Interaction of differentiated human adipocytes with macrophages leads to trogocytosis and selective IL-6 secretion

Suppression of Inflammation in Adipocyte-Macrophage Coculture by Passion Fruit Seed Extract: Insights into the p38 and NF-ҡB Pathway

Obesity, which is characterized by chronic low-grade inflammation, involves the infiltration of immune cells into adipose tissue, leading to the secretion of inflammatory cytokines and subsequent inflammation. Therefore, the aim of this study was to examine the potential of passion fruit seed extract (PSEE) in mitigating lipopolysaccharide (LPS)-induced inflammation in a coculture system comprising macrophages and adipocytes. PSEE demonstrated significant reductions in reactive oxygen species (ROS) and nitric oxide (NO) levels, primarily achieved through the downregulation of inducible nitric oxide synthase (iNOS) protein expression in LPS-induced adipocyte-macrophage cocultures. Furthermore, PSEE effectively suppressed the secretion of TNF-α and IL-1β by attenuating the gene expression of these cytokines, as well as other inflammation-related genes such as MMP-2, IL-6, and MCP-1. Notably, PSEE exhibited potent inhibitory effects on the p38 and NF-κB signaling pathways, thus alleviating inflammation in the LPS-induced adipocyte-macrophage cocultures. Additionally, PSEE led to a decrease in the expression of ACC, HSL, and FaSN, while aP2 and ATGL showed increased expression in LPS-induced cocultured macrophages and adipocytes. These findings suggest that passion fruit seed extract effectively combats inflammation by suppressing the p38 and NF-κB signaling pathways, resulting in reduced levels of proinflammatory cytokines, NO, and ROS production.

Human iPSC-Derived Proinflammatory Macrophages cause Insulin Resistance in an Isogenic White Adipose Tissue Microphysiological System

Chronic white adipose tissue (WAT) inflammation has been recognized as a critical early event in the pathogenesis of obesity-related disorders. This process is characterized by the increased residency of proinflammatory M1 macrophages in WAT. However, the lack of an isogenic human macrophage-adipocyte model has limited biological studies and drug discovery efforts, highlighting the need for human stem cell-based approaches. Here, human induced pluripotent stem cell (iPSC) derived macrophages (iMACs) and adipocytes (iADIPOs) are cocultured in a microphysiological system (MPS). iMACs migrate toward and infiltrate into the 3D iADIPOs cluster to form crown-like structures (CLSs)-like morphology around damaged iADIPOs, recreating classic histological features of WAT inflammation seen in obesity. Significantly more CLS-like morphologies formed in aged and palmitic acid-treated iMAC-iADIPO-MPS, showing the ability to mimic inflammatory severity. Importantly, M1 (proinflammatory) but not M2 (tissue repair) iMACs induced insulin resistance and dysregulated lipolysis in iADIPOs. Both RNAseq and cytokines analyses revealed a reciprocal proinflammatory loop in the interactions of M1 iMACs and iADIPOs. This iMAC-iADIPO-MPS thus successfully recreates pathological conditions of chronically inflamed human WAT, opening a door to study the dynamic inflammatory progression and identify clinically relevant therapies.

ClC-7 drives intraphagosomal chloride accumulation to support hydrolase activity and phagosome resolution

Degradative organelles contain enzymes that function optimally at the acidic pH generated by the V-ATPase. The resulting transmembrane H+ gradient also energizes the secondary transport of several solutes, including Cl-. We report that Cl- influx, driven by the 2Cl-/H+ exchanger ClC-7, is necessary for the resolution of phagolysosomes formed by macrophages. Cl- transported via ClC-7 had been proposed to provide the counterions required for electrogenic H+ pumping. However, we found that deletion of ClC-7 had a negligible effect on phagosomal acidification. Instead, luminal Cl- was found to be required for activation of a wide range of phagosomal hydrolases including proteases, nucleases, and glycosidases. These findings argue that the primary role of ClC-7 is the accumulation of (phago)lysosomal Cl- and that the V-ATPases not only optimize the activity of degradative hydrolases by lowering the pH but, importantly, also play an indirect role in their activation by providing the driving force for accumulation of luminal Cl- that stimulates hydrolase activity allosterically.

Gold Nanobipyramid-Mediated Apoptotic Camouflage of Adipocytes for Obesity Immunotherapy

Obesity treatment is a global public health challenge due to inadequate weight loss and weight regain even after endeavors with multimodal treatments. Considering the abundance of resident macrophages in adipose tissues, precise regulation of the interactions between macrophages and adipocytes may provide chances for immunotherapy of obesity. Herein, inspired by the phagocytosis of macrophages to clear apoptotic cells in homeostasis, an immunotherapy strategy for obesity treatment is proposed for the first time through apoptotic camouflage of adipocytes by _PA Au BPs to activate macrophages for clearance, where _PA Au BPs are gold nanobipyramids engineered with adipose-targeting and apoptotic cell-mimicking functions. During clearance, the macrophage is switched from pro-inflammatory M1 to anti-inflammatory M2, remarkably modulating the immune microenvironment of adipose tissues to prevent weight regain. After inguinal injection with _PA Au BPs, the body weights of obese mice are effectively decreased by 24.4% and can be decreased by 33.3% when combined with photothermal lipolysis, and little weight regain is associated with these treatments. This study demonstrates that the strategy of camouflaging adipocytes with apoptotic features holds great potential for obesity immunotherapy.

Efficacy of Siwan Traditional Therapy on Erythrocyte Sedimentation Rate, Lipid Profile, and Atherogenic Index as Cardiac Risk Factors Related to Rheumatoid Arthritis

Background and Objectives: The most frequent cause of mortality in rheumatoid arthritis (RA) patients is cardiovascular disease (CVD). Inflammation, dyslipidemia, and decreased physical activity are some of the main risk factors for CVD. Siwan sand therapy is a type of traditional therapy used in Egypt to treat RA. The approach of this therapy depends on the experience of the healers. The aim of the current study was to compare the effects of three sessions of Siwan traditional therapy to five sessions on common CVD risk factors and physical function in rheumatoid arthritis patients. Materials and Methods: Thirty patients (9 male and 21 female) were assigned into two groups of equal size: group (A) received three sessions of Siwan traditional therapy in the form of a sand bath. Group (B) received the same form of therapy for five days. Erythrocyte sedimentation rate (ESR), lipid profile, atherogenic index of plasma (AIP), and a health assessment questionnaire (HAQ) were measured before and after treatment. Results: There was a significant increase above normal within group (A) for ESR (p = 0.001), triglycerides (TG; p = 0.015), total cholesterol (Tot-Chol; p = 0.0001), and low-density lipoprotein (LDL; p = 0.0001). However, there were no considerable differences in high-density lipoprotein (HDL; p = 0.106), very low-density lipoprotein (VLDL; p = 0.213), AIP (p = 0.648), and HAQ (p = 0.875). For the second group, there were significant changes within group B only in Tot-Chol (p = 0.0001), HDL (p = 0.0001), VLDL (p = 0.0001), AIP (p = 0.008), and HAQ (p = 0.014). There was a significant difference between both groups regarding HDL (p = 0.027), LDL (p = 0.005), AIP (p = 0.029), ESR (p = 0.016), and HAQ (p = 0.036). Conclusions: For RA patients, five days of Siwan traditional therapy caused significant changes regarding inflammation, Tot-Chol, LDL, HDL, AIP, and functional activity when compared to three days of Siwan hot sand therapy.

