Long-term growth and steroidogenic potential of human granulosa-lutein cells immortalized with SV40 large T antigen

Current Advances in Cellular Approaches for Pathophysiology and Treatment of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a prevalent gynecological and endocrine disorder that results in irregular menstruation, incomplete follicular development, disrupted ovulation, and reduced fertility rates among affected women of reproductive age. While these symptoms can be managed through appropriate medication and lifestyle interventions, both etiology and treatment options remain limited. Here we provide a comprehensive overview of the latest advancements in cellular approaches utilized for investigating the pathophysiology of PCOS through in vitro cell models, to avoid the confounding systemic effects such as in vitro fertilization (IVF) therapy. The primary objective is to enhance the understanding of abnormalities in PCOS-associated folliculogenesis, particularly focusing on the aberrant roles of granulosa cells and other relevant cell types. Furthermore, this article encompasses analyses of the mechanisms and signaling pathways, microRNA expression and target genes altered in PCOS, and explores the pharmacological approaches considered as potential treatments. By summarizing the aforementioned key findings, this article not only allows us to appreciate the value of using in vitro cell models, but also provides guidance for selecting suitable research models to facilitate the identification of potential treatments and understand the pathophysiology of PCOS at the cellular level.

Co-cultivation of human granulosa cells with ovarian cancer cells leads to a significant increase in progesterone production

PURPOSE

In humans, granulosa cells (GCs) are part of the follicle and nourish the growing oocyte. GCs produce estrogen and, after ovulation, progesterone. They are embedded in a multicellular tissue structure of the ovary, which consists of a variety of different cell types that are essential for the physiological function of the ovary. However, the extent to which individual ovarian cell types contribute to overall functionality has not yet been fully elucidated. In this study, we aim to investigate the effects of co-culturing human granulosa cells with ovarian cancer cells on their progesterone and estrogen production in an in vitro model.

METHODS

After seeding, the cells were stimulated with 200 µM forskolin in DMEM for 72 h and the medium of the different cell culture experiments was collected. Subsequently, progesterone and oestradiol concentrations were determined using an Elisa assay.

RESULTS

Morphologically, it was striking that the cells self-organize and form spatially separated areas. Compared to culturing granulosa cells alone, co-culturing human granulosa cells together with the ovarian cancer cell line OvCar-3 resulted in a significant increase in progesterone production (20.3 ng/ml versus 50.2 ng/ml; p < 0.01).

CONCLUSIONS

Using a simple in vitro model, we highlight the importance of cellular crosstalk between different ovarian cells in a complex cellular network and that it strongly influences granulosa cell hormone production. This could have potential implications for the procedure of transplanting endocrine tissues after cryopreservation, as it highlights the importance of survival of all cells for the functionality of the transplanted tissue.

Diverse actions of sirtuin-1 on ovulatory genes and cell death pathways in human granulosa cells

BACKGROUND

Human granulosa-lutein cells (hGLCs) amply express sirtuin-1 (SIRT1), a NAD + -dependent deacetylase that is associated with various cellular functions. SIRT1 was shown to elevate cAMP on its own and additively with human chorionic gonadotropin (hCG), it is therefore interesting to examine if SIRT1 affects other essential hGLC functions.

METHODS

Primary hGLCs, obtained from the follicular aspirates of women undergoing IVF and SV40-transfected, immortalized hGLCs (SVOG cells), were used. Primary cells were treated with SIRT1 specific activator SRT2104, as well as hCG or their combination. Additionally, siRNA-targeting SIRT1 construct was used to silence endogenous SIRT1 in SVOG cells. PTGS2, EREG, VEGFA and FGF2 expression was determined using quantitative polymerase chain reaction (qPCR). Apoptotic and necroptotic proteins were determined by specific antibodies in western blotting. Cell viability/apoptosis was determined by the XTT and flow cytometry analyses. Data were analyzed using student t-test or Mann-Whitney U test or one-way ANOVA followed by Tukey HSD post hoc test.

RESULTS

In primary and immortalized hGLCs, SRT2104 significantly upregulated key ovulatory and angiogenic genes: PTGS2, EREG, FGF2 and VEGFA, these effects tended to be further augmented in the presence of hCG. Additionally, SRT2104 dose and time-dependently decreased viable cell numbers. Flow cytometry of Annexin V stained cells confirmed that SIRT1 reduced live cell numbers and increased late apoptotic and necrotic cells. Moreover, we found that SIRT1 markedly reduced anti-apoptotic BCL-XL and MCL1 protein levels and increased cleaved forms of pro-apoptotic proteins caspase-3 and PARP. SIRT1 also significantly induced necroptotic proteins RIPK1 and MLKL. RIPK1 inhibitor, necrostatin-1 mitigated SIRT1 actions on RIPK1 and MLKL but also on cleaved caspase-3 and PARP and in accordance on live and apoptotic cells, implying a role for RIPK1 in SIRT1-induced cell death. SIRT1 silencing produced inverse effects on sorted cell populations, anti-apoptotic, pro-apoptotic and necroptotic proteins, corroborating SIRT1 activation.

