Pituitary gland development and disease: from stem cell to hormone production

Many aspects of pituitary development have become better understood in the past two decades. The signaling pathways regulating pituitary growth and shape have emerged, and the balancing interactions between the pathways are now appreciated. Markers for multipotent progenitor cells are being identified, and signature transcription factors have been discovered for most hormone-producing cell types. We now realize that pulsatile hormone secretion involves a 3D integration of cellular networks. About a dozen genes are known to cause pituitary hypoplasia when mutated due to their essential roles in pituitary development. Similarly, a few genes are known that predispose to familial endocrine neoplasia, and several genes mutated in sporadic pituitary adenomas are documented. In the next decade, we anticipate gleaning a deeper appreciation of these processes at the molecular level, insight into the development of the hypophyseal portal blood system, and evolution of better therapeutics for congenital and acquired hormone deficiencies and for common craniopharyngiomas and pituitary adenomas.

Surfactant protein-A (SP-A) selectively inhibits prostaglandin F2alpha (PGF2alpha) production in term decidua: implications for the onset of labor

CONTEXT

Labor is characterized by "decidual activation" with production of inflammatory mediators. Recent data suggest that surfactant protein-A (SP-A) may be critical to the onset of labor in mice. Whether this is also true in humans is unclear.

OBJECTIVES

The aim was to investigate: 1) the expression of SP-A at the maternal-fetal interface; 2) the effect of SP-A on the production of inflammatory mediators by human decidua; and 3) the association between single nucleotide polymorphisms in maternal SP-A genes and spontaneous preterm birth.

RESEARCH DESIGN AND METHODS

In situ expression of SP-A was investigated by immunohistochemistry and quantitative RT-PCR. Term decidual stromal cells were isolated, purified, and treated with/without SP-A (1-100 μg/ml), IL-1β, and/or thrombin. Levels of inflammatory mediators [IL-6, IL-8, TNFα, matrix metalloproteinase-3, monocyte chemotactic protein-1, IL-1β, PGE(2), prostaglandin F(2α) (PGF(2α))] and angiogenic factors (soluble fms-like tyrosine kinase-1, vascular endothelial growth factor) were measured in conditioned supernatant by ELISA and corrected for protein content. The effect of SP-A on eicosanoid gene expression was measured by quantitative RT-PCR.

RESULTS

SP-A localized to endometrium/decidua. High-dose SP-A (100 μg/ml) inhibited PGF(2α) by term decidual stromal cells without affecting the production of other inflammatory mediators, and this effect occurred at a posttranscriptional level. Decidual SP-A expression decreased significantly with labor. Single nucleotide polymorphisms in the SP-A genes do not appear to be associated with preterm birth.

CONCLUSIONS

SP-A is produced by human endometrium/decidua, where it significantly and selectively inhibits PGF(2α) production. Its expression decreases with labor. These novel observations suggest that decidual SP-A likely plays a critical role in regulating prostaglandin production within the uterus, culminating at term in decidual activation and the onset of labor.

Antioxidants induce apoptosis of rat ovarian theca-interstitial cells

Regulation of growth of ovarian theca-interstitial tissues is essential for normal ovarian development and function. Reactive oxygen species are involved in modulation of signal transduction pathways, including regulation of tissue growth and apoptosis. Previously, we have demonstrated that antioxidants inhibit proliferation of theca-interstitial cells. This report evaluates the effects of antioxidants on apoptosis of rat theca-interstitial cells. The cells were cultured in chemically defined media without or with vitamin E succinate and ebselen. Apoptosis was evaluated by cytochemical assessment of nuclear morphology, activity of executioner caspases 3 and 7, and determination of staining with annexin V in combination with propidium iodide. Both tested antioxidants induced significant morphological changes consistent with apoptosis, including chromatin condensation, nuclear shrinkage, and pyknosis. Antioxidants also induced other hallmarks of apoptosis including increased activity of caspases 3/7 as well as increased staining with annexin V. The present findings demonstrate that antioxidants with distinctly different mechanisms of action induce a series of events consistent with the process of apoptosis in ovarian mesenchyme. These observations may be of translational-clinical relevance, providing mechanistic support for the use of antioxidants in the treatment of PCOS, a condition associated with excessive growth and activity of theca-interstitial cells.

Progestin inhibits and thrombin stimulates the plasminogen activator/inhibitor system in term decidual stromal cells: implications for parturition

OBJECTIVE

Labor is associated with 'decidual activation' with increased proteolysis and extracellular matrix degradation. The balance between plasminogen activator inhibitor-1 (PAI-1) and urokinase (uPA) and tissue-type plasminogen activator (tPA) is an important determinant of proteolytic activity at the maternal-fetal interface. Thrombin released at the time of placental abruption (decidual hemorrhage) is known to promote decidual proteolysis and uterine contractions. This study investigates the separate and interactive effects of steroid hormones and thrombin on PAI-1, uPA, and tPA expression by term decidual cells (DCs).

