Beta-trace gene expression is regulated by a core promoter and a distal thyroid hormone response element

β-Trace protein: a marker of GFR and other biological pathways

β-Trace protein (BTP), also known as lipocalin prostaglandin D2 synthase (L-PGDS; encoded by the PTGDS gene), is a low-molecular-weight glycoprotein and an emerging novel marker of glomerular filtration rate. BTP is an important constituent of cerebral spinal fluid and is found in much lower concentrations in blood. Its serum origin and renal handling remain poorly understood. Unlike serum creatinine, BTP is not physiologically inert. It possesses both ligand-binding and enzymatic properties. BTP catalyzes the conversion of prostaglandin H2 (PGH2) to PGD2. PGD2 is an eicosanoid involved in a variety of important physiologic processes, including platelet aggregation, vasodilation, inflammation, adipogenesis, and bone remodeling. Several studies now have documented BTP's strong association with glomerular filtration rate, end-stage renal disease, cardiovascular disease, and death in a variety of different patient populations. This review provides an overview of the biochemistry, physiology and metabolism, biological functions, and measurement of BTP; summarizes the evidence for BTP as a marker of both kidney function and cardiovascular disease; and then considers the interplay between its biological properties, serum concentration, and patient outcomes.

Beta-trace protein as a marker of GFR--history, indications, and future research

OBJECTIVES

Recent findings suggest that beta-trace protein (BTP), a small molecular weight protein, is at least equal if not superior to serum creatinine as a marker of glomerular filtration rate (GFR), particularly since it is independent from height, gender, age, and muscle mass. The authors sought to summarize knowledge on BTP and its use as a marker of GFR using the most recent literature available.

DESIGN AND METHODS

The authors compiled key articles and all relevant recent literature on this topic. Physical and chemical features of the molecule are described, as well as factors that may affect its expression. The use of BTP in estimating GFR as a whole and in specific patient groups, including pregnant women, neonates and infants, children and adolescents, and patients who have undergone renal transplantation is discussed. The use of BTP as a marker for cardiovascular risk factors is also briefly addressed.

RESULTS

Although its performance in the general population is marginally inferior to cystatin C, studies have suggested that it may be superior in accurately estimating GFR in select patient groups such as pregnant women and neonates.

CONCLUSIONS

This novel marker shows promise, but further research is required to clarify findings from available data.

Modulation of lipocalin-type prostaglandin D2 synthase expression in catfish seminal vesicles by thyroid disrupting agents and hormones

Thyroid hormones play crucial role in several biological processes including reproduction. Disruption of normal thyroid status by environmental contaminants can cause severe impairment in reproductive functions. In our previous study, we reported down-regulation of a protein in seminal vesicular fluid of air-breathing catfish, Clarias gariepinus during experimentally induced hyperthyroidism. N-terminal amino acid sequence analysis followed by search in sequence database denoted it to be lipocalin-type prostaglandin D2 synthase (ptgds-b). In the present study, we cloned full-length cDNA of ptgds-b based on the N-terminal amino acid sequence. Surprisingly, Northern blot as well as RT-PCR analysis demonstrated the presence of ptgds-b transcript predominantly in seminal vesicles and developing testis. Further, ptgds-b mRNA significantly decreased in seminal vesicles following L-thyroxine overdose while there was an increased expression of ptgds-b after depletion of thyroid hormone by thiourea and withdrawal of the treatments reverted this effect. Treatment of catfish with human chorionic gonadotropin and estradiol significantly reduced ptgds-b expression. Taken together, we report ptgds-b as a thyroid hormone regulated protein in the seminal vesicles in addition to gonadotropin and estradiol. Further studies might explain the exclusive presence of ptgds-b in seminal vesicles and developing testis yet present data evaluated it as a putative biomarker for thyroid hormone disruption.

Neurochemical measures co-vary with personality traits: forensic psychiatric findings replicated in a general population sample

Neurobiological markers in cerebrospinal fluid (CSF) and in serum, previously found to co-vary with destructive personality traits in violent offenders, were explored in a general population sample of 21 patients undergoing knee surgery. Results on the Karolinska Scales of Personality (KSP) and the Temperament and Character Inventory (TCI) were compared with CSF/serum albumin ratios and serum concentrations of beta-trace protein (betaTP) (as markers for blood-brain barrier (BBB) permeability), to CSF/serum albumin ratios between the dopamine and serotonin metabolites homovanillic acid (HVA)/5-hydroxyindoleacetic acid (HIAA) and to CSF and serum ratios between activated thyroid hormone (T3) and its precursor T4. Serum betaTP concentrations correlated with CSF/serum albumin ratios (P=0.018), but not with preoperative serum creatinine concentrations. Serum betaTP correlated significantly with Monotony Avoidance and Impulsiveness; CSF HVA/5-HIAA ratios with Irritability and low Cooperativeness. The betaTP is a potential serum marker for the integrity of the BBB that does not necessitate lumbar puncture. Thyroid hormones did not correlate with personality traits. As reported in forensic psychiatric patients, aggressive, unempathic personality traits were thus associated with increased dopaminergic activity in relation to the serotonergic activity and impulsivity to increased BBB permeability also in a general population group.

