Steroidogenic response of rat and pig luteal cells to estradiol-17 beta and catecholestrogens in vitro

Changes in Porcine Corpus Luteum Proteome Associated with Development, Maintenance, Regression, and Rescue during Estrous Cycle and Early Pregnancy

Corpus luteum (CL), a transitory gland, undergoes rapid growth in a limited time to produce progesterone (P4) followed by its regression. A complex molecular signaling is involved in controlling luteal P4 production. In the present study, 2D gel electrophoresis-based proteomics and in silico functional analysis were used to identify changes in key proteins and pathways in CL along the different stages of the estrous cycle as its development progresses from early (Day 3) to mid-luteal phase (Day 9), effective functioning (Day 12) followed by regression (Day 15) or, in the case of pregnancy, rescue of function (Day 15). A total of 273 proteins were identified by MALDI-MS/MS analysis that showed significant changes in abundances at different stages of CL development or regression and rescue. Functional annotation of differentially abundant proteins suggested enrichment of several important pathways and functions during CL development and function maintenance including cell survival, endocytosis, oxidative stress response, estradiol metabolism, and angiogenesis. On the other hand, differentially abundant proteins during CL regression were associated with decreased steroid synthesis and metabolism and increased apoptosis, necrosis, and infiltration of immune cells. Establishment of pregnancy rescues CL from regression by maintaining the expression of proteins that support steroidogenesis as pathways such as the super-pathway of cholesterol biosynthesis, RhoA signaling, and functions such as fatty acid metabolism and sterol transport were enriched in CL of pregnancy. In this study, some novel proteins were identified along CL development that advances our understanding of CL survival and steroidogenesis.

Progesterone and Luteinizing hormone secretion patterns in early pregnant gilts

We studied luteinizing hormone (LH) pulsatility and episodic progesterone release of the corpus luteum (CL) on Day 11 and Day 21 in inseminated gilts and aimed to establish a relationship between these two hormones. Blood was collected at 15-min intervals for 12 hr on Days 11, 16 and 21 from a vena cava caudalis catheter. At euthanasia, eight gilts were pregnant and six gilts were not pregnant. Progesterone parameters (basal, mean, pulse frequency and pulse amplitude) did not differ between pregnant and non-pregnant gilts on Day 11, LH pulse frequency and amplitude tended to differ (p = .07 and p = .079). In pregnant gilts, basal and mean progesterone, progesterone pulse amplitude and frequency declined significantly from Day 11 to Day 21 (p < .05). A significant decline was also seen in the LH pulse amplitude from Day 11 to Day 21 (p < .05). None of the LH pulses was followed by a progesterone pulse within 1 hr on Day 21. On Day 11 and Day 21 appeared a synchronicity in the LH pulse pattern, as there were two or three LH pulses in 12 hr and these LH pulses appeared in the same time window. We conclude that on Day 11 and Day 21 of pregnancy in gilts, progesterone pulses do not follow an LH pulse within one hour. Further we demonstrated that the successful or not successful formation of a CL of pregnancy is independent of progesterone release on Day 11 after insemination. We confirmed the decline of progesterone from Day 11 to Day 21 in the vena cava caudalis and could demonstrate that this decline is partly due to lower progesterone pulse amplitude and frequency and that the decline occurs simultaneously with a decline in LH pulse amplitude.

Seasonal changes in luteal progesterone concentration and mRNA expressions of progesterone synthesis-related proteins in the corpus luteum of mares

Although circulating progesterone (P₄) levels tend to change with the season, little is known about the seasonal changes of P₄ synthesis-related proteins in the corpus luteum (CL) of mares. To examine these changes, seventy-four ovaries containing a CL were collected from Anglo-Norman mares at a local abattoir in Kumamoto, Japan (~N32°), five times during one year. The stages of the CLs were classified as early, mid and regressed by macroscopic observation of the CL and follicles. The mid CL, which had the highest P₄ concentration, was used to evaluate the seasonal changes in P₄ synthesis. The luteal P₄ concentration and mRNA expression of luteinizing hormone receptor (LHCGR) were lowest during early winter and highest during late winter. The mRNA expressions of steroidogenic acute regulatory protein (StAR), P450 cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) were lowest during early winter and increased during late winter. These results suggest that P₄ synthesis in the CL is affected by the seasonal changes in the mRNA expressions of P₄ synthesis-related proteins in mares.