Obesity Programs Macrophages to Support Cancer Progression

Obesity induces multifactorial effects such as dyslipidemia, insulin resistance, and arterial hypertension that influence the progression of many diseases. Obesity is associated with an increased incidence of cancers, and multiple mechanisms link obesity with cancer initiation and progression. Macrophages participate in the homeostasis of adipose tissue and play an important role in cancer. Adipose tissue expansion in obesity alters the balance between pro- and anti-inflammatory macrophages, which is a primary cause of inflammation. Chronic low-grade inflammation driven by macrophages is also an important characteristic of cancer. Adipocytes secrete various adipokines, including adiponectin, leptin, IL6, and TNFα, that influence macrophage behavior and tumor progression. Furthermore, other metabolic effects of obesity, such as hyperlipidemia, hyperglycemia, and hypercholesterolemia, can also regulate macrophage functionality in cancer. This review summarizes how obesity influences macrophage-tumor cell interactions and the role of macrophages in the response to anticancer therapies under obese conditions.

The crosstalk between parenchymal cells and macrophages: A keeper of tissue homeostasis

Non-parenchymal cells (NPCs) and parenchymal cells (PCs) collectively perform tissue-specific functions. PCs play significant roles and continuously adjust the intrinsic functions and metabolism of organs. Tissue-resident macrophages (TRMs) are crucial members of native NPCs in tissues and are essential for immune defense, tissue repair and development, and homeostasis maintenance. As a plastic-phenotypic and prevalent cluster of NPCs, TRMs dynamically assist PCs in functioning by producing cytokines, inflammatory and anti-inflammatory signals, growth factors, and proteolytic enzymes. Furthermore, the PCs of tissues modulate the functional activity and polarization of TRMs. Dysregulation of the PC-TRM crosstalk axis profoundly impacts many essential physiological functions, including synaptogenesis, gastrointestinal motility and secretion, cardiac pulsation, gas exchange, blood filtration, and metabolic homeostasis. This review focuses on the PC-TRM crosstalk in mammalian vital tissues, along with their interactions with tissue homeostasis maintenance and disorders. Thus, this review highlights the fundamental biological significance of the regulatory network of PC-TRM in tissue homeostasis.

GATA3 as an immunomodulator in obesity-related metabolic dysfunction associated with fatty liver disease, insulin resistance, and type 2 diabetes

Obesity is the leading risk factor associated with Metabolic dysfunction Associated with Fatty Liver Disease (MAFLD), Insulin Resistance (IR), and type 2 diabetes (T2DM). Notably, MAFLD affects 25% of the world's adult population, ranging from 13.5% in Africa to 31.8% in the Middle East. The prevalence of MAFLD is 80-90% in obese adults and 30-50% in patients with diabetes. According to the recent WHO update, more than 400 million people will experience T2DM by 2025. Furthermore, the worldwide obesity incidence rate has risen in the preceding years. Adipogenesis deterioration is a critical step in the induction of obesity correlated with MAFLD, IR and T2DM. The well-known transcription factor GATA3 is highly expressed in the preadipocytes-adipocytes transition of embryonic stem cells and obese people with IR. In this regard, the reduction of GATA3 improves the differentiation of adipocytes. Omental adipose tissue inflammation by upregulation of macrophages infiltration is strongly linked with body mass index in insulin tolerance of obese people. In particular, the dynamic interaction between macrophages and adipocytes significantly regulates obese adipose tissue's inflammatory status and influences IR by reducing the differentiation of adipocytes, macrophage function, and glucose transport. Emerging evidence demonstrated that GATA3 is a master regulator for macrophage polarization and infiltration. Hence, we will shed light on GATA3 as an emerging target for immunomodulation in human obesity associated with MAFLD, IR, and T2DM by reducing macrophages' recruitment and inflammation of muscles and liver.

CXCL16/CXCR6 Axis in Adipocytes Differentiated from Human Adipose Derived Mesenchymal Stem Cells Regulates Macrophage Polarization

Adipocytes interact with adipose tissue macrophages (ATMs) that exist as a form of M2 macrophage in healthy adipose tissue and are polarized into M1 macrophages upon cellular stress. ATMs regulate adipose tissue inflammation by secreting cytokines, adipokines, and chemokines. CXC-motif receptor 6 (CXCR6) is the chemokine receptor and interactions with its specific ligand CXC-motif chemokine ligand 16 (CXCL16) modulate the migratory capacities of human adipose-derived mesenchymal stem cells (hADMSCs). CXCR6 is highly expressed on differentiated adipocytes that are non-migratory cells. To evaluate the underlying mechanisms of CXCR6 in adipocytes, THP-1 human monocytes that can be polarized into M1 or M2 macrophages were co-cultured with adipocytes. As results, expression levels of the M1 polarization-inducing factor were decreased, while those of the M2 polarization-inducing factor were significantly increased in differentiated adipocytes in a co-cultured environment with additional CXCL16 treatment. After CXCL16 treatment, the anti-inflammatory factors, including p38 MAPK ad ERK1/2, were upregulated, while the pro-inflammatory pathway mediated by Akt and NF-κB was downregulated in adipocytes in a co-cultured environment. These results revealed that the CXCL16/CXCR6 axis in adipocytes regulates M1 or M2 polarization and displays an immunosuppressive effect by modulating pro-inflammatory or anti-inflammatory pathways. Our results may provide an insight into a potential target as a regulator of the immune response via the CXCL16/CXCR6 axis in adipocytes.

Innate-Immunity Genes in Obesity

The main functions of adipose tissue are thought to be storage and mobilization of the body’s energy reserves, active and passive thermoregulation, participation in the spatial organization of internal organs, protection of the body from lipotoxicity, and ectopic lipid deposition. After the discovery of adipokines, the endocrine function was added to the above list, and after the identification of crosstalk between adipocytes and immune cells, an immune function was suggested. Nonetheless, it turned out that the mechanisms underlying mutual regulatory relations of adipocytes, preadipocytes, immune cells, and their microenvironment are complex and redundant at many levels. One possible way to elucidate the picture of adipose-tissue regulation is to determine genetic variants correlating with obesity. In this review, we examine various aspects of adipose-tissue involvement in innate immune responses as well as variants of immune-response genes associated with obesity.

