Luteal regression in the normally cycling rat: apoptosis, monocyte chemoattractant protein-1, and inflammatory cell involvement

The stromal microenvironment and ovarian aging: mechanisms and therapeutic opportunities

For decades, most studies of ovarian aging have focused on its functional units, known as follicles, which include oocytes and granulosa cells. However, in the ovarian stroma, there are a variety of somatic components that bridge the gap between general aging and ovarian senescence. Physiologically, general cell types, microvascular structures, extracellular matrix, and intercellular molecules affect folliculogenesis and corpus luteum physiology alongside the ovarian cycle. As a result of damage caused by age-related metabolite accumulation and external insults, the microenvironment of stromal cells is progressively remodeled, thus inevitably perturbing ovarian physiology. With the established platforms for follicle cryopreservation and in vitro maturation and the development of organoid research, it is desirable to develop strategies to improve the microenvironment of the follicle by targeting the perifollicular environment. In this review, we summarize the role of stromal components in ovarian aging, describing their age-related alterations and associated effects. Moreover, we list some potential techniques that may mitigate ovarian aging based on their effect on the stromal microenvironment.

Macrophages: an indispensable piece of ovarian health

Macrophages are the most abundant immune cells in the ovary. In addition to their roles in the innate immune system, these heterogeneous tissue-resident cells are responsive to tissue-derived signals, adapt to their local tissue environment, and specialize in unique functions to maintain tissue homeostasis. Research in the past decades has established a strong link between macrophages and various aspects of ovarian physiology, indicating a pivotal role of macrophages in ovarian health. However, unlike other intensively studied organs, the knowledge of ovarian macrophages dates back to the time when the heterogeneity of ontogeny, phenotype, and function of macrophages was not fully understood. In this review, we discuss the evolving understanding of the biology of ovarian tissue-resident macrophages, highlight their regulatory roles in normal ovarian functions, review the association between certain ovarian pathologies and disturbed macrophage homeostasis, and finally, discuss the technologies that are essential for addressing key questions in the field.

Serum progesterone concentration, volume, and apoptosis of corpora lutea in early, middle and late diestrus in the bitch

The aim was to study number, volume, apoptosis of corpora lutea (CL), and serum P₄ concentrations in early, middle, and late diestrus of dogs. Thirty-six bitches were ovari-hysterectomized (OVX): Early Diestrus (Group [G]1; OVX 20 days after end of estrus [DEH]); Mid-diestrus (GII; OVX between 21 and 40 days after DEH), and Late-diestrus (GIII; OVX between 41 and 60 days after DEH). Before OVX a blood sample was collected to quantify P₄. After OVX, the number of CL (NCL) was recorded, CL measured using both ultrasonography (US) and caliper (CAL), and the volume (mm³) was calculated. Based on abundances of caspase-3, apoptotic luteal cells were detected. Bitches in early-diestrus had greater P₄ concentrations than bitches in mid- and late-diestrus (23.52 ± 3.78 and 10.86 ± 3.88 ng/mL; P < 0.05). The NCL, cumulative USCLV, and CALCLV were similar among diestrus stages (P > 0.30). Bitches with CL (≥5) had twice the serum P₄ concentrations as bitches with CL1-2 and CL3-4 (22.71 ± 3.70 and 10.97 ± 4.06 ng/mL; P < 0.05). There were correlations between P₄ concentrations with USCLV, CALCLV, and NCL (r = 0.64, r = 0.67, r = 0.44; P < 0.0001). When serum P₄ concentrations were adjusted for stages of diestrus, however, there were only correlations during early diestrus. The percentage of apoptotic cells was greater in GIII compared with GI and GII (13.75 ± 2.26 % compared with 4.5 ± 0.68 % and 4.6 ± 1.5 %, respectively; P < 0.05). As days of diestrus increased, number of apoptotic cells increased, and serum P₄ concentrations decreased.

The role of BH3-only proteins in apoptosis within the ovary

BH3-only proteins are pro-apoptotic members of the BCL2 family that play pivotal roles in embryonic development, tissue homeostasis and immunity by triggering cell death through the intrinsic apoptosis pathway. Recent in vitro and in vivo studies have demonstrated that BH3-only proteins are also essential mediators of apoptosis within the ovary and are responsible for the initiation of the cell death signalling cascade in a cell type and stimulus-specific fashion. This review gives a brief overview of the intrinsic apoptosis pathway and summarise the roles of individual BH3-only proteins in the promotion of apoptosis in embryonic germ cells, oocytes, follicular granulosa cells and luteal cells. The role of these proteins in activating apoptosis in response to developmental cues and cell stressors, such as exposure to chemotherapy, radiation and environmental toxicants, is described. Studies on the function of BH3-only proteins in the ovary are providing valuable insights into the regulation of oocyte number and quality, as well as ovarian endocrine function, which collectively influence the female reproductive lifespan and health.

Temporal expression of tenascin-C and type I collagen in response to gonadotropins in the immature rat ovary

Ovarian morphogenesis and physiology in mammals take place in the context of hormones, paracrine factors and extracellular matrix molecules. Both fibrillar type I collagen and the multidomain tenascin-C are matrix molecules capable of modulating the behavior of both normal and neoplastic cells in many organs. Therefore, the objective of this qualitative study was to simultaneously examine the distribution of both tenascin-C and type I collagen in ovarian follicles and corpora lutea induced to develop in response to gonadotropin treatments. In preantral follicles both matrix proteins were present in the focimatrix, theca externa and the interstitium. Equine gonadotropin induced the appearance of both proteins in the theca interna. Subsequent to administration with human chorionic gonadotropin, tenascin-C appearance in the thecal capillaries preceded type I collagen expression. Tenascin-C was also observed in the capillaries of functional and regressing corpora lutea, while type I collagen was predominantly present in the interstitium and tunica albuginea. Western blots showed both an increase in and degradation of tenascin-C in the regressing corpora lutea. The ovarian surface epithelium also showed immunoreactivity for both tenascin-C and type I collagen. The study reveals that tenascin-C and type I collagen may participate in the morphogenesis of ovarian follicles, and in the formation and regression of corpora lutea.

Histological characteristics of the regression of corpora lutea in wistar hannover rats: the comparisons with sprague-dawley rats

We examined the ovaries of 44 Wistar Hannover (RccHan^TM:WIST) (WH) and 30 Sprague-Dawley (SD) rats at 32-weeks of age to determine whether the ovarian structure and formation/regression of the corpora lutea (CLs) differ between the two strains. The average ovary weight was higher in WH rats. The average number of all CLs, including currently formed and previously formed CLs, was higher in WH rats in all cycles; however, no appreciable difference was detected in the number of newly or currently formed CLs between the two strains. CLs regression characterized by degeneration and necrosis of luteal cells began to appear in diestrus in both strains; however, the distribution of degenerated/necrotic cells in CLs differed. Necrotic cells were scattered in SD rats but were focally observed in the center of the CL in WH rats. The reduction in size of previously formed CLs accompanied by regression started about 2 or more stages later in WH rats than in those of SD rats. In conclusion, the higher number of CLs in WH rats is considered to be due to slow CL regression compared with in SD rats.

Downregulation of lymphatic vessel formation factors in PGF2α-induced luteolysis in the cow

Prostaglandin F2α (PGF2α) induces luteolysis in cows and causes infiltration of immune cells, which resembles inflammatory immune response. Since the general immune response is mediated by the lymphatic system, we hypothesized that luteolysis is associated with generation of an immune response that involves lymphatic vessels in the bovine corpus luteum (CL). The CL was obtained from Holstein cows at the mid-luteal phase (days 10-12, ovulation = day 0) by ovariectomy at various time points after PGF2α injection. Lymphatic endothelial cell (LyEC) marker, endothelial hyaluronan receptor 1 (LYVE1), levels decreased significantly 12 h after PGF2α injection. Podoplanin, another LyEC marker, decreased from 15 min after PGF2α injection. PGF2α also diminished mRNA expression of lymphangiogenic factors, such as vascular endothelial growth factor (VEGF) C, VEGFD and VEGF receptor 3 (VEGFR3). During PGF2α-induced luteolysis, the levels of mRNA expression of tumor necrosis factor α (TNFα; the major pro-inflammatory cytokine) and chemokine (C-X-C motif) ligand 1 (neutrophil chemokine) were increased. On the other hand, chemokine (C-C motif) ligand 21, which regulates outflow of immune cells from tissues via the lymphatic vessels during an immune response, was decreased. This study demonstrated that the lymphatic network in the CL is disrupted during luteolysis and suggests that during luteolysis, immune cells can induce a local immune response in the CL without using the lymphatic vessels.