Effects of cholesterol and cAMP on progesterone production in cultured luteal cells isolated from pseudopregnant cat ovaries

The present study was designed to incubate luteal cells isolated from pseudopregnant cats and to investigate the effects of cholesterol and cAMP on luteal progesterone production. Corpora lutea were collected from the cats on days 10 and 15 of pseudopregnancy. Luteal cells were isolated from the ovaries by collagenase digestion. Steroidogenic luteal cells were stained for 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity. Cells (2 x 10(4)) staining positive for 3beta-HSD were cultured for up to 7 days. The cells were treated with 22(R)-hydroxycholesterol (22R-HC) and dibutyryl cyclic AMP (dbcAMP) on days 1, 3 and 7. Treatment of cells with 22R-HC resulted in a dose-dependent increase (p<0.001) in progesterone production. When 22R-HC was used at a concentration of 10 microg/ml, it resulted in 2.7- and 5.1-fold increases in progesterone production on days 3 and 5, respectively. When the dose was doubled (20 microg/ml), treated cells produced four times more progesterone on days 3 and 7, and three times more on day 5. By day 7, progesterone production increased up to 9.1 times more than the control. Incubation of cells with both concentrations of dbcAMP (0.1 mM and 1 mM) resulted in significant stimulations of progesterone on days 5 and 7 (p<0.001). However, on day 3, only higher doses of dbcAMP (1 mM) resulted in significant stimulation (p<0.05). Progesterone production was increased up to 2- and 2.9-fold of the control when cells were treated with lower concentration of dbcAMP (0.1 mM) on days 5 and 7, respectively. Incubation of cells with 1 mM concentrations of dbcAMP induced a 3.2-fold increase on day 5 and a 5-fold increase on day 7. In conclusion, a successful incubation was performed for long-life culturing of luteal cells collected from pseudopregnant cats. The method works well and allows for optimal growth and development of cells in the culture. The present study also demonstrated that incubating cat luteal cells with 22R-HC and dbcAMP induces a significant increase in luteal progesterone synthesis.

HPLC-electrochemical detection of ovarian estradiol-17beta and catecholestrogens in the catfish Heteropneustes fossilis: seasonal and periovulatory changes

A high performance liquid chromatography-electrochemical (HPLC-EC) detection method was used to characterize estradiol-17beta (E2) and its metabolites (2-hydroxyE2, 4-hydroxyE2, and 2-methoxyE2) and investigate their seasonal and periovulatory changes in the ovary of the catfish Heteropneustes fossilis. The retention times in minutes of standards determined by individual and mixture applications are: 2-OHE2-6.6, 4-OHE2-7.0, 4-OHE1-11.2, E2-12.0, and 2-methoxyE2-15.2. Since the retention times of 2-OHE2 and 4-OHE2 merged at higher concentrations, the elution peaks of the sample were taken as due to both (2/4-OHE2) for analysis. The steroids were not detectable in the resting and postspawning phases and 2-methoxyE2 was not detectable in the recrudescent (preparatory, prespawning, and spawning) phases as well. E2 and 2/4-OHE2 have maintained an inverse relationship in the recrudescent phase. The E2 concentration was the highest in the preparatory phase (April) with active vitellogenic activity and declined significantly across prespawning and spawning phases (P<0.001, one way ANOVA; P<0.05, Newman-Keuls' test). On the other hand, the concentration of 2/4-OHE2, which was the lowest in the preparatory phase, increased significantly to the peak level in the spawning phase. A single intraperitoneal injection of hCG (100 IU/fish) stimulated significantly the formation of 2/4-OHE2 at 8 h with a simultaneous reduction in E2. 2-MethoxyE2 was detected only after 16 h of the hCG injection. The functional significance of catecholestrogens in the seasonal reproductive cycle and during the hCG-induced ovulation of the catfish was discussed.

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).

Blockade of estrogen synthesis with an aromatase inhibitor affects luteal function of the pseudopregnant rat

The luteotropic action of estrogen (E) was investigated using immature pseudopregnant rat as the model and CGS 16949A (Fadrozole hydrochloride), a potent aromatase inhibitor (AI), to block E synthesis. Aromatase activity could be inhibited by administering CGS 16949A (50 micrograms/day/rat) via a mini osmotic Alzet pump (model 2002) for 3 days during pseudopregnancy. This resulted in significant reduction of serum (40%, P < 0.05) and intraovarian 70.6%, P < 0.001) estradiol-17 beta (E2) levels. The serum and intraovarian progesterone (P4) levels as analyzed on day 4 of pseudopregnancy were also reduced by > or = 50% (for both, P < 0.01). Simultaneous administration of estradiol-3-benzoate (E2B) via an Alzet pump during the AI treatment period at a dose of 1 microgram/day could completely reverse the AI induced reduction in P4 secretion. The luteal cells of experimental rats depleted of E in vivo showed a significantly reduced response upon incubation with hCG or dbcAMP in vitro (P < 0.05 and 0.001, respectively). Addition of E2 (500 pg/tube) at the time of in vitro incubation was able to partially increase the responsiveness to hCG. The luteal cell LH/hCG receptor content and the affinity of hCG binding to the receptor remained unchanged following AI treatment in vivo. Both esterified and total cholesterol content of luteal cells of rats treated with AI in vivo was significantly high (P < 0.05) suggesting that E lack results in an impairment in cholesterol utilization for steroidogenesis. The results clearly show that E regulates luteal function in the pseudopregnant rat by acting at a non-cAMP mediated event and this perhaps involves facilitation of cholesterol utilization at the mitochondrial level for P4 synthesis.

