Differential effects of calcium on progesterone production in small and large bovine luteal cells

Analysis of changes in the proteomic profile of porcine corpus luteum during different stages of the oestrous cycle: effects of PPAR gamma ligands

CONTEXT

The corpus luteum (CL) is an endocrine gland in the ovary of mature females during the oestrous cycle and pregnancy. There is evidence of a relationship between the secretory function of the CL and PPARs.

AIMS

In this study, we investigated the changes in the proteome of the CL in relation to the phase of the oestrous cycle and the impact of PPARγ ligands on the proteomic profile of the CL during the mid- and late-luteal phase of the oestrous cycle.

METHODS

The porcine CL explants were incubated in vitro for 6h in the presence of PPARγ ligands (agonist pioglitazone, antagonist T0070907) or without ligands. Global proteomic analysis was performed using the TMT-based LC-MS/MS method.

KEY RESULTS

The obtained results showed the disparity in proteomic profile of the untreated CL - different abundance of 23 and 28 proteins for the mid- and late-luteal phase, respectively. Moreover, seven proteins were differentially regulated in the CL tissue treated with PPARγ ligands. In the mid-luteal phase, one protein, CAND1, was downregulated after treatment with T0070907. In the late-luteal phase, the proteins SPTAN1, GOLGB1, TP53BP1, MATR3, RRBP1 and SRRT were upregulated by pioglitazone.

CONCLUSIONS

Comparative proteomic analysis revealed that certain proteins constitute a specific proteomic signature for each examined phase. Moreover, the study showed that the effect of PPARγ ligands on the CL proteome was rather limited.

IMPLICATIONS

The results provide a broader insight into the processes that may be responsible for the structural luteolysis of the porcine CL, in addition to apoptosis and autophagy.

Mercury affects uterine myogenic activity even without producing any apparent toxicity in rats: Involvement of calcium-signaling cascades

BACKGROUND

Mercury is an established environmental toxicant reported to cause reproductive disorders in women, however, its direct action on myometrial activity is yet to be understood. Earlier we have reported the underlying mechanism of mercury-induced myometrial contractions following in vitro exposure; however, no such information on the effect of mercury on myometrial activity following in vivo exposure is available, therefore, the present study was undertaken.

OBJECTIVE

Present study was designed to evaluate the effect of mercury on myometrial activity following in vivo exposure of rats and unravel the possible underlying mechanism.

METHODS

Female Wistar rats were orally exposed to mercury (5, 50 and 500 μg/L in drinking water) for 28 days to investigate the toxicodynamics of mercuric chloride (HgCl₂)-induced alterations in myometrial activity. Response of the isolated myometrial strips to different spasmogens was recorded using polyphysiograph. Blood and uterine calcium, mercury, iron and zinc levels were estimated by atomic absorption spectrophotometry. Blood biochemicals and serum hormonal profiles (estradiol, progesterone) were also determined.

RESULTS

No systemic toxicity of mercury was observed in any of the treatment groups (5, 50 and 500 μg/L) in terms of alterations in body weight, organ weights, blood biochemical parameters including hormonal profile. Interestingly, mercury at 5 μg/L concentration significantly increased the receptor-dependent (PGF_2α-induced) and receptor-independent (CaCl₂-induced and high K⁺-depolarizing solution-induced) myometrial contractions and it was coupled with corresponding increase in the uterine calcium levels. However, mercury at higher dose levels (50 and 500 μg/L) did not significantly alter the myometrial response.

CONCLUSION

Our results evidently suggest that mercury at low level (5 μg/L) produced detrimental effect on myometrial activity by altering calcium entry into the smooth muscle and/or the release of calcium from intracellular stores without causing any apparent systemic toxicity in rats.

Apoptotic Effects of Xanthium strumarium via PI3K/AKT/mTOR Pathway in Hepatocellular Carcinoma

Xanthium strumarium (XS) has been traditionally used as a medicinal herb for treating inflammatory diseases, such as appendicitis, chronic bronchitis, rheumatism, and rhinitis. In this study, we yielded ethanol extracts from XS and investigated whether they could inhibit the progression of hepatocellular carcinoma (HCC) and its underlying mechanism. The XS-5 and XS-6 extracts dose-dependently inhibited the growth and proliferation in HCC cell lines. The apoptotic effects of them were observed via increased levels of cleaved caspase-3 and cleaved PARP, as well as elevated numbers of terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling- (TUNEL-) positive apoptotic cells. They also decreased XIAP and Mcl-1 expression via loss of mitochondrial membrane potential. Additionally, they inhibited the invasion and migration of HCC cells. In an ex vivo model, the extracts significantly inhibited tumor cell growth and induced apoptosis by increasing the expression of the cleaved caspase-3. A mechanistic study revealed that they effectively suppressed PI3K/AKT/mTOR signaling pathways in HCC cells. Taken together, our findings demonstrate that they could efficiently not only induce apoptosis but also inhibit cell growth, migration, and invasion of human HCC cells by blocking the PI3K/AKT/mTOR pathway. We suggest XS-5 and XS-6 as novel natural anti-HCC agents.

