Adiponectin attenuates human eosinophil adhesion and chemotaxis: implications in allergic inflammation

Adiponectin: friend or foe in obesity and inflammation

Adiponectin is an adipokine predominantly produced by fat cells, circulates and exerts insulin-sensitizing, cardioprotective and anti-inflammatory effects. Dysregulation of adiponectin and/or adiponectin signaling is implicated in a number of metabolic diseases such as obesity, insulin resistance, diabetes, and cardiovascular diseases. However, while the insulin-sensitizing and cardioprotective effects of adiponectin have been widely appreciated in the field, the obesogenic and anti-inflammatory effects of adiponectin are still of much debate. Understanding the physiological function of adiponectin is critical for adiponectin-based therapeutics for the treatment of metabolic diseases.

Elevated Serum Leptin Levels in Patients With Eosinophilic Chronic Rhinosinusitis

Background: Eosinophilic chronic sinusitis (ECRS) is a subtype of CRS with nasal polyps (CRSwNP) that is frequently comorbid with asthma. Notably, ECRS patients often show a high recurrence of NPs after surgical resection. Leptin is a hormone produced by adipocytes that has been implicated in airway inflammatory diseases. However, to date, the role of leptin in ECRS has not been investigated. Objective: To determine whether the serum levels of leptin are altered in patients with ECRS. Methods: In total, 40 patients with ECRS, 15 patients with non-eosinophilic CRS (non-ECRS), and 12 individuals without CRS (control) were included in this study. Patient's serum leptin levels were assessed, and the number of eosinophils in their NPs were measured through a histological evaluation of the three densest areas with cellular infiltrate beneath the epithelial surface. Finally, nasal fibroblast cultures established from NPs were stimulated with varying concentrations of recombinant leptin in vitro to determine whether leptin affects eotaxin-3 (Chemokine (C-C motif) ligand 26 :26: CCL26) expression. Results: The serum leptin levels in both the ECRS and non-ECRS groups were significantly higher than those in the control subjects (p < 0.0001 vs. ECRS; p < 0.05 vs. non-ECRS). Furthermore, ECRS patients displayed significantly elevated serum leptin levels compared to non-ECRS patients (p < 0.001), although there was no difference in body mass index between the groups. Notably, serum leptin levels were correlated with the proportion of eosinophils in peripheral blood (r = 0.3575, p < 0.01) and the number of eosinophils in NPs (r = 0.5109, p < 0.0001). Serum leptin levels were also correlated with eotaxin-3 mRNA expression in NPs (r = 0.5374, p < 0.01). Finally, leptin significantly augmented eotaxin-3 expression in nasal fibroblasts established in vitro from NPs in a leptin receptor-dependent manner (p < 0.05). Conclusion: Leptin levels are elevated in ECRS patients and may both promote and indicate the severity of ECRS as well as systemic type 2-biased inflammatory responses. Combined, these data indicate that circulating leptin may play a significant role in the development of eosinophilic inflammation in NPs.

The Role of Adiponectin in the Skin

Adiponectin (Ad), a 30 kDa molecule, is an anti-diabetic adipokine; although derived from adipose tissue, it performs numerous activities in various other tissues. It binds to its own receptors, namely adiponectin receptor 1(AdipoR1), adiponectin receptor 2 (AdipoR2), and T-cadherin (CDH13). Ad plays several roles, especially as a regulator. It modulates lipid and glucose metabolism and promotes insulin sensitivity. This demonstrates that Ad has a robust correlation with fat metabolism. Furthermore, although Ad is not in direct contact with other tissues, including the skin, it can be delivered to them by diffusion or secretion via the endocrine system. Recently it has been reported that Ad can impact skin cell biology, underscoring its potential as a therapeutic biomarker of skin diseases. In the present review, we have discussed the association between skin cell biology and Ad. To elaborate further, we described the involvement of Ad in the biology of various types of cells in the skin, such as keratinocytes, fibroblasts, melanocytes, and immune cells. Additionally, we postulated that Ad could be employed as a therapeutic target to maintain skin homeostasis.

