A Stat6/Pten Axis Links Regulatory T Cells with Adipose Tissue Function

Cell-cell crosstalk between fat cells and immune cells

Obesity is a metabolic disorder with pandemic-like implications, lacking viable pharmaceutical treatments currently. Thermogenic adipose tissues, including brown and beige adipose tissues, play an essential role in regulating systemic energy homeostasis and have emerged as appealing therapeutic targets for the treatment of obesity and obesity-related diseases. The function of adipocytes is subject to complex regulation by a cellular network of immune signaling pathways in response to environmental signals. However, the specific regulatory roles of immune cells in thermogenesis and relevant involving mechanisms are still not well understood. Here, we concentrate on our present knowledge of the interaction between thermogenic adipocytes and immune cells and present an overview of cellular and molecular mechanisms underlying immunometabolism in adipose tissues. We discuss cytokines, especially interleukins, which originate from widely variable sources, and their impacts on the development and function of thermogenic adipocytes. Moreover, we summarize the neuroimmune regulation in heat production and expand a new mode of intercellular communication mediated by mitochondrial transfer. The crosstalk between immune cells and adipocytes achieves adipose tissue homeostasis and systemic energy balance. A deep understanding of this intricate interaction would provide evidence for improving thermogenic efficiency by remodeling the immune microenvironment. Interventions based on these factors show a high potential to prevent adverse metabolic outcomes in patients with obesity.

M6A modification and T cells in adipose tissue inflammation

Adipose tissue in the obese state can lead to low-grade chronic inflammation while inducing or exacerbating obesity-related metabolic diseases and impairing overall health.T cells, which are essential immune cells similar to macrophages, are widely distributed in adipose tissue and perform their immunomodulatory function; they also cross-talk with other cells in the vascular stromal fraction. Based on a large number of studies, it has been found that N6 methyl adenine (m6A) is one of the most representative of epigenetic modifications, which affects the crosstalk between T cells, as well as other immune cells, in several ways and plays an important role in the development of adipose tissue inflammation and related metabolic diseases. In this review, we first provide an overview of the widespread presence of T cells in adipose tissue and summarize the key role of T cells in adipose tissue inflammation. Next, we explored the effects of m6A modifications on T cells in adipose tissue from the perspective of adipose tissue inflammation. Finally, we discuss the impact of m6a-regulated crosstalk between T cells and immune cells on the prospects for improving adipose tissue inflammation research, providing additional new ideas for the treatment of obesity.

Lack of p38 activation in T cells increases IL-35 and protects against obesity by promoting thermogenesis

Obesity is characterized by low-grade inflammation, energy imbalance and impaired thermogenesis. The role of regulatory T cells (Treg) in inflammation-mediated maladaptive thermogenesis is not well established. Here, we find that the p38 pathway is a key regulator of T cell-mediated adipose tissue (AT) inflammation and browning. Mice with T cells specifically lacking the p38 activators MKK3/6 are protected against diet-induced obesity, leading to an improved metabolic profile, increased browning, and enhanced thermogenesis. We identify IL-35 as a driver of adipocyte thermogenic program through the ATF2/UCP1/FGF21 pathway. IL-35 limits CD8+ T cell infiltration and inflammation in AT. Interestingly, we find that IL-35 levels are reduced in visceral fat from obese patients. Mechanistically, we demonstrate that p38 controls the expression of IL-35 in human and mouse Treg cells through mTOR pathway activation. Our findings highlight p38 signaling as a molecular orchestrator of AT T cell accumulation and function.

Dynamic changes of immunocyte subpopulations in thermogenic activation of adipose tissues

Objectives

The effects of cold exposure on whole-body metabolism in humans have gained increasing attention. Brown or beige adipose tissues are crucial in cold-induced thermogenesis to dissipate energy and thus have the potential to combat metabolic disorders. Despite the immune regulation of thermogenic adipose tissues, the overall changes in vital immune cells during distinct cold periods remain elusive. This study aimed to discuss the overall changes in immune cells under different cold exposure periods and to screen several potential immune cell subpopulations on thermogenic regulation.

Methods

Cibersort and mMCP-counter algorithms were employed to analyze immune infiltration in two (brown and beige) thermogenic adipose tissues under distinct cold periods. Changes in some crucial immune cell populations were validated by reanalyzing the single-cell sequencing dataset (GSE207706). Flow cytometry, immunofluorescence, and quantitative real-time PCR assays were performed to detect the proportion or expression changes in mouse immune cells of thermogenic adipose tissues under cold challenge.

Results

The proportion of monocytes, naïve, and memory T cells increased, while the proportion of NK cells decreased under cold exposure in brown adipose tissues.

Conclusion

Our study revealed dynamic changes in immune cell profiles in thermogenic adipose tissues and identified several novel immune cell subpopulations, which may contribute to thermogenic activation of adipose tissues under cold exposure.

mTORC1 in energy expenditure: consequences for obesity

In eukaryotic cells, the mammalian target of rapamycin complex 1 (sometimes referred to as the mechanistic target of rapamycin complex 1; mTORC1) orchestrates cellular metabolism in response to environmental energy availability. As a result, at the organismal level, mTORC1 signalling regulates the intake, storage and use of energy by acting as a hub for the actions of nutrients and hormones, such as leptin and insulin, in different cell types. It is therefore unsurprising that deregulated mTORC1 signalling is associated with obesity. Strategies that increase energy expenditure offer therapeutic promise for the treatment of obesity. Here we review current evidence illustrating the critical role of mTORC1 signalling in the regulation of energy expenditure and adaptive thermogenesis through its various effects in neuronal circuits, adipose tissue and skeletal muscle. Understanding how mTORC1 signalling in one organ and cell type affects responses in other organs and cell types could be key to developing better, safer treatments targeting this pathway in obesity.

Niche-specific control of tissue function by regulatory T cells-Current challenges and perspectives for targeting metabolic disease

Tissue regulatory T cells (Tregs) exert pivotal functions in both immune and metabolic regulation, maintaining local tissue homeostasis, integrity, and function. Accordingly, Tregs play a crucial role in controlling obesity-induced inflammation and supporting efficient muscle function and repair. Depending on the tissue context, Tregs are characterized by unique transcriptomes, growth, and survival factors and T cell receptor (TCR) repertoires. This functional specialization offers the potential to selectively target context-specific Treg populations, tailoring therapeutic strategies to specific niches, thereby minimizing potential side effects. Here, we discuss challenges and perspectives for niche-specific Treg targeting, which holds promise for highly efficient and precise medical interventions to combat metabolic disease.

