The prostaglandin D2 receptor 1 (DP1), a G protein-coupled receptor encoded by the PTGDR1 gene (also termed PTGDR), is primarily a receptor for prostaglandin D2 (PGD2). [5] The receptor is a member of the prostaglandin receptors belonging to the subfamily A14 of rhodopsin-like receptors. Activation of DP1 by PGD2 or other cognate receptor ligands is associated with a variety of physiological and pathological responses in animal models.
The PTGDR1 gene is located on chromosome 14 at position q22.1, (i.e. 14q22.1), a chromosomal locus associated with asthma and other allergic disorders. [6] PTGDR1, which consists of 4 introns and 5 exons, encodes for a ~44 kilodalton protein but also multiple alternative spliced transcript variants. [7]
DP1 is expressed primarily by cells involved in mediating allergic and inflammatory reactions, i.e. human and rodent mast cells, basophils, and eosinophils, Th2 cells, and dendritic cells, and by cells contributing to these reactions, i.e. human and/or rodent airway epithelial cells, vascular endothelium, mucus-secreting goblet cells in the nasal and colonic mucosa, and serous gland cells of the nose. [8] [9] DP1 protein is expressed in mouse placenta and testes [10] and mRNA transcripts have also been detected in the meninges of the mouse brain by multiple reports and, by single reports, in the rat meninges as well as the mouse thalamus, hippocampus, cerebellum, brainstem, and retina. [11] [12]
PGD2 binds to and activates DP1 at concentrations in the 0.5 to 1 nanomolar range. Relative potencies in binding to and activating DP1 for the following prostanoids are: PGD2>>PGE2>Prostaglandin F2alpha>PGI2=thromboxane A2, with PGD2 being more than 100-fold more potent than PGE2 in binding to and stimulating DP1. [13] PDJ2, Δ12-PDJ2, and 15-deoxy-Δ12,14-PGJ2, which form in vitro and in vivo rapidly as non-enzymatic rearrangements of PGD2 (see cyclopentenone prostaglandins), also bind to and activate DP1, with PDJ2 doing so almost as effectively as PDG2 and the latter two PGJs doing so 100-fold and 300-fold less potently than PDG2. [14] [15] Other compounds, e.g. L-644,698, BW 245C, BW A868C, and ZK 110841, have been synthesized, found to be about as potent as PGD2 in binding to and stimulating DP1, and used to study the function of this receptor. [14]
The drug treprostinil is a high affinity ligand for and potent activator of not only DP1 but also two other prostanoid receptors, EP2 and IP. [16]
Asapiprant (S-555739) and laropiprant are selective receptor antagonists of DP1 whereas vidupiprant is a receptor antagonist for both DP1 and DP2. [17]
Among the 8 human prostanoid receptors, DP1, along with IP, EP2, and EP4, are classified as relaxant prostanoid receptors; each, including DP1, is a G protein-coupled receptors that works by activating G-S proteins which in turn raises cellular cAMP levels thereby mobilizing cyclic adenosine monophosphate-activated cell signaling pathways which regulate cell function. [8] [18] DP1 activation also causes the mobilization of calcium in HEK293 cells transfected with this receptor. It does so by a mechanism that is independent of inositol trisphosphate signaling; [10] [12] Ligand-activated DP1 also mobilizes G protein-coupled receptor kinase 2 (GRK2, also known as β-adrenergic receptor kinase 2 [BARK1]) and arrestin 2 (also known as arrestin beta 1 [ARRB1]). These agents act to uncouple DP1 from its G proteins and to internalize in a process that limits the DP1's cell-activation life-time in a process termed homologous desensitization. [19] Activation of protein kinase Cs likewise trigger DP1 to uncouple from G proteins and internalize although in model studies DP1 has not been shown to cause the activation of PKC (see Protein kinase C#Function). [19]
Studies in mouse as well as human tissues and cells find that DP1 stimulation has numerous pro-allergic effects. DP1 activation blocks the production of interleukin 12 by dendritic cells; this biases the development of naïve T lymphocytes to Th-2 rather than Th-1 helper cells and thereby promotes allergic rather than non-allergic inflammatory responses (see T helper cell#Th1/Th2 Model for helper T cells and T helper cell#Limitations to the Th1/Th2 model. DH1 activation also promotes allergic reactions by suppressing the function of natural killer cells, prolonging the survival of eosinophils, and stimulation the maturation of dermal mast cell. [20] [21]
Studies of experimentally-induced allergic responses in animals further implicate DP1 in allergy. DP1 gene knockout and/or DP1 inhibition by receptor antagonists markedly reduces airway inflammation, obstruction, hypersensitivity, and pro-allergic cytokine and chemokine production in a mouse model of ovalbumin-induced asthma as well as allergic symptoms in a guinea pig model of allergic conjunctivitis, rhinitis, and asthma. [8] [9] The administration of PGD2 into the skin of rats or into the eyes of rabbits causes local symptoms of allery. These responses are thought, but not yet proved, to be mediated by DP1 activation. [9] In contrast to these results, however, activation of DP1 by intratrachael administration of a selective DP1 activator activated DP1 on dendritic cells to suppress airway allergic inflammation by increasing the number of Foxp3+ CD4+ regulatory T cells. [22] Furthermore, DP1 activation reduces eosinophilia in allergic inflammation and blocks antigen-presenting langerhans cell function in mice. [23] This results suggest that DP1 can promote or suppress allergic responses depending on the animal model tested and, perhaps, the type of allergic reaction investigated.
