Luteinizing hormone activates chloride currents in hen ovarian granulosa cells

Reproductive endocrinology of environmental nitrate

Nitrate is a widespread contaminant of aquatic ecosystems and drinking water. It is also broadly active in organismal physiology, and as such, has the potential to both enhance and disrupt normal physiological function. In animals, nitrate is a proposed endocrine disrupter that is converted in vivo to nitrite and nitric oxide. Nitric oxide, in particular, is a potent cell signaling molecule that participates in diverse biological pathways and events. Here, we review in vivo nitrate cycling and downstream mechanistic physiology, with an emphasis on reproductive outcomes. However, in many cases, the research produces contradictory results, in part because there is good evidence that nitrate follows a non-monotonic dose-response curve. This conundrum highlights an array of opportunities for scientists from different fields to collaborate for a full understanding of nitrate physiology. Opposing conclusions are especially likely when in vivo/in vitro, long term/short term, high dose/low dose, or hypoxia/normoxia studies are compared. We conclude that in vivo studies are most appropriate for testing an organism's integrated endocrine response to nitrate. Based on the limited available studies, there is a generalized trend that shorter term studies (less than 1 month) or studies involving low doses (≤5 mg/L NO₃-N) cause steroid hormone levels to decline. Studies that last more than a month and/or involve higher, but still environmentally relevant, exposures (>50-100 mg/L NO₃-N) cause steroid hormone levels to increase. Very high nitrate doses (>500 mg/L NO₃-N) are cytotoxic in many species. Hypoxia and acidity are likely to intensify the effects of nitrate. For study design, degree of study animal reproductive maturity or activity is important, with immature/reproductively quiescent animals responding to nitrate differently, compared with reproductively active animals. A detailed table of studies is presented.

Anoctamin 1 calcium-activated chloride channel downregulates estrogen production in mouse ovarian granulosa cells

Calcium-dependent chloride conductances have been described in chicken and human granulosa cells (GCs) and may be involved in steroidogenesis. However, the molecular identities of corresponding chloride channels remain unknown. The purpose of this study was to explore the expression and function of the Anoctamin 1 (ANO1) calcium-activated chloride channel (CaCC) in mouse ovary. ANO1 mRNA and protein expression was identified in mouse ovary GCs by RT-PCR, immunoblot, and immunostaining. Patch-clamp analysis on freshly isolated GCs identified an outwardly rectifying Ca(2+)-activated Cl(-) current that was completely blocked by a selective ANO1 inhibitor T16Ainh-A01. Knockdown of ANO1 mRNA or incubation with a selective inhibitor T16Ainh-A01 enhanced estradiol production, whereas a selective ANO1 activator Eact significantly inhibited estradiol production in primary cultured GCs. The ANO1 expression or activation increases the phosphorylation of ERK1/2 and decreases aromatase expression. The ANO1 expression level is remarkably higher at the proestrous and estrous stages in the estrous cycle. In vivo study indicated a profound induction of ANO1 expression in ovarian GCs by pregnant mare serum gonadotropin (PMSG) that can be further augmented by hCG treatment, suggesting that both FSH and LH may upregulate ANO1 expression at the proestrous and estrous stages. ANO1 expression was remarkably reduced in DHEA-induced PCOS ovary. These data identified for the first time the expression of ANO1 Ca(2+) activated Cl(-) channel in mouse ovarian GCs and determined its negative regulation on estrogen production possibly through MEK-ERK signaling cascade. The present study provided new insights into the molecular mechanisms for the regulation of folliculogenesis and ovulation.

Activation of Cl- channels by human chorionic gonadotropin in luteinized granulosa cells of the human ovary modulates progesterone biosynthesis

