Evidence that TLR4 Is Not a Receptor for Saturated Fatty Acids but Mediates Lipid-Induced Inflammation by Reprogramming Macrophage Metabolism

Dietary wheat gluten induces astro- and microgliosis in the hypothalamus of male mice

Gluten, which is found in cereals such as wheat, rye and barley, makes up a major dietary component in most western nations, and has been shown to promote body mass gain and peripheral inflammation in mice. In the current study, we investigated the impact of gluten on central inflammation that is typically associated with diet-induced obesity. While we found no effect of gluten when added to a low-fat diet (LFD), male mice fed high fat diet (HFD) enriched with gluten increased body mass and adiposity compared with mice fed HFD without gluten. We furthermore found that gluten, when added to the LFD, increases circulating C-reactive protein levels. Gluten regardless of whether it was added to LFD or HFD led to a profound increase in the number of microglia and astrocytes in the arcuate nucleus of the hypothalamus, as detected by immunohistochemistry for ionised calcium binding adaptor molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP), respectively. In mice fed LFD, gluten mimicked the immunogenic effects of HFD exposure and when added to HFD led to a further increase in the number of immunoreactive cells. Taken together, our results confirm a moderate obesogenic effect of gluten when fed to mice exposed to HFD and for the first-time report gluten-induced astro- and microgliosis suggesting the development of hypothalamic injury in rodents.

Dietary fat differentially modulates the response of bone marrow-derived macrophages to TLR4 and NOD2 agonists

Consumption of diets high in fat has been linked to the development of obesity and related metabolic complications. Such associations originate from the enhanced, chronic, low-grade inflammation mediated by macrophages in response to translocated bacteria, bacterial products, or dietary constituents such as fatty acids (FAs). Nucleotide-binding Oligomerization Domain 2 (NOD2) senses muramyl dipeptide (MDP), a component of bacterial peptidoglycan. The inability to sense peptidoglycan through NOD2 has been demonstrated to lead to dysbiosis, increased bacterial translocation, inflammation and metabolic dysfunction. Currently, it is unknown how consumption of HFDs with different FA compositions might influence NOD2-dependent responses. In this study, we subjected WT mice to a control diet or to HFDs comprised of various ratios of unsaturated to saturated fats and determined the macrophage response to TLR4 and NOD2 agonists. A HFD with equal ratios of saturated and unsaturated fats enhanced subsequent responsiveness of macrophages to LPS but not to MDP. However, a high-unsaturated fat diet (HUFD) or a high-saturated fat diet (HSFD) both decreased the responsiveness to NOD2 agonists compared to that observed in control diet (CD) fed mice. These data suggest that dietary fatty acid composition can influence the subsequent macrophage responsiveness to bacterial products.

Obesity and the risk of cardiometabolic diseases

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

O-linked N-acetylglucosamine modification is essential for physiological adipose expansion induced by high-fat feeding

Adipose tissues accumulate excess energy as fat and heavily influence metabolic homeostasis. O-linked N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), which involves the addition of N-acetylglucosamine to proteins by O-GlcNAc transferase (Ogt), modulates multiple cellular processes. However, little is known about the role of O-GlcNAcylation in adipose tissues during body weight gain due to overnutrition. Here, we report on O-GlcNAcylation in mice with high-fat diet (HFD)-induced obesity. Mice with knockout of Ogt in adipose tissue achieved using adiponectin promoter-driven Cre recombinase (Ogt-FKO) gained less body weight than control mice under HFD. Surprisingly, Ogt-FKO mice exhibited glucose intolerance and insulin resistance, despite their reduced body weight gain, as well as decreased expression of de novo lipogenesis genes and increased expression of inflammatory genes, resulting in fibrosis at 24 weeks of age. Primary cultured adipocytes derived from Ogt-FKO mice showed decreased lipid accumulation. Both primary cultured adipocytes and 3T3-L1 adipocytes treated with OGT inhibitor showed increased secretion of free fatty acids. Medium derived from these adipocytes stimulated inflammatory genes in RAW 264.7 macrophages, suggesting that cell-to-cell communication via free fatty acids might be a cause of adipose inflammation in Ogt-FKO mice. In conclusion, O-GlcNAcylation is important for healthy adipose expansion in mice. Glucose flux into adipose tissues may be a signal to store excess energy as fat.NEW & NOTEWORTHY We evaluated the role of O-GlcNAcylation in adipose tissue in diet-induced obesity using adipose tissue-specific Ogt knockout mice. We found that O-GlcNAcylation in adipose tissue is essential for healthy fat expansion and that Ogt-FKO mice exhibit severe fibrosis upon long-term overnutrition. O-GlcNAcylation in adipose tissue may regulate de novo lipogenesis and free fatty acid efflux to the degree of overnutrition. We believe that these results provide new insights into adipose tissue physiology and obesity research.

The Impacts of Animal-Based Diets in Cardiovascular Disease Development: A Cellular and Physiological Overview

Cardiovascular disease (CVD) is the leading cause of death in the United States, and diet plays an instrumental role in CVD development. Plant-based diets have been strongly tied to a reduction in CVD incidence. In contrast, animal food consumption may increase CVD risk. While increased serum low-density lipoprotein (LDL) cholesterol concentrations are an established risk factor which may partially explain the positive association with animal foods and CVD, numerous other biochemical factors are also at play. Thus, the aim of this review is to summarize the major cellular and molecular effects of animal food consumption in relation to CVD development. Animal-food-centered diets may (1) increase cardiovascular toll-like receptor (TLR) signaling, due to increased serum endotoxins and oxidized LDL cholesterol, (2) increase cardiovascular lipotoxicity, (3) increase renin-angiotensin system components and subsequent angiotensin II type-1 receptor (AT1R) signaling and (4) increase serum trimethylamine-N-oxide concentrations. These nutritionally mediated factors independently increase cardiovascular oxidative stress and inflammation and are all independently tied to CVD development. Public policy efforts should continue to advocate for the consumption of a mostly plant-based diet, with the minimization of animal-based foods.

Anti-Inflammatory Activity of Black Soldier Fly Oil Associated with Modulation of TLR Signaling: A Metabolomic Approach

Dietary intervention in the treatment of ulcerative colitis involves, among other things, modifications in fatty acid content and/or profile. For example, replacing saturated long chain fatty acids with medium chain fatty acids (MCFAs) has been reported to ameliorate inflammation. The Black Soldier Fly Larvae's (BSFL) oil is considered a sustainable dietary ingredient rich in the MCFA C12:0; however, its effect on inflammatory-related conditions has not been studied until now. Thus, the present study aimed to investigate the anti-inflammatory activity of BSFL oil in comparison to C12:0 using TLR4- or TLR2-activated THP-1 and J774A.1 cell lines and to assess its putative protective effect against dextran sulfate sodium (DSS)-induced acute colitis in mice. BSFL oil and C12:0 suppressed proinflammatory cytokines release in LPS-stimulated macrophages; however, only BSFL oil exerted anti-inflammatory activity in Pam3CSK4-stimulated macrophages. Transcriptome analysis provided insight into the possible role of BSFL oil in immunometabolism switch, involving mTOR signaling and an increase in PPAR target genes promoting fatty acid oxidation, exhibiting a discrepant mode of action compared to C12:0 treatment, which mainly affected cholesterol biosynthesis pathways. Additionally, we identified anti-inflammatory eicosanoids, oxylipins, and isoprenoids in the BSFL oil that may contribute to an orchestrated anti-inflammatory response. In vivo, a BSFL oil-enriched diet (20%) ameliorated the clinical signs of colitis, as indicated by improved body weight recovery, reduced colon shortening, reduced splenomegaly, and an earlier phase of secretory IgA response. These results indicate the novel beneficial use of BSFL oil as a modulator of inflammation.

Microbiota and Glucidic Metabolism: A Link with Multiple Aspects and Perspectives

The global prevalence of overweight and obesity has dramatically increased in the last few decades, with a significant socioeconomic burden. In this narrative review, we include clinical studies aiming to provide the necessary knowledge on the role of the gut microbiota in the development of diabetic pathology and glucose-metabolism-related disorders. In particular, the role of a certain microbial composition of the fermentative type seems to emerge without a specific link to the development in certain subjects of obesity and the chronic inflammation of the adipose tissues, which underlies the pathological development of all the diseases related to glucose metabolism and metabolic syndrome. The gut microbiota plays an important role in glucose tolerance. Conclusion. New knowledge and new information is presented on the development of individualized therapies for patients affected by all the conditions related to reduced glucose tolerance and insulin resistance.