Membrane receptor cross talk in gonadotropin-, IGF-I-, and insulin-mediated steroidogenesis in fish ovary: An overview

Gonadal steroidogenesis is critical for survival and reproduction of all animals. The pathways that regulate gonadal steroidogenesis are therefore conserved among animals from the steroidogenic enzymes to the intracellular signaling molecules and G protein-coupled receptors (GPCRs) that mediate the activity of these enzymes. Regulation of fish ovarian steroidogenesis in vitro by gonadotropin (GtH) and GPCRs revealed interaction between adenylate cyclase and calcium/calmodulin-dependent protein kinases (CaMKs) and also MAP kinase pathway. Recent studies revealed another important pathway in GtH-induced fish ovarian steroidogenesis: cross talk between GPCRs and membrane receptor tyrosine kinases. Gonadotropin binding to Gαs-coupled membrane receptor in fish ovary leads to production of cAMP which in turn trans-activate the membrane-bound epidermal growth factor receptor (EGFR). This is followed by activation of ERK1/2 signaling that promotes steroid production. Interestingly, GtH-induced trans-activation of EGFR in the fish ovary uniquely requires matrix-metalloproteinase-mediated release of EGF. Inhibition of these proteases blocks GtH-induced steroidogenesis. Increased cAMP production in fish ovarian follicle upregulate follicular cyp19a1a mRNA expression and aromatase activity leading to increased biosynthesis of 17β-estradiol (E2). Evidence for involvement of SF-1 protein in inducing cyp19a1a mRNA and aromatase activity has also been demonstrated. In addition to GtH, insulin-like growth factor (IGF-I) and bovine insulin can alone induced steroidogenesis in fish ovary. In intact follicles and isolated theca cells, IGF-I and insulin had no effect on GtH-induced testosterone and 17a,hydroxysprogeaterone production. GtH-stimulated E2 and 17,20bdihydroxy-4-pregnane 3-one production in granulosa cells however, was significantly increased by IGF-I and insulin. Both IGF-I and insulin mediates their signaling via receptor tyrosine kinases leading to activation of PI3 kinase/Akt and MAP kinase. These kinase signals then activates steroidogenic enzymes which promotes steroid production. PI3 kinase, therefore considered to be an initial component of the signal transduction pathways which precedes MAP kinase in IGF-1 and insulininduced steroidogenesis in fish ovary. Thus, investigation on the mechanism of signal transduction regulating fish ovarian steroidogenesis have shown that multiple, apparently independent signal transduction pathways are needed to convey the message of single hormone or growth factor.

After 65 years, research is still fun

In 1946, at the end of World War II, I entered graduate school at Cornell University, where I remained for 44 years. During that time, my laboratory produced more than 300 publications in the field of reproductive biology, including studies on nutrition and reproduction, the role of the hypothalamus in pituitary gonadotropin release, corpus luteum formation and function, hormone assays, and estrous cycle synchronization. At age seventy, I retired from Cornell and accepted the Gordon Cain Endowed Professorship at Louisiana State University, where I continued my work on the bovine corpus luteum and added research on the collection, maturation, in vitro fertilization, and culture of bovine oocytes. In 1994, I moved to the Pennington Biomedical Research Center and soon thereafter started the research that led to development of the lytic peptide-gonadotropin conjugates, which target and destroy cancer cell membranes. I am continuing my work on the development of targeted cancer cell drugs and, yes, research is still fun!

