Remodeling Phenotype of Human Subcutaneous Adipose Tissue Macrophages

Unraveling the complex roles of macrophages in obese adipose tissue: an overview

Macrophages, a heterogeneous population of innate immune cells, exhibit remarkable plasticity and play pivotal roles in coordinating immune responses and maintaining tissue homeostasis within the context of metabolic diseases. The activation of inflammatory macrophages in obese adipose tissue leads to detrimental effects, inducing insulin resistance through increased inflammation, impaired thermogenesis, and adipose tissue fibrosis. Meanwhile, adipose tissue macrophages also play a beneficial role in maintaining adipose tissue homeostasis by regulating angiogenesis, facilitating the clearance of dead adipocytes, and promoting mitochondrial transfer. Exploring the heterogeneity of macrophages in obese adipose tissue is crucial for unraveling the pathogenesis of obesity and holds significant potential for targeted therapeutic interventions. Recently, the dual effects and some potential regulatory mechanisms of macrophages in adipose tissue have been elucidated using single-cell technology. In this review, we present a comprehensive overview of the intricate activation mechanisms and diverse functions of macrophages in adipose tissue during obesity, as well as explore the potential of drug delivery systems targeting macrophages, aiming to enhance the understanding of current regulatory mechanisms that may be potentially targeted for treating obesity or metabolic diseases.

SLC40A1 in iron metabolism, ferroptosis, and disease: A review

Solute carrier family 40 member 1 (SLC40A1) plays an essential role in transporting iron from intracellular to extracellular environments. When SLC40A1 expression is abnormal, cellular iron metabolism becomes dysregulated, resulting in an overload of intracellular iron, which induces cell ferroptosis. Numerous studies have confirmed that ferroptosis is closely associated with the development of many diseases. Here, we review recent findings on SLC40A1 in ferroptosis and its association with various diseases, intending to explore new directions for research on disease pathogenesis and new therapeutic targets for prevention and treatment. This article is categorized under: Cancer > Genetics/Genomics/Epigenetics Metabolic Diseases > Molecular and Cellular Physiology.

The phenotype and related gene expressions of macrophages in adipose tissue of T2D mice following MSCs infusion

BACKGROUND

Infusion of mesenchymal stem cells (MSCs) induces polarization of M2 macrophages in adipose tissue of type 2 diabetes (T2D) mice. Studies have shown that M2 macrophages were divided into four sub-phenotypes (M2a, M2b, M2c and M2d) with different functions, and manuscripts have also confirmed that macrophages co-cultured with MSCs were not matched with known four phenotype macrophages. Therefore, our study explored the phenotype and related gene expressions of macrophages in the adipose tissue of T2D mice with/without MSCs infusion.

METHODS

We induced a T2D mouse model by using high-fat diets and streptozotocin (STZ) injection. The mice were divided into three groups: the control group, the T2D group, and the MSCs group. MSCs were systemically injected once a week for 6 weeks. The phenotype of macrophages in adipose tissue was detected via flow cytometric analysis. We also investigated the gene expression of macrophages in different groups via SMART-RNA-sequencing and quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR).

RESULTS

The present study found that the macrophages of adipose tissue in the MSCs group were polarized to the M2 phenotype mixed with four sub-phenotypes. Besides, M2a and M2c held a dominant position, while M2b and M2d (tumor-associated macrophages, TAMs) exhibited a decreasing trend after infusion of MSCs. Moreover, the MSCs group did not appear to express higher levels of tumor-associated, inflammation-associated, or fibrosis-associated genes in comparison to the T2D group.

CONCLUSION

The present results unveiled that the macrophage phenotype was inclined to be present in a hybridity state of four M2 sub-phenotypes and the genes related to tumor-promoting, pro-inflammation and pro-fibrosis were not increased after MSCs injection.

Association of inflammatory cytokines with obesity and pulmonary function testing

BACKGROUND

The World Health Organization (WHO) reported that the prevalence of obesity in the Kingdom of Saudi Arabia (KSA) is 33.7% (women 39.5% and men 29.5%), respectively. The effects of obesity on airway inflammation and respiratory mechanics as well as the function of adipose tissue has a key role in the development of various lung diseases. Therefore, this study aimed to compare the level of cytokines between obese (BMI ≥ 30) and non-obese participants and to assess their association with BMI, airways inflammation and pulmonary function.

METHOD

One-hundred and seven non-smoking students (18-25 years of age) were recruited using convenience sampling technique for comparative cross-sectional study. Of them, 80 students were eligible and included in the analysis; 54 were non-obese (BMI<30) and 26 were obese (BMI ≥ 30). All the participants underwent anthropometric measurements, fractional exhaled nitric oxide (FeNO) measurement, spirometry and cytokines measurement (IL-6, IL-1β, GM-CSF, IL-7, IL-8 and IL-10). Measurements were compared between obese and non-obese groups. Then a correlation test was made between pro- and anti-inflammatory cytokines with BMI, pulmonary function test finding and FeNO.

RESULTS

The prevalence of obesity was 32.5% in the study population. Levels of pro-inflammatory cytokine IL-6 levels was significantly higher in obese than non-obese participants (p = 0.044). The level of FeNO log was significantly higher in obese participants than non-obese (p = 0.002). The pro-inflammatory cytokine IL-6 showed positive correlation with BMI while GMCSF showed negative correlation with FVC (p<0.05).

CONCLUSION

The levels of pro-inflammatory cytokine IL-6 was found to be significantly higher in obese participants than non-obese participants. Furthermore, it showed positive correlation with BMI whereas pro-inflammatory cytokine GMCSF showed negative correlation with FVC.

The role of three-dimensional in vitro models in modelling the inflammatory microenvironment associated with obesity in breast cancer

Obesity is an established risk factor for breast cancer in postmenopausal women. However, the underlying biological mechanisms of how obesity contributes to breast cancer remains unclear. The inflammatory adipose microenvironment is central to breast cancer progression and has been shown to favour breast cancer cell growth and to reduce efficacy of anti-cancer treatments. Thus, it is imperative to further our understanding of the inflammatory microenvironment seen in breast cancer patients with obesity. Three-dimensional (3D) in vitro models offer a key tool in increasing our understanding of such complex interactions within the adipose microenvironment. This review discusses some of the approaches utilised to recapitulate the breast tumour microenvironment, including various co-culture and 3D in vitro models. We consider how these model systems contribute to the understanding of breast cancer research, with particular focus on the inflammatory tumour microenvironment. This review aims to provide insight and prospective future directions on the utility of such model systems for breast cancer research.

Irisin: A Possible Marker of Adipose Tissue Dysfunction in Obesity

Adipose tissue (AT) secretes pro- and anti-inflammatory cytokines involved in AT homeostasis, including tumor necrosis factor-α (TNFα) and irisin. The functionality of AT is based on a regulated equilibrium between adipogenesis and extracellular matrix (ECM) remodeling. We investigated the contributions of adipose progenitors (ASCs) and adipocytes (AMCs) to TNFα-induced ECM remodeling and a possible implication of irisin in AT impairment in obesity. ASCs and AMCs were exposed to TNFα treatment and nuclear factor-kappa (NF-kB) pathway was investigated: Tissue Inhibitor of Metalloproteinase (TIMP-1), Twist Family Transcription Factor 1 (TWIST-1), and peroxisome proliferator-activated receptor-γ (PPARγ) expression levels were analyzed. The proteolytic activity of matrix metalloproteinases (MMPs) -2 and -9 was analyzed by zymography, and the irisin protein content was measured by ELISA. In inflamed AMCs, a TIMP-1/TWIST-1 imbalance leads to a drop in PPARγ. Adipogenesis and lipid storage ability impairment come with local tissue remodeling due to MMP-9 overactivation. In vitro and ex vivo measurements confirm positive correlations among inflammation, adipose secreting irisin levels, and circulating irisin levels in patients with visceral obesity. Our findings identify the NF-kB downstream effectors as molecular initiators of AT dysfunction and suggest irisin as a possible AT damage and obesity predictive factor.

