Involvement of prostaglandin receptors (EPR2–4) in in vivo immunosuppression of PGE2 in rat skin transplant model

Inhibition of Prostaglandin-Degrading Enzyme 15-PGDH Mitigates Acute Murine Lung Allograft Rejection

PURPOSE

Acute rejection is a frequent complication among lung transplant recipients and poses substantial therapeutic challenges. 15-hydroxyprostaglandin dehydrogenase (15-PGDH), an enzyme responsible for the inactivation of prostaglandin E2 (PGE2), has recently been implicated in inflammatory lung diseases. However, the role of 15-PGDH in lung transplantation rejection remains elusive. The present study was undertaken to examine the expression of 15-PGDH in rejected lung allografts and whether inhibition of 15-PGDH ameliorates acute lung allograft rejection.

METHODS

Orthotopic mouse lung transplantations were performed between donor and recipient mice of the same strain or allogeneic mismatched pairs. The expression of 15-PGDH in mouse lung grafts was measured. The efficacy of a selective 15-PGDH inhibitor (SW033291) in ameliorating acute rejection was assessed through histopathological examination, micro-CT imaging, and pulmonary function tests. Additionally, the mechanism underlying the effects of SW033291 treatment was explored using CD8+ T cells isolated from mouse lung allografts.

RESULTS

Increased 15-PGDH expression was observed in rejected allografts and allogeneic CD8+ T cells. Treatment with SW033291 led to an accumulation of PGE2, modulation of CD8+ T-cell responses and mitochondrial activity, and improved allograft function and survival.

CONCLUSION

Our study provides new insights into the role of 15-PGDH in acute lung rejection and highlights the therapeutic potential of inhibiting 15-PGDH for enhancing graft survival. The accumulation of PGE2 and modulation of CD8+ T-cell responses represent potential mechanisms underlying the benefits of 15-PGDH inhibition in this model. Our findings provide impetus for further exploring 15-PGDH as a target for improving lung transplantation outcomes.

Role of prostaglandin E2 in allogeneic mesenchymal stem cell therapy for cardiac repair

Ischemic heart disease is among the primary causes of cardiovascular-related deaths worldwide. Conventional treatments including surgical interventions and medical therapies aid in preventing further damage to heart muscle but are unable to provide a permanent solution. In recent years, stem cell therapy has emerged as an attractive alternative to restore damaged myocardium after myocardial injury. Allogeneic (donor-derived) mesenchymal stem cells (MSCs) have shown great promise in preclinical and clinical studies, making them the most widely accepted candidates for cardiac cell therapy. MSCs promote cardiac repair by modulating host immune system and secreting various soluble factors, of which prostaglandin E2 (PGE2) is an important one. PGE2 plays a significant role in regulating cardiac remodeling following myocardial injury. In this review, we provide an overview of allogeneic MSCs as candidates for myocardial regeneration with a focus on the role of the PGE2/cyclooxygenase-2 (COX2) pathway in mediating these effects.

Differential Expression of Prostaglandin E2 Receptors in Porcine Kidney Transplants

BACKGROUND

Acute rejection of a kidney allograft results from adaptive immune responses and marked inflammation. The eicosanoid prostaglandin E2 (PGE2) modulates the inflammatory response, is generated by cyclooxygenase 2 (COX-2), and binds to 1 of the 4 G protein-coupled E prostanoid cell surface receptors (EP1-4). Receptor activation results in in proinflammatory (EP1 and EP3) or anti-inflammatory (EP2 and EP4) responses. We theorized that expression of the components of the COX-PGE2-EP signaling pathway correlates with acute rejection in a porcine model of allogeneic renal transplantation.

METHOD

COX-2 enzyme and EP receptor protein expression were quantitated with western blotting and immunohistochemistry from allotransplants (n = 18) and autotransplants (n = 5). Linear regression analysis was used to correlate EP receptor expression with the Banff category of rejection.

RESULTS

Pigs with advanced rejection demonstrated significant increases in serum PGE2 metabolites, while pigs with less rejection demonstrated higher tissue concentrations of PGE2 metabolites. A significant negative correlation between COX-2 expression and Banff category of rejection (R = -0.877) was shown. Rejection decreased expression of EP2 and EP4. For both receptors, there was a significant negative correlation with the extent of rejection (R = -0.760 and R = -0.891 for EP2 and EP4, respectively). Rejection had no effect on the proinflammatory receptors EP1 and EP3.