Resolvin D1 reduces inflammation in co-cultures of primary human macrophages and adipocytes by triggering macrophages

Obesity leads to chronic inflammation of the adipose tissue which is tightly associated with the metabolic syndrome, type 2 diabetes and cardiovascular disease. Inflammation of the adipose tissue is mainly characterized by the presence of crown-like structures composed of inflammatory macrophages in the neighborhood of adipocytes. Resolvin D1 (RvD1), a potent anti-inflammatory and pro-resolving lipid mediator derived from the omega-3 fatty acid docosahexaenoic acid, has been shown to reduce the inflammatory tone of adipose tissue in animal models but the underlying mechanism is not clear. We investigated the effect of RvD1 on the inflammatory state of a human co-culture system of adipocytes and macrophages. For this, human mesenchymal stem cells were differentiated into mature adipocytes and overlaid with human primary macrophages. In this co-culture, 10-500 nM RvD1 dose-dependently reduced the secretion of the pro-inflammatory cytokine IL-6 (-21%) and its soluble receptor IL-6Rα (-22%), of the chemokine MCP-1 (-13%), and of the adipokine leptin (-22%). Similarly, we observed a reduction in secretion of the soluble receptor IL-6Rα (-20%), and TNF-α (-11%) when macrophages alone were treated with RvD1, while no change of cytokine secretion was observed when adipocytes were treated with RvD1. We conclude that RvD1 polarizes macrophages to an anti-inflammatory phenotype, which in turn modulates inflammation in adipocytes.

Irisin Stimulates the Release of CXCL1 From Differentiating Human Subcutaneous and Deep-Neck Derived Adipocytes via Upregulation of NFκB Pathway

Thermogenic brown and beige adipocytes might open up new strategies in combating obesity. Recent studies in rodents and humans have indicated that these adipocytes release cytokines, termed "batokines". Irisin was discovered as a polypeptide regulator of beige adipocytes released by myocytes, primarily during exercise. We performed global RNA sequencing on adipocytes derived from human subcutaneous and deep-neck precursors, which were differentiated in the presence or absence of irisin. Irisin did not exert an effect on the expression of characteristic thermogenic genes, while upregulated genes belonging to various cytokine signaling pathways. Out of the several upregulated cytokines, CXCL1, the highest upregulated, was released throughout the entire differentiation period, and predominantly by differentiated adipocytes. Deep-neck area tissue biopsies also showed a significant release of CXCL1 during 24 h irisin treatment. Gene expression data indicated upregulation of the NFκB pathway upon irisin treatment, which was validated by an increase of p50 and decrease of IκBα protein level, respectively. Continuous blocking of the NFκB pathway, using a cell permeable inhibitor of NFκB nuclear translocation, significantly reduced CXCL1 release. The released CXCL1 exerted a positive effect on the adhesion of endothelial cells. Together, our findings demonstrate that irisin stimulates the release of a novel adipokine, CXCL1, via upregulation of NFκB pathway in neck area derived adipocytes, which might play an important role in improving tissue vascularization.

BMP7 Increases UCP1-Dependent and Independent Thermogenesis with a Unique Gene Expression Program in Human Neck Area Derived Adipocytes

White adipocytes contribute to energy storage, accumulating lipid droplets, whereas brown and beige adipocytes mainly function in dissipating energy as heat primarily via the action of uncoupling protein 1 (UCP1). Bone morphogenic protein 7 (BMP7) was shown to drive brown adipocyte differentiation in murine interscapular adipose tissue. Here, we performed global RNA-sequencing and functional assays on adipocytes obtained from subcutaneous (SC) and deep-neck (DN) depots of human neck and differentiated with or without BMP7. We found that BMP7 did not influence differentiation but upregulated browning markers, including UCP1 mRNA and protein in SC and DN derived adipocytes. BMP7 also enhanced mitochondrial DNA content, levels of oxidative phosphorylation complex subunits, along with PGC1α and p-CREB upregulation, and fragmentation of mitochondria. Furthermore, both UCP1-dependent proton leak and UCP1-independent, creatine-driven substrate cycle coupled thermogenesis were augmented upon BMP7 addition. The gene expression analysis also shed light on the possible role of genes unrelated to thermogenesis thus far, including ACAN, CRYAB, and ID1, which were among the highest upregulated ones by BMP7 treatment in both types of adipocytes. Together, our study shows that BMP7 strongly upregulates thermogenesis in human neck area derived adipocytes, along with genes, which might have a supporting role in energy expenditure.

Chronic and Transient Hyperglycemia Induces Changes in the Expression Patterns of IL6 and ADIPOQ Genes and Their Associated Epigenetic Modifications in Differentiating Human Visceral Adipocytes

Adipokines secreted by hypertrophic visceral adipose tissue (VAT) instigate low-grade inflammation, followed by hyperglycemia (HG)-related metabolic disorders. The latter may develop with the participation of epigenetic modifications. Our aim was to assess how HG influences selected epigenetic modifications and the expression of interleukin 6 (IL-6) and adiponectin (APN; gene symbol ADIPOQ) during the adipogenesis of human visceral preadipocytes (HPA-v). Adipocytes (Ads) were chronically or transiently HG-treated during three stages of adipogenesis (proliferation, differentiation, maturation). We measured adipokine mRNA, protein, proven or predicted microRNA expression (RT-qPCR and ELISA), and enrichment of H3K9/14ac, H3K4me3, and H3K9me3 at gene promoter regions (chromatin immunoprecipitation). In chronic HG, we detected different expression patterns of the studied adipokines at the mRNA and protein levels. Chronic and transient HG-induced changes in miRNA (miR-26a-5p, miR-26b-5p, let-7d-5p, let-7e-5p, miR-365a-3p, miR-146a-5p) were mostly convergent to altered IL-6 transcription. Alterations in histone marks at the IL6 promoter were also in agreement with IL-6 mRNA. The open chromatin marks at the ADIPOQ promoter mostly reflected the APN transcription during NG adipogenesis, while, in the differentiation stage, HG-induced changes in all studied marks were in line with APN mRNA levels. In summary, HG dysregulated adipokine expression, promoting inflammation. Epigenetic changes coexisted with altered expression of adipokines, especially for IL-6; therefore, epigenetic marks induced by transient HG may act as epi-memory in Ads. Such changes in the epigenome and expression of adipokines could be instrumental in the development of inflammation and metabolic deregulation of VAT.

Adipocytes, Innate Immunity and Obesity: A Mini-Review

The role of adipose tissue (AT) inflammation in obesity and its multiple related-complications is a rapidly expanding area of scientific interest. Within the last 30 years, the role of the adipocyte as an endocrine and immunologic cell has been progressively established. Like the macrophage, the adipocyte is capable of linking the innate and adaptive immune system through the secretion of adipokines and cytokines; exosome release of lipids, hormones, and microRNAs; and contact interaction with other immune cells. Key innate immune cells in AT include adipocytes, macrophages, neutrophils, and innate lymphoid cells type 2 (ILC2s). The role of the innate immune system in promoting adipose tissue inflammation in obesity will be highlighted in this review. T cells and B cells also play important roles in contributing to AT inflammation and are discussed in this series in the chapter on adaptive immunity.

