Prostaglandin E2-induced IL-23p19 subunit is regulated by cAMP-responsive element-binding protein and C/AATT enhancer-binding protein β in bone marrow-derived dendritic cells

Stem cell transplantation uncovers TDO-AHR regulation of lung dendritic cells in herpesvirus-induced pathology

The aryl-hydrocarbon receptor (AHR) is an intracellular sensor of aromatic hydrocarbons that sits at the top of various immunomodulatory pathways. Here, we present evidence that AHR plays a role in controlling IL-17 responses and the development of pulmonary fibrosis in response to respiratory pathogens following bone marrow transplant (BMT). Mice infected intranasally with gamma-herpesvirus 68 (γHV-68) following BMT displayed elevated levels of the AHR ligand, kynurenine (kyn), in comparison with control mice. Inhibition or genetic ablation of AHR signaling resulted in a significant decrease in IL-17 expression as well as a reduction in lung pathology. Lung CD103⁺ DCs expressed AHR following BMT, and treatment of induced CD103⁺ DCs with kyn resulted in altered cytokine production in response to γHV-68. Interestingly, mice deficient in the kyn-producing enzyme indolamine 2-3 dioxygenase showed no differences in cytokine responses to γHV-68 following BMT; however, isolated pulmonary fibroblasts infected with γHV-68 expressed the kyn-producing enzyme tryptophan dioxygenase (TDO2). Our data indicate that alterations in the production of AHR ligands in response to respiratory pathogens following BMT results in a pro-Th17 phenotype that drives lung pathology. We have further identified the TDO2/AHR axis as a potentially novel form of intercellular communication between fibroblasts and DCs that shapes immune responses to respiratory pathogens.

Angiogenesis in Lymph Nodes Is a Critical Regulator of Immune Response and Lymphoma Growth

Tumor-induced remodeling of the microenvironment in lymph nodes (LNs) includes the formation of blood vessels, which goes beyond the regulation of metabolism, and shaping a survival niche for tumor cells. In contrast to solid tumors, which primarily rely on neo-angiogenesis, hematopoietic malignancies usually grow within pre-vascularized autochthonous niches in secondary lymphatic organs or the bone marrow. The mechanisms of vascular remodeling in expanding LNs during infection-induced responses have been studied in more detail; in contrast, insights into the conditions of lymphoma growth and lodging remain enigmatic. Based on previous murine studies and clinical trials in human, we conclude that there is not a universal LN-specific angiogenic program applicable. Instead, signaling pathways that are tightly connected to autochthonous and infiltrating cell types contribute variably to LN vascular expansion. Inflammation related angiogenesis within LNs relies on dendritic cell derived pro-inflammatory cytokines stimulating vascular endothelial growth factor-A (VEGF-A) expression in fibroblastic reticular cells, which in turn triggers vessel growth. In high-grade B cell lymphoma, angiogenesis correlates with poor prognosis. Lymphoma cells immigrate and grow in LNs and provide pro-angiogenic growth factors themselves. In contrast to infectious stimuli that impact on LN vasculature, they do not trigger the typical inflammatory and hypoxia-related stroma-remodeling cascade. Blood vessels in LNs are unique in selective recruitment of lymphocytes via high endothelial venules (HEVs). The dissemination routes of neoplastic lymphocytes are usually disease stage dependent. Early seeding via the blood stream requires the expression of the homeostatic chemokine receptor CCR7 and of L-selectin, both cooperate to facilitate transmigration of tumor and also of protective tumor-reactive lymphocytes via HEV structures. In this view, the HEV route is not only relevant for lymphoma cell homing, but also for a continuous immunosurveillance. We envision that HEV functional and structural alterations during lymphomagenesis are not only key to vascular remodeling, but also impact on tumor cell accessibility when targeted by T cell-mediated immunotherapies.

Distinct Populations of Immune-Suppressive Macrophages Differentiate from Monocytic Myeloid-Derived Suppressor Cells in Cancer

Here, we report that functional heterogeneity of macrophages in cancer could be determined by the nature of their precursors: monocytes (Mons) and monocytic myeloid-derived suppressor cells (M-MDSCs). Macrophages that are differentiated from M-MDSCs, but not from Mons, are immune suppressive, with a genomic profile matching that of M-MDSCs. Immune-suppressive activity of M-MDSC-derived macrophages is dependent on the persistent expression of S100A9 protein in these cells. S100A9 also promotes M2 polarization of macrophages. Tissue-resident- and Mon-derived macrophages lack expression of this protein. S100A9-dependent immune-suppressive activity of macrophages involves transcription factor C/EBPβ. The presence of S100A9-positive macrophages in tumor tissues is associated with shorter survival in patients with head and neck cancer and poor response to PD-1 antibody treatment in patients with metastatic melanoma. Thus, this study reveals the pathway of the development of immune-suppressive macrophages and suggests an approach to their selective targeting.

The Protective Effects of the Ethyl Acetate Part of Er MiaoSan on Adjuvant Arthritis Rats by Regulating the Function of Bone Marrow-Derived Dendritic Cells

