Peroxisome proliferator-activated receptor α and γ agonists together with TGF-β convert human CD4+CD25- T cells into functional Foxp3+ regulatory T cells

Abnormal energy metabolism in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease with significant socioeconomic impact worldwide. Orderly energy metabolism is essential for normal immune function, and disordered energy metabolism is increasingly recognized as an important contributor to the pathogenesis of SLE. Disorders of energy metabolism are characterized by increased reactive oxygen species, ATP deficiency, and abnormal metabolic pathways. Oxygen and mitochondria are critical for the production of ATP, and both mitochondrial dysfunction and hypoxia affect the energy production processes. In addition, several signaling pathways, including mammalian target of rapamycin (mTOR)/adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling and the hypoxia-inducible factor (HIF) pathway also play important regulatory roles in energy metabolism. Furthermore, drugs with clear clinical effects on SLE, such as sirolimus, metformin, and tacrolimus, have been proven to improve the disordered energy metabolism of immune cells, suggesting the potential of targeting energy metabolism for the treatment of SLE. Moreover, several metabolic modulators under investigation are expected to have potential therapeutic effects in SLE. This review aimed to gain insights into the role and mechanism of abnormal energy metabolism in the pathogenesis of SLE, and summarizes the progression of metabolic modulator in the treatment of SLE.

Roles of PPAR activation in cancer therapeutic resistance: Implications for combination therapy and drug development

Therapeutic resistance is a major obstacle to successful treatment or effective containment of cancer. Peroxisome proliferator-activated receptors (PPARs) play an essential role in regulating energy homeostasis and determining cell fate. Despite of the pleiotropic roles of PPARs in cancer, numerous studies have suggested their intricate relationship with therapeutic resistance in cancer. In this review, we provided an overview of the roles of excessively activated PPARs in promoting resistance to modern anti-cancer treatments, including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. The mechanisms through which activated PPARs contribute to therapeutic resistance in most cases include metabolic reprogramming, anti-oxidant defense, anti-apoptosis signaling, proliferation-promoting pathways, and induction of an immunosuppressive tumor microenvironment. In addition, we discussed the mechanisms through which activated PPARs lead to multidrug resistance in cancer, including drug efflux, epithelial-to-mesenchymal transition, and acquisition and maintenance of the cancer stem cell phenotype. Preliminary studies investigating the effect of combination therapies with PPAR antagonists have suggested the potential of these antagonists in reversing resistance and facilitating sustained cancer management. These findings will provide a valuable reference for further research on and clinical translation of PPAR-targeting treatment strategies.

Zinc Modulates Glutamine Metabolism in T Cells

SCOPE

Zinc and glutamine are well known to be essential for the function and polarization of immune cells. TH 17 cells are more frequently induced during zinc deficiency and cover their energy requirement mainly through glutaminolysis. A dysregulation of TH 17 cells can contribute to the development of autoimmune diseases. Both inhibition of glutaminolysis and zinc supplementation suppress experimental autoimmune encephalomyelitis in mice. Therefore, the aim of this study is to investigate whether zinc modulates glutaminolysis in T cells.

METHODS AND RESULTS

CD3/CD28 stimulation and mixed lymphocytes culture are used as in vitro models for T cell activation. Then, the glutaminolysis is investigated on mRNA, protein, and functional level. Zinc deficiency and glutaminase (GLS) inhibition decrease immune responses in vitro. Furthermore, extracellular zinc and glutamine levels both modulate glutaminolysis by changing the expression of glutamine transporters and key enzymes. Intriguingly, zinc directly interferes with the activity of GLS both in a cell free system and in the cytosol.

CONCLUSION

Besides T cell subset differentiation, zinc also impacts on the cellular metabolism by inhibiting glutaminolysis. This suggests that zinc deficiency can contribute to the development of autoimmune diseases whereas zinc supplementation can support their therapy.

Peroxisome proliferator-activated receptors as therapeutic target for cancer

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to the nuclear receptor family. There are three subtypes of PPARs, including PPAR-α, PPAR-β/δ and PPAR-γ. They are expressed in different tissues and act by regulating the expression of target genes in the form of binding to ligands. Various subtypes of PPAR have been shown to have significant roles in a wide range of biological processes including lipid metabolism, body energy homeostasis, cell proliferation and differentiation, bone formation, tissue repair and remodelling. Recent studies have found that PPARs are closely related to tumours. They are involved in cancer cell growth, angiogenesis and tumour immune response, and are essential components in tumour progression and metastasis. As such, they have become a target for cancer therapy research. In this review, we discussed the current state of knowledge on the involvement of PPARs in cancer, including their role in tumourigenesis, the impact of PPARs in tumour microenvironment and the potential of using PPARs combinational therapy to treat cancer by targeting essential signal pathways, or as adjuvants to boost the effects of current chemo and immunotherapies. Our review highlights the complexity of PPARs in cancer and the need for a better understanding of the mechanism in order to design effective cancer therapies.

Differentiated Embryo-Chondrocyte Expressed Gene1 and Parkinson's Disease: New Insights and Therapeutic Perspectives

Differentiated embryo-chondrocyte expressed gene1 (DEC1), an important transcription factor with a basic helix-loop-helix domain, is ubiquitously expressed in both human embryonic and adult tissues. DEC1 is involved in neural differentiation and neural maturation in the central nervous system (CNS). Recent studies suggest that DEC1 protects against Parkinson's disease (PD) by regulating apoptosis, oxidative stress, lipid metabolism, immune system, and glucose metabolism disorders. In this review, we summarize the recent progress on the role of DEC1 in the pathogenesis of PD and provide new insights into the prevention and treatment of PD and neurodegenerative diseases.

The effect of PPAR isoform (de)activation on the lipid composition in full-thickness skin models

Human skin equivalents (HSEs) are 3D-cultured human skin models that mimic many aspects of native human skin (NHS). Although HSEs resemble NHS very closely, the barrier located in the stratum corneum (SC) is impaired. This is caused by an altered lipid composition in the SC of HSEs compared with NHS. One of the most pronounced changes in this lipid composition is a high level of monounsaturation. One key enzyme in this change is stearoyl-CoA desaturase-1 (SCD1), which catalyses the monounsaturation of lipids. In order to normalize the lipid composition, we aimed to target a group of nuclear receptors that are important regulators in the lipid synthesis. This group of receptors are known as the peroxisome proliferating activating receptors (PPARs). By (de)activating each isoform (PPAR-α, PPAR-δ and PPAR-γ), the PPAR isoforms may have normalizing effects on the lipid composition. In addition, another PPAR-α agonist Wy14643 was included as this supplement demonstrated normalizing effects in the lipid composition in a more recent study. After PPAR (ant)agonists supplementation, the mRNA of downstream targets, lipid synthesis genes and lipid composition were investigated. The PPAR downstream targets were activated, indicating that the supplements reached the keratinocytes to trigger their effect. However, minimal impact was observed on the lipid composition after PPAR isoform (de) activation. Only the highest concentration Wy14643 resulted in strong, but negative effects on CER composition. Although the novel tested modifications did not result in an improvement, more insight is gained on the nuclear receptors PPARs and their effects on the lipid barrier in full-thickness skin models.

PPARα at the crossroad of metabolic-immune regulation in cancer

Rewiring metabolism to sustain cell growth, division, and survival is the most prominent feature of cancer cells. In particular, dysregulated lipid metabolism in cancer has received accumulating interest, since lipid molecules serve as cell membrane structure components, secondary signaling messengers, and energy sources. Given the critical role of immune cells in host defense against cancer, recent studies have revealed that immune cells compete for nutrients with cancer cells in the tumor microenvironment and accordingly develop adaptive metabolic strategies for survival at the expense of compromised immune functions. Among these strategies, lipid metabolism reprogramming toward fatty acid oxidation is closely related to the immunosuppressive phenotype of tumor-infiltrated immune cells, including macrophages and dendritic cells. Therefore, it is important to understand the lipid-mediated crosstalk between cancer cells and immune cells in the tumor microenvironment. Peroxisome proliferator-activated receptors (PPARs) consist of a nuclear receptor family for lipid sensing, and one of the family members PPARα is responsible for fatty acid oxidation, energy homeostasis, and regulation of immune cell functions. In this review, we discuss the emerging role of PPARα-associated metabolic-immune regulation in tumor-infiltrated immune cells, and key metabolic events and pathways involved, as well as their influences on antitumor immunity.

