Adipocyte death triggers a pro-inflammatory response and induces metabolic activation of resident macrophages

The endoplasmic reticulum stress protein GRP94 modulates cathepsin L activity in M2 macrophages in conditions of obesity-associated inflammation and contributes to their pro-inflammatory profile

BACKGROUND/OBJECTIVES

Adipose tissue macrophages (ATM) are key actors in the pathophysiology of obesity-related diseases. They have a unique intermediate M2-M1 phenotype which has been linked to endoplasmic reticulum (ER) stress. We previously reported that human M2 macrophages treated with the ER stress inducer thapsigargin switched to a pro-inflammatory phenotype that depended on the stress protein GRP94. In these conditions, GRP94 promoted cathepsin L secretion and was co-secreted with complement C3. As cathepsin L and complement C3 have been reported to play a role in the pathophysiology of obesity, in this work we studied the involvement of GRP94 in the pro-inflammatory phenotype of ATM.

METHODS

GRP94, cathepsin L and C3 expression were analyzed in CD206 + ATM from mice, WT or obesity-resistant transgenic fat-1, fed a high-fat diet (HFD) or a standard diet. GRP94 colocalization with cathepsin L and C3 and its effects were analyzed in human primary macrophages using thapsigargin as a control to induce ER stress and palmitic acid (PA) as a driver of metabolic activation.

RESULTS

In WT, but not in fat-1 mice, fed a HFD, we observed an increase in crown-like structures consisting of CD206 + pSTAT1+ macrophages showing high expression of GRP94 that colocalized with cathepsin L and C3. In vitro experiments showed that PA favored a M2-M1 switch depending on GRP94. This switch was prevented by omega-3 fatty acids. PA-induced GRP94-cathepsin L colocalization and a decrease in cathepsin L enzymatic activity within the cells (while the enzymatic activity in the extracellular medium was increased). These effects were prevented by the GRP94 inhibitor PU-WS13.

CONCLUSIONS

GRP94 is overexpressed in macrophages both in in vivo and in vitro conditions of obesity-associated inflammation and is involved in changing their profile towards a more pro-inflammatory profile. It colocalizes with complement C3 and cathepsin L and modulates cathepsin L activity.

Immunotherapy targeting the obese white adipose tissue microenvironment: Focus on non-communicable diseases

Obesity triggers inflammatory responses in the microenvironment of white adipose tissue, resulting in chronic systemic inflammation and the subsequent development of non-communicable diseases, including type 2 diabetes, coronary heart disease, and breast cancer. Current therapy approaches for obesity-induced non-communicable diseases persist in prioritizing symptom remission while frequently overlooking the criticality of targeting and alleviating inflammation at its source. Accordingly, this review highlights the importance of the microenvironment of obese white adipose tissue and the promising potential of employing immunotherapy to target it as an effective therapeutic approach for non-communicable diseases induced by obesity. Additionally, this review discusses the challenges and offers perspective about the immunotherapy targeting the microenvironment of obese white adipose tissue.

Nanomodulator-Mediated Restructuring of Adipose Tissue Immune Microenvironments for Antiobesity Treatment

In obesity, the interactions between proinflammatory macrophages and adipocytes in white adipose tissues are known to play a crucial role in disease progression by providing inflammatory microenvironments. Here, we report that the functional nanoparticle-mediated modulation of crosstalk between adipocytes and macrophages can remodel adipocyte immune microenvironments. As a functional nanomodulator, we designed antivascular cell adhesion molecule (VCAM)-1 antibody-conjugated and amlexanox-loaded polydopamine nanoparticles (VAPN). Amlexanox was used as a model drug to increase energy expenditure. Compared to nanoparticles lacking antibody modification or amlexanox, VAPN showed significantly greater binding to VCAM-1-expressing adipocytes and lowered the interaction of adipocytes with macrophages. In high fat diet-fed mice, repeated subcutaneous administration of VAPN increased the populations of beige adipocytes and ameliorated inflammation in white adipose tissues. Moreover, the localized application of VAPN in vivo exerted a systemic metabolic effect and reduced metabolic disorders, including insulin tolerance and liver steatosis. These findings suggested that VAPN had potential to modulate the immune microenvironments of adipose tissues for the immunologic treatment of obesity. Although we used amlexanox as a model drug and anti-VCAM-1 antibody in VAPN, the concept of immune nanomodulators can be widely applied to the immunological treatment of obesity.

TM4SF19-mediated control of lysosomal activity in macrophages contributes to obesity-induced inflammation and metabolic dysfunction

Adipose tissue (AT) adapts to overnutrition in a complex process, wherein specialized immune cells remove and replace dysfunctional and stressed adipocytes with new fat cells. Among immune cells recruited to AT, lipid-associated macrophages (LAMs) have emerged as key players in obesity and in diseases involving lipid stress and inflammation. Here, we show that LAMs selectively express transmembrane 4 L six family member 19 (TM4SF19), a lysosomal protein that represses acidification through its interaction with Vacuolar-ATPase. Inactivation of TM4SF19 elevates lysosomal acidification and accelerates the clearance of dying/dead adipocytes in vitro and in vivo. TM4SF19 deletion reduces the LAM accumulation and increases the proportion of restorative macrophages in AT of male mice fed a high-fat diet. Importantly, male mice lacking TM4SF19 adapt to high-fat feeding through adipocyte hyperplasia, rather than hypertrophy. This adaptation significantly improves local and systemic insulin sensitivity, and energy expenditure, offering a potential avenue to combat obesity-related metabolic dysfunction.