Temporal changes of the plasma levels of cystatin C, β‐trace protein, β2‐microglobulin, urate and creatinine during pregnancy indicate continuous alterations in the renal filtration process

OBJECTIVE

To determine the plasma levels of the renal functional markers creatinine, urate, cystatin C, beta2-microglobulin and beta-trace protein in samples from the first, second, early third and late third trimesters of 398 healthy women with uncomplicated singleton pregnancies.

MATERIAL AND METHODS

Plasma samples from 58 healthy non-pregnant women served as controls. The creatinine levels were significantly lower at all time-points in pregnancy, whereas the urate levels were lower during the first and second trimesters but increased in the late third trimester. The cystatin C, beta2-microglobulin and beta-trace protein levels displayed similar changes with increased levels in the third trimester but unaltered levels during the first and second trimesters.

RESULTS

The results indicate an increased filtration of low-molecular weight molecules during pregnancy, particularly during the first and second trimesters, whereas filtration of 10-30 kDa molecules is decreased in the third but unaltered in the first and second trimesters. The levels of albumin and alph2-macroglobulin were measured in the same samples.

CONCLUSIONS

The albumin levels decreased in the second and third trimesters, whereas the levels of chi2-macroglobulin were unchanged, which is compatible with a virtually unaltered transfer of chi2-macroglobulin between the intra- and extravascular space during pregnancy and a significantly increased extravascular fraction of albumin.

Biochemical, functional, and pharmacological characterization of AT-56, an orally active and selective inhibitor of lipocalin-type prostaglandin D synthase

We report here that 4-dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)-butyl]-piperidine (AT-56) is an orally active and selective inhibitor of lipocalin-type prostaglandin (PG) D synthase (L-PGDS). AT-56 inhibited human and mouse L-PGDSs in a concentration (3–250 μm)-dependent manner but did not affect the activities of hematopoietic PGD synthase (H-PGDS), cyclooxygenase-1 and -2, and microsomal PGE synthase-1. AT-56 inhibited the L-PGDS activity in a competitive manner against the substrate PGH₂ (K_m = 14 μm) with a K_i value of 75 μm but did not inhibit the binding of 13-cis-retinoic acid, a nonsubstrate lipophilic ligand, to L-PGDS. NMR titration analysis revealed that AT-56 occupied the catalytic pocket, but not the retinoid-binding pocket, of L-PGDS. AT-56 inhibited the production of PGD₂ by L-PGDS-expressing human TE-671 cells after stimulation with Ca²⁺ ionophore (5 μm A23187) with an IC₅₀ value of about 3 μm without affecting their production of PGE₂ and PGF_2α but had no effect on the PGD₂ production by H-PGDS-expressing human megakaryocytes. Orally administered AT-56 (<30 mg/kg body weight) decreased the PGD₂ production to 40% in the brain of H-PGDS-deficient mice after a stab wound injury in a dose-dependent manner without affecting the production of PGE₂ and PGF_2α and also suppressed the accumulation of eosinophils and monocytes in the bronco-alveolar lavage fluid from the antigen-induced lung inflammation model of human L-PGDS-transgenic mice.

Enhancement of prostaglandin D(2) production through cyclooxygenase-2 and lipocalin-type prostaglandin D synthase by upstream stimulatory factor 1 in human brain-derived TE671 cells under serum starvation

We found that prostaglandin (PG) D(2) production was induced through transcriptional activation of cyclooxygenase (COX)-2 and lipocalin-type PGD synthase (L-PGDS) genes under serum-starved conditions in human brain-derived TE671 cells. Analysis of promoter and intron regions of the human L-PGDS gene demonstrated that an atypical E-box within intron 4 mediated serum starvation-induced up-regulation of L-PGDS gene expression. The results of electrophoretic mobility shift assay and chromatin immunoprecipitation assay showed that upstream stimulatory factor (USF) 1 bound to this atypical E-box. USF1 gene expression was also enhanced during serum starvation in TE671 cells through activation of p38 mitogen activated protein kinase, and the efficiency of the binding of USF1 to the atypical E-box was clearly increased by serum starvation. Administration of USF1 siRNA suppressed both L-PGDS and COX-2 gene expression and PGD(2) production. Moreover, NS-398, a COX-2 inhibitor and AT-56, an L-PGDS inhibitor, suppressed PGD(2) production in TE671 cells cultured under the serum-starved condition. These results indicate that PGD(2) production stimulated by serum starvation is mediated by both COX-2 and L-PGDS through enhancement of USF1 in TE671 cells.

