Investigations concerning the relationship of ovarian eosinophilia to ovulation and luteal function in the sheep

Description of the Follicular Fluid Cytokine and Hormone Profiles in Human Physiological Natural Cycles

PURPOSE

Exogenous gonadotrophins administration during in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles could significantly alter the endogenous follicular regulation system and could influence oocyte quality. The analysis of the follicular fluid (FF) cytokine and hormone profiles in physiological natural cycles is crucial to appreciate the role of FF milieu on follicle development. So far, the FF cytokine profile has been analyzed only in controlled ovarian stimulation cycles and in modified natural cycles. Our study defines, in physiological natural cycles, the cytokine and hormone profiles of individual FF aspirated from antral follicles.

METHODS

A total of 203 FFs obtained from 83 women with regular menstrual cycles undergoing ovarian tissue cryopreservation were analyzed: 115 FFs from Group 1 (10 to 29 years of age) and 88 FFs from Group 2 (30 to 40 years of age). In individual FF, 27 cytokines were measured with xMAP technology, and progesterone, estrone, estradiol, testosterone, androstenedione concentrations were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

FF hormone profiles were not different in follicular and luteal phase, suggesting that FF hormones are regulated independently of the endogenous gonadotrophins-possibly because 74% of the punctured follicles, which were ≤6 mm, did not require cyclic pituitary function. The follicle size was influenced not only by the FF cytokine profile but also by the FF hormone profile, both of which are dependent on age.

MAIN CONCLUSIONS

In physiological natural cycles, FF hormones seems to be regulated independently of the endogenous gonadotropins. Age influences FF hormone and cytokine profiles and the compelling relationship between FF hormones and FF cytokines could influence the follicle development.

Multistep analysis reveals the relationship between blood indices at the time of ovum pick-up and in vitro embryo production in heifers

The inflammatory factors of complete blood count (CBC) are associated with a decrease in the in vitro embryo production (IVP) outcome in women. The relation between the blood indices and in vitro fertilization (IVF) outcomes in bovines remains to be elucidated. Using ovum pick-up (OPU), oocytes were retrieved from heifers (n = 60) and inseminated separately with sperm. The blastocyst formation was recorded on day 7 after insemination for each animal and the blood indices were evaluated at the time of OPU. Then, heifers were classified on the basis of (1) blastocyst formation, cleaved vs. failed, or (2) inflammation, low-grade inflammation (lymphocyte counts > 5.6 × 10⁹/L) vs. no inflammation (lymphocyte counts < 5.6 × 10⁹/L). Oocytes derived from heifers with higher lymphocytes, red blood cells (RBC), platelets, hematocrit, red cell distribution width (RDW-SD) and plateletcrit values and lower monocytes, eosinophils, mean corpuscular hemoglobin (MCH) and MCH concentration (MCHC) successfully developed to the blastocyst stage. Heifers with low-grade inflammation numerically had a higher percentage of blastocyst formation than normal heifers. The principle component analysis (PCA) showed that blastocyst formation had the strongest positive association with RDW-cv and RDW-SD, while having a strong negative association with mean corpuscular volume (MCV), hemoglobin, MCHC and MCH. The PCA determined that the number of grade A COCs and the percentage of COCs reached the cleavage stage had a negative association with white blood cells (WBC), lymphocytes, basophils and monocytes, and a positive correlation with platelet to lymphocyte ratio, platelet distribution width (PDW) and plateletcrit. Network mapping detected close similarities between BFR and RDW-SD, MPV, and lymphocytes. The area under the receiver operating characteristic curve (AUC) identified that, eosinophils (AUC 0.80), RDW-SD (AUC 0.76), monocytes (AUC 0.76) and lymphocytes (AUC 0.76) had a good predictive ability to detect heifers with high OPU-IVP outcome (≥60%). In conclusion, these findings suggest that CBC indices at the time of OPU were associated with the IVF outcome and may be incorporated into protocols for the identification of heifers with high potential for blastocyst formation.

Contribution of the immune system to follicle differentiation, ovulation and early corpus luteum formation

Much of what we know about the involvement of the immune system in periovulatory follicle differentiation, ovulation and subsequent formation of the corpus luteum in cattle is drawn from the findings of studies in several mammalian livestock species. By integrating published histological data from cattle, sheep and pigs and referring back to the more comprehensive knowledge bank that exists for mouse and humans we can sketch out the key cells of the immune system and the cytokines and growth factors that they produce that are involved in follicle differentiation and luteinization, ovulation and early follicle development. These contributions are reviewed and the key findings, discussed.

