive multiplex assays. We used principal component analysis (PCoA) to reveal distinct differences in the levels of cytokines and chemokines between each of the study groups. Further, a random forest classification model was developed to identify the panel of markers that could predict diseases. The protein-protein network analysis was performed to determine the various signaling pathways associated with the disease-specific panel of markers. Serum concentrations of TNF-α, IL-1β, IL-1ra, G-CSF, PDGF-BB, MCP-1, MIP-1a, MIP-1b, RANTES, eotaxin, IL-8 and IP-10 were significantly increased in NASH group as compared to control group. Furthermore, serum concentrations of IL-9 and IL-13 were significantly lower in the NASH group, whereas IL-2 levels were significantly decreased in the NAFL group when compared to the control group. PCoA results demonstrated statistically significant differences in cytokines and chemokines between each of the study groups (PERMANOVA p = 0.001; R2 = 0.102). RANTES, IL-1ra, MIP-1b, IL-2, and G-CSF could differentiate the NAFL group from the controls; G-CSF, IL-1ra, TNF-α, RANTES, and IL-9 could differentiate the NASH group from the controls; and G-CSF, IL-9, IL-13, eotaxin, and TNF- α could differentiate the NASH group from the NAFL group. Our protein-protein network revealed that these markers are involved in cytokine-cytokine receptor interaction, Th1 and Th2 cell differentiation, TNF, chemokine, JAK/STAT, P13K/Akt, TLR, NOD-like receptor, NF-kB, and adipocytokine signaling pathways which might be responsible for disease pathogenesis. Our study findings revealed a set of distinct cytokine and chemokine markers and they might be considered as biomarkers in distinguishing NASH from NAFL. Future multicentre studies with larger sample size are recommended to determine the potential utility of these panels of markers.

Bardoxolone methyl prevents metabolic dysfunction-associated steatohepatitis by inhibiting macrophage infiltration

BACKGROUND AND PURPOSE

Bardoxolone methyl (2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid methyl ester, CDDO-Me) is a potent activator of nuclear factor erythroid 2-related factor 2 (Nrf2), which induces the expression of antioxidative-associated genes. CDDO-Me exerts protective effects against chronic inflammatory diseases in the kidneys and lungs. However, its pharmacological effects on metabolic dysfunction-associated steatohepatitis (MASH) caused by fat accumulation remain unknown. In this study, we examined the hepatoprotective effects of CDDO-Me in a diet-induced MASH mouse model and elucidated its pharmacological mechanisms using RNA-seq analysis.

EXPERIMENTAL APPROACH

CDDO-Me was orally administered to mice fed a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD), and histological, biochemical, and transcriptomic analyses were performed on livers of mice that developed MASH.

KEY RESULTS

CDDO-Me administration induced the expression of antioxidant genes and cholesterol transporters downstream of Nrf2 and significantly prevented the symptoms of MASH. Whole-transcriptome analysis revealed that CDDO-Me inhibited the inflammatory pathway that led to phagocyte recruitment, in addition to activating the Nrf2-dependent pathway. Among inflammatory pathways, CC chemokine ligands (CCL)3 and CCL4, which are downstream of NF-κB and are associated with the recruitment of macrophages expressing CC chemokine receptors (CCR)1 and CCR5, were released into the blood in MASH mice. However, CDDO-Me directly inhibited the expression of CCL3-CCR1 and CCL4-CCR5 in macrophages.

CONCLUSIONS AND IMPLICATIONS

Overall, we revealed the potent hepatoprotective effect of CDDO-Me in a MASH mouse model and demonstrated that its pharmacological effects were closely associated with a reduction of macrophage infiltration, through CCL3-CCR1 and CCL4-CCR5 inhibition, in addition to Nrf2-mediated hepatoprotective effects.

CCL2-CCR2 signaling axis in obesity and metabolic diseases

Obesity and metabolic diseases, such as insulin resistance, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular ailments, represent formidable global health challenges, bearing considerable implications for both morbidity and mortality rates. It has become increasingly evident that chronic, low-grade inflammation plays a pivotal role in the genesis and advancement of these conditions. The involvement of C-C chemokine ligand 2 (CCL2) and its corresponding receptor, C-C chemokine receptor 2 (CCR2), has been extensively documented in numerous inflammatory maladies. Recent evidence indicates that the CCL2/CCR2 pathway extends beyond immune cell recruitment and inflammation, exerting a notable influence on the genesis and progression of metabolic syndrome. The present review seeks to furnish a comprehensive exposition of the CCL2-CCR2 signaling axis within the context of obesity and metabolic disorders, elucidating its molecular mechanisms, functional roles, and therapeutic implications.

History and future perspectives of adipose tissue macrophage biology

Macrophages contribute to adipose tissue homeostasis; however, they are also thought to be responsible for insulin resistance in obesity. Macrophages, which were oversimplified in past methodologies, have become rather difficult to understand comprehensively as recent developments in research methodology have revealed their diversity. This review highlights recent studies on adipose tissue macrophages, identifies controversial issues that need to be resolved and proposes a scenario for further development of adipose tissue macrophage biology.

Interaction between peripheral blood mononuclear cells and Trypanosoma cruzi-infected adipocytes: implications for treatment failure and induction of immunomodulatory mechanisms in adipose tissue

Background/Introduction

Adipose tissue (AT) has been highlighted as a promising reservoir of infection for viruses, bacteria and parasites. Among them is Trypanosoma cruzi, which causes Chagas disease. The recommended treatment for the disease in Brazil is Benznidazole (BZ). However, its efficacy may vary according to the stage of the disease, geographical origin, age, immune background of the host and sensitivity of the strains to the drug. In this context, AT may act as an ally for the parasite survival and persistence in the host and a barrier for BZ action. Therefore, we investigated the immunomodulation of T. cruzi-infected human AT in the presence of peripheral blood mononuclear cells (PBMC) where BZ treatment was added.

Methods

We performed indirect cultivation between T. cruzi-infected adipocytes, PBMC and the addition of BZ. After 72h of treatment, the supernatant was collected for cytokine, chemokine and adipokine assay. Infected adipocytes were removed to quantify T. cruzi DNA, and PBMC were removed for immunophenotyping.

Results

Our findings showed elevated secretion of interleukin (IL)-6, IL-2 and monocyte chemoattractant protein-1 (MCP-1/CCL2) in the AT+PBMC condition compared to the other controls. In contrast, there was a decrease in tumor necrosis factor (TNF) and IL-8/CXCL-8 in the groups with AT. We also found high adipsin secretion in PBMC+AT+T compared to the treated condition (PBMC+AT+T+BZ). Likewise, the expression of CD80+ and HLA-DR+ in CD14+ cells decreased in the presence of T. cruzi.

Discussion

Thus, our findings indicate that AT promotes up-regulation of inflammatory products such as IL-6, IL-2, and MCP-1/CCL2. However, adipogenic inducers may have triggered the downregulation of TNF and IL-8/CXCL8 through the peroxisome proliferator agonist gamma (PPAR-g) or receptor expression. On the other hand, the administration of BZ only managed to reduce inflammation in the microenvironment by decreasing adipsin in the infected culture conditions. Therefore, given the findings, we can see that AT is an ally of the parasite in evading the host's immune response and the pharmacological action of BZ.

Air pollution exposure and cardiometabolic risk

The Global Burden of Disease assessment estimates that 20% of global type 2 diabetes cases are related to chronic exposure to particulate matter (PM) with a diameter of 2·5 μm or less (PM2·5). With 99% of the global population residing in areas where air pollution levels are above current WHO air quality guidelines, and increasing concern in regard to the common drivers of air pollution and climate change, there is a compelling need to understand the connection between air pollution and cardiometabolic disease, and pathways to address this preventable risk factor. This Review provides an up to date summary of the epidemiological evidence and mechanistic underpinnings linking air pollution with cardiometabolic risk. We also outline approaches to improve awareness, and discuss personal-level, community, governmental, and policy interventions to help mitigate the growing global public health risk of air pollution exposure.

