CRTH2 Research Articles

The endogenous bioactive lipid prostaglandin D2-glycerol ester reduces murine colitis via DP1 and PPARγ receptors.

Cyclooxygenase-2 (COX-2) has long been implicated in the pathogenesis of inflammatory bowel diseases (IBDs). COX-2 is mostly known for the production of prostaglandins (PGs) from arachidonic acid. However, it also metabolizes the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide into the less well-studied bioactive lipids PG-glycerol esters (PG-Gs) and PG-ethanolamides (PG-EAs or prostamides). We previously showed that PGD2-G, a product of 2-AG oxygenation by COX-2, has anti-inflammatory effects. Therefore, we used the dextran sulfate sodium (DSS)-induced model of colitis in mice to explore the role of PGD2-G in murine models of IBD. Colon inflammation was assessed using macroscopic and histologic scores, myeloperoxidase activity, and expression of inflammatory mediators by real-time quantitative PCR and ELISA. We also compared the effects of PGD2-G with those of PGD2 and PGD2-EA. Finally, we used receptor antagonists to gain mechanistic insight into the receptors responsible for the observed effects. PGD2-G reduced DSS-induced colitis, but PGD2 and PGD2-EA did not have the same effect. Furthermore, we showed that PGD2-G is an agonist of the PGD2 receptor 1 (DP1) and that some of the effects of PGD2-G were blocked by antagonism of peroxisome proliferator-activated receptor γ and DP1. Therefore, PGD2-G could be one of the products from the COX-2/prostaglandin D synthase axis to exert beneficial effects in colitis.-Alhouayek, M., Buisseret, B., Paquot, A., Guillemot-Legris, O., Muccioli, G. G. The endogenous bioactive lipid prostaglandin D2-glycerol ester reduces murine colitis via DP1 and PPARγ receptors.

DP1 receptor signaling prevents the onset of intrinsic apoptosis in eosinophils and functions as a transcriptional modulator

Prostaglandin (PG) D2 is the ligand for the G‐protein coupled receptors DP1 (D‐type prostanoid receptor 1) and DP2 (also known as chemoattractant receptor homologous molecule, expressed on Th2 cells; CRTH2). Both, DP1 and DP2 are expressed on the cellular surface of eosinophils; although it has become quite clear that PGD2 induces eosinophil migration mainly via DP2 receptors, the role of DP1 in eosinophil responses has remained elusive. In this study, we addressed how DP1 receptor signaling complements the pro‐inflammatory effects of DP2. We found that PGD2 prolongs the survival of eosinophils via a DP1 receptor‐mediated mechanism that inhibits the onset of the intrinsic apoptotic cascade. The DP1 agonist BW245c prevented the activation of effector caspases in eosinophils and protected mitochondrial membranes from depolarization which—as a consequence—sustained viability of eosinophils. DP1 activation in eosinophils enhanced the expression of the anti‐apoptotic gene BCL‐XL, but also induced pro‐inflammatory genes, such as VLA‐4 and CCR3. In HEK293 cells that overexpress recombinant DP1 and/or DP2 receptors, activation of DP1, but not DP2, delayed cell death and stimulated proliferation, along with induction of serum response element (SRE), a regulator of anti‐apoptotic, early‐response genes. We conclude that DP1 receptors promote the survival via SRE induction and induction of pro‐inflammatory genes. Therefore, targeting DP1 receptors, along with DP2, may contribute to anti‐inflammatory therapy in eosinophilic diseases.

The Role of the K2P Channels TASK‐1, TREK‐1 and TREK‐2 in the Use of Treprostinil Therapy in Pulmonary Arterial Hypertension

