Interferon-α-producing plasmacytoid dendritic cells drive the loss of adipose tissue regulatory T cells during obesity

Gut Microbiota-Butyrate-PPARγ Axis Modulates Adipose Regulatory T Cell Population

Gut microbiota is essential for the function of peripherally-induced regulatory T (pTreg) cells. However, how commensal bacteria affect thymically derived fat-resident Treg cells that harbor a unique expression of peroxisome proliferator-activated receptor (PPAR)-γ and suppress inflammation in visceral adipose tissue (VAT), is not well defined. Here it is revealed that microbiota depletion causes a drastic decline in Treg cell population in VAT, particularly those expressing ST2 (ST2+ Treg), which are largely restored after gut microbiome reconstruction. Mechanistically, gut microbiota-derived butyrate increases VAT ST2+ Treg cells through binding PPARγ. Butyrate supplementation and high fiber diet increase VAT ST2+ Treg population in obese mice, and ameliorated glucose tolerance and visceral inflammation. Furthermore, human omental adipose Treg cells show positive correlation with fecal butyrate and certain butyrate-producing microbes. This study identifies the critical role of gut microbiota-butyrate-PPARγ axis in maintaining VAT Treg population, pinpointing a potential approach to augment VAT Treg population and ameliorate inflammation.

Predictive factors for responders to deucravacitinib treatment in patients with psoriasis

The tyrosine kinase 2 inhibitor deucravacitinib is therapeutically effective for psoriasis. However, predictive factors for high responses to deucravacitinib have not been examined in a real-world clinical study. Our study aimed to identify predictive factors for responders to deucravacitinib. Therefore, a retrospective study was conducted on 74 patients with psoriasis treated with deucravacitinib (6 mg/day) at week 16 of treatment from January 2023 to February 2024. Patients were classified into responders (achievers of a static Physician's Global Assessment [sPGA] of 0 or 1 with ≥2-point improvement from basal sPGA) and non-responders (non-achievers). We compared baseline values of clinical and laboratory indexes between responders and non-responders. Multivariate logistic regression analysis was used to identify variables predicting responders. Forty-one patients (55.4%) were considered as responders at week 16. Multivariate logistic regression analysis revealed that the response to deucravacitinib was associated with higher age (odds ratio [OR] 1.04; 95% confidence interval [CI] 1.01-1.08; p = 0.0222) and lower body mass index (BMI) (OR 0.825; 95% CI 0.713-0.955; p = 0.0101). Higher age and lower BMI may predict a higher response to deucravacitinib (6 mg/day) at week 16 of treatment.

Immunometabolism of Tregs: mechanisms, adaptability, and therapeutic implications in diseases

Immunometabolism is an emerging field that explores the intricate interplay between immune cells and metabolism. Regulatory T cells (Tregs), which maintain immune homeostasis in immunometabolism, play crucial regulatory roles. The activation, differentiation, and function of Tregs are influenced by various metabolic pathways, such as the Mammalian targets of rapamycin (mTOR) pathway and glycolysis. Correspondingly, activated Tregs can reciprocally impact these metabolic pathways. Tregs also possess robust adaptive capabilities, thus enabling them to adapt to various microenvironments, including the tumor microenvironment (TME). The complex mechanisms of Tregs in metabolic diseases are intriguing, particularly in conditions like MASLD, where Tregs are significantly upregulated and contribute to fibrosis, while in diabetes, systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA), they show downregulation and reduced anti-inflammatory capacity. These phenomena suggest that the differentiation and function of Tregs are influenced by the metabolic environment, and imbalances in either can lead to the development of metabolic diseases. Thus, moderate differentiation and inhibitory capacity of Tregs are critical for maintaining immune system balance. Given the unique immunoregulatory abilities of Tregs, the development of targeted therapeutic drugs may position them as novel targets in immunotherapy. This could contribute to restoring immune system balance, resolving metabolic dysregulation, and fostering innovation and progress in immunotherapy.

Obesity reshapes regulatory T cells in the visceral adipose tissue by disrupting cellular cholesterol homeostasis

Regulatory T cells (Tregs) accumulate in the visceral adipose tissue (VAT) to maintain systemic metabolic homeostasis but decline during obesity. Here, we explored the metabolic pathways controlling the homeostasis, composition, and function of VAT Tregs under normal and high-fat diet feeding conditions. We found that cholesterol metabolism was specifically up-regulated in ST2hi VAT Treg subsets. Treg-specific deletion of Srebf2, the master regulator of cholesterol homeostasis, selectively reduced ST2hi VAT Tregs, increasing VAT inflammation and insulin resistance. Single-cell RNA/T cell receptor (TCR) sequencing revealed a specific loss and reduced clonal expansion of ST2hi VAT Treg subsets after Srebf2 deletion. Srebf2-mediated cholesterol homeostasis potentiated strong TCR signaling, which preferentially promoted ST2hi VAT Treg accumulation. However, long-term high-fat diet feeding disrupted VAT Treg cholesterol homeostasis and impaired clonal expansion of the ST2hi subset. Restoring Treg cholesterol homeostasis rescued VAT Treg accumulation in obese mice, suggesting that modulation of cholesterol homeostasis could be a promising strategy for Treg-targeted therapies in obesity-associated metabolic diseases.

Dynamics of tissue repair regulatory T cells and damage in acute Trypanosoma cruzi infection

Tissue-repair regulatory T cells (trTregs) comprise a specialized cell subset essential for tissue homeostasis and repair. While well-studied in sterile injury models, their role in infection-induced tissue damage and antimicrobial immunity is less understood. We investigated trTreg dynamics during acute Trypanosoma cruzi infection, marked by extensive tissue damage and strong CD8+ immunity. Unlike sterile injury models, trTregs significantly declined in secondary lymphoid organs and non-lymphoid target tissues during infection, correlating with systemic and local tissue damage, and downregulation of function-associated genes in skeletal muscle. This decline was linked to decreased systemic IL-33 levels, a key trTreg growth factor, and promoted by the Th1 cytokine IFN-γ. Early recombinant IL-33 treatment increased trTregs, type 2 innate lymphoid cells, and parasite-specific CD8+ cells at specific time points after infection, leading to reduced tissue damage, lower parasite burden, and improved disease outcome. Our findings not only provide novel insights into trTregs during infection but also highlight the potential of optimizing immune balance by modulating trTreg responses to promote tissue repair while maintaining effective pathogen control during infection-induced injury.

