Association of PTGDR gene polymorphisms with asthma in two Caucasian populations

The Biased Activities of Prostanoids and Their Receptors: Review and Beyond

Since the discovery of β-arrestin, a new concept/viewpoint has arisen in G-protein coupled receptor (GPCR)-mediated signaling. The Lock and Key concept of GPCR was previously recognized as basically a single- or mono-originated pathway activated from a single receptor. However, the new concept/viewpoint allows for many- or more-than-one-originated pathways activated from a single receptor; namely, biased activities. It is well-recognized that prostanoids exhibit preferences for their corresponding cognate receptors, while promiscuous cross-reactivities have also been reported among endogenous prostanoids and their receptor family. However, of particular interest, such cross-reactivities have led to reports of their physiologically significant roles. Thus, this review discusses and considers that the endogenous prostanoids are not showing random cross-reactivities but what are showing important physiological and pathological activities as biased ligands. Moreover, why and how the biased activities are evoked by endogenous structurally similar prostanoid ligands are discussed. Furthermore, when the biased activities of endogenous prostanoids first arose is also discussed and considered. These biased activities of endogenous prostanoids are also discussed from the perspective that they may provide many benefits and/or disadvantages for all living things, any-where on this planet, who/which are utilizing, had utilized, and will utilize the prostanoids and their receptor system, as a marked driving force for evolution.

The differential functional coupling of phosphodiesterase 4 to human DP and EP2 prostanoid receptors stimulated with PGD2 or PGE2

BACKGROUND

Human DP and EP2 receptors are two of the most homologically related receptors coupling with G_αs-protein, which stimulate adenylyl cyclase to produce cAMP. Indeed, both receptors are considered to be generated by tandem duplication. It has been reported that other highly homologous and closely related β1- and β2-adrenergic receptors interact distinctly with and differentially regulate cAMP-specific phosphodiesterase (PDE) 4 recruitment.

METHODS

First, we focused on the cAMP degradation pathways of DP and EP2 receptors stimulated by prostaglandin (PG) D₂ or PGE₂ using HEK cells stably expressing either human DP receptors or EP2 receptors. Then, distances between ligands and amino acids of the receptors were evaluated by molecular dynamics (MD) analysis.

RESULTS

We found that PGD₂/EP2 receptors exerted a greater effect on PDE4 activity than PGE₂/EP2 receptors. Moreover, by MD analysis, either the PGD₂ or EP2 receptor was moved and the distance was shortened between them. According to the results, DP receptors retain reactivity for PGE₂, but EP2 receptors may be activated only by PGE₂, at least in terms of cAMP formation, through the differential functional coupling of PDE4 probably with β-arrestin.

CONCLUSION

Since DP receptors and EP2 receptors are considered to be duplicated genes, DP receptors may still be in a rapid evolutionary stage as a duplicated copy of EP2 receptors and have not yet sufficient selectivity for their cognate ligand, PGD₂.

Genetic Mechanisms of Asthma and the Implications for Drug Repositioning

Asthma is a chronic disease that is caused by airway inflammation. The main features of asthma are airway hyperresponsiveness (AHR) and reversible airway obstruction. The disease is mainly managed using drug therapy. The current asthma drug treatments are divided into two categories, namely, anti-inflammatory drugs and bronchodilators. However, disease control in asthma patients is not very efficient because the pathogenesis of asthma is complicated, inducing factors that are varied, such as the differences between individual patients. In this paper, we delineate the genetic mechanisms of asthma, and present asthma-susceptible genes and genetic pharmacology in an attempt to find a diagnosis, early prevention, and treatment methods for asthma. Finally, we reposition some clinical drugs for asthma therapy, based on asthma genetics.

