Eosinophil function in adipose tissue is regulated by Krüppel-like factor 3 (KLF3)

The Sympathetic-Immune Milieu in Metabolic Health and Diseases: Insights from Pancreas, Liver, Intestine, and Adipose Tissues

Sympathetic innervation plays a crucial role in maintaining energy balance and contributes to metabolic pathophysiology. Recent evidence has begun to uncover the innervation landscape of sympathetic projections and sheds light on their important functions in metabolic activities. Additionally, the immune system has long been studied for its essential roles in metabolic health and diseases. In this review, the aim is to provide an overview of the current research progress on the sympathetic regulation of key metabolic organs, including the pancreas, liver, intestine, and adipose tissues. In particular, efforts are made to highlight the critical roles of the peripheral nervous system and its potential interplay with immune components. Overall, it is hoped to underscore the importance of studying metabolic organs from a comprehensive and interconnected perspective, which will provide valuable insights into the complex mechanisms underlying metabolic regulation and may lead to novel therapeutic strategies for metabolic diseases.

KLF3 promotes colorectal cancer growth by activating WNT1

OBJECTIVE

The function of Kruppel-like factor 3 (KLF3) remains largely unexplored in colorectal cancer (CRC).

METHODS

KLF3 expression in CRC was assessed through qPCR, western blotting, immunohistochemical assays, and The Cancer Genome Atlas (TCGA) database. The tumor-promoting capacity of KLF3 was explored by performing in vitro functional experiments using CRC cells. A subcutaneous nude mouse tumor assay was employed to evaluate tumor growth. To further elucidate the interaction between KLF3 and other factors, luciferase reporter assay, agarose gel electrophoresis, and ChIP analysis were performed.

RESULTS

KLF3 was downregulated in CRC tissue and cells. Silencing of KLF3 increased the potential of CRC cells for proliferation, migration, and invasion, while its activation decreased these processes. Downregulated KLF3 was associated with accelerated tumor growth in vivo. Mechanistically, KLF3 was discovered to target the promoter sequence of WNT1. Consequently, the diminished expression of KLF3 led to the buildup of WNT1 and the WNT/β-catenin pathway activation, consequently stimulating the progression of CRC.

CONCLUSIONS

This investigation suggests that the involvement of KLF3/WNT1 regulatory pathway contributes to the progression of CRC, thereby emphasizing its promise as an important focus for future therapies aimed at treating CRC.

The regulatory role of eosinophils in adipose tissue depends on autophagy

Introduction

Obesity is a metabolic condition that elevates the risk of all-cause mortality. Brown and beige adipose tissues, known for their thermogenic properties, offer potential therapeutic targets for combating obesity. Recent reports highlight the role of immune cells, including eosinophils, in adipose tissue homeostasis, while the underlying mechanisms are poorly understood.

Methods

To study the role of autophagy in eosinophils in this process, we used a genetic mouse model lacking autophagy-associated protein 5 (Atg5), specifically within the eosinophil lineage (Atg5 eoΔ).

Results

The absence of Atg5 in eosinophils led to increased body weight, impaired glucose metabolism, and alterations in the cellular architecture of adipose tissue. Our findings indicate that Atg5 modulates the functional activity of eosinophils within adipose tissue rather than their abundance. Moreover, RNA-seq analysis revealed upregulation of arginase 2 (Arg2) in Atg5-knockout eosinophils. Increased Arg2 activity was shown to suppress adipocyte beiging. Furthermore, we observed enrichment of the purine pathway in the absence of Atg5 in eosinophils, leading to a pro-inflammatory shift in macrophages and a further reduction in beiging.

Discussion

The data shed light on the importance of autophagy in eosinophils and its impact on adipose tissue homeostasis by suppressing Arg2 expression and limiting inflammation in adipose tissue.

Immune cells in adipose tissue microenvironment under physiological and obese conditions

PURPOSE

This review will focus on the immune cells in adipose tissue microenvironment and their regulatory roles in metabolic homeostasis of adipose tissue and even the whole body under physiological and obese conditions.

METHODS

This review used PubMed searches of current literature to examine adipose tissue immune cells and cytokines, as well as the complex interactions between them.

RESULTS

Aside from serving as a passive energy depot, adipose tissue has shown specific immunological function. Adipose tissue microenvironment is enriched with a large number of immune cells and cytokines, whose physiological regulation plays a crucial role for metabolic homeostasis. However, obesity causes pro-inflammatory alterations in these adipose tissue immune cells, which have detrimental effects on metabolism and increase the susceptibility of individuals to the obesity related diseases.

