Toll-like receptor 4 deficiency promotes the alternative activation of adipose tissue macrophages

The involvement of endogenous melatonin in LPS-induced M1-like macrophages and its underlying synthesis mechanism regulated by IRF3

Melatonin (MLT) has been shown to induce polarization of macrophages towards M2-like phenotype and inhibit polarization of macrophages towards M1-like phenotype through exogenous administration, which affects the development of many macrophage polarization-related diseases, such as infectious diseases, cardiovascular diseases, bone diseases, and tumors. However, whether endogenous melatonin has similar influences on macrophage polarization as exogenous melatonin is still under investigation. This study revealed that the process of lipopolysaccharide (LPS) inducing macrophages to polarize towards M1-like phenotype was accompanied by an increase in endogenous MLT secretion. To explore the role of increased endogenous MLT in the polarization process of macrophages, whether similar to the function of exogenous MLT in inhibiting polarization of macrophages towards M1-like phenotype, we established LPS-induced MLT deficiency models in vitro to investigate the effects of endogenous MLT on the secretion of cytokines, co-stimulatory molecules, ROS, and phagocytic function in LPS-induced M1-like macrophages. Additionally, we aimed to elucidate the mechanism by which LPS affects the secretion of endogenous MLT by macrophages. Our results confirm that LPS induces transcription of Aanat through the TLR4/TRIF pathway, consequently facilitating the secretion of MLT by macrophages. In this way, IRF3 is the main transcription factor that regulates Aanat transcription. Endogenous MLT plays a role in inhibiting the polarization of macrophages towards M1 phenotype and delaying cell apoptosis during LPS-induced polarization towards M1 phenotype. This phenomenon may be a form of self-protection that occurs when macrophages engulf pathogens while avoiding oxidative stress and apoptosis caused by LPS. This conclusion clarifies the role of endogenous MLT in the clearance of pathogens by macrophages, providing a theoretical basis for understanding its role in innate immunity.

The Interplay between Obesity and Inflammation

Obesity is an important condition affecting the quality of life of numerous patients and increasing their associated risk for multiple diseases, including tumors and immune-mediated disorders. Inflammation appears to play a major role in the development of obesity and represents a central point for the activity of cellular and humoral components in the adipose tissue. Macrophages play a key role as the main cellular component of the adipose tissue regulating the chronic inflammation and modulating the secretion and differentiation of various pro- and anti-inflammatory cytokines. Inflammation also involves a series of signaling pathways that might represent the focus for new therapies and interventions. Weight loss is essential in decreasing cardiometabolic risks and the degree of associated inflammation; however, the latter can persist for long after the excess weight is lost, and can involve changes in macrophage phenotypes that can ensure the metabolic adjustment. A clear understanding of the pathophysiological processes in the adipose tissue and the interplay between obesity and chronic inflammation can lead to a better understanding of the development of comorbidities and may ensure future targets for the treatment of obesity.

The impact of metabolic disorders on management of periodontal health in children

Periodontitis is a chronic inflammatory disease caused by plaque biofilm which shares risk factors with systemic chronic diseases such as diabetes, cardiovascular disease, and osteoporosis. Many studies have found increased prevalence and rate of progression of periodontal disease in children with common metabolic disorders. Although the causal relationship and specific mechanism between them has not been determined yet. The aim of this paper is to progress on the impact of metabolic disorders on periodontal health in children and the underlying mechanisms, which provides new evidences for the prevention and intervention of metabolic disorders and periodontitis in children.

Zerumbone reduces TLR2 stimulation-induced M1 macrophage polarization pattern via upregulation of Nrf-2 expression in murine macrophages

Hyperuricemia contributes significantly to gout arthritis pathogenesis, which promotes urate crystal deposition in the joints and activates joint-resident macrophages and circulating monocytes to initiate a state of inflammatory arthritis. In the joint, macrophages have an immune defense role where the presence of urate crystals results in the inflammatory mediators secretion, inflammatory cells recruitment to the joint, and shift macrophage population toward M1 pro-inflammatory phenotypes. Current treatment modalities of gout arthritis have side effects that limit their use in the elderly. A novel treatment that targets macrophage polarization to re-establish homeostasis may initiate a drug discovery program of novel disease-modifying agents for gout. Zerumbone (Zer) is a sesquiterpenoid bioactive compound found in the rhizome of Zingiberaceae family and possesses anti-inflammatory, antioxidant, and anti-proliferative activity. Our study hypothesized that soluble uric acid (sUA) and Pam3CSK4 (TLR2 agonist) reduce the anti-inflammatory function of murine M2 bone marrow-derived macrophages and change the expression of M2 genetic markers toward M1 phenotypes. We observed that priming of M2 macrophages with sUA and Pam3CSK4 significantly decreased M2 specific markers expression, e.g., Arg-1, Ym-1, and Fizz-1, enhanced mRNA expression of IL-1β, TNF-α, CXCL2, and iNOS and increased oxidative stress in M2 macrophages, as exhibited by a reduction in Nrf2 expression. We also aimed to study the impact of Zer on reducing the pro-inflammatory effect of sUA in TLR2-stimulated M2 macrophages. We noticed that Zer treatment significantly reduced L-1β and TNF-α production following Pam3CSK4 + sUA treatment on M2 macrophages. Furthermore, Zer reduced the caspase-1 activity without altering cytosolic NLRP3 content in challenged M2 BMDMs. We also observed that Zer significantly enhanced M2-associated marker's expression, e.g., Arg-1, Ym-1, and Fizz-1, and augmented Nrf-2 and other antioxidant proteins, including HMOX1 and srxn1expression following Pam3CSK4 + sUA treatment. We draw the conclusion that Zer is a potentially effective anti-inflammatory treatment for gout arthritis linked to hyperuricemia.

Reappraisal of Adipose Tissue Inflammation in Obesity

Chronic low-grade inflammation is a central component in the pathogenesis of obesity-related expansion of adipose tissue and complications in other metabolic tissues. Five different signaling pathways are defined as dominant determinants of adipose tissue inflammation: These are increased circulating endotoxin due to dysregulation in the microbiota-gut-brain axis, systemic oxidative stress, macrophage accumulation, and adipocyte death. Finally, the nucleotide-binding and oligomerization domain (NOD) leucine-rich repeat family pyrin domain-containing 3 (NLRP3) inflammasome pathway is noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome and associated metabolic inflammation play an important role in the relationships among fatty acids and obesity. Several highly active molecules, including primarily leptin, resistin, adiponectin, visfatin, and classical cytokines, are abundantly released from adipocytes. The most important cytokines that are released by inflammatory cells infiltrating obese adipose tissue are tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1) (CCL-2), and IL-1. All these molecules mentioned above act on immune cells, causing local and then general inflammation. Three metabolic pathways are noteworthy in the development of adipose tissue inflammation: toll-like receptor 4 (TLR4)/phosphatidylinositol-3'-kinase (PI3K)/Protein kinase B (Akt) signaling pathway, endoplasmic reticulum (ER) stress-derived unfolded protein response (UPR), and inhibitor of nuclear factor kappa-B kinase beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway. In fact, adipose tissue inflammation is an adaptive response that contributes to a visceral depot barrier that effectively filters gut-derived endotoxin. Excessive fatty acid release worsens adipose tissue inflammation and contributes to insulin resistance. However, suppression of adipose inflammation in obesity with anti-inflammatory drugs is not a rational solution and paradoxically promotes insulin resistance, despite beneficial effects on weight gain. Inflammatory pathways in adipocytes are indeed indispensable for maintaining systemic insulin sensitivity. Cannabinoid type 1 receptor (CB1R) is important in obesity-induced pro-inflammatory response; however, blockade of CB1R, contrary to anti-inflammatory drugs, breaks the links between insulin resistance and adipose tissue inflammation. Obesity, however, could be decreased by improving leptin signaling, white adipose tissue browning, gut microbiota interactions, and alleviating inflammation. Furthermore, capsaicin synthesized by chilies is thought to be a new and promising therapeutic option in obesity, as it prevents metabolic endotoxemia and systemic chronic low-grade inflammation caused by high-fat diet.