Vitamin D and obesity

An inverse association between vitamin D status and obesity has been reported across diverse populations and age groups in humans. In animal model of diet-induced obesity, dysregulation of vitamin D metabolism has been observed. However, the causal relationship between vitamin D status and obesity is not conclusive. Several explanations, such as volumetric dilution, sequestration of vitamin D into adipose tissue, and limited sunlight exposure, have been suggested as the underlying mechanisms linking poor vitamin D status and obesity. Vitamin D can modulate adipose tissue biology, spanning from adipocyte differentiation to adipocyte apoptosis and energy metabolism, indicating its potential impact on adiposity. In this chapter, we will review the prevalence of vitamin D deficiency and determinants of vitamin D deficiency among different populations, as well as changes in vitamin D metabolism associated with obesity. Additionally, we will review vitamin D's regulation of adipogenesis and lipogenesis at the cellular level in order to gain a deeper understanding of the underlying mechanisms linking vitamin D levels and obesity.

Histological Comparison of Nanofat and Lipoconcentrate: Enhanced Effects of Lipoconcentrate on Adipogenesis and Angiogenesis

BACKGROUND

Nanofat and lipoconcentrate contain adipose-derived stem cells and growth factors, and have wide clinical applications in the regenerative field. This study aimed to investigate the microenvironmental changes associated with nanofat and lipoconcentrate.

METHODS

Conventional fat, nanofat, or lipoconcentrate (0.2 mL each, n = 5 per group) were injected subcutaneously into the dorsal flanks of athymic nude mice. The graft weights were measured at postoperative week 4; the grafts and their overlying skin were used for histological analyses.

RESULTS

Weights of the lipoconcentrate grafts were significantly greater than those of the conventional fat (p < 0.05) and nanofat (p < 0.01) grafts. There was no significant difference in inflammation, oil cysts, and fibrosis between the conventional fat and nanofat groups. Histological examination of the lipoconcentrate grafts showed less macrophage infiltration and the formation of fibrosis and oil cysts. Additionally, adipogenesis and angiogenesis were induced more in the lipoconcentrate grafts than in the nanofat grafts (p < 0.01). Lipoconcentrate and nanofat improved dermal thickness (p < 0.001 and p < 0.01, respectively, versus the baseline).

CONCLUSION

Lipoconcentrate grafts had greater volume and shape retention than conventional fat and nanofat grafts. They had better histological structure and acted as scaffolds for adipogenesis and angiogenesis. Both products showed regenerative effects on dermal thickness; however, only lipoconcentrate grafts had the required volume and regenerative effects, allowing it to serve as a novel adipose-free grafting method for facial rejuvenation and contouring.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Lipid parameters, adipose tissue distribution and prognosis prediction in chronic kidney Disease patients

BACKGROUND

Lipid management in clinic is critical to the prevention and treatment of Chronic kidney disease (CKD), while the manifestations of lipid indicators vary in types and have flexible association with CKD prognosis.

PURPOSE

Explore the associations between the widely used indicators of lipid metabolism and their distribution in clinic and CKD prognosis; provide a reference for lipid management and inform treatment decisions for patients with non-dialysis CKD stage 3-5.

METHODS

This is a retrospective cohort study utilizing the Self-Management Program for Patients with Chronic Kidney Disease Cohort (SMP-CKD) database of 794 individuals with CKD stages 3-5. It covers demographic data, clinical diagnosis and medical history collection, laboratory results, circulating lipid profiles and lipid distribution assessments. Primary endpoint was defined as a composite outcome(the initiation of chronic dialysis or renal transplantation, sustained decline of 40% or more in estimated glomerular filtration rate (eGFR), doubled of serum creatinine (SCr) from the baseline, eGFR less than 5 mL/min/1.73m2, or all-cause mortality). Exposure variables were circulating lipid profiles and lipid distribution measurements. Association were assessed using Relative risks (RRs) (95% confidence intervals (CIs)) computed by multivariate Poisson models combined with least absolute shrinkage and selection operator (LASSO) regression according to categories of lipid manifestations. The best model was selected via akaike information criterion (AIC), area under curve (AUC), receiver operating characteristic curve (ROC) and net reclassification index (NRI). Subgroup analysis and sensitivity analysis were performed to assess the interaction effects and robustness..

RESULTS

255 individuals reached the composite outcome. Median follow-up duration was 2.03 [1.06, 3.19] years. Median age was 58.8 [48.7, 67.2] years with a median eGFR of 33.7 [17.6, 47.8] ml/min/1.73 m2. Five dataset were built after multiple imputation and five category-based Possion models were constructed for each dataset. Model 5 across five datasets had the best fitness with smallest AIC and largest AUC. The pooled results of Model 5 showed that total cholesterol (TC) (RR (95%CI) (per mmol/L) :1.143[1.023,1.278], P = 0.018) and percentage of body fat (PBF) (RR (95%CI) (per percentage):0.976[0.961,0.992], P = 0.003) were significant factors of composite outcome. The results indicated that comprehensive consideration of lipid metabolism and fat distribution is more critical in the prediction of CKD prognosis..

CONCLUSION

Comprehensive consideration of lipid manifestations is optimal in predicting the prognosis of individuals with non-dialysis CKD stages 3-5.

Whole-Mount Imaging of Adipose Tissue Macrophages

The adipose tissue comprises highly heterogeneous macrophage populations, which play critical roles in the regulation of adipose tissue function and dysfunction during health and disease. Whole-amount staining is a powerful technique for macrophage characterization within the 3D environment of the adipose tissue, enabling the visualization of different macrophage populations and their interaction with other cells within their in vivo niche. Due to the high-fat content and softness, freezing and sectioning of adipose tissue is difficult, and distortion of tissue morphology typically occurs, especially in the case of white adipose tissue. We describe here a whole-mount staining alternative for adipose tissue imaging that preserves all structures and allows high-resolution image acquisition. We address in a step-by-step manner how to perform immunofluorescence staining of different fat pads and how to optimally visualize cellular and acellular (extracellular matrix) constituents of the adipose tissue and its vasculature, as well as resident and infiltrating macrophage populations.