CONCLUSIONS

Adipose tissue microenvironment is enriched with various immune cells and cytokines, which regulate metabolic homeostasis of adipose tissue and even the whole body, whether under physiological or obese conditions. Targeting key immune cells and cytokines in adipose tissue microenvironment for obesity treatment becomes an attractive research point.

Eosinophils at diagnosis are elevated in amyotrophic lateral sclerosis

Introduction

Amyotrophic lateral sclerosis (ALS) is a rare, devastating neurodegenerative disease that affects upper and lower motor neurons. To date, no effective treatment or reliable biomarker for ALS has been developed. In recent years, many factors have been proposed as possible biomarkers of ALS; however, no consensus has been reached. Therefore, a reliable biomarker is urgently needed. Eosinophils may play a crucial role in healthy humans and diseases, and serve as a biomarker for many chronic diseases.

Methods

Routine blood test results were collected from 66 healthy controls and 59 patients with ALS. The percentages and total numbers of each cell population were analyzed, and the correlation between these indicators and patient ALS functional rating scale-revised (ALSFRS-R) score or disease progression rate (ΔFS score) was analyzed.

Results

Compared to healthy controls, the number of blood leukocytes, neutrophils, monocytes, and basophils was significantly decreased in patients with ALS (p = 0.002, p = 0.001, p = 0.049, and p < 0.0001, respectively). There was an increase in the number of eosinophils (p < 0.0001), but no difference in the number of lymphocytes between patients with ALS and healthy controls was found (p = 0.563). Compared to healthy controls, the percentage of neutrophils was decreased and the percentage of lymphocytes and eosinophils was increased in patients with ALS (p = 0.01, p = 0.012, and p = 0.001, respectively). There was no difference between patients with ALS and healthy controls in the percentage of monocytes and basophils (p = 0.622 and p = 0.09, respectively). However, only the percentage and number of eosinophils had a correlation with the ΔFS score. Further multivariate analysis revealed a significant correlation between the disease duration, eosinophil count and percentage, and the disease progression rate (p < 0.0001, p = 0.048, and p = 0.023, respectively). The neutrophil-to-eosinophil ratio (NER), lymphocyte-to-eosinophil ratio (LER), and monocyte-to-eosinophil ratio (MER) were significantly lower in patients with ALS than in healthy controls. However, only the LER was significantly correlated with the ΔFS score.

Conclusion

These observations implicate neutrophils, lymphocytes, and eosinophils as important factors, and increasing eosinophil counts were negatively correlated with the ΔFS score in patients with ALS.

Eosinophils in obesity and obesity-associated disorders

Despite the rising prevalence and costs for the society, obesity etiology, and its precise cellular and molecular mechanisms are still insufficiently understood. The excessive accumulation of fat by adipocytes plays a key role in obesity progression and has many repercussions on total body physiology. In recent years the immune system as a gatekeeper of adipose tissue homeostasis has been evidenced and has become a focal point of research. Herein we focus on eosinophils, an important component of type 2 immunity, assuming fundamental, yet ill-defined, roles in the genesis, and progression of obesity and related metabolic disorders. We summarize eosinophilopoiesis and eosinophils recruitment into adipose tissue and discuss how the adipose tissue environments shape their function and vice versa. Finally, we also detail how obesity transforms the local eosinophil niche. Understanding eosinophil crosstalk with the diverse cell types within the adipose tissue environment will allow us to framework the therapeutic potential of eosinophils in obesity.

Pan-cancer analysis of Krüppel-like factor 3 and its carcinogenesis in pancreatic cancer

Background

Krüppel-like factor 3 (KLF3) is a key transcriptional repressor, which is involved in various biological functions such as lipogenesis, erythropoiesis, and B cell development, and has become one of the current research hotspots. However, the role of KLF3 in the pan-cancer and tumor microenvironment remains unclear.

