Characterization of prostaglandin F2 alpha production in pregnant and cycling mice

Prostaglandins F2α and E2 in rat placenta and fetal membrane: a comprehensive immunohistochemistry of their synthetic enzymes and in vivo tissue levels during normal pregnancy

We determined a comprehensive immunohistochemistry of putative isoforms of enzymes for prostaglandin (PG) F₂α and PGE₂ biosynthesis and these PGs levels in placenta and fetal membrane of normal pregnant rats in vivo. Placenta and fetal membrane showed positive immunoreactions for phospholipase A₂ group 4A, but not group 2A, and cyclooxygenase (COX)-1 rather than COX-2. They showed positive immunoreactions for at least one isoform of each of PGF synthase and PGE synthase with tissue-dependent variations. PGF₂α and PGE₂ levels in both tissues were highest on day 12 and declined and remained low thereafter. Obtained data would be the basic information on the primary PGs synthesis in rat placenta and fetal membrane in normal pregnancy.

Development and evaluation of a simultaneous and efficient quantification strategy for final prostanoid metabolites in urine

Prostanoids (PNs) play critical roles in various physiological and pathological processes. Therefore, it is important to understand the alternation of PN expression profiles. However, a simultaneous and efficient quantification system for final PN metabolites in urine has not yet been established. Here, we developed and evaluated a novel method to quantify all final PN metabolites. By purification using a reverse phase solid phase extraction (SPE) column, the matrix effects against the final PGD₂, PGE₂, and PGF_2α metabolites were low, and their accuracies were nearly 100%. The matrix effects against the final PGI₂ and TXA₂ metabolites were high using reverse phase SPE column purification alone. By applying a tandem SPE method that combined reverse phase and ion exchange SPE columns, the matrix effects decreased so that the accuracy was nearly 100%. To validate the reliability of the method, each final metabolite was quantified from mouse urine to which the PNs (PGD₂, PGE₂, and PGI₂) were intravenously administered. As a result, the amounts of PN metabolites were correlated with those of the PNs administered to the blood in a dose-dependent manner. To validate the method using human samples, the urinary metabolites of Crohn's disease (CD, a PN-related disease) patients and healthy individuals were quantified. All five metabolites were successfully quantified. Only final PGE₂ metabolite levels were significantly higher in CD patients than those in healthy individuals, so that the urinary metabolite profiles of CD patients is determined. In conclusion, we developed a novel method to quantify all final PN metabolites simultaneously and efficiently and demonstrated the practicality of the method using human CD patient samples.

A comprehensive immunohistochemistry of prostaglandins F2α and E2 synthetic enzymes in rat ovary and uterus around parturition

A comprehensive immunohistochemistry with the isoform-distinguishable antibodies against prostaglandin (PG) F2α and PGE2 biosynthetic enzymes was undertaken to identify the cellular types and enzyme isoforms in rat ovary and uterus around parturition. In general ovarian and uterine cells showed positive immunoreactions for phospholipase A2 groups 4A and 6A, but not group 2A, and cyclooxygenase (COX)-1 rather than COX-2. Their immunoreactions for PGF2α synthase and PGE2 synthase were cell type-dependently variable. The putative PGF2α and PGE2 producing cell types included, as expected, ovarian luteal cells, uterine endometrial epithelium and myometrium, and cervical connective tissue and, unexpectedly, ovarian stromal cells and basal lamina of cervical endometrium. Obtained data indicate the generation of PGF2α and PGE2 by multiple sites, which are entirely the same as established sites of actions, in parturition processes and tissue-dependent differential usage of PG biosynthetic pathway.

Dual effect of nitric oxide on uterine prostaglandin synthesis in a murine model of preterm labour

BACKGROUND AND PURPOSE

Maternal infections are one of the main causes of adverse developmental outcomes including embryonic resorption and preterm labour. In this study a mouse model of inflammation-associated preterm delivery was developed, and used to study the relationship between nitric oxide (NO) and prostaglandins (PGs).

EXPERIMENTAL APPROACH

The murine model of preterm labour was achieved by assaying different doses of bacterial lipopolysaccharides (LPS). Once established, it was used to analyse uterine levels of prostaglandins E(2) and F(2α) (by radioimmunoassay), cyclooxygenases (COX) and NOS proteins (by Western blot) and NO synthase (NOS) activity. Effects of inhibitors of COX and NOS on LPS-induced preterm labour were also studied. In vitro assays with a nitric oxide donor (SNAP) were performed to analyse the modulation of prostaglandin production by NO.

KEY RESULTS

Lipopolysaccharide increased uterine NO and PG synthesis and induced preterm delivery. Co-administration of meloxicam, a cyclooxygenase-2 inhibitor, or aminoguanidine, an inducible NOS inhibitor, prevented LPS-induced preterm delivery and blocked the increase in PGs and NO. Notably, the levels of NO were found to determine its effect on PG synthesis; low concentrations of NO reduced PG synthesis whereas high concentrations augmented them.