The Effect of an Innovative Combination of Bergamot Polyphenolic Fraction and Cynara cardunculus L. Extract on Weight Gain Reduction and Fat Browning in Obese Mice

Obesity is one of the world's most serious public health issues, with a high risk of developing a wide range of diseases. As a result, focusing on adipose tissue dysfunction may help to prevent the metabolic disturbances commonly associated with obesity. Nutraceutical supplementation may be a crucial strategy for improving WAT inflammation and obesity and accelerating the browning process. The aim of this study was to perform a preclinical "proof of concept" study on Bergacyn®, an innovative formulation originating from a combination of bergamot polyphenolic fraction (BPF) and Cynara cardunculus (CyC), for the treatment of adipose tissue dysfunction. In particular, Bergacyn® supplementation in WD/SW-fed mice at doses of 50 mg/kg given orally for 12 weeks, was able to reduce body weight and total fat mass in the WD/SW mice, in association with an improvement in plasma biochemical parameters, including glycemia, total cholesterol, and LDL levels. In addition, a significant reduction in serum ALT levels was highlighted. The decreased WAT levels corresponded to an increased weight of BAT tissue, which was associated with a downregulation of PPARγ as compared to the vehicle group. Bergacyn® was able to restore PPARγ levels and prevent NF-kB overexpression in the WAT of mice fed a WD/SW diet, suggesting an improved oxidative metabolism and inflammatory status. These results were associated with a significant potentiation of the total antioxidant status in WD/SW mice. Finally, our data show, for the first time, that Bergacyn® supplementation may be a valuable approach to counteract adipose tissue dysfunction and obesity-associated effects on cardiometabolic risk.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

Blockade of C5aR1 alleviates liver inflammation and fibrosis in a mouse model of NASH by regulating TLR4 signaling and macrophage polarization

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is an advanced form of chronic fatty liver disease, which is a driver of hepatocellular carcinoma. However, the roles of the C5aR1 in the NASH remain poorly understood. Here, we aimed to investigate the functions and mechanisms of the C5aR1 on hepatic inflammation and fibrosis in murine NASH model.

METHODS

Mice were fed a normal chow diet with corn oil (ND + Oil), a Western diet with corn oil (WD + Oil) or a Western diet with carbon tetrachloride (WD + CCl4) for 12 weeks. The effects of the C5a-C5aR1 axis on the progression of NASH were analyzed and the underlying mechanisms were explored.

RESULTS

Complement factor C5a was elevated in NASH mice. C5 deficiency reduced hepatic lipid droplet accumulation in the NASH mice. The hepatic expression levels of TNFα, IL-1β and F4/80 were decreased in C5-deficient mice. C5 loss alleviated hepatic fibrosis and downregulated the expression levels of α-SMA and TGFβ1. C5aR1 deletion reduced inflammation and fibrosis in NASH mice. Transcriptional profiling of liver tissues and KEGG pathway analysis revealed that several pathways such as Toll-like receptor signaling, NFκB signaling, TNF signaling, and NOD-like receptor signaling pathway were enriched between C5aR1 deficiency and wild-type mice. Mechanistically, C5aR1 deletion decreased the expression of TLR4 and NLRP3, subsequently regulating macrophage polarization. Moreover, C5aR1 antagonist PMX-53 treatment mitigated the progression of NASH in mice.

CONCLUSIONS

Blockade of the C5a-C5aR1 axis reduces hepatic steatosis, inflammation, and fibrosis in NASH mice. Our data suggest that C5aR1 may be a potential target for drug development and therapeutic intervention of NASH.

Research progress into adipose tissue macrophages and insulin resistance

In recent years, there has been an increasing incidence of metabolic syndrome, type 2 diabetes, and cardiovascular events related to insulin resistance. As one of the target organs for insulin, adipose tissue is essential for maintaining in vivo immune homeostasis and metabolic regulation. Currently, the specific adipose tissue mechanisms involved in insulin resistance remain incompletely understood. There is increasing evidence that the process of insulin resistance is mostly accompanied by a dramatic increase in the number and phenotypic changes of adipose tissue macrophages (ATMs). In this review, we discuss the origins and functions of ATMs, some regulatory factors of ATM phenotypes, and the mechanisms through which ATMs mediate insulin resistance. We explore how ATM phenotypes contribute to insulin resistance in adipose tissue. We expect that modulation of ATM phenotypes will provide a novel strategy for the treatment of diseases associated with insulin resistance.

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.

Obesity and Adipose Tissue Dysfunction: From Pediatrics to Adults

Obesity is a growing health problem that affects both children and adults. The increasing prevalence of childhood obesity is associated with comorbidities such as cardiovascular disease, type 2 diabetes and metabolic syndrome due to chronic low-grade inflammation present at early stages of the disease. In pediatric patients suffering from obesity, the role of epigenetics, the gut microbiome and intrauterine environment have emerged as causative factors Interestingly, pediatric obesity is strongly associated with low birth weight. Accelerated weight gain oftentimes occurs in these individuals during the post-natal period, which can lead to increased risk of adiposity and metabolic disease. The pathophysiology of obesity is complex and involves biological and physiological factors compounded by societal factors such as family and community. On a cellular level, adipocytes contained within adipose tissue become dysregulated and further contribute to development of comorbidities similar to those present in adults with obesity. This review provides an overview of the current understanding of adipose tissue immune, inflammatory and metabolic adaptation of the adipose tissue in obesity. Early cellular changes as well as the role of immune cells and inflammation on the progression of disease in pivotal pediatric clinical trials, adult studies and mouse models are emphasized. Understanding the initial molecular and cellular changes that occur during obesity can facilitate new and improved treatments aimed at early intervention and subsequent prevention of adulthood comorbidities.

The role of probiotic supplementation on insulin resistance in obesity associated diabetes: A mini review

Obesity and diabetes are two metabolic disorders linked by an inflammatory process named insulin resistance (IR). Various research on the role of gut microbiota in developing obesity and its associated disorders has led to the growing interest in probiotic supplementation. Considering the life-threatening complications of diabesity this mini review explored the effects of probiotic supplementation on IR in obesity associated diabetes. This review is based on recent articles from 2005-2020, studying the role of probiotic supplementation on glucose and insulin parameters in healthy and diabetic mouse model. Probiotic supplementation altered the gut microbiota composition, increased short chain fatty acid production, and decreased pro inflammatory cytokines. Additionally, they decreased intestinal permeability, circulating lipopolysaccharides and metabolic endotoxemia, hence improved insulin sensitivity and reduced obesity. Although multi-strain probiotic supplementation showed greater benefits than single strain interventions, variations in the concentration of probiotics used and the duration of treatment also influenced the results.  Probiotic supplementation could manipulate the gut microbiota by reducing intestinal permeability, inflammation and ameliorate IR and obesity associated diabetes in animal models which requires further long-term clinical studies in humans. 