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.

Loss of Visceral Fat is Associated with a Reduction in Inflammatory Status in Patients with Metabolic Syndrome

SCOPE

Excessive visceral adipose tissue (VAT) is associated with higher secretion of pro-inflammatory molecules, contributing to systemic inflammation and obesity-related metabolic disturbances.

METHODS AND RESULTS

This prospective analysis includes 117 overweight/obese adults (55-75 years) from the PREDIMED-Plus study. Fourteen inflammatory markers and adipokines are measured using a Bio-Plex assay with multiplex technology: insulin, glucagon, IL-6, visfatin, ghrelin, GLP-1, TNF-α, MCP-1, PAI-1, resistin, C-peptide, leptin, adipsin, and adiponectin. Participants are categorized into tertiles according to changes in VAT after 1-year of follow-up, determined by dual-energy X-Ray absorptiometry. Participants allocate in tertile 3, which represent an increase of VAT content after 1-year of follow-up compared to tertile 1, show significant differences in insulin (T3 vs T1, fully adjusted model: p = 0.037, p for trend 0.042), PAI-1 (fully adjusted model: p = 0.05, p for trend 0.06), c-peptide (fully adjusted model: p = 0.037, p for trend 0.042), and TNF-α (fully adjusted model p = 0.037, p for trend 0.042).

CONCLUSION

The results evidence that a reduction in VAT is associated with clinical improvements in several inflammatory and adiposity markers, mainly in insulin, c-peptide, and PAI-1 levels, and these improvements may contribute to a reduction in cardiometabolic disturbances observe in obesity.

Inflammaging and body composition: New insights in diabetic and hypertensive elderly men

Age-related changes in the body's physiological responses play a critical role in systemic arterial hypertension (SAH) and type 2 Diabetes mellitus (T2DM). SAH and T2DM have clinically silent low-grade inflammation as a common risk factor. This inflammation has a relevant element, the excess of fatty tissue. In this scenario, little is known about how inflammatory markers interact with each other. Therefore, this work evaluated the interplay among anthropometric, biochemical, and inflammatory markers in the elderly with SAH and T2DM. Men aged 60-80 years old with SAH and T2DM were classified by body mass index (BMI) as eutrophic elderly (EE, 24 individuals) or overweight elderly (OE, 25 individuals). Body composition analysis was performed using bioimpedance. Blood samples were collected to perform inflammatory and biochemical evaluations. The cytokines IL-17A, IL-1β, IFN-y, TNF-α, and IL-10, were evaluated by ELISA. Triglycerides, total and fractions of cholesterol, and glucose were measured by spectrophotometry. Overweight elderly men had a higher glycemic index and an increase in most anthropometric markers, as well as higher means for all pro-inflammatory cytokines analyzed (IL-17A, IL-1β, IFN-y, and TNF-α) in comparison to their eutrophic elderly counterparts. However, there was a decrease in IL-10 anti-inflammatory cytokine and IL-10/IL-17A ratio compared to their eutrophic elderly counterparts. Although overweight elderly men have worsening inflammatory parameters, the magnitude of their correlations with anthropometric and biochemical parameters becomes less evident. The Bayesian networks highlight that in the eutrophic elderly, IL-17A and TNF-α are the cytokines most associated with interactions, and most of these interactions occur with biochemical parameters. It is worth highlighting the role of IFN-y in overweight elderly men. This cytokine influences IL-10 and TNF-α production, contributing to the inflammatory profile exacerbated in this group.

Aberrant Mesenteric Adipose Extracellular Matrix Remodelling is Involved in Adipocyte Dysfunction in Crohn's Disease: The Role of TLR-4-mediated Macrophages

BACKGROUND AND AIMS

Hypertrophic mesenteric adipose tissue [htMAT] is involved in the disease progression of Crohn's disease [CD] through expressing proinflammatory adipokines from dysfunctional adipocytes by unknown mechanism. Adipocyte function is affected by dynamic adipose tissue extracellular matrix [ECM] remodelling that is mainly mediated by macrophages, and our study aimed to reveal whether aberrant ECM remodelling was present in CD-htMAT and its effects on adipocyte dysfunction, as well as the mechanism.

METHODS

ECM remodelling was examined in MAT samples from CD patients and controls. Mice with dinitrobenzene sulphonic acid [DNBS]-induced colitis were used in vivo study, and lipopolysaccharide [LPS]-induced remodelling behaviour in macrophages was examined in vitro. Macrophages or TLR4 inhibition were used to analyse ECM remodelling mechanisms and their effects on adipocyte function.

RESULTS

Aberrant ECM remodelling: was observed in CD-htMAT, which was characterised by a widened and deformed ECM structure accompanied by dysregulated matrix synthesis and degradation; served as a reservoir for inflammatory factors/cells dominated by macrophages; and was involved in adipocyte dysfunction. In addition, macrophages were the main source of ECM remodelling regulatory factors with activation of Toll-like receptor 4 [TLR4] in htMAT. In vivo, macrophage depletion or TLR4 inhibition largely attenuated mesenteric ECM remodelling while improving mesenteric adipocyte dysfunction during chronic enteritis. In vitro, antagonizing TLR4 significantly inhibited LPS-induced macrophage ECM remodelling behavior.

CONCLUSIONS

The aberrant ECM remodelling in CD-htMAT contributed to mesenteric adipocyte dysfunction, which may be caused at least partly by TLR4-mediated macrophage remodelling behavior. Inhibiting ECM remodelling may be a potential therapeutic strategy for CD.

Adipose tissue macrophages: Regulators of adipose tissue immunometabolism during obesity

BACKGROUND

Adipose tissue macrophages (ATMs) are a well characterized regulator of adipose tissue inflammatory tone. Previously defined by the M1 vs M2 classification, we now have a better understanding of ATM diversity that departs from the old paradigm and reports a spectrum of ATM function and phenotypes in both brown and white adipose tissue.

SCOPE OF REVIEW

This review provides an updated overview of ATM activation and function, ATM diversity in humans and rodents, and novel ATM functions that contribute to metabolic homeostasis and disease.

MAJOR CONCLUSIONS

While the paradigm that resident ATMs predominate in the lean state and obesity leads to the accumulation of lipid-associated and inflammatory ATMs still broadly remains rigorously supported, the details of this model continue to be refined and single cell data provide new insight into ATM subtypes and states.

Estradiol treatment increases M2-like visceral adipose tissue macrophages in obese ovariectomized mice regardless of its anorectic action

Estradiol (E2) treatment has been known to induce changes in food intake, energy expenditure, and weight gain. However, its direct effects on adipose tissue macrophages (ATM) in vivo are not fully understood. Thus, we aimed to explore this aspect at cellular and molecular levels in ovariectomized obese mice. We examined the changes in ATMs after eight weeks of a high-fat diet (HFD) in male, female, and ovariectomized (OVX) mice. After eight weeks, osmotic pumps were inserted into OVX mice to provide two weeks of E2 treatment. We additionally set up a vehicle Pair-Fed (PF) control group that supplied the same amount of HFD consumed by the E2-treated group. We then investigated the in vivo phenotypic changes of visceral adipose tissue (VAT) macrophages. The percentage of M1-like ATMs decreased by the anorectic effect of E2, while M2-like ATMs increased regardless of the anorexia. E2 treatment increased the expression of anti-inflammatory genes but decreased pro-inflammatory genes in VAT. Monocyte recruitment and local proliferation contributed to M2-like ATMs. Furthermore, M2-like phenotypes were induced by E2 treatment in human macrophages. E2 treatment increases M2-like macrophages and improves the tissue milieu of VAT regardless of the anorectic reaction of E2.