CONCLUSIONS AND IMPLICATIONS

An infection-associated model of preterm labour showed that preterm delivery can be prevented by decreasing PG or NO production. NO was found to have a dual effect on PG synthesis depending on its concentration. These data contribute to the understanding of the interaction between NO and PGs in pregnancy and parturition, and could help to improve neonatal outcomes.

Lack of functional and expression homology between human and mouse aldo-keto reductase 1C enzymes: implications for modelling human cancers

Background

Over recent years, enzymes of the aldo-keto reductase (AKR) 1C subfamily have been implicated in the progression of prostate, breast, endometrial and leukemic cancers. This is due to the ability of AKR1C enzymes to modify androgens, estrogens, progesterone and prostaglandins (PGs) in a tissue-specific manner, regulating the activity of nuclear receptors and other downstream effects. Evidence supporting a role for AKR1C enzymes in cancer derives mostly from studies with isolated primary cells from patients or immortalized cell lines. Mice are ideal organisms for in vivo studies, using knock-out or over-expression strains. However, the functional conservation of AKR1C enzymes between human and mice has yet to be described.

Results

In this study, we have characterized and compared the four human (AKR1C1,-1C2, -1C3 and -1C4) and the eight murine (AKR1C6, -1C12, -1C13, -1C14, -1C18, -1C19, -1C20 and -1C21) isoforms in their phylogeny, substrate preference and tissue distribution. We have found divergent evolution between human and murine AKR1C enzymes that was reflected by differing substrate preference. Murine enzymes did not perform the 11β-ketoreduction of prostaglandin (PG) D₂, an activity specific to human AKR1C3 and important in promoting leukemic cell survival. Instead, murine AKR1C6 was able to perform the 9-ketoreduction of PGE₂, an activity absent amongst human isoforms. Nevertheless, reduction of the key steroids androstenedione, 5α-dihydrotestosterone, progesterone and estrone was found in murine isoforms. However, unlike humans, no AKR1C isoforms were detected in murine prostate, testes, uterus and haemopoietic progenitors.

Conclusions

This study exposes significant lack of phylogenetic and functional homology between human and murine AKR1C enzymes. Therefore, we conclude that mice are not suitable to model the role of AKR1C in human cancers and leukemia.

Involvement of prostaglandin F 2 alpha receptor in ATP-induced mechanical allodynia

Nociceptive primary afferents have the capacity to induce a state of increased excitability in the dorsal horn neurons of the spinal cord. It is well accepted that capsaicin-sensitive C-fibers transduce noxious stimulation and acute pain and that capsaicin-insensitive A beta-fibers are responsible for touch and innocuous sensation. It has been reported that the intrathecal (i.t.) administration of prostaglandin F(2 alpha) (PGF(2 alpha)) and ATP induces mechanical allodynia via the capsaicin-insensitive primary afferent pathway. In the present study, we investigated the interaction of purinoceptor P2X and the PGF(2 alpha) receptor (FP) in the induction of allodynia by use of mice lacking FP (FP(-/-)). Both PGF(2 alpha) and the P2X receptor agonist alphabeta-methylene ATP administered i.t. strongly induced allodynia for 50 min by tactile stimuli to the flank of mice. The allodynia induced by alphabeta-methylene ATP, but not that by PGF(2 alpha), was suppressed by simultaneous i.t. administration of P2X receptor antagonists pyridoxalphosphate-6-azophenyl-2,4-disulphonic acid and A-317491. In contrast, the allodynia induced by alphabeta-methylene ATP as well as that by PGF(2 alpha) was not observed in FP(-/-) mice. Immunostaining of beta-galactosidase, a reporter knocked into the endogenous FP locus in FP(-/-) mice, showed that the FP receptor was co-localized with P2X(2) and P2X(3) receptors in neurons of the spinal cord. alphabeta-Methylene ATP evoked a transient or sustained [Ca(2+)](i) increase in most of the PGF(2 alpha)-responsive cells in the deeper layer of the spinal cord, and the alphabeta-methylene ATP-evoked increase was blocked by the FP receptor antagonist AL-8810 in two-thirds of the cells. Neither PGF(2 alpha) nor alphabeta-methylene ATP induced the activation of spinal microglia. The present study demonstrates that the alphabeta-methylene ATP-evoked allodynia is mediated by the FP receptor, possibly via the functional coupling between the activation of P2X(2/3) receptors on the central terminal of capsaicin-insensitive fibers and FP receptors on spinal neurons.