Estradiol regulation of progesterone synthesis in the brain

Steroidogenesis is now recognized as a global phenomenon in the brain, but how it is regulated and its relationship to circulating steroids of peripheral origin have remained more elusive issues. Neurosteroids, steroids synthesized de novo in nervous tissue, have a large range of actions in the brain, but it is only recently that the role of neuroprogesterone in the regulation of arguably the quintessential steroid-dependent neural activity, regulation of the reproduction has been appreciated. Circuits involved in controlling the LH surge and sexual behaviors were thought to be influenced by estradiol and progesterone synthesized in the ovary and perhaps the adrenal. It is now apparent that estradiol of ovarian origin regulates the synthesis of neuroprogesterone, and it is the locally produced neuroprogesterone that is involved in the initiation of the LH surge and subsequent ovulation. In this model, estradiol induces the transcription of progesterone receptors while stimulating synthesis of neuroprogesterone. Although the complete signaling cascade has not been elucidated, many of the features have been characterized. The synthesis of neuroprogesterone occurs primarily in astrocytes and requires the interaction of membrane-associated estrogen receptor-alpha with metabotropic glutamate receptor-1a. This G protein-coupled receptor activates a phospholipase C that in turn increases inositol trisphosphate (IP3) levels mediating the release of intracellular stores of Ca2+ via an IP3 receptor gated Ca2+ channel. The large increase in free cytoplasmic Ca2+ ([Ca2+]i) stimulates the synthesis of progesterone, which can then diffuse out of the astrocyte and activate estradiol-induced progesterone receptors in local neurons to trigger the neural cascade to produce the LH surge. Thus, it is a cooperative action of astrocytes and neurons that is needed for estrogen positive feedback and stimulation of the LH surge.

Membrane estrogen receptors acting through metabotropic glutamate receptors: an emerging mechanism of estrogen action in brain

It has been over 60 years since the first studies have been published describing the effects of steroid hormones on brain function. For over 30 years, estrogen has been presumed to directly affect gene expression and protein synthesis through a specific receptor. More than 20 years ago, the first estrogen receptor was cloned and identified as a transcription factor. Yet, throughout their course of study, estrogens have also been observed to affect nervous system function via mechanisms independent of intracellular receptor regulation of gene expression. Up until recently, the membrane estrogen receptors responsible for these rapid actions have remained elusive. Recent studies have demonstrated that a large number of these rapid, membrane-initiated actions of estradiol are due to surface expression of classical estrogen receptors. This review focuses on the importance of membrane estrogen receptor interactions with metabotropic glutamate receptors for understanding rapid estradiol signaling mechanisms and downstream effectors, as well as their significance in a variety of physiological processes.

Synthesis and function of hypothalamic neuroprogesterone in reproduction

The physiology and regulation of steroid synthesis in the brain have emerged as important for understanding brain function. Neurosteroids, those steroids synthesized de novo in nervous tissue, have been associated with numerous central nervous system functions, including myelination, mental retardation, and epilepsy. Central regulation of reproduction was thought to depend on steroids of peripheral origin. Only recently has the role of neurosteroids in reproduction been appreciated. This minireview describes our work trying to understand how circulating estradiol modulates the synthesis of neuroprogesterone. The synthesis of neuroprogesterone occurs primarily in astrocytes, and requires the interaction of membrane-associated estrogen receptor with metabotropic glutamate receptor and the release of intracellular calcium stores. The newly synthesized neuroprogesterone acts on estradiol-induced progesterone receptors in nearby neurons to initiate the LH surge.

Luteolytic effect of prostaglandin F 2 alpha on bovine corpus luteum depends on cell composition and contact

Prostaglandin F(2 alpha) (PGF(2 alpha)) is a main luteolytic factor in vivo; however, its direct luteolytic influence on steroidogenic cells of bovine corpus luteum (CL) is controversial and not fully understood. The aim of the study was to clarify PGF(2 alpha) action on bovine CL in different in vivo and in vitro conditions and to examine whether the contact among all main types of CL cells is necessary for luteolytic PGF(2 alpha) action. In experiment 1, the bovine CL (day 15 of the oestrous cycle) was perfused using in vivo microdialysis system with dinoprost (an analogue of PGF(2 alpha)) for 0.5 h. Dinoprost caused a short-time increase in progesterone (P4), whose concentration decreased thereafter (at 6-, 10-, 12- and 24-h after treatment). In experiment 2, the direct effect of PGF(2 alpha) on P4 accumulation in CL steroidogenic cells cultured in monolayer (day 15 of the cycle) was determined. PGF(2 alpha) after 24 h of incubation increased P4 accumulation in steroidogenic CL cells. In experiment 3 steroidogenic, endothelial CL and immune cells (day 15 of the cycle) were incubated with PGF(2 alpha) in cocultures for 24 h in glass tubes and the levels of P4, stable metabolites of nitric oxide (NO) and leukotriene (LT) C(4) were determined. Although PGF(2 alpha) treatment increased P4 secretion in homogeneous steroidogenic CL cell culture, the decrease in P4 secretion in cocultures of all types of CL cells was observed. The secretion of NO and LTC(4) increased after the treatment of PGF(2 alpha) both in pure cultures of CL cells and in cocultures. The interactions between endothelial and immune cells with steroidogenic CL cells are needed for luteolytic PGF(2 alpha) action within the bovine CL. Our results indicate that the cell coculture model, including the main types of CL cells, is the most approximate to study PGF(2 alpha) role in vitro.