Allergen inhalation challenge of humans produces rises in the PGD2 levels in their bronchoalveolar lavage fluids. Furthermore, the administration of PGD2 into the nose or skin of human volunteers produces local symptoms of allergy and the inhalation of PGD2 into asthmatics causes constriction of the airways as well as the potentiation of airway constriction responses. [9] These reactions, similar to those produced in animal studies, may be mediated by DP1.
PGD2 is the most abundant prostanoid in the brains of humans and other mammals and DP1 receptors are located on arachnoid mater trabecular cells in mouse basal forebrain. The PGD2-DP1 pathway is involved in the regulation of non-rapid eye movement sleep in rodents: infusion of PGD2 into the lateral ventricle of mice or the brain of rats induces an increase in the amount of non-rapid eye movement sleep in wild-type (WT) but not DP1-deficient animals. This sleep-induction appears to involve the DP1-dependent stimulation of adenosine formation and subsequent simulation of the adenosine A2A receptor by adenosine. [24] [25] In humans, a genetic variant of ADA associated with the reduced metabolism of adenosine to inosine has been reported to deep sleep and SWA during sleep. These studies suggest that DP1 has a similar role in the sleep of humans. [25]
Pulmonary arterial hypertension, Who group 1 (see Pulmonary hypertension#Causes), in humans in commonly treated with specific pulmonary artery vasodilators that increase survival such as the prostacyclin I2 (PGI2) mimetics including treprostinil, epoprostanol, iloprost, and beraprost. Recent studies find that DP1 as well as the PGI2 receptor protein are expressed in human pulmonary arteries and veins; that treprostinil but not iloprost caused pulmonary vein relaxation in part by acting through DP1 in insolated human pulmonary vascular preparations; and that the effect of treprostinil on DP1 in human pulmonary veins may contribute to its therapeutic efficacy in primary pulmonary hypertension. [26]
Studies in male mice indicate that DP1 activation induces the translocation of SOX9 into the nucleus thereby signaling for the maturation of Sertoli cells and embryonic gonads. Disruption of this DP1-activated circuit leads to disordered maturation of the male reproductive organs such as cryptorchidism (i.e. failure of testes descent into the scrotum) in mice and, it is suggested, may also do so in humans. [10]
Human genomics studies have associated single-nucleotide polymorphism variants with an increased incidence of allergic diseases. Studies in two different populations have replicated associations between -549T>C, -441C>T, and -197T>C variants and a study in a single population has associated the -613C>T variation with increased incidences of nasal polyposis, asthma, and/or aspirin sensitivity; the -197T>C and -613 C>T variants were also associated with increased incidences of allergic reactions to pollen and mites. A single population study associated the -731A>C variant and studies in two different population associated the 6651C>T variant with increased incidences of asthma and/or bronchial hyper-reactivity. The intrinsic variants rs17831675, rs17831682, and rs58004654 (now termed rs7709505) have been associated with an increased incidence of asthma in single population studies. [27] A metaanalasis −549 C/T, −441 C/T, and −197 C/T found that of these three variants, only −549 C/T conferred susceptibility to asthma in Europeans and that this susceptibility was limited to adults. [6]
Prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derived enzymatically from the fatty acid arachidonic acid. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. They are a subclass of eicosanoids and of the prostanoid class of fatty acid derivatives.