IntroductionPulmonary arterial hypertension (PAH) is a progressive and ultimately fatal disease affecting ~6 people per million, per year (1). Recent studies have reported mutations in the two‐pore domain potassium (K2P) channel TASK‐1 (KCNK3) giving rise to PAH (2). Treprostinil is a stable prostacyclin analogue often administered as a therapy in PAH, to keep blood vessels open. Its mode of action is thought to occur through an interaction with prostanoid receptors, DP2, EP2 and IP (3). Patients undergoing continuous subcutaneous treprostinil infusion can often exhibit severe pain at the site of delivery (4). In this study we investigate the action of treprostinil on TASK‐1 and on two other K2P channels, TREK‐1 (KCNK2) and TREK‐2 (KCNK10), which regulate the excitability of sensory neurons and are implicated in pain (5).MethodUsing the whole‐cell patch‐clamp technique, currents were measured through human TASK‐1, TREK‐1 and TREK‐2 channels transiently expressed in tsA‐201 cells. TASK‐1 was also co‐expressed with prostanoid receptors (IP, DP2 and EP2). Data are expressed as mean ± SEM (n = cells) of current measured at −40 mV and mean % change ± SEM (n = cells), with statistical analysis performed using a paired t‐test.ResultsAcute application of treprostinil (1 μM) on cells expressing TASK‐1 channels had no effect on current (control: 234 ± 80 pA; treprostinil: 240 ± 53 pA, n = 5, p > 0.05). Co‐expression of TASK‐1 with various prostanoid receptors, followed by acute application of treprostinil (1 μM) resulted in varying effects on TASK‐1 current. In cells expressing WT TASK‐1 and IP receptors, the average TASK‐1 current significantly decreased by 50% in the presence of treprostinil (control: 333 ± 82 pA; treprostinil (1 μM): 173 ± 46 pA, n = 6, p < 0.05). Whilst co‐expression of TASK‐1 with EP2 receptors saw a 30% increase in TASK‐1 current (control: 294 ± 65 pA; treprostinil (1 μM): 368 ± 78 pA, n = 8, p < 0.05). Co‐expression of TASK‐1 with DP2 receptors saw no significant change (3%) in TASK‐1 current (control: 387 ± 45 pA; treprostinil (1 μM): 398 ± 54 pA, n = 5, p > 0.05). Interestingly, treprostinil had a potent inhibitory effect on TREK‐1 (80 ± 8%, n = 5, p < 0.05) and TREK‐2 channels (59 ± 9%, n = 5, p < 0.05) in the absence of prostanoid receptors.ConclusionIn this study, acutely applied treprostinil did not appear to have a direct action on the TASK‐1 channels, themselves, instead its effects appeared to occur through the activation of prostanoid receptors and their associated signalling pathways. Conversely, treprostinil demonstrated a direct inhibitory effect on TREK‐1 and TREK‐2 channels. This effect of treprostinil may explain infusion site pain, a common side‐effect of patients on subcutaneous treatment (4). Acute enhancement of TREK channel activity at the infusion site could therefore help to reduce discomfort in PAH patients.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prostaglandin D2 amplifies lupus disease through basophil accumulation in lymphoid organs

In systemic lupus erythematosus (SLE), autoantibody production can lead to kidney damage and failure, known as lupus nephritis. Basophils amplify the synthesis of autoantibodies by accumulating in secondary lymphoid organs. Here, we show a role for prostaglandin D2 (PGD2) in the pathophysiology of SLE. Patients with SLE have increased expression of PGD2 receptors (PTGDR) on blood basophils and increased concentration of PGD2 metabolites in plasma. Through an autocrine mechanism dependent on both PTGDRs, PGD2 induces the externalization of CXCR4 on basophils, both in humans and mice, driving accumulation in secondary lymphoid organs. Although PGD2 can accelerate basophil-dependent disease, antagonizing PTGDRs in mice reduces lupus-like disease in spontaneous and induced mouse models. Our study identifies the PGD2/PTGDR axis as a ready-to-use therapeutic modality in SLE.

Prostaglandin D2-Mediated DP2 and AKT Signal Regulate the Activation of Androgen Receptors in Human Dermal Papilla Cells.