PKC epsilon and an increase in intracellular calcium concentration are necessary for PGF2 alpha to inhibit LH-stimulated progesterone secretion in cultured bovine steroidogenic luteal cells

The hypotheses that PKC epsilon is necessary for: 1) PGF2 alpha to inhibit LH-stimulated progesterone (P4) secretion, and 2) for the expression of key prostaglandin synthesizing/metabolizing enzymes were tested in bovine luteal cells in which PKC epsilon expression had been ablated using a validated siRNA protocol. Steroidogenic cells from Day -6 bovine corpus luteum (CL) were isolated and transfected to reduce PKC epsilon expression after 48, 72 and 96 h. A third tested hypothesis was that an increase in intracellular calcium concentration ([Ca(2+)]i) is the cellular mechanism through which PGF2 alpha inhibits luteal progesterone. The hypothesis was tested with two pharmacological agents. In the first test, the dose-dependent effects on raising the [Ca(2+)]i with the ionophore, A23187, on basal and LH-stimulated P4 secretion in cells collected from early (Day -4) and mid-cycle (Day -10) bovine CL was examined. In the second test, the ability of PGF2 alpha to inhibit LH-stimulated P4 secretion in Day-10 luteal cells was examined under conditions in which an elevation in [Ca(2+)]i had been buffered by means of the intracellular calcium chelator, Bapta-AM.PKC epsilon expression was reduced 65 and 75% by 72 and 96 h after transfection, respectively. In cells in which PKC epsilon expression was ablated by 75%, the inhibitory effect of PGF2 alpha on LH-stimulated P4 secretion was only 29% lower than in the LH-stimulated group. In contrast, it was reduced by 75% in the group where PKC epsilon expression had not been reduced (P < 0.05). Real time PCR analysis indicated that there were no differences in the expression of cyclooxygenase-2 (COX-2), aldoketoreductase 1B5 (AKR1B5), prostaglandin E synthase (PGES), hydroxyprostaglandin-15 dehydrogenase (PGDH) and PGE2 -9-reductase as a function of PKC epsilon down-regulation. Finally, LH stimulated secretion of P4 at each luteal stage (Day -4 and -10), and PGF2 alpha inhibited this only in Day -10 cells (P < 0.05). When A23187 was used at concentrations greater than 0.1 mumol, the induced elevation in [Ca(2+)]i inhibited the effect of LH on secretion of P4 in Day -4 and -10 cells (P < 0.05, Fig. 5). The inhibitory effect of PGF2 alpha on LH-stimulated P4 in Day -10 cells was reduced if an increase in [Ca(2+)]i was prevented with Bapta-AM. These results support the hypothesis that differential expression of PKC epsilon and an elevation of [Ca(2+)]i are important for acquisition of luteolytic response to PGF2 alpha.

Calcium-mediated aponecrosis plays a central role in the pathogenesis of estrogenic chemical-induced neurotoxicity

Estrogen is traditionally associated with females but is also present in males, and influences aspects of brain chemistry and brain morphology in males, females and also during prenatal development. Humans as well as animals are additionally exposed to environmental products that mimic estrogen activity, also known as endocrine disrupters (EDCs). This hypothesis article investigates the role of estrogen (and also EDCs) in the brain and how it influences the Ca2+ pathway. Ca2+ and its movement in and out of the cell is an extremely important ion controlling normal cell physiology. Any dysfunction in the movement from outside to inside the cell or between organelles may have fundamentally negative effects and the disturbance may even lead to apoptosis and/or necrosis. Therefore we consider whether estrogen and EDCs may alter the Ca2+ physiology and whether these changes may be one of the main causes of interference in physiology that is seen when humans and animals are exposed to EDCs. We come to the conclusion that on a molecular level Ca2+ and Ca2+ fluxes ([Ca2+]i, endocrine disrupting chemicals, redox modulation, mitochondria and cytochrome c followed by apoptosis, necrosis or most likely aponecrosis may contribute to chemical-mediated developmental toxicity. Similarly, we hypothesize that calcium-mediated aponecrosis do not only play a central role in the pathophysiology of estrogenic chemical-induced neurotoxicity, but can contribute to chemical-mediated developmental toxicity in general, thereby affecting almost all cells and organs of the living organism.