Regulation of PPAR-γ activity in lipid-laden hepatocytes affects macrophage polarization and inflammation in nonalcoholic fatty liver disease

BACKGROUND

Lipid metabolism disorder and inflammatory-immune activation are vital triggers in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Various studies have shown that PPAR-γ exerts potent anti-inflammatory and immunomodulatory properties. However, little is known about the regulation of PPAR-γ activity in modulating cell crosstalk in NAFLD.

AIM

To investigate whether the regulation of PPAR-γ activity in lipid-laden hepatocytes affects macrophage polarization and inflammation.

METHODS

Primary hepatocytes were isolated from wild-type C57BL6/J mice or hepatocyte-specific PPAR-γ knockout mice and incubated with free fatty acids (FFAs). Macrophages were incubated with conditioned medium (CM) from lipid-laden hepatocytes with or without a PPAR-γ agonist. Wild-type C57BL/6J mice were fed a high-fat (HF) diet and administered rosiglitazone.

RESULTS

Primary hepatocytes exhibited significant lipid deposition and increased ROS production after incubation with FFAs. CM from lipid-laden hepatocytes promoted macrophage polarization to the M1 type and activation of the TLR4/NF-κB pathway. A PPAR-γ agonist ameliorated oxidative stress and NLRP3 inflammasome activation in lipid-laden hepatocytes and subsequently prevented M1 macrophage polarization. Hepatocyte-specific PPAR-γ deficiency aggravated oxidative stress and NLRP3 inflammasome activation in lipid-laden hepatocytes, which further promoted M1 macrophage polarization. Rosiglitazone administration improved oxidative stress and NLRP3 inflammasome activation in HF diet-induced NAFLD mice in vivo.

CONCLUSION

Upregulation of PPAR-γ activity in hepatocytes alleviated NAFLD by modulating the crosstalk between hepatocytes and macrophages via the reactive oxygen species-NLRP3-IL-1β pathway.

Flightless I Negatively Regulates Macrophage Surface TLR4, Delays Early Inflammation, and Impedes Wound Healing

TLR4 plays a pivotal role in orchestrating inflammation and tissue repair. Its expression has finally been balanced to initiate the early, robust immune response necessary for efficient repair without excessively amplifying and prolonging inflammation, which impairs healing. Studies show Flightless I (Flii) is an immunomodulator that negatively regulates macrophage TLR4 signalling. Using macrophages from Flii^+/−, WT, and Flii^Tg/Tg mice, we have shown that elevated Flii reduces early TLR4 surface expression, delaying and reducing subsequent TNF secretions. In contrast, reduced Flii increases surface TLR4, leading to an earlier robust TNF peak. In Flii^+/− mice, TLR4 levels peak earlier during wound repair, and overall healing is accelerated. Fewer neutrophils, monocytes and macrophages are recruited to Flii^+/− wounds, leading to fewer TNF-positive macrophages, alongside an early peak and a robust shift to M2 anti-inflammatory, reparative Ym1⁺ and IL-10⁺ macrophages. Importantly, in diabetic mice, high Flii levels are found in plasma and unwounded skin, with further increases observed in their wounds, which have impaired healing. Lowering Flii in diabetic mice results in an earlier shift to M2 macrophages and improved healing. Overall, this suggests Flii regulation of TLR4 reduces early inflammation and decreases the M2 macrophage phenotype, leading to impaired healing.

Proteoglycan 4 (PRG4) treatment enhances wound closure and tissue regeneration

The wound healing response is one of most primitive and conserved physiological responses in the animal kingdom, as restoring tissue integrity/homeostasis can be the difference between life and death. Wound healing in mammals is mediated by immune cells and inflammatory signaling molecules that regulate tissue resident cells, including local progenitor cells, to mediate closure of the wound through formation of a scar. Proteoglycan 4 (PRG4), a protein found throughout the animal kingdom from fish to elephants, is best known as a glycoprotein that reduces friction between articulating surfaces (e.g. cartilage). Previously, PRG4 was also shown to regulate the inflammatory and fibrotic response. Based on this, we asked whether PRG4 plays a role in the wound healing response. Using an ear wound model, topical application of exogenous recombinant human (rh)PRG4 hastened wound closure and enhanced tissue regeneration. Our results also suggest that rhPRG4 may impact the fibrotic response, angiogenesis/blood flow to the injury site, macrophage inflammatory dynamics, recruitment of immune and increased proliferation of adult mesenchymal progenitor cells (MPCs) and promoting chondrogenic differentiation of MPCs to form the auricular cartilage scaffold of the injured ear. These results suggest that PRG4 has the potential to suppress scar formation while enhancing connective tissue regeneration post-injury by modulating aspects of each wound healing stage (blood clotting, inflammation, tissue generation and tissue remodeling). Therefore, we propose that rhPRG4 may represent a potential therapy to mitigate scar and improve wound healing.

Galectin-3 S-glutathionylation regulates its effect on adipocyte insulin signaling

Protein-S-glutathionylation promotes redox signaling in physiological and oxidative distress conditions. Galectin-3 (Gal-3) promotes insulin resistance by down-regulating adipocyte insulin signaling, however, its S-glutathionylation and significance is not known. In this context, we report reversible S-glutathionylation of Gal-3. Site-directed mutagenesis established Gal-3 Cys187 as the putative S-glutathionylation site. Glutathionylated Gal-3 prevents Gal-3(WT)-Insulin Receptor interaction and facilitates insulin-induced murine adipocyte p-IRS1(tyr895) and p-AKT(ser473) signaling and glucose uptake in a Gal-3 Cys187 glutathionylation dependent manner in murine adipocytes, as assessed by Western blotting and 2-NBDG uptake assay respectively. Pre-glutathionylated Gal-3 at Cys187 resisted irreversible oxidation by H₂O₂. M2 macrophages showed enhanced Gal-3 S-glutathionylation when compared to M1 phenotype. Serum and stromal vascular fraction (SVF) isolated from control mice showed increased Gal-3 S-glutathionylation as compared to db/db mice. A significant increase in Gal-3 S-glutathionylation was observed in metformin-treated db/db mice when compared to db/db mice alone. Similar to murine, enhanced Gal-3 S-glutathionylation is observed in primary human monocyte derived M2 macrophages when compared to the M1 macrophage phenotype and Gal-3 regulates primary human adipocyte insulin signaling in a glutathionylation dependent manner. Collectively, we identified Gal-3 S-glutathionylation as a protective phenomenon, which relieves its inhibitory effect on adipocyte insulin signaling.

Host-microbial interactions in metabolic diseases: from diet to immunity

Growing evidence suggests that the gut microbiome is an important contributor to metabolic diseases. Alterations in microbial communities are associated with changes in lipid metabolism, glucose homeostasis, intestinal barrier functions, and chronic inflammation, all of which can lead to metabolic disorders. Therefore, the gut microbiome may represent a novel therapeutic target for obesity, type 2 diabetes, and nonalcoholic fatty liver disease. This review discusses how gut microbes and their products affect metabolic diseases and outlines potential treatment approaches via manipulation of the gut microbiome. Increasing our understanding of the interactions between the gut microbiome and host metabolism may help restore the healthy symbiotic relationship between them.