Prostaglandin D2 (PGD2) and prostaglandin D2 receptor 2 (DP2) is known to be an important factor in androgenetic alopecia (AGA). However, the effect of PGD2 in human dermal papilla cells (hDPCs) is not fully understood. The function of PGD2-induced expression of the androgen receptor (AR), DP2, and AKT (protein kinase B) signal were examined by using real time-PCR (qRT-PCR), western blot analysis, immunocytochemistry (ICC), and siRNA transfection system. PGD2 stimulated AR expression and AKT signaling through DP2. PGD2 stimulated AR related factors (transforming growth factor beta 1 (TGFβ1), Creb, lymphoid enhancer binding factor 1 (LEF1), and insulin-like growth factor 1, (IGF-1)) and AKT signaling (GSK3β and Creb) on the AR expression in hDPCs. However, these factors were down-regulated by DP2 antagonist (TM30089) and AKT inhibitor (LY294002) as well as DP2 knockdown in hDPCs decreased AR expression and AKT signaling. Finally, we confirmed that PGD2 stimulates the expression of AR related target genes, and that AKT and its downstream substrates are involved in AR expression on hDPCs. Taken together, our data suggest that PGD2 promotes AR and AKT signal via DP2 in hDPCs, thus, PGD2 and DP2 signal plays a critical role in AR expression. These findings support the additional explanation for the development of AGA involving PGD2-DP2 in hDPCs.

Prostaglandin D2 Receptor DP1 Antibodies Predict Vaccine-induced and Spontaneous Narcolepsy Type 1: Large-scale Study of Antibody Profiling

BackgroundNeuropathological findings support an autoimmune etiology as an underlying factor for loss of orexin-producing neurons in spontaneous narcolepsy type 1 (narcolepsy with cataplexy; sNT1) as well as in Pandemrix influenza vaccine-induced narcolepsy type 1 (Pdmx-NT1). The precise molecular target or antigens for the immune response have, however, remained elusive. MethodsHere we have performed a comprehensive antigenic repertoire analysis of sera using the next-generation phage display method - mimotope variation analysis (MVA). Samples from 64 children and adolescents were analyzed: 10 with Pdmx-NT1, 6 with sNT1, 16 Pandemrix-vaccinated, 16 H1N1 infected, and 16 unvaccinated healthy individuals. The diagnosis of NT1 was defined by the American Academy of Sleep Medicine international criteria of sleep disorders v3. FindingsOur data showed that although the immunoprofiles toward vaccination were generally similar in study groups, there were also striking differences in immunoprofiles between sNT1 and Pdmx-NT1 groups as compared with controls. Prominent immune response was observed to a peptide epitope derived from prostaglandin D2 receptor (DP1), as well as peptides homologous to B cell lymphoma 6 protein. Further validation confirmed that these can act as true antigenic targets in discriminating NT1 diseased along with a novel epitope of hemagglutinin of H1N1 to delineate exposure to H1N1. InterpretationWe propose that DP1 is a novel molecular target of autoimmune response and presents a potential diagnostic biomarker for NT1. DP1 is involved in the regulation of non-rapid eye movement (NREM) sleep and thus alterations in its functions could contribute to the disturbed sleep regulation in NT1 that warrants further studies. Together our results also show that MVA is a helpful method for finding novel peptide antigens to classify human autoimmune diseases, possibly facilitating the design of better therapies.

Fevipiprant in the treatment of asthma

ABSTRACTIntroduction: Asthma is common and in many, particularly those with more severe disease, there remains a substantial unmet need. Success with biologics targeting eosinophilic inflammation underscore the value of treating inflammation in asthma beyond corticosteroids. Fevipiprant (QAW039) is an oral treatment for asthma. It competitively and reversibly antagonises the prostaglandin D2 receptor 2 (DP2) expressed on inflammatory and structural cells.Areas covered: We reviewed fevipiprant’s mode of action and efficacy against other current and emerging pharmacological interventions for moderate-to-severe asthma. We undertook a literature review using the PubMed/Medline database, the U.S. National Library of Medicine’s Clinical Trials website and from manufacturers’ press releases with the search terms: ‘QAW039’, ‘Fevipiprant’, ‘CRTH2 antagonists’, ‘DP2’, ‘DP1’, ‘monoclonal antibody’, ‘eosinophil’ with ‘asthma’ plus the names of individual drugs. Three Phase 2 trials have been conducted and three Phase 3 trials (NCT02563067, NCT03052517, NCT02555683) are in progress. To date Fevipiprant’s greatest success has been in targeting severe eosinophilic asthma.Expert opinion: Fevipiprant presents the possibility of a new orally active therapy for asthma. If successful in phase 3 trials it will have an enormous impact on the treatment paradigm for asthma and will potentially widen access for pre-biologic treatment to a larger population.

