Molecular cloning and spatio-temporal expression of the prostaglandin transporter: a basis for the action of prostaglandins in the bovine reproductive system

Expression and localization of prostaglandin transporter in Alzheimer disease brains and age-matched controls

Neuroinflammation, a major contributor to neurodegenerative diseases, involves the contribution of activated microglia, reactive astrocytes, and infiltrating inflammatory cells. Stress and various acute or chronic brain injuries stimulate the generation of free radicals and glutamate, triggering inflammatory pathways that lead to increases in chemokines, cytokines, and prostaglandins. Prostaglandins are lipid mediators of inflammation that are produced from arachidonic acid by cyclooxygenase enzymes. They are generally believed to be in all tissues and organs. Their transport through the lipid bilayers of the cell membranes/organelles is facilitated by the prostaglandin transporter (PGT). In this study, middle frontal gyrus brain tissue from patients diagnosed with Alzheimer disease (AD) and that of age-matched control brains were examined to determine the protein expression pattern of PGT and its possible role in modulating neuroinflammation associated with AD. Immunohistochemical and immunofluorescent studies showed that PGT protein was expressed in all the brain tissues examined and was localized in neurons, microglia, and astrocytes. Interestingly, Western blot analysis revealed that the PGT level was significantly less in AD than in age-matched control brain homogenates. Further work is warranted to address the possibility and implications that prostaglandins might not be cleared at a proper rate in AD brains.

Molecular cloning and characterization of prostaglandin (PG) transporter in ovine endometrium: role for multiple cell signaling pathways in transport of PGF2alpha

In ruminants, endometrial prostaglandin F(2alpha) (PGF(2alpha)) is the luteolytic hormone. Cellular transport of PGF(2alpha) in the uterine endometrium is critical for regulation of the estrous cycle. Molecular mechanisms responsible for control of PGF(2alpha) transport in endometrium during luteolysis are largely unknown. In the present study, we characterized the prostaglandin transporter (PGT) in ovine endometrium. Ovine PGT cDNA consists of 1935 nucleotides that encode 644 amino acids. In ovine endometria, PGT is highly expressed during the period of luteolysis, between d 14 and 16 of the estrous cycle, in luminal and glandular epithelia. Pharmacological and genomic inhibition of PGT indicates that it is responsible for influx and efflux of PGF(2alpha) in ovine endometrial epithelial cells. Inhibition of PGT during the period of luteolysis prevents the release of oxytocin-induced PGF(2alpha) pulses, and maintains functional corpus luteum and its secretion of progesterone. In ovine endometrial epithelial cells, protein kinase A and protein kinase C pathways are involved in regulating the influx of PGF(2alpha), whereas epidermal growth factor receptor pathways are implicated in regulation of influx and efflux of PGF(2alpha.) The ERK1/2 pathway is associated with efflux of PGF(2alpha), whereas Jun-amino-terminal kinase/stress-activated protein kinase pathways are involved in both efflux and influx of PGF(2alpha.) Phosphatidylinositol 3-kinase pathways are not involved in either influx or efflux of PGF(2alpha) in ovine endometrial epithelial cells. These are the first results to demonstrate a functional role for PGT in regulation of PGF(2alpha) efflux and influx in ovine endometrial cells that influence luteolytic mechanisms in ruminants.

Gene expression profiles and functional characterization of human immortalized endometriotic epithelial and stromal cells

OBJECTIVE

To determine whether immortalized endometriotic cells can be used as potential models to unravel pathophysiology/pathogenesis of endometriosis in humans.

DESIGN

In vitro study. Human immortalized endometriotic epithelial and stromal cells.

SETTING

College of Veterinary Medicine and Biomedical Sciences, Texas A&M University.

PATIENT(S)

Not applicable.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Gene expression pattern and prostaglandin E(2) production and activity of matrix metalloproteinase 2 and matrix metalloproteinase 9.