CONCLUSION

Downregulation of COX-2 and the anti-inflammatory EP2 and EP4 receptors is associated with acute rejection in unmatched pig kidney transplants, suggesting that the COX-2-PGE2-EP pathway may modulate inflammation in this model. Enhancing EP2 and/or EP4 activity may offer novel therapeutic approaches to controlling the inflammation of acute allograft rejection.

PGE2 stimulates COX-2 expression via EP2/4 receptors and acts in synergy with IL-1β in human follicular dendritic cell-like cells

PGE2 is the major lipid mediator of inflammation produced by multiple cell types including follicular dendritic cells (FDCs) of the lymphoid tissue. We have investigated the immunoregulatory function of PGE2 and its production mechanism using FDC-like cells isolated from human tonsil. Our recent observation of COX-2-inducing effect of PGE2 prompted us to identify the responsible receptor in this study. Pharmacologic approaches were adopted and Western blotting was utilized to measure protein expression levels. Agonists selective for EP2 and EP4 significantly stimulated COX-2 expression, while antagonists for these receptors prevented PGE2 from triggering COX-2 induction. The combined addition of EP2 and EP4 antagonists resulted in further inhibition of PGE2. In contrast, EP1 and EP3 antagonists failed to exhibit the inhibitory effect on PGE2-induced COX-2 expression. Since PGE2 achieves COX-2 induction by repressing Akt activation in FDC-like cells, we confirmed EP2 and EP4 being the targets of PGE2 by examining the effects of E-prostanoid (EP) agonists and antagonists on the level of Akt phosphorylation. After the identification of PGE2 receptor, we examined the effect of PGE2 on IL-1β-induced COX-2 expression. PGE2 and IL-1β brought about a synergistic induction of COX-2 expression. Taken together, this study implies the impact of the combined role of eicosanoids and cytokines in inflammatory milieu.

Prostaglandin EP2 receptor: Novel therapeutic target for human cancers (Review)

Prostaglandin E2 (PGE2) receptor 2 subtype (EP2), which is a metabolite of arachidonic acid that binds with and regulates cellular responses to PGE2, is associated with numerous physiological and pathological events in a wide range of tissues. As a stimulatory G protein‑coupled receptor, PGE2‑induced EP2 activation can activate adenylate cyclase, leading to increased cytoplasmic cAMP levels and activation of protein kinase A. The EP2 receptor can also activate the glycogen synthase kinase 3β and β‑catenin pathways. The present study aimed to review the roles of the EP2 receptor in tumor development, including immunity, chronic inflammation, angiogenesis, metastasis and multidrug resistance. Furthermore, the involvement of the EP2 receptor signaling pathway in cancer was discussed. Understanding the role and mechanisms of action of the EP2 receptor, and its importance in targeted therapy, may help identify novel methods to improve management of numerous types of cancer.

Activated Platelets Induce an Anti-Inflammatory Response of Monocytes/Macrophages through Cross-Regulation of PGE2 and Cytokines

Platelets are well known for their role in hemostasis and are also increasingly recognized for their roles in the innate immune system during inflammation and their regulation of macrophage activation. Here, we aimed to study the influence of platelets on the production of inflammatory mediators by monocytes and macrophages. Analyzing cocultures of platelets and murine bone marrow-derived macrophages or human monocytes, we found that collagen-activated platelets release high amounts of prostaglandin E₂ (PGE₂) that leads to an increased interleukin- (IL-) 10 release and a decreased tumor necrosis factor (TNF) α secretion out of the monocytes or macrophages. Platelet PGE₂ mediated the upregulation of IL-10 in both cell types via the PGE₂ receptor EP2. Notably, PGE₂-mediated IL-10 synthesis was also mediated by EP4 in murine macrophages. Inhibition of TNFα synthesis via EP2 and EP4, but not EP1, was mediated by IL-10, since blockade of the IL-10 receptor abolished the inhibitory effect of both receptors on TNFα release. This platelet-mediated cross-regulation between PGE₂ and cytokines reveals one mechanism how monocytes and macrophages can attenuate excessive inflammatory responses induced by activated platelets in order to limit inflammatory processes.