Adipose failure through adipocyte overload and autoimmunity

Metabolic syndrome poses a great worldwide threat to the health of the patients. Increased visceral adiposity is recognized as the main determinant of the detrimental clinical effects of insulin resistance. Inflammation and immune system activation in the adipose tissue (AT) have a central role in the pathophysiology of metabolic syndrome, but the mechanisms linking increased adiposity to immunity in the AT remain in part elusive. In this review, we support the central role of adipocyte overload and relative adipose failure as key determinants in triggering immune aggression to AT. This provides a mechanistic explanation of the relative metabolic wellness of metabolically normal obese people and the disruption in insulin signaling in metabolically obese lean people.

IL-6 signaling drives self-renewal and alternative activation of adipose tissue macrophages

Introduction

Obesity is associated with chronic low-grade inflammation of adipose tissue (AT) and an increase of AT macrophages (ATMs) that is linked to the onset of type 2 diabetes. We have recently shown that neutralization of interleukin (IL)-6 in obese AT organ cultures inhibits proliferation of ATMs, which occurs preferentially in alternatively activated macrophage phenotype.

Methods

In this study, we investigated AT biology and the metabolic phenotype of mice with myeloid cell-specific IL-6Rα deficiency (Il6ra Δmyel) after normal chow and 20 weeks of high-fat diet focusing on AT inflammation, ATM polarization and proliferation. Using organotypical AT culture and bone marrow derived macrophages (BMDMs) of IL-4Rα knockout mice (Il4ra -/-) we studied IL-6 signaling.

Results

Obese Il6ra Δmyel mice exhibited no differences in insulin sensitivity or histological markers of AT inflammation. Notably, we found a reduction of ATMs expressing the mannose receptor 1 (CD206), as well as a decrease of the proliferation marker Ki67 in ATMs of Il6ra Δmyel mice. Importantly, organotypical AT culture and BMDM data of Il4ra -/- mice revealed that IL-6 mediates a shift towards the M2 phenotype independent from the IL-6/IL-4Rα axis.

Discussion

Our results demonstrate IL-4Rα-independent anti-inflammatory effects of IL-6 on macrophages and the ability of IL-6 to maintain proliferation rates in obese AT.

Diet-Induced Obesity Increases Monocyte/Macrophage Proliferation during Skin Wound Healing in Mice

Obesity is associated with low-grade chronic inflammation and impaired glucose metabolism, both of which are detrimental to wound healing. C-C motif chemokine receptor 2 (CCR2) plays an important role in cell recruitment during healing, and our recent studies revealed the significance of CCR2-CCL2 signaling in promoting the proliferation of pro-inflammatory monocytes/macrophages in wounds. Therefore, we sought to determine whether diet-induced obesity increases monocyte/macrophage proliferation and their accumulation in skin wounds. We first confirmed that wound closure was delayed in obese CCR2RFP/+ mice fed with a high-fat diet (HFD) compared to mice fed with a normal diet (ND). Using in vivo imaging and flow cytometry analysis, we found that HFD mice had significantly increased accumulation of CCR2+ monocytes/macrophages, particularly pro-inflammatory CCR2+Ly6C+ cells in wounds compared to their ND counterparts. Importantly, HFD mice exhibited an increased proliferation of wound CCR2+Ly6C+ compared to ND mice. Together, our data suggest that obesity leads to an increased proliferation and accumulation of pro-inflammatory CCR2+Ly6C+ monocytes/macrophages in skin wounds, which may contribute to delayed healing.

Contribution of NKT cells and CD1d-expressing cells in obesity-associated adipose tissue inflammation

Natural killer T (NKT) cell are members of the innate-like T lymphocytes and recognizes lipid antigens presented by CD1d-expressing cells. Obesity-associated inflammation in adipose tissue (AT) leads to metabolic dysfunction, including insulin resistance. When cellular communication is properly regulated among AT-residing immune cells and adipocytes during inflammation, a favorable balance of Th1 and Th2 immune responses is achieved. NKT cells play crucial roles in AT inflammation, influencing the development of diet-induced obesity and insulin resistance. NKT cells interact with CD1d-expressing cells in AT, such as adipocytes, macrophages, and dendritic cells, shaping pro-inflammatory or anti-inflammatory microenvironments with distinct characteristics depending on the antigen-presenting cells. Additionally, CD1d may be involved in the inflammatory process independently of NKT cells. In this mini-review, we provide a brief overview of the current understanding of the interaction between immune cells, focusing on NKT cells and CD1d signaling, which control AT inflammation both in the presence and absence of NKT cells. We aim to enhance our understanding of the mechanisms of obesity-associated diseases.

Orchestration of the Adipose Tissue Immune Landscape by Adipocytes

Obesity is epidemic and of great concern because of its comorbid and costly inflammatory-driven complications. Extensive investigations in mice have elucidated highly coordinated, well-balanced interactions between adipocytes and immune cells in adipose tissue that maintain normal systemic metabolism in the lean state, while in obesity, proinflammatory changes occur in nearly all adipose tissue immune cells. Many of these changes are instigated by adipocytes. However, less is known about obesity-induced adipose-tissue immune cell alterations in humans. Upon high-fat diet feeding, the adipocyte changes its well-known function as a metabolic cell to assume the role of an immune cell, orchestrating proinflammatory changes that escalate inflammation and progress during obesity. This transformation is particularly prominent in humans. In this review, we (a) highlight a leading and early role for adipocytes in promulgating inflammation, (b) discuss immune cell changes and the time course of these changes (comparing humans and mice when possible), and (c) note how reversing proinflammatory changes in most types of immune cells, including adipocytes, rescues adipose tissue from inflammation and obese mice from insulin resistance.

A macrophage-collagen fragment axis mediates subcutaneous adipose tissue remodeling in mice

Efficient removal of fibrillar collagen is essential for adaptive subcutaneous adipose tissue (SAT) expansion that protects against ectopic lipid deposition during weight gain. Here, we used mice to further define the mechanism for this collagenolytic process. We show that loss of collagen type-1 (CT1) and increased CT1-fragment levels in expanding SAT are associated with proliferation of resident M2-like macrophages that display increased CD206-mediated engagement in collagen endocytosis compared to chow-fed controls. Blockage of CD206 during acute high-fat diet-induced weight gain leads to SAT CT1-fragment accumulation associated with elevated inflammation and fibrosis markers. Moreover, these SAT macrophages' engagement in collagen endocytosis is diminished in obesity associated with elevated levels collagen fragments that are too short to assemble into triple helices. We show that such short fragments provoke M2-macrophage proliferation and fibroinflammatory changes in fibroblasts. In conclusion, our data delineate the importance of a macrophage-collagen fragment axis in physiological SAT expansion. Therapeutic targeting of this process may be a means to prevent pathological adipose tissue remodeling, which in turn may reduce the risk for obesity-related metabolic disorders.

