Leptin deficiency impairs maturation of dendritic cells and enhances induction of regulatory T and Th17 cells

Orchestration of the Adipose Tissue Immune Landscape by Adipocytes

Obesity is epidemic and of great concern because of its comorbid and costly inflammatory-driven complications. Extensive investigations in mice have elucidated highly coordinated, well-balanced interactions between adipocytes and immune cells in adipose tissue that maintain normal systemic metabolism in the lean state, while in obesity, proinflammatory changes occur in nearly all adipose tissue immune cells. Many of these changes are instigated by adipocytes. However, less is known about obesity-induced adipose-tissue immune cell alterations in humans. Upon high-fat diet feeding, the adipocyte changes its well-known function as a metabolic cell to assume the role of an immune cell, orchestrating proinflammatory changes that escalate inflammation and progress during obesity. This transformation is particularly prominent in humans. In this review, we (a) highlight a leading and early role for adipocytes in promulgating inflammation, (b) discuss immune cell changes and the time course of these changes (comparing humans and mice when possible), and (c) note how reversing proinflammatory changes in most types of immune cells, including adipocytes, rescues adipose tissue from inflammation and obese mice from insulin resistance.

Leptin/lipopolysaccharide-treated dendritic cell vaccine improved cellular immune responses in an animal model of breast cancer

PURPOSE

In dendritic cells (DCs), leptin as an immune-regulating hormone, increases the IL-12 generation whereas it reduces the IL-10 production, thus contributing to TH1 cell differentiation. Using a murine model of breast cancer (BC), we evaluated the impacts of the Leptin and/or lipopolysaccharide (LPS)-treated DC vaccine on various T-cell-related immunological markers.

MATERIALS AND METHODS

Tumors were established in mice by subcutaneously injecting 7 × 105 4T1 cells into the right flank. Mice received the DC vaccines pretreated with Leptin, LPS, and both Leptin/LPS, on days 12 and 19 following tumor induction. The animals were sacrificed on day 26 and after that the frequency of the splenic cytotoxic T lymphocytes (CTLs) and TH1 cells; interferon gamma (IFN-γ), interleukin 12 (IL-12) and tumor growth factor beta (TGF-β) generation by tumor lysate-stimulated spleen cells, and the mRNA expression of T-bet, FOXP3 and Granzyme B in the tumors were measured with flow cytometry, ELISA and real-time PCR methods, respectively.

RESULTS

Leptin/LPS-treated mDC group was more efficient in blunting tumor growth (p = .0002), increasing survival rate (p = .001), and preventing metastasis in comparison with the untreated tumor-bearing mice (UT-control). In comparison to the UT-control group, treatment with Leptin/LPS-treated mDC also significantly increased the splenic frequencies of CTLs (p < .001) and TH1 cells (p < .01); promoted the production of IFN-γ (p < .0001) and IL-12 (p < .001) by splenocytes; enhanced the T-bet (p < .05) and Granzyme B (p < .001) expression, whereas decreased the TGF-β and FOXP3 expression (p < .05).

CONCLUSION

Compared to the Leptin-treated mDC and LPS-treated mDC vaccines, the Leptin/LPS-treated mDC vaccine was more effective in inhibiting BC development and boosting immune responses against tumor.

Multifaceted effects of obesity on cancer immunotherapies: Bridging preclinical models and clinical data

Obesity, defined by excessive body fat, is a highly complex condition affecting numerous physiological processes, such as metabolism, proliferation, and cellular homeostasis. These multifaceted effects impact cells and tissues throughout the host, including immune cells as well as cancer biology. Because of the multifaceted nature of obesity, common parameters used to define it (such as body mass index in humans) can be problematic, and more nuanced methods are needed to characterize the pleiotropic metabolic effects of obesity. Obesity is well-accepted as an overall negative prognostic factor for cancer incidence, progression, and outcome. This is in part due to the meta-inflammatory and immunosuppressive effects of obesity. Immunotherapy is increasingly used in cancer therapy, and there are many different types of immunotherapy approaches. The effects of obesity on immunotherapy have only recently been studied with the demonstration of an "obesity paradox", in which some immune therapies have been demonstrated to result in greater efficacy in obese subjects despite the direct adverse effects of obesity and excess body fat acting on the cancer itself. The multifactorial characteristics that influence the effects of obesity (age, sex, lean muscle mass, underlying metabolic conditions and drugs) further confound interpretation of clinical data and necessitate the use of more relevant preclinical models mirroring these variables in the human scenario. Such models will allow for more nuanced mechanistic assessment of how obesity can impact, both positively and negatively, cancer biology, host metabolism, immune regulation, and how these intersecting processes impact the delivery and outcome of cancer immunotherapy.

Roles of four targets in the pathogenesis of graves' orbitopathy

Graves' orbitopathy (GO) is an autoimmune disease that involves complex immune systems. The mainstays of clinical management for this disease are surgery, targeted drugs therapy, and no-targeted drugs drug therapy. targeted drugs can improve therapeutic efficacy and enhance the quality of life for GO patients. However, as a second-line treatment for GO, targeted drugs such as tocilizumab and rituximab have very limited therapeutic effects and may be accompanied by side effects. The introduction of Teprotumumab, which targets IGF-IR, has made significant progress in the clinical management of GO. The pathophysiology of GO still remains uncertain as it involves a variety of immune cells and fibroblast interactions as well as immune responses to relevant disease targets of action. Therfore, learning more about immune response feedback pathways and potential targets of action will assist in the treatment of GO. In this discussion, we explore the pathogenesis of GO and relevant work, and highlight four potential targets for GO: Interleukin-23 receptor (IL-23 R), Leptin receptor (LepR), Orbital fibroblast activating factors, and Plasminogen activator inhibitor-1 (PAI-1). A deeper understanding of the pathogenesis of GO and the role of potential target signaling pathways is crucial for effective treatment of this disease.

The development and function of human monocyte-derived dendritic cells regulated by metabolic reprogramming

Human monocyte-derived dendritic cells (moDCs) that develop from monocytes play a key role in innate inflammatory responses as well as T cell priming. Steady-state moDCs regulate immunogenicity and tolerogenicity by changing metabolic patterns to participate in the body's immune response. Increased glycolytic metabolism after danger signal induction may strengthen moDC immunogenicity, whereas high levels of mitochondrial oxidative phosphorylation were associated with the immaturity and tolerogenicity of moDCs. In this review, we discuss what is currently known about differential metabolic reprogramming of human moDC development and distinct functional properties.

Promoted Generation of T Helper 1-Like Regulatory T Cells After Transient Middle Cerebral Artery Occlusion in Type-2 Diabetic Mice

BACKGROUND

Regulatory T cells (Tregs) play a remarkable role in modulating post-ischemic neuroinflammation. However, the characteristics of Tregs in diabetic ischemic stroke remain unknown.

METHODS

Transient middle cerebral artery occlusion (MCAO) was conducted on leptin receptor-mutated db/db mice and db/+ mice. The number, cytokine production, and signaling features of Tregs in peripheral blood and ipsilateral hemispheres were evaluated by flow cytometry. Treg plasticity was assessed by the adoptive transfer of splenic Tregs into mice. The effect of ipsilateral macrophages/microglia on Treg plasticity was determined by in vitro co-culture analysis.

