Altered endothelin expression in granulosa-lutein cells of women with polycystic ovary syndrome

Reduced Endothelin-2 and Hypoxic Signaling Pathways in Granulosa-Lutein Cells of PCOS Women

Granulosa-lutein cells (GLCs) from PCOS women display reduced HIF-1α and EDN2 levels, suggesting their role in PCOS etiology. Here, we investigated the mechanisms involved in aberrant EDN2 expression in PCOS, and its association with HIF-1α. Various HIF-1α-dependent factors were studied in GLCs from PCOS and compared to normally ovulating women. MicroRNA-210 (miR-210), its target genes (SDHD and GPD1L), and HIF-1α-responsive genes (EDN2 and VEGFA) differed in GLCs from PCOS, compared with those of healthy women. Levels of miR-210—designated hypoxiamiR—and EDN2 were reduced in the PCOS GLCs; concomitantly, GPD1L and SDHD levels were elevated. Cultured GLCs retained low EDN2 expression and had low HIF-1α levels, providing evidence for a disrupted hypoxic response in the PCOS GLCs. However, VEGFA expression was elevated in these cells. Next, miR-210 levels were manipulated. miR-210-mimic stimulated EDN2 twice as much as the miR-NC-transfected cells, whereas miR-210-inhibitor diminished EDN2, emphasizing the importance of hypoxiamiR for EDN2 induction. Intriguingly, VEGFA transcripts were reduced by both miR-210-mimic and -inhibitor, demonstrating that EDN2 and VEGFA are distinctly regulated. Disrupted hypoxic response in the GLCs of periovulatory follicles in PCOS women may play a role in ovulation failure, and in the reduced fertility prevalent in this syndrome.

Sirtuin-1 inhibits endothelin-2 expression in human granulosa-lutein cells via hypoxia inducible factor 1 alpha and epigenetic modifications†

Endothelin-2 (EDN2) expression in granulosa cells was previously shown to be highly dependent on the hypoxic mediator, hypoxia inducible factor 1 alpha (HIF1A). Here, we investigated whether sirtuin-1 (SIRT1), by deacetylating HIF1A and class III histones, modulates EDN2 in human granulosa-lutein cells (hGLCs). We found that HIF1A was markedly suppressed in the presence of resveratrol or a specific SIRT1 activator, SRT2104. In turn, hypoxia reduced SIRT1 levels, implying a mutually inhibitory interaction between hypoxia (HIF1A) and SIRT1. Consistent with reduced HIF1A transcriptional activity, SIRT1 activators, resveratrol, SRT2104, and metformin, each acting via different mechanisms, significantly inhibited EDN2. In support, knockdown of SIRT1 with siRNA markedly elevated EDN2, whereas adding SRT2104 to SIRT1-silenced cells abolished the stimulatory effect of siSIRT1 on EDN2 levels further demonstrating that EDN2 is negatively correlated with SIRT1. Next, we investigated whether SIRT1 can also mediate the repression of the EDN2 promoter via histone modification. Chromatin immunoprecipitation (ChIP) analysis revealed that SIRT1 is indeed bound to the EDN2 promoter and that elevated SIRT1 induced a 40% decrease in the acetylation of histone H3, suggesting that SIRT1 inhibits EDN2 promoter activity by inducing a repressive histone configuration. Importantly, SIRT1 activation, using SRT2104 or resveratrol, decreased the viable numbers of hGLC, and silencing SIRT1 enhanced hGLC viability. This effect may be mediated by reducing HIF1A and EDN2 levels, shown to promote cell survival. Taken together, these findings propose novel, physiologically relevant roles for SIRT1 in downregulating EDN2 and survival of hGLCs.

The cAMP pathway promotes sirtuin-1 expression in human granulosa-lutein cells

Sirtuin-1 (SIRT1), a NAD+-dependent deacetylase, is present in the ovarian granulosa cells (GCs) of various species. This study examined the regulation of SIRT1 expression in human granulosa-lutein cells (hGLCs). Two different, structurally unrelated SIRT1 activators, SRT2104 and resveratrol, dose- and time-dependently enhanced SIRT1 (∼2- and 1.5-fold increase at 50 μmol/L for mRNA and protein levels, respectively), whereas EX-527, an inhibitor of SIRT1 deacetylase activity, significantly suppressed SIRT1 protein induced by these activators. Transfecting cells with SIRT1 siRNA molecules efficiently silenced SIRT1 (∼70 % decrease in 48 h post-transfection). Furthermore, the stimulatory effects of SRT2104 on SIRT1 expression observed in non-transfected or in scrambled siRNA-transfected cells were diminished with SIRT1 silencing. The findings described above imply that SIRT1 autoregulates its own expression. Interestingly, SRT2104 elevated cAMP accumulation (1.4-fold) in the culture media of hGLCs which was further augmented in the presence of hCG (2.2-fold); these effects were evident after 12 h of incubation. This additive effect of hCG and SRT2104 on cAMP accumulation may explain the incremental outcome observed on SIRT1 expression (∼3-fold increase from basal level and ∼1.6-fold stimulation for each compound alone) with these two compounds. SIRT1 knockdown diminished SIRT1 induced by forskolin, providing additional evidence that cAMP promotes SIRT1. These findings imply that by activating adenylyl cyclase (hCG or forskolin) and inhibiting phosphodiesterases (SIRT1 activators), these two signals converge to produce an incremental, positive feedback loop on SIRT1 expression. Such a mechanism highlights the importance of maintaining high SIRT1 levels in human luteinized GCs.