FEVIPIPRANT REDUCES AIRWAY SMOOTH MUSCLE MASS IN ASTHMATICS VIA PGD2 RECEPTOR ANTAGONISM

RespirologyVolume 22, Issue S3 p. 11-11 Asthma 1 FEVIPIPRANT REDUCES AIRWAY SMOOTH MUSCLE MASS IN ASTHMATICS VIA PGD2 RECEPTOR ANTAGONISM First published: 20 November 2017 https://doi.org/10.1111/resp.13206_15Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume22, IssueS3Supplement: 22nd Congress of the Asian Pacific Society of Respirology, International Convention Centre, Sydney, Australia, 23–26 November 2017November 2017Pages 11-11 RelatedInformation

PTGDR gene expression and response to dexamethasone treatment in an in vitro model.

Asthma is a multifactorial pathology influenced by environmental and genetic factors. Glucocorticoid treatment decreases symptoms by regulating genes involved in the inflammatory process through binding to specific DNA sequences. Polymorphisms located in the promoter region of the Prostaglandin D Receptor (PTGDR) gene have been related to asthma. We aimed to analyze the effect of PTGDR promoter haplotypes on gene expression and response to corticosteroid therapy. A549 lung epithelial cells were transfected with vectors carrying four different PTGDR haplotypes (CTCT, CCCC, CCCT and TCCT), and treated with dexamethasone. Different approaches to study the promoter activity (Dual Luciferase Reporter System), gene expression levels (qPCR) and cytokine secretion (Multiplexed Bead-based Flow Cytometric) were used. In addition, in silico analysis was also performed. Cells carrying the TCCT haplotype showed the lowest promoter activity (p-value<0.05) and mRNA expression levels in basal conditions. After dexamethasone treatment, cells carrying the wild-type variant CTCT showed the highest response, and those carrying the TCCT variant the lowest (p-value<0.05) in luciferase assays. Different transcription factor binding patterns were identified in silico. Moreover, differences in cytokine secretion were also found among different promoter haplotypes. Polymorphisms of PTGDR gene influence basal promoter activity and gene expression, as well as the cytokine secretory pattern. Furthermore, an association between these positions and response to corticoid treatment was observed.

Prostaglandin D2 Uses Components of ROS Signaling to Enhance Testosterone Production in Keratinocytes.

Elevated levels of prostaglandin D2 (PGD2) have been shown to be present in the bald scalp of androgenic alopecia (AGA) patients and to functionally inhibit hair growth. However, its precise mechanism in AGA has yet to be clearly defined. Although testosterone plays a critical role in the initiation and progression of AGA, the existence of a possible link between PGD2 and testosterone in skin has not been investigated. Here we show that human keratinocytes treated with PGD2 show enhanced capacity to convert the weak androgen, androstenedione, to testosterone. At the same time, treatment with PGD2 induced reactive oxygen species as indicated by generation of the lipid peroxidation product, 4-hydroxynonenal. To determine whether these two events are linked, we used the reactive oxygen species scavenger N-acetyl-cysteine, which blocked the enhanced testosterone production from PGD2-treated keratinocytes. Our study suggests the existence of a possible crosstalk between the PGD2-reactive oxygen species axis and testosterone metabolism in keratinocytes. Thus, we propose that AGA patients might benefit from the use of N-acetyl-cysteine or other antioxidants as a supplement to currently available or emerging AGA therapies such as finasteride, minoxidil, and PGD2 receptor blockers.

Efficacy of Laropiprant in Minimizing Brain Injury Following Experimental Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is one of the most devastating and disabling forms of stroke, yet effective treatments are still lacking. Prostaglandins and their receptors have been implicated in playing vital roles in ICH outcomes. Recently, laropiprant, a DP1 receptor antagonist, has been used in combination with niacin to abolish the prostaglandin D2-(PGD2)-induced flushing. Here, we test the hypothesis that laropiprant limits bleeding and rescues the brain from ICH. Wildtype (WT) and DP1−/− mice were subjected ICH and neurologic deficits and hemorrhagic lesion outcomes were evaluated at 72 hours after the ICH. To test the therapeutic potential of laropiprant, WT mice subjected to ICH were treated with laropiprant at 1 hour after the ICH. The putative effect of laropiprant on limiting hematoma expansion was tested by an in vivo tail bleeding cessation method and an ex vivo coagulation method. Finally, the roles of laropiprant on gliosis and iron accumulation were also investigated. A significant decrease in the injury volume was observed in DP1−/− as well as laropiprant-treated WT mice. The tail bleeding time was significantly lower in laropiprant group as compared with the vehicle group. Significantly lower Iba-1 and Perls’ iron staining in DP1−/− and laropiprant-treated WT groups were observed. Altogether, the data suggest that laropiprant treatment post-ICH attenuates brain damage by targeting primary as well as secondary injuries.