The contribution of the maternal immune system to the establishment of pregnancy in cattle

Immune cells play an integral role in affecting successful reproductive function. Indeed, disturbed or aberrant immune function has been identified as primary mechanisms behind infertility. In contrast to the extensive body of literature that exists for human and mouse, studies detailing the immunological interaction between the embryo and the maternal endometrium are quite few in cattle. Nevertheless, by reviewing the existing studies and extrapolating from sheep, pig, mouse, and human data, we can draw a reasonably comprehensive picture. Key contributions of immune cell populations include granulocyte involvement in follicle differentiation and gamete transfer, monocyte invasion of the peri-ovulatory follicle and their subsequent role in corpus luteum formation and the pivotal roles of maternal macrophage and dendritic cells in key steps of the establishment of pregnancy, particularly, the maternal immune response to the embryo. These contributions are reviewed in detail below and key findings are discussed.

Physiology and Endocrinology Symposium: role of immune cells in the corpus luteum

The immune system is essential for optimal function of the reproductive system. The corpus luteum (CL) is an endocrine organ that secretes progesterone, which is responsible for regulating the length of the estrous cycle, and for the establishment and maintenance of pregnancy in mammals. This paper reviews literature that addresses 2 areas; i) how immune cells are recruited to the CL, and ii) how immune cells communicate with luteal cells to affect the formation, development, and regression of the CL. Immune cells, primarily recruited to the ovulatory follicle from lymphoid organs after the LH surge, facilitate ovulation and populate the developing CL. During the luteal phase, changes in the population of macrophages, eosinophils, neutrophils, and T lymphocytes occur at critical functional stages of the CL. In addition to their role in facilitating ovulation, immune cells may have an important role in luteal function. Evidence shows that cytokines secreted by immune cells modulate both luteotropic and luteolytic processes. However, the decision to pursue either function may depend on the environment provided by luteal cells. It is suggested that understanding the role immune cells play could lead to identification of new strategies to improve fertility in dairy cattle and other species.

Dexamethasone-induced eosinopenia is associated with lower progesterone production in cattle

Eosinophilic cells accumulate in the capillaries of the bovine Graafian follicle shortly before ovulation and in the early developing corpus luteum (CL). Suppressing the migration of these eosinophilic cells by dexamethasone allowed us to evaluate their possible function in the CL development. Brown Swiss cows (n = 10) were randomly subdivided into two groups (n = 5). Every group was used once as control group and once as experimental group with two oestrous cycles between each treatment. Eighteen hours (h) after oestrus synchronization, dexamethasone or saline was given. Ovulation was induced 24 h later with gonadotropin-releasing hormone. Another injection of dexamethasone or saline was given 12 h later. Eosinophilic cells in the blood were counted daily until day 7 after the first dexamethasone injection. The collection of ovaries took place at days 1, 2 and 5. Gene expression, protein concentration and location of angiogenic factors, chemokines, insulin-like growth factor 1 (IGF1) and eosinophilic cells were studied. No eosinophilic cells were found in the CL of the treatment group. Blood progesterone decreased significantly in the dexamethasone group from day 8 to 17. The protein concentration of FGF2 increased significantly in CL tissue at day 2 and VEGFA decreased. Local IGF1 gene expression in the CL was not regulated. We assume from our data that the migration of eosinophilic cells into the early CL is not an essential, but an important stimulus for angiogenesis during early CL development in cattle.

Pathophysiological roles of chemokines in human reproduction: an overview

Chemokines are a group of small cytokines that have an ability to induce leukocyte migration. Chemokines exert their functions by binding and activating specific G protein-coupled receptors. Studies have unveiled pleiotropic bioactivities of chemokines in various phenomena ranging from immunomodulation, embryogenesis, and homeostasis to pathogenesis. In the mammalian reproductive system, chemokines unexceptionally serve in multimodal events that are closely associated with establishment, maintenance, and deterioration of fecundity. The aim of this review is to update the knowledge on chemokines in male and female genital organs, with a focus on their potential pathophysiological roles in human reproduction.