Human DP and EP2 prostanoid receptors take on distinct forms depending on the diverse binding of different ligands

Human D-type prostanoid (DP) and E-type prostanoid 2 (EP2) receptors are G protein-coupled receptors and are regarded as the most closely related receptors among prostanoid receptors because they are generated by tandem duplication. The DP receptor-cognate ligand, prostaglandin D₂ (PGD₂ ) has the ability to activate not only DP receptors but also EP2 receptors. Likewise, the EP2 receptor-cognate ligand, prostaglandin E₂ (PGE₂ ) has the ability to activate DP receptors in addition to EP receptors in order to stimulate cAMP formation. However, since PGD₂ and/or PGE₂ activate DP and EP2 receptors to similar maximal levels, that is, their similar efficacies, differences between the ligands in each receptor have not yet been determined in detail except for their different affinities. Herein we demonstrated, using an in silico simulation to predict binding patterns among DP or EP2 receptors and PGD₂ , PGE₂ , or prostaglandin F_2α as the reference prostanoid, that DP and EP2 receptors plausibly take on distinct forms depending on the diverse binding of different ligands. Since these ligands have the potential to make these receptors form distinct conformations with discrete signaling pathways, they are consequently regarded as endogenous biased ligands. Moreover, by using functional assays, the susceptibilities of the DP receptors to the noncognate ligands were approximately 10 times lower than those of EP2 receptors. Thus, EP2 receptors seem to be able to distinguish endogenous ligands better than DP receptors, thereby both receptors are plausibly gaining role-sharing functions with respect to one another as the copies of duplicated gene.

Pharmacogenomics of Prostaglandin and Leukotriene Receptors

Individual genetic background together with environmental effects are thought to be behind many human complex diseases. A number of genetic variants, mainly single nucleotide polymorphisms (SNPs), have been shown to be associated with various pathological and inflammatory conditions, representing potential therapeutic targets. Prostaglandins (PTGs) and leukotrienes (LTs) are eicosanoids derived from arachidonic acid and related polyunsaturated fatty acids that participate in both normal homeostasis and inflammatory conditions. These bioactive lipid mediators are synthesized through two major multistep enzymatic pathways: PTGs by cyclooxygenase and LTs by 5-lipoxygenase. The main physiological effects of PTGs include vasodilation and vascular leakage (PTGE2); mast cell maturation, eosinophil recruitment, and allergic responses (PTGD2); vascular and respiratory smooth muscle contraction (PTGF2), and inhibition of platelet aggregation (PTGI2). LTB4 is mainly involved in neutrophil recruitment, vascular leakage, and epithelial barrier function, whereas cysteinyl LTs (CysLTs) (LTC4, LTD4, and LTE4) induce bronchoconstriction and neutrophil extravasation, and also participate in vascular leakage. PTGs and LTs exert their biological functions by binding to cognate receptors, which belong to the seven transmembrane, G protein-coupled receptor superfamily. SNPs in genes encoding these receptors may influence their functionality and have a role in disease susceptibility and drug treatment response. In this review we summarize SNPs in PTGs and LTs receptors and their relevance in human diseases. We also provide information on gene expression. Finally, we speculate on future directions for this topic.

Identification of Susceptibility Genes of Adult Asthma in French Canadian Women

Susceptibility genes of asthma may be more successfully identified by studying subgroups of phenotypically similar asthma patients. This study aims to identify single nucleotide polymorphisms (SNPs) associated with asthma in French Canadian adult women. A pooling-based genome-wide association study was performed in 240 allergic asthmatic and 120 allergic nonasthmatic women. The top associated SNPs were selected for individual genotyping in an extended cohort of 349 asthmatic and 261 nonasthmatic women. The functional impact of asthma-associated SNPs was investigated in a lung expression quantitative trait loci (eQTL) mapping study (n = 1035). Twenty-one of the 38 SNPs tested by individual genotyping showed P values lower than 0.05 for association with asthma. Cis-eQTL analyses supported the functional contribution of rs17801353 associated with C3AR1 (P = 7.90E - 10). The asthma risk allele for rs17801353 is associated with higher mRNA expression levels of C3AR1 in lung tissue. In silico functional characterization of the asthma-associated SNPs also supported the contribution of C3AR1 and additional genes including SYNE1, LINGO2, and IFNG-AS1. This pooling-based GWAS in French Canadian adult women followed by lung eQTL mapping suggested C3AR1 as a functional locus associated with asthma. Additional susceptibility genes were suggested in this homogenous subgroup of asthma patients.