Metabolic factors in the regulation of hypothalamic innate immune responses in obesity

The hypothalamus is a central regulator of body weight and energy homeostasis. There is increasing evidence that innate immune activation in the mediobasal hypothalamus (MBH) is a key element in the pathogenesis of diet-induced obesity. Microglia, the resident immune cells in the brain parenchyma, have been shown to play roles in diverse aspects of brain function, including circuit refinement and synaptic pruning. As such, microglia have also been implicated in the development and progression of neurological diseases. Microglia express receptors for and are responsive to a wide variety of nutritional, hormonal, and immunological signals that modulate their distinct functions across different brain regions. We showed that microglia within the MBH sense and respond to a high-fat diet and regulate the function of hypothalamic neurons to promote food intake and obesity. Neurons, glia, and immune cells within the MBH are positioned to sense and respond to circulating signals that regulate their capacity to coordinate aspects of systemic energy metabolism. Here, we review the current knowledge of how these peripheral signals modulate the innate immune response in the MBH and enable microglia to regulate metabolic control.

Hematopoietic Progenitors and the Bone Marrow Niche Shape the Inflammatory Response and Contribute to Chronic Disease

It is now well understood that the bone marrow (BM) compartment can sense systemic inflammatory signals and adapt through increased proliferation and lineage skewing. These coordinated and dynamic alterations in responding hematopoietic stem and progenitor cells (HSPCs), as well as in cells of the bone marrow niche, are increasingly viewed as key contributors to the inflammatory response. Growth factors, cytokines, metabolites, microbial products, and other signals can cause dysregulation across the entire hematopoietic hierarchy, leading to lineage-skewing and even long-term functional adaptations in bone marrow progenitor cells. These alterations may play a central role in the chronicity of disease as well as the links between many common chronic disorders. The possible existence of a form of “memory” in bone marrow progenitor cells is thought to contribute to innate immune responses via the generation of trained immunity (also called innate immune memory). These findings highlight how hematopoietic progenitors dynamically adapt to meet the demand for innate immune cells and how this adaptive response may be beneficial or detrimental depending on the context. In this review, we will discuss the role of bone marrow progenitor cells and their microenvironment in shaping the scope and scale of the immune response in health and disease.

The Association between Gut Microbiota and Osteoarthritis: Does the Disease Begin in the Gut?

Some say that all diseases begin in the gut. Interestingly, this concept is actually quite old, since it is attributed to the Ancient Greek physician Hippocrates, who proposed the hypothesis nearly 2500 years ago. The continuous breakthroughs in modern medicine have transformed our classic understanding of the gastrointestinal tract (GIT) and human health. Although the gut microbiota (GMB) has proven to be a core component of human health under standard metabolic conditions, there is now also a strong link connecting the composition and function of the GMB to the development of numerous diseases, especially the ones of musculoskeletal nature. The symbiotic microbes that reside in the gastrointestinal tract are very sensitive to biochemical stimuli and may respond in many different ways depending on the nature of these biological signals. Certain variables such as nutrition and physical modulation can either enhance or disrupt the equilibrium between the various species of gut microbes. In fact, fat-rich diets can cause dysbiosis, which decreases the number of protective bacteria and compromises the integrity of the epithelial barrier in the GIT. Overgrowth of pathogenic microbes then release higher quantities of toxic metabolites into the circulatory system, especially the pro-inflammatory cytokines detected in osteoarthritis (OA), thereby promoting inflammation and the initiation of many disease processes throughout the body. Although many studies link OA with GMB perturbations, further research is still needed.

The emerging roles of IL-36, IL-37, and IL-38 in diabetes mellitus and its complications

Diabetes mellitus is a metabolic disease caused by a combination of genetics and environmental factors. The importance of the inflammatory response occurring in the pancreas and adipose tissue in the occurrence and progression of diabetes has been gradually accepted. Excess blood glucose and free fatty acids produce large amounts of inflammatory cytokines and chemokines through oxidative stress and endoplasmic reticulum stress. There is sufficient evidence that proinflammatory mediators, such as interleukin (IL)-1β, IL-6, macrophage chemotactic protein-1, and tumor necrosis factor-α, are engaged in the insulin resistance in peripheral adipose tissue and the apoptosis of pancreatic β-cells. IL-36, IL-37, and IL-38, as new members of the IL-1 family, play an indispensable effect in the regulation of immune system homeostasis and are involved in the pathogenesis of inflammatory and autoimmune diseases. Recently, the abnormal expression of IL-36, IL-37, and IL-38 in diabetes has been reported. In this review, we discuss the emerging functions, potential mechanisms, and future research directions on the role of IL-36, IL-37, and IL-38 in diabetes mellitus and its complications.

Cross-Talk Between Gut Microbiota and Adipose Tissues in Obesity and Related Metabolic Diseases

The rapid increase of obesity and associated diseases has become a major global health problem. Adipose tissues are critical for whole-body homeostasis. The gut microbiota has been recognized as a significant environmental factor in the maintenance of energy homeostasis and host immunity. A growing body of evidence suggests that the gut microbiota regulates host metabolism through a close cross-talk with adipose tissues. It modulates energy expenditure and alleviates obesity by promoting energy expenditure, but it also produces specific metabolites and structural components that may act as the central factors in the pathogenesis of inflammation, insulin resistance, and obesity. Understanding the relationship between gut microbiota and adipose tissues may provide potential intervention strategies to treat obesity and associated diseases. In this review, we focus on recent advances in the gut microbiota and its actions on adipose tissues and highlight the joint actions of the gut microbiota and adipose tissue with each other in the regulation of energy metabolism.

Chronic tissue inflammation and metabolic disease

In this review, Lee and Olefsky discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Deoxyhypusine synthase promotes a pro-inflammatory macrophage phenotype

The metabolic inflammation (meta-inflammation) of obesity is characterized by proinflammatory macrophage infiltration into adipose tissue. Catalysis by deoxyhypusine synthase (DHPS) modifies the translation factor eIF5A to generate a hypusine (Hyp) residue. Hypusinated eIF5A (eIF5A^Hyp) controls the translation of mRNAs involved in inflammation, but its role in meta-inflammation has not been elucidated. Levels of eIF5A^Hyp were found to be increased in adipose tissue macrophages from obese mice and in murine macrophages activated to a proinflammatory M1-like state. Global proteomics and transcriptomics revealed that DHPS deficiency in macrophages altered the abundance of proteins involved in NF-κB signaling, likely through translational control of their respective mRNAs. DHPS deficiency in myeloid cells of obese mice suppressed M1 macrophage accumulation in adipose tissue and improved glucose tolerance. These findings indicate that DHPS promotes the post-transcriptional regulation of a subset of mRNAs governing inflammation and chemotaxis in macrophages and contributes to a proinflammatory M1-like phenotype.

Obesity and inflammation: colorectal cancer engines

The prevalence of obesity continues to increase to the extent that it became a worldwide pandemic. An accumulating body of evidence has associated obesity with the development of different types of cancer, including colorectal cancer, which is a notorious disease with a high mortality rate. At the molecular level, colorectal cancer is a heterogenous disease characterized by a myriad of genetic and epigenetic alterations associated with various forms of genomic instability (detailed in Supplementary Materials). Recently, the microenvironment has emerged as a major factor in carcinogenesis. Our aim is to define the different molecular alterations leading to the development of colorectal cancer in obese patients with a focus on the role of the microenvironment in carcinogenesis. We also highlight all existent molecules in clinical trials that target the activated pathways in obesity-associated colorectal cancer, whether used as single treatments or in combination. Obesity predisposes to colorectal cancer via creating a state of chronic inflammation with dysregulated adipokines, inflammatory mediators, and other factors such as immune cell infiltration. A unifying theme in obesity-mediated colorectal cancer is the activation of the PI3K/AKT, mTOR/MAPK, and STAT3 signaling pathways. Different inhibitory molecules towards these pathways exist, increasing the therapeutic choice of obesity-associated colon cancer. However, obese patients are more likely to suffer from chemotherapy overdosing. Preventing obesity through maintaining a healthy and active lifestyle remains to be the best remedy.

