Granulosa cell production of anti-Müllerian hormone is increased in polycystic ovaries

CONTEXT

There has been renewed interest in anti-Müllerian hormone (AMH) because of its role in the ovary. Data on its actions are sparse, but it appears to inhibit follicle growth. Interestingly, serum AMH is two to three times higher in women with polycystic ovary (PCO) syndrome than women with normal ovaries.

OBJECTIVE

We examined the production of AMH by cells from a range of follicle sizes from normal ovaries and compared this with production by ovulatory and anovulatory (anov) PCOs.

DESIGN

Granulosa cells (GCs) and theca and follicular fluid (ff) were isolated from intact follicles. Cells were cultured for 48 h +/- FSH or LH, and AMH was measured in ff and cell-conditioned media (CM).

RESULTS

AMH levels in ff and GC-CM ranged from 42 to 2240 and 0.025 to 1.7 ng/ml, respectively, and were low or undetectable in ff and GC-CM from follicles greater than 9 mm, luteinized cells, and theca and stroma. The mean level of AMH was four times higher in GC-CM from ovulatory PCOs [mean (range) 1.56 (0.025-7)] and 75 times higher from anovPCO [21.4 (17.2-43 ng/ml)] than normal ovaries [0.37 (0.025-1.7)]. Neither LH nor FSH had an effect on AMH production by GCs from normal ovaries, but in cells from PCOs, FSH significantly decreased AMH, and in contrast, LH increased AMH.

CONCLUSIONS

The reduction of AMH in follicles greater than 9 mm from normal ovaries appears to be an important requirement for the selection of the dominant follicle. AMH production per GC was 75 times higher in anovPCOs, compared with normal ovaries. This increase in AMH may contribute to failure of follicle growth and ovulation seen in polycystic ovary syndrome.

Anti-Müllerian hormone and polycystic ovary syndrome: a mountain too high?

Anti-Müllerian hormone (AMH) was initially thought to be produced solely by the foetal male during sexual differentiation to promote regression of the Müllerian ducts. Over the last decade, however, a new and interesting role has emerged for AMH in the ovary. In human ovaries, AMH is produced by granulosa cells from 36 weeks of gestation until menopause, with the highest expression being in small antral follicles. AMH production gradually declines as follicles grow; once follicles reach a size at which they are dominant, it has largely disappeared. Its removal from these larger follicles appears to be an important requirement for dominant follicle selection and progression to ovulation as AMH has an inhibitory role in the ovary, reducing both primordial follicle initiation and follicle sensitivity to FSH by inhibition of aromatase. It is for this reason that AMH is a focus of interest in polycystic ovary syndrome (PCOS). Serum levels are doubled, and granulosa cell production is greatly increased. Interestingly, there appear to be two groups of women with PCOS who can be distinguished by their AMH level: one group consists of those who have high levels which do not reduce with treatment and who respond less well to induction of ovulation, and a second group consists of those in whom the level is less elevated and reduces on treatment and who seem to respond rather better. Understanding the reason for the raised AMH in PCOS may give clues as to the mechanism of anovulation. To conclude, AMH appears to have a major inhibitory role during folliculogenesis, which may contribute to anovulation in PCOS.

Metformin inhibits aromatase via an extracellular signal-regulated kinase-mediated pathway

Metformin treatment, now widely prescribed in polycystic ovary syndrome, is aimed at correcting the associated insulin resistance, but it has also been shown to directly inhibit ovarian steroidogenesis. The mechanisms, however, by which metformin inhibits estradiol production in human granulosa cells remains unknown. Granulosa luteal cells were incubated with metformin, insulin, or combined metformin and insulin treatment, and aromatase mRNA expression was quantified using real-time RT-PCR. Enzyme activity was assessed by the conversion of (3)H-androstenedione to estrone and estradiol. Metformin's effect on the expression of specific untranslated first exon aromatase promoters was analyzed using semiquantitative PCR. The involvement of MAPK kinase (MEK)/ERK pathway was investigated by immunoblotting for aromatase, phosphorylated, and total ERK-1,2 from cells cultured as above with/without the MEK inhibitor PD98059. Metformin significantly inhibited basal and insulin-stimulated aromatase mRNA expression, with parallel results from the aromatase activity assay and protein assessment. This suppression was via down-regulation of aromatase promoter II, I.3, and 1.4 expression and was reversed by the addition of PD98059. Involvement of the ERK signaling pathway was demonstrated by the significant increase in phosphorylated ERK-1,2 with the combined metformin and insulin treatment. We have shown for the first time in human granulosa cells that metformin signficantly attenuated basal and insulin-stimulated P450 aromatase mRNA expression and activity, via silencing of key promoters. This occurred by activation of MEK/ERK pathway, which negatively regulated aromatase production. This is an important consideration given metformin's widespread use in polycystic ovary syndrome and may further support a possible therapeutic indication in estrogen-dependent breast tumors.