RESULT(S)

Several genes associated with estrogen and progesterone biosynthesis and signaling, cell cycle regulation, extracellular matrix degradation, angiogenesis, cell growth and survival, cytokine production, and prostaglandin E(2) biosynthesis, transport, and signaling were expressed in human immortalized endometriotic cells. These endometriotic epithelial and stromal cells exhibited migrating and invading potential, produced a high quantity of prostaglandin E(2), and showed higher matrix metalloproteinase 2 and matrix metalloproteinase 9 activity compared to normal endometrial, epithelial, and stromal cells.

CONCLUSION(S)

Human immortalized endometriotic epithelial and stromal cells could be used as ideal models to study the molecular and cellular aspects of endometriosis in humans.

Differential expression and regulation of prostaglandin transporter and metabolic enzymes in mouse uterus during blastocyst implantation

OBJECTIVE

To examine the spatiotemporal expression and regulation of prostaglandin transporter (PGT), 15-hydroxy-PG dehydrogenase (15-PGDH), and carbonyl reductase 1 (CBR1) messenger RNA (mRNA) and protein in the mouse uterus during embryo implantation and in related models.

DESIGN

Experimental animal study.

SETTING

University research laboratory.

ANIMAL(S)

Sexually mature female Kunming strain white mice.

INTERVENTION(S)

Delayed and activated implantation, artificial decidualization, and subcutaneous injection of progesterone (P) and E(2) in ovariectomized mouse.

MAIN OUTCOME MEASURE(S)

The expression of mRNA and protein were detected by in situ hybridization and immunohistochemistry in mouse uterus.

RESULT(S)

Prostaglandin transporter mRNA and protein were expressed in the subluminal stroma at implantation site on day 5 of pregnancy and then in decidua but were not detected at the interimplantation sites and in preimplantation or pseudopregnant uterus. The presence of an active blastocyst was required for PGT expression at the implantation site. Both 15-PGDH and CBR1 mRNA were detected in glandular epithelium on day 4 of pregnancies. The expression of 15-PGDH and CBR1 mRNA was also detected in postimplantation embryos.

CONCLUSION(S)

These data suggest that differentially expressed PGT and 15-PGDH may participate in PG signaling in mouse uterus during implantation and decidualization.

Regulation, action and transport of prostaglandins during the periovulatory period in cattle

Follicular production of prostaglandins (PGs) is essential for mammalian ovulation, but the factors that mediate production and the cell-specific action(s) of PGE and PGF2alpha during the ovulatory cascade remain largely unknown. The aims of these experiments were: (1) to investigate the potential role of oxytocin (OT) in ovulatory PG production, (2) to determine cellular and temporal patterns of expression of mRNA for specific PG receptors during the periovulatory interval, (3) to determine cell-specific effects of PGE2 on progesterone secretion, and (4) to investigate the potential for an active transport mechanism that may regulate the effect of PGs during the ovulatory cascade, using cattle as the animal model. Heifers were treated sequentially with PGF2alpha and GnRH to induce luteal regression, a follicular phase and the LH/FSH surge (ovulation occurs approximately 30 h after GnRH). In experiment 1, OT increased the secretion of PGE and PGF2alpha by granulosa cells collected from preovulatory follicles (before the LH/FSH surge) and OT production by pieces of follicle wall from periovulatory follicles (after the LH/FSH surge) was regulated by progesterone acting through the progesterone receptor. In experiment 2, levels of mRNA for the PGF2alpha receptor and three PGE receptor subtypes were determined by semi-quantitative RT-PCR in theca interna and granulosa cells from pre- and periovulatory follicles collected at 0, 6, 12, 18 and 24 h post-GnRH. Time- and cell-specific patterns of change in mRNA for PG receptors were observed, suggesting multiple effects of both PGE and PGF2alpha in both theca interna and granulosa cells throughout the ovulatory cascade. Cell-specificity of PG action was confirmed in experiment 3; PGE2 increased the secretion of progesterone by theca interna but not granulosa cells collected from late periovulatory follicles. The results of experiment 4 revealed the expression of mRNA for the bovine PG transporter in theca interna and granulosa cells and its regulation during the periovulatory period, thus revealing the presence of a potential transport mechanism that could regulate cellular distribution of PGs throughout the ovulatory cascade. Taken together, these results provide new insight into mechanisms that regulate the production, distribution and site of action of PGE and PGF2alpha during the ovulatory cascade.