Vascular and immune regulation of corpus luteum development, maintenance, and regression in the cow

The bovine corpus luteum (CL) is a unique, transient organ with well-coordinated mechanisms by which its development, maintenance, and regression are effectively controlled. Angiogenic factors, such as vascular endothelial growth factor A and basic fibroblast growth factor, play an essential role in promoting progesterone secretion, cell proliferation, and angiogenesis. These processes are critically regulated, through both angiogenic and immune systems, by the specific immune cells, including macrophages, eosinophils, and neutrophils, that are recruited into the developing CL. The bovine luteolytic cascade appears to be similar to that of general acute inflammation in terms of time-dependent infiltration by immune cells (neutrophils, macrophages, and T lymphocytes) and drastic changes in vascular tonus and blood flow, which are regulated by luteal nitric oxide and the vasoconstrictive factors endothelin-1 and angiotensin II. Over the period of maternal recognition of pregnancy, the maternal immune system should be well controlled to accept the semiallograft fetus. The information on the presence of the developing embryo in the genital tract is suggested to be transmitted to the ovary by both the endocrine system and the circulating immune cells. In the bovine CL, the lymphatic system, but not the blood vascular system, is reconstituted during early pregnancy, and interferon tau from the embryo could trigger this novel phenomenon. Collectively, the angiogenic and vasoactive factors produced by luteal cells and the time-dependently recruited immune cells within the CL and their interactions appear to play critical roles in regulating luteal functions throughout the life span of the CL.

Rapid accumulation of polymorphonuclear neutrophils in the Corpus luteum during prostaglandin F(2α)-induced luteolysis in the cow

Prostaglandin F_2α (PGF_2α) induces luteolysis within a few days in cows, and immune cells increase in number in the regressing corpus luteum (CL), implying that luteolysis is an inflammatory-like immune response. We investigated the rapid change in polymorphonuclear neutrophil (PMN) numbers in response to PGF_2α administration as the first cells recruited to inflammatory sites, together with mRNA of interleukin-8 (IL-8: neutrophil chemoattractant) and P-selectin (leukocyte adhesion molecule) in the bovine CL. CLs were collected by ovariectomy at various times after PGF_2α injection. The number of PMNs was increased at 5 min after PGF_2α administration, whereas IL-8 and P-selectin mRNA increased at 30 min and 2 h, respectively. PGF_2α directly stimulated P-selectin protein expression at 5–30 min in luteal endothelial cells (LECs). Moreover, PGF_2α enhanced PMN adhesion to LECs, and this enhancement by PGF_2α was inhibited by anti-P-selectin antibody, suggesting that P-selectin expression by PGF_2α is crucial in PMN migration. In conclusion, PGF_2α rapidly induces the accumulation of PMNs into the bovine CL at 5 min and enhances PMN adhesion via P-selectin expression in LECs. It is suggested that luteolytic cascade by PGF_2α may involve an acute inflammatory-like response due to rapidly infiltrated PMNs.

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.

Induction of mRNA for chemokines and chemokine receptors by prostaglandin F2α is dependent upon stage of the porcine corpus luteum and intraluteal progesterone

This study tested the hypotheses that prostaglandin (PG) F(2α) increases expression of genes related to recruitment of leukocytes in mature but not early corpus luteum (CL) and that insensitivity to PGF(2α) action in early CL is dependent on high intraluteal progesterone (P4) concentrations. Experiment 1 examined early (0.5 h) and late (10 h) in vivo effects of PGF(2α) on mature (d 17 of pseudopregnancy) and early (d 9) porcine CL. Real-time PCR was used to measure mRNA for chemokines (IL8, CXCL2, CCL2, CCL8, CCL4, CCL11) and chemokine receptors (CCR1, CCR2, CXCR2, CCR5). Western blotting was used to measure protein expression and phosphorylation of nuclear factor-κB proteins. Treatment with PGF(2α) for 10 h increased mRNA for almost all of these genes (all expect CXCL2 and CCL11) in d 17 CL but not d 9 CL. Treatment with PGF(2α) also led to greater phosphorylation of nuclear factor-κB-1A protein in d 17 than d 9 CL. Experiment 2 had a 2 × 2 factorial design with d 9 gilts treated or not treated with epostane (3β-hydroxysteroid dehydrogenase inhibitor to suppress intraluteal P4) and treated or not treated with PGF(2α). Treatment with PGF(2α) (10 h) or epostane alone did not induce expression of any of these genes in d 9 CL. However, PGF(2α) + epostane increased expression of all of these genes except CCL11. In conclusion, PGF(2α) increases mRNA for chemokines and chemokine receptors in mature CL with similar PGF(2α) effects induced in early CL if intraluteal P4 is suppressed prior to PGF(2α) treatment.

Deciphering the luteal transcriptome: potential mechanisms mediating stage-specific luteolytic response of the corpus luteum to prostaglandin F2α

The objective of this study was to identify prostaglandin F2α (PG)-induced changes in the transcriptome of bovine corpora lutea (CL) that are specific to mature, PG-responsive (day 11) CL vs. developing (day 4) CL, which do not undergo luteolysis in response to PG administration. CL were collected at 0, 4, and 24 h after PG injection on days 4 and 11 of the estrous cycle ( n = 5 per day and time point), and microarray analysis was performed with GeneChip Bovine Genome Arrays. Data normalization was performed with affy package and significance testing with maanova from Bioconductor. Significance (relative to 0 h time point) was declared at fold change >2.0 or <0.5 and false discovery rate of <5%. At 4 and 24 h after PG, 221 (day 4) and 661 (day 11) and 248 (day 4) and 1,421 (day 11) regulated genes, respectively, were identified. The accentuated gene expression response in day 11 CL was accompanied by specific enrichment of PG-regulated genes in distinctive gene ontology categories (immune related and other), particularly at 24 h after injection. Specificity in putative transcription factor binding sites was observed among PG-regulated genes on day 11 vs. day 4, including a potential association of ETS transcription factors with acute PG-induced gene expression specific to day 11 CL. Temporal and PG-induced regulation of abundance of mRNA for ETS transcription factor family members linked to the stage-specific response to PG was not observed. Increased abundance of protein and/or mRNA for six PG-regulated putative ETS-responsive genes was noted in day 11 but not day 4 CL. Results reveal insight into stage-specific gene expression in bovine CL in response to PG and potential transcriptional mediators of luteolysis.

Phosphorylation state of tyrosine hydroxylase in the stalk-median eminence is decreased by progesterone in cycling female rats

Progesterone has the capacity to suppress hypothalamic dopaminergic neuronal activity on proestrous afternoon and prolong or amplify the preovulatory prolactin surge in rats. In the present study, we examined enzyme activity and phosphorylation state of tyrosine hydroxylase (TH) in the stalk-median eminence of cycling female rats on proestrus and estrus and related these to circulating progesterone levels. Phospho-TH levels were evaluated by Western blot analysis. TH activity was determined from the rate of 3,4-dihydroxyphenylalanine (DOPA) accumulation. Phospho-TH levels at Ser-19, Ser-31, and Ser-40 were similar at 1100, 1300, and 1500 h on proestrus but declined at 1700, 1900, and 2200 h, coincident with rising serum progesterone levels. Similarly, DOPA accumulation was 30-50% lower at 1700, 1900, and 2200 h as compared with 1100-1500 h on proestrus. Ser-31 and Ser-40 phosphorylation states were increased by 1100 h on estrus to a level similar to 1100 h on proestrus, whereas DOPA accumulation was 30% greater on estrous as compared with proestrous morning. There were no significant differences among the several time points on proestrus and estrus with regard to TH protein or beta-tubulin levels. Exogenous progesterone administration (7.5 mg/kg, sc) before the preovulatory progesterone surge decreased TH activity and phospho-TH at Ser-19, Ser-31, and Ser-40, accompanied by premature increased serum prolactin. Our study suggests that decreased TH phosphorylation at Ser-19, Ser-31, and Ser-40 contributes to the decline in TH activity in the stalk-median eminence on proestrous afternoon and that progesterone may cause this initial cytoplasmic response of TH dephosphorylation.