Metformin inhibits follicle-stimulating hormone (FSH) action in human granulosa cells: relevance to polycystic ovary syndrome

BACKGROUND

Women with anovulatory polycystic ovary syndrome (PCOS) are generally insulin-resistant and as a consequence are often treated with the biguanide metformin. Results with metformin have, however, been variable with some studies demonstrating induction of regular cycles and an increase in ovulation, whereas others do not. Hence more understanding is needed regarding the mechanism of metformin's actions in ovarian granulosa cells especially in light of previous demonstrations of direct actions.

OBJECTIVE

The aim of this study was to investigate metformin's interaction with the FSH/cAMP/protein kinase A pathway, which is the primary signaling pathway controlling CYP19A1 (aromatase) expression in the ovary.

METHODS

The effect of metformin on FSH and forskolin-stimulated aromatase expression in human granulosa cells was measured by quantitative real-time PCR. Activity was assessed after transfection with a promoter II-luciferase construct, and by an RIA measuring conversion of androgen to estrogens. The effect on FSH receptor (FSHR) mRNA was assessed by quantitative PCR. Levels of phosphorylated cAMP response element binding protein (CREB) and CREB-regulated transcription coactivator 2 (CRTC2) were measured by Western blotting and cAMP by a bioluminescent assay.

RESULTS

Metformin markedly reduced FSH but not forskolin-stimulated aromatase expression and activity. This effect was exerted by inhibition of basal and ligand-induced up-regulation of FSHR expression. Metformin also reduced FSH-induced phosphorylation of CREB and hence CRE activity, which could potentially disrupt the CREB-CREB-binding protein-CRTC2 coactivator complex that binds to CRE in promoter II of the aromatase gene. This is mediated in an AMP-activated protein kinase-independent manner, and does not involve alteration of cAMP levels.

CONCLUSION

These finding have implications for the use of metformin in the treatment of anovulation in women with PCOS.

Pharmacological activators of AMP-activated protein kinase have different effects on Na+ transport processes across human lung epithelial cells

BACKGROUND AND PURPOSE

AMP-activated protein kinase (AMPK) is activated by metformin, phenformin, and the AMP mimetic, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). We have completed an extensive study of the pharmacological effects of these drugs on AMPK activation, adenine nucleotide concentration, transepithelial amiloride-sensitive (I(amiloride)) and ouabain-sensitive basolateral (I(ouabain)) short circuit current in H441 lung epithelial cells.

EXPERIMENTAL APPROACH

H441 cells were grown on permeable filters at air interface. I(amiloride), I(ouabain) and transepithelial resistance were measured in Ussing chambers. AMPK activity was measured as the amount of radiolabelled phosphate transferred to the SAMS peptide. Adenine nucleotide concentration was analysed by reverse phase HPLC and NAD(P)H autofluorescence was measured using confocal microscopy.

KEY RESULTS

Phenformin, AICAR and metformin increased AMPK (alpha1) activity and decreased I(amiloride). The AMPK inhibitor Compound C prevented the action of metformin and AICAR but not phenformin. Phenformin and AICAR decreased I(ouabain) across H441 monolayers and decreased monolayer resistance. The decrease in I(amiloride) was closely related to I(ouabain) with phenformin, but not in AICAR treated monolayers. Metformin and phenformin increased the cellular AMP:ATP ratio but only phenformin and AICAR decreased cellular ATP.

CONCLUSIONS AND IMPLICATIONS

Activation of alpha1-AMPK is associated with inhibition of apical amiloride-sensitive Na(+) channels (ENaC), which has important implications for the clinical use of metformin. Additional pharmacological effects evoked by AICAR and phenformin on I(ouabain), with potential secondary effects on apical Na+ conductance, ENaC activity and monolayer resistance, have important consequences for their use as pharmacological activators of AMPK in cell systems where Na+K+ATPase is an important component.

Action of metformin on the insulin-signaling pathway and on glucose transport in human granulosa cells

CONTEXT

Hyperinsulinemia in polycystic ovary syndrome is widely treated with the insulin sensitizer metformin, which, in addition to its systemic effects, directly affects the ovarian insulin-stimulated steroidogenesis pathway.

OBJECTIVE

Our aim was to investigate the interaction of metformin with the other insulin-stimulated ovarian pathway, namely that leading to glucose uptake.