The interface of the immune and reproductive systems in the ovary: lessons learned from the corpus luteum of domestic animal models

The dynamic changes that characterize the female reproductive system are regulated by hormones. However, local cell-to-cell interactions may mediate responsiveness of tissues to hormonal signals. The corpus luteum (CL) is an excellent model for understanding how immune cells are recruited into tissues and the role played by those cells in regulating tissue homeostasis or demise. Leukocytes are recruited into the CL throughout its lifespan, and leukocyte-derived cytokines have been found in corpora lutea of all species examined. The proinflammatory cytokines inhibit gonadotropin-stimulated steroidogenesis, profoundly stimulate prostaglandin synthesis by luteal cells, and promote apoptosis. However, there is mounting evidence that leukocytes and luteal cells communicate in different ways to maintain homeostasis within the functional CL. Domestic animals have provided important information regarding the presence and role of immune cells in the CL.

Expression and localisation of extracellular matrix degrading proteases and their inhibitors during the oestrous cycle and after induced luteolysis in the bovine corpus luteum

The corpus luteum (CL) offers the opportunity to study high proliferative processes during its development and degradation processes during its regression. We examined the mRNA expression of matrix metalloproteases (MMP)-1, MMP-2, MMP-9, MMP-14, MMP-19, tissue inhibitor of MMP (TIMP)-1, TIMP-2, tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), uPA-receptor (uPAR), PA-inhibitors (PAI)-1, PAI-2 in follicles 20 h after GnRH application, CLs during days 1–2, 3–4, 5–7 and 8–12 of the oestrous cycle as well as after induced luteolysis. Cows in the mid-luteal phase were injected with Cloprostenol and the CLs were collected at 0.5, 2, 4, 12, 24, 48 and 64 h after PGF2α injection. Real-time RT-PCR determined mRNA expressions. Expression from 20 h after GnRH to day 12: MMP-1, MMP-2, MMP-14 and tPA showed a clear expression, but no regulation. TIMP-1 and uPAR mRNA increased when compared with the follicular phase. TIMP-2, MMP-9, MMP-19 and uPA increased from the follicular phase to days 8–12. PAI-1 and PAI-2 expression increased from days 1–7 and decreased to days 8–12. Induced luteolysis: MMP-1, MMP-2, MMP-9, MMP-14, MMP-19 and TIMP-1 all increased at different time points and intensities, whereas TIMP-2 was constantly decreased from 24 to 64 h. The plasminogen activator system and their inhibitors were up-regulated from 2 to 64 h, tPA was already increased after 0.5 h. Immunohistochemistry for MMP-1, MMP-2, MMP-14: an increased staining for MMP-1 and MMP-14 was seen in large luteal cells beginning 24 h after PGF2α application. MMP-2 showed a strong increase in staining in endothelial cells at 48 h.

Prostaglandins and reproduction in female farm animals

Prostaglandins impact on ovarian, uterine, placental, and pituitary function to regulate reproduction in female livestock. They play important roles in ovulation, luteal function, maternal recognition of pregnancy, implantation, maintenance of gestation, microbial-induced abortion, parturition, postpartum uterine and ovarian infections, and resumption of postpartum ovarian cyclicity. Prostaglandins have both positive and negative effects on reproduction; they are used to synchronize oestrus, terminate pseudopregnancy in mares, induce parturition, and treat retained placenta, luteinized cysts, pyometra, and chronic endometritis. Improved therapeutic uses for prostaglandins will be developed when we understand better their involvement in implantation, maintenance of luteal function, and establishment and maintenance of pregnancy.

Bovine eotaxin (CCL11)--an unusual member of the eotaxin group--attracts eosinophils in vitro but is not responsible for eosinophilia in the ovary