15-Hydroxyprostaglandin dehydrogenase in the bovine endometrium during the oestrous cycle and early pregnancy

Prostaglandins (PG) are primary regulators of reproductive function. In ruminants, the relative production of PGE2and PGF2αdetermines the return to a new oestrous cycle or to the establishment of pregnancy in response to a viable embryo. PG action depends on biosynthesis, transport and interaction with their receptors, which are all expressed differentially during the oestrous cycle. PGs are, however, local mediators and thus the onsite degradation by enzymes such as 15-hydroxyprostaglandin dehydrogenase (HPGD), also known as 15-PGDH, is another factor to consider in the regulation of physiological action. Little information is available on PG catabolism in the endometrium during the oestrous cycle or early pregnancy. The purpose of this study was to clone the bovine 15-PGDH, produce the recombinant protein and generate a specific antibody to study its activity and its expression in the endometrium during the oestrous cycle. We have found that the bovine 15-PGDH is highly homologous to the rat and human isoforms. 15-PGDH is localized principally in the glandular epithelium and to a lesser extent in stromal and luminal epithelial cells. The enzyme expression is regulated during the oestrous cycle and it reaches its maximal level on days 16–18. Transient expression is observed in luminal epithelial and trophoblast cells on day 21 of pregnancy. The mRNA is expressed at a constant high level throughout the cycle. The activity of the recombinant 15-PGDH was also tested and was found comparable for PGF2αand PGE2. These data suggest that 15-PGDH contributes to the tight regulation of PG action in the endometrium especially at the critical period of recognition of pregnancy.

The protease-activated receptor2 (PAR2)-prostaglandin E2-prostanoid EP receptor axis: a potential bronchoprotective unit in the respiratory tract?

Protease-activated receptor2 (PAR2) is a subtype of G protein-coupled receptor that is widely expressed within the respiratory tract. Stimulation of PAR2 by proteases such as trypsin and tryptase, or by small peptidic activators induces a complex array of effects within the airways. One such PAR2-mediated effect by basal airway epithelial cells is the generation of prostaglandin E2. Prostaglandin E2 produces a raft of anti-inflammatory effects within the airways, principally through the activation of the prostanoid EP2 and EP3 receptor subtypes. This article reviews the PAR2-prostaglandin E2-prostanoid EP receptor axis and discusses approaches through which its activation may provide beneficial effects in respiratory disease.

Functional characterization of prostaglandin transporter and terminal prostaglandin synthases during decidualization of human endometrial stromal cells

BACKGROUND

Decidualization of endometrial stromal cells is essential for successful implantation and pregnancy. Prostaglandins (PG) have been shown to be required for the initiation and maintenance of decidualization in animal models. The transport of PG across the plasma membrane is mediated by carriers such as prostaglandin transporter (PGT). Our recent data have shown the expression of human PGT (hPGT) in the endometrium during the menstrual cycle. The objective of the present study was to characterize hPGT in decidualized stromal cells.

METHODS AND RESULTS

Human endometrial stromal cells were treated with a combination of cAMP and medroxyprogesterone acetate to induce decidualization. Decidualization was confirmed by morphological differentiation and increased secretion of prolactin. A large increase in hPGT mRNA level, as measured by real-time PCR analysis, was observed in decidual cells compared with control. Similarly, a 2-fold up-regulation of hPGT and 3-12-fold increase in PG biosynthetic enzymes were obtained at the protein level. Decidual cells exhibited a higher isotopic PGE2 uptake and greater intracellular PG levels than control.

