STAT4 deficiency reduces obesity-induced insulin resistance and adipose tissue inflammation

Inflammation-related miRNAs in obesity, CVD, and NAFLD

Obesity, cardiovascular diseases (CVD), and nonalcoholic fatty liver disease (NAFLD) pose significant worldwide health challenges, characterized by complex interplay among inflammatory pathways that underlie their development. In this review, we examine the contribution of inflammation and associated signaling molecules to the pathogenesis of these conditions, while also emphasizing the significant participation of non-coding RNAs (ncRNAs) in modulating inflammatory pathways. In the context of obesity, aberrant expression patterns of inflammatory-associated miRNAs play a contributory role in adipose tissue inflammation and insulin resistance, thereby exacerbating disturbances in metabolic homeostasis. Similarly, in CVD, dysregulated miRNA expression alters inflammatory reactions, disrupts endothelial function, and induces cardiac remodeling, thereby impacting the advancement of the disease. Moreover, in the context of NAFLD, inflammatory-associated miRNAs are implicated in mediating hepatic inflammation, lipid deposition, and fibrosis, underscoring their candidacy as promising therapeutic targets. Additionally, the competing endogenous RNA (ceRNA) network has emerged as a novel regulatory mechanism in the etiology of CVD, obesity, and NAFLD, wherein ncRNAs assume pivotal roles in facilitating communication across diverse molecular pathways. Moreover, in the concluding section, we underscored the potential efficacy of directing interventions towards inflammatory-related miRNAs utilizing herbal remedies and therapies based on exosome delivery systems as a promising strategy for ameliorating pathologies associated with inflammation in obesity, CVD, and NAFLD.

USP18 Curbs the Progression of Metabolic Hypertension by Suppressing JAK/STAT Pathway

Hypertension is a pathological state of the metabolic syndrome that increases the risk of cardiovascular disease. Managing hypertension is challenging, and we aimed to identify the pathogenic factors and discern therapeutic targets for metabolic hypertension (MHR). An MHR rat model was established with the combined treatment of a high-sugar, high-fat diet and ethanol. Histopathological observations were performed using hematoxylin-eosin and Sirius Red staining. Transcriptome sequencing was performed to screen differentially expressed genes. The role of ubiquitin-specific protease 18 (USP18) in the proliferation, apoptosis, and oxidative stress of HUVECs was explored using Cell Counting Kit-8, flow cytometry, and enzyme-linked immunosorbent assays. Moreover, USP18 downstream signaling pathways in MHR were screened, and the effects of USP18 on these signaling pathways were investigated by western blotting. In the MHR model, total cholesterol and low-density lipoprotein levels increased, while high-density lipoprotein levels decreased. Moreover, high vessel thickness and percentage of collagen were noted along with increased malondialdehyde, decreased superoxide dismutase and catalase levels. The staining results showed that the MHR model exhibited an irregular aortic intima and disordered smooth muscle cells. There were 78 differentially expressed genes in the MHR model, and seven hub genes, including USP18, were identified. USP18 overexpression facilitated proliferation and reduced apoptosis and oxidative stress in HUVECs treated with Ang in vitro. In addition, the JAK/STAT pathway was identified as a USP18 downstream signaling pathway, and USP18 overexpression inhibited the expression of JAK/STAT pathway-related proteins. Conclusively, USP18 restrained MHR progression by promoting cell proliferation, reversing apoptosis and oxidative stress, and suppressing the JAK/STAT pathway.

Adipose tissue lymphocytes and obesity

Obesity is associated with chronic inflammation in adipose tissue (AT), mainly evidenced by infiltration and phenotypic changes of various types of immune cells. Macrophages are the major innate immune cells and represent the predominant immune cell population within AT. Lymphocytes, including T cells and B cells, are adaptive immune cells and constitute another important immune cell population in AT. In obesity, CD8+ effector memory T cells, CD4+ Th1 cells, and B2 cells are increased in AT and promote AT inflammation, while regulatory T cells and Th2 cells, which usually function as immune regulatory or type 2 inflammatory cells, are reduced in AT. Immune cells may regulate the metabolism of adipocytes and other cells through various mechanisms, contributing to the development of metabolic diseases, including insulin resistance and type 2 diabetes. Efforts targeting immune cells and inflammation to prevent and treat obesity-linked metabolic disease have been explored, but have not yielded significant success in clinical studies. This review provides a concise overview of the changes in lymphocyte populations within AT and their potential role in AT inflammation and the regulation of metabolic functions in the context of obesity.

Adipose cDC1s contribute to obesity-associated inflammation through STING-dependent IL-12 production

Obesity is associated with chronic low-grade white adipose tissue (WAT) inflammation that can contribute to the development of insulin resistance in mammals. Previous studies have identified interleukin (IL)-12 as a critical upstream regulator of WAT inflammation and metabolic dysfunction during obesity. However, the cell types and mechanisms that initiate WAT IL-12 production remain unclear. Here we show that conventional type 1 dendritic cells (cDC1s) are the cellular source of WAT IL-12 during obesity through analysis of mouse and human WAT single-cell transcriptomic datasets, IL-12 reporter mice and IL-12p70 protein levels by enzyme-linked immunosorbent assay. We demonstrate that cDC1s contribute to obesity-associated inflammation by increasing group 1 innate lymphocyte interferon-γ production and inflammatory macrophage accumulation. Inducible depletion of cDC1s increased WAT insulin sensitivity and systemic glucose tolerance during diet-induced obesity. Mechanistically, endocytosis of apoptotic bodies containing self-DNA by WAT cDC1s drives stimulator of interferon genes (STING)-dependent IL-12 production. Together, these results suggest that WAT cDC1s act as critical regulators of adipose tissue inflammation and metabolic dysfunction during obesity.