Under physiological conditions normally characterised by low tissue infiltration of eosinophils, a conspicuous number of these cells are attracted into the human and ruminant ovary. Eosinophils suddenly increase in the thecal layer of the preovulatory follicle and corpus luteum at very early development. Currently, we only have a limited understanding of the mechanism for the recruitment of the ovarian eosinophils. Eotaxin (CCL11) may be one of the chemoattractants involved in stimulating eosinophils to migrate selectively into ovary. As a prerequisite for the analysis of eotaxin expression in the bovine ovary, we determined the complete bovine eotaxin mRNA sequence since it was not available from databases. The bovine eotaxin is the first member of the monocyte chemoattractant protein (MCP)/eotaxin subfamily with two mRNA isoforms varying in length in the untranslated 3'-untranslated region. The unusual amino-acid sequence of bovine eotaxin contains structural features that are so far known to be characteristic for MCP, but not eotaxin. In our microchemotaxis assays, recombinant bovine eotaxin showed a functional pattern orthologous to known eotaxins. Thus, the chimeric structure of bovine eotaxin did not affect the favoured chemotactic activity on eosinophils. Semiquantitative RT-PCR was used to investigate the expression of eotaxin in different regions of the bovine ovary. We only detected faint eotaxin mRNA signals that did not indicate physiological significance even in stimulated granulosa cell cultures, follicle-derived macrophages or fibroblasts. Taken together, bovine eotaxin attracts eosinophils in vitro but is not responsible for eosinophilia in the ovary. Its unusual chimeric structure confirms the unity of the MCP/eotaxin subfamily of CC chemokines and distinguishes it from other CC chemokine subfamilies.

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.

Chemokines in the corpus luteum: implications of leukocyte chemotaxis

Chemokines are small molecular weight peptides responsible for adhesion, activation, and recruitment of leukocytes into tissues. Leukocytes are thought to influence follicular atresia, ovulation, and luteal function. Many studies in recent years have focused attention on the characterization of leukocyte populations within the ovary, the importance of leukocyte-ovarian cell interactions, and more recently, the mechanisms of ovarian leukocyte recruitment. Information about the role of chemokines and leukocyte trafficking (chemotaxis) during ovarian function is important to understanding paracrine-autocrine relationships shared between reproductive and immune systems. Recent advances regarding chemokine expression and leukocyte accumulation within the ovulatory follicle and the corpus luteum are the subject of this mini-review.

The expression of substance P and its neurokinin-1 receptor mRNA in the bovine corpus luteum of early developmental stage

Related to all leukocytes, 90% of eosinophils are recruited into the bovine corpus luteum of early developmental stage. We here describe a simultaneous appearance of substance P (SP)-positive fibre-like structures and the neurokinin-1 (NK-1) receptor mRNA for SP. Substance P was depicted by using indirect immunohistology and immunofluorescence localization. The dot blot analysis confirmed the presence of SP at the protein level. Using nested reverse transcribed-polymerase chain reaction (RT-PCR) analysis, a 358 bp long partial bovine receptor mRNA for SP (NK-1) was sequenced in the spinal cord. The mRNA for SP and for the NK-1 receptor were then detected in the corpus luteum of early developmental stage with RT-PCR and nested RT-PCR. We conclude: The production of SP and the expression of NK-1 receptor mRNA may be involved in the selective recruitment of eosinophils into the bovine corpus luteum of early developmental stage.

Vascular morphogenesis in the ovary

Vascular morphogenesis through mechanisms of vasculogenesis, angiogenesis and intussusception is associated primarily with embryonic and fetal development and is down-regulated in the healthy adult. Physiological angiogenesis in the adult is restricted to the female reproductive system where it occurs cyclically in the ovary and the uterus as well as pregnancy-associated in the placenta and in the mammary gland. Of all the different organs, the cyclic corpus luteum of the ovary is the organ site with the strongest physiological angiogenesis. The hormonally regulated cyclic processes in the corpus luteum are characterized by discrete phases of blood vessel growth, vessel maturation and vessel regression. This chapter discusses the morphological changes of the vasculature in the cyclic corpus luteum in relation to the regulating molecular mechanisms. These data establish the dynamic processes in the ovarian corpus luteum as a unique system for studying all steps of the angiogenic cascade, including vessel maturation and vessel regression. Inhibition of angiogenesis impairs the normal ovarian cycle, reflecting that angiogenesis is rate-limiting for ovulation and growth of the corpus luteum and may, thus, be a potential target for therapeutic intervention in the reproductive function.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Cloning of bovine RANTES mRNA and its expression and regulation in ovaries in the periovulatory period

RANTES may be one of the chemoattractants involved in stimulating eosinophils and macrophages to migrate selectively into bovine dominant follicles and into developing corpora lutea. We sequenced a 736 bp fragment of the bovine RANTES mRNA encoding the complete protein and defined the ovarian source of RANTES mRNA. As demonstrated by competitive RT-PCR, follicle-derived macrophages showed a 100-1000 times higher RANTES mRNA level compared to unpurified granulosa cells or follicle-derived fibroblasts. By means of in situ hybridization, RANTES mRNA positive macrophages were located in the former thecal layer of the developing corpora lutea.