Adiponectin and Asthma: Knowns, Unknowns and Controversies

Adiponectin is an adipokine associated with the healthy obese phenotype. Adiponectin increases insulin sensitivity and has cardio and vascular protection actions. Studies related to adiponectin, a modulator of the innate and acquired immunity response, have suggested a role of this molecule in asthma. Studies based on various asthma animal models and on the key cells involved in the allergic response have provided important insights about this relation. Some of them indicated protection and others reversed the balance towards negative effects. Many of them described the cellular pathways activated by adiponectin, which are potentially beneficial for asthma prevention or for reduction in the risk of exacerbations. However, conclusive proofs about their efficiency still need to be provided. In this article, we will, briefly, present the general actions of adiponectin and the epidemiological studies supporting the relation with asthma. The main focus of the current review is on the mechanisms of adiponectin and the impact on the pathobiology of asthma. From this perspective, we will provide arguments for and against the positive influence of this molecule in asthma, also indicating the controversies and sketching out the potential directions of research to complete the picture.

Adiponectin/AdipoR1 Axis Promotes IL-10 Release by Human Regulatory T Cells

Background

Adiponectin is an important immunomodulatory mediator in inflammatory conditions. While we previously showed that adiponectin receptor 1 (AdipoR1) is expressed in murine regulatory T cells (Tregs), its expression in human Tregs remain unknown. Here, we examined the expression of AdipoR1 in human Tregs and whether its ligand, globular adiponectin (gAd) affects the Treg ability to secrete IL-10 and the role of Type 2 (T2) inflammation in such process.

Methods

Human Tregs from peripheral blood were analyzed by flow cytometry for AdipoR1, Helios and IL-10 expression. CD4⁺ T cells enriched from peripheral blood mononuclear cells (PBMCs) were cultured in the presence or the absence of gAd or the chemical adiponectin receptor agonist, AdipoRon, or in a T2 cytokine milieu. Flow cytometry was then used to assess intracellular IL-10, IL-10 secreting cells, FOXP3 and Helios expression, and phosphorylated p38 MAP kinase (MAPK). IL-10 levels in CD4⁺ T cell supernatants were quantified by ELISA.

Results

We found that a subset of human Tregs expressed AdipoR1. Importantly, more Helios^- cells expressed AdipoR1 than Helios⁺ cells. Likewise, there was a higher frequency of IL-10⁺ cells within Helios^- AdipoR1⁺ Tregs compared to Helios⁺ AdipoR1⁺ Tregs. In contrast, the IL-10 mean fluorescence intensity (MFI) was higher in Helios⁺ AdipoR1⁺ Tregs compared to Helios^-AdipoR1⁺ Tregs. When human CD4⁺ T cells were treated with gAd or AdipoRon, a significant increase in IL-10 secretion, FOXP3 expression, and p38 MAPK phosphorylation was observed in Helios^- AdipoR1⁺ Tregs. Interestingly, gAd under T2 cytokine milieu significantly increased the intracellular levels of IL-10, mainly in Helios⁺ AdipoR1⁺ Tregs, and IL-10 levels in supernatants of CD4⁺ T cells.

Conclusions

Collectively, our findings suggest that adiponectin/AdipoR1 axis promotes IL-10 release by Tregs, mainly in Helios^- Tregs, and the effect was amplified by T2 inflammation in Helios⁺ Tregs.

The pathophysiological role of adipokines in the development of bronchial asthma combined with obesity

The combined course of bronchial asthma (BA) and obesity is one of the urgent medical and social problems that requires a comprehensive and careful study in connection with a decrease in the quality of life of such patients, an increase in the frequency, duration of hospitalization and a high economic burden for the state as a whole. The relationship between BA and obesity is now confirmed by numerous studies, at the same time, despite the variability of the proposed mechanisms of pathogenetic effects of obesity on asthma, metabolic aspects of the relationship of these diseases need further study. Adipose tissue hormones are responsible for the energy homeostasis of the body therefore, excessive accumulation of adipose tissue is accompanied by the development of an imbalance in metabolic processes in various organs and tissues. Due to the emergence of new scientific data on the role and function of adipokines in the body, metabolic effects of adipokines are considered in the focus of their pathophysiological association with obesity and asthma. This literary review highlights the current understanding of the role of metabolic effects of the most studied adipokines (resistin, retinol-binding protein, leptin and adiponectin) in the development of obesity and BA. Gender and age-dependent features of adipokine levels in BA and obesity are described. Data on the confirmed role of adiponectin and leptin in the progression of BA combined with obesity are presented. It has been shown that the role of resistin and retinol-binding protein in the development of BA combined with obesity has not been studied. It is demonstrated that further study of metabolic activity of adipokines in BA is an actual and perspective direction of researches which will allow to develop new diagnostic and therapeutic strategies in patients with BA with obesity.