Role of TrkA signalling and mast cells in the initiation of osteoarthritis pain in the monoiodoacetate model.

Aiming to delineate novel neuro-immune mechanisms for NGF/TrkA signalling in osteoarthritis (OA) pain, we evaluated inflammatory changes in the knee joints following injection of monoiodoacetate (MIA) in mice carrying a TrkA receptor mutation (P782S; TrkA KI mice). In behavioural studies we monitored mechanical hypersensitivity following intra-articular MIA and oral prostaglandin D2 (PGD2) synthase inhibitor treatments. In immunohistochemical studies we quantified joint mast cell numbers, calcitonin gene-related peptide expression in synovia and dorsal root ganglia, spinal cord neuron activation and microgliosis. We quantified joint leukocyte infiltration by flow cytometry analysis, and PGD2 generation and cyclooxygenase-2 (COX-2) expression in mast cell lines by ELISA and Western blot. In TrkA KI mice we observed rapid development of mechanical hypersensitivity and amplification of dorsal horn neurons and microglia activation 7 days after MIA. In TrkA KI knee joints we detected significant leukocyte infiltration and mast cells located in the vicinity of synovial nociceptive fibres. We demonstrated that mast cells exposure to NGF results in up-regulation of COX-2 and increase of PGD2 production. Finally, we observed that a PGD2 synthase inhibitor prevented MIA-mechanical hypersensitivity in TrkA KI, at doses which were ineffective in wild type (WT) mice. Using the TrkA KI mouse model, we delineated a novel neuro-immune pathway and suggest that NGF-induced production of PGD2 in joint mast cells is critical for referred mechanical hypersensitivity in OA, probably through the activation of PGD2 receptor 1 in nociceptors: TrkA blockade in mast cells constitutes a potential target for OA pain.

Does Inhibition of Aldose Reductase Contribute to the Anti-Inflammatory Action of Setipiprant?

The aim of this study was to investigate aldose reductase inhibitory action of setipiprant as a potential additional mechanism contributing to its anti-inflammatory action. Aldose reductase activity was determined by spectrophotometric measuring of NADPH consumption. Setipiprant was found to inhibit aldose reductase/NADPH-mediated reduction of 4-hydroxynonenal, 4-hydroxynonenal glutathione and prostaglandin H2 substrates, all relevant to the process of inflammation. Molecular modeling simulations into the aldose reductase inhibitor binding site revealed an interaction pattern of setipiprant. Considering multifactorial etiology of inflammatory pathologies, it is suggested that, in addition to the antagonizing prostaglandin D2 receptor, inhibition of aldose reductase may contribute to the reported anti-inflammatory action of setipiprant.

Exacerbation of Aging-Associated and Instability-Induced Murine Osteoarthritis With Deletion of D Prostanoid Receptor 1, a Prostaglandin D2 Receptor.

D prostanoid receptor 1 (DP1), a receptor for prostaglandin D2 , plays important roles in inflammation and cartilage metabolism. However, its role in the pathogenesis of osteoarthritis (OA) remains unknown. This study was undertaken to explore the roles of DP1 in the development of OA in murine models and to evaluate the efficacy of a DP1 selective agonist in the treatment of OA. The development of aging-associated OA and destabilization of the medial meniscus (DMM)-induced OA was compared between DP1-deficient (DP1-/- ) and wild-type (WT) mice. The progression of OA was assessed by histology, immunohistochemistry, and micro-computed tomography. Cartilage explants from DP1-/- and WT mice were treated with interleukin-1α (IL-1α) ex vivo, to evaluate proteoglycan degradation. The effect of intraperitoneal administration of the DP1 selective agonist BW245C on OA progression was evaluated in WT mice. Compared to WT mice, DP1-/- mice had exacerbated cartilage degradation in both models of OA, and this was associated with increased expression of matrix metalloproteinase 13 and ADAMTS-5. In addition, DP1-/- mice demonstrated enhanced subchondral bone changes. Cartilage explants from DP1-/- mice showed enhanced proteoglycan degradation following treatment with IL-1α. Intraperitoneal injection of BW245C attenuated the severity of DMM-induced cartilage degradation and bony changes in WT mice. These findings indicate a critical role for DP1 signaling in OA pathogenesis. Modulation of the functions of DP1 may constitute a potential therapeutic target for the development of novel OA treatments.