Extracellular vesicles as tools and targets in therapy for diseases

Extracellular vesicles (EVs) are nano-sized, membranous structures secreted into the extracellular space. They exhibit diverse sizes, contents, and surface markers and are ubiquitously released from cells under normal and pathological conditions. Human serum is a rich source of these EVs, though their isolation from serum proteins and non-EV lipid particles poses challenges. These vesicles transport various cellular components such as proteins, mRNAs, miRNAs, DNA, and lipids across distances, influencing numerous physiological and pathological events, including those within the tumor microenvironment (TME). Their pivotal roles in cellular communication make EVs promising candidates for therapeutic agents, drug delivery systems, and disease biomarkers. Especially in cancer diagnostics, EV detection can pave the way for early identification and offers potential as diagnostic biomarkers. Moreover, various EV subtypes are emerging as targeted drug delivery tools, highlighting their potential clinical significance. The need for non-invasive biomarkers to monitor biological processes for diagnostic and therapeutic purposes remains unfulfilled. Tapping into the unique composition of EVs could unlock advanced diagnostic and therapeutic avenues in the future. In this review, we discuss in detail the roles of EVs across various conditions, including cancers (encompassing head and neck, lung, gastric, breast, and hepatocellular carcinoma), neurodegenerative disorders, diabetes, viral infections, autoimmune and renal diseases, emphasizing the potential advancements in molecular diagnostics and drug delivery.

Adipose tissue macrophage heterogeneity in the single-cell genomics era

It is now well-accepted that obesity-induced inflammation plays an important role in the development of insulin resistance and type 2 diabetes. A key source of the inflammation is the murine epididymal and human visceral adipose tissue. The current paradigm is that obesity activates multiple proinflammatory immune cell types in adipose tissue, including adipose-tissue macrophages (ATMs), T Helper 1 (Th1) T cells, and natural killer (NK) cells, while concomitantly suppressing anti-inflammatory immune cells such as T Helper 2 (Th2) T cells and regulatory T cells (Tregs). A key feature of the current paradigm is that obesity induces the anti-inflammatory M2 ATMs in lean adipose tissue to polarize into proinflammatory M1 ATMs. However, recent single-cell transcriptomics studies suggest that the story is much more complex. Here we describe the single-cell genomics technologies that have been developed recently and the emerging results from studies using these technologies. While further studies are needed, it is clear that ATMs are highly heterogeneous. Moreover, while a variety of ATM clusters with quite distinct features have been found to be expanded by obesity, none truly resemble classical M1 ATMs. It is likely that single-cell transcriptomics technology will further revolutionize the field, thereby promoting our understanding of ATMs, adipose-tissue inflammation, and insulin resistance and accelerating the development of therapies for type 2 diabetes.

M2 Macrophage Membrane-Camouflaged Fe3 O4 -Cy7 Nanoparticles with Reduced Immunogenicity for Targeted NIR/MR Imaging of Atherosclerosis

Atherosclerosis （AS） is the primary reason behind cardiovascular diseases, leading to approximately one-third of global deaths. Developing a novel multi-model probe to detect AS is urgently required. Macrophages are the primary cells from which AS genesis occurs. Utilizing natural macrophage membranes coated on the surface of nanoparticles is an efficient delivery method to target plaque sites. Herein, Fe3 O4 -Cy7 nanoparticles (Fe3 O4 -Cy7 NPs), functionalized using an M2 macrophage membrane and a liposome extruder for Near-infrared fluorescence and Magnetic resonance imaging, are synthesized. These macrophage membrane-coated nanoparticles (Fe3 O4 @M2 NPs) enhance the recognition and uptake using active macrophages. Moreover, they inhibit uptake using inactive macrophages and human coronary artery endothelial cells. The macrophage membrane-coated nanoparticles (Fe3 O4 @M0 NPs, Fe3 O4 @M1 NPs, Fe3 O4 @M2 NPs) can target specific sites depending on the macrophage membrane type and are related to C-C chemofactor receptor type 2 protein content. Moreover, Fe3 O4 @M2 NPs demonstrate excellent biosafety in vivo after injection, showing a significantly higher Fe concentration in the blood than Fe3 O4 -Cy7 NPs. Therefore, Fe3 O4 @M2 NPs effectively retain the physicochemical properties of nanoparticles and depict reduced immunological response in blood circulation. These NPs mainly reveal enhanced targeting imaging capability for atherosclerotic plaque lesions.

Macrophage Development and Function

Macrophages were first described over a hundred years ago. Throughout the years, they were shown to be essential players in their tissue-specific environment, performing various functions during homeostatic and disease conditions. Recent reports shed more light on their ontogeny as long-lived, self-maintained cells with embryonic origin in most tissues. They populate the different tissues early during development, where they help to establish and maintain homeostasis. In this chapter, the history of macrophages is discussed. Furthermore, macrophage ontogeny and core functions in the different tissues are described.

Macrophage and T cell networks in adipose tissue

The signals and structure of the tissues in which leukocytes reside critically mould leukocyte function and development and have challenged our fundamental understanding of how to define and categorize tissue-resident immune cells. One specialized tissue niche that has a powerful effect on immune cell function is adipose tissue. The field of adipose tissue leukocyte biology has expanded dramatically and has revealed how tissue niches can shape immune cell function and reshape them in a setting of metabolic stress, such as obesity. Most notably, adipose tissue macrophages and T cells are under intense investigation due to their contributions to adipose tissue in the lean and obese states. Both adipose tissue macrophages and T cells have features associated with the metabolic function of adipose tissue that are distinct from features of macrophages and T cells that are classically characterized in other tissues. This Review provides state-of-the-art understanding of adipose tissue macrophages and T cells and discusses how their unique niche can help us to better understand diversity in leukocyte responses.

FAP expression in adipose tissue macrophages promotes obesity and metabolic inflammation

Adipose tissue macrophages (ATM) are key players in the development of obesity and associated metabolic inflammation which contributes to systemic metabolic dysfunction. We here found that fibroblast activation protein α (FAP), a well-known marker of cancer-associated fibroblast, is selectively expressed in murine and human ATM among adipose tissue-infiltrating leukocytes. Macrophage FAP deficiency protects mice against diet-induced obesity and proinflammatory macrophage infiltration in obese adipose tissues, thereby alleviating hepatic steatosis and insulin resistance. Mechanistically, FAP specifically mediates monocyte chemokine protein CCL8 expression by ATM, which is further upregulated upon high-fat-diet (HFD) feeding, contributing to the recruitment of monocyte-derived proinflammatory macrophages with no effect on their classical inflammatory activation. CCL8 overexpression restores HFD-induced metabolic phenotypes in the absence of FAP. Moreover, macrophage FAP deficiency enhances energy expenditure and oxygen consumption preceding differential body weight after HFD feeding. Such enhanced energy expenditure is associated with increased levels of norepinephrine (NE) and lipolysis in white adipose tissues, likely due to decreased expression of monoamine oxidase, a NE degradation enzyme, by Fap-/- ATM. Collectively, our study identifies FAP as a previously unrecognized regulator of ATM function contributing to diet-induced obesity and metabolic inflammation and suggests FAP as a potential immunotherapeutic target against metabolic disorders.

Alterations in the mammary gland and tumor microenvironment of formerly obese mice

BACKGROUND

Obesity is a risk factor for breast cancer, and women with obesity that develop breast cancer have a worsened prognosis. Within the mammary gland, obesity causes chronic, macrophage-driven inflammation and adipose tissue fibrosis. Weight loss is a recommended intervention to resolve obesity, but the impact of weight loss on the mammary gland microenvironment and in tumors has not been well identified.

METHODS

To examine the effects of weight loss following obesity, mice were fed a high-fat diet for 16 weeks to induce obesity, then switched to a low-fat diet for 6 weeks. We examined changes in immune cells, including fibrocytes, which are myeloid lineage cells that have attributes of both macrophages and myofibroblasts, and collagen deposition within the mammary glands of non-tumor-bearing mice and within the tumors of mice that were transplanted with estrogen receptor alpha positive TC2 tumor cells.