Family-based and case-control studies reveal no association of lipocalin-type prostaglandin D2 synthase with schizophrenia

Several observations point to the involvement of disturbed lipid biology in schizophrenia. Reduced response to niacin flushing test, which involves vasodilatation induced by prostaglandin D2 (PGD2), is among the evidences, together with decreased CSF levels of lipocalin-type prostaglandin D2 synthase (PTGDS), the enzyme responsible for the synthesis of PGD2 in the brain. Since PTGDS is also a carrier for lipophilic molecules such as retinoids and thyroid hormones, altered PTGDS levels might influence both PGD2-mediated signaling, and vitamin A and thyroid hormone availability. To test whether genetic variants of PTGDS are involved in the etiology of schizophrenia, we searched for variants in the coding and regulatory regions of the gene. We identified four previously described polymorphisms. Using two case-control samples from Portugal and Brazil, none of the polymorphisms tested was associated with the disease. In addition, no transmission distortion was observed in an independent parents-offspring sample from the Azorean Islands. Our data do not support the involvement of the PTGDS gene in the etiology of schizophrenia.

SOX9 Regulates Prostaglandin D Synthase Gene Transcription in Vivo to Ensure Testis Development

In mammals, male sex is determined by the Y-chromosomal gene Sry (sex-determining region of Y chromosome). The expression of Sry and subsequently Sox9 (SRY box containing gene 9) in precursors of the supporting cell lineage results in the differentiation of these cells into Sertoli cells. Sertoli cells in turn orchestrate the development of all other male-specific cell types. To ensure that Sertoli cells differentiate in sufficient numbers to induce normal testis development, the early testis produces prostaglandin D(2) (PGD(2)), which recruits cells of the supporting cell lineage to a Sertoli cell fate. Here we show that the gene encoding prostaglandin D synthase (Pgds), the enzyme that produces PGD(2), is expressed in Sertoli cells immediately after the onset of Sox9 expression. Promoter analysis in silico and in vitro identified a paired SOX/SRY binding site. Interestingly, only SOX9, and not SRY, was able to bind as a dimer to this site and transactivate the Pgds promoter. In line with this, a transgenic mouse model showed that Pgds expression is not affected by ectopic Sry expression. Finally, chromatin immunoprecipitation proved that SOX9 but not SRY binds to the Pgds promoter in vivo.

Zebrafish and chicken lipocalin-type prostaglandin D synthase homologues: Conservation of mammalian gene structure and binding ability for lipophilic molecules, and difference in expression profile and enzyme activity

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is a bifunctional protein possessing both the ability to synthesize PGD(2) and to serve as a carrier protein for lipophilic molecules. L-PGDS has been extensively studied in mammalian species, whereas little is known about non-mammalian forms. Here, we identified and characterized the L-PGDS homologues from non-mammals such as zebrafish and chicken. Phylogenetic analysis revealed that L-PGDSs of mammalian and non-mammalian organisms form a "L-PGDS sub-family" that has been evolutionally separated from other lipocalin gene family proteins. The genes for zebrafish and chicken L-PGDS homologues consisted of 6 exons, and all of the exon/intron boundaries were completely identical to those of mammalian L-PGDS genes. Zebrafish and chicken L-PGDS genes were clustered with several lipocalin genes in the chromosome, as in the case of mouse and human genes. Gene expression profiles were different among chicken, mouse, human, except for conservation of abundant expression in the brain and heart. The chicken L-PGDS homologue carried weak PGDS activity, whereas the zebrafish protein did not show any of the activity. However, when the amino-terminal region of the zebrafish L-PGDS homologue was exchanged for that of mouse L-PGDS carrying the Cys residue essential for PGDS activity, this chimeric protein showed weak PGDS activity. Both zebrafish and chicken L-PGDS homologues bound thyroxine and all-trans retinoic acid, like mammalian L-PGDSs and other lipocalin gene family proteins. These results indicate that non-mammalian and mammalian L-PGDS genes evolved from the same ancestral gene and that the non-mammalian L-PGDS homologue was the primordial form of L-PGDS but whose major function was and is to serve as a carrier protein for lipophilic molecules. During molecular evolution, the mammalian L-PGDS protein might have acquired effective PGDS activity through substitution of several amino acid residues, especially in the amino-terminal region including the Cys residue, which is essential for PGDS activity.

