Effects of indomethacin on ovarian leukocytes during the periovulatory period in the rat

Ovarian follicles are resistant to monocyte perturbations-implications for ovarian health with immune disruption†

Monocytes and macrophages are the most abundant immune cell populations in the adult ovary, with well-known roles in ovulation and corpus luteum formation and regression. They are activated and proliferate in response to immune challenge and are suppressed by anti-inflammatory treatments. It is also likely they have a functional role in the healthy ovary in supporting the maturing follicle from the primordial through to the later stages; however, this role has been unexplored until now. Here, we utilized a Cx3cr1-Dtr transgenic Wistar rat model that allows a conditional depletion of circulating monocytes, to investigate their role in ovarian follicle health. Our findings show that circulating monocyte depletion leads to a significant depletion of ovarian monocytes and monocyte-derived macrophages. Depletion of monocytes was associated with a transient reduction in circulating anti-Müllerian hormone (AMH) at 5 days postdepletion. However, the 50-60% ovarian monocyte/macrophage depletion had no effect on ovarian follicle numbers, follicle atresia, or apoptosis, within 5-21 days postdepletion. These data reveal that the healthy adult ovary is remarkably resistant to perturbations of circulating and ovarian monocytes despite acute changes in AMH. These data suggest that short-term anti-inflammatory therapies that transiently impact on circulating monocytes are unlikely to disrupt ovarian follicle health, findings that have significant implications for fertility planning relative to the experience of an immune challenge or immunosuppression.

Expression of cytokine-induced neutrophil chemoattractant suppresses tumor necrosis factor alpha expression and thereby prevents the follicles from undergoing atresia and apoptosis

Aim

Cytokine-induced neutrophil chemoattractant (CINC/gro) is a CXC family chemokine, similar to interleukin-8 in rats, and is one of the factors that regulates ovulation. However, the mechanism that regulates atresia of the ovaries postovulation is not clearly defined.

Methods

Whether antibody-blocking of CINC/gro can alter the number of ovulated oocytes and modulate neutrophil infiltration was investigated. The effect of the antibody on the level of inflammatory cytokine production and follicular atresia was examined. Apoptosis was measured by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method and via analysis of the messenger RNA expression of Bcl-2 and Bcl2-associated X (Bax).

Results

The anti-CINC/gro antibody treatment decreased the number of ovulated oocytes. The messenger RNA levels of cyclooxygenase-2 and interleukin-1 beta were decreased by the antibody treatment, whereas that of tumor necrosis factor (TNF) alpha was increased. The TUNEL analysis revealed a larger number of apoptotic cells in the antibody group, compared with those in the control group, as well as a significant increase in the Bax/Bcl-2 ratio 24 hours after human chorionic gonadotropin administration.

Conclusion

These findings suggest that ovulation is accelerated by neutrophil infiltration into the theca layer. The CINC/gro appears to synergize with interleukin-1 beta for ovulation. By contrast, the data suggest that CINC/gro expression suppresses TNF alpha expression and that CINC/gro expression therefore prevents the follicles from undergoing atresia and apoptosis.

Chemokine Ligand 20: A Signal for Leukocyte Recruitment During Human Ovulation?

Ovulation is one of the cornerstones of female fertility. Disruption of the ovulatory process results in infertility, which affects approximately 10% of couples. Using a unique model in which the dominant follicle is collected across the periovulatory period in women, we have identified a leukocyte chemoattractant, chemokine ligand 20 (CCL20), in the human ovary. CCL20 mRNA is massively induced after an in vivo human chorionic gonadotropin (hCG) stimulus in granulosa (>10 000-fold) and theca (>4000-fold) cells collected during the early ovulatory (12-18 h) and late ovulatory (18-34 h) periods after hCG administration. Because the LH surge sets in motion an inflammatory reaction characterized by an influx of leukocytes and CCL20 is known to recruit leukocytes in other systems, the composition of ovarian leukocytes (CD45+) containing the CCL20 receptor CCR6 was determined immediately prior to ovulation. CD45+/CCR6+ cells were primarily natural killer cells (41%) along with B cells (12%), T cells (11%), neutrophils (10%), and monocytes (9%). Importantly, exogenous CCL20 stimulated ovarian leukocyte migration 59% within 90 minutes. Due to the difficulties in obtaining human follicles, an in vitro model was developed using granulosa-lutein cells to explore CCL20 regulation. CCL20 expression increased 40-fold within 6 hours after hCG, was regulated partially by the epithelial growth factor pathway, and was positively correlated with progesterone production. These results demonstrate that hCG dramatically increases CCL20 expression in the human ovary, that ovarian leukocytes contain the CCL20 receptor, and that CCL20 stimulates leukocyte migration. Our findings raise the prospect that CCL20 may aid in the final ovulatory events and contribute to fertility in women.