RESULTS

db/db mice had more infiltrating Tregs in their ipsilateral hemispheres than db/+ mice. Infiltrating Tregs in db/db mice expressed higher transforming growth factor-β (TGF-β), interleukin-10 (IL-10), forkhead box P3 (Foxp3), interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and T-box expressed in T cells (T-bet) in comparison to infiltrating Tregs in db/+ mice, suggesting promoted generation of T helper 1 (Th1)-like Tregs in the brains of db/db mice after stroke. The post-ischemic brain microenvironment of db/db mice significantly up-regulated IFN-γ, TNF-α, T-bet, IL-10, and TGF-β in infiltrating Tregs. Moreover, ipsilateral macrophages/microglia remarkably enhanced the expression of IFN-γ, TNF-α, and T-bet but not IL-10 and TGF-β in Tregs. db/db macrophages/microglia were more potent in up-regulating IFN-γ, TNF-α, and T-bet than db/+ macrophages/microglia. Interleukin-12 (IL-12) blockage partially abolished the modulatory effect of macrophages/microglia on Tregs.

CONCLUSION

The generation of Th1-like Tregs was promoted in the brains of type 2 diabetic mice after stroke. Our study reveals significant Treg plasticity in diabetic stroke.Abbreviations: Foxp3: forkhead box P3; IFN-γ: interferon-γ; IL-10: interleukin-10; IL-12: interleukin-12; MCAO: middle cerebral artery occlusion; PBS: phosphate-buffered saline; STAT1: Signal transducer and activator of transcription 1; STAT5: Signal transducer and activator of transcription 1; T-bet: T-box expressed in T cells; TGF-β: transforming growth factor-β; Th1: T helper 1; TNF-α: tumor necrosis factor-α; Tregs: regulatory T cells. Foxp3: forkhead box P3; IFN-γ: interferon-γ; IL-10: interleukin-10; IL-12: interleukin-12; MCAO: middle cerebral artery occlusion; PBS: phosphate-buffered saline; STAT1: Signal transducer and activator of transcription 1; STAT5: Signal transducer and activator of transcription 1; T-bet: T-box expressed in T cells; TGF-β: transforming growth factor-β; Th1: T helper 1; TNF-α: tumor necrosis factor-α; Tregs: regulatory T cells.

Deficient leptin receptor signaling in T cells of human SLE

BACKGROUND

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease mainly mediated by IgG autoantibody. While follicular helper T (Tfh) cells are crucial for supporting IgG autoantibody generation in human SLE, underlying mechanisms for Tfh cell mal-differentiation remain unclear.

METHODS

In total, 129 SLE patients and 37 healthy donors were recruited for this study. Circulating leptin was determined by ELISA from patients with SLE and healthy individuals. CD4 T cells isolated from SLE patients and healthy donors were activated with anti-CD3/CD28 beads under cytokine-unbiased conditions in the presence or absence of recombinant leptin protein, followed by detection for Tfh cell differentiation by quantifying intracellular transcription factor Bcl-6 and cytokine IL-21. AMPK activation was assessed by analyzing phosphor-AMPK using phosflow cytometry and immunoblots. Leptin receptor expression was determined using flow cytometry and its overexpression was achieved by transfection with an expression vector. Humanized SLE chimeras were induced by injecting patients' immune cells into immune-deficient NSG mice and used for translational studies.

RESULTS

Circulating leptin was elevated in patients with SLE, inversely associated with disease activity. In healthy individuals, leptin efficiently inhibited Tfh cell differentiation through inducing AMPK activation. Meanwhile, leptin receptor deficiency was a feature of CD4 T cells in SLE patients, impairing the inhibitory effect of leptin on the differentiation of Tfh cells. As a result, we observed the coexistence of high circulating leptin and increased Tfh cell frequencies in SLE patients. Accordingly, overexpression of leptin receptor in SLE CD4 T cells abrogated Tfh cell mal-differentiation and IgG anti-dsDNA generation in humanized lupus chimeras.

CONCLUSION

Leptin receptor deficiency blocks the inhibitory effect of leptin on SLE Tfh cell differentiation, serving as a promising therapeutic target for lupus management.

Leptin regulates thymic plasmacytoid dendritic cell ability to influence the thymocyte distribution in vitro

Leptin, the adipocyte-derived hormone, involved in regulating food intake and body weight, plays an important role in immunity and reproduction. Leptin signals via the specific membrane receptors expressed in most types of immune cells including dendritic cells (DCs) and thymocytes. Leptin enhances thymopoiesis and modulates T-cell-mediated immunity. Thymic plasmacytoid DCs (pDCs) are predominated in the thymus. They play an important role in thymocyte differentiation. We have analyzed whether leptin mediates its effects on human thymocytes by influencing on pDCs. We used leptin at concentration corresponding to its level during II-III trimesters of physiological pregnancy. We cultivated leptin-primed pDCs with autologous thymocytes and estimated the main thymocyte subsets expressing αβ chains of the T-cell receptor (αβTCR), natural regulatory T-cells (tTreg), natural T-helpers producing interleukin-17 (nTh17) and invariant natural killer T-cells (iNKT) in vitro. We have shown that leptin augmented CD86, CD276 expressions and depressed IL-10 productions by pDCs. Leptin-primed pDCs decreased the percentage of CD4⁺CD8⁺αβTCR⁺ thymocytes, increased CD4^hiCD8^-/loαβTCR⁺ cells. pDCs cultivated with leptin decreased the number of iNKT precursors, and did not change the number of tTreg and nTh17 precursors. Thus, leptin's important role in regulation of thymic pDC abilities to influence on the thymocyte distribution was indicated in vitro.

A class of anti-inflammatory lipids decrease with aging in the central nervous system

Lipids contribute to the structure, development, and function of healthy brains. Dysregulated lipid metabolism is linked to aging and diseased brains. However, our understanding of lipid metabolism in aging brains remains limited. Here we examined the brain lipidome of mice across their lifespan using untargeted lipidomics. Co-expression network analysis highlighted a progressive decrease in 3-sulfogalactosyl diacylglycerols (SGDGs) and SGDG pathway members, including the potential degradation products lyso-SGDGs. SGDGs show an age-related decline specifically in the central nervous system and are associated with myelination. We also found that an SGDG dramatically suppresses LPS-induced gene expression and release of pro-inflammatory cytokines from macrophages and microglia by acting on the NF-κB pathway. The detection of SGDGs in human and macaque brains establishes their evolutionary conservation. This work enhances interest in SGDGs regarding their roles in aging and inflammatory diseases and highlights the complexity of the brain lipidome and potential biological functions in aging.

Leptin's Immune Action: A Review Beyond Satiety

The adipose tissue is an endocrine organ that secretes adipokines such as leptin, which is one of the most important hormones for controlling satiety, metabolism, and energy homeostasis. This hormone acts in the regulation of innate and adaptive immune responses since immune cells have leptin receptors from which this hormone initiates its biological action. These receptors have been identified in hematopoietic stem cells in the bone marrow and mature immune cells, inducing signaling pathways mediated by JAK/STAT, PI3K, and ERK 1/2. It is known that the bone marrow also contains leptin-producing adipocytes, which are crucial for regulating hematopoiesis through largely unknown mechanisms. Therefore, we have reviewed the roles of leptin inside and outside the bone marrow, going beyond its action in the control of satiety.

Leptin and Asthma: What Are the Interactive Correlations?