Aims. The aim of this study was to evaluate the protective effects of Er Miao San (EMS) and the regulative function of bone marrow-derived dendritic cells (BMDCs) on adjuvant arthritis (AA) in rats. Methods. The ethyl acetate part of EMS (3 g/kg, 1.5 g/kg, and 0.75 g/kg) was orally administered from day 15 after immunization to day 29. The polyarthritis index and paw swelling were measured, the ankle joint pathological changes were observed using hematoxylin-eosin (HE) staining, and the spleen and thymus index were determined. Moreover, T and B cell proliferation were determined using the CCK-8 assay. The expression of BMDC surface costimulatory molecules and inflammatory factors were determined using flow cytometry and ELISA kits, respectively. Results. Compared with the AA model rats, the ethyl acetate fraction of EMS obviously reduced paw swelling (from 1.0 to 0.7) and the polyarthritis index (from 12 to 9) $\left(P<0.01\right)$ and improved the severity of histopathology $\left(P<0.01\right)$ . The treatment using ethyl acetate fraction of EMS significantly reduced the spleen and thymus index $\left(P<0.01\right)$ and inhibited T and B cell proliferation $\left(P<0.01\right)$ . Moreover, EMS significantly modulated the expression of surface costimulatory molecules in BMDCs, including CD40, CD80, CD86, and major histocompatibility complex class II (MHC-II) $\left(P<0.01\right)$ . The results also showed that the ethyl acetate part of EMS significant inhibited the levels of proinflammatory cytokines interleukin- (IL-) 23 tumor necrosis factor- (TNF-) α and inflammatory factor prostaglandin (PG) E2 in the supernatant of BMDCs. However, the level of anti-inflammatory cytokine IL-10 was significantly increased $\left(P<0.01\right)$ . Conclusion. These results suggest that the ethyl acetate part of EMS has better protective effects on AA rats, probably by regulating the function of BMDCs and modulating the balance of cytokines.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Current Concepts on 6-sulfo LacNAc Expressing Monocytes (slanMo)

The human mononuclear phagocytes system consists of dendritic cells (DCs), monocytes, and macrophages having different functions in bridging innate and adaptive immunity. Among the heterogeneous population of monocytes the cell surface marker slan (6-sulfo LacNAc) identifies a specific subset of human CD14^- CD16⁺ non-classical monocytes, called slan⁺ monocytes (slanMo). In this review we discuss the identity and functions of slanMo, their contributions to immune surveillance by pro-inflammatory cytokine production, and cross talk with T cells and NK cells. We also consider the role of slanMo in the regulation of chronic inflammatory diseases and cancer. Finally, we highlight unresolved questions that should be the focus of future research.

Prostaglandin-cytokine crosstalk in chronic inflammation

Chronic inflammation underlies various debilitating disorders including autoimmune, neurodegenerative, vascular and metabolic diseases as well as cancer, where aberrant activation of the innate and acquired immune systems is frequently seen. Since non-steroidal anti-inflammatory drugs exert their effects by inhibiting COX and suppressing PG biosynthesis, PGs have been traditionally thought to function mostly as mediators of acute inflammation. However, an inducible COX isoform, COX-2, is often highly expressed in tissues of the chronic disorders, suggesting an as yet unidentified role of PGs in chronic inflammation. Recent studies have shown that in addition to their short-lived actions in acute inflammation, PGs crosstalk with cytokines and amplify the cytokine actions on various types of inflammatory cells and drive pathogenic conversion of these cells by critically regulating their gene expression. One mode of such PG-mediated amplification is to induce the expression of relevant cytokine receptors, which is typically observed in Th1 cell differentiation and Th17 cell expansion, events leading to chronic immune inflammation. Another mode of amplification is cooperation of PGs with cytokines at the transcription level. Typically, PGs and cytokines synergistically activate NF-κB to induce the expression of inflammation-related genes, one being COX-2 itself, which makes PG-mediated positive feedback loops. This signalling consequently enhances the expression of various NF-κB-induced genes including chemokines to macrophages and neutrophils, which enables sustained infiltration of these cells and further amplifies chronic inflammation. In addition, PGs are also involved in tissue remodelling such as fibrosis and angiogenesis. In this article, we review these findings and discuss their relevance to human diseases.

CD11c-Specific Deletion Reveals CREB as a Critical Regulator of DC Function during the Germinal Center Response

Dendritic cells (DCs) are crucial for the balance between immune response and tolerance, but the molecular mechanism regulating development, differentiation, and homeostasis are poorly understood. The transcriptional activator CREB is involved in regulating different cells of the innate and adaptive immune system and is a transcriptional regulator of development, survival, activation, or proliferation in macrophages, dendritic cells, B cells, and T cells. To directly examine the role of CREB in the regulation of DCs, the CREB gene was targeted for deletion with a CD11c-cre transgene. The deletion of CREB in CD11c⁺ cells did not involve any developmental or systemic defects within DC populations. However, CREB deficiency in CD11c⁺ cells reduced germinal center (GC) B cells in steady state, and immunization with NP-CGG resulted in a reduced formation of GCs, paralleled by the reduced production of IgGs in sera of immunized mice. In conclusion, we demonstrate that CREB expression in CD11c⁺ cells enhances germinal center responses, most likely by altering DC function, which might have implications for autoimmune diseases that are associated with dysregulated GC responses.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Stromal C-type lectin receptor COLEC12 integrates H. pylori, PGE2-EP2/4 axis and innate immunity in gastric diseases

Tissue stroma is known to be important in regulating Hp-mediated inflammation, but its interaction with Hp and dendritic cells (DCs) remains to be determined. To this end, the potential crosstalk between H. pylori (Hp) infected gastric stromal cells (Hp-GSCs) and DCs was investigated. Primary GSCs from cancerous and adjacent normal tissues were generated from gastric cancer patients, and monocyte-derived DCs were obtained from healthy individuals. Levels of cytokines and prostaglandin E₂ (PGE₂) were measured by ELISA, and C-type lectin expression in GSCs was assessed by flow cytometry and immunohistochemistry. In a trans-well co-culture system, significantly upregulated DC-derived IL-23 expression was found when DCs were co-cultured with Hp-infected GSCs (Hp-GSCs). Further, PGE₂ from Hp-GSCs was discovered to possess the priming effect, which could be inhibited by anti-COLEC12 (Collectin subfamily member 12) Abs, COLEC12 knockdown or when alpha3-fucosyltransferase-null (futB; HP0651) strain of Hp was used. Also, the expression of COLEC12 was co-localized with CD90⁺ stromal cells in cancerous tissues. Hp-GSCs-conditioned DCs were able to induce the expression of IL-17 from CD4⁺ T cells, which could be inhibited by IL-23-neutralizing Abs. These results suggested the importance of COLEC12 as a receptor involved in Hp-stromal cell interaction and its subsequent conditioning effect on DCs.