Toxic effects of four cardiovascular drugs on the development and epigenetics of zebrafish (Danio rerio)

Due to the prevalence of cardiovascular diseases, therapeutic drugs such as atenolol (ATE), metoprolol (MET), atorvastatin (ATO), and bezafibrate (BZB) have been widely used and thus frequently detected in surface water at ng·L^-1-μg·L^-1 level. In this study, the developmental toxicity of these drugs (0.5 μg·L^-1-500 μg·L^-1) to zebrafish, an aquatic model organism, was investigated; and the epigenetic toxicity of BZB was also explored. For all four drugs, the results showed that the drugs exposure could cause sublethal toxic effects on zebrafish larvae, such as decreases in hatching rate, body length, and heart rate. ATO also induced the swelling of the eyes of larvae by 5 %-15 %. Yolk sac edema, pericardial edema, bent spine, and tail malformation were observed in larvae exposed to the drugs, and yolk sac edema was the most common malformation. In addition, the spontaneous movement and free-swimming activity could be inhibited by the drugs. Combined with RNA-seq results, the adverse development of larvae in exposure groups may be caused by the disruption of lipid and carbohydrate metabolism, and the development and function of eye and nervous system. After a 30-day uptake period, the accumulation of BZB and the decrease of global DNA methylation level were observed in the liver, kidneys, gut, gills, and brain of adult zebrafish (4-month-old) exposed to 0.5 μg·L^-1 to 500 μg·L^-1 BZB. The liver was the main organ for BZB accumulation and the occurrence of DNA hypomethylation. In the liver, overexpression (1.5-7.6 times) of genes related to lipid metabolism (PPARα), DNA methylation (Dnmt1), and apoptosis (p53) was also observed. The results of the current study suggest that long-term exposure to low-concentrations of cardiovascular drugs may pose significant threats to aquatic ecosystems.

Suppression of Hepatic PPARα in Primary Biliary Cholangitis Is Modulated by miR-155

Background: PPARα is a ligand-activated transcription factor that shows protective effects against metabolic disorders, inflammation and apoptosis. Primary biliary cholangitis and primary sclerosing cholangitis result in the intrahepatic accumulation of bile acids that leads to liver dysfunction and damage. Small, non-coding RNAs such as miR-155 and miR-21 are associated with silencing PPARα. Methods: The expression of miR-155, miR-21 and PPARα were evaluated using real-time PCR on liver tissue, as well as on human hepatocytes (HepG2) or cholangiocytes (NHCs) following exposure to lipopolysaccharide (LPS), glycodeoxycholic acid (GCDCA), lithocholic acid (LCA) and/or ursodeoxycholic acid (UDCA). Results: A reduction of PPARα in primary biliary cholangitis (PBC) livers was associated with miR-21 and miR-155 upregulation. Experimental overexpression of either miR-155 or miR-21 inhibited PPARα in hepatocytes, whereas, in cholangiocytes, only miR-21 suppressed PPARα. Both GCDCA and LCA induced the cell type-specific upregulation of miR-155 or miR-21. In HepG2, LPS-induced miR-155 expression was blocked by a cotreatment with UDCA and was associated with PPARα upregulation. In NHC cells, the expression of miR-21 was induced by LPS but did not affect PPARα expression. Conclusions: Hepatic PPARα expression is reduced in PBC livers as a likely result of miR-155 overexpression. UDCA effectively reduced both baseline and LPS-induced miR-155 expression, thus preventing the suppression of PPARα.

Crosstalk between incretin hormones, Th17 and Treg cells in inflammatory diseases

Intestinal epithelial cells constantly crosstalk with the gut microbiota and immune cells of the gut lamina propria. Enteroendocrine cells, secrete hormones, such as incretin hormones, which participate in host physiological events, such as stimulating insulin secretion, satiety, and glucose homeostasis. Interestingly, evidence suggests that the incretin pathway may influence immune cell activation. Consequently, drugs targeting the incretin hormone signaling pathway may ameliorate inflammatory diseases such as inflammatory bowel diseases, cancer, and autoimmune diseases. In this review, we discuss how these hormones may modulate two subsets of CD4 + T cells, the regulatory T cells (Treg)/Th17 axis important for gut homeostasis: thus, preventing the development and progression of inflammatory diseases. We also summarize the main experimental and clinical findings using drugs targeting the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP-1) signaling pathways and their great impact on conditions in which the Treg/Th17 axis is disturbed such as inflammatory diseases and cancer. Understanding the role of incretin stimulation in immune cell activation and function, might contribute to new therapeutic designs for the treatment of inflammatory diseases, autoimmunity, and tumors.

Peroxisome Proliferator-Activated Receptors Regulate Hepatic Immunity and Assist in the Treatment of Primary Biliary Cholangitis

Fibrates, which are agonists of peroxisome proliferator-activated receptor alpha, have received increasing attention in the treatment of primary biliary cholangitis. Reduced alkaline phosphatase levels and improved clinical outcomes were observed in patients with primary biliary cholangitis with an inadequate response to ursodeoxycholic acid (UDCA) monotherapy4 when treated with bezafibrate or fenofibrate combined with UDCA. In contrast to obeticholic acid, which exacerbates pruritus in patients, fibrates have been shown to relieve pruritus. Clinical trial outcomes show potential for the treatment of primary biliary cholangitis by targeting peroxisome proliferator-activated receptors. It is currently agreed that primary biliary cholangitis is an autoimmune-mediated cholestatic liver disease, and peroxisome proliferator-activated receptor is a nuclear receptor that regulates the functions of multiple immune cells, thus playing an important role in regulating innate and adaptive immunity. Therefore, this review focuses on the immune disorder of primary biliary cholangitis and summarizes the regulation of hepatic immunity when peroxisome proliferator-activated receptors are targeted for treating primary biliary cholangitis.

PPARβ mediates mangiferin-induced neuronal differentiation of neural stem cells through DNA demethylation

Adult hippocampal neurogenesis (AHN) is heavily implicated in the pathogenesis of various neuropsychiatric disorders. The mangiferin (MGF), a bioactive compound of the mango, reportedly produces biological effects on a variety of neuropsychiatric disorders. However, the function and underlying mechanisms of MGF in regulating hippocampal neurogenesis remain unknown. Here we discovered that the transcriptome and methylome of MGF-induced neural stem cells (NSCs) are distinct from the control. RNA-seq analysis revealed that the diferentially expressed genes (DEGs) were signifcantly enriched in the PPARs. Furthermore, we found that MGF enhanced neuronal differentiation and proliferation of neural stem cells (NSCs) via PPARβ but not PPARα and PPARγ. The combination of WGBS and RNA-seq analysis showed that the expression of some neurogenesis genes was negatively correlated with the DNA methylation level generally. We further found that PPARβ increased demethylation of Mash1 promoter by modulating the expressions of active and passive DNA demethylation enzymes in MGF-treated NSCs. Importantly, genetic deficiency of PPARβ decreased hippocampal neurogenesis in the adult mice, whereas the defective neurogenesis was notably rescued by Mash1 overexpression. Our findings uncover a model that PPARβ-mediated DNA demethylation of Mash1 contributes to MGF-induced neuronal genesis, and advance the concept that targeting PPARβ-TET1/DNMT3a-Mash1 axis regulation of neurogenesis might serve as a novel neurotherapeutic strategy.

The activation of PPARγ enhances Treg responses through up-regulating CD36/CPT1-mediated fatty acid oxidation and subsequent N-glycan branching of TβRII/IL-2Rα

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARγ) is an enhancer of Treg responses, but the mechanisms remain elusive. This study aimed to solve this problem in view of cellular metabolism.

METHODS

Three recognized PPARγ agonists (synthetic agonist: rosiglitazone; endogenous ligand: 15d-PGJ2; natural product: morin) were used as the tools to activate PPARγ. The fatty acid oxidation (FAO) was evaluated through the detection of fatty acid uptake, oxygen consumption rate, mitochondrial mass, mitochondrial membrane potential and acetyl-CoA level. The involvement of UDP-GlcNAc/N-linked glycosylation axis and the exact role of PPARγ in the action of PPARγ agonists were determined by flow cytometry, Q-PCR, western blotting, a commercial kit for enzyme activity and CRISPR/Cas9-mediated knockout.