Effects of melatonin on the synthesis of estradiol and gene expression in pig granulosa cells

The interaction of granulosa cells (GCs) with oocytes is important to regulate follicle development. The exogenous melatonin promoting the maturation of oocytes by GCs has been approved in pig, however, the transcriptome profile and the functions of the genes regulated by melatonin in GCs have not yet to be fully characterized. In this study, we found melatonin could stimulate the synthesis of estradiol in pig GCs. The RNA-seq was used to explore the effects of melatonin on gene expression, a total of 89 differentially expressed genes (DEGs) were identified. Gene ontology analysis showed DEGs which associated with regulation of cell proliferation, cell cycle, and anti-apoptosis were significantly enriched. The functions of two DEGs, NOTCH2 and FILIP1L, were studied in pig GCs. The results showed that NOTCH2 inhibited the synthesis of estradiol, but FILIP1L promoted the synthesis of estradiol. Furthermore, inhibiting NOTCH2 in granulosa cells cocultured with cumulus-oocyte-complexes had no obvious effect on the maturation of pig oocyte, but could upregulate the cleavage rate of oocyte. We proved that FILIP1L had no effect on the maturation and cleavage of pig oocytes. Our work deepens the understanding of melatonin's effects on GCs and oocyte. The DEGs we found will be beneficial to reveal mechanisms of melatonin acting on GCs and oocytes and design the pharmacological interventions.

Endothelin-1 promotes human germinal vesicle-stage oocyte maturation by downregulating connexin-26 expression in cumulus cells

STUDY QUESTION

Does endothelin-1 (ET-1) promote human oocyte maturation and by what mechanism?

SUMMARY ANSWER

Addition of ET-1 to the medium in which human germinal vesicle (GV)-stage immature oocytes are cultured enhances the GV breakdown (GVBD) rate; the resumption of meiosis may be initiated by ET-1 downregulating the expression of connexin-26 (Cx26) in cumulus cells via endothelin receptor type B (ETRB), leading to decreased cAMP levels in the oocyte.

WHAT IS KNOWN ALREADY

The paracrine factor ET-1 is secreted by ovarian somatic cells in pre-ovulatory follicles and regulates oocyte maturation in mice. Connexins, or gap junction proteins, form intercellular membrane channels that play important roles in the resumption of meiosis.

STUDY DESIGN, SIZE, DURATION

This laboratory study was conducted over a 1-year period. The effects of ET-1 on meiotic resumption were evaluated in human GV-stage cumulus-oocyte complexes (COCs; 70 oocytes/group). The transcriptome profiles of ET-1-treated or untreated cumulus cells were compared to explore the possible mechanisms by which ET-1 may regulate oocyte maturation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The ET-1, ETRA and ETRB expression levels in human cumulus cells from oocytes at different stages of maturation were evaluated using real-time quantitative PCR. Human GV-stage COCs collected from patients undergoing IVF at a university-affiliated infertility centre were cultured with or without ET-1, and cumulus cells were subsequently denuded using hyaluronidase and cultured in α-MEM. A GeneChip® Human Transcriptome Array was applied to explore differences in the whole-genome transcriptome profiles of cumulus cells treated with or without ET-1. Real-time quantitative PCR and Western blotting were used respectively to examine Cx26 mRNA and protein levels in cumulus cells. Changes in cAMP levels in both oocytes and cumulus cells after ET-1 treatment were measured using an enzyme-linked immunosorbent assay.

MAIN RESULTS AND THE ROLE OF CHANCE

Cumulus cells from MII-stage oocytes exhibited upregulated ET-1 expression, compared to those from GV-stage oocytes. The addition of ET-1 to the culture medium enhanced the GVBD rate of cumulus cell-enclosed human oocytes. Whole-genome transcriptome microarray analyses revealed significantly downregulated Cx26 expression in cumulus cells after ET-1 treatment, and this action was blocked by an ETRB antagonist. The involvement of Cx26 was further supported by the finding that ET-1 treatment led to decreased cAMP levels in oocytes but increased cAMP levels in cumulus cells.

