A possible interrelationship between gonadotrophin stimulation and prostaglandin F2alpha inhibition of steroidogenesis by granulosa-luteal cells in vitro

Autophagy regulates sex steroid hormone synthesis through lysosomal degradation of lipid droplets in human ovary and testis

Autophagy is an evolutionarily conserved process that aims to maintain the energy homeostasis of the cell by recycling long-lived proteins and organelles. Previous studies documented the role of autophagy in sex steroid hormone biosynthesis in different animal models and human testis. Here we demonstrate in this study that sex steroid hormones estrogen and progesterone are produced through the same autophagy-mediated mechanism in the human ovary in addition to the human testis. In brief, pharmacological inhibition and genetic interruption of autophagy through silencing of autophagy genes (Beclin1 and ATG5) via siRNA and shRNA technologies significantly reduced basal and gonadotropin-stimulated estradiol (E₂), progesterone (P₄) and testosterone (T) production in the ex vivo explant tissue culture of ovary and testis and primary and immortalized granulosa cells. Consistent with the findings of the previous works, we observed that lipophagy, a special form of autophagy, mediates the association of the lipid droplets (LD)s with lysosome to deliver the lipid cargo within the LDs to lysosomes for degradation in order to release free cholesterol required for steroid synthesis. Gonadotropin hormones are likely to augment the production of sex steroid hormones by upregulating the expression of autophagy genes, accelerating autophagic flux and promoting the association of LDs with autophagosome and lysosome. Moreover, we detected some aberrations at different steps of lipophagy-mediated P₄ production in the luteinized GCs of women with defective ovarian luteal function. The progression of autophagy and the fusion of the LDs with lysosome are markedly defective, along with reduced P₄ production in these patients. Our data, together with the findings of the previous works, may have significant clinical implications by opening a new avenue in understanding and treatment of a wide range of diseases, from reproductive disorders to sex steroid-producing neoplasms, sex steroid-dependent malignancies (breast, endometrium, prostate) and benign disorders (endometriosis).

Effect of periovulatory prostaglandin F2alpha on pregnancy rates and luteal function in the mare

The objective of this study was to determine whether periovulatory treatments with PGF2alpha affects the development of the CL, and whether the treatment was detrimental to the establishment of pregnancy. Reproductively sound mares were assigned randomly to one of the following treatment groups during consecutive estrus cycles: 1. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol (PGF2alpha analogue) on Days 0, 1, and 2 after ovulation (n=8), 2. 2 mL sterile water injection within 24 hours before artificial insemination and 500 microg cloprostenol on Days 0, 1, and 2 after ovulation (n=8); 3. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol on Day 2 after ovulation (n=8); or 4. 3,000 IU hCG within 24 hours before artificial insemination and 2 mL of sterile water on Days 0, 1, and 2 after ovulation (controls; n=8). Blood samples were collected from the jugular vein on Days 0, 1, 2, 5, 8, 11, and 14 after ovulation. Plasma progesterone concentrations were determined by the use of a solid phase 125I radioimmunoassay. All mares were examined for pregnancy by the use of transrectal ultrasonography at 14 days after ovulation. Mares in Group 1 and 2 had lower plasma progesterone concentrations at Day 2 and 5, compared to mares in the control group (P < 0.001). No difference was detected between group 1 and 2. Plasma progesterone concentrations in group 3 were similar to the control group until the day of treatment, but decreased after treatment and were significantly lower than the control group at Day 5 (P < 0.001). Plasma progesterone concentrations increased in all treatment groups after Day 5, and were comparable among all groups at Day 14 after ovulation. Cloprostenol treatment had a significant effect on pregnancy rates (P < 0.01). The pregnancy rate was 12.5% in Group 1, 25% in Group 2, 38% in Group 3, and 62.5% in Group 4. It was concluded that periovulatory treatment with PGF2alpha has a detrimental effect on early luteal function and pregnancy.

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.

