The selective prostaglandin EP4 agonist, APS-999 Na, induces follicular growth and maturation in the rat ovary

Depletion of GPSM1 enhances ovarian granulosa cell apoptosis via cAMP-PKA-CREB pathway in vitro

BACKGROUND

Genetic causes of premature ovarian insufficiency (POI) account for approximately 20 ~ 25% of patients. So far, only a few genes have been identified.

RESULTS

Here, we first identified the c.1840C > A on G-protein signaling modulator 1 (GPSM1) as a susceptibility locus for POI in 10 sporadic POI patients by whole-exome sequencing. The frequency of GPSM1 c.1840C > A was then verified as 3/20 in a POI sample of 20 patients (including the above 10 patients) by Sanger sequencing. RT-PCR and western blot analysis showed the expression of GPSM1 in rat ovaries was increased in the large antral follicle stage compared to the primordial follicle stage (P < 0.01). The cell proliferation assay (CCK8) and flow cytometry suggested that the small-interfering RNA-induced silencing of Gpsm1 significantly increased apoptosis and decreased proliferation of rat ovarian granulosa cells (GCs) (P < 0.01). Furthermore, suppression of Gpsm1 in GCs reduced levels of cAMP, PKAc, p-CREB as well as the ratio of Bcl-2/Bax, and increased the expression of Caspase-3 and Cleaved Caspase-3 (P < 0.01).

CONCLUSIONS

In summary, this study identified a susceptibility variant GPSM1 c.1840C > A of POI for the first time. Gpsm1 was related to rat follicle development, and silencing of Gpsm1 increased apoptosis and decreased proliferation in rat GCs, possibly through inhibition of the cAMP-PKA-CREB pathway.

Improved homology modeling of the human & rat EP4 prostanoid receptors

Background

The EP₄ prostanoid receptor is one of four GPCRs that mediate the diverse actions of prostaglandin E₂ (PGE₂). Novel selective EP₄ receptor agonists would assist to further elucidate receptor sub-type function and promote development of therapeutics for bone healing, heart failure, and other receptor associated conditions. The rat EP₄ (rEP₄) receptor has been used as a surrogate for the human EP₄ (hEP₄) receptor in multiple SAR studies. To better understand the validity of this traditional approach, homology models were generated by threading for both receptors using the RaptorX server. These models were fit to an implicit membrane using the PPM server and OPM database with refinement of intra and extracellular loops by Prime (Schrödinger). To understand the interaction between the receptors and known agonists, induced-fit docking experiments were performed using Glide and Prime (Schrödinger), with both endogenous agonists and receptor sub-type selective, small-molecule agonists. The docking scores and observed interactions were compared with radioligand displacement experiments and receptor (rat & human) activation assays monitoring cAMP.

Results

Rank-ordering of in silico compound docking scores aligned well with in vitro activity assay EC₅₀ and radioligand binding K_i. We observed variations between rat and human EP₄ binding pockets that have implications in future small-molecule receptor-modulator design and SAR, specifically a S103G mutation within the rEP4 receptor. Additionally, these models helped identify key interactions between the EP₄ receptor and ligands including PGE₂ and several known sub-type selective agonists while serving as a marked improvement over the previously reported models.

Conclusions

This work has generated a set of novel homology models of the rEP₄ and hEP₄ receptors. The homology models provide an improvement upon the previously reported model, largely due to improved solvation. The hEP₄ docking scores correlates best with the cAMP activation data, where both data sets rank order Rivenprost>CAY10684 > PGE₁ ≈ PGE₂ > 11-deoxy-PGE₁ ≈ 11-dexoy-PGE₂ > 8-aza-11-deoxy-PGE₁. This rank-ordering matches closely with the rEP₄ receptor as well. Species-specific differences were noted for the weak agonists Sulprostone and Misoprostol, which appear to dock more readily within human receptor versus rat receptor.

Electronic supplementary material

The online version of this article (10.1186/s12860-019-0212-5) contains supplementary material, which is available to authorized users.

Mapping PTGERs to the Ovulatory Follicle: Regional Responses to the Ovulatory PGE2 Signal

Prostaglandin E2 (PGE2) is a key intrafollicular mediator of ovulation in many, if not all, mammalian species. PGE2 acts at follicular cells via four distinct PGE2 receptors (PTGERs). Within the ovulatory follicle, each cell type (e.g., oocyte, cumulus granulosa cell, mural granulosa cell, theca cell, endothelial cell) expresses a different subset of the four PTGERs. Expression of a subset of PTGERs has consequences for the generation of intracellular signals and ultimately the unique functions of follicular cells that respond to PGE2. Just as the ovulatory LH surge regulates PGE2 synthesis, the LH surge also regulates expression of the four PTGERs. The pattern of expression of the four PTGERs among follicular cells before and after the LH surge forms a spatial and temporal map of PGE2 responses. Differential PTGER expression, coupled with activation of cell-specific intracellular signals, may explain how a single paracrine mediator can have pleotropic actions within the ovulatory follicle. Understanding the role of each PTGER in ovulation may point to previously unappreciated opportunities to both promote and prevent fertility.