Independent Dose-Response Associations between Fetuin-A and Lean Nonalcoholic Fatty Liver Disease

Patients with lean NAFLD make up an increasing subset of liver disease patients. The association between lean NAFLD and feutin-A, which serves as a hepatokine and adipokine, has never been examined. Our study aimed to explore the association of serum fetuin-A among lean and non-lean patients. The study comprised 606 adults from the community, stratified into lean or non-lean (BMI </≥ 24 kg/m²) and NAFLD or non-NAFLD (scoring of ultrasonographic fatty liver indicator, US-FLI ≥ 2/< 2). Multivariate logistic regression analyses were performed to estimate the odds ratio of having NAFLD among the tertiles of fetuin-A after adjustment. The least square means were computed by general linear models to estimate marginal means of the serum fetuin-A concentrations in relation to the NAFLD groups. The odds ratio (OR) of having NAFLD for the highest versus the lowest tertile of fetuin-A was 2.62 (95% CI: 1.72–3.98; p for trend < 0.001). Stratifying by BMI, the OR of having lean NAFLD for the highest versus the lowest tertile of fetuin-A was 2.09 (95% CI: 1.09–3.98; p for trend 0.026), while non-lean NAFLD had no significant association with the fetuin-A gradient after adjustments. Fetuin-A was positively associated with lean NAFLD after adjusting for central obesity and insulin resistance.

Toll-like receptor-4 null mutation causes fetal loss and fetal growth restriction associated with impaired maternal immune tolerance in mice

Maternal immune adaptation to accommodate pregnancy depends on sufficient availability of regulatory T (Treg) cells to enable embryo implantation. Toll-like receptor 4 is implicated as a key upstream driver of a controlled inflammatory response, elicited by signals in male partner seminal fluid, to initiate expansion of the maternal Treg cell pool after mating. Here, we report that mice with null mutation in Tlr4 (Tlr4^−/−) exhibit impaired reproductive outcomes after allogeneic mating, with reduced pregnancy rate, elevated mid-gestation fetal loss, and fetal growth restriction, compared to Tlr4^+/+ wild-type controls. To investigate the effects of TLR4 deficiency on early events of maternal immune adaptation, TLR4-regulated cytokines and immune regulatory microRNAs were measured in the uterus at 8 h post-mating by qPCR, and Treg cells in uterus-draining lymph nodes were evaluated by flow cytometry on day 3.5 post-coitum. Ptgs2 encoding prostaglandin-endoperoxide synthase 2, cytokines Csf2, Il6, Lif, and Tnf, chemokines Ccl2, Cxcl1, Cxcl2, and Cxcl10, and microRNAs miR-155, miR-146a, and miR-223 were induced by mating in wild-type mice, but not, or to a lesser extent, in Tlr4^−/− mice. CD4⁺ T cells were expanded after mating in Tlr4^+/+ but not Tlr4^−/− mice, with failure to expand peripheral CD25⁺FOXP3⁺ NRP1⁻ or thymic CD25⁺FOXP3⁺ NRP1⁺ Treg cell populations, and fewer Treg cells expressed Ki67 proliferation marker and suppressive function marker CTLA4. We conclude that TLR4 is an essential mediator of the inflammation-like response in the pre-implantation uterus that induces generation of Treg cells to support robust pregnancy tolerance and ensure optimal fetal growth and survival.

Potential of Nutraceutical Supplementation in the Modulation of White and Brown Fat Tissues in Obesity-Associated Disorders: Role of Inflammatory Signalling

The high incidence of obesity is associated with an increasing risk of several chronic diseases such as cardiovascular disease, type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). Sustained obesity is characterized by a chronic and unsolved inflammation of adipose tissue, which leads to a greater expression of proinflammatory adipokines, excessive lipid storage and adipogenesis. The purpose of this review is to clarify how inflammatory mediators act during adipose tissue dysfunction in the development of insulin resistance and all obesity-associated diseases. In particular, we focused our attention on the role of inflammatory signaling in brown adipose tissue (BAT) thermogenic activity and the browning of white adipose tissue (WAT), which represent a relevant component of adipose alterations during obesity. Furthermore, we reported the most recent evidence in the literature on nutraceutical supplementation in the management of the adipose inflammatory state, and in particular on their potential effect on common inflammatory mediators and pathways, responsible for WAT and BAT dysfunction. Although further research is needed to demonstrate that targeting pro-inflammatory mediators improves adipose tissue dysfunction and activates thermogenesis in BAT and WAT browning during obesity, polyphenols supplementation could represent an innovative therapeutic strategy to prevent progression of obesity and obesity-related metabolic diseases.

Inflammatory Mechanisms Underlying Nonalcoholic Steatohepatitis and the Transition to Hepatocellular Carcinoma

Nonalcoholic fatty liver disease (NAFLD) is a rising chronic liver disease and comprises a spectrum from simple steatosis to nonalcoholic steatohepatitis (NASH) to end-stage cirrhosis and risk of hepatocellular carcinoma (HCC). The pathogenesis of NAFLD is multifactorial, but inflammation is considered the key element of disease progression. The liver harbors an abundance of resident immune cells, that in concert with recruited immune cells, orchestrate steatohepatitis. While inflammatory processes drive fibrosis and disease progression in NASH, fueling the ground for HCC development, immunity also exerts antitumor activities. Furthermore, immunotherapy is a promising new treatment of HCC, warranting a more detailed understanding of inflammatory mechanisms underlying the progression of NASH and transition to HCC. Novel methodologies such as single-cell sequencing, genetic fate mapping, and intravital microscopy have unraveled complex mechanisms behind immune-mediated liver injury. In this review, we highlight some of the emerging paradigms, including macrophage heterogeneity, contributions of nonclassical immune cells, the role of the adaptive immune system, interorgan crosstalk with adipose tissue and gut microbiota. Furthermore, we summarize recent advances in preclinical and clinical studies aimed at modulating the inflammatory cascade and discuss how these novel therapeutic avenues may help in preventing or combating NAFLD-associated HCC.

Obesity-induced inflammation: The impact of the hematopoietic stem cell niche

Obesity and obesity-related diseases like type 2 diabetes (T2D) are prominent global health issues; therefore, there is a need to better understand the mechanisms underlying these conditions. The onset of obesity is characterized by accumulation of proinflammatory cells, including Ly6c^hi monocytes (which differentiate into proinflammatory macrophages) and neutrophils, in metabolic tissues. This shift toward chronic, low-grade inflammation is an obese-state hallmark and highly linked to metabolic disorders and other obesity comorbidities. The mechanisms that induce and maintain increased inflammatory myelopoiesis are of great interest, with a recent focus on how obesity affects more primitive hematopoietic cells. The hematopoietic system is constantly replenished by proper regulation of hematopoietic stem and progenitor (HSPC) pools in the BM. While early research suggests that chronic obesity promotes expansion of myeloid-skewed HSPCs, the involvement of the hematopoietic stem cell (HSC) niche in regulating obesity-induced myelopoiesis remains undefined. In this review, we explore the role of the multicellular HSC niche in hematopoiesis and inflammation, and the potential contribution of this niche to the hematopoietic response to obesity. This review further aims to summarize the potential HSC niche involvement as a target of obesity-induced inflammation and a driver of obesity-induced myelopoiesis.