Effects of oestrogen on progesterone synthesis and arachidonic acid metabolism in human luteal cells

OBJECTIVE

Locally produced oestrogens and prostaglandins (PGs) are implicated in the regulation of luteal lifespan in the human ovary. This study (1) assesses direct effects of these factors on progesterone synthesis in isolated luteal cells, and (2) explores interactions between luteal age and treatment with gonadotrophin or oestrogen on the metabolism of arachidonic acid (prostaglandin precursor) by steroidogenic luteal cells in vitro.

DESIGN

Primary monolayer cultures of human luteal cells obtained at different stages of the luteal phase were used to investigate the effect of oestradiol, catechol oestrogens (2- and 4-hydroxyoestradiol), diethylstilboestrol, PGE2 and PGF2 alpha on basal and human chorionic gonadotrophin (hCG) stimulated progesterone production in vitro. The role of PGs as modulators of luteal cell function was further investigated by studying the metabolic fate of radioactively labelled arachidonic acid in hormone treated (oestradiol and hCG) and control cultures, assessed by high performance liquid chromatography.

PATIENTS

Corpora lutea were enucleated from nine women with regular ovulatory cycles undergoing microsurgical reversal of tubal sterilization. Granulosa cell aspirates were obtained from three patients undergoing in-vitro fertilization treatment.

RESULTS

PGE2 and PGF2 alpha at various concentrations did not have a consistent effect, whereas oestradiol, diethylstilboestrol (and 2-hydroxyoestradiol in early luteal cell cultures) significantly inhibited basal and hCG stimulated progesterone biosynthesis. Evidence for direct inhibition of 3 beta-hydroxysteroid dehydrogenase enzymic activity by oestradiol was obtained. Both major metabolic pathways of arachidonic acid (lipoxygenase and cyclo-oxygenase) were operative in steroidogenic luteal cells recovered throughout the luteal phase. The ratio of PGE2 to PGF2 alpha synthesis in vitro by human luteal cells from endogenously incorporated arachidonic acid did not change significantly with corpus luteum age, with PGE2 tending to predominate. Oestradiol treatment shifted arachidonic acid metabolism from the lipoxygenase towards the cyclooxygenase pathway in cells isolated from ageing corpora lutea.

CONCLUSIONS

Oestradiol, at relatively high concentrations, is a potent inhibitor of basal and hCG induced luteal cell steroidogenesis in vitro. No support is provided for the concept that luteolysis is mediated by local production of PGF2 alpha. The putative luteolytic effect of oestradiol may entail reduced metabolism of arachidonic acid to lipoxygenase derived products by luteal cells rather than direct stimulation of prostaglandin production by itself.

Calcium and potassium currents in porcine granulosa cells maintained in follicular or monolayer tissue culture

We studied membrane currents in granulosa cells (GC), immediately after collection or after variable culture time in the everted-follicle wall or in the monolayer. GC in both systems express an inward calcium current (ICa) with T-type kinetics and voltage dependence. GC in the everted-follicle culture express an outward potassium current (IK) kinetics, which remains unchanged during three days in culture. IK has delayed-rectifier kinetics, but is insensitive to TEA, 4-AP and apamine. GC in monolayer culture develop a new, inactivating delayed-rectifier potassium current (InK), which progressively dominates as cells advance from day one to day three in culture. A similar InK was recorded in large luteal cells. A possible link between luteinization and the appearance of InK is hypothesized.

Influence of luteinizing hormone and prostaglandin F2α on progesterone secretion in superfused minced bovine luteal tissue in the early stage of the estrous cycle