Lymphocytes and Trogocytosis-Mediated Signaling

Trogocytosis is the intercellular transfer of membrane and membrane-associated molecules. This underappreciated process has been described in a variety of biological settings including neuronal remodeling, fertilization, viral and bacterial spread, and cancer, but has been most widely studied in cells of the immune system. Trogocytosis is performed by multiple immune cell types, including basophils, macrophages, dendritic cells, neutrophils, natural killer cells, B cells, γδ T cells, and CD4⁺ and CD8⁺ αβ T cells. Although not expressed endogenously, the presence of trogocytosed molecules on cells has the potential to significantly impact an immune response and the biology of the individual trogocytosis-positive cell. Many studies have focused on the ability of the trogocytosis-positive cells to interact with other immune cells and modulate the function of responders. Less understood and arguably equally important is the impact of these molecules on the individual trogocytosis-positive cell. Molecules that have been reported to be trogocytosed by cells include cognate ligands for receptors on the individual cell, such as activating NK cell ligands and MHC:peptide. These trogocytosed molecules have been shown to interact with receptors on the trogocytosis-positive cell and mediate intracellular signaling. In this review, we discuss the impact of this trogocytosis-mediated signaling on the biology of the individual trogocytosis-positive cell by focusing on natural killer cells and CD4⁺ T lymphocytes.

Biodistribution of surfactant-free poly(lactic-acid) nanoparticles and uptake by endothelial cells and phagocytes in zebrafish: Evidence for endothelium to macrophage transfer

In the development of therapeutic nanoparticles (NP), there is a large gap between in vitro testing and in vivo experimentation. Despite its prominence as a model, the mouse shows severe limitations for imaging NP and the cells with which they interact. Recently, the transparent zebrafish larva, which is well suited for high-resolution live-imaging, has emerged as a powerful alternative model to investigate the in vivo behavior of NP. Poly(D,L lactic acid) (PLA) is widely accepted as a safe polymer to prepare therapeutic NP. However, to prevent aggregation, many NP require surfactants, which may have undesirable biological effects. Here, we evaluate 'safe-by-design', surfactant-free PLA-NP that were injected intravenously into zebrafish larvae. Interaction of fluorescent NPs with different cell types labelled in reporter animals could be followed in real-time at high resolution; furthermore, by encapsulating colloidal gold into the matrix of PLA-NP we could follow their fate in more detail by electron microscopy, from uptake to degradation. The rapid clearance of fluorescent PLA-NP from the circulation coincided with internalization by endothelial cells lining the whole vasculature and macrophages. After 30 min, when no NP remained in circulation, we observed that macrophages continued to internalize significant amounts of NP. More detailed video-imaging revealed a new mechanism of NP transfer where NP are transmitted along with parts of the cytoplasm from endothelial cells to macrophages.

Human macrophages stimulate expression of inflammatory mediators in adipocytes; effects of second-generation antipsychotics and glucocorticoids on cellular cross-talk

OBJECTIVE

Adipose tissue inflammation and distorted macrophage-adipocyte communication are positively associated with metabolic disturbances. Some pharmacological agents, such as second-generation antipsychotics (SGAs) and synthetic glucocorticoid (GC) dexamethasone, tend to induce adverse metabolic side effects and the underlying mechanisms are not fully understood. Our work aimed to study whether SGAs and dexamethasone affect macrophage phenotype and macrophage-adipocyte communication on gene expression level. We selected the model involving THP-1-derived macrophages, polarized into M0, M1, and M2 phenotypes, and primary human mature subcutaneous adipocytes.

METHODS

Abdominal subcutaneous adipose tissue needle biopsies were obtained from 6 healthy subjects (4F/2M; age: 22-64 yr; BMI: 21.7-27.6 kg/m2) followed by isolation of mature adipocytes. THP-1-human monocytic cell line was used for the study. THP-1 monocytes were differentiated and polarized into M0 (naïve), M1 (classically activated), and M2 (alternatively activated) macrophages. During and after polarization the macrophages were treated for 24 h without (control) or with therapeutic and supra-therapeutic concentrations of olanzapine (0.2 µM and 2.0 µM), aripiprazole (1.0 µM and 10 µM) and its active metabolite dehydroaripiprazole (0.4 µM and 4.0 µM). Isolated mature human adipocytes were co-incubated with THP-1-derived polarized macrophages pre-treated with SGAs after their polarization. Adipocytes and macrophages were collected before and after co-culture for mRNA expression analysis of genes involved in inflammation.

RESULTS

Co-incubation of mature human adipocytes with human macrophages, regardless of polarization, resulted in a marked induction of pro-inflammatory cytokines in adipocytes, including IL1B, IL6, TNFA, and IL10. Remarkably, it did not affect the expression of adipokines and genes involved in the regulation of energy, lipid, and glucose metabolism in adipocytes. Dexamethasone markedly reduced gene expression of pro-inflammatory cytokines in macrophages and prevented macrophage-induced inflammatory response in adipocytes. In contrast, SGAs did not affect macrophage-adipocyte communication and had a minute anti-inflammatory effect in macrophages at supra-therapeutic concentrations. Interestingly, the adipocytes co-incubated with M1 macrophages pre-treated with dexamethasone and SGAs particularly the supra-therapeutic concentration of olanzapine, reduced expression of LPL, LIPE, AKT1, and SLC2A4, suggesting that the expression of metabolic genes in adipocytes was dependent on the presence of pro-inflammatory M1 macrophages.

CONCLUSION

Together, these data suggest that macrophages induce expression of pro-inflammatory genes in human subcutaneous adipocytes without affecting the expression of adipokines or genes involved in energy regulation. Furthermore, our findings demonstrated that SGAs and dexamethasone had a mild effect on macrophage-adipocyte communication in M1 macrophage phenotype.

Trogocytosis between Non-Immune Cells for Cell Clearance, and among Immune-Related Cells for Modulating Immune Responses and Autoimmunity

The term trogocytosis refers to a rapid bidirectional and active transfer of surface membrane fragment and associated proteins between cells. The trogocytosis requires cell-cell contact, and exhibits fast kinetics and the limited lifetime of the transferred molecules on the surface of the acceptor cells. The biological actions of trogocytosis include information exchange, cell clearance of unwanted tissues in embryonic development, immunoregulation, cancer surveillance/evasion, allogeneic cell survival and infectious pathogen killing or intercellular transmission. In the present review, we will extensively review all these aspects. In addition to its biological significance, aberrant trogocytosis in the immune system leading to autoimmunity and immune-mediated inflammatory diseases will also be discussed. Finally, the prospective investigations for further understanding the molecular basis of trogocytosis and its clinical applications will also be proposed.

Modeling Adipogenesis: Current and Future Perspective

Adipose tissue is contemplated as a dynamic organ that plays key roles in the human body. Adipogenesis is the process by which adipocytes develop from adipose-derived stem cells to form the adipose tissue. Adipose-derived stem cells’ differentiation serves well beyond the simple goal of producing new adipocytes. Indeed, with the current immense biotechnological advances, the most critical role of adipose-derived stem cells remains their tremendous potential in the field of regenerative medicine. This review focuses on examining the physiological importance of adipogenesis, the current approaches that are employed to model this tightly controlled phenomenon, and the crucial role of adipogenesis in elucidating the pathophysiology and potential treatment modalities of human diseases. The future of adipogenesis is centered around its crucial role in regenerative and personalized medicine.