JAK-STAT signaling in inflammation and stress-related diseases: implications for therapeutic interventions

The Janus kinase-signal transducer and transcription activator pathway (JAK-STAT) serves as a cornerstone in cellular signaling, regulating physiological and pathological processes such as inflammation and stress. Dysregulation in this pathway can lead to severe immunodeficiencies and malignancies, and its role extends to neurotransduction and pro-inflammatory signaling mechanisms. Although JAK inhibitors (Jakinibs) have successfully treated immunological and inflammatory disorders, their application has generally been limited to diseases with similar pathogenic features. Despite the modest expression of JAK-STAT in the CNS, it is crucial for functions in the cortex, hippocampus, and cerebellum, making it relevant in conditions like Parkinson's disease and other neuroinflammatory disorders. Furthermore, the influence of the pathway on serotonin receptors and phospholipase C has implications for stress and mood disorders. This review expands the understanding of JAK-STAT, moving beyond traditional immunological contexts to explore its role in stress-related disorders and CNS function. Recent findings, such as the effectiveness of Jakinibs in chronic conditions such as rheumatoid arthritis, expand their therapeutic applicability. Advances in isoform-specific inhibitors, including filgotinib and upadacitinib, promise greater specificity with fewer off-target effects. Combination therapies, involving Jakinibs and monoclonal antibodies, aiming to enhance therapeutic specificity and efficacy also give great hope. Overall, this review bridges the gap between basic science and clinical application, elucidating the complex influence of the JAK-STAT pathway on human health and guiding future interventions.

Myeloid cell deficiency of the inflammatory transcription factor Stat4 protects long-term synaptic plasticity from the effects of a high-fat, high-cholesterol diet

Neuroinflammation is associated with neurodegenerative diseases, including Alzheimer's and Parkinson's. The cytokine interleukin-12 activates signal transducer and activator of transcription 4 (Stat4), and consumption of a high-fat, high-cholesterol diet (HFD-C) and Stat4 activity are associated with inflammation, atherosclerosis, and a diabetic metabolic phenotype. In studies of in vitro hippocampal slices from control Stat4fl/flLdlr-/- mice fed a HFD-C diabetogenic diet, we show that Schaffer collateral-CA1 synapses exhibited larger reductions in activity-dependent, long-term potentiation (LTP) of synaptic transmission, compared to mice fed a standard diet. Glucose tolerance and insulin sensitivity shifts produced by HFD-C diet were reduced in Stat4ΔLysMLdlr-/- mice compared to Stat4fl/flLdlr-/- controls. Stat4ΔLysMLdlr-/- mice, which lack Stat4 under control of the LysMCre promoter, were resistant to HFD-C induced impairments in LTP. In contrast, Schaffer collateral-CA1 synapses in Stat4ΔLysMLdlr-/- mice fed the HFD-C diet showed larger LTP than control Stat4fl/flLdlr-/- mice. Expression of a number of neuroinflammatory and synaptic plasticity genes was reduced by HFD-C diet in control mice, and less affected by HFD-C diet in Stat4ΔLysMLdlr-/- mice. These data suggest that suppression of Stat4 activation may protect against effects of Western diet on cognition, type 2 diabetes, and reduce risk of Alzheimer's disease and other neurodegenerative disorders associated with neuroinflammation.

The water extract of Potentilla discolor Bunge (PDW) ameliorates high-sugar diet-induced type II diabetes model in Drosophila melanogaster via JAK/STAT signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Potentilla discolor Bunge (PD) is a member of the Rosaceae family. It has been traditionally used in folk medicine for the treatment of diabetes. Additionally, people in folk also eat fresh and tender PD stems as vegetables or brew them as tea.

AIM OF THE STUDY

The aim of this study was to explore the antidiabetic effects and underlying mechanisms of the water extract of Potentilla discolor (PDW) in a fruit fly model of high-sugar diet-induced type 2 diabetes.

MATERIALS AND METHODS

The antidiabetic efficacy of PDW was evaluated in a fruit fly model of diabetes induced by a high-sugar diet (HSD). Various physiological parameters were tested to evaluate the anti-diabetic effect of PDW. Gene expression levels related to insulin signaling pathways, glucose metabolism, lipid metabolism, and JAK/STAT signaling pathways were primarily analyzed using RT-qPCR to investigate the therapeutic mechanisms.

RESULTS

In this study, we found that the water extract of Potentilla discolor (PDW) can ameliorate type II diabetes phenotypes induced by the HSD in fruit flies. These phenotypes include growth rate, body size, hyperglycemia, glycogen metabolism, fat storage, and intestinal microflora homeostasis. PDW also improved the body size of s6k and rheb knockdown flies, suggesting its potential to activate the downstream insulin pathway and alleviate insulin resistance. Furthermore, we demonstrated that PDW reduced the expression of two target genes of the JAK/STAT signaling pathway, namely the insulin antagonist Impl2 and insulin receptor inhibitor Socs36E, which act as regulators inhibiting the activation of the insulin signaling pathway.