Unique adipose tissue invariant natural killer T cell subpopulations control adipocyte turnover in mice

Adipose tissue invariant natural killer T (iNKT) cells are a crucial cell type for adipose tissue homeostasis in obese animals. However, heterogeneity of adipose iNKT cells and their function in adipocyte turnover are not thoroughly understood. Here, we investigate transcriptional heterogeneity in adipose iNKT cells and their hierarchy using single-cell RNA sequencing in lean and obese mice. We report that distinct subpopulations of adipose iNKT cells modulate adipose tissue homeostasis through adipocyte death and birth. We identify KLRG1+ iNKT cells as a unique iNKT cell subpopulation in adipose tissue. Adoptive transfer experiments showed that KLRG1+ iNKT cells are selectively generated within adipose tissue microenvironment and differentiate into a CX3CR1+ cytotoxic subpopulation in obese mice. In addition, CX3CR1+ iNKT cells specifically kill enlarged and inflamed adipocytes and recruit macrophages through CCL5. Furthermore, adipose iNKT17 cells have the potential to secrete AREG, and AREG is involved in stimulating adipose stem cell proliferation. Collectively, our data suggest that each adipose iNKT cell subpopulation plays key roles in the control of adipocyte turnover via interaction with adipocytes, adipose stem cells, and macrophages in adipose tissue.

Fast histological assessment of adipose tissue inflammation by label-free mid-infrared optoacoustic microscopy

Conventional histology, as well as immunohistochemistry or immunofluorescence, enables the study of morphological and phenotypical changes during tissue inflammation with single-cell accuracy. However, although highly specific, such techniques require multiple time-consuming steps to apply exogenous labels, which might result in morphological deviations from native tissue structures. Unlike these techniques, mid-infrared (mid-IR) microspectroscopy is a label-free optical imaging method that retrieves endogenous biomolecular contrast without altering the native composition of the samples. Nevertheless, due to the strong optical absorption of water in biological tissues, conventional mid-IR microspectroscopy has been limited to dried thin (5-10 µm) tissue preparations and, thus, it also requires time-consuming steps-comparable to conventional imaging techniques. Here, as a step towards label-free analytical histology of unprocessed tissues, we applied mid-IR optoacoustic microscopy (MiROM) to retrieve intrinsic molecular contrast by vibrational excitation and, simultaneously, to overcome water-tissue opacity of conventional mid-IR imaging in thick (mm range) tissues. In this proof-of-concept study, we demonstrated application of MiROM for the fast, label-free, non-destructive assessment of the hallmarks of inflammation in excised white adipose tissue; i.e., formation of crown-like structures and changes in adipocyte morphology.

Pathophysiological Links Between Obesity and Dementia

Obesity is a major global health concern, with prevalence rates rapidly rising due to increased availability of highly processed foods rich in fats and/or sugars and technological advances promoting more sedentary behaviour. There is increasing evidence to suggest that obesity predisposes individuals to developing cognitive impairment and dementia. However, the relationship between the brain and the peripheral metabolic state is complex, and many of the underlying mechanisms of cognitive impairment in obesity are yet to be fully elucidated. To better understand the links between obesity and dementia, further work is required to determine pathological changes occurring in the brain during obesity. In this mini-review, we discuss the role of two pathological features of obesity (the gut-brain axis and systemic inflammation) and their potential contribution to dementia.

Visceral adipocyte size links obesity with dysmetabolism more than fibrosis, and both can be estimated by circulating miRNAs

OBJECTIVE

In obesity, adipocyte hypertrophy is detrimental to health, but its' interrelation with fibrosis in the visceral adipose tissue (VAT) depot remains unclear. Because VAT is less accessible via biopsy, biomarkers for VAT quality are needed. The authors hypothesized that VAT adipocyte size and fibrosis are interrelated and can be estimated by circulating microRNAs (circ-miRNAs), contributing to subphenotyping obesity.

METHODS

Adipocyte size and AT fibrosis were estimated in n = 43 participants (BMI ≥ 30 kg/m2 ). Circ-miRNAs were sequenced (Next Generation Sequencing).

RESULTS

Participants with above- versus below-median VAT adipocyte area exhibited metabolic dysfunction but lower total and pericellular fibrosis. VAT adipocyte size remained associated with metabolic dysfunction even when controlling for BMI or VAT fibrosis in the entire cohort, as in matched-pairs subanalyses. Next Generation Sequencing uncovered 22 and 6 circ-miRNAs associated with VAT adipocyte size and fibrosis, respectively, with miRNA-130b-3p common to both analyses. The combination of miRNA-130b-3p + miR-150-5p + high-density lipoprotein cholesterol discriminated among those with large versus small VAT adipocytes (receiver operating characteristic-area under the curve: 0.872 [95% CI: 0.747-0.996]), whereas miRNA-130b-3p + miRNA-15a-5p + high-density lipoprotein cholesterol discriminated among those with low and high fibrosis (receiver operating characteristic-area under the curve: 0.823 [95% CI: 0.676-0.97]).

CONCLUSIONS

These findings suggest that VAT adipocyte size and fibrosis are inversely correlated in obesity and can be estimated by distinct circ-miRNAs, providing a potential tool to subphenotype obesity via a liquid biopsy-like approach to assess VAT health in nonsurgical patients.