Pituitary-ovary-spleen axis in ovulation

Leukocytes are rapidly recruited to the preovulatory ovary and play a crucial role as facilitators of ovulation and luteal formation. In this article, recent findings on leukocyte trafficking to the ovary, as well as the physiological role of leukocytes in the ovary, will be summarized and discussed. We then explore the novel hypothesis that the hypothalamus-pituitary-ovary (HPO) axis might include the spleen as a reservoir of leukocytes by summarizing recent reports on this topic, both in the fields of immunology and reproductive biology.

Periovulatory leukocyte infiltration in the rat ovary

Ovulation is preceded by intraovarian inflammatory reactions that occur in response to the preovulatory gonadotropin surge. As a main inflammatory event, leukocytes infiltrate the ovary and release proteolytic enzymes that degrade the extracellular matrix weakening the follicular wall, a required step for follicle rupture. This study aimed to quantitatively measure the infiltrating leukocytes, determine their cell types, and localize infiltration sites in the periovulatory rat ovary. Cycling adult and gonadotropin-stimulated immature rats were used as animal models. Ovaries were collected at five different stages of estrous cycle in the adult rats (diestrus, 1700 h; proestrus, 1500 h; proestrus, 2400 h; estrus, 0600 h; and metestrus, 1700 h) and at five different time points after superovulation induction in the immature rats (pregnant mare's serum gonadotrophin, 0 h; pregnant mare's serum gonadotrophin, 48 h; human chorionic gonadotropin, 6 h; human chorionic gonadotropin, 12 h; and human chorionic gonadotropin, 24 h). The ovaries were either dissociated into a single cell suspension for flow cytometric analysis or fixed for immunohistochemical localization of the leukocytes. Similar numbers of leukocytes were seen throughout the estrous cycle (approximately 500,000/ovary), except proestrus 2400 when 2-fold higher numbers of leukocytes were found (approximately 1.1 million/ovary). A similar trend of periovulatory rise of leukocyte numbers was seen in the superovulation-induced immature rat model, recapitulating a dramatic increase in leukocyte numbers upon gonadotropin stimulation. Both macrophage/granulocytes and lymphocytes were among the infiltrating leukocytes and were localized in the theca and interstitial tissues, where platelet-endothelial cell adhesion molecule-1 and intercellular adhesion molecule-1 may play roles in the transmigration of leukocytes, because their expressions correlates spatiotemporally with the infiltrating leukocytes. In addition, a strong inverse relationship between leukocyte numbers in the ovary and spleen, as well as significant reduction of leukocyte infiltration in the splenectomized rats, were seen, indicating that the spleen may serve as an immediate supplier of leukocytes to the periovulatory ovary.

Occurrence of immunoreactivity for adipocyte-type fatty acid binding protein in degenerating granulosa cells in atretic antral follicles of mouse ovary

The localization of adipocyte-type fatty acid binding protein (A-FABP) in the mature mouse ovary was examined by immuno-light and electron microscopy. Solitary round cells showing the distinct immunoreactivity for A-FABP were detected in 1-6 antral follicles. In sets of two consecutive sections in a mirror alignment on slide glasses which were treated for immunoreactivity for A-FABP and TUNEL reaction separately, cells immunoreactive for A-FABP appeared in the same antral follicles as containing cells exhibiting TUNEL-reaction. In immunoelectron microscopy, A-FABP-immunopositive cells were found to contain highly electron-dense nuclei of round, irregular or crescent shapes together with cytoplasmic remnants without any features of macrophages or cells of extrinsic origin. Therefore the cells were identified as apoptotic granulosa cells. The apoptotic cells immunoreactive for A-FABP were often seen to be enclosed/engulfed in adjacent cells exhibiting normal ultrastructures without containing numerous lysosomes. The present findings suggest that A-FABP is involved in the apoptosis of ovarian granulosa cells, probably through its interaction with peroxisome proliferator activated receptors.