Fibrosis in fat: From other diseases to Crohn’s disease

Creeping fat is a specific feature of Crohn’s disease (CD) and is characterized by mesenteric fat wrapping around the intestine. It highly correlates with intestinal transmural inflammation, muscular hypertrophy, fibrosis, and stricture formation. However, the pathogenesis of creeping fat remains unclear. Molecular crosstalk exists between mesenteric fat and the intestine. Indeed, creeping fat contains different types of cells, including adipocytes and immune cells. These cell types can produce various cytokines, fatty acids, and growth factors, which affect the mesenteric fat function and modulate intestinal inflammation and immunity. Moreover, adipocyte progenitors can produce extracellular matrix to adapt to fat expansion. Previous studies have shown that fat fibrosis is an important feature of adipose tissue malfunction and exists in other diseases, including metabolic disorders, cancer, atrial fibrillation, and osteoarthritis. Furthermore, histological sections of CD showed fibrosis in the creeping fat. However, the role of fibrosis in the mesenteric fat of CD is not well understood. In this review, we summarized the possible mechanisms of fat fibrosis and its impact on other diseases. More specifically, we illustrated the role of various cells (adipocyte progenitors, macrophages, mast cells, and group 1 innate lymphoid cells) and molecules (including hypoxia-inducible factor 1-alpha, transforming growth factor-beta, platelet-derived growth factor, and peroxisome proliferator-activated receptor-gamma) in the pathogenesis of fat fibrosis in other diseases to understand the role of creeping fat fibrosis in CD pathogenesis. Future research will provide key information to decipher the role of fat fibrosis in creeping fat formation and intestinal damage, thereby helping us identify novel targets for the diagnosis and treatment of CD.

Role of adipose tissue macrophages in obesity-related disorders

The obesity epidemic has led researchers and clinicians to reconsider the etiology of this disease and precisely decipher its molecular mechanisms. The excessive accumulation of fat by cells, most notably adipocytes, which play a key role in this process, has many repercussions in tissue physiology. Herein, we focus on how macrophages, immune cells well known for their tissue gatekeeping functions, assume fundamental, yet ill-defined, roles in the genesis and development of obesity-related metabolic disorders. We first discuss the determinants of the biology of these cells before introducing the specifics of the adipose tissue environment, while highlighting its heterogeneity. Finally, we detail how obesity transforms both adipose tissue and local macrophage populations. Understanding macrophage diversity and their cross talk with the diverse cell types constituting the adipose tissue environment will allow us to frame the therapeutic potential of adipose tissue macrophages in obesity.

Targeted Suppression of miRNA-33 Using pHLIP Improves Atherosclerosis Regression

BACKGROUND

miRNA therapeutics have gained attention during the past decade. These oligonucleotide treatments can modulate the expression of miRNAs in vivo and could be used to correct the imbalance of gene expression found in human diseases such as obesity, metabolic syndrome, and atherosclerosis. The in vivo efficacy of current anti-miRNA technologies hindered by physiological and cellular barriers to delivery into targeted cells and the nature of miRNAs that allows one to target an entire pathway that may lead to deleterious off-target effects. For these reasons, novel targeted delivery systems to inhibit miRNAs in specific tissues will be important for developing effective therapeutic strategies for numerous diseases including atherosclerosis.

METHODS

We used pH low-insertion peptide (pHLIP) constructs as vehicles to deliver microRNA-33-5p (miR-33) antisense oligonucleotides to atherosclerotic plaques. Immunohistochemistry and histology analysis was performed to assess the efficacy of miR-33 silencing in atherosclerotic lesions. We also assessed how miR-33 inhibition affects gene expression in monocytes/macrophages by single-cell RNA transcriptomics.

RESULTS

The anti-miR-33 conjugated pHLIP constructs are preferentially delivered to atherosclerotic plaque macrophages. The inhibition of miR-33 using pHLIP-directed macrophage targeting improves atherosclerosis regression by increasing collagen content and decreased lipid accumulation within vascular lesions. Single-cell RNA sequencing analysis revealed higher expression of fibrotic genes (Col2a1, Col3a1, Col1a2, Fn1, etc) and tissue inhibitor of metalloproteinase 3 (Timp3) and downregulation of Mmp12 in macrophages from atherosclerotic lesions targeted by pHLIP-anti-miR-33.

CONCLUSIONS

This study provides proof of principle for the application of pHLIP for treating advanced atherosclerosis via pharmacological inhibition of miR-33 in macrophages that avoid the deleterious effects in other metabolic tissues. This may open new therapeutic opportunities for atherosclerosis-associated cardiovascular diseases via selective delivery of other protective miRNAs.

Use of Physical Activity and Exercise to Reduce Inflammation in Children and Adolescents with Obesity

Childhood obesity is a leading public health problem worldwide, as it is increasingly prevalent and therefore responsible for serious obesity-related comorbidities, not only in childhood but also in adulthood. In addition to cardio-metabolic obesity-related disorders, recent evidence suggests that excess adipose tissue in turn is associated with immune cell infiltration, increased adipokine release, and the development of low-grade systemic inflammation obesity. Exercise is considered a non-pharmacological intervention that can delay obesity-related comorbidities, improving cardiovascular fitness and modulating the inflammatory processes. It has been reported that the anti-inflammatory effect of regular exercise may be mediated by a reduction in visceral fat mass, with a subsequent decrease in the release of adipokines from adipose tissue (AT) and/or by the induction of an anti-inflammatory environment. In this narrative review, we discuss the role of AT as an endocrine organ associated with chronic inflammation and its role in obesity-related complications, focusing on the effect of exercise in reducing inflammation in children and adolescents with obesity. Regular physical exercise must be considered as a natural part of a healthy lifestyle, and promoting physical activity starting from childhood is useful to limit the negative effects of obesity on health. The crucial role of the immune system in the development of obesity-induced inflammatory processes and the efficacy of exercise as an anti-inflammatory, non-pharmacological intervention may provide possible targets for the development of new treatments and early preventive strategies.

Periprostatic Adipose Tissue Displays a Chronic Hypoxic State that Limits Its Expandability

White adipose tissue accumulates at various sites throughout the body, some adipose tissue depots exist near organs whose function they influence in a paracrine manner. Prostate gland is surrounded by a poorly characterized adipose depot called periprostatic adipose tissue (PPAT), which plays emerging roles in prostate-related disorders. Unlike all other adipose depots, PPAT secretes proinflammatory cytokines even in lean individuals and does not increase in volume during obesity. These unique features remain unexplained because of the poor structural and functional characterization of this tissue. This study characterized the structural organization of PPAT in patients compared with abdominopelvic adipose tissue (APAT), an extraperitoneal adipose depot, the accumulation of which is correlated to body mass index. Confocal microscopy followed by three-dimensional reconstructions showed a sparse vascular network in PPAT when compared with that in APAT, suggesting that this tissue is hypoxic. Unbiased comparisons of PPAT and APAT transcriptomes found that most differentially expressed genes were related to the hypoxia response. High levels of the hypoxia-inducible factor 2α confirmed the presence of an adaptive response to hypoxia in PPAT. This chronic hypoxic state was associated with inflammation and fibrosis, which were not further up-regulated by obesity. This fibrosis and inflammation explain the failure of PPAT to expand in obesity and open new mechanistic avenues to explain its role in prostate-related disorders, including cancer.