CONCLUSIONS

These findings reveal that in hGLCs, SIRT1 enhances the expression of ovulatory and angiogenic genes while eventually advancing cell death pathways. Interestingly, these seemingly contradictory events may have occurred in a cAMP-dependent manner.

Activin a promotes hyaluronan production and upregulates versican expression in human granulosa cells via the ALK4-SMAD2/3-SMAD4 signaling pathway

Hyaluronan is a structural component of the expanded cumulus matrix, and hyaluronan synthase 2 (HAS2) is the major enzyme for the synthesis of hyaluronan in humans. Versican cross-links the hyaluronan-rich matrix to cumulus cells and is critical for successful ovulation. Activin A is a critical intrafollicular regulator of ovarian function. Although activin A has been shown to promote cumulus matrix expansion in mice, the functional role of activin A in the regulation of cumulus expansion in the human ovary remains to be elucidated. Using primary and immortalized human granulosa-lutein (hGL) cells as study models, we provide the first data showing that activin A increased the production of hyaluronan by upregulating the expression of HAS2 in these cells. Additionally, activin A also promoted the expression of the hyaluronan-binding protein versican. Moreover, using inhibitor- and siRNA-mediated inhibition approaches, we found that these stimulatory effects of activin A are most likely mediated through the type I receptor ALK4-mediated SMAD2/SMAD3-SMAD4 signaling pathway. Notably, the ChIP analyses demonstrated that SMAD4 could bind to human HAS2 and VERSICAN promoters. The results obtained from this in vitro study suggest that locally produced activin A plays a functional role in the regulation of hyaluronan production and stabilization in hGL cells.

Connective tissue growth factor mediates bone morphogenetic protein 2-induced increase in hyaluronan production in luteinized human granulosa cells

BACKGROUND

Hyaluronan is the main component of the cumulus-oocyte complex (COC) matrix, and it maintains the basic structure of the COC during ovulation. As a member of the transforming growth factor β (TGF-β) superfamily, bone morphogenetic protein 2 (BMP2) has been identified as a critical regulator of mammalian folliculogenesis and ovulation. However, whether BMP2 can regulate the production of hyaluronan in human granulosa cells has never been elucidated.

METHODS

In the present study, we investigated the effect of BMP2 on the production of hyaluronan and the underlying molecular mechanism using both immortalized (SVOG) and primary human granulosa-lutein (hGL) cells. The expression of three hyaluronan synthases (including HAS1, HAS2 and HAS3) were examined following cell incubation with BMP2 at different concentrations. The concentrations of the hyaluronan cell culture medium were determined by enzyme-linked immunosorbent assay (ELISA). The TGF-β type I receptor inhibitors (dorsomorphin and DMH-1) and small interfering RNAs targeting ALK2, ALK3, ALK6 and SMAD4 were used to investigate the involvement of TGF-β type I receptor and SMAD-dependent pathway.

RESULTS

Our results showed that BMP2 treatment significantly increased the production of hyaluronan by upregulating the expression of hyaluronan synthase 2 (HAS2). In addition, BMP2 upregulates the expression of connective tissue growth factor (CTGF), which subsequently mediates the BMP2-induced increases in HAS2 expression and hyaluronan production because overexpression of CTGF enhances, whereas knockdown of CTGF reverses, these effects. Notably, using kinase inhibitor- and siRNA-mediated knockdown approaches, we demonstrated that the inductive effect of BMP2 on the upregulation of CTGF is mediated by the ALK2/ALK3-mediated SMAD-dependent signaling pathway.

CONCLUSIONS

Our findings provide new insight into the molecular mechanism by which BMP2 promotes the production of hyaluronan in human granulosa cells.