CONCLUSIONS

This study provides evidence for the anti-diabetic activity of PDW and suggests that its underlying mechanism may involve the improvement of insulin resistance by inhibiting the JAK/STAT signaling pathway.

High-fat-diet induced obesity and diabetes mellitus in Th1 and Th2 biased mice strains: A brief overview and hypothesis

Obesity and diabetes mellitus are common metabolic diseases prevalent worldwide. Mice are commonly used to study the pathogenesis of these two conditions. Obesity and diabetes mellitus are induced by administering a high-fat diet in many studies although other diet-induced models are also used. Several factors may influence the outcome of the studies done to study diet-induced obesity in mice. The immune system plays a crucial role in the susceptibility of mice to develop obesity and metabolic disease. In this article, the reasons for differences in susceptibility to develop obesity and diabetes mellitus in mice in response to high-fat-diet feeding and the influence of immunological bias of the mice strain used in studies are evaluated. Mice strains that induce proinflammatory and Th1-type immune responses are found to be susceptible to high-fat-diet-induced obesity. A few studies which directly compared the effect of a high-fat diet on obesity and diabetic phenotype in Th1- and Th2-biased mice strains were briefly analyzed. Based on the observations, it is proposed that the liver and adipose tissue may respond differently to high-fat-diet feeding regimens in Th1- and Th2-biased mice strains. For instance, in Th1-biased mice, adipose tissue fat content was high both in the baseline as well as in response to a high-fat diet whereas in the liver, it was found to be less. It can be inferred that the immune responses to diet-induced models may provide insights into the pathogenesis of obesity and diabetes mellitus.

Epigenetic regulation of macrophage polarization in wound healing

The immune microenvironment plays a critical role in regulating skin wound healing. Macrophages, the main component of infiltrating inflammatory cells, play a pivotal role in shaping the immune microenvironment in the process of skin wound healing. Macrophages comprise the classic proinflammatory M1 subtype and anti-inflammatory M2 population. In the early inflammatory phase of skin wound closure, M1-like macrophages initiate and amplify the local inflammatory response to disinfect the injured tissue. In the late tissue-repairing phase, M2 macrophages are predominant in wound tissue and limit local inflammation to promote tissue repair. The biological function of macrophages is tightly linked with epigenomic organization. Transcription factors are essential for macrophage polarization. Epigenetic modification of transcription factors determines the heterogeneity of macrophages. In contrast, transcription factors also regulate the expression of epigenetic enzymes. Both transcription factors and epigenetic enzymes form a complex network that regulates the plasticity of macrophages. Here, we describe the latest knowledge concerning the potential epigenetic mechanisms that precisely regulate the biological function of macrophages and their effects on skin wound healing.

Anti-Inflammatory Mechanisms of Dietary Flavones: Tapping into Nature to Control Chronic Inflammation in Obesity and Cancer

Flavones are natural phytochemicals broadly distributed in our diet. Their anti-inflammatory properties provide unique opportunities to control the innate immune system and inflammation. Here, we review the role of flavones in chronic inflammation with an emphasis on their impact on the molecular mechanisms underlying inflammatory diseases including obesity and cancer. Flavones can influence the innate immune cell repertoire restoring the immune landscape. Flavones impinge on NF-κB, STAT, COX-2, or NLRP3 inflammasome pathways reestablishing immune homeostasis. Devoid of adverse side effects, flavones could present alternative opportunities for the treatment and prevention of chronic inflammation that contributes to obesity and cancer.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

STAT4 regulates cardiomyocyte apoptosis in rat models of diabetic cardiomyopathy

OBJECTIVE

This study aimed to investigate the protective role of the signal transducer and activator of transcription 4 (STAT4) in diabetic cardiomyopathy.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats (6-8 weeks old) were purchased from the Experimental Animal Center of Zhengzhou University. The rats were randomly divided into the control and diabetic cardiomyopathy groups. Rat models of diabetic cardiomyopathy were established by a high-sugar and high-fat diet combined with a peritoneal injection of streptozocin. Pathological changes in the heart were visualized using Hematoxylin-eosin (HE) staining and Masson's staining. Moreover, cell apoptosis was detected using terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labeling (TUNEL) staining and Annexin V apoptosis detection kit. Furthermore, H9C2 cells were transfected with lentivirus overexpressing STAT4 and treated with high glucose. The CCK-8 assay was performed to determine cell viability. Finally, Western blotting was used to determine the expression of STAT4, Bax, and Bcl-2.

RESULTS

The myocardial tissue of the diabetic cardiomyopathy models showed hypertrophy, myocardial fibrosis and collagen deposition. Furthermore, TUNEL staining showed increased apoptosis and decreased expression of STAT4 in the myocardial cells. Moreover, the myocardial tissues of the DCM models showed increased expression of Bax/Bcl-2 and a high percentage of Annexin V positive cells. The H9C2 cells showed decreased expression of STAT4 following high glucose treatment. However, the H9C2 cells overexpressing STAT4 showed decreased expression of Bax/Bcl-2 and reduced percentage of Annexin V positive cells.

CONCLUSION

The DCM group had decreased myocardial expression of STAT4. Furthermore, overexpression of STAT4 was shown to reduce high glucose-induced apoptosis.