Molecular cloning and spatiotemporal expression of prostaglandin F synthase and microsomal prostaglandin E synthase-1 in porcine endometrium

Endometrial prostaglandins (PGs) and the PGE2/PGF2alpha ratio play an important role in regulating the estrous cycle and establishment of pregnancy. The enzymes downstream of cyclooxygenase-2 may determine the PGE2/PGF2alpha ratio in the porcine uterus. Thus, we have cloned porcine PGF synthase (PGFS) and microsomal PGE synthase-1 (mPGES-1) and characterized their expression in porcine endometrium during the estrous cycle and early pregnancy. PGFS and mPGES-1 amino acid sequences possessed a high degree (>67% and >77%, respectively) of identity with the other mammalian homologs. There was little modulation of mPGES-1 throughout the estrous cycle; however, PGFS expression was highly up-regulated in endometrium around the time of luteolysis. During early pregnancy, PGFS at the protein level showed a time-dependent increase (low on d 10-13, intermediate on d 14-23, and high on d 24-25). In pregnancy, expression of mPGES-1 was intermediate on d 10-11 and low on d 14-17 and then increased after d 22, reaching the maximum on d 24-25. Immunohistochemistry showed localization of PGFS and mPGES-1 proteins mainly in luminal and glandular epithelium. Concluding, the spatiotemporal expression of PGFS throughout the estrous cycle indicates an involvement of PGFS in regulating luteolysis in the pig. The comparison of endometrial PGFS and mPGES-1 expression on d 10-13 of the estrous cycle and pregnancy suggest a supportive role of these enzymes in determining the increase of uterine PGE2/PGF2alpha ratio during maternal recognition of pregnancy. Moreover, high expression of both PG synthases after initiation of implantation may indicate their significant role in placentation.

Functional characterization of prostaglandin F2alpha receptor in the spinal cord for tactile pain (allodynia)

Prostaglandin F2alpha (PGF2alpha) binds to its receptor (FP) to increase the intracellular-free calcium concentration ([Ca2+]i) by coupling of FP with Gq protein. Spinal intrathecal administration of PGF2alpha to mouse induces touch-evoked pain (mechanical allodynia), in which capsaicin-insensitive primary afferent Abeta-fibres and N-methyl-d-aspartate receptor epsilon 4 subunit are involved. FP in the spinal cord, however, was not well characterized. Here, we showed constitutive expression of FP mRNA in mouse spinal cord, and functionally characterized spinal FP-expressing cells which were involved in PGF2alpha-induced mechanical allodynia. The method for repetitive administration of oligodeoxyribonucleotides through tubing to conscious mice was established for mechanical allodynia evaluation. We identified an antisense oligodeoxyribonucleotide targeting FP mRNA, causing both disappearance of PGF2alpha-induced mechanical allodynia and decrease of FP mRNA. With saline-administered mice, PGF2alpha rapidly increased [Ca2+]i of the cells in the deeper layer of the dorsal horn. In contrast, when the FP antisense oligodeoxyribonucleotide was repeatedly administered, the population of PGF2alpha-responsive cells in the slices reduced, and PGF2alpha-induced [Ca2+]i increase of these cells diminished. These data strongly suggested that, in the dorsal horn of the spinal cord, there are the FP-expressing cells which are involved in PGF2alpha-induced mechanical allodynia.

Mouse placental prostaglandins are associated with uterine activation and the timing of birth

We explored a potential mechanism linking placental prostaglandins (PGs) with a fall in plasma progesterone and increased expression of uterine activation proteins in the mouse. PG endoperoxide H synthase 2 (PGHS-2) mRNA expression increased in placenta in late gestation in association with an 8-fold increase in PGF(2alpha) concentration, reaching a peak on Gestational Day (GD) 18. This peak coincided with the final descent in plasma progesterone and birth on GD 19.3 +/- 0.2. Implantation of a progesterone-releasing pellet in intact pregnant dams on GD 16 delayed birth at term until GD 20.9 +/- 0.4 and inhibited the GD 18 increase in placental PGF(2alpha) levels in conjunction with a delayed fall in plasma progesterone that reached its lowest level 1 day after term birth. The mRNA levels of uterine activation proteins, connexin-43 (CX-43), oxytocin receptor, PGF(2alpha) receptor (FP), and PGHS-2, and the concentration of uterine PGF(2alpha) all increased at normal term birth. At progesterone-delayed term birth on GD 19.3, even though tissue PGF(2alpha) concentrations were at the same high levels observed at normal term birth, CX-43 and FP mRNA levels were lower than those at normal term birth, thereby possibly contributing to the delay of birth. These data are consistent with the hypotheses that fetal placental PGs affect the timing of birth by hastening luteolysis, that uterine activation initiates labor, and that birth may be delayed by blocking or decreasing the expression of two of the uterine activation proteins.

Cloning and characterization of two novel aldo-keto reductases (AKR1C12 and AKR1C13) from mouse stomach

In contrast to hepatic hydrosteroid dehydrogenases (HSDs) of the aldo-keto reductase family (AKR1C), little is known about a stomach one. From a mouse stomach cDNA library, we isolated two clones encoding proteins of 323 amino acid residues. They exhibited 93.2% amino acid sequence identity and 64-68% with any known HSDs. Recombinant proteins expressed in Escherichia coli reduced 9,10-phenanthraquinone with NAD(P)H as cofactor. The mRNAs were exclusively expressed in stomach, liver and ileum. The present study demonstrates that these proteins are new members of the HSD subfamily and they are named AKR1C12 and AKR1C13. Immunohistochemical analysis suggests that they are involved in detoxification of xenobiotics in the stomach.