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

The role of lipoxin A4 in endometrial biology and endometriosis

Lipoxin A4 (LXA4), an endogenous anti-inflammatory and immunomodulatory mediator studied in many disease states, is recently appreciated as a potentially significant player in the endometrium. This eicosanoid, synthesized from arachidonic acid via the action of lipoxygenase enzymes, is likely regulated in endometrial tissue during the menstrual cycle. Recent studies revealed that LXA4 acts as an estrogen receptor agonist in endometrial epithelial cells, antagonizing some estrogen-mediated activities in a manner similar to the weak estrogen estriol, with which it shares structural similarity. LXA4 may also be an anti-inflammatory molecule in the endometrium, though its precise function in various physiological and pathological scenarios remains to be determined. The expression patterns for LXA4 and its receptor in the female reproductive tract suggest a role in pregnancy. The present review provides an oversight of its known and putative roles in the context of immuno-endocrine crosstalk. Endometriosis, a common inflammatory condition and a major cause of infertility and pain, is currently treated by surgery or anti-hormone therapies that are contraceptive and associated with undesirable side effects. LXA4 may represent a potential therapeutic and further research to elucidate its function in endometrial tissue and the peritoneal cavity will undoubtedly provide valuable insights.

Systems modeling of molecular mechanisms controlling cytokine-driven CD4+ T cell differentiation and phenotype plasticity

Differentiation of CD4+ T cells into effector or regulatory phenotypes is tightly controlled by the cytokine milieu, complex intracellular signaling networks and numerous transcriptional regulators. We combined experimental approaches and computational modeling to investigate the mechanisms controlling differentiation and plasticity of CD4+ T cells in the gut of mice. Our computational model encompasses the major intracellular pathways involved in CD4+ T cell differentiation into T helper 1 (Th1), Th2, Th17 and induced regulatory T cells (iTreg). Our modeling efforts predicted a critical role for peroxisome proliferator-activated receptor gamma (PPARγ) in modulating plasticity between Th17 and iTreg cells. PPARγ regulates differentiation, activation and cytokine production, thereby controlling the induction of effector and regulatory responses, and is a promising therapeutic target for dysregulated immune responses and inflammation. Our modeling efforts predict that following PPARγ activation, Th17 cells undergo phenotype switch and become iTreg cells. This prediction was validated by results of adoptive transfer studies showing an increase of colonic iTreg and a decrease of Th17 cells in the gut mucosa of mice with colitis following pharmacological activation of PPARγ. Deletion of PPARγ in CD4+ T cells impaired mucosal iTreg and enhanced colitogenic Th17 responses in mice with CD4+ T cell-induced colitis. Thus, for the first time we provide novel molecular evidence in vivo demonstrating that PPARγ in addition to regulating CD4+ T cell differentiation also plays a major role controlling Th17 and iTreg plasticity in the gut mucosa.

CD4+ T cells can differentiate into different phenotypes depending on the cytokine milieu. Due to the complexity of this process, we have constructed a computational and mathematical model with sixty ordinary differential equations representing a CD4+ T cell differentiating into either Th1, Th2, Th17 or iTreg cells. The model includes cytokines, nuclear receptors and transcription factors that define fate and function of CD4+ T cells. Computational simulations illustrate how a proinflammatory Th17 cell can undergo reprogramming into an anti-inflammatory iTreg phenotype following PPARγ activation. This modeling-derived hypothesis has been validated with in vitro and in vivo experiments. Experimental data support the modeling-derived prediction and demonstrate that the loss of PPARγ enhances a proinflammatory response characterized by Th17 in colitis-induced mice. Moreover, pharmacological activation of PPARγ in vivo can affect the Th17/iTreg balance by upregulating FOXP3 and downregulating IL-17A and RORγt. In summary, we demonstrate that computational simulations using our CD4+ T cell model provide novel unforeseen hypotheses related to the molecular mechanisms controlling differentiation and function of CD4+ T cells. In vivo findings validated the modeling prediction that PPARγ modulates differentiation and plasticity of CD4+ T cells in mice.

