Macrophages In Visceral Adipose Tissue Research Articles

Role for BLT1 in regulating inflammation within adipose tissue immune cells of aged mice

BackgroundAging is a complex biological process characterized by obesity and immunosenescence throughout the organism. Immunosenescence involves a decline in immune function and the increase in chronic-low grade inflammation, called inflammaging. Adipose tissue expansion, particularly that of visceral adipose tissue (VAT), is associated with an increase in pro-inflammatory macrophages that play an important role in modulating immune responses and producing inflammatory cytokines. The leukotriene B4 receptor 1 (BLT1) is a regulator of obesity-induced inflammation. Its ligand, LTB4, acts as a chemoattractant for immune cells and induces inflammation. Studies have shown that BLT1 is crucial for cytokine production during lipopolysaccharide (LPS) endotoxemia challenge in younger organisms. However, the expression patterns and function of BLT1 in older organisms remains unknown.ResultsIn this study, we investigated BLT1 expression in immune cell subsets within the VAT of aged male and female mice. Moreover, we examined how antagonizing BLT1 signaling could alter the inflammatory response to LPS in aged mice. Our results demonstrate that aged mice exhibit increased adiposity and inflammation, characterized by elevated frequencies of B and T cells, along with pro-inflammatory macrophages in VAT. BLT1 expression is the highest in VAT macrophages. LPS and LTB4 treatment result in increased BLT1 in young and aged bone marrow-derived macrophages (BMDMs). However, LTB4 treatment resulted in amplified Il6 from aged, but not young BMDMs. Treatment of aged mice with the BLT1 antagonist, U75302, followed by LPS-induced endotoxemia resulted in an increase in anti-inflammatory macrophages, reduced phosphorylated NFκB and reduced Il6.ConclusionsThis study provides valuable insights into the age- and sex- specific changes in BLT1 expression on immune cell subsets within VAT. This study offers support for the potential of BLT1 in modulating inflammation in aging.

Four-and-a-Half LIM-Domain Protein 2 (FHL2) Induces Neuropeptide Y (NPY) in Macrophages in Visceral Adipose Tissue and Promotes Diet-Induced Obesity.

Obesity is characterized by the expansion of the adipose tissue, usually accompanied by inflammation, with a prominent role of macrophages infiltrating the visceral adipose tissue (VAT). This chronic inflammation is a major driver of obesity-associated comorbidities. Four-and-a-half LIM-domain protein 2 (FHL2) is a multifunctional adaptor protein that is involved in the regulation of various biological functions and the maintenance of the homeostasis of different tissues. In this study, we aimed to gain new insights into the expression and functional role of FHL2 in VAT in diet-induced obesity. We found enhanced FHL2 expression in the VAT of mice with Western-type diet (WTD)-induced obesity and obese humans and identified macrophages as the cellular source of enhanced FHL2 expression in VAT. In mice with FHL2 deficiency (FHL2KO), WTD feeding resulted in reduced body weight gain paralleled by enhanced energy expenditure and uncoupling protein 1 (UCP1) expression, indicative of activated thermogenesis. In human VAT, FHL2 was inversely correlated with UCP1 expression. Furthermore, macrophage infiltration and the expression of the chemokine MCP-1, a known promotor of macrophage accumulation, was significantly reduced in WTD-fed FHL2KO mice compared with wild-type (wt) littermates. While FHL2 depletion did not affect the differentiation or lipid metabolism of adipocytes in vitro, FHL2 depletion in macrophages resulted in reduced expressions of MCP-1 and the neuropeptide Y (NPY). Furthermore, WTD-fed FHL2KO mice showed reduced NPY expression in VAT compared with wt littermates, and NPY expression was enhanced in VAT resident macrophages of obese individuals. Stimulation with recombinant NPY induced not only UCP1 expression and lipid accumulation but also MCP-1 expression in adipocytes. Collectively, these findings indicate that FHL2 is a positive regulator of NPY and MCP-1 expression in macrophages and herewith closely linked to the mechanism of obesity-associated lipid accumulation and inflammation in VAT. Thus, FHL2 appears as a potential novel target to interfere with the macrophage-adipocyte crosstalk in VAT for treating obesity and related metabolic disorders.

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

ABSTRACT 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.

Adipocyte size, adipose tissue fibrosis, macrophage infiltration and disease risk are different in younger and older individuals with childhood versus adulthood onset obesity.