Immunological roles for resistin and related adipokines in obesity-associated tumors

Rationale Obesity is an independent risk factor for the occurrence and development of tumors. Obesity is influenced by signaling of adipokines, which are secreted factors from adipocytes and resident immune cells within adipose tissues that mediate lipid metabolism. More recently, adipokines have been implicated in chronic inflammation as well as in tumor formation and growth. Among them, resistin has received increasing attention in research related to the growth and expansion of solid tumors and hematological cancers through various signaling pathways. Objective and findings We reviewed the physiological, biochemical, and immune functions of adipose tissue, with a focus on the structure and expression of resistin and adipokines within multiple adipose cell types, their signaling pathways and putative effects on tumor cells, as well as their in vivo regulation. Current evidence indicates that adipokines such as resistin act as pro-inflammatory factors to stimulate immune cells which, in turn, promotes tumor angiogenesis, connective tissue proliferation, and matrix fibrosis. Concurrently, in states of metabolic dysfunction and lipotoxicity in obese individuals, the numbers and functions of immune cells are compromised, leading to an immunosuppressive environment that fosters tumor cell survival and weak cancer immune monitoring. Conclusion Adipokines such as resistin are important to the development of obesity-related tumors. Clarifying the roles for obesity-related factors in immune regulation and tumor progression may lead to the discovery of novel anti-tumor strategies for targeting obesity factors such as resistin to limit tumor growth and manage obesity, or both.

Multi-omics landscape of childhood simple obesity: novel insights into pathogenesis and biomarkers discovery

BACKGROUND

The increasing incidence of childhood obesity annually has led to a surge in physical and mental health risks, making it a significant global public health concern. This study aimed to discover novel biomarkers of childhood simple obesity through integrative multi-omics analysis, uncovering their potential connections and providing fresh research directions for the complex pathogenesis and treatment strategies.

METHODS

Transcriptome, untargeted metabolome, and 16 S rDNA sequencing were conducted on subjects to examine transcripts, metabolites in blood, and gut microflora in stool.

RESULTS

Transcriptomic analysis identified 599 differentially expressed genes (DEGs), of which 25 were immune-related genes, and participated in immune pathways such as antimicrobial peptides, neutrophil degranulation, and interferons. The optimal random forest model based on these genes exhibited an AUC of 0.844. The metabolomic analysis examined 71 differentially expressed metabolites (DEMs), including 12 immune-related metabolites. Notably, lauric acid showed an extremely strong positive correlation with BMI and showed a good discriminative power for obesity (AUC = 0.82). DEMs were found to be significantly enriched in four metabolic pathways, namely "Aminoacyl-tRNA biosynthesis", "Valine leucine and isoleucine biosynthesis, and Glycine", "Serine and threonine metabolism", and "Biosynthesis of unsaturated fatty acids". Microbiome analysis revealed 12 differential gut microbiotas (DGMs) at the phylum and genus levels, with p_Firmicutes dominating in the obese group and g_Escherichia-Shigella in the normal group. Subsequently, a Random Forest model was developed based on the DEMs, immune-related DEGs, and metabolites with an AUC value of 0.912. The 14 indicators identified by this model could potentially serve as a set of biomarkers for obesity. The analysis of the inter-omics correlation network found 233 pairs of significant correlations. DEGs BPIFA1, BPI, and SAA1, DEMs Dimethy(tetradecyl)amine, Deoxycholic acid, Pathalic anhydride, and DL-Alanine, and DGMs g_Intestinimonas and g_Turicibacter showed strong connectivity within the network, constituting a large proportion of interactions.

CONCLUSION

This study presents the first comprehensive description of the multi-omics characteristics of childhood simple obesity, recognizing promising biomarkers. Immune-related markers offer a new perspective for researching the immunological mechanisms underlying obesity and its associated complications. The revealed interactions among these biomarkers contribute to a deeper understanding the intricate biological regulatory networks associated with obesity.

Host metabolic inflammation fueled by bacterial DNA

Metabolic diseases, characterized by chronic low-grade inflammation, exhibit a compromised gut barrier allowing the translocation of bacteria-derived products to bloodstream and distant metabolic organs. Bacterial DNA can be detected in metabolic tissues during the onset of these diseases, highlighting its role in the development of metabolic diseases. Extracellular vesicles (EVs) are involved in the delivery of bacterial DNA to the local tissues, and its sensing by the host triggers local and system inflammation. Understanding bacterial DNA translocation and its induced inflammation is crucial in deciphering metabolic disease pathways. Here, we delve into the mechanisms dictating the interaction between host physiology and bacterial DNA, focusing on its origin and delivery, host immune responses against it, and its roles in metabolic disorders.

Macrophages and T cells in metabolic disorder-associated cancers

Cancer and metabolic disorders have emerged as major global health challenges, reaching epidemic levels in recent decades. Often viewed as separate issues, metabolic disorders are shown by mounting evidence to heighten cancer risk and incidence. The intricacies underlying this connection are still being unraveled and encompass a complex interplay between metabolites, cancer cells and immune cells within the tumour microenvironment (TME). Here, we outline the interplay between metabolic and immune cell dysfunction in the context of three highly prevalent metabolic disorders, namely obesity; two associated liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH); and type 2 diabetes. We focus primarily on macrophages and T cells, the critical roles of which in dictating inflammatory response and immune surveillance in metabolic disorder-associated cancers are widely reported. Moreover, considering the ever-increasing number of patients prescribed with metabolism disorder-altering drugs and diets in recent years, we discuss how these therapies modulate systemic and local immune phenotypes, consequently impacting cancer malignancy. Collectively, unraveling the determinants of metabolic disorder-associated immune landscape and their role in fuelling cancer malignancy will provide a framework essential to therapeutically address these highly prevalent diseases.

Exogenous MSC based tissue regeneration: a review of immuno-protection strategies from biomaterial scaffolds

Mesenchymal stem cell (MSC)-based tissue engineering holds great potential for regenerative medicine as a means of replacing damaged or lost tissues to restore their structure and function. However, the efficacy of MSC-based regeneration is frequently limited by the low survival rate and limited survival time of transplanted MSCs. Despite the inherent immune privileges of MSCs, such as low expression of major histocompatibility complex antigens, tolerogenic properties, local immunosuppressive microenvironment creation, and induction of immune tolerance, immune rejection remains a major obstacle to their survival and regenerative potential. Evidence suggests that immune protection strategies can enhance MSC therapeutic efficacy by prolonging their survival and maintaining their biological functions. Among various immune protection strategies, biomaterial-based scaffolds or cell encapsulation systems that mediate the interaction between transplanted MSCs and the host immune system or spatially isolate MSCs from the immune system for a specific time period have shown great promise. In this review, we provide a comprehensive overview of these biomaterial-based immune protection strategies employed for exogenous MSCs, highlighting the crucial role of modulating the immune microenvironment. Each strategy is critically examined, discussing its strengths, limitations, and potential applications in MSC-based tissue engineering. By elucidating the mechanisms behind immune rejection and exploring immune protection strategies, we aim to address the challenges faced by MSC-based tissue engineering and pave the way for enhancing the therapeutic outcomes of MSC therapies. The insights gained from this review will contribute to the development of more effective strategies to protect transplanted MSCs from immune rejection and enable their successful application in regenerative medicine.