Bone marrow immune cells stop weight regain

Weight regain is a major challenge in the long-term management of obesity; however, the underlying mechanisms remain unclear. Zhou et al. found that bone-marrow-derived CD7+ monocytes respond to fluctuating nutritional stress and suppress weight regain by promoting beige fat thermogenesis.

Multifaceted roles of T cells in obesity and obesity-related complications: A narrative review

Obesity is characterized by chronic low-grade inflammatory responses in the adipose tissue, accompanied by pronounced insulin resistance and metabolic anomalies. It affects almost all body organs and eventually leads to diseases such as fatty liver disease, type 2 diabetes mellitus, and atherosclerosis. Recently, T cells have emerged as interesting therapeutic targets because the dysfunction of T cells and their cytokines in the adipose tissue is implicated in obesity-induced inflammation and their complicated onset. Although several recent narrative reviews have provided a brief overview of related evidence in this area, they have mainly focused on either obesity-associated T cell metabolism or modulation of T cell activation in obesity. Moreover, at present, no published review has reported on the multifaceted roles of T cells in obesity and obesity-related complications, even though there has been a significant increase in studies on this topic since 2019. Therefore, this narrative review aims to comprehensively summarize current advances in the mechanistic roles of T cells in the development of obesity and its related complications. Further, we aim to discuss relevant drugs for weight loss as well as the contradictory role of T cells in the same disease so as to highlight key findings regarding this topic and provide a valid basis for future treatment strategies.

Regulatory T cells require IL6 receptor alpha signaling to control skeletal muscle function and regeneration

Muscle-residing regulatory T cells (Tregs) control local tissue integrity and function. However, the molecular interface connecting Treg-based regulation with muscle function and regeneration remains largely unexplored. Here, we show that exercise fosters a stable induction of highly functional muscle-residing Tregs with increased expression of amphiregulin (Areg), EGFR, and ST2. Mechanistically, we find that mice lacking IL6Rα on T cells (TKO) harbor significant reductions in muscle Treg functionality and satellite and fibro-adipogenic progenitor cells, which are required for muscle regeneration. Using exercise and sarcopenia models, IL6Rα TKO mice demonstrate deficits in Tregs, their functional maturation, and a more pronounced decline in muscle mass. Muscle injury models indicate that IL6Rα TKO mice have significant disabilities in muscle regeneration. Treg gain of function restores impaired muscle repair in IL6Rα TKO mice. Of note, pharmacological IL6R blockade in WT mice phenocopies deficits in muscle function identified in IL6Rα TKO mice, thereby highlighting the clinical implications of the findings.

The role of Th17 cells in endocrine organs: Involvement of the gut, adipose tissue, liver and bone

T Helper 17 (Th17) cells are adaptive immune cells that play myriad roles in the body. Immune-endocrine interactions are vital in endocrine organs during pathological states. Th17 cells are known to take part in multiple autoimmune diseases over the years. Current evidence has moved from minimal to substantial that Th17 cells are closely related to endocrine organs. Diverse tissue Th17 cells have been discovered within endocrine organs, including gut, adipose tissue, liver and bone, and these cells are modulated by various secretions from endocrine organs. Th17 cells in these endocrine organs are key players in the process of an array of metabolic disorders and inflammatory conditions, including obesity, insulin resistance, nonalcoholic fatty liver disease (NAFLD), primary sclerosing cholangitis (PSC), osteoporosis and inflammatory bowel disease (IBD). We reviewed the pathogenetic or protective functions played by Th17 cells in various endocrine tissues and identified potential regulators for plasticity of it. Furthermore, we discussed the roles of Th17 cells in crosstalk of gut-organs axis.

Adipose tissue aging is regulated by an altered immune system

Adipose tissue is a widely distributed organ that plays a critical role in age-related physiological dysfunctions as an important source of chronic sterile low-grade inflammation. Adipose tissue undergoes diverse changes during aging, including fat depot redistribution, brown and beige fat decrease, functional decline of adipose progenitor and stem cells, senescent cell accumulation, and immune cell dysregulation. Specifically, inflammaging is common in aged adipose tissue. Adipose tissue inflammaging reduces adipose plasticity and pathologically contributes to adipocyte hypertrophy, fibrosis, and ultimately, adipose tissue dysfunction. Adipose tissue inflammaging also contributes to age-related diseases, such as diabetes, cardiovascular disease and cancer. There is an increased infiltration of immune cells into adipose tissue, and these infiltrating immune cells secrete proinflammatory cytokines and chemokines. Several important molecular and signaling pathways mediate the process, including JAK/STAT, NFκB and JNK, etc. The roles of immune cells in aging adipose tissue are complex, and the underlying mechanisms remain largely unclear. In this review, we summarize the consequences and causes of inflammaging in adipose tissue. We further outline the cellular/molecular mechanisms of adipose tissue inflammaging and propose potential therapeutic targets to alleviate age-related problems.

Differential IL18 signaling via IL18 receptor and Na-Cl co-transporter discriminating thermogenesis and glucose metabolism regulation

White adipose tissue (WAT) plays a role in storing energy, while brown adipose tissue (BAT) is instrumental in the re-distribution of stored energy when dietary sources are unavailable. Interleukin-18 (IL18) is a cytokine playing a role in T-cell polarization, but also for regulating energy homeostasis via the dimeric IL18 receptor (IL18r) and Na-Cl co-transporter (NCC) on adipocytes. Here we show that IL18 signaling in metabolism is regulated at the level of receptor utilization, with preferential role for NCC in brown adipose tissue (BAT) and dominantly via IL18r in WAT. In Il18r^-/-Ncc^-/- mice, high-fat diet (HFD) causes more prominent body weight gain and insulin resistance than in wild-type mice. The WAT insulin resistance phenotype of the double-knockout mice is recapitulated in HFD-fed Il18r^-/- mice, whereas decreased thermogenesis in BAT upon HFD is dependent on NCC deletion. BAT-selective depletion of either NCC or IL18 reduces thermogenesis and increases BAT and WAT inflammation. IL18r deletion in WAT reduces insulin signaling and increases WAT inflammation. In summary, our study contributes to the mechanistic understanding of IL18 regulation of energy metabolism and shows clearly discernible roles for its two receptors in brown and white adipose tissues.