RESULTS

Rosiglitazone, 15d-PGJ2 and morin all increased the frequency of CD4⁺Foxp3⁺ Treg cells generated from naïve CD4⁺ T cells, boosted the transcription of Foxp3, IL-10, CTLA4 and TIGIT, and facilitated the function of Treg cells. They significantly promoted FAO in differentiating Treg cells by up-regulating the levels of CD36 and CPT1 but not other enzymes involved in FAO such as ACADL, ACADM, HADHA or HADHB, and siCD36 or siCPT1 dampened PPARγ agonists-promoted Treg responses. Moreover, PPARγ agonists enhanced UDP-GlcNAc biosynthesis and subsequent N-linked glycosylation, but did not affect the expressions of N-glycan branching enzymes Mgat1, 2, 4 and 5. Notably, the enzyme activity of phosphofructokinase (PFK) was inhibited by PPARγ agonists and the effect was limited by siCD36 or siCPT1, implying PFK to be a link between PPARγ agonists-promoted FAO and UDP-GlcNAc biosynthesis aside from acetyl-CoA. Furthermore, PPARγ agonists facilitated the cell surface abundance of TβRII and IL-2Rα via N-linked glycosylation, thereby activating TGF-β/Smads and IL-2/STAT5 signaling, and the connection between N-linked glycosylation and Treg responses was revealed by tunicamycin. However, the increased surface abundance of CD36 was demonstrated to be mainly owing to PPARγ agonists-up-regulated overall expression. Finally, PPARγ antagonist GW9662 or CRISPR/Cas9-mediated knockout of PPARγ constrained the effects of rosiglitazone, 15d-PGJ2 and morin, confirming the exact role of PPARγ.

CONCLUSIONS

The activation of PPARγ enhances Treg responses through up-regulating CD36/CPT1-mediated fatty acid oxidation and subsequent N-glycan branching of TβRII/IL-2Rα, which is beneficial for inflammatory and autoimmune diseases. Video Abstract.

Sophora flavescens Alkaloids and Corticosteroid Synergistically Augment IL-10/IL-5 Ratio with Foxp3-Gene-Epigenetic Modification in Asthma PBMCs

Background

It has been demonstrated that ASHMI (antiasthma-simplified herbal medicine intervention) can improve airway function and reduce inflammation in human asthmatic patients with high safety and tolerability. In addition, ASHMI significantly suppresses Th2 cytokine production and increases Th1 cytokine production in treating asthma.

Objective

Allergic asthma is associated with dysregulation of cytokines. We focused on IL-5 and IL-10 as signature Th2 and Treg cytokines to characterize ASHMI immunomodulatory components.

Methods

The effects of ASHMI and individual herbal constituents on IL-5 and IL-10 production by PBMCs from asthmatic subjects were determined ex vivo. Sophora flavescens (SF)-F2, containing alkaloid compounds, effects on PBMC IL-10 and IL-5 production in the presence or absence of dexamethasone (Dex), and on DNA methylation levels at the foxp3 gene promoter were determined.

Results

The ratio of anti-CD3/CD28 stimulated IL-10/IL-5 production by PBMCs from asthmatic subjects was significantly reduced compared to healthy subjects. In PBMCs from asthmatic subjects, ASHMI significantly reduced IL-5 production and increased IL-10 secretion in a dose-dependent manner (p < 0.05–0.01). SF-F2 was most effective in increasing IL-10, whereas SF-F4 (flavonoid compounds) was most effective in suppressing IL-5 production. Dex-treated PBMCs from asthma subjects showed a trend of increasing ratio of IL-10/IL-5 while demonstrating reduced levels in both IL-5 and IL-10 (p < 0.05). Co-culture with Dex and SF-F2 significantly prevented Dex suppression of IL-10, while retained Dex-suppression of IL-5 production, and increased IL-10/IL-5 ratio by Dex. Co-culture with SF-F2 and Dex significantly reduced DNA methylation levels at the foxp3 gene promoter at CpG⁻¹²⁶.

Conclusion

The SF alkaloid-rich fraction may be responsible for ASHMI induction of IL-10 production by PBMCs and plays a synergistic effect with Dex for augmenting IL-10/IL-5 ratio.

Mitochondrial Exhaustion of Memory CD4 T-Cells in Treated HIV-1 Infection

People living with HIV (PLWH) who are immune non-responders (INR) to therapy are unable to restore their CD4 T-cell count and remain at great risk of morbidity and mortality. Here the mitochondrial defects that characterize memory CD4 T-cells in INR and causes of this mitochondrial exhaustion are reviewed. This review also describes the various reagents used to induce the expression of the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), the master regulator of mitochondrial biogenesis, which can restore mitochondria fitness and CD4 T-cell proliferation in INR. Due to sustained heightened inflammation in INR, the mitochondrial network is unable to be rejuvenated and requires attenuation of mediators of inflammation to rescue mitochondria and CD4 T-cell counts in INR.

Mechanistic Insight into PPARγ and Tregs in Atherosclerotic Immune Inflammation

Atherosclerosis (AS) is the main pathological cause of acute cardiovascular and cerebrovascular diseases, such as acute myocardial infarction and cerebral apoplexy. As an immune-mediated inflammatory disease, the pathogenesis of AS involves endothelial cell dysfunction, lipid accumulation, foam cell formation, vascular smooth muscle cell (VSMC) migration, and inflammatory factor infiltration. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) plays an important role in lipid metabolism, inflammation, and apoptosis by antagonizing the Wnt/β-catenin pathway and regulating cholesterol efflux and inflammatory factors. Importantly, PPARγ-dependant fatty acid uptake is critical for metabolic programming. Activated PPARγ can exert an anti-atherosclerotic effect by inhibiting the expression of various inflammatory factors, improving endothelial cell function, and restraining the proliferation and migration of VSMCs. Regulatory T cells (Tregs) are the only subset of T lymphocytes that have a completely negative regulatory effect on the autoimmune response. They play a critical role in suppressing excessive immune responses and inflammatory reactions and widely affect AS-associated foam cell formation, plaque rupture, and other processes. Recent studies have shown that PPARγ activation promotes the recruitment of Tregs to reduce inflammation, thereby exerting its anti-atherosclerotic effect. In this review, we provide an overview of the anti-AS roles of PPARγ and Tregs by discussing their pathological mechanisms from the perspective of AS and immune-mediated inflammation, with a focus on basic research and clinical trials of their efficacies alone or in combination in inhibiting atherosclerotic inflammation. Additionally, we explore new ideas for AS treatment and plaque stabilization and establish a foundation for the development of natural PPARγ agonists with Treg recruitment capability.

The MS Remyelinating Drug Bexarotene (an RXR Agonist) Promotes Induction of Human Tregs and Suppresses Th17 Differentiation In Vitro

The retinoid X receptor agonist bexarotene promotes remyelination in patients with multiple sclerosis. Murine studies have also demonstrated that RXR agonists have anti-inflammatory effects by enhancing the ability of all-trans-retinoic acid (atRA) to promote T-regulatory cell (Treg) induction and reduce Th17 differentiation in vitro. By stimulating human naïve CD4 T-cells in the presence of Treg or Th17 skewing cytokines, we show that bexarotene also tips the human Treg/Th17 axis in favor of Treg induction, but unlike murine cells this occurs independently of atRA and retinoic acid receptor signaling. Tregs induced in the presence of bexarotene express canonical markers of T-regulation and are functionally suppressive in vitro. Circulating Treg numbers did not increase in the blood of trial patients receiving bexarotene; we believe this is because Treg induction is likely to occur within tissues. These findings lend support to developing RXR agonists as treatments of autoimmune diseases, in particular multiple sclerosis.

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.

The role of peroxisome proliferator-activated receptors (PPAR) in immune responses

Peroxisome proliferator-activated receptors (PPARs) are fatty acid-activated transcription factors of nuclear hormone receptor superfamily that regulate energy metabolism. Currently, three PPAR subtypes have been identified: PPARα, PPARγ, and PPARβ/δ. PPARα and PPARδ are highly expressed in oxidative tissues and regulate genes involved in substrate delivery and oxidative phosphorylation (OXPHOS) and regulation of energy homeostasis. In contrast, PPARγ is more important in lipogenesis and lipid synthesis, with highest expression levels in white adipose tissue (WAT). In addition to tissues regulating whole body energy homeostasis, PPARs are expressed in immune cells and have an emerging critical role in immune cell differentiation and fate commitment. In this review, we discuss the actions of PPARs in the function of the innate and the adaptive immune system and their implications in immune-mediated inflammatory conditions.