Species-related differences in the mechanism of apoptosis during structural luteolysis

Luteolysis is defined as the loss of function and subsequent involution of the luteal structure. The luteolytic process is usually subdivided, whereby the decline in progesterone is described as functional luteolysis and the structural involution is described as structural luteolysis. After the corpus luteum ceases to produce progesterone, it decreases in size, experiences a loss of cellular integrity, and then disappears from the ovary as a result of apoptosis of luteal cells. However, the control mechanisms responsible for initiating and mediating apoptosis during structural luteolysis seem more complex than originally envisioned. Furthermore, efforts to elucidate the apoptotic mechanisms have been complicated by the fact that different mammalian species have different mechanisms for controlling luteal function. Therefore, it is of interest to know whether different mammalian species have different apoptotic mechanisms. The goal of this review was to focus on species-related differences in the mechanism of apoptosis during structural luteolysis in rodents, cattle and humans, the species that are used most for luteolysis research.

Apoptotic myocytes generate monocyte chemoattractant protein-1 and mediate macrophage recruitment

The mechanisms by which apoptotic myocytes are removed by macrophages have not been fully elucidated. This study examined whether apoptotic myocytes actively recruit macrophages by generating monocyte chemoattractant protein-1 (MCP-1) in experiments in vitro and in vivo. Neonatal rat cardiac myocytes were incubated for 4 h in the presence or absence of staurosporine (STS, 0.2-1 mumol/l), an apoptosis inducer. Nuclear staining with DAPI showed that STS induced apoptosis in a dose-dependent fashion. STS (1 mumol/l) caused extensive DNA fragmentation and increased caspase-3 activity compared with a serum-deprived control. MCP-1 mRNA and protein levels in myocytes increased twofold and fourfold, respectively, on STS treatment, and immunochemical staining revealed that apoptotic myocytes expressed MCP-1. To elucidate the role of MCP-1 expressed in apoptotic myocytes to recruit macrophages/monocytes, rat monocytes were incubated in the supernatant of STS-treated myocytes using a trans-well system. The culture medium of STS-treated myocytes recruited monocytes in a MCP-1-dependent fashion. In addition, experiments were performed in vivo using ischemia-reperfused rat hearts. Rats were subjected to 30 min of ligation of the left coronary artery followed by 24 h of reperfusion. After the reperfusion, in the ischemic border myocardium, 17.1 +/- 1.1% of myocytes were terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) positive. Moreover, double staining using the TUNEL technique and immunohistochemistry with MCP-1 antibody showed that 69.8 +/- 3.9% of TUNEL-positive myocytes expressed MCP-1 protein. Concomitantly, activated macrophages infiltrated the areas of apoptosis remarkably. These results suggest that apoptotic myocytes produce MCP-1, which have a critical role in the active recruitment of macrophages.

Elevated Plasma Levels of Interleukin 1β, Tumour Necrosis Factor α and Monocyte Chemotactic Protein 1 Are Associated with Pregnancy Toxaemia in Ewes

Pregnancy toxaemia is a metabolic disorder that results from an inadequate energy supply to the growing maternal-fetal unit. The mechanism underlying the pathogenesis of the syndrome has not been fully clarified; however, a key role for cytokines and chemokines including interleukin 1 beta (IL-1 beta), tumour necrosis factor alpha (TNF-alpha) and monocyte chemotactic protein 1 (MCP-1) has been indicated in women and experimental animals. However, information on the maternal plasma levels of IL-1 beta, TNF-alpha and MCP-1 in ewes with pregnancy toxaemia is limited. Thus, the present study was designed to determine plasma IL-1 beta, TNF-alpha and MCP-1 concentrations in ewes with severe (n=6) and mild (n=4) naturally occurring pregnancy toxaemia and in uncomplicated pregnant ewes (n=10) using enzyme-linked immunosorbent assay (ELISA). All ewes with pregnancy toxaemia had significantly lower body temperature and respiratory rate than uncomplicated pregnant ewes (p<0.05). With the highest concentrations in severe cases, heart rate, proteinuria and serum uric acid levels as well as plasma IL-1 beta, TNF-alpha and MCP-1 were significantly different among all three groups (p<0.05). The plasma concentrations of IL-1 beta in control ewes and ewes with mild and severe toxaemia were 15.81 +/- 3.90 pg/ml, 23.83 +/- 2.42 pg/ml and 34.55 +/- 8.03 pg/ml, respectively. The plasma concentrations of TNF-alpha in control ewes and ewes with mild and severe toxaemia were 7.71 +/- 1.61 pg/ml, 16.13 +/- 3.63 pg/ml, and 22.85 +/- 3.64 pg/ml, respectively. The plasma concentrations of MCP-1 in control ewes and ewes with mild and severe toxaemia were 101.70 +/- 9.86 pg/ml, 134.75 +/- 6.24 pg/ml, and 157.67 +/- 9.69 pg/ml, respectively. Moreover, plasma IL-1 beta, TNF-alpha and MCP-1 levels were positively correlated with clinical and well-establish biochemical parameters of pregnancy toxaemia, serum uric acid and proteinuria (p<0.01). Concomitant increase of plasma IL-1 beta, TNF-alpha and MCP-1 concentrations along with serum uric acid, proteinuria, and worsening of the clinical signs indicates that such cytokines are involved in the aetiopathogenesis and in perpetuation of the local and systemic inflammatory reactions in pregnancy toxaemia in ewes. Hence, plasma IL-1 beta, TNF-alpha and MCP-1 may potentially serve as markers to monitor prognosis of pregnancy toxaemia in ewes.

Cell death induced by serum deprivation in luteal cells involves the intrinsic pathway of apoptosis

The corpus luteum is a transient endocrine gland specializing in the production of progesterone. The regression of the corpus luteum involves an abrupt decline in its capacity for producing progesterone followed by its structural involution, which is associated with apoptosis of the luteal cells. An in vitro experimental approach is needed to study the molecular mechanisms underlying hormonal regulation of luteal cell death under defined experimental conditions. In this study, we investigated simian virus-40-transformed luteal cells to determine whether they can be driven to apoptosis and, if so, to define the intracellular pathway involved. Luteal cells were cultured in the presence or absence of fetal bovine serum for 24 or 48 h. Under serum starvation conditions, the luteal cells underwent growth arrest accompanied by cell death as evaluated by dye exclusion, and confirmed by two-color fluorescence cell viability/cytotoxicity assay. We next studied whether serum starvation-induced death of luteal cells occurred by apoptosis. Morphologic features of apoptosis were observed in cells stained with hematoxylin after being subjected to serum starvation for 48 h. The apoptotic nature was further confirmed by in situ 3'-end labeling and fragmentation of genomic DNA. Apoptosis of serum-deprived luteal cells was dependent upon caspase activation. Serum starvation induced cleavage of poly (ADP-ribose) polymerase (PARP), suggesting that caspase-3 had been activated under the stress of withdrawal of growth factors. This was confirmed by cleavage of full-length procaspase-3. Finally, the fact that serum starvation promoted the cleavage of full-length procaspase-9 and the decrease in the expression of endogenous Bid, a BH-3-only proapoptotic protein of the Bcl-2 family, indicates that the intrinsic (i.e., mitochondrial) pathway of apoptosis was activated. In summary, we have characterized an in vitro experimental model of luteal cell death that can be utilized to evaluate the role of hormones in apoptosis of luteal cells under defined culture conditions, and to study the mechanism of luteal regression.