STUDY DESIGN

Term DCs were isolated by enzymatic digestion, purified, and depleted of leukocytes. Cells were treated with estradiol (10(-8) mol [E2]), medroxyprogesterone acetate (10(-7) mol [MPA]), both, or vehicle for 7 days. After 24-hour incubation with or without thrombin (0.1-2.5 U/mL), levels of PAI-1, uPA, and tPA in conditioned supernatant were measured by specific ELISA and Western blotting. Levels of PAI-1 and uPA mRNA were measured by quantitative RT-PCR.

RESULTS

In the cultured term DCs, ELISA measurements indicated that basal output of PAI-1 was about 2 logs higher than that of either uPA or tPA (2.5 +/- 0.7 ng/mL per microg protein, 13.4 +/- 6.3 pg/mL per microg protein, and 25.4 +/- 10.8 pg/mL per microg protein, respectively). Although E2 alone did not affect PAI-1 output, MPA and E2+MPA significantly enhanced PAI-1 production (2.5 +/- 0.7 vs 8.2 +/- 2.0 ng/mL per microg protein for E2+MPA [3.3-fold]; P < .01). By contrast, uPA output was inhibited by exposure to MPA (13.4 +/- 6.3 vs 2.6 +/- 1.1 pg/mL per microg protein [0.2-fold]; P < .05), whereas tPA production was not affected by MPA. Thrombin did not significantly affect uPA and tPA production by term DCs. In contrast, in E2+MPA-treated term DCs, thrombin, a hemostatic proinflammatory cytokine, selectively increased PAI-1 output in a dose-dependent fashion, which could be blocked by the selective thrombin inhibitor, hirudin. Western blotting confirmed the effects of MPA and thrombin in elevating secreted levels of PAI-1. Unlike the increase in PAI-1 output elicited by thrombin, term DCs were unresponsive to either of the classic proinflammatory cytokines, TNFalpha or IL-1beta. Corresponding effects on PAI-1 mRNA levels were elicited by MPA and thrombin as seen for PAI-1 protein expression, suggesting that these up-regulatory effects are transcriptionally mediated.

CONCLUSION

Progestin enhanced PAI-1 and inhibited uPA expression by term DCs, which may explain in part the pregnancy-prolonging properties of progesterone as a consequence of inhibited proteolytic activity at the maternal-fetal interface. Thrombin augmented PAI-1 expression in the absence of increased uPA or tPA expression by term DCs, suggesting that abruption-associated decidual proteolysis and preterm labor is mediated primarily by thrombin-enhanced matrix metalloproteinase expression rather than an indirect effect on the plasminogen activator/inhibitor system.

Mevastatin inhibits proliferation of rat ovarian theca–interstitial cells by blocking the mitogen-activated protein kinase pathway

OBJECTIVE

To evaluate mechanisms involved in mevastatin-induced inhibition of proliferation of ovarian theca-interstitial cells.

DESIGN

In vitro study.

SETTING

Academic laboratory.

ANIMAL(S)

Immature Sprague-Dawley female rats.

INTERVENTION(S)

Ovarian theca-interstitial cells were cultured without and with mevastatin in the presence and absence of serum, mevalonic acid, and/or insulin.

MAIN OUTCOME MEASURE(S)

Proliferation was assessed by determination of DNA synthesis by thymidine incorporation assay. Activation of extracellular signal-regulated kinase (Erk1/2) and of Akt/protein kinase B (PKB) was determined by ELISA.

RESULT(S)

Mevastatin induced a concentration-dependent inhibition of theca-interstitial cell proliferation in the absence and in the presence of serum. Inhibitory effects of mevastatin were partly abrogated by mevalonic acid and by insulin. Mevastatin blocked basal and insulin-induced phosphorylation of ERK1/2. In contrast, mevastatin had no significant effect on either basal or insulin-induced phosphorylation of Akt/PKB.

CONCLUSION(S)

Mevastatin inhibits proliferation of theca-interstitial cells by a mechanism that involves depletion of mevalonic acid and selective inhibition of basal and insulin-induced activity of Erk1/2 pathway, but not Akt/PKB pathway. These effects of mevastatin may be a result of decreased isoprenylation of small GTPases.