Decreased levels and activity of Sirt1 are modulated by increased miR-34a expression in adipose tissue mononuclear cells from subjects with overweight and obesity: A pilot study

BACKGROUND AND AIMS

Overweight and obesity are important risk factors for chronic disorders. Fat accumulation is one of the central manifestations; it occurs via a complex mechanism where multiple metabolic signals converge. Sirtuins are an enzyme family with deacetylase functions that are implicated in the regulation of several genes. Sirt1 and its upstream regulator (miR-34a) are elements of a converging mechanism that integrates the dynamic metabolic state. In this work, we hypothesized that elevated levels of miR-34a in overweight/obese group inhibits Sirt1 activity. Therefore, we studied the miR-34a/Sirt1 axis in mononuclear cells obtained from adipose tissue.

METHODS

Adipose tissue samples were collected from 36 subjects, and they were categorized according to body mass index (BMI) as overweight/obesity and normoweight. Subcutaneous adipose tissue samples were enzymatically dissociated, and mononuclear cells from adipose tissue were isolated by Ficoll Hypaque. Sirt1-positive cells and relative Sirt1 expression were determined by flow cytometry and real-time polymerase chain reaction (qPCR), respectively. Finally, Sirt1 activity was measured with a luminescence assay.

RESULTS

The percentage of Sirt1-positive mononuclear cells from adipose tissue decreased along with Sirt1 enzymatic activity in overweight/obese participants. miR-34a expression increased in the overweight/obese group compared to normoweight individuals. There was a negative association between the relative miR-34a expression and Sirt1-positive cells and a synergistic effect on Sirt1-positive cells mediated by the miR-34a inhibitor and Sirt1 agonist.

CONCLUSIONS

Our results describe for the first time the presence of miR-34a and Sirt1 in mononuclear cells isolated from subcutaneous adipose tissue. Additionally, these results suggest altered sirtuin function in overweight/obese patients and open the possibility for new therapies that involve these metabolic targets.

Assessing in vitro and in vivo Trogocytosis By Murine CD4+ T cells

Recognition of antigens by lymphocytes (B, T, and NK) on the surface of an antigen-presenting cell (APC) leads to lymphocyte activation and the formation of an immunological synapse between the lymphocyte and the APC. At the immunological synapse APC membrane and associated membrane proteins can be transferred to the lymphocyte in a process called trogocytosis. The detection of trogocytosed molecules provides insights to the activation state, antigen specificity, and effector functions and differentiation of the lymphocytes. Here we outline our protocol for identifying trogocytosis-positive CD4+ T cells in vitro and in vivo. In vitro, antigen presenting cells are surface biotinylated and pre-loaded with magnetic polystyrene beads before incubating for a short time with in vitro activated CD4+ T cell blasts (90 min) or naïve T cells (3-24 h). After T cell recovery and APC depletion by magnetic separation trogocytosis positive (trog+) cells are identified by streptavidin staining of trogocytosed, biotinylated APC membrane proteins. Their activation phenotype, effector function, and effector differentiation are subsequently analyzed by flow cytometry immediately or after subsequent incubation. Similarly, trogocytosis-positive cells can be identified and similarly analyzed by flow cytometry. Previous studies have described methods for analyzing T cell trogocytosis to identify antigen-specific cells or the antigenic epitopes recognized by the cells. With the current protocol, the effects of trogocytosis on the individual T cell or the ability of trog+ T cells to modulate the activation and function of other immune cells can be assessed over an extended period of time.

The Role of MKP-5 in Adipocyte-Macrophage Interactions during Obesity

OBJECTIVE

In obese individuals, chronic low-grade inflammation resulting from adipocyte-macrophage interactions is a major cause of adipose tissue dysfunction and metabolic disease. This study investigated the role of MAP kinase phosphatase-5 (MKP-5) in obesity-induced inflammation during macrophage and adipocyte interactions.

METHODS

High-fat diet-induced obese mice were used to explore the role of MKP-5 in obesity-induced adipose tissue inflammation. Macrophage polarization was determined by inflammatory cytokine expression in MKP-5-overexpressed or -silenced Raw264.7 cells exposed to palmitate (PA) or M1/M2 macrophage inducers. To uncover the role of MKP-5 during macrophage-adipocyte interactions, a coculture system composed of differentiated 3T3-L1 and Raw264.7 cells was employed. MAPK inhibitors were used to investigate the involvement of MAPK signaling.

RESULTS

Increased MKP-5 expression was observed in adipose stromal vascular cells (SVCs) of obese mice. In Raw264.7 cells, MKP-5 promoted the switching of M1 macrophages to an M2 phenotype. Notably, MKP-5 reduced inflammation during the interaction of macrophages and adipocytes. MKP-5 overexpression in primary SVCs attenuated the expression of inflammatory mediators and increased the number of obesity-induced adipose tissue macrophages. MKP-5 suppressed PA-induced inflammation through the inactivation of P38, JNK, and ERK MAPKs.

CONCLUSIONS

MKP-5 promotes macrophages to switch from the M1 to the M2 phenotype and is an inflammatory inhibitor involved in obesity-induced adipose tissue inflammation and PA-triggered macrophage inflammation via the P38, JNK, and ERK MAPK pathways. MKP-5 may be developed into a potential therapeutic target for obesity-related diseases, including type 2 diabetes mellitus and insulin resistance.

Resolvin D1 promotes the targeting and clearance of necroptotic cells

Inflammation-resolution is a protective response that is mediated by specialized pro-resolving mediators (SPMs). The clearance of dead cells or efferocytosis is a critical cellular program of inflammation-resolution. Impaired efferocytosis can lead to tissue damage in prevalent human diseases, like atherosclerosis. Therefore understanding mechanisms associated with swift clearance of dead cells is of utmost clinical importance. Recently, the accumulation of necroptotic cells (NCs) was observed in human plaques and we postulated that this is due to defective clearance programs. Here we present evidence that NCs are inefficiently taken up by macrophages because they have increased surface expression of a well-known "don't eat me" signal called CD47. High levels of CD47 on NCs stimulated RhoA-pMLC signaling in macrophages that promoted "nibbling", rather than whole-cell engulfment of NCs. Anti-CD47 blocking antibodies limited RhoA-p-MLC signaling and promoted whole-cell NC engulfment. Treatment with anti-CD47 blocking antibodies to Ldlr^-/- mice with established atherosclerosis decreased necrotic cores, limited the accumulation of plaque NCs and increased lesional SPMs, including Resolvin D1 (RvD1) compared with IgG controls. Mechanistically, RvD1 promoted whole-cell engulfment of NCs by decreasing RhoA signaling and activating CDC42. RvD1 specifically targeted NCs for engulfment by facilitating the release of the well-known "eat me signal" called calreticulin from macrophages in a CDC42 dependent manner. Lastly, RvD1 enhanced the clearance of NCs in advanced murine plaques. Together, these results suggest new molecules and signaling associated with the clearance of NCs, provide a new paradigm for the regulation of inflammation-resolution, and offer a potential treatment strategy for diseases where NCs underpin the pathology.