Adipose invariant NKT cells interact with CD1d-expressing macrophages to regulate obesity-related inflammation

Obesity is accompanied by and accelerated with chronic inflammation in adipose tissue, especially visceral adipose tissue (VAT). This low-level inflammation predisposes the host to the development of metabolic disease, most notably type 2 diabetes. We have focused on the capacity of glycolipid-reactive, CD1d-restricted natural killer T (NKT) cells to modulate obesity and its associated metabolic sequelae. We previously reported that CD1d knockout (KO) mice are partially protected against the development of obesity-associated insulin-resistance, and these findings were recapitulated in mice with an adipocyte-specific CD1d deficiency, suggesting that NKT cell-adipocyte interactions play a critical role in exacerbating disease. However, many other CD1d-expressing cells contribute to the in vivo responses of NKT cells to lipid antigens. In the present study, we examined the role of CD1d expression by macrophages (Mϕ) to the development of obesity-associated metabolic inflammation using LysMcre-cd1d1^f/f mice where the CD1d1 gene is disrupted in a Mϕ-specific manner. Unexpectedly, these animals contained a higher frequency of T-bet⁺ CD4⁺ T cells in VAT with increased production of Th1-cytokines that aggravated VAT inflammation. Mϕ from mutant mice displayed increased production of IL-12p40, suggesting M1 polarization. These findings indicate that interactions of CD1d on Mϕ with NKT cells play a beneficial role in obesity-associated VAT inflammation and insulin resistance with a sharp contrast to an aggravating role of CD1d on another type of antigen presenting cell, dendritic cells.

Adipocyte-Derived Versican and Macrophage-Derived Biglycan Control Adipose Tissue Inflammation in Obesity

Obesity is characterized by adipose tissue inflammation. Because proteoglycans regulate inflammation, here we investigate their role in adipose tissue inflammation in obesity. We find that adipose tissue versican and biglycan increase in obesity. Versican is produced mainly by adipocytes and biglycan by adipose tissue macrophages. Both proteoglycans are also present in adipose tissue from obese human subjects undergoing gastric bypass surgery. Deletion of adipocyte-specific versican or macrophage-specific biglycan in mice reduces macrophage accumulation and chemokine and cytokine expression, although only adipocyte-specific versican deletion leads to sustained improvement in glucose tolerance. Macrophage-derived biglycan activates inflammatory genes in adipocytes. Versican expression increases in cultured adipocytes exposed to excess glucose, and adipocyte-conditioned medium stimulates inflammation in resident peritoneal macrophages, in part because of a versican breakdown product, versikine. These findings provide insights into the role of adipocyte- and macrophage-derived proteoglycans in adipose tissue inflammation in obesity.

Innate Immunity in Diabetic Wound Healing: Focus on the Mastermind Hidden in Chronic Inflammatory

A growing body of evidence suggests that the interaction between immune and metabolic responses is essential for maintaining tissue and organ homeostasis. These interacting disorders contribute to the development of chronic diseases associated with immune-aging such as diabetes, obesity, atherosclerosis, and nonalcoholic fatty liver disease. In Diabetic wound (DW), innate immune cells respond to the Pathogen-associated molecular patterns (PAMAs) and/or Damage-associated molecular patterns (DAMPs), changes from resting to an active phenotype, and play an important role in the triggering and maintenance of inflammation. Furthermore, the abnormal activation of innate immune pathways secondary to immune-aging also plays a key role in DW healing. Here, we review studies of innate immune cellular molecular events that identify metabolic disorders in the local microenvironment of DW and provide a historical perspective. At the same time, we describe some of the recent progress, such as TLR receptor-mediated intracellular signaling pathways that lead to the activation of NF-κB and the production of various pro-inflammatory mediators, NLRP3 inflammatory via pyroptosis, induction of IL-1β and IL-18, cGAS-STING responds to mitochondrial injury and endoplasmic reticulum stress, links sensing of metabolic stress to activation of pro-inflammatory cascades. Besides, JAK-STAT is also involved in DW healing by mediating the action of various innate immune effectors. Finally, we discuss the great potential of targeting these innate immune pathways and reprogramming innate immune cell phenotypes in DW therapy.

Metabolic tissue-resident CD8+ T cells: A key player in obesity-related diseases

Obesity-induced low-grade chronic inflammation in the metabolic tissues, such as adipose tissue (AT) and liver tissue, in individuals with obesity is a major etiological factor for several diseases, such as insulin resistance, type 2 diabetes, fatty liver disease, atherosclerosis and cardiovascular problems, as well as cancer and autoimmune diseases. Previous studies have revealed that tissue-resident macrophages play a crucial role in this process. However, the mechanisms responsible for recruiting and activating macrophages and initiating chronic inflammation in the metabolic tissues have not yet been clearly elucidated. In the most recent decade, there has been a growing emphasis on the critical role of the adaptive CD8⁺ T cells in obesity-induced chronic inflammation and related metabolic diseases. In this review, we will summarize the relevant studies in both mice and human regarding the role of metabolic tissue-resident CD8⁺ T cells in obesity-related inflammation and diseases, as well as the possible mechanisms underlying the regulation of CD8⁺ T cell recruitment, activation and function in the metabolic tissues, and discuss their potential as therapeutic targets for obesity-related diseases.