Leptin is an adipokine directly correlated with the proinflammatory obese-associated phenotype. Leptin has been demonstrated to inhibit adipogenesis, promote fat demarcation, promote a chronic inflammatory state, increase insulin sensitivity, and promote angiogenesis. Leptin, a regulator of the immune response, is implicated in the pathology of asthma. Studies involved in the key cell reaction and animal models of asthma have provided vital insights into the proinflammatory role of leptin in asthma. Many studies described the immune cell and related cellular pathways activated by leptin, which are beneficial in asthma development and increasing exacerbations. Subsequent studies relating to animal models support the role of leptin in increasing inflammatory cell infiltration, airway hyperresponsiveness, and inflammatory responses. However, the conclusive effects of leptin in asthma are not well elaborated. In the present study, we explored the general functions and the clinical cohort study supporting the association between leptin and asthma. The main objective of our review is to address the knowns and unknowns of leptin on asthma. In this perspective, the arguments about the different faces of leptin in asthma are provided to picture the potential directions, thus yielding a better understanding of asthma development.

The emerging role of leptin in obesity-associated cardiac fibrosis: evidence and mechanism

Cardiac fibrosis is a hallmark of various cardiovascular diseases, which is quite commonly found in obesity, and may contribute to the increased incidence of heart failure arrhythmias, and sudden cardiac death in obese populations. As an endogenous regulator of adiposity metabolism, body mass, and energy balance, obesity, characterized by increased circulating levels of the adipocyte-derived hormone leptin, is a critical contributor to the pathogenesis of cardiac fibrosis. Although there are some gaps in our knowledge linking leptin and cardiac fibrosis, this review will focus on the interplay between leptin and major effectors involved in the pathogenesis underlying cardiac fibrosis at both cellular and molecular levels based on the current reports. The profibrotic effect of leptin is predominantly mediated by activated cardiac fibroblasts but may also involve cardiomyocytes, endothelial cells, and immune cells. Moreover, a series of molecular signals with a known profibrotic property is closely involved in leptin-induced fibrotic events. A more comprehensive understanding of the underlying mechanisms through which leptin contributes to the pathogenesis of cardiac fibrosis may open up a new avenue for the rapid emergence of a novel therapy for preventing or even reversing obesity-associated cardiac fibrosis.

Leptin Signaling Suppression in Macrophages Improves Immunometabolic Outcomes in Obesity

Obesity is a major concern for global health care systems. Systemic low-grade inflammation in obesity is a major risk factor for insulin resistance. Leptin is an adipokine secreted by the adipose tissue that functions by controlling food intake, leading to satiety. Leptin levels are increased in obesity. Here, we show that leptin enhances the effects of LPS in macrophages, intensifying the production of cytokines, glycolytic rates, and morphological and functional changes in the mitochondria through an mTORC2-dependent, mTORC1-independent mechanism. Leptin also boosts the effects of IL-4 in macrophages, leading to increased oxygen consumption, expression of macrophage markers associated with a tissue repair phenotype, and wound healing. In vivo, hyperleptinemia caused by diet-induced obesity increases the inflammatory response by macrophages. Deletion of leptin receptor and subsequently of leptin signaling in myeloid cells (ObR-/-) is sufficient to improve insulin resistance in obese mice and decrease systemic inflammation. Our results indicate that leptin acts as a systemic nutritional checkpoint to regulate macrophage fitness and contributes to obesity-induced inflammation and insulin resistance. Thus, specific interventions aimed at downstream modulators of leptin signaling may represent new therapeutic targets to treat obesity-induced systemic inflammation.

Use of Physical Activity and Exercise to Reduce Inflammation in Children and Adolescents with Obesity

Childhood obesity is a leading public health problem worldwide, as it is increasingly prevalent and therefore responsible for serious obesity-related comorbidities, not only in childhood but also in adulthood. In addition to cardio-metabolic obesity-related disorders, recent evidence suggests that excess adipose tissue in turn is associated with immune cell infiltration, increased adipokine release, and the development of low-grade systemic inflammation obesity. Exercise is considered a non-pharmacological intervention that can delay obesity-related comorbidities, improving cardiovascular fitness and modulating the inflammatory processes. It has been reported that the anti-inflammatory effect of regular exercise may be mediated by a reduction in visceral fat mass, with a subsequent decrease in the release of adipokines from adipose tissue (AT) and/or by the induction of an anti-inflammatory environment. In this narrative review, we discuss the role of AT as an endocrine organ associated with chronic inflammation and its role in obesity-related complications, focusing on the effect of exercise in reducing inflammation in children and adolescents with obesity. Regular physical exercise must be considered as a natural part of a healthy lifestyle, and promoting physical activity starting from childhood is useful to limit the negative effects of obesity on health. The crucial role of the immune system in the development of obesity-induced inflammatory processes and the efficacy of exercise as an anti-inflammatory, non-pharmacological intervention may provide possible targets for the development of new treatments and early preventive strategies.

Influence of adipose tissue immune dysfunction on childhood obesity

In recent decades, a dramatic rise has been observed in the prevalence of obesity in childhood and adolescence, along with an increase in fetal microsomia rates. The increased risk of obesity during this key period in development negatively affects the health of the individual later in life. Immune cells residing and recruited to white adipose tissue have been highlighted as important factors contributing to the pathogenesis of childhood obesity. Immune dysfunction in the context of obesity begins early in childhood, which is different from the pathological characteristics and influencing factors of adipose immunity in adults. Here, we explore the current understanding of the roles of childhood and early life events that result in high risks for obesity by influencing adipose tissue immune dysfunction under the pathological condition of obesity. Such knowledge will help in determining the mechanisms of childhood and early life obesity in efforts to ameliorate chronic inflammation-related metabolic diseases.

Psoriasis and metabolic syndrome: implications for the management and treatment of psoriasis

Psoriasis is a chronic systemic inflammatory disorder associated with several comorbidities in addition to the characteristic skin lesions. Metabolic syndrome (MetS) is the most frequent comorbidity in psoriasis and a risk factor for cardiovascular disease, a major cause of death among patients with psoriasis. Although the exact causal relationship between these two disorders is not fully established, the underlying pathophysiology linking psoriasis and MetS seems to involve overlapping genetic predispositions and inflammatory pathways. Dysregulation of the IL‐23/Th‐17 immune signalling pathway is central to both pathologies and may be key to promoting susceptibility to metabolic and cardiovascular diseases in individuals with and without psoriasis. Thus, biological treatments for psoriasis that interrupt these signals could both reduce the psoriatic inflammatory burden and also lessen the risk of developing atherosclerosis and cardiometabolic diseases. In support of this hypothesis, improvement of skin lesions was associated with improvement in vascular inflammation in recent imaging studies, demonstrating that the beneficial effect of biological agents goes beyond the skin and could help to prevent cardiovascular disease. This review will summarize current knowledge on underlying inflammatory mechanisms shared between psoriasis and MetS and discuss the most recent clinical evidence for the potential for psoriasis treatment to reduce cardiovascular risk.

Change of Dendritic Cell Subsets Involved in Protection Against Listeria monocytogenes Infection in Short-Term-Fasted Mice

The gastrointestinal tract is the first organ directly affected by fasting. However, little is known about how fasting influences the intestinal immune system. Intestinal dendritic cells (DCs) capture antigens, migrate to secondary lymphoid organs, and provoke adaptive immune responses. We evaluated the changes of intestinal DCs in mice with short-term fasting and their effects on protective immunity against Listeria monocytogenes (LM). Fasting induced an increased number of CD103⁺CD11b⁻ DCs in both small intestinal lamina propria (SILP) and mesenteric lymph nodes (mLN). The SILP CD103⁺CD11b⁻ DCs showed proliferation and migration, coincident with increased levels of GM-CSF and C-C chemokine receptor type 7, respectively. At 24 h post-infection with LM, there was a significant reduction in the bacterial burden in the spleen, liver, and mLN of the short-term-fasted mice compared to those fed ad libitum. Also, short-term-fasted mice showed increased survival after LM infection compared with ad libitum-fed mice. It could be that significantly high TGF-β2 and Aldh1a2 expression in CD103⁺CD11b⁻ DCs in mice infected with LM might affect to increase of Foxp3⁺ regulatory T cells. Changes of major subset of DCs from CD103⁺ to CD103⁻ may induce the increase of IFN-γ–producing cells with forming Th1-biased environment. Therefore, the short-term fasting affects protection against LM infection by changing major subset of intestinal DCs from tolerogenic to Th1 immunogenic.