The timing of obesity onset and age have been shown to affect the risk of obesity-related comorbidities, although the impact of each of these factors on markers of adipose tissue function remains unclear. The aim of this study was to determine whether differences in regional adipose tissue characteristics vary with age and age of obesity onset, and whether these differences are associated with the markers of cardiometabolic health. Adipose tissue samples were obtained from 80 female bariatric surgery candidates who were classified by age of obesity onset and age into 4 groups: (1) younger adults (<40 y) with childhood-onset obesity (<18 y) (Child-Young); (2) younger adults with adulthood-onset obesity (>18 y) (Adult-Young); (3) older adults (>55 y) with childhood-onset obesity (Child-Old); and (4) older adults with adulthood-onset obesity (Adult-Old). Adipocyte diameter, adipose tissue fibrosis, and macrophage infiltration were determined in subcutaneous (SAT) and visceral adipose tissue (VAT). Clinical parameters were obtained from participants' medical records. Visceral adipocyte size in the Child-Young group was the smallest of all the groups. Age affected visceral infiltration of M1-like cells with greater percent of M1-like cells in the Adult-Old and Child-Old groups. Though not significant, a stepwise increase in M2-like macrophages in VAT was observed with Adult-Young having the smallest followed by Adult-Old, Child-Young, and Child-Old having the greatest percent of M2-like macrophages. Pericellular fibrosis accumulation in SAT and VAT varied with both age and onset, particularly in the Child-Old group, which had the lowest fibrosis levels. Markers of cardiometabolic health (fasting glucose, glycated hemoglobin, total, HDL- and LDL-cholesterol and triglyceride concentrations) were positively and well-associated with adipose tissue characteristics of the Child-Old group but not of the Adult-Young group. Older adults with childhood-onset obesity, who had the greatest duration of obesity exposure, were particularly vulnerable to the cardiometabolic effects associated with perturbations in adipose tissue characteristics. These results suggest that age and age of obesity onset may have independent and cumulative effects on obesity pathology.

Early-life dietary exposures mediate persistent shifts in the gut microbiome and visceral fat metabolism.

In utero dietary exposures are linked to the development of metabolic syndrome in adult offspring. These dietary exposures can potentially impact gut microbial composition and offspring metabolic health. Female BALB/c mice were administered a lard, lard + flaxseed oil, high sugar, or control diet 4 wk before mating, throughout mating, pregnancy, and lactation. Female offspring were offered low-fat control diet at weaning. Fecal 16S sequencing was performed. Untargeted metabolomics was performed on visceral adipose tissue (VAT) of adult female offspring. Immunohistochemistry was used to determine adipocyte size, VAT collagen deposition, and macrophage content. Hippurate was administered via weekly intraperitoneal injections to low-fat and high-fat diet-fed female mice and VAT fibrosis and collagen 1A (COL1A) were assessed by immunohistochemistry. Lard diet exposure was associated with elevated body and VAT weight and dysregulated glucose metabolism. Lard + flaxseed oil attenuated these effects. Lard diet exposures were associated with increased adipocyte diameter and VAT macrophage count. Lard + flaxseed oil reduced adipocyte diameter and fibrosis compared with the lard diet. Hippurate-associated bacteria were influenced by lard versus lard + flax exposures that persisted to adulthood. VAT hippurate was increased in lard + flaxseed oil compared with lard diet. Hippurate supplementation mitigated VAT fibrosis pathology. Maternal high-fat lard diet consumption resulted in long-term metabolic and gut microbiome programming in offspring, impacting VAT inflammation and fibrosis, and was associated with reduced VAT hippurate content. These traits were not observed in maternal high-fat lard + flaxseed oil diet-exposed offspring. Hippurate supplementation reduced VAT fibrosis. These data suggest that detrimental effects of early-life high-fat lard diet exposure can be attenuated by dietary omega-3 polyunsaturated fatty acid supplementation.

Dextran-Mimetic Quantum Dots for Multimodal Macrophage Imaging In Vivo, Ex Vivo, and In Situ.