LARGE SCALE DATA

Microarray data are published in the GEO database (GSE97684).

LIMITATIONS, REASONS FOR CAUTION

The heterogeneity of human COCs collected from patients undergoing IVF might affect the maturation results in vitro. Although we focused on the effects of ET-1 on human oocyte maturation in the present study, mammalian oocyte maturation is a complicated process involving many endocrine and paracrine factors.

WIDER IMPLICATIONS OF THE FINDINGS

Our present study suggests that in vitro, human GV-stage oocyte maturation could be enhanced by adding ET-1 to the culture medium. In the present study, we explored the molecular mechanisms by which ET-1 initiates the resumption of meiosis and demonstrated that ET-1 promotes oocyte maturation by downregulating the expression of the gap junction protein Cx26 in cumulus cells. These results expand our understanding of the molecular mechanisms underlying mammalian oocyte maturation and provide a basis for better in-vitro maturation strategies.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by grants from the China Natural Science Foundation (Grant Nos. 81170567 and 81370761). The authors declare that they have no conflicts of interest associated with this manuscript.

miR-210 and GPD1L regulate EDN2 in primary and immortalized human granulosa-lutein cells

Endothelin-2 (EDN2), expressed at a narrow window during the periovulatory period, critically affects ovulation and corpus luteum (CL) formation. LH (acting mainly via cAMP) and hypoxia are implicated in CL formation; therefore, we aimed to elucidate how these signals regulate EDN2 using human primary (hGLCs) and immortalized (SVOG) granulosa-lutein cells. The hypoxiamiR, microRNA-210 (miR-210) was identified as a new essential player in EDN2 expression. Hypoxia (either mimetic compound-CoCl₂, or low O₂) elevated hypoxia-inducible factor 1A (HIF1A), miR-210 and EDN2 Hypoxia-induced miR-210 was suppressed in HIF1A-silenced SVOG cells, suggesting that miR-210 is HIF1A dependent. Elevated miR-210 levels in hypoxia or by miR-210 overexpression, increased EDN2 Conversely, miR-210 inhibition reduced EDN2 levels, even in the presence of CoCl₂, indicating the importance of miR-210 in the hypoxic induction of EDN2 A molecule that destabilizes HIF1A protein, glycerol-3-phosphate dehydrogenase 1-like gene-GPD1L, was established as a miR-210 target in both cell types. It was decreased by miR-210-mimic and was increased by miR-inhibitor. Furthermore, reducing GPD1L by endogenously elevated miR-210 (in hypoxia), miR-210-mimic or by GPD1L siRNA resulted in elevated HIF1A protein and EDN2 levels, implying a vital role for GPD1L in the hypoxic induction of EDN2 Under normoxic conditions, forskolin (adenylyl cyclase activator) triggered changes typical of hypoxia. It elevated HIF1A, EDN2 and miR-210 while inhibiting GPD1L Furthermore, HIF1A silencing greatly reduced forskolin's ability to elevate EDN2 and miR-210. This study highlights the novel regulatory roles of miR-210 and its gene target, GPD1L, in hypoxia and cAMP-induced EDN2 by human granulosa-lutein cells.

Current status of the role of endothelins in regulating ovarian follicular function: A review

Endothelins (EDN) are a group of vasoactive 21 amino acid peptides reported to play roles in steroidogenesis, folliculogenesis, and ovulation. EDN1, EDN2 and EDN3 have all been shown to affect granulosa cell (GC) function in a variety of mammalians species. Herewithin, the role of EDN in regulating steroidogenesis and ovarian follicular development is reviewed, focusing on the localization and function of EDN and their receptors in ovarian follicular function emphasizing species differences. For example, in single ovulating species such as humans and cattle, in the presence of trophic hormones such as FSH and IGF1, EDN1 and EDN2 significantly inhibited GC estradiol production in 2 of 4 studies, while no effect was observed for GC progesterone production in 2 of 4 studies. In contrast, EDN1 exhibited inhibitory effects on progesterone production by GC in 3 of 3 studies in pigs and 3 of 4 studies in rats. Also, EDN1 inhibited GC estradiol production in 4 of 5 studies in rats. Altogether, these results indicate that EDN are produced by ovarian follicles and are involved in the regulation of steroidogenesis of GC of several mammalian species including humans, cattle, pigs and rats, but that these effects may vary with species and culture condition.