The Interleukin-6 trans-signaling promotes progesterone production in human granulosa-lutein cells

As a critical paracrine regulator of multiple reproductive functions, the cytokine interleukin-6 (IL-6) is expressed in human granulosa cells and can be detected in follicular fluid. At present, the functional role of IL-6 in the regulation of ovarian steroidogenesis is controversial. Moreover, the detailed molecular mechanisms by which IL-6 regulates the production of progesterone in human granulosa cells remain to be elucidated. In the present study, we used primary and immortalized human granulosa-lutein (hGL) cells to investigate the effects of IL-6 on progesterone synthesis and the underlying molecular mechanisms. We found that IL-6 trans-signaling by the combined addition of IL-6 and soluble IL-6 receptor (sIL-6Rα) induced StAR expression and progesterone production in hGL cells. Additionally, IL-6/sIL-6Rα activated the phosphorylation of Janus activated kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), and the cellular effects were abolished by AG490 (JAK2 inhibitor), C188–9 (STAT3 inhibitor), or siRNA-mediated knockdown of STAT3. IL-6 trans-signaling-induced activation of JAK2/STAT3 also upregulated the expression of suppressor of cytokine signaling 3 (SOCS3), which, in turn, negatively regulated the JAK2/STAT3 pathway by suppressing STAT3 activation and its downstream effects. Our findings provide insight into the molecular mechanisms by which IL-6 trans-signaling modulates steroidogenesis in hGL cells.

Bone morphogenetic protein 2 inhibits growth differentiation factor 8-induced cell signaling via upregulation of gremlin2 expression in human granulosa-lutein cells

BACKGROUND

Bone morphogenetic protein 2 (BMP2), growth differentiation factor 8 (GDF8) and their functional receptors are expressed in human ovarian follicles, and these two intrafollicular factors play essential roles in regulating follicle development and luteal function. As BMP antagonists, gremlin1 (GREM1) and gremlin2 (GREM2) suppress BMP signaling through blockage of ligand-receptor binding. However, whether BMP2 regulates the expression of GREM1 and GREM2 in follicular development remains to be determined.

METHODS

In the present study, we investigated the effect of BMP2 on the expression of GREM1 and GREM2 and the underlying mechanisms in human granulosa-lutein (hGL) cells. An established immortalized human granulosa cell line (SVOG) and primary hGL cells were used as study models. The expression of GREM1 and GREM2 were examined following cell incubation with BMP2 at different concentrations and time courses. The TGF-β type I inhibitors (dorsomorphin, DMH-1 and SB431542) and small interfering RNAs targeting ALK2, ALK3, SMAD2/3, SMAD1/5/8 and SMAD4 were used to investigate the involvement of the SMAD-dependent pathway.

RESULTS

Our results showed that BMP2 significantly increased the expression of GREM2 (but not GREM1) in a dose- and time-dependent manner. Using a dual inhibition approach combining kinase inhibitors and siRNA-mediated knockdown, we found that the BMP2-induced upregulation of GREM2 expression was mediated by the ALK2/3-SMAD1/5-SMAD4 signaling pathway. Moreover, we demonstrated that BMP2 pretreatment significantly attenuated the GDF8-induced phosphorylation of SMAD2 and SMAD3, and this suppressive effect was reversed by knocking down GREM2 expression.

CONCLUSIONS

Our findings provide new insight into the molecular mechanisms by which BMP2 modulates the cellular activity induced by GDF8 through the upregulated expression of their antagonist (GREM2).

BMP6 increases CD68 expression by up-regulating CTGF expression in human granulosa-lutein cells

Bone morphogenetic protein 6 (BMP6) and connective tissue growth factor (CTGF) are critical growth factors required for normal follicular development and luteal function. Cluster of Differentiation 68 (CD68) is an intraovarian marker of macrophages that plays an important role in modulating the physiological regression of the corpus luteum. The aim of this study was to investigate the effect of BMP6 on the expression of CTGF and the subsequent increase in CD68 expression as well as its underlying mechanisms. Primary and immortalized (SVOG) human granulosa cells obtained from infertile women undergoing in vitro fertilization treatment were used as cell models to conduct the in vitro experiments. Our results showed that BMP6 treatment significantly increased the expression levels of CTGF and CD68. Using BMP type I receptor inhibitors (dorsomorphin, DMH-1 and SB431542), we demonstrated that both activin receptor-like kinase (ALK)2 and ALK3 are involved in BMP6-induced stimulatory effects on the expression of CTGF and CD68. Additionally, SMAD4-knock down reversed the BMP6-induced up-regulation of CTGF and CD68, indicating that the canonical SMAD signaling pathway is required for these effects. Moreover, CTGF-knock down abolished the BMP6-induced up-regulation of CD68 expression. These findings indicate that intrafollicular CTGF mediates BMP6-induced increases in CD68 expression through the ALK2/ALK3-mediated SMAD-dependent signaling pathway.