Eicosanoids are signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, around 20 carbon units in length. Eicosanoids are a sub-category of oxylipins, i.e. oxidized fatty acids of diverse carbon units in length, and are distinguished from other oxylipins by their overwhelming importance as cell signaling molecules. Eicosanoids function in diverse physiological systems and pathological processes such as: mounting or inhibiting inflammation, allergy, fever and other immune responses; regulating the abortion of pregnancy and normal childbirth; contributing to the perception of pain; regulating cell growth; controlling blood pressure; and modulating the regional flow of blood to tissues. In performing these roles, eicosanoids most often act as autocrine signaling agents to impact their cells of origin or as paracrine signaling agents to impact cells in the proximity of their cells of origin. Eicosanoids may also act as endocrine agents to control the function of distant cells.
Interleukin 13 (IL-13) is a protein that in humans is encoded by the IL13 gene. IL-13 was first cloned in 1993 and is located on chromosome 5q31.1 with a length of 1.4kb. It has a mass of 13 kDa and folds into 4 alpha helical bundles. The secondary structural features of IL-13 are similar to that of Interleukin 4 (IL-4); however it only has 25% sequence identity to IL-4 and is capable of IL-4 independent signaling. IL-13 is a cytokine secreted by T helper type 2 (Th2) cells, CD4 cells, natural killer T cell, mast cells, basophils, eosinophils and nuocytes. Interleukin-13 is a central regulator in IgE synthesis, goblet cell hyperplasia, mucus hypersecretion, airway hyperresponsiveness, fibrosis and chitinase up-regulation. It is a mediator of allergic inflammation and different diseases including asthma.
The thromboxane receptor (TP) also known as the prostanoid TP receptor is a protein that in humans is encoded by the TBXA2R gene, The thromboxane receptor is one among the five classes of prostanoid receptors and was the first eicosanoid receptor cloned. The TP receptor derives its name from its preferred endogenous ligand thromboxane A2.
A prostaglandin antagonist is a hormone antagonist acting upon one or more prostaglandins, a subclass of eicosanoid compounds which function as signaling molecules in numerous types of animal tissues.
Most of the eicosanoid receptors are integral membrane protein G protein-coupled receptors (GPCRs) that bind and respond to eicosanoid signaling molecules. Eicosanoids are rapidly metabolized to inactive products and therefore are short-lived. Accordingly, the eicosanoid-receptor interaction is typically limited to a local interaction: cells, upon stimulation, metabolize arachidonic acid to an eicosanoid which then binds cognate receptors on either its parent cell or on nearby cells to trigger functional responses within a restricted tissue area, e.g. an inflammatory response to an invading pathogen. In some cases, however, the synthesized eicosanoid travels through the blood to trigger systemic or coordinated tissue responses, e.g. prostaglandin (PG) E2 released locally travels to the hypothalamus to trigger a febrile reaction. An example of a non-GPCR receptor that binds many eicosanoids is the PPAR-γ nuclear receptor.
Prostaglandin D2 (or PGD2) is a prostaglandin that binds to the receptor PTGDR (DP1), as well as CRTH2 (DP2). It is a major prostaglandin produced by mast cells – recruits Th2 cells, eosinophils, and basophils. In mammalian organs, large amounts of PGD2 are found only in the brain and in mast cells. It is critical to development of allergic diseases such as asthma. Research carried out in 1989 found PGD2 is the primary mediator of vasodilation (the "niacin flush") after ingestion of niacin (nicotinic acid).
Prostaglandin receptors or prostanoid receptors represent a sub-class of cell surface membrane receptors that are regarded as the primary receptors for one or more of the classical, naturally occurring prostanoids viz., prostaglandin D2,, PGE2, PGF2alpha, prostacyclin (PGI2), thromboxane A2 (TXA2), and PGH2. They are named based on the prostanoid to which they preferentially bind and respond, e.g. the receptor responsive to PGI2 at lower concentrations than any other prostanoid is named the Prostacyclin receptor (IP). One exception to this rule is the receptor for thromboxane A2 (TP) which binds and responds to PGH2 and TXA2 equally well.
Cyclopentenone prostaglandins are a subset of prostaglandins (PGs) or prostanoids that has 15-deoxy-Δ12,14-prostaglandin J2 (15-d-Δ12,14-PGJ2), Δ12-PGJ2, and PGJ2 as its most prominent members but also including PGA2, PGA1, and, while not classified as such, other PGs. 15-d-Δ12,14-PGJ2, Δ12-PGJ2, and PGJ2 share a common mono-unsaturated cyclopentenone structure as well as a set of similar biological activities including the ability to suppress inflammation responses and the growth as well as survival of cells, particularly those of cancerous or neurological origin. Consequently, these three cyclopentenone-PGs and the two epoxyisoprostanes are suggested to be models for the development of novel anti-inflammatory and anti-cancer drugs. The cyclopenentone prostaglandins are structurally and functionally related to a subset of isoprostanes viz., two cyclopentenone isoprostanes, 5,6-epoxyisoprostane E2 and 5,6-epoxisoprostane A2.