Developmental Sensitivity of the Bovine Corpus Luteum to Prostaglandin F2α (PGF2α) and Endothelin-1 (ET-1): Is ET-1 a Mediator of the Luteolytic Actions of PGF2α or a Tonic Inhibitor of Progesterone Secretion?1

We examined the responsiveness of large luteal cells (LLC), small luteal cells (SLC), and endothelial cells of the Day 4 and Day 10 bovine corpus luteum (CL) to prostaglandin (PG) F2alpha and endothelin (ET)-1. Using a single-cell approach, we tested the ability of each agonist to increase the cytoplasmic concentration of calcium ions ([Ca2+]i) as function of luteal development. All tested concentrations of agonists significantly (P = 0.05) increased [Ca2+]i in all cell populations isolated from Day 4 and Day 10 CL. Day 10 steroidogenic cells were more responsive than Day 4 cells to PGF2alpha and ET-1. Response amplitudes and number of responding cells were affected significantly by agonist concentration, luteal development, and cell type. Response amplitudes were greater in LLC than in SLC; responses of maximal amplitude were elicited with lower agonist concentrations in Day 10 cells than in Day 4 cells. Furthermore, on Day 10, as the concentration of PGF2alpha increased, larger percentages of SLC responded. Endothelial cells responded maximally, regardless of agonist concentration and luteal development. In experiment 2, we tested the developmental responsiveness of total dispersed and steroidogenic-enriched cells to the inhibitory actions of PGF2alpha and ET-1 on basal and LH-stimulated progesterone accumulation. The potency of PGF2alpha steroidogenic-enriched cells on Day 4 was lower than on Day 10; in contrast, the potency of ET-1 was not different. Therefore, ET-1 was a tonic inhibitor of progesterone accumulation rather than a mediator of PGF2alpha action. The lower efficacy of PGF2alpha in the early CL more likely is related to signal transduction differences associated with its receptor at these two developmental stages than to the inability of PGF2alpha to up-regulate ET-1.

Effects of selective protein kinase c isozymes in prostaglandin2alpha-induced Ca2+ signaling and luteinizing hormone-induced progesterone accumulation in the mid-phase bovine corpus luteum

A single-cell approach for measuring the concentration of cytoplasmic calcium ions ([Ca(2+)](i)) and a protein kinase C-epsilon (PKCepsilon)-specific inhibitor were used to investigate the developmental role of PKCepsilon in the prostaglandin F(2alpha)(PGF(2alpha))-induced rise in [Ca(2+)](i) and the induced decline in progesterone accumulation in cultures of cells isolated from the bovine corpus luteum. PGF(2alpha) increased [Ca(2+)](i) in Day 4 large luteal cells (LLCs), but the response was significantly lower than in Day 10 LLCs (4.3 +/- 0.6, n = 116 vs. 21.3 +/- 2.3, n = 110). Similarly, the fold increase in the PGF(2alpha)-induced rise in [Ca(2+)](i) in Day 4 small luteal cells (SLCs) was lower than in Day 10 SLCs (1.6 +/- 0.2, n = 198 vs. 2.7 +/- 0.1, n = 95). A PKCepsilon inhibitor reduced the PGF(2alpha)-elicited calcium responses in both Day 10 LLCs and SLCs to 3.5 +/- 0.3 (n = 217) and 1.3 +/- 0.1 (n = 205), respectively. PGF(2alpha) inhibited LH-stimulated progesterone (P(4)) accumulation only in the incubation medium of Day 10 luteal cells. Both conventional and PKCepsilon-specific inhibitors reversed the ability of PGF(2alpha) to decrease LH-stimulated P(4) accumulation, and the PKCepsilon inhibitor was more effective at this than the conventional PKC inhibitor. In conclusion, the evidence indicates that PKCepsilon, an isozyme expressed in corpora lutea with acquired PGF(2alpha) luteolytic capacity, has a regulatory role in the PGF(2alpha)-induced Ca(2+) signaling in luteal steroidogenic cells, and that this in turn may have consequences (at least in part) on the ability of PGF(2alpha) to inhibit LH-stimulated P(4) synthesis at this developmental stage.

Up-regulation of basal transcriptional activity of the cytochrome P450 cholesterol side-chain cleavage (CYP11A) gene by isoform-specific calcium-calmodulin-dependent protein kinase in primary cultures of ovarian granulosa cells