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.

Dissecting the species-specific recognition of Neoseptin 3 by TLR4/MD2 via molecular dynamics simulations

Toll-like receptor 4 (TLR4) is crucial in the innate immune response with species-specific recognition. As a novel small-molecule agonist for mouse TLR4/MD2, Neoseptin 3 fails to activate human TLR4/MD2, while the underlying mechanism is unclear. Herein, molecular dynamics simulations were performed to investigate the species-specific molecular recognition of Neoseptin 3. Lipid A, a classic TLR4 agonist showing no apparent species-specific sensing by TLR4/MD2, was also investigated for comparison. Neoseptin 3 and lipid A showed similar binding patterns with mouse TLR4/MD2. Although the binding free energies of Neoseptin 3 interacting with TLR4/MD2 from mouse and human species were similar, protein-ligand interactions and the details of the dimerization interface were substantially different between Neoseptin 3-bound mouse and human heterotetramers at the atomic level. Neoseptin 3 binding made human (TLR4/MD2)2 more flexible than human (TLR4/MD2/Lipid A)2, especially at the TLR4 C-terminus and MD2, which drives human (TLR4/MD2)2 fluctuating away from the active conformation. In contrast to mouse (TLR4/MD2/2*Neoseptin 3)2 and mouse/human (TLR4/MD2/Lipid A)2 systems, Neoseptin 3 binding to human TLR4/MD2 led to the separating trend of the C-terminus of TLR4. Furthermore, the protein-protein interactions at the dimerization interface between TLR4 and the neighboring MD2 in the human (TLR4/MD2/2*Neoseptin 3)2 system were much weaker than those of the lipid A-bound human TLR4/MD2 heterotetramer. These results explained the inability of Neoseptin 3 to activate human TLR4 signaling and accounted for the species-specific activation of TLR4/MD2, which provides insight for transforming Neoseptin 3 as a human TLR4 agonist.

Dietary Effects on Monocyte Phenotypes in Subjects With Hypertriglyceridemia and Metabolic Syndrome

In patients with hypertriglyceridemia, a short-term low-saturated fat vs high-saturated fat diet induced lower plasma lipids and improved monocyte phenotypes. These findings highlight the role of diet fat content and composition for monocyte phenotypes and possibly cardiovascular disease risk in these patients. (Effects of Dietary Interventions on Monocytes in Metabolic Syndrome; NCT03591588).

Anthocyanins ameliorate obesity-associated metainflammation: Preclinical and clinical evidence

The growing rates of obesity worldwide call for intervention strategies to help control the pathophysiological consequences of weight gain. The use of natural foods and bioactive compounds has been suggested as such a strategy because of their recognized antioxidant and anti-inflammatory properties. For example, polyphenols, especially anthocyanins, are candidates for managing obesity and its related metabolic disorders. Obesity is well known for the presence of metainflammation, which has been labeled as an inflammatory activation that leads to a variety of metabolic disorders, usually related to increased oxidative stress. Considering this, anthocyanins may be promising natural compounds able to modulate several intracellular mechanisms, mitigating oxidative stress and metainflammation. A wide variety of foods and extracts rich in anthocyanins have become the focus of research in the field of obesity. Here, we bring together the current knowledge regarding the use of anthocyanins as an intervention tested in vitro, in vivo, and in clinical trials to modulate metainflammation. Most recent research applies a wide variety of extracts and natural sources of anthocyanins, in diverse experimental models, which represents a limitation of the research field. However, the literature is sufficiently consistent to establish that the in-depth molecular analysis of gut microbiota, insulin signaling, TLR4-triggered inflammation, and oxidative stress pathways reveals their modulation by anthocyanins. These targets are interconnected at the cellular level and interact with one another, leading to obesity-associated metainflammation. Thus, the positive findings with anthocyanins observed in preclinical models might directly relate to the positive outcomes in clinical studies. In summary and based on the entirety of the relevant literature, anthocyanins can mitigate obesity-related perturbations in gut microbiota, insulin resistance, oxidative stress and inflammation and therefore may contribute as a therapeutic tool in people living with obesity.

Administration of an LXR agonist promotes atherosclerotic lesion remodelling in murine inflammatory arthritis

Objectives

The leading cause of mortality in patients with rheumatoid arthritis is atherosclerotic cardiovascular disease (CVD). We have shown that murine arthritis impairs atherosclerotic lesion regression, because of cellular cholesterol efflux defects in haematopoietic stem and progenitor cells (HSPCs), causing monocytosis and impaired atherosclerotic regression. Therefore, we hypothesised that improving cholesterol efflux using a Liver X Receptor (LXR) agonist would improve cholesterol efflux and improve atherosclerotic lesion regression in arthritis.

Methods

Ldlr -/- mice were fed a western-type diet for 14 weeks to initiate atherogenesis, then switched to a chow diet to induce lesion regression and divided into three groups; (1) control, (2) K/BxN serum transfer inflammatory arthritis (K/BxN) or (3) K/BxN arthritis and LXR agonist T0901317 daily for 2 weeks.

Results

LXR activation during murine inflammatory arthritis completely restored atherosclerotic lesion regression in arthritic mice, evidenced by reduced lesion size, macrophage abundance and lipid content. Mechanistically, serum from arthritic mice promoted foam cell formation, demonstrated by increased cellular lipid accumulation in macrophages and paralleled by a reduction in mRNA of the cholesterol efflux transporters Abca1, Abcg1 and Apoe. T0901317 reduced lipid loading and increased Abca1 and Abcg1 expression in macrophages exposed to arthritic serum and increased ABCA1 levels in atherosclerotic lesions of arthritic mice. Moreover, arthritic clinical score was also attenuated with T0901317.

Conclusion

Taken together, we show that the LXR agonist T0901317 rescues impaired atherosclerotic lesion regression in murine arthritis because of enhanced cholesterol efflux transporter expression and reduced foam cell development in atherosclerotic lesions.

Protective Effect of Glycomacropeptide on the Inflammatory Response of U937 Macrophages

Macrophages play crucial roles in inflammation and oxidative stress associated with noncommunicable diseases, such as cardiovascular diseases, diabetes, and cancer. Glycomacropeptide (GMP) is a bioactive peptide derived from milk κ-casein that contains abundant sialic acid and has shown anti-inflammatory, antioxidative, anti-obesity, and anti-diabetic properties when is orally administered. The aim of this study was to evaluate the effect of GMP on the regulation of the inflammatory response in human macrophages and the participation of sialic acid in this activity. GMP pretreatment decreased by 35%, 35%, and 49% the production of nitrites, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α, respectively, in activated human macrophages U937. The same effect was obtained when cells were pretreated with asialo GMP, and no change on the gene expression of the lectins associated with the recognition of sialic acids, SIGLEC5, 7, and 9, was induced by GMP on macrophages, which suggests that sialic acid might not be involved in this immunoregulatory effect. Interestingly, GMP increased 8.9- and 3.5-fold the gene expression of the canonical anti-inflammatory protein SOCS3 and the antioxidant enzyme HMOX1, respectively, in U937 cells. Thus, GMP exerts anti-inflammatory and antioxidative activities on activated macrophages in a sialic acid-independent manner, which might be related to its in vivo reported bioactivity.

A new frontier for fat: dietary palmitic acid induces innate immune memory

Dietary saturated fats have recently been appreciated for their ability to modify innate immune cell function, including monocytes, macrophages, and neutrophils. Many dietary saturated fatty acids (SFAs) embark on a unique pathway through the lymphatics following digestion, and this makes them intriguing candidates for inflammatory regulation during homeostasis and disease. Specifically, palmitic acid (PA) and diets enriched in PA have recently been implicated in driving innate immune memory in mice. PA has been shown to induce long-lasting hyper-inflammatory capacity against secondary microbial stimuli in vitro and in vivo, and PA-enriched diets alter the developmental trajectory of stem cell progenitors in the bone marrow. Perhaps the most relevant finding is the ability of exogenous PA to enhance clearance of fungal and bacterial burdens in mice; however, the same PA treatment enhances endotoxemia severity and mortality. Westernized countries are becoming increasingly dependent on SFA-enriched diets, and a deeper understanding of SFA regulation of innate immune memory is imperative in this pandemic era.