Leptin receptor antagonist attenuates experimental autoimmune thyroiditis in mice by regulating Treg/Th17 cell differentiation

Leptin has been found to be involved in the development and progression of many autoimmune diseases. As an organ-specific autoimmune disease, the pathogenesis of Hashimoto's thyroiditis has not been fully elucidated. It has been reported that serum leptin level is increased in Hashimoto's thyroiditis, but other studies have not shown any difference. We replicated a mouse model of experimental autoimmune thyroiditis (EAT) with a high-iodine diet and found that injection of the leptin receptor antagonist Allo-aca reduced thyroid follicle destruction and inflammatory cell infiltration in EAT mice, and thyroxine and thyroid autoimmune antibody levels. Further investigation revealed that Allo-aca promotes the differentiation of Treg cells and inhibits the differentiation of Th17 cells. We believe that Allo-aca can alter the differentiation of Treg/Th17 cells by inhibiting the leptin signaling pathway, thereby alleviating thyroid injury in EAT mice. Interfering with the leptin signaling pathway may be a novel new approach to treat treating and ameliorating Hashimoto's thyroiditis.

The role and research progress of the balance and interaction between regulatory T cells and other immune cells in obesity with insulin resistance

Metabolic homoeostasis in adipose tissue plays a major role in obesity-related insulin resistance (IR). Regulatory T (Treg) cells have been recorded to regulate metabolic homoeostasis in adipose tissue. However, their specific mechanism is not yet known. This review aims to present the role of Treg cells and other immune cells in obesity-associated IR, focusing on the balance of numbers and functions of Treg cells and other immune cells as well as the crucial role of their interactions in maintaining adipose tissue homoeostasis. Th1 cells, Th17 cells, CD8⁺ T cells, and pro-inflammatory macrophages mediate the occurrence of obesity and IR by antagonizing Treg cells, while anti-inflammatory dendritic cells, eosinophils and type 2 innate lymphoid cells (ILC2s) regulate the metabolic homoeostasis of adipose tissue by promoting the proliferation and differentiation of Treg cells. γ δ T cells and invariant natural killer T (iNKT) cells have complex effects on Treg cells, and their roles in obesity-associated IR are controversial. The balance of Treg cells and other immune cells can help maintain the metabolic homoeostasis of adipose tissue. Further research needs to explore more specific molecular mechanisms, thus providing more precise directions for the treatment of obesity with IR.

A Tale of Three Systems: Toward a Neuroimmunoendocrine Model of Obesity

The prevalence of obesity is on the rise. What was once considered a simple disease of energy imbalance is now recognized as a complex condition perpetuated by neuro- and immunopathologies. In this review, we summarize the current knowledge of the neuroimmunoendocrine mechanisms underlying obesity. We examine the pleiotropic effects of leptin action in addition to its established role in the modulation of appetite, and we discuss the neural circuitry mediating leptin action and how this is altered with obesity, both centrally (leptin resistance) and in adipose tissues (sympathetic neuropathy). Finally, we dissect the numerous causal and consequential roles of adipose tissue macrophages in obesity and highlight recent key studies demonstrating their direct role in organismal energy homeostasis.

Leptin promotes glycolytic metabolism to induce dendritic cells activation via STAT3-HK2 pathway

Leptin is over-secreted in many autoimmune diseases, which can promote dendritic cells (DCs) maturation and up-regulate the expression of inflammatory cytokines, but the underlying mechanisms are not fully elucidated. Considering the major role of leptin in maintaining energy balance and the significant role of glycolysis in DCs activation, our study aims to investigate whether leptin promotes the activation of DCs via glycolysis and its underlying mechanisms. We demonstrated that leptin promoted the activation of DCs, including up-regulating the expression of co-stimulatory molecules and inflammatory cytokines, enhancing the proliferation and T helper 17 (Th17) cell ratio in peripheral blood mononuclear cells (PBMC) co-cultured with leptin-stimulated DCs. Leptin also enhanced DCs glycolysis with increased glucose consumption, lactate production, and the expression of hexokinase 2 (HK2). In addition, the activation of DCs stimulated by leptin could be inhibited by the glycolysis inhibitor 2-deoxy-d-glucose (2-DG). To explore the signaling pathways involved in leptin-induced HK2 expression, we observed that the inhibitors of STAT3 (NSC74859) could repress the enhancement of HK2 triggered by leptin stimulation. Therefore, our results indicated that leptin promoted glycolytic metabolism to induce DCs activation via STAT3-HK2 pathway.

Emerging role of leptin in joint inflammation and destruction

Rheumatoid arthritis (RA) is an autoimmune disease characterized by tumor-like hyperplasia and inflammation of the synovium, which causes synovial cell invasion into the bone and cartilage. In RA pathogenesis, various molecules in effector cells (i.e., immune cells and mesenchymal cells) are dysregulated by genetic and environmental factors. Consistent with the early stages of RA, these pathogenic cells cooperate and activate each other directly by cell-to-cell contact or indirectly via humoral factors. Recently, growing evidence has revealed essential role of adipokines, which are multifunctional signal transduction molecules, in the immune system. In this review, we summarize the current understanding of the cross-talk between leptin, one of the most well-known and best-characterized adipokines, and osteoimmunology. Furthermore, we discuss the contribution of leptin to the pathogenesis of RA and its potential mechanisms.

The Role of Leptin in Childhood Immune Thrombocytopenia (ITP): An Anti-Inflammatory Agent?

To investigate the effect of leptin in childhood ITP, we measured plasma leptin in 39 children with acute ITP, after treatment and in remission, and in 33 healthy age/BMI-matched controls. We also cultured ITP and control peripheral blood mononuclear cells (PBMCs) with recombinant leptin to assess its direct effect on pro/anti-inflammatory cytokine gene expression. A significant increase in leptin was observed in children with active disease compared to controls. A significant inverse correlation of leptin with platelet count was also observed in children with acute ITP. Leptin remained high after treatment with IVIg, whereas steroid treatment lowered leptin below control levels. In remission, leptin was in the control range. Cytokine gene expression was significantly increased in children with acute ITP compared with controls, with highest expression for IFN-γ and IL-10. IVIg/steroid treatment significantly decreased IFN-γ and IL-10 expression. In remission, IFN-γ and IL-10 expression remained low. Addition of leptin to PBMCs isolated from patients in remission resulted in a significant increase in IL-10 gene expression compared to controls. Further experiments with purified T-cells and monocytes identified monocytes as the source of leptin-induced IL-10. We suggest that leptin acts as an active anti-inflammatory agent in childhood ITP by promoting IL-10 secretion by monocytes.