What role do fat cells play in pancreatic tissue?

Background

It is now generally accepted that obesity is a major risk factor for type 2 diabetes mellitus (T2DM). Hepatic steatosis in particular, as well as visceral and ectopic fat accumulation within tissues, is associated with the development of the disease. We recently presented the first study on isolated human pancreatic adipocytes and their interaction with islets [Gerst, F., Wagner, R., Kaiser, G., Panse, M., Heni, M., Machann, J., et al., 2017. Metabolic crosstalk between fatty pancreas and fatty liver: effects on local inflammation and insulin secretion. Diabetologia 60(11):2240–2251.]. The results indicate that the function of adipocytes depends on the overall metabolic status in humans which, in turn, differentially affects islet hormone release.

Scope of Review

This review summarizes former and recent studies on factors derived from adipocytes and their effects on insulin-secreting β-cells, with particular emphasis on the human pancreas. The adipocyte secretome is discussed with a special focus on its influence on insulin secretion, β-cell survival and apoptotic β-cell death.

Major Conclusions

Human pancreatic adipocytes store lipids and release adipokines, metabolites, and pro-inflammatory molecules in response to the overall metabolic, humoral, and neuronal status. The differentially regulated adipocyte secretome impacts on endocrine function, i.e., insulin secretion, β-cell survival and death which interferes with glycemic control. This review attempts to explain why the extent of pancreatic steatosis is associated with reduced insulin secretion in some studies but not in others.

Trogocytosis-Mediated Intracellular Signaling in CD4+ T Cells Drives TH2-Associated Effector Cytokine Production and Differentiation

CD4⁺ T cells have been observed to acquire APC-derived membrane and membrane-associated molecules through trogocytosis in diverse immune settings. Despite this, the consequences of trogocytosis on the recipient T cell remain largely unknown. We previously reported that trogocytosed molecules on CD4⁺ T cells engage their respective surface receptors, leading to sustained TCR signaling and survival after APC removal. Using peptide-pulsed bone marrow-derived dendritic cells and transfected murine fibroblasts expressing antigenic MHC:peptide complexes as APC, we show that trogocytosis-positive CD4⁺ T cells display effector cytokines and transcription factor expression consistent with a T_H2 phenotype. In vitro-polarized T_H2 cells were found to be more efficient at performing trogocytosis than T_H1 or nonpolarized CD4⁺ cells, whereas subsequent trogocytosis-mediated signaling induced T_H2 differentiation in polarized T_H1 and nonpolarized cells. Trogocytosis-positive CD4⁺ T cells generated in vivo also display a T_H2 phenotype in both TCR-transgenic and wild-type models. These findings suggest that trogocytosis-mediated signaling impacts CD4⁺ T cell differentiation and effector cytokine production and may play a role in augmenting or shaping a T_H2-dominant immune response.

Interleukin-6 released from differentiating human beige adipocytes improves browning

Brown and beige adipocytes contribute significantly to the regulation of whole body energy expenditure and systemic metabolic homeostasis not exclusively by thermogenesis through mitochondrial uncoupling. Several studies have provided evidence in rodents that brown and beige adipocytes produce a set of adipokines ("batokines") which regulate local tissue homeostasis and have beneficial effects on physiological functions of the entire body. We observed elevated secretion of Interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1, but not tumor necrosis factor alpha (TNFα) or IL-1β pro-inflammatory cytokines, by ex vivo differentiating human beige adipocytes (induced by either PPARγ agonist or irisin) compared to white. Higher levels of IL-6, IL-8 and MCP-1 were released from human deep neck adipose tissue biopsies (enriched in browning cells) than from subcutaneous ones. IL-6 was produced in a sustained manner and mostly by the adipocytes and not by the undifferentiated progenitors. Continuous blocking of IL-6 receptor by specific antibody during beige differentiation resulted in downregulation of brown marker genes and increased morphological changes that are characteristic of white adipocytes. The data suggest that beige adipocytes adjust their production of IL-6 to reach an optimal level for differentiation in the medium enhancing browning in an autocrine manner.

Adipose-on-a-chip: a dynamic microphysiological in vitro model of the human adipose for immune-metabolic analysis in type II diabetes

Infiltration of immune cells into adipose tissue is associated with chronic low-grade inflammation in obese individuals. To better understand the crosstalk between immune cells and adipocytes, in vivo-like in vitro models are required. Conventionally transwell culture plates are used for studying the adipocyte-immune cell interaction; however, the static culture nature of this approach falls short of closely recapitulating the physiological environment. Here we present a compartmentalized microfluidic co-culture system which provides a constant-rate of nutrient supply as well as waste removal, resembling the microvascular networks of the in vivo environment. Human adipocytes and U937 cells were co-cultured in close proximity in an enclosed system. The porous barrier between the adjacent compartments comprises an array of microchannels, which enables paracrine interaction between cells in adjacent compartments and improved perfusion-based long term cell feeding. Human pre-adipocytes were fully differentiated into adipocytes on the chip and remained viable for several weeks. Upon co-culturing with immune cells, adipocytes showed a tendency to develop insulin resistance. The immune-metabolic correlation has been studied by monitoring adiponectin and IL-6 expression, as well as glucose uptake upon treatment with insulin. Our microfluidic system can be potentially used to develop physiologically relevant adipose tissue models to study obesity-associated diseases such as insulin resistance and type 2 diabetes and therefore, facilitate drug development to treat these diseases.

Induction of fat apoptosis by a non-thermal device: Mechanism of action of non-invasive high-intensity electromagnetic technology in a porcine model

Objectives

While controlled thermal changes in subcutaneous tissue have been used to trigger apoptosis of fat cells and have been proven clinically efficacious, another mechanism of electromagnetic stress suggests that fat apoptosis could be achieved by a non‐thermal manner as well. This animal model study investigates the use of a non‐invasive high‐intensity magnetic field device to induce apoptosis in fat cells.

Methods

Yorkshire pigs (N = 2) received one treatment (30 minutes) in the abdominal area using a High‐Intensity Focused Electromagnetic (HIFEM) device. Punch biopsy samples of fat tissue and blood samples were collected at the baseline, 1 and 8 hours after the treatment. Biopsy samples were sectioned and evaluated for the levels of an apoptotic index (AI) by the TUNEL method. Statistical significance was examined using the rANOVA and Tukey's test (α 5%). Biopsy samples were also assessed for molecular biomarkers. Blood samples were evaluated to determine changes related to fat and muscle metabolism. Free fatty acids (FFA), triacylglycerol (TG), glycerol and glucose (Glu) were used as the main biomarkers of fat metabolism. Creatinine, creatinine kinase (CK), lactate dehydrogenase (LDH) and interleukin 6 (IL6) served as the main biomarkers to evaluate muscle metabolism.