Domeless receptor loss in fat body tissue reverts insulin resistance induced by a high-sugar diet in Drosophila melanogaster

Insulin resistance is a hallmark of type 2 diabetes resulting from the confluence of several factors, including genetic susceptibility, inflammation, and diet. Under this pathophysiological condition, the dysfunction of the adipose tissue triggered by the excess caloric supply promotes the loss of sensitivity to insulin at the local and peripheral level, a process in which different signaling pathways are involved that are part of the metabolic response to the diet. Besides, the dysregulation of insulin signaling is strongly associated with inflammatory processes in which the JAK/STAT pathway plays a central role. To better understand the role of JAK/STAT signaling in the development of insulin resistance, we used a simple organism, Drosophila melanogaster, as a type 2 diabetes model generated by the consumption of a high-sugar diet. In this model, we studied the effects of inhibiting the expression of the JAK/STAT pathway receptor Domeless, in fat body, on adipose metabolism and glycemic control. Our results show that the Domeless receptor loss in fat body cells reverses both hyperglycemia and the increase in the expression of the insulin resistance marker Nlaz, observed in larvae fed a high sugar diet. This effect is consistent with a significant reduction in Dilp2 mRNA expression and an increase in body weight compared to wild-type flies fed high sugar diets. Additionally, the loss of Domeless reduced the accumulation of triglycerides in the fat body cells of larvae fed HSD and also significantly increased the lifespan of adult flies. Taken together, our results show that the loss of Domeless in the fat body reverses at least in part the dysmetabolism induced by a high sugar diet in a Drosophila type 2 diabetes model.

Metabolic Inflammation and Insulin Resistance in Obesity

Obesity is becoming an epidemic in the United States and worldwide and increases risk for many diseases, particularly insulin resistance, type 2 diabetes mellitus, and cardiovascular disease. The mechanisms linking obesity with these diseases remain incompletely understood. Over the past 2 to 3 decades, it has been recognized that in obesity, inflammation, with increased accumulation and inflammatory polarization of immune cells, takes place in various tissues, including adipose tissue, skeletal muscle, liver, gut, pancreatic islet, and brain and may contribute to obesity-linked metabolic dysfunctions, leading to insulin resistance and type 2 diabetes mellitus. Therapies targeting inflammation have shed light on certain obesity-linked diseases, including type 2 diabetes mellitus and atherosclerotic cardiovascular disease, but remain to be tested further and confirmed in clinical trials. This review focuses on inflammation in adipose tissue and its potential role in insulin resistance associated with obesity.

STAT4: an immunoregulator contributing to diverse human diseases

Signal transducer and activator of transcription 4 (STAT4) is a member of the STAT family and localizes to the cytoplasm. STAT4 is phosphorylated after a variety of cytokines bind to the membrane, and then dimerized STAT4 translocates to the nucleus to regulate gene expression. We reviewed the essential role played by STAT4 in a wide variety of cells and the pathogenesis of diverse human diseases, especially many kinds of autoimmune and inflammatory diseases, via activation by different cytokines through the Janus kinase (JAK)-STAT signaling pathway.

STAT4 silencing underlies a novel inhibitory role of microRNA-141-3p in inflammation response of mice with experimental autoimmune myocarditis

As an inflammatory disease afflicting the heart muscle, autoimmune myocarditis (AM) represents one of the foremost causes of heart failure. Accumulating evidence has implicated microRNAs (miRNAs) in the process of inflammation and autoimmunity. Hence, the current study aimed to investigate the mechanism by which miR-141-3p influences experimental AM (EAM). An EAM mouse model was established using 6-wk old male BALB/c mice, after which the expression of miR-141-3p and STAT4 was measured. Gain-of-function and loss-of-function investigations were performed to identify the functional role of miR-141-3p and STAT4 in EAM. Heart weight-to-body weight ratio, cardiac function, and degree of inflammation, as well as the levels of inflammation factors (IFN-γ, TNF-α, IL-2, IL-6, and IL-17) in the serum were detected. STAT4 was subsequently verified to be upregulated, and miR-141-3p was downregulated in the EAM mice. Furthermore, the overexpression of miR-141-3p or silencing of STAT4 was observed to reduce the heart weight-to-body weight ratio of EAM mice and improve cardiac function, while alleviating the degree of inflammatory cell infiltration in the myocardial tissue. Meanwhile, the overexpression of miR-141-3p was identified to diminish serum inflammatory factor levels by downregulating STAT4. Additionally, miR-141-3p could bind to STAT4 to downregulate its expression, ultimately mitigating inflammation and inducing an anti-inflammatory effect in EAM mice. Taken together, upregulation of miR-141-3p alleviates the inflammatory response in EAM mice by inhibiting STAT4, providing a promising intervention target for the molecular treatment of AM.NEW & NOTEWORTHY miR-141-3p is poorly expressed, and STAT4 is upregulated in experimental autoimmune myocarditis (EAM) mice. Overexpressing miR-141-3p inhibits EAM. miR-141-3p binds to and suppresses STAT4 expression. miR-141-3p overexpression inhibits inflammatory factors by downregulating STAT4. This study provides new insights into the treatment of autoimmune myocarditis.

