A Novel Role for Triglyceride Metabolism in Foxp3 Expression

Evolution and global research trends of immunity in diabetic nephropathy: a bibliometric and visual analysis from 2004 to 2023

BACKGROUND

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, with an increasing prevalence worldwide, but its pathomechanisms remain incompletely understood. Accumulating evidence suggests that immunity plays an important role in the development of DN. Many papers have been published in the field over the last 20 years, but there has been no bibliometric review of the research hotspots and trends in the field. This study aimed to assess the current research status and future trends of the link between immune and DN using bibliometric analysis.

METHODS

Publications on the association between immunity and DN from 2004 to 2023 were retrieved from the Web of Science Core Collection database and screened according to inclusion criteria. VOSviewer and CiteSpace software were employed to visualize research trends and hotspots in the field. Data including author, institution, country, journal, reference, and keyword were analyzed.

RESULTS

Ultimately 1246 publications meeting the criteria were included in the bibliometric analysis, involving 838 articles (84.96%) and 408 reviews (15.04%). The literature covered 81 countries and regions, 1751 institutions, and 6584 authors. The top 2 countries in terms of the number of publications were China (435) and the United States (318), and they collaborated most frequently. The United States had the highest number of citations for published papers (18,161), far exceeding the other countries. England had 38 publications but had the highest average number of citations (92.32). The University of California system was the most prolific institution (25 papers, 1062 citations, 42.48 citations per paper). Frontiers in Immunology was the most prolific journal in the field (30 papers). The most cited journal was Kidney International (863 citations). The analysis of keywords and references showed that inflammation, ferroptosis, and lipid metabolism may be future research hotspots in this field.

CONCLUSIONS

The number of publications related to immunity and DN has increased annually over the past 20 years, with a significant increase in the last 3 years especially. Our results identified research hotspots and trends in the field. These findings provide valuable perspectives for future research, enhancing our understanding of the immune-related mechanisms of DN and exploring potential therapeutic strategies.

The immunosuppressive landscape in tumor microenvironment

Recent advances in cancer immunotherapy, especially immune checkpoint inhibitors (ICIs), have revolutionized the clinical outcome of many cancer patients. Despite the fact that impressive progress has been made in recent decades, the response rate remains unsatisfactory, and many patients do not benefit from ICIs. Herein, we summarized advanced studies and the latest insights on immune inhibitory factors in the tumor microenvironment. Our in-depth discussion and updated landscape of tumor immunosuppressive microenvironment may provide new strategies for reversing tumor immune evasion, enhancing the efficacy of ICIs therapy, and ultimately achieving a better clinical outcome.

Deciphering the developmental trajectory of tissue-resident Foxp3+ regulatory T cells

Foxp3+ TREG cells have been at the focus of intense investigation for their recognized roles in preventing autoimmunity, facilitating tissue recuperation following injury, and orchestrating a tolerance to innocuous non-self-antigens. To perform these critical tasks, TREG cells undergo deep epigenetic, transcriptional, and post-transcriptional changes that allow them to adapt to conditions found in tissues both at steady-state and during inflammation. The path leading TREG cells to express these tissue-specialized phenotypes begins during thymic development, and is further driven by epigenetic and transcriptional modifications following TCR engagement and polarizing signals in the periphery. However, this process is highly regulated and requires TREG cells to adopt strategies to avoid losing their regulatory program altogether. Here, we review the origins of tissue-resident TREG cells, from their thymic and peripheral development to the transcriptional regulators involved in their tissue residency program. In addition, we discuss the distinct signalling pathways that engage the inflammatory adaptation of tissue-resident TREG cells, and how they relate to their ability to recognize tissue and pathogen-derived danger signals.

The Role of Neutral Sphingomyelinase-2 (NSM2) in the Control of Neutral Lipid Storage in T Cells

The accumulation of lipid droplets (LDs) and ceramides (Cer) is linked to non-alcoholic fatty liver disease (NAFLD), regularly co-existing with type 2 diabetes and decreased immune function. Chronic inflammation and increased disease severity in viral infections are the hallmarks of the obesity-related immunopathology. The upregulation of neutral sphingomyelinase-2 (NSM2) has shown to be associated with the pathology of obesity in tissues. Nevertheless, the role of sphingolipids and specifically of NSM2 in the regulation of immune cell response to a fatty acid (FA) rich environment is poorly studied. Here, we identified the presence of the LD marker protein perilipin 3 (PLIN3) in the intracellular nano-environment of NSM2 using the ascorbate peroxidase APEX2-catalyzed proximity-dependent biotin labeling method. In line with this, super-resolution structured illumination microscopy (SIM) shows NSM2 and PLIN3 co-localization in LD organelles in the presence of increased extracellular concentrations of oleic acid (OA). Furthermore, the association of enzymatically active NSM2 with isolated LDs correlates with increased Cer levels in these lipid storage organelles. NSM2 enzymatic activity is not required for NSM2 association with LDs, but negatively affects the LD numbers and cellular accumulation of long-chain unsaturated triacylglycerol (TAG) species. Concurrently, NSM2 expression promotes mitochondrial respiration and fatty acid oxidation (FAO) in response to increased OA levels, thereby shifting cells to a high energetic state. Importantly, endogenous NSM2 activity is crucial for primary human CD4+ T cell survival and proliferation in a FA rich environment. To conclude, our study shows a novel NSM2 intracellular localization to LDs and the role of enzymatically active NSM2 in metabolic response to enhanced FA concentrations in T cells.