CONCLUSIONS

The higher uptake of PG by decidual cells is highly likely to be mediated via hPGT. PGT is a newly identified regulator of PG action at the cellular level and likely contributes to the regulation of PG action in female reproductive processes.

Identification of a new class of prostaglandin transporter inhibitors and characterization of their biological effects on prostaglandin E2 transport

Prostaglandins (PGs) are involved in several major signaling pathways. Their effects are terminated when they are transported across cell membranes and oxidized intracellularly. The transport step of PG metabolism is carried out by the prostaglandin transporter (PGT). Inhibition of PGT would therefore be expected to change local or circulating concentrations of prostaglandins, and thus their biological effects. To develop PGT-specific inhibitors with high affinity, we designed a library of triazine compounds and screened 1842 small molecules by using Madin-Darby canine kidney cells stably expressing rat PGT. We found several effective PGT inhibitors. Among them, the most potent inhibitor had a Ki of 3.7 +/- 0.2 microM. These inhibitors allowed us to isolate the efflux process of PGE2 and to demonstrate that PGT does not transport PGE2 outwardly under physiological conditions.

Inhibitors of Prostaglandin Transport and Metabolism Augment Protease-Activated Receptor-2-Mediated Increases in Prostaglandin E2 Levels and Smooth Muscle Relaxation in Mouse Isolated Trachea

Stimulants of protease-activated receptor-2 (PAR(2)), such as Ser-Leu-Ile-Gly-Arg-Leu-NH(2) (SLIGRL), cause airway smooth muscle relaxation via the release of the bronchodilatory prostanoid prostaglandin E(2) (PGE(2)). The principal aim of the current study was to determine whether compounds that inhibit PGE(2) reuptake by the prostaglandin transporter [bromocresol green and U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy PGF2alpha) and PGE(2) metabolism by 15-hydroxyprostaglandin dehydrogenase (thiazolidenedione compounds rosiglitazone and ciglitazone) significantly enhanced the capacity of SLIGRL to elevate PGE(2) levels and produce relaxation in isolated segments of upper and lower mouse trachea. SLIGRL produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, although both effects were significantly greater in lower tracheal segments than in upper tracheal segments. SLIGRL-induced increases in PGE(2) levels were significantly enhanced in the presence of ciglitazone and rosiglitazone, and these effects were not inhibited by GW9662 (2-chloro-5-nitrobenzanilide), a peroxisome proliferator-activated receptor-gamma antagonist. SLI-GRL-induced relaxation responses were also significantly enhanced by ciglitazone and rosiglitazone, whereas responses to isoprenaline, a PGE(2)-independent smooth muscle relaxant, were unaltered. Ciglitazone and rosiglitazone alone produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, and these responses were inhibited by indomethacin, a cyclooxygenase inhibitor. Bromocresol green, an inhibitor of prostaglandin transport, significantly enhanced SLIGRL-induced increases in PGE(2) levels and relaxation. Immunohistochemical staining for 15-hydroxyprostaglandin dehydrogenase was relatively intense over airway smooth muscle, as was staining for the prostaglandin transporter over both airway smooth muscle and epithelium. In summary, inhibitors of PGE(2) reuptake and metabolism significantly potentiate PAR(2)-mediated increases in PGE(2) levels and smooth muscle relaxation in murine-isolated airways.

Mechanical strain opens connexin 43 hemichannels in osteocytes: a novel mechanism for the release of prostaglandin