TGF-β1 inhibits microvascular-like formation by decreasing VCAM1 and ICAM1 via the upregulation of SNAIL in human granulosa cells

Three major endothelial cell junctional adhesion molecules (VCAM1, ICAM1 and E-SELECTIN) play important roles in the process of angiogenesis, a progression of extensive physiological vascularization that occurs during the formation of the corpus luteum. Our previous studies demonstrated that TGF-β1 is a negative regulator of luteinization and progesterone production in luteinized human granulosa (hGL) cells. Whether TGF-β1 can regulate the expression of these endothelial cell adhesion molecules and subsequent angiogenesis in hGL cells remains to be elucidated. Using dual inhibition approaches (small molecular inhibitors and siRNA-based knockdown), we provided the first data showing that TGF-β1 significantly upregulates the expression of the SNAIL transcription factor, which in turn suppresses the expression of VCAM1 and ICAM1 in hGL cells. Additionally, we demonstrate that the suppressive effects on the expression of VCAM1 and ICAM1 induced by TGF-β1 treatment were most likely via an ALK5-mediated SMAD-dependent signaling pathway. Furthermore, functional studies showed that hGL cells cultured on Matrigel exhibited two typical endothelial cell phenotypes, microvascular-like formation and a sprouting microvascular pattern. Notably, these phenotypes were significantly suppressed by either TGF-β1 treatment or knockdown of VCAM1 and ICAM1. Our findings suggest that TGF-β1 plays a potential role in the inhibition of granulosa cell angiogenesis by downregulating the expression of VCAM1 and ICAM1 during follicular development and corpus luteum formation.

Bone morphogenetic protein 2 upregulates SERPINE2 expression through noncanonical SMAD2/3 and p38 MAPK signaling pathways in human granulosa-lutein cells

Serine protease inhibitor-E2 (SERPINE2) is highly expressed in the granulosa cells of growing follicles and the dynamic changes in SERPINE2 expression are correlated with follicular development and ovulation in several mammals, including mice, cattle, sheep, and humans. Bone morphogenetic proteins (BMPs) and their functional receptors are extensively expressed in the ovary and play critical roles in the regulation of ovarian folliculogenesis and luteal function. To date, whether BMPs regulate the expression of SERPINE2 during human follicular development remains to be elucidated. The aim of this study was to investigate the effects of BMPs on the regulation of SERPINE2 expression (a major regulator of plasminogen activators [PA]) and the underlying mechanisms using primary and immortalized human granulosa-lutein (hGL) cells. Our results demonstrated that these BMPs (BMP2, BMP4, BMP6, BMP7, and BMP15) induced differential upregulation of SERPINE2 expression. In this regard, BMP2 is the major modulator that has the best cellular activity, which further decreased the production of urokinase PA and tissue PA in hGL cells. In addition to canonical SMAD1/5/8 signaling, BMP2 also activates noncanonical SMAD2/3 and p38 mitogen-activated protein kinase (MAPK) signaling. Using two inhibition approaches (kinase receptor inhibitors and siRNA-mediated knockdown), we found that SMAD2/3-SMAD4 and p38 MAPK, but not SMAD1/5/8 signaling, was involved in the BMP2-induced upregulation of SERPINE2 expression via activin receptor-like kinase 3. These findings deepen our understanding of the differential effect of BMPs in regulating follicular function and provide new insights of the molecular mechanisms by which BMP2 regulates the expression of SERPINE2 in human granulosa cells.

The IL6/sIL-6Rα trans-signaling increases PGE2 production in human granulosa cells

As a potent autocrine regulator, the proinflammatory cytokine interleukin 6 (IL6) is expressed in granulosa cells and follicular fluid and is involved in the modulation of various follicular functions, including follicular development and ovulation. At present, the detailed molecular mechanisms by which IL6 regulates the event of ovulation remain to be elucidated. In the present study, primary and immortalized (SVOG) human granulosa-lutein (hGL) cells were used to investigate the effects of IL6 on the expression of prostaglandin-endoperoxide synthase 2 (PTGS2) and the subsequent synthesis of prostaglandin E2 (PGE2) and to investigate the underlying molecular mechanisms. We found that instead of classic signaling, IL6/sIL-6Rα trans-signaling induced the expression of PTGS2 and production of PGE2 in both SVOG cells and primary hGL cells. Moreover, IL6/sIL-6Rα activated the phosphorylation of Janus activated kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), which in turn induced STAT3 nuclear translocation. Additionally, these effects were suppressed by the addition of inhibitors (AG490 for JAK2 and C188-9 for STAT3) and by the siRNA-mediated knockdown of STAT3. Additionally, suppressor of cytokine signaling 3 (SOCS3) acts as a negative-feedback regulator in IL6/sIL-6Rα-induced cellular activities, including the activation and nuclear translocation of STAT3, upregulation of PTGS2 expression, and increase in PGE2 production in SVOG cells. In conclusion, IL6 trans-signaling upregulates the expression of PTGS2 and increases the production of PGE2 via the JAK2/STAT3/SOCS3 signaling pathway in hGL cells. Our findings provide insights into the molecular mechanisms by which IL6 trans-signaling may potentially modulate the event of ovulation in human ovaries.