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

Update on Obesity and Cardiovascular Risk: From Pathophysiology to Clinical Management

Obesity is an epidemic worldwide. Overweight and multiple obesity-related mechanisms, including dysmetabolic alterations, contribute to cardiovascular deleterious effects. Hence, overweight and obesity have been independently associated with increased cardiovascular risk, whose assessment is crucial for preserving life quality and reducing mortality, and to address appropriate therapeutic strategies in obese patients. Beyond the standard of care in managing overweight and obesity in adults (i.e., diet and physical exercise), several relevant pharmacotherapies have been approved, and several procedures and device types for weight loss have been recommended. In such a contest, medical weight management remains one option for treating excess weight. Most drugs used for obesity reduce appetite and increase satiety and, secondarily, slow gastric emptying to reduce body weight and, therefore, act also to improve metabolic parameters. In this contest, agonists of the glucagon-like peptide-1 receptor (GLP-1RAs) modulate different metabolic pathways associated with glucose metabolism, energy homeostasis, antioxidation, and inflammation. Moreover, this class of drugs has shown efficacy in improving glycemic control, reducing the incidence of cardiovascular events in type 2 diabetic patients, and reducing body weight independently of the presence of diabetes. Recently, in overweight or obese patients with pre-existing cardiovascular disease but without diabetes, the GLP-1RA semaglutide reduced the incidence of cardiovascular and cerebrovascular events and death from cardiovascular causes. Thus, semaglutide has been approved for secondary prevention in obese people with cardiovascular disease. Nevertheless, whether this class of drugs is equally effective for primary prevention in obese people has to be demonstrated. In this review, we will summarize updates on the pathophysiology of obesity, the effects of obesity on cardiovascular risk, the impact of different obesity phenotypes on cardiovascular diseases, and the novelties in the clinical management of obesity for cardiovascular prevention.

Revisiting the Immunometabolic Basis for the Metabolic Syndrome from an Immunonutritional View

Metabolic syndrome (MetS) implies different conditions where insulin resistance constitutes a major hallmark of the disease. The disease incurs a high risk for the development of cardiovascular complications, and takes its toll in regard to the gut-liver axis (pancreas, primary liver and colorectal)-associated immunity. The modulation of immunometabolic responses by immunonutritional factors (IFs) has emerged as a key determinant of the gut-liver axis' metabolic and immune health. IFs from plant seeds have shown in vitro and pre-clinical effectiveness primarily in dealing with various immunometabolic and inflammatory diseases. Only recently have immunonutritional studies established the engagement of innate intestinal immunity to effectively control immune alterations in inflamed livers preceding the major features of the MetS. However, integrative analyses and the demonstration of causality between IFs and specific gut-liver axis-associated immunometabolic imbalances for the MetS remain ill-defined in the field. Herein, a better understanding of the IFs with a significant role in the MetS, as well as within the dynamic interplay in the functional differentiation of innate immune key effectors (i.e., monocytes/macrophages), worsening or improving the disease, could be of crucial relevance. The development of an adequate intermediary phenotype of these cells can significantly contribute to maintaining the function of Tregs and innate lymphoid cells for the prevention and treatment of MetS and associated comorbidities.

Obesity-induced chronic low-grade inflammation in adipose tissue: A pathway to Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of cognitive impairment worldwide. Overweight and obesity are strongly associated with comorbidities, such as hypertension, diabetes, and insulin resistance (IR), which contribute substantially to the development of AD and subsequent morbidity and mortality. Adipose tissue (AT) is a highly dynamic organ composed of a diverse array of cell types, which can be classified based on their anatomic localization or cellular composition. The expansion and remodeling of AT in the context of obesity involves immunometabolic and functional shifts steered by the intertwined actions of multiple immune cells and cytokine signaling within AT, which contribute to the development of metabolic disorders, IR, and systemic markers of chronic low-grade inflammation. Chronic low-grade inflammation, a prolonged, low-dose stimulation by specific immunogens that can progress from localized sites and affect multiple organs throughout the body, leads to neurodystrophy, increased apoptosis, and disruption of homeostasis, manifesting as brain atrophy and AD-related pathology. In this review, we sought to elucidate the mechanisms by which AT contributes to the onset and progression of AD in obesity through the mediation of chronic low-grade inflammation, particularly focusing on the roles of adipokines and AT-resident immune cells.

Dual Regulation Mechanism of Obesity: DNA Methylation and Intestinal Flora

Obesity is a multifactorial chronic inflammatory metabolic disorder, with pathogenesis influenced by genetic and non-genetic factors such as environment and diet. Intestinal microbes and their metabolites play significant roles in the occurrence and development of obesity by regulating energy metabolism, inducing chronic inflammation, and impacting intestinal hormone secretion. Epigenetics, which involves the regulation of host gene expression without changing the nucleotide sequence, provides an exact direction for us to understand how the environment, lifestyle factors, and other risk factors contribute to obesity. DNA methylation, as the most common epigenetic modification, is involved in the pathogenesis of various metabolic diseases. The epigenetic modification of the host is induced or regulated by the intestinal microbiota and their metabolites, linking the dynamic interaction between the microbiota and the host genome. In this review, we examined recent advancements in research, focusing on the involvement of intestinal microbiota and DNA methylation in the etiology and progression of obesity, as well as potential interactions between the two factors, providing novel perspectives and avenues for further elucidating the pathogenesis, prevention, and treatment of obesity.

Transcriptional and hormonal control of adipose Treg heterogeneity and function

Adipose tissue stores excess energy and produces a broad range of factors that regulate multiple physiological processes including systemic energy homeostasis. Visceral adipose tissue (VAT) plays a particularly important role in glucose metabolism as its endocrine function underpins food uptake and energy expenditure. Caloric excess triggers VAT inflammation which can impair insulin sensitivity and cause metabolic deregulation. Regulatory T cells (Tregs) that reside in the VAT suppress inflammation and protect from metabolic disease. The cellular components of VAT and its secretory products play a vital role in fostering the differentiation and maintenance of VAT Tregs. Critically, the physiology and inflammatory tone of VAT exhibit sex-specific disparities, resulting in substantial VAT Treg heterogeneity. Indeed, cytokines and sex hormones promote the differentiation of distinct populations of mature VAT Tregs, each characterized by unique phenotypes, homeostatic requirements, and functions. This review focuses on key findings that have significantly advanced our understanding of VAT Treg biology and the current state of the field, while also discussing open questions that require further exploration.