The Model of PPARγ-Downregulated Signaling in Psoriasis

Interactions of genes in intersecting signaling pathways, as well as environmental influences, are required for the development of psoriasis. Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and transcription factor which inhibits the expression of many proinflammatory genes. We tested the hypothesis that low levels of PPARγ expression promote the development of psoriatic lesions. We combined experimental results and network functional analysis to reconstruct the model of PPARγ-downregulated signaling in psoriasis. We hypothesize that the expression of IL17, STAT3, FOXP3, and RORC and FOSL1 genes in psoriatic skin is correlated with the level of PPARγ expression, and they belong to the same signaling pathway that regulates the development of psoriasis lesion.

PPARα Inhibition Overcomes Tumor-Derived Exosomal Lipid-Induced Dendritic Cell Dysfunction

Dendritic cells (DCs) orchestrate the initiation, programming, and regulation of anti-tumor immune responses. Emerging evidence indicates that the tumor microenvironment (TME) induces immune dysfunctional tumor-infiltrating DCs (TIDCs), characterized with both increased intracellular lipid content and mitochondrial respiration. The underlying mechanism, however, remains largely unclear. Here, we report that fatty acid-carrying tumor-derived exosomes (TDEs) induce immune dysfunctional DCs to promote immune evasion. Mechanistically, peroxisome proliferator activated receptor (PPAR) α responds to the fatty acids delivered by TDEs, resulting in excess lipid droplet biogenesis and enhanced fatty acid oxidation (FAO), culminating in a metabolic shift toward mitochondrial oxidative phosphorylation, which drives DC immune dysfunction. Genetic depletion or pharmacologic inhibition of PPARα effectively attenuates TDE-induced DC-based immune dysfunction and enhances the efficacy of immunotherapy. This work uncovers a role for TDE-mediated immune modulation in DCs and reveals that PPARα lies at the center of metabolic-immune regulation of DCs, suggesting a potential immunotherapeutic target.

Yin et al. reveal that tumor-derived exosomes (TDEs), as fatty acid carriers, induce a metabolic shift toward oxidative phosphorylation, driving DC immune dysfunction. Transcriptomic analysis identifies PPARα as the fatty acid sensor mediating the immunosuppressive effects of TDEs on DCs. PPARα blockade effectively restores DC function and enhances the efficacy of immunotherapy.

Epigenetics: Linking Early Postnatal Nutrition to Obesity Programming?

Despite constant research and public policy efforts, the obesity epidemic continues to be a major public health threat, and new approaches are urgently needed. It has been shown that nutrient imbalance in early life, from conception to infancy, influences later obesity risk, suggesting that obesity could result from “developmental programming”. In this review, we evaluate the possibility that early postnatal nutrition programs obesity risk via epigenetic mechanisms, especially DNA methylation, focusing on four main topics: (1) the dynamics of epigenetic processes in key metabolic organs during the early postnatal period; (2) the epigenetic effects of alterations in early postnatal nutrition in animal models or breastfeeding in humans; (3) current limitations and remaining outstanding questions in the field of epigenetic programming; (4) candidate pathways by which early postnatal nutrition could epigenetically program adult body weight set point. A particular focus will be given to the potential roles of breast milk fatty acids, neonatal metabolic and hormonal milieu, and gut microbiota. Understanding the mechanisms by which early postnatal nutrition can promote lifelong metabolic modifications is essential to design adequate recommendations and interventions to “de-program” the obesity epidemic.

Meglumine acridone acetate, the ionic salt of CMA and N-methylglucamine, induces apoptosis in human PBMCs via the mitochondrial pathway

Meglumine acridone acetate (MA) is used in Russia for the treatment of influenza and other acute respiratory viral infections. It was assumed, until recently, that its antiviral effect was associated with its potential ability to induce type I interferon. Advanced studies, however, have shown the failure of 10-carboxymethyl-9-acridanone (CMA) to activate human STING. As such, MA’s antiviral properties are still undergoing clarification. To gain insight into MA’s mechanisms of action, we carried out RNA-sequencing analysis of global transcriptomes in MA-treated (MA+) human peripheral blood mononuclear cells (PBMCs). In response to treatment, approximately 1,223 genes were found to be differentially expressed, among which 464 and 759 were identified as either up- or down-regulated, respectively. To clarify the cellular and molecular processes taking place in MA+ cells, we performed a functional analysis of those genes. We have shown that evident MA subcellular localizations are: at the nuclear envelope; inside the nucleus; and diffusely in perinuclear cytoplasm. Postulating that MA may be a nuclear receptor agonist, we carried out docking simulations with PPARα and RORα ligand binding domains including prediction and molecular dynamics-based analysis of potential MA binding poses. Finally, we confirmed that MA treatment enhanced nuclear apoptosis in human PBMCs. The research presented here, in our view, indicates that: (i) MA activity is mediated by nuclear receptors; (ii) MA is a possible PPARα and/or RORα agonist; (iii) MA has an immunosuppressive effect; and (iv) MA induces apoptosis through the mitochondrial signaling pathway.

Crosstalk between PPARγ Ligands and Inflammatory-Related Pathways in Natural T-Regulatory Cells from Type 1 Diabetes Mouse Model

Immunomodulation, as a means of immunotherapy, has been studied in major research and clinical laboratories for many years. T-Regulatory (Treg) cell therapy is one of the modulators used in immunotherapy approaches. Similarly, nuclear receptor peroxisome proliferator activated receptor gamma (PPARγ) has extensively been shown to play a role as an immuno-modulator during inflammation. Given their mutual roles in downregulating the immune response, current study examined the influence of PPARγ ligands i.e., thiazolidinedione (TZD) class of drugs on Forkhead Box P3 (Foxp3) expression and possible crosstalk between PPARγ and nTreg cells of Non-Obese Diabetes (NOD) and Non-Obese Diabetes Resistant (NOR) mice. Results showed that TZD drug, ciglitazone and natural ligand of PPARγ 15d-prostaglandin downregulated Foxp3 expression in activated nTreg cells from both NOD and NOR mice. Interestingly, addition of the PPARγ inhibitor, GW9662 further downregulated Foxp3 expression in these cells from both mice. We also found that PPARγ ligands negatively regulate Foxp3 expression in activated nTreg cells via PPARγ-independent mechanism(s). These results demonstrate that both natural and synthetic PPARγ ligands capable of suppressing Foxp3 expression in activated nTreg cells of NOD and NOR mice. This may suggest that the effect of PPARγ ligands in modulating Foxp3 expression in activated nTreg cells is different from their reported effects on effector T cells. Given the capability to suppress Foxp3 gene, it is possible to be tested as immunomodulators in cancer-related studies. The co-lateral use of PPARγ ligands in nTreg cells in inducing tolerance towards pseudo-self antigens as in tumor microenvironment may uphold beneficial outcomes.

PPAR-γ Agonist Alleviates Liver and Spleen Pathology via Inducing Treg Cells during Schistosoma japonicum Infection

Background

Peroxisome proliferator-activated receptor- (PPAR-) γ plays critical roles in human metabolic disorders and has recently been implicated as a regulator of cellular proliferation and inflammatory responses. Regulatory T cells (Tregs), which express high levels of PPAR-γ protein, have the ability to maintain immune tolerance to self-antigens and regulate immune response to Schistosoma infection. However, mechanisms involved in the resolution of these responses are elusive.

Methods

Liver and spleen tissue samples in Schistosoma japonicum-infected mice after administration of pioglitazone (a PPAR-γ agonist) were collected. The hepatic and splenic pathologies were detected by H&E and Masson staining. The percentages of Th1/2 and Treg cells in the liver and spleen of each mouse were determined using flow cytometry. Levels of gene expression of PPAR-γ and Foxp3 in tissues or cells were determined using real-time PCR (RT-PCR). Macrophages were treated with pioglitazone in vitro or cocultured with normal purified CD4⁺ T cells for detecting Treg cells by flow cytometry. The interactions of PPAR-γ with Foxp3 in CD4⁺ T cells were detected by coimmunoprecipitation.

Results

Administration of pioglitazone resulted in the prevention of the development of hepatic and splenic pathologies. Activation of PPAR-γ by pioglitazone resulted in increased percentages of CD4⁺CD25⁺Foxp3⁺ Treg cells and decreased percentages of CD3⁺CD4⁺IFN-γ⁺ and CD3⁺CD4⁺IL-4⁺ cells in the liver and spleen of Schistosoma japonicum-infected mice. In addition, the PPAR-γ agonist can induce Treg cells in vitro directly or by modulating the macrophage's function indirectly. Furthermore, through interaction with Foxp3 in CD4⁺ T cells, the PPAR-γ agonist can promote the expression of Foxp3; however, the inhibitor of PPAR-γ weakened the expression of Foxp3 by modifying the coexpression of Foxp3 and PPAR-γ.