Exogenous estradiol enhances apoptosis in regressing post-partum rat corpora lutea possibly mediated by prolactin

BACKGROUND

In pregnant rats, structural luteal regression takes place after parturition and is associated with cell death by apoptosis. We have recently shown that the hormonal environment is responsible for the fate of the corpora lutea (CL). Changing the levels of circulating hormones in post-partum rats, either by injecting androgen, progesterone, or by allowing dams to suckle, was coupled with a delay in the onset of apoptosis in the CL. The objectives of the present investigation were: i) to examine the effect of exogenous estradiol on apoptosis of the rat CL during post-partum luteal regression; and ii) to evaluate the post-partum luteal expression of the estrogen receptor (ER) genes.

METHODS

In a first experiment, rats after parturition were separated from their pups and injected daily with vehicle or estradiol benzoate for 4 days. On day 4 post-partum, animals were sacrificed, blood samples were taken to determine serum concentrations of hormones, and the ovaries were isolated to study apoptosis in situ. In a second experiment, non-lactating rats after parturition received vehicle, estradiol benzoate or estradiol benzoate plus bromoergocryptine for 4 days, and their CL were isolated and used to study apoptosis ex vivo. In a third experiment, we obtained CL from rats on day 15 of pregnancy and from non-lactating rats on day 4 post-partum, and studied the expression of the messenger RNAs (mRNAs) encoding the ERalpha and ERbeta genes.

RESULTS

Exogenous administration of estradiol benzoate induced an increase in the number of apoptotic cells within the CL on day 4 post-partum when compared with animals receiving vehicle alone. Animals treated with the estrogen had higher serum prolactin and progesterone concentrations, with no changes in serum androstenedione. Administration of bromoergocryptine blocked the increase in serum prolactin and progesterone concentrations, and DNA fragmentation induced by the estrogen treatment. ERalpha and ERbeta mRNAs were expressed in CL of day 4 post-partum animals at levels similar to those found in CL of day 15 pregnant animals.

CONCLUSION

We have established that estradiol accelerates apoptosis in the CL during post-partum luteal regression through a mechanism that possibly involves the secretion of pituitary prolactin. We have also shown that the post-partum rat CL express ERalpha and ERbeta mRNAs suggesting that they can be targeted by estrogen.

Regulation mechanism of selective atresia in porcine follicles: regulation of granulosa cell apoptosis during atresia

More than 99% of follicles undergo a degenerative process known as "atresia", in mammalian ovaries, and only a few follicles ovulate during ovarian follicular development. We have investigated the molecular mechanism of selective follicular atresia in mammalian ovaries, and have reported that follicular selection dominantly depends on granulosa cell apoptosis. However, we have little knowledge of the molecular mechanisms that control apoptotic cell death in granulosa cells during follicle selection. To date, at least five cell death ligand-receptor systems [tumor necrosis factor (TNF)alpha and receptors, Fas (also called APO-1/CD95) ligand and receptors, TNF-related apoptosis-inducing ligand (TRAIL; also called APO-2) and receptors, APO-3 ligand and receptors, and PFG-5 ligand and receptors] have been reported in granulosa cells of porcine ovaries. Some cell death ligand-receptor systems have "decoy" receptors, which act as inhibitors of cell death ligand-induced apoptosis in granulosa cells. Moreover, we showed that the porcine granulosa cell is a type II apoptotic cell, which has the mitochondrion-dependent apoptosis-signaling pathway. Briefly, the cell death receptor-mediated apoptosis signaling pathway in granulosa cells has been suggested to be as follows. (1) A cell death ligand binds to the extracellular domain of a cell death receptor, which contains an intracellular death domain (DD). (2) The intracellular DD of the cell death receptor interacts with the DD of the adaptor protein (Fas-associated death domain: FADD) through a homophilic DD interaction. (3) FADD activates an initiator caspase (procaspase-8; also called FLICE), which is a bipartite molecule, containing an N-terminal death effector domain (DED) and a C-terminal DD. (4) Procaspase-8 begins auto-proteolytic cleavage and activation. (5) The auto-activated caspase-8 cleaves Bid protein. (6) The truncated Bid releases cytochrome c from mitochondrion. (7) Cytochrome c and ATP-dependent oligimerization of apoptotic protease-activating factor-1 (Apaf-1) allows recruitment of procaspase-9 into the apoptosome complex. Activation of procaspase-9 is mediated by means of a conformational change. (8) The activated caspase-9 cleaves downstream effector caspases (caspase-3). (9) Finally, apoptosis is induced. Recently, we found two intracellular inhibitor proteins [cellular FLICE-like inhibitory protein short form (cFLIPS) and long form (cFLIPL)], which were strongly expressed in granulosa cells, and they may act as anti-apoptotic/survival factors. Further in vivo and in vitro studies will elucidate the largely unknown molecular mechanisms, e. g. which cell death ligand-receptor system is the dominant factor controlling the granulosa cell apoptosis of selective follicular atresia in mammalian ovaries. If we could elucidate the molecular mechanism of granulosa cell apoptosis (follicular selection), we could accurately diagnose the healthy ovulating follicles and precisely evaluate the oocyte quality. We hope that the mechanism will be clarified and lead to an integrated understanding of the regulation mechanism.

Effects of prolactin level on burn-induced aberrations in myelopoiesis

In this study, we sought to determine if prolactin (PRL) had any influence on burn-induced alterations in myelopoiesis and serum IL-6, IL-10, IL-12, IFN-gamma, TNF-alpha, and MCP-1 levels. To do this, we used mice that were PRL normal, PRL deficient, or hyperprolactinemic and had received a 15% total body surface area burn, sham treatment, or no treatment. We performed clonogenic assays of bone marrow cells, and we found that sham treatment significantly decreased monocyte/macrophage (M) colony formation relative to the control group in the PRL-deficient and PRL-normal mice (P < 0.01). Hyperprolactinemia attenuated the sham-induced decrease in M colony formation. Burn injury significantly increased M colony formation relative to the sham group with an equal significance in the PRL-deficient and PRL-normal mice (P < 0.05). We also showed that burn led to a significant increase in GM colony formation relative to the sham group. This burn-induced increase was significant in the PRL-normal (P < 0.05) and the PRL-deficient (P < 0.01) mice. In the PRL-normal mice, burn injury caused a 2.1-fold increase in the GM colony number, whereas in the PRL-deficient mice burn led to a 2.6-fold increase in GM colony number. When comparing the effects of burn injury on colony formation to the control groups, there were no significant differences seen, irrespective of the PRL level. We observed that all of the cytokines studied, with the exception of IL-10, were influenced by either sham treatment, burn injury, or both forms of stress. This stress-induced response occurred most often in animals that were either hypo- or hyperprolactinemic. We conclude that the PRL level was able to influence the sham-induced and burn-induced alterations in GM and M colony formation. Under euprolactinemic conditions, mice exhibited less often with stress-induced serum cytokine level alterations. We did not find any significant correlations with any of the serum cytokine levels and the ability to form colonies. Importantly, the sham treatment led to immune alterations independent of, and sometimes opposite of burn-induced effects.

Concomitant induction of apoptosis and expression of monocyte chemoattractant protein-1 in cultured rat luteal cells by nuclear factor-kappaB and oxidative stress

It has previously been shown that expression of monocyte chemoattractant protein (mcp)-1 and apoptosis of luteal cells occur concomitantly during the estrous cycle in the rat corpus luteum; however, luteal cells containing mcp-1 mRNA did not seem to be apoptotic. In the present study, the relationship between the induction of apoptosis and mcp-1 expression in cultures of dispersed rat luteal cells was examined. Both apoptosis and mcp-1 expression were spontaneously induced in cultured luteal cells in a manner inhibitable by antioxidative reagents or an inhibitor of nuclear translocation of nuclear factor-kB. However, the cells containing mcp-1 mRNA were distinct from those undergoing apoptosis, and the inhibition of apoptosis by the pan-caspase inhibitor z-VAD-fmk did not influence the induction of mcp-1 expression. These results collectively indicate that oxidative stress simultaneously, but independently, induces apoptosis and mcp-1 expression in luteal cells through the activation of nuclear factor-kB. This phenomenon might help to explain how monocytes/macrophages accumulate in regressive corpora lutea where their target apoptotic cells exist.