Attenuation of islet-specific T cell responses is associated with C-peptide improvement in autoimmune type 2 diabetes patients

The clinical efficacy of peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists in cell-mediated autoimmune diseases results from down-regulation of inflammatory cytokines and autoimmune effector cells. T cell islet autoimmunity has been demonstrated to be common in patients with phenotypic type 2 diabetes mellitus (T2DM) and islet-specific T cells (T(+) ) to be correlated positively with more severe beta cell dysfunction. We hypothesized that the beneficial effects of the PPAR-γ agonist, rosiglitazone, therapy in autoimmune T2DM patients is due, in part, to the immunosuppressive properties on the islet-specific T cell responses. Twenty-six phenotypic T2DM patients positive for T cell islet autoimmunity (T(+) ) were identified and randomized to rosiglitazone (n = 12) or glyburide (n = 14). Beta cell function, islet-specific T cell responses, interleukin (IL)-12 and interferon (IFN)-γ responses and islet autoantibodies were followed for 36 months. Patients treated with rosiglitazone demonstrated significant (P < 0·03) down-regulation of islet-specific T cell responses, although no change in response to tetanus, a significant decrease (P < 0·05) in IFN-γ production and significantly (P < 0·001) increased levels of adiponectin compared to glyburide-treated patients. Glucagon-stimulated beta cell function was observed to improve significantly (P < 0·05) in the rosiglitazone-treated T2DM patients coinciding with the down-regulation of the islet-specific T cell responses. In contrast, beta cell function in the glyburide-treated T2DM patients was observed to drop progressively throughout the study. Our results suggest that down-regulation of islet-specific T cell autoimmunity through anti-inflammatory therapy may help to improve beta cell function in autoimmune phenotypic T2DM patients.

mTOR, metabolism, and the regulation of T-cell differentiation and function

Upon antigen recognition, naive T cells undergo rapid expansion and activation. The energy requirements for this expansion are formidable, and T-cell activation is accompanied by dramatic changes in cellular metabolism. Furthermore, the outcome of antigen engagement is guided by multiple cues derived from the immune microenvironment. Mammalian target of rapamycin (mTOR) is emerging as a central integrator of these signals playing a critical role in driving T-cell differentiation and function. Indeed, multiple metabolic programs are controlled by mTOR signaling. In this review, we discuss the role of mTOR in regulating metabolism and how these pathways intersect with the ability of mTOR to integrate cues that guide the outcome of T-cell receptor engagement.

Retinoid and TGF-β families: crosstalk in development, neoplasia, immunity, and tissue repair

Transforming growth factor-β (TGF-β) isoforms are profibrotic cytokines, par excellence, and have complex multifunctional effects on many systems, depending on the biologic setting. Retinoids are vitamin A derivatives that also have diverse effects in development, physiology, and disease. The interactions between these classes of molecules are, not surprisingly, highly complex and are dependent on the tissue, cellular, and molecular settings.

Time-Qualified Patterns of Variation of PPARγ, DNMT1, and DNMT3B Expression in Pancreatic Cancer Cell Lines

Carcinogenesis is related to the loss of homeostatic control of cellular processes regulated by transcriptional circuits and epigenetic mechanisms. Among these, the activities of peroxisome proliferator-activated receptors (PPARs) and DNA methyltransferases (DNMTs) are crucial and intertwined. PPARγ is a key regulator of cell fate, linking nutrient sensing to transcription processes, and its expression oscillates with circadian rhythmicity. Aim of our study was to assess the periodicity of PPARγ and DNMTs in pancreatic cancer (PC). We investigated the time-related patterns of PPARG, DNMT1, and DNMT3B expression monitoring their mRNA levels by qRT-PCR at different time points over a 28-hour span in BxPC-3, CFPAC-1, PANC-1, and MIAPaCa-2 PC cells after synchronization with serum shock. PPARG and DNMT1 expression in PANC-1 cells and PPARG expression in MIAPaCa-2 cells were characterized by a 24 h period oscillation, and a borderline significant rhythm was observed for the PPARG, DNMT1, and DNMT3B expression profiles in the other cell lines. The time-qualified profiles of gene expression showed different shapes and phase relationships in the PC cell lines examined. In conclusion, PPARG and DNMTs expression is characterized by different time-qualified patterns in cell lines derived from human PC, and this heterogeneity could influence cell phenotype and human disease behaviour.

