A positive feedback loop between progesterone and microsomal prostaglandin E synthase-1-mediated PGE2 promotes production of both in mouse granulosa cells

Nuclear progesterone receptor regulates ptger4b and PLA2G4A expression in zebrafish (Danio rerio) ovulation

Previous studies have implicated the nuclear progesterone receptor (Pgr or nPR) as being critical to ovulation in fishes. This study investigated the expression of Pgr in zebrafish ovarian follicles throughout development as well as putative downstream targets of Pgr by searching the promoter regions of selected genes for specific DNA sequences to which Pgr binds and acts as a transcription factor. Expression of Pgr mRNA increases dramatically as follicles grow and mature. In silico analysis of selected genes linked to ovulation showed that the prostaglandin receptors ptger4a and ptger4b contained the progesterone responsive element (PRE) GRCCGGA in their promoter regions. Studies using full-grown follicles incubated in vitro revealed that ptger4b was upregulated in response to 17,20β-P. Our studies also showed that the expression of phospholipase A2 (PLA2G4A) mRNA and protein, a key enzyme in prostaglandin synthesis, was upregulated in response to 17,20β-P treatment. pla2g4a was not found to contain a PRE, indicating that it is regulated indirectly by 17,20β-P or that it may contain an as-of-yet unidentified PRE in its promoter region. Collectively, these studies provide further evidence of the importance of Pgr during the periovulatory periods through its involvement in prostaglandin production and function by controlling expression of PLA2G4A and the receptor EP4b and that these genes appear to be regulated through the actions of 17,20β-P.

Characteristics of lipid droplets and the expression of proteins involved in lipolysis in the murine cervix during mid-pregnancy

Lipid droplets (LDs) are reservoirs of arachidonoyl lipids for prostaglandin (PG) E2 synthesis, and progesterone can stimulate PGE2 synthesis; however, the relationship between progesterone and LD metabolism in the murine cervix remains unclear. In the present study we examined LD distribution and changes in the expression of proteins involved in lipolysis and autophagy in the murine cervix during pregnancy, and compared the findings with those in dioestrous mice. During mid-pregnancy, LDs were predominantly distributed in the cervical epithelium. Electron microscopy revealed the transfer of numerous LDs from the basal to apical region in the luminal epithelium, marked catabolism of LDs, an elevated number of LDs and autophagosomes and a higher LD:mitochondrion size ratio in murine cervical epithelial cells (P<0.05). In addition, immunohistochemical and western blotting analyses showed significantly higher cAMP-dependent protein kinase, adipose triglyceride lipase and hormone-sensitive lipase expression, and a higher light chain 3 (LC3) II:LC3I ratio in the stroma and smooth muscles and, particularly, in murine cervical epithelial cells, during mid-pregnancy than late dioestrus. In conclusion, these results suggest that the enhanced lipolysis of LDs and autophagy in murine cervical tissues were closely related to pregnancy and were possibly controlled by progesterone because LD catabolism may be necessary for energy provision and PGE2 synthesis to maintain a closed pregnant cervix.

Intravital Imaging Identifies the VEGF-TXA2 Axis as a Critical Promoter of PGE2 Secretion from Tumor Cells and Immune Evasion

Prostaglandin E₂ (PGE₂) promotes tumor progression through evasion of antitumor immunity. In stark contrast to cyclooxygenase-dependent production of PGE₂, little is known whether PGE₂ secretion is regulated within tumor tissues. Here, we show that VEGF-dependent release of thromboxane A₂ (TXA₂) triggers Ca²⁺ transients in tumor cells, culminating in PGE₂ secretion and subsequent immune evasion in the early stages of tumorigenesis. Ca²⁺ transients caused cPLA2 activation and triggered the arachidonic acid cascade. Ca²⁺ transients were monitored as the surrogate marker of PGE₂ secretion. Intravital imaging of Braf^V600E mouse melanoma cells revealed that the proportion of cells exhibiting Ca²⁺ transients is markedly higher in vivo than in vitro. The TXA₂ receptor was indispensable for the Ca²⁺ transients in vivo, high intratumoral PGE₂ concentration, and evasion of antitumor immunity. Notably, treatment with a VEGF receptor antagonist and an anti-VEGF antibody rapidly suppressed Ca²⁺ transients and reduced TXA₂ and PGE₂ concentrations in tumor tissues. These results identify the VEGF-TXA₂ axis as a critical promoter of PGE₂-dependent tumor immune evasion, providing a molecular basis underlying the immunomodulatory effect of anti-VEGF therapies. SIGNIFICANCE: This study identifies the VEGF-TXA₂ axis as a potentially targetable regulator of PGE₂ secretion, which provides novel strategies for prevention and treatment of multiple types of malignancies.

Contribution of Prostaglandin Transporter OATP2A1/SLCO2A1 to Placenta-to-Maternal Hormone Signaling and Labor Induction

We evaluated the contribution of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a high-affinity carrier for prostaglandins (PGs), to the parturition process. At gestational day (GD) 15.5, OATP2A1 is co-localized with 15-hydroxy-PG dehydrogenase in the mouse placental junctional zone and facilitates PG degradation by delivering PGs to the cytoplasm. Slco2a1 (+/-) females mated with Slco2a1 (-/-) males frequently showed elevated circulating progesterone at GD18.5 and delayed parturition. Progesterone receptor inhibition by RU486 treatment at GD18.5 blocked the delay of parturition. In the junctional zone, PGE2 stimulated placental lactogen II (PL-II) production, resulting in higher expression of PL-II in Slco2a1 (-/-) placenta at GD18.5. Indomethacin treatment at GD15.5 suppressed the PL-II overproduction at GD18.5 in Slco2a1 (-/-) embryo-bearing dams, which promoted progesterone withdrawal and corrected the delayed parturition. These results suggest that extracellular PGE2 reduction by OATP2A1 at mid-pregnancy would be associated with progesterone withdrawal by suppressing PL-II production, triggering parturition onset.