Results

In treated pigs, a statistically significant increase in the apoptotic index (AI) (P = 1.17E‐4) was observed. A significant difference was found between AI at baseline (AI = 18.75%) and 8‐hours post‐treatment (AI = 35.95%). Serum levels of fat and muscle metabolism indicated trends (FFA −0.32 mmol · l⁻¹, −28.1%; TG −0.24 mmol · l⁻¹, −51.8%; Glycerol −5.68 mg · l⁻¹, −54.8%; CK +67.58 μkat · l⁻¹, +227.8%; LDH +4.9 μkat · l⁻¹,+35.4%) suggesting that both adipose and muscle tissue were affected by HIFEM treatment. No adverse events were noted to skin and surrounding tissue.

Conclusions

Application of a high‐intensity electromagnetic field in a porcine model results in adipocyte apoptosis. The analysis of serum levels suggests that HIFEM treatment influences fat and muscle metabolism. Lasers Surg. Med. 51:47–53, 2019. © 2018 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

M1 macrophage subtypes activation and adipocyte dysfunction worsen during prolonged consumption of a fructose-rich diet

Fructose-rich diet (FRD) has been associated with obesity development, which is characterized by adipocytes hypertrophy and chronic low-grade inflammation. Interaction of adipocytes and immune cells plays a key role in adipose tissue (AT) alterations in obesity. We assessed the metabolic and immune impairments in AT in a murine obesity model induced by FRD at different periods. Adult Swiss mice were divided into groups of 6 and 10 weeks of fructose (FRD 6wk, FRD 10wk) or water intake (CTR 6wk, CTR 10wk). FRD induced increased in body weight, epidydimal AT mass, and plasmatic and liver Tg, and impaired insulin sensitivity. Also, hypertrophic adipocytes from FRD 6wk-10wk mice showed higher IL-6 when stimulated with LPS and leptin secretion. Several of these alterations worsened in FRD 10wk. Regarding AT inflammation, FRD mice have increased TNFα, IL-6 and IL1β, and decrease in IL-10 and CD206 mRNA levels. Using CD11b, LY6C, CD11c and CD206 as macrophages markers, we identified for first time in AT M1 (M1a: Ly6C^+/-CD11c⁺CD206^- and M1b: Ly6C^+/-CD11c⁺CD206⁺) and M2 subtypes (Ly6C^+/-CD11c^-CD206⁺). M1a phenotype increased from 6 weeks onward, while Ly6C^+/- M1b phenotype increased only after 10 weeks. Finally, co-culture of RAW264.7 (monocytes cell line) and CTR or FRD adipocytes showed that FRD 10wk adipocytes increased IL-6 expression in non- or LPS-stimulated monocytes. Our results showed that AT dysfunction got worse as the period of fructose consumption was longer. Inflammatory macrophage subtypes increased depending on the period of FRD intake, and hypertrophic adipocytes were able to create an environment that favored M1 phenotype in vitro.

Pro-atherogenic and pro-oxidant crosstalk between adipocytes and macrophages

PURPOSE

Obesity, which is characterized by triglyceride accumulation mainly in adipocytes but also in arterial wall cells such as macrophages, is a major risk factor for developing atherosclerosis. We aimed to identify the crosstalk related to lipid metabolism and oxidation status between adipocytes and macrophages.

METHODS

We used a co-culture model system with J477A.1 cultured macrophages and 3T3L1 cultured adipocytes. For an in-vivo co-culture system, we used C57BL/6 mouse peritoneal macrophages and visceral or subcutaneous adipose tissue.

RESULTS

Adipocytes significantly increased reactive oxygen species generation, up to twofold, and decreased cholesterol content by 22% in the co-cultured macrophages. Macrophages significantly increased triglyceride-biosynthesis rate by twofold and decreased triglyceride-degradation rate by 30%, resulting in increased triglyceride accumulation in the co-cultured adipocytes by up to 72%. In the in-vivo mouse model, visceral adipose tissue crosstalk with macrophages resulted in a significant pro-atherogenic phenotype with respect to cellular cholesterol metabolism. In contrast, the interaction between subcutaneous adipose tissue and macrophages mostly affected cellular triglyceride metabolism. There were no significant effects on mitochondrial respiration capacity in the macrophages. Upon oxidative-stress reduction in the co-cultured cells using the polyphenol-rich antioxidant, pomegranate juice, the expression of genes related to cellular lipid accumulation was significantly reduced.

CONCLUSIONS

We reveal, for the first time, that paracrine interactions between adipocytes and macrophages result in oxidative stress and lipids metabolic alterations in both cells, toward increased atherogenicity which can be reversed by phenolic antioxidants.

The Phagocytic Function of Macrophage-Enforcing Innate Immunity and Tissue Homeostasis

Macrophages are effector cells of the innate immune system that phagocytose bacteria and secrete both pro-inflammatory and antimicrobial mediators. In addition, macrophages play an important role in eliminating diseased and damaged cells through their programmed cell death. Generally, macrophages ingest and degrade dead cells, debris, tumor cells, and foreign materials. They promote homeostasis by responding to internal and external changes within the body, not only as phagocytes, but also through trophic, regulatory, and repair functions. Recent studies demonstrated that macrophages differentiate from hematopoietic stem cell-derived monocytes and embryonic yolk sac macrophages. The latter mainly give rise to tissue macrophages. Macrophages exist in all vertebrate tissues and have dual functions in host protection and tissue injury, which are maintained at a fine balance. Tissue macrophages have heterogeneous phenotypes in different tissue environments. In this review, we focused on the phagocytic function of macrophage-enforcing innate immunity and tissue homeostasis for a better understanding of the role of tissue macrophages in several pathological conditions.

Minocycline modulates NFκB phosphorylation and enhances antimicrobial activity against Staphylococcus aureus in mesenchymal stromal/stem cells

Background

Mesenchymal stromal/stem cells (MSCs) have demonstrated pro-healing properties due to their anti-inflammatory, angiogenic, and even antibacterial properties. We have shown previously that minocycline enhances the wound healing phenotype of MSCs, and MSCs encapsulated in poly(ethylene glycol) and gelatin-based hydrogels with minocycline have antibacterial properties against Staphylococcus aureus (SA). Here, we investigated the signaling pathway that minocycline modulates in MSCs which results in their enhanced wound healing phenotype and determined whether preconditioning MSCs with minocycline has an effect on antimicrobial activity. We further investigated the in-vivo antimicrobial efficacy of MSC and antibiotic-loaded hydrogels in inoculated full-thickness cutaneous wounds.

Methods

Modulation of cell signaling pathways in MSCs with minocycline was analyzed via western blot, immunofluorescence, and ELISA. Antimicrobial efficacy of MSCs pretreated with minocycline was determined by direct and transwell coculture with SA. MSC viability after SA coculture was determined via a LIVE/DEAD® stain. Internalization of SA by MSCs pretreated with minocycline was determined via confocal imaging. All protein and cytokine analysis was done via ELISA. The in-vivo antimicrobial efficacy of MSC and antibiotic-loaded hydrogels was determined in Sprague–Dawley rats inoculated with SA. Two-way ANOVA for multiple comparisons was used with Bonferroni test assessment and an unpaired two-tailed Student’s t test was used to determine p values for all assays with multiple or two conditions, respectively.