Conclusions

Our study reveals a previously unrecognized role for PPAR-γ/Foxp3 signaling in regulating the immunopathology that occurs during Schistosoma infection through induction of Treg cells.

IDO decreases glycolysis and glutaminolysis by activating GCN2K, while it increases fatty acid oxidation by activating AhR, thus preserving CD4+ T‑cell survival and proliferation

It is generally hypothesized in the literature that indoleamine 2,3‑dioxygenase (IDO), by degrading L‑tryptophan along the kynurenine pathway, suppresses CD4+ T‑cell function by inducing apoptosis, inhibiting proliferation and promoting differentiation towards a regulatory phenotype. These effects are either accompanied or directly lead to alterations in cell metabolism. The present study evaluated the pathways that govern the effect of IDO on the utilization of the three main energy sources in CD4+ T‑cells. Two‑way mixed lymphocyte reactions were performed with or without oleate and/or the IDO inhibitor 1‑methyl‑DL‑tryptophan. In addition, isolated CD4+ T‑cells cultured in an oleate‑containing medium were activated in the presence or not of the general control nonderepressible 2 kinase (GCN2K) activator tryptophanol. L‑tryptophan, glucose and free fatty acid consumption, cell proliferation, apoptosis and the levels of key proteins involved in IDO‑mediated signal transduction, and glucose, glutamine and free fatty acid utilization were assessed. The results indicate that IDO decreased glycolysis and glutaminolysis by activating GCN2K, resulting in activation of AMP‑activated protein kinase (AMPK). In parallel with AMPK activation, IDO‑induced activation of aryl hydrocarbon receptor increased the expression of all carnitine palmitoyltransferase I isoenzymes, leading ultimately to increased free fatty acid oxidation and preservation of CD4+ T‑cell survival and proliferation. Thus, contrary to what is generally hypothesized, in a normal environment containing fatty acids, the immunosuppressive effect of IDO may not be due to a decrease in CD4+ T‑cell survival and proliferation, since IDO supplies the required energy for cell survival and proliferation by increasing free fatty acid oxidation.

Sex Effects at the Ramparts: Nutrient- and Microbe-Mediated Regulation of the Immune-Metabolic Interface

The relationships between dietary compounds, derivative metabolites, and host metabolism and immunity are controlled by diverse molecular mechanisms. Essential contributions to these dynamics come from the community of microbes (the microbiome) inhabiting the human digestive tract. The composition and function of the microbiome are shaped by available nutrients, and reciprocally, these organisms produce an as yet poorly defined repertoire of molecules that communicate with the epithelial barrier and the mucosal immune system. We present evidence that diet-derived vitamins and lipids regulate immunity and metabolic function and highlight the diverse mechanisms through which these effects are impacted by sex. We discuss exciting new data emerging from studies using high-throughput sequencing technology, specialized mouse models, and bio-specimens, and clinical data from human subjects that have begun to reveal the complexity of these interactions. Also profiled in this chapter are the striking sex differences in pathways by which dietary nutrients and gut microbes modify metabolism, immunity, and immune- and inflammation-mediated diseases. Although the incidence, severity, and therapeutic responses of many autoimmune diseases differ by sex, the molecular mechanisms of these effects remain poorly understood.

Cell death and restoration of TRAIL-sensitivity by ciglitazone in resistant cervical cancer cells

Known activators of the Peroxisome Proliferator-Activated Receptor γ (PPARγ), thiazolidinediones (TZD) induce apoptosis in a variety of cancer cells through dependent and/or independent mechanisms of the receptor. We tested a panel of TZD (Rosiglitazone, Pioglitazone, Ciglitazone) to shed light on their potential therapeutic effects on three cervical cancer cell lines (HeLa, Ca Ski, C-33 A). In these cells, only ciglitazone triggered apoptosis through PPARγ-independent mechanisms and in particular via both extrinsic and intrinsic pathways in Ca Ski cells containing Human PapillomaVirus (HPV) type 16. It also inhibits cervical cancer xenograft development in nude mice. Ciglitazone kills cervical cancer cells by activating death receptor signalling pathway, caspase cascade and BH3 interacting-domain death agonist (Bid) cleavage through the up-regulation of Death Receptor 4 (DR4)/DR5 and soluble and membrane-bound TNF related apoptosis inducing ligand (TRAIL). Importantly, the drug let TRAIL-resistant Ca Ski cells to respond to TRAIL through the downregulation of cellular FLICE-Like Inhibitory Protein (c-FLIP) level. For the first time, we revealed that ciglitazone is able to decrease E6 viral oncoprotein expression known to block TRAIL pathway and this was associated with cell death. Our results highlight the capacity of ciglitazone to restore TRAIL sensitivity and to prevent E6 blocking action to induce apoptosis in cervical cancer cells.

The ex vivo toll-like receptor 7 tolerance induction in donor lymphocytes prevents murine acute graft-versus-host disease

BACKGROUND AIMS

Acute graft-versus-host disease (aGVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation, mediated by alloreactive donor T cells. Toll-like receptors (TLRs), a family of conserved pattern-recognition receptors (PRRs), represent key players in donors' T-cell activation during aGVHD; however, a regulatory, tolerogenic role for certain TLRs has been recognized in a different context. We investigated whether the ex vivo-induced TLR-2,-4,-7 tolerance in donor cells could prevent alloreactivity in a mismatched transplantation model.

METHODS

TLR-2,-4,-7 tolerance was induced in mouse splenocytes, after stimulation with low doses of corresponding ligands. Cellular and molecular changes of the TLR-tolerant splenocytes and purified T cells were assessed by immunophenotypic and gene expression analyses. Incidence of aGVHD was evaluated by the clinical score and survival as well as histopathology of target tissues.

RESULTS

Only the R848-induced TLR7 tolerance prevented aGVHD. The TLR7 ligand-induced tolerance lasted for a critical post-transplant period and was associated with distinct cellular and molecular signatures characterized by induction of regulatory T cells, reduced alloreactivity and balanced regulation of inflammatory signaling and innate immune responses. The TLR7-tolerant T cells preserved the immunological memory and generated in vitro virus-specific T cells upon antigen stimulation. The anti-aGVHD tolerization effect was direct and specific to TLR7 and required the receptor-ligand interaction; TLR7^-/- T cells isolated from B6 TLR7^-/- mice presented a distinct gene expression profile but failed to prevent aGVHD.

DISCUSSION

We propose an effective and clinically applicable ex vivo approach for aGVHD prevention through a transient and reversible immune reprogramming exerted by TLR7-tolerant donor lymphocytes.

Downregulation of DEC1 contributes to the neurotoxicity induced by MPP+ by suppressing PI3K/Akt/GSK3β pathway

AIM

Differentiated embryonic chondrocyte gene 1 (DEC1) is involved in the neuronal differentiation and development. The aim of this study is to investigate the role of DEC1 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPP+ )-induced PD model.

METHODS

The location of DEC1 and tyrosine hydroxylase (TH)-positive neurons were detected by immunofluorescence. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse subacute model of PD was established to evaluate the change of DEC1 expression in midbrain. Then, SH-SY5Y cells were used to investigate the role of DEC1 in MPP+ -induced neurotoxicity.

RESULTS

We showed that the co-expressed DEC1 and TH neurons took up more than 80% of the expressed TH neurons in the midbrain of mice. DEC1/TH double-positive neurons decreased by 40.6% in SNpc and 28.8% in VTA of MPTP-injured mice. Consistently, DEC1, TH and dopamine transporter (DAT) expression decreased in the midbrain of MPTP mice. In SY-SY5Y cells, MPP+ significantly suppressed DEC1 expression and increased the cleaved caspase 3/caspase 3 and Bax/Bcl-2. DEC1 overexpression relieved, whereas DEC1 knockdown aggravated MPP+ -induced cytotoxicity. Likewise, DEC1 overexpression and knockdown inversely regulated the expression of β-catenin and PI3Kp110α (PIK3CA), an essential role in Wnt/β-catenin and PI3K/Akt signaling pathways. Interestingly, LY294002, an inhibitor of PI3K/Akt signaling, aggravated, whereas LiCl, an activator of Wnt/β-catenin signaling, abolished the reduction in DEC1 by MPP+ . It is established that these two pathways are interconnected by the phosphorylation status of GSK3β. DEC1 overexpression increased but MPP+ and DEC1 knockdown decreased GSK3β phosphorylation.