Adipokines and Chronic Rheumatic Diseases: from Inflammation to Bone Involvement

Besides its well-known role as energy storage tissue, adipose tissue is a biologically active tissue that can also be considered as an endocrine organ, as it is able to secrete adipokines. These bioactive factors, similar in structure to cytokines, are involved in several physiological and pathological conditions, such as glucose homeostasis, angiogenesis, blood pressure regulation, control of food intake, and also inflammation and bone homeostasis via endocrine, paracrine, and autocrine mechanisms. Given their pleiotropic functions, the role of adipokines has been evaluated in chronic rheumatic osteoarticular inflammatory diseases, particularly focusing on their effects on inflammatory and immune response and on bone alterations. Indeed, these diseases are characterized by different bone complications, such as local and systemic bone loss and new bone formation. The aim of this review is to summarize the role of adipokines in rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, osteoarthritis, and osteoporosis, especially considering their role in the pathogenesis of bone complications typical of these conditions.

Adipose Tissue Immunomodulation: A Novel Therapeutic Approach in Cardiovascular and Metabolic Diseases

Adipose tissue is a critical regulator of systemic metabolism and bodily homeostasis as it secretes a myriad of adipokines, including inflammatory and anti-inflammatory cytokines. As the main storage pool of lipids, subcutaneous and visceral adipose tissues undergo marked hypertrophy and hyperplasia in response to nutritional excess leading to hypoxia, adipokine dysregulation, and subsequent low-grade inflammation that is characterized by increased infiltration and activation of innate and adaptive immune cells. The specific localization, physiology, susceptibility to inflammation and the heterogeneity of the inflammatory cell population of each adipose depot are unique and thus dictate the possible complications of adipose tissue chronic inflammation. Several lines of evidence link visceral and particularly perivascular, pericardial, and perirenal adipose tissue inflammation to the development of metabolic syndrome, insulin resistance, type 2 diabetes and cardiovascular diseases. In addition to the implication of the immune system in the regulation of adipose tissue function, adipose tissue immune components are pivotal in detrimental or otherwise favorable adipose tissue remodeling and thermogenesis. Adipose tissue resident and infiltrating immune cells undergo metabolic and morphological adaptation based on the systemic energy status and thus a better comprehension of the metabolic regulation of immune cells in adipose tissues is pivotal to address complications of chronic adipose tissue inflammation. In this review, we discuss the role of adipose innate and adaptive immune cells across various physiological and pathophysiological states that pertain to the development or progression of cardiovascular diseases associated with metabolic disorders. Understanding such mechanisms allows for the exploitation of the adipose tissue-immune system crosstalk, exploring how the adipose immune system might be targeted as a strategy to treat cardiovascular derangements associated with metabolic dysfunctions.

The role of adipokines in the modulation of lymphoid lineage cell development and activity: An overview

Adipokines are predominantly known to play a vital role in the control of food intake, energy homeostasis and regulation of glucose and lipid metabolism. However, evidence supporting the concept of their extensive involvement in immune system defence mechanisms and inflammatory processes continues to grow. Some of the adipokines, that is, leptin and resistin, have been recognized to exhibit mainly pro-inflammatory properties, whereas others such as visfatin, chemerin, apelin and vaspin have been found to exert regulatory effects. In contrast, adiponectin or omentin are known for their anti-inflammatory activities. Hence, adipokines influence the activity of various cells engaged in innate immune response and inflammatory processes mainly by affecting adhesion molecule expression, chemotaxis, apoptosis and phagocytosis, as well as mediators production and release. However, much less is known about the role of adipokines in processes involving lymphoid lineage cells. This review summarizes the current knowledge regarding the importance of different adipokines in the lymphopoiesis, recirculation, differentiation and polarization of lymphoid lineage cells. It also provides insight into the influence of selected adipokines on the activity of those cells in tissues.