Protein Kinase C Activates Human Lipocalin-type Prostaglandin D Synthase Gene Expression through De-repression of Notch-HES Signaling and Enhancement of AP-2β Function in Brain-derived TE671 Cells

Here we investigated the regulatory mechanism of lipocalin-type prostaglandin D synthase (L-PGDS) gene expression in human TE671 (medulloblastoma of cerebellum) cells. Reporter analysis of the promoter region from -730 to +75 of the human L-PGDS gene demonstrated that deletion or mutation of the N-box at -337 increased the promoter activity 220-300%. The N-box was bound by Hes-1, a mammalian homologue of Drosophila Hairy and enhancer of split, as examined by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Functional expression of the Notch intracellular domain significantly increased Hes-1 expression and decreased L-PGDS expression level in TE671 cells. Moreover, knock-down of Hes-1 mRNA by RNA interference significantly enhanced the L-PGDS mRNA level, indicating that the L-PGDS gene expression is repressed by the Notch-Hes signaling. When the AP-2 element at -98 of the promoter region was deleted or mutated, the promoter activity was drastically decreased to approximately 10% of normal. The AP-2 element was bound by AP-2beta dominantly expressed in TE671 cells, according to the results of electrophoretic mobility shift assay and chromatin immunoprecipitation assay. L-PGDS expression was induced by 12-O-tetradecanoylphorbol-13-acetate in TE671 cells, and this induction was inhibited by a protein kinase C inhibitor. Stimulation of TE671 cells with 12-O-tetradecanoylphorbol-13-acetate or transfection with protein kinase Calpha expression vector induced phosphorylation of Hes-1, inhibition of DNA binding of Hes-1 to the N-box, and activation of the AP-2beta function to up-regulate L-PGDS gene expression. These results reveal a novel transcriptional regulatory mechanism responsible for the high level expression of the human L-PGDS gene in TE671 cells.

Activator Protein-1 Mediates Shear Stress–Induced Prostaglandin D Synthase Gene Expression in Vascular Endothelial Cells

OBJECTIVE

We attempted to determine the molecular mechanism of fluid shear stress-induced lipocalin-type prostaglandin D synthase (l-PGDS) expression in vascular endothelial cells.

METHODS AND RESULTS

We examined the promoter region of the l-PGDS gene by loading laminar shear stress (20 dyne/cm2), using a parallel-plate flow chamber, on endothelial cells transfected with luciferase reporter vectors containing the 5'-flanking regions of the human l-PGDS gene. A deletion mutant analysis revealed that a shear stress-responsive element resided in the region between -2607 and -2523 bp. A mutation introduced into the putative binding site for activator protein-1 (AP-1) within this region eliminated the response to shear stress. In an electrophoretic mobility shift assay, shear stress stimulated nuclear protein binding to the AP-1 binding site, which was supershifted by antibodies to c-Fos and c-Jun. Shear stress elevated the c-Jun phosphorylation level in a time-dependent manner, similar to that of l-PGDS gene expression. SP600125, a c-Jun N-terminal kinase inhibitor, decreased the c-Jun phosphorylation, DNA binding of AP-1, and l-PGDS expression induced by shear stress. Additionally, an mRNA chase experiment using actinomycin D demonstrated that shear stress did not stabilize l-PGDS mRNA.

CONCLUSIONS

Shear stress induces l-PGDS expression by transcriptional activation through the AP-1 binding site.

Identification of gene polymorphism in lipocalin-type prostaglandin D synthase and its association with carotid atherosclerosis in Japanese hypertensive patients

Recent reports suggested that lipocalin-type prostaglandin D synthase (L-PGDS) is implicated in atherogenesis. In the present study, we investigated the polymorphism of the L-PGDS gene and examined its relationship with the severity of carotid atherosclerosis which is determined as the maximum intima-media thickness in the common carotid artery (C-IMT(max)). We identified 6 single nucleotide polymorphisms (SNPs) of the L-PGDS gene in Japanese. A rare SNP with an amino acid change (1535C>G in exon 4, Leu79Val) and a common SNP (4111 A>C in 3'-untranslated region) were selected for genotyping in 782 Japanese hypertensive subjects. There was no significant difference among genotypes in 1535C>G, however, in 4111 A>C, serum levels of high-density lipoprotein (HDL) cholesterol were significantly higher in subjects with A/A genotype than those with A/C and C/C genotypes. C-IMT(max) was significantly smaller in subjects with A/A genotype than those with A/C and C/C. Logistic regression analysis revealed that the presence of A/A genotype significantly reduced the risk for increased C-IMT(max), even after adjustment for other known risk factors [adjusted odds ratio: 0.71 (95% CI: 0.58-0.88)]. Our results suggested that 4111 A>C polymorphism in the L-PGDS gene contributes to the development of carotid atherosclerosis in Japanese hypertensive patients.