Tissue adaptation of regulatory T cells in adipose tissue

Foxp3⁺ regulatory T (Treg) cells critically suppress over-activated immune responses and therefore maintain immune homeostasis. Adipose tissue-resident Treg (AT Treg) cells are known for modulating immunity and metabolism in adipose tissue microenvironment through various physiological signals, as well as their heterogeneous subsets, which potentially play disparate roles in aging and obesity. Recent single-cell studies of Treg cells have revealed specialized trajectories of their tissue adaptation and development in lymphoid tissues and at barrier sites. Here, we reviewed a T Cell Receptor (TCR)-primed environmental cue-boosted model of adipose Treg cells' tissue adaptation, especially in response to IL-33, IFN-α, insulin, and androgen signals, which trigger sophisticated transcriptional cascades and ultimately establish unique transcriptional modules in adipose Treg cell subsets. In addition, we further discuss potential therapeutic strategies against aging and obesity by blocking detrimental environmental cues, strengthening the functions of specific AT Treg subsets and modifying the communications between AT Treg subsets and adipocytes.

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.

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.

An OGT-STAT5 Axis in Regulatory T Cells Controls Energy and Iron Metabolism

The immunosuppressive regulatory T (Treg) cells exert emerging effects on adipose tissue homeostasis and systemic metabolism. However, the metabolic regulation and effector mechanisms of Treg cells in coping with obesogenic insults are not fully understood. We have previously established an indispensable role of the O-linked N-Acetylglucosamine (O-GlcNAc) signaling in maintaining Treg cell identity and promoting Treg suppressor function, via STAT5 O-GlcNAcylation and activation. Here, we investigate the O-GlcNAc transferase (OGT)-STAT5 axis in driving the immunomodulatory function of Treg cells for metabolic homeostasis. Treg cell-specific OGT deficiency renders mice more vulnerable to high-fat diet (HFD)-induced adiposity and insulin resistance. Conversely, constitutive STAT5 activation in Treg cells confers protection against adipose tissue expansion and impaired glucose and insulin metabolism upon HFD feeding, in part by suppressing adipose lipid uptake and redistributing systemic iron storage. Treg cell function can be augmented by targeting the OGT-STAT5 axis to combat obesity and related metabolic disorders.

Integrative understanding of immune-metabolic interaction

Recent studies have revealed that the immune system plays a critical role in various physiological processes beyond its classical pathogen control activity. Even under a sterile condition, various cells and tissues can utilize the immune system to meet a specific demand for proper physiological functions. Particularly, a strong link between immunity and metabolism has been identified. Studies have identified the reciprocal regulation between these two systems. For example, immune signals can regulate metabolism, and metabolism (cellular or systemic) can regulate immunity. In this review, we will summarize recent findings on this reciprocal regulation between immunity and metabolism, and discuss potential biological rules behind this interaction with integrative perspectives.

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.

Tissue Resident Foxp3+ Regulatory T Cells: Sentinels and Saboteurs in Health and Disease

Foxp3⁺ regulatory T (Treg) cells are a CD4 T cell subset with unique immune regulatory function that are indispensable in immunity and tolerance. Their indisputable importance has been investigated in numerous disease settings and experimental models. Despite the extensive efforts in determining the cellular and molecular mechanisms operating their functions, our understanding their biology especially in vivo remains limited. There is emerging evidence that Treg cells resident in the non-lymphoid tissues play a central role in regulating tissue homeostasis, inflammation, and repair. Furthermore, tissue-specific properties of those Treg cells that allow them to express tissue specific functions have been explored. In this review, we will discuss the potential mechanisms and key cellular/molecular factors responsible for the homeostasis and functions of tissue resident Treg cells under steady-state and inflammatory conditions.

Adipocyte-derived PGE2 is required for intermittent fasting-induced Treg proliferation and improvement of insulin sensitivity

The intermittent fasting (IF) diet has profound benefits for diabetes prevention. However, the precise mechanisms underlying IF's beneficial effects remain poorly defined. Here, we show that the expression levels of cyclooxygenase-2 (COX-2), an enzyme that produces prostaglandins, are suppressed in white adipose tissue (WAT) of obese humans. In addition, the expression of COX-2 in WAT is markedly upregulated by IF in obese mice. Adipocyte-specific depletion of COX-2 led to reduced fractions of CD4+Foxp3+ Tregs and a substantial decrease in the frequency of CD206+ macrophages, an increase in the abundance of γδT cells in WAT under normal chow diet conditions, and attenuation of IF-induced antiinflammatory and insulin-sensitizing effects, despite a similar antiobesity effect in obese mice. Mechanistically, adipocyte-derived prostaglandin E2 (PGE2) promoted Treg proliferation through the CaMKII pathway in vitro and rescued Treg populations in adipose tissue in COX-2-deficient mice. Ultimately, inactivation of Tregs by neutralizing anti-CD25 diminished IF-elicited antiinflammatory and insulin-sensitizing effects, and PGE2 restored the beneficial effects of IF in COX-2-KO mice. Collectively, our study reveals that adipocyte COX-2 is a key regulator of Treg proliferation and that adipocyte-derived PGE2 is essential for IF-elicited type 2 immune response and metabolic benefits.

Immune Cells in Thermogenic Adipose Depots: The Essential but Complex Relationship

Brown adipose tissue (BAT) is a unique organ in mammals capable of dissipating energy in form of heat. Additionally, white adipose tissue (WAT) can undergo browning and perform thermogenesis. In recent years, the research community has aimed to harness thermogenic depot functions for new therapeutic strategies against obesity and the metabolic syndrome; hence a comprehensive understanding of the thermogenic fat microenvironment is essential. Akin to WAT, immune cells also infiltrate and reside within the thermogenic adipose tissues and perform vital functions. As highly plastic organs, adipose depots rely on crucial interplay with these tissue resident cells to conserve their healthy state. Evidence has accumulated to show that different immune cell populations contribute to thermogenic adipose tissue homeostasis and activation through complex communicative networks. Furthermore, new studies have identified -but still not fully characterized further- numerous immune cell populations present in these depots. Here, we review the current knowledge of this emerging field by describing the immune cells that sway the thermogenic adipose depots, and the complex array of communications that influence tissue performance.