Thromboxane A2-TP axis promotes adipose tissue macrophages M1 polarization leading to insulin resistance in obesity

Aberrant arachidonic acid metabolism has been implicated in multiple pathophysiological conditions, and the downstream prostanoids levels are associated with adipocyte dysfunction in obesity. However, the role of thromboxane A₂ (TXA₂) in obesity remains unclear. We observed that TXA₂, through its receptor TP, is a candidate mediator in obesity and metabolic disorders. Obese mice with upregulated TXA₂ biosynthesis (TBXAS1) and TXA₂ receptor (TP) expression in caused insulin resistance and macrophage M1 polarization in white adipose tissue (WAT), which can be prevented by treatment with aspirin. Mechanistically, the activation of TXA₂-TP signaling axis leads to accumulation of protein kinase Cɛ (PKCɛ), thereby enhancing free fat acid (FFA) induced Toll-like receptor4 (TLR4) proinflammatory macrophage activation and the tumor necrosis factor-a (TNF-a) production in adipose tissues. Importantly, TP knockout mice reduced the accumulation of proinflammatory macrophages and adipocyte hypertrophy in WAT. Thus, our findings demonstrate that TXA₂-TP axis plays a crucial role in obesity-induced adipose macrophage dysfunction, and rational targeting TXA₂ pathway may improve obesity and its associated metabolic disorders in future. In this work, we establish previously unknown role of TXA₂-TP axis in WAT. These findings might provide new insight into the molecular pathogenesis of insulin resistance, and indicate rational targeting TXA₂ pathway to improve obesity and its associated metabolic disorders in future.

[Role of metaflammation as a systemic manifestation of metabolic diseases]

Visceral obesity as a component of the metabolic syndrome is characterized by systemic and local inflammation, which can be quantified in organs (metaflammation). This process can be regarded as a chronic, sterile, and low-grade state of inflammation without infection, trauma, tumor or autoimmunity. It is caused by an inflammation of the visceral adipose tissue (adipose inflammation or adipoflammation) due to adipocyte hypertrophy and hyperplasia with increased infiltration by monocytes and macrophages. Important is the presence of proinflammatory, so-called polarized M1 macrophages that are induced by interferon gamma (IFN-γ) and lipopolysaccharides (LPS) with secretion of interleukin (IL)-6, tumor necrosis factor (TNF) and IL‑1. In contrast, the anti-inflammatory, so-called polarized M2 macrophages induced by IL‑4 and IL-13 with secretion of IL‑8 and IL-10 decrease. In addition, the secreted adipokine pattern changes from anti-inflammatory to proinflammatory. Adipocyte necrosis, local hypoxia, dysregulated autophagy, activation of inflammasomes, modulation of toll-like receptors, and epigenetic factors play a complex role. This mechanism results in local insulin resistance and subsequently a systemic insulin resistance of peripheral organs as well as a spillover of local mediators of inflammation into the systemic circulation (measured as obesity C‑reactive protein, CRP). The activation of inflammatory signal transduction cascades leads to inhibitory phosphorylation of the insulin signaling pathway and a weakening of the effect of insulin. In parallel, ectopic lipid accumulation occurs in the liver, musculature, pancreas, pericardium and lungs. Diacylglycerol (DAG) activates specific isoforms of protein kinase C (ε in the liver and τ in the musculature), which in turn lead to inhibition of the insulin signaling pathway. Insulin resistance in obesity and type 2 diabetes mellitus is an inflammatory disease. The aim of future translational approaches is an anti-inflammatory, molecularly individualized (precision medicine) treatment in adipose tissue (targeted therapy) and in organs of insulin resistance.

Inflammatory crosstalk between saturated fatty acids and gut microbiota-white adipose tissue axis

PURPOSE

High-fat diets have different metabolic responses via gut dysbiosis. In this review, we discuss the complex interaction between the intake of long- and medium-chain saturated fatty acids (SFAs), gut microbiota, and white adipose tissue (WAT) dysfunction, particularly focusing on the type of fat.

RESULTS

The evidence for the impact of dietary SFAs on the gut microbiota-WAT axis has been mostly derived from in vitro and animal models, but there is now also evidence emerging from human studies. Most current reports show that, in response to high long- and medium-chain SFA diets, WAT functions are altered and can be modulated from microbial metabolites in several manners; and it appears to be also modified under conditions of obesity. SFAs overconsumption can reduce bacterial content and disrupt the gut environment. Both long- and medium-chain SFAs may contribute to proinflammatory cytokines release and TLR4 cascade signaling, either by regulation of endotoxemia markers or myristoylated protein. Palmitic and stearic acids have pathological effects on the intestinal epithelium, microbes, and inflammatory and lipogenic WAT profiles. While myristic and lauric acids display somewhat controversial outcomes, from probiotic effects and contribution to weight loss to cardiometabolic alterations from WAT inflammation.

CONCLUSION

Identifying an interference of distinct types of SFA in the binomial gut microbiota-WAT may elucidate essential mechanisms of metabolic endotoxemia, which may be the key to triggering obesity, innovating the therapeutic tools for this disease.

Omega-3-Supplemented Fat Diet Drives Immune Metabolic Response in Visceral Adipose Tissue by Modulating Gut Microbiota in a Mouse Model of Obesity

Obesity is a chronic, relapsing, and multifactorial disease characterized by excessive accumulation of adipose tissue (AT), and is associated with inflammation mainly in white adipose tissue (WAT) and an increase in pro-inflammatory M1 macrophages and other immune cells. This milieu favors the secretion of cytokines and adipokines, contributing to AT dysfunction (ATD) and metabolic dysregulation. Numerous articles link specific changes in the gut microbiota (GM) to the development of obesity and its associated disorders, highlighting the role of diet, particularly fatty acid composition, in modulating the taxonomic profile. The aim of this study was to analyze the effect of a medium-fat-content diet (11%) supplemented with omega-3 fatty acids (D2) on the development of obesity, and on the composition of the GM compared with a control diet with a low fat content (4%) (D1) over a 6-month period. The effect of omega-3 supplementation on metabolic parameters and the modulation of the immunological microenvironment in visceral adipose tissue (VAT) was also evaluated. Six-weeks-old mice were adapted for two weeks and then divided into two groups of eight mice each: a control group D1 and the experimental group D2. Their body weight was recorded at 0, 4, 12, and 24 weeks post-differential feeding and stool samples were simultaneously collected to determine the GM composition. Four mice per group were sacrificed on week 24 and their VAT was taken to determine the immune cells phenotypes (M1 or M2 macrophages) and inflammatory biomarkers. Blood samples were used to determine the glucose, total LDL and HDL cholesterol LDL, HDL and total cholesterol, triglycerides, liver enzymes, leptin, and adiponectin. Body weight measurement showed significant differences at 4 (D1 = 32.0 ± 2.0 g vs. D2 = 36.2 ± 4.5 g, p-value = 0.0339), 12 (D1 = 35.7 ± 4.1 g vs. D2 = 45.3 ± 4.9 g, p-value = 0.0009), and 24 weeks (D1 = 37.5 ± 4.7 g vs. D2 = 47.9 ± 4.7, p-value = 0.0009). The effects of diet on the GM composition changed over time: in the first 12 weeks, α and β diversity differed considerably according to diet and weight increase. In contrast, at 24 weeks, the composition, although still different between groups D1 and D2, showed changes compared with previous samples, suggesting the beneficial effects of omega-3 fatty acids in D2. With regard to metabolic analysis, the results did not reveal relevant changes in biomarkers in accordance with AT studies showing an anti-inflammatory environment and conserved structure and function, which is in contrast to reported findings for pathogenic obesity. In conclusion, the results suggest that the constant and sustained administration of omega-3 fatty acids induced specific changes in GM composition, mainly with increases in Lactobacillus and Ligilactobacillus species, which, in turn, modulated the immune metabolic response of AT in this mouse model of obesity.