Immune and non-immune functions of adipose tissue leukocytes

Adipose tissue is a complex dynamic organ with whole-body immunometabolic influence. Much of the work into understanding the role of immune cells in adipose tissue has been in the context of obesity. These investigations have also uncovered a range of typical (immune) and non-typical functions exerted by adipose tissue leukocytes. Here we provide an overview of the adipose tissue immune system, including its role as an immune reservoir in the whole-body response to infection and as a site of parasitic and viral infections. We also describe the functional roles of specialized immunological structures found within adipose tissue. However, our main focus is on the recently discovered 'non-immune' functions of adipose tissue immune cells, which include the regulation of adipocyte homeostasis, as well as responses to changing nutrient status and body temperature. In doing so, we outline the therapeutic potential of the adipose tissue immune system in health and disease.

Prognostic significance of crown-like structures to trastuzumab response in patients with primary invasive HER2 + breast carcinoma

Obesity can initiate, promote, and maintain systemic inflammation via metabolic reprogramming of macrophages that encircle adipocytes, termed crown-like structures (CLS). In breast cancer the presence of CLS has been correlated to high body mass index (BMI), larger mammary adipocyte size and postmenopausal status. However, the prognostic significance of CLS in HER2 + breast cancer is still unknown. We investigated the prognostic significance of CLS in a cohort of 69 trastuzumab-naïve and 117 adjuvant trastuzumab-treated patients with primary HER2 + breast cancer. Immunohistochemistry of tumour blocks was performed for CLS and correlated to clinical outcomes. CLS were more commonly found at the adipose-tumour border (B-CLS) (64.8% of patients). The presence of multiple B-CLS was associated with reduced time to metastatic disease (TMD) in trastuzumab treated patients with BMI ≥ 25 kg/m2 but not those with BMI < 25 kg/m2. Phenotypic analysis showed the presence of CD32B + B-CLS was strongly correlated to BMI ≥ 25 kg/m2 and reduced TMD in trastuzumab treated patients. Multivariable analysis suggested that CD32B + B-CLS positive tumours are associated with shorter TMD in trastuzumab-treated patients (HR 4.2 [95%CI, (1.01-17.4). This study indicates adipose-tumour border crown-like structures that are CD32B + potentially represent a biomarker for improved personalisation of treatment in HER2-overexpressed breast cancer patients.

Sex differences in regional adipose tissue depots pose different threats for the development of Type 2 diabetes in males and females

Type 2 diabetes mellitus (T2DM) affects males and females disproportionately. In midlife, more males have T2DM than females. The sex difference in T2DM prevalence is, in part, explained by differences in regional adipose tissue characteristics. With obesity, changes to regional adipokine and cytokine release increases the risk of T2DM in both males and females with males having greater levels of TNFα and females having greater levels of leptin, CRP, and adiponectin. Regional immune cell infiltration appears to be pathogenic in both sexes via different routes as males with obesity have greater VAT ATM and a decrease in the protective Treg cells, whereas females have greater SAT ATM and T cells. Lastly, the ability of female adipose tissue to expand all regions through hyperplasia, rather than hypertrophy, protects them against the development of large insulin-resistant adipocytes that dominate male adipose tissue. The objective of this review is to discuss how sex may affect regional differences in adipose tissue characteristics and how these differences may distinguish the development of T2DM in males and females. In doing so, we will show that the origins of T2DM development differ between males and females.

Gut Microbiota, Macrophages and Diet: An Intriguing New Triangle in Intestinal Fibrosis

Intestinal fibrosis is a common complication in inflammatory bowel disease (IBD) without specific treatment. As macrophages are the key actors in inflammatory responses and the wound healing process, they have been extensively studied in chronic diseases these past decades. By their exceptional ability to integrate diverse stimuli in their surrounding environment, macrophages display a multitude of phenotypes to underpin a broad spectrum of functions, from the initiation to the resolution of inflammation following injury. The hypothesis that distinct macrophage subtypes could be involved in fibrogenesis and wound healing is emerging and could open up new therapeutic perspectives in the treatment of intestinal fibrosis. Gut microbiota and diet are two key factors capable of modifying intestinal macrophage profiles, shaping their specific function. Defects in macrophage polarisation, inadequate dietary habits, and alteration of microbiota composition may contribute to the development of intestinal fibrosis. In this review, we describe the intriguing triangle between intestinal macrophages, diet, and gut microbiota in homeostasis and how the perturbation of this discreet balance may lead to a pro-fibrotic environment and influence fibrogenesis in the gut.

Slc7a8 Deletion Is Protective against Diet-Induced Obesity and Attenuates Lipid Accumulation in Multiple Organs

Simple Summary

The development of obesity can be attributed to adipocyte hypertrophy or hyperplasia which lead to increased adiposity. The C57BL/6 mouse is an excellent model to study metabolic syndromes often associated with obesity development. Mice fed on a high-fat diet are susceptible to weight gain, leading to the development of obesity and its associated metabolic syndrome. Here, we report findings from targeting a novel potential human adipogenic gene (SLC7A8) under conditions of obesity development using a mouse model of diet-induced obesity (DIO). The results indicate that deleting slc7a8 in mice significantly protects against DIO and improves glucose metabolism. Deficiency in slc7a8 was observed to significantly attenuate adipocyte hypertrophy in white and brown adipose tissue and to reduce lipid accumulation in many organs. Furthermore, inflammation was significantly reduced in the adipose tissue and liver of slc7a8-deficient mice with DIO. Overall, the results from this study show that slc7a8 is an important molecular regulator of obesity development and mediates its function by reducing lipid accumulation in multiple organs. Hence, SLC7A8 could serve as a potential therapeutic target to combat the development of obesity and other pathophysiological conditions associated with excess lipid accumulation.

Abstract

Adipogenesis, through adipocyte hyperplasia and/or hypertrophy, leads to increased adiposity, giving rise to obesity. A genome-wide transcriptome analysis of in vitro adipogenesis in human adipose-derived stromal/stem cells identified SLC7A8 (Solute Carrier Family 7 Member 8) as a potential novel mediator. The current study has investigated the role of SLC7A8 in adipose tissue biology using a mouse model of diet-induced obesity. slc7a8 knockout (KO) and wildtype (WT) C57BL/6J mice were fed either a control diet (CD) or a high-fat diet (HFD) for 14 weeks. On the HFD, both WT and KO mice (WTHFD and KOHFD) gained significantly more weight than their CD counterparts. However, KOHFD gained significantly less weight than WTHFD. KOHFD had significantly reduced levels of glucose intolerance compared with those observed in WTHFD. KOHFD also had significantly reduced adipocyte mass and hypertrophy in inguinal, mesenteric, perigonadal, and brown adipose depots, with a corresponding decrease in macrophage infiltration. Additionally, KOHFD had decreased lipid accumulation in the liver, heart, gastrocnemius muscle, lung, and kidney. This study demonstrates that targeting slc7a8 protects against diet-induced obesity by reducing lipid accumulation in multiple organs and suggests that if targeted, has the potential to mitigate the development of obesity-associated comorbidities.

Human CD206+ macrophages associate with diabetes and adipose tissue lymphoid clusters

Increased adipose tissue macrophages (ATMs) correlate with metabolic dysfunction in humans and are causal in development of insulin resistance in mice. Recent bulk and single-cell transcriptomics studies reveal a wide spectrum of gene expression signatures possible for macrophages that depends on context, but the signatures of human ATM subtypes are not well defined in obesity and diabetes. We profiled 3 prominent ATM subtypes from human adipose tissue in obesity and determined their relationship to type 2 diabetes. Visceral adipose tissue (VAT) and s.c. adipose tissue (SAT) samples were collected from diabetic and nondiabetic obese participants to evaluate cellular content and gene expression. VAT CD206+CD11c- ATMs were increased in diabetic participants, were scavenger receptor-rich with low intracellular lipids, secreted proinflammatory cytokines, and diverged significantly from 2 CD11c+ ATM subtypes, which were lipid-laden, were lipid antigen presenting, and overlapped with monocyte signatures. Furthermore, diabetic VAT was enriched for CD206+CD11c- ATM and inflammatory signatures, scavenger receptors, and MHC II antigen presentation genes. VAT immunostaining found CD206+CD11c- ATMs concentrated in vascularized lymphoid clusters adjacent to CD206-CD11c+ ATMs, while CD206+CD11c+ were distributed between adipocytes. Our results show ATM subtype-specific profiles that uniquely contribute to the phenotypic variation in obesity.