PTGDR gene in asthma: a functional, genetic, and epigenetic study

BACKGROUND

Asthma affects more than 300 million individuals in the world. Several studies have demonstrated the importance of the genetic component. The aim of this study is to develop a holistic approach, including genetic, epigenetic, and expression analysis to study the Prostaglandin D2 receptor gene (PTGDR) in asthmatic patients.

METHODS

In this study, 637 Caucasian individuals were included. Genetic variants were characterized by sequencing, and haplotype and diplotype combinations were established. Electrophoretic mobility shift assays (EMSAs) were performed with different promoter variants. An epigenetic analysis of PTGDR was for the first time developed by MassArray assays, and gene expression was determined by real-time polymerase chain reaction.

RESULTS

The -197T > C (Fisher's P = 0.028) and -613C > T (Fisher's P < 0.001) polymorphisms were found to be significantly associated with allergic asthma and allergy to pollen and mites, respectively. In addition, several haplotype and diplotype combinations were associated with different allergy and asthma phenotypes. The presence of the -613C > T SNP determined variations in the EMSAs. Moreover, consistent differences in the methylation and expression patterns were observed between asthmatic patients and controls determining a 2.34-fold increase of PTGDR gene expression in asthmatic patients.

CONCLUSIONS

Genetic combinations described have functional implications in the PTGDR promoter activity by changing the transcription factors affinity that will help characterize different risk groups. The differences observed in the transcription factors affinity and in the methylation pattern bring insight into different transcription regulation in these patients. To the best of our knowledge, this is the first work in which the implication of genetic and epigenetic factors of PTGDR has been characterized pointing to putative therapeutic targets.

Functional haplotypes in the PTGDR gene fail to associate with asthma in two Australian populations

BACKGROUND AND OBJECTIVE

Haplotypes in the promoter region of the prostanoid DP receptor (PTGDR) gene have been shown to functionally influence gene transcription and to be associated with asthma in two previous case-control studies in Caucasians. This study tested the association of PTGDR haplotypes with asthma phenotypes in two large Caucasian-Australian populations. These results were incorporated in a meta-analysis with previously published data to determine the overall role for these haplotypes in the risk of asthma.

METHODS

Three PTGDR promoter-region single nucleotide polymorphisms (SNP) were genotyped in 368 individuals from the Western Australian Twin Child Health study and 2988 individuals from the Busselton Health Study. Logistic regression and transition disequilibrium tests were used to assess whether SNP genotypes and three SNP haplotypes were associated with doctor-diagnosed asthma or intermediate quantitative traits. Longitudinal data from the Busselton Health Study were used to examine whether PTGDR influences changes in lung function over time. Meta-analysis incorporated the findings of this study with those of two previous studies in Caucasian populations.

RESULTS

Cross-sectional associations between PTGDR haplotypes and asthma phenotypes were non-significant (P > 0.05) in both populations. Longitudinal analyses of PTGDR and lung function were also non-significant. Meta-analysis, however, suggested that haplotype TCT was significantly associated with decreased risk of asthma (OR = 0.76; P = 0.02) while haplotype CCC was not significantly associated with asthma (OR = 1.30; P = 0.07).

CONCLUSIONS

These results suggest that despite the non-significant findings in the present study populations, PTGDR promoter haplotypes may account for a small but significant proportion of the risk of asthma in Caucasian populations.

Prostaglandin D₂ and T(H)2 inflammation in the pathogenesis of bronchial asthma

Prostaglandin D₂ (PGD₂) is a major prostanoid, produced mainly by mast cells, in allergic diseases, including bronchial asthma. PGD₂-induced vasodilatation and increased permeability are well-known classical effects that may be involved in allergic inflammation. Recently, novel functions of PGD₂ have been identified. To date, D prostanoid receptor (DP) and chemoattractant receptor homologous molecule expressed on T(H)2 cells (CRTH2) have been shown to be major PGD₂-related receptors. These two receptors have pivotal roles mediating allergic diseases by regulating the functions of various cell types, such as T(H)2 cells, eosinophils, basophils, mast cells, dendritic cells, and epithelial cells. This review will focus on the current understanding of the roles of PGD₂ and its metabolites in T(H)2 inflammation and the pathogenesis of bronchial asthma.