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

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

Long-term dasatinib plus quercetin effects on aging outcomes and inflammation in nonhuman primates: implications for senolytic clinical trial design

Cellular senescence increases with aging and results in secretion of pro-inflammatory factors that induce local and systemic tissue dysfunction. We conducted the first preclinical trial in a relevant middle-aged nonhuman primate (NHP) model to allow estimation of the main translatable effects of the senolytic combination dasatinib (D) and quercetin (Q), with and without caloric restriction (CR). A multi-systemic survey of age-related changes, including those on immune cells, adipose tissue, the microbiome, and biomarkers of systemic organ and metabolic health are reported. Age-, weight-, sex-, and glycemic control-matched NHPs (D + Q, n = 9; vehicle [VEH] n = 7) received two consecutive days of D + Q (5 mg/kg + 50 mg/kg) monthly for 6 months, where in month six, a 10% CR was implemented in both D + Q and VEH NHPs to induce equal weight reductions. D + Q reduced senescence marker gene expressions in adipose tissue and circulating PAI-1 and MMP-9. Improvements were observed in immune cell types with significant anti-inflammatory shifts and reductions in microbial translocation biomarkers, despite stable microbiomes. Blood urea nitrogen showed robust improvements with D + Q. CR resulted in significant positive body composition changes in both groups with further improvement in immune cell profiles and decreased GDF15 (p = 0.05), and the interaction of D + Q and CR dramatically reduced glycosylated hemoglobin A1c (p = 0.03). This work indicates that 6 months of intermittent D + Q exposure is safe and may combat inflammaging via immune benefits and improved intestinal barrier function. We also saw renal benefits, and with CR, improved metabolic health. These data are intended to provide direction for the design of larger controlled intervention trials in older patients.

Selective reduction of visceral adipose tissue with injectable ice slurry

Reduction in visceral adipose tissue (VAT) mass reduces body weight and metabolic disease risk in obese patients. However surgical removal of VAT is highly invasive and thus not clinically feasible. We developed an injectable ice slurry for selective reduction of adipose tissue through cryolipolysis. The aim of this study was to investigate safety, feasibility and mechanism of ice slurry-induced cryolipolysis of VAT. Perigonadal VAT in diet-induced obese mice and rats was subjected to slurry or sham treatment. Body weight and blood chemistry were monitored for 56 days post-treatment. Histological analysis and molecular studies were performed to elucidate mechanisms of fat reduction. Treatment of VAT was well tolerated in all animals. Slurry induced adipocyte cell death via selective cryolipolysis; significant weight loss was noted at day 21 post-treatment. RNA sequencing from treated VAT samples showed increased expression of genes involved in inflammation, immune response, collagen biosynthesis and wound healing, and decreased expression of adipokines. This study demonstrates that slurry treatment is safe and effective in inducing cryolipolysis of VAT and subsequent weight loss in mice. Ice slurry is promising as a minimally-invasive treatment to reduce visceral adipose tissue.

Efferocytosis: An Emerging Therapeutic Strategy for Type 2 Diabetes Mellitus and Diabetes Complications

Increasing evidence indicates that chronic, low-grade inflammation is a significant contributor to the fundamental pathogenesis of type 2 diabetes mellitus (T2DM). Efferocytosis, an effective way to eliminate apoptotic cells (ACs), plays a critical role in inflammation resolution. Massive accumulation of ACs and the proliferation of persistent inflammation caused by defective efferocytosis have been proven to be closely associated with pancreatic islet β cell destruction, adipose tissue inflammation, skeletal muscle dysfunction, and liver metabolism abnormalities, which together are considered the most fundamental pathological mechanism underlying T2DM. Therefore, here we outline the association between the molecular mechanisms of efferocytosis in glucose homeostasis, T2DM, and its complications, and we analyzed the present constraints and potential future prospects for therapeutic targets in T2DM and its complications.

Leptin: A Heavyweight Player in Obesity-Related Cancers

Obesity, defined as the abnormal or excessive expansion of white adipose tissue, has reached pandemic proportions and is recognized as an important health concern since it is a common root for several comorbidities, including malignancies. Indeed, the current knowledge of the white adipose tissue, which shifts its role from an energy storage tissue to an important endocrine and metabolic organ, has opened up new avenues for the discovery of obesity's effects on tumor biology. In this review, we will report the epidemiological studies concerning the strong impact of obesity in several types of cancer and describe the mechanisms underlying the heterotypic signals between cancer cell lines and adipocytes, with particular emphasis on inflammation, the insulin/IGF-1 axis, and adipokines. Among the adipokines, we will further describe the in vitro, in vivo, and clinical data concerning the role of leptin, recognized as one of the most important mediators of obesity-associated cancers. In fact, leptin physiologically regulates energy metabolism, appetite, and reproduction, and several studies have also described the role of leptin in affecting cancer development and progression. Finally, we will summarize the newest pharmacological strategies aimed at mitigating the protumorigenic effects of leptin, underlining their mechanisms of action.