T Regulatory Cells in the Visceral Adipose Tissues

CD4⁺ Foxp3⁺ T regulatory cells (Tregs) residing in the visceral adipose tissues (VAT) have profound effects on local and systemic metabolism. Although many of the molecular characteristics of VAT resident Tregs have been identified, how these cells promote metabolic homeostasis is still unclear. Several new publications help to illuminate the molecular mechanisms that underpin VAT resident Treg function and will be discussed here.

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

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

Resident and migratory adipose immune cells control systemic metabolism and thermogenesis

Glucose is a vital source of energy for all mammals. The balance between glucose uptake, metabolism and storage determines the energy status of an individual, and perturbations in this balance can lead to metabolic diseases. The maintenance of organismal glucose metabolism is a complex process that involves multiple tissues, including adipose tissue, which is an endocrine and energy storage organ that is critical for the regulation of systemic metabolism. Adipose tissue consists of an array of different cell types, including specialized adipocytes and stromal and endothelial cells. In addition, adipose tissue harbors a wide range of immune cells that play vital roles in adipose tissue homeostasis and function. These cells contribute to the regulation of systemic metabolism by modulating the inflammatory tone of adipose tissue, which is directly linked to insulin sensitivity and signaling. Furthermore, these cells affect the control of thermogenesis. While lean adipose tissue is rich in type 2 and anti-inflammatory cytokines such as IL-10, obesity tips the balance in favor of a proinflammatory milieu, leading to the development of insulin resistance and the dysregulation of systemic metabolism. Notably, anti-inflammatory immune cells, including regulatory T cells and innate lymphocytes, protect against insulin resistance and have the characteristics of tissue-resident cells, while proinflammatory immune cells are recruited from the circulation to obese adipose tissue. Here, we review the key findings that have shaped our understanding of how immune cells regulate adipose tissue homeostasis to control organismal metabolism.

The Effect of miR-520b on Macrophage Polarization and T Cell Immunity by Targeting PTEN in Breast Cancer

Background

Breast cancer is the most common cancer in women. miR-520b had binding sites with PTEN through the bioinformatics prediction. But few studies have been conducted on miR-520b and PTEN in breast cancer. We aimed to explore the effect of miR-520b and PTEN on breast cancer and the mechanisms involved.

Methods

Clinical samples of breast cancer were collected. Bioinformatics analysis was performed to screen the differentially expressed miRNAs. CD4 T cells and CD8 T cells were cocultured with MCF-7 cells in the Transwell system. Moreover, MCF-7 cells and M0 macrophage cocultured cell lines were constructed. qRT-PCR, IF, western blot, flow cytometry, and ELISA were performed to detect related factors expression. Starbase and dual-luciferase reporter assay verified the binding of miR-520b to PTEN. The tumor formation model was established to study miR-520b and PTEN effects in vivo.

Results

The differentially expressed miR-520b was screened via miRNAs sequencing and cell verification. miR-520b expression was high, PTEN was low in tumor tissues, T cells and NK cells were inhibited, and macrophages were transformed into M2 type, promoting immune escape. In addition, miR-520b bound to PTEN. Then, splenic CD4 T cells and CD8 T cells were successfully sorted. During CD4 T cell differentiation to Th1 and Treg, Th1 was inhibited, and Treg was activated. We found the polarization of macrophages was related to breast cancer. The proportion of CD206 cells increased and CD68 cells decreased in the miR-520b mimics group compared with the mimic NC group. Compared with the inhibitor NC group, the proportion of CD206 cells decreased, and CD68 cells increased in the miR-520b inhibitor group. In vivo experiments showed that miR-520b inhibitor inhibited tumor growth and promoted PTEN expression. The proportion of CD3, CD4, CD8, NK1.1, CD4+IFNγ, and CD68 cells increased, while FOXP3 and CD206 cells decreased in the miR-520b inhibitor group compared with the inhibitor NC group. However, the proportion of CD3, CD4, CD8, NK1.1, CD4+IFNγ, and CD68 cells decreased, while FOXP3 and CD206 cells increased after the addition of siPTEN.

Conclusions

miR-520b inhibited PTEN and aggravated breast tumors. miR-520b inhibitor enhanced CD4 and CD8 cell populations in the tumor immune microenvironment and inhibited tumor growth.

Phenotypic and Functional Diversity in Regulatory T Cells

The concept that a subset of T cells exists that specifically suppresses immune responses was originally proposed over 50 years ago. It then took the next 30 years to solidify the concept of regulatory T cells (Tregs) into the paradigm we understand today - namely a subset of CD4+ FOXP3+ T-cells that are critical for controlling immune responses to self and commensal or environmental antigens that also play key roles in promoting tissue homeostasis and repair. Expression of the transcription factor FOXP3 is a defining feature of Tregs, while the cytokine IL2 is necessary for robust Treg development and function. While our initial conception of Tregs was as a monomorphic lineage required to suppress all types of immune responses, recent work has demonstrated extensive phenotypic and functional diversity within the Treg population. In this review we address the ontogeny, phenotype, and function of the large number of distinct effector Treg subsets that have been defined over the last 15 years.

Tissue regulatory T cells: regulatory chameleons

The FOXP3⁺CD4⁺ regulatory T (T_reg) cells located in non-lymphoid tissues differ in phenotype and function from their lymphoid organ counterparts. Tissue T_reg cells have distinct transcriptomes, T cell receptor repertoires and growth and survival factor dependencies that arm them to survive and operate in their home tissue. Their functions extend beyond immune surveillance to tissue homeostasis, including regulation of local and systemic metabolism, promotion of tissue repair and regeneration, and control of the proliferation, differentiation and fate of non-lymphoid cell progenitors. T_reg cells in diverse tissues share a common FOXP3⁺CD4⁺ precursor located within lymphoid organs. This precursor undergoes definitive specialization once in the home tissue, following a multilayered array of common and tissue-distinct transcriptional programmes. Our deepening knowledge of tissue T_reg cell biology will inform ongoing attempts to harness T_reg cells for precision immunotherapeutics.