Chloride permeability pathways and progesterone (P4) secretion elicited by human chorionic gonadotropin (hCG) in human granulosa cells were studied by electrophysiological techniques and single-cell volume, membrane potential and Ca2+i measurements. Reduction in extracellular Cl(-) and equimolar substitution by the membrane-impermeant anions glutamate or gluconate significantly increased hCG-stimulated P4 accumulation. A similar result was achieved by exposing the cells to hCG in the presence of a hypotonic extracellular solution. Conversely, P4 accumulation was drastically reduced in cells challenged with hCG exposed to a hypertonic solution. Furthermore, conventional Cl(-) channel inhibitors abolished hCG-mediated P4 secretion. In contrast, 25-hydroxycholesterol-mediated P4 accumulation was unaffected by Cl(-) channel blockers. In human granulosa cells, hCG triggered the activation of a tamoxifen-sensitive outwardly rectifying Cl(-) current comparable to the volume-sensitive outwardly rectifying Cl(-) current. Exposure of human granulosa cells to hCG induced a rapid 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid-sensitive cell membrane depolarization that was paralleled with an approximately 20% decrease in cell volume. Treatment with hCG evoked oscillatory and nonoscillatory intracellular Ca2+ signals in human granulosa cells. Extracellular Ca2+ removal and 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid abolished the nonoscillatory component while leaving the Ca2+ oscillations unaffected. It is concluded that human granulosa cells express functional the volume-sensitive outwardly rectifying Cl(-) channels that are activated by hCG, which are critical for plasma membrane potential changes, Ca2+ influx, and P4 production.

The expression of hyperpolarization activated cyclic nucleotide gated (HCN) channels in the rat ovary are dependent on the type of cell and the reproductive age of the animal: a laboratory investigation

BACKGROUND

Aim of this study was to test the hypothesis that levels of hyperpolarization activated cyclic nucleotide gated channels 1 to 4 (HCN1-4) are linked to the reproductive age of the ovary.

METHODS

Young, adult, and reproductively aged ovaries were collected from Sprague-Dawley rats. RT-PCR and western blot analysis of ovaries was performed to investigate the presence of mRNA and total protein for HCN1-4. Immunohistochemistry with semiquantitative H score analysis was performed using whole ovarian histologic sections.

RESULTS

RT-PCR analysis showed the presence of mRNA for HCN1-4. Western blot analysis revealed HCN1-3 proteins in all ages of ovarian tissues. Immunohistochemistry with H score analysis demonstrated distinct age-related changes in patterns of HCN1-3 in the oocytes, granulosa cells, theca cells, and corpora lutea. HCN4 was present only in the oocytes, with declining levels during the reproduction lifespan.

CONCLUSION

The evidence presented here demonstrates cell-type and developmental age patterns of HCN1-4 channel expression in rat ovaries. Based on this, we hypothesize that HCN channels have functional significance in rat ovaries and may have changing roles in reproductive aging.

The Cebpd (C/EBPdelta) gene is induced by luteinizing hormones in ovarian theca and interstitial cells but is not essential for mouse ovary function

The CCAAT/enhancer binding protein (CEBP) family of transcription factors includes five genes. In the ovary, both Cebpa and Cebpb are essential for granulosa cell function. In this study we have explored the role of the Cebpd gene in ovarian physiology by expression and functional studies. Here we report that Cebpd (C/EBPdelta) is expressed in the mouse ovary in a highly restricted temporal and spatial pattern. In response to luteinizing hormone (LH/hCG), CEBPD expression is transiently induced in interstitial cells and in theca cells of follicles from the primary to pre-ovulatory stage, and overlaps in part with expression of the alpha-smooth muscle actin protein. Efficient down-regulation of CEBPD was dependent on a functional Cebpb gene. Proliferating human theca cells in culture also express Cebpd. Cells from patients with polycystic ovarian syndrome (PCOS) exhibited higher Cebpd expression levels. However, deletion of Cebpd in mice had no overt effect on ovarian physiology and reproductive function. Very little is known at present about the molecular mechanisms underlying theca/interstitial cell functions. The expression pattern of CEBPD reported here identifies a novel functional unit of mouse theca cells of primary through tertiary follicles responding to LH/hCG together with a subset of interstitial cells. This acute stimulation of CEBPD expression may be exploited to further characterize the hormonal regulation and function of theca and interstitial cells.

Gonadotropins and ovarian cancer

Ovarian epithelial cancer (OEC) accounts for 90% of all ovarian cancers and is the leading cause of death from gynecological cancers in North America and Europe. Despite its clinical significance, the factors that regulate the development and progression of ovarian cancer are among the least understood of all major human malignancies. The two gonadotropins, FSH and LH, are key regulators of ovarian cell functions, and the potential role of gonadotropins in the pathogenesis of ovarian cancer is suggested. Ovarian carcinomas have been found to express specific receptors for gonadotropins. The presence of gonadotropins in ovarian tumor fluid suggests the importance of these factors in the transformation and progression of ovarian cancers as well as being prognostic indicators. Functionally, there is evidence showing a direct action of gonadotropins on ovarian tumor cell growth. This review summarizes the key findings and recent advances in our understanding of these peptide hormones in ovarian cancer development and progression and their role in potential future cancer therapy. We will first discuss the supporting evidence and controversies in the "gonadotropin theory" and the use of animal models for exploring the involvement of gonadotropins in the etiology of ovarian cancer. The role of gonadotropins in regulating the proliferation, survival, and metastasis of OEC is next summarized. Relevant data from ovarian surface epithelium, which is widely believed to be the precursor of OEC, are also described. Finally, we will discuss the clinical applications of gonadotropins in ovarian cancer and the recent progress in drug development.