Minced luteal tissue of bovine corpora lutea from Day 4, 5, and 6 of the estrous cycle (n = 4 corpora lutea each) was superfused for 9 h, and the progesterone secretion under the influence of 100 ng luteinizing hormone (LH)/ml and/or 1,000 ng prostaglandin F(2alpha) (PGF(2alpha))/ml was determined. In vivo, this period of the estrous cycle is characterized by a transition from PGF(2alpha) refractoriness to PGF(2alpha) sensitivity. The investigations were carried out in order to examine whether this transition is reflected by a change in the hormone secretion pattern in vitro. The basal secretion was higher on Day 6 than on Day 4 and 5 (P < 0.01). PGF(2alpha) slightly increased the progesterone secretion, but there was no statistically significant difference (P > 0.05). LH, however, stimulated the progesterone secretion by about 30% in luteal tissue collected from Day 4 and 5 (P < 0.01). In luteal tissue collected from Day 6, the LH-induced increase in hormone secretion was not statistically significant due to two corpora lutea that showed no response at all to LH. The progesterone secretion of the two other corpora lutea, however, was increased by 30% (P < 0.01). When PGF(2alpha) and LH were simultaneously added, the LH-induced progesterone secretion was not inhibited; PGF(2alpha) even seemed to intensify the action of LH. The difference between the hormone secretion under the influence of LH alone and that under the influence of a combination of LH and PGF(2alpha), however, was not statistically significant. It is concluded that in cattle the end of the refractoriness to PGF(2alpha) in vivo is not reflected by a corresponding change of the hormone secretion pattern in vitro.

Modulation of cyclic AMP formation and progesterone secretion by human chorionic gonadotropin, epinephrine, buserelin and prostaglandins in normal or human chorionic gonadotropin desensitized rat immature luteal cells in monolayer culture

It is now well recognized that hCG-induced luteolysis is associated with hCG-induced desensitization, but the physiological significance of luteal cell GnRH, PGS and beta-receptors is still undefined. Therefore, we intend in this study to observe the effects of prostaglandin F2 alpha and prostaglandin E2 and the interactions between epinephrine, a potent LHRH agonist [(D-Ser-(TBu)6, des-Gly-NH2(10)) LHRH ethylamide: Buserelin] and hCG in normal and in vitro hCG-desensitized rat immature luteal cells in monolayer culture, on basal, hCG or cholera toxin stimulated intracellular and extracellular cyclic AMP and progesterone secretion. The present report shows that incubation of immature rat luteal cells in monolayer culture with Buserelin, led to 25-50% inhibition of the epinephrine--as well as PGE2--induced cyclic AMP and progesterone responses. The LHRH agonist can also reverse the stimulatory effects of cholera toxin in the presence of hCG and led with PGF2 alpha, to additive inhibitory effects on extracellular cyclic AMP accumulation induced by cholera toxin. Both Buserelin and PGF2 alpha can reverse the hCG-induced cyclic AMP and progesterone release but no effect could be observed when the incubation was carried out with either substance in the absence of hCG. Prostaglandin E2, in acute conditions of incubation, seems to share agonist properties with hCG when both were incubated with luteal cells. Buserelin reversed the stimulatory effects of PGE2, hCG, epinephrine, and cholera toxin on cyclic AMP and progesterone responses to these substances. These results suggest that Buserelin and PGF2 alpha have luteolytic-like effects and that there may be a complementary action for the two substances. Preincubation of rat luteal cells in monolayer culture with 1 nM hCG for a 24 h period led to the inhibition of cyclic AMP and progesterone responses after a subsequent exposure to hCG and epinephrine. Luteal cells were no longer responsive to hCG while the presence of epinephrine in hCG-desensitized cells led to a 40% stimulation of cAMP and progesterone production. These observations suggest that there occurred a partial alteration of the N component activity of the adenylyl cyclase system.

Modulation of cyclic AMP formation and progesterone secretion by human chorionic gonadotropin, epinephrine, buserelin and prostaglandins in normal or human chorionic gonadotropin desensitized rat immature luteal cells in monolayer culture