Expression pattern and functional studies of matrix degrading proteases and their inhibitors in the mouse corpus luteum

The formation of the corpus luteum (CL) is accompanied with angiogenesis and tissue remodeling and its regression involves tissue degradation. Matrix degrading proteases such as plasminogen activators (PAs) and matrix metalloproteinases (MMPs) are thought to play important roles in such controlled proteolytic processes. In this study, in situ hybridization has been used to examine the regulation and expression pattern of mRNAs coding for proteases and protease inhibitors belonging to the PA- and MMP-systems during the life cycle of the CL in an adult pseudopregnant mouse model. Of the nine proteases and five protease inhibitors that were studied, the majority were found to be temporally expressed during the formation and/or the regression of the CL. However, the mRNAs coding for urokinase type PA (uPA), membrane-type 1 MMP (MT1-MMP), and tissue inhibitor of metalloproteinases type-3 (TIMP-3) were constantly expressed in the mouse CL throughout its whole life span. To study the functional role of uPA in the CL, we analyzed luteal formation and function in uPA deficient mice. Our results revealed no significant difference in ovarian weight, serum progesterone levels, and blood vessel density in the functional CL between uPA deficient and wild type control mice. The temporal and spatial expression pattern of proteases and protease inhibitors during the CL life span suggests that members of the PA- and MMP-systems may play important roles in the angiogenesis and tissue remodeling processes during CL formation, as well as in the tissue degradation during luteal regression. However, the absence of reproductive phenotypes in mice lacking uPA and several other matrix degrading proteases indicates that there are redundancies among different matrix degrading proteases or that tissue remodeling in the ovary may involve other additional unique elements.

In vivo hormonal environment leads to differential susceptibility of the corpus luteum to apoptosis in vitro

We evaluated the involvement of the in vivo hormonal environment on the ability of the rat corpus luteum (CL) to undergo apoptosis. Gel electrophoretic DNA fragmentation analysis revealed no apoptosis in CL isolated either the 2 last days of pregnancy (Days 21 and 22) or throughout the 4 days following parturition, suggesting that the number of cells undergoing apoptosis at the same time is not sufficient to allow for visualization of DNA breakdown. In contrast, CL incubated in serum-free medium underwent significant apoptosis, as evaluated by chromatin condensation and DNA fragmentation, regardless of their developmental stage in pregnancy. However, CL obtained on Day 7 of pregnancy and on Day 4 postpartum demonstrated higher sensitivity to apoptosis in vitro, but lactation reduced significantly the capacity of the CL to undergo apoptosis when maintained in culture. These data suggest that the exposure of the CL to different hormonal environments throughout pregnancy and after parturition is responsible for the differential susceptibility to apoptosis observed in vitro. We have previously shown that progesterone is a direct factor for survival of the CL. Prolactin stimulates luteal progesterone production; therefore, we examined whether prolactin prevents apoptosis in luteal cells independently of its stimulatory action on progesterone production. We used a luteal cell line (GG-CL) that expresses the prolactin receptor but does not produce progesterone. These cells undergo apoptosis under conditions of serum starvation, and addition of prolactin to the culture medium significantly reduced DNA fragmentation. These results indicate that the extent of luteal cell death induced by incubation of CL under serum-free conditions depends on the hormonal environment to which this endocrine gland is exposed in vivo. These results also indicate an important role for lactation in preventing apoptosis, which is further supported by the antiapoptotic activity of prolactin observed in luteal cells.

Role of tumor necrosis factor-alpha and the modulating effect of the caspases in rat corpus luteum apoptosis

Tumor necrosis factor-alpha (TNFalpha) is a pleiotropic cytokine that has been implicated in apoptosis of many cell systems. However, the signal transduction of TNFalpha during the structural and functional regression of the corpus luteum (CL) is largely unknown. In this study, we investigate the role of TNFalpha in rat CL apoptosis and the involvement of monocyte chemoattractant protein-1 (MCP-1) and the modulating effect of the caspases in this process. An in vivo study of CL during pregnancy and postpartum using immunohistochemistry and Western blot analysis indicated that increases in TNFalpha correspond with luteal apoptosis approaching term (Day 22) and at postpartum (Day 3). CL apoptosis was further investigated using a whole-CL culture model of tropic withdrawal. An increase was observed in both low molecular weight (MW) DNA fragmentation and TUNEL staining from 0 h to 8 h in culture. CL apoptosis in vitro was associated with increased protein expression of both TNFalpha and MCP-1 as measured by immunohistochemistry and Western blot analysis. Using a whole-CL culture model, apoptosis was induced in vitro by TNFalpha as demonstrated by a dose-dependent increase in DNA fragmentation. Treatment of luteal cells with TNFalpha and both specific caspase inhibitors (Z-DEVD-FMK, Z-VEID-FMK, Z-IETD-FMK) or a general caspase inhibitor (Boc-D-FMK) prevented the effect of TNFalpha. CL regression involves the apoptotic deletion of luteal cells; the results of this study suggest that TNFalpha is possibly involved in this process. The observed increases in MCP-1 expression suggest the coordination of TNFalpha expression with the infiltration and activation of macrophages. Furthermore, the results demonstrate the importance of the caspases in the TNFalpha signal transduction pathway and suggest a hierarchy within the caspase family.

Progesterone promotes survival of the rat corpus luteum in the absence of cognate receptors

Progesterone production by the corpus luteum (CL) is essential for preparation of the endometrium for implantation and for the maintenance of gestation. Progesterone modulates its own production and opposes functional luteal regression induced by exogenous agents, such as prostaglandin F(2alpha). In the present study, we evaluated whether progesterone is also capable of interfering with the process of structural luteal regression, which is characterized by a decrease in weight and size of the gland because of programmed cell death (i.e., apoptosis). We have found that a low number of luteal cells undergo apoptosis throughout gestation. On the day of parturition, but following the initial decline in endogenous progesterone production, a small increase in the number of luteal cells undergoing cell death was observed. This increase in apoptotic cells continued postpartum, reaching dramatic levels by Day 4 postpartum, and was accompanied by a marked decrease in average luteal weight. We have established that the exogenous administration of progesterone significantly reduces the decline in luteal weight observed during structural luteal regression postpartum. This effect was associated with a decrease in the number of cells undergoing apoptosis and with enhanced circulating levels of androstenedione. Furthermore, in vivo administration of progesterone delayed the occurrence of DNA fragmentation in postpartum CL incubated in serum-free conditions. Finally, we have shown that neither the CL of gestation nor the newly formed CL after postpartum ovulation express the classic progesterone-receptor mRNA. In summary, the present results support a protective action of progesterone on the function and survival of the CL through inhibition of apoptosis and stimulation of androstenedione production. Furthermore, this effect is carried out in the absence of classic progesterone receptors.

Interleukin-1beta in the functional and structural luteolysis. Relationship with the nitric oxide system

The aim of the present report was to investigate the in vitro effect of interleukin-1beta(IL-1beta) on corpus luteum (CL) function and some aspects of this mechanism involved. Ovarian rat dispersates from mid-luteal phase were exposed to different doses of IL-1beta (1, 10, 20 ng/ml). Meanwhile 1, 10 and 20 ng/ml of IL-1beta decreased progesterone (P4) production, only the highest doses of IL-1beta increased prostaglandin F2alpha (PGF2alpha) levels. To investigate the possible relationship between PGs production and P4 synthesis, we incubated together IL-1beta (20 ng/ml) and indomethacin (0.1 mM) a potent inhibitor of cyclooxygenase pathway. We found that P4 inhibition induced by IL-1beta was completely prevented by addition of indomethacin. On the other hand, when ovarian rat tissue were exposed at 20 ng/ml of IL-1beta (doses that affected both PGF2alpha and P4 production) the nitric oxide synthase (NOS) activity was augmented. Moreover, IL-1beta effects on PGF2alpha and P4 levels were impaired when a NOS inhibitor N(W)-nitro- L -arginine methyl ester (L-NAME, 600 microM) was added to the incubation media. These data demonstrate that: (i) at the tested doses (1-20 ng/ml), IL-1beta is involved in CL function through the diminution of P4 production of whole ovarian dispersate culture; (ii) at the highest doses assayed (20 ng/ml) IL-1beta increased PGF2alpha production; (iii) at these doses, IL-1beta decreased P4 production by means of a cyclooxygenase pathway and (iv) the NO system would be a key intermediary second messenger in the IL-1beta actions.