Macrophages are white blood cells with diverse functions contributing to a healthy immune response as well as the pathogenesis of cancer, osteoarthritis, atherosclerosis, and obesity. Due to their pleiotropic and dynamic nature, tools for imaging and tracking these cells at scales spanning the whole body down to microns could help to understand their role in disease states. Here we report fluorescent and radioisotopic quantum dots (QDs) for multimodal imaging of macrophage cells in vivo, ex vivo, and in situ. Macrophage specificity is imparted by click-conjugation to dextran, a biocompatible polysaccharide that natively targets these cell types. The emission spectral band of the crystalline semiconductor core was tuned to the near-infrared for optical imaging deep in tissue, and probes were covalently conjugated to radioactive iodine for nuclear imaging. The performance of these probes was compared with all-organic dextran probe analogues in terms of their capacity to target macrophages in visceral adipose tissue using in vivo positron emission tomography/computed tomography (PET/CT) imaging, in vivo fluorescence imaging, ex vivo fluorescence, post-mortem isotopic analyses, and optical microscopy. All probe classes exhibited equivalent physicochemical characteristics in aqueous solution and similar in vivo targeting specificity. However, dextran-mimetic QDs provided enhanced signal-to-noise ratio for improved optical quantification, long-term photostability, and resistance to chemical fixation. In addition, the vascular circulation time for the QD-based probes was extended 9-fold compared with dextran, likely due to differences in conformational flexibility. The enhanced photophysical and photochemical properties of dextran-mimetic QDs may accelerate applications in macrophage targeting, tracking, and imaging across broad resolution scales, particularly advancing capabilities in single-cell and single-molecule imaging and quantification.

Myeloid Cell-Specific IL-4 Receptor Knockout Partially Protects from Adipose Tissue Inflammation.

IL-4 receptor signaling is supposed to play a major role in anti-inflammatory polarization and proliferation of adipose tissue macrophages. In this study, we examined the metabolic and inflammatory phenotype of C57BL/6J mice (IIl4ra) with LysM-dependent knockout (IIl4ra Δmyel) of the IL-4 receptor α-chain (IL-4Rα), the mandatory signaling component of IL-4 and IL-13, on chow and high-fat diet. Lean IIl4ra Δmyel mice showed decreased insulin sensitivity, no divergent adipose tissue macrophage polarization, but an increased percentage of CD8+ T cells in visceral adipose tissue. After 20 wk of a high-fat diet, IIl4ra Δmyel mice exhibited higher glucose tolerance, no changes in the lymphocyte compartment and fewer M1 macrophages in visceral adipose tissue. In vivo adipose tissue macrophage proliferation measured by BrdU incorporation was unaffected by Il4ra knockout. Interestingly, we show that IL-4Rα signaling directly augmented Itgax (Cd11c) gene expression in bone marrow-derived macrophages and increased the amount of CD11c+ macrophages in adipose tissue explants. Myeloid cell-specific knockout of Il4ra deteriorated insulin sensitivity in lean mice but improved parameters of glucose homeostasis and partially protected from adipose tissue inflammation in obese mice. Hence, IL-4Rα signaling probably plays a minor role in maintaining the macrophage M2 population and proliferation rates in vivo. Moreover, our data indicate that IL-4 signaling plays a proinflammatory role in adipose tissue inflammation by directly upregulating CD11c on adipose tissue macrophages.

Role of RAGE in obesity-induced adipose tissue inflammation and insulin resistance

AbatractObesity is known to be associated with adipose tissue inflammation and insulin resistance. Importantly, in obesity, the accumulation of proinflammatory macrophages in adipose tissue correlates with insulin resistance. We hypothesized that the receptor for advanced glycation end products (RAGE) and associated ligands are involved in adipose tissue insulin resistance, and that the activation of the AGE–RAGE axis plays an important role in obesity-associated inflammation. C57BL/6J mice (WT) and RAGE deficient (RAGE−/−) mice were fed a high fat diet (HFD) and subjected to glucose and insulin tolerance tests. Epdidymal adipose tissue (eAT) was collected and adipose stromal vascular cells isolated using flow cytometry. Visceral adipose tissue macrophage polarization was assessed by quantitative real time PCR. Immunoblotting was performed to evaluate the insulin signaling in adipose tissues. In additional studies, cell trafficking was assessed by injecting labeled blood monocytes into recipient mice. RAGE−/− mice displayed improved insulin sensitivity and glucose tolerance, accompanied by decreased body weight and eAT mass. Exogenous methylglyoxal (MGO) impaired insulin-stimulated AKT signaling in adipose tissues from WT mice fed a normal chow diet, but not in RAGE−/− mice. In contrast, in obese mice, treatment with MGO did not reduce insulin-induced phosphorylation of AKT in WT-HFD mice. Moreover, insulin-induced AKT phosphorylation was found to be impaired in adipose tissue from RAGE−/−-HFD mice. RAGE−/− mice displayed improved inflammatory profiles and evidence for increased adipose tissue browning. This observation is consistent with the finding of reduced plasma levels of FFA, glycerol, IL-6, and leptin in RAGE−/− mice compared to WT mice. Collectively the data demonstrate that RAGE-mediated adipose tissue inflammation and insulin-signaling are potentially important mechanisms that contribute to the development of obesity-associated insulin resistance.