ERJPodcast August 2017: Fevipiprant in allergic asthma not controlled by low-dose inhaled corticosteroids

As part of the August issue, the European Respiratory Journal presents the latest in its series of podcasts. Chief editor Marc Humbert discusses the publication of the results of a trial of fevipiprant, an oral prostaglandin in DP2 receptor (CRTh2) antagonist, in allergic asthma that is not controlled by low-dose inhaled corticosteroids with Prof. Eric D. Bateman from the University of Cape Town, South Africa.

Prostaglandins and Their Receptors in Eosinophil Function and As Therapeutic Targets.

Of the known prostanoid receptors, human eosinophils express the prostaglandin D2 (PGD2) receptors DP1 [also D-type prostanoid (DP)] and DP2 (also chemoattractant receptor homologous molecule, expressed on Th2 cells), the prostaglandin E2 receptors EP2 and EP4, and the prostacyclin (PGI2) receptor IP. Prostanoids can bind to either one or multiple receptors, characteristically have a short half-life in vivo, and are quickly degraded into metabolites with altered affinity and specificity for a given receptor subtype. Prostanoid receptors signal mainly through G proteins and naturally activate signal transduction pathways according to the G protein subtype that they preferentially interact with. This can lead to the activation of sometimes opposing signaling pathways. In addition, prostanoid signaling is often cell-type specific and also the combination of expressed receptors can influence the outcome of the prostanoid impulse. Accordingly, it is assumed that eosinophils and their (patho-)physiological functions are governed by a sensitive prostanoid signaling network. In this review, we specifically focus on the functions of PGD2, PGE2, and PGI2 and their receptors on eosinophils. We discuss their significance in allergic and non-allergic diseases and summarize potential targets for drug intervention.

Effects of icariin on asthma mouse model are associated with regulation of prostaglandin D2 level

BackgroundWe aimed to observe the effect of icariin on an asthma mouse model and explore the potential underlying mechanisms. MethodsThe asthma mouse model was established by ovalbumin (OVA) sensitisation and respiratory syncytial virus (RSV) infection and then treated with icariin. Airway resistance was assessed by whole body plethysmograph. In addition, pathological slides were stained with haematoxylin–eosin, and the peribronchial inflammation was observed microscopically. The concentration of prostaglandin D2 (PGD2) in serum and bronchoalveolar lavage fluid (BALF) was detected by enzyme-linked immuno sorbent assay (ELISA). The relative level of prostaglandin D2 receptor 2 (CRTH2) mRNA was assessed by real-time quantitative PCR. ResultsCompared with the icariin-untreated group, there was a significant reduction of Penh in the treated group. Total leucocyte amount and all sorts of leukocytes were lower in the treated group than in the untreated group. HE staining results revealed that a large number of inflammatory cells infiltrated into the peribronchial tissues of untreated group, and the degree of airway inflammation decreased significantly in the treated group. PGD2 in serum and BALF, as well as CRTH2 mRNA level in lung tissues were lower in the treated group than in the untreated group. ConclusionIcariin is a promising therapeutic strategy for asthma, and PGD2 might be a new target for asthma therapy in OVA-induced and RSV-infected asthma model.