Fatty acid overproduction by gut commensal microbiota exacerbates obesity

Although recent studies have highlighted the impact of gut microbes on the progression of obesity and its comorbidities, it is not fully understood how these microbes promote these disorders, especially in terms of the role of microbial metabolites. Here, we report that Fusimonas intestini, a commensal species of the family Lachnospiraceae, is highly colonized in both humans and mice with obesity and hyperglycemia, produces long-chain fatty acids such as elaidate, and consequently facilitates diet-induced obesity. High fat intake altered the expression of microbial genes involved in lipid production, such as the fatty acid metabolism regulator fadR. Monocolonization with a FadR-overexpressing Escherichia coli exacerbated the metabolic phenotypes, suggesting that the change in bacterial lipid metabolism is causally involved in disease progression. Mechanistically, the microbe-derived fatty acids impaired intestinal epithelial integrity to promote metabolic endotoxemia. Our study thus provides a mechanistic linkage between gut commensals and obesity through the overproduction of microbe-derived lipids.

Towards early detection of neurodegenerative diseases: A gut feeling

The gastrointestinal tract communicates with the nervous system through a bidirectional network of signaling pathways called the gut-brain axis, which consists of multiple connections, including the enteric nervous system, the vagus nerve, the immune system, endocrine signals, the microbiota, and its metabolites. Alteration of communications in the gut-brain axis is emerging as an overlooked cause of neuroinflammation. Neuroinflammation is a common feature of the pathogenic mechanisms involved in various neurodegenerative diseases (NDs) that are incurable and debilitating conditions resulting in progressive degeneration and death of neurons, such as in Alzheimer and Parkinson diseases. NDs are a leading cause of global death and disability, and the incidences are expected to increase in the following decades if prevention strategies and successful treatment remain elusive. To date, the etiology of NDs is unclear due to the complexity of the mechanisms of diseases involving genetic and environmental factors, including diet and microbiota. Emerging evidence suggests that changes in diet, alteration of the microbiota, and deregulation of metabolism in the intestinal epithelium influence the inflammatory status of the neurons linked to disease insurgence and progression. This review will describe the leading players of the so-called diet-microbiota-gut-brain (DMGB) axis in the context of NDs. We will report recent findings from studies in model organisms such as rodents and fruit flies that support the role of diets, commensals, and intestinal epithelial functions as an overlooked primary regulator of brain health. We will finish discussing the pivotal role of metabolisms of cellular organelles such as mitochondria and peroxisomes in maintaining the DMGB axis and how alteration of the latter can be used as early disease makers and novel therapeutic targets.

Blood orange juice intake modulates plasma and PBMC microRNA expression in overweight and insulin-resistant women: impact on MAPK and NFκB signaling pathways

Blood orange consumption presents potential health benefits and may modulate epigenetic mechanisms such as microRNAs (miRNAs) expression. MiRNAs are non-coding RNAs responsible for post-transcriptional gene regulation, and these molecules can also be used as biomarkers in body fluids. This study was designed to investigate the effect of chronic blood orange juice (BOJ) intake on the inflammatory response and miRNA expression profile in plasma and blood cells in overweight women. The study cohort was comprised of twenty women aged 18-40 years old, diagnosed as overweight, who consumed 500 mL/d of BOJ for four weeks. Clinical data were collected at baseline and after 4 weeks of juice consumption, e.g., anthropometric and hemodynamic parameters, food intake, blood cell count, and metabolic and inflammatory biomarkers. BOJ samples were analyzed and characterized. Additionally, plasma and blood cells were also collected for miRNA expression profiling and evaluation of the expression of genes and proteins in the MAPK and NFκB signaling pathways. BOJ intake increased the expression of miR-144-3p in plasma and the expression of miR-424-5p, miR-144-3p, and miR-130b-3p in peripheral blood mononuclear cells (PBMC). Conversely, the beverage intake decreased the expression of let-7f-5p and miR-126-3p in PBMC. Computational analyses identified different targets of the dysregulated miRNA on inflammatory pathways. Furthermore, BOJ intake increased vitamin C consumption and the pJNK/JNK ratio and decreased the expression of IL6 mRNA and NFκB protein. These results demonstrate that BOJ regulates the expression of genes involved in the inflammatory process and decreases NFкB-protein expression in PBMC.

Immune and metabolic cross-links in the pathogenesis of comorbid non-alcoholic fatty liver disease

In recent years, there has been a steady growth of interest in non-alcoholic fatty liver disease (NAFLD), which is associated with negative epidemiological data on the prevalence of the disease and its clinical significance. NAFLD is closely related to the metabolic syndrome and these relationships are the subject of active research. A growing body of evidence shows cross-linkages between metabolic abnormalities and the innate immune system in the development and progression of NAFLD. These links are bidirectional and largely still unclear, but a better understanding of them will improve the quality of diagnosis and management of patients. In addition, lipid metabolic disorders and the innate immune system link NAFLD with other diseases, such as atherosclerosis, which is of great clinical importance.

Molecular tracking of insulin resistance and inflammation development on visceral adipose tissue

Background

Visceral adipose tissue (VAT) is one of the most important sources of proinflammatory molecules in obese people and it conditions the appearance of insulin resistance and diabetes. Thus, understanding the synergies between adipocytes and VAT-resident immune cells is essential for the treatment of insulin resistance and diabetes.

Methods

We collected information available on databases and specialized literature to construct regulatory networks of VAT resident cells, such as adipocytes, CD4+ T lymphocytes and macrophages. These networks were used to build stochastic models based on Markov chains to visualize phenotypic changes on VAT resident cells under several physiological contexts, including obesity and diabetes mellitus.

Results

Stochastic models showed that in lean people, insulin produces inflammation in adipocytes as a homeostatic mechanism to downregulate glucose intake. However, when the VAT tolerance to inflammation is exceeded, adipocytes lose insulin sensitivity according to severity of the inflammatory condition. Molecularly, insulin resistance is initiated by inflammatory pathways and sustained by intracellular ceramide signaling. Furthermore, our data show that insulin resistance potentiates the effector response of immune cells, which suggests its role in the mechanism of nutrient redirection. Finally, our models show that insulin resistance cannot be inhibited by anti-inflammatory therapies alone.

Conclusion

Insulin resistance controls adipocyte glucose intake under homeostatic conditions. However, metabolic alterations such as obesity, enhances insulin resistance in adipocytes, redirecting nutrients to immune cells, permanently sustaining local inflammation in the VAT.

A systematic review of the biological mediators of fat taste and smell

Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and obesity. Thus there is growing interest in the study of the biological mediators of fat taste and associated olfaction as potential targets for pharmacologic and nutritional interventions in the context of obesity and health. The number of studies examining mechanisms underlying fat taste and smell has grown rapidly in the last 5 years. Therefore, the purpose of this systematic review is to summarize emerging evidence examining the biological mechanisms of fat taste and smell. A literature search was conducted of studies published in English between 2014 and 2021 in adult humans and animal models. Database searches were conducted using PubMed, EMBASE, Scopus, and Web of Science for key terms including fat/lipid, taste, and olfaction. Initially, 4,062 articles were identified through database searches, and a total of 84 relevant articles met inclusion and exclusion criteria and are included in this review. Existing literature suggests that there are several proteins integral to fat chemosensation, including cluster of differentiation 36 (CD36) and G protein-coupled receptor 120 (GPR120). This systematic review will discuss these proteins and the signal transduction pathways involved in fat detection. We also review neural circuits, key brain regions, ingestive cues, postingestive signals, and genetic polymorphism that play a role in fat perception and consumption. Finally, we discuss the role of fat taste and smell in the context of eating behavior and obesity.

Obese visceral fat tissue inflammation: from protective to detrimental?

Obesity usually is accompanied by inflammation of fat tissue, with a prominent role of visceral fat. Chronic inflammation in obese fat tissue is of a lower grade than acute immune activation for clearing the tissue from an infectious agent. It is the loss of adipocyte metabolic homeostasis that causes activation of resident immune cells for supporting tissue functions and regaining homeostasis. Initially, the excess influx of lipids and glucose in the context of overnutrition is met by adipocyte growth and proliferation. Eventual lipid overload of hypertrophic adipocytes leads to endoplasmic reticulum stress and the secretion of a variety of signals causing increased sympathetic tone, lipolysis by adipocytes, lipid uptake by macrophages, matrix remodeling, angiogenesis, and immune cell activation. Pro-inflammatory signaling of adipocytes causes the resident immune system to release increased amounts of pro-inflammatory and other mediators resulting in enhanced tissue-protective responses. With chronic overnutrition, these protective actions are insufficient, and death of adipocytes as well as senescence of several tissue cell types is seen. This structural damage causes the expression or release of immunostimulatory cell components resulting in influx and activation of monocytes and many other immune cell types, with a contribution of stromal cells. Matrix remodeling and angiogenesis is further intensified as well as possibly detrimental fibrosis. The accumulation of senescent cells also may be detrimental via eventual spread of senescence state from affected to neighboring cells by the release of microRNA-containing vesicles. Obese visceral fat inflammation can be viewed as an initially protective response in order to cope with excess ambient nutrients and restore tissue homeostasis but may contribute to tissue damage at a later stage.