RESULTS

In formerly obese mice, we observed reduced numbers of crown-like structures and fibrocytes in mammary glands, while collagen deposition was not resolved with weight loss. Following transplant of TC2 tumor cells into the mammary glands of lean, obese, and formerly obese mice, diminished collagen deposition and cancer-associated fibroblasts were observed in tumors from formerly obese mice compared to obese mice. Within tumors of obese mice, increased myeloid-derived suppressor cells and diminished CD8+ T cells were identified, while the microenvironment of tumors of formerly obese mice were more similar to tumors from lean mice. When TC2 tumor cells were mixed with CD11b+CD34+ myeloid progenitor cells, which are the cells of origin for fibrocytes, and transplanted into mammary glands of lean and obese mice, collagen deposition within the tumors of both lean and obese was significantly greater than when tumor cells were mixed with CD11b+CD34- monocytes or total CD45+ immune cells.

CONCLUSIONS

Overall, these studies demonstrate that weight loss resolved some of the microenvironmental conditions within the mammary gland that may contribute to tumor progression. Additionally, fibrocytes may contribute to early collagen deposition in mammary tumors of obese mice leading to the growth of desmoplastic tumors.

Identification of major hub genes involved in high-fat diet-induced obese visceral adipose tissue based on bioinformatics approach

High-fat diet (HFD) can cause obesity, inducing dysregulation of the visceral adipose tissue (VAT). This study aimed to explore potential biological pathways and hub genes involved in obese VAT, and for that, bioinformatic analysis of multiple datasets was performed. The expression profiles (GSE30247, GSE167311 and GSE79434) were downloaded from Gene Expression Omnibus. Overlapping differentially expressed genes (ODEGs) between normal diet and HFD groups in GSE30247 and GSE167311 were selected to run protein-protein interaction network, GO and KEGG analysis. The hub genes in ODEGs were screened by Cytoscape software and further verified in GSE79434 and obese mouse model. A total of 747 ODEGs (599 up-regulated and 148 down-regulated) were screened, and the GO and KEGG analysis showed that the up-regulated ODEGs were significantly enriched in inflammatory response and extracellular matrix receptor interaction pathways. On the other hand, the down-regulated ODEGs were involved in metabolic pathways; however, there were no significant KEGG pathways. Furthermore, six hub genes, Mki67, Rac2, Itgb2, Emr1, Tyrobp and Csf1r were acquired. These pathways and genes were verified in GSE79434 and VAT of obese mice. This study revealed that HFD induced VAT expansion, inflammation and fibrosis, and the hub genes could be used as therapeutic biomarkers in obesity.

Metaflammation in obesity and its therapeutic targeting

Obesity-associated inflammation is a systemic process that affects all metabolic organs. Prominent among these is adipose tissue, where cells of the innate and adaptive immune system are markedly changed in obesity, implicating these cells in a range of processes linking immune memory to metabolic regulation. Furthermore, weight loss and weight cycling have unexpected effects on adipose tissue immune populations. Here, we review the current literature on the roles of various immune cells in lean and obese adipose tissue. Within this context, we discuss pharmacological and nonpharmacological approaches to obesity treatment and their impact on systemic inflammation.

Eosinophils in obesity and obesity-associated disorders

Despite the rising prevalence and costs for the society, obesity etiology, and its precise cellular and molecular mechanisms are still insufficiently understood. The excessive accumulation of fat by adipocytes plays a key role in obesity progression and has many repercussions on total body physiology. In recent years the immune system as a gatekeeper of adipose tissue homeostasis has been evidenced and has become a focal point of research. Herein we focus on eosinophils, an important component of type 2 immunity, assuming fundamental, yet ill-defined, roles in the genesis, and progression of obesity and related metabolic disorders. We summarize eosinophilopoiesis and eosinophils recruitment into adipose tissue and discuss how the adipose tissue environments shape their function and vice versa. Finally, we also detail how obesity transforms the local eosinophil niche. Understanding eosinophil crosstalk with the diverse cell types within the adipose tissue environment will allow us to framework the therapeutic potential of eosinophils in obesity.

Adipose tissue‑derived extracellular vesicles: Systemic messengers in health and disease (Review)

Adipose tissue (AT) is a complicated metabolic organ consisting of a heterogeneous population of cells that exert wide‑ranging effects on the regulation of systemic metabolism and in maintaining metabolic homeostasis. Various obesity‑related complications are associated with the development of dysfunctional AT. As an essential transmitter of intercellular information, extracellular vesicles (EVs) have recently been recognized as crucial in regulating multiple physiological functions. AT‑derived extracellular vesicles (ADEVs) have been shown to facilitate cellular communication both inside and between ATs and other peripheral organs. Here, the role of EVs released from ATs in the homeostasis of metabolic and cardiovascular diseases, cancer, and neurological disorders by delivering lipids, proteins, and nucleic acids between different cells is summarized. Furthermore, the differences in the sources of ADEVs, such as adipocytes, AT macrophages, AT‑derived stem cells, and AT‑derived mesenchymal stem cells, are also discussed. This review may provide valuable information for the potential application of ADEVs in metabolic syndrome, cardiovascular diseases, cancer, and neurological disorders.

Comparative efficacy of four exercise types on obesity-related outcomes in breast cancer survivors: A Bayesian network meta-analysis

PURPOSE

Exercise training is associated with improving the prognosis of breast cancer survivors, but no studies have evaluated the optimal exercise intervention. We aimed to investigate the most effective exercise intervention to improve obesity-related outcomes in breast cancer survivors.

METHODS

A comprehensive search strategy was conducted in Medline, Embase, Web of Science, Cochrane Library, and Chinese biomedical literature databases from the time of library construction to April 2, 2023. We included randomized controlled trials reporting the effects of four types of exercise interventions (aerobic exercise; aerobic combined with resitance exercise, resitstance exercise and mind-body exercise ) on obesity-related outcomes in breast cancer survivors. A Bayesian network meta-analysis was used to analyze and rank the effectiveness of four exercise types.

RESULTS

A total of 76 randomized controlled trials that contained 5610 breast cancer survivors were included. The treatment effect of combined aerobic and resistance exercise (mean difference = -0.59; 95% credible interval: 1.15, -0.08) was significantly better than that of the control groups in terms of body mass index. For percentage of body fat, combined aerobic and resistance exercise (mean difference = -1.74; 95% credible interval: 0.87, -0.90) and aerobic exercise (mean difference = -1.16; 95% credible interval: 2.15, -0.16) were significantly better than controls. Subgroup analysis suggested that combined aerobic and resistance exercise significantly affected body mass index at an intervention duration >12 weeks or weekly time on exercise >150 min.

CONCLUSION

Our network meta-analysis found combined aerobic and resistance exercise may be the most effective intervention to improve obesity-related outcomes in breast cancer survivors. In addition, intervention duration and participant adherence are important factors that influence the effectiveness of exercise interventions.

Osteopontin-driven T-cell accumulation and function in adipose tissue and liver promoted insulin resistance and MAFLD

OBJECTIVE

This study investigated the contribution of osteopontin/secreted phosphoprotein 1 (SPP1) to T-cell regulation in initiation of obesity-driven adipose tissue (AT) inflammation and macrophage infiltration and the subsequent impact on insulin resistance (IR) and metabolic-associated fatty liver disease (MAFLD) development.

METHODS

SPP1 and T-cell marker expression was evaluated in AT and liver according to type 2 diabetes and MAFLD in human individuals with obesity. The role of SPP1 on T cells was evaluated in Spp1-knockout mice challenged with a high-fat diet.