Association analysis of RGS7BP gene polymorphisms with aspirin intolerance in asthmatic patients

BACKGROUND

Signal-regulated palmitoylation of RGS7BP(regulator of G-protein-signaling 7-binding protein) initiates the activation of G-protein-coupled receptors (GPCRs), including muscarinic receptors, which contribute to the development of asthma and its subphenotypes.

OBJECTIVE

To determine the association of RGS7BP gene polymorphisms with the development of aspirin-exacerbated respiratory disease (AERD).

METHODS

We evaluated the association of RGS7BP gene polymorphisms with response to oral aspirin challenge and with responsiveness to methacholine challenge. RGS7BP messenger RNA splice variants in peripheral blood platelets from patients with different single-nucleotide polymorphisms were analyzed by reverse-transcription polymerase chain reaction.

RESULTS

Logistic regression analysis of RGS7BP gene polymorphisms in patients with AERD (n = 102) and aspirin-tolerant asthma (n = 429) revealed that a haplotype of block 3 consisting of rare alleles +98092 C>G, +98853 C>T, and +104450 T>G of the RGS7BP gene was associated with AERD. Multiple linear regression analysis showed that asthmatic patients carrying ht2/ht2 in block 3 were more responsive to aspirin challenge than those not carrying ht2 (P = .008 in a codominant model). The log-transformed provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% for methacholine was significantly dependent on the BL3-ht2 haplotype. No significant differences in platelet expression of different RGS7BP messenger RNA splice variants were detected between those with and without the BL3-ht2 haplotype.

CONCLUSION

BL3-ht2 of RGS7BP may be an important genetic variant associated with AERD. The haplotype of block 3 may play a protective role against aspirin hypersensitivity in asthma, perhaps by altering the responsiveness of muscarinic receptors.

An inosine 5'-monophosphate dehydrogenase 2 single-nucleotide polymorphism impairs the effect of mycophenolic acid

Mycophenolic acid (MPA) is a selective inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme of de novo synthesis of guanine nucleotides. The isoenzyme IMPDH2 predominates in activated lymphocytes, and its inhibition by MPA is part of standard immunosuppressive regimens. Yet, there are significant unexplained differences in efficacy and tolerability among patients. The objective of this study was to analyze whether frequent variants in the IMPDH2 gene lead to changes in IMPDH activity and to differences in responsiveness to MPA therapy. All 14 exons and intron-exon boundary regions of IMPDH2 were sequenced from genomic DNA probes from 100 healthy individuals. Two novel exonic single-nucleotide polymorphisms were identified in 1% and one intronic polymorphism (rs11706052) in 19% of the study population. Lymphocyte IMPDH activity and proliferation under three MPA concentrations (2.5, 10 and 25 micromol l(-1)) were compared in rs11706052 carriers and wild-type individuals. The presence of rs11706052 polymorphism reduced the antiproliferative effect of MPA on lymphocytes by approximately 50% compared with the IMPDH2 wild-type form at therapeutic relevant concentrations of 10 micromol l(-1) and 25 micromol l(-1). We conclude that a poorer response to MPA therapy can be explained in some individuals by the presence of the rs11706052 polymorphism.