Methods

TCGA and GTEx databases were used to evaluate the expression difference of KLF3 in pan-cancer and normal tissues. The cBioPortal database and the GSCALite platform analyzed the genetic variation and methylation modification of KLF3. The prognostic role of KLF3 in pan-cancer was identified using Cox regression and Kaplan-Meier analysis. Correlation analysis was used to explore the relationship between KLF3 expression and tumor mutation burden, microsatellite instability, and immune-related genes. The relationship between KLF3 expression and tumor immune microenvironment was calculated by ESTIMATE, EPIC, and MCPCOUNTER algorithms. TISCH and CancerSEA databases analyzed the expression distribution and function of KLF3 in the tumor microenvironment. TIDE, GDSC, and CTRP databases evaluated KLF3-predicted immunotherapy response and sensitivity to small molecule drugs. Finally, we analyzed the role of KLF3 in pancreatic cancer by in vivo and in vitro experiments.

Results

KLF3 was abnormally expressed in a variety of tumors, which could effectively predict the prognosis of patients, and it was most obvious in pancreatic cancer. Further experiments verified that silencing KLF3 expression inhibited pancreatic cancer progression. Functional analysis and gene set enrichment analysis found that KLF3 was involved in various immune-related pathways and tumor progression-related pathways. In addition, based on single-cell sequencing analysis, it was found that KLF3 was mainly expressed in CD4Tconv, CD8T, monocytes/macrophages, endothelial cells, and malignant cells in most of the tumor microenvironment. Finally, we assessed the value of KLF3 in predicting response to immunotherapy and predicted a series of sensitive drugs targeting KLF3.

Conclusion

The role of KLF3 in the tumor microenvironment of various types of tumors cannot be underestimated, and it has significant potential as a biomarker for predicting the response to immunotherapy. In particular, it plays an important role in the progression of pancreatic cancer.

Metabolism in type 2 immune responses

The immune response is tailored to the environment in which it takes place. Immune cells sense and adapt to changes in their surroundings, and it is now appreciated that in addition to cytokines made by stromal and epithelial cells, metabolic cues provide key adaptation signals. Changes in immune cell activation states are linked to changes in cellular metabolism that support function. Furthermore, metabolites themselves can signal between as well as within cells. Here, we discuss recent progress in our understanding of how metabolic regulation relates to type 2 immunity firstly by considering specifics of metabolism within type 2 immune cells and secondly by stressing how type 2 immune cells are integrated more broadly into the metabolism of the organism as a whole.

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.

Immune cell involvement in brown adipose tissue functions

Brown adipose tissue (BAT) contains many immune cells. The presence of macrophages, monocytes, dendritic cells, T cells, B cells, and mast cells was documented in BAT. However, in comparison to white adipose tissue, relatively little is known on the impact of immune cells on BAT function. By directly interacting with BAT stromal cells, or by secreting pro- and anti-inflammatory mediators, immune cells modulate BAT activation and subsequently influence on adaptative thermogenesis and heat generation. In the current manuscript, we will focus on the diversity and functions of BAT immune cells.

Adipose tissue-to-breast cancer crosstalk: Comprehensive insights

The review focuses on mechanistic evidence for the link between obesity and breast cancer. According to the IARC study, there is sufficient evidence that obesity is closely related to a variety of cancers. Among them, breast cancer is particularly disturbed by adipose tissue due to the unique histological structure of the breast. The review introduces the relationship between obesity and breast cancer from two aspects, including factors that promote tumorigenesis or metastasis. We summarize alterations in adipokines and metabolic pathways that contribute to breast cancer development. Breast cancer metastasis is closely related to obesity-induced pro-inflammatory microenvironment, adipose stem cells, and miRNAs. Based on the mechanism by which obesity causes breast cancer, we list possible therapeutic directions, including reducing the risk of breast cancer and inhibiting the progression of breast cancer. We also discussed the risk of autologous breast remodeling and fat transplantation. Finally, the causes of the obesity paradox and the function of enhancing immunity are discussed. Evaluating the balance between obesity-induced inflammation and enhanced immunity warrants further study.

Immune cell cholinergic signaling in adipose thermoregulation and immunometabolism

Research focusing on adipose immunometabolism has been expanded from inflammation in white fat during obesity development to immune cell function regulating thermogenic fat, energy expenditure, and systemic metabolism. This opinion discusses our current understanding of how resident immune cells within the thermogenic fat niche may regulate whole-body energy homeostasis. Furthermore, various types of immune cells can synthesize acetylcholine (ACh) and regulate important physiological functions. We highlight a unique subset of cholinergic macrophages within subcutaneous adipose tissue, termed cholinergic adipose macrophages (ChAMs); these macrophages interact with beige adipocytes through cholinergic receptor nicotinic alpha 2 subunit (CHRNA2) signaling to induce adaptive thermogenesis. We posit that these newly identified thermoregulatory macrophages may broaden our view of immune system functions for maintaining metabolic homeostasis and potentially treating obesity and metabolic disorders.