Genetic variation of the transcription factor GATA3, not STAT4, is associated with the risk of type 2 diabetes in the Bangladeshi population

Type 2 diabetes mellitus is a multifactorial metabolic disorder caused by environmental factors and has a strong association with hereditary issues. These hereditary issues result in an imbalance in CD4⁺T cells and a decreased level of naïve CD4⁺T cells, which may be critical in the pathogenesis of type 2 diabetes. Transcription factors GATA3 and STAT4 mediate the cytokine-induced development of naïve T cells into Th1 or Th2 types. In the present study, genetic analyses of GATA3 SNP rs3824662 and STAT4 SNP rs10181656 were performed to investigate the association of allelic and genotypic variations with the risk of T2D in the Bangladeshi population. A total of 297 unrelated Bangladeshi patients with type 2 diabetes and 247 healthy individuals were included in the study. The allelic and genotypic frequencies of rs10181656 located in the STAT4 gene were not found to be associated with risk of type 2 diabetes. The GATA3 rs3824662 T allele and mutant TT genotype had a significant association with the risk of T2D [OR: 1.52 (1.15–2.02), X² = 8.66, p = 0.003 and OR: 2.98 (1.36–6.55), X² = 7.98, p = 0.04, respectively]. Thus, the present study postulates that the genetic variation of the transcription factor GATA3, not STAT4, is associated with the risk of type 2 diabetes in the Bangladeshi population.

JAK/STAT - Emerging Players in Metabolism

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is crucial for transducing signals from a variety of metabolically relevant hormones and cytokines including growth hormone, leptin, erythropoietin, IL4, IL6 and IFNγ. A growing body of evidence suggests that this pathway is dysregulated in the context of obesity and metabolic disease. Recent development of animal models has been instrumental in identifying the role of JAK/STAT signaling in the peripheral metabolic organs including adipose, liver, muscle, pancreas, and the immune system. In this review we summarize current knowledge about the function of JAK/STAT proteins in the regulation of metabolism, and highlight new potential therapeutic targets for the treatment of obesity and diabetes.

A vicious circle in chronic lymphoedema pathophysiology? An adipocentric view

Chronic lymphoedema is a disease caused by a congenital or acquired damage to the lymphatic system and characterized by complex chains of pathophysiologic events such as lymphatic fluid stasis, chronic inflammation, lymphatic vessels impairment, adipose tissue deposition and fibrosis. These events seem to maintain and reinforce themselves through a positive feedback loop: regardless of the initial cause of lymphatic stasis, the dysfunctional adipose tissue and its secretion products can worsen lymphatic vessels' function, aggravating lymph leakage and stagnation, which can promote further adipose tissue deposition and fibrosis, similar to what may happen in obesity. In addition to the current knowledge about the tight and ancestral interrelation between immunity system and metabolism, there is evidence for similarities between obesity-related and lymphatic damage-induced lymphoedema. Together, these observations indicate strong reciprocal relationship between lymphatics and adipose tissue and suggest a possible key role of the adipocyte in the pathophysiology of chronic lymphoedema's vicious circle.

Modulation of T Cell Activation in Obesity

SIGNIFICANCE

Immune T cells are present in adipose tissues (AT), and the stoichiometry of the different T cell subsets is altered during diet-induced obesity (DIO). T cells contribute to the early steps of AT inflammation during DIO. Recent Advances: Many factors could potentially be responsible for this altered pro-inflammatory versus anti-inflammatory T cell balance.

CRITICAL ISSUES

T cells are potentially activated in AT, which vitamin D might contribute to, as will be discussed in this article. In addition, we will review the different possible contributors to T cell activation in AT, such as the CD28 and CD154 T cell costimulatory molecules in AT.

FUTURE DIRECTIONS

The potential antigen presentation capacities of adipocytes should be further investigated. Moreover, the properties of these AT resident (or migrating to AT) T cells must be further assessed. Antioxid. Redox Signal. 26, 489-500.

Key Role of STAT4 Deficiency in the Hematopoietic Compartment in Insulin Resistance and Adipose Tissue Inflammation

Visceral adipose tissue (AT) inflammation is linked to the complications of obesity, including insulin resistance (IR) and type 2 diabetes. Recent data from our lab showed that germline deficiency in STAT4 reduces inflammation and improves IR in obese mice. The objective of this study was to determine the contribution of selective STAT4 deficiency in subsets of hematopoietic cells to IR and AT inflammation. To determine the contribution of hematopoietic lineage, we sublethally irradiated Stat4^-/-C57Bl6 mice and reconstituted them with bone marrow cells (BMC) from Stat4^+/+C57Bl6 congenic donors. We also established the contribution of selective STAT4 deficiency in CD4+ or CD8+ T cells using adoptive transfer in Rag1-/- mice. All mice received a HFD for 15 weeks (n = 7-12 mice/group). BMC that expressed STAT4 induced increases in glucose intolerance and IR compared to STAT4-deficient cells. Also, AT inflammation was increased and the numbers of CD8+ cells infiltrating AT were higher in mice with STAT4 expressing BMC. Studies in Rag1-/- mice further confirmed the prominent role of CD8+ cells expressing STAT4 in insulin resistance and AT and islet inflammation. Collectively our results show specific and dominant contribution of STAT4 in the hematopoietic compartment to metabolic health and inflammation in diet-induced obesity.