Role of Peroxisome Proliferator-Activated Receptor-γ in Vascular Inflammation

Vascular inflammation plays a crucial role in atherosclerosis, and its regulation is important to prevent cerebrovascular and coronary artery disease. The inflammatory process in atherogenesis involves a variety of immune cells including monocytes/macrophages, lymphocytes, dendritic cells, and neutrophils, which all express peroxisome proliferator-activated receptor-γ (PPAR-γ). PPAR-γ is a nuclear receptor and transcription factor in the steroid superfamily and is known to be a key regulator of adipocyte differentiation. Increasing evidence from mainly experimental studies has demonstrated that PPAR-γ activation by endogenous and synthetic ligands is involved in lipid metabolism and anti-inflammatory activity. In addition, recent clinical studies have shown a beneficial effect of thiazolidinediones, synthetic PPAR-γ ligands, on cardiovascular disease beyond glycemic control. These results suggest that PPAR-γ activation is an important regulator in vascular inflammation and is expected to be a therapeutic target in the treatment of atherosclerotic complications. This paper reviews the recent findings of PPAR-γ involvement in vascular inflammation and the therapeutic potential of regulating the immune system in atherosclerosis.

Fenofibrate enhances the in vitro differentiation of foxp3(+) regulatory T cells in mice

Foxp3⁺ regulatory T cells (Tregs) play a critical role in maintaining immune self-tolerance. Reduced number and activity of Tregs are usually found in autoimmune and inflammatory diseases, and enhancing the differentiation of Tregs may be a promising therapeutic strategy. Some reports suggested an anti-inflammatory and anti-autoimmune potential for fenofibrate, a hypolipidemic drug used worldwide, whose lipid effects are mediated by the activation of peroxisome proliferator-activated receptor α (PPARα). In the present paper, we found that fenofibrate dose-dependently increased transforming growth factor-β and interleukin-2-induced Treg differentiation in vitro, by 1.96-fold from 0 to 20 μM (12.59 ± 1.34% to 24.69 ± 3.03%, P < 0.05). Other PPARα activators, WY14643 (100 μM), gemfibrozil (50 μM), and bezafibrate (30 μM), could not enhance Treg differentiation. In addition, PPARα could not upregulate the promoter activity of the Treg-specific transcription factor Foxp3. Fenofibrate might exert its function by enhancing Smad3 phosphorylation, a critical signal in Treg differentiation, via Akt suppression. Our work reveals a new PPARα independent anti-inflammatory mechanism of fenofibrate in up-regulating mouse Treg differentiation.

Lysophosphatidylcholine enhances the suppressive function of human naturally occurring regulatory T cells through TGF-β production

Naturally occurring CD4(+)CD25(+) regulatory T cells (nTregs) play a pivotal role in the maintenance of self-tolerance and immune homeostasis. To gain insight into the mechanism of action of nTregs in pathological and physiological immune responses, it is important to analyze bioactive molecules that modulate the maintenance and function of nTregs. From a library of bioactive lipids, we obtained lysophosphatidylcholine (LPC) as a molecule that enhanced the Foxp3 expression and suppressive function of human nTregs significantly in comparison with those of DMSO-treated nTregs (control). The expression levels of TGF-β1 mRNA and protein in LPC-treated nTregs were significantly higher than those in control nTregs. After treatment with anti-TGF-β1 antibody, the increases in Foxp3 expression and the suppressive properties of LPC-treated nTregs returned to the levels observed in control nTregs. These findings indicate that LPC enhances Foxp3 expression and the suppressive function of nTregs through TGF-β1 produced by nTregs themselves. Experimental knockdown of G2A and GPR4 showed that this LPC-induced TGF-β1 expression in nTregs was due to G2A signaling, and did not involve GPR4. Moreover, JNK was a major contributor to LPC-induced TGF-β1 expression in nTregs, although LPC activated MAPKs including ERK1/2, p38 MAPK, and JNK via G2A. LPC is a bioactive lysolipid highly abundant in the circulation. Therefore, LPC may contribute to the maintenance and function of human nTregs in vivo.