ILC2s and Adipose Tissue Homeostasis: Progress to Date and the Road Ahead

Group 2 innate lymphoid cells (ILC2s) were initially identified as a new type of lymphocytes that produce vigorous amounts of type 2 cytokines in adipose tissue. Subsequent studies revealed that ILC2s are present not only in adipose tissue but also in various other tissues such as lung and skin. ILC2s are generally recognized as tissue-resident immune cells that regulate tissue homeostasis. ILC2s express receptors for various humoral factors and thus can change their functions or distribution depending on the environment and circumstances. In this review, we will outline our recent understanding of ILC2 biology and discuss future directions for ILC2 research, particularly in adipose tissue and metabolic homeostasis.

Immune and non-immune functions of adipose tissue leukocytes

Adipose tissue is a complex dynamic organ with whole-body immunometabolic influence. Much of the work into understanding the role of immune cells in adipose tissue has been in the context of obesity. These investigations have also uncovered a range of typical (immune) and non-typical functions exerted by adipose tissue leukocytes. Here we provide an overview of the adipose tissue immune system, including its role as an immune reservoir in the whole-body response to infection and as a site of parasitic and viral infections. We also describe the functional roles of specialized immunological structures found within adipose tissue. However, our main focus is on the recently discovered 'non-immune' functions of adipose tissue immune cells, which include the regulation of adipocyte homeostasis, as well as responses to changing nutrient status and body temperature. In doing so, we outline the therapeutic potential of the adipose tissue immune system in health and disease.

Role of Innate lymphoid Cells in Obesity and Insulin Resistance

Obesity, a growing chronic metabolic disease, greatly increases the risk of metabolic syndrome which includes type 2 diabetes, fatty liver and cardiovascular diseases. Obesity-associated metabolic diseases significantly contribute to mortality and reduce life expectancy. Recently, innate lymphoid cells (ILCs) have emerged as crucial regulators of metabolic homeostasis and tissue inflammation. This review focuses on the roles of ILCs in different metabolic tissues, including adipose tissue, liver, pancreas, and intestine. We briefly outline the relationship between obesity, inflammation, and insulin resistance. We then discuss how ILCs in distinct metabolic organs may function to maintain metabolic homeostasis and contribute to obesity and its associated metabolic diseases. The potential of ILCs as the therapeutic target for obesity and insulin resistance is also addressed.

IL-33 causes thermogenic failure in aging by expanding dysfunctional adipose ILC2

Aging impairs the integrated immunometabolic responses, which have evolved to maintain core body temperature in homeotherms to survive cold stress, infections, and dietary restriction. Adipose tissue inflammation regulates the thermogenic stress response, but how adipose tissue-resident cells instigate thermogenic failure in the aged are unknown. Here, we define alterations in the adipose-resident immune system and identify that type 2 innate lymphoid cells (ILC2s) are lost in aging. Restoration of ILC2 numbers in aged mice to levels seen in adults through IL-33 supplementation failed to rescue old mice from metabolic impairment and increased cold-induced lethality. Transcriptomic analyses revealed intrinsic defects in aged ILC2, and adoptive transfer of adult ILC2s are sufficient to protect old mice against cold. Thus, the functional defects in adipose ILC2s during aging drive thermogenic failure.

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.

Innate Immune System Orchestrates Metabolic Homeostasis and Dysfunction in Visceral Adipose Tissue During Obesity

Arising incidence of metabolic disorders and related diseases caused by obesity is a global health concern. Elucidating the role of the immune system in this process will help to understand the related mechanisms and develop treatment strategies. Here, we have focused on innate immune cells in visceral adipose tissue (VAT) and summarized the roles of these cells in maintaining the homeostasis of VAT. Furthermore, this review reveals the importance of quantitative and functional changes of innate immune cells when the metabolic microenvironment changes due to obesity or excess lipids, and confirms that these changes eventually lead to the occurrence of chronic inflammation and metabolic diseases of VAT. Two perspectives are reviewed, which include sequential changes in various innate immune cells in the steady state of VAT and its imbalance during obesity. Cross-sectional interactions between various innate immune cells at the same time point are also reviewed. Through delineation of a comprehensive perspective of VAT homeostasis in obesity-induced chronic inflammation, and ultimately metabolic dysfunction and disease, we expect to clarify the complex interactive networks among distinct cell populations and propose that these interactions should be taken into account in the development of biotherapeutic strategies.