Finasteride Enhances the Generation of Human Myeloid-Derived Suppressor Cells by Up-Regulating the COX2/PGE2 Pathway

Myeloid-derived suppressor cells (MDSCs) have been known to be a key factor in the regulation of the immune system under numerous conditions such as tumors, infections, autoimmune diseases, and transplantations. In contrast to the proposed deleterious role of MDSCs in tumors and infections, MDSCs with their suppressive function are now proved to have the beneficial potential of suppressing the autoimmune response and promoting tolerance to transplantation. Therefore, the expansion of MDSCs could be a promising therapeutic strategy for many diseases. In this study, we aimed to identify FDA-approved drugs that could aid in the expansion of functional MDSCs. We performed a high-throughput screening (HTS) of FDA-approved drugs based on the in vitro human MDSC-differentiation system and identified finasteride (FIN) to have the best potency to aid the generation of human MDSCs. The FIN-induced MDSCs were quite similar to monocytic MDSCs with regard to their surface phenotype, morphology, immunosuppressive function, and related gene expression. Next, we aimed to determine the mechanism of action of FIN and found that FIN induced the expansion of MDSCs through up-regulation of the COX2/PGE2 pathway by enhancing the activity of COX2 promoter. In addition, the administration of indomethacin (IND), a COX2 inhibitor, abrogated the effect of FIN. Based on these results, we suggested that FIN could find applications in the future in the expansion of MDSCs. Further development of FIN-like compounds could be a novel strategy for generating functional MDSCs for immunosuppressive therapies in various immune disorder conditions.

Myeloid-derived suppressor cells in transplantation and cancer

Myeloid-derived suppressor cells (MDSC) are myeloid cells that suppress the immune response, a definition that reflects both their origin and their function. As negative regulators of the immune response, MDSC represent a novel therapeutic approach for manipulating the immune system toward tolerance or immunity. MDSC are present in cancer patients and tumor-bearing mice and are in part responsible for the inhibition of the cell-mediated immune response against the tumor. Our laboratories investigate the immunologic mechanisms of tumor acceptance mediated by MDSC, which can be exploited to prevent allograft rejection in transplantation. A better understanding of MDSC biology will open new avenues for therapeutic intervention, either by inhibiting their function (i.e. in cancer patients), or by enhancing their suppressive effects and promoting their expansion (i.e. in organ transplantation and alloimmune responses). In this review, we summarize some of the critical aspects of the immunoregulatory function of MDSC in cancer and transplantation and discuss their potential clinical applications.

The eicosanoid response to high dose UVR exposure of individuals prone and resistant to sunburn

High personal UVR doses can be gained during leisure activities, causing intense self-resolving inflammation (sunburn) of unprotected skin. UVR activates release of membrane fatty acids and upregulates their metabolism by cyclooxygenases (COX) and lipoxygenases (LOX) to different eicosanoids. While COX-derived prostaglandin (PG)E(2) is a potent mediator of sunburn vasodilatation, LOX-derived 15-hydroxyeicosatetraenoic acid (HETE) and its lipoxin metabolites may contribute to sunburn limitation. We explored the relationships between expression of these lipid mediators and the clinical and histological outcomes, comparing responses of individuals prone and more resistant to sunburn. An acute UVR exposure of 12 SED (standard erythema dose) was applied to buttock skin of 32 white Caucasians (n = 16 phototype I/II, n = 16 phototype III/IV), and over the subsequent 72 h assessments were made of skin erythema, immunohistochemical expression of leukocyte markers, COX-2, 12-LOX, 15-LOX and nitric oxide synthase (NOS), and eicosanoid levels by LC/ESI-MS/MS. Evidence of a significant inflammatory response was seen earlier in phototype I/II with regard to expression of erythema (4 h, p < 0.001), neutrophil infiltration (24 h, p = 0.01), epidermal COX-2 (24 h, p < 0.05) and 12-LOX (24 h, p < 0.01), and dermal eNOS (24 h, p < 0.05) proteins, although CD3+ lymphocyte infiltration showed an earlier increase in phototype III/IV (24 h, p < 0.05). Although erythema was equivalent at 72 h in both groups, phototype I/II showed higher PGE(2) accompanied by elevated 15-HETE, and a strong positive correlation was seen between these mediators (n = 18, r = 0.805, p = 0.0001). Hence anti-inflammatory eicosanoid 15-HETE may temper the pro-inflammatory milieu in sunburn, having greater influence in those prone to sunburn than those more resistant, given the same high UVR exposure conditions.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

The regulation of CD4+ T cell immune responses toward Th2 cell development by prostaglandin E2