Zfp335 establishes eTreg lineage and neonatal immune tolerance by targeting Hadha-mediated fatty acid oxidation

Regulatory T cells (Tregs) are instrumental in maintaining immune tolerance and preventing destructive autoimmunity, but how heterogeneous Treg populations are established remains largely unknown. Here, we show that Zfp335 deletion in Tregs failed to differentiate into effector Tregs (eTregs) and lose Treg-suppressive function and that KO mice exhibited early-onset lethal autoimmune inflammation with unrestricted activation of conventional T cells. Single-cell RNA-Seq analyses revealed that Zfp335-deficient Tregs lacked a eTreg population and showed dramatic accumulation of a dysfunctional Treg subset. Mechanistically, Zfp335-deficient Tregs displayed reduced oxidative phosphorylation and dysfunctional mitochondrial activity. Further studies revealed that Zfp335 controlled eTreg differentiation by regulating fatty acid oxidation (FAO) through direct targeting of the FAO enzyme Hadha. Importantly, we demonstrate a positive correlation between ZNF335 and HADHA expression in human eTregs. Our findings reveal that Zfp335 controls FAO-driven eTreg differentiation to establish immune tolerance.

Platelet-Derived Extracellular Vesicles as Lipid Carriers in Severe Allergic Inflammation

The resolution of inflammation is a complex process that is critical for removing inflammatory cells and restoring tissue function. The dysregulation of these mechanisms leads to chronic inflammatory disorders. Platelets, essential cells for preserving homeostasis, are thought to play a role in inflammation as they are a source of immunomodulatory factors. Our aim was to identify key metabolites carried by platelet-derived extracellular vesicles (PL-EVs) in a model of allergic inflammation. PL-EVs were isolated by serial ultracentrifugation using platelet-rich plasma samples obtained from platelet apheresis from severely (n = 6) and mildly (n = 6) allergic patients and non-allergic individuals used as controls (n = 8). PL-EVs were analysed by a multiplatform approach using liquid and gas chromatography coupled to mass spectrometry (LC-MS and GC-MS, respectively). PL-EVs obtained from severely and mildly allergic patients and control individuals presented comparable particle concentrations and sizes with similar protein concentrations. Strikingly, PL-EVs differed in their lipid and metabolic content according to the severity of inflammation. L-carnitine, ceramide (Cer (d18:0/24:0)), and several triglycerides, all of which seem to be involved in apoptosis and regulatory T functions, were higher in PL-EVs from patients with mild allergic inflammation than in those with severe inflammation. In contrast, PL-EVs obtained from patients with severe allergic inflammation showed an alteration in the arachidonic acid pathway. This study demonstrates that PL-EVs carry specific lipids and metabolites according to the degree of inflammation in allergic patients and propose novel perspectives for characterising the progression of allergic inflammation.

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.

Nasopharyngeal carcinoma cells promote regulatory T cell development and suppressive activity via CD70-CD27 interaction

Despite the intense CD8+ T-cell infiltration in the tumor microenvironment of nasopharyngeal carcinoma, anti-PD-1 immunotherapy shows an unsatisfactory response rate in clinical trials, hindered by immunosuppressive signals. To understand how microenvironmental characteristics alter immune homeostasis and limit immunotherapy efficacy in nasopharyngeal carcinoma, here we establish a multi-center single-cell cohort based on public data, containing 357,206 cells from 50 patient samples. We reveal that nasopharyngeal carcinoma cells enhance development and suppressive activity of regulatory T cells via CD70-CD27 interaction. CD70 blocking reverts Treg-mediated suppression and thus reinvigorate CD8+ T-cell immunity. Anti-CD70+ anti-PD-1 therapy is evaluated in xenograft-derived organoids and humanized mice, exhibiting an improved tumor-killing efficacy. Mechanistically, CD70 knockout inhibits a collective lipid signaling network in CD4+ naïve and regulatory T cells involving mitochondrial integrity, cholesterol homeostasis, and fatty acid metabolism. Furthermore, ATAC-Seq delineates that CD70 is transcriptionally upregulated by NFKB2 via an Epstein-Barr virus-dependent epigenetic modification. Our findings identify CD70+ nasopharyngeal carcinoma cells as a metabolic switch that enforces the lipid-driven development, functional specialization and homeostasis of Tregs, leading to immune evasion. This study also demonstrates that CD70 blockade can act synergistically with anti-PD-1 treatment to reinvigorate T-cell immunity against nasopharyngeal carcinoma.