Results

Minocycline leads to the phosphorylation of transcriptional nuclear factor-κB (NFκB), but not c-Jun NH₂-terminal kinase (JNK) or mitogen-activated protein kinase (ERK). Inhibition of NFκB activation prevented the minocycline-induced increase in VEGF secretion. Preconditioning of MSCs with minocycline led to a reduced production of the antimicrobial peptide LL-37, but enhanced antimicrobial activity against SA via an increased production of IL-6 and SA internalization. MSC and antibiotic-loaded hydrogels reduced SA bioburden in inoculated wounds over 3 days and accelerated reepithelialization.

Conclusions

Minocycline modulates the NFκB pathway in MSCs that leads to an enhanced production of IL-6 and internalization of SA. This mechanism may have contributed to the in-vivo antibacterial efficacy of MSC and antibiotic-loaded hydrogels.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0623-1) contains supplementary material, which is available to authorized users.

Macrophage functions in lean and obese adipose tissue

Interactions between macrophages and adipocytes influence both metabolism and inflammation. Obesity-induced changes to macrophages and adipocytes lead to chronic inflammation and insulin resistance. This paper reviews the various functions of macrophages in lean and obese adipose tissue and how obesity alters adipose tissue macrophage phenotypes. Metabolic disease and insulin resistance shift the balance between numerous pro- and anti-inflammatory regulators of macrophages and create a feed-forward loop of increasing inflammatory macrophage activation and worsening adipocyte dysfunction. This ultimately leads to adipose tissue fibrosis and diabetes. The molecular mechanisms underlying these processes have therapeutic implications for obesity, metabolic syndrome, and diabetes.

Clearance of autophagy-associated dying retinal pigment epithelial cells - a possible source for inflammation in age-related macular degeneration

Retinal pigment epithelial (RPE) cells can undergo different forms of cell death, including autophagy-associated cell death during age-related macular degeneration (AMD). Failure of macrophages or dendritic cells (DCs) to engulf the different dying cells in the retina may result in the accumulation of debris and progression of AMD. ARPE-19 and primary human RPE cells undergo autophagy-associated cell death upon serum depletion and oxidative stress induced by hydrogen peroxide (H₂O₂). Autophagy was revealed by elevated light-chain-3 II (LC3-II) expression and electron microscopy, while autophagic flux was confirmed by blocking the autophago-lysosomal fusion using chloroquine (CQ) in these cells. The autophagy-associated dying RPE cells were engulfed by human macrophages, DCs and living RPE cells in an increasing and time-dependent manner. Inhibition of autophagy by 3-methyladenine (3-MA) decreased the engulfment of the autophagy-associated dying cells by macrophages, whereas sorting out the GFP-LC3-positive/autophagic cell population or treatment by the glucocorticoid triamcinolone (TC) enhanced it. Increased amounts of IL-6 and IL-8 were released when autophagy-associated dying RPEs were engulfed by macrophages. Our data suggest that cells undergoing autophagy-associated cell death engage in clearance mechanisms guided by professional and non-professional phagocytes, which is accompanied by inflammation as part of an in vitro modeling of AMD pathogenesis.

Effects of iron supplementation in mice with hypoferremia induced by obesity

Iron is an important micronutrient, but it can also act as a dangerous element by interfering with glucose homeostasis and inflammation, two features that are already disturbed in obese subjects. In this work, we study the effects of systemic iron supplementation on metabolic and inflammatory responses in mice with hypoferremia induced by obesity to better characterize whether iron worsens the parameters that are already altered after 24 weeks of a high-fat diet (HFD). Mice were maintained on a control diet or a HFD for 24 weeks and received iron-III polymaltose (50 mg/kg/every 2 days) during the last two weeks. Glucose homeostasis (basal glucose and insulin test tolerance) and systemic and visceral adipose tissue (VAT) inflammation were assessed. Iron levels were measured in serum. The Prussian blue reaction was used in isolated macrophages to detect iron deposition. Iron supplementation resulted in an increased number of VAT macrophages that were positive for Prussian blue staining as well as increased serum iron levels. Systemic hepcidin, leptin, resistin, and monocyte chemoattractant protein-1 (MCP-1) levels were not altered by iron supplementation. Local adipose tissue inflammation was also not made worse by iron supplementation because the levels of hepcidin, MCP-1, leptin, and interleukin (IL)-6 were not altered. In contrast, iron supplementation resulted in an increased production of IL-10 by adipose tissue and VAT macrophages. Leukocytosis and VAT plasminogen activator inhibitor-1 (PAI-1) level were reduced, but insulin resistance was not altered after iron supplementation. In conclusion, systemic iron supplementation in mice with hypoferremia induced by obesity did not worsen inflammatory marker or adipose tissue inflammation or the metabolic status established by obesity. Iron deposition was observed in adipose tissue, mainly in macrophages, suggesting that these cells have mechanisms that promote iron incorporation without increasing the production of inflammatory mediators.

Obesity-Driven Gut Microbiota Inflammatory Pathways to Metabolic Syndrome

The intimate interplay between immune system, metabolism, and gut microbiota plays an important role in controlling metabolic homeostasis and possible obesity development. Obesity involves impairment of immune response affecting both innate and adaptive immunity. The main factors involved in the relationship of obesity with inflammation have not been completely elucidated. On the other hand, gut microbiota, via innate immune receptors, has emerged as one of the key factors regulating events triggering acute inflammation associated with obesity and metabolic syndrome. Inflammatory disorders lead to several signaling transduction pathways activation, inflammatory cytokine, chemokine production and cell migration, which in turn cause metabolic dysfunction. Inflamed adipose tissue, with increased macrophages infiltration, is associated with impaired preadipocyte development and differentiation to mature adipose cells, leading to ectopic lipid accumulation and insulin resistance. This review focuses on the relationship between obesity and inflammation, which is essential to understand the pathological mechanisms governing metabolic syndrome.

The interplay between inflammation and metabolism in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by extensive synovitis resulting in erosions of articular cartilage and marginal bone that lead to joint destruction. The autoimmune process in RA depends on the activation of immune cells, which use intracellular kinases to respond to external stimuli such as cytokines, immune complexes, and antigens. An intricate cytokine network participates in inflammation and in perpetuation of disease by positive feedback loops promoting systemic disorder. The widespread systemic effects mediated by pro-inflammatory cytokines in RA impact on metabolism and in particular in lymphocyte metabolism. Moreover, RA pathobiology seems to share some common pathways with atherosclerosis, including endothelial dysfunction that is related to underlying chronic inflammation. The extent of the metabolic changes and the types of metabolites seen may be good markers of cytokine-mediated inflammatory processes in RA. Altered metabolic fingerprints may be useful in predicting the development of RA in patients with early arthritis as well as in the evaluation of the treatment response. Evidence supports the role of metabolomic analysis as a novel and nontargeted approach for identifying potential biomarkers and for improving the clinical and therapeutical management of patients with chronic inflammatory diseases. Here, we review the metabolic changes occurring in the pathogenesis of RA as well as the implication of the metabolic features in the treatment response.