Deciphering visceral adipose tissue regulatory T cells: Key contributors to metabolic health

Regulatory T cells (Tregs) within the visceral adipose tissue (VAT) play a crucial role in controlling tissue inflammation and maintaining metabolic health. VAT Tregs display a unique transcriptional profile and T cell receptor (TCR) repertoire, and closely interact with adipocytes, stromal cells, and other immune components within the local VAT microenvironment. However, in the context of obesity, there is a notable decline in VAT Tregs, resulting in heightened VAT inflammation and insulin resistance. A comprehensive understanding of the biology of VAT Tregs is essential for the development of Treg-based therapies for mitigating obesity-associated metabolic diseases. Recent advancements in lineage tracing tools, genetic mouse models, and various single cell "omics" techniques have significantly progressed our understandings of the origin, differentiation, and regulation of this unique VAT Treg population at steady state and during obesity. The identification of VAT-Treg precursor cells in the secondary lymphoid organs has also provided important insights into the timing, location, and mechanisms through which VAT Tregs acquire their distinctive phenotype that enables them to function within a lipid-rich microenvironment. In this review, we highlight key recent breakthroughs in the VAT-Treg field while discussing pivotal questions that remain unanswered.

T cells in obesity-associated inflammation: The devil is in the details

Obesity presents a significant health challenge, affecting 41% of adults and 19.7% of children in the United States. One of the associated health challenges of obesity is chronic low-grade inflammation. In both mice and humans, T cells in circulation and in the adipose tissue play a pivotal role in obesity-associated inflammation. Changes in the numbers and frequency of specific CD4+ Th subsets and their contribution to inflammation through cytokine production indicate declining metabolic health, that is, insulin resistance and T2D. While some Th subset alterations are consistent between mice and humans with obesity, some changes mainly characterize male mice, whereas female mice often resist obesity and inflammation. However, protection from obesity and inflammation is not observed in human females, who can develop obesity-related T-cell inflammation akin to males. The decline in female sex hormones after menopause is also implicated in promoting obesity and inflammation. Age is a second underappreciated factor for defining and regulating obesity-associated inflammation toward translating basic science findings to the clinic. Weight loss in mice and humans, in parallel with these other factors, does not resolve obesity-associated inflammation. Instead, inflammation persists amid modest changes in CD4+ T cell frequencies, highlighting the need for further research into resolving changes in T-cell function after weight loss. How lingering inflammation after weight loss affecting the common struggle to maintain lower weight is unknown. Semaglutide, a newly popular pharmaceutical used for treating T2D and reversing obesity, holds promise for alleviating obesity-associated health complications, yet its impact on T-cell-mediated inflammation remains unexplored. Further work in this area could significantly contribute to the scientific understanding of the impacts of weight loss and sex/hormones in obesity and obesity-associated metabolic decline.

Adipose-tissue Treg cells restrain differentiation of stromal adipocyte precursors to promote insulin sensitivity and metabolic homeostasis

Regulatory T (Treg) cells in epidydimal visceral adipose tissue (eVAT) of lean mice and humans regulate metabolic homeostasis. We found that constitutive or punctual depletion of eVAT-Treg cells reined in the differentiation of stromal adipocyte precursors. Co-culture of these precursors with conditional medium from eVAT-Treg cells limited their differentiation in vitro, suggesting a direct effect. Transcriptional comparison of adipocyte precursors, matured in the presence or absence of the eVAT-Treg-conditioned medium, identified the oncostatin-M (OSM) signaling pathway as a key distinction. Addition of OSM to in vitro cultures blocked the differentiation of adipocyte precursors, while co-addition of anti-OSM antibodies reversed the ability of the eVAT-Treg-conditioned medium to inhibit in vitro adipogenesis. Genetic depletion of OSM (specifically in Treg) cells or of the OSM receptor (specifically on stromal cells) strongly impaired insulin sensitivity and related metabolic indices. Thus, Treg-cell-mediated control of local progenitor cells maintains adipose tissue and metabolic homeostasis, a regulatory axis seemingly conserved in humans.

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.

Ontogeny and Function of Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) represent a unique cell type within the innate immune system. Their defining property is the recognition of pathogen-derived nucleic acids through endosomal Toll-like receptors and the ensuing production of type I interferon and other soluble mediators, which orchestrate innate and adaptive responses. We review several aspects of pDC biology that have recently come to the fore. We discuss emerging questions regarding the lineage affiliation and origin of pDCs and argue that these cells constitute an integral part of the dendritic cell lineage. We emphasize the specific function of pDCs as innate sentinels of virus infection, particularly their recognition of and distinct response to virus-infected cells. This essential evolutionary role of pDCs has been particularly important for the control of coronaviruses, as demonstrated by the recent COVID-19 pandemic. Finally, we highlight the key contribution of pDCs to systemic lupus erythematosus, in which therapeutic targeting of pDCs is currently underway.

[Latest Findings on the Role of α-Ketoglutarate in Metabolic Syndrome]

Alpha-ketoglutarate (α-KG), an endogenous intermediate of the tricarboxylic acid cycle, is involved in a variety of cellular metabolic pathways. It serves as an energy donor, a precursor of amino acid biosynthesis, and an epigenetic regulator. α-KG plays physiological functions in immune regulation, oxidative stress, and anti-aging as well. In recent years, it has been reported that the level of α-KG in the body is closely associated with metabolic syndrome, including obesity, hyperglycemia, and other pathological factors. Exogenous supplementation of α-KG improves obesity, blood glucose levels, and cardiovascular disease risks associated with metabolic syndrome. Furthermore, α-KG regulates the common pathological mechanisms of metabolic syndrome, suggesting the potential application prospect of α-KG in metabolic syndrome. In order to provide a theoretical basis for further exploration of the application of α-KG in metabolic syndrome, we focused on α-KG and metabolic syndrome in this article and summarized the latest research progress in the role of α-KG in improving the pathological condition and disease progression of metabolic syndrome. For the next step, researchers may focus on the co-pathogenesis of metabolic syndrome and investigate whether α-KG can be used to achieve the therapeutic goal of "homotherapy for heteropathy" in the treatment of metabolic syndrome.

CRISPR-Cas9 applications in T cells and adoptive T cell therapies

T cell immunity is central to contemporary cancer and autoimmune therapies, encompassing immune checkpoint blockade and adoptive T cell therapies. Their diverse characteristics can be reprogrammed by different immune challenges dependent on antigen stimulation levels, metabolic conditions, and the degree of inflammation. T cell-based therapeutic strategies are gaining widespread adoption in oncology and treating inflammatory conditions. Emerging researches reveal that clustered regularly interspaced palindromic repeats-associated protein 9 (CRISPR-Cas9) genome editing has enabled T cells to be more adaptable to specific microenvironments, opening the door to advanced T cell therapies in preclinical and clinical trials. CRISPR-Cas9 can edit both primary T cells and engineered T cells, including CAR-T and TCR-T, in vivo and in vitro to regulate T cell differentiation and activation states. This review first provides a comprehensive summary of the role of CRISPR-Cas9 in T cells and its applications in preclinical and clinical studies for T cell-based therapies. We also explore the application of CRISPR screen high-throughput technology in editing T cells and anticipate the current limitations of CRISPR-Cas9, including off-target effects and delivery challenges, and envisioned improvements in related technologies for disease screening, diagnosis, and treatment.