Determination of cell type specificity and estrous cycle dependency of monocyte chemoattractant protein-1 expression in corpora lutea of normally cycling rats in relation to apoptosis and monocyte/macrophage accumulation

In regressive corpora lutea, apoptosis of luteal cells, expression of monocyte chemoattractant protein-1 (MCP-1), and accumulation of monocytes/macrophages occur. However, whether these three events are correlated and what cell type expresses MCP-1 have yet to be determined. To clarify these issues, we performed histochemical examinations to determine the localization and the numbers of MCP-1 mRNA-containing cells, apoptotic cells, and monocytes/macrophages in corpora lutea of normally cycling rats. We found that the Mcp-1 gene is expressed in nonapoptotic steroidogenic luteal cells. Corpora lutea that contained MCP-1 mRNA-expressing cells increased in number at estrus together with those containing apoptotic luteal cells. When individual corpora lutea at estrus were analyzed, those with many MCP-1-expressing cells contained few apoptotic cells, and vice versa. These results collectively suggest the following pathway for apoptosis- and MCP-1-dependent regression of the corpus luteum: 1) luteal cells are induced to undergo apoptosis at estrus, and the activation of Mcp-1 gene expression follows in nonapoptotic luteal cells; 2) monocytes/macrophages are chemoattracted by MCP-1 toward corpora lutea containing apoptotic luteal cells; and 3) monocytes/macrophages invade corpora lutea and eliminate apoptotic luteal cells by phagocytosis.

Androstenedione interferes in luteal regression by inhibiting apoptosis and stimulating progesterone production

Androgens, in concert with lactogenic hormones, contribute to the maintenance of function of the corpus luteum (CL) in pregnant rats. Whereas some of the androgenic actions in the CL are clearly mediated by intracrine conversion to estrogen, pure androgenic effects are also implicated in the regulation of this transient endocrine gland. In this report, we have established, to our knowledge for the first time, the expression of androgen receptor (AR) mRNA and protein throughout gestation in the rat CL. We have found that the AR remains expressed in the CL of gestation on Day 4 postpartum and becomes expressed in the newly formed CL after postpartum ovulation. An AR immunoreactive protein was identified in the CL of pregnancy as well as in prostate and epididymis, which were used as positive controls. The luteal AR protein had mainly nuclear localization, yet some diffuse cytoplasmic staining was also observed. Moreover, we have established that androstenedione, the main circulating androgen in pregnant rats, significantly reduces the decline in luteal weight observed during postpartum structural regression. This effect was correlated with a decrease in the number of cells undergoing apoptosis and with enhanced levels of circulating progesterone. In addition, in vivo administration of androstenedione delayed the occurrence of DNA fragmentation in postpartum CL incubated in serum-free conditions. Finally, we have shown that the interference with apoptosis in vitro elicited by androstenedione is accompanied by an increased capacity of the CL to secrete progesterone. In summary, the results of this study have established that the rat CL expresses AR throughout pregnancy and after parturition, and they have defined a potential role for androstenedione in opposing postpartum luteal regression through inhibition of apoptosis and stimulation of progesterone production.

Prolactin, a lymphocyte growth and survival factor

Evidence accumulated over the past 20 y indicates that the anterior pituitary hormone, prolactin (PRL), is a critical, physiologically relevant immunomodulator. Results from early hormone-ablation studies in animals implicated PRL as a factor that contributes to maintenance of immunocompetence. However, the discovery of PRL receptors on T and B lymphocytes and the observation that these cells synthesize and secrete PRL spurred intensive investigation into the actions and underlying mechanisms triggered by the hormone in the immune system. In numerous cell culture systems, PRL was found to act as a co-mitogen, enhancing the efficacy of plant lectins and cytokines in the stimulation of lymphocyte proliferation. In addition, results from more recent studies suggest that PRL may promote survival of certain lymphocyte subsets presumably due to its capacity to augment expression of anti-apoptotic genes. In this review, we focus on the proliferative actions of PRL and its survival promoting properties in immune cells.

Expression, hormonal regulation, and cyclic variation of chemokines in the rat ovary: key determinants of the intraovarian residence of representatives of the white blood cell series

A growing body of evidence suggests that mammalian ovulation bears similarities to local inflammatory reactions. Monocytes/macrophages, eosinophils, and neutrophils are known to infiltrate the area surrounding the dominant follicle before ovulation. Candidate local chemoattractants may include a family of small cytokines, also known as chemokines. In the present study, quantitative RT-PCR was used to initially identify and quantify the chemokines expressed in the preovulatory rat ovary. The chemokines monocyte chemotatic protein 1 (MCP-1), MCP-3, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, MIP-1gamma, regulated upon activation normal T cell expressed and secreted, eotaxin, interferon-inducible protein of 10 kDa, growth-regulated oncogene, lymphotactin, and fractalkine were all expressed in the PMSG-primed rat ovary 6 h post human CG. C10, T cell activation gene 3, exodus, exodus-2, cytokine-induced neutrophil chemoattractant-2, MIP-2, and lipopolysaccharide-induced C-X-C were not expressed in the PMSG-primed rat ovary 6 h post human CG. The cyclic variation of the ovary-positive chemokines was also evaluated throughout the course of a superovulated ovarian cycle. Significant preovulatory up-regulation relative to the untreated control state was documented for MCP-1 (18-fold), MCP-3 (12-fold), and growth-regulated oncogene (25-fold). In contrast, the preovulatory ovarian expression of eotaxin, fractalkine and regulated upon activation normal T cell expressed and secreted was not increased. These observations suggest that intraovarian chemokines may be responsible for the cyclic intraovarian residence of representatives of the white blood cell series.

Matrix remodeling in the ovary: regulation and functional role of the plasminogen activator and matrix metalloproteinase systems

In each reproductive cycle, extensive tissue remodeling takes place in the ovary during follicular development, ovulation, formation and regression of corpus luteum (CL) and follicular atresia. Several lines of indirect evidence suggest that these changes are mediated, in part, by proteases belonging to the plasminogen activator (PA) and the matrix metalloproteinase (MMP) systems. These two enzyme systems include both proteinases and associated inhibitors, that are thought to act in concert via a cascade of proteolytic events, the end result of which is the generation of a broad spectrum proteolytic activity, that can mediate physiological tissue remodeling throughout the body. The current review highlights the key features of these two enzyme systems and focuses on their regulation and functional role during the dynamic remodeling processes that takes place in the ovary during each reproductive cycle.

Expression of monocyte chemoattractant protein-1 and distribution of immune cell populations in the bovine corpus luteum throughout the estrous cycle

This study characterizes the expression of monocyte chemoattractant protein-1 (MCP-1) and the relative distribution of immune cell populations in the bovine corpus luteum throughout the estrous cycle. Immunodetectable MCP-1 was evident in corpora lutea of cows at Days 6, 12, and 18 postovulation (Day 0 = ovulation, n = 4 cows/stage). Day 6 corpora lutea contained minimal MCP-1 that was confined primarily to blood vessels. In contrast, relatively intense staining for MCP-1 was observed in corpora lutea from Days 12 and 18 postovulation. MCP-1 was again most evident in the cells of the vasculature, but it was also observed surrounding individual luteal cells, particularly by Day 18. An increase in immunohistochemical expression of MCP-1 on Days 12 and 18 postovulation corresponded with increases in MCP-1 mRNA and protein in corpora lutea as determined by Northern blot analysis and ELISA. Monocytes and macrophages were the most abundant immune cells detected in the bovine corpus luteum, followed by CD8+ and CD4+ T lymphocytes. In all instances, Day 6 corpora lutea contained fewer immune cells than corpora lutea from Days 12 and 18. In conclusion, increased expression of MCP-1 was accompanied by the accumulation of immune cells in the corpora lutea of cows during the latter half of the estrous cycle (Days 12-18 postovulation). These results support the hypothesis that MCP-1 promotes immune cell recruitment into the corpus luteum to facilitate luteal regression. These results also raise a provocative issue, however, concerning the recruitment of immune cells several days in advance of the onset of luteal regression.