FOXP3 Expression in GARP-Transduced Helper T Cells Is Not Associated with FOXP3 TSDR Demethylation

AIM: Glycoprotein A repetitions predominant (GARP or LRRC32) represents a human regulatory CD4+ CD25(hi) FOXP3+ T (T(reg)) cell-specific receptor that controls FOXP3. Ectopic expression of GARP in helper T (T(h)) cells has been shown to be sufficient for the induction of FOXP3 and generation of a stable regulatory phenotype. Since expression of FOXP3 in Treg cells is epigenetically controlled by a conserved motif, the so-called T(reg)-specific demethylated region (TSDR), we asked whether GARP-mediated upregulation of FOXP3 in Th cells is similarly accompanied by demethylation of the TSDR. METHODS: DNA methylation of the FOXP3 TSDR was analyzed by direct sequencing of polymerase chain reaction (PCR) products from bisulfite-treated genomic DNA. RESULTS: Although GARP-transduced T(h) cells exhibit constitutive FOXP3 expression and a regulatory phenotype, the FOXP3 TSDR is completely methylated as in naive T(h) cells. GARP-mediated FOXP3 upregulation in T(h) cells is not associated with T(reg)-specific demethylation of the FOXP3 TSDR. CONCLUSION: Although GARP-engineered T(h) cells exhibit stable FOXP3 expression and a phenotypic reprogramming towards T(reg) cells in vitro, these cells do not completely mimic the epigenotype of natural T(reg) cells. Thus, concepts based on the genetic modification of T(h) cells as cellular therapies to treat autoimmune diseases or to control transplantation tolerance should be critically tested before any clinical application.

Peroxisome proliferator-activated receptor gamma is required for CD4+ T cell-mediated lymphopenia-associated autoimmunity

The nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) was shown to play an immunoregulatory role in many immune-related cell types, and activation of PPARγ was reported to be an effective therapeutic approach in murine and human autoimmune disease. However, despite an association between lymphopenia and autoimmunity, there has been no study on the role of T cell PPARγ in lymphopenia-associated autoimmunity. In the present studies, we examined the role of PPARγ in CD4(+) T cells in two murine models of lymphopenia-associated autoimmunity. Surprisingly, we found that PPARγ expression in CD4(+) CD25(-) T cells (T effector cells [Teffs]) is actually required for development of autoimmunity under lymphopenic conditions. Mechanistically, the inability of PPARγ-deficient (T-PPAR) Teffs to mediate lymphopenic autoimmunity is associated with a significant decrease in accumulation of Teffs in the spleen, lymph nodes, and tissues after adoptive transfer. This abnormal accumulation of T-PPAR Teffs was associated with defects in both in vivo proliferation and survival. Additionally, T-PPAR Teffs demonstrated decreased cytokine production in inflammatory sites and decreased expression of the homing receptor α4β7. Finally, these abnormalities in T-PPAR Teff function were not elicited by lymphopenia alone but also required the additional activation involved in the mediation of autoimmunity. Thus, in contrast to its documented immunosuppressive role, we identified an unexpected function for PPARγ in Teffs: a role in Teff proliferation and survival in lymphopenia-associated autoimmunity. These findings highlight both the multifunctional role of PPARγ in T cells and the complexity of PPARγ as a potential therapeutic target in autoimmunity.

Rationale for HDAC inhibitor therapy in autoimmunity and transplantation

While there are currently more than 70 ongoing clinical trials of inhibitors of so-called classical HDACs (HDACi) as anticancer therapies, given their potency as antiproliferative and angiostatic agents, HDACi also have considerable therapeutic potential as anti-inflammatory and immunosuppressive drugs. The utility of HDACi as anti-inflammatory agents is dependent upon their proving safe and effective in experimental models. Current pan-HDACi compounds are not well suited to this role, given the broad distribution of target HDACs and their complex and multifaceted mechanisms of action. In contrast, the development of isoform-selective HDACi may provide important new tools for therapy in autoimmunity and transplantation. This chapter discusses which HDACs are worthwhile targets in inflammation and progress toward their therapeutic inhibition, including the use of HDAC subclass and isoform-selective HDACi to promote the functions of Foxp3+ T regulatory cells.