Hepatic Meteorin-like and Krüppel-like Factor 3 are Associated with Weight Loss and Liver Injury

OBJECTIVE

Laparoscopic adjustable gastric banding (LAGB) was found to be effective in reducing body weight and improving insulin resistance in patients with obesity and non-alcoholic fatty liver disease (NAFLD). The adipokine/myokine meteorin-like (METNRL) is an important regulator of whole-body energy expenditure. Krüppel-like factor 3 (KLF3), a regulator of METRNL expression in eosinophils, inhibits the beiging of adipose tissue in mice and therefore regulates adipose tissue development.

METHODS

Thirty-three obese patients undergoing LAGB were included in the study. The hepatic and adipose tissue expression of METNRL and KLF3 was determined before (t0) and 6 months after (t6) LABG. The human liver cancer cell line (HepG2) was stimulated with cytokines and fatty acids and METNRL and KLF3 expressions were analyzed.

RESULTS

LAGB-associated weight loss was correlated with decreased hepatic METNRL expression. The expression of METNRL and KLF3 in hepatic-and adipose tissues correlated before and after LAGB. Individuals with augmented LAGB-induced weight loss (>20 kg) showed lower hepatic METNRL and KLF3 expression before and after LAGB than patients with <20 kg weight loss. METNRL and KLF3 levels were higher in patients with higher NAFLD activity scores. HepG2 stimulation with interleukin-1β, tumor necrosis factor-α, palmitic acid but not interleukin-6, oleic acid, or lipopolysaccharide, induced the expression of one or both investigated adipokines.

CONCLUSIONS

The novel description of METRNL and KLF3 as hepatokines could pave the way to target their production and/or signaling in obesity, NAFLD, and related disorders. Both proteins may act as possible biomarkers to estimate weight loss after bariatric surgery.

IL-25-induced shifts in macrophage polarization promote development of beige fat and improve metabolic homeostasis in mice

Beige fat dissipates energy and functions as a defense against cold and obesity, but the mechanism for its development is unclear. We found that interleukin (IL)-25 signaling through its cognate receptor, IL-17 receptor B (IL-17RB), increased in adipose tissue after cold exposure and β3-adrenoceptor agonist stimulation. IL-25 induced beige fat formation in white adipose tissue (WAT) by releasing IL-4 and IL-13 and promoting alternative activation of macrophages that regulate innervation and up-regulate tyrosine hydroxylase (TH) up-regulation to produce more catecholamine including norepinephrine (NE). Blockade of IL-4Rα or depletion of macrophages with clodronate-loaded liposomes in vivo significantly impaired the beige fat formation in WAT. Mice fed with a high-fat diet (HFD) were protected from obesity and related metabolic disorders when given IL-25 through a process that involved the uncoupling protein 1 (UCP1)-mediated thermogenesis. In conclusion, the activation of IL-25 signaling in WAT may have therapeutic potential for controlling obesity and its associated metabolic disorders.

Epigenetic Analysis of the Chromatin Landscape Identifies a Repertoire of Murine Eosinophil-Specific PU.1-Bound Enhancers

Eosinophils develop in the bone marrow from hematopoietic progenitors into mature cells capable of a plethora of immunomodulatory roles via the choreographed process of eosinophilopoiesis. However, the gene regulatory elements and transcription factors (TFs) orchestrating this process remain largely unknown. The potency and resulting diversity fundamental to an eosinophil's complex immunomodulatory functions and tissue specialization likely result from dynamic epigenetic regulation of the eosinophil genome, a dynamic eosinophil regulome. In this study, we applied a global approach using broad-range, next-generation sequencing to identify a repertoire of eosinophil-specific enhancers. We identified over 8200 active enhancers located within 1-20 kB of expressed eosinophil genes. TF binding motif analysis revealed PU.1 (Spi1) motif enrichment in eosinophil enhancers, and chromatin immunoprecipitation coupled with massively parallel sequencing confirmed PU.1 binding in likely enhancers of genes highly expressed in eosinophils. A substantial proportion (>25%) of these PU.1-bound enhancers were unique to murine, culture-derived eosinophils when compared among enhancers of highly expressed genes of three closely related myeloid cell subsets (macrophages, neutrophils, and immature granulocytes). Gene ontology analysis of eosinophil-specific, PU.1-bound enhancers revealed enrichment for genes involved in migration, proliferation, degranulation, and survival. Furthermore, eosinophil-specific superenhancers were enriched in genes whose homologs are associated with risk loci for eosinophilia and allergic diseases. Our collective data identify eosinophil-specific enhancers regulating key eosinophil genes through epigenetic mechanisms (H3K27 acetylation) and TF binding (PU.1).