Molecular Characterization of Equine P-Selectin (CD62P) and Its Regulation in Ovarian Follicles During the Ovulatory Process1

Ovulation is accompanied by a marked infiltration of leukocytes into thecal layers after the gonadotropin surge. P-selectin is known to play a critical role in the initial steps of leukocyte recruitment from the bloodstream during inflammation. Thus, the objective was to investigate the potential regulation of P-selectin by gonadotropins in equine preovulatory follicles. The full-length equine P-selectin cDNA was cloned by a combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'- and 3'-rapid amplification of cDNA ends. Results showed that equine P-selectin cDNA encodes an 829-amino acid protein that is highly conserved when compared to the human protein (80% identity). Semiquantitative RT-PCR/Southern blot analyses were performed to study the regulation of P-selectin transcript in preovulatory follicles isolated during estrus at 0, 12, 24, 30, 33, 36, and 39 h after an ovulatory dose of hCG (ovulation occurs between 39 and 42 h post-hCG in this model). Results showed that levels of P-selectin mRNA remained very low or undetectable throughout the ovulatory process in extracts prepared from the granulosa cell layer. In contrast, a significant increase in P-selectin transcript was observed between 30 and 39 h post-hCG in extracts obtained from thecal layers (P < 0.05). Likewise, immunohistochemistry revealed an increase of immunoreactive P-selectin protein in the vascular endothelium present in thecal layers of follicles isolated 36 and 39 h post-hCG. Thus, the present study describes, to our knowledge for the first time, the primary structure of equine P-selectin and the regulation of P-selectin transcript and protein in follicular thecal endothelial cells before ovulation.

Guinea-pig interpubic joint (symphysis pubica) relaxation at parturition: underlying cellular processes that resemble an inflammatory response

BACKGROUND

At term, cervical ripening in coordination with uterine contractions becomes a prerequisite for a normal vaginal delivery. Currently, cervical ripening is considered to occur independently from uterine contractions. Many evidences suggest that cervical ripening resembles an inflammatory process. Comparatively little attention has been paid to the increased flexibility of the pelvic symphysis that occurs in many species to enable safe delivery. The aim of this study was to investigate whether the guinea-pig interpubic joint relaxation process observed during late pregnancy and parturition resembles an inflammatory process.

METHODS

Samples of pubic symphysis were taken from pregnant guinea-pigs sacrificed along gestation, parturition and postpartum. Serial sections of paraffin-embedded tissues were used to measure the interpubic distance on digitalized images, stained with Giemsa to quantify leukocyte infiltration and to describe the vascular area changes, or studied by the picrosirius-polarization method to evaluate collagen remodeling. P4 and E2 serum levels were measured by a sequential immunometric assay.

RESULTS

Data showed that the pubic relaxation is associated with an increase in collagen remodeling. In addition, a positive correlation between E2 serum levels and the increase in the interpubic distance was found. On the other hand, a leukocyte infiltration in the interpubic tissue around parturition was described, with the presence of almost all inflammatory cells types. At the same time, histological images show an increase in vascular area (angiogenesis). Eosinophils reached their highest level immediately before parturition; whereas for the neutrophilic and mononuclear infiltration higher values were recorded one day after parturition. Correlation analysis showed that eosinophils and mononuclear cells were positively correlated with E2 levels, but only eosinophilic infiltration was associated with collagen remodeling. Additionally, we observed typical histological images of dissolution of the connective tissue matrix around eosinophils.

CONCLUSION

The present study shows that a timely regulated influx of infiltrating leukocytes is associated with an extensive collagen remodeling process that allows the pubic separation for a normal delivery in guinea-pig. Thus, the findings in this study support the hypothesis that the guinea-pig pubic symphyseal relaxation at parturition resembles an inflammatory process.