The cAMP-EPAC Pathway Mediates PGE2-Induced FGF2 in Bovine Granulosa Cells

During the periovulatory period, the profile of fibroblast growth factor 2 (FGF2) coincides with elevated prostaglandin E2 (PGE2) levels. We investigated whether PGE2 can directly stimulate FGF2 production in bovine granulosa cells and, if so, which prostaglandin E2 receptor (PTGER) type and signaling cascades are involved. PGE2 temporally stimulated FGF2. Accordingly, endoperoxide-synthase2-silenced cells, exhibiting low endogenous PGE2 levels, had reduced FGF2. Furthermore, elevation of viable granulosa cell numbers by PGE2 was abolished with FGF2 receptor 1 inhibitor, suggesting that FGF2 mediates this action of PGE2. Epiregulin (EREG), a known PGE2-inducible gene, was studied alongside FGF2. PTGER2 agonist elevated cAMP as well as FGF2 and EREG levels. However, a marked difference between cAMP-induced downstream signaling was observed for FGF2 and EREG. Whereas FGF2 upregulated by PGE2, PTGER2 agonist, or forskolin was unaffected by the protein kinase A (PKA) inhibitor H89, EREG was significantly inhibited. FGF2 was dose-dependently stimulated by the exchange protein directly activated by cAMP (EPAC) activator; a similar induction was observed for EREG. However, forskolin-stimulated FGF2, but not EREG, was inhibited in EPAC1-silenced cells. These findings ascribe a novel autocrine role for PGE2, namely, elevating FGF2 production in granulosa cells. This study also reveals that cAMP-activated EPAC1, rather than PKA, mediates the effect of PGE2/PTGER2 on the expression of FGF2. Stimulation of EREG by PGE2 is also mediated by PTGER2 but, in contrast to FGF2, EREG was found to be PKA sensitive. PGE2-stimulated FGF2 can act to maintain granulosa cell survival; it can also act on ovarian endothelial cells to promote angiogenesis.

Raging the War Against Inflammation With Natural Products

Over the last few decade Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are the drugs of choice for treating numerous inflammatory diseases including rheumatoid arthritis. The NSAIDs produces anti-inflammatory activity via inhibiting cyclooxygenase enzyme, responsible for the conversation of arachidonic acid to prostaglandins. Likewise, cyclooxegenase-2 inhibitors (COX-2) selectively inhibit the COX-2 enzyme and produces significant anti-inflammatory, analgesic, and anti-pyretic activity without producing COX-1 associated gastrointestinal and renal side effects. In last two decades numerous selective COX-2 inhibitors (COXIBs) have been developed and approved for various inflammatory conditions. However, data from clinical trials have suggested that the prolong use of COX-2 inhibitors are also associated with life threatening cardiovascular side effects including ischemic heart failure and myocardial infection. In these scenario secondary metabolites from natural product offers a great hope for the development of novel anti-inflammatory compounds. Although majority of the natural product based compounds exhibit more selectively toward COX-1. However, the data suggest that slight structural modification can be helpful in developing COX-2 selective secondary metabolites with comparative efficacy and limited side effects. This review is an effort to highlight the secondary metabolites from terrestrial and marine source with significant COX-2 and COX-2 mediated PGE2 inhibitory activity, since it is anticipated that isolates with ability to inhibit COX-2 mediated PGE2 production would be useful in suppressing the inflammation and its classical sign and symptoms. Moreover, this review has highlighted the potential lead compounds including berberine, kaurenoic acid, α-cyperone, curcumin, and zedoarondiol for further development with the help of structure-activity relationship (SAR) studies and their current status.

Prostaglandins in teleost ovulation: A review of the roles with a view to comparison with prostaglandins in mammalian ovulation

Prostaglandins are well known to be central regulators of vertebrate ovulation. Studies addressing the role of prostaglandins in mammalian ovulation have established that they are involved in the processes of oocyte maturation and cumulus oocyte complex expansion. In contrast, despite the first indication of the role of prostaglandins in teleost ovulation appearing 40 years ago, the mechanistic background of their role has long been unknown. However, studies conducted on medaka over the past decade have provided valuable information. Emerging evidence indicates an indispensable role of prostaglandin E₂ and its receptor subtype Ptger4b in the process of follicle rupture. In this review, we summarize studies addressing the role of prostaglandins in teleost ovulation and describe recent advances. To help understand differences from and similarities to ovulation in mammalian species, the findings on the roles of prostaglandins in mammalian ovulation are discussed in parallel.

Potential role of polyunsaturated fatty acids, with particular regard to the signaling pathways of arachidonic acid and its derivatives in the process of maturation of the oocytes: Contemporary review

Oocyte meiotic maturation is one of the significant physiological requirements for ovulation and fertility. It is believed that Cyclic Adenosine Monophosphate, protein kinase A and protein kinase C pathways along with eicosanoids, particularly prostaglandin E_2, and steroids are the key factors regulating mammalian oocyte maturation. The aim of the current study was to highlight the molecular events triggered by arachidonic acid during oocyte meiotic arrest and resumption at the time of gonadotrophin surge. It should be noted that arachidonic acid release is tightly regulated by Follicle-stimulating and Luteinizing hormones during oocyte development.