DESIGN

Human granulosa-luteal cells were cultured with metformin (10(-7) M), insulin (10 ng/ml) or metformin and insulin (met + ins) combined. Insulin receptor (IR) involvement was assessed by culture with an (anti)-insulin receptor (IR) antibody.

MAIN OUTCOME MEASURES

The effect of metformin on insulin-receptor substrate proteins 1 and 2 (IRS-1 and -2) mRNA and protein expression was determined. The KGN granulosa-cell line was used to investigate the effect of insulin and metformin on Akt activation and glucose transporter-4 (Glut-4) expression. Glut-4 translocation from the cytosol to the membrane was determined in cytoplasmic and membrane-enriched fractions of protein lysates.

RESULTS

IRS-1 mRNA and protein increased with all treatments. In contrast, basal IRS-2 mRNA levels were barely detectable, but transcription was up-regulated by metformin. The anti-IR antibody reduced treatment-stimulated IRS-1 to basal levels and IRS-2 expression to an even greater extent than IRS-1, showing greater dependence on the IR than IRS-1. Metformin in the presence of insulin activated Akt and this was dependent on phosphoinositide-3 kinase, as was translocation of Glut-4 to the membrane. Metformin was able to substantially enhance the insulin-stimulated translocation of Glut-4 transporters from the cytosol to the membrane.

CONCLUSION

This net increase in Glut-4 transporters in the plasma membrane has the potential to increase glucose uptake and metabolism by granulosa cells of the insulin-resistant polycystic ovary, thereby facilitating follicle growth.

The regulation and signalling of anti-Müllerian hormone in human granulosa cells: relevance to polycystic ovary syndrome

STUDY QUESTION

What prevents the fall in anti-Müllerian hormone (AMH) levels in polycystic ovary syndrome (PCOS) and what are the consequences of this for follicle progression in these ovaries?

SUMMARY ANSWER

Exposure of granulosa cells (GCs) to high levels of androgens, equivalent to that found in PCOS, prevented the fall in AMH and was associated with dysregulated AMH-SMAD signalling leading to stalled follicle progression in PCOS.

WHAT IS KNOWN ALREADY

In normal ovaries, AMH exerts an inhibitory role on antral follicle development and a fall in AMH levels is a prerequisite for ovulation. Levels of AMH are high in PCOS, contributing to the dysregulated follicle growth that is a common cause of anovulatory infertility in these women.

STUDY DESIGN, SIZE, DURATION

Human KGN-GC (the cell line that corresponds to immature GC from smaller antral follicles (AF)) were cultured with a range of doses of various androgens to determine the effects on AMH production. KGN-GC were also treated with PHTPP (an oestrogen receptor β (ERβ) antagonist) to examine the relationship between AMH expression and the ratio of ERα:ERβ. The differential dose-related effect of AMH on gene expression and SMAD signalling was investigated in human granulosa-luteal cells (hGLC) from women with normal ovaries, with polycystic ovarian morphology (PCOM) and with PCOS. KGN-GC were also cultured for a prolonged period with AMH at different doses to assess the effect on cell proliferation and viability.

PARTICIPANTS/MATERIALS, SETTING, METHODS

AMH protein production by cells exposed to androgens was measured by ELISA. The effect of PHTPP on the mRNA expression levels of AMH, ERα and ERβ was assessed by real-time quantitative PCR (qPCR). The influence of AMH on the relative mRNA expression levels of aromatase, AMH and its receptor AMHRII, and the FSH and LH receptor (FSHR and LHR) in control, PCOM and PCOS hGLCs was quantified by qPCR. Western blotting was used to assess changes in levels of SMAD proteins (pSMAD-1/5/8; SMAD-4; SMAD-6 and SMAD-7) after exposure of hGLCs from healthy women and women with PCOS to AMH. The ApoTox-Glo Triplex assay was used to evaluate the effect of AMH on cell viability, cytotoxicity and apoptosis.