Metabolism and Metabolic Disorders and the Microbiome: The Intestinal Microbiota Associated With Obesity, Lipid Metabolism, and Metabolic Health-Pathophysiology and Therapeutic Strategies

Changes in the intestinal microbiome have been associated with obesity and type 2 diabetes, in epidemiological studies and studies of the effects of fecal transfer in germ-free mice. We review the mechanisms by which alterations in the intestinal microbiome contribute to development of metabolic diseases, and recent advances, such as the effects of the microbiome on lipid metabolism. Strategies have been developed to modify the intestinal microbiome and reverse metabolic alterations, which might be used as therapies. We discuss approaches that have shown effects in mouse models of obesity and metabolic disorders, and how these might be translated to humans to improve metabolic health.

Role of TLR4 in the induction of inflammatory changes in adipocytes and macrophages

In obesity, high levels of saturated fatty acids (SFAs) contribute to adipose tissue inflammation and dysfunction. Obesity-induced macrophage infiltration leads to insulin resistance, but the adipocyte itself may play a role in generating the inflammatory milieu. Given our recent findings of the role of TLR4 in myeloid biasing in obesity, we next investigated the role of TLR4 in adipocyte generated inflammatory responses to SFAs and lipopolysaccharides. We used WT and Tlr4^-/- ear mesenchymal stem cell derived adipocytes (EMSC Ad) and bone marrow dendritic cells (BMDCs) to evaluate cell specific responses. Our work demonstrates a role for TLR4 in adipocyte- immune cell crosstalk and that SFA derived metabolites from adipocytes may induce proinflammatory stimulation of immune cells in a TLR4 independent manner.

Nitrate Esters Alleviated Coronary Atherosclerosis Through Inhibition of NF-κB-Regulated Macrophage Polarization Shift in Epicardial Adipose Tissue

Nitrate esters have been used in clinical practice for more than one century for the treatment of angina. Their clinical effectiveness is due to vasodilator activity in arteries through a method of delivering nitric oxide or a nitric oxide-like compound. Recently, an increasing numbers of functions of this molecule in biology and pathophysiology have been discovered. Macrophage polarization shift in epicardial adipose tissue (EAT) has been demonstrated to be correlated with the severity of coronary artery disease (CAD). In this study, we aimed to investigate whether nitrate esters could improve coronary atherosclerosis through inhibition of macrophage polarization shift in EAT. A case-control study enrolled 48 subjects in 2 groups: CAD patients with or without nitrate esters treatment. Infiltration of M1/M2 macrophages and the expressions of pro-inflammatory and anti-inflammatory cytokines in EAT and subcutaneous white adipose tissue were investigated by immunohistochemical stain among subjects undergoing coronary artery bypass graft surgery. The expression levels of metabolic genes were investigated by real-time reverse transcription-polymerase chain reaction (RT-PCR). We found that nitrate ester treatment significantly inhibited NF-кB activity and decreased macrophage infiltration and M1/M2 macrophage ratio in EAT in patients with CAD. The expressions of pro-inflammatory cytokines were significantly decreased, along with significantly elevated expressions of anti-inflammatory cytokines in CAD patients with nitrate ester treatment, corresponding EAT dysfunction was ameliorated and the severity of patients with CAD (Gensini score) was significantly decreased. The protective effects on macrophage polarization and EAT function through NF-кB activity inhibition suggested a potential mechanism of nitrate esters in alleviating the severity of CAD.

Obese Adipose Tissue Secretion Induces Inflammation in Preadipocytes: Role of Toll-Like Receptor-4

In obesity, the dysfunctional adipose tissue (AT) releases increased levels of proinflammatory adipokines such as TNFα, IL-6, and IL-1β and free fatty acids (FFAs), characterizing a chronic, low-grade inflammation. Whilst FFAs and proinflammatory adipokines are known to elicit an inflammatory response within AT, their relative influence upon preadipocytes, the precursors of mature adipocytes, is yet to be determined. Our results demonstrated that the conditioned medium (CM) derived from obese AT was rich in FFAs, which guided us to evaluate the role of TLR4 in the induction of inflammation in preadipocytes. We observed that CM derived from obese AT increased reactive oxygen species (ROS) levels and NF-ĸB nuclear translocation together with IL-6, TNFα, and IL-1β in 3T3-L1 cells in a TLR4-dependent manner. Furthermore, TLR4 signaling was involved in the increased expression of C/EBPα together with the release of leptin, adiponectin, and proinflammatory mediators, in response to the CM derived from obese AT. Our results suggest that obese AT milieu secretes lipokines, which act in a combined paracrine/autocrine manner, inducing inflammation in preadipocytes via TLR4 and ROS, thus creating a paracrine loop that facilitates the differentiation of adipocytes with a proinflammatory profile.

Fgr kinase is required for proinflammatory macrophage activation during diet-induced obesity

Proinflammatory macrophages are key in the development of obesity. In addition, reactive oxygen species (ROS), which activate the Fgr tyrosine kinase, also contribute to obesity. Here we show that ablation of Fgr impairs proinflammatory macrophage polarization while preventing high-fat diet (HFD)-induced obesity in mice. Systemic ablation of Fgr increases lipolysis and liver fatty acid oxidation, thereby avoiding steatosis. Knockout of Fgr in bone marrow (BM)-derived cells is sufficient to protect against insulin resistance and liver steatosis following HFD feeding, while the transfer of Fgr-expressing BM-derived cells reverts protection from HFD feeding in Fgr-deficient hosts. Scavenging of mitochondrial peroxides is sufficient to prevent Fgr activation in BM-derived cells and HFD-induced obesity. Moreover, Fgr expression is higher in proinflammatory macrophages and correlates with obesity traits in both mice and humans. Thus, our findings reveal the mitochondrial ROS-Fgr kinase as a key regulatory axis in proinflammatory adipose tissue macrophage activation, diet-induced obesity, insulin resistance and liver steatosis.

Metabolic and Molecular Mechanisms of Macrophage Polarisation and Adipose Tissue Insulin Resistance

Inflammation plays a key role in the development and progression of type-2 diabetes (T2D), a disease characterised by peripheral insulin resistance and systemic glucolipotoxicity. Visceral adipose tissue (AT) is the main source of inflammation early in the disease course. Macrophages are innate immune cells that populate all peripheral tissues, including AT. Dysregulated AT macrophage (ATM) responses to microenvironmental changes are at the root of aberrant inflammation and development of insulin resistance, locally and systemically. The inflammatory activation of macrophages is regulated at multiple levels: cell surface receptor stimulation, intracellular signalling, transcriptional and metabolic levels. This review will cover the main mechanisms involved in AT inflammation and insulin resistance in T2D. First, we will describe the physiological and pathological changes in AT that lead to inflammation and insulin resistance. We will next focus on the transcriptional and metabolic mechanisms described that lead to the activation of ATMs. We will discuss more novel metabolic mechanisms that influence macrophage polarisation in other disease or tissue contexts that may be relevant to future work in insulin resistance and T2D.