Immunological aspects of ovarian function: role of the cytokines

Interaction between the immune system and reproduction is multiple. Either directly or indirectly through their products, immune cells are associated with the regulation of every level of the hypothalamus-pituitary-ovarian axis. Immune cells are present in the ovaries and their numbers increase during the cycle. During the follicular development cytokines assist granulosa cell growth while inhibiting their differentiation. During the LH peak, an influx of immune cells occurs and several cytokines are released. The rupture of the follicle is considered as an inflammatory reaction. IL-1, TNF-alpha are the main cytokines involved in this process. During the luteal phase, the installation of the corpus luteum needs the setting up of neovascularization. Cytokines are probable candidates for this function, but they also promote cellular differentiation resulting in steroid synthesis. In the absence of pregnancy T lymphocytes and eosinophils are involved in corpus luteum regression. Their products are directly cytotoxic for the luteal cells. They attract macrophages which are locally activated to phagocytose the damaged luteal cells. They can induce apoptosis of endothelial and luteal cells through gene expression. Cytokines are members of a larger regulatory network residing in the ovary and involving hormones and growth factors. The various stages of ovarian cycle will be shown from an immunological point of view. Understanding the role of the cytokines should enable us to go beyond a purely descriptive stage, and allow us to envisage new ovulation induction therapy and treatment in certain cases of premature menopause.

Ovulation as a tissue remodelling process. Proteolysis and cumulus expansion

Ovulation, recurring every midcycle of the mammalian female and triggered by a surge of luteinizing hormone (LH) released from the pituitary, is an essential prerequisite for fertilization and subsequent embryonic development. Here we shall describe two of the biological components of the ovulatory response, cumulus expansion (frequently denoted as cumulus maturation) and the rupture of follicular wall, both crucial for the release of a fertilizable ovum. The role of a proteolytic cascade and its regulation by eicosanoids will be emphasized in relation to follicle rupture. The new data implicating cumulus maturation as an essential step for the release of the ovum and the apparent mediatory role of interleukin-1 in this process will be presented. LH/hCG stimulates, in the preovulatory follicles, a cascade of proteolytic enzymes, including plasminogen activator (PA), plasmin and matrix metalloproteinase 1 (MMP-1). These enzymes bring about the degradation of perifollicular matrix and, most notably, the decomposition of the meshwork of collagen fibers which provides the strength to follicular wall. Furthermore, pharmacological blockage of any of these enzymes resulted in inhibition of follicle rupture. LH/hCG stimulates, in addition, an increase in ovarian production of eicosanoids. These include prostaglandins, obtained from arachidonic acid via the cyclooxygenase pathway and leukotrienes, the products of lipoxygenase. Previous studies from our and other laboratories have demonstrated the ability of inhibitors of cyclooxygenase and of lipoxygenases to suppress ovulation in several mammalian species. MK-886, which inhibits the translocation of 5-lipoxygenase (5-LO) from the cytosol and its binding to the membranal 5-LO activating enzyme, suppressed dose-dependently follicular rupture from the treated ovary. Zymographic analysis of ovarian extracts from PMSG/hCG-stimulated rats revealed a band of collagenolytic activity at 52kD, corresponding to human MMP-1 and at 72kD, corresponding to human MMP-2. Both activities were markedly stimulated by administration of hCG and were significantly inhibited by indomethacin, NDGA or MK-886. Thus, eicosanoids seem to mediate LH stimulation of follicular collagenase. Interleukin-1 (IL-1) has been recently implicated in ovulation. The ability of an IL-1 receptor antagonist (ra) to block ovulation in vivo and in vitro has been demonstrated recently. Morphological examination of the ovulatory follicles failing to ovulate suggests that this effect is exerted by inhibiting cumulus oophorus expansion and detachment from mural granulosa cells. In vitro, IL-1ra attenuated the action of hCG and FSH on cumulus expansion and follicular hyaluronic acid synthesis. Thus, IL-1 seems to mediate and/or facilitate gonadotropin action on cumulus expansion, and hence on ovulation.