It is now well recognized that hCG-induced luteolysis is associated with hCG-induced desensitization, but the physiological significance of luteal cell GnRH, PGs and beta-receptors is still undefined. Therefore, we intend in this study to observe the effects of prostaglandin F2 alpha and prostaglandin E2 and the interactions between epinephrine, a potent LHRH agonist [(D-Ser-(TBu)6, des-Gly-NH10(2) LHRH ethylamide: Buserelin] and hCG in normal and in vitro hCG-desensitized rat immature luteal cells in monolayer culture, on basal, hCG or cholera toxin stimulated intracellular and extracellular cAMP and progesterone secretion. The present report shows that incubation of immature rat luteal cells in monolayer culture with Buserelin, led to 25-50% inhibition of the epinephrine-as well as PGE2-induced cAMP and progesterone responses. The LHRH agonist can also reverse the stimulatory effects of cholera toxin in the presence of hCG and led with PGF2 alpha, to additive inhibitory effects on extracellular cAMP accumulation induced by cholera toxin. Both Buserelin and PGF2 alpha can reverse the hCG-induced cAMP and progesterone release but no effect could be observed when the incubation was carried out with either substance in the absence of hCG. Prostaglandin E2, in acute conditions of incubation, seems to share agonist properties with hCG when both were incubated with luteal cells. Buserelin reversed the stimulatory effects of PGE2, hCG, epinephrine and cholera toxin on cAMP and progesterone responses to these substances. These results suggest that Buserelin and PGF2 alpha have luteolytic-like effects and that there may be a complementary action for the two substances. Preincubation of rat luteal cells in monolayer culture with 1 nM hCG for a 24 h period led to the inhibition of cAMP and progesterone responses after a subsequent exposure to hCG and epinephrine. Luteal cells were no longer responsive to hCG while the presence of epinephrine in hCG-desensitized cells led to a 40% stimulation of cAMP and progesterone production. These observations suggest that occurred a partial alteration of the N component activity of the adenylyl cyclase system.

Inhibitory characteristics of prostaglandin F2 alpha in the rat luteal cell

Enzymatically dispersed and enriched preparations of rat luteal cells were used to characterize the antigonadotropic effects of prostaglandin (PG) F2 alpha. The half-maximal dose (ED50) of LH for stimulation of cAMP accumulation and progesterone secretion was 100 and 25 ng/ml, respectively. Methylisobutylxanthine (MIX) had no effect on the ED50 of LH on cAMP accumulation but reduced the ED50 of LH on progesterone secretion from 25 to 10 ng/ml. PGF2 alpha inhibited the tropic responses to LH by 55-70% within minutes at concentrations of PGF2 alpha within the physiological range. For example, 2-4 nM PGF2 alpha inhibited LH-stimulated cAMP accumulation by 50% (IC50). PGF2 alpha reduced the maximum cAMP response to LH but had no effect on the ED50 of LH for cAMP accumulation whereas PGF2 alpha increased the ED50 of LH on progesterone secretion by 5-7-fold. Inhibition by PGF2 alpha appeared to be unrelated to an effect on cAMP phosphodiesterase activity or to changes in parameters of LH receptor binding activity. No inhibition by PGF2 alpha was evident on LH-stimulated cAMP accumulation in isolated membranes. PGF2 alpha had little effect on cAMP accumulation in response to cholera toxin or forskolin but produced significant inhibition of progesterone secretion in response to cholera toxin or dibutyryl cAMP [Bu)2cAMP). It is concluded that the antigonadotropic effect of PGF2 alpha in the luteal cell is due to two interrelated actions: inhibition of activation of cAMP accumulation by LH and inhibition of the luteal cell response to cAMP. Since PGF2 alpha had no effect in the broken cells, it is suggested that the action of PGF2 alpha may be mediated by a second messenger in the intact cell.

Prostaglandin F2 alpha inhibition of epinephrine stimulated cyclic AMP and progesterone production by rat corpora lutea of various ages

Epinephrine can mimic the stimulatory effects of LH in vitro on cyclic AMP (cAMP) and progesterone production by isolated rat corpora lutea. The aim of the present study was to test whether the effects of epinephrine in vitro on the rat corpus luteum, as with LH, can be inhibited by prostaglandin F2 alpha (PGF2 alpha). The stimulatory effect of epinephrine on tissue levels of cAMP in 1-day-old corpora lutea was not inhibited by PGF2 alpha. A dose-dependent inhibition by PGF2 alpha (0.5-50 microM) was seen for 3-day-old corpora lutea and this inhibition could not be overcome by higher concentrations of epinephrine (0.165-165 microM). The stimulation by epinephrine on progesterone production was inhibited by PGF2 alpha (5 microM) in 3- and 5-day-old, but not in 1-day-old corpora lutea. Thus, PGF2 alpha can inhibit the stimulatory effect of epinephrine in 3- and 5-day-old corpora lutea, but not in the newly formed corpora lutea (1-day-old) and PGF2 alpha shows in this respect the same age dependent inhibitory pattern as in relation to LH stimulation.