NOD-like Receptors-Emerging Links to Obesity and Associated Morbidities

Obesity and its associated metabolic morbidities have been and still are on the rise, posing a major challenge to health care systems worldwide. It has become evident over the last decades that a low-grade inflammatory response, primarily proceeding from the adipose tissue (AT), essentially contributes to adiposity-associated comorbidities, most prominently insulin resistance (IR), atherosclerosis and liver diseases. In mouse models, the release of pro-inflammatory cytokines such as TNF-alpha (TNF-α) and interleukin (IL)-1β and the imprinting of immune cells to a pro-inflammatory phenotype in AT play an important role. However, the underlying genetic and molecular determinants are not yet understood in detail. Recent evidence demonstrates that nucleotide-binding and oligomerization domain (NOD)-like receptor (NLR) family proteins, a group of cytosolic pattern recognition receptors (PRR), contribute to the development and control of obesity and obesity-associated inflammatory responses. In this article, we review the current state of research on the role of NLR proteins in obesity and discuss the possible mechanisms leading to and the outcomes of NLR activation in the obesity-associated morbidities IR, type 2 diabetes mellitus (T2DM), atherosclerosis and non-alcoholic fatty liver disease (NAFLD) and discuss emerging ideas about possibilities for NLR-based therapeutic interventions of metabolic diseases.

Obesity, Preserved Ejection Fraction Heart Failure, and Left Ventricular Remodeling

Owing to the overwhelming obesity epidemic, preserved ejection fraction heart failure commonly ensues in patients with severe obesity and the obese phenotype of preserved ejection fraction heart failure is now commonplace in clinical practice. Severe obesity and preserved ejection fraction heart failure share congruent cardiovascular, immune, and renal derangements that make it difficult to ascertain whether the obese phenotype of preserved ejection fraction heart failure is the convergence of two highly prevalent conditions or severe obesity enables the development and progression of the syndrome of preserved ejection fraction heart failure. Nevertheless, the obese phenotype of preserved ejection fraction heart failure provides a unique opportunity to assess whether sustained and sizeable loss of excess body weight via metabolic bariatric surgery reverses the concentric left ventricular remodeling that patients with preserved ejection fraction heart failure commonly display.

Adipose Tissue Macrophage-Mediated Inflammation in Obesity: A Link to Posttranslational Modification

Adipose tissue macrophages (ATM) are an essential type of immune cells in adipose tissue. Obesity induces the inflammation of adipose tissues, as expressed by ATM accumulation, that is more likely to become a source of systemic metabolic diseases, including insulin resistance. The process is characterized by the transcriptional regulation of inflammatory pathways by virtue of signaling molecules such as cytokines and free fatty acids. Notably, posttranslational modification (PTM) is a key link for these signaling molecules to trigger the proinflammatory or anti-inflammatory phenotype of ATMs. This review focuses on summarizing the functions and molecular mechanisms of ATMs regulating inflammation in obese adipose tissue. Furthermore, the role of PTM is elaborated, hoping to identify new horizons of treatment and prevention for obesity-mediated metabolic disease.

Adipose tissue macrophages and their role in obesity-associated insulin resistance: an overview of the complex dynamics at play

Obesity, a major global health concern, is characterized by serious imbalance between energy intake and expenditure leading to excess accumulation of fat in adipose tissue (AT). A state of chronic low-grade AT inflammation is prevalent during obesity. The adipose tissue macrophages (ATM) with astounding heterogeneity and complex regulation play a decisive role in mediating obesity-induced insulin resistance. Adipose-derived macrophages were broadly classified as proinflammatory M1 and anti-inflammatory M2 subtypes but recent reports have proclaimed several novel and intermediate profiles, which are crucial in understanding the dynamics of macrophage phenotypes during development of obesity. Lipid-laden hypertrophic adipocytes release various chemotactic signals that aggravate macrophage infiltration into AT skewing toward mostly proinflammatory status. The ratio of M1-like to M2-like macrophages is increased substantially resulting in copious secretion of proinflammatory mediators such as TNFα, IL-6, IL-1β, MCP-1, fetuin-A (FetA), etc. further worsening insulin resistance. Several AT-derived factors could influence ATM content and activation. Apart from being detrimental, ATM exerts beneficial effects during obesity. Recent studies have highlighted the prime role of AT-resident macrophage subpopulations in not only effective clearance of excess fat and dying adipocytes but also in controlling vascular integrity, adipocyte secretions, and fibrosis within obese AT. The role of ATM subpopulations as friend or foe is determined by an intricate interplay of such factors arising within hyperlipidemic microenvironment of obese AT. The present review article highlights some of the key research advances in ATM function and regulation, and appreciates the complex dynamics of ATM in the pathophysiologic scenario of obesity-associated insulin resistance.

The Role of IL-13 and IL-4 in Adipose Tissue Fibrosis

White adipose tissue (WAT) fibrosis, characterized by an excess of extracellular (ECM) matrix components, is strongly associated with WAT inflammation and dysfunction due to obesity. Interleukin (IL)-13 and IL-4 were recently identified as critical mediators in the pathogenesis of fibrotic diseases. However, their role in WAT fibrosis is still ill-defined. We therefore established an ex vivo WAT organotypic culture system and demonstrated an upregulation of fibrosis-related genes and an increase of α-smooth muscle actin (αSMA) and fibronectin abundance upon dose-dependent stimulation with IL-13/IL-4. These fibrotic effects were lost in WAT lacking il4ra, which encodes for the underlying receptor controlling this process. Adipose tissue macrophages were found to play a key role in mediating IL-13/IL-4 effects in WAT fibrosis as their depletion through clodronate dramatically decreased the fibrotic phenotype. IL-4-induced WAT fibrosis was partly confirmed in mice injected intraperitoneally with IL-4. Furthermore, gene correlation analyses of human WAT samples revealed a strong positive correlation of fibrosis markers with IL-13/IL-4 receptors, whereas IL13 and IL4 correlations failed to confirm this association. In conclusion, IL-13 and IL-4 can induce WAT fibrosis ex vivo and partly in vivo, but their role in human WAT remains to be further elucidated.