RESULTS

In humans with obesity, elevated SPP1 expression in AT was parallel to T-cell marker expression (CD4, CD8A) and IR. Weight loss reversed AT inflammation with decreased SPP1 and CD8A expression. In liver, elevated SPP1 expression correlated with MAFLD severity and hepatic T-cell markers. In mice, although Spp1 deficiency did not impact obesity, it did improve AT IR associated with prevention of proinflammatory T-cell accumulation at the expense of regulatory T cells. Spp1 deficiency also decreased ex vivo helper T cell, subtype 1 (Th1) polarization of AT CD4+ and CD8+ T cells. In addition, Spp1 deficiency significantly reduced obesity-associated liver steatosis and inflammation.

CONCLUSIONS

Current findings highlight a critical role of SPP1 in the initiation of obesity-driven chronic inflammation by regulating accumulation and/or polarization of T cells. Early targeting of SPP1 could be beneficial for IR and MAFLD treatment.

Circulating Levels of IL-8 and MCP-1 in Healthy Adults: Changes after an Acute Aerobic Exercise and Association with Body Composition and Energy Metabolism

The most recent WHO recommendations about physical activity emphasise the importance of total exercise volume above the significance of the duration of each bout. This study examined whether acute aerobic exercise changes circulating levels of IL-8 and MCP-1 and if these changes are associated with body composition and energy metabolism. Healthy adult volunteers completed a 10 min walking-running exercise on a treadmill. Indirect calorimetry was used to determine their resting metabolic rate (RMR) and energy expenditure (EE) during the exercise. Pre-exercise levels of IL-8 and MCP-1 were similar in both sexes. There were positive correlations of pre-exercise IL-8 with body mass, waist circumference, and lean body mass in men and pre-exercise MCP-1 with RMR in women. The exercise led to an increase in IL-8 of 68% and a decrease in MCP-1 of 74% of participants. An increase in post-exercise IL-8 in men was associated with greater walking EE and a greater increase in walking EE. The increase in post-exercise MCP-1 was associated with a lower RMR and running EE in women. There are both sex and individual variations in changes in chemokine secretion in response to the same exercise situation and their associations with values of metabolic parameters.

Sex-specific Association Between Adipose Tissue Inflammation and Vascular and Metabolic Complications of Obesity

CONTEXT

Adipose tissue (AT) inflammation predisposes to insulin resistance and metabolic syndrome in obesity.

OBJECTIVE

To investigate the association between adipocyte size, AT inflammation, systemic inflammation, and metabolic and atherosclerotic complications of obesity in a sex-specific manner.

DESIGN

Cross-sectional cohort study.

SETTING

University hospital in the Netherlands.

PARTICIPANTS

A total of 302 adult subjects with a body mass index (BMI) ≥ 27 kg/m2.

MAIN OUTCOME MEASURES

We obtained subcutaneous abdominal fat biopsies and systematically assessed, in a sex-specific manner, associations of several parameters of AT inflammation (including adipocyte size, macrophage content, crown-like structures, and gene expression) to biomarkers of systemic inflammation, leukocyte number and function, and to the presence of metabolic syndrome, insulin resistance, and carotid atherosclerotic plaques, assessed with ultrasound.

RESULTS

Adipocyte size was associated with metabolic syndrome and AT macrophage content with insulin resistance. In contrast, none of the AT parameters was associated with carotid atherosclerosis, although mRNA expression of the anti-inflammatory IL-37 was associated with a lower intima-media thickness. We revealed profound sex-specific differences, with an association between BMI and adipocyte size, and between adipocyte size and metabolic syndrome in men only. Also, only men showed an association between adipocyte size, AT expression of leptin and MCP-1, and AT macrophage numbers, and between AT inflammation (crown-like structure number) and several circulating inflammatory proteins, including high specificity C-reactive protein, and IL-6.

CONCLUSIONS

Inflammation in abdominal subcutaneous adipose tissue is more related to the metabolic than the atherosclerotic complications of obesity, and there are profound sex-specific differences in the association between BMI, adipocyte size, AT inflammation, and systemic inflammation, which are much stronger in men than women.

A novel role of RNase L in the development of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and affects about 25% of the population globally. NAFLD has the potential to cause significant liver damage in many patients because it can progress to nonalcoholic steatohepatitis (NASH) and cirrhosis, which substantially increases disease morbidity and mortality. Despite the key role of innate immunity in the disease progression, the underlying molecular and pathogenic mechanisms remain to be elucidated. RNase L is a key enzyme in interferon action against viral infection and displays pleiotropic biological functions such as control of cell proliferation, apoptosis, and autophagy. Recent studies have demonstrated that RNase L is involved in innate immunity. In this study, we revealed that RNase L contributed to the development of NAFLD, which further progressed to NASH in a time-dependent fashion after RNase L wild-type (WT) and knockout mice were fed with a high-fat and high-cholesterol diet. RNase L WT mice showed significantly more severe NASH, evidenced by widespread macro-vesicular steatosis, hepatocyte ballooning degeneration, inflammation, and fibrosis, although physiological and biochemical data indicated that both types of mice developed obesity, hyperglycemia, hypercholesterolemia, dysfunction of the liver, and systemic inflammation at different extents. Further investigation demonstrated that RNase L was responsible for the expression of some key genes in lipid metabolism, inflammation, and fibrosis signaling. Taken together, our results suggest that a novel therapeutic intervention for NAFLD may be developed based on regulating the expression and activity of RNase L.

The miR-23-27-24 clusters drive lipid-associated macrophage proliferation in obese adipose tissue

Identifying molecular circuits that control adipose tissue macrophage (ATM) function is necessary to understand how ATMs contribute to tissue homeostasis and obesity-induced insulin resistance. In this study, we find that mice with a myeloid-specific knockout of the miR-23-27-24 clusters of microRNAs (miRNAs) gain less weight on a high-fat diet but exhibit worsened glucose and insulin tolerance. Analysis of ATMs from these mice shows selectively reduced numbers and proliferation of a recently reported subset of lipid-associated CD9+Trem2+ ATMs (lipid-associated macrophages [LAMs]). Leveraging the role of miRNAs to control networks of genes, we use RNA sequencing (RNA-seq), functional screens, and biochemical assays to identify candidate target transcripts that regulate proliferation-associated signaling. We determine that miR-23 directly targets the mRNA of Eif4ebp2, a gene that restricts protein synthesis and proliferation in macrophages. Altogether, our study demonstrates that control of proliferation of a protective subset of LAMs by noncoding RNAs contributes to protection against diet-induced obesity metabolic dysfunction.

CCR2 inhibitor strengthens the adiponectin effects against myocardial injury after infarction

Little evidence demonstrated the effects of nitric oxide (NO) hydrogel with adipocytes in vivo. We aimed to investigate the effects of adiponectin (ADPN) and CCR2 antagonist on cardiac functions and macrophage phenotypes after myocardial infarction (MI) using chitosan caged nitric oxide donor (CSNO) patch with adipocytes. 3T3-L1 cell line was induced to adipocytes and ADPN expression was knocked down. CSNO was synthesized and patch was constructed. MI model was constructed and patch was placed on the infarcted area. ADPN knockdown adipocytes or control was incubated with CSNO patch, and CCR2 antagonist was also used to investigate the ADPN effects on myocardial injury after infarction. On day 7 after operation, cardiac functions of the mice using CSNO with adipocytes or ADPN knockdown adipocytes improved more than in mice only using CSNO for treatment. Lymphangiogenesis increased much more in the MI mice using CSNO with adipocytes. After treating with CCR2 antagonist, Connexin43+ CD206+ cells and ZO-1+ CD206+ cells increased, suggesting that CCR2 antagonist promoted M2 polarization after MI. Besides, CCR2 antagonist promoted ADPN expression in adipocytes and cardiomyocytes. ELISA was also used and CKMB expression was much lower than other groups at 3 days after operation. On day 7 after operation, the VEGF and TGFβ expressions were high in the adipocytes CSNO group, illustrating that higher ADPN led to better treatment. In all, CCR2 antagonist enhanced the ADPN effects on macrophage M2 polarization and cardiac functions. The combination used in border zone and infarcted areas may help improve patients' prognosis in surgery, such as CABG.