Impacts of lipid-related metabolites, adiposity, and genetic background on blood eosinophil counts: the Nagahama study

Blood eosinophil count is a useful measure in asthma or COPD management. Recent epidemiological studies revealed that body mass index (BMI) is positively associated with eosinophil counts. However, few studies focused on the role of adiposity and fatty acid-related metabolites on eosinophil counts, including the effect of genetic polymorphism. In this community-based study involving 8265 participants (30-74 year old) from Nagahama city, we investigated the relationship between eosinophil counts and serum levels of fatty acid-related metabolites. The role of MDC1, a gene that is related to eosinophil counts in our previous study and encodes a protein that is thought to be involved in the repair of deoxyribonucleic acid damage, was also examined taking into account its interaction with adiposity. Serum levels of linoleic acid (LA) and β-hydroxybutyric acid (BHB) were negatively associated with eosinophil counts after adjustment with various confounders; however, there were positive interactions between serum LA and BMI and between serum BHB and BMI/body fat percentages in terms of eosinophil counts. In never-smokers, there was positive interaction for eosinophil counts between the CC genotype of MDC1 rs4713354 and BMI/body fat percentages. In conclusion, both serum LA and BHB have negative impacts on eosinophil counts, while adiposity shows robust positive effects on eosinophil counts, partly via genetic background in never-smokers.

Sirtuin 6 promotes eosinophil differentiation by activating GATA-1 transcription factor

There is evidence emerging that exposure to cold temperatures enhances alternative activation of macrophages in white adipose tissue (WAT), which promotes adipocyte beiging and adaptive thermogenesis. Although we recently reported that NAD⁺‐dependent deacetylase sirtuin 6 (Sirt6) drives alternatively activated (M2) macrophage polarization, the role of myeloid Sirt6 in adaptive thermogenesis had remained elusive. In this study, we demonstrate that myeloid Sirt6 deficiency impaired both thermogenic responses and M2 macrophage infiltration in subcutaneous WAT (scWAT) during cold exposure. Moreover, the infiltration of Siglec‐F‐positive eosinophils in scWAT and Th2 cytokines levels was reduced in myeloid Sirt6 knockout mice. An ex vivo bone marrow‐derived cell culture experiment indicated that Sirt6 was required for eosinophil differentiation independent of its deacetylase activity. Data from our in vitro experiments show that Sirt6 acted as a transcriptional cofactor of GATA‐1, independent of its catalytic function as a deacetylase or ADP‐ribosyltransferase. Specifically, Sirt6 physically interacted with GATA‐1, and enhanced GATA‐1’s acetylation and transcriptional activity by facilitating its cooperation with p300. Overall, our results suggest that myeloid Sirt6 plays an important role in eosinophil differentiation and fat beiging/adaptive thermogenesis, which is at least in part due to its ability to bind GATA‐1 and stimulate its transcriptional activity.

Type 2 immunity is maintained during cancer-associated adipose tissue wasting

Objectives: Cachexia is a systemic metabolic disorder characterized by loss of fat and muscle mass, which disproportionately impacts patients with gastrointestinal malignancies such as pancreatic cancer. While the immunologic shifts contributing to the development of other adipose tissue (AT) pathologies such as obesity have been well described, the immune microenvironment has not been studied in the context of cachexia.

Methods: We performed bulk RNA-sequencing, cytokine arrays, and flow cytometry to characterize the immune landscape of visceral AT (VAT) in the setting of pancreatic and colorectal cancers.

Results: The cachexia inducing factor IL-6 is strongly elevated in the wasting VAT of cancer bearing mice, but the regulatory type 2 immune landscape which characterizes healthy VAT is maintained. Pathologic skewing toward Th1 and Th17 inflammation is absent. Similarly, the VAT of patients with colorectal cancer is characterized by a Th2 signature with abundant IL-33 and eotaxin-2, albeit also with high levels of IL-6.

Conclusions: Wasting AT during the development of cachexia may not undergo drastic changes in immune composition like those seen in obese AT. Our approach provides a framework for future immunologic analyses of cancer associated cachexia.