EoTHINophils: Eosinophils as key players in adipose tissue homeostasis

Eosinophils are granular cells of the innate immune system that are found in almost all vertebrates and some invertebrates. Knowledge of their wide-ranging roles in health and disease has largely been attained through studies in mice and humans. Although eosinophils are typically associated with helminth infections and allergic diseases such as asthma, there is building evidence that beneficial homeostatic eosinophils residing in specific niches are important for tissue development, remodelling and metabolic control. In recent years, the importance of immune cells in the regulation of adipose tissue homeostasis has been a focal point of research efforts. There is an abundance of anti-inflammatory innate immune cells in lean white adipose tissue, including macrophages, eosinophils and group 2 innate lymphoid cells, which promote energy homeostasis and stimulate the development of thermogenic beige adipocytes. This review will evaluate evidence for the role of adipose-resident eosinophils in local tissue homeostasis, beiging and systemic metabolism, highlighting where more research is needed to establish the specific effector functions that adipose eosinophils perform in response to different internal and external cues.

Adipocytokines leptin and adiponectin function as mast cell activity modulators

A growing body of data indicates that adipocytokines, including leptin and adiponectin, are critical components not only of metabolic regulation but also of the immune system, mainly by influencing the activity of cells participating in immunological and inflammatory processes. As mast cells (MCs) are the key players in the course of those mechanisms, this study aimed to evaluate the impact of leptin and adiponectin on some aspects of MC activity. We documented that in vivo differentiated mature tissue MCs from the rat peritoneal cavity express a receptor for leptin (OB-R), as well as receptors for adiponectin (AdipoR1 and AdipoR2). We established that leptin, but not adiponectin, stimulates MCs to release of histamine as well as to generation of cysteinyl leukotrienes (cysLTs) and chemokine CCL2. We also found that both adipocytokines affect mRNA expression of various cytokines/chemokines. Leptin and adiponectin also activate MCs to produce reactive oxygen species. Moreover, we documented that leptin significantly augments the surface expression of receptors for cysLTs, i.e. CYSLTR1, CYSLTR2, and GPR17 on MCs, while adiponectin increases only GPR17 expression, and decreases CYSLTR2. Finally, we showed that both adipocytokines serve as potent chemoattractants for MCs. In intracellular signaling in MCs activated by leptin Janus-activated kinase 2, phospholipase C, phosphatidylinositol 3-kinase (PI3K), extracellular signal-regulated kinase (ERK1/2), and p38 molecules play a part whereas the adiponectin-induced activity of MCs is mediated through PI3K, p38, and ERK1/2 pathways. Our observations that leptin and adiponectin regulate MC activity might indicate that adipocytokines modulate the different processes in which MCs are involved.

Reciprocal Inhibition of Adiponectin and Innate Lung Immune Responses to Chitin and Aspergillus fumigatus

Chitin is a structural biopolymer found in numerous organisms, including pathogenic fungi, and recognized as an immune-stimulating pathogen associated molecular pattern by pattern recognition molecules of the host immune system. However, programming and regulation of lung innate immunity to chitin inhalation in the context of inhalation of fungal pathogens such as Aspergillus fumigatus is complex and our understanding incomplete. Here we report that the systemic metabolism-regulating cytokine adiponectin is decreased in the lungs and serum of mice after chitin inhalation, with a concomitant decrease in surface expression of the adiponectin receptor AdipoR1 on lung leukocytes. Constitutive lung expression of acidic mammalian chitinase resulted in decreased inflammatory cytokine gene expression and neutrophil recruitment, but did not significantly affect lung adiponectin transcription. Exogenous recombinant adiponectin specifically dampened airway chitin-mediated eosinophil recruitment, while adiponectin deficiency resulted in increased airway eosinophils. The presence of adiponectin also resulted in decreased CCL11-mediated migration of bone marrow-derived eosinophils. In contrast to purified chitin, aspiration of viable conidia from the high chitin-expressing A. fumigatus isolate Af5517 resulted in increased neutrophil recruitment and inflammatory cytokine gene expression in adiponectin-deficient mice, while no significant changes were observed in response to the isolate Af293. Our results identify a novel role for the adiponectin pathway in inhibition of lung inflammatory responses to chitin and A. fumigatus inhalation.