T regulatory cells metabolism: The influence on functional properties and treatment potential

CD4+CD25highFoxP3+ regulatory T cells (Tregs) constitute a small but substantial fraction of lymphocytes in the immune system. Tregs control inflammation associated with infections but also when it is improperly directed against its tissues or cells. The ability of Tregs to suppress (inhibit) the immune system is possible due to direct interactions with other cells but also in a paracrine fashion via the secretion of suppressive compounds. Today, attempts are made to use Tregs to treat autoimmune diseases, allergies, and rejection after bone marrow or organ transplantation. There is strong evidence that the metabolic program of Tregs is connected with the phenotype and function of these cells. A modulation towards a particular metabolic stage of Tregs may improve or weaken cells’ stability and function. This may be an essential tool to drive the immune system keeping it activated during infections or suppressed when autoimmunity occurs.

G9a Modulates Lipid Metabolism in CD4 T Cells to Regulate Intestinal Inflammation

BACKGROUND & AIMS

Although T-cell intrinsic expression of G9a has been associated with murine intestinal inflammation, mechanistic insight into the role of this methyltransferase in human T-cell differentiation is ill defined, and manipulation of G9a function for therapeutic use against inflammatory disorders is unexplored.

METHODS

Human naive T cells were isolated from peripheral blood and differentiated in vitro in the presence of a G9a inhibitor (UNC0642) before being characterized via the transcriptome (RNA sequencing), chromatin accessibility (assay for transposase-accessible chromatin by sequencing), protein expression (cytometry by time of flight, flow cytometry), metabolism (mitochondrial stress test, ultrahigh performance liquid chromatography-tandem mas spectroscopy) and function (T-cell suppression assay). The in vivo role of G9a was assessed using 3 murine models.

RESULTS

We discovered that pharmacologic inhibition of G9a enzymatic function in human CD4 T cells led to spontaneous generation of FOXP3+ T cells (G9a-inibitors-T regulatory cells [Tregs]) in vitro that faithfully reproduce human Tregs, functionally and phenotypically. Mechanistically, G9a inhibition altered the transcriptional regulation of genes involved in lipid biosynthesis in T cells, resulting in increased intracellular cholesterol. Metabolomic profiling of G9a-inibitors-Tregs confirmed elevated lipid pathways that support Treg development through oxidative phosphorylation and enhanced lipid membrane composition. Pharmacologic G9a inhibition promoted Treg expansion in vivo upon antigen (gliadin) stimulation and ameliorated acute trinitrobenzene sulfonic acid-induced colitis secondary to tissue-specific Treg development. Finally, Tregs lacking G9a expression (G9a-knockout Tregs) remain functional chronically and can rescue T-cell transfer-induced colitis.

CONCLUSION

G9a inhibition promotes cholesterol metabolism in T cells, favoring a metabolic profile that facilitates Treg development in vitro and in vivo. Our data support the potential use of G9a inhibitors in the treatment of immune-mediated conditions including inflammatory bowel disease.

The role of metabolism on regulatory T cell development and its impact in tumor and transplantation immunity

Regulatory CD4⁺ T (Treg) cells play a key role in the induction of immune tolerance and in the prevention of autoimmune diseases. Treg cells are defined by the expression of transcription factor FOXP3, which ensures proliferation and induction of the suppressor activity of this cell population. In a tumor microenvironment, after transplantation or during autoimmune diseases, Treg cells can respond to various signals from their environment and this property ensures their suppressor function. Recent studies showed that a metabolic signaling pathway of Treg cells are essential in the control of Treg cell proliferation processes. This review presents the latest research highlights on how the influence of extracellular factors (e.g. nutrients, vitamins and metabolites) as well as intracellular metabolic signaling pathways regulate tissue specificity of Treg cells and heterogeneity of this cell population. Understanding the metabolic regulation of Treg cells should provide new insights into immune homeostasis and disorders along with important therapeutic implications for autoimmune diseases, cancer and other immune-system-mediated disorders.

ANGPTL3 deficiency associates with the expansion of regulatory T cells with reduced lipid content

BACKGROUND AND AIMS

Angiopoietin-like 3 (ANGPTL3) regulates lipid and glucose metabolism. Loss-of-function mutations in its gene, leading to ANGPTL3 deficiency, cause in humans the familial combined hypolipidemia type 2 (FHBL2) phenotype, characterized by very low concentrations of circulating lipoproteins and reduced risk of atherosclerotic cardiovascular disease. Whether this condition is accompanied by immune dysfunctions is unknown. Regulatory T cells (Tregs) are CD4 T lymphocytes endowed with immune suppressive and atheroprotective functions and sensitive to metabolic signals. By investigating FHBL2, we explored the hypothesis that Tregs expand in response to extreme hypolipidemia, through a modulation of the Treg-intrinsic lipid metabolism.