Kallikrein-Kinin System Suppresses Type I Interferon Responses: A Novel Pathway of Interferon Regulation

The Kallikrein–Kinin System (KKS), comprised of kallikreins (klks), bradykinins (BKs) angiotensin-converting enzyme (ACE), and many other molecules, regulates a number of physiological processes, including inflammation, coagulation, angiogenesis, and control of blood pressure. In this report, we show that KKS regulates Type I IFN responses, thought to be important in lupus pathogenesis. We used CpG (TLR9 ligand), R848 (TLR7 ligand), or recombinant IFN-α to induce interferon-stimulated genes (ISGs) and proteins, and observed that this response was markedly diminished by BKs, klk1 (tissue kallikrein), or captopril (an ACE inhibitor). BKs significantly decreased the ISGs induced by TLRs in vitro and in vivo (in normal and lupus-prone mice), and in human PBMCs, especially the induction of Irf7 gene (p < 0.05), the master regulator of Type I IFNs. ISGs induced by IFN-α were also suppressed by the KKS. MHC Class I upregulation, a classic response to Type I IFNs, was reduced by BKs in murine dendritic cells (DCs). BKs decreased phosphorylation of STAT2 molecules that mediate IFN signaling. Among the secreted pro-inflammatory cytokines/chemokines analyzed (IL-6, IL12p70, and CXCL10), the strongest suppressive effect was on CXCL10, a highly Type I IFN-dependent cytokine, upon CpG stimulation, both in normal and lupus-prone DCs. klks that break down into BKs, also suppressed CpG-induced ISGs in murine DCs. Captopril, a drug that inhibits ACE and increases BK, suppressed ISGs, both in mouse DCs and human PBMCs. The effects of BK were reversed with indomethacin (compound that inhibits production of PGE2), suggesting that BK suppression of IFN responses may be mediated via prostaglandins. These results highlight a novel regulatory mechanism in which members of the KKS control the Type I IFN response and suggest a role for modulators of IFNs in the pathogenesis of lupus and interferonopathies.

Cyclic AMP-Responsive Element-Binding Protein (CREB) is Critical in Autoimmunity by Promoting Th17 but Inhibiting Treg Cell Differentiation

The molecular mechanisms that govern differential T cell development into pro-inflammatory Th17 vs. regulatory T (Treg) cells remain unclear. Here, we show that selective deletion of CREB in T cells or Th17 cells impaired Th17 cell differentiation in vitro and in vivo, and led to resistance to autoimmune diseases. Mechanistically, CREB, activated by CD3-PKC-ϴ signaling, plays a key role in regulating Th17 cell differentiation, at least in part through directly binding to the Il17-Il17f gene locus. Unexpectedly, although dispensable for FOXP3 expression and for the homeostasis and suppressive function of thymus-derived Treg cells, CREB negatively regulates the survival of TGF-β-induced Treg cells, and deletion of CREB resulted in increased FOXP3 + Treg cells in the intestine and protection in a colitis model. Thus, CREB is critical in autoimmune diseases by promoting Th17 cell and inhibiting de novo Treg cell generation.

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CREB is critical for autoimmunity.

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CREB plays a T cell- and Th17 cell-instrinsic role in controlling IL-17 expression and Th17 cell differentiation.

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CREB is dispensable for FOXP3 expression and the homeostasis of nTreg cells.

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CREB negatively regulates the survival of iTreg cells.

The balance of Th17 and Treg cells dictates development of numerous autoimmune and inflammatory diseases, and targeting Th17 cell-related pathways has been proved to be effective in treatment of related diseases. Here, we identified CREB as a critical transcription factor in regulating the differentiation of Th17 cells and survival of Treg cells in both in vitro experimental systems and mouse models of autoimmune diseases. The findings in this study might be useful for developing therapeutics against Th17 cell-related immune diseases.

Endoplasmic Reticulum Stress Sensor IRE1α Enhances IL-23 Expression by Human Dendritic Cells

Human monocyte-derived dendritic cells (DCs) exposed to pathogen-associated molecular patterns (PAMPs) undergo bioenergetic changes that influence the immune response. We found that stimulation with PAMPs enhanced glycolysis in DCs, whereas oxidative phosphorylation remained unaltered. Glucose starvation and the hexokinase inhibitor 2-deoxy-d-glucose (2-DG) modulated cytokine expression in stimulated DCs. Strikingly, IL23A was markedly induced upon 2-DG treatment, but not during glucose deprivation. Since 2-DG can also rapidly inhibit protein N-glycosylation, we postulated that this compound could induce IL-23 in DCs via activation of the endoplasmic reticulum (ER) stress response. Indeed, stimulation of DCs with PAMPs in the presence of 2-DG robustly activated inositol-requiring protein 1α (IRE1α) signaling and to a lesser extent the PERK arm of the unfolded protein response. Additional ER stressors such as tunicamycin and thapsigargin also promoted IL-23 expression by PAMP-stimulated DCs. Pharmacological, biochemical, and genetic analyses using conditional knockout mice revealed that IL-23 induction in ER stressed DCs stimulated with PAMPs was IRE1α/X-box binding protein 1-dependent upon zymosan stimulation. Interestingly, we further evidenced PERK-mediated and CAAT/enhancer-binding protein β-dependent trans-activation of IL23A upon lipopolysaccharide treatment. Our findings uncover that the ER stress response can potently modulate cytokine expression in PAMP-stimulated human DCs.