Phylogeny and regulation of four lipocalin genes clustered in the chicken genome: evidence of a functional diversification after gene duplication

A novel lipocalin gene is here reported that represents the fourth member of a cluster we have identified in the chicken genome. This cluster also includes Chondrogenesis-Associated Lipocalins beta and gamma (CAL beta, CAL gamma) and Extracellular Fatty Acid Binding Protein (Ex-FABP). The new gene codes for a 22-kDa secreted protein with three cysteine residues and a series of sequence features well conserved in the lipocalin family. All the genes in the cluster are structurally similar presenting comparable exon/intron boundary positions and exon sizes. A phylogenetic analysis indicates the monophyletic grouping of these genes, and their relationship with the lipocalins alpha-1-microglobulin (A1mg), complement factor 8 gamma chain (C8GC), prostaglandin D synthase (PGDS), and neutrophil-gelatinase-associated lipocalin (NGAL). The new cluster gene appears to be the ortholog of the mammalian C8GC and was thus named Ggal-C8GC. This orthology also suggests that this lipocalin was present in the ancestor common to reptiles and mammals. In addition to other expressing tissues, Ex-FABP, CAL beta and CAL gamma genes are highly transcribed in chondrocytes at late stages of chondrogenesis during endochondral bone formation and/or upon inflammatory stimulation. Here, we show that they are also transcriptionally induced when chondrocytes are subjected to various biological events as cell quiescence, cell shape transition, and hormonal stimulation. By contrast, Ggal-C8GC transcripts are only barely detectable in chondrocytes, but are more abundant in liver, kidney, brain, heart, skeletal muscle and particularly in skin. Moreover, no expression induction was observed neither during chondrocyte differentiation, nor upon any of the stimulations mentioned above. This indicates that the Ggal-C8GC gene was co-opted for a novel function after the duplication events that gave rise to the cluster. The peculiar coordinated regulation of Ex-FABP, CAL beta and CAL gamma, and the apparent divergent role of Ggal-C8GC suggest that these gene duplications may have been maintained during evolution by a sub-functionalization mechanism where some common function(s) are shared by several members of the cluster and some other specialized function(s) are unique to other members.

Perspectives in the study of thyroid hormone action on brain development and function

The purpose of this review is to provide an up-to-date report on the molecular and physiologic processes involved in the role of thyroid hormone as an epigenetic factor in brain maturation. We summarize the available data on the control of brain gene expression by thyroid hormone, the correlation between gene expression and physiologic effects, and the likely mechanisms of action of thyroid hormone on brain gene expression. In addition we propose a role for unliganded thyroid hormone receptors in the pathogenesis of hypothyroidism. Finally, we review recent data indicating that thyroid hormone receptors have an impact on behavior.

Regulation of lipocalin-type prostaglandin D synthase gene expression by Hes-1 through E-box and interleukin-1 beta via two NF-kappa B elements in rat leptomeningeal cells

The promoter function of the rat lipocalin-type prostaglandin D synthase (L-PGDS) gene was characterized in primary cultures of leptomeningeal cells prepared from the neonatal rat brain. Luciferase reporter assays with deletion and site-directed mutation of the promoter region (-1250 to +77) showed that an AP-2 element at -109 was required for activation and an E-box at +57, for repression. Binding of nuclear factors to each of these cis-elements was demonstrated by an electrophoretic mobility shift assay. Several components of the Notch-Hes signaling pathway, Jagged, Notch1, Notch3, and Hes-1, were expressed in the leptomeningeal cells. Human Hes-1 co-expressed in the leptomeningeal cells bound to the E-box of the rat L-PGDS gene, and repressed the promoter activity of the rat L-PGDS gene in a dose-dependent manner. The L-PGDS gene expression was up-regulated slowly by interleukin-1 beta to the maximum level at 24 h. The reporter assay with deletion and mutation revealed that two NF-kappa B elements at -1106 and -291 were essential for this up-regulation. Binding of two NF-kappa B subunits, p65 and c-Rel, to these two NF-kappa B elements occurred after the interleukin-1 beta treatment. Therefore, the L-PGDS gene is the first gene identified as the target for the Notch-Hes signal through the E-box among a variety of genes involved in the prostanoid biosynthesis, classified to the lipocalin family, and expressed in the leptomeninges. Moreover, the L-PGDS gene is a unique gene that is activated slowly by the NF-kappa B system.