Intracellular calcium ions (Ca2+) regulate steroidogenesis in the placenta, adrenal gland, testis, and ovary. Earlier data indicate that Ca2+/calmodulin-dependent protein kinase (CamK) may mediate Ca(2+)-dependent up-regulation of CYP11A (cholesterol side-chain cleavage). To examine this notion further, we assessed the expression and actions of isotype-specific CamK on in vitro transcription of the swine CYP11A gene promoter in primary cultures of ovarian granulosa-luteal cells. RT-PCR and oligodeoxynucleotide sequencing identified gene transcripts encoding CamKII and IV in granulosa and theca cells and corpora lutea. DNA sequence homology with the cognate human and rat genes was 97 and 94% (CamKII) and 96 and 88% (CamKIV), respectively. SDS-PAGE and isoform-specific immunoblotting corroborated expression of CamKII (approximately 52 kDa) and CamKIV (approximately 60 kDa) proteins. To monitor transcriptional control, granulosa-luteal cells were transfected transiently with a putative 5'-upstream regulatory region of the homologous CYP11A gene -2320 to +23 bp from the transcriptional start site driving luciferase (CYP11A/luc). Coexpression of constitutively active CamKIV elevated basal transcription by 3.5 +/- 0.2-fold (P < 0.001), whereas inactive mutant CamKIV and native CamKII had no effect. Forskolin, an activator of adenylyl cyclase, stimulated expression of CYP11A/luciferase by 4.5 +/- 0.9-fold (P < 0.001) and did not enhance transcriptional drive by exogenous CamKIV. Preliminary promoter-deletional analyses showed that a proximal 5'-fragment -100 to +23 bp, but not -50/+23 bp, retained full responsiveness to CamKIV (4.5 +/- 0.4-fold; P < 0.001). Threefold cotransfection of -100/+23 bp CYP11A/luciferase, active CamKIV, and a dominant-negative mutant of the cAMP-responsive element binding protein (10, 100, and 250 ng) inhibited CamKIV-stimulated transcriptional activity by 17, 47, and 48% (pooled sem+/- 2%) [P < 0.01]. The dominant-negative mutant of the cAMP-responsive element binding protein also repressed forskolin's stimulation of -100/+23 CYP11A/luciferase by 12, 38, and 52% (P < 0.01). Based on these ensemble outcomes, we postulate that endogenous CamKIV may serve as a Ca(2+)-dependent effector mechanism to maintain basal CYP11A gene expression in ovarian granulosa-luteal cells.

Estrogen induces de novo progesterone synthesis in astrocytes

The brain is an established target for peripheral steroids, but also expresses steroidogenic enzymes and is capable of de novo 'sex' steroid synthesis (neurosteroidogenesis) independent of peripheral steroidogenic organs. In adrenalectomized and ovariectomized rats that do not have peripheral sources of steroids, estrogen treatment increased progesterone levels specifically in the hypothalamus, indicating that estrogen stimulates progesterone neurosteroidogenesis. Recent studies have demonstrated that specific cell types preferentially secrete specific steroids, and that astrocytes are the primary progesterone synthesizing cells in the nervous system. We hypothesized that estrogen could directly induce de novo synthesis of progesterone in astrocytes. To determine whether estrogen stimulates progesterone synthesis in astrocytes, astrocyte-enriched cultures were grown to confluence, then grown for an additional 48 h in an estrogen- and phenol-free Dulbecco's Modified Eagle Medium (DMEM) and then treated with either 17beta-estradiol or steroid-free media. After culturing for 48 h in steroid-free, phenol red-free DMEM, low levels of progesterone were detected in the media, whereas progesterone levels were significantly increased in the media of astrocytes cultured in DMEM with 17beta-estradiol (10(-7)-10(-4)M). To determine whether estrogen regulated the mRNA expression of progesterone synthetic enzymes, P-450 side-chain cleavage and 3beta-hydroxysteroid dehydrogenase, control and 17beta-estradiol-treated astrocytes were harvested and prepared for Northern and slot blot analysis. Expression levels of enzyme mRNAs were very low and 17beta-estradiol did not significantly increase mRNA levels of either steroidogenic enzyme. These results suggest that estrogen directly stimulated the de novo synthesis of neuroprogesterone in astrocytes, and demonstrate the potential for estrogen to regulate reproductive physiology and behavior through the paracrine actions of astrocyte-derived progesterone.

Calcium ions positively modulate follicle-stimulating hormone- and exogenous cyclic 3',5'-adenosine monophosphate-driven transcription of the P450(scc) gene in porcine granulosa cells