Complement Activation and STAT4 Expression Are Associated with Early Inflammation in Diabetic Wounds

Diabetic non-healing wounds are a major clinical problem. The mechanisms leading to poor wound healing in diabetes are multifactorial but unresolved inflammation may be a major contributing factor. The complement system (CS) is the most potent inflammatory cascade in humans and contributes to poor wound healing in animal models. Signal transducer and activator of transcription 4 (STAT4) is a transcription factor expressed in immune and adipose cells and contributes to upregulation of some inflammatory chemokines and cytokines. Persistent CS and STAT4 expression in diabetic wounds may thus contribute to chronic inflammation and delayed healing. The purpose of this study was to characterize CS and STAT4 in early diabetic wounds using db/db mice as a diabetic skin wound model. The CS was found to be activated early in the diabetic wounds as demonstrated by increased anaphylatoxin C5a in wound fluid and C3-fragment deposition by immunostaining. These changes were associated with a 76% increase in nucleated cells in the wounds of db/db mice vs.

CONTROLS

The novel classical CS inhibitor, Peptide Inhibitor of Complement C1 (PIC1) reduced inflammation when added directly or saturated in an acellular skin scaffold, as reflected by reduced CS components and leukocyte infiltration. A significant increase in expression of STAT4 and the downstream macrophage chemokine CCL2 and its receptor CCR2 were also found in the early wounds of db/db mice compared to non-diabetic controls. These studies provide evidence for two new promising targets to reduce unresolved inflammation and to improve healing of diabetic skin wounds.

The JAK/STAT pathway in obesity and diabetes

Diabetes mellitus are complex, multi-organ metabolic pathologies characterized by hyperglycemia. Emerging evidence shows that the highly conserved and potent JAK/STAT signaling pathway is required for normal homeostasis, and, when dysregulated, contributes to the development of obesity and diabetes. In this review, we analyze the role of JAK/STAT activation in the brain, liver, muscle, fat and pancreas, and how this affects the course of the disease. We also consider the therapeutic implications of targeting the JAK/STAT pathway in treatment of obesity and diabetes.

Contribution of the STAT4 rs7574865 gene polymorphism to the susceptibility to autoimmune thyroiditis in healthy Turk population and psoriatic subgroups

Introduction

STAT4 is an important transcription factor that activates gene transcription as a response to cytokines. Recently, the influence of STAT4 gene on autoimmune disease has been widely studied in many different immune-related diseases. Autoimmune, metabolic and cardiovascular disorders are more common in psoriatic patients. STAT4 may be a unique gene that switches on in autoimmune-related thyroid disease in psoriatic patients.

The aim of the study: To explore the association of a STAT4 rs7574865 polymorphism to autoimmune thyroid diseases in the general Turkish population and psoriatic subgroups.

Material and methods

A total of 132 psoriatic patients and 118 non-psoriatic volunteers were genotyped for STAT4 rs7574865 using real time PCR. Twenty-four of the psoriatic patients and 15 of the non-psoriatic volunteers have autoimmune-related thyroid diseases.

Results

The prevalence of the T allele [OR = 4.37; 95% CI: 1.05-19; p = 0.03] of the STAT4 rs7574865 was higher in individuals with autoimmune-related thyroid diseases among the all non-psoriatic volunteers. The volunteers with autoimmune-related thyroid diseases has an increased allele positivity and carriers having at least one of the risk allele was significantly higher than in counterparts with a GG wild genotype [ORGT/TT vs. GG: 1.73; 95% CI: 0.09-32; p = 0.03]. Yet, there was no evidence of an association between rs7574865 and autoimmune-related thyroid disease in psoriatic patients.

Conclusions

The STAT4 rs7574865 polymorphism increases autoimmune-related thyroid disease susceptibility among the general population but not in psoriatic patients.

STAT4 contributes to adipose tissue inflammation and atherosclerosis

Adipose tissue (AT) inflammation is an emerging factor contributing to cardiovascular disease. STAT4 is a transcription factor expressed in adipocytes and in immune cells and contributes to AT inflammation and insulin resistance in obesity. The objective of this study was to determine the effect of STAT4 deficiency on visceral and peri-aortic AT inflammation in a model of atherosclerosis without obesity. Stat4(-/-)Apoe(-/-) mice and Apoe(-/-) controls were kept either on chow or Western diet for 12 weeks. Visceral and peri-aortic AT were collected and analyzed for immune composition by flow cytometry and for cytokine/chemokine expression by real-time PCR. Stat4(-/-)Apoe(-/-) and Apoe(-/-) mice had similar body weight, plasma glucose, and lipids. Western diet significantly increased macrophage, CD4+, CD8+, and NK cells in peri-aortic and visceral fat in Apoe(-/-) mice. In contrast, in Stat4(-/-)Apoe(-/-) mice, a Western diet failed to increase the percentage of immune cells infiltrating the AT. Also, IL12p40, TNFa, CCL5, CXCL10, and CX3CL1 were significantly reduced in the peri-aortic fat in Stat4(-/-)Apoe(-/-) mice. Importantly, Stat4(-/-)Apoe(-/-) mice on a Western diet had significantly reduced plaque burden vs Apoe(-/-) controls. In conclusion, STAT4 deletion reduces inflammation in peri-vascular and visceral AT and this may contribute via direct or indirect effects to reduced atheroma formation.