Endocrine signaling in ovarian surface epithelium and cancer

Ovarian cancer is the sixth most common cancer and the fifth leading cause of cancer-related death among women in developed countries. Greater than 85% of human ovarian cancer arises within the ovarian surface epithelium (OSE), with the remainder derived from granulosa cells or, rarely, stroma or germ cells. The pathophysiology of ovarian cancer is the least understood among all major human malignancies because of a poor understanding of the aetiological factors and mechanisms of ovarian cancer progression. There is increasing evidence suggesting that several key reproductive hormones, such as GnRH, gonadotrophins and sex steroids, regulate the growth of normal OSE and ovarian cancer cells. The objective of this review was to highlight the effects of these endocrine factors on ovarian cancer cell growth and to summarize the signalling mechanisms involved in normal human OSE and its neoplastic counterparts.

Ion channels of primate ovarian endocrine cells: identification and functional significance

Ion channels are crucially involved in cellular functions, but little is known about molecular identity, subunit composition and the specific role of ion channels in ovarian endocrine cells in human and nonhuman primates. Using human luteinizing granulosa cells, a few groups have started to address these questions and have begun to show molecular identity of ion channels, electrophysiological functions and the relationship to hormone production, as well as regulation by hormones and intraovarian factors. Functional ion channels that have been identified so far include T- and L-type Ca²⁺ channels (Ca_v3.2, Ca_v1.2), a voltage-dependent Na⁺ channel (Na_v1.7), as well as voltage- (K_v4.2) and Ca²⁺-dependent K⁺ channels (BK_Ca). Since all these ion channels were found to be involved in steroid hormone synthesis and are expressed by endocrine ovarian cells in human and nonhuman ovary, it has been proposed that they are physiological key molecules for ovarian function. Furthermore, they may be novel targets for modulating ovarian functions.

4-aminopyridine decreases progesterone production by porcine granulosa cells

BACKGROUND

Ion channels occur as large families of related genes with cell-specific expression patterns. Granulosa cells have been shown to express voltage-gated potassium channels from more than one family. The purpose of this study was to determine the effects of 4-aminopyridine (4-AP), an antagonist of KCNA but not KCNQ channels.

METHODS

Granulosa cells were isolated from pig follicles and cultured with 4-AP, alone or in combination with FSH, 8-CPT-cAMP, estradiol 17beta, and DIDS. Complimentary experiments determined the effects of 4-AP on the spontaneously established pig granulosa cell line PGC-2. Granulosa cell or PGC-2 function was assessed by radio-immunoassay of media progesterone accumulation. Cell viability was assessed by trypan blue exclusion. Drug-induced changes in cell membrane potential and intracellular potassium concentration were documented by spectrophotometric determination of DiBAC4(3) and PBFI fluorescence, respectively. Expression of proliferating cell nuclear antigen (PCNA) and steroidogenic acute regulatory protein (StAR) was assessed by immunoblotting. Flow cytometry was also used to examine granulosa cell viability and size.

RESULTS

4-AP (2 mM) decreased progesterone accumulation in the media of serum-supplemented and serum-free granulosa cultures, but inhibited cell proliferation only under serum-free conditions. 4-AP decreased the expression of StAR, the production of cAMP and the synthesis of estradiol by PGC-2. Addition of either 8-CPT-cAMP or estradiol 17beta to serum-supplemented primary cultures reduced the inhibitory effects of 4-AP. 4-AP treatment was also associated with increased cell size, increased intracellular potassium concentration, and hyperpolarization of resting membrane potential. The drug-induced hyperpolarization of resting membrane potential was prevented either by decreasing extracellular chloride or by adding DIDS to the media. DIDS also prevented 4-AP inhibition of progesterone production.