Saturated very long-chain fatty acids regulate macrophage plasticity and invasiveness

Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD) due to inherited dysfunction of the peroxisomal VLCFA transporter ABCD1. In its severest form, X-ALD causes cerebral myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Here, whole transcriptome sequencing of X-ALD macrophages indicated that VLCFAs prime human macrophage membranes for inflammation and increased expression of factors involved in chemotaxis and invasion. When added externally to mimic lipid release in demyelinating X-ALD lesions, VLCFAs did not activate toll-like receptors in primary macrophages. In contrast, VLCFAs provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix-degrading enzymes and chemokine release. Following pro-inflammatory LPS activation, VLCFA levels increased also in healthy macrophages. With the onset of the resolution, VLCFAs were rapidly cleared in control macrophages by increased peroxisomal VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression upon LPS treatment. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.

The metabolic nature of inflammatory bowel diseases

Crohn's disease and ulcerative colitis, phenotypically comprising a spectrum of inflammatory bowel diseases (IBDs), spread globally during the westernization of lifestyle and dietary habits over the past few decades. Here, we review experimental and clinical evidence for the metabolic nature of gut inflammation in IBD and delineate distinct parallels to the inflammatory state in metabolic diseases. Experimental evidence indicates that excessive intake of specific macronutrients in a Western diet fuels an inflammatory response in the gut by exploiting sensors of innate immunity and perturbation of gut microbial metabolism. Genetic IBD risk partly affects metabolism and stress signalling of innate immunity, and immunometabolism controls susceptibility to gut inflammation. Epidemiological and clinical studies indicate that specific nutrients in the Western diet pose a risk for the development of IBD and a poor disease course. Translational studies in IBD indicate perturbation of energy metabolism in immune cells and perturbation of gut microbial metabolism, which can be shaped by diet. In turn, dietary restriction by exclusive enteral nutrition induces remission in patients with IBD. Collectively, these studies support a metabolic underpinning of gut inflammation in IBD as described for metabolic inflammation in obesity and related disorders.

Anti-inflammatory mechanisms of polyphenols in adipose tissue: role of gut microbiota, intestinal barrier integrity and zinc homeostasis

Obesity is associated with an imbalance of micro-and macro-nutrients, gut dysbiosis, and a "leaky" gut phenomenon. Polyphenols, such as curcumin, resveratrol, and anthocyanins may alleviate the systemic effects of obesity, potentially by improving gut microbiota, intestinal barrier integrity (IBI), and zinc homeostasis. The essential micronutrient zinc plays a crucial role in the regulation of enzymatic processes, including inflammation, maintenance of the microbial ecology, and intestinal barrier integrity. In this review, we focus on IBI- which prevents intestinal lipopolysaccharide (LPS) leakage - as a critical player in polyphenol-mediated protective effects against obesity-associated white adipose tissue (WAT) inflammation. This occurs through mechanisms that block the movement of the bacterial endotoxin LPS across the gut barrier. Available research suggests that polyphenols reduce WAT and systemic inflammation via crosstalk with inflammatory NF-κB, the mammalian target of rapamycin (mTOR) signaling and zinc homeostasis.

Formulated Phospholipids as Non-Canonical TLR4 Agonists

Immunogenic agents known as adjuvants play a critical role in many vaccine formulations. Adjuvants often signal through Toll-like receptor (TLR) pathways, including formulations in licensed vaccines that target TLR4. While TLR4 is predominantly known for responding to lipopolysaccharide (LPS), a component of Gram-negative bacterial membranes, it has been shown to be a receptor for a number of molecular structures, including phospholipids. Therefore, phospholipid-based pharmaceutical formulations might have off-target effects by signaling through TLR4, confounding interpretation of pharmaceutical bioactivity. In this study we examined the individual components of a clinical stage oil-in-water vaccine adjuvant emulsion (referred to as a stable emulsion or SE) and their ability to signal through murine and human TLR4s. We found that the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) activated TLR4 and elicited many of the same immune phenotypes as canonical TLR4 agonists. This pathway was dependent on the saturation, size, and headgroup of the phospholipid. Interestingly, DMPC effects on human cells were evident but overall appeared less impactful than emulsion oil composition. Considering the prevalence of DMPC and other phospholipids used across the pharmaceutical space, these findings may contextualize off-target innate immune responses that could impact preclinical and clinical development.

Omega-3 pleiad: The multipoint anti-inflammatory strategy

Omega 3 (ω3) fatty acids have been described since the 1980s as promising anti-inflammatory substances. Prostaglandin and leukotriene modulation were exhaustively explored as the main reason for ω3 beneficial outcomes. However, during the early 2000s, after the human genome decoding advent, the nutrigenomic approaches exhibited an impressive plethora of ω3 targets, now under the molecular point of view. Different G protein-coupled receptors (GPCRs) recognizing ω3 and its derivatives appear to be responsible for blocking inflammation and insulin-sensitizing effects. A new class of ω3-derived substances, such as maresins, resolvins, and protectins, increases ω3 actions. Inflammasome disruption, the presence of GPR120 on immune cell surfaces, and intracellular crosstalk signaling mediated by PPARγ compose the last discoveries regarding the multipoint anti-inflammatory targets for this nutrient. This review shows a detailed mechanistic proposal to understand ω3 fatty acid action over the inflammatory environment in the background of several chronic diseases.

Effect of acute TLR4 inhibition on insulin resistance in humans

BackgroundStudies in cell cultures and rodents suggest that TLR4 is involved in the pathogenesis of insulin resistance, but direct data in humans are limited. We tested the hypothesis that pharmacologic blockade of TLR4 with the competitive inhibitor eritoran would improve insulin resistance in humans.MethodsIn protocol I, 10 lean, healthy individuals received the following 72-hour i.v. infusions in a randomized crossover design: saline (30 mL/h) plus vehicle; Intralipid (30 mL/h) plus vehicle; or Intralipid (30 mL/h) plus eritoran (12 mg i.v. every 12 hours). In protocol II, also a randomized crossover design, 9 nondiabetic individuals with obesity received eritoran or vehicle for 72 hours. The effect of eritoran was assessed with euglycemic hyperinsulinemic clamps.ResultsIn protocol I, lipid infusion significantly decreased peripheral insulin sensitivity (M value) by 14% and increased fasting plasma glucose (FPG) concentrations, fasting plasma insulin (FPI) concentrations, and the homeostatic model assessment of insulin resistance (HOMA-IR) index by 7%, 22%, and 26%, respectively. Eritoran did not prevent lipid-induced alterations of these metabolic parameters. Eritoran also failed to improve any baseline metabolic parameters (M, FPG, FPI, HOMA-IR) in individuals with obesity and insulin resistance (protocol II).ConclusionsAcute TLR4 inhibition with eritoran did not protect against lipid-induced insulin resistance. Short-term eritoran administration also failed to improve obesity-associated insulin resistance. These data do not support a role for TLR4 in insulin resistance. Future studies with a different class of TLR4 inhibitors, longer drug exposure, and/or lipid-enhancing interventions richer in saturated fats may be needed to further clarify the role of TLR4 in metabolic dysfunction in humans.Trial registrationClinicalTrials.gov NCT02321111 and NCT02267317.FundingNIH grants R01DK080157, P30AG044271, P30AG013319, and UL1TR002645.