As an important immune mediator, PGE2 plays an important role in the immune tolerance, autoimmune diseases, immune regulation and tumor immunotolerance. PGE2 is considered to be a promising candidate for the control of the immune diseases. To further understand the immuno-modulating effects of PGE2 on CD4+ T cells, in vitro investigation was conducted in the present study. The results showed that PGE2 inhibited the proliferation of T cells in vitro in a dose-dependent manner. Gene expression profiling showed that 1716 genes were down regulated and 73 genes were up regulated with a change of 1.5 fold. Several signal transduction pathways were involved, such as TNF-α and NF-kB signaling pathway, T cell receptor signaling pathway, IL-2 signaling pathway, and MAPK pathway. The results showed that PGE2 inhibited IFN-γ, TNF-α and IL-4 production by CD4+ T cells 24h after cell culture. A comparison between IFN-γ and IL-4 production showed that PGE2 enhanced the relative ratio of IL-4 to IFN-γ in CD4+ T cells culture, and regulated CD4+ T cells toward Th2 cell development. The results of the present study indicated that PGE2 has the potential to treat Th1-mediated inflammatory diseases by regulating CD4+ T cells toward Th2 cell immune response.

The peroxisome proliferator-activated receptor gamma system regulates ultraviolet B-induced prostaglandin e(2) production in human epidermal keratinocytes

Studies using PPARgamma agonists in mouse skin have suggested that peroxisome proliferator-activated receptor gamma (PPARgamma) is irrelevant to cutaneous photobiology. However, in several epithelial cell lines, ultraviolet B (UVB) has been shown to induce the nonenzymatic production of oxidized phospholipids that act as PPARgamma agonists. UVB is also a potent inducer of prostaglandin E(2) (PGE(2)) production and COX-2 expression in keratinocytes and PPARgamma is coupled to increased PGE(2) production in other cell lines. In this current study, we demonstrate that PPARgamma agonists, but not PPARalpha or PPARbeta/delta agonists, induce PGE(2) production and COX-2 expression in primary human keratinocytes (PHKs). Importantly, PPARgamma agonist-induced COX-2 expression and PGE(2) production were partially inhibited by the PPARgamma antagonist, GW9662, indicating that both PPARgamma-dependent and -independent pathways are likely involved. GW9662 also suppressed UVB and tert-butylhydroperoxide- (TBH-) induced PGE(2) production in PHKs and intact human epidermis and partially inhibited UVB-induced COX-2 expression in PHKs. These findings provide evidence that PPARgamma is relevant to cutaneous photobiology in human epidermis.

The IL-10 and IFN-gamma pathways are essential to the potent immunosuppressive activity of cultured CD8+ NKT-like cells

Global gene expression profiling of in vitro cultured CD8⁺ T cells that express natural killer cell markers revealed differential expression of about 3,000 genes between these cells and naïve CD8⁺ T cells.

Background

CD8⁺ NKT-like cells are naturally occurring but rare T cells that express both T cell and natural killer cell markers. These cells may play key roles in establishing tolerance to self-antigens; however, their mechanism of action and molecular profiles are poorly characterized due to their low frequencies. We developed an efficient in vitro protocol to produce CD8⁺ T cells that express natural killer cell markers (CD8⁺ NKT-like cells) and extensively characterized their functional and molecular phenotypes using a variety of techniques.

Results

Large numbers of CD8⁺ NKT-like cells were obtained through culture of naïve CD8⁺ T cells using anti-CD3/anti-CD28-coated beads and high dose IL-2. These cells possess potent activity in suppressing the proliferation of naïve responder T cells. Gene expression profiling suggests that the cultured CD8⁺ NKT-like cells and the naïve CD8⁺ T cells differ by more than 2-fold for about 3,000 genes, among which 314 are upregulated by more than 5-fold and 113 are upregulated by more than 10-fold in the CD8⁺ NKT-like cells. A large proportion of the highly upregulated genes are soluble factors or surface markers that have previously been implicated in immune suppression or are likely to possess immunosuppressive properties. Many of these genes are regulated by two key cytokines, IL-10 and IFN-γ. The immunosuppressive activities of cells cultured from IL-10^-/- and IFN-γ^-/- mice are reduced by about 70% and about 50%, respectively, compared to wild-type mice.

Conclusion

Immunosuppressive CD8⁺ NKT-like cells can be efficiently produced and their immunosuppressive activity is related to many surface and soluble molecules regulated by IL-10 and IFN-γ.