MAIN RESULTS AND THE ROLE OF CHANCE

Testosterone reduced AMH protein secreted from KGN-GC at 10-9-10-7 M (P < 0.05; P < 0.005, multiple uncorrected comparisons Fishers least squares difference), but at equivalent hyperandrogenemic levels no change was seen in AMH levels. 5α-DHT produced a significant dose-related increase in AMH protein secreted into the media (P = 0.022, ANOVA). Increasing the mRNA ratio of ERα:ERβ produced a corresponding increase in AMH mRNA expression (P = 0.015, two-way ANOVA). AMH increased mRNA levels of aromatase (P < 0.05, one-way ANOVA) and FSHR (P < 0.0001, one-way ANOVA) in hGLCs from women with PCOM, but not from normal cells or PCOS (normal n = 7, PCOM n = 5, PCOS n = 4). In contrast to hGLCs from ovulatory ovaries, in PCOS AMH reduced protein levels (cell content) of stimulatory pSMAD-1/5/8 and SMAD-4 but increased inhibitory SMAD-6 and -7 (P < 0.05, normal n = 6, PCOS n = 3). AMH at 20 and 50 ng/ml decreased KGN-GC cell proliferation but not viability after 8 days of treatment (P < 0.005, two-way ANOVA).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Luteinised GC from women undergoing IVF have a relatively low expression of AMH/AMHRII but advantageously continue to display responses inherent to the ovarian morphology from which they are collected. To compensate, we also utilised the KGN cell line which has been characterised to be at a developmental stage close to that of immature GC. The lack of flutamide influence on testosterone effects is not in itself sufficient evidence to conclude that the effect on AMH is mediated via conversion to oestrogen, and the effect of aromatase inhibitors or oestrogen-specific inhibitors should be tested. The effect of flutamide was tested on testosterone but not DHT.

WIDER IMPLICATIONS OF THE FINDINGS

Normal folliculogenesis and ovulation are dependent on the timely reduction in AMH production from GC at the time of follicle selection. Our findings reveal for the first time that theca-derived androgens may play a role in this model but that this inhibitory action is lost at levels of androgens equivalent to those seen in PCOS. The AMH decline may either be a direct effect of androgens or an indirect one via conversion to oestradiol and acting through the upregulation of ERα, which is known to stimulate the AMH promoter. Interestingly, the ability of GCs to respond to this continually elevated AMH level appears to be reduced in cells from women with PCOS due to an adaptive alteration in the SMAD signalling pathway and lower expression of AMHRII, indicating a form of 'AMH resistance'.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Thomas Addison Scholarship, St Georges Hospital Trust. The authors report no conflict of interest in this work and have nothing to disclose.

TRIAL REGISTRATION NUMBER

N/A.

Neonatal 5HT activity antagonizes the masculinizing effect of testosterone on the luteinizing hormone release response to gonadal steroids and on brain structures in rats

Hypothalamic 5HT concentrations are transiently lower in male compared to female Wistar rats in the second week post partum (pp) and our previous findings have shown that pharmacologically potentiating 5HT activity over this period feminizes certain aspects of sexually differentiated behaviours in adult males and androgenized females. In order to investigate whether neonatal testosterone and 5HT interact to influence physiological and morphological brain sexual differences, females, androgenized females and males were treated with the 5HT2 agonist (-) [2,5 dimethoxy-4-iodophenyl]-2-amino propane HCl [(-) DOI], over days 8-16 pp. In androgenized females (250 microg testosterone proprionate, day 2 pp) (-) DOI prevented the delay in vaginal opening, but did not prevent the androgen-induced constant oestrus in females treated with 100 microg TP, day 2 pp. (-) DOI overcame the neonatal androgen effect in suppressing the positive feedback of ovarian steroids in a few males and androgenized females. (-) DOI had a feminizing effect on the volume of the anteroventral periventricular nucleus (normally smaller in males), by significantly increasing its volume in male and androgenized females. It also had a significant antagonistic effect on the testosterone-induced increase in the volume of the sexually dimorphic nucleus of the preoptic area in males and androgenized females. These findings support the view that raised 5HT activity in the second week of life antagonizes the masculinizing effect of neonatal testosterone.

Phosphorylation and activation of AMP-activated protein kinase (AMPK) by metformin in the human ovary requires insulin

Metformin is commonly used to treat women with polycystic ovary syndrome, but its precise mechanism of action is unclear, and it even appears to have direct ovarian effects. At the cellular level, it may act either via an insulin-dependent pathway or an independent pathway by activating AMP-activated protein kinase (AMPK). In the ovary, metformin directly decreased estradiol and progesterone production by human granulosa cells, and inhibition of progesterone production by metformin in rat granulosa cells caused an increase in phosphorylated AMPK (pAMPK). We investigated whether metformin activates AMPK in the human ovary by looking for changes in phosphorylation of AMPK and its downstream target acetyl CoA carboxylase (ACC). mRNA and protein for α1 and α2 AMPK subunits were present in all human ovarian tissue. Neither 100 nm nor 2 mm of metformin affected subunit expression. After 1 or 4 h, neither dose of metformin increased pAMPK or pACC, although after 1 h, the addition of insulin significantly enhanced pAMPK, whereas insulin alone had no effect on phosphorylation of either AMPK or ACC. The addition of compound C, an inhibitor of AMPK, negated the effect of metformin in the presence of insulin on pAMPK. This effect on AMPK was not due to a change in the ADP/ATP ratio measured by HPLC. In summary, the presence of insulin was required to cause a metformin-induced increase in pAMPK in these human ovarian cells. Although previous data suggest that metformin may act via an insulin-independent pathway, our results therefore imply that insulin may be required to initiate an effect.