Diabetes-Induced Changes in Macrophage Biology Might Lead to Reduced Risk for Abdominal Aortic Aneurysm Development

Type 2 diabetes patients are less likely to develop an abdominal aortic aneurysm (AAA). Since macrophages play a crucial role in AAA development, we hypothesized that this decrease in AAA risk in diabetic patients might be due to diabetes-induced changes in macrophage biology. To test this hypothesis, we treated primary macrophages obtained from healthy human volunteers with serum from non-diabetic vs. diabetic AAA patients and observed differences in extracellular acidification and the expression of genes involved in glycolysis and lipid oxidation. These results suggest an increase in metabolism in macrophages treated with serum from diabetic AAA patients. Since serum samples used did not differ in glucose content, these changes are not likely to be caused by differences in glycemia. Macrophage functions have been shown to be linked to their metabolism. In line with this, our data suggest that this increase in macrophage metabolism is accompanied by a shift towards an anti-inflammatory state. Together, these results support a model where diabetes-induced changes in metabolism in macrophages might lead to a reduced risk for AAA development.

Adipose tissue macrophages and atherogenesis – a synergy with cholesterolaemia

Excessive LDL cholesterol concentration together with subclinical inflammation, in which macrophages play a central role, are linked pathologies. The process starts with the accumulation of macrophages in white adipose tissue and the switch of their polarization toward a pro-inflammatory phenotype. The proportion of pro-inflammatory macrophages in adipose tissue is related to the main risk predictors of cardiovascular disease. The cholesterol content of phospholipids of cell membranes seems to possess a crucial role in the regulation of membrane signal transduction and macrophage polarization. Also, different fatty acids of membrane phospholipids influence phenotypes of adipose tissue macrophages with saturated fatty acids stimulating pro-inflammatory whereas ω3 fatty acids anti-inflammatory changes. The inflammatory status of white adipose tissue, therefore, reflects not only adipose tissue volume but also adipose tissue macrophages feature. The beneficial dietary change leading to an atherogenic lipoprotein decrease may therefore synergically reduce adipose tissue driven inflammation.

An optimized 3D-printed perfusion bioreactor for homogeneous cell seeding in bone substitute scaffolds for future chairside applications

A clinical implementation of cell-based bone regeneration in combination with scaffold materials requires the development of efficient, controlled and reproducible seeding procedures and a tailor-made bioreactor design. A perfusion system for efficient, homogeneous, and rapid seeding with human adipogenic stem cells in bone substitute scaffolds was designed. Variants concerning medium inlet and outlet port geometry, i.e. cylindrical or conical diffuser, cell concentration, perfusion mode and perfusion rates were simulated in silico. Cell distribution during perfusion was monitored by dynamic [¹⁸F]FDG micro-PET/CT and validated by laser scanning microscopy with three-dimensional image reconstruction. By iterative feedback of the in silico and in vitro experiments, the homogeneity of cell distribution throughout the scaffold was optimized with adjustment of flow rates, cell density and perfusion properties. Finally, a bioreactor with a conical diffusor geometry was developed, that allows a homogeneous cell seeding (hoover coefficient: 0.24) in less than 60 min with an oscillating perfusion mode. During this short period of time, the cells initially adhere within the entire scaffold and stay viable. After two weeks, the formation of several cell layers was observed, which was associated with an osteogenic differentiation process. This newly designed bioreactor may be considered as a prototype for chairside application.

Understanding the heterogeneity and functions of metabolic tissue macrophages

Growing evidence places tissue-resident macrophages as essential gatekeepers of metabolic organ homeostasis, including the adipose tissue and the pancreatic islets. Therein, macrophages may adopt specific phenotypes and ensure local functions. Recent advances in single cell genomic analyses provide a comprehensive map of adipose tissue macrophage subsets and their potential roles are now better apprehended. Whether they are beneficial or detrimental, macrophages overall contribute to the proper adipose tissue expansion under steady state and during obesity. By contrast, macrophages residing inside pancreatic islets, which may exert fundamental functions to fine tune insulin secretion, have only started to attract attention and their cellular heterogeneity remains to be established. The present review will focus on the latest findings exploring the phenotype and the properties of macrophages in adipose tissue and pancreatic islets, questioning early beliefs and future perspectives in the field of immunometabolism.

Retinol-binding protein 4 in obesity and metabolic dysfunctions

Excessive increased adipose tissue mass in obesity is associated with numerous co-morbid disorders including increased risk of type 2 diabetes, fatty liver disease, hypertension, dyslipidemia, cardiovascular diseases, dementia, airway disease and some cancers. The causal mechanisms explaining these associations are not fully understood. Adipose tissue is an active endocrine organ that secretes many adipokines, cytokines and releases metabolites. These biomolecules referred to as adipocytokines play a significant role in the regulation of whole-body energy homeostasis and metabolism by influencing and altering target tissues function. Understanding the mechanisms of adipocytokine actions represents a hot topic in obesity research. Among several secreted bioactive signalling molecules from adipose tissue and liver, retinol-binding protein 4 (RBP4) has been associated with systemic insulin resistance, dyslipidemia, type 2 diabetes and other metabolic diseases. Here, we aim to review and discuss the current knowledge on RBP4 with a focus on its role in the pathogenesis of obesity comorbid diseases.

Obesity cardiomyopathy: evidence, mechanisms, and therapeutic implications

The prevalence of heart failure is on the rise and imposes a major health threat, in part, due to the rapidly increased prevalence of overweight and obesity. To this point, epidemiological, clinical, and experimental evidence supports the existence of a unique disease entity termed “obesity cardiomyopathy,” which develops independent of hypertension, coronary heart disease, and other heart diseases. Our contemporary review evaluates the evidence for this pathological condition, examines putative responsible mechanisms, and discusses therapeutic options for this disorder. Clinical findings have consolidated the presence of left ventricular dysfunction in obesity. Experimental investigations have uncovered pathophysiological changes in myocardial structure and function in genetically predisposed and diet-induced obesity. Indeed, contemporary evidence consolidates a wide array of cellular and molecular mechanisms underlying the etiology of obesity cardiomyopathy including adipose tissue dysfunction, systemic inflammation, metabolic disturbances (insulin resistance, abnormal glucose transport, spillover of free fatty acids, lipotoxicity, and amino acid derangement), altered intracellular especially mitochondrial Ca²⁺ homeostasis, oxidative stress, autophagy/mitophagy defect, myocardial fibrosis, dampened coronary flow reserve, coronary microvascular disease (microangiopathy), and endothelial impairment. Given the important role of obesity in the increased risk of heart failure, especially that with preserved systolic function and the recent rises in COVID-19-associated cardiovascular mortality, this review should provide compelling evidence for the presence of obesity cardiomyopathy, independent of various comorbid conditions, underlying mechanisms, and offer new insights into potential therapeutic approaches (pharmacological and lifestyle modification) for the clinical management of obesity cardiomyopathy.