METHODS

Treg frequency, phenotype, and intracellular lipid content were assessed ex vivo from FHBL2 subjects and age- and sex-matched controls, through multiparameter flow cytometry. The response of CD4 T cells from healthy controls to marked hypolipidemia was tested in vitro in low-lipid culture conditions.

RESULTS

The ex vivo analysis revealed that FHBL2 subjects showed higher percentages of Tregs with a phenotype undistinguishable from controls and with a lower lipid content, which directly correlated with the concentrations of circulating lipoproteins. In vitro, lipid restriction induced the upregulation of genes of the mevalonate pathway, including those involved in isoprenoid biosynthesis, and concurrently increased the expression of the Treg markers FOXP3 and Helios. The latter event was found to be prenylation-dependent, and likely related to increased IL-2 production and signaling.

CONCLUSIONS

Our study demonstrates that FHBL2 is characterized by high Treg frequencies, a feature which may concur to the reduced atherosclerotic risk in this condition. Mechanistically, hypolipidemia may directly favor Treg expansion, through the induction of the mevalonate pathway and the prenylation of key signaling proteins.

Regulatory T cells as metabolic sensors

Compelling experimental evidence links immunity and metabolism. In this perspective, we propose forkhead-box-P3 (FoxP3)⁺CD4⁺CD25⁺ regulatory T (Treg) cells as key metabolic sensors controlling the immunological state in response to their intrinsic capacity to perceive nutritional changes. Treg cell high anabolic state in vivo, residency in metabolically crucial districts, and recirculation between lymphoid and non-lymphoid sites enable them to recognize the metabolic cues and adapt their intracellular metabolism and anti-inflammatory function at the paracrine and systemic levels. As privileged regulators at the interface between neuroendocrine and immune systems, the role of Treg cells in maintaining metabolic homeostasis makes these cells promising targets of therapeutic strategies aimed at restoring organismal homeostasis not only in autoimmune but also metabolic disorders.

Metabolomic and transcriptomic signatures of influenza vaccine response in healthy young and older adults

Seasonal influenza causes mild to severe respiratory infections and significant morbidity, especially in older adults. Transcriptomic analysis in populations across multiple flu seasons has provided insights into the molecular determinants of vaccine response. Still, the metabolic changes that underlie the immune response to influenza vaccination remain poorly characterized. We performed untargeted metabolomics to analyze plasma metabolites in a cohort of younger and older subjects before and after influenza vaccination to identify vaccine-induced molecular signatures. Metabolomic and transcriptomic data were combined to define networks of gene and metabolic signatures indicative of high and low antibody response in these individuals. We observed age-related differences in metabolic baselines and signatures of antibody response to influenza vaccination and the abundance of α-linolenic and linoleic acids, sterol esters, fatty-acylcarnitines, and triacylglycerol metabolism. We identified a metabolomic signature associated with age-dependent vaccine response, finding increased tryptophan and decreased polyunsaturated fatty acids (PUFAs) in young high responders (HRs), while fatty acid synthesis and cholesteryl esters accumulated in older HRs. Integrated metabolomic and transcriptomic analysis shows that depletion of PUFAs, which are building blocks for prostaglandins and other lipid immunomodulators, in young HR subjects at Day 28 is related to a robust immune response to influenza vaccination. Increased glycerophospholipid levels were associated with an inflammatory response in older HRs to flu vaccination. This multi-omics approach uncovered age-related molecular markers associated with influenza vaccine response and provides insight into vaccine-induced metabolic responses that may help guide development of more effective influenza vaccines.

pH sensing controls tissue inflammation by modulating cellular metabolism and endo-lysosomal function of immune cells

Extracellular acidification occurs in inflamed tissue and the tumor microenvironment; however, a systematic study on how pH sensing contributes to tissue homeostasis is lacking. In the present study, we examine cell type-specific roles of the pH sensor G protein-coupled receptor 65 (GPR65) and its inflammatory disease-associated Ile231Leu-coding variant in inflammation control. GPR65 Ile231Leu knock-in mice are highly susceptible to both bacterial infection-induced and T cell-driven colitis. Mechanistically, GPR65 Ile231Leu elicits a cytokine imbalance through impaired helper type 17 T cell (TH17 cell) and TH22 cell differentiation and interleukin (IL)-22 production in association with altered cellular metabolism controlled through the cAMP-CREB-DGAT1 axis. In dendritic cells, GPR65 Ile231Leu elevates IL-12 and IL-23 release at acidic pH and alters endo-lysosomal fusion and degradation capacity, resulting in enhanced antigen presentation. The present study highlights GPR65 Ile231Leu as a multistep risk factor in intestinal inflammation and illuminates a mechanism by which pH sensing controls inflammatory circuits and tissue homeostasis.