The Alterations in and the Role of the Th17/Treg Balance in Metabolic Diseases

Chronic inflammation plays an important role in the development of metabolic diseases. These include obesity, type 2 diabetes mellitus, and metabolic dysfunction-associated fatty liver disease. The proinflammatory environment maintained by the innate immunity, including macrophages and related cytokines, can be influenced by adaptive immunity. The function of T helper 17 (Th17) and regulatory T (Treg) cells in this process has attracted attention. The Th17/Treg balance is regulated by inflammatory cytokines and various metabolic factors, including those associated with cellular energy metabolism. The possible underlying mechanisms include metabolism-related signaling pathways and epigenetic regulation. Several studies conducted on human and animal models have shown marked differences in and the important roles of Th17/Treg in chronic inflammation associated with obesity and metabolic diseases. Moreover, Th17/Treg seems to be a bridge linking the gut microbiota to host metabolic disorders. In this review, we have provided an overview of the alterations in and the functions of the Th17/Treg balance in metabolic diseases and its role in regulating immune response-related glucose and lipid metabolism.

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.

Intercellular and inter-organ crosstalk in browning of white adipose tissue: molecular mechanism and therapeutic complications

Adipose tissue (AT) is highly plastic and heterogeneous in response to environmental and nutritional changes. The development of heat-dissipating beige adipocytes in white AT (WAT) through a process known as browning (or beiging) has garnered much attention as a promising therapeutic strategy for obesity and its related metabolic complications. This is due to its inducibility in response to thermogenic stimulation and its association with improved metabolic health. WAT consists of adipocytes, nerves, vascular endothelial cells, various types of immune cells, adipocyte progenitor cells, and fibroblasts. These cells contribute to the formation of beige adipocytes through the release of protein factors that significantly influence browning capacity. In addition, inter-organ crosstalk is also important for beige adipocyte biogenesis. Here, we summarize recent findings on fat depot-specific differences, secretory factors participating in intercellular and inter-organ communications that regulate the recruitment of thermogenic beige adipocytes, as well as challenges in targeting beige adipocytes as a potential anti-obese therapy.

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

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

Mirabegron: The most promising adipose tissue beiging agent

Accumulation of white adipose tissue (WAT) underlies the obesity epidemic, leading to current therapeutic techniques that are being investigated for their ability to activate/“beige” this tissue. Adipose tissue (AT) beiging has been reported through intermittent cold exposure (CE), exercise, and β3‐Adrenergic Receptor (β3AR) agonists. But how AT beiging can help in the treatment of metabolic disorders like obesity and type 2 diabetes (T2D) remains largely unexplored. This review summarizes recent research on the use of β3AR agonist, mirabegron (Myrbetriq®), in stimulating beiging in AT. Researchers have only recently been able to determine the optimal therapeutic dose of mirabegron for inducing beiging in subcutaneous/ inguinal WAT, where the benefits of AT activation are evident without the undesired cardiovascular side effects. To determine whether the effects that mirabegron elicits are metabolically beneficial, a comparison of the undisputed findings resulting from intermittent CE‐induced beiging and the disputed findings from exercise‐induced beiging was conducted. Given the recent in vivo animal and clinical studies, the understanding of how mirabegron can be metabolically beneficial for both lean and obese individuals is more clearly understood. These studies have demonstrated that circulating adipokines, glucose metabolism, and lipid droplet (LD) size are all positively affected by mirabegron administration. Recent studies have also demonstrated that mirabegron has similar outcomes to intermittent CE and displays more direct evidence for beiging than those produced with exercise. With these current findings, mirabegron is considered the most promising and safest β3AR agonist currently available that has the potential to be used in the therapeutic treatment of metabolic disorders, and future studies into its interaction with different conditions may prove to be useful as part of a treatment plan in combination with a healthy diet and exercise.

T reg-specific insulin receptor deletion prevents diet-induced and age-associated metabolic syndrome

Adipose tissue (AT) regulatory T cells (T regs) control inflammation and metabolism. Diet-induced obesity causes hyperinsulinemia and diminishes visceral AT (VAT) T reg number and function, but whether these two phenomena were mechanistically linked was unknown. Using a T reg–specific insulin receptor (Insr) deletion model, we found that diet-induced T reg dysfunction is driven by T reg–intrinsic insulin signaling. Compared with Foxp3^cre mice, after 13 wk of high-fat diet, Foxp3^creInsr^fl/fl mice exhibited improved glucose tolerance and insulin sensitivity, effects associated with lower AT inflammation and increased numbers of ST2⁺ T regs in brown AT, but not VAT. Similarly, Foxp3^creInsr^fl/fl mice were protected from the metabolic effects of aging, but surprisingly had reduced VAT T regs and increased VAT inflammation compared with Foxp3^cre mice. Thus, in both diet- and aging-associated hyperinsulinemia, excessive Insr signaling in T regs leads to undesirable metabolic outcomes. Ablation of Insr signaling in T regs represents a novel approach to mitigate the detrimental effects of hyperinsulinemia on immunoregulation of metabolic syndrome.

Advances in Human Immune System Mouse Models for Personalized Treg-Based Immunotherapies

Immunodeficient mice engrafted with a functional human immune system [Human immune system (HIS) mice] have paved the way to major advances for personalized medicine and translation of immune-based therapies. One prerequisite for advancing personalized medicine is modeling the immune system of individuals or disease groups in a preclinical setting. HIS mice engrafted with peripheral blood mononuclear cells have provided fundamental insights in underlying mechanisms guiding immune activation vs. regulation in several diseases including cancer. However, the development of Graft-vs.-host disease restrains relevant long-term studies in HIS mice. Alternatively, engraftment with hematopoietic stem cells (HSCs) enables mimicking different disease stages, however, low frequencies of HSCs in peripheral blood of adults impede engraftment efficacy. One possibility to overcome those limitations is the use of patient-derived induced pluripotent stem cells (iPSCs) reprogrammed into HSCs, a challenging process which has recently seen major advances. Personalized HIS mice bridge research in mice and human diseases thereby facilitating the translation of immunomodulatory therapies. Regulatory T cells (Tregs) are important mediators of immune suppression and thereby contribute to tumor immune evasion, which has made them a central target for cancer immunotherapies. Importantly, studying Tregs in the human immune system in vivo in HIS mice will help to determine requirements for efficient Treg-targeting. In this review article, we discuss advances on personalized HIS models using reprogrammed iPSCs and review the use of HIS mice to study requirements for efficient targeting of human Tregs for personalized cancer immunotherapies.