Prostaglandin E2 receptor 4 (EP4) is a prostaglandin receptor for prostaglandin E2 (PGE2) encoded by the PTGER4 gene in humans; it is one of four identified EP receptors, the others being EP1, EP2, and EP3, all of which bind with and mediate cellular responses to PGE2 and also, but generally with lesser affinity and responsiveness, certain other prostanoids (see Prostaglandin receptors). EP4 has been implicated in various physiological and pathological responses in animal models and humans.
Prostaglandin D2 receptor 2 (DP2 or CRTH2) is a human protein encoded by the PTGDR2 gene and GPR44. DP2 has also been designated as CD294 (cluster of differentiation 294). It is a member of the class of prostaglandin receptors which bind with and respond to various prostaglandins. DP2 along with Prostaglandin DP1 receptor are receptors for prostaglandin D2 (PGD2). Activation of DP2 by PGD2 or other cognate receptor ligands has been associated with certain physiological and pathological responses, particularly those associated with allergy and inflammation, in animal models and certain human diseases.
Cysteinyl leukotriene receptor 2, also termed CYSLTR2, is a receptor for cysteinyl leukotrienes (LT). CYSLTR2, by binding these cysteinyl LTs contributes to mediating various allergic and hypersensitivity reactions in humans. However, the first discovered receptor for these CsLTs, cysteinyl leukotriene receptor 1 (CysLTR1), appears to play the major role in mediating these reactions.
Prostaglandin E2 receptor 1 (EP1) is a 42kDa prostaglandin receptor encoded by the PTGER1 gene. EP1 is one of four identified EP receptors, EP1, EP2, EP3, and EP4 which bind with and mediate cellular responses principally to prostaglandin E2) (PGE2) and also but generally with lesser affinity and responsiveness to certain other prostanoids (see Prostaglandin receptors). Animal model studies have implicated EP1 in various physiological and pathological responses. However, key differences in the distribution of EP1 between these test animals and humans as well as other complicating issues make it difficult to establish the function(s) of this receptor in human health and disease.
Prostaglandin E2 receptor 2, also known as EP2, is a prostaglandin receptor for prostaglandin E2 (PGE2) encoded by the human gene PTGER2: it is one of four identified EP receptors, the others being EP1, EP3, and EP4, which bind with and mediate cellular responses to PGE2 and also, but with lesser affinity and responsiveness, certain other prostanoids (see Prostaglandin receptors). EP has been implicated in various physiological and pathological responses.
Prostaglandin EP3 receptor (53kDa), also known as EP3, is a prostaglandin receptor for prostaglandin E2 (PGE2) encoded by the human gene PTGER3; it is one of four identified EP receptors, the others being EP1, EP2, and EP4, all of which bind with and mediate cellular responses to PGE2 and also, but generally with lesser affinity and responsiveness, certain other prostanoids (see Prostaglandin receptors). EP has been implicated in various physiological and pathological responses.
Prostaglandin F receptor (FP) is a receptor belonging to the prostaglandin (PG) group of receptors. FP binds to and mediates the biological actions of Prostaglandin F2α (PGF2α). It is encoded in humans by the PTGFR gene.
The Prostacyclin receptor, also termed the prostaglandin I2 receptor or just IP, is a receptor belonging to the prostaglandin (PG) group of receptors. IP binds to and mediates the biological actions of prostacyclin (also termed Prostaglandin I2, PGI2, or when used as a drug, epoprostenol). IP is encoded in humans by the PTGIR gene. While possessing many functions as defined in animal model studies, the major clinical relevancy of IP is as a powerful vasodilator: stimulators of IP are used to treat severe and even life-threatening diseases involving pathological vasoconstriction.
PGDS protein is a protein that in humans is encoded by the HPGDS gene.
Setipiprant (INN; developmental code names ACT-129968, KYTH-105) is an investigational drug developed for the treatment of asthma and scalp hair loss. It was originally developed by Actelion and acts as a selective, orally available antagonist of the prostaglandin D2 receptor 2 (DP2). The drug is being developed as a novel treatment for male pattern baldness by Allergan.
The prostaglandin D2 (PGD2) receptors are G protein-coupled receptors that bind and are activated by prostaglandin D2. Also known as PTGDR or DP receptors, they are important for various functions of the nervous system and inflammation. They include the following proteins:
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