Overview of Cellular and Soluble Mediators in Systemic Inflammation Associated with Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is currently the most prevalent chronic liver disease in Western countries, affecting approximately 25% of the adult population. This condition encompasses a spectrum of liver diseases characterized by abnormal accumulation of fat in liver tissue (non-alcoholic fatty liver, NAFL) that can progress to non-alcoholic steatohepatitis (NASH), characterized by the presence of liver inflammation and damage. The latter form often coexists with liver fibrosis which, in turn, may progress to a state of cirrhosis and, potentially, hepatocarcinoma, both irreversible processes that often lead to the patient's death and/or the need for liver transplantation. Along with the high associated economic burden, the high mortality rate among NAFLD patients raises interest, not only in the search for novel therapeutic approaches, but also in early diagnosis and prevention to reduce the incidence of NAFLD-related complications. In this line, an exhaustive characterization of the immune status of patients with NAFLD is mandatory. Herein, we attempted to gather and compare the current and relevant scientific evidence on this matter, mainly on human reports. We addressed the current knowledge related to circulating cellular and soluble mediators, particularly platelets, different leukocyte subsets and relevant inflammatory soluble mediators.

Adipose tissue aging is regulated by an altered immune system

Adipose tissue is a widely distributed organ that plays a critical role in age-related physiological dysfunctions as an important source of chronic sterile low-grade inflammation. Adipose tissue undergoes diverse changes during aging, including fat depot redistribution, brown and beige fat decrease, functional decline of adipose progenitor and stem cells, senescent cell accumulation, and immune cell dysregulation. Specifically, inflammaging is common in aged adipose tissue. Adipose tissue inflammaging reduces adipose plasticity and pathologically contributes to adipocyte hypertrophy, fibrosis, and ultimately, adipose tissue dysfunction. Adipose tissue inflammaging also contributes to age-related diseases, such as diabetes, cardiovascular disease and cancer. There is an increased infiltration of immune cells into adipose tissue, and these infiltrating immune cells secrete proinflammatory cytokines and chemokines. Several important molecular and signaling pathways mediate the process, including JAK/STAT, NFκB and JNK, etc. The roles of immune cells in aging adipose tissue are complex, and the underlying mechanisms remain largely unclear. In this review, we summarize the consequences and causes of inflammaging in adipose tissue. We further outline the cellular/molecular mechanisms of adipose tissue inflammaging and propose potential therapeutic targets to alleviate age-related problems.

The PI3K/Akt Pathway in Meta-Inflammation

Obesity is a global epidemic representing a serious public health burden as it is a major risk factor for the development of cardiovascular disease, stroke and all-cause mortality. Chronic low-grade systemic inflammation, also known as meta-inflammation, is thought to underly obesity's negative health consequences, which include insulin resistance and the development of type 2 diabetes. Meta-inflammation is characterized by the accumulation of immune cells in adipose tissue, a deregulation in the synthesis and release of adipokines and a pronounced increase in the production of proinflammatory factors. In this state, the infiltration of macrophages and their metabolic activation contributes to complex paracrine and autocrine signaling, which sustains a proinflammatory microenvironment. A key signaling pathway mediating the response of macrophages and adipocytes to a microenvironment of excessive nutrients is the phosphoinositide 3-kinase (PI3K)/Akt pathway. This multifaceted network not only transduces metabolic information but also regulates macrophages' intracellular changes, which are responsible for their phenotypic switch towards a more proinflammatory state. In the present review, we discuss how the crosstalk between macrophages and adipocytes contributes to meta-inflammation and provide an overview on the involvement of the PI3K/Akt signaling pathway, and how its impairment contributes to the development of insulin resistance.

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.

Combined genetic deletion of GDF15 and FGF21 has modest effects on body weight, hepatic steatosis and insulin resistance in high fat fed mice

OBJECTIVES

Obesity in humans and mice is associated with elevated levels of two hormones responsive to cellular stress, namely GDF15 and FGF21. Over-expression of each of these is associated with weight loss and beneficial metabolic changes but where they are secreted from and what they are required for physiologically in the context of overfeeding remains unclear.

METHODS

Here we used tissue selective knockout mouse models and human transcriptomics to determine the source of circulating GDF15 in obesity. We then generated and characterized the metabolic phenotypes of GDF15/FGF21 double knockout mice.

RESULTS

Circulating GDF15 and FGF21 are both largely derived from the liver, rather than adipose tissue or skeletal muscle, in obese states. Combined whole body deletion of FGF21 and GDF15 does not result in any additional weight gain in response to high fat feeding but it does result in significantly greater hepatic steatosis and insulin resistance than that seen in GDF15 single knockout mice.

CONCLUSIONS

Collectively the data suggest that overfeeding activates a stress response in the liver which is the major source of systemic rises in GDF15 and FGF21. These hormones then activate pathways which reduce this metabolic stress.

Inflammation: the incubator of the tumor microenvironment

An inflammatory microenvironment, either conferred by an underlying chronic overt or smoldering inflammatory condition constitutes a prerequisite and fuel to essentially all cancers. The complex reciprocal interplay of different cell types in the tumor microenvironment (TME) determines patient outcome. Apart from the actual tumor cells, local and recruited nonmalignant cells as well as the intestinal microbiome actively shape polarization and plasticity of cells in the TME, thereby augmenting protumorigenic and prometastatic inflammatory processes. Here, we address the universality of inflammation in carcinogenesis, review distinct forms of tumor related inflammation and highlight critical processes in the TME actively sustaining a nurturing incubator for cancer progression and therapy resistance.