Therapeutic opportunities to modulate immune tolerance through the metabolism-chromatin axis

The ability of the immune system to discriminate external stimuli from self-components - namely immune tolerance - occurs through a coordinated cascade of events involving a dense network of immune cells. Among them, CD4⁺CD25⁺ T regulatory cells are crucial to balance immune homeostasis and function. Growing evidence supports the notion that energy metabolites can dictate T cell fate and function via epigenetic modifications, which affect gene expression without altering the DNA sequence. Moreover, changes in cellular metabolism couple with activation of immune pathways and epigenetic remodeling to finely tune the balance between T cell activation and tolerance. This Review summarizes these aspects and critically evaluates novel possibilities for developing therapeutic strategies to modulate immune tolerance through metabolism via epigenetic drugs.

A Deep Insight Into Regulatory T Cell Metabolism in Renal Disease: Facts and Perspectives

Kidney disease encompasses a complex set of diseases that can aggravate or start systemic pathophysiological processes through their complex metabolic mechanisms and effects on body homoeostasis. The prevalence of kidney disease has increased dramatically over the last two decades. CD4⁺CD25⁺ regulatory T (Treg) cells that express the transcription factor forkhead box protein 3 (Foxp3) are critical for maintaining immune homeostasis and preventing autoimmune disease and tissue damage caused by excessive or unnecessary immune activation, including autoimmune kidney diseases. Recent studies have highlighted the critical role of metabolic reprogramming in controlling the plasticity, stability, and function of Treg cells. They are also likely to play a vital role in limiting kidney transplant rejection and potentially promoting transplant tolerance. Metabolic pathways, such as mitochondrial function, glycolysis, lipid synthesis, glutaminolysis, and mammalian target of rapamycin (mTOR) activation, are involved in the development of renal diseases by modulating the function and proliferation of Treg cells. Targeting metabolic pathways to alter Treg cells can offer a promising method for renal disease therapy. In this review, we provide a new perspective on the role of Treg cell metabolism in renal diseases by presenting the renal microenvironment、relevant metabolites of Treg cell metabolism, and the role of Treg cell metabolism in various kidney diseases.

Lipid metabolism in T cell signaling and function

T cells orchestrate adaptive immunity against pathogens and other immune challenges, but their dysfunction can also mediate the pathogenesis of cancer and autoimmunity. Metabolic adaptation in response to immunological and microenvironmental signals contributes to T cell function and fate decision. Lipid metabolism has emerged as a key regulator of T cell responses, with selective lipid metabolites serving as metabolic rheostats to integrate environmental cues and interplay with intracellular signaling processes. Here, we discuss how extracellular, de novo synthesized and membrane lipids orchestrate T cell biology. We also describe the roles of lipids as regulators of intracellular signaling at the levels of transcriptional, epigenetic and post-translational regulation in T cells. Finally, we summarize therapeutic targeting of lipid metabolism and signaling, and conclude with a discussion of important future directions. Understanding the molecular and functional interplay between lipid metabolism and T cell biology will ultimately inform therapeutic intervention for human disease.

Favorable Genotypes of Type III Interferon Confer Risk of Dyslipidemia in the Population With Obesity

BACKGROUND

Studies have indicated that the chronic state of inflammation caused by obesity leads to dyslipidemia. However, how the polymorphisms involved in these inflammatory pathways affect the lipid metabolism in people with obesity is poorly understood. We investigated the associations of inflammation-related gene polymorphisms with dyslipidemia in individuals with obesity living in China.

METHODS

This case-control study in a population with obesity involved 194 individuals with dyslipidemia and 103 individuals without dyslipidemia. Anthropometric indices of obesity, fasting plasma glucose, blood pressure, blood lipids, and C-reactive protein were evaluated. The genes we tested were IL6 (interleukin 6), IL6R (interleukin 6 receptor), FOXP3 (forkhead box P3), TLR2 (toll-like receptor 2), TLR4 (toll-like receptor 4), IFNL3 (interferon lambda 3, formerly known as IL28B), and IFNL4 (interferon lambda 4, formerly known as IL29). Polymorphisms were genotyped using matrix-assisted laser desorption/ionization-time of flight mass spectrometry.

RESULTS

There were significant differences in the allelic and genotype frequencies of IFNL3 (IL28B) rs12971396, rs8099917, rs11882871, rs12979860, rs4803217 between non-dyslipidemia and dyslipidemia groups in people with obesity. These single nucleotide polymorphisms (SNPs) of IFNL3 were highly linked (D' and r > 0.90), so the result of one SNP could represent the result of other SNPs. For IFNL3 rs12971396, people with the homozygous genotype (the major group) carried a higher risk of dyslipidemia than people with the heterozygous genotype (P < 0.001, OR = 4.46, 95%CI, 1.95-10.22).

CONCLUSIONS

The favorable genotypes of type III interferon, which have a beneficial role in anti-virus function, were associated with dyslipidemia in a Chinese population with obesity. Type III interferon could have a pathologic role and confer risk of dyslipidemia in people with obesity and chronic inflammation.