E-type prostanoid receptor 4 (EP4) in disease and therapy

The large variety of biological functions governed by prostaglandin (PG) E2 is mediated by signaling through four distinct E-type prostanoid (EP) receptors. The availability of mouse strains with genetic ablation of each EP receptor subtype and the development of selective EP agonists and antagonists have tremendously advanced our understanding of PGE2 as a physiologically and clinically relevant mediator. Moreover, studies using disease models revealed numerous conditions in which distinct EP receptors might be exploited therapeutically. In this context, the EP4 receptor is currently emerging as most versatile and promising among PGE2 receptors. Anti-inflammatory, anti-thrombotic and vasoprotective effects have been proposed for the EP4 receptor, along with its recently described unfavorable tumor-promoting and pro-angiogenic roles. A possible explanation for the diverse biological functions of EP4 might be the multiple signaling pathways switched on upon EP4 activation. The present review attempts to summarize the EP4 receptor-triggered signaling modules and the possible therapeutic applications of EP4-selective agonists and antagonists.

Effects of hypo- and hyperthyroidism on proliferation, angiogenesis, apoptosis and expression of COX-2 in the corpus luteum of female rats

Although thyroid dysfunction occurs frequently in humans and some animal species, the mechanisms by which hypo- and hyperthyroidism affect the corpus luteum have not been thoroughly elucidated. This study evaluated the levels of proliferative activity, angiogenesis, apoptosis and expression of cyclooxygenase-2 in the corpus luteum of female rats with thyroid dysfunction. These processes may be important in understanding the reproductive changes caused by thyroid dysfunction. A total of 18 adult female rats were divided into three groups (control, hypothyroid and hyperthyroid) with six animals per group. Three months after treatment to induce thyroid dysfunction, the rats were euthanized in the dioestrus phase. The ovaries were collected and immunohistochemically analysed for expression of the cell proliferation marker CDC-47, vascular endothelial growth factor (VEGF), VEGF receptor Flk-1 and cyclooxygenase-2 (COX-2). Apoptosis was evaluated using the TUNEL assay. Hypothyroidism reduced the intensity and area of COX-2 expression in the corpus luteum (p < 0.05), while hyperthyroidism did not alter COX-2 expression in the dioestrus phase. Hypothyroidism significantly reduced the expression of CDC-47 in endothelial cells and pericytes in the corpus luteum, whereas hyperthyroidism did not induce a detectable change in CDC-47 expression (p > 0.05). Hypothyroidism reduced the level of apoptosis in luteal cells (p < 0.05) and increased VEGF expression in the corpus luteum. In contrast, hyperthyroidism increased the level of apoptosis in the corpus luteum (p < 0.05). In conclusion, thyroid dysfunction differentially affects the levels of proliferative activity, angiogenesis and apoptosis and COX-2 expression in the corpus luteum of female rats.

Drosophila Pxt: a cyclooxygenase-like facilitator of follicle maturation

Prostaglandins are local transient hormones that mediate a wide variety of biological events, including reproduction. The study of prostaglandin biology in a genetically tractable invertebrate model organism has been limited by the lack of clearly identified prostaglandin-mediated biological processes and prostaglandin metabolic genes, particularly analogs of cyclooxygenase (COX), the rate-limiting step in vertebrate prostaglandin synthesis. Here, we present pharmacological data that Drosophila ovarian follicle maturation requires COX-like activity and genetic evidence that this activity is supplied in vivo by the Drosophila peroxidase Pxt. pxt mutant females are sterile, and maturing follicles show defects in actin filament formation, nurse cell membrane stability and border cell migration. Maturation of pxt follicles in vitro is stimulated by prostaglandin treatment and fertility is restored in vivo to pxt mutants by expressing mammalian Cox1 protein. Our experiments suggest that prostaglandins promote Drosophila follicle maturation, in part by modulating the actin cytoskeleton, and establish Drosophila oogenesis as a model for understanding these critical biological regulators.

Prostaglandin E2 increases cyp19 expression in rat granulosa cells: implication of GATA-4

The expression of Cyp19, the key gene of estrogen biosynthesis, in granulosa cells (GC) is essential for follicular growth and coordination of the ovulatory process. The goal of this study was to examine the effect of PGE2 and PGF2alpha on Cyp19 expression in undifferentiated and luteinized GC (UGC and LGC). In UGC, PGE2 increased Cyp19 mRNA and Cyp19 protein levels whereas PGF2alpha had no effect. In LGC, PGF2alpha decreased Cyp19 expression whereas PGE2 had no effect. Gene-reporter experiments demonstrated that PGE2 increases Cyp19 transcription in UGC. A protein kinase A inhibitor blocked PGE2-induced increase in Cyp19 promoter activity. PGE2 increased GATA-4 binding to the Cyp19 promoter. Mutation of the GATA binding site resulted in the loss of PGE2 stimulation. This study demonstrates that PGE2 stimulates Cyp19 expression in rat GC and suggests that GATA-4 may mediate (at least in part) the stimulatory effect of PGE2.