PTGDR is not a major candidate gene for asthma and atopy in Chinese children

Airway sensitization requires the expression of prostanoid DP receptor in mice. Recent studies reported that polymorphisms in the gene encoding prostanoid DP receptor (PTGDR) were associated with asthma in White people and Black people, but this association could not be replicated among Latinos and Koreans. This study investigated the association between asthma-related traits and six single nucleotide polymorphisms (SNPs) of PTGDR in Chinese children, consisted of 308 asthmatics and 368 non-allergic controls. Plasma total and aeroallergen-specific immunoglobulin E were measured by immunoassays. PTGDR SNPs were determined by multiplex SNaPshot genotyping. All polymorphic markers followed Hardy-Weinberg equilibrium except G1044A in the controls (p = 0.021). The linkage disequilibrium (LD) scores for these SNPs were moderate to high, and in particular, T-549C and C-441T were in strong LD. Significant interethnic variations in PTGDR alleles and haplotypes (up to 41%) were found in our subjects when compared with White people or Latinos. Asthma diagnosis, atopy and aeroallergen sensitization did not differ among children with different PTGDR genotypes (p > 0.15 for all). Linear regression showed weakly significant associations between T-197C and G1044A of PTGDR and spirometric variables. PTGDR haplotypes were not associated with asthma and atopy phenotypes (p > 0.09 for all). Our results do not support PTGDR to be a major candidate gene for asthma traits in Chinese children.

Brief bout of exercise alters gene expression in peripheral blood mononuclear cells of early- and late-pubertal males

Peripheral blood mononuclear cells (PBMCs) are stimulated by exercise and contribute not only to host defense, but also to growth, repair, and disease pathogenesis. Whether PBMC gene expression is altered by exercise in children is not known. Ten early pubertal boys (8-12 y) and 10 late pubertal boys (15-18 y) performed ten 2-min bouts of strenuous, constant work rate exercise with 1-min rest intervals. PBMCs were isolated before and after exercise and microarray (Affymetrix U133 + 2 chips) analyzed. Statistical criterion to identify gene expression changes was less than 5% false discovery rate (FDR) with 95% confidence interval. One thousand two hundred forty-six genes were altered in older boys (517 up, 729 down), but only 109 were altered in the younger group (79 up, 30 down). In older boys, 13 gene pathways (using Expression Analysis Systematic Explorer, p < 0.05) were found (e.g. natural killer cell cytotoxicity, apoptosis). Epiregulin gene expression (EREG, a growth factor involved in wound healing) increased in older boys. In older boys exercise altered genes such as TBX21, GZMA, PGTDR, and CCL5 also play roles in pediatric inflammatory diseases like asthma. Sixty-six genes were changed significantly in both groups. The pattern of PBMC gene expression suggests the initiation of an immunologic "danger" signal associated with a sudden change in energy expenditure.

A new PTGDR promoter polymorphism in a population of children with asthma

Recently, functional genetic variants of the PTGDR gene have been associated with asthma. The objective of this work was to study polymorphisms of the promoter region of PTGDR and their haplotype and diplotype combinations in a Spanish population of children with asthma. In this study, 200 Caucasian individuals were included. Asthma was specialist-physician diagnosed according to the ATS criteria. The polymorphisms were analyzed by direct sequencing. In the study, the new polymorphism (-613C > T) in the promoter region of PTGDR was analyzed. The CT genotype was more common in controls (17%) than in patients with asthma (1%) (p-value = 0.0003; OR, 0.057; 95% CI, 0.007-0.441). The CCCT CCCC diplotype (promoter positions -613, -549, -441, and -197) was more frequent in the group of patients with asthma [Fisher's p-value = 0.012; OR, 10.24; 95% CI (1.25-83.68)]; this diplotype is unambiguous. To our knowledge, this is the first study of -613C > T PTGDR polymorphism in patients. This analysis provides more complete information on influence of diplotype combinations of PTGDR polymorphisms in asthma.

The TaqMan method for SNP genotyping

Single nucleotide polymorphisms (SNPs) are common DNA sequence variations that occur at single bases within the genome. SNPs have been instrumental in elucidating the genetic basis of common, complex diseases using genome-wide association studies, candidate gene case-control association studies, and genome-wide linkage analyses. A key to these studies is genotyping of SNPs. Various methods for SNP genotyping have been developed. For a particular genotyping project, the choice of method is dependent on the number of SNPs (n) and the number of DNA samples (m) to be genotyped. For a genome-wide or large-scale project with very high n and small m, the Affymetrix SNP GeneChip and Illumina GoldenGate BeadChips assays are the ideal methods. For a project involving a small number of SNPs (small n) and a large population (high m), the TaqMan assay is the preferred technology as it has high throughput and is highly accurate, precise, time-efficient, and cost-effective. Here, we describe the detailed procedures for TaqMan SNP genotyping assay, including preparation of high-quality DNA samples, the operating protocol, clarification of technical issues, and discussion of several cautionary notes.