Human Visceral Adipose Tissue (VAT) Inflammation Is Not Associated With Perforin Deficiency in Type 2 Diabetes Mellitus (DM) Subjects as Compared to Health Controls

Abstract Introduction: Role of T cells in VAT inflammation is poorly characterised. Perforin deficiency is associated with autoimmune inflammatory diseases like Hemophagocytosis Lymphohistiocytosis,as also in context of type 1 DM pathogenesis. Data from animal models suggest that perforin deficiency leads to VAT inflammation1Objective: We hypothesized CD8+/perf+ and CD56+/perf+ cells to be decreased in type 2 DM as compared to healthy controls. The present study also explored the difference in activation of T/NK cells between two groups Methods: 2×2 cm omental tissue was obtained from subjects undergoing elective abdominal surgery. The sample was transported in RPMI solution and stored in -80 ℃. Processing involved thawing, incubation at 37.6 ℃ for 24 hours with type IV Collagenase (1 mg/ml, Sigma Aldrich) 1ml/g of tissue,centrifuge (32g for 10 min at 10℃). The resultant Stromal Vascular fraction (SVF) was suspended in phosphate buffer saline (PBS), passed through cell strainer to make single cell suspension. It was again centrifuged and tagged with CD markers of interest. Fc block was added and single cell solution with FACS fluid prepared. It was run in BD CANTO-2 flow cytometer as described2Results: Of seventeen samples analysed, twelve samples of type 2 diabetes subjects were compared with five healthy controls. All results are presented in median. The diabetics had higher HbA1c (8.1 % vs 6%), higher BMI (28 kg/m2 vs 24 kg/m2), hsCRP(2.1 mg/dl Vs 0.9 mg/dl) but there was no difference in HOMA-Ir (5 vs 5.2 mU/L/mg/dl). The percentage of CD4+ + CD8+ cells/g of VAT was similar in both cases and control (20 × 103 Vs 23× 103). CD8+/CD45+/perf+ and CD56+/CD45+/perf+ could not be identified in any of the samples. Although CD8+/CD45+/perf-- and CD56+/CD45+/perf-- cells were identified. Next, we analysed the same cells for cytotoxic activation by 107a. The percentage of 107a positivity was low in CD 8+ (7% and 4 % respectively in cases and control) and CD 56+ cells (10% and 9 % respectively in cases and control),Although clinically type 2 DM subjects were obese and had inflammation (i.e higher hsCRP), there was no difference in VAT activation of immune cells studied. Also, we could not delineate perforin in any of the samples. Conclusion: Taken together this work suggests VAT T cell immune milieu in human Type 2 DM is different from mouse model. It is neither characterised by perforin deficiency nor activation of T cell/NK cell. This study points towards the probability that, the role of T cell/NK cells in human VAT infiltration could be fundamentally different from mice models. Further studies should be focussed on functional characteristics of these cells and interaction with VAT macrophages.

Abstract 13039: Loss of Visceral Adipose Tissue Macrophage Subsets Induces Myocardial Infarction Induced Insulin Resistance: Role of Adiponectin