Distinct Associations of BMI and Fatty Acids With DNA Methylation in Fasting and Postprandial States in Men

We have previously shown that blood global DNA methylation (DNAm) differs between postprandial state (PS) and fasting state (FS) and is associated with BMI and polyunsaturated fatty acid (PUFA) (negatively and positively, respectively) in 12 metabolically healthy adult Mexican men (AMM cohort) equally distributed among conventional BMI classes. Here, we detailed those associations at CpG dinucleotide level by exploiting the Infinium methylation EPIC array (Illumina). We sought differentially methylated CpG (dmCpG) that were (1) associated with BMI (BMI-dmCpG) and/or fatty acids (FA) (FA-dmCpG) in FS or PS and (2) different across FS and PS within a BMI class. BMI-dmCpG and FA-dmCpG were more numerous in FS compared to PS and largely prandial state-specific. For saturated and monounsaturated FA, dmCpG overlap was higher across than within the respective saturation group. Several BMI- and FA-dmCpG mapped to genes involved in metabolic disease and in some cases matched published experimental data sets. Notably, SETDB1 and MTHFS promoter dmCpG could explain the previously observed associations between global DNAm, PUFA content, and BMI in FS. Surprisingly, overlap between BMI-dmCpG and FA-dmCpG was limited and the respective dmCpG were differentially distributed across functional genomic elements. BMI-dmCpG showed the highest overlap with dmCpG of the saturated FA palmitate, monounsaturated C20:1 and PUFA C20:2. Of these, selected promoter BMI-dmCpG showed opposite associations with palmitate compared to C20:1 and C20:2. As for the comparison between FS and PS within BMI classes, dmCpG were strikingly more abundant and variably methylated in overweight relative to normoweight or obese subjects (∼70–139-fold, respectively). Overweight-associated dmCpG-hosting genes were significantly enriched in targets for E47, SREBP1, and RREB1 transcription factors, which are known players in obesity and lipid homeostasis, but none overlapped with BMI-dmCpG. We show for the first time that the association of BMI and FA with methylation of disease-related genes is distinct in FS and PS and that limited overlap exists between BMI- and FA-dmCpG within and across prandial states. Our study also identifies a transcriptional regulation circuitry in overweight that might contribute to adaptation to that condition or to transition to obesity. Further work is necessary to define the pathophysiological implications of these findings.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Divergent immunometabolic changes in adipose tissue and skeletal muscle with ageing in healthy humans

KEY POINTS

Ageing is associated with increased systemic inflammation and metabolic dysfunction that contributes to the development of age-associated diseases. The role of adipose tissue in immunometabolic alterations that take place with ageing is unknown in humans. We show, in healthy, active and lean older adults, that adipose tissue, but not skeletal muscle, displays considerable pro-inflammatory transcriptomic, cellular and secretory changes, as well as a reduction in insulin signalling proteins compared to younger adults. These findings indicate that adipose tissue undergoes substantial immunometabolic alterations with ageing, and that these changes are tissue-specific and more profound than those observed in skeletal muscle or in the circulation. These results identify adipose tissue as an important tissue in the biological ageing process in humans, which may exhibit signs of immunometabolic dysfunction prior to systemic manifestation.

ABSTRACT

Ageing and obesity are both characterized by inflammation and a deterioration in metabolic health. It is now clear that adipose tissue plays a major role in inflammation and metabolic control in obesity, although little is known about the role of adipose tissue in human ageing. To understand how ageing impacts adipose tissue, we characterized subcutaneous adipose tissue and skeletal muscle samples from twelve younger (27 ± 4 years [Young]) and twelve older (66 ± 5 years [Old]) active/non-obese males. We performed a wide-range of whole-body and tissue measures, including RNA-sequencing and multicolour flow cytometry. We also measured a range of inflammatory and metabolic proteins in the circulation and their release by adipose tissue, ex vivo. Both adipose tissue and muscle had ∼2-fold more immune cells per gram of tissue with ageing. In adipose tissue, this immune cell infiltration was driven by increased memory/effector T-cells, whereas, in muscle, the accumulation was driven by memory/effector T-cells and macrophages. Transcriptomic analysis revealed that, with ageing, adipose tissue, but not muscle, was enriched for inflammatory transcripts/pathways related to acquired and innate immunity. Ageing also increased the adipose tissue pro-inflammatory secretory profile. Insulin signalling protein content was reduced in adipose tissue, but not muscle. Our findings indicate that adipose tissue undergoes substantial immunometabolic changes with ageing in humans, and that these changes are tissue-specific and more profound than those observed in the circulation and skeletal muscle.