Adiponectin alleviates exacerbation of airway inflammation and oxidative stress in obesity-related asthma mice partly through AMPK signaling pathway

Adiponectin plays a role in asthma and obesity, but its effects and mechanism in obesity-related asthma remain elusive. This study aimed to evaluate the effects of adiponectin on airway inflammation and oxidative stress and to determine its mechanism in obesity-related asthma. Male C57BL6/J mice fed with a high-fat diet to induce obesity were sensitized and challenged with ovalbumin to induce asthma, and treated with adiponectin (1 mg/kg) and AMP-activated protein kinase (AMPK) inhibitor compound C (20 mg/kg) twice before the first ovalbumin challenge. We found exogenous adiponectin significantly reduced airway resistance, inflammatory infiltration in lung tissue, and cell counts in bronchoalveolar lavage fluid. Adiponectin inhibited great levels of eotaxin, myeloperoxidase, tumor necrosis factor-α, 8‑hydroxy‑2'‑deoxyguanosine, and nitric oxide in obesity-related asthma mice. Moreover, we found increased nuclear factor kappa B p65, inducible nitric oxide synthase and B-cell lymphoma 2 protein expression were down-regulated with adiponectin administration. Additionally, adiponectin elevated the lower levels of pAMPK and AMPK activity in lung tissue. These protective effects of adiponectin were reversed after treatment with the AMPK inhibitor compound C. Thus, we conclude that adiponectin alleviates exacerbation of airway inflammation and oxidative stress in a murine model of obesity-related asthma partly through AMPK signaling pathway.

Adipocytokine Involvement in Innate Immune Mechanisms

The innate immune response is defined as an immensely complex and sophisticated process aimed at defending the organism against any disturbance in the body homeostasis, including invading pathogens. It requires a close cooperation of a vast amount of different cell types, recognized as inflammatory migrating cells, as well as stationary cells that form tissues. Moreover, innate immune mechanisms require an efficient functioning of various humoral components that exert a significant impact on physiological and pathological processes. Apart from commonly mentioned humoral factors, this group also includes a family of proteins known as adipocytokines that may act as pro- or anti-inflammatory agents or act both ways. Leptin, predominantly characterized as a proinflammatory adipokine, plays a crucial role in endothelium remodeling and regulation, as well as in cell survival and production of numerous cytokines. Adiponectin, similar to leptin, acts on the endothelial cells and the phagocytic properties of immune cells; however, it exerts an anti-inflammatory impact. Resistin has a documented role in the control of angiogenesis and stimulation of proinflammatory mediator generation and release. Furthermore, there are adipokines, ie, visfatin and chemerin, whose participation in the inflammatory processes is ambiguous. This review focuses on the current knowledge on the extensive role of selected adipokines in innate immune response.

Leptin Elicits LTC4 Synthesis by Eosinophils Mediated by Sequential Two-Step Autocrine Activation of CCR3 and PGD2 Receptors