Introduction: Myocardial infarction (MI) is the major cause of morbidity and mortality in the western world. Insulin resistance is a major complication in patients with MI. Hypothesis: Loss of visceral adipose tissue (VAT) resident macrophages in MI results in diminished adiponectin production causing systemic insulin resistance. Methods: To understand if MI results in insulin resistance, we analyzed UPMC patient records and identified patients who had normal fasting blood glucose levels on average 15 days before ST elevation myocardial infarction (STEMI) and checked their fasting blood glucose levels 30 days after STEMI. To understand the mechanisms of MI-induced insulin resistance, we used a mouse model of coronary ligation in C57BL/6 mice and analyzed the features of insulin resistance by measuring serum insulin, serum adiponectin, AKT activation status in the liver and muscle. Results: We found that 50% of non-diabetic patients (fasting blood glucose levels 99±2.5 mg/ dl) developed hyperglycemia (141±13 mg/dl) after MI, suggesting that MI causes insulin resistance. Consistently, mice with MI had higher fasting blood insulin, and reduced p-Akt levels in the liver and skeletal muscles confirming insulin resistance. Concomitantly, mice and patients with MI had reduced number of visceral adipose tissue (VAT) resident macrophages. In line with this, MI resulted in marked reduction in the level of macrophage colony stimulating factor (M-CSF), a cytokine required for tissue resident macrophage survival. M-CSF supplementation in mice with MI improved insulin sensitivity and decreased inflammatory phenotype of VAT macrophages. Furthermore, the systemic level of adiponectin, which is reported to augment insulin sensitivity, was profoundly reduced in mice after MI. Specific depletion of VAT resident macrophages resulted in lower levels of adiponectin in the serum, indicating that this macrophage subset is necessary for adiponectin production by adipocytes. Conclusions: Our data demonstrate that diminished M-CSF levels after MI triggers apoptosis of VAT resident macrophages, resulting in reduced adiponectin secretion and systemic insulin resistance.

Apoptosis of hematopoietic progenitor-derived adipose tissue-resident macrophages contributes to insulin resistance after myocardial infarction.

Patients with insulin resistance have high risk of cardiovascular disease such as myocardial infarction (MI). However, it is not known whether MI can initiate or aggravate insulin resistance. We observed that patients with ST-elevation MI and mice with MI had de novo hyperglycemia and features of insulin resistance, respectively. In mouse models of both myocardial and skeletal muscle injury, we observed that the number of visceral adipose tissue (VAT)-resident macrophages decreased because of apoptosis after these distant organ injuries. Patients displayed a similar decrease in VAT-resident macrophage numbers and developed systemic insulin resistance after ST-elevation MI. Loss of VAT-resident macrophages after MI injury led to systemic insulin resistance in non-diabetic mice. Danger signaling-associated protein high mobility group box 1 was released by the dead myocardium after MI in rodents and triggered macrophage apoptosis via Toll-like receptor 4. The VAT-resident macrophage population in the steady state in mice was transcriptomically distinct from macrophages in the brain, skin, kidney, bone marrow, lungs, and liver and was derived from hematopoietic progenitor cells just after birth. Mechanistically, VAT-resident macrophage apoptosis and de novo insulin resistance in mouse models of MI were linked to diminished concentrations of macrophage colony-stimulating factor and adiponectin. Collectively, these findings demonstrate a previously unappreciated role of adipose tissue-resident macrophages in sensing remote organ injury and promoting MI pathogenesis.

Exercise training reduces inflammatory metabolic activity of visceral fat assessed by18F‐FDG PET/CT in obese women

Obesity plays pivotal roles in the increased risk of cardiometabolic disease via induction of the inflammatory reaction from macrophages in visceral adipose tissue (VAT), which may elevate the inflammatory activity of VAT. This prospective study aimed to evaluate whether the inflammatory activity of VAT existed in association with systemic inflammation, and whether exercise could ameliorate the inflammatory activity of VAT assessed by 18 F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in obese women. A total of 23 obese women who participated in an exercise program were included. Subjects underwent 18 F-FDG PET/CT before the start of the exercise program (baseline) and after the completion of the 3-month exercise program. For the assessment of VAT metabolic activity, the maximum standardized uptake value (SUVmax) and the mean standardized uptake value (SUVmean) were measured. The SUVmax of spleen, bone marrow (BM) and the high-sensitivity C-reactive protein (hsCRP) were used as a surrogate marker for systemic inflammation. Baseline SUVmax of VAT was positively correlated with the SUVmax of spleen, BM and hsCRP, whereas VAT SUVmean was not correlated. Exercise reduced SUVmax of VAT in addition to adiposity, the SUVmax of spleen, BM and hsCRP. However, VAT SUVmean was not significantly changed. Furthermore, the association of SUVmax of VAT, and the SUVmax of spleen, BM and hsCRP was no longer relevant after exercise. In obese women, the SUVmax of VAT assessed by 18 F-FDG PET/CT was associated with systemic inflammation and exercise reduced the SUVmax of VAT and abrogated its association with systemic inflammation.

Macrophages protect against loss of adipose tissue during cancer cachexia.

