Association between visceral adipose tissue and asthma based on the NHANES and Mendelian randomization study

BACKGROUND

Obesity is a crucial risk factor for asthma. Observational studies have examined the association between abdominal obesity and asthma symptoms. This study aimed to investigate the causal relationship between visceral adipose tissue (VAT) and asthma and its potential as an independent indicator.

METHODS

This study utilized data from the National Health and Nutrition Examination Survey spanning 2011-8. Multivariable logistic regression and stratified variable selection were employed to identify associations between asthma and VAT. Moreover, a two-sample Mendelian randomization analysis, using 221 genetic variants as instrumental variables, was conducted to assess this relationship further.

RESULTS

Our findings indicated that individuals with higher VAT levels were more likely to develop asthma. Visceral obesity remained a significant risk factor for asthma after adjusting for demographic characteristics. Genetic predictions suggest a positive association between VAT and an elevated risk of asthma (odds ratio [OR] = 1.393, 95% confidence interval [CI]: 1.266-1.534, and P = 1.43E-11). No significant polymorphisms were detected using the Mendelian randomization-Egger intercept test.

CONCLUSIONS

This study presents potential evidence supporting the causal role of VAT in asthma development. Furthermore, the findings from the Mendelian randomization analysis further reinforce the relationship between VAT and asthma risk.

Bovine Serum Albumin Elicits IL-33-Dependent Adipose Tissue Eosinophilia: Potential Relevance to Ovalbumin-induced Models of Allergic Disease

All cells of the immune system reside in adipose tissue (AT), and increasing type 2 immune cells may be a therapeutic strategy to improve metabolic health. In our previous study using i.p. IL-5 injections to increase eosinophils, we observed that a standard vehicle control of 0.1% BSA also elicited profound AT eosinophilia. In this study, we aimed to determine whether BSA-induced AT eosinophilia results in metabolic benefits in murine models of diet-induced obesity. I.p. 0.1% BSA injections increased AT eosinophils after 4 wk. Despite elevating eosinophils to >50% of immune cells in the AT, body weight and glucose tolerance were not different between groups. Interestingly, BSA elicited epithelial IL-33 production, as well as gene expression for type 2 cytokines and IgE production that were dependent on IL-33. Moreover, multiple models of OVA sensitization also drove AT eosinophilia. Following transplantation of a donor fat pad with BSA-induced eosinophilia, OVA-sensitized recipient mice had higher numbers of bronchoalveolar lavage eosinophils that were recipient derived. Interestingly, lungs of recipient mice contained eosinophils, macrophages, and CD8 T cells from the donor AT. These trafficked similarly from BSA- and non-BSA-treated AT, suggesting even otherwise healthy AT serves as a reservoir of immune cells capable of migrating to the lungs. In conclusion, our studies suggest that i.p. injections of BSA and OVA induce an allergic response in the AT that elicits eosinophil recruitment, which may be an important consideration for those using OVA in animal models of allergic disease.

Blood and adipose-resident eosinophils are defined by distinct transcriptional profiles

Eosinophils are granular leukocytes of the innate immune system that play important functions in host defense. Inappropriate activation of eosinophils can occur in pathologies such as asthma and esophagitis. However, eosinophils also reside within adipose tissue, where they play homeostatic roles and are important in the activation of thermogenic beige fat. Here we performed bulk RNA sequencing in mouse adipose tissue-resident eosinophils isolated from both subcutaneous and gonadal depots, for the first time, and compared gene expression to blood eosinophils. We found a predominantly conserved transcriptional landscape in eosinophils between adipose depots that is distinct from blood eosinophils in circulation. Through exploration of differentially expressed transcription factors and transcription factors with binding sites enriched in adipose-resident eosinophil genes, we identified KLF, CEBP, and Fos/Jun family members that may drive functional specialization of eosinophils in adipose tissue. These findings increase our understanding of tissue-specific eosinophil heterogeneity, with implications for targeting eosinophil function to treat metabolic disorders such as obesity.

EoTHINophils: Eosinophils as key players in adipose tissue homeostasis

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

Extrinsic and Intrinsic Immunometabolism Converge: Perspectives on Future Research and Therapeutic Development for Obesity

PURPOSE OF REVIEW

Research over the past decade has shown that immunologic and metabolic pathways are intricately linked. This burgeoning field of immunometabolism includes intrinsic and extrinsic pathways and is known to be associated with obesity-accelerated metabolic disease. Intrinsic immunometabolism includes the study of fuel utilization and bioenergetic pathways that influence immune cell function. Extrinsic immunometabolism includes the study of immune cells and products that influence systemic metabolism.

RECENT FINDINGS

Th2 immunity, macrophage iron handling, adaptive immune memory, and epigenetic regulation of immunity, which all require intrinsic metabolic changes, play a role in systemic metabolism and metabolic function, linking the two arms of immunometabolism. Together, this suggests that targeting intrinsic immunometabolism can directly affect immune function and ultimately systemic metabolism. We highlight important questions for future basic research that will help improve translational research and provide therapeutic targets to help establish new treatments for obesity and associated metabolic disorders.

Increased eosinophils in adipose tissue of metabolic syndrome

AIMS

Metabolic Syndrome (MetS) is a common global disorder that predisposes to both Type 2 diabetes mellitus (T2DM) and cardiovascular disease (ASCVD). Adipose tissue (AT) contributes significantly to increased inflammation and insulin resistance (IR) in MetS which appear to be the crucial underpinnings of MetS. Compared to macrophages and lymphocytes in human subcutaneous AT (SAT), there is sparse data on the role of other immune cells, especially eosinophils (EOS). In this study, we investigated the abundance of EOS in the SAT of 19 patients with MetS without diabetes, ASCVD, smoking or any inflammatory condition, and matched controls.

METHODS

SAT EOS were quantified by immunohistochemistry.

RESULTS

Both circulating and SAT EOS were significantly increased 2-fold in MetS and correlated with each other. Circulating EOS correlated significantly with triglycerides (TG), high-sensitivity CRP, leptin, and IL-6. SAT EOS correlated significantly with plasma glucose, TG, FFA, adipose-IR, leptin, IL-6, endotoxin, chemerin and inversely with adiponectin. They also correlated with SAT markers of fibrosis: collagen and Sirius red staining of SAT.

CONCLUSION

We make the novel and seminal observation that eosinophils are increased in SAT of MetS patients, and are associated with the pro-inflammatory state. Hence, in humans, they appear to contribute to the dysregulation of SAT biology in MetS.