Adipose Tissue Immunomodulation and Treg/Th17 Imbalance in the Impaired Glucose Metabolism of Children with Obesity

In the last few decades, obesity has increased dramatically in pediatric patients. Obesity is a chronic disease correlated with systemic inflammation, characterized by the presence of CD4 and CD8 T cell infiltration and modified immune response, which contributes to the development of obesity related diseases and metabolic disorders, including impaired glucose metabolism. In particular, Treg and Th17 cells are dynamically balanced under healthy conditions, but imbalance occurs in inflammatory and pathological states, such as obesity. Some studies demonstrated that peripheral Treg and Th17 cells exhibit increased imbalance with worsening of glucose metabolic dysfunction, already in children with obesity. In this review, we considered the role of adipose tissue immunomodulation and the potential role played by Treg/T17 imbalance on the impaired glucose metabolism in pediatric obesity. In the patient care, immune monitoring could play an important role to define preventive strategies of pediatric metabolic disease treatments.

Peripheral leptin signaling persists in innate immune cells during diet-induced obesity

Leptin is a pleiotropic adipokine that regulates immunometabolism centrally and peripherally. Obese individuals present increased levels of leptin in the blood and develop hypothalamic resistance to this adipokine. Here we investigated whether leptin effects on the periphery are maintained despite the hypothalamic resistance. We previously reported that leptin injection induces in vivo neutrophil migration and peritoneal macrophage activation in lean mice through TNF-α- and CXCL1-dependent mechanisms. However, leptin effects on leukocyte biology during obesity remain unclear. In this study, we investigated the in vivo responsiveness of leukocytes to i.p. injected leptin in mice with diet-induced obesity (DIO). After 14-16 wk, high-sucrose, high-fat diet (HFD)-fed mice showed hyperglycemia, hyperleptinemia, and dyslipidemia compared to normal-sucrose, normal-fat diet (ND). Exogenous leptin did not reduce food intake in DIO mice in contrast to control mice, indicating that DIO mice were centrally resistant to leptin. Regardless of the diet, we found increased levels of TNF-α and CXCL1 in the animals injected with leptin, alongside a pronounced neutrophil migration to the peritoneal cavity and enhanced biogenesis of lipid droplets in peritoneal macrophages. Supporting our in vivo results, data from ex vivo leptin stimulation experiments confirmed hypothalamic resistance in DIO mice, whereas bone marrow cells responded to leptin stimulation through mTOR signaling despite obesity. Altogether, our results show that leukocytes responded equally to leptin in ND- or HFD-fed mice. These results support a role for leptin in the innate immune response also in obesity, contributing to the inflammatory status that leads to the development of metabolic disease.

Immunometabolic regulation of adipose tissue resident immune cells

Adipose tissue (AT) performs immunoregulatory functions beyond fat storage. In addition to adipocytes, AT has a diverse spectrum of resident and infiltrating immune cells in health and disease. Immune cells contribute to the homeostatic function of AT by adapting their metabolism in accordance with the microenvironment. However, how the metabolic reprogramming of immune cells affects their inflammatory profile and the subsequent implication for adipocyte function is not completely elucidated. Here, we discuss the available data on metabolic regulatory processes implicated in the control of adipose tissue-resident immune cells and their crosstalk with adipocytes.

The pleiotropic roles of leptin in metabolism, immunity, and cancer

The discovery of the archetypal adipocytokine leptin and how it regulates energy homeostasis have represented breakthroughs in our understanding of the endocrine function of the adipose tissue and the biological determinants of human obesity. Investigations on leptin have also been instrumental in identifying physio-pathological connections between metabolic regulation and multiple immunological functions. For example, the description of the promoting activities of leptin on inflammation and cell proliferation have recognized the detrimental effects of leptin in connecting dysmetabolic conditions with cancer and with onset and/or progression of autoimmune disease. Here we review the multiple biological functions and complex framework of operations of leptin, discussing why and how the pleiotropic activities of this adipocytokine still pose major hurdles in the development of effective leptin-based therapeutic opportunities for different clinical conditions.

Undernutrition and HIV Infection in Sub-Saharan Africa: Health Outcomes and Therapeutic Interventions

PURPOSE OF REVIEW

Sub-Saharan Africa (SSA) is disproportionately burdened by the twin epidemics of food insecurity and HIV infection, and protein-calorie undernutrition is common among persons with HIV (PWH) initiating antiretroviral therapy (ART) in the region. In this review, we discuss the intersection of HIV infection and undernutrition, health outcomes among undernourished PWH starting ART, and the demonstrated and potential benefits of therapeutic interventions such as micro/macronutrient supplementation and pharmacological agents.

RECENT FINDINGS

A low body mass index (BMI), used as a general indicator of poor nutrition in most studies, is associated with impaired immune recovery and increased mortality in the early ART period. The increased risk of mortality is multifactorial, and contributors include undernutrition-related immune system dysfunction, increased susceptibility to opportunistic infections, and metabolic and cardiovascular dysregulation. Clinical trials of micro/macronutrient supplementary feeding, appetite stimulants (hormones and anabolic agents), and recombinant adipokines have shown a benefit for weight gain and metabolic health, but there are few data on mortality or immune recovery. A substantial proportion of PWH in SSA are undernourished, and undernutrition contributes to an increased risk of mortality and other adverse health outcomes. To date, there have been few prospective trials of nutritional supplementation and/or pharmacologic therapy among undernourished PWH in SSA, though findings from other settings suggest a potential benefit in this population.

The impact of obesity on immune function in pediatric asthma

PURPOSE OF REVIEW

Pediatric obese asthma is a complex disease that remains poorly understood. The increasing worldwide incidence of both asthma and obesity over the last few decades, their current high prevalence and the challenges in treating obese asthmatic patients all highlight the importance of a better understanding of the pathophysiological mechanisms in obese asthma. While it is well established that patients with obesity are at an increased risk of developing asthma, the mechanisms by which obesity drives the onset of asthma, and modifies existing asthma, remain unclear. Here, we will focus on mechanisms by which obesity alters immune function in asthma.

RECENT FINDINGS

Lung parenchyma has an altered structure in some pediatric obese asthmatics, known as dysanapsis. Central adiposity is linked to reduced pulmonary function and a better predictor of asthma risk in children than BMI. Obesity in young children is associated with an increased risk of developing asthma, as well as early puberty, and hormonal alterations are implicated in obese asthma. Obesity and asthma each yield immunometabolic dysregulation separately and we are learning more about alterations in these pathways in pediatric obese asthma and the potential impact of bariatric surgery on those processes.

SUMMARY

The recent progress in clarifying the connections between childhood obesity and asthma and their combined impacts on immune function moves us closer to the goals of improved understanding of the pathophysiological mechanisms underpinning obese asthma and improved therapeutic target selection. However, this common inflammatory disease remains understudied, especially in children, and much remains to be learned.

The role of immune dysfunction in obesity-associated cancer risk, progression, and metastasis

Obesity has been linked to an increased risk of and a worse prognosis for several types of cancer. A number of interrelated mediators contribute to obesity's pro-tumor effects, including chronic adipose inflammation and other perturbations of immune cell development and function. Here, we review studies examining the impact of obesity-induced immune dysfunction on cancer risk and progression. While the role of adipose tissue inflammation in obesity-associated cancer risk has been well characterized, the effects of obesity on immune cell infiltration and activity within the tumor microenvironment are not well studied. In this review, we aim to highlight the impact of both adipose-mediated inflammatory signaling and intratumoral immunosuppressive signaling in obesity-induced cancer risk, progression, and metastasis.