BackgroundCancer cachexia represents a central obstacle in medical oncology as it is associated with poor therapy response and reduced overall survival. Systemic inflammation is considered to be a key driver of cancer cachexia; however, clinical studies with anti‐inflammatory drugs failed to show distinct cachexia‐inhibiting effects. To address this contradiction, we investigated the functional importance of innate immune cells for hepatocellular carcinoma (HCC)‐associated cachexia.MethodsA transgenic HCC mouse model was intercrossed with mice harbouring a defect in myeloid cell‐mediated inflammation. Body composition of mice was analysed via nuclear magnetic resonance spectroscopy and microcomputed tomography. Quantitative PCR was used to determine adipose tissue browning and polarization of adipose tissue macrophages. The activation state of distinct areas of the hypothalamus was analysed via immunofluorescence. Multispectral immunofluorescence imaging and immunoblot were applied to characterize sympathetic neurons and macrophages in visceral adipose tissue. Quantification of pro‐inflammatory cytokines in mouse serum was performed with a multiplex immunoassay. Visceral adipose tissue of HCC patients was quantified via the L3 index of computed tomography scans obtained during routine clinical care.ResultsWe identified robust cachexia in the HCC mouse model as evidenced by a marked loss of visceral fat and lean mass. Computed tomography‐based analyses demonstrated that a subgroup of human HCC patients displays reduced visceral fat mass, complementing the murine data. While the myeloid cell‐mediated inflammation defect resulted in reduced expression of pro‐inflammatory cytokines in the serum of HCC‐bearing mice, this unexpectedly did not translate into diminished but rather enhanced cachexia‐associated fat loss. Defective myeloid cell‐mediated inflammation was associated with decreased macrophage abundance in visceral adipose tissue, suggesting a role for local macrophages in the regulation of cancer‐induced fat loss.ConclusionsMyeloid cell‐mediated inflammation displays a rather unexpected beneficial function in a murine HCC model. These results demonstrate that immune cells are capable of protecting the host against cancer‐induced tissue wasting, adding a further layer of complexity to the pathogenesis of cachexia and providing a potential explanation for the contradictory results of clinical studies with anti‐inflammatory drugs.

Physical Activity and Inflammation Phenotype Conversion

ABSTRACTInflammation is a protective response to infection or injury; however, persistent microtraumas at the tissue level may result in chronic low-grade inflammation that plays both direct and indirect roles in the development of many diseases and aging. The purpose of this review is to describe the underlying physiology of low-grade inflammation and highlight potential inflammation lowering effects of physical activity (PA). Unique contributions of this review are to introduce the concept of inflammation phenotype flexibility in contrast to the low-grade inflammation state and describe how PA influences inflammation phenotype by altering muscle, gut, adipose, and postprandial metabolism. Pro-inflammatory M1 macrophages and cytokines—such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6—contribute to low-grade inflammation. Among the mechanisms that commonly contribute to low-grade inflammation are dysfunctional adipose tissue, a leaky gut, gut microbiota that promotes inflammation, and large postprandial glycemic and lipidemic responses. Physical activity may lower inflammation by decreasing M1 macrophages in visceral adipose tissue, decreasing adipose tissue volume, production of anti-inflammatory myokines, promotion of butyrate-producing members of the gut microbiota, improved gut barrier function, and lowering of postprandial glycemic and lipidemic responses. While exercise has many anti-inflammatory mechanisms, phenotype conversion is complex, multifaceted, and difficult to achieve. Our understanding of how PA influences inflammation must include acute exercise-induced anti-inflammatory effects, contribution to the inflammation state from multiple sources in the body, and phenotypic shifts underpinning low-grade inflammation.

Macrophages of the subcutaneous and omental fatty tissue in obese patients: Immunohistochemical phenotyping of M2 subtypes in relation to type 2 diabetes.