Leptin is a cytokine, produced mainly by mature adipocytes, that regulates the central nervous system, mainly to suppress appetite and stimulate energy expenditure. Leptin also regulates the immune response by controlling activation of immunomodulatory cells, including eosinophils. While emerging as immune regulatory cells with roles in adipose tissue homeostasis, eosinophils have a well-established ability to synthesize pro-inflammatory molecules such as lipid mediators, a key event in several inflammatory pathologies. Here, we investigated the impact and mechanisms involved in leptin-driven activation of eicosanoid-synthesizing machinery within eosinophils. Direct in vitro activation of human or mouse eosinophils with leptin elicited synthesis of lipoxygenase as well as cyclooxygenase products. Displaying selectivity, leptin triggered synthesis of LTC₄ and PGD₂, but not PGE₂, in parallel to dose-dependent induction of lipid body/lipid droplets biogenesis. While dependent on PI3K activation, leptin-driven eosinophil activation was also sensitive to pertussis toxin, indicating the involvement of G-protein coupled receptors on leptin effects. Leptin-induced lipid body-driven LTC₄ synthesis appeared to be mediated through autocrine activation of G-coupled CCR3 receptors by eosinophil-derived CCL5, inasmuch as leptin was able to trigger rapid CCL5 secretion, and neutralizing anti-RANTES or anti-CCR3 antibodies blocked lipid body assembly and LTC₄ synthesis induced by leptin. Remarkably, autocrine activation of PGD₂ G-coupled receptors DP1 and DP2 also contributes to leptin-elicited lipid body-driven LTC₄ synthesis by eosinophils in a PGD₂-dependent fashion. Blockade of leptin-induced PGD₂ autocrine/paracrine activity by a specific synthesis inhibitor or DP1 and DP2 receptor antagonists, inhibited both lipid body biogenesis and LTC₄ synthesis induced by leptin stimulation within eosinophils. In addition, CCL5-driven CCR3 activation appears to precede PGD₂ receptor activation within eosinophils, since neutralizing anti-CCL5 or anti-CCR3 antibodies inhibited leptin-induced PGD₂ secretion, while it failed to alter PGD₂-induced LTC₄ synthesis. Altogether, sequential activation of CCR3 and then PGD₂ receptors by autocrine ligands in response to leptin stimulation of eosinophils culminates with eosinophil activation, characterized here by assembly of lipidic cytoplasmic platforms synthesis and secretion of the pleiotropic lipid mediators, PGD₂, and LTC₄.

Eosinophilic Otitis Media: the Aftermath of Eosinophil Extracellular Trap Cell Death

PURPOSE OF REVIEW

Eosinophilic otitis media (EOM) is a refractory disease characterized by the accumulation of eosinophils in middle ear effusion and mucosa. We summarize current knowledge regarding the clinical characteristics and management of EOM. Although eosinophil activation in inflamed foci is involved in the pathogenesis of EOM, little is known about the fate of the eosinophils and aftermath of their cell death. We discuss the possibility that eosinophils undergo non-apoptotic cell death that worsens tissue damage and increases effusion viscosity.

RECENT FINDINGS

Unlike chronic otitis media, EOM is strongly associated with an allergic background. Corticosteroids are currently the only effective pharmacological treatment, and surgical intervention is often required. Mucosal eosinophils infiltrate extensively into the middle ear cavity where they are stimulated by locally produced activators including interleukin-5 and eotaxin. The eosinophils undergo cytolysis in the effusion, which represents a major fate of activated eosinophils in vivo. Recent data revealed cytolysis could be renamed as extracellular trap cell death (ETosis). ETosis represents suicidal cell death involving total cell degranulation and development of sticky chromatin structures (extracellular traps (ETs)). The characteristics of eosinophil- and neutrophil-derived ET polymers might contribute to the difference in viscosity of secretions between EOM and common chronic otitis media. The extracellular products remaining after eosinophil ETosis are an important aspect of EOM pathology. The concept of ETosis also has novel implications for potential therapeutic modalities in various eosinophilic disorders.

Adiponectin promotes human jaw bone marrow mesenchymal stem cell chemotaxis via CXCL1 and CXCL8

Adiponectin (APN) is known to promote the osteogenic differentiation of human jaw bone marrow mesenchymal stem cells (h‐JBMMSCs). However, the underlying mechanism has not been fully elucidated. Previously, we showed that APN could promote h‐JBMMSC osteogenesis via APPL1‐p38 by up‐regulating osteogenesis‐related genes. Here, we aimed to determine whether APN could promote h‐JBMMSC chemotaxis through CXCL1/CXCL8. The CCK‐8, wound healing and transwell assays were used to evaluate the proliferation, migration and chemotaxis of h‐JBMMSCs with or without APN treatment. Chemotaxis‐related genes were screened using RNA‐seq, and the results were validated using real‐time PCR and ELISA. We also performed Western blot using the AMPK inhibitor, WZ4003, and the p38 MAPK inhibitor, SB203580, to identify the signalling pathway involved. We found that APN could promote h‐JBMMSC chemotaxis in the co‐culture transwell system. CXCL1 and CXCL8 were screened and confirmed as the up‐regulated target genes. The APN‐induced CXCL1/8 up‐regulation to promote chemotaxis could be blocked by CXCR2 inhibitor SB225002. Western blot revealed that the phosphorylation of AMPK and p38 MAPK increased in a time‐dependent manner with APN treatment. Additionally, WZ4003 and SB203580 could suppress the APN‐induced overexpression of CXCL1 and CXCL8. The results of the transwell chemotaxis assay also supported the above results. Our data suggest that APN can promote h‐JBMMSC chemotaxis by up‐regulating CXCL1 and CXCL8.