The Weight of Obesity in Immunity from Influenza to COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has emerged in December 2019 and rapidly outspread worldwide endangering human health. The coronavirus disease 2019 (COVID-19) manifests itself through a wide spectrum of symptoms that can evolve to severe presentations as pneumonia and several non-respiratory complications. Increased susceptibility to COVID-19 hospitalization and mortality have been linked to associated comorbidities as diabetes, hypertension, cardiovascular diseases and, recently, to obesity. Similarly, individuals living with obesity are at greater risk to develop clinical complications and to have poor prognosis in severe influenza pneumonia. Immune and metabolic dysfunctions associated with the increased susceptibility to influenza infection are linked to obesity-associated low-grade inflammation, compromised immune and endocrine systems, and to high cardiovascular risk. These preexisting conditions may favor virological persistence, amplify immunopathological responses and worsen hemodynamic instability in severe COVID-19 as well. In this review we highlight the main factors and the current state of the art on obesity as risk factor for influenza and COVID-19 hospitalization, severe respiratory manifestations, extrapulmonary complications and even death. Finally, immunoregulatory mechanisms of severe influenza pneumonia in individuals with obesity are addressed as likely factors involved in COVID-19 pathophysiology.

The Role of the Adipokine Leptin in Immune Cell Function in Health and Disease

Leptin is a critical mediator of the immune response to changes in overall nutrition. Leptin is produced by adipocytes in proportion to adipose tissue mass and is therefore increased in obesity. Despite having a well-described role in regulating systemic metabolism and appetite, leptin displays pleiotropic actions, and it is now clear that leptin has a key role in influencing immune cell function. Indeed, many immune cells have been shown to respond to leptin directly via the leptin receptor, resulting in a largely pro-inflammatory phenotype. Understanding the role of adipose-tissue derived mediators in inflammation is critical to determining the pathophysiology of multiple obesity-associated diseases, such as type 2 diabetes, autoimmune disease, and infection. This review, therefore, focuses on the latest data regarding the role of leptin in modulating inflammation.

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4

Adipose tissue (AT) inflammation contributes to systemic insulin resistance. In obesity and type 2 diabetes (T2D), retinol binding protein 4 (RBP4), the major retinol carrier in serum, is elevated in AT and has proinflammatory effects which are mediated partially through Toll-like receptor 4 (TLR4). We now show that RBP4 primes the NLRP3 inflammasome for interleukin-1β (IL1β) release, in a glucose-dependent manner, through the TLR4/MD2 receptor complex and TLR2. This impairs insulin signaling in adipocytes. IL1β is elevated in perigonadal white AT (PGWAT) of chow-fed RBP4-overexpressing mice and in serum and PGWAT of high-fat diet-fed RBP4-overexpressing mice vs. wild-type mice. Holo- or apo-RBP4 injection in wild-type mice causes insulin resistance and elevates PGWAT inflammatory markers, including IL1β. TLR4 inhibition in RBP4-overexpressing mice reduces PGWAT inflammation, including IL1β levels and improves insulin sensitivity. Thus, the proinflammatory effects of RBP4 require NLRP3-inflammasome priming. These studies may provide approaches to reduce AT inflammation and insulin resistance in obesity and diabetes.

Immunolocalization of leptin and leptin receptor in colorectal mucosa of ulcerative colitis, Crohn's disease and control subjects with no inflammatory bowel disease

The expression of leptin and leptin receptor (Ob-R) has been partially elucidated in colon of patients with inflammatory bowel diseases (IBDs), even though leptin is involved in angiogenesis and inflammation. We previously reported overexpression of GLUT5 fructose transporter, in aberrant clusters of lymphatic vessels in lamina propria of IBD and controls. Here, we examine leptin and Ob-R expression in the same biopsies. Specimens were obtained from patients with ulcerative colitis (UC), Crohn’s disease (CD) and controls who underwent screening for colorectal cancer, follow-up after polypectomy or with a history of lower gastrointestinal symptoms. Immunohistochemistry revealed leptin in apical and basolateral membranes of short epithelial portions, Ob-R on the apical pole of epithelial cells. Leptin and Ob-R were also identified in structures and cells scattered in the lamina propria. In UC, a significant correlation between leptin and Ob-R in the lamina propria was found in all inflamed samples, beyond non-inflamed samples of the proximal tract, while in CD, it was found in inflamed distal samples. Most of the leptin and Ob-R positive areas in the lamina propria were also GLUT5 immunoreactive in inflamed and non-inflamed mucosa. A significant correlation of leptin or Ob-R expression with GLUT5 was observed in the inflamed distal samples from UC. Our findings suggest that there are different sites of leptin and Ob-R expression in large intestine and those in lamina propria do not reflect the status of mucosal inflammation. The co-localization of leptin and/or Ob-R with GLUT5 may indicate concomitance effects in colorectal lamina propria areas.

Anti-inflammatory effects of troxerutin are mediated through elastase inhibition

CONTEXT

Obesity is a chronic low-grade inflammatory state associated with immune cell infiltration into the adipose tissue (AT). We hypothesize that the anti-obesity and anti-inflammatory effects of troxerutin (TX) are mediated through inhibition of elastase.

OBJECTIVE

To determine the inhibitory effect of TX on elastase in vitro and in tumor necrosis factor alpha (TNFα) induced 3T3-L1 adipocytes and the molecular interaction of TX with human neutrophil elastase (HNE).

MATERIALS AND METHODS

Differentiated 3T3-L1 adipocytes were pretreated with TX, elastatinal (ELAS) or sodium salicylate (SAL) before exposure to TNFα. Lipid accumulation, reactive oxygen species (ROS) generation and oxidant-antioxidant balance were examined. The mRNA and protein expression of TNFα, interleukin-6, monocyte chemoattractant protein-1, adiponectin, leptin, resistin, chemerin, and elastase were analyzed. Elastase inhibition by TX and ELAS in a cell free system and docking studies for HNE with TX and ELAS were performed.

RESULTS

TX, ELAS or SAL pretreatment had lowered lipid droplets formation and TG content. TX suppressed ROS generation, oxidative stress and improved antioxidant status. The expression of inflammatory cytokines and elastase was downregulated while that of adiponectin was upregulated by TX. The concentration required to produce 50% inhibition in vitro (IC₅₀) was 11.5 μM for TX and 16.9 μM for ELAS. TX showed hydrogen bonding and hydrophobic interactions with elastase.

DISCUSSION

TNFα induces inflammation of 3T3-L1 cells through elastase activation. TX inhibits elastase activity, downregulates expression and binds with elastase.

CONCLUSION

The antioxidant and anti-inflammatory activities of TX in AT could be of relevance in the management of obesity.

Obesity Expands a Distinct Population of T Cells in Adipose Tissue and Increases Vulnerability to Infection

Obesity in humans is associated with poorer health outcomes after infections compared with non-obese individuals. Here, we examined the effects of white adipose tissue and obesity on T cell responses to viral infection in mice. We show that lymphocytic choriomeningitis virus (LCMV) grows to high titer in adipose tissue. Virus-specific T cells enter the adipose tissue to resolve infection but then remain as a memory population distinct from memory T cells in lymphoid tissues. Memory T cells in adipose tissue are abundant in lean mice, and diet-induced obesity further increases memory T cell number in adipose tissue and spleen. Upon re-challenge infection, memory T cells rapidly cause severe pathogenesis, leading to increases in lipase levels, calcification of adipose tissue, pancreatitis, and reduced survival in obese mice but not lean mice. Thus, obesity leads to a unique form of viral pathogenesis involving memory T cell-dependent adipocyte destruction and damage to other tissues.

Obesity is associated with increased morbidity and mortality after viral infections. Using a mouse model of obesity, Misumi et al. identify a distinct population of memory T cells in white adipose tissue and a memory cell-dependent pathogenic response to infection that leads to acute fat necrosis, pancreatitis, and lethality.