Insulin and oxidative stress modulate proliferation of rat ovarian theca-interstitial cells through diverse signal transduction pathways

Insulin and moderate oxidative stress stimulate proliferation of ovarian theca-interstitial cells. The effects of these agents on selected signal transduction pathways were examined. PD98059 (inhibitor of MAP2K1, also known as MEK-1, upstream of extracellular signal-regulated protein kinases MAPK3/1, also known as ERK1/2), wortmannin (inhibitor of PIK3C2A, also known as PI3K), and rapamycin (inhibitor of FRAP1, also known as mTOR, upstream of RPS6KB1) each significantly decreased insulin and oxidative stress-induced proliferation of theca-interstitial cells. The greatest inhibition was observed in the presence of rapamycin; this effect occurred without a significant change in cell viability. Phosphorylation of AKT was stimulated by insulin only, while phosphorylation of MAPK3/1 and RPS6KB1 was increased by insulin and oxidative stress. Insulin-induced and oxidative stress-induced phosphorylation of RPS6KB1 was partly inhibited by wortmannin and partly by PD98059; the greatest inhibition was observed in the presence of a combination of wortmannin plus PD98059. Effects of insulin and oxidative stress on phosphorylation of RPS6KB1 were confirmed by kinase activity assays. These findings indicate that actions of insulin and oxidative stress converge on MAPK3/1 and RPS6KB1. Furthermore, we speculate that activation of RPS6KB1 may be in part induced via the MAPK3/1 pathway.

Placental growth factor in the cerebrospinal fluid of women with preeclampsia

OBJECTIVE

Recent data suggest that excess circulating soluble fms-like tyrosine kinase-1 (sFlt-1) may causally relate to preeclampsia. This study investigates the levels of sFlt-1, VEGF, and PlGF in cerebrospinal fluid (CSF) of patients with preeclampsia and normotensive controls.

METHODS

CSF was collected from preeclamptic patients (n=15) and controls (n=7) at the time of spinal anesthesia and assayed for PlGF, sFlt-1, and VEGF (total and free) by specific immunoassays.

RESULTS

All sought angiogenic factors were measurable. Levels of free PlGF but not sFlt-1 or VEGF (total or free) were increased in CSF of preeclamptic women. There was no significant difference in the ratios of angiogenic factors in the CSF of women with preeclampsia. There was no correlation between levels of angiogenic factors and CSF cell counts or severity of symptoms.

CONCLUSION

Elevated levels of PlGF in CSF preeclamptic women may promote vascular permeability and contribute to the hypertensive encephalopathy seen in such patients.

Changes in the Expression of Steroidogenic and Antioxidant Genes in the Mouse Corpus Luteum During Luteolysis1

Luteal cell death plays a key role in the regulation of the reproductive process in all mammals. It is also known that prostaglandin (PG) F 2alpha is one of the main factors that cause luteal demise; still, the effects of PGF 2alpha on luteal gene transcription have not been fully explored. Using microarray and reverse transcription-polymerase chain reaction, we have profiled gene expression in the corpus luteum (CL) of wild-type and PGF 2alpha receptor knockout mice on Day 19 of pregnancy. Western blot analysis of selected genes was also performed. Because luteolysis has been shown to be associated with increased oxygen radical production and decreased progesterone synthesis, we report here changes observed in the expression of antioxidant and steroidogenic genes. We found that luteal cells express all genes necessary for progesterone synthesis, whether or not they had undergone luteolysis; however, an increase in mRNA levels of enzymes involved in androgen production, along with a decrease in the expression of enzymes implicated in estrogen synthesis, was observed. We also identified six genes committed to the elimination of free radical species that are dramatically down-regulated in the CL of wild-type animals with respect to PGF 2alpha receptor knockout mice. Similar changes in the expression of steroidogenic and antioxidant genes were found in the CL of wild-type animals between Days 15 and 19 of pregnancy. It is proposed that an increase in the androgen:estrogen biosynthesis ratio, along with a significantly reduced expression of free radical scavenger proteins, may play an important role in the luteolytic process.

Pituitary gland and pregnancy

The hypothalamic-pituitary-adrenal axis is central to mammalian reproductive function, including conception, pregnancy maintenance, parturition, and breastfeeding. Pregnancy is associated with substantial physiologic changes within this endocrine axis to meet the demands of pregnancy, which include support of the fetus (volume support, nutritional and oxygen supply, clearance of fetal waste), protection of the fetus (from starvation, drugs, toxins), preparation of the uterus for labor, and protection of the mother from potential cardiovascular injury at delivery. This article reviews the anatomy, embryology, and physiology of the pituitary. The effect of pregnancy on pituitary structure and function, in health and disease, also is discussed.

Effects of oxidants and antioxidants on proliferation of endometrial stromal cells

OBJECTIVE

To evaluate the effects of oxidative stress and antioxidants on proliferation of endometrial stromal cells.

DESIGN

In vitro study.

SETTING

Academic laboratory.

PATIENT(S)

Women, with and without endometriosis, of reproductive age.