Obese visceral adipose dendritic cells downregulate regulatory T cell development through IL-33

Regulatory T cells (Tregs) residing in visceral adipose tissue (VAT) play a pivotal role in regulating tissue inflammation and metabolic dysfunction associated with obesity. However, the specific phenotypic and functional characteristics of Tregs in obese VAT, as well as the regulatory mechanisms shaping them, remain elusive. This study demonstrates that obesity selectively reduces Tregs in VAT, characterized by restrained proliferation, heightened PD-1 expression, and diminished ST2 expression. Additionally, obese VAT displays distinctive maturation of dendritic cells (DCs), marked by elevated expressions of MHC-II, CD86, and PD-L1, which are inversely correlated with VAT Tregs. In an in vitro co-culture experiment, only obese VAT DCs, not macrophages or DCs from subcutaneous adipose tissue (SAT) and spleen, result in decreased Treg differentiation and proliferation. Furthermore, Tregs differentiated by obese VAT DCs exhibit distinct characteristics resembling those of Tregs in obese VAT, such as reduced ST2 and IL-10 expression. Mechanistically, obesity lowers IL-33 production in VAT DCs, contributing to the diminished Treg differentiation. These findings collectively underscore the critical role of VAT DCs in modulating Treg generation and shaping Treg phenotype and function during obesity, potentially contributing to the regulation of VAT Treg populations.

Adipose Tissue Inflammation: Linking Physiological Stressors to Disease Susceptibility

The study of adipose tissue (AT) is enjoying a renaissance. White, brown, and beige adipocytes are being investigated in adult animals, and the critical roles of small depots like perivascular AT are becoming clear. But the most profound revision of the AT dogma has been its cellular composition and regulation. Single-cell transcriptomic studies revealed that adipocytes comprise well under 50% of the cells in white AT, and a substantial portion of the rest are immune cells. Altering the function of AT resident leukocytes can induce or correct metabolic syndrome and, more surprisingly, alter adaptive immune responses to infection. Although the field is dominated by obesity research, conditions such as rapid lipolysis, infection, and heat stress impact AT immune dynamics as well. Recent findings in rodents lead to critical questions that should be explored in domestic livestock as potential avenues for improved animal resilience to stressors, particularly as animals age.

Orchestration of the Adipose Tissue Immune Landscape by Adipocytes

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

Adipose-tissue regulatory T cells are a consortium of subtypes that evolves with age and diet

Foxp3+CD4+ regulatory T (Treg) cells found within tissues regulate local immunity, inflammation, and homeostasis. Tregs in epididymal visceral adipose tissue (eVAT) are critical regulators of local and systemic inflammation and metabolism. During aging and under obesogenic conditions, eVAT Tregs undergo transcriptional and phenotypic changes and are important for containing inflammation and normalizing metabolic indices. We have employed single-cell RNA sequencing, single-cell Tra and Trb sequencing, adoptive transfers, photoconvertible mice, cellular interaction analyses, and in vitro cultures to dissect the evolving heterogeneity of eVAT Tregs with aging and obesity. Distinct Treg subtypes with distinguishable gene expression profiles and functional roles were enriched at differing ages and with differing diets. Like those in lean mice, eVAT Tregs in obese mice were not primarily recruited from the circulation but instead underwent local expansion and had a distinct and diversified T cell receptor repertoire. The different eVAT-Treg subtypes were specialized in different functions; for example, the subtypes enriched in lean, but not obese, mice suppressed adipogenesis. The existence of functionally divergent eVAT-Treg subtypes in response to obesogenic conditions presents possibilities for precision therapeutics in the context of obesity.

Macrophage and T cell networks in adipose tissue

The signals and structure of the tissues in which leukocytes reside critically mould leukocyte function and development and have challenged our fundamental understanding of how to define and categorize tissue-resident immune cells. One specialized tissue niche that has a powerful effect on immune cell function is adipose tissue. The field of adipose tissue leukocyte biology has expanded dramatically and has revealed how tissue niches can shape immune cell function and reshape them in a setting of metabolic stress, such as obesity. Most notably, adipose tissue macrophages and T cells are under intense investigation due to their contributions to adipose tissue in the lean and obese states. Both adipose tissue macrophages and T cells have features associated with the metabolic function of adipose tissue that are distinct from features of macrophages and T cells that are classically characterized in other tissues. This Review provides state-of-the-art understanding of adipose tissue macrophages and T cells and discusses how their unique niche can help us to better understand diversity in leukocyte responses.

Regulatory T cells shield muscle mitochondria from interferon-γ-mediated damage to promote the beneficial effects of exercise

Exercise enhances physical performance and reduces the risk of many disorders such as cardiovascular disease, type 2 diabetes, dementia, and cancer. Exercise characteristically incites an inflammatory response, notably in skeletal muscles. Although some effector mechanisms have been identified, regulatory elements activated in response to exercise remain obscure. Here, we have addressed the roles of Foxp3+CD4+ regulatory T cells (Tregs) in the healthful activities of exercise via immunologic, transcriptomic, histologic, metabolic, and biochemical analyses of acute and chronic exercise models in mice. Exercise rapidly induced expansion of the muscle Treg compartment, thereby guarding against overexuberant production of interferon-γ and consequent metabolic disruptions, particularly mitochondrial aberrancies. The performance-enhancing effects of exercise training were dampened in the absence of Tregs. Thus, exercise is a natural Treg booster with therapeutic potential in disease and aging contexts.

Immunometabolism of dendritic cells in health and disease

Dendritic cells (DCs) are crucial mediators that bridge the innate and adaptive immune responses. Cellular rewiring of metabolism is an emerging regulator of the activation, migration, and functional specialization of DC subsets in specific microenvironments and immunological conditions. DCs undergo metabolic adaptation to exert immunogenic or tolerogenic effects in different contexts. Also, beyond their intracellular metabolic and signaling roles, metabolites and nutrients mediate the intercellular crosstalk between DCs and other cell types, and such crosstalk orchestrates DC function and immune responses. Here, we provide a comprehensive review of the metabolic regulation of DC biology in various contexts and summarize the current understanding of such regulation in directing immune homeostasis and inflammation, specifically with respect to infections, autoimmunity, tolerance, cancer, metabolic diseases, and crosstalk with gut microbes. Understanding context-specific metabolic alterations in DCs may identify mechanisms for physiological and pathological functions of DCs and yield potential opportunities for therapeutic targeting of DC metabolism in many diseases.