Leptin: an unappreciated key player in SLE

Leptin is the forerunner of the adipokine superfamily and plays a key role in regulating energy expenditure and neuroendocrine function. Researches into leptin put emphasize not only on the metabolic role but also its immunoregulatory effect on immune response through immunocyte activation and cytokine secretion. Leptin acts on receptors that are widespread throughout the body and that are expressed across many tissue types. As a consequence, the abnormal expression of leptin has been found to correlate with a number of diseases, including cancers, autoimmune diseases, and cardiovascular diseases. The significance of leptin in the development of autoimmune diseases is becoming increasingly prominent. Systemic lupus erythematosus (SLE) is a severe atypical autoimmune disease that causes damage to multiple organ systems. It is characterised by the following: impaired clearance of apoptotic cells, loss of tolerance to self-antigens, aberrant activation of T cells and B cells, and chronic inflammation. The heightened immunocyte response in SLE means that these physiological systems are particularly vulnerable to regulation by leptin in addition to being of great significance to the research field. Our current review provides insight into the regulatory roles that leptin plays on immune effector cells in SLE.

Obesity worsens central inflammation and disability in multiple sclerosis

BACKGROUND

Previous studies evidenced a link between metabolic dysregulation, inflammation, and neurodegeneration in multiple sclerosis (MS).

OBJECTIVES

To explore whether increased adipocyte mass expressed as body mass index (BMI) and increased serum lipids influence cerebrospinal fluid (CSF) inflammation and disease severity.

METHODS

In this cross-sectional study, 140 consecutive relapsing-remitting (RR)-MS patients underwent clinical assessment, BMI evaluation, magnetic resonance imaging scan, and blood and CSF collection before any specific drug treatment. The CSF levels of the following cytokines, adipocytokines, and inflammatory factors were measured: interleukin (IL)-6, IL-13, granulocyte macrophage colony-stimulating factor, leptin, ghrelin, osteoprotegerin, osteopontin, plasminogen activator inhibitor-1, resistin, and Annexin A1. Serum levels of triglycerides, total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C) were assessed.

RESULTS

A positive correlation emerged between BMI and Expanded Disability Status Scale score. Obese RR-MS patients showed higher clinical disability, increased CSF levels of the proinflammatory molecules IL-6 and leptin, and reduced concentrations of the anti-inflammatory cytokine IL-13. Moreover, both the serum levels of triglycerides and TC/HDL-C ratio showed a positive correlation with IL-6 CSF concentrations.

CONCLUSION

Obesity and altered lipid profile are associated with exacerbated central inflammation and higher clinical disability in RR-MS at the time of diagnosis. Increased adipocytokines and lipids can mediate the negative impact of high adiposity on RR-MS course.

Mechanisms of Leptin and Ghrelin Action on Maturation and Functions of Dendritic Cells

Molecular mechanisms of the immunomodulatory effects of leptin and ghrelin in concentrations typical for pregnancy on the maturation and functional activity of dendritic cells (DCs) generated from the peripheral blood monocytes of women are investigated. The presence of leptin during DC maturation did not affect the levels of CD83⁺CD1c⁺, CD86⁺CD1c⁺, and HLA-DR⁺CD1c⁺ DCs, but increased the amount and the activity of the enzyme indoleamine 2,3-dioxygenase (IDO). Cell culturing in the presence of ghrelin or combination of leptin and ghrelin reduced the percentage of CD86⁺CD1c⁺ DCs but did not affect the levels of CD83⁺CD1c⁺ and HLA-DR⁺CD1c⁺ DCs. In addition, ghrelin reduced the number of IDO molecules without affecting its activity. Simultaneous presence of leptin and ghrelin increased induced IDO activity without affecting the amount of the enzyme in DCs. The effects of leptin and ghrelin on the investigated functions of DCs in some cases correlated with high levels of cAMP. New mechanisms for leptin and ghrelin regulation of tolerogenic functions of DCs in pregnancy are proposed.

Stressed: The Unfolded Protein Response in T Cell Development, Activation, and Function

The unfolded protein response (UPR) is a highly conserved pathway that allows cells to respond to stress in the endoplasmic reticulum caused by an accumulation of misfolded and unfolded protein. This is of great importance to secretory cells because, in order for proteins to traffic from the endoplasmic reticulum (ER), they need to be folded appropriately. While a wealth of literature has implicated UPR in immune responses, less attention has been given to the role of UPR in T cell development and function. This review discusses the importance of UPR in T cell development, homeostasis, activation, and effector functions. We also speculate about how UPR may be manipulated in T cells to ameliorate pathologies.

Leptin Induces Proadipogenic and Proinflammatory Signaling in Adipocytes

Background: Leptin is an adipokine with well-known effects on the central nervous system including the induction of energy expenditure and satiety. Leptin also has major relevance when activating immune cells and modulating inflammatory response. In obesity, increases in white adipose tissue accumulation and leptin levels are accompanied by hypothalamic resistance to leptin. Even though the adipose tissue is a leptin-rich environment, the local actions of leptin regarding adipogenesis were not thoroughly investigated until now. Here we evaluate the contributions of leptins direct signaling in preadipocytes and adipose tissue-derived stromal cells (ASCs) for adipogenesis. Methods: Adipocytes were differentiated from the murine lineage of preadipocytes 3T3-L1 or ASCs from subcutaneous and visceral (retroperitoneal) fat depots from C57Bl/6J mice. Differentiating cells were treated with leptin in addition to or in replacement of insulin. The advance of adipogenesis was assessed by the expression and secretion of adipogenesis- and lipogenesis-related proteins by Western blot and immunoenzimatic assays, and the accumulation of lipid droplets by fluorescence microscopy. Results: Leptin treatment in 3T3-L1 preadipocytes or ASCs increased the production of the adipogenesis- and lipogenesis-related proteins PLIN1, CAV-1, PPARγ, SREBP1C, and/or adiponectin at earlier stages of differentiation. In 3T3-L1 preadipocytes, we found that leptin induced lipid droplets' formation in an mTOR-dependent manner. Also, leptin induced a proinflammatory cytokine profile in 3T3-L1 and ASCs, modulating the production of TNF-α, IL-10, and IL-6. Since insulin is considered an essential factor for preadipocyte differentiation, we asked whether leptin would support adipogenesis in the absence of insulin. Importantly, leptin induced the formation of lipid droplets and the expression of adipogenesis-related proteins independently of insulin during the differentiation of 3T3-L1 cells and ASCs. Conclusions: Our results demonstrate that leptin induces intracellular signaling in preadipocytes and adipocytes promoting adipogenesis and modulating the secretion of inflammatory mediators. Also, leptin restores adipogenesis in the absence of insulin. These findings contribute to the understanding of the local signaling of leptin in precursor and mature adipose cells. The proadipogenic role of leptin unraveled here may be of especial relevance during obesity, when its central signaling is defective.