Mechanosensing bone osteocytes express large amounts of connexin (Cx)43, the component of gap junctions; yet, gap junctions are only active at the small tips of their dendritic processes, suggesting another function for Cx43. Both primary osteocytes and the osteocyte-like MLO-Y4 cells respond to fluid flow shear stress by releasing intracellular prostaglandin E2 (PGE2). Cells plated at lower densities release more PGE2 than cells plated at higher densities. This response was significantly reduced by antisense to Cx43 and by the gap junction and hemichannel inhibitors 18 beta-glycyrrhetinic acid and carbenoxolone, even in cells without physical contact, suggesting the involvement of Cx43-hemichannels. Inhibitors of other channels, such as the purinergic receptor P2X7 and the prostaglandin transporter PGT, had no effect on PGE2 release. Cell surface biotinylation analysis showed that surface expression of Cx43 was increased by shear stress. Together, these results suggest fluid flow shear stress induces the translocation of Cx43 to the membrane surface and that unapposed hemichannels formed by Cx43 serve as a novel portal for the release of PGE2 in response to mechanical strain.

Expression of prostaglandin transporter in the bovine uterus and fetal membranes during pregnancy

Uteroplacental prostaglandins (PGs) play pivotal roles in the maintenance and termination of pregnancy in mammals. In the present study, we have characterized the expression of prostaglandin transporter (PGT) in placentome caruncles, intercaruncular tissues, fetal membranes, and utero-ovarian plexus during pregnancy in cattle. Pregnant bovine uteri were collected and classified into six groups covering the entire gestational length. In caruncles and intercaruncular tissues, PGT mRNA (also known as SLC02A1) and PGT protein were highly expressed at the late stage of pregnancy compared to the early and mid stages, whereas the level of expression is constant and low in fetal membranes throughout pregnancy. PGT mRNA and PGT protein were expressed at a constant level in the utero-ovarian plexus both ipsilateral and contralateral to corpus luteum throughout the course of pregnancy. Overall, the relative expression of PGT mRNA and PGT protein were higher in caruncles than in intercaruncular tissue and fetal membranes, whereas no differences were detected between intercaruncular tissues and fetal membranes at any stage of gestation. Immunohistochemistry indicated that PGT was preferentially expressed in caruncular epithelial cells of placentomes and endometrial luminal epithelial and myometrial smooth muscle cells of the intercaruncular regions. The level of PGT expression was comparatively higher in maternal components than in fetal components. In conclusion, differential spatiotemporal tissue-specific expression of PGT in uterine and intrauterine tissues suggests a role for this transporter in the exchange of PGs between the maternal and the fetal compartments, as well as for intrauterine metabolism of PGs during pregnancy.

Three's company: two or more unrelated receptors pair with the same ligand

Intercellular communication relies on signal transduction mediated by extracellular ligands and their receptors. Although the ligand-receptor interaction is usually a two-player event, there are selective examples of one polypeptide ligand interacting with more than one phylogenetically unrelated receptor. Likewise, a few receptors interact with more than one polypeptide ligand, and sometimes with more than one coreceptor, likely through an interlocking of unique protein domains. Phylogenetic analyses suggest that for certain triumvirates, the matching events could have taken place at different evolutionary times. In contrast to a few polypeptide ligands interacting with more than one receptor, we found that many small nonpeptide ligands have been paired with two or more plasma membrane receptors, nuclear receptors, or channels. The observation that many small ligands are paired with more than one receptor type highlights the utilitarian use of a limited number of cellular components during metazoan evolution. These conserved ligands are ubiquitous cell metabolites likely favored by natural selection to establish novel regulatory networks. They likely possess structural features useful for designing agonistic and antagonistic drugs to target diverse receptors.

Effect of interferon-tau on prostaglandin biosynthesis, transport, and signaling at the time of maternal recognition of pregnancy in cattle: evidence of polycrine actions of prostaglandin E2