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

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

Gut-derived short-chain fatty acids bridge cardiac and systemic metabolism and immunity in heart failure

Heart failure (HF) represents a group of complex clinical syndromes with high morbidity and mortality and has a significant global health burden. Inflammation and metabolic disorders are closely related to the development of HF, which are complex and depend on the severity and type of HF and common metabolic comorbidities such as obesity and diabetes. An increasing body of evidence indicates the importance of short-chain fatty acids (SCFAs) in regulating cardiac function. In addition, SCFAs represent a unique class of metabolites and play a distinct role in shaping systemic immunity and metabolism. In this review, we reveal the role of SCFAs as a link between metabolism and immunity, which regulate cardiac and systemic immune and metabolic systems by acting as energy substrates, inhibiting the expression of histone deacetylase (HDAC) regulated genes and activating G protein-coupled receptors (GPCRs) signaling. Ultimately cardiac efficiency is improved, cardiac inflammation alleviated and cardiac function in failing hearts enhanced. In conclusion, SCFAs represent a new therapeutic approach for HF.

Hypertension-Driven Regulatory T-Cell Perturbations Accelerate Myocardial Ischemia-Reperfusion Injury

BACKGROUND

Patients with a history of hypertension have elevated inflammation and a worse prognosis after acute myocardial infarction (AMI). Regulatory T cells (Tregs) are reported to lose their immunosuppressive capacity under pathological conditions. However, whether hypertension leads to Treg dysfunction, thus accelerating myocardial ischemia-reperfusion injury, is still unknown.

METHODS

Studies were performed in hypertensive rats and mice with myocardial ischemia-reperfusion injury. The frequencies and phenotypes of Tregs were analyzed by flow cytometry and immunohistochemistry. Reconstruction Treg experiments were performed to evaluate the effect of Tregs on ischemia-reperfusion injury. Patients with AMI were enrolled to assess circulating Tregs, inflammatory cytokines, and cardiac function.

RESULTS

In this study, we found that hypertension leads to proinflammatory Th1 (T helper 1 cell)-like Treg subsets with compromised suppressive capacity. Reconstruction Treg experiments identified that dysfunctional Tregs induced by hypertension play a pathogenic role in the progression of myocardial ischemia-reperfusion injury. In particular, we identified HDAC6 (histone deacetylase 6) as a central regulator in the perturbed Tregs. Clinical studies revealed that the hypertension-induced reduction in circulating Tregs strongly correlated with the higher occurrence rate of microvascular obstruction in AMI patients with hypertension.

CONCLUSIONS

Our study provided promising clues to explain the poor prognosis of hypertensive AMI patients due to alterations in Tregs. Targeting disturbed Tregs may be a new strategy to treat AMI patients with hypertension.

Fat and inflammation: adipocyte-myeloid cell crosstalk in atherosclerosis

Adipose tissue inflammation has been implicated in various chronic inflammatory diseases and cancer. Perivascular adipose tissue (PVAT) surrounds the aorta as an extra layer and was suggested to contribute to atherosclerosis development. PVAT regulates the function of endothelial and vascular smooth muscle cells in the aorta and represent a reservoir for various immune cells which may participate in aortic inflammation. Recent studies demonstrate that adipocytes also express various cytokine receptors and, therefore, may directly respond to inflammatory stimuli. Here we will summarize current knowledge on immune mechanisms regulating adipocyte activation and the crosstalk between myeloid cells and adipocytes in pathogenesis of atherosclerosis.

Mitochondrial sourcing of interferogenic ligands and an autoantigen in human obesity-associated metaflammation

OBJECTIVE

Visceral adipose tissue (VAT) inflammation contributes to metabolic dysregulation in obesity. VAT recruitment and activation of plasmacytoid dendritic cells (pDCs) through toll-like receptor 9 (TLR9) recognition of self-DNA, leading to induction of type I interferons, are crucial innate triggers for this VAT inflammation. It was hypothesized that mitochondrial DNA (mtDNA) can contribute to TLR9 activation in VAT-recruited pDCs in obesity, and this study aimed to identify the carrier protein for ligand access to TLR9 and to explore whether this also provides for a source of autoantigens in this context.

METHODS

VAT samples, used for gene expression studies as well as adipose explant cultures, were collected from patients with obesity (n = 54) and lean patients (n = 10). Supernatants from human pDC cultures, treated with adipose explant culture supernatants, were used for interferon α ELISA. Venous plasma, from patients with (n = 114) and without (n = 45) obesity, was used for an ELISA for autoantibodies.

RESULTS

MtDNA from VAT in obesity, in complex with mitochondrial transcription factor A protein (TFAM), acts as interferogenic ligands for pDCs. Humoral autoreactivity against TFAM is also induced in obesity.

CONCLUSIONS

Interferogenic ligands and an autoantigen can be sourced from dysfunctional mitochondria in VAT of humans with obesity. Further therapeutic and prognostic potential for this immune mechanism in obesity warrants exploration.

Obesity-induced dysregulation of skin-resident PPARγ+ Treg cells promotes IL-17A-mediated psoriatic inflammation

Obesity is a major risk factor for psoriasis, but how obesity disrupts the regulatory mechanisms that keep skin inflammation in check is unclear. Here, we found that skin was enriched with a unique population of CD4+Foxp3+ regulatory T (Treg) cells expressing the nuclear receptor peroxisome proliferation-activated receptor gamma (PPARγ). PPARγ drove a distinctive transcriptional program and functional suppression of IL-17A+ γδ T cell-mediated psoriatic inflammation. Diet-induced obesity, however, resulted in a reduction of PPARγ+ skin Treg cells and a corresponding loss of control over IL-17A+ γδ T cell-mediated inflammation. Mechanistically, PPARγ+ skin Treg cells preferentially took up elevated levels of long-chain free fatty acids in obese mice, which led to cellular lipotoxicity, oxidative stress, and mitochondrial dysfunction. Harnessing the anti-inflammatory properties of these PPARγ+ skin Treg cells could have therapeutic potential for obesity-associated inflammatory skin diseases.