Galectin-1-induced tolerogenic dendritic cells combined with apoptotic lymphocytes prolong liver allograft survival

Donor-derived tolerogenic dendritic cells (DCs) and apoptotic lymphocytes (ALs) are practical tools for controlling rejection after transplantation by targeting direct and indirect allorecognition pathways, respectively. To date, few studies have investigated the combination of donor-derived tolerogenic DCs and ALs infusion in organ transplantation protection. In the present study, we generated galectin-1-induced tolerogenic DCs (DC_gal-1s) and ultraviolet irradiation-induced ALs with stable immune characteristics in vitro and potential immune regulatory activity in vivo. A rat model of acute liver transplant rejection was established, and the intrinsic tolerogenic profiles associated with the short-term alleviation of rejection and the long-term maintenance of tolerance in the absence of immunosuppressive drugs were evaluated. The DC_gal-1-AL treatment prolonged allograft survival more significantly than a transfusion of DC_gal-1s or ALs alone. This benefit was associated with CD4⁺ Treg cell expansion and decreased interferon (IFN)-γ⁺ T cell levels. Moreover, DC_gal-1-AL treatment led to different cytokine/chemokine changes in the allograft and peripheral blood, that indicated an alleviation of local and systemic inflammation on day 7 post-transplantation. TGF-β1 and TGF-β2 were significantly increased in the long-term surviving allografts after DC_gal-1-AL treatment. Our results indicate that the combination of DC_gal-1s with ALs effectively prolongs liver allograft survival and represents a novel therapeutic strategy for liver transplant rejection.

Orai1 is involved in leptin-sensitive cell maturation in mouse dendritic cells

Store operated calcium entry(SOCE) is known to play a pivotal role in DCs functions including migration, maturation and antigen-presenting ability. Orai1, the major component of SOCE which mainly pairs with Stim1, is surely involved in the regulation of DCs functions. Leptin is recently found to mature DCs, we aim to evaluate the role of Orai1 in leptin-induced dendritic cells(DCs) maturation process and elucidate the mechanism. To this end, Flow cytometry and ELISA were utilized to detect the costimulatory molecule CD86 expression and IL-12 secretion, respectively. Transwell assay was used to examine DCs migration capacity. To evaluate the activity of SOCE, calcium(Ca²⁺) imaging was performed. Firstly, we confirmed the positive effects of leptin upon SOCE and Orai1 expression in DCs isolated from mouse bone marrow. Secondly, we showed that the effects of leptin on DCs migration and maturation are Orai1 dependent. Moreover, Janus kinase 2(Jak2) silencing inhibited leptin-induced Orai1 expression and influenced DCs functions including migration and maturation as well as IL-12 secretion. In conclusion, our results imply that leptin regulates Orai1 by activating Jak2 signaling pathway, hence facilitating DCs migration and maturation.

Leptin/osteopontin axis contributes to enhanced T helper 17 type responses in allergic rhinitis

BACKGROUND

Recent studies suggest that T helper 17 (Th17) cell subset, a distinct pro-inflammatory CD4 +  T cell lineage, may play an important role in the pathophysiology of allergic rhinitis (AR). However, the regulation of Th17 response in allergic disease is not well characterized.

METHODS

Thirty AR and 30 healthy children were enrolled. Serum leptin and OPN levels were measured, and their correlation with IL-17 expression was analyzed using enzyme-linked immunosorbent assay (ELISA). Th17 cell differentiation and cytokine production in peripheral blood mononuclear cell (PBMCs) stimulated by leptin and OPN and related inhibitors were analyzed by ELISA. AR mice models were also established to verify the effect of leptin and OPN on Th17 cell regulation. Immunoprecipitation was performed to explore the interaction between OPN and leptin in Th17 cells.

RESULTS

Our results showed that elevated serum leptin and OPN in AR children were correlated with serum IL-17 level (r = .53, P < .01). The recombinant leptin and OPN enhanced Th17 responses from PBMCs synergistically through nuclear factor κB (NF-κB), mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK) pathway and β3 integrin receptor. The AR mice showed as more severe Th17 responses and symptoms compared with control mice. Immunoprecipitation showed that OPN and leptin may interact with each other directly, and this process may be mediated by β3 integrin.

CONCLUSIONS

Our data provide evidence that upregulation of leptin and OPN promotes Th17 responses in AR, and this process may be achieved through NF-κB, MAPK, and JNK pathway and β3 integrin.

Obesity, Fat Mass and Immune System: Role for Leptin

Obesity is an epidemic disease characterized by chronic low-grade inflammation associated with a dysfunctional fat mass. Adipose tissue is now considered an extremely active endocrine organ that secretes cytokine-like hormones, called adipokines, either pro- or anti-inflammatory factors bridging metabolism to the immune system. Leptin is historically one of most relevant adipokines, with important physiological roles in the central control of energy metabolism and in the regulation of metabolism-immune system interplay, being a cornerstone of the emerging field of immunometabolism. Indeed, leptin receptor is expressed throughout the immune system and leptin has been shown to regulate both innate and adaptive immune responses. This review discusses the latest data regarding the role of leptin as a mediator of immune system and metabolism, with particular emphasis on its effects on obesity-associated metabolic disorders and autoimmune and/or inflammatory rheumatic diseases.

Adipokines and inflammation: is it a question of weight?

Obesity has reached epidemic proportions in the Western society and is increasing in the developing world. It is considered as one of the major contributors to the global burden of disability and chronic diseases, including autoimmune, inflammatory and degenerative diseases. Research conducted on obesity and its complications over the last two decades has transformed the outdated concept of white adipose tissue (WAT) merely serving as an energy depot. WAT is now recognized as an active and inflammatory organ capable of producing a wide variety of factors known as adipokines. These molecules participate through endocrine, paracrine, autocrine or juxtacrine crosstalk mechanisms in a great variety of physiological or pathophysiological processes, regulating food intake, insulin sensitivity, immunity and inflammation. Although initially restricted to metabolic activities (regulation of glucose and lipid metabolism), adipokines currently represent a new family of proteins that can be considered key players in the complex network of soluble mediators involved in the pathophysiology of immune/inflammatory diseases. However, the complexity of the adipokine network in the pathogenesis and progression of inflammatory diseases has posed, since the beginning, the important question of whether it may be possible to target the mechanism(s) by which adipokines contribute to disease selectively without suppressing their physiological functions. Here, we explore in depth the most recent findings concerning the involvement of adipokines in inflammation and immune responses, in particular in rheumatic, inflammatory and degenerative diseases. We also highlight several possible strategies for therapeutic development and propose that adipokines and their signalling pathways may represent innovative therapeutic strategies for inflammatory disorders.

Frontline Science: High fat diet and leptin promote tumor progression by inducing myeloid-derived suppressor cells

Obesity is a risk factor for cancer incidence and cancer mortality. The association of obesity and cancer is attributed to multiple factors, but the tightest linkage is with the chronic, low-grade inflammation that accompanies obesity. Myeloid-derived suppressor cells (MDSC) are known facilitators of cancer progression that act by suppressing the activation and function of tumor-reactive T cells. Because MDSC quantity and function are driven by chronic inflammation, we hypothesized that MDSC may accumulate in obese individuals and facilitate tumor growth by suppressing antitumor immunity. To test this hypothesis, tumor-bearing mice on a high fat or low fat diet (HFD or LFD) were assessed for tumor progression and the metabolic dysfunction associated with obesity. HFD enhanced the accumulation of MDSC, and the resulting MDSC had both beneficial and detrimental effects. HFD-induced MDSC protected mice against diet-induced metabolic dysfunction and reduced HFD-associated inflammation, but also increased the accumulation of fat, enhanced tumor progression, and spontaneous metastasis and reduced survival time. HFD-induced MDSC facilitated tumor growth by limiting the activation of tumor-reactive CD8⁺ T cells. Leptin, an adipokine that regulates appetite satiety and is overexpressed in obesity, undergoes crosstalk with MDSC in which leptin drives the accumulation of MDSC while MDSC down-regulate the production of leptin. Collectively, these studies demonstrate that although MDSC protect against some metabolic dysfunction associated with HFD they enhance tumor growth in HFD mice and that leptin is a key regulator linking HFD, chronic inflammation, immune suppression, and tumor progression.