Bioactive compounds modulating Toll-like 4 receptor (TLR4)-mediated inflammation: pathways involved and future perspectives

Chronic inflammation is associated with the development and progression of several noncommunicable diseases, such as diabetes, cardiovascular disease, chronic kidney disease, cancer, and nonalcoholic fatty liver disease. Evidence suggests that pattern recognition receptors that identify pathogen-associated molecular patterns and danger-associated molecular patterns are crucial in chronic inflammation. Among the pattern recognition receptors, Toll-like receptor 4 (TLR4) stimulates several inflammatory pathway agonists, such as nuclear factor-κB, interferon regulator factor 3, and nod-like receptor pyrin domain containing 3 pathways, which consequently trigger the expression of pro-inflammatory biomarkers, increasing the risk of noncommunicable disease development and progression. Studies have focused on the antagonistic potential of bioactive compounds, following the concept of food as a medicine, in which nutritional strategies may mitigate inflammation via TLR4 modulation. Thus, this review discusses preclinical evidence concerning bioactive compounds from fruit, vegetable, spice, and herb extracts (curcumin, resveratrol, catechin, cinnamaldehyde, emodin, ginsenosides, quercetin, allicin, and caffeine) that may regulate the TLR4 pathway and reduce the inflammatory response. Bioactive compounds can inhibit TLR4-mediated inflammation through gut microbiota modulation, improvement of intestinal permeability, inhibition of lipopolysaccharide-TLR4 binding, and decreasing TLR4 expression by modulation of microRNAs and antioxidant pathways. The responses directly mitigated inflammation, especially nuclear factor-κB activation and inflammatory cytokines release. These findings should be considered for further clinical studies on inflammation-mediated diseases.

Obese male Zucker rats exhibit dendritic remodeling in neurons of the hippocampal trisynaptic circuit as well as spatial memory deficits

Obesity is characterized by excessive fat accumulation. The Zucker rat displays genetic obesity due to a mutation in the leptin receptor gene; this model is of great interest because of its similarity to human obesity. Brain regions may be affected by obesity, but detailed information is lacking. In the present study, we analyzed the morphology of neurons in the hippocampal trisynaptic circuit as well as the spatial memory of obese Zucker rats. We performed two experiments. Each experiment contained two experimental groups: the control group (male Long Evans rats) and the study group (obese male Zucker rats). We monitored the body weights of all rats over 4 weeks. In the first experiment, we analyzed the morphology of hippocampal neurons. Under anesthesia, we measured the abdominal and hip circumferences and collected at least 1 ml of blood to assess serum glucose (GLU), triglyceride (TGC), and cholesterol (COL) concentrations. We perfused the brains of these rats with 0.9% saline solution, incubated the brains in Golgi-Cox solution, and subsequently evaluated the morphology of pyramidal neurons in the hippocampus (the CA1-CA3 regions) and the entorhinal cortex as well as the morphology of granule neurons in the dentate gyrus. In the second experiment, we assessed the spatial memory of animals with the Morris water maze. The Zucker rats had an obese phenotype, as indicated by their elevated body weight and increased abdominal and hip circumferences as well as elevated GLU, COL, and TGC concentrations. Analysis of neurons from the specified regions in obese male Zucker rats indicated reduced dendritic arborization and reduced dendritic spine density. In terms of spatial learning and memory, the obese Zucker rats exhibited intact spatial learning (i.e., of platform location) but deficits in spatial memory. These data provide evidence that obesity alters the morphology and function of hippocampal neurons.

REDD1 promotes obesity-induced metabolic dysfunction via atypical NF-κB activation

Regulated in development and DNA damage response 1 (REDD1) expression is upregulated in response to metabolic imbalance and obesity. However, its role in obesity-associated complications is unclear. Here, we demonstrate that the REDD1-NF-κB axis is crucial for metabolic inflammation and dysregulation. Mice lacking Redd1 in the whole body or adipocytes exhibited restrained diet-induced obesity, inflammation, insulin resistance, and hepatic steatosis. Myeloid Redd1-deficient mice showed similar results, without restrained obesity and hepatic steatosis. Redd1-deficient adipose-derived stem cells lost their potential to differentiate into adipocytes; however, REDD1 overexpression stimulated preadipocyte differentiation and proinflammatory cytokine expression through atypical IKK-independent NF-κB activation by sequestering IκBα from the NF-κB/IκBα complex. REDD1 with mutated Lys^219/220Ala, key amino acid residues for IκBα binding, could not stimulate NF-κB activation, adipogenesis, and inflammation in vitro and prevented obesity-related phenotypes in knock-in mice. The REDD1-atypical NF-κB activation axis is a therapeutic target for obesity, meta-inflammation, and metabolic complications.

Enriched dietary saturated fatty acids induce trained immunity via ceramide production that enhances severity of endotoxemia and clearance of infection

Trained immunity is an innate immune memory response that is induced by a primary inflammatory stimulus that sensitizes monocytes and macrophages to a secondary pathogenic challenge, reprogramming the host response to infection and inflammatory disease. Dietary fatty acids can act as inflammatory stimuli, but it is unknown if they can act as the primary stimuli to induce trained immunity. Here we find mice fed a diet enriched exclusively in saturated fatty acids (ketogenic diet; KD) confer a hyper-inflammatory response to systemic lipopolysaccharide (LPS) and increased mortality, independent of diet-induced microbiome and hyperglycemia. We find KD alters the composition of the hematopoietic stem cell compartment and enhances the response of bone marrow macrophages, monocytes, and splenocytes to secondary LPS challenge. Lipidomics identified enhanced free palmitic acid (PA) and PA-associated lipids in KD-fed mice serum. We found pre-treatment with physiologically relevant concentrations of PA induces a hyper-inflammatory response to LPS in macrophages, and this was dependent on the synthesis of ceramide. In vivo, we found systemic PA confers enhanced inflammation and mortality in response to systemic LPS, and this phenotype was not reversible for up to 7 days post-PA-exposure. Conversely, we find PA exposure enhanced clearance of Candida albicans in Rag1-/- mice. Lastly, we show that oleic acid, which depletes intracellular ceramide, reverses PA-induced hyper-inflammation in macrophages and enhanced mortality in response to LPS. These implicate enriched dietary SFAs, and specifically PA, in the induction of long-lived innate immune memory and highlight the plasticity of this innate immune reprogramming by dietary constituents.

Adipose tissue macrophage in obesity-associated metabolic diseases

Adipose tissue macrophage (ATM) has been appreciated for its critical contribution to obesity-associated metabolic diseases in recent years. Here, we discuss the regulation of ATM on both metabolic homeostatsis and dysfunction. In particular, the macrophage polarization and recruitment as well as the crosstalk between ATM and adipocyte in thermogenesis, obesity, insulin resistance and adipose tissue fibrosis have been reviewed. A better understanding of how ATM regulates adipose tissue remodeling may provide novel therapeutic strategies against obesity and associated metabolic diseases.

Secreted fungal virulence effector triggers allergic inflammation via TLR4

Invasive fungal pathogens are major causes of human mortality and morbidity^1,2. Although numerous secreted effector proteins that reprogram innate immunity to promote virulence have been identified in pathogenic bacteria, so far, there are no examples of analogous secreted effector proteins produced by human fungal pathogens. Cryptococcus neoformans, the most common cause of fungal meningitis and a major pathogen in AIDS, induces a pathogenic type 2 response characterized by pulmonary eosinophilia and alternatively activated macrophages^3-8. Here, we identify CPL1 as an effector protein secreted by C. neoformans that drives alternative activation (also known as M2 polarization) of macrophages to enable pulmonary infection in mice. We observed that CPL1-enhanced macrophage polarization requires Toll-like receptor 4, which is best known as a receptor for bacterial endotoxin but is also a poorly understood mediator of allergen-induced type 2 responses^9-12. We show that this effect is caused by CPL1 itself and not by contaminating lipopolysaccharide. CPL1 is essential for virulence, drives polarization of interstitial macrophages in vivo, and requires type 2 cytokine signalling for its effect on infectivity. Notably, C. neoformans associates selectively with polarized interstitial macrophages during infection, suggesting a mechanism by which C. neoformans generates its own intracellular replication niche within the host. This work identifies a circuit whereby a secreted effector protein produced by a human fungal pathogen reprograms innate immunity, revealing an unexpected role for Toll-like receptor 4 in promoting the pathogenesis of infectious disease.