Luteolytic effect of prolactin is dependent on the degree of differentiation of luteal cells in the rat

We studied the morphological and quantitative changes in cyclic corpora lutea (CCL) and in CL of pregnancy (CLP) during structural luteolysis. Elimination of CCL takes several cycles, and cell death occurs as successive apoptotic bursts, from 2100 h in proestrus to 1300 h in estrus. Each apoptotic burst determined a 60% decrease in the CL volume and an 80% decrease in the number of steroidogenic cells (SC). All these changes were inhibited by blocking the preovulatory prolactin (PRL) surge with bromocryptine (CB154). Neither apoptotic cells nor changes in the number of SC were found in regressing CLP from Day 21 of pregnancy to Day 2 postpartum, although there was a 50% decrease in the CLP volume and a 30% decrease in the mean cross-sectional area of SC. Treatment with CB154 on the day of parturition did not modify these regressive changes. On Day 5 postpartum, the volume of the CLP and the number of SC were equivalent in lactating rats (showing high PRL concentrations induced by pup suckling) and nonlactating noncycling rats (in which cyclicity and, therefore PRL surges, were blocked by treatment with LHRH antagonist). However, on Day 10 postpartum, the CLP volume and the number of SC were significantly decreased in lactating rats, and apoptotic cells were frequent. In postpartum cycling rats, the CLP did not show apoptotic cells on the day of the second postpartum estrus (on Day 5 postpartum), whereas on the day of the third postpartum estrus (on Day 9 postpartum), apoptotic cells were abundant. These results indicate that PRL does not induce apoptosis in the CLP before Day 5 postpartum and strongly suggest that the proapoptotic effect of PRL is dependent on the degree of differentiation of luteal cells.

Prolactin and lipopolysaccharide treatment increased apoptosis and atresia in rat ovarian follicles

Follicular atresia is associated with the presence of increased macrophages within the follicle. What is not known is whether, in the adult rat, macrophages are instrumental in inducing apoptosis and/or atresia or whether they are simply secondary to a hormonally mediated event. As prolactin is an immunoreactive hormone and stimulates the expression of monocyte chemoattractant, the present experiments compared the effects of prolactin treatment with that of an immune challenge with lipopolysaccharide (LPS) on the invasion of macrophages into the follicular and luteal compartments of the ovary and the occurrence of apoptosis/atresia in relation to macrophage invasion. Rats were treated for 3 days with either prolactin or LPS and ovaries obtained at pro-oestrus or oestrus. Prolactin and LPS increased the number of atretic vs. healthy follicles (P < 0.008, chi2) in pro-oestrus ovaries and increased the mean number of apoptotic cells and macrophages (P < 0.05 for some groups). Macrophages were typically observed in the thecal layer, apoptotic cells in the granulosa cell layer, although 84% follicles which had macrophages within the granulosa cell layer also contained relatively high numbers of apoptotic nuclei. Prolactin and LPS treatment in vivo reduced the progesterone response to follicle stimulating hormone (FSH) (P < 0.001) in cultures of ovarian dispersates but did not inhibit the response to forskolin. In contrast, prolactin or LPS added in vitro to the cultures inhibited the progesterone response to forskolin. Results show that both prolactin and LPS increase follicular apoptosis and atresia and reduce the progesterone response to FSH.

Spatiotemporal messenger ribonucleic acid expression of ovarian tissue inhibitors of metalloproteinases throughout the rat estrous cycle

The tissue inhibitors of metalloproteinases (TIMPs) within the ovary closely regulate the matrix metalloproteinases, enzymes capable of degrading components of the extracellular matrix. The purpose of this study was to examine the spatial and temporal messenger RNA (mRNA) expression of the TIMPs in the ovaries of normally cycling rats. Ovaries were collected at 1100 h on each day of the 4-day estrous cycle, and TIMP mRNA expression was examined by Northern blot, RT-PCR, or in situ hybridization. TIMP-1 mRNA levels were significantly higher on estrus than on any other day. Although the 1.0-kb TIMP-2 transcript did not change across the cycle, the 3.5-kb transcript decreased significantly between metestrus and diestrus. Expression of TIMP-3 mRNA decreased significantly between proestrus and estrus. TIMP-1, TIMP-2, and TIMP-3 mRNAs were primarily localized to the theca, stroma, and corpora lutea (CL) on all days of the cycle, but with distinct cyclic changes. Thecal expression of TIMP-1 and TIMP-2 mRNAs was especially high immediately before and after ovulation. TIMP-1 and TIMP-3 mRNAs, which were low to undetectable in the granulosa cells of preovulatory follicles, were greatly increased in the luteinizing cells of newly forming CL on estrus. Although the presence of TIMP-1 mRNA in the granulosa cells of preovulatory follicles by in situ hybridization was near background levels, it was specifically identified in granulosa cells of follicles on all days of the cycle using laser capture microdissection and RT-PCR. Both TIMP-2 and TIMP-3 transcripts were up-regulated in luteinized follicles on proestrus and were present throughout the cycle in regressing CL. In summary, the unique and dynamic expression patterns of the TIMPs suggest that they have important, yet distinct, functions in the ovary. The high levels of TIMP-1 mRNA in the CL on estrus indicate a likely role for this inhibitor in luteal formation. The presence of TIMP-2 mRNA in regressing CL suggests an involvement in luteal demise, whereas TIMP-3 may play a role in the health of the follicle as well as in CL regression.

Monocyte chemotactic protein-1 and -2 messenger ribonucleic acids in the ovine uterus: regulation by pregnancy, progesterone, and interferon-tau

Endometrial leukocytes may play important roles during pregnancy. Because chemokines are regulators of immune cell activity and trafficking, this study determined if mRNAs for monocyte chemotactic proteins (MCP) were present in the ovine uterus and regulated by progesterone (P) and/or recombinant ovine interferon tau (roIFN-tau). Uteri of normal cycling and pregnant ewes (experiment 1) and uteri of ovariectomized ewes receiving intrauterine infusions of IFN-tau and/or i.m. injections of P (experiment 2) were used to detect MCP-1 and MCP-2 mRNA. In experiment 1, slot-blot hybridization analysis of endometrial total RNA revealed that MCP-1 and MCP-2 mRNA levels did not change during the estrous cycle but increased between Days 13 and 19 of pregnancy. Using in situ hybridization, MCP-1 and MCP-2 mRNA were localized to immune cells in the subepithelial compact stroma. Histomorphological studies and in situ hybridization for major basic protein (MBP) indicated that MCP-positive immune cells were eosinophils. In experiment 2, treatment with P and roIFN-tau increased (P < 0.05) the number of MCP-1- and MCP-2-expressing eosinophils in the endometrium compared to ewes treated with P alone. Injection of the P receptor antagonist (ZK 137,316) inhibited effects of P and/or roIFN-tau to recruit eosinophils expressing MCP-1 and MCP-2 mRNAs. Endometrial production of MCPs by eosinophils during early pregnancy may play a role(s) in central implantation and/or placentation in ewes that is crucial for successful establishment of pregnancy.