Macrophages are linked to the initiation of the chronic inflammation believed to underlie the changes taking place in the white fatty tissue of obese people. Both the number of macrophages, but their functional status, play an important role in the development of inflammation. Classically, macrophages are divided into two types: pro-inflammatory (M1) and anti-inflammatory (M2) types, and based on current immunological studies, further views on the functional distribution of macrophages are suggested. In this study, we evaluated the M1 and M2 macrophages ratio in obese subjects with, or without diabetes. To identify all macrophages, we used CD68 expression, while CD204 expression is typically used for the M2 macrophage. During bariatric surgery, carried out in obese people with and without type 2 diabetes (T2D), we obtained subcutaneous adipose tissue from the navel and omental adipose tissue. We also obtained the same tissue from people with a physiological range of BMI from a judicial autopsy. Applying immunohistochemical staining anti-CD68 and anti-CD204, we carried out a quantitative evaluation of the number of macrophages. We found CD68+ and CD204+ positive macrophages in perivascular spaces and between fat cells, both isolated and in larger infiltrates. They were also present in so-called "crown-like structures" (CLS) around dying adipocytes. Quantitative analysis showed an increased number of macrophages in all obese patients compared to the control group of non-obese, individuals without T2D. The most striking observation was the macrophage increase in the visceral fatty tissue of diabetics. The number of CD68 and CD204 positive macrophages was statistically significantly smaller in patients without T2D. We demonstrated a significantly greater number of macrophages in visceral adipose tissue, especially in patients with T2D. Our results also show a positive correlation between the presence of T2D and the total number of macrophages; a significantly greater number of macrophages were found in visceral adipose tissue, especially in patients with T2D.

Human Visceral Adipose Tissue Macrophages Are Not Adequately Defined by Standard Methods of Characterization.

Obesity is associated with a state of chronic low-grade inflammation both systemically and within specific tissues, including adipose tissue (AT). In murine models of obesity, there is a shift in the inflammatory profile of the AT immune cells, with an accumulation of proinflammatory M1 macrophages that surround the expanding adipocyte. However, much less is known about the immune cell composition and how to best define AT macrophages in humans. Objective. The goals of the current study were to determine the contribution of macrophages to the stromal vascular fraction (SVF) in lean versus obese human visceral AT (VAT); examine the expression of common M1, M2, and pan macrophage markers; and determine the association of specific macrophage types with known biomarkers of obesity-related cardiometabolic disease. Research Design and Methods. VAT biopsies were obtained from obese (n = 50) and lean (n = 8) patients during elective surgery. Adipocytes and SVF were isolated, and the SVF was subjected to flow cytometry analyses. Results. Our results indicate that VAT macrophages are increased in obesity and associate with biomarkers of CVD but that many macrophages do not fall into currently defined M1/M2 classification system based on CD206 receptor expression levels. Conclusions. VAT macrophages are increased in obese subjects, but the current markers used to define macrophage populations are inadequate to distinguish differences in human obesity. Further studies are needed to delineate the function of AT macrophages in the maintenance and progression of human AT inflammation in obesity.

Single-Cell RNA Sequencing of Visceral Adipose Tissue Leukocytes Reveals that Caloric Restriction Following Obesity Promotes the Accumulation of a Distinct Macrophage Population with Features of Phagocytic Cells.

Obesity can lead to type 2 diabetes and is an epidemic. A major contributor to its adverse effects is inflammation of the visceral adipose tissue (VAT). Life-long caloric restriction (CR), in contrast, results in extended lifespan, enhanced glucose tolerance/insulin sensitivity, and other favorable phenotypes. The effects of CR following obesity are incompletely established, but studies show multiple benefits. Many leukocyte types, macrophages predominantly, reside in VAT in homeostatic and pathological states. CR following obesity transiently increases VAT macrophage content prior to resolution of inflammation and obesity, suggesting that macrophage content and phenotype play critical roles. Here, we examined the heterogeneity of VAT leukocytes and the effects of obesity and CR. In general, our single-cell RNA-sequencing data demonstrate that macrophages are the most abundant and diverse subpopulation of leukocytes in VAT. Obesity induced significant transcriptional changes in all 15 leukocyte subpopulations, with many genes showing coordinated changes in expression across the leukocyte subpopulations. Additionally, obese VAT displayed expansion of one major macrophage subpopulation, which, in silico, was enriched in lipid binding and metabolic processes. This subpopulation returned from dominance in obesity to lean proportions after only 2 weeks of CR, although the pattern of gene expression overall remained similar. Surprisingly, CR VAT is dominated by a different macrophage subpopulation, which is absent in lean conditions. This subpopulation is enriched in genes related to phagocytosis and we postulate that its function includes clearance of dead cells, as well as excess lipids, contributing to limiting VAT inflammation and restoration of the homeostatic state.