In Vitro Systematic Drug Testing Reveals Carboplatin, Paclitaxel, and Alpelisib as a Potential Novel Combination Treatment for Adult Granulosa Cell Tumors

Adult granulosa cell tumors (AGCTs) arise from the estrogen-producing granulosa cells. Treatment of recurrence remains a clinical challenge, as systemic anti-hormonal treatment or chemotherapy is only effective in selected patients. We established a method to rapidly screen for drug responses in vitro using direct patient-derived cell lines in order to optimize treatment selection. The response to 11 monotherapies and 12 combination therapies, including chemotherapeutic, anti-hormonal, and targeted agents, were tested in 12 AGCT-patient-derived cell lines and an AGCT cell line (KGN). Drug screens were performed within 3 weeks after tissue collection by measurement of cell viability 72 h after drug application. The potential synergy of drug combinations was assessed. The human maximum drug plasma concentration (Cmax) and steady state (Css) thresholds obtained from available phase I/II clinical trials were used to predict potential toxicity in patients. Patient-derived AGCT cell lines demonstrated resistance to all monotherapies. All cell lines showed synergistic growth inhibition by combination treatment with carboplatin, paclitaxel, and alpelisib at a concentration needed to obtain 50% cell death (IC50) that are below the maximum achievable concentration in patients (IC50 < Cmax). We show that AGCT cell lines can be rapidly established and used for patient-specific in vitro drug testing, which may guide treatment decisions. Combination treatment with carboplatin, paclitaxel, and alpelisib was consistently effective in AGCT cell lines and should be further studied as a potential effective combination for AGCT treatment in patients.

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.

Development of a novel dual reproductive organ on a chip: recapitulating bidirectional endocrine crosstalk between the uterine endometrium and the ovary

Conventional 2D or even 3Din vitroculture models for human reproductive organs cannot properly recapitulate the bidirectional endocrine crosstalk between the uterine endometrium and the ovary. This crosstalk is essential for maintaining the various physiological features and functions of each tissue. Moreover, mostin vitromodels for the female reproductive tract also fail to mimic its multicellular structure. We therefore developed a novel 'dual reproductive organ on a chip' that reflects the bidirectional endocrine cross-talk and the complex multicellular structures by integrating various cellular components of both the human uterine endometrium and the ovary with several biodegradable natural polymers. Indeed, the bidirectional endocrine crosstalk between these two tissues is achieved through media sharing between channels, and it can markedly improve the viability of loaded cells within each chamber of the chip platform. In addition, we also identified a reliable reproductive toxicity marker, SERPINB2, which is significantly increased in response to various toxic exposures in both endometrial and ovarian follicular cells. Based on these findings, we next established a SERPINB2 luciferase reporter system that was specifically designed for detecting and quantifying the toxicity of certain substances. By introducing this SERPINB2 luciferase reporter system into the loaded cells within the chip platform, we ultimately developed an effective 'dual reproductive organ-on-chip' that was successfully used to predict the reproductive toxicity of various hazardous materials.

BMP2 increases the production of BDNF through the upregulation of proBDNF and furin expression in human granulosa-lutein cells

Locally produced in human granulosa cells of the developing follicle, bone morphogenetic protein 2 (BMP2) plays a crucial role in the regulation of ovarian folliculogenesis and luteal formation. Brain-derived neurotrophic factor (BDNF) is an intraovarian neurotrophic factor that has been shown to promote oocyte maturation and subsequent fertilization competency. At present, little is known regarding the intracellular regulation, assembly and secretion of endogenous BDNF in human granulosa cells. The aim of this study was to explore the effect of BMP2 on the expression and production of BDNF in human granulosa cells and the molecular mechanisms underlying this effect. An immortalized human granulosa cell line (SVOG) and primary human granulosa-lutein (hGL) cells were utilized as in vitro study models. Our results showed that BMP2 significantly increased the mRNA and secreted levels of BDNF. Additionally, BMP2 upregulated the expression of furin at the transcriptional and translational levels. Knockdown of endogenous furin partially attenuated the BMP2-induced increase in BDNF production, indicating that furin is involved in the maturation process of BDNF. Using pharmacological (kinase receptor inhibitors) and siRNA-mediated inhibition approaches, we demonstrated that BMP2-induced upregulation of BDNF and furin expression is most likely mediated by the activin receptor-like kinase (ALK)2/ALK3-SMAD4 signaling pathway. Notably, analysis using clinical samples revealed that there was a positive correlation between follicular fluid concentrations of BMP2 and those of BDNF. These results indicate that BMP2 increases the production of mature BDNF by upregulating the precursor BDNF and promoting the proteolytic processing of mature BDNF. Finally, we also investigated the effects of BMP2 on ovarian steroidogenesis and the results showed that BMP2 treatment significantly increased the accumulated level of estradiol (by upregulating the expression of FSH receptor and cytochrome P450 aromatase), whereas it decreased the accumulated level of progesterone (by downregulating the expression of LH receptors and steroidogenic acute regulatory protein) in primary hGL cells. Our findings provide a novel paracrine mechanism underlying the regulation of an intraovarian growth factor in human granulosa cells.