STAT4 deficiency reduces the development of atherosclerosis in mice

Atherosclerosis is a chronic inflammatory process that leads to plaque formation in large and medium sized vessels. T helper 1 (Th1) cells constitute the majority of plaque infiltrating pro-atherogenic T cells and are induced via IFNγ-dependent activation of T-box (Tbet) and/or IL-12-dependent activation of signal transducer and activator of transcription 4 (STAT4). We thus aimed to define a role for STAT4 in atherosclerosis. STAT4-deficiency resulted in a ∼71% reduction (p < 0.001) in plaque burden in Stat4(-/-)Apoe(-/-) vs Apoe(-/-) mice fed chow diet and significantly attenuated atherosclerosis (∼31%, p < 0.01) in western diet fed Stat4(-/-)Apoe(-/-) mice. Surprisingly, reduced atherogenesis in Stat4(-/-)Apoe(-/-) mice was not due to attenuated IFNγ production in vivo by Th1 cells, suggesting an at least partially IFNγ-independent pro-atherogenic role of STAT4. STAT4 is expressed in T cells, but also detected in macrophages (MΦs). Stat4(-/-)Apoe(-/-)in vitro differentiated M1 or M2 MΦs had reduced cytokine production compare to Apoe(-/-) M1 and M2 MΦs that was accompanied by reduced induction of CD69, I-A(b), and CD86 in response to LPS stimulation. Stat4(-/-)Apoe(-/-) MΦs expressed attenuated levels of CCR2 and demonstrated reduced migration toward CCL2 in a transwell assay. Importantly, the percentage of aortic CD11b(+)F4/80(+)Ly6C(hi) MΦs was reduced in Stat4(-/-)Apoe(-/-) vs Apoe(-/-) mice. Thus, this study identifies for the first time a pro-atherogenic role of STAT4 that is at least partially independent of Th1 cell-derived IFNγ, and primarily involving the modulation of MΦ responses.

Prostaglandin profiling reveals a role for haematopoietic prostaglandin D synthase in adipose tissue macrophage polarisation in mice and humans

BACKGROUND/OBJECTIVES

Obesity has been associated with both changes in adipose tissue lipid metabolism and inflammation. A key class of lipid-derived signalling molecules involved in inflammation are the prostaglandins. In this study, we aimed to determine how obesity affects the levels of prostaglandins within white adipose tissue (WAT) and determine which cells within adipose tissue produce them. To avoid the effects of cellular stress on prostaglandin levels, we developed a multivariate statistical approach in which metabolite concentrations and transcriptomic data were integrated, allowing the assignment of metabolites to cell types.

SUBJECTS/METHODS

Eicosanoids were measured by liquid chromatography-tandem mass spectrometry and mRNA levels using real-time PCR. Eicosanoid levels and transcriptomic data were combined using principal component analysis and hierarchical clustering in order to associate metabolites with cell types. Samples were obtained from C57Bl/6 mice aged 16 weeks. We studied the ob/ob genetically obese mouse model and diet-induced obesity model. We extended our results in mice to a cohort of morbidly obese humans undergoing bariatric surgery.

RESULTS

Using our modelling approach, we determined that prostglandin D₂ (PGD₂) in adipose tissue was predominantly produced in macrophages by the haematopoietic isoform of prostaglandin D synthase (H-Pgds). Analysis of sub-fractionated WAT confirmed that H-Pgds was expressed in adipose tissue macrophages (ATMs). Furthermore, H-Pgds expression in ATMs isolated from lean and obese mice was consistent with it affecting macrophage polarisation. Functionally, we demonstrated that H-PGDS-produced PGD₂ polarised macrophages toward an M2, anti-inflammatory state. In line with a potential anti-inflammatory role, we found that H-PGDS expression in ATMs was positively correlated with both peripheral insulin and adipose tissue insulin sensitivity in humans.

CONCLUSIONS

In this study, we have developed a method to determine the cellular source of metabolites within an organ and used it to identify a new role for PGD₂ in the control of ATM polarisation.

Therapeutic potential of STAT4 in autoimmunity

INTRODUCTION

STAT4, which acts as the major signaling transducing STATs in response to IL-12, is a central mediator in generating inflammation during protective immune responses and immune-mediated diseases.

AREAS COVERED

This review summarizes that STAT4 is essential for the differentiation and function of a wide variety of immune cells, including natural killer cells, mast cells, dendritic cells and T helper cells. In addition, STAT4-mediated signaling promoted the production of autoimmune-associated components, which are implicated in the pathogenesis of autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and psoriasis.

EXPERT OPINION

Due to its crucial roles in inflammation and autoimmunity, STAT4 may have promise as an effective therapeutic target for autoimmune diseases. Understanding the molecular mechanisms driving STAT4, together with knowledge on the ability of current immunosuppressive treatment to target this process, may open an avenue to novel therapeutic options.

Morphological and inflammatory changes in visceral adipose tissue during obesity

Obesity is a major health burden worldwide and is a major factor in the development of insulin resistance and metabolic complications such as type II diabetes. Chronic nutrient excess leads to visceral adipose tissue (VAT) expansion and dysfunction in an active process that involves the adipocytes, their supporting matrix, and immune cell infiltrates. These changes contribute to adipose tissue hypoxia, adipocyte cell stress, and ultimately cell death. Accumulation of lymphocytes, macrophages, and other immune cells around dying adipocytes forms the so-called "crown-like structure", a histological hallmark of VAT in obesity. Cross talk between immune cells in adipose tissue dictates the overall inflammatory response, ultimately leading to the production of pro-inflammatory mediators which directly induce insulin resistance in VAT. In this review, we summarize recent studies demonstrating the dramatic changes that occur in visceral adipose tissue during obesity leading to low-grade chronic inflammation and metabolic disease.