Adiponectin: a versatile player of innate immunity

Adiponectin acts as a key regulator of the innate immune system and plays a major role in the progression of inflammation and metabolic disorders. Macrophages and monocytes are representative components of the innate immune system, and their proliferation, plasticity, and polarization are a key component of metabolic adaption. Innate-like lymphocytes such as group 2 innate lymphoid cells (ILC2s), natural killer T (NKT) cells, and gamma delta T (γδ T) cells are also members of the innate immune system and play important roles in the development of obesity and its related diseases. Adiponectin senses metabolic stress and modulates metabolic adaption by targeting the innate immune system under physiological and pathological conditions. Defining the mechanisms underlying the role of adiponectin in regulating innate immunity is crucial to adiponectin-based therapeutic intervention.

The impact of diet on asthma and allergic diseases

The incidence of allergic diseases is increasing, both in developed and developing countries, concomitantly with the rise in living standards and the adoption of a 'western lifestyle'. For two decades, the hygiene hypothesis - which proposes that the lack of early childhood exposure to infectious agents increases susceptibility to allergic diseases in later life - provided the conceptual framework for unravelling the mechanisms that could account for the increased incidence of allergic diseases. In this Review, we discuss recent evidence that highlights the role of diet as a key factor influencing immune homeostasis and the development of allergic diseases through a complex interplay between nutrients, their metabolites and immune cell populations. Although further investigations are still required to understand these complex relationships, recent data have established a possible connection between metabolic homeostasis and allergic diseases.

The adiponectin levels and asthma control in non-obese children with asthma

OBJECTIVE

To determine the relationship between adiponectin levels and asthma control in non-obese asthmatic children.

METHODS

Eighty-two children with asthma who had been followed up in a single center were included. The control group included 28 children with no evidence of allergic disease. Adiponectin levels were analyzed in all children. Additionally, skin prick tests and pulmonary function tests were also performed in patients.

RESULTS

Three groups were designated with respect to asthma control as; well-controlled group (n = 28), partially controlled group (n = 34) and uncontrolled group (n = 20). There was no significant difference of gender, age, height, weight, BMI and adiponectin levels between study and control groups (p > 0.05). The duration of illness, presence of atopy and sensitivities to mite, pollens, dander and cockroaches were similar between the groups (p > 0.05). Adiponectin, FEV1, FVC, and FEV1/FVC levels were significantly lower in uncontrolled group (p < 0.05). Sensitivity to Alternaria alternata was significantly higher in the uncontrolled group (p < 0.05). In logistic regression analysis, as dependent parameter, adiponectin, FEV1, FVC and FEV1/FVC levels were found to be statistically significant for uncontrolled asthma.

CONCLUSION

Adiponectin levels in non-obese asthmatics were not different from controls. Lower levels of adiponectin were associated with uncontrolled asthma. Low adiponectin level can therefore be used as an indicator of uncontrolled asthma.

G-protein-coupled estrogen receptor agonist suppresses airway inflammation in a mouse model of asthma through IL-10