The p38 signaling pathway mediates the TGF-β1-induced increase in type I collagen deposition in human granulosa cells

Type I collagen, which is mainly composed of collagen type I alpha 1 chain (COL1A1), is the most abundant extracellular matrix (ECM) protein in the mammalian ovary; and the cyclical remodeling of the ECM plays an essential role in the regulation of corpus luteum formation. Our previous studies have demonstrated that TGF-β1 is a potent inhibitor of luteinization in human granulosa-lutein (hGL) cells. Whether TGF-β1 can regulate the expression of COL1A1 during the luteal phase remains to be elucidated. The aim of this study was to investigate the effect of TGF-β1 on the regulation of COL1A1 expression and the underlying molecular mechanisms using an immortalized hGL cell line (SVOG cells) and primary hGL cells (obtained from 20 consenting patients undergoing IVF treatment). The results showed that TGF-β1 significantly upregulated the expression of COL1A1. Using inhibition approaches, including pharmacological inhibition (a specific p38 inhibitor, SB203580, and a specific ERK1/2 inhibitor, U0126) and specific siRNA-mediated knockdown inhibition, we demonstrated that TGF-β1 promoted the expression and production of COL1A1 in hGL cells, most likely via the ALK5-mediated p38 signaling pathway. Our findings provide insights into the molecular mechanisms by which TGF-β1 promotes the deposition of type I collagen during the late follicular phase in humans.

SMAD-dependent signaling mediates morphogenetic protein 6-induced stimulation of connective tissue growth factor in luteinized human granulosa cells†

Connective tissue growth factor (also known as CTGF or CCN2) is a secreted matricellular protein that belongs to the CCN family. With wide-ranging biological activities and tissue expression patterns, CTGF plays a critical role in regulating various cellular functions. In the female reproductive system, CTGF is highly expressed in granulosa cells in growing ovarian follicles and is involved in the regulation of follicular development, ovulation, and luteal function. In the mammalian ovary, bone morphogenetic protein 6 (BMP6) is an important intraovarian modulator of follicular development. In this study, we demonstrated that BMP6 treatment significantly increased the expression of CTGF in both primary and immortalized human granulosa cells. Using both pharmacological inhibitors and Small interfering RNA-mediated knockdown approaches, we showed that ALK2 and ALK3 type I receptors are required for BMP6-induced cellular activities. Furthermore, this effect is most likely mediated by a Sma- and Mad-related protein (SMAD)-dependent pathway. Our studies provide novel insight into the molecular mechanisms by which an intraovarian growth factor affects the production of another factor via a paracrine effect in human granulosa cells.

Establishment and characterization of a PCOS and a normal human granulosa cell line

Oocyte maturation is an important phase in fertility and any disorder in this process could lead to infertility. The most common disorder during folliculogenesis is polycystic ovary syndrome (PCOS). Due to the secretive activity of granulosa cells (GCs), they play a vital role in folliculogenesis. Although scientists use various cellular and molecular methods to have a better understanding of the mechanism of these cells, some limitations still exist in GC culture such as low primary cell yield and proliferation capability. Therefore, immortalization of primary cells is an approach to overcome these limitations. In the current study, GCs were obtained from two females, one with PCOS and one with normal folliculogenesis. In the first stage, we established two human GC (hGC) lines by immortalizing them through retrovirus-mediated transfer of the human telomerase reverse transcriptase (hTERT) and c-Myc genes. Subsequently, the normal and PCOS cell lines were characterized and were investigated for their growth features. The cell lines were also examined in terms of immortal markers of hTERT, follicle stimulating hormone receptor (FSHR), aromatase, anti-Müllerian hormone (AMH), growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), estrogen, and progesterone. Our results indicated that the normal and PCOS cell lines both showed similar characteristics to GCs during the follicular stage in normal and PCOS women. The normal and PCOS cell lines demonstrate molecular mechanisms similar to that of GCs such as folliculogenesis, oogenesis, and steroidogenesis, which enable researchers to perform further investigations in future.