Abrogation of Toll-Like Receptor 4 Mitigates Obesity-Induced Oxidative Stress, Proinflammation, and Insulin Resistance Through Metabolic Reprogramming of Mitochondria in Adipose Tissue

Aims: Obesity-induced excessive visceral fat (VF) accumulation is associated with insulin resistance (IR), systemic oxidative stress, and chronic inflammation. As toll-like receptor 4 (TLR4) plays an important role in innate immunity, we herein investigate the effect of TLR4 knockout (T4KO) in a high-fat high-sucrose diet (HFD)-induced obesity mouse model. Results: C57BL6 wild-type (WT) and T4KO mice were fed with either control diet (CD) or HFD for 12 months, rendering four experimental groups: WT+CD, WT+HFD, T4KO+CD, and T4KO+HFD. Compared with WT+CD, WT+HFD demonstrated significant increase in VF accumulation, oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and development of IR. Compared with WT+HFD, T4KO+HFD presented increased BW and body fat with higher subcutaneous fat (SF)/VF ratio, but lower body temperature, as well as decreased oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and IR. Unlike WT+HFD, T4KO+HFD exhibited an increase in mitochondrial electron transport chain activity but a decrease of uncoupling protein 2 (UCP2) level. While T4KO hindered HFD-induced increasing mitochondrial oxygen consumption rate, a shift toward a higher extracellular acidification rate in VF was observed. Notably, T4KO inhibits HFD-induced mitochondrial translocation of nuclear factor of activated T cells 2 (NFATC2), which contributed to mitochondrial metabolic reprogramming. Both fat distribution shifting from VF to SF and mitochondrial metabolic reprogramming may alleviate systemic oxidative stress and chronic inflammation. Innovation and Conclusion: Abrogation of TLR4 contributes to reduction of oxidative stress through metabolic reprogramming of mitochondria in VF, mitigating obesity-induced IR. The study provides critical insight into associating innate immunity-mitochondria interplay with prevention of diabetes.

The Relationship Between Gut Microbiota and Inflammatory Diseases: The Role of Macrophages

Gut microbiota, an integral part of the human body, comprise bacteria, fungi, archaea, and protozoa. There is consensus that the disruption of the gut microbiota (termed “gut dysbiosis”) is influenced by host genetics, diet, antibiotics, and inflammation, and it is closely linked to the pathogenesis of inflammatory diseases, such as obesity and inflammatory bowel disease (IBD). Macrophages are the key players in the maintenance of tissue homeostasis by eliminating invading pathogens and exhibit extreme plasticity of their phenotypes, such as M1 or M2, which have been demonstrated to exert pro- and anti-inflammatory functions. Microbiota-derived metabolites, short-chain fatty acids (SCFAs) and Gram-negative bacterial lipopolysaccharides (LPS), exert anti-inflammatory or pro-inflammatory effects by acting on macrophages. Understanding the role of macrophages in gut microbiota-inflammation interactions might provide us a novel method for preventing and treating inflammatory diseases. In this review, we summarize the recent research on the relationship between gut microbiota and inflammation and discuss the important role of macrophages in this context.

Deciphering the cellular interplays underlying obesity-induced adipose tissue fibrosis

Obesity originates from an imbalance between caloric intake and energy expenditure that promotes adipose tissue expansion, which is necessary to buffer nutrient excess. Patients with higher visceral fat mass are at a higher risk of developing severe complications such as type 2 diabetes and cardiovascular and liver diseases. However, increased fat mass does not fully explain obesity's propensity to promote metabolic diseases. With chronic obesity, adipose tissue undergoes major remodeling, which can ultimately result in unresolved chronic inflammation leading to fibrosis accumulation. These features drive local tissue damage and initiate and/or maintain multiorgan dysfunction. Here, we review the current understanding of adipose tissue remodeling with a focus on obesity-induced adipose tissue fibrosis and its relevance to clinical manifestations.

Epigenetic Regulation of TLR4 in Diabetic Macrophages Modulates Immunometabolism and Wound Repair

Macrophages are critical for the initiation and resolution of the inflammatory phase of wound healing. In diabetes, macrophages display a prolonged inflammatory phenotype preventing tissue repair. TLRs, particularly TLR4, have been shown to regulate myeloid-mediated inflammation in wounds. We examined macrophages isolated from wounds of patients afflicted with diabetes and healthy controls as well as a murine diabetic model demonstrating dynamic expression of TLR4 results in altered metabolic pathways in diabetic macrophages. Further, using a myeloid-specific mixed-lineage leukemia 1 (MLL1) knockout (Mll1^f/fLyz2^Cre+ ), we determined that MLL1 drives Tlr4 expression in diabetic macrophages by regulating levels of histone H3 lysine 4 trimethylation on the Tlr4 promoter. Mechanistically, MLL1-mediated epigenetic alterations influence diabetic macrophage responsiveness to TLR4 stimulation and inhibit tissue repair. Pharmacological inhibition of the TLR4 pathway using a small molecule inhibitor (TAK-242) as well as genetic depletion of either Tlr4 (Tlr4^-/- ) or myeloid-specific Tlr4 (Tlr4^f/fLyz2^Cre+) resulted in improved diabetic wound healing. These results define an important role for MLL1-mediated epigenetic regulation of TLR4 in pathologic diabetic wound repair and suggest a target for therapeutic manipulation.

Mechanisms of Macrophage Polarization in Insulin Signaling and Sensitivity

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

The Exercise Training Modulatory Effects on the Obesity-Induced Immunometabolic Dysfunctions

Reduced physical activity rate in people's lifestyle is a global concern associated with the prevalence of health disorders such as obesity and metabolic disturbance. Ample evidence has indicated a critical role of the immune system in the aggravation of obesity. The type, duration, and production of adipose tissue-released mediators may change subsequent inactive lifestyle-induced obesity, leading to the chronic systematic inflammation and monocyte/macrophage (MON/MФ) phenotype polarization. Preliminary adipose tissue expansion can be inhibited by changing the lifestyle. In this context, exercise training is widely recommended due to a definite improvement of energy balance and the potential impacts on the inflammatory signaling cascades. How exercise training affects the immune system has not yet been fully elucidated, because its anti-inflammatory, pro-inflammatory, or even immunosuppressive impacts have been indicated in the literature. A thorough understanding of the mechanisms triggered by exercise can suggest a new approach to combat meta-inflammation-induced metabolic diseases. In this review, we summarized the obesity-induced inflammatory pathways, the roles of MON/MФ polarization in adipose tissue and systemic inflammation, and the underlying inflammatory mechanisms triggered by exercise during obesity.

TLR4 Polymorphisms (896A>G and 1196C>T) Affect the Predisposition to Diabetic Nephropathy in Type 2 Diabetes Mellitus

PURPOSE

Type 2 diabetes mellitus (T2DM) is a disease with a steadily increasing incidence throughout the world. Some molecules regulating the innate immune responses such as toll-like receptor 4 (TLR4) have shown to be involved in late diabetic complications. This study aimed to investigate the association of TLR4 gene polymorphisms with clinicopathological aspects of T2DM in the Iranian population.

PATIENTS AND METHODS

Two TLR4 896A>G and 1196C>T polymorphisms were assessed in 100 T2DM patients and 100 healthy controls using sequence-specific primers PCR. Demographic, anthropometric, and biochemical parameters were obtained from the participants.

RESULTS

After logistic regression, in 1196C>T, a significant association was shown between diabetic nephropathy (DN) and CT genotype (P= 0.04, OR= 4.35, CI= (1.04-18.1)). TG level has increased significantly in both T2DM and control subjects with CT genotype (P= 0.027, OR= 1.005, 95% CI= (1.001-1.01)). For 896A>G variant, a significant association was also detected between AG genotype and increased oral glucose tolerance test (OGTT) level (P= 0.048, OR= 1.003, 95% CI= (1.00-1.005)).