The phosphodiesterase 4 inhibitor apremilast inhibits Th1 but promotes Th17 responses induced by 6-sulfo LacNAc (slan) dendritic cells

BACKGROUND

The phosphodiesterase 4 (PDE4) inhibitor apremilast increases cellular cAMP levels and has proven effective in the treatment of psoriasis and psoriasis arthritis. We recently described 6-sulfo LacNAc dendritic cells (slanDCs) as immature DCs in blood and as a subset of inflammatory dermal DCs in psoriasis with a pronounced capacity to produce proinflammatory cytokines and to program Th17/Th1 T cell responses.

OBJECTIVE

The aim of this study was to investigate possible immune regulatory effects of the PDE4 inhibitor apremilast on slanDCs.

METHODS

In vitro studies were performed analyzing the effects of apremilast on the proinflammatory function of slanDCs and their capacity to induce Th1/Th17-biased T cell responses.

RESULTS

Increasing cAMP levels in slanDCs by PDE4 inhibition strongly reduced production of IL-12 and TNF-α. In line with these findings, co-culture experiments with apremilast-pulsed slanDCs and allogeneic T cells either from psoriasis patients or healthy controls, revealed a significant reduction of IFN-γ production and expression of the transcription factor T-bet. In parallel, production of IL-23 and IL-1ß by slanDCs was increased and co-cultured T cells revealed a largely augmented IL-17 production and an upregulated RORyt expression.

CONCLUSIONS

We here demonstrate anti-inflammatory as well as Th17-promoting effects of apremilast when studying blood precursors of human inflammatory dermal dendritic cells. In the concert of the broad anti-inflammatory effects of apremilast on keratinocytes, fibroblasts and endothelial cells, the dual effect on slan⁺ inflammatory dermal DCs should be taken into account and may constrain therapeutic responses.

Prostaglandin E2 Inhibition of IL-27 Production in Murine Dendritic Cells: A Novel Mechanism That Involves IRF1

IL-27, a multifunctional cytokine produced by APCs, antagonizes inflammation by affecting conventional dendritic cells (cDC), inducing IL-10, and promoting development of regulatory Tr1 cells. Although the mechanisms involved in IL-27 induction are well studied, much less is known about the factors that negatively impact IL-27 expression. PGE₂, a major immunomodulatory prostanoid, acts as a proinflammatory agent in several models of inflammatory/autoimmune disease, promoting primarily Th17 development and function. In this study, we report on a novel mechanism that promotes the proinflammatory function of PGE₂ We showed previously that PGE₂ inhibits IL-27 production in murine bone marrow-derived DCs. In this study, we show that, in addition to bone marrow-derived DCs, PGE₂ inhibits IL-27 production in macrophages and in splenic cDC, and we identify a novel pathway consisting of signaling through EP2/EP4→induction of cAMP→downregulation of IFN regulatory factor 1 expression and binding to the p28 IFN-stimulated response element site. The inhibitory effect of PGE₂ on p28 and irf1 expression does not involve endogenous IFN-β, STAT1, or STAT2, and inhibition of IL-27 does not appear to be mediated through PKA, exchange protein activated by cAMP, PI3K, or MAPKs. We observed similar inhibition of il27p28 expression in vivo in splenic DC following administration of dimethyl PGE₂ in conjunction with LPS. Based on the anti-inflammatory role of IL-27 in cDC and through the generation of Tr1 cells, we propose that the PGE₂-induced inhibition of IL-27 in activated cDC represents an important additional mechanism for its in vivo proinflammatory functions.

IL-23 Inhibits Melanoma Development by Augmenting DNA Repair and Modulating T Cell Subpopulations

In animal models, IL-12 and IL-23 participate in the development of malignant neoplasms of keratinocytes. However, the role of these cytokines in pigmented lesion development and their progression to melanoma has received little attention. IL-12p35, IL-23p19, and IL-12/IL-23p40 knockout mice on a C3H/HeN background, subjected to a melanomagenesis protocol, demonstrated profound differences in susceptibility to nevus initiation, transformation, tumorigenicity, and metastatic potential. IL-23 was found to be essential for melanocyte homeostasis, whereas IL-12 supported nevus development. A direct action of IL-23 on primary melanocytes, shown to be IL-23R⁺, demonstrated that DNA repair of damaged melanocytes requires IL-23. Furthermore, IL-23 modulated the cutaneous microenvironment by limiting regulatory T cells and IFN-γ and inhibiting IL-10 production. Neutralizing Ab to IFN-γ, but not IL-17, inhibited nevus development (p < 0.01).

Neuroimmune interactions: dendritic cell modulation by the sympathetic nervous system

Dendritic cells are of paramount importance bridging innate and adaptive immune responses. Depending on the context, after sensing environmental antigens, commensal microorganisms, pathogenic agents, or antigens from the diet, dendritic cells may drive either different effector adaptive immune responses or tolerance, avoiding tissue damage. Although the plasticity of the immune response and the capacity to regulate itself are considered essential to orchestrate appropriate physiological responses, it is known that the nervous system plays a relevant role controlling immune cell function. Dendritic cells present in the skin, the intestine, and lymphoid organs, besides expressing adrenergic receptors, can be reached by neurotransmitters released by sympathetic fibers innervating these tissues. These review focus on how neurotransmitters from the sympathetic nervous system can modulate dendritic cell function and how this may impact the immune response and immune-mediated disorders.