The Role of Macrophage Populations in Skeletal Muscle Insulin Sensitivity: Current Understanding and Implications

Insulin resistance is a crucial factor in the development of type 2 diabetes mellitus (T2DM) and other metabolic disorders. Skeletal muscle, the body's largest insulin-responsive tissue, plays a significant role in the pathogenesis of T2DM due to defects in insulin signaling. Recently, there has been growing evidence that macrophages, immune cells essential for tissue homeostasis and injury response, also contribute to the development of skeletal muscle insulin resistance. This review aims to summarize the current understanding of the role of macrophages in skeletal muscle insulin resistance. Firstly, it provides an overview of the different macrophage populations present in skeletal muscle and their specific functions in the development of insulin resistance. Secondly, it examines the underlying mechanisms by which macrophages promote or alleviate insulin resistance in skeletal muscle, including inflammation, oxidative stress, and altered metabolism. Lastly, the review discusses potential therapeutic strategies targeting macrophages to improve skeletal muscle insulin sensitivity and metabolic health.

NAFLD and AATD Are Two Diseases with Unbalanced Lipid Metabolism: Similarities and Differences

Non-alcoholic fatty liver disease (NAFLD) is a type of steatosis commonly associated with obesity, dyslipidemia, hypertension, and diabetes. Other diseases such as inherited alpha-1 antitrypsin deficiency (AATD) have also been related to the development of liver steatosis. The primary reasons leading to hepatic lipid deposits can be genetic and epigenetic, and the outcomes range from benign steatosis to liver failure, as well as to extrahepatic diseases. Progressive hepatocellular damage and dysregulated systemic immune responses can affect extrahepatic organs, specifically the heart and lungs. In this review, we discuss the similarities and differences between the molecular pathways of NAFLD and AATD, and the putative value of hepatic organoids as novel models to investigate the physio pathological mechanisms of liver steatosis.

Diesel Exhaust Particle (DEP)-induced glucose intolerance is driven by an intestinal innate immune response and NLRP3 activation in mice

BACKGROUND

We previously found that air pollution particles reaching the gastrointestinal tract elicit gut inflammation as shown by up-regulated gene expression of pro-inflammatory cytokines and monocyte/macrophage markers. This inflammatory response was associated with beta-cell dysfunction and glucose intolerance. So far, it remains unclear whether gut inflammatory changes upon oral air pollution exposure are causally linked to the development of diabetes. Hence, our aim was to assess the role of immune cells in mediating glucose intolerance instigated by orally administered air pollutants.

METHODS

To assess immune-mediated mechanisms underlying air pollution-induced glucose intolerance, we administered diesel exhaust particles (DEP; NIST 1650b, 12 µg five days/week) or phosphate-buffered saline (PBS) via gavage for up to 10 months to wild-type mice and mice with genetic or pharmacological depletion of innate or adaptive immune cells. We performed unbiased RNA-sequencing of intestinal macrophages to elucidate signaling pathways that could be pharmacologically targeted and applied an in vitro approach to confirm these pathways.

RESULTS

Oral exposure to air pollution particles induced an interferon and inflammatory signature in colon macrophages together with a decrease of CCR2^- anti-inflammatory/resident macrophages. Depletion of macrophages, NLRP3 or IL-1β protected mice from air pollution-induced glucose intolerance. On the contrary, Rag2-/- mice lacking adaptive immune cells developed pronounced gut inflammation and glucose intolerance upon oral DEP exposure.

CONCLUSION

In mice, oral exposure to air pollution particles triggers an immune-mediated response in intestinal macrophages that contributes to the development of a diabetes-like phenotype. These findings point towards new pharmacologic targets in diabetes instigated by air pollution particles.

Fibrocytes enhance mammary gland fibrosis in obesity

Obesity rates continue to rise, and obese individuals are at higher risk for multiple types of cancer, including breast cancer. Obese mammary fat is a site of chronic, macrophage-driven inflammation, which enhances fibrosis within adipose tissue. Elevated fibrosis within the mammary gland may contribute to risk for obesity-associated breast cancer. To understand how inflammation due to obesity enhanced fibrosis within mammary tissue, we utilized a high-fat diet model of obesity and elimination of CCR2 signaling in mice to identify changes in immune cell populations and their impact on fibrosis. We observed that obesity increased a population of CD11b⁺ cells with the ability to form myofibroblast-like colonies in vitro. This population of CD11b⁺ cells is consistent with fibrocytes, which have been identified in wound healing and chronic inflammatory diseases but have not been examined in obesity. In CCR2-null mice, which have limited ability to recruit myeloid lineage cells into obese adipose tissue, we observed reduced mammary fibrosis and diminished fibrocyte colony formation in vitro. Transplantation of myeloid progenitor cells, which are the cells of origin for fibrocytes, into the mammary glands of obese CCR2-null mice resulted in significantly increased myofibroblast formation. Gene expression analyses of the myeloid progenitor cell population from obese mice demonstrated enrichment for genes associated with collagen biosynthesis and extracellular matrix remodeling. Together these results show that obesity enhances recruitment of fibrocytes to promote obesity-induced fibrosis in the mammary gland.

Obesity and the risk of cardiometabolic diseases

The prevalence of obesity has reached pandemic proportions, and now approximately 25% of adults in Westernized countries have obesity. Recognized as a major health concern, obesity is associated with multiple comorbidities, particularly cardiometabolic disorders. In this Review, we present obesity as an evolutionarily novel condition, summarize the epidemiological evidence on its detrimental cardiometabolic consequences and discuss the major mechanisms involved in the association between obesity and the risk of cardiometabolic diseases. We also examine the role of potential moderators of this association, with evidence for and against the so-called 'metabolically healthy obesity phenotype', the 'fatness but fitness' paradox or the 'obesity paradox'. Although maintenance of optimal cardiometabolic status should be a primary goal in individuals with obesity, losing body weight and, particularly, excess visceral adiposity seems to be necessary to minimize the risk of cardiometabolic diseases.

Link between obesity and atopic dermatitis: Does obesity predispose to atopic dermatitis, or vice versa?

Two serious health conditions, obesity and atopic dermatitis (AD), share some pathological features such as insulin resistance, leptin resistance and inflammation, and a growing body of evidence suggests a link between obesity and AD. Obesity predisposes an individual to and/or worsens AD, whereas AD increases the risk of obesity. Obesity and AD's interactions are mediated by cytokines, chemokines and immune cells. Obese individuals with AD are more resistant to anti-inflammatory therapy, while weight loss can alleviate AD. In this review, we summarize the evidence linking AD and obesity. We also discuss the pathogenic role of obesity in AD, and vice versa. Because of the connection between these two conditions, mitigation of one could possibly prevent the development of or alleviate the other condition. Effective management of AD and weight loss can enhance the wellness of individuals with both of these conditions. However, proper clinical studies are warranted to validate this speculation.