Recognition and establishment of pregnancy involve several molecular and cellular interactions among the conceptus, uterus, and corpus luteum (CL). In ruminants, interferon-tau (IFNtau) of embryonic origin is recognized as the pregnancy recognition signal. Endometrial prostaglandin F(2alpha) (PGF(2alpha)) is the luteolysin, whereas PGE(2) is considered a luteoprotective or luteotrophic mediator at the time of establishment of pregnancy. The interplay between IFNtau and endometrial PGs production, transport, and signaling at the time of maternal recognition of pregnancy (MRP) is not well understood. We have studied the expression of enzymes involved in metabolism of PGE(2) and PGF(2alpha), cyclooxygenase-1 (COX-1) and COX-2, PG synthases (PGES and PGFS), PG 15-dehydrogenase, and PG transporter as well as PGE(2) (EP2 and EP3) and PGF(2alpha) receptors. IFNtau influences cell-specific expression of COX-2, PGFS, EP2, and EP3 in endometrium, myometrium, and CL in a spatio-temporal and tissue-specific manner, whereas it does not alter COX-1, PGES, PG 15-dehydrogenase, PG transporter, or PGF(2alpha) receptor expression in any of these tissues. In endometrium, IFNtau decreases PGFS in epithelial cells and increases EP2 in stroma. In myometrium, IFNtau decreases PGFS and increases EP2 in smooth muscle cells. In CL, IFNtau increases PGES and decreases EP3. Together, our results show that IFNtau directly or indirectly increases PGE(2) biosynthesis and EP2-associated signaling in endometrium, myometrium, and CL during MRP. Thus, PGE(2) may play pivotal roles in endometrial receptivity, myometrial quiescence, and luteal maintenance, indicating polycrine (endocrine, exocrine, paracrine, and autocrine) actions of PGE(2) at the time of MRP. Therefore, the establishment of pregnancy may depend not only on inhibition of endometrial PGF(2alpha), but also on increased PGE(2) production in cattle.

Prostaglandin receptor signalling and function in human endometrial pathology

Prostaglandins are bioactive lipids that exert an autocrine or paracrine function by binding to specific G-protein-coupled receptors (GPCRs) to activate intracellular signalling and gene transcription. Prostaglandins are key regulators of reproductive processes, including ovulation, implantation and menstruation. Prostaglandins have been ascertained to have a role in various pathological changes of the reproductive tract including menorrhagia, dysmenorrhea, endometriosis and cancer. Although the mechanism by which prostaglandins modulate these changes remains unclear, much evidence suggests that prostaglandins and their receptors and downstream signalling pathways are involved in angiogenesis and in alterations in cell adhesion, morphology, motility, invasion and metastases. The potential role of prostaglandin receptors in pathological changes of the endometrium has significance for the future development of therapeutic interventions.

Prostaglandin biosynthesis, transport, and signaling in corpus luteum: a basis for autoregulation of luteal function

The corpus luteum (CL) is a transient ovarian endocrine gland formed from the ovulated follicle. Progesterone is the primary secretory product of CL and is essential for establishment of pregnancy in mammals. In the cyclic female, the life span of CL is characterized by luteal development, maintenance, and regression regulated by complex interactions between luteotrophic and luteolytic mediators. It is universally accepted that prostaglandin (PG) F(2a) is the luteolysin whereas PGE(2) is considered as a luteotropin in most mammals. New emerging concepts emphasize the autocrine and paracrine actions of luteal PGs in CL function. However, there is no report on selective biosynthesis and cellular transport of luteal PGE(2) and PGF(2alpha) in the CL of any species. We have studied the expression of enzymes involved in the metabolism of PGE(2) and PGF(2alpha), cyclooxygenase (COX)-1 and -2, PGE and F synthases, PG 15-dehydrogenase, and PG transporter as well as receptors (EP2, EP3, and FP) throughout the CL life span using a bovine model. COX-1, PGF synthase, and PG 15-dehydrogenase are expressed at constant levels whereas COX-2, PGE synthase, PG transporter, EP2, EP3, and FP are highly modulated during different phases of the CL life span. The PG components are preferentially expressed in large luteal cells. The results indicate that PGE(2) biosynthesis, transport, and signaling cascades are selectively activated during luteal maintenance. By contrast the PGF(2alpha) system is activated during luteal regression. Collectively, our results suggest an integrated role for luteal PGE(2) and PGF(2alpha) in autoregulation of CL function.