HIF1A-dependent increase in endothelin 2 levels in granulosa cells: role of hypoxia, LH/cAMP, and reactive oxygen species

Hypoxia-inducible factor 1 alpha (HIF1A) and endothelin 2 (EDN2) are transiently expressed during the same time window in the developing corpus luteum (CL). In this study, we sought to investigate the involvement of LH/cAMP, reactive oxygen species (ROS), and a hypoxia-mimetic compound (CoCl2) on HIF1A expression and how it affected EDN2 levels, using transformed human granulosa cells (thGCs) and primary bovine granulosa cells (GCs). CoCl2 elevated HIF1A protein levels in thGCs in a dose-dependent manner. Forskolin alone had no significant effect; however, forskolin and CoCl2 together further induced HIF1A protein and EDN2 mRNA expression in thGCs. Similarly, in primary GCs, LH with CoCl2 synergistically augmented HIF1A protein levels, which resulted in higher expression of EDN2 and another well-known hypoxia-inducible gene, VEGF (VEGFA). Importantly, LH alone elevated HIF1A mRNA but not its protein. The successful knockdown of HIF1A in thGCs using siRNA abolished hypoxia-induced EDN2 and also the additive effect of forskolin and CoCl2. We then examined the roles of ROS in thGCs: hydrogen peroxide (20 and 50 μM) elevated HIF1A protein as well as the expression of EDN2, implying that induction of HIF1A protein levels is sufficient to stimulate the expression of EDN2 (and VEGF) in normoxia. A broad-range ROS scavenger, butylated hydroxyanisole, inhibited CoCl2-induced HIF1A protein with a concomitant reduction in the mRNA expression of EDN2 and VEGF in thGCs. The results obtained in this study suggest that HIF1A, induced by various stimuli, is an essential mediator of EDN2 mRNA expression. The results may also explain the rise in the levels of HIF1A-dependent genes (EDN2 and VEGF) in the developing CL.

Expression and clinical significance of the HIF-1a/ET-2 signaling pathway during the development and treatment of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a major health problem in reproductive-aged women worldwide, but the precise pathogenesis of PCOS remains unclear. Our previous study revealed that hypoxia-inducible factor (HIF)-1a mediated endothelin (ET)-2 signaling plays an important role in ovulation in rats. Therefore, the present study used a PCOS rat model to test the hypotheses that HIF-1a signaling is expressed and inhibited in ovaries during PCOS formation and that the HIF-1a/ET-2 signaling pathway is a target of dimethyldiguanide (DMBG) in the clinical treatment of PCOS. First, the development of a PCOS model and the effect of DMBG treatment were examined through ovarian histology and serum hormone levels, which were consistent with previous reports. Second, HIF-1a and ET-2 expression were detected by immunohistochemistry and western blot. The results showed decreased HIF-1a/ET-2 expression in the ovaries of PCOS rats, whereas DMBG treatment reversed the protein decreases and improved the PCOS symptoms. Third, to understand the molecular mechanism, HIF-1a/ET-2 mRNA expression was also examined. Interestingly, HIF-1a mRNA increased in the ovaries of PCOS rats, while ET-2 mRNA decreased, indicating that HIF-1a protein degradation may be involved in POCS development and treatment. Finally, HIF prolyl hydroxylase (PHD) activity was examined to further clarify the contribution of HIF-1a signaling to the development and treatment of PCOS. The results suggested that the inhibition of HIF-1a/ET-2 signaling may be caused by increased PHD activity in PCOS. DMBG-treated PCOS may further activate HIF-1a signaling at least partly through inhibiting PHD activity. Taken together, these results indicate that HIF-1a signaling is inhibited in a PCOS rat model through increasing PHD activity. DMBG treatment improved PCOS by rescuing this pathway, suggesting that HIF-1a signaling plays an important role in the development and treatment of PCOS. This HIF-1a-mediated ET-2 signaling pathway may be an important mechanism regulating PCOS formation and treatment in mammalian ovaries in vivo and should be a new clinical target for PCOS prevention and treatment in the future.

Linking the beneficial effects of current therapeutic approaches in diabetes to the vascular endothelin system

The rising epidemic of diabetes worldwide is of significant concern. Although the ultimate objective is to prevent the development and find a cure for the disease, prevention and treatment of diabetic complications is very important. Vascular complications in diabetes, or diabetic vasculopathy, include macro- and microvascular dysfunction and represent the principal cause of morbidity and mortality in diabetic patients. Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vasculopathy. Endothelin-1 (ET-1), an endothelial cell-derived peptide, is a potent vasoconstrictor with mitogenic, pro-oxidative and pro-inflammatory properties that are particularly relevant to the pathophysiology of diabetic vasculopathy. Overproduction of ET-1 is reported in patients and animal models of diabetes and the functional effects of ET-1 and its receptors are also greatly altered in diabetic conditions. The current therapeutic approaches in diabetes include glucose lowering, sensitization to insulin, reduction of fatty acids and vasculoprotective therapies. However, whether and how these therapeutic approaches affect the ET-1 system remain poorly understood. Accordingly, in the present review, we will focus on experimental and clinical evidence that indicates a role for ET-1 in diabetic vasculopathy and on the effects of current therapeutic approaches in diabetes on the vascular ET-1 system.