Action of thyroid hormone in brain

Among the most critical actions of thyroid hormone in man and other mammals are those exerted on brain development. Severe hypothyroidism during the neonatal period leads to structural alterations, including hypomyelination and defects of cell migration and differentiation, with long-lasting, irreversible effects on behavior and performance. A complex regulatory mechanism operates in brain involving regulation of the concentration of the active hormone, T3, and the control of gene expression. Most brain T3 is formed locally from its precursor, T4, by the action of type II deiodinase which is expressed in glial cells, tanycytes, and astrocytes. Type III deiodinase (DIII) is also involved in the regulation of T3 concentrations, especially during the embryonic and early post-natal periods. DIII is expressed in neurons and degrades T4 and T3 to inactive metabolites. The action of T3 is mediated through nuclear receptors, which are expressed mainly in neurons. The receptors are ligand-modulated transcription factors, and a number of genes have been identified as regulated by thyroid hormone in brain. The regulated genes encode proteins of myelin, mitochondria, neurotrophins and their receptors, cytoskeleton, transcription factors, splicing regulators, cell matrix proteins, adhesion molecules, and proteins involved in intracellular signaling pathways. The role of thyroid hormone is to accelerate changes of gene expression that take place during development. Surprisingly, null-mutant mice for the T3 receptors show almost no signs of central nervous system involvement, in contrast with the severe effects of hypothyroidism. The resolution of this paradox is essential to understand the role of thyroid hormone and its receptors in brain development and function.

Biochemical, structural, genetic, physiological, and pathophysiological features of lipocalin-type prostaglandin D synthase

Lipocalin-type prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2), a common precursor of various prostanoids, to produce PGD(2), a potent endogenous somnogen and nociceptive modulator, in the presence of sulfhydryl compounds. PGDS is an N-glycosylated monomeric protein with an M(r) of 20000-31000 depending on the size of the glycosyl moiety. PGDS is localized in the central nervous system and male genital organs of various mammals and in the human heart and is secreted into the cerebrospinal fluid, seminal plasma, and plasma, respectively, as beta-trace. The PGDS concentrations in these body fluids are useful for the diagnosis of several neurological disorders, dysfunction of sperm formation, and cardiovascular and renal diseases. The cDNA and gene for PGDS have been isolated from several animal species, and the tissue distribution and cellular localization have also been determined. This enzyme is considered to be a dual functional protein; i.e. it acts as a PGD(2)-producing enzyme and also as a lipophilic ligand-binding protein, because the enzyme binds biliverdin, bilirubin (K(d)=30 nM), retinaldehyde, retinoic acid (K(d)=80 nM) with high affinities. X-ray crystallographic analyses revealed that PGDS possesses a beta-barrel structure with a hydrophobic pocket in which an active thiol, Cys(65), the active center for the catalytic reaction, was located facing to the inside of the pocket. Gene-knockout and transgenic mice for PGDS were generated and found to have abnormalities in the regulation of nociception and sleep.

Dexamethasone induces lipocalin-type prostaglandin D synthase gene expression in mouse neuronal cells

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is responsible for the production of PGD(2), the main PG in the CNS. PGD(2) is an endogenous sleep inducer, and it is involved in the control of odor and pain responses and body temperature. In addition, PGD synthase transports lipophilic molecules in the subarachnoid space and CSF. By northern and western assays we show that the synthetic glucocorticoid dexamethasone, an inhibitor of PG production in most tissues, induces L-PGDS mRNA and protein in a dose- and time-dependent fashion in mouse neuronal GT1-7 cells. Accordingly, dexamethasone increases cellular L-PGDS enzymatic activity. Dexamethasone induced L-PGDS gene transcription in run-on assays and activated the mouse L-PGDS gene promoter in transiently transfected cells. It is interesting that the tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA), which induces the synthesis of PGs in many tissues, inhibited the increase in L-PGDS expression induced by dexamethasone. In contrast, neither dexamethasone nor TPA affected the expression of cyclooxygenases-1 and -2. Our data demonstrate that dexamethasone induces L-PGDS gene transcription in neuronal cells.