Obesity and adipose tissue impact on T-cell response and cancer immune checkpoint blockade therapy

Many different types of cancer are now well known to have increased occurrence or severity in individuals with obesity. The influence of obesity on cancer and the immune cells in the tumor microenvironment has been thought to be a pleiotropic effect. As key endocrine and immune organs, the highly plastic adipose tissues play crucial roles in obesity pathophysiology, as they show alterations according to environmental cues. Adipose tissues of lean subjects present mostly anti-inflammatory cells that are crucial in tissue remodeling, favoring uncoupling protein 1 expression and non-shivering thermogenesis. Oppositely, obese adipose tissues display massive proinflammatory immune cell infiltration, dying adipocytes, and enhanced crown-like structure formation. In this review, we discuss how obesity can lead to derangements and dysfunctions in antitumor CD8+ T lymphocytes dysfunction. Moreover, we explain how obesity can affect the efficiency of cancer immunotherapy, depicting the mechanisms involved in this process. Cancer immunotherapy management includes monoclonal antibodies targeting the immune checkpoint blockade. Exhausted CD8+ T lymphocytes show elevated programmed cell death-1 (PD-1) expression and highly glycolytic tumors tend to show a good response to anti-PD-1/PD-L1 immunotherapy. Although obesity is a risk factor for the development of several neoplasms and is linked with increased tumor growth and aggressiveness, obesity is also related to improved response to cancer immunotherapy, a phenomenon called the obesity paradox. However, patients affected by obesity present higher incidences of adverse events related to this therapy. These limitations highlight the necessity of a deeper investigation of factors that influence the obesity paradox to improve the application of these therapies.

The role of lipid metabolism in shaping the expansion and the function of regulatory T cells

Metabolic inflammation, defined as a chronic low-grade inflammation, is implicated in numerous metabolic diseases. In recent years, the role of regulatory T cells (Tregs) as key controllers of metabolic inflammation has emerged, but our comprehension on how different metabolic pathways influence Treg functions needs a deeper understanding. Here we focus on how circulating and intracellular lipid metabolism, in particular cholesterol metabolism, regulates Treg homeostasis, expansion, and functions. Cholesterol is carried through the bloodstream by circulating lipoproteins (chylomicrons, very low-density lipoproteins, low-density lipoproteins). Tregs are equipped with a wide array of metabolic sensors able to perceive and respond to changes in the lipid environment through the activation of different intracellular pathways thus conferring to these cells a crucial metabolic and functional plasticity. Nevertheless, altered cholesterol transport, as observed in genetic dyslipidemias and atherosclerosis, impairs Treg proliferation and function through defective cellular metabolism. The intracellular pathway devoted to the cholesterol synthesis is the mevalonate pathway and several studies have shown that this pathway is essential for Treg stability and suppressive activity. High cholesterol concentrations in the extracellular environment may induce massive accumulation of cholesterol inside the cell thus impairing nutrients sensors and inhibiting the mevalonate pathway. This review summarizes the current knowledge regarding the role of circulating and cellular cholesterol metabolism in the regulation of Treg metabolism and functions. In particular, we will discuss how different pathological conditions affecting cholesterol transport may affect cellular metabolism in Tregs.

Lipid Droplets, the Central Hub Integrating Cell Metabolism and the Immune System

Lipid droplets (LDs) are commonly found in various biological cells and are organelles related to cell metabolism. LDs, the number and size of which are heterogeneous across cell type, are primarily composed of polar lipids and proteins on the surface with neutral lipids in the core. Neutral lipids stored in LDs can be degraded by lipolysis and lipophagocytosis, which are regulated by various proteins. The process of LD formation can be summarized in four steps. In addition to energy production, LDs play an extremely pivotal role in a variety of physiological and pathological processes, such as endoplasmic reticulum stress, lipid toxicity, storage of fat-soluble vitamins, regulation of oxidative stress, and reprogramming of cell metabolism. Interestingly, LDs, the hub of integration between metabolism and the immune system, are involved in antitumor immunity, anti-infective immunity (viruses, bacteria, parasites, etc.) and some metabolic immune diseases. Herein, we summarize the role of LDs in several major immune cells as elucidated in recent years, including T cells, dendritic cells, macrophages, mast cells, and neutrophils. Additionally, we analyze the role of the interaction between LDs and immune cells in two typical metabolic immune diseases: atherosclerosis and Mycobacterium tuberculosis infection.

The potential targets in immunotherapy of atherosclerosis

Cardiovascular disease is the most common cause of death, which has the highest mortality rate worldwide. Although a diverse range of inflammatory diseases can affect the cardiovascular system, however, heart failure and stroke occur due to atherosclerosis. Atherosclerosis is a chronic autoinflammatory disease of small to large vessels in which different immune mediators are involved in lipid plaque formation and inflammatory vascular remodeling process. A better understanding of the pathophysiology of atherosclerosis may lead to uncovering immunomodulatory therapies. Despite present diagnostic and therapeutic methods, the lack of immunotherapy in the prevention and treatment of atherosclerosis is perceptible. In this review, we will discuss the promising immunological-based therapeutics and novel preventive approaches for atherosclerosis. This study could provide new insights into a better perception of targeted therapeutic pathways and biological therapies.