The phosphodiesterase 4 inhibitor roflumilast augments the Th17-promoting capability of dendritic cells by enhancing IL-23 production, and impairs their T cell stimulatory activity due to elevated IL-10

Phosphodiesterase 4 (PDE4) inhibitors serve to prevent degradation of the intracellular second messenger cAMP, resulting in broad anti-inflammatory effects on different cell types including immune cells. Agents that elevate cAMP levels via activation of adenylate cyclase have been shown to imprint a Th17-promoting capacity in dendritic cells (DCs). Therefore, we studied the potential of therapeutically relevant PDE inhibitors to induce a pronounced Th17-skewing capacity in DCs. Here we show that mouse bone marrow-derived (BM-) DCs when treated with the PDE4 inhibitor roflumilast (ROF, trade name: Daxas) in the course of stimulation with LPS (ROF-DCs) evoked elevated IL-17 levels in cocultured allogeneic T cells. In addition, as compared with control settings, levels of IFN-γ remained unaltered, while contents of Th2 cytokines (IL-5, IL-10) were diminished. ROF enhanced expression of the Th17-promoting factor IL-23 in BM-DCs. In line, neutralizing antibodies specific for IL-23 or IL-6 when applied to DC/T cell cocultures partially inhibited the IL17-promoting effect of ROF-DCs. Furthermore, ROF-DCs displayed a markedly diminished allogeneic T cell stimulatory capacity due to enhanced production of IL-10, which was restored upon application of IL-10 specific neutralizing antibody to DC/T cell cocultures. Both the IL-17-inducing and impaired T cell stimulatory capacity of BM-DCs were mimicked by a specific activator of protein kinase A, while stimulation of EPACs (exchange proteins of activated cAMP) did not yield such effects. Taken together, our findings suggest that PDE4 inhibitors aside from their broad overall anti-inflammatory effects may enhance the Th17-polarizing capacity in DCs as an unwanted side effect.

Stromal fibroblasts support dendritic cells to maintain IL-23/Th17 responses after exposure to ionizing radiation

Cross talk between DCs and FBs in understanding the effects of IR in DC function.

Dendritic cell function is modulated by stromal cells, including fibroblasts. Although poorly understood, the signals delivered through this crosstalk substantially alter dendritic cell biology. This is well illustrated with release of TNF-α/IL-1β from activated dendritic cells, promoting PGE₂ secretion from stromal fibroblasts. This instructs dendritic cells to up-regulate IL-23, a key Th17-polarizing cytokine. We previously showed that ionizing radiation inhibited IL-23 production by human dendritic cells in vitro. In the present study, we investigated the hypothesis that dendritic cell-fibroblast crosstalk overcomes the suppressive effect of ionizing radiation to support appropriately polarized Th17 responses. Radiation (1–6 Gy) markedly suppressed IL-23 secretion by activated dendritic cells (P < 0.0001) without adversely impacting their viability and consequently, inhibited the generation of Th17 responses. Cytokine suppression by ionizing radiation was selective, as there was no effect on IL-1β, -6, -10, and -27 or TNF-α and only a modest (11%) decrease in IL-12p70 secretion. Coculture with fibroblasts augmented IL-23 secretion by irradiated dendritic cells and increased Th17 responses. Importantly, in contrast to dendritic cells, irradiated fibroblasts maintained their capacity to respond to TNF-α/IL-1β and produce PGE₂, thus providing the key intermediary signals for successful dendritic cell-fibroblasts crosstalk. In summary, stromal fibroblasts support Th17-polarizing cytokine production by dendritic cells that would otherwise be suppressed in an irradiated microenvironment. This has potential ramifications for understanding the immune response to local radiotherapy. These findings underscore the need to account for the impact of microenvironmental factors, including stromal cells, in understanding the control of immunity.

Norepinephrine Controls Effector T Cell Differentiation through β2-Adrenergic Receptor-Mediated Inhibition of NF-κB and AP-1 in Dendritic Cells

Despite accumulating evidence indicating that neurotransmitters released by the sympathetic nervous system can modulate the activity of innate immune cells, we still know very little about how norepinephrine impacts signaling pathways in dendritic cells (DC) and the consequence of that in DC-driven T cell differentiation. In this article, we demonstrate that β2-adrenergic receptor (β2AR) activation in LPS-stimulated DC does not impair their ability to promote T cell proliferation; however, it diminishes IL-12p70 secretion, leading to a shift in the IL-12p70/IL-23 ratio. Although β2AR stimulation in DC induces protein kinase A-dependent cAMP-responsive element-binding protein phosphorylation, the effect of changing the profile of cytokines produced upon LPS challenge occurs in a protein kinase A-independent manner and, rather, is associated with inhibition of the NF-κB and AP-1 signaling pathways. Moreover, as a consequence of the inverted IL-12p70/IL-23 ratio following β2AR stimulation, LPS-stimulated DC promoted the generation of CD4(+) T cells that, upon TCR engagement, produced lower amounts of IFN-γ and higher levels of IL-17. These findings provide new insights into molecular and cellular mechanisms by which β2AR stimulation in murine DC can influence the generation of adaptive immune responses and may explain some aspects of how sympathetic nervous system activity can modulate immune function.

Pharmacological inhibition of eicosanoids and platelet-activating factor signaling impairs zymosan-induced release of IL-23 by dendritic cells

The engagement of the receptors for fungal patterns induces the expression of cytokines, the release of arachidonic acid, and the production of PGE2 in human dendritic cells (DC), but few data are available about other lipid mediators that may modulate DC function. The combined antagonism of leukotriene (LT) B4, cysteinyl-LT, and platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) inhibited IL23A mRNA expression in response to the fungal surrogate zymosan and to a lower extent TNFA (tumor necrosis factor-α) and CSF2 (granulocyte macrophage colony-stimulating factor) mRNA. The combination of lipid mediators and the lipid extract of zymosan-conditioned medium increased the induction of IL23A by LPS (bacterial lipopolysaccharide), thus suggesting that unlike LPS, zymosan elicits the production of mediators at a concentration enough for optimal response. Zymosan induced the release of LTB4, LTE4, 12-hydroxyeicosatetraenoic acid (12-HETE), and PAF C16:0. DC showed a high expression and detectable Ser663 phosphorylation of 5-lipoxygenase in response to zymosan, and a high expression and activity of LPCAT1/2 (lysophosphatidylcholine acyltransferase 1 and 2), the enzymes that incorporate acetate from acetyl-CoA into choline-containing lysophospholipids to produce PAF. Pharmacological modulation of the arachidonic acid cascade and the PAF receptor inhibited the binding of P-71Thr-ATF2 (activating transcription factor 2) to the IL23A promoter, thus mirroring their effects on the expression of IL23A mRNA and IL-23 protein. These results indicate that LTB4, cysteinyl-LT, and PAF, acting through their cognate G protein-coupled receptors, contribute to the phosphorylation of ATF2 and play a central role in IL23A promoter trans-activation and the cytokine signature induced by fungal patterns.