UCP2 KO mice exhibit ameliorated obesity and inflammation induced by high-fat diet feeding

Uncoupling protein 2 (Ucp2) was first introduced as a member of Uncoupling protein family and a regulator of ROS formation; however, its role in adipose tissue is not fully understood. In the present study, we have investigated the role of Ucp2 against high-fat diet (HFD)-induced obesity in epididymal white adipose tissue (eWAT) and browning of inguinal white adipose tissue (iWAT). Diet-induced obesity is closely related to macrophage infiltration and the secretion of pro-inflammatory cytokines. Macrophages surround adipocytes and form a crown-like-structure (CLS). Some reports have suggested that CLS formation requires adipocyte apoptosis. After 12 weeks of HFD challenge, Ucp2 knockout (KO) mice maintained relatively lean phenotypes compared to wild-type (WT) mice. In eWAT, macrophage infiltration, CLS formation, and inflammatory cytokines were reduced in HFD KO mice compared to HFD WT mice. Surprisingly, we found that apoptotic signals were also reduced in the Ucp2 KO mice. Our study suggests that Ucp2 deficiency may prevent diet-induced obesity by regulating adipocyte apoptosis. However, Ucp2 deficiency did not affect the browning capacity of iWAT.

Palmitoleic Acid Acts on Adipose-Derived Stromal Cells and Promotes Anti-Hypertrophic and Anti-Inflammatory Effects in Obese Mice

Adipose tissue (AT) secretes adipokines, modulators of low-grade chronic inflammation in obesity. Molecules that induce the emergence of new and functional adipocytes in AT can alleviate or prevent inflammatory and metabolic disorders. The objective of this study was to investigate the role of palmitoleic acid (n7) in 3T3-L1 and primary pre-adipocyte differentiation and AT inflammation. C57BL/6j mice were submitted to a control or high-fat diet (HFD) for 8 weeks, and treated with n7 for 4 weeks. Mice consuming a HFD presented an increase in body weight, epididymal (Epi) fat mass, and Epi adipocytes size. N7 treatment attenuated the body weight gain and completely prevented the hypertrophy of Epi adipocytes, but not the increment in Epi mass induced by the HFD, suggesting a greater adipocytes hyperplasia in animals treated with n7. It was agreed that n7 increased 3T3-L1 proliferation and differentiation, as well as the expression of genes involved in adipogenesis, such as Cebpa, Pparg, aP2, Perilipin, and Scl2a4. Furthermore, n7 decreased the inflammatory cytokines Mcp1, Tnfa, Il6, Cxcl10, and Nos2 genes in Epi vascular stromal cells, but not in the whole AT. These findings show that n7 exerts anti-hypertrophic effects in adipocytes which influence the surrounding cells by attenuating the overexpression of pro-inflammatory cytokines triggered by a HFD.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

Discovery and functional assessment of a novel adipocyte population driven by intracellular Wnt/β-catenin signaling in mammals

Wnt/β-catenin signaling has been well established as a potent inhibitor of adipogenesis. Here, we identified a population of adipocytes that exhibit persistent activity of Wnt/β-catenin signaling, as revealed by the Tcf/Lef-GFP reporter allele, in embryonic and adult mouse fat depots, named as Wnt⁺ adipocytes. We showed that this β-catenin-mediated signaling activation in these cells is Wnt ligand- and receptor-independent but relies on AKT/mTOR pathway and is essential for cell survival. Such adipocytes are distinct from classical ones in transcriptomic and genomic signatures and can be induced from various sources of mesenchymal stromal cells including human cells. Genetic lineage-tracing and targeted cell ablation studies revealed that these adipocytes convert into beige adipocytes directly and are also required for beige fat recruitment under thermal challenge, demonstrating both cell autonomous and non-cell autonomous roles in adaptive thermogenesis. Furthermore, mice bearing targeted ablation of these adipocytes exhibited glucose intolerance, while mice receiving exogenously supplied such cells manifested enhanced glucose utilization. Our studies uncover a unique adipocyte population in regulating beiging in adipose tissues and systemic glucose homeostasis.

Pharmacological manipulation of macrophage autophagy effectively rejuvenates the regenerative potential of biodegrading vascular graft in aging body

Declined regenerative potential and aggravated inflammation upon aging create an inappropriate environment for arterial regeneration. Macrophages are one of vital effector cells in the immune microenvironment, especially during biomaterials mediated repairing process. Here, we revealed that the macrophage autophagy decreased with aging, which led to aggravated inflammation, thereby causing poor vascular remodeling of artificial grafts in aging body. Through loading the autophagy-targeted drugs, rapamycin and 3-MA (3-methyladenine), in PCL (polycaprolactone) sheath of the PGS (poly glycerol sebacate) - PCL vascular graft, the essential role of macrophage autophagy was confirmed in regulating macrophage polarization and biomaterial degradation. Moreover, the utilization of rapamycin promoted anti-inflammatory polarization of macrophage by activating autophagy, which further promoted myogenic differentiation of vascular progenitor cells and accelerated endothelialization. Our study elucidated the contribution of pharmacological manipulation of macrophage autophagy in promoting regeneration of small caliber artery, which may pave a new avenue for clinical translation of vascular grafts in aging body.