CONCLUSION

Downregulation of DEC1 contributes to MPP+ -induced neurotoxicity by suppressing PI3K/Akt/GSK3β pathway.

PPAR-γ promotes type 2 immune responses in allergy and nematode infection

A hallmark of immunity to worm infections and many allergies is a strong type 2 immune response. This is characterized by the production of cytokines interleukin-5 (IL-5) and IL-13 by adaptive T helper 2 (T_H2) cells and/or type 2 innate lymphoid cells. Peroxisome proliferator activated receptor-γ (PPAR-γ) is typically regarded as an anti-inflammatory factor. We report that T_H2 cells express high levels of PPAR-γ in response to the allergen house dust mite and after infection with the parasite Heligmosomoides polygyrus Mice lacking PPAR-γ in T cells failed to effectively differentiate into IL-5- and IL-13-secreting cells and, hence, did not develop T_H2 cell-associated pathologies, including goblet cell metaplasia and eosinophilia, in response to allergen challenge. Furthermore, these mice could not mount protective immune responses to nematode infection. In addition, mice lacking PPAR-γ in T cells had greatly reduced frequencies of T_H2 cells in visceral adipose tissue. Mechanistically, PPAR-γ appeared to promote the expression of the IL-33 receptor on the surface of T_H2 cells. These results pinpoint PPAR-γ as a factor that drives type 2 responses in allergy, worm infection, and visceral adipose tissue.

Therapeutic Treatment of Arthritic Mice with 15-Deoxy Δ12,14-Prostaglandin J2 (15d-PGJ2) Ameliorates Disease through the Suppression of Th17 Cells and the Induction of CD4+CD25-FOXP3+ Cells

The prostaglandin, 15-deoxy Δ^12,14-prostaglandin J₂ (15d-PGJ₂), is a lipid mediator that plays an important role in the control of chronic inflammatory disease. However, the role of prostanoid in rheumatoid arthritis (RA) is not well determined. We demonstrated the therapeutic effect of 15d-PGJ₂ in an experimental model of arthritis. Daily administration of 15d-PGJ₂ attenuated the severity of CIA, reducing the clinical score, pain, and edema. 15d-PGJ₂ treatment was associated with a marked reduction in joint levels of proinflammatory cytokines. Although the mRNA expression of ROR-γt was profoundly reduced, FOXP3 was enhanced in draining lymph node cells from 15d-PGJ₂-treated arthritic mice. The specific and polyclonal CD4⁺ Th17 cell responses were limited during the addition of prostaglandin to cell culture. Moreover, in vitro 15d-PGJ₂ increased the expression of FOXP3, GITR, and CTLA-4 in the CD4⁺CD25⁻ population, suggesting the induction of Tregs on conventional T cells. Prostanoid addition to CD4⁺CD25⁻ cells selectively suppressed Th17 differentiation and promoted the enhancement of FOXP3 under polarization conditions. Thus, 15d-PGJ₂ ameliorated symptoms of collagen-induced arthritis by regulating Th17 differentiation, concomitant with the induction of Tregs, and, consequently, protected mice from diseases aggravation. Altogether, these results indicate that 15d-PGJ₂ may represent a potential therapeutic strategy in RA.

Human tolerogenic dendritic cells generated with protein kinase C inhibitor are optimal for functional regulatory T cell induction - A comparative study

Tolerogenic dendritic cells (tDCs) are a promising therapeutic tool for specific induction of immunological tolerance. Human tDCs can be generated ex vivo using various compounds. However, the compound(s) most suitable for clinical application remain undefined. We compared the tolerogenic properties of tDCs treated with protein kinase C inhibitor (PKCI), dexamethasone, vitamin D3 (Vit D3), rapamycin (Rapa), interleukin (IL)-10, transforming growth factor (TGF)-β, and a combination of peroxisome proliferator-activated receptor γ agonist and retinoic acid. All tDCs had a semi-mature DC phenotype. PKCI-, TGF-β-, and Rapa-tDCs showed CCR7 expression and migration to CCL19, but other tDCs showed little or none. PKCI- and IL-10-tDCs induced functional regulatory T cells more strongly than other tDCs. The tolerogenic properties of all tDCs were stable against proinflammatory stimuli. Furthermore, PKCI-tDCs were generated from patients with rheumatoid arthritis and primary Sjögren's syndrome. Therefore, PKCI-tDCs showed the characteristics best suited for tolerance-inducing therapy.

Peroxisome proliferator-activated receptor alpha deficiency impairs regulatory T cell functions: Possible application in the inhibition of melanoma tumor growth in mice

Regulatory T (Treg) cells are important to induce and maintain immunological self-tolerance. Although the progress accomplished in understanding the functional mechanism of Treg cells, intracellular molecules that control the mechanisms of their suppressive capacity are still on investigation. The present study showed that peroxisome proliferator-activated receptor-alpha deficiency impaired the suppressive activity of Treg cells on CD4⁺CD25^- and CD8⁺ T cell proliferation. In Treg cells, PPARα gene deletion also induced a decrease of migratory abilities, and downregulated the expression of chemokine receptors (CCR-4, CCR-8 and CXCR-4) and p27^KIP1 mRNA. Treg cells from PPARα^-/- mice also lost their anergic property. Since low Treg activity, as observed in PPARα^-/- mice, is known to be associated with the inhibition of tumor growth, we inoculated these mice with B16 melanoma cells and assessed tumor proliferation. In PPARα^-/- mice, cancer growth was significantly curtailed, and it was correlated with high expression of granzyme B and perforin mRNA in tumor bed. Degranulation of cytolytic molecules by CD8⁺ T cells, assessed by a perforin-release marker CD107a expression, was higher in PPARα^-/- mice than that in wild-type mice. Tumor-infiltrating lymphocytes (TIL) in melanoma tumors in PPARα^-/- mice exhibited high pro-inflammatory Th1 phenotype. Consistently, adoptive transfer into lymphopenic RAG2^-/- mice of total PPARα^-/-splenic T cells inhibited more the growth rate of B16 tumor than the wild type splenic T cells. Our findings suggest that PPARα deficiency, by diminishing Treg cell functions and upregulating pro-inflammatory T cell phenotype, exerts an in vivo anti-cancer properties.

The role of nuclear receptors in regulation of Th17/Treg biology and its implications for diseases

Nuclear receptors in the cell play essential roles in environmental sensing, differentiation, development, homeostasis,and metabolism and are thus highly conserved across multiple species. The anti-inflammatory role of nuclear receptors in immune cells has recently gained recognition. Nuclear receptors play critical roles in both myeloid and lymphoid cells, particularly in helper CD41 T-cell type 17 (Th17) and regulatory T cells (Treg). Th17 and Treg are closely related cell fates that are determined by orchestrated cytokine signaling. Recent studies have emphasized the interactions between nuclear receptors and the known cytokine signals and how such interaction affects Th17/Treg development and function.This review will focus on the most recent discoveries concerning the roles of nuclear receptors in the context of therapeutic applications in autoimmune diseases.

RNA Seq profiling reveals a novel expression pattern of TGF-β target genes in human blood eosinophils

Despite major advances in our understanding of TGF-β signaling in multiple cell types, little is known about the direct target genes of this pathway in human eosinophils. These cells constitute the major inflammatory component present in the sputum and lung of active asthmatics and their numbers correlate well with disease severity. During the transition from acute to chronic asthma, TGF-β levels rise several fold in the lung which drives fibroblasts to produce extracellular matrix (ECM) and participate in airway and parenchymal remodeling. In this report, we use purified blood eosinophils from healthy donors and analyze baseline and TGF-β responsive genes by RNA Seq, and demonstrate that eosinophils (PBE) express 7981 protein-coding genes of which 178 genes are up-regulated and 199 genes are down-regulated by TGF-β. While 18 target genes have been previously associated with asthma and eosinophilic disorders, the vast majority have been implicated in cell death and survival, differentiation, and cellular function. Ingenuity pathway analysis revealed that 126 canonical pathways are activated by TGF-β including iNOS, TREM1, p53, IL-8 and IL-10 signaling. As TGF-β is an important cytokine for eosinophil function and survival, and pulmonary inflammation and fibrosis, our results represent a significant step toward the identification of novel TGF-β responsive genes and provide a potential therapeutic opportunity by selectively targeting relevant genes and pathways.