Cellular Heterogeneity in Adipose Tissues

Adipose tissue depots in distinct anatomical locations mediate key aspects of metabolism, including energy storage, nutrient release, and thermogenesis. Although adipocytes make up more than 90% of adipose tissue volume, they represent less than 50% of its cellular content. Here, I review recent advances in genetic lineage tracing and transcriptomics that reveal the identities of the heterogeneous cell populations constituting mouse and human adipose tissues. In addition to mature adipocytes and their progenitors, these include endothelial and various immune cell types that together orchestrate adipose tissue development and functions. One salient finding is the identification of progenitor subtypes that can modulate adipogenic capacity through paracrine mechanisms. Another is the description of fate trajectories of monocyte/macrophages, which can respond maladaptively to nutritional and thermogenic stimuli, leading to metabolic disease. These studies have generated an extraordinary source of publicly available data that can be leveraged to explore commonalities and differences among experimental models, providing new insights into adipose tissues and their role in metabolic disease.

DsbA-L deficiency in T cells promotes diet-induced thermogenesis through suppressing IFN-γ production

Adipose tissue-resident T cells have been recognized as a critical regulator of thermogenesis and energy expenditure, yet the underlying mechanisms remain unclear. Here, we show that high-fat diet (HFD) feeding greatly suppresses the expression of disulfide-bond A oxidoreductase-like protein (DsbA-L), a mitochondria-localized chaperone protein, in adipose-resident T cells, which correlates with reduced T cell mitochondrial function. T cell-specific knockout of DsbA-L enhances diet-induced thermogenesis in brown adipose tissue (BAT) and protects mice from HFD-induced obesity, hepatosteatosis, and insulin resistance. Mechanistically, DsbA-L deficiency in T cells reduces IFN-γ production and activates protein kinase A by reducing phosphodiesterase-4D expression, leading to increased BAT thermogenesis. Taken together, our study uncovers a mechanism by which T cells communicate with brown adipocytes to regulate BAT thermogenesis and whole-body energy homeostasis. Our findings highlight a therapeutic potential of targeting T cells for the treatment of over nutrition-induced obesity and its associated metabolic diseases.

Bone marrow Tregs mediate stromal cell function and support hematopoiesis via IL-10

The nonimmune roles of Tregs have been described in various tissues, including the BM. In this study, we comprehensively phenotyped marrow Tregs, elucidating their key features and tissue-specific functions. We show that marrow Tregs are migratory and home back to the marrow. For trafficking, marrow Tregs use S1P gradients, and disruption of this axis allows for specific targeting of the marrow Treg pool. Following Treg depletion, the function and phenotype of both mesenchymal stromal cells (MSCs) and hematopoietic stem cells (HSCs) was impaired. Transplantation also revealed that a Treg-depleted niche has a reduced capacity to support hematopoiesis. Finally, we found that marrow Tregs are high producers of IL-10 and that Treg-secreted IL-10 has direct effects on MSC function. This is the first report to our knowledge revealing that Treg-secreted IL-10 is necessary for stromal cell maintenance, and our work outlines an alternative mechanism by which this cytokine regulates hematopoiesis.

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.

Regulatory T cell heterogeneity and therapy in autoimmune diseases

Regulatory T (Treg) cells are a group of CD4⁺ T cell with high expression of CD25 and cell linage specific transcription factor forkhead box P3 (Foxp3) and play a vital role in maintaining immune homeostasis. In the last two decades, researchers have shown that Treg cells involved in the occurrence, development and prognosis of many diseases, especially in autoimmune diseases. Treg targeted therapies, such as low-dose interleukin-2 (IL-2) treatment and Treg infusion therapy, which are aimed at restoring the number or function of Treg cells, have become a hot topic in clinical trials of these diseases. It is believed that Treg cells are heterogeneous. Different subsets of Treg cells have various functions and play different parts in immunomodulatory. Gaining insights into Treg heterogeneity will help us further understand the function of Treg cells and provide news ideas for the selective therapeutic manipulation of Treg cells. In this review, we mainly summarize the heterogeneity of Treg cells and their potential therapeutic value in autoimmune diseases.

Adipose PTEN acts as a downstream mediator of a brain-fat axis in environmental enrichment

Background/Objectives

Environmental enrichment (EE) is a physiological model to investigate brain-fat interactions. We previously discovered that EE activates the hypothalamic-sympathoneural adipocyte (HSA) axis via induction of brain-derived neurotrophic factor (BDNF), thus leading to sympathetic stimulation of white adipose tissue (WAT) and an anti-obesity phenotype. Here, we investigate whether PTEN acts as a downstream mediator of the HSA axis in the EE.

Methods

Mice were housed in EE for 4- and 16-week periods to determine how EE regulates adipose PTEN. Hypothalamic injections of adeno-associated viral (AAV) vectors expressing BDNF and a dominant negative form of its receptor were performed to assess the role of the HSA axis in adipose PTEN upregulation. A β-blocker, propranolol, and a denervation agent, 6-hydroydopamine, were administered to assess sympathetic signaling in the observed EE-PTEN phenotype. To determine whether inducing PTEN is sufficient to reproduce certain EE adipose remodeling, we overexpressed PTEN in WAT using an AAV vector. To determine whether adipose PTEN is necessary for the EE-mediated reduction in adipocyte size, we injected a rAAV vector expressing Cre recombinase to the WAT of adult PTEN^flox mice and placed the mice in EE.

Results

EE upregulated adipose PTEN expression, which was associated with suppression of AKT and ERK phosphorylation, increased hormone-sensitive lipase (HSL) phosphorylation, and reduced adiposity. PTEN regulation was found to be controlled by the HSA axis—with the hypothalamic BDNF acting as the upstream mediator—and dependent on sympathetic innervation. AAV-mediated adipose PTEN overexpression recapitulated EE-mediated adipose changes including suppression of AKT and ERK phosphorylation, increased HSL phosphorylation, and reduced adipose mass, whereas PTEN knockdown blocked the EE-induced reduction of adipocyte size.

Conclusions

These data suggest that adipose PTEN responds to environmental stimuli and serves as downstream mediator of WAT remodeling in the EE paradigm, resulting in decreased adipose mass and decreased adipocyte size.