Noncanonical Regulation of cAMP-Dependent Insulin Secretion and Its Implications in Type 2 Diabetes

Impaired glucose tolerance (IGT) and β-cell dysfunction in insulin resistance associated with obesity lead to type 2 diabetes (T2D). Glucose-stimulated insulin secretion (GSIS) from β-cells occurs via a canonical pathway that involves glucose metabolism, ATP generation, inactivation of K ATP channels, plasma membrane depolarization, and increases in cytosolic concentrations of [Ca 2+ ] c . However, optimal insulin secretion requires amplification of GSIS by increases in cyclic adenosine monophosphate (cAMP) signaling. The cAMP effectors protein kinase A (PKA) and exchange factor activated by cyclic-AMP (Epac) regulate membrane depolarization, gene expression, and trafficking and fusion of insulin granules to the plasma membrane for amplifying GSIS. The widely recognized lipid signaling generated within β-cells by the β-isoform of Ca 2+ -independent phospholipase A 2 enzyme (iPLA 2 β) participates in cAMP-stimulated insulin secretion (cSIS). Recent work has identified the role of a G-protein coupled receptor (GPCR) activated signaling by the complement 1q like-3 (C1ql3) secreted protein in inhibiting cSIS. In the IGT state, cSIS is attenuated, and the β-cell function is reduced. Interestingly, while β-cell-specific deletion of iPLA 2 β reduces cAMP-mediated amplification of GSIS, the loss of iPLA 2 β in macrophages (MØ) confers protection against the development of glucose intolerance associated with diet-induced obesity (DIO). In this article, we discuss canonical (glucose and cAMP) and novel noncanonical (iPLA 2 β and C1ql3) pathways and how they may affect β-cell (dys)function in the context of impaired glucose intolerance associated with obesity and T2D. In conclusion, we provide a perspective that in IGT states, targeting noncanonical pathways along with canonical pathways could be a more comprehensive approach for restoring β-cell function in T2D. © 2023 American Physiological Society. Compr Physiol 13:5023-5049, 2023.

Regulation of systemic metabolism by tissue-resident immune cell circuits

Recent studies have demonstrated that tissue homeostasis and metabolic function are dependent on distinct tissue-resident immune cells that form functional cell circuits with structural cells. Within these cell circuits, immune cells integrate cues from dietary contents and commensal microbes in addition to endocrine and neuronal signals present in the tissue microenvironment to regulate structural cell metabolism. These tissue-resident immune circuits can become dysregulated during inflammation and dietary overnutrition, contributing to metabolic diseases. Here, we review the evidence describing key cellular networks within and between the liver, gastrointestinal tract, and adipose tissue that control systemic metabolism and how these cell circuits become dysregulated during certain metabolic diseases. We also identify open questions in the field that have the potential to enhance our understanding of metabolic health and disease.

Macrophages and the development and progression of non-alcoholic fatty liver disease

The liver is the site of first pass metabolism, detoxifying and metabolizing blood arriving from the hepatic portal vein and hepatic artery. It is made up of multiple cell types, including macrophages. These are either bona fide tissue-resident Kupffer cells (KC) of embryonic origin, or differentiated from circulating monocytes. KCs are the primary immune cells populating the liver under steady state. Liver macrophages interact with hepatocytes, hepatic stellate cells, and liver sinusoidal endothelial cells to maintain homeostasis, however they are also key contributors to disease progression. Generally tolerogenic, they physiologically phagocytose foreign particles and debris from portal circulation and participate in red blood cell clearance. However as immune cells, they retain the capacity to raise an alarm to recruit other immune cells. Their aberrant function leads to the development of non-alcoholic fatty liver disease (NAFLD). NAFLD refers to a spectrum of conditions ranging from benign steatosis of the liver to steatohepatitis and cirrhosis. In NAFLD, the multiple hit hypothesis proposes that simultaneous influences from the gut and adipose tissue (AT) generate hepatic fat deposition and that inflammation plays a key role in disease progression. KCs initiate the inflammatory response as resident immune effectors, they signal to neighbouring cells and recruit monocytes that differentiated into recruited macrophages in situ. Recruited macrophages are central to amplifying the inflammatory response and causing progression of NAFLD to its fibro-inflammatory stages. Given their phagocytic capacity and their being instrumental in maintaining tissue homeostasis, KCs and recruited macrophages are fast-becoming target cell types for therapeutic intervention. We review the literature in the field on the roles of these cells in the development and progression of NAFLD, the characteristics of patients with NAFLD, animal models used in research, as well as the emerging questions. These include the gut-liver-brain axis, which when disrupted can contribute to decline in function, and a discussion on therapeutic strategies that act on the macrophage-inflammatory axis.

Obesity and Fibrosis: Setting the Stage for Breast Cancer

Obesity is a rising health concern and is linked to a worsened breast cancer prognosis. Tumor desmoplasia, which is characterized by elevated numbers of cancer-associated fibroblasts and the deposition of fibrillar collagens within the stroma, may contribute to the aggressive clinical behavior of breast cancer in obesity. A major component of the breast is adipose tissue, and fibrotic changes in adipose tissue due to obesity may contribute to breast cancer development and the biology of the resulting tumors. Adipose tissue fibrosis is a consequence of obesity that has multiple sources. Adipocytes and adipose-derived stromal cells secrete extracellular matrix composed of collagen family members and matricellular proteins that are altered by obesity. Adipose tissue also becomes a site of chronic, macrophage-driven inflammation. Macrophages exist as a diverse population within obese adipose tissue and mediate the development of fibrosis through the secretion of growth factors and matricellular proteins and interactions with other stromal cells. While weight loss is recommended to resolve obesity, the long-term effects of weight loss on adipose tissue fibrosis and inflammation within breast tissue are less clear. Increased fibrosis within breast tissue may increase the risk for tumor development as well as promote characteristics associated with tumor aggressiveness.

Obesity contributes to hepatocellular carcinoma development via immunosuppressive microenvironment remodeling

It is generally recognized that the initiation of obesity-related hepatocellular carcinoma (HCC) is closely associated with hepatic inflammation. However, the paradoxical role of inflammation in the initiation and progression of HCC is highlighted by the fact that the inflammatory HCC is accompanied by significant immune effector cells infiltration compared to non-inflammatory HCC and HCC with enhanced immune response exhibits better survival. Importantly, the cancer progression has been primarily attributed to the immunosuppression, which can also be induced by obesity. Furthermore, the increased risk of viral infection and thus viral-HCC in obese individuals supports the view that obesity contributes to HCC via immunosuppression. Here, we have reviewed the various mechanisms responsible for obesity-induced tumor immune microenvironment and immunosuppression in obesity-related HCC. We highlight that the obesity-induced immunosuppression originates from lipid disorder as well as metabolic reprogramming and propose potential therapeutic strategy for HCC based on the current success of immunotherapy.

Bioactive compounds from Polygonatum genus as anti-diabetic agents with future perspectives

Diabetes mellitus (DM) is one of the most serious health problems worldwide. Species in the genus Polygonatum are traditional food and medicinal plants, which play an important role in controlling blood glucose. In this reveiw, we systematically summarized the traditional and modern applications of the genus Polygonatum in DM, focused on the material bases of polysaccharides, flavonoids and saponins. We highlighted their mechanisms of action in preventing obese diabetes, improving insulin resistance, promoting insulin secretion, regulating intestinal microecology, inhibiting advanced glycation end products (AGEs) accumulation, suppressing carbohydrate digestion and obsorption and modulating gluconeogenesis. Based on the safety and efficacy of this 'medicinal food' and its utility in the prevention and treatment of diabetes, we proposed a research and development program that includs diet design (supplementary food), medical nutrition therapy and new drugs, which could provide new pathways for the use of natural plants in prevention and treatment of DM.