Regulatory T cell differentiation is controlled by αKG-induced alterations in mitochondrial metabolism and lipid homeostasis

Suppressive regulatory T cell (Treg) differentiation is controlled by diverse immunometabolic signaling pathways and intracellular metabolites. Here we show that cell-permeable α-ketoglutarate (αKG) alters the DNA methylation profile of naive CD4 T cells activated under Treg polarizing conditions, markedly attenuating FoxP3+ Treg differentiation and increasing inflammatory cytokines. Adoptive transfer of these T cells into tumor-bearing mice results in enhanced tumor infiltration, decreased FoxP3 expression, and delayed tumor growth. Mechanistically, αKG leads to an energetic state that is reprogrammed toward a mitochondrial metabolism, with increased oxidative phosphorylation and expression of mitochondrial complex enzymes. Furthermore, carbons from ectopic αKG are directly utilized in the generation of fatty acids, associated with lipidome remodeling and increased triacylglyceride stores. Notably, inhibition of either mitochondrial complex II or DGAT2-mediated triacylglyceride synthesis restores Treg differentiation and decreases the αKG-induced inflammatory phenotype. Thus, we identify a crosstalk between αKG, mitochondrial metabolism and triacylglyceride synthesis that controls Treg fate.

Effect of Intralipid infusion on peripheral blood T cells and plasma cytokines in women undergoing assisted reproduction treatment

Objectives

Intravenous infusion of Intralipid is an adjunct therapy in assisted reproduction treatment (ART) when immune‐associated infertility is suspected. Here, we evaluated the effect of Intralipid infusion on regulatory T cells (Treg cells), effector T cells and plasma cytokines in peripheral blood of women undertaking IVF.

Methods

This prospective, observational pilot study assessed Intralipid infusion in 14 women exhibiting recurrent implantation failure, a clinical sign of immune‐associated infertility. Peripheral blood was collected immediately prior to and 7 days after intravenous administration of Intralipid. Plasma cytokines were measured by Luminex, and T‐cell subsets were analysed by flow cytometry.

Results

A small increase in conventional CD8⁺ T cells occurred after Intralipid infusion, but no change was seen in CD4⁺ Treg cells, or naïve, memory or effector memory T cells. Proliferation marker Ki67, transcription factors Tbet and RORγt, and markers of suppressive capacity CTLA4 and HLA‐DR were unchanged. Dimensionality‐reduction analysis using the tSNE algorithm confirmed no phenotype shift within Treg cells or other T cells. Intralipid infusion increased plasma CCL2, CCL3, CXCL8, GM‐CSF, G‐CSF, IL‐6, IL‐21, TNF and VEGF.

Conclusion

Intralipid infusion elicited elevated pro‐inflammatory cytokines, and a minor increase in CD8⁺ T cells, but no change in pro‐tolerogenic Treg cells. Notwithstanding the limitation of no placebo control, the results do not support Intralipid as a candidate intervention to attenuate the Treg cell response in women undergoing ART. Future placebo‐controlled studies are needed to confirm the potential efficacy and clinical significance of Intralipid in attenuating cytokine induction and circulating CD8⁺ T cells.

LXR directly regulates glycosphingolipid synthesis and affects human CD4+ T cell function

The liver X receptor (LXR) is a key transcriptional regulator of cholesterol, fatty acid, and phospholipid metabolism. Dynamic remodeling of immunometabolic pathways, including lipid metabolism, is a crucial step in T cell activation. Here, we explored the role of LXR-regulated metabolic processes in primary human CD4⁺ T cells and their role in controlling plasma membrane lipids (glycosphingolipids and cholesterol), which strongly influence T cell immune signaling and function. Crucially, we identified the glycosphingolipid biosynthesis enzyme glucosylceramide synthase as a direct transcriptional LXR target. LXR activation by agonist GW3965 or endogenous oxysterol ligands significantly altered the glycosphingolipid:cholesterol balance in the plasma membrane by increasing glycosphingolipid levels and reducing cholesterol. Consequently, LXR activation lowered plasma membrane lipid order (stability), and an LXR antagonist could block this effect. LXR stimulation also reduced lipid order at the immune synapse and accelerated activation of proximal T cell signaling molecules. Ultimately, LXR activation dampened proinflammatory T cell function. Finally, compared with responder T cells, regulatory T cells had a distinct pattern of LXR target gene expression corresponding to reduced lipid order. This suggests LXR-driven lipid metabolism could contribute to functional specialization of these T cell subsets. Overall, we report a mode of action for LXR in T cells involving the regulation of glycosphingolipid and cholesterol metabolism and demonstrate its relevance in modulating T cell function.

Regulatory T cells and transplantation tolerance: Emerging from the darkness?