Gene expression and peptide localization for epidermal growth factor receptor and its ligands in porcine luteal cells

The present study was undertaken to determine the expression of the genes for epidermal growth factor receptor (EGF-R), and two of its ligands, epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) in isolated large (LLC) and small (SLC) porcine luteal cells by reverse transcription-polymerase chain reaction (RT-PCR), and to localize their peptides in whole corpora lutea (CL) as well in isolated LLC and SLC by immunocytochemistry. RT-PCR revealed strong cDNA signals for EGF-R and EGF in both LLC and SLC, and for TGF-alpha in LLC. The signal for TGF-alpha message in SLC was relatively weaker but detectable. Immunocytochemistry revealed intense EGF-R staining in LLC and SLC in both isolated and intact CL preparations. On the other hand, immunoreactive EGF and TGF-alpha appeared to be present only in LLC in intact CL sections, and isolated luteal cell preparations confirmed their presence in LLC and absence in SLC. These results suggest an autocrine/paracrine role for EGF and TGF-alpha in luteal functions.

Localization of epidermal growth factor (EGF) receptor in the rat corpus luteum, and EGF and transforming growth factor-alpha stimulation of luteal cell steroidogenesis in vitro

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) have potent mitogenic effects on granulosa and theca cells. However, their effects on steroidogenesis by these cells is controversial, and there is limited information regarding their effects on luteal cell steroidogenesis. The present study investigated the cellular distribution of the EGF receptor (EGF-R) in the rat corpus luteum (CL) by immunocytochemical staining, and the effects of EGF and TGF-alpha on progesterone and 20 alpha-dihydroprogesterone (20 alpha-OH-P) production in cultures of luteal cells. Using a primary antibody directed against the human EGF-R peptide, specific EGF-R staining was obtained in the CL. Both small and large luteal cells had EGF-R staining. In initial cell culture experiments, treatment of freshly isolated luteal cells with EGF or TGF-alpha (0.5-50 ng/ml) for 24 h had no effect on progesterone and 20 alpha-OH-P accumulation. Addition of LH (250 ng/ml) alone caused a 3.5-fold increase in both progestins, but co-treatment with EGF or TGF-alpha produced no further enhancement of progestin accumulation. However, when cells were seeded overnight and the attached cells were washed prior to growth factor treatment for 3 days with media change every 24 h, both EGF and TGF-alpha caused dose-dependent increases in progesterone accumulation/24 h period (up to 2-fold at 50 ng/ml growth factor) on days 1 and 2 but not day 3 of treatment. 20 alpha-OH-P accumulation was similarly stimulated (up to 2.5-fold) by EGF and TGF-alpha under these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholestrogen modulation of steroid production by rat luteal cells: mechanism of action

This study investigated the mechanisms underlying 2-hydroxyestradiol (2-OHE2) effect on luteal steroidogenesis using serum-free cultures of mixed luteal cells from day 8 pseudopregnant rats. Initially, interactions between 2-OHE2 and LH or dibutyryl (db)cAMP on progesterone production were investigated. LH (250 ng/ml) and 2-OHE2 (2.5 microg/ml) had comparable effects on progesterone accumulation, while dbcAMP (5 mM) was more stimulatory. When applied together, 2-OHE2 did not synergize with LH or dbcAMP to further enhance progesterone accumulation. Furthermore, in time course experiments, the dose-dependent effect of 2-OHE2 was to reduce and eventually abolish the time-dependent increase in cAMP accumulation. In contrast LH stimulated cAMP accumulation at all times. Experiments in which cells were co-treated with 2-OHE2, 22-OH-cholesterol and cyanoketone, or with 2-OHE2 and 22-OH-cholesterol or pregnenolone indicated that 2-OHE2 not only had a stimulatory effect on the cholesterol side-chain cleavage and 3beta-hydroxysteroid dehydrogenase enzymes, but it also appeared to inhibit the 20alpha-hydroxysteroid dehydrogenase leading to a relative increase in progesterone accumulation. Experiments with hormone antagonists suggested that the actions of 2-OHE2 were not mediated by the estrogen, alpha- or beta-adrenergic receptors. The results of this study support the concept of a physiological role for catecholestrogens in rat luteal steroidogenesis.