Estrogen influences the disease severity and sexual dimorphism in asthma, which is caused by complex mechanisms. Besides classical nuclear estrogen receptors (ERαβ), G-protein-coupled estrogen receptor (GPER) was recently established as an estrogen receptor on the cell membrane. Although GPER is associated with immunoregulatory functions of estrogen, the pathophysiological role of GPER in allergic inflammatory lung disease has not been examined. We investigated the effect of GPER-specific agonist G-1 in asthmatic mice. GPER expression in asthmatic lung was confirmed by immunofluorescent staining. OVA-sensitized BALB/c and C57BL/6 mice were treated with G-1 by daily subcutaneous injections during an airway challenge phase, followed by histological and biochemical examination. Strikingly, administration of G-1 attenuated airway hyperresponsiveness, accumulation of inflammatory cells, and levels of Th2 cytokines (IL-5 and IL-13) in BAL fluid. G-1 treatment also decreased serum levels of anti-OVA IgE antibodies. The frequency of splenic Foxp3+CD4+ regulatory T cells and IL-10-producing GPER+CD4+ T cells was significantly increased in G-1-treated mice. Additionally, splenocytes isolated from G-1-treated mice showed greater IL-10 production. G-1-induced amelioration of airway inflammation and IgE production were abolished in IL-10-deficient mice. Taken together, these results indicate that extended GPER activation negatively regulates the acute asthmatic condition by altering the IL-10-producing lymphocyte population. The current results have potential importance for understanding the mechanistic aspects of function of estrogen in allergic inflammatory response.

Functional analysis of free fatty acid receptor GPR120 in human eosinophils: implications in metabolic homeostasis

Recent evidence has shown that eosinophils play an important role in metabolic homeostasis through Th2 cytokine production. GPR120 (FFA4) is a G protein-coupled receptor (GPCR) for long-chain fatty acids that functions as a regulator of physiological energy metabolism. In the present study, we aimed to investigate whether human eosinophils express GPR120 and, if present, whether it possesses a functional capacity on eosinophils. Eosinophils isolated from peripheral venous blood expressed GPR120 at both the mRNA and protein levels. Stimulation with a synthetic GPR120 agonist, GW9508, induced rapid down-regulation of cell surface expression of GPR120, suggesting ligand-dependent receptor internalization. Although GPR120 activation did not induce eosinophil chemotactic response and degranulation, we found that GW9508 inhibited eosinophil spontaneous apoptosis and Fas receptor expression. The anti-apoptotic effect was attenuated by phosphoinositide 3-kinase (PI3K) inhibitors and was associated with inhibition of caspase-3 activity. Eosinophil response investigated using ELISpot assay indicated that stimulation with a GPR120 agonist induced IL-4 secretion. These findings demonstrate the novel functional properties of fatty acid sensor GPR120 on human eosinophils and indicate the previously unrecognized link between nutrient metabolism and the immune system.

Asthma and metabolic syndrome: Current knowledge and future perspectives

Asthma and obesity are epidemiologically linked; however, similar relationships are also observed with other markers of the metabolic syndrome, such as insulin resistance and dyslipidemia, which cannot be accounted for by increased body mass alone. Obesity appears to be a predisposing factor for the asthma onset, both in adults and in children. In addition, obesity could make asthma more difficult to control and to treat. Although obesity may predispose to increased Th2 inflammation or tendency to atopy, other mechanisms need to be considered, such as those mediated by hyperglycaemia, hyperinsulinemia and dyslipidemia in the context of metabolic syndrome. The mechanisms underlying the association between asthma and metabolic syndrome are yet to be determined. In the past, these two conditions were believed to occur in the same individual without any pathogenetic link. However, the improvement in asthma symptoms following weight reduction indicates a causal relationship. The interplay between these two diseases is probably due to a bidirectional interaction. The purpose of this review is to describe the current knowledge about the possible link between metabolic syndrome and asthma, and explore potential application for future studies and strategic approaches.

Is there a link between obesity and asthma?

Increasing epidemiological data identify a link between obesity and asthma incidence and severity. Based on experimental data, it is possible that shared inflammatory mechanisms play a role in determining this linkage. Although controversial, the role of adipokines may be central to this association and the maintenance of the asthma phenotype. While leptin and adiponectin have a causal link to experimental asthma in mice, data in humans are less conclusive. Recent studies demonstrate that adipokines can regulate the survival and function of eosinophils and that these factors can affect eosinophil trafficking from the bone marrow to the airways. In addition, efferocytosis, the clearance of dead cells, by airway macrophages or blood monocytes appears impaired in obese asthmatics and is inversely correlated with glucocorticoid responsiveness. This review examines the potential mechanisms linking obesity to asthma.