INTERVENTION(S)

Culture of endometrial stromal cells with antioxidants or with agents inducing oxidative stress.

MAIN OUTCOME MEASURE(S)

Proliferation of endometrial stromal cells as determined by thymidine incorporation assay and 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay.

RESULT(S)

Antioxidants induced a dose-dependent inhibition of thymidine incorporation: vitamin E succinate was inhibitory at 10-100 microM (by 43%-95%), ebselen at 10-30 microM (by 29%-77%), and N-acetylcysteine at 10-30 mM (by 52%-85%). In contrast, modest oxidative stress induced by hypoxanthine/xanthine oxidase (1 mM/3-30 microU/mL) stimulated proliferation by 40%-62%. H2O2 (1 microM) increased DNA synthesis by 56%. Comparable findings were obtained using MTT proliferation assay. Antioxidants inhibited proliferation: vitamin E succinate (100 microM) by 91%, ebselen (30 microM) by 81%, and N-acetylcysteine (30 mM) by 95%. Hypoxanthine/xanthine oxidase (1 mM/30 microU/mL) and H2O2 (1 microM) stimulated growth by 122% and 58%, respectively.

CONCLUSION(S)

Reactive oxygen species may modulate growth of endometrial stroma. Under pathologic conditions such as endometriosis, increased oxidative stress and depletion of antioxidants may contribute to excessive growth of endometrial stromal cells.

Mevastatin inhibits ovarian theca-interstitial cell proliferation and steroidogenesis

OBJECTIVE

Statins reduce cardiovascular risks by improving hypercholesterolemia, reducing vascular smooth muscle proliferation, and ameliorating inflammation. Polycystic ovary syndrome (PCOS) is associated with increased cardiovascular risks and is characterized by ovarian theca-interstitial hyperplasia and hyperandrogenism. This study tested the hypothesis that mevastatin limits theca-interstitial proliferation and decreases steroidogenesis.

DESIGN

In vitro study.

SETTING

Academic laboratory.

PATIENT(S)

None.

INTERVENTION(S)

Effects of mevastatin on cultured theca-interstitial cells.

MAIN OUTCOME MEASURE(S)

Proliferation was evaluated by determination of DNA synthesis using thymidine incorporation assay and by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay. Production of P and T was determined by specific radioimmunoassays.

RESULT(S)

Mevastatin induced a profound concentration-dependent inhibition of DNA synthesis. At the highest concentration (30 microM), mevastatin inhibited DNA synthesis by 92%. Similarly, in the MTT proliferation assay, mevastatin induced a concentration-dependent decrease in cell number. Mevastatin decreased production of P (by up to 49%) and T (by up to 52%); these effects remained significant when the effect on cell culture protein content was accounted for.

CONCLUSION(S)

Mevastatin inhibits proliferation of theca-interstitial cells; it also inhibits P and T production independently of the effects on cell growth. These findings provide a foundation for studies evaluating statins as potential therapeutic agents in the treatment of ovarian mesenchymal hyperplasia and hyperandrogenism characteristic of PCOS.

Proliferation of ovarian theca-interstitial cells is modulated by antioxidants and oxidative stress

BACKGROUND

Maintenance of ovarian homeostasis requires precise regulation of proliferation of thecal- interstitial (T-I) cells. Recent evidence indicates that oxidative stress and antioxidants modulate proliferation of various tissues under both physiological and pathological conditions. This study evaluated the effects of oxidative stress and antioxidants on T-I proliferation.

METHODS

Rat T-I cells were cultured in serum-free medium and proliferation was assessed by determination of DNA synthesis using the thymidine incorporation assay, by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and by direct counting of steroidogenically active cells and steroidogenically inactive cells.

RESULTS

Antioxidants and reactive oxygen scavengers induced a dose-dependent decrease of T-I proliferation. Vitamin E succinate was inhibitory at 10-100 micro mol/l, ebselen was inhibitory at 0.3-30 micro mol/l, and superoxide dismutase was inhibitory at 300-1000 IU/ml. In contrast, oxidative stress resulted in a biphasic effect. Modest oxidative stress induced by 1 mmol/l hypoxanthine and xanthine oxidase (3-30 micro U/ml) stimulated proliferation of T-I cells, while greater oxidative stress induced by xanthine oxidase (1 mU/ml) profoundly inhibited proliferation. Direct cell counting demonstrated comparable effects on steroidogenically active and inactive cells.

CONCLUSIONS

Reactive oxygen species may play a role in the regulation of growth of ovarian mesenchyme. Under pathological conditions, such as those encountered in polycystic ovary syndrome, excessive oxidative stress and depletion of antioxidants may contribute to ovarian mesenchymal hyperplasia.