The Harm of Metabolically Healthy Obese and the Effect of Exercise on Their Health Promotion

Obesity and obesity-related diseases [type 2 diabetes, cardiovascular disease (CVD), and cancer] are becoming more common, which is a major public health concern. Metabolically healthy obesity (MHO) has become a type of obesity, accounting for a large proportion of obese people. MHO is still harmful to health. It was discovered that MHO screening criteria could not well reflect health hazards, whereas visceral fat, adiponectin pathway, oxidative stress, chronic inflammation, and histological indicators at the microlevel could clearly distinguish MHO from health control, and the biological pathways involved in these micro indicators were related to MHO pathogenesis. This review reveals that MHO’s micro metabolic abnormality is the initial cause of the increase of disease risk in the future. Exploring the biological pathway of MHO is important in order to develop an effective mechanism-based preventive and treatment intervention strategy. Exercise can correct the abnormal micro metabolic pathway of MHO, regulate metabolic homeostasis, and enhance metabolic flexibility. It is a supplementary or possible alternative to the traditional healthcare prevention/treatment strategy as well as an important strategy for reducing MHO-related health hazards.

A label-free SPR biosensor for specific detection of TLR4 expression; introducing of 10-HDA as an antagonist

Toll-like receptor 4 (TLR4) is actively involved in many health-related problems, including transplantation rejection and autoimmune diseases. Therefore, it is important to identify an antagonist to inhibit the TLR4-induced immune cell activation. In our previous study, 10-hydroxy-2-decanoic acid (10-HDA) was introduced as a potential antagonist for TLR4; however, possible interaction between 10-HDA and TLR4 needed to be detected. Due to the ability of surface plasmon resonance (SPR) biosensor to confirm the specific interactions between receptors and ligands, a new configuration of SPR biosensor proposed to detect the possible interaction between 10-HDA and TLR4. Hence, 10-HDA was immobilized using the (3-aminopropyl) triethoxysilane (APTES) polymer as a crosslinking agent on the Ag-MgF₂ surface. Besides, genetically modified HEK293T cells with high TLR4 expression were used to study the possible interaction between 10-HDA and TLR4. Surprisingly, the SPR angle was significantly reduced in the presence of HEK cells expressing TLR4, while HEK cells without TLR4 did not affect the SPR angle. So, the proposed SPR biosensor successfully detected the interaction betweenTLR4 and 10-HDA. The sensitivity and detection limit of the biosensor were achieved at 0.05 and 0.5 million cells expressing TLR4, respectively, with a two-fold dynamic range.

Contribution of specific ceramides to obesity-associated metabolic diseases

Ceramides are a heterogeneous group of bioactive membrane sphingolipids that play specialized regulatory roles in cellular metabolism depending on their characteristic fatty acyl chain lengths and subcellular distribution. As obesity progresses, certain ceramide molecular species accumulate in metabolic tissues and cause cell-type-specific lipotoxic reactions that disrupt metabolic homeostasis and lead to the development of cardiometabolic diseases. Several mechanisms for ceramide action have been inferred from studies in vitro, but only recently have we begun to better understand the acyl chain length specificity of ceramide-mediated signaling in the context of physiology and disease in vivo. New discoveries show that specific ceramides affect various metabolic pathways and that global or tissue-specific reduction in selected ceramide pools in obese rodents is sufficient to improve metabolic health. Here, we review the tissue-specific regulation and functions of ceramides in obesity, thus highlighting the emerging concept of selectively inhibiting production or action of ceramides with specific acyl chain lengths as novel therapeutic strategies to ameliorate obesity-associated diseases.

Fungal Patterns Induce Cytokine Expression through Fluxes of Metabolic Intermediates That Support Glycolysis and Oxidative Phosphorylation

Cytokine expression is fine-tuned by metabolic intermediates, which makes research on immunometabolism suitable to yield drugs with a wider prospect of application than the biological therapies that block proinflammatory cytokines. Switch from oxidative phosphorylation (OXPHOS) to glycolysis has been considered a characteristic feature of activated immune cells. However, some stimuli might enhance both routes concomitantly. The connection between the tricarboxylic acid cycle and cytokine expression was scrutinized in human monocyte-derived dendritic cells stimulated with the fungal surrogate zymosan. Results showed that nucleocytosolic citrate and ATP-citrate lyase activity drove IL1B, IL10, and IL23A expression by yielding acetyl-CoA and oxaloacetate, with the latter one supporting glycolysis and OXPHOS by maintaining cytosolic NAD⁺ and mitochondrial NADH levels through mitochondrial shuttles. Succinate dehydrogenase showed a subunit-specific ability to modulate IL23A and IL10 expression. Succinate dehydrogenase A subunit activity supported cytokine expression through the control of the 2-oxoglutarate/succinate ratio, whereas C and D subunits underpinned cytokine expression by conveying electron flux from complex II to complex III of the electron transport chain. Fatty acids may also fuel the tricarboxylic acid cycle and influence cytokine expression. Overall, these results show that fungal patterns support cytokine expression through a strong boost of glycolysis and OXPHOS supported by the use of pyruvate, citrate, and succinate, along with the compartmentalized NAD(H) redox state maintained by mitochondrial shuttles.

You aren't IMMUNE to the ceramides that accumulate in cardiometabolic disease

Obesity leads to persistent increases in immune responses that contribute to cardiometabolic pathologies such as diabetes and cardiovascular disease. Pro-inflammatory macrophages infiltrate the expanding fat mass, which leads to increased production of cytokines such as tumor necrosis factor-alpha. Moreover, saturated fatty acids enhance signaling through the toll-like receptors involved in innate immunity. Herein we discuss the evidence that ceramides-which are intermediates in the biosynthetic pathway that produces sphingolipids-are essential intermediates that link these inflammatory signals to impaired tissue function. We discuss the mechanisms linking these immune insults to ceramide production and review the numerous ceramide actions that alter cellular metabolism, induce oxidative stress, and stimulate apoptosis. Lastly, we evaluate the correlation of ceramides in humans with inflammation-linked cardiometabolic disease and discuss preclinical studies which suggest that ceramide-lowering interventions may be an effective strategy to treat or prevent such maladies.

Oxidation of Polyunsaturated Fatty Acids as a Promising Area of Research in Infertility

In this review, the role of fatty acids (FA) in human pathological conditions, infertility in particular, was considered. FA and FA-derived metabolites modulate cell membrane composition, membrane lipid microdomains and cell signaling. Moreover, such molecules are involved in cell death, immunological responses and inflammatory processes. Human health and several pathological conditions are specifically associated with both dietary and cell membrane lipid profiles. The role of FA metabolism in human sperm and spermatogenesis has recently been investigated. Cumulative findings indicate F₂ isoprostanes (oxygenated products from arachidonic acid metabolism) and resolvins (lipid mediators of resolution of inflammation) as promising biomarkers for the evaluation of semen and follicular fluid quality. Advanced knowledge in this field could lead to new scenarios in the treatment of infertility.

Anti-Inflammatory Diet for Women with Interstitial Cystitis/Bladder Pain Syndrome: The AID-IC Pilot Study

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic condition characterized by pelvic pain coupled with urinary frequency and urgency. The underlying cause of IC/BPS is unknown; there is no cure. Dietary components exacerbate symptoms. The Anti-Inflammatory Diet for Interstitial Cystitis (AID-IC) employs a randomized, crossover design to evaluate the effect of a plant-based, low saturated fat diet on the quality of life of women with IC/BPS. Insights on the implementation of the protocol and reflections on the facilitators and barriers experienced during the pilot study follow. The logistics of the protocol proved time-consuming; however, the barriers were surmountable. Quantitative and qualitative findings suggest that the AID-IC therapeutic diet may have lessened symptoms and improved the quality of life for many of the women in the study.