Given the evident modulation of FSH-induced steroidogenesis by Ca2+ in granulosa cells, we here test the hypothesis that Ca2+ controls expression of the enzymatically rate-limiting cytochrome P450(scc) (CYP11A) gene. To test this postulate, we quantitated the ability of Ca2+ to regulate: 1) transcriptional activity of a transiently transfected luciferase reporter gene driven by a 2.32-kb 5'-upstream fragment of the porcine P450(scc) gene promoter region; and 2) accumulation of endogenous P450(scc) transcripts in primary monolayer cultures of porcine granulosa cells. To this end, granulosa cells were stimulated for 4 h with FSH (15 ng/ml, NIDDK-oFSH-20) or 8-Bromo-cAMP (8 Br-cAMP, 1 mM) in serum-free medium containing either 1.8 mM Ca2- or no added Ca2+ with 100 microM EGTA or 100 microM CoCl2. In the presence of extracellular Ca2+, FSH and 8 Br-cAMP stimulated expression of the transfected P450(scc) promoter-reporter fusion construct by 5.6 +/- 1.1 and 3.6 +/- 0.67-fold, respectively over Ca2+-containing unstimulated control (P < or = 0.04, n = 5-6 experiments). The foregoing two agonists augmented 4-h progesterone production by cultured granulosa cells by 1.8 +/- 0.11 and 1.6 +/- 0.16-fold, respectively (P < or = 0.001 for FSH and P < or = 0.01 for 8 Br-cAMP). FSH and 8 Br-cAMP also significantly elevated endogenous P450(scc) transcript levels as measured by homologous solution-hybridization RNase protection assay; i.e. by 3.1 +/- 0.49 and 2.9 +/- 0.45-fold, respectively (P < or = 0.001). In Ca2+-free/EGTA-supplemented medium, basal luciferase reporter-gene activity and endogenous P450(scc) messenger RNA accumulation in granulosa cells declined to 34 +/- 12% and 78 +/- 12%, respectively, of corresponding values in control (unstimulated Ca2+-containing) cultures. Extracellular Ca2+ deprivation inhibited the stimulatory effect of FSH (and 8 Br-cAMP) on P450(scc) promoter-luciferase reporter expression to 58 +/- 30% (and 58 +/- 23%), and restrained endogenous P450(scc) message accumulation to 86 +/- 15% (and 96 +/- 18%) of the value in Ca2+-containing control. Extracellular Ca2+ withdrawal suppressed FSH (and 8 Br-cAMP)-driven progesterone production over 4 h to basal levels but did not alter FSH-stimulated cAMP accumulation by granulosa cells. Ca2+-deprived cells exposed to serum-containing media regained P450(scc) responsiveness to both agonists. Antagonism of cellular uptake of Ca2+ and other divalent cations via administration of cobalt chloride (100 microM) inhibited FSH and 8 Br-cAMP's stimulation of endogenous (but not exogenous promoter-driven) P450(scc) gene expression. In contrast, granulosa-cell concentrations of messenger RNA's encoding sterol-carrier protein-2 (SCP-2) and the low density lipoprotein receptor were not altered by Ca2+ withdrawal. In summary, uptake of extracellular Ca2+ by porcine granulosa cells significantly potentiates transactivation of the endogenously expressed and exogenously transfected P450(scc) gene by FSH and 8 Br-cAMP. The agonistic impact of Ca2+ on P450(scc) promoter activity is requisite downstream of FSH-induced cAMP second-messenger signaling.

Sensitivity of bovine corpora lutea to prostaglandin F2alpha is dependent on progesterone, oxytocin, and prostaglandins

Prostaglandin (PG) F2alpha that is released from the uterus is essential for spontaneous luteolysis in cattle. Although PGF2alpha and its analogues are extensively used to synchronize the estrous cycle by inducing luteolysis, corpora lutea (CL) at the early stage of the estrous cycle are resistant to the luteolytic effect of PGF2alpha. We examined the sensitivity of bovine CL to PGF2alpha treatment in vitro and determined whether the changes in the response of CL to PGF2alpha are dependent on progesterone (P4), oxytocin (OT), and PGs produced locally. Bovine luteal cells from early (Days 4-5 of the estrous cycle) and mid-cycle CL (Days 8-12 of the estrous cycle) were preexposed for 12 h to a P4 antagonist (onapristone: OP; 10(-4) M), an OT antagonist (atosiban: AT; 10(-6) M), or indomethacin (INDO; 10(-4) M) before stimulation with PGF2alpha. Although OP reduced P4 secretion (p < 0.001) only in early CL, it reduced OT secretion in the cells of both phases examined (p < 0.001). OP also reduced PGF2alpha and PGE2 secretion (p < 0.01) from early CL. However, it stimulated PGF2alpha secretion in mid-cycle luteal cells (p < 0.001). AT reduced P4 secretion in early and mid-cycle CL (p < 0.05). Moreover, PGF2alpha secretion was inhibited (p < 0.05) by AT in early CL. The OT secretion and the intracellular level of free Ca2+ ([Ca2+]i) were measured as indicators of CL sensitivity to PGF2alpha. PGF2alpha had no influence on OT secretion, although [Ca2+]i increased (p < 0.05) in the early CL. However, the effect of PGF2alpha was augmented (p < 0.01) in cells after pretreatment with OP, AT, and INDO in comparison with the controls. In mid-cycle luteal cells, PGF2alpha induced 2-fold increases in OT secretion and [Ca2+]i. However, in contrast to results in early CL, these increases were magnified only by preexposure of the cells to AT (p < 0.05). These results indicate that luteal P4, OT, and PGs are components of an autocrine/paracrine positive feedback cascade in bovine early to mid-cycle CL and may be responsible for the resistance of the early bovine CL to the exogenous PGF2alpha action.