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.

The Pathognomonic FOXL2 C134W Mutation Alters DNA-Binding Specificity

The somatic missense point mutation c.402C>G (p.C134W) in the FOXL2 transcription factor is pathognomonic for adult-type granulosa cell tumors (AGCT) and a diagnostic marker for this tumor type. However, the molecular consequences of this mutation and its contribution to the mechanisms of AGCT pathogenesis remain unclear. To explore these mechanisms, we engineered V5-FOXL2^WT- and V5-FOXL2^C134W-inducible isogenic cell lines and performed chromatin immunoprecipitation sequencing and transcriptome profiling. FOXL2^C134W associated with the majority of the FOXL2 wild-type DNA elements as well as a large collection of unique elements genome wide. This model enabled confirmation of altered DNA-binding specificity for FOXL2^C134W and identification of unique targets of FOXL2^C134W including SLC35F2, whose expression increased sensitivity to YM155. Our results suggest FOXL2^C134W drives AGCT by altering the binding affinity of FOXL2-containing complexes to engage an oncogenic transcriptional program. SIGNIFICANCE: A mechanistic understanding of FOXL2^C134W-induced regulatory state alterations drives discovery of a rationally designed therapeutic strategy.

TGF-β1 promotes vitamin D-induced prostaglandin E2 synthesis by upregulating vitamin D receptor expression in human granulosa-lutein cells

There is increasing evidence showing the importance of vitamin D (Vit D) and its nuclear receptor, the Vit D receptor (VDR), in female reproductive health. Transforming growth factor-β1 (TGF-β1) and its functional receptors are expressed in human oocytes and granulosa cells that participate in follicular development and ovulation. Recently, Sma- and Mad-related protein 3 (SMAD3; a downstream effector of TGF-β1) has been proposed to mediate crosstalk between the Vit D and TGF-β1 signaling pathways, but this relationship has not been fully explored and has yet to be tested in human granulosa-lutein (hGL) cells. In this study, we showed that TGF-β1 significantly promoted the expression of VDR, and this stimulatory effect occurred through the activin receptor-like kinase 5 type I receptor-mediated SMAD3 and ERK1/2 signaling pathways in hGL cells. Additionally, we showed that Vit D increased the expression of cyclooxygenase 2 (COX-2) and the synthesis of prostaglandin E2 (PGE2) in a time- and dose-dependent manner. Furthermore, we demonstrated a synergistic effect of TGF-β1 and Vit D on the expression of COX-2 and synthesis of PGE2, and this effect could be attenuated by silencing the expression of VDR. Our findings indicate that TGF-β1 upregulates the expression of VDR, which promotes Vit D-induced COX-2 expression and subsequent PGE2 production by activating the SMAD3 and ERK1/2 signaling pathways in hGL cells.

ALK4-SMAD3/4 mediates the effects of activin A on the upregulation of PAI-1 in human granulosa lutein cells

In the mammalian ovary, the proteolysis of the extracellular matrix is dynamically regulated by plasminogen activator and plasminogen activator inhibitor (PAI), and it is a critical event that influences various physiological and pathological processes. Activin A is a member of the transforming growth factor-β superfamily and is expressed at a high level in human luteal cells that play an essential role in the regulation of the luteal function. At present, it is not known whether activin A can regulate the expression and production of PAI in human granulosa lutein (hGL) cells. The present study aimed to examine the effects of activin A on the expression and production of intraovarian PAI-1 and the underlying molecular mechanisms. Using primary and immortalized hGL cells as the cell model, we demonstrated that activin A upregulated the expression of PAI-1 and increased the production of PAI-1 in an autocrine/paracrine manner. Additionally, using a dual inhibition approach (molecular inhibitors and siRNA-mediated knockdown), we showed that this biological function is mediated by the ALK4-mediated SMAD3-SMAD4-dependent signaling pathway. Our findings suggest that activin A may be involved in the regulation of luteal function via the induction of PAI-1 expression and an increase in PAI-1 production.