CD4+ T cells regulate glucose homeostasis independent of adipose tissue dysfunction in mice

Obesity is frequently associated with a chronic low-grade inflammation in the adipose tissue (AT) and impaired glucose homeostasis. Adipose tissue macrophages (ATMs) have been shown to accumulate in the inflamed AT either by means of recruitment from the blood or local proliferation. ATM proliferation and activation can be stimulated by TH2 cytokines, such as IL-4 and IL-13, suggesting involvement of CD4-positive T cells in ATM proliferation and activation. Furthermore, several studies have associated T cells to alterations in glucose metabolism. Therefore, we sought to examine a direct impact of CD4-positive T cells on ATM activation, ATM proliferation and glucose homeostasis using an in vivo depletion model. Surprisingly, CD4 depletion did not affect ATM activation, ATM proliferation, or insulin sensitivity. However, CD4 depletion led to a significant improvement of glucose tolerance. In line with this, we found moderate disturbances in pancreatic endocrine function following CD4 depletion. Hence, our data suggest that the effect on glucose metabolism observed after CD4 depletion might be mediated by organs other than AT and independent of AT inflammation.

Insulin action in adipocytes, adipose remodeling, and systemic effects

On this 100th anniversary of the discovery of insulin, we recognize the critical role that adipocytes, which are exquisitely responsive to insulin, have played in determining the mechanisms for insulin action at the cellular level. Our understanding of adipose tissue biology has evolved greatly, and it is now clear that adipocytes are far more complicated than simple storage depots for fat. A growing body of evidence documents how adipocytes, in response to insulin, contribute to the control of whole-body nutrient homeostasis. These advances highlight adipocyte plasticity, heterogeneity, and endocrine function, unique features that connect adipocyte metabolism to the regulation of other tissues important for metabolic homeostasis (e.g., liver, muscle, pancreas).

Cancer-associated adipocytes as immunomodulators in cancer

Cancer-associated adipocytes (CAAs), as a main component of the tumor-adipose microenvironment (TAME), have various functions, including remodeling the extracellular matrix and interacting with tumor cells or infiltrated leukocytes through a variety of mutual signals. Here, we summarize the primary interplay among CAAs, the immune response and cancer with a focus on the mechanistic aspects of these relationships. Finally, unifying our understanding of CAAs with the immune cell function may be an effective method to enhance the efficacy of immunotherapeutic and conventional treatments.

Adipose tissue inflammation and metabolic dysfunction in obesity

Several lines of preclinical and clinical research have confirmed that chronic low-grade inflammation of adipose tissue is mechanistically linked to metabolic disease and organ tissue complications in the overweight and obese organism. Despite this widely confirmed paradigm, numerous open questions and knowledge gaps remain to be investigated. This is mainly due to the intricately intertwined cross-talk of various pro- and anti-inflammatory signaling cascades involved in the immune response of expanding adipose depots, particularly the visceral adipose tissue. Adipose tissue inflammation is initiated and sustained over time by dysfunctional adipocytes that secrete inflammatory adipokines and by infiltration of bone marrow-derived immune cells that signal via production of cytokines and chemokines. Despite its low-grade nature, adipose tissue inflammation negatively impacts remote organ function, a phenomenon that is considered causative of the complications of obesity. The aim of this review is to broadly present an overview of adipose tissue inflammation by highlighting the most recent reports in the scientific literature and summarizing our overall understanding of the field. We also discuss key endogenous anti-inflammatory mediators and analyze their mechanistic role(s) in the pathogenesis and treatment of adipose tissue inflammation. In doing so, we hope to stimulate studies to uncover novel physiological, cellular, and molecular targets for the treatment of obesity.

Nomogram Including Neutrophil-to-Lymphocyte Ratio for the Prediction of Stroke-Associated Infections

Stroke has been a leading cause of mortality in China. Stroke-associated infections (SAI) are common complications, occurring in 5–65% of stroke patients. Faced with SAI, clinicians often are placed in a considerable dilemma. On the one hand, preventive overuse of antibiotics will lead to the emergence of drug-resistant bacteria. On the other hand, treatment delay of the infection will likely result in a poor outcome. Therefore, it is necessary to determine the early predictors of post-stroke infection to screen patients with high infection risk for early clinical intervention, thereby promoting and improving survival rates. We assessed 257 patients with acute ischemic stroke from a consecutive retrospective cohort. Data of these patients were obtained from three hospitals (TongJi Hospital and its two branches) between August 2018 and June 2019. Of these patients, 59 (23.0%) developed SAI. SAI was defined according to the modified Centers for Disease Control and Prevention criteria. There were 38 patients (64.4%) who developed pneumonia, 11 with urinary tract infections (18.6%), and 10 with other infections (16.9%). We found that a higher neutrophil-to-lymphocyte ratio (adjusted odds ratio [aOR] = 1.16; 95% confidence interval [CI], 1.01–1.33; P = 0.034), National Institutes of Health Stroke Scale score (aOR = 1.18; CI, 1.09–1.27; p < 0.001), and dysphagia (aOR = 2.95; CI, 1.40–6.22; P = 0.004) were risk factors for SAI. Of note, hypertriglyceridemia (aOR = 0.35; CI, 0.13–0.90; P = 0.029) was a protective factor, lowering the risk of SAI. To this end, a reliable nomogram was constructed for the prediction of SAI in our study (mean C-index value ± standard deviation = 0.821 ± 0.03). It has the potential to be widely used and may help identify patients at high risk for SAI and make timely clinical decisions. Given our study was based on relatively small dataset, the results should be interpreted with care and external validation in independent datasets is very necessary.

Impact of human visceral and glutealfemoral adipose tissue transplant on glycemic control in a mouse model of diet-induced obesity

Regional distribution of adipose tissue is an important factor in conferring cardiometabolic risk and obesity-related morbidity. We tested the hypothesis that human visceral adipose tissue (VAT) impairs glucose homeostasis, whereas subcutaneous glutealfemoral adipose tissue (GFAT) protects against the development of impaired glucose homeostasis in mice. VAT and GFAT were collected from patients undergoing bariatric surgery and grafted onto the epididymal adipose tissue of weight- and age-matched severe, combined immunodeficient mice. SHAM mice underwent surgery without transplant of tissue. Mice were fed a high-fat diet after xenograft. Energy homeostasis, glucose metabolism, and insulin sensitivity were assessed 6 wk later. Xenograft of human adipose tissues was successful, as determined by histology, immunohistochemical evaluation of collagen deposition and angiogenesis, and maintenance of lipolytic function. Adipose tissue transplant did not affect energy expenditure, food intake, whole body substrate partitioning, or plasma free fatty acid, triglyceride, and insulin levels. Fasting blood glucose was significantly reduced in GFAT and VAT compared with SHAM, whereas glucose tolerance was improved only in mice transplanted with VAT compared with SHAM mice. This improvement was not associated with differences in whole body insulin sensitivity or plasma insulin between groups. Together, these data suggest that VAT improves glycemic control and GFAT does not protect against the development of high-fat diet-induced glucose intolerance. Hence, the intrinsic properties of VAT and GFAT do not necessarily explain the postulated negative and positive effects of these adipose tissue depots on metabolic health.