The role of metabolic reprogramming of tumor-associated macrophages in shaping the immunosuppressive tumor microenvironment

Macrophages are potent immune effector cells in innate immunity and exert dual-effects in the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) make up a significant portion of TME immune cells. Similar to M1/M2 macrophages, TAMs are also highly plastic, and their functions are regulated by cytokines, chemokines and other factors in the TME. The metabolic changes in TAMs are significantly associated with polarization towards a protumour or antitumour phenotype. The metabolites generated via TAM metabolic reprogramming in turn promote tumor progression and immune tolerance. In this review, we explore the metabolic reprogramming of TAMs in terms of energy, amino acid and fatty acid metabolism and the potential roles of these changes in immune suppression.

Macrophage function in adipose tissue homeostasis and metabolic inflammation

Obesity-related metabolic organ inflammation contributes to cardiometabolic disorders. In obese individuals, changes in lipid fluxes and storage elicit immune responses in the adipose tissue (AT), including expansion of immune cell populations and qualitative changes in the function of these cells. Although traditional models of metabolic inflammation posit that these immune responses disturb metabolic organ function, studies now suggest that immune cells, especially AT macrophages (ATMs), also have important adaptive functions in lipid homeostasis in states in which the metabolic function of adipocytes is taxed. Adverse consequences of AT metabolic inflammation might result from failure to maintain local lipid homeostasis and long-term effects on immune cells beyond the AT. Here we review the complex function of ATMs in AT homeostasis and metabolic inflammation. Additionally, we hypothesize that trained immunity, which involves long-term functional adaptations of myeloid cells and their bone marrow progenitors, can provide a model by which metabolic perturbations trigger chronic systemic inflammation.

Fatty Liver Disease, Metabolism and Alcohol Interplay: A Comprehensive Review

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, and its incidence has been increasing in recent years because of the high prevalence of obesity and metabolic syndrome in the Western population. Alcohol-related liver disease (ArLD) is the most common cause of cirrhosis and constitutes the leading cause of cirrhosis-related deaths worldwide. Both NAFLD and ArLD constitute well-known causes of liver damage, with some similarities in their pathophysiology. For this reason, they can lead to the progression of liver disease, being responsible for a high proportion of liver-related events and liver-related deaths. Whether ArLD impacts the prognosis and progression of liver damage in patients with NAFLD is still a matter of debate. Nowadays, the synergistic deleterious effect of obesity and diabetes is clearly established in patients with ArLD and heavy alcohol consumption. However, it is still unknown whether low to moderate amounts of alcohol are good or bad for liver health. The measurement and identification of the possible synergistic deleterious effect of alcohol consumption in the assessment of patients with NAFLD is crucial for clinicians, since early intervention, advising abstinence and controlling cardiovascular risk factors would improve the prognosis of patients with both comorbidities. This article seeks to perform a comprehensive review of the pathophysiology of both disorders and measure the impact of alcohol consumption in patients with NAFLD.

Glucocorticoid activation of anti-inflammatory macrophages protects against insulin resistance

Insulin resistance (IR) during obesity is linked to adipose tissue macrophage (ATM)-driven inflammation of adipose tissue. Whether anti-inflammatory glucocorticoids (GCs) at physiological levels modulate IR is unclear. Here, we report that deletion of the GC receptor (GR) in myeloid cells, including macrophages in mice, aggravates obesity-related IR by enhancing adipose tissue inflammation due to decreased anti-inflammatory ATM leading to exaggerated adipose tissue lipolysis and severe hepatic steatosis. In contrast, GR deletion in Kupffer cells alone does not alter IR. Co-culture experiments show that the absence of GR in macrophages directly causes reduced phospho-AKT and glucose uptake in adipocytes, suggesting an important function of GR in ATM. GR-deficient macrophages are refractory to alternative ATM-inducing IL-4 signaling, due to reduced STAT6 chromatin loading and diminished anti-inflammatory enhancer activation. We demonstrate that GR has an important function in macrophages during obesity by limiting adipose tissue inflammation and lipolysis to promote insulin sensitivity.

Adipose tissue macrophages as potential targets for obesity and metabolic diseases

Macrophage infiltration into adipose tissue is a key pathological factor inducing adipose tissue dysfunction and contributing to obesity-induced inflammation and metabolic disorders. In this review, we aim to present the most recent research on macrophage heterogeneity in adipose tissue, with a focus on the molecular targets applied to macrophages as potential therapeutics for metabolic diseases. We begin by discussing the recruitment of macrophages and their roles in adipose tissue. While resident adipose tissue macrophages display an anti-inflammatory phenotype and promote the development of metabolically favorable beige adipose tissue, an increase in pro-inflammatory macrophages in adipose tissue has negative effects on adipose tissue function, including inhibition of adipogenesis, promotion of inflammation, insulin resistance, and fibrosis. Then, we presented the identities of the newly discovered adipose tissue macrophage subtypes (e.g. metabolically activated macrophages, CD9+ macrophages, lipid-associated macrophages, DARC+ macrophages, and MFehi macrophages), the majority of which are located in crown-like structures within adipose tissue during obesity. Finally, we discussed macrophage-targeting strategies to ameliorate obesity-related inflammation and metabolic abnormalities, with a focus on transcriptional factors such as PPARγ, KLF4, NFATc3, and HoxA5, which promote macrophage anti-inflammatory M2 polarization, as well as TLR4/NF-κB-mediated inflammatory pathways that activate pro-inflammatory M1 macrophages. In addition, a number of intracellular metabolic pathways closely associated with glucose metabolism, oxidative stress, nutrient sensing, and circadian clock regulation were examined. Understanding the complexities of macrophage plasticity and functionality may open up new avenues for the development of macrophage-based treatments for obesity and other metabolic diseases.

Diet-induced obesity alters intestinal monocyte-derived and tissue-resident macrophages and increases intestinal permeability in female mice independent of tumor necrosis factor

Macrophages are essential for homeostatic maintenance of the anti-inflammatory and tolerogenic intestinal environment, yet monocyte-derived macrophages can promote local inflammation. Proinflammatory macrophage accumulation within the intestines may contribute to the development of systemic chronic inflammation and immunometabolic dysfunction in obesity. Using a model of high-fat diet-induced obesity in C57BL/6J female mice, we assessed intestinal paracellular permeability by in vivo and ex vivo assays and quantitated intestinal macrophages in ileum and colon tissues by multicolor flow cytometry after short (6 wk), intermediate (12 wk), and prolonged (18 wk) diet allocation. We characterized monocyte-derived CD4^-TIM4^- and CD4⁺TIM4^- macrophages, as well as tissue-resident CD4⁺TIM4⁺ macrophages. Diet-induced obesity had tissue- and time-dependent effects on intestinal permeability, as well as monocyte and macrophage numbers, surface marker phenotype, and intracellular production of the cytokines IL-10 and tumor necrosis factor (TNF). We found that obese mice had increased paracellular permeability, in particular within the ileum, but this did not elicit recruitment of monocytes nor a local proinflammatory response by monocyte-derived or tissue-resident macrophages in either the ileum or colon. Proliferation of monocyte-derived and tissue-resident macrophages was also unchanged. Wild-type and TNF^-/- littermate mice had similar intestinal permeability and macrophage population characteristics in response to diet-induced obesity. These data are unique from reported effects of diet-induced obesity on macrophages in metabolic tissues, as well as outcomes of acute inflammation within the intestines. These experiments also collectively indicate that TNF does not mediate effects of diet-induced obesity on paracellular permeability or intestinal monocyte-derived and tissue-resident intestinal macrophages in young female mice.NEW & NOTEWORTHY We found that diet-induced obesity in female mice has tissue- and time-dependent effects on intestinal paracellular permeability as well as monocyte-derived and tissue-resident macrophage numbers, surface marker phenotype, and intracellular production of the cytokines IL-10 and TNF. These changes were not mediated by TNF.