Dexamethasone suppresses allergic rhinitis and amplifies CD4(+) Foxp3(+) regulatory T cells in vitro

BACKGROUND

Glucocorticosteroids (GCs) are highly effective in mitigating allergic inflammation. In this study, we investigate the effects of dexamethasone (DEX) on regulatory T cells (Tregs) in a murine model of allergic rhinitis (AR).

METHODS

BALB/c mice were sensitized to ovalbumin (OVA) followed by intranasal OVA challenge. Mice in the treatment group received DEX by intraperitoneal injection (5 mg/kg/day) 1 hour before the OVA challenge. Further, CD4(+) CD25(-) T cells from the spleens were cultured in presence of DEX. The effects of DEX on CD4(+) Foxp3(+) T cells were then assessed in vivo as well as in vitro.

RESULTS

Frequencies of sneezing and scratching decreased significantly in the DEX-treated group compared to that in the OVA group. Histopathological analyses showed that DEX restored the destroyed and discontinuous ciliated epithelium of the nasal mucosa in the OVA group. Moreover, DEX inhibited the production of interleukin (IL)-4, IL-5, and IL-13 in the nasal cavity lavage fluid in this group. We also observed a significant increase in the percentage of CD4(+) Foxp3(+) T cells in the OVA group. In vivo, DEX treatment significantly decreased the number of CD4(+) Foxp3(+) T cells. However, in vitro, the proportion of these cells increased in the presence of DEX. Furthermore, the number of late stage apoptotic CD4(+) T cells was also significantly increased upon exposure to DEX.

CONCLUSION

DEX therapy effectively suppresses AR symptoms, but does not result in the expected increase in the frequency of Tregs in vivo. Thus, whether GCs exert immunosuppressive effects by influencing the number of Tregs remains unresolved.

Differentiated embryonic chondrocytes 1 expression of periodontal ligament tissue and gingival tissue in the patients with chronic periodontitis

OBJECTIVE

To evaluate the DEC1 expression of periodontal ligament tissue and gingival tissue in the patients with chronic periodontitis.

METHODS

20 non-smoking patients with chronic periodontitis and 20 healthy individuals were enrolled. Periodontal ligament tissue and gingival tissue samples from healthy subjects were collected during teeth extraction for orthodontic reason or the third molar extraction. The parallel samples from patients with chronic periodontitis were obtained during periodontal flap operations or teeth extraction as part of periodontal treatment. The DEC1 expression and the alkaline phosphatase (ALP) activity of both the periodontal ligament tissue and gingival tissue were determined by Western blot, Immunohistochemistry and ALP Detection Kit.

RESULTS

The DEC1 expression of periodontal ligament tissue in the patients with chronic periodontitis decreased significantly along with the decreased ALP activity. On the contrary, the DEC1 expression of gingival tissue in the patients with chronic periodontitis increased significantly. Further study found that the DEC1 expression of gingival tissue increased mainly in the suprabasal layer of gingival epithelial cells but decreased in the gingival connective tissue of the patients with chronic periodontitis.

CONCLUSION

The DEC1 expression decreases in the periodontal ligament tissue which is related to the osteogenic capacity, whereas the DEC1 expression increases in the suprabasal layer of gingival epithelial cells which are involved in immune inflammatory response in the patients with chronic periodontitis. The findings provide a new target to explore the pathology and the therapy of periodontitis.

Ectosomes released by platelets induce differentiation of CD4+T cells into T regulatory cells

Accumulating evidence suggests an immune-modulatory role for platelets (PLT) and PLT-derived microvesicles. In particular, ectosomes, i.e. vesicles budding from PLT surface, have been shown to exert immunosuppressive activities on phagocytes. Here we investigated the effects mediated by PLT-derived ectosomes (PLT-Ecto) on CD4+ T cells. Exposure of activated CD4+ T cells to PLT-Ecto decreased their release of IFNγ, TNFα and IL-6, and increased the production of TGF-β1. Concomitantly, PLT-Ecto-exposed CD4+ T cells displayed increased frequencies of CD25high Foxp3+ cells. These phenomena were dose-dependent and PLT-Ecto specific, since they were not observed in the presence of polymorphonuclear- and erythrocyte-derived ectosomes. Analysis of specific T cell subsets revealed that PLT-Ecto induced differentiation of naïve T cells into Foxp3+ cells, but had no effect on pre-differentiated Foxp3+ regulatory T cells (Tregs). Importantly, PLT-Ecto-induced Foxp3+ cells were as effective as peripheral blood Tregs in suppressing CD8+ T cell proliferation. PLT-Ecto-mediated effects were partly dependent on PLT-derived TGF-β1, as they were to some extent inhibited by PLT-Ecto pretreatment with TGF-β1-neutralising antibodies. Interestingly, ectosome-derived TGF-β1 levels correlated with Foxp3+ T cell frequencies in blood of healthy donors. In conclusion, PLT-Ecto induce differentiation of CD4+ T cells towards functional Tregs. This may represent a mechanism by which PLT-Ecto enhance peripheral tolerance.

Nutrient Sensing via mTOR in T Cells Maintains a Tolerogenic Microenvironment

We have proposed that tolerance can be maintained through the induction, by Treg cells, of a tolerogenic microenvironment within tolerated tissues that inhibits effector cell activity but which supports the generation of further Treg cells by “infectious tolerance.” Two important components of this tolerogenic microenvironment depend on metabolism and nutrient sensing. The first is due to the up-regulation of multiple enzymes that consume essential amino acids, which are sensed in naïve T cells primarily via inhibition of the mechanistic target of rapamycin (mTOR) pathway, which in turn encourages their further differentiation into FOXP3⁺ Treg cells. The second mechanism is the metabolism of extracellular ATP to adenosine by the ectoenzymes CD39 and CD73. These two enzymes are constitutively co-expressed on Treg cells, but can also be induced on a wide variety of cell types by TGFβ and the adenosine generated can be shown to be a potent inhibitor of T cell proliferation. This review will focus on mechanisms of nutrient sensing in T cells, how these are integrated with TCR and cytokine signals via the mTOR pathway, and what impact this has on intracellular metabolism and subsequently the control of differentiation into different effector or regulatory T cell subsets.

Role of PPAR, LXR, and PXR in epidermal homeostasis and inflammation

Epidermal lipid synthesis and metabolism are regulated by nuclear hormone receptors (NHR) and in turn epidermal lipid metabolites can serve as ligands to NHR. NHR form a large superfamily of receptors modulating gene transcription through DNA binding. A subgroup of these receptors is ligand-activated and heterodimerizes with the retinoid X receptor including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and pregnane X receptor (PXR). Several isotypes of these receptors exist, all of which are expressed in skin. In keratinocytes, ligand activation of PPARs and LXRs stimulates differentiation, induces lipid accumulation, and accelerates epidermal barrier regeneration. In the cutaneous immune system, ligand activation of all three receptors, PPAR, LXR, and PXR, has inhibitory properties, partially mediated by downregulation of the NF-kappaB pathway. PXR also has antifibrotic effects in the skin correlating with TGF-beta inhibition. In summary, ligands of PPAR, LXR and PXR exert beneficial therapeutic effects in skin disease and represent promising targets for future therapeutic approaches in dermatology. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Modulation of T Cell Metabolism and Function through Calcium Signaling

As a vital second messenger in the activation of lymphocytes, the divalent cation Ca(2+) plays numerous roles in adaptive immune responses. Importantly, Ca(2+) signaling is essential for T cell activation, tolerance of self-antigens, and homeostasis. Supporting the essential role of Ca(2+) signaling in T cell biology, the Ca(2+) regulated protein phosphatase calcineurin is a key target of pharmacologic inhibition for preventing allograft rejection and for autoimmune therapy. Recent studies have highlighted the unique role of Stim1 and Orai1/2 proteins in the regulation of store-operated/calcium release activated calcium (CRAC) channels in the context of T cells. While Ca(2+) is known to modulate T cell activation via effects on calcineurin and its target, nuclear factor of activated T cells (NFAT), this second messenger also regulates other pathways, including protein kinase C, calmodulin kinases, and cytoskeletal proteins. Ca(2+) also modulates the unique metabolic changes that occur during in distinct T cell stages and subsets. Herein, we discuss the means by which Ca(2+) mobilization modulates cellular metabolism following T cell receptor ligation. Further, we highlight the crosstalk between mitochondrial metabolism, reactive oxygen species (ROS) generation, and CRAC channel activity. As a target of mitochondrial ROS and Ca(2+) regulation, we describe the involvement of the serine/threonine kinase DRAK2 in the context of these processes. Given the important roles for Ca(2+) dependent signaling and cellular metabolism in adaptive immune responses, the crosstalk between these pathways is likely to be important for the regulation of T cell activation, tolerance, and homeostasis.