Nicotinamide N-methyltransferase (NNMT) regulates the glucocorticoid signaling pathway during the early phase of adipogenesis

Obesity is associated with adipose tissue dysfunction through the differentiation and expansion of pre-adipocytes to adipocytes (hyperplasia) and/or increases in size of pre-existing adipocytes (hypertrophy). A cascade of transcriptional events coordinates the differentiation of pre-adipocytes into fully differentiated adipocytes; the process of adipogenesis. Although nicotinamide N-methyltransferase (NNMT) has been associated with obesity, how NNMT is regulated during adipogenesis, and the underlying regulatory mechanisms, remain undefined. In present study we used genetic and pharmacological approaches to elucidate the molecular signals driving NNMT activation and its role during adipogenesis. Firstly, we demonstrated that during the early phase of adipocyte differentiation NNMT is transactivated by CCAAT/Enhancer Binding Protein beta (CEBPB) in response to glucocorticoid (GC) induction. We found that Nnmt knockout, using CRISPR/Cas9 approach, impaired terminal adipogenesis by influencing the timing of cellular commitment and cell cycle exit during mitotic clonal expansion, as demonstrated by cell cycle analysis and RNA sequencing experiments. Biochemical and computational methods showed that a novel small molecule, called CC-410, stably binds to and highly specifically inhibits NNMT. CC-410 was, therefore, used to modulate protein activity during pre-adipocyte differentiation stages, demonstrating that, in line with the genetic approach, chemical inhibition of NNMT at the early stages of adipogenesis impairs terminal differentiation by deregulating the GC network. These congruent results conclusively demonstrate that NNMT is a key component of the GC-CEBP axis during the early stages of adipogenesis and could be a potential therapeutic target for both early-onset obesity and glucocorticoid-induced obesity.

Obesity contributes to hepatocellular carcinoma development via immunosuppressive microenvironment remodeling

It is generally recognized that the initiation of obesity-related hepatocellular carcinoma (HCC) is closely associated with hepatic inflammation. However, the paradoxical role of inflammation in the initiation and progression of HCC is highlighted by the fact that the inflammatory HCC is accompanied by significant immune effector cells infiltration compared to non-inflammatory HCC and HCC with enhanced immune response exhibits better survival. Importantly, the cancer progression has been primarily attributed to the immunosuppression, which can also be induced by obesity. Furthermore, the increased risk of viral infection and thus viral-HCC in obese individuals supports the view that obesity contributes to HCC via immunosuppression. Here, we have reviewed the various mechanisms responsible for obesity-induced tumor immune microenvironment and immunosuppression in obesity-related HCC. We highlight that the obesity-induced immunosuppression originates from lipid disorder as well as metabolic reprogramming and propose potential therapeutic strategy for HCC based on the current success of immunotherapy.

Dysregulated systemic metabolism in a Down syndrome mouse model

OBJECTIVE

Trisomy 21 is one of the most complex genetic perturbations compatible with postnatal survival. Dosage imbalance arising from the triplication of genes on human chromosome 21 (Hsa21) affects multiple organ systems. Much of Down syndrome (DS) research, however, has focused on addressing how aneuploidy dysregulates CNS function leading to cognitive deficit. Although obesity, diabetes, and associated sequelae such as fatty liver and dyslipidemia are well documented in the DS population, only limited studies have been conducted to determine how gene dosage imbalance affects whole-body metabolism. Here, we conduct a comprehensive and systematic analysis of key metabolic parameters across different physiological states in the Ts65Dn trisomic mouse model of DS.

METHODS

Ts65Dn mice and euploid littermates were subjected to comprehensive metabolic phenotyping under basal (chow-fed) state and the pathophysiological state of obesity induced by a high-fat diet (HFD). RNA sequencing of liver, skeletal muscle, and two major fat depots were conducted to determine the impact of aneuploidy on tissue transcriptome. Pathway enrichments, gene-centrality, and key driver estimates were performed to provide insights into tissue autonomous and non-autonomous mechanisms contributing to the dysregulation of systemic metabolism.

RESULTS

Under the basal state, chow-fed Ts65Dn mice of both sexes had elevated locomotor activity and energy expenditure, reduced fasting serum cholesterol levels, and mild glucose intolerance. Sexually dimorphic deterioration in metabolic homeostasis became apparent when mice were challenged with a high-fat diet. While obese Ts65Dn mice of both sexes exhibited dyslipidemia, male mice also showed impaired systemic insulin sensitivity, reduced mitochondrial activity, and elevated fibrotic and inflammatory gene signatures in the liver and adipose tissue. Systems-level analysis highlighted conserved pathways and potential endocrine drivers of adipose-liver crosstalk that contribute to dysregulated glucose and lipid metabolism.

CONCLUSIONS

A combined alteration in the expression of trisomic and disomic genes in peripheral tissues contribute to metabolic dysregulations in Ts65Dn mice. These data lay the groundwork for understanding the impact of aneuploidy on in vivo metabolism.

Dendritic cells in energy balance regulation

Besides their well-known role in initiating adaptive immune responses, several groups have studied the role of dendritic cells (DCs) in the context of chronic metabolic inflammation, such as in diet-induced obesity (DIO) or metabolic-associated fatty liver disease. DCs also have an important function in maintaining metabolic tissue homeostasis in steady-state conditions. In this review, we will briefly describe the different DC subsets, the murine models available to assess their function, and discuss the role of DCs in regulating energy balance and maintaining tissue homeostasis.

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.

Extensive Summary of the Important Roles of Indole Propionic Acid, a Gut Microbial Metabolite in Host Health and Disease

Increasing evidence suggests that metabolites produced by the gut microbiota play a crucial role in host-microbe interactions. Dietary tryptophan ingested by the host enters the gut, where indole-like metabolites such as indole propionic acid (IPA) are produced under deamination by commensal bacteria. Here, we summarize the IPA-producing bacteria, dietary patterns on IPA content, and functional roles of IPA in various diseases. IPA can not only stimulate the expression of tight junction (TJ) proteins to enhance gut barrier function and inhibit the penetration of toxic factors, but also modulate the immune system to exert anti-inflammatory and antioxidant effects to synergistically regulate body physiology. Moreover, IPA can act on target organs through blood circulation to form the gut-organ axis, which helps maintain systemic homeostasis. IPA shows great potential for the diagnosis and treatment of various clinical diseases, such as NAFLD, Alzheimer's disease, and breast cancer. However, the therapeutic effect of IPA depends on dose, target organ, or time. In future studies, further work should be performed to explore the effects and mechanisms of IPA on host health and disease to further improve the existing treatment program.

Interferon Family Cytokines in Obesity and Insulin Sensitivity

Obesity and its associated complications are global public health concerns. Metabolic disturbances and immune dysregulation cause adipose tissue stress and dysfunction in obese individuals. Immune cell accumulation in the adipose microenvironment is the main cause of insulin resistance and metabolic dysfunction. Infiltrated immune cells, adipocytes, and stromal cells are all involved in the production of proinflammatory cytokines and chemokines in adipose tissues and affect systemic homeostasis. Interferons (IFNs) are a large family of pleiotropic cytokines that play a pivotal role in host antiviral defenses. IFNs are critical immune modulators in response to pathogens, dead cells, and several inflammation-mediated diseases. Several studies have indicated that IFNs are involved in the pathogenesis of obesity. In this review, we discuss the roles of IFN family cytokines in the development of obesity-induced inflammation and insulin resistance.