Fisetin Alleviates Hepatic and Adipocyte Fibrosis and Insulin Resistance in Diet-Induced Obese Mice

The present study aimed to investigate the protective role of the flavonoid fisetin (FI) on inflammation-mediated metabolic diseases, especially tissue fibrosis and insulin resistance (IR) in high-fat diet (HFD)-induced obese mice. C57BL/6J mice were fed with normal-fat diet, HFD (40 kcal% fat), or HFD +0.02% (w/w) FI for 16 weeks. Dietary FI supplementation improved hepatic steatosis by restricting lipogenesis, while promoting lipolysis in the liver. FI also prevented adiposity via an increase in the expression of genes involved in FA oxidation and a decrease in the expression of genes involved in lipogenesis in white adipose tissue. In addition, FI increased brown adipose tissue (BAT) and skeletal muscle weights, thermogenic gene mRNA expression in BAT, and tricarboxylic acid cycle-related gene expression in skeletal muscle, which may be linked to the prevention of nonalcoholic fatty liver disease as well as adiposity. Moreover, FI supplementation decreased excessive reactive oxygen species production by increasing paraoxonase activity, adipokine dysregulation, proinflammatory cytokine production, and extracellular matrix amassment in the liver. FI supplementation ameliorated IR, in part, by normalizing pancreatic islet dysfunction, and it declined hepatic gluconeogenesis and proinflammatory responses. Taken together, the present findings indicate that FI can protect against HFD-induced inflammation-mediated disorders, including fibrosis and IR.

Natural constituents from food sources as therapeutic agents for obesity and metabolic diseases targeting adipose tissue inflammation

Adipose tissue, an endocrine and paracrine organ, plays critical roles in the regulation of whole-body metabolic homeostasis. Obesity is accompanied with a chronic low-grade inflammation status in adipose tissue, which disrupts its endocrine function and results in metabolic derangements, such as type 2 diabetes. Dietary bioactive components, such as flavonoids, polyphenols and unsaturated fatty acids from fruits and vegetables, have been widely revealed to alleviate both systemic and adipose tissue inflammation, and improve metabolic disorders. Remarkably, some dietary bioactive components mitigate the inflammatory response in adipocytes, macrophages, and other immune cells, and modulate the crosstalk between adipocytes and macrophages or other immune cells, in adipose tissue. Epidemiological and preclinical studies related to these substances have indicated beneficial effects on adipose tissue inflammation. The main purpose of this review is to provide a comprehensive and up-to-date state of knowledge on dietary components targeting adipose tissue inflammation and their underlying mechanisms. These natural products have great potential to be developed as functional food or lead compounds for treating and/or preventing metabolic disorders.

Whole transcriptome analysis and validation of metabolic pathways in subcutaneous adipose tissues during FGF21-induced weight loss in non-human primates

Fibroblast growth factor 21 (FGF21) induces weight loss in mouse, monkey, and human studies. In mice, FGF21 is thought to cause weight loss by stimulating thermogenesis, but whether FGF21 increases energy expenditure (EE) in primates is unclear. Here, we explore the transcriptional response and gene networks active in adipose tissue of rhesus macaques following FGF21-induced weight loss. Genes related to thermogenesis responded inconsistently to FGF21 treatment and weight loss. However, expression of gene modules involved in triglyceride (TG) synthesis and adipogenesis decreased, and this was associated with greater weight loss. Conversely, expression of innate immune cell markers was increased post-treatment and was associated with greater weight loss. A lipogenesis gene module associated with weight loss was evaluated by testing the function of member genes in mice. Overexpression of NRG4 reduced weight gain in diet-induced obese mice, while overexpression of ANGPTL8 resulted in elevated TG levels in lean mice. These observations provide evidence for a shifting balance of lipid storage and metabolism due to FGF21-induced weight loss in the non-human primate model, and do not fully recapitulate increased EE seen in rodent and in vitro studies. These discrepancies may reflect inter-species differences or complex interplay of FGF21 activity and counter-regulatory mechanisms.

A Review of Adropin as the Medium of Dialogue between Energy Regulation and Immune Regulation

Adropin is a secretory protein encoded by the energy balance gene and is closely associated with regulation of energy metabolism and insulin resistance. The clinical findings demonstrated its decreased expression in various inflammatory diseases, its negative correlation with the expression levels of inflammatory cytokines, and its potential anti-inflammatory effects. We speculate that adropin plays a pivotal regulatory role in immune cells and inflammatory factors. In this study, we reviewed the advances in researches concentrated on immunological effects of adropin.

Adipose Tissue Distribution, Inflammation and Its Metabolic Consequences, Including Diabetes and Cardiovascular Disease

Adipose tissue plays essential roles in maintaining lipid and glucose homeostasis. To date several types of adipose tissue have been identified, namely white, brown, and beige, that reside in various specific anatomical locations throughout the body. The cellular composition, secretome, and location of these adipose depots define their function in health and metabolic disease. In obesity, adipose tissue becomes dysfunctional, promoting a pro-inflammatory, hyperlipidemic and insulin resistant environment that contributes to type 2 diabetes mellitus (T2DM). Concurrently, similar features that result from adipose tissue dysfunction also promote cardiovascular disease (CVD) by mechanisms that can be augmented by T2DM. The mechanisms by which dysfunctional adipose tissue simultaneously promote T2DM and CVD, focusing on adipose tissue depot-specific adipokines, inflammatory profiles, and metabolism, will be the focus of this review. The impact that various T2DM and CVD treatment strategies have on adipose tissue function and body weight also will be discussed.

Mechanisms of Macrophage Polarization in Insulin Signaling and Sensitivity

Type-2 diabetes (T2D) is a disease of two etiologies: metabolic and inflammatory. At the cross-section of these etiologies lays the phenomenon of metabolic inflammation. Whilst metabolic inflammation is characterized as systemic, a common starting point is the tissue-resident macrophage, who's successful physiological or aberrant pathological adaptation to its microenvironment determines disease course and severity. This review will highlight the key mechanisms in macrophage polarization, inflammatory and non-inflammatory signaling that dictates the development and progression of insulin resistance and T2D. We first describe the known homeostatic functions of tissue macrophages in insulin secreting and major insulin sensitive tissues. Importantly we highlight the known mechanisms of aberrant macrophage activation in these tissues and the ways in which this leads to impairment of insulin sensitivity/secretion and the development of T2D. We next describe the cellular mechanisms that are known to dictate macrophage polarization. We review recent progress in macrophage bio-energetics, an emerging field of research that places cellular metabolism at the center of immune-effector function. Importantly, following the advent of the metabolically-activated macrophage, we cover the known transcriptional and epigenetic factors that canonically and non-canonically dictate macrophage differentiation and inflammatory polarization. In closing perspectives, we discuss emerging research themes and highlight novel non-inflammatory or non-immune roles that tissue macrophages have in maintaining microenvironmental and systemic homeostasis.

The Interplay Between Tissue Niche and Macrophage Cellular Metabolism in Obesity

Obesity is associated with the development of metabolic diseases such as type 2 diabetes and non-alcoholic fatty liver disease. The presence of chronic, low-grade inflammation appears to be an important mechanistic link between excess nutrients and clinical disease. The onset of these metabolic disorders coincides with changes in the number and phenotype of macrophages in peripheral organs, particularly in the liver and adipose tissue. Macrophage accumulation in these tissues has been implicated in tissue inflammation and fibrosis, contributing to metabolic disease progression. Recently, the concept has emerged that changes in macrophage metabolism affects their functional phenotype, possibly triggered by distinct environmental metabolic cues. This may be of particular importance in the setting of obesity, where both liver and adipose tissue are faced with a high metabolic burden. In the first part of this review we will discuss current knowledge regarding macrophage dynamics in both adipose tissue and liver in obesity. Then in the second part, we will highlight data linking macrophage metabolism to functional phenotype with an emphasis on macrophage activation in metabolic disease. The importance of understanding how tissue niche influences macrophage function in obesity will be highlighted. In addition, we will identify important knowledge gaps and outstanding questions that are relevant for future research in this area and will facilitate the identification of novel targets for therapeutic intervention in associated metabolic diseases.