Predictive computational modeling of the mucosal immune responses during Helicobacter pylori infection

T helper (Th) cells play a major role in the immune response and pathology at the gastric mucosa during Helicobacter pylori infection. There is a limited mechanistic understanding regarding the contributions of CD4+ T cell subsets to gastritis development during H. pylori colonization. We used two computational approaches: ordinary differential equation (ODE)-based and agent-based modeling (ABM) to study the mechanisms underlying cellular immune responses to H. pylori and how CD4+ T cell subsets influenced initiation, progression and outcome of disease. To calibrate the model, in vivo experimentation was performed by infecting C57BL/6 mice intragastrically with H. pylori and assaying immune cell subsets in the stomach and gastric lymph nodes (GLN) on days 0, 7, 14, 30 and 60 post-infection. Our computational model reproduced the dynamics of effector and regulatory pathways in the gastric lamina propria (LP) in silico. Simulation results show the induction of a Th17 response and a dominant Th1 response, together with a regulatory response characterized by high levels of mucosal Treg) cells. We also investigated the potential role of peroxisome proliferator-activated receptor γ (PPARγ) activation on the modulation of host responses to H. pylori by using loss-of-function approaches. Specifically, in silico results showed a predominance of Th1 and Th17 cells in the stomach of the cell-specific PPARγ knockout system when compared to the wild-type simulation. Spatio-temporal, object-oriented ABM approaches suggested similar dynamics in induction of host responses showing analogous T cell distributions to ODE modeling and facilitated tracking lesion formation. In addition, sensitivity analysis predicted a crucial contribution of Th1 and Th17 effector responses as mediators of histopathological changes in the gastric mucosa during chronic stages of infection, which were experimentally validated in mice. These integrated immunoinformatics approaches characterized the induction of mucosal effector and regulatory pathways controlled by PPARγ during H. pylori infection affecting disease outcomes.

Retinoid X receptor agonists modulate Foxp3⁺ regulatory T cell and Th17 cell differentiation with differential dependence on retinoic acid receptor activation

Retinoic acid (RA) enhances TGF-β-dependent differentiation of Foxp3(+) inducible regulatory T cells (iTregs) and inhibits Th17 differentiation by binding to the RA receptor (RAR)/retinoid X receptor (RXR) heterodimer. The major physiologic RA, all-trans-RA, binds to RAR but not to RXR at physiological concentrations. It remained unclear whether RXR-mediated stimulation affected the iTregs and Th17 differentiation. We found in this study that the RXR agonists, PA024 and tributyltin, augmented the ability of all-trans-RA or the RAR agonist Am80 to enhance CD4(+)CD25(-) T cells to acquire Foxp3 expression and suppressive function. However, they failed to enhance Foxp3 expression in the presence of the RAR antagonist LE540, suggesting that the effect depends on RAR-mediated signals. They exerted the effect largely by augmenting the ability of all-trans-RA to suppress the production of IL-4, IL-21, and IFN-γ that inhibited Foxp3 expression. Agonists of peroxisome proliferator-activated receptors and liver X receptors (LXRs), permissive partners of RXR, failed to enhance Foxp3 expression. In contrast, RXR agonists and LXR agonists suppressed IL-17 expression. The RXR-mediated suppression was not canceled by blocking RAR stimulation but was likely to involve permissive activation of LXRs. All-trans-RA and an agonist of RXR or LXR additively suppressed IL-17 expression when the all-trans-RA concentration was low. RXR agonists also suppressed Ccr6 expression that is essential for Th17 cells to enter the CNS. Accordingly, tributyltin treatment of mice ameliorated experimental autoimmune encephalomyelitis through regulating Th17 cell activities. These results suggest that RXR stimulation modulates Foxp3(+) iTreg and Th17 differentiation with differential dependence on RAR-mediated stimulation.

Protein kinase C inhibitor generates stable human tolerogenic dendritic cells

Tolerogenic dendritic cells (DCs) are a promising tool for a specific form of cellular therapy whereby immunological tolerance can be induced in the context of transplantation and autoimmunity. From libraries of bioactive lipids, nuclear receptor ligands, and kinase inhibitors, we screened conventional protein kinase C inhibitors (PKCIs) bisindolylmaleimide I, Gö6983, and Ro32-0432 with strong tolerogenic potential. PKCI-treated human DCs were generated by subjecting them to a maturation process after differentiation of immature DCs. The PKCI-treated DCs had a semimature phenotype, showing high production of IL-10, and efficiently induced IL-10-producing T cells and functional Foxp3(+) regulatory T cells from naive CD4(+) T cells, thus eliciting a strong immunosuppressive function. They also showed CCR7 expression and sufficient capacity for migration toward CCR7 ligands. Additionally, PKCI-treated DCs were highly stable when exposed to inflammatory stimuli such as proinflammatory cytokines or LPS. Conventional PKCIs inhibited NF-κB activation of both the canonical and noncanonical pathways of DC maturation, thus suppressing the expression of costimulatory molecules and IL-12 production. High production of IL-10 in PKCI-treated DCs was due to not only an increase of intracellular cAMP, but also a synergistic effect of increased cAMP and NF-κB inhibition. Moreover, PKCI-treated mouse DCs that had properties similar to PKCI-treated human DCs prevented graft-versus-host disease in a murine model of acute graft-versus-host disease. Conventional PKCI-treated DCs may be useful for tolerance-inducing therapy, as they satisfy the required functional characteristics for clinical-grade tolerogenic DCs.

Metabolic control of the Treg/Th17 axis

The interplay of the immune system with other aspects of physiology is continually being revealed and in some cases studied in considerable mechanistic detail. A prime example is the influence of metabolic cues on immune responses. It is well appreciated that upon activation, T cells take on a metabolic profile profoundly distinct from that of their quiescent and anergic counterparts; however, a number of recent breakthroughs have greatly expanded our knowledge of how aspects of cellular metabolism can shape a T-cell response. Particularly important are findings that certain environmental cues can tilt the delicate balance between inflammation and immune tolerance by skewing T-cell fate decisions toward either the T-helper 17 (Th17) or T-regulatory (Treg) cell lineage. Recognizing the unappreciated immune-modifying potential of metabolic factors and particularly those involved in the generation of these functionally opposing T-cell subsets will likely add new and potent therapies to our repertoire for treating immune mediated pathologies. In this review, we summarize and discuss recent findings linking certain metabolic pathways, enzymes, and by-products to shifts in the balance between Th17 and Treg cell populations. These advances highlight numerous opportunities for immune modulation.

High beta-palmitate fat controls the intestinal inflammatory response and limits intestinal damage in mucin Muc2 deficient mice

BACKGROUND

Palmitic-acid esterified to the sn-1,3 positions of the glycerol backbone (alpha, alpha'-palmitate), the predominant palmitate conformation in regular infant formula fat, is poorly absorbed and might cause abdominal discomfort. In contrast, palmitic-acid esterified to the sn-2 position (beta-palmitate), the main palmitate conformation in human milk fat, is well absorbed. The aim of the present study was to examine the influence of high alpha, alpha'-palmitate fat (HAPF) diet and high beta-palmitate fat (HBPF) diet on colitis development in Muc2 deficient (Muc2(-/-)) mice, a well-described animal model for spontaneous enterocolitis due to the lack of a protective mucus layer.

METHODS

Muc2(-/-) mice received AIN-93G reference diet, HAPF diet or HBPF diet for 5 weeks after weaning. Clinical symptoms, intestinal morphology and inflammation in the distal colon were analyzed.

RESULTS

Both HBPF diet and AIN-93G diet limited the extent of intestinal erosions and morphological damage in Muc2(-/-) mice compared with HAPF diet. In addition, the immunosuppressive regulatory T (Treg) cell response as demonstrated by the up-regulation of Foxp3, Tgfb1 and Ebi3 gene expression levels was enhanced by HBPF diet compared with AIN-93G and HAPF diets. HBPF diet also increased the gene expression of Pparg and enzymatic antioxidants (Sod1, Sod3 and Gpx1), genes all reported to be involved in promoting an immunosuppressive Treg cell response and to protect against colitis.

CONCLUSIONS

This study shows for the first time that HBPF diet limits the intestinal mucosal damage and controls the inflammatory response in Muc2(-/-) mice by inducing an immunosuppressive Treg cell response.