CONCLUSION

4-AP inhibits basal and FSH-stimulated progesterone production by pig granulosa cells via drug action at multiple interacting steps in the steroidogenic pathway. These inhibitory effects of 4-AP on steroidogenesis may reflect drug-induced changes in intracellular concentrations of K+and Cl- as well as granulosa cell resting membrane potential.

Basal lamina of ovarian follicle regulates an inward Cl(-) current in differentiated granulosa cells

Patch-clamp experiments were conducted to study the effects of basal lamina (basement membrane) of preovulatory chicken ovarian follicle on membrane currents in differentiated chicken granulosa cells in a homologous system. The membrane capacitance (measure of total membrane area) was smaller in cells cultured on intact basal lamina than that of control cells. The granulosa cells expressed outward and two inward currents. A small fraction of the cells (3%) expressed only a transient fast-activating and -inactivating inward current carried by Ca(2+). The majority of the cells, however, expressed a slowly activating and inactivating inward current (carried by Cl(-)) that was superimposed on the transient Ca(2+) current. All cells expressed an outward current characteristic of the delayed-rectifier K(+) current. The removal of extracellular Ca(2+) led to elimination of the slow inward Cl(-) current, indicating that it is a Ca(2+)-dependent Cl(-) current. Both peak amplitude and current density of the inward Cl(-) current were significantly lower in cells cultured on freshly isolated intact basal lamina (or basal lamina stored at 4 degrees C for 12 mo) than those of control cells; however, basal lamina had no significant effect on the density of the outward current. Similar to the observations made for intact basal lamina, solubilized basal lamina suppressed the inward Cl(-) current in differentiated granulosa cells. These data show that homologous basal lamina modulates a Ca(2+)-dependent Cl(-) current in differentiated granulosa cells. These findings provide a partial explanation for the mechanisms that subserve the reported effects of basal lamina (basement membrane) on the metabolic functions of differentiated granulosa cells.

Effect of large dietary doses of beta-carotene on plasma retinoid and beta-carotene levels and on progesterone production in the granulosa cells of Japanese quail

An experiment was conducted to study the effect of large-dose beta-carotene supplementation on blood retinoid and beta-carotene levels as well as on the progesterone secretion of the granulosa cells in Japanese quail. Laying quails were assigned to three dietary groups. The control group (Group C) received the basal diet (laying feed containing 9000 IU vitamin A/kg). In the treated groups (Groups BC1 and BC2) the basal diet was supplemented with 10(2) and 10(3) mg/kg beta-carotene (BC), respectively. At the end of the two-week feeding period, 10 birds from each group were euthanised. Blood samples were analysed for retinol, retinyl palmitate and beta-carotene concentrations. Granulosa cells were isolated from ovarian follicles (F1 and F2), and PMSG-induced in vitro progesterone (P4) secretion was measured. Similar retinol concentrations were found in both beta-carotene supplemented groups, indicating saturation of the retinol-transporting system. beta-carotene supplementation was accompanied by hypercarotenaemia, but did not increase the retinyl palmitate levels in the blood. PMSG-induced P4 production of the granulosa cells decreased significantly in Groups BC1 and BC2 in a dose-dependent manner.

Low extracellular Ca(2+) activates a transient Cl(-) current in chicken ovarian granulosa cells

The effects of low Ca(2+) on ion currents in hen ovarian granulosa cells were examined. A fast activating and inactivating transient outward current (TOC) and a slowly activating outward current (SOC) could be observed. In the presence of normal Ca(2+) concentration (2. 5 mM) and with a holding potential of -80 mV, SOC was activated in all cells with command pulses more positive than -20 mV. In 2.5 mM Ca(2+), TOC appeared in 10% of cells at the command pulse of +80 mV and in 60-85% of cells at +100 to +120 mV. In low-Ca(2+) solution and command potential of +80 mV (holding potential of -80 mV), the amplitude of TOC was enhanced in cells that expressed it in normal Ca(2+), and TOC appeared in 43% of the cells that did not express it initially in normal Ca(2+). At both normal and low Ca(2+) levels, TOC decreased as the holding potential became more positive. TOC was reduced in Cl(-)-deficient solution and in the presence of 5-nitro-2-(3-phenylpropylamino)benzoic acid, a Cl(-) channel blocker. These findings suggest that chicken granulosa cells express a Ca(2+)-inactivated TOC carried by Cl(-). This current may serve as a signal for some of the reduced metabolic functions of granulosa cells associated with Ca(2+) deficiency.