Actions of prostaglandin F2alpha and prolactin on intercellular adhesion molecule-1 expression and monocyte/macrophage accumulation in the rat corpus luteum

Expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of monocytes/macrophages are inflammatory events that occur during PRL (PRL)-induced regression of the rat corpus luteum. Here we have compared the ability of prostaglandin F2alpha (PGF) and PRL to induce, in rat corpora lutea, inflammatory events thought to perpetuate luteal regression. Immature rats were ovulated with eCG-hCG and then hypophysectomized (Day 0), which resulted in a single cohort of persistent, functional corpora lutea. On Days 9-11, the rats received twice daily injections of saline, PGF (Lutalyse, 250 microg/injection), or PRL (312 microg/injection) to induce luteal regression. Surprisingly, luteal weight and plasma progestin concentrations (progesterone and 20alpha-dihydroprogesterone) did not differ between PGF-treated rats and controls; whereas both luteal weight and plasma progestins declined significantly in PRL-treated rats. Furthermore, corpora lutea of PGF-treated rats and controls contained relatively minimal ICAM-1 staining and few monocytes/macrophages. In contrast, but as expected, corpora lutea of PRL-treated rats stained intensely for ICAM-1 and contained numerous monocytes/macrophages. In an additional experiment, there was no indication that luteal prostaglandin F2alpha receptor mRNA diminished as a result of hypophysectomy. These findings suggest that prolactin, not PGF, induces the inflammatory events that accompany regression of the rat corpus luteum.

Repeated exposure to prolactin is required to induce luteal regression in the hypophysectomized rat

We investigated whether prolactin (PRL) treatments resembling the intermittent PRL surges of estrous cycles could induce luteal regression in hypophysectomized rats. Immature female rats were stimulated to ovulate and form corpora lutea with exogenous gonadotropins, and were hypophysectomized following ovulation. A single s.c. injection of either vehicle (VEH) or PRL was administered to each rat on post-hypophysectomy Day 8 and again on Day 11. The four resulting treatment groups consisted of rats that received two injections of VEH, VEH followed by PRL, PRL followed by VEH, or two injections of PRL. Rats were killed 24 or 72 h following the second injection. Plasma 20alpha-dihydroprogesterone, luteal weight, and total luteal protein were determined. One ovary was sectioned for immunohistochemistry for monocytes/macrophages, apoptotic nuclei, and major histocompatibility class II (MHC II) molecules. No effect of time (following injection) was observed on any endpoint, indicating that PRL does not have an ongoing regressive action. Time groups from within each treatment group were therefore pooled for analysis. Significant declines (P: < 0.05) in plasma concentrations of 20alpha-dihydroprogesterone, luteal weight, and protein per corpus luteum occurred only after two injections of PRL. Numbers of luteal monocytes/macrophages, apoptotic nuclei, and MHC II-positive cells were low in all groups; numbers of luteal monocytes/macrophages increased following two injections of PRL (P: < 0.05). We conclude that PRL has a cumulative regressive effect on the corpus luteum of the hypophysectomized rat. Drawing a parallel with the estrous cycle, we suggest that continued exposure to PRL, over several cycles, is necessary to induce full luteal regression.

Prolactin-induced expression of intercellular adhesion molecule-1 and the accumulation of monocytes/macrophages during regression of the rat corpus luteum

Intercellular adhesion molecule-1 (ICAM-1) is thought to facilitate the recruitment and migration of monocytes/macrophages to sites of inflammation. Here we investigated whether the luteolytic effect of prolactin in the hypophysectomized rat is associated with the expression of ICAM-1. In addition, we examined the effect of exogenous testosterone (or its potential conversion to estradiol endogenously) on the corpus luteum to address recent speculation that ovarian steroids might augment luteal regression. Immature, 30-day-old rats were ovulated with eCG and hCG and then hypophysectomized; this resulted in a single cohort of persistent corpora lutea. The rats were assigned randomly into four treatment groups: vehicle treatment without or with testosterone (VEH-T4, VEH+T4) and prolactin treatment without or with testosterone (PRL-T4, PRL+T4). Corpora lutea of control rats exhibited minimal ICAM-1 staining and contained relatively few monocytes/macrophages. In contrast, corpora lutea of prolactin-treated rats exhibited prominent ICAM-1 staining and contained numerous monocytes/macrophages. Testosterone did not overtly affect ICAM-1 staining, numbers of monocytes/macrophages, or concentrations of plasma progestins (progesterone and 20alpha-dihydroprogesterone) in either VEH or prolactin treatment groups; notwithstanding, luteal weights increased significantly in response to testosterone in VEH+T4 rats compared to VEH-T4 rats and prolactin-treated rats. We conclude that ICAM-1 expression and monocyte/macrophage accumulation are associated with prolactin-induced luteal regression in the rat and that these aspects are not influenced by testosterone.

Molecular analysis of the inhibition of monocyte chemoattractant protein-1 gene expression by estrogens and xenoestrogens in MCF-7 cells

Xenoestrogens (XEs) are a diverse group of chemicals that mimic estrogenic actions and may have adverse effects on human health. The influence of these compounds on cytokine production or immune system function remains unclear. In this study we have examined the effects of 17beta-estradiol (E2) and XEs on chemoattractant cytokine (chemokine) production and analyzed the molecular mechanism. Monocyte chemoattractant protein-1 (MCP-1), also termed monocyte chemotactic and activating factor, is a member of the chemokine family and attracts mainly blood monocytes. Human mammary tumor cell line MCF-7 cells produce a large quantity of MCP-1 in response to interleukin-1alpha (IL-1alpha). Addition of E2 to MCF-7 cells inhibited MCP-1 production in a dose-dependent manner. XEs, bisphenol A, and NP also inhibited MCP-1 production, although the potency was 3-4 orders of magnitude lower than that of E2. E2, bisphenol A, and NP inhibited MCP-1 messenger RNA expression in MCF-7 cells. Two closely located nuclear factor-kappaB sites, A1 and A2, have been identified in the promoter of the human MCP-1 gene. A luciferase construct containing this enhancer region (pGLM-ENH) was activated by IL-1alpha, and a mutation at either the A1 or A2 site resulted in a loss of IL-1alpha responsiveness. Treatment with E2 or XEs decreased the IL-1alpha-inducible pGLM-ENH luciferase activity significantly. In an electrophoretic mobility shift assay and supershift analysis, we found that treatment with E2 or XEs diminished the IL-1alpha-induced complex formation with both A1 and A2 probes, which was identified immunochemically to consist of nuclear factor-kappaB, p50, and p65. The IL-1alpha-induced p50/c-Rel complex to the A2 probe was also, to a lesser extent, decreased by E2 or XE treatment. The effects of E2 and XEs on the expression of MCP-1 seem to be much more dramatic than the effects of these agents on the promoters used in the luciferase assay, suggesting the involvement of an additional site(s) of the promoter region of the MCP-1 gene or posttranscriptional regulation of MCP-1 gene expression by E2 and XEs. This work represents the first report describing possible regulation of immune system function by XEs through inhibiting chemokine production.

The proestrous prolactin surge is not the sole initiator of regressive changes in corpora lutea of normally cycling rats

During the estrous cycle, secretion of prolactin is largely restricted to a surge on proestrus. We investigated whether this proestrous prolactin surge initiates regression of the corpora lutea of the preceding cycle. Adult rats were killed prior to the prolactin surge (Proestrus group), following the prolactin surge (Estrus group), after chemical blockade of the prolactin surge with bromocryptine (Estrus+BRC group), and after blockade of the prolactin surge and administration of prolactin (Estrus+BRC+PRL group). Corpora lutea of the current (proestrus) or preceding (estrus) cycle were dissected out, weighed, and sectioned for immunohistochemistry or cultured for examination of in vitro progestin production. Numbers of luteal monocytes/macrophages, differentiated macrophages, and apoptotic nuclei per high-power field were greater for Estrus and Estrus+BRC+PRL than for Estrus+BRC, which in turn had greater numbers than Proestrus (P< 0.05). In contrast, BRC completely reversed the decline in luteal weight observed between Proestrus and Estrus (P<0.05). Number of major histocompatibility complex II-positive cells was not different between groups (P>0.05). Finally, progestin production by corpora lutea in vitro was lower for Proestrus than for the other groups (P<0.05). The results indicate that the prolactin surge alone is not responsible for initiation of apoptosis or immune cell infiltration in regressing corpora lutea of the estrous cycle, although prolactin increases these markers of regression. Prolactin does cause a decline in luteal weight; however, the corpora lutea retain the capacity for steroidogenesis. We conclude that although prolactin has a role in luteal regression, it is not solely responsible for the initiation of this process.