Fluid shear stress induces lipocalin-type prostaglandin D(2) synthase expression in vascular endothelial cells

Ligands for peroxisome proliferator-activated receptor gamma, such as the thiazolidinedione class of antidiabetic drugs and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), modulate various processes in atherogenesis. In search of cells that generate prostaglandin D(2) (PGD(2)), the metabolic precursor of 15d-PGJ(2), we identified PGD(2) from culture medium of endothelial cells. To study how PGD(2) production is regulated in endothelial cells, we investigated the role of fluid shear stress in the metabolism of PGD(2). Endothelial cells expressed the mRNA for the lipocalin-type PGD(2) synthase (L-PGDS) both in vitro and in vivo. Loading laminar shear stress using a parallel-plate flow chamber markedly enhanced the gene expression of L-PGDS, with the maximal effect being obtained at 15 to 30 dyne/cm(2). The expression began to increase within 6 hours after loading shear stress and reached the maximal level at 18 to 24 hours. In contrast, shear stress did not alter the expression levels of PGI(2) synthase and thromboxane A(2) synthase. In parallel with the increase in the expression level of L-PGDS, endothelial cells released PGD(2) and 15d-PGJ(2) into culture medium. These results demonstrate that shear stress promotes PGD(2) production by stimulating L-PGDS expression and suggest the possibility that a peroxisome proliferator-activated receptor gamma ligand is produced in vascular wall in response to blood flow.

Prostaglandin D synthase: structure and function

Prostaglandin (PG) D synthase catalyzes the isomerization of PGH2, a common precursor of various prostanoids, to produce PGD2 in the presence of sulfhydryl compounds. PGD2 induces sleep, regulates nociception, inhibits platelet aggregation, acts as an allergic mediator, and is further converted to 9 alpha, 11 beta-PGF2 or the J series of prostanoids, such as PGJ2, delta 12-PGJ2, and 15-deoxy-delta 12,14-PGJ2. We have purified two distinct types of PGD synthase; one is the lipocalin-type enzyme and the other is the hematopoietic enzyme. We isolated the cDNA and the gene for each enzyme and determined the tissue distribution profile and the cellular localization in several animal species. Lipocalin-type PGD synthase is localized in the central nervous system and male genital organs of various mammals and the human heart and is secreted into cerebrospinal fluid, seminal plasma, and plasma, respectively. The human enzyme was identified as beta-trace, which is a major protein in human cerebrospinal fluid. This enzyme is considered to be a dual-function protein; it acts as a PGD2-producing enzyme and also as a lipophilic ligand-binding protein, because the enzyme binds retinoids, thyroids, and bile pigments, with high affinities. Hematopoietic PGD synthase is widely distributed in the peripheral tissues and localized in the antigen-presenting cells, mast cells, and megakaryocytes. The hematopoietic enzyme is the first recognized vertebrate homolog of the sigma class of glutathione S-transferase. X-ray crystallographic analyses and generation of gene-knockout and transgenic mice for each enzyme have been performed.

Immunocytochemical localization of lipocalin-type prostaglandin D synthase in the bull testis and epididymis and on ejaculated sperm

Previously, we identified a 26-kDa fertility-associated protein in bull seminal plasma as lipocalin-type prostaglandin D synthase. The objective of the present study was to immunohistochemically localize this enzyme to the various cell types within the bull testis and seven subsegments of the epididymis, and on ejaculated sperm in order to gain further insight into its potential function in male reproduction. In the testis, immunoperoxidase staining was localized within the elongating spermatids and Sertoli cells of the seminiferous tubules, varying with the stage of the spermatogenic cycle. The highest level of staining occurred during stages III-VII. The cuboidal epithelial cells of the rete testis and efferent ducts were also immunoreactive. Expression of lipocalin-type prostaglandin D synthase was not uniform in the seven epididymal subsegments, suggesting a possible role in sperm maturation. In all epididymal regions, expression was limited to the epithelial principal cells; no immunoreactivity was apparent in other cell types. Lipocalin-type prostaglandin D synthase was strikingly localized in the caput epididymidis, while moderate to weak staining was observed in the remainder of the epididymis. Droplets of reaction product observed within the lumen increased progressively from the caput to cauda. Using fluorescence microscopy, we also localized lipocalin-type prostaglandin D synthase to the apical ridge of the acrosome on ejaculated sperm.

Prostaglandin D2 and sleep regulation

Prostaglandin (PG) D2 is recognized as the most potent endogenous sleep-promoting substance whose action mechanism is the best characterized among the various sleep-substances thus far reported. The PGD2 concentration in rat cerebrospinal fluid (CSF) shows a circadian change coupled to the sleep-wake cycle and elevates with an increase in sleep propensity during sleep deprivation. Lipocalin-type PGD synthase is dominantly produced in the arachnoid membrane and choroid plexus of the brain, and is secreted into the CSF to become beta-trace, a major protein component of the CSF. The PGD synthase as well as the PGD2 thus produced circulates in the ventricular system, subarachnoidal space, and extracellular space in the brain system. PGD2 then interacts with DP receptors in the chemosensory region of the ventro-medial surface of the rostral basal forebrain to initiate the signal to promote sleep probably via the activation of adenosine A2A receptive neurons. The activation of DP receptors in the PGD2-sensitive chemosensory region results in activation of a cluster of neurons within the ventrolateral preoptic area, which may promote sleep by inhibiting tuberomammillary nucleus, the source of the ascending histaminergic arousal system.