Obesity and Leptin Resistance in the Regulation of the Type I Interferon Early Response and the Increased Risk for Severe COVID-19

Obesity, and obesity-associated conditions such as hypertension, chronic kidney disease, type 2 diabetes, and cardiovascular disease, are important risk factors for severe Coronavirus disease-2019 (COVID-19). The common denominator is metaflammation, a portmanteau of metabolism and inflammation, which is characterized by chronically elevated levels of leptin and pro-inflammatory cytokines. These induce the “Suppressor Of Cytokine Signaling 1 and 3” (SOCS1/3), which deactivates the leptin receptor and also other SOCS1/3 sensitive cytokine receptors in immune cells, impairing the type I and III interferon early responses. By also upregulating SOCS1/3, Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 adds a significant boost to this. The ensuing consequence is a delayed but over-reactive immune response, characterized by high-grade inflammation (e.g., cytokine storm), endothelial damage, and hypercoagulation, thus leading to severe COVID-19. Superimposing an acute disturbance, such as a SARS-CoV-2 infection, on metaflammation severely tests resilience. In the long run, metaflammation causes the “typical western” conditions associated with metabolic syndrome. Severe COVID-19 and other serious infectious diseases can be added to the list of its short-term consequences. Therefore, preventive measures should include not only vaccination and the well-established actions intended to avoid infection, but also dietary and lifestyle interventions aimed at improving body composition and preventing or reversing metaflammation.

Effects of co-incubation of LPS-stimulated RAW 264.7 macrophages on leptin production by 3T3-L1 adipocytes: a method for co-incubating distinct adipose tissue cell lines

BACKGROUND

Adipose tissue is a major endocrine organ capable of releasing inflammatory adipokines that are linked to changes occurring in the overfed state, where tissue remodeling results in hypertrophic adipocytes that recruit monocytes to infiltrate the tissue and take on an inflammatory phenotype. Increases in macrophage-specific inflammatory mediator levels contribute to the inflamed state and worsen the inflammatory loop between the macrophages and adipocytes. Although most inflammatory adipokines are released by macrophages, adipocytes can also release immunomodulatory adipokines, such as leptin. The objective of this research was to determine if co-incubation of activated macrophages with mature adipocytes, using transwell inserts, affected adipocyte leptin release. We also examined if there were differences in levels of cell-secreted products quantified in cell-conditioned media collected from macrophage-containing (transwell insert) and adipocyte-containing (well) compartments.

METHODS

Mature adipocytes were co-incubated with control and lipopolysaccharide-stimulated (0.01 mg/ml) murine macrophages, and nitric oxide, interleukin-6, and leptin levels were quantified in the cell-conditioned media from both compartments.

RESULTS

Activation status of the macrophages did not affect leptin release by the adipocytes. We observed higher amounts of leptin in wells compared to transwells. Nitric oxide and interleukin-6 levels were similar between transwells and wells, suggesting that these adipokines travel through the transwell inserts and are reaching equilibrium between the two compartments.

CONCLUSION

Our results suggest that co-incubating activated macrophages and adipocytes using transwell inserts can result in distinct microenvironments in the different cellular compartments and that separate sampling of these compartments is required to detect the subtle signaling dynamics that exist between these cells.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s42269-022-00747-7.

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

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

The Role of T Cells in Obesity-Associated Inflammation and Metabolic Disease

Chronic inflammation plays a critical role in the development of obesity-associated metabolic disorders such as insulin resistance. Obesity alters the microenvironment of adipose tissue and the intestines from anti-inflammatory to pro-inflammatory, which promotes low grade systemic inflammation and insulin resistance in obese mice. Various T cell subsets either help maintain metabolic homeostasis in healthy states or contribute to obesity-associated metabolic syndromes. In this review, we will discuss the T cell subsets that reside in adipose tissue and intestines and their role in the development of obesity-induced systemic inflammation.

Adipoclast: a multinucleated fat-eating macrophage

Cell membrane fusion and multinucleation in macrophages are associated with physiologic homeostasis as well as disease. Osteoclasts are multinucleated macrophages that resorb bone through increased metabolic activity resulting from cell fusion. Fusion of macrophages also generates multinucleated giant cells (MGCs) in white adipose tissue (WAT) of obese individuals. For years, our knowledge of MGCs in WAT has been limited to their description as part of crown-like structures (CLS) surrounding damaged adipocytes. However, recent evidence indicates that these cells can phagocytose oversized lipid remnants, suggesting that, as in osteoclasts, cell fusion and multinucleation are required for specialized catabolic functions. We thus reason that WAT MGCs can be viewed as functionally analogous to osteoclasts and refer to them in this article as adipoclasts. We first review current knowledge on adipoclasts and their described functions. In view of recent advances in single cell genomics, we describe WAT macrophages from a ‘fusion perspective’ and speculate on the ontogeny of adipoclasts. Specifically, we highlight the role of CD9 and TREM2, two plasma membrane markers of lipid-associated macrophages in WAT, which have been previously described as regulators of fusion and multinucleation in osteoclasts and MGCs. Finally, we consider whether strategies aiming to target WAT macrophages can be more selectively directed against adipoclasts.

Adipose Tissue Immunometabolism and Apoptotic Cell Clearance

The safe removal of apoptotic debris by macrophages—often referred to as efferocytosis—is crucial for maintaining tissue integrity and preventing self-immunity or tissue damaging inflammation. Macrophages clear tissues of hazardous materials from dying cells and ultimately adopt a pro-resolving activation state. However, adipocyte apoptosis is an inflammation-generating process, and the removal of apoptotic adipocytes by so-called adipose tissue macrophages triggers a sequence of events that lead to meta-inflammation and obesity-associated metabolic diseases. Signals that allow apoptotic cells to control macrophage immune functions are complex and involve metabolites released by the apoptotic cells and also metabolites produced by the macrophages during the digestion of apoptotic cell contents. This review provides a concise summary of the adipocyte-derived metabolites that potentially control adipose tissue macrophage immune functions and, hence, may induce or alleviate adipose tissue inflammation.