PGE2 Elevates IL-23 Production in Human Dendritic Cells via a cAMP Dependent Pathway

PGE2 elevates IL-23 production in mouse dendritic cells while inhibits IL-23 production in isolated human monocytes. Whether this differential effect of PGE2 on IL-23 production is cell-type- or species-specific has not been investigated in detail. The present study was designed to investigate the effect of PGE2 on IL-23 production in human DCs and the possible underlying mechanisms. Human monocytes derived dendritic cells (Mo-DCs) were pretreated with or without PGE2. Then the cells were incubated with zymosan. Our results demonstrated that PGE2 promoted zymosan-induced IL-23 production in a concentration dependent manner. In addition, it was found that PGE2 is also able to elevate MyD88-mediated IL-23 p19 promoter activity. More importantly, ELISA data demonstrated that db-cAMP, a cAMP analog, and forskolin, an adenylate cyclase activator, can mimic the effect of PGE2 on zymosan-induced IL-23 production, and rp-cAMP, a protein kinase A (PKA) inhibitor, can block the effect of PGE2. Moreover, PGE2 can increase zymosan-induced expression of the mRNA levels of both p19 and p40 subunits, which was mimicked by db-cAMP and forskolin. Our data suggest that PGE2 elevates the production of IL-23 in human Mo-DCs via a cAMP dependent pathway.

Prostaglandin E2-EP4 signaling persistently amplifies CD40-mediated induction of IL-23 p19 expression through canonical and non-canonical NF-κB pathways

While there is mounting evidence that interleukin (IL)-23-IL-17 axis plays a critical role in the pathogenesis of various autoimmune diseases, much remains to be elucidated on how IL-23 is induced in the pathological processes. IL-23 is a heterodimer composed of p19 and p40, the latter being shared with IL-12. We previously reported that prostaglandin (PG) E2 promotes CD40-mediated induction of Il23a (p19) expression through its E receptor subtype 4 (EP4) receptor in splenic dendritic cells (DCs). Here, we have analyzed signaling pathways regulating Il23a induction in the cross talk between EP4 and CD40 in bone marrow-derived DCs. We found that PGE2 synergistically induced Il23a transcription with CD40 signaling. An EP4 agonist, but not agonists of EP1, EP2, or EP3, reproduced this action. Stimulation of CD40 with an agonist antibody evoked biphasic induction of Il23a expression, with the early phase peaking at 1 h and the late phase peaking at 12 h and lasting up to 36 h after stimulation, whereas induction by lipopolysaccharide or tumor necrosis factor-α was transient. The early phase induction by CD40 stimulation was absent in DCs derived from Nfkb1-deficient mice, and the late phase induction was eliminated by RNA interference of nuclear factor-kappa B (NF-κB) p100 subunit. Further, cAMP response element-binding protein (CREB) depletion completely eliminated the induction of Il23a by CD40 stimulation. The addition of the EP4 agonist amplified the induction in both phases through the cAMP-protein kinase A (PKA) pathway. These results suggest that Il23a expression in DCs is synergistically triggered by the PG E2-EP4-cAMP-PKA pathway and canonical/non-canonical NF-κB pathways and CREB activated by CD40 stimulation.

Functional polymorphisms in interleukin-23 receptor and susceptibility to coronary artery disease

As a key element in the T-helper 17 (Th17) cell-mediated inflammatory process, interleukin-23 receptor (IL-23R) may play a crucial role in the pathogenesis of atherosclerosis. Single nucleotide polymorphisms (SNPs) in IL-23R have been studied in several diseases. However, its association with coronary artery disease (CAD) remains unclear. This study examined whether genetic polymorphisms in IL-23R were associated with susceptibility to CAD. Two IL-23R SNPs, rs1884444 and rs6682925, were genotyped in 462 CAD patients and 486 healthy controls. Data showed that percentages of rs6682925TC and CC genotypes were significantly higher in patients than in controls (odds ratio [OR]=1.23, 95% confidence interval [CI]: 1.04-1.79, p=0.022; OR=2.35, 95% CI: 1.52-3.43, p<0.001, respectively). Frequency of the rs1884444 polymorphism did not reveal any significant differences between patients and healthy donors. Further analyses demonstrated a significantly increased number of rs6682925CC genotype in patients with hypertension. Moreover, we investigated the effect of IL-23R polymorphisms on gene expression by assessing mRNA level of IL-23R in peripheral blood mononucleated cells (PBMCs). Results showed that subjects carrying rs6682925TC and CC genotypes had significantly increased mRNA level of IL-23R in PBMCs than those with TT genotype. These data suggest that IL-23R rs6682925T/C polymorphism may act as a risk factor of CAD.