Loss of periostin ameliorates adipose tissue inflammation and fibrosis in vivo

Recent evidence suggests that the accumulation of macrophages as a result of obesity-induced adipose tissue hypoxia is crucial for the regulation of tissue fibrosis, but the molecular mechanisms underlying adipose tissue fibrosis are still unknown. In this study, we revealed that periostin (Postn) is produced at extraordinary levels by adipose tissue after feeding with a high-fat diet (HFD). Postn was secreted at least from macrophages in visceral adipose tissue during the development of obesity, possibly due to hypoxia. Postn−/− mice had lower levels of crown-like structure formation and fibrosis in adipose tissue and were protected from liver steatosis. These mice also showed amelioration in systemic insulin resistance compared with HFD-fed WT littermates. Mice deficient in Postn in their hematopoietic compartment also had lower levels of inflammation in adipose tissue, in parallel with a reduction in ectopic lipid accumulation compared with the controls. Our data indicated that the regulation of Postn in visceral fat could be beneficial for the maintenance of healthy adipose tissue in obesity.

Evaluation of Visceral Adipose Tissue Oxygenation by Blood Oxygen Level-Dependent MRI in Zucker Diabetic Fatty Rats.

This study aimed to investigate the feasibility of blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) to evaluate visceral adipose tissue (VAT) oxygenation in Zucker diabetic fatty (ZDF) rats and its associations with systemic metaflammation. Five-week-old ZDF rats and Zucker lean (ZL) rats were fed a high-fat diet (HFD) for 18 weeks. A baseline BOLD-MRI scan of perirenal adipose tissue was performed after 8 weeks of HFD feeding, and then the rats were randomized to receive pioglitazone or a vehicle for the following 10 weeks. At sacrifice, BOLD-MRI scan, Hypoxyprobe-1 injection, and circulating T helper 17 (Th17), regulatory T (Treg) cells, and monocyte subtype flow cytometry analysis were performed. HFD feeding led to a significant increase in VAT BOLD-MRI R2* signals (20.14 ± 0.23 per second vs. 21.53 ± 0.20 per second; P = 0.012), an indicator for decreased oxygenation. R2* signal was significantly correlated with VAT pimonidazole adduct-positive area, insulin resistance, Th17 and Treg cells, CD43 + and CD43+ + monocyte subtypes, and VAT macrophage infiltration. Pioglitazone treatment improved the insulin resistance and was associated with a delayed progression of VAT oxygenation. This work demonstrated the feasibility of BOLD-MRI for detecting the VAT oxygenation status in ZDF rats, and the BOLD-MRI signals were associated with insulin resistance and systemic metaflammation in ZDF rats during the development of obesity.

Effect of dietary fish oil on selected inflammatory markers in pigs

The present study tested a hypothesis that dietary fish oil (eicosapentaenoic acid+docosahexaenoic acid) in a commonly achievable dose ameliorates a systemic inflammation in pigs. Two groups of pigs of 16 animals each were fed a diet with either 2.5% of fish oil (F) or a control diet with 2.5% of palm oil (P). After 70 days of fattening, eight F and eight P pigs were challenged (F+; P+) i.v. by lipopolysaccharide. After 3 h, all pigs were sacrificed and blood, liver and visceral adipose tissue (VAT) samples were taken. No significant effect (P>0.05) of dietary oil on the feed intake and daily weight gain was found out. Less neutrophils (16.8% v. 28.8%; P<0.05) were found in the F+-leukocytes of the peripheral blood; F+ pigs had lower (P<0.05) percentage of the swine leukocyte antigen-D-related CD163+ (SLA-DR+ CD163+) macrophages in the VAT (15.4% v. 21.8%) and lower expression of the SLA-DR-CD163+ surface molecules of the VAT macrophages. No difference (P>0.05) between F+ and P+ pigs in the peroxisome proliferator-activated receptor γ, GPR120, Adipor1 and Adipor2 (adiponectin receptor) gene expression, respectively, was established; plasma adiponectin was the same (21.1 ng/ml) in F+ and P+ pigs. In comparison with the P+ pigs, increased expression of the lipopolysaccharide-binding protein (LBP) gene and intercellular adhesion molecule 1 (ICAM1) gene was found out in the liver of the F+ pigs; expression of the tumor necrosis factor α (TNFα) gene was higher in the liver but lower in the VAT of the F+ pigs (P<0.05). The F+ pigs had higher (P<0.05) plasma concentration of both anti-inflammatory cytokine interleukin-4 (0.46 v. 0.04 ng/ml) and pro-inflammatory TNF-α (13.41 v. 7.72 ng/ml). It was concluded that dietary fish oil at the tested amount had a negligible effect on expression of the evaluated receptor genes and plasma adiponectin, and had an ambiguous effect on expression of cytokine genes and plasma cytokine levels.