Extracellular Matrix Remodeling of Adipose Tissue in Obesity and Metabolic Diseases

The extracellular matrix (ECM) is a network of different proteins and proteoglycans that controls differentiation, migration, repair, survival, and development, and it seems that its remodeling is required for healthy adipose tissue expansion. Obesity drives an excessive lipid accumulation in adipocytes, which provokes immune cells infiltration, fibrosis (an excess of deposition of ECM components such as collagens, elastin, and fibronectin) and inflammation, considered a consequence of local hypoxia, and ultimately insulin resistance. To understand the mechanism of this process is a challenge to treat the metabolic diseases. This review is focused at identifying the putative role of ECM in adipose tissue, describing its structure and components, its main tissue receptors, and how it is affected in obesity, and subsequently the importance of an appropriate ECM remodeling in adipose tissue expansion to prevent metabolic diseases.

Exercise training prevents the perivascular adipose tissue-induced aortic dysfunction with metabolic syndrome

The aim of the study was to determine the effects of exercise training on improving the thoracic perivascular adipose tissue (tPVAT) phenotype (inflammation, oxidative stress, and proteasome function) in metabolic syndrome and its subsequent actions on aortic function.

Methods

Lean and obese (model of metabolic syndrome) Zucker rats (n=8/group) underwent 8-weeks of control conditions or treadmill exercise (70% of max speed, 1 h/day, 5 days/week). At the end of the intervention, the tPVAT was removed and conditioned media was made. The cleaned aorta was attached to a force transducer to assess endothelium-dependent and independent dilation in the presence or absence of tPVAT-conditioned media. tPVAT gene expression, inflammatory /oxidative phenotype, and proteasome function were assessed.

Results

The main findings were that Ex induced: (1) a beige-like, anti-inflammatory tPVAT phenotype; (2) a greater abundance of ^•NO in tPVAT; (3) a reduction in tPVAT oxidant production; and (4) an improved tPVAT proteasome function. Regarding aortic function, endothelium-dependent dilation was greater in exercised lean and obese groups vs. controls (p < 0.05). Lean control tPVAT improved aortic relaxation, whereas obese control tPVAT decreased aortic relaxation. In contrast, the obese Ex-tPVAT increased aortic dilation, whereas the lean Ex-tPVAT did not affect aortic dilation.

Conclusion

Overall, exercise had the most dramatic impact on the obese tPVAT reflecting a change towards an environment with less oxidant load, less inflammation and improved proteasome function. Such beneficial changes to the tPVAT micro-environment with exercise likely played a significant role in mediating the improvement in aortic function in metabolic syndrome following 8 weeks of exercise.

Tissue Immune Cells Fuel Obesity-Associated Inflammation in Adipose Tissue and Beyond

Obesity-associated inflammation stems from a combination of cell-intrinsic changes of individual immune cell subsets and the dynamic crosstalk amongst a broad array of immune cells. Although much of the focus of immune cell contributions to metabolic disease has focused on adipose tissue-associated cells, these potent sources of inflammation inhabit other metabolic regulatory tissues, including liver and gut, and recirculate to promote systemic inflammation and thus obesity comorbidities. Tissue-associated immune cells, especially T cell subpopulations, have become a hotspot of inquiry based on their contributions to obesity, type 2 diabetes, non-alcoholic fatty liver diseases and certain types of cancers. The cell-cell interactions that take place under the stress of obesity are mediated by intracellular contact and cytokine production, and constitute a complicated network that drives the phenotypic alterations of immune cells and perpetuates a feed-forward loop of metabolic decline. Herein we discuss immune cell functions in various tissues and obesity-associated cancers from the viewpoint of inflammation. We also emphasize recent advances in the understanding of crosstalk amongst immune cell subsets under obese conditions, and suggest future directions for focused investigations with clinical relevance.

Androgen receptor deficiency in monocytes/macrophages does not alter adiposity or glucose homeostasis in male mice

Androgen deprivation in men leads to increased adiposity, but the mechanisms underlying androgen regulation of fat mass have not been fully defined. Androgen receptor (AR) is expressed in monocytes/macrophages, which are resident in key metabolic tissues and influence energy metabolism in surrounding cells. Male mice bearing a cell-specific knockout of the AR in monocytes/macrophages (M-ARKO) were generated to determine whether selective loss of androgen signaling in these cells would lead to altered body composition. Wild-type (WT) and M-ARKO mice (12–22 weeks of age, n = 12 per group) were maintained on a regular chow diet for 8 weeks and then switched to a high-fat diet for 8 additional weeks. At baseline and on both the regular chow and high-fat diets, no differences in lean mass or fat mass were observed between groups. Consistent with the absence of differential body weight or adiposity, no differences in food intake (3.0 ± 0.5 g per day for WT mice vs 2.8 ± 0.4 g per day for M-ARKO mice) or total energy expenditure (0.6 ± 0.1 Kcal h⁻¹ for WT mice vs 0.5 ± 0.1 Kcal h⁻¹ for M-ARKO mice) were evident between groups during high-fat feeding. Liver weight was greater in M-ARKO than that in WT mice (1.5 ± 0.1 g vs 1.3 ± 0.0 g, respectively, P = 0.02). Finally, M-ARKO mice did not exhibit impairments in glucose tolerance or insulin sensitivity relative to WT mice at any study time point. In aggregate, these findings suggest that AR signaling specifically in monocytes/macrophages does not contribute to the regulation of systemic energy balance, adiposity, or insulin sensitivity in male mice.

Adipose-derived stromal/stem cells from different adipose depots in obesity development

The increasing prevalence of obesity is alarming because it is a risk factor for cardiovascular and metabolic diseases (such as type 2 diabetes). The occurrence of these comorbidities in obese patients can arise from white adipose tissue (WAT) dysfunctions, which affect metabolism, insulin sensitivity and promote local and systemic inflammation. In mammals, WAT depots at different anatomical locations (subcutaneous, preperitoneal and visceral) are highly heterogeneous in their morpho-phenotypic profiles and contribute differently to homeostasis and obesity development, depending on their ability to trigger and modulate WAT inflammation. This heterogeneity is likely due to the differential behavior of cells from each depot. Numerous studies suggest that adipose-derived stem/stromal cells (ASC; referred to as adipose progenitor cells, in vivo) with depot-specific gene expression profiles and adipogenic and immunomodulatory potentials are keys for the establishment of the morpho-functional heterogeneity between WAT depots, as well as for the development of depot-specific responses to metabolic challenges. In this review, we discuss depot-specific ASC properties and how they can contribute to the pathophysiology of obesity and metabolic disorders, to provide guidance for researchers and clinicians in the development of ASC-based therapeutic approaches.

Dietary Eriodictyol Alleviates Adiposity, Hepatic Steatosis, Insulin Resistance, and Inflammation in Diet-Induced Obese Mice

The present study aimed to investigate the molecular mechanisms underlying the anti-obesity effect of flavonoid eriodictyol (ED) supplementation in mice fed with a high-fat diet (HFD). C57BL/6N mice were fed with normal diet (ND), HFD (40 kcal% fat), or HFD + 0.005% (w/w) ED for 16 weeks. In HFD-induced obese mice, dietary ED supplementation significantly alleviated dyslipidemia and adiposity by downregulating the expression of lipogenesis-related genes in white adipose tissue (WAT), while enhancing fecal lipid excretion. ED additionally improved hepatic steatosis and decreased the production of pro-inflammatory cytokines by downregulating the expression of hepatic enzymes and the genes involved in lipogenesis and upregulating the expression of hepatic fatty acid oxidation-related enzymes and genes. In addition, ED improved insulin resistance (IR) by suppressing hepatic gluconeogenesis, enhancing glucose utilization, and modulating the production and release of two incretin hormones, namely gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Taken together, the current findings indicated that ED can protect against diet-induced obesity and related metabolic disturbances, including dyslipidemia, inflammation, fatty liver disease, and IR in diet-induced obese mice.