The unfolded protein response and the phosphorylations of activating transcription factor 2 in the trans-activation of il23a promoter produced by β-glucans

Current views on the control of IL-23 production focus on the regulation of il23a, the gene encoding IL-23 p19, by NF-κB in combination with other transcription factors. C/EBP homologous protein (CHOP), X2-Box-binding protein 1 (XBP1), activator protein 1 (AP1), SMAD, CCAAT/enhancer-binding protein (C/EBPβ), and cAMP-response element-binding protein (CREB) have been involved in response to LPS, but no data are available regarding the mechanism triggered by the fungal mimic and β-glucan-containing stimulus zymosan, which produces IL-23 and to a low extent the related cytokine IL-12 p70. Zymosan induced the mobilization of CHOP from the nuclear fractions to phagocytic vesicles. Hypha-forming Candida also induced the nuclear disappearance of CHOP. Assay of transcription factor binding to the il23a promoter showed an increase of Thr(P)-71-Thr(P)-69-activating transcription factor 2 (ATF2) binding in response to zymosan. PKC and PKA/mitogen- and stress-activated kinase inhibitors down-regulated Thr(P)-71-ATF2 binding to the il23a promoter and il23a mRNA expression. Consistent with the current concept of complementary phosphorylations on N-terminal Thr-71 and Thr-69 of ATF2 by ERK and p38 MAPK, MEK, and p38 MAPK inhibitors blunted Thr(P)-69-ATF2 binding. Knockdown of atf2 mRNA with siRNA correlated with inhibition of il23a mRNA, but it did not affect the expression of il12/23b and il10 mRNA. These data indicate the following: (i) zymosan decreases nuclear proapoptotic CHOP, most likely by promoting its accumulation in phagocytic vesicles; (ii) zymosan-induced il23a mRNA expression is best explained through coordinated κB- and ATF2-dependent transcription; and (iii) il23a expression relies on complementary phosphorylation of ATF2 on Thr-69 and Thr-71 dependent on PKC and MAPK activities.

Myeloid-derived suppressor cell function is diminished in aspirin-triggered allergic airway hyperresponsiveness in mice

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) have recently been implicated in the pathogenesis of asthma, but their regulation in patients with aspirin-intolerant asthma (AIA) remains unclear.

OBJECTIVE

We sought to characterize MDSC accumulation and pathogenic functions in allergic airway inflammation mediated by COX-1 deficiency or aspirin treatment in mice.

METHODS

Allergic airway inflammation was induced in mice by means of ovalbumin challenge. The distribution and function of MDSCs in mice were analyzed by using flow cytometry and pharmacologic/gene manipulation approaches.

RESULTS

CD11b(+)Gr1(high)Ly6G(+)Ly6C(int) MDSCs (polymorphonuclear MDSCs [PMN-MDSCs]) recruited to the lungs are negatively correlated with airway inflammation in allergen-challenged mice. Aspirin-treated and COX-1 knockout (KO) mice showed significantly lower accumulation of PMN-MDSCs in the inflamed lung and immune organs accompanied by increased TH2 airway responses. The TH2-suppressive function of PMN-MDSCs was notably impaired by COX-1 deletion or inhibition, predominantly through downregulation of arginase-1. COX-1-derived prostaglandin E2 promoted PMN-MDSC generation in bone marrow through E prostanoid 2 and 4 receptors (EP2 and EP4), whereas the impaired arginase-1 expression in PMN-MDSCs in COX-1 KO mice was mediated by dysregulation of the prostaglandin E2/EP4/cyclic AMP/protein kinase A pathway. EP4 agonist administration alleviated allergy-induced airway hyperresponsiveness in COX-1 KO mice. Moreover, the immunosuppressive function of PMN-MDSCs from patients with AIA was dramatically decreased compared with that from patients with aspirin-tolerant asthma.

CONCLUSION

The immunosuppressive activity of PMN-MDSCs was diminished in both allergen-challenged COX-1 KO mice and patients with AIA, probably through an EP4-mediated signaling pathway, indicating that activation of PMN-MDSCs might be a promising therapeutic strategy for asthma, particularly AIA.

Possible roles of the cAMP-mediators EPAC and RAP1 in decidualization of rat uterus

The optimal decidualization of endometrial stromal cells (ESCs) following embryo implantation is one of the critical steps to establish pregnancy in rodents and humans. This step is intricately regulated by ovarian hormones. Using in vitro human ESCs model, we previously showed that activation of a cAMP mediator, exchange protein directly activated by cAMP (EPAC), promotes ovarian steroid- or cAMP analog-induced decidualization. However, expressions and functions of EPAC and RAP1 in the uterus during pregnancy have not yet been examined. In this study, we found that the expression of EPAC2 and RAP1 was markedly upregulated in the decidual cells at the implantation sites on days 7 and 9 of pregnancy in rats. Furthermore, both delayed-implantation and artificial decidualization models showed that EPAC2 and RAP1 expression was enhanced in decidual cells. Significant activation of cAMP-responsive element-binding protein (CREB), a central transcriptional factor of cAMP signaling, was observed in decidual cells. These spatiotemporal expressions of protein related EPAC pathway are overlapped by sites with activated cAMP signaling, indicating the association of EPAC signaling with decidualization. Strikingly, further studies in in vitro rat decidualization model showed that the cAMP analog and medroxyprogesterone stimulated the expression of decidual markers, while knockdown of EPAC1/2 and RAP1 attenuated the expressions of these markers. Together, these findings suggest that EPAC and RAP1 are the crucial factors for endometrial decidualization in rat pregnancy.

Diverse roles of prostaglandins in blastocyst implantation

Prostaglandins (PGs), derivatives of arachidonic acid, play an indispensable role in embryo implantation. PGs have been reported to participate in the increase in vascular permeability, stromal decidualization, blastocyst growth and development, leukocyte recruitment, embryo transport, trophoblast invasion, and extracellular matrix remodeling during implantation. Deranged PGs syntheses and actions will result in implantation failure. This review summarizes up-to-date literatures on the role of PGs in blastocyst implantation which could provide a broad perspective to guide further research in this field.