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Environmental enrichment (EE) induces adipose PTEN expression and is associated with (1) suppression of AKT phosphorylation, (2) increased hormone-sensitive lipase phosphorylation, and (3) decreased adiposity

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The hypothalamic-sympathoneural-adipocyte (HSA) axis mediates EE-induced adipose PTEN

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rAAV-mediated gene delivery of PTEN to adipose tissues mimics EE-related adipose remodeling

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Knockdown of adipose PTEN blocks EE-induced reductions in adipocyte size

Aging and Immunometabolic Adaptations to Thermogenesis

Brown and subcutaneous adipose tissues play a key role in non-shivering thermogenesis both in mice and human, and their activation by adrenergic stimuli promotes energy expenditure, reduces adiposity, and protects against age-related metabolic diseases such as type 2 diabetes (T2D). Low-grade inflammation and insulin resistance characterize T2D. Even though the decline of thermogenic adipose tissues is well-established during ageing, the mechanisms by which this event affects immune system and contributes to the development of T2D is still poorly defined. It is emerging that activation of thermogenic adipose tissues promotes type 2 immunity skewing, limiting type 1 inflammation. Of note, metabolic substrates sustaining type 1 inflammation (e.g. glucose and succinate) are also used by activated adipocytes to promote thermogenesis. Keeping in mind this aspect, a nutrient competition between adipocytes and adipose tissue immune cell infiltrates could be envisaged. Herein, we reviewed the metabolic rewiring of adipocytes during thermogenesis in order to give important insight into the anti-inflammatory role of thermogenic adipose tissues and delineate how their decline during ageing may favor the setting of low-grade inflammatory states that predispose to type 2 diabetes in elderly. A brief description about the contribution of adipokines secreted by thermogenic adipocytes in modulation of immune cell activation is also provided. Finally, we have outlined experimental flow chart procedures and provided technical advices to investigate the physiological processes leading to thermogenic adipose tissue impairment that are behind the immunometabolic decline during aging.

Functional Inactivation of Mast Cells Enhances Subcutaneous Adipose Tissue Browning in Mice

Adipose tissue browning and systemic energy expenditure provide a defense mechanism against obesity and associated metabolic diseases. In high-cholesterol Western diet-fed mice, mast cell (MC) inactivation ameliorates obesity and insulin resistance and improves the metabolic rate, but a direct role of adipose tissue MCs in thermogenesis and browning remains unproven. Here, we report that adrenoceptor agonist norepinephrine-stimulated metabolic rate and subcutaneous adipose tissue (SAT) browning are enhanced in MC-deficient Kit^w-sh/w-sh mice and MC-stabilized wild-type mice on a chow diet. MC reconstitution to SAT in Kit^w-sh/w-sh mice blocks these changes. Mechanistic studies demonstrate that MC inactivation elevates SAT platelet-derived growth factor receptor A (PDGFRα⁺) adipocyte precursor proliferation and accelerates beige adipocyte differentiation. Using the tryptophan hydroxylase 1 (TPH1) inhibitor and TPH1-deficient MCs, we show that MC-derived serotonin inhibits SAT browning and systemic energy expenditure. Functional inactivation of MCs or inhibition of MC serotonin synthesis in SAT promotes adipocyte browning and systemic energy metabolism in mice.

The Heating Microenvironment: Intercellular Cross Talk Within Thermogenic Adipose Tissue

Adipose tissue serves as the body's primary energy storage site; however, findings in recent decades have transformed our understanding of the multifaceted roles of this adaptable organ. The ability of adipose tissue to undergo energy expenditure through heat generation is termed adaptive thermogenesis, a process carried out by thermogenic adipocytes. Adipocytes are the primary parenchymal cell type in adipose tissue, yet these cells are sustained within a rich stromal vascular microenvironment comprised of adipose stem cells and progenitors, immune cells, neuronal cells, fibroblasts, and endothelial cells. Intricate cross talk between these diverse cell types is essential in regulating the activation of thermogenic fat, and the past decade has shed significant light on how this intercellular communication functions. This review will draw upon recent findings and current perspectives on the sophisticated repertoire of cellular and molecular features that comprise the adipose thermogenic milieu.

Adoptive Cell Transfer of Regulatory T Cells Exacerbates Hepatic Steatosis in High-Fat High-Fructose Diet-Fed Mice

Background and Aims: Non-alcoholic steatohepatitis (NASH) is a multisystem condition, involving the liver, adipose tissue, and immune system. Regulatory T (Treg) cells are a subset of T cells that exert an immune-controlling effect. Previously, a reduction of Treg cells in the visceral adipose tissue (VAT) was shown to be associated with a more severe degree of liver disease. We aimed to correct this immune disruption through adoptive cell transfer (ACT) of Treg cells. Methods: Male 8-week-old C57BL/6J mice were fed a high-fat high-fructose diet (HFHFD) for 20 weeks. Treg cells were isolated from the spleens of healthy 8 to 10-week-old C57BL/6J mice and were adoptively transferred to HFHFD-fed mice. PBS-injected mice served as controls. Plasma ALT and lipid levels were determined. Liver and adipose tissue were assessed histologically. Cytotoxic T (Tc), Treg, T helper (Th) 1 and Th17 cells were characterized in VAT, liver, subcutaneous adipose tissue (SAT), blood, and spleen via flow cytometry. Gene expression analysis was performed in SAT and VAT of mice fed either the HFHFD or a control diet for 10-32 weeks. Results: ACT increased Treg cells in SAT, but not in any of the other tissues. Moreover, the ACT induced a decrease in Th1 cells in SAT, liver, blood, and spleen. Higher plasma ALT levels and a higher degree of steatosis were observed in ACT mice, whereas the other HFHFD-induced metabolic and histologic disruptions were unaffected. Expression analysis of genes related to Treg-cell proliferation revealed a HFHFD-induced decrease in all investigated genes in the SAT, while in the VAT the expression of these genes was largely unaffected, except for a decrease in Pparg. Conclusion: ACT of Treg cells in HFHFD-fed mice exacerbated hepatic steatosis, which was possibly related to the increase of Treg cells in the SAT and/or the general decrease in Th1 cells. Moreover, the HFHFD-induced decrease in Pparg expression appeared critical in the decrease of Treg cells at the level of the VAT and the inability to replenish the amount of Treg cells by the ACT, while the mechanism of Treg cell accumulation at the level of the SAT remained unclear.

Immunometabolism and atherosclerosis: perspectives and clinical significance: a position paper from the Working Group on Atherosclerosis and Vascular Biology of the European Society of Cardiology

Inflammation is an important driver of atherosclerosis, and the favourable outcomes of the Canakinumab Anti-inflammatory Thrombosis Outcome Study (CANTOS) trial revealed the large potential of anti-inflammatory drugs for the treatment of cardiovascular disease, especially in patients with a pro-inflammatory constitution. However, the complex immune reactions driving inflammation in the vascular wall in response to an atherosclerotic microenvironment are still being unravelled. Novel insights into the cellular processes driving immunity and inflammation revealed that alterations in intracellular metabolic pathways are strong drivers of survival, growth, and function of immune cells. Therefore, this position paper presents a brief overview of the recent developments in the immunometabolism field, focusing on its role in atherosclerosis. We will also highlight the potential impact of immunometabolic markers and targets in clinical cardiovascular medicine.