Role of prostaglandin D(2) and its receptors in the pathophysiology of asthma

Prostaglandin D(2) (PGD(2)) is one of the most abundant lipid mediators present in the airways of asthmatics. However, little was known of the role it plays in the pathophysiology of asthma, until the identification of DP (DP1, PTGDR) and CRTH2 (DP2), two PGD(2)-specific transmembrane receptors with different distribution and intracellular signaling. Pharmacological tools, such as receptor-specific agonists and antagonists, and genetically-engineered mice, which lack either DP or CRTH2, have helped understand the complex effects of PGD(2) in allergic inflammation of the airways. Furthermore, genetic association studies have shown a positive linkage of the genetic polymorphisms in DP and CRTH2, with asthma phenotypes from specific ethnic backgrounds, further highlighting the importance of PGD(2) and its receptors in the pathophysiology of asthma.

Interleukin 18 receptor 1 gene polymorphisms are associated with asthma

The interleukin 18 receptor (IL18R1) gene is a strong candidate gene for asthma. It has been implicated in the pathophysiology of asthma and maps to an asthma susceptibility locus on chromosome 2q12. The possibility of association between polymorphisms in IL18R1 and asthma was examined by genotyping seven SNPs in 294, 342 and 100 families from Denmark, United Kingdom and Norway and conducting family-based association analyses for asthma, atopic asthma and bronchial hyper-reactivity (BHR) phenotypes. Three SNPs in IL18R1 were associated with asthma (0.01131 < or = P < or = 0.01377), five with atopic asthma (0.00066 < or = P < or = 0.00405) and two with BHR (0.01450 < or = P < or = 0.03203) in the Danish population; two SNPs were associated with atopic asthma (0.00397 < or = P < or = 0.01481) and four with BHR (0.00435 < or = P < or = 0.03544) in the UK population; four SNPs showed associations with asthma (0.00015 < or = P < or = 0.03062), two with atopic asthma (0.01269 < or = P < or = 0.04042) and three with BHR (0.00259 < or = P < or = 0.01401) in the Norwegian population; five SNPs showed associations with asthma (0.00005 < or = P < or = 0.03744), five with atopic asthma (0.00001 < or = P < or = 0.04491) and three with BHR (0.03568 < or = P < or = 0.04778) in the combined population. Three intronic SNPs (rs1420099, rs1362348 and rs1974675) showed replicated association for at least one asthma-related phenotype. These results demonstrate significant association between polymorphisms in IL18R1 and asthma.

Polymorphisms in the endothelin-1 (EDN1) are associated with asthma in two populations

Endothelin-1 (EDN1) has been reported to be implicated in the pathophysiology of asthma. Literature results on the genetic association of EDN1 in asthma are inconsistent. Eleven single nucleotide polymorphisms in EDN1 were genotyped in 342 and 100 families from UK and Norway, respectively. Asthma, bronchial hyperreactivity (BHR) and atopic asthma phenotypes were analyzed for the family-based association. Five single nucleotide polymorphisms (SNPs) were associated with asthma (0.0017<or=P<or=0.0291), five with BHR (0.0026<or=P<or=0.0315) and three with atopic asthma (0.0016<or=P<or=0.041) in the UK population. Three SNPs were associated with asthma (0.0041<or=P<or=0.019), seven with BHR (0.0018<or=P<or=0.041) and two with atopic asthma (0.0123<or=P<or=0.0153) in the Norwegian population. A polymorphism (rs1800541) in the promoter region of EDN1 was replicated in the two populations. A nonsynonymous coding polymorphism (rs5370) resulting in a change of amino acid Asn to Lys at position 198 was also replicated. The results of haplotype-based association analyses strongly supported the ones of single SNP associations. This study demonstrates the significant evidence of association between polymorphisms in EDN1 and asthma.