Ovarian 11β-hydroxysteroid dehydrogenase (11βHSD) activity is suppressed in women with anovulatory polycystic ovary syndrome (PCOS): apparent role for ovarian androgens

CONTEXT

Altered hepatic cortisol-cortisone metabolism by type 1 11β-hydroxysteroid dehydrogenase (11βHSD1) has previously been linked with polycystic ovary (PCO) syndrome (PCOS).

OBJECTIVES

Our objectives were to establish whether ovarian 11βHSD activities are also altered in PCOS and to determine whether any changes in ovarian cortisol metabolism might reflect exposure to elevated concentrations of insulin or androgens.

DESIGN

Cortisol and cortisone concentrations were measured in follicular fluid aspirated from size-matched follicles dissected from normal, ovulatory, and anovulatory PCOs. Human granulosa-lutein cells, recovered during oocyte retrieval for assisted conception, were maintained in primary culture for 4 days, after which 11βHSD1 activities were measured as the net oxidation of [(3)H]cortisol (100 nmol/L) in the absence and presence of insulin (100 nmol/L) with or without metformin (1 μmol/L) or a range of androgens/oxy-androgen metabolites (0.01-10 μmol/L).

RESULTS

Intrafollicular cortisol to cortisone ratios were elevated in anovulatory PCOs (2.1 ± 0.4, P < .05, n = 13) but did not differ between follicles from ovulatory PCOs (1.6 ± 0.1, n = 24) and normal ovaries (1.2 ± 0.1, n = 14). 11βHSD1 activities were lower in granulosa-lutein cells recovered from patients with PCOS compared with all other causes of infertility (median = 5.8 vs 14.9 pmol cortisone/4 h, respectively; P < .05). Cortisol oxidation was unaffected by insulin with or without metformin, dehydroepiandrosterone, and androstenedione, but was inhibited in a concentration-dependent manner by testosterone, 11β-hydroxyandrostenedione, and 7α- and 7β-hydroxy-dehydroepiandrosterone (P < .01).

CONCLUSIONS

There is decreased inactivation of cortisol in follicles from anovulatory PCOS. This may reflect inhibition of 11βHSD1 by androgens and their 7/11-oxy-metabolites, local concentrations of which are increased in PCOS, and may contribute to the block to folliculogenesis seen in PCOS.

Action of Metformin on the Insulin-Signaling Pathway and on Glucose Transport in Human Granulosa Cells

Context:

Hyperinsulinemia in polycystic ovary syndrome is widely treated with the insulin sensitizer metformin, which, in addition to its systemic effects, directly affects the ovarian insulin-stimulated steroidogenesis pathway.

Objective:

Our aim was to investigate the interaction of metformin with the other insulin-stimulated ovarian pathway, namely that leading to glucose uptake.

Design:

Human granulosa-luteal cells were cultured with metformin (10−7m), insulin (10 ng/ml) or metformin and insulin (Met + Ins) combined. Insulin receptor (IR) involvement was assessed by culture with an (anti)-insulin receptor (IR) antibody.

Main Outcome Measures:

The effect of metformin on insulin-receptor substrate proteins 1 and 2 (IRS-1 and -2) mRNA and protein expression was determined. The KGN granulosa-cell line was used to investigate the effect of insulin and metformin on Akt activation and glucose transporter-4 (Glut-4) expression. Glut-4 translocation from the cytosol to the membrane was determined in cytoplasmic and membrane-enriched fractions of protein lysates.

Results:

IRS-1 mRNA and protein increased with all treatments. In contrast, basal IRS-2 mRNA levels were barely detectable, but transcription was up-regulated by metformin. The anti-IR antibody reduced treatment-stimulated IRS-1 to basal levels and IRS-2 expression to an even greater extent than IRS-1, showing greater dependence on the IR than IRS-1. Metformin in the presence of insulin activated Akt and this was dependent on phosphoinositide-3 kinase, as was translocation of Glut-4 to the membrane. Metformin was able to substantially enhance the insulin-stimulated translocation of Glut-4 transporters from the cytosol to the membrane.

Conclusion:

This net increase in Glut-4 transporters in the plasma membrane has the potential to increase glucose uptake and metabolism by granulosa cells of the insulin-resistant polycystic ovary, thereby facilitating follicle growth.