Prostaglandin D2 enhances lipid accumulation through suppression of lipolysis via DP2 (CRTH2) receptors in adipocytes

Prostaglandin (PG) D2 enhanced lipid accumulation in adipocytes. However, its molecular mechanism remains unclear. In this study, we investigated the regulatory mechanisms of PGD2-elevated lipid accumulation in mouse adipocytic 3T3-L1 cells. The Gi-coupled DP2 (CRTH2) receptors (DP2R), one of the two-types of PGD2 receptors were dominantly expressed in adipocytes. A DP2R antagonist, CAY10595, but not DP1 receptor antagonist, BWA868C cleared the PGD2-elevated intracellular triglyceride level. While, a DP2R agonist, 15R-15-methyl PGD2 (15R) increased the mRNA levels of the adipogenic and lipogenic genes, and decreased the glycerol release level. In addition, the forskolin-mediated increase of cAMP-dependent protein kinase A (PKA) activity and phosphorylation of hormone-sensitive lipase (HSL) was repressed by the co-treatment with 15R. Moreover, the lipolysis was enhanced in the adipocyte-differentiated DP2R gene-knockout mouse embryonic fibroblasts. These results indicate that PGD2 suppressed the lipolysis by repression of the cAMP-PKA-HSL axis through DP2R in adipocytes.

Targeting the PGD2/CRTH2/DP1 Signaling Pathway in Asthma and Allergic Disease: Current Status and Future Perspectives

Prostaglandin D2 (PGD2) released by degranulating mast cells is believed to play a key role in orchestrating mechanisms of inflammation in allergies and asthma. The biological effects of PGD2 are mediated by D-prostanoid (DP1), CRTH2 (DP2), and thromboxane prostanoid (TP) receptors. The CRTH2 receptor is involved in induction of migration and activation of T helper type 2 (Th2) lymphocytes, eosinophils, and basophils; up-regulation of adhesion molecules; and promotion of pro-inflammatory Th2-type cytokines (interleukin [IL]-4, 5, 13), whereas the DP receptor is associated with relaxation of smooth muscles, vasodilation, inhibition of cell migration, and apoptosis of eosinophils. A number of CRTH2/PGD2 receptor antagonists have been investigated in asthma and allergic diseases. The CRTH2 antagonist (OC000459) or dual CRTH2 and TP receptor antagonist (ramatroban) were effective in reducing eosinophilia, nasal mucosal swelling, and clinical symptoms of allergic rhinitis, with the latter drug registered for clinical use in this indication. OC000459 and setipiprant reduced the late but not early phase of response in an allergen challenge in atopic asthmatics. In persistent asthma, some molecules induced limited improvement in lung function, quality of life, and asthma symptoms (OC000459, BI671800), but in other trials with AMG 853 and AZ1981 these findings were not confirmed. The clear discrepancy between animal studies and clinical efficacy of CRTH2 antagonism in allergic rhinitis, and lack of efficacy in a general cohort of asthmatics, highlight the issue of patient phenotyping. There is no doubt that the PGD2/CATH2/DP1 pathway plays a key role in allergic inflammation and further studies with selective or combined antagonisms in well defined cohorts of patients are needed.

DP1 receptor agonist, BW245C inhibits diet-induced obesity in ApoE−/− mice

Lipocalin Prostaglandin D2 synthase (LPGDS) contributes to the production of PGD2, which has been associated with adipogenesis. In this study, we aimed to investigate the role of PGD2 on obesity through its DP1 and DP2 receptor signaling using intraperitoneal injection of their respective agonists and antagonists. ApoE-/- mice were divided into five groups: vehicle control (n=5), DP1 receptor agonist (n=5), DP1 receptor antagonist (n=5), DP2 receptor agonist (n=5), and DP2 receptor antagonist (n=5), and the study was carried out for 10 weeks. Despite being on high fat diet, mice receiving DP1 receptor agonist sustained a significant inhibition of weight gain throughout the study gaining only 11.4% body weight compared to the controls gaining 61% body weight. Interestingly, parallel to the body weight, the DP1 receptor agonist group showed a significant reduction in food intake throughout the study. Consistently, fasting leptin, insulin and bile acids levels were elevated in the DP1 receptor agonist group compared to controls. As expected, there was a significant reduction in fasting glucose level in DP1 receptor agonist group. At last, as a result of weight gain inhibition, DP1 receptor agonist also imparted cardiovascular benefits showing significant reduction in aortic wall thickness, intima, adventia and lumen size. Based on the obtained results, we believe DP1 receptor agonism inhibited diet induced weight gain possibly through controlling appetite which consequently imparted beneficial cardiometabolic effects. DP1 receptor agonism may represent a novel therapeutic target for the management of obesity.