The human RC3 gene homolog, NRGN contains a thyroid hormone-responsive element located in the first intron

NRGN is the human homolog of the neuron-specific rat RC3/neurogranin gene. This gene encodes a postsynaptic 78-amino acid protein kinase substrate that binds calmodulin in the absence of calcium, and that has been implicated in dendritic spine formation and synaptic plasticity. In the rat brain RC3 is under thyroid hormone control in specific neuronal subsets in both developing and adult animals. To evaluate whether the human gene is also a target of thyroid hormone we have searched for T3-responsive elements in NRGN cloned genomic fragments spanning the whole gene. Labeled DNA fragments were incubated with T3 receptors (T3R) and 9-cis-retinoic acid receptors and immunoprecipitated using an anti T3R antibody. A receptor-binding site was localized in the first intron, 3000 bp downstream from the origin of transcription. Footprinting analysis revealed the sequence GGATTAAATGAGGTAA, closely related to the consensus T3-responsive element of the direct repeat (DR4) type. This sequence binds the T3R-9-cis-retinoic acid receptors heterodimers, but not T3R monomers or homodimers, and is able to confer regulation by T3R and T3 when fused upstream of the NRGN or thymidine kinase promoters. The data reported in this work suggest that NRGN is a direct target of thyroid hormone in human brain, and that control of expression of this gene could underlay many of the consequences ofhypothyroidism on mental states during development as well as in adult subjects.

Identification of a thyroid hormone response element in the promoter region of the rat lipocalin-type prostaglandin D synthase (beta-trace) gene

We have previously reported that mRNA levels for the rat lipocalin-type prostaglandin (PG) D synthase/beta-trace (PGDS) gene, the enzyme responsible for the production of PGD2 in the central nervous system, are regulated by thyroid hormone in vivo. In this study, we describe the identification of a thyroid hormone (T3) response element (T3RE) in the 5'-flanking region of the rat PGDS gene. By radioimmunoprecipitation of genomic fragments using thyroid hormone receptor (TR) protein and specific anti-TR antibodies, gel-shift, foot-printing, mutational analysis, and transactivation assays we have identified a spaced four imperfect direct repeat (DR4) element, GGTTCACTTCAGGGTA (positions -586/-571), which functions as a T3RE when fused to a heterologous promoter. Our results suggest that thyroid hormone regulates the expression of the rat lipocalin-type PGDS gene through this element. Remarkably, the element identified also confers regulation by retinoic acid. Giving the important roles proposed for the PGDS enzyme and its product, PGD2, the major PG in the mammalian brain, the altered expression of the PGDS gene may contribute to the deleterious effects of hypothyroidism in the central nervous system.

Expression of lipocalin-type prostaglandin D synthase (beta-trace) in human heart and its accumulation in the coronary circulation of angina patients

Lipocalin-type prostaglandin D synthase (L-PGDS) is localized in the central nervous system and male genital organs of various mammals and is secreted as beta-trace into the closed compartment of these tissues separated from the systemic circulation. In this study, we found that the mRNA for the human enzyme was expressed most intensely in the heart among various tissues examined. In human autopsy specimens, the enzyme was localized immunocytochemically in myocardial cells, atrial endocardial cells, and a synthetic phenotype of smooth muscle cells in the arteriosclerotic intima, and accumulated in the atherosclerotic plaque of coronary arteries with severe stenosis. In patients with stable angina (75-99% stenosis), the plasma level of L-PGDS was significantly (P < 0.05) higher in the great cardiac vein (0.694 +/- 0.054 microg/ml, n = 7) than in the coronary artery (0.545 +/- 0.034 microg/ml), as determined by a sandwich enzyme immunoassay. However, the veno-arterial difference in the plasma L-PGDS concentration was not observed in normal subjects without stenosis. After a percutaneous transluminal coronary angioplasty was performed to compress the stenotic atherosclerotic plaques, the L-PGDS concentration in the cardiac vein decreased significantly (P < 0.05) to 0.610 +/- 0.051 microg/ml at 20 min and reached the arterial level within 1 h. These findings suggest that L-PGDS is present in both endocardium and myocardium of normal subjects and the stenotic site of patients with stable angina and is secreted into the coronary circulation.