The field of tissue transplantation has revolutionized the treatment of patients with failing organs. Its success, thus far, has depended on combinations of immunosuppressive drugs that damp host immunity, while also imposing numerous unwanted side-effects. There is a longstanding recognition that better treatment outcomes, will come from replacing these drugs, fully or in part, by taking advantage of tractable physiological mechanisms of self-tolerance. The past 50 years have seen many advances in the field of self-tolerance, but perhaps, the most tractable of these has been the more recent discovery of a subset T-cells (Treg) whose role is to regulate or damp immunity. This article is intended to first provide the reader with some historical background to explain why we have been slow to identify these cells, despite numerous clues to their existence, and also to indicate how little we know about how they achieve their regulatory function in averting transplant rejection. However, as is often the case in immunology, the therapeutic needs often dictate that our advances move to translation even before detailed explanations of the science are available. The final part of the article will briefly summarize how Treg are being harnessed as agents to interface with or perhaps, replace current drug combinations.

BATF Regulates T Regulatory Cell Functional Specification and Fitness of Triglyceride Metabolism in Restraining Allergic Responses

Preserving appropriate function and metabolism in regulatory T (Treg) cells is crucial for controlling immune tolerance and inflammatory responses. Yet how Treg cells coordinate cellular metabolic programs to support their functional specification remains elusive. In this study, we report that BATF couples the T_H2-suppressive function and triglyceride (TG) metabolism in Treg cells for controlling allergic airway inflammation and IgE responses. Mice with Treg-specific ablation of BATF developed an inflammatory disorder characterized by T_H2-type dominant responses and were predisposed to house dust mite-induced airway inflammation. Loss of BATF enabled Treg cells to acquire T_H2 cell-like characteristics. Moreover, BATF-deficient Treg cells displayed elevated levels of cellular TGs, and repressing or elevating TGs, respectively, restored or exacerbated their defects. Mechanistically, TCR/CD28 costimulation enhanced expression and function of BATF, which sustained IRF4 activity to preserve Treg cell functionality. Thus, our studies reveal that BATF links Treg cell functional specification and fitness of cellular TGs to control allergic responses, and suggest that therapeutic targeting of TG metabolism could be used for the treatment of allergic disease.

Tissue Nutrient Environments and Their Effect on Regulatory T Cell Biology

Regulatory T cells (Tregs) are essential for mitigating inflammation. Tregs are found in nearly every tissue and play either beneficial or harmful roles in the host. The availability of various nutrients can either enhance or impair Treg function. Mitochondrial oxidative metabolism plays a major role in supporting Treg differentiation and fitness. While Tregs rely heavily on oxidation of fatty acids to support mitochondrial activity, they have found ways to adapt to different tissue types, such as tumors, to survive in competitive environments. In addition, metabolic by-products from commensal organisms in the gut also have a profound impact on Treg differentiation. In this review, we will focus on the core metabolic pathways engaged in Tregs, especially in the context of tissue nutrient environments, and how they can affect Treg function, stability and differentiation.

Regulatory T cell metabolism at the intersection between autoimmune diseases and cancer

Regulatory T cells (Tregs) are critical for peripheral immune tolerance and homeostasis, and altered Treg behavior is involved in many pathologies, including autoimmunity and cancer. The expression of the transcription factor FoxP3 in Tregs is fundamental to maintaining their stability and immunosuppressive function. Recent studies have highlighted the crucial role that metabolic reprogramming plays in controlling Treg plasticity, stability, and function. In this review, we summarize how the availability and use of various nutrients and metabolites influence Treg metabolic pathways and activity. We also discuss how Treg-intrinsic metabolic programs define and shape their differentiation, FoxP3 expression, and suppressive capacity. Lastly, we explore how manipulating the regulation of Treg metabolism might be exploited in different disease settings to achieve novel immunotherapies.

Mechanisms of TREG cell adaptation to inflammation

Inflammation is an important defense mechanism. In this complex and dynamic process, drastic changes in the tissue micro-environment play key roles in dictating the nature of the evolving immune response. However, uncontrolled inflammation is detrimental, leading to unwanted cellular damage, loss of physiological functions, and even death. As such, the immune system possesses tools to limit inflammation while ensuring rapid and effective clearance of the inflammatory trigger. Foxp3⁺ regulatory T (T_REG ) cells, a potently immunosuppressive CD4⁺ T cell subset, play a crucial role in immune tolerance by controlling the extent of the response to self and non-self Ags, all-the-while promoting a quick return to immune homeostasis. T_REG cells adapt to changes in the local micro-environment enabling them to migrate, proliferate, survive, differentiate, and tailor their suppressive ability at inflamed sites. Several inflammation-associated factors can impact T_REG cell functional adaptation in situ including locally released alarmins, oxygen availability, tissue acidity and osmolarity and nutrient availability. Here, we review some of these key signals and pathways that control the adaptation of T_REG cell function in inflammatory settings.