Regulatory T cells promote adipocyte beiging in subcutaneous adipose tissue

Regulatory T cells (Tregs) play essential roles in obesity and diabetes. Here, we report a role of Tregs in enhancing β3-adrenergic receptor agonist CL316243 (CL)-stimulated thermogenic program in subcutaneous adipose tissue (SAT), but not in visceral fat. CL treatment for 7 days increased SAT adipocyte beiging and thermogenic gene expression in male or female mice. Adoptive transfer of Tregs enhanced this CL activity. Such Treg activity lost in male epididymal white adipose tissue (eWAT) and female gonadal gWAT. Adipocyte culture yielded the same conclusion. Tregs enhanced the expression of CL-induced thermogenic genes in SAT from male and female mice. This activity of Tregs reduced or disappeared in adipocytes from eWAT or gWAT. Both CL and Tregs induced much higher UCP-1 (uncoupling protein-1) expression in SAT from females than that from males. A mechanistic study demonstrated a role of Tregs in suppressing the expression of M1 macrophage markers (Tnfa, Il6, iNos, Ip10) and promoting the expression of M2 macrophage markers (Mrc1, Arg1, Il10) in bone-marrow-derived macrophages or in SAT from male or female mice. In female mice with pre-established obesity, Treg adoptive transfer reduced the gWAT weight in 2 weeks. Together with CL treatment, Treg adoptive transfer reduced the SAT weight and further improved CL-induced glucose metabolism and insulin sensitivity in female obese mice, but did not affect CL-induced body weight loss in male or female obese mice. This study revealed a predominant role of Tregs in female mice in promoting adipocyte beiging and thermogenesis in SAT, in part by slanting M2 macrophage polarization.

mTOR signaling in Brown and Beige adipocytes: implications for thermogenesis and obesity

Brown and beige adipocytes are mainly responsible for nonshivering thermogenesis or heat production, despite the fact that they have distinguished features in distribution, developmental origin, and functional activation. As a nutrient sensor and critical regulator of energy metabolism, mechanistic target of rapamycin (mTOR) also plays an important role in the development and functional maintenance of adipocytes. While the recent studies support the notion that mTOR (mTORC1 and mTORC2) related signaling pathways are of great significance for thermogenesis and the development of brown and beige adipocytes, the exact roles of mTOR in heat production are controversial. The similarities and disparities in terms of thermogenesis might be ascribed to the use of different animal models and experimental systems, distinct features of brown and beige adipocytes, and the complexity of regulatory networks of mTORC1 and mTORC2 in energy metabolism.

Short-term cold exposure supports human Treg induction in vivo

Objective

Obesity and type-2 diabetes (T2D) are metabolic diseases that represent a critical health problem worldwide. Metabolic disease is differentially associated with fat distribution, while visceral white adipose tissue (VAT) is particularly prone to obesity-associated inflammation. Next to their canonical function of immune suppression, regulatory T cells (Tregs) are key in controlling adipose tissue homeostasis. Towards understanding the molecular underpinnings of metabolic disease, we focus on how environmental-metabolic stimuli impinge on the functional interplay between Tregs and adipose tissue. Here, cold exposure or beta3-adrenergic signaling are a promising tool to increase energy expenditure by activating brown adipose tissue, as well as by reducing local inflammation within fat depots by supporting immunosuppressive Tregs. However, in humans, the underlying mechanisms that enable the environmental-immune crosstalk in the periphery and in the respective tissue remain currently unknown.

Methods

We used combinatorial approaches of next generation humanized mouse models and in vitro and in vivo experiments together with beta3-adrenergic stimulation to dissect the underlying mechanisms of human Treg induction exposed to environmental stimuli such as cold. To test the translational relevance of our findings, we analyzed samples from the FREECE study in which human subjects were exposed to individualized cooling protocols. Samples were analyzed ex vivo and after in vitro Treg induction using qRT-PCR, immunofluorescence, as well as with multicolor flow cytometry and cell sorting.

Results

In vivo application of the beta3-adrenergic receptor agonist mirabegron in humanized mice induced thermogenesis and improved the Treg induction capacity of naïve T cells isolated from these animals. Using samples from the human FREECE study, we demonstrate that a short-term cold stimulus supports human Treg induction in vitro and in vivo. Mechanistically, we identify BORCS6 encoding the Ragulator-interacting protein C17orf59 to be significantly induced in human CD4⁺ T cells upon short-term cold exposure. Strong mTOR signaling is known to limit successful Treg induction and thus likely by interfering with mTOR activation at lysosomal surfaces, C17orf59 improves the Treg induction capacity of human naïve T cells upon cold exposure.

Conclusions

These novel insights into the molecular underpinnings of human Treg induction suggest an important role of Tregs in linking environmental stimuli with adipose tissue function and metabolic diseases. Moreover, these discoveries shed new light on potential approaches towards tailored anti-inflammatory concepts that support human adipose tissue homeostasis by enabling Tregs.

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Beta3-adrenergic stimulation enhances human Tregs in humanized mice.

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Short-term cold stimulation increases human Treg induction in vitro and in vivo.

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Short-term cold exposure elevates human Treg signatures genes.

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Short-term cold induces BORCS6 encoding C17orf59 in human CD4⁺T cells.

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C17orf59 limits mTOR signaling and thereby supports human Treg induction.

Immune Cells Gate White Adipose Tissue Expansion

The immune system plays a critical role in white adipose tissue (WAT) energy homeostasis and, by extension, whole-body metabolism. Substantial evidence from mouse and human studies firmly establishes that insulin sensitivity deteriorates as a result of subclinical inflammation in the adipose tissue of individuals with diabetes. However, the relationship between adipose tissue expandability and immune cell infiltration remains a complex problem important for understanding the pathogenesis of obesity. Notably, a large body of work challenges the idea that all immune responses are deleterious to WAT function. This review highlights recent advances that describe how immune cells and adipocytes coordinately enable WAT expansion and regulation of energy homeostasis.