Neuroimmune regulation of white adipose tissues

The white adipose tissues (WAT) are located in distinct depots throughout the body. They serve as an energy reserve, providing fatty acids for other tissues via lipolysis when needed, and function as an endocrine organ to regulate systemic metabolism. Their activities are coordinated through intercellular communications among adipocytes and other cell types such as residential and infiltrating immune cells, which are collectively under neuronal control. The adipocytes and immune subtypes including macrophages/monocytes, eosinophils, neutrophils, group 2 innate lymphoid cells (ILC2s), T and B cells, dendritic cells (DCs), and natural killer (NK) cells display cellular and functional diversity in response to the energy states and contribute to metabolic homeostasis and pathological conditions. Accumulating evidence reveals that neuronal innervations control lipid deposition and mobilization via regulating lipolysis, adipocyte size, and cellularity. Vice versa, the neuronal innervations and activity are influenced by cellular factors in the WAT. Though the literature describing adipose tissue cells is too extensive to cover in detail, we strive to highlight a selected list of neuronal and immune components in this review. The cell-to-cell communications and the perspective of neuroimmune regulation are emphasized to enlighten the potential therapeutic opportunities for treating metabolic disorders.

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.

Cytokine and metabolic regulation of adipose tissue Tregs

Since their discovery over a decade ago, much has been learned regarding the importance and function of visceral adipose tissue (VAT)-resident regulatory T cells (Tregs). VAT Tregs play a critical role in controlling VAT inflammation and alleviating metabolic disease. However, this population is disrupted in obesity which exacerbates VAT inflammation and metabolic abnormalities. Therefore, understanding the factors governing the accumulation and maintenance of VAT Tregs, both at steady state and under disease conditions, is crucial for identifying the mechanisms underlying obesity-associated metabolic disease and developing novel therapies. Expansion and maintenance of the VAT Treg compartment is strongly influenced by factors in the local tissue microenvironment, including cytokines, T-cell receptor ligands, hormones, and various metabolites. This mini-review will primarily focus on recent advances in our understandings regarding the regulation of mouse epididymal VAT (eVAT) Tregs, which are the most thoroughly characterized VAT Treg population, by tissue microenvironmental factors and cellular metabolic processes. We will also briefly discuss the limited knowledge available regarding the regulation of mouse ovarian VAT (oVAT) Tregs and human omental VAT Tregs, highlight some lingering questions, and provide a prospective view on where the field is heading.

Adipose Tissue Plasticity in Aging

As a dynamic endocrine organ, white adipose tissue (WAT) stores lipids and plays a critical role in maintaining whole-body energy homeostasis and insulin sensitivity. A large group of the population over 65 years old suffer from increased WAT mass, especially in the visceral location. Visceral adiposity accelerates aging through promoting age-associated chronic conditions, significantly shortening life expectancy. Unlike WAT, brown adipose tissue (BAT) functions as an effective energy sink that burns and disposes of excess lipids and glucose upon activation of thermogenesis. Unfortunately, the thermogenic activity of BAT declines during aging. New appreciation of cellular and functional remodeling of WAT and BAT during aging has emerged in recent years. Efforts are underway to explore the potential underlying mechanisms behind these age-associated alterations in WAT and BAT and the impact of these alterations on whole-body metabolism. Lastly, it is intriguing to translate our knowledge obtained from animal models to the clinic to prevent and treat age-associated metabolic disorders. © 2022 American Physiological Society. Compr Physiol 12: 4119-4132, 2022.

Tregs in visceral adipose tissue up-regulate circadian-clock expression to promote fitness and enforce a diurnal rhythm of lipolysis

Regulatory T cells (Tregs) in nonlymphoid organs provide critical brakes on inflammation and regulate tissue homeostasis. Although so-called "tissue Tregs" are phenotypically and functionally diverse, serving to optimize their performance and survival, up-regulation of pathways related to circadian rhythms is a feature they share. Yet the diurnal regulation of Tregs and its consequences are controversial and poorly understood. Here, we profiled diurnal variations in visceral adipose tissue (VAT) and splenic Tregs in the presence and absence of core-clock genes. VAT, but not splenic, Tregs up-regulated their cell-intrinsic circadian program and exhibited diurnal variations in their activation and metabolic state. BMAL1 deficiency specifically in Tregs led to constitutive activation and poor oxidative metabolism in VAT, but not splenic, Tregs. Disruption of core-clock components resulted in loss of fitness: BMAL1-deficient VAT Tregs were preferentially lost during competitive transfers and in heterozygous TregBmal1Δ females. After 16 weeks of high-fat diet feeding, VAT inflammation was increased in mice harboring BMAL1-deficient Tregs, and the remaining cells lost the transcriptomic signature of bona fide VAT Tregs. Unexpectedly, VAT Tregs suppressed adipocyte lipolysis, and BMAL1 deficiency specifically in Tregs abrogated the characteristic diurnal variation in adipose tissue lipolysis, resulting in enhanced suppression of lipolysis throughout the day. These findings argue for the importance of the cell-intrinsic clock program in optimizing VAT Treg function and fitness.

Obesity in HIV infection: host-pathogen interaction

OBJECTIVE

Both obesity and HIV infection are characterized by a state of chronic inflammation associated with increased morbidity and mortality. This review aims to assess the available literature on immune dysregulation in obesity and people with HIV infection (PWH).

DESIGN

A systematic review of peer-reviewed literature.

METHODS

We conducted a systematic literature search of PubMed, Embase, Scopus, and international conference abstracts for articles on the epidemiology of obesity in the general population and in PWH and the pathogenesis of obesity with a focus on inflammation and immune activation.

RESULTS

Of the 631 articles selected after title review, 490 met the inclusion criteria and 90 were included in the final selection. The selected studies highlight the increasing prevalence of obesity in PWH and a substantial role for antiretroviral treatment (ART) in its development. Pathogenesis of obesity and its associated inflammation derives from disturbances in adipose tissue (AT) immune function, focused on T-cell and macrophage function, with a switch to pro-inflammatory immune phenotype and resulting increases in pro-inflammatory chemokines, which contribute to the development of metabolic syndrome. Although dysregulation of these pathways is seen in both obesity and HIV, there remains a lack of human studies on AT inflammation in HIV.

CONCLUSION

Obesity is an emerging comorbidity in PWH, with a substantial overlap in immune dysregulation patterns seen in both conditions. How this immune dysfunction impacts on development of metabolic complications for both obesity and HIV infection, and whether targeting of AT-derived inflammation will improve outcomes in PWH requires further study.