Lipid-induced monokine cyclophilin-A promotes adipose tissue dysfunction implementing insulin resistance and type 2 diabetes in zebrafish and mice models of obesity

Several studies have implicated obesity-induced macrophage-adipocyte cross-talk in adipose tissue dysfunction and insulin resistance. However, the molecular cues involved in the cross-talk of macrophage and adipocyte causing insulin resistance are currently unknown. Here, we found that a lipid-induced monokine cyclophilin-A (CyPA) significantly attenuates adipocyte functions and insulin sensitivity. Targeted inhibition of CyPA in diet-induced obese zebrafish notably reduced adipose tissue inflammation and restored adipocyte function resulting in improvement of insulin sensitivity. Silencing of macrophage CyPA or pharmacological inhibition of CyPA by TMN355 effectively restored adipocytes' functions and insulin sensitivity. Interestingly, CyPA incubation markedly increased adipocyte inflammation along with an impairment of adipogenesis, however, mutation of its cognate receptor CD147 at P309A and G310A significantly waived CyPA's effect on adipocyte inflammation and its differentiation. Mechanistically, CyPA-CD147 interaction activates NF-κB signaling which promotes adipocyte inflammation by upregulating various pro-inflammatory cytokines gene expression and attenuates adipocyte differentiation by inhibiting PPARγ and C/EBPβ expression via LZTS2-mediated downregulation of β-catenin. Moreover, inhibition of CyPA or its receptor CD147 notably restored palmitate or CyPA-induced adipose tissue dysfunctions and insulin sensitivity. All these results indicate that obesity-induced macrophage-adipocyte cross-talk involving CyPA-CD147 could be a novel target for the management of insulin resistance and type 2 diabetes.

Maternal diet and obesity shape offspring central and peripheral inflammatory outcomes in juvenile non-human primates

The obesity epidemic affects 40% of adults in the US, with approximately one-third of pregnant women classified as obese. Previous research suggests that children born to obese mothers are at increased risk for a number of health conditions. The mechanisms behind this increased risk are poorly understood. Increased exposure to in-utero inflammation induced by maternal obesity is proposed as an underlying mechanism for neurodevelopmental alterations in offspring. Utilizing a non-human primate model of maternal obesity, we hypothesized that maternal consumption of an obesogenic diet will predict offspring peripheral (e.g., cytokines and chemokines) and central (microglia number) inflammatory outcomes via the diet's effects on maternal adiposity and maternal inflammatory state during the third trimester. We used structural equation modeling to simultaneously examine the complex associations among maternal diet, metabolic state, adiposity, inflammation, and offspring central and peripheral inflammation. Four latent variables were created to capture maternal chemokines and pro-inflammatory cytokines, and offspring cytokine and chemokines. Model results showed that offspring microglia counts in the basolateral amygdala were associated with maternal diet (β = -0.622, p < 0.01), adiposity (β = 0.593, p < 0.01), and length of gestation (β = 0.164, p < 0.05) but not with maternal chemokines (β = 0.135, p = 0.528) or maternal pro-inflammatory cytokines (β = 0.083, p = 0.683). Additionally, we found that juvenile offspring peripheral cytokines (β = -0.389, p < 0.01) and chemokines (β = -0.298, p < 0.05) were associated with a maternal adiposity-induced decrease in maternal circulating chemokines during the third trimester (β = -0.426, p < 0.01). In summary, these data suggest that maternal diet and adiposity appear to directly predict offspring amygdala microglial counts while maternal adiposity influences offspring peripheral inflammatory outcomes via maternal inflammatory state.

Bile acid coordinates microbiota homeostasis and systemic immunometabolism in cardiometabolic diseases

Cardiometabolic disease (CMD), characterized with metabolic disorder triggered cardiovascular events, is a leading cause of death and disability. Metabolic disorders trigger chronic low-grade inflammation, and actually, a new concept of metaflammation has been proposed to define the state of metabolism connected with immunological adaptations. Amongst the continuously increased list of systemic metabolites in regulation of immune system, bile acids (BAs) represent a distinct class of metabolites implicated in the whole process of CMD development because of its multifaceted roles in shaping systemic immunometabolism. BAs can directly modulate the immune system by either boosting or inhibiting inflammatory responses via diverse mechanisms. Moreover, BAs are key determinants in maintaining the dynamic communication between the host and microbiota. Importantly, BAs via targeting Farnesoid X receptor (FXR) and diverse other nuclear receptors play key roles in regulating metabolic homeostasis of lipids, glucose, and amino acids. Moreover, BAs axis per se is susceptible to inflammatory and metabolic intervention, and thereby BAs axis may constitute a reciprocal regulatory loop in metaflammation. We thus propose that BAs axis represents a core coordinator in integrating systemic immunometabolism implicated in the process of CMD. We provide an updated summary and an intensive discussion about how BAs shape both the innate and adaptive immune system, and how BAs axis function as a core coordinator in integrating metabolic disorder to chronic inflammation in conditions of CMD.

Macrophage scavenger receptor 1 mediates lipid-induced inflammation in non-alcoholic fatty liver disease

BACKGROUND & AIMS

Obesity-associated inflammation is a key player in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the role of macrophage scavenger receptor 1 (MSR1, CD204) remains incompletely understood.

METHODS

A total of 170 NAFLD liver biopsies were processed for transcriptomic analysis and correlated with clinicopathological features. Msr1^-/- and wild-type mice were subjected to a 16-week high-fat and high-cholesterol diet. Mice and ex vivo human liver slices were treated with a monoclonal antibody against MSR1. Genetic susceptibility was assessed using genome-wide association study data from 1,483 patients with NAFLD and 430,101 participants of the UK Biobank.

RESULTS

MSR1 expression was associated with the occurrence of hepatic lipid-laden foamy macrophages and correlated with the degree of steatosis and steatohepatitis in patients with NAFLD. Mice lacking Msr1 were protected against diet-induced metabolic disorder, showing fewer hepatic foamy macrophages, less hepatic inflammation, improved dyslipidaemia and glucose tolerance, and altered hepatic lipid metabolism. Upon induction by saturated fatty acids, MSR1 induced a pro-inflammatory response via the JNK signalling pathway. In vitro blockade of the receptor prevented the accumulation of lipids in primary macrophages which inhibited the switch towards a pro-inflammatory phenotype and the release of cytokines such as TNF-ɑ. Targeting MSR1 using monoclonal antibody therapy in an obesity-associated NAFLD mouse model and human liver slices resulted in the prevention of foamy macrophage formation and inflammation. Moreover, we identified that rs41505344, a polymorphism in the upstream transcriptional region of MSR1, was associated with altered serum triglycerides and aspartate aminotransferase levels in a cohort of over 400,000 patients.

CONCLUSIONS

Taken together, our data suggest that MSR1 plays a critical role in lipid-induced inflammation and could thus be a potential therapeutic target for the treatment of NAFLD.

LAY SUMMARY

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease primarily caused by excessive consumption of fat and sugar combined with a lack of exercise or a sedentary lifestyle. Herein, we show that the macrophage scavenger receptor MSR1, an innate immune receptor, mediates lipid uptake and accumulation in Kupffer cells, resulting in liver inflammation and thereby promoting the progression of NAFLD in humans and mice.

Molecular mechanism of crosstalk between immune and metabolic systems in metabolic syndrome

Chronic inflammation is currently considered as a molecular basis of metabolic syndrome. Particularly, obesity-induced inflammation in adipose tissue is the origin of chronic inflammation of metabolic syndrome. Adipose tissue contains not only mature adipocytes with large lipid droplets, but also a variety of stromal cells including adipocyte precursors, vascular component cells, immune cells, and fibroblasts. However, crosstalk between those various cell types in adipose tissue in obesity still remains to be fully understood. We focus on two innate immune receptors, Toll-like receptor 4 (TLR4) and macrophage-inducible C-type lectin (Mincle). We provided evidence that adipocyte-derived saturated fatty acids (SFAs) activate macrophage TLR4 signaling pathway, thereby forming a vicious cycle of inflammatory responses during the development of obesity. Intriguingly, the TLR4 signaling pathway is modulated metabolically and epigenetically: SFAs augment TLR4 signaling through the integrated stress response and chromatin remodeling, such as histone methylation, regulates dynamic transcription patterns downstream of TLR4 signaling. Another innate immune receptor Mincle senses cell death, which is a trigger of chronic inflammatory diseases including obesity. Macrophages form a histological structure termed “crown-like structure (CLS)”, in which macrophages surround dead adipocytes to engulf cell debris and residual lipids. Mincle is exclusively expressed in macrophages forming the CLS in obese adipose tissue and regulates adipocyte death-triggered adipose tissue fibrosis. In addition to adipose tissue, we found a structure similar to CLS in the liver of nonalcoholic steatohepatitis (NASH) and the kidney after acute kidney injury. This review article highlights the recent progress of the crosstalk between immune and metabolic systems in metabolic syndrome, with a focus on innate immune receptors.