CONCLUSION

Although minor alleles of 1196C>T and 896A>G variants have not directly been associated with type 2 diabetes, by involving in the dysregulation of serum TG and blood sugar levels, they might increase the risk of DN.

Obesity, Insulin Resistance, and Type 2 Diabetes: Associations and Therapeutic Implications

Obesity is a triggering factor for diabetes associated with insulin resistance. In individuals who are obese, higher amounts of non-esterified fatty acids, glycerol, hormones, and pro-inflammatory cytokines that could participate in the development of insulin resistance are released by adipose tissue. Besides, endoplasmic reticulum stress, adipose tissue hypoxia, oxidative stress, lipodystrophy, and genetic background have a role in insulin resistance. However, no effective drug therapy was developed for type 2 diabetes mellitus targeting these physiological factors. This is might be due to a lack of agreement on the comprehensive mechanism of insulin resistance. Therefore, this review assesses the cellular components of each physiologic and pathophysiologic factors that are involved in obesity associated insulin resistance, and may encourage further drug development in this field.

A global perspective on the crosstalk between saturated fatty acids and Toll-like receptor 4 in the etiology of inflammation and insulin resistance

Obesity is featured by chronic systemic low-grade inflammation that eventually contributes to the development of insulin resistance. Toll-like receptor 4 (TLR4) is an important mediator that triggers the innate immune response by activating inflammatory signaling cascades. Human, animal and cell culture studies identified saturated fatty acids (SFAs), the dominant non-esterified fatty acid (NEFA) in the circulation of obese subjects, as non-microbial agonists that trigger the inflammatory response via activating TLR4 signaling, which acts as an important causative link between fatty acid overload, chronic low-grade inflammation and the related metabolic aberrations. The interaction between SFAs and TLR4 may be modulated through the myeloid differentiation primary response gene 88-dependent and independent signaling pathway. Greater understanding of the crosstalk between dietary SFAs and TLR4 signaling in the pathogenesis of metabolic imbalance may facilitate the design of a more efficient pharmacological strategy to alleviate the risk of developing chronic diseases elicited in part by fatty acid overload. The current review discusses recent advances in the impact of crosstalk between SFAs and TLR4 on inflammation and insulin resistance in multiple cell types, tissues and organs in the context of metabolic dysregulation.

Pattern Recognition Receptor-Mediated Chronic Inflammation in the Development and Progression of Obesity-Related Metabolic Diseases

Obesity-induced chronic inflammation is known to promote the development of many metabolic diseases, especially insulin resistance, type 2 diabetes mellitus, nonalcoholic fatty liver disease, and atherosclerosis. Pattern recognition receptor-mediated inflammation is an important determinant for the initiation and progression of these metabolic diseases. Here, we review the major features of the current understanding with respect to obesity-related chronic inflammation in metabolic tissues, focus on Toll-like receptors and nucleotide-binding oligomerization domain-like receptors with an emphasis on how these receptors determine metabolic disease progression, and provide a summary on the development and progress of PRR antagonists for therapeutic intervention.

Toll-like receptor 4 deficiency or inhibition does not modulate survival and neurofunctional outcome in a murine model of cardiac arrest and resuscitation

Background

Patients experiencing cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) often die or suffer from severe neurological impairment. Post resuscitation syndrome is characterized by a systemic inflammatory response. Toll-like receptor 4 (TLR4) is a major mediator of inflammation and TLR4 has been implicated in the pathogenesis of post-resuscitation encephalopathy. The aim of this study was to evaluate whether TLR4 deficiency or inhibition can modulate survival and neurofunctional outcome after CA/CPR.

Methods

Following intubation and central venous cannulation, CA was induced in wild type (C57Bl/6J, n = 38), TLR4 deficient (TLR4^-/-, n = 37) and TLR4 antibody treated mice (5mg/kg MTS510, n = 15) by high potassium. After 10min, CPR was performed using a modified sewing machine until return of spontaneous circulation (ROSC). Cytokines and cerebral TNFalpha levels were measured 8h after CA/CPR. Survival, early neurological recovery, locomotion, spatial learning and memory were assessed over a period of 28 days.

Results

Following CA/CPR, all mice exhibited ROSC and 31.5% of wild type mice survived until day 28. Compared to wild type mice, neither TLR4^-/- nor MTS510 treated wild type mice had statistically significant altered survival following CA/CPR (51.3 and 26.7%, P = 0.104 and P = 0.423 vs. WT, respectively). Antibody-treated but not TLR4^-/- mice had higher IL-1β and IL-6 levels and TLR4^-/- mice had higher IL-10 and cerebral TNFalpha levels. No differences existed between mice of all groups in early neurological recovery, locomotion, spatial learning ability or remembrance.

Conclusion

Therapeutic strategies targeting TLR4 may not be suitable for the reduction of mortality or neurofunctional impairment after CA/CPR.

Ghrelin Signaling in Immunometabolism and Inflamm-Aging

Intracellular changes in immune cells lead to metabolic dysfunction, which is termed immunometabolism. Chronic inflammation is a hallmark of aging; this phenomenon is described as inflamm-aging. Immunometabolism and inflamm-aging are closely linked to obesity, insulin resistance, type 2 diabetes (T2D), cardiovascular diseases, and cancers, which consequently reduce life span and health span of the elderly. Ghrelin is an orexigenic hormone that regulates appetite and food intake. Ghrelin's functions are mediated through its receptor, growth hormone secretagogue receptor (GHS-R). Ghrelin and GHS-R have important roles in age-associated obesity, insulin resistance, and T2D. In this chapter, we have discussed the roles of ghrelin signaling in diet-induced obesity and normal aging as it relates to energy metabolism and inflammation in key metabolic tissues and organs. The new findings reveal that ghrelin signaling is an important regulatory mechanism for immunometabolism and inflamm-aging. Ghrelin signaling offers an exciting novel therapeutic strategy for treatment of obesity and insulin resistance of the elderly.

Alcohol-induced adipose tissue macrophage phenotypic switching is independent of myeloid Toll-like receptor 4 expression

Alcoholic liver disease results from a combination of immune and metabolic pathogenic events. In addition to liver injury, chronic alcohol consumption also causes adipose tissue inflammation. The specific immune mechanisms that drive this process are unknown. Here, we sought to determine the role of the innate immune receptor Toll-like receptor 4 (TLR4) in alcohol-induced adipose tissue inflammation. Using a model of chronic, multiple-binge alcohol exposure, we showed that alcohol-mediated accumulation of proinflammatory adipose tissue macrophages was absent in global TLR4 knockout mice. Proinflammatory macrophage accumulation did not depend on macrophage TLR4 expression; LysMCre-driven deletion of Tlr4 from myeloid cells did not affect circulating endotoxin or the accumulation of M1 macrophages in adipose tissue following alcohol exposure. Proinflammatory cytokine/chemokine production in the adipose stromal vascular fraction also occurred independently of TLR4. Finally, the levels of other adipose immune cells, such as dendritic cells, neutrophils, B cells, and T cells, were modulated by chronic, multiple-binge alcohol and the presence of TLR4. Together, these data indicate that TLR4 expression on cells, other than myeloid cells, is important for the alcohol-induced increase in proinflammatory adipose tissue macrophages.