Polarization of the innate immune response by prostaglandin E2: a puzzle of receptors and signals

Eicosanoids tailor the innate immune response by supporting local inflammation and exhibiting immunomodulatory properties. Prostaglandin (PG) E2 is the most abundant eicosanoid in the inflammatory milieu due to the robust production elicited by pathogen-associated molecular patterns on cells of the innate immune system. The different functions and cell distribution of E prostanoid receptors explain the difficulty encountered thus far to delineate the actual role of PGE2 in the immune response. The biosynthesis of eicosanoids includes as the first step the Ca(2+)- and kinase-dependent activation of the cytosolic phospholipase A2, which releases arachidonic acid from membrane phospholipids, and later events depending on the transcriptional regulation of the enzymes of the cyclooxygenase routes, where PGE2 is the most relevant product. Acting in an autocrine/paracrine manner in macrophages, PGE2 induces a regulatory phenotype including the expression of interleukin (IL)-10, sphingosine kinase 1, and the tumor necrosis factor family molecule LIGHT. PGE2 also stabilizes the suppressive function of myeloid-derived suppressor cells, inhibits the release of IL-12 p70 by macrophages and dendritic cells, and may enhance the production of IL-23. PGE2 is a central component of the inflammasome-dependent induction of the eicosanoid storm that leads to massive loss of intravascular fluid, increases the mortality rate associated with coinfection by Candida ssp. and bacteria, and inhibits fungal phagocytosis. These effects have important consequences for the outcome of infections and the polarization of the immune response into the T helper cell types 2 and 17 and can be a clue to develop pharmacological tools to address infectious, autoimmune, and autoinflammatory diseases.

The multiple faces of prostaglandin E2 G-protein coupled receptor signaling during the dendritic cell life cycle

Many processes regulating immune responses are initiated by G-protein coupled receptors (GPCRs) and report biochemical changes in the microenvironment. Dendritic cells (DCs) are the most potent antigen-presenting cells and crucial for the regulation of innate and adaptive immune responses. The lipid mediator Prostaglandin E2 (PGE2) via four GPCR subtypes (EP1-4) critically regulates DC generation, maturation and migration. The role of PGE₂ signaling in DC biology was unraveled by the characterization of EP receptor subtype expression in DC progenitor cells and DCs, the identification of the signaling pathways initiated by these GPCR subtypes and the classification of DC responses to PGE₂ at different stages of differentiation. Here, we review the advances in PGE₂ signaling in DCs and describe the efforts still to be made to understand the spatio-temporal fine-tuning of PGE₂ responses by DCs.

Regulation of decidualization in human endometrial stromal cells through exchange protein directly activated by cyclic AMP (Epac)

INTRODUCTION

Human endometrial stromal cells (ESCs) undergo differentiation during the decidualization process. Decidualization is characterized by their enhanced production of IGF binding protein-1 (IGFBP-1), prolactin (PRL), and the forkhead transcriptional factor FOXO1, and transformation into more rounded cells, during the secretory phase of the menstrual cycle and subsequent pregnancy. Protein kinase A (PKA)-mediated cAMP signaling is crucial for this process. The present study was undertaken to examine the involvement of a mediator of cAMP signaling, exchange protein directly activated by cAMP (Epac), in decidualization of cultured ESCs.

RESULTS

Treatment of ESCs with the Epac-selective cAMP analog 8-CPT-2-OMe-cAMP (CPT) had no effect on IGFBP-1, PRL, and FOXO1 mRNA expression. However, CPT potentiated IGFBP-1 and PRL expression stimulated by the PKA-selective cAMP analog N(6)-Phe-cAMP (Phe) and activated Rap1, a downstream regulator of Epac signaling. Knock-down of Epac1, Epac2, or Rap1 significantly inhibited the Phe- or Phe/CPT-induced increase in IGFBP-1 and PRL expression, as well as Rap1 activation. Furthermore, CPT enhanced IGFBP-1 and PRL expression and the morphological differentiation induced by ovarian steroids, whereas Epac1, Epac2, or Rap1 knock-down suppressed these events.

CONCLUSION

These data provide evidence for the involvement of the Epac/Rap1 signaling pathway in cAMP-mediated decidualization of human ESCs.

PGE2 differentially regulates monocyte-derived dendritic cell cytokine responses depending on receptor usage (EP2/EP4)

Dendritic cells (DCs) are central players in coordinating immune responses, both innate and adaptive. While the role of lipid mediators in the immune response has been the subject of many investigations, the precise role of prostaglandins has often been plagued by contradictory studies. In this study, we examined the role of PGE(2) on human DC function. Although studies have suggested that PGE(2) specifically plays a role in DC motility and cytokine release profile, the precise receptor usage and signaling pathways involved remain unclear. In this report we found that irrespective of the human donor, monocyte-derived dendritic cells (MoDCs) express three of the four PGE(2) receptor subtypes (EP(2-4)), although only EP(2) and EP(4) were active with respect to cytokine production. Using selective EP receptor antagonists and agonists, we demonstrate that PGE(2) coordinates control of IL-23 release (a promoter of Th17, an autoimmune associated T cell subset) in a dose-dependent manner by differential use of EP(2) and EP(4) receptors in LPS-activated MoDCs. This is in contrast to IL-12, which is dose dependently inhibited by PGE(2) through both receptor subtypes. Low concentrations (∼1-10nM) of PGE(2) promoted IL-23 production via EP(4) receptors, while at higher (>50 nM), but still physiologically relevant concentrations, IL-23 is suppressed by an EP(2) dependent mechanism. These results can be explained by differential regulation of the common subunit, IL-12p40, and IL-23p19, by EP(2) and EP(4). By these means, PGE(2) can act as a regulatory switch of immune responses depending on its concentration in the microenvironment. In addition, we believe these results may also explain why seemingly conflicting biological functions assigned to PGE(2) have been reported in the literature, as the concentration of ligand (PGE(2)) fundamentally alters the nature of the response. This finding also highlights the potential of designing therapeutics which differentially target these receptors.