Obesity, Adipose Tissue and Vascular Dysfunction

Cardiovascular diseases are the leading cause of death worldwide. Overweight and obesity are strongly associated with comorbidities such as hypertension and insulin resistance, which collectively contribute to the development of cardiovascular diseases and resultant morbidity and mortality. Forty-two percent of adults in the United States are obese, and a total of 1.9 billion adults worldwide are overweight or obese. These alarming numbers, which continue to climb, represent a major health and economic burden. Adipose tissue is a highly dynamic organ that can be classified based on the cellular composition of different depots and their distinct anatomical localization. Massive expansion and remodeling of adipose tissue during obesity differentially affects specific adipose tissue depots and significantly contributes to vascular dysfunction and cardiovascular diseases. Visceral adipose tissue accumulation results in increased immune cell infiltration and secretion of vasoconstrictor mediators, whereas expansion of subcutaneous adipose tissue is less harmful. Therefore, fat distribution more than overall body weight is a key determinant of the risk for cardiovascular diseases. Thermogenic brown and beige adipose tissue, in contrast to white adipose tissue, is associated with beneficial effects on the vasculature. The relationship between the type of adipose tissue and its influence on vascular function becomes particularly evident in the context of the heterogenous phenotype of perivascular adipose tissue that is strongly location dependent. In this review, we address the abnormal remodeling of specific adipose tissue depots during obesity and how this critically contributes to the development of hypertension, endothelial dysfunction, and vascular stiffness. We also discuss the local and systemic roles of adipose tissue derived secreted factors and increased systemic inflammation during obesity and highlight their detrimental impact on cardiovascular health.

Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation

The protein α-actinin-3 expressed in fast-twitch skeletal muscle fiber is absent in 1.5 billion people worldwide due to homozygosity for a nonsense polymorphism in ACTN3 (R577X). The prevalence of the 577X allele increased as modern humans moved to colder climates, suggesting a link between α-actinin-3 deficiency and improved cold tolerance. Here, we show that humans lacking α-actinin-3 (XX) are superior in maintaining core body temperature during cold-water immersion due to changes in skeletal muscle thermogenesis. Muscles of XX individuals displayed a shift toward more slow-twitch isoforms of myosin heavy chain (MyHC) and sarcoplasmic reticulum (SR) proteins, accompanied by altered neuronal muscle activation resulting in increased tone rather than overt shivering. Experiments on Actn3 knockout mice showed no alterations in brown adipose tissue (BAT) properties that could explain the improved cold tolerance in XX individuals. Thus, this study provides a mechanism for the positive selection of the ACTN3 X-allele in cold climates and supports a key thermogenic role of skeletal muscle during cold exposure in humans.

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

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

Can eosinophils in adipose tissue add fuel to the fire?

In inguinal adipose tissue, beige adipocytes are interspersed among white adipocytes and in close communication with dynamic populations of immune cells. Recent data have demonstrated that anti-inflammatory macrophages (M2) increase thermogenic activity of beige adipocytes, although the mechanism is currently under debate. ILC2, cells via secretion, of methionine enkephalin peptide were found to be able to increase beige thermogenesis. Knights et al. have recently generated a whole-body knock-out of KLF3 (KLF3-/-) to explore its contribution to thermogenesis and weight gain in a diet-induced obesity animal model.

Characterization and Treatment of Inflammation and Insulin Resistance in Obese Adipose Tissue

Adipose tissue is the largest energy storage and protection organ. It is distributed subcutaneously and around the internal organs. It regulates metabolism by storing and releasing fatty acids and secreting adipokines. Excessive nutritional intake results in adipocyte hypertrophy and proliferation, leading to local hypoxia in adipose tissue and changes in the release of adipokines. These lead to recruit of more immune cells into adipose tissue and release of inflammatory signaling factors. Excess free fatty acids and inflammatory factors interfere with intracellular insulin signaling. In this review, we summarize the characteristics of obese adipose tissue and analyze how its inflammation causes insulin resistance. We further discuss the latest clinical research progress on the control of insulin resistance and inflammation resulting from obesity through anti-inflammatory therapy and bariatric surgery. Our review shows that targeted anti-inflammatory therapy is of great significance for obese patients with insulin resistance.