The functional activity of adult mouse Leydig cells in monolayer culture. Effect of lutropin and foetal calf serum

Purified Leydig cells were obtained from adult mouse testes by mechanical dispersion followed by Percoll density-gradient centrifugation as described by Schumacher et al. (1978). The cells were then established in monolayer culture by maintaining them in medium and 10% serum at 32 degrees C in 95% O2, 5% CO2. The cells rapidly attached to the culture dishes, gradually flattened and became epitheloid in appearance. Testosterone production by the cells in response to maximum stimulating levels of LH (100 ng/ml) and dibutyryl cyclic AMP (1 mM) was maintained for at least 2 days (approximately 1 microgram/10(6) cells/2h) and then declined to lower levels by days 3-4. Cyclic AMP production in response to LH was higher on day 1 than day 0 and then declined to lower levels by days 3-4. Binding of [125I]hCG was similar on day 0 and day 1 (approximately 20 fmoles/10(6) cells) and then declined to lower levels by days 3-4. The functional activity of the cells cultured in 0, 1 and 10% foetal calf serum was also examined; no significant effect of the serum on LH-stimulated testosterone or cyclic AMP production was found; however, a decrease of up to 50% in the binding of [125I]hCG to the Leydig cells occurred in the presence of serum. These results demonstrate that the function of differentiated adult Leydig cells can be maintained for at least 2 days in culture.

Progesterone, 20alpha-dihydroprogesterone and PGF; interrelated hormonal changes during pseudo-pregnancy in the rat

Ovarian and uterine tissue concentrations of progesterone, 20alpha-dihydroprogesterone (20alphaOHP) and prostaglandin F (PGF) were measured during hormonally-induced pseudopregnancy, as were plasma levels of progesterone and 20alphaOHP, in hysterectomised and sham-operated rats. Elevated levels of PGF in uterine and ovarian tissues were coincident with declining concentrations of progesterone and increasing concentrations of 20alphaOHP in the sham-operated rats. Maximum PGF concentrations were apparent in uterine tissue 14 days after hCG injection, coincident with the plasma, ovarian and uterine nadir concentrations of progesterone. A small but statistically significant increase in ovarian PGF was apparent at this time in sham-operated rats. This elevation of ovarian PGF was abolished by hysterectomy.

Mechanism of the rapid antigonadotropic action of prostaglandins in cultured luteal cells

A reproducible method for dissociation and culture of rat luteal cells is described. The concentration of LH required to produce half-maximal stimulation of progesterone secretion was 50 ng/ml. The effects of prostaglandin E(2) (PGE(2)) and prostaglandin F(2alpha) (PGF(2alpha)) on basal and luteinizing hormone (LH)-stimulated progesterone production were examined. Both prostaglandins stimulated basal progesterone production but PGE(2) was about twice as active, showing a 2-fold maximal stimulation at 0.75 muM. When either prostaglandin was incubated simultaneously with LH, a dose-dependent inhibition of progesterone secretion occurred; PGF(2alpha) was 4 times more active than PGE(2), showing 50% inhibition at a concentration of 40 x nM. Thus, both prostaglandins are more active as antagonists than as agonists of LH with respect to progesterone secretion. PGF(2alpha) also inhibited LH-stimulated adenylate cyclase activity and cyclic AMP accumulation. The block in progesterone secretion was reversed by addition of dibutyryl cyclic AMP (1 mM) but not by theophylline (5 mM) alone. These data and the finding that PGF(2alpha) did not affect the specific binding activity of the LH receptor in intact luteal cells indicate that the rapid action of prostaglandins in luteal cells is due to a block of LH-dependent production of cyclic AMP which results in a decrease in progesterone secretion.