Gap junctional intercellular communication of bovine luteal cells from several stages of the estrous cycle: effects of prostaglandin F2 alpha, protein kinase C and calcium

Cellular interactions mediated by both contact-dependent and contact-independent mechanisms are probably important to maintain luteal function. The present studies were performed to evaluate the effects of luteotropic and luteolytic hormones, and also intracellular regulators, on contact-dependent gap junctional intercellular communication (GJIC) of bovine luteal cells from several stages of luteal development. Bovine corpora lutea (CL) from the early, mid and late luteal phases of the estrous cycle were dispersed with collagenase and incubated with no treatment, LH, PGF or LH + PGF (Experiment 1), or with no treatment, or agonists or antagonists of protein kinase C (TPA or H-7) or calcium (A23187 or EGTA; Experiment 2). After incubation, media were collected for determination of progester-one concentrations. Then the rate of GJIC was evaluated for small luteal cells in contact with small luteal cells, and large luteal cells in contact with small luteal cells by using the fluorescence recovery after photobleaching technique and laser cytometry. Luteal cells from each stage of the estrous cycle exhibited GJIC, but the rate of GJIC was least (P < 0.05) for luteal cells from the late luteal phase. LH increased (P < 0.05) GJIC between small luteal cells from the mid and late but not the early luteal phase. PGF increased (P < 0.05) GJIC between small luteal cells from the mid luteal phase and diminished (P < 0.05) LH-stimulatory effects on GJIC between small luteal cells from the late luteal phase. Throughout the estrous cycle, TPA decreased (P < 0.05) the rate of GJIC between large and small, and between small luteal cells, and A23187 decreased (P < 0.05) the rate of GJIC between large and small luteal cells. LH and LH + PGF, but not PGF alone increased (P < 0.05) progesterone secretion by luteal cells from the mid and late luteal phases. Agonists or antagonists of PKC or calcium did not affect progesterone secretion by luteal cells. These data demonstrate that both luteal cell types communicate with small luteal cells, and the rate of communication depends on the stage of luteal development. LH and PGF affect GJIC between small luteal cells during the fully differentiated (mid-luteal) and regressing (late luteal) stages of the estrous cycle. In contrast, at all stages of luteal development, activation of PKC decreases GJIC between small and between large and small luteal cells, whereas calcium ionophore decreases GJIC only between large and small luteal cells. Luteotropic and luteolytic hormones, and intracellular regulators, may be involved in regulation of cellular interactions within bovine CL which likely is an important mechanism for coordination of luteal function.

The effects of gonadotropin on the phosphatidylinositol pathway in the primate corpus luteum

The current study was designed to investigate the effects of gonadotropin on basal and prostaglandin (PG) F2 alpha-induced activity of the phosphatidylinositol pathway in corpora lutea (CL) of rhesus monkeys. Luteal progesterone production in vitro was significantly stimulated (P < 0.05) by human chorionic gonadotropin (hCG). Neither basal nor PGF2 alpha-induced phosphatidylinositol 4,5-bisphosphate hydrolysis was significantly influenced by hCG in CL of various ages (P > 0.10). Gonadotropin did induce a slight, yet sustained, increase (P < 0.05) in [Ca2+]i in approximately 70% of luteal cells. The maximal increase in [Ca2+]i in response to hCG (approximately 100 nM) was about one-tenth that induced by PGF2 alpha (approximately 1000 nM). hCG treatment did not alter (P > 0.10) the increase in [Ca2+]i induced by PGF2 alpha Treatment-induced changes in [Ca2+]i did not differ between small (17-21 microns) and large (23-28 microns) luteal cells. Therefore, luteolytic agents are more potent activators of the phosphatidylinositol pathway than luteotropins. This is consistent with the hypothesis that the phosphatidylinositol pathway is involved in primate luteal regression. The inability of hCG to acutely alter the responsiveness of this pathway to PGF2 alpha suggests that CG may rescue the CL of early pregnancy via a mechanism other than direct inhibition of the luteolytic actions of PGF2 alpha.