TGF-β1 induces VEGF expression in human granulosa-lutein cells: a potential mechanism for the pathogenesis of ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is one of the most serious and iatrogenic complications that can occur during in vitro fertilization treatment. Although the pathogenesis of OHSS is not fully understood, vascular endothelial growth factor (VEGF) has been recognized as an important mediator of the development of OHSS. Transforming growth factor-beta-1 (TGF-β1) is known to regulate various ovarian functions. However, whether VEGF can be regulated by TGF-β1 in human granulosa cells has not been determined. In addition, the role of TGF-β1 in the pathogenesis of OHSS remains unknown. In the present study, we demonstrate that TGF-β1 stimulates VEGF expression in and secretion from both immortalized human granulosa-lutein (hGL) cells and primary hGL cells. Our results demonstrate that the SMAD2/3, ERK1/2, and p38 MAPK signaling pathways are involved in TGF-β1-induced VEGF expression and secretion. Using a mouse OHSS model, we show that the expression levels of TGF-β1 and VEGF are increased in the ovaries of OHSS mice. Blocking TGF-β1 signaling inhibits the development of OHSS by attenuating VEGF expression. Moreover, clinical results reveal that the protein levels of TGF-β1 and VEGF are increased in the follicular fluid of patients with OHSS, and that the levels of these two proteins in the follicular fluid are positively correlated. The results of this study help to elucidate the mechanisms by which VEGF expression is regulated in hGL cells, which could lead to the development of alternative therapeutic approaches for treating OHSS.

Insights into abnormal protein activity involved in ovarian hyperstimulation syndrome (OHSS) could inform future therapies. OHSS is a serious complication of fertility treatment where the body responds excessively to medication taken to help eggs grow, causing blood clots, pain, and even death. Scientists believe that high levels of the vascular endothelial growth factor (VEGF) protein trigger OHSS. Another protein involved in cell proliferation,transforming growth factor beta-1 (TGF-β1), may influence VEGF activity. Ying-Pu Sun and Jung-Chien Cheng at the First Affiliated Hospital of Zhengzhou University, Henan, China, and co-workers conducted experiments on human cell lines and OHSS mouse models. They found that TGF-β1 stimulates VEGF expression in human cells, and identified the associated signaling pathways. Both TGF-β1 and VEGF were increased in the ovaries of mice with OHSS, while blocking TGF-β1 halted OHSS progression.

TGF-β1 Increases GDNF Production by Upregulating the Expression of GDNF and Furin in Human Granulosa-Lutein Cells

Glial cell line-derived neurotrophic factor (GDNF) is expressed at a high level in the human ovary and GDNF signaling is involved in the direct control of follicular activation and oocyte maturation. Transforming growth factor-β1 (TGF-β1) plays an important role in the regulation of various ovarian functions. Furin is an intracellular serine endopeptidase of the subtilisin family that is closely associated with the activation of multiple protein precursors. Despite the important roles of GDNF and TGF-β1 in the regulation of follicular development, whether TGF-β is able to regulate the expression and production of GDNF in human granulosa cells remains to be determined. The aim of this study was to investigate the effect of TGF-β1 on the production of GDNF and its underlying mechanisms in human granulosa-lutein (hGL) cells. We used two types of hGL cells (primary hGL cells and an established immortalized hGL cell line, SVOG cells) as study models. Our results show that TGF-β1 significantly induced the expression of GDNF and furin, which, in turn, increased the production of mature GDNF. Using a dual inhibition approach combining RNA interference and kinase inhibitors against cell signaling components, we showed that the TβRII type II receptor and ALK5 type I receptor are the principal receptors that mediated TGF-β1-induced cellular activity in hGL cells. Additionally, Sma- and Mad-related protein (SMAD)3 and SMAD4 are the downstream signaling transducers that mediate the biological response induced by TGF-β1. Furthermore, furin is the main proprotein convertase that induces the production of GDNF. These findings provide additional regulatory mechanisms by which an intrafollicular factor influences the production of another growth factor through a paracrine or autocrine interaction in hGL cells.

Bone morphogenetic protein 6 affects cell-cell communication by altering the expression of Connexin43 in human granulosa-lutein cells

Connexin 43 (Cx43)-coupled gap junctions in granulosa cells play an important role in follicular development, oocyte maturation, and corpus luteum maintenance. Bone morphogenetic protein 6 (BMP6) is highly expressed in human oocytes and granulosa cells and is involved in the regulation of female reproduction. Currently, whether oocyte- and granulosa cell-derived BMP6 affects the expression of Cx43 and its related gap junction intercellular communication (GJIC) activity in human granulosa cells remains unknown. In this study, we demonstrate that BMP6 treatment significantly suppressed the expression of Cx43 in both primary and immortalized (SVOG) human granulosa-lutein cells. Using both pharmacological inhibitors and small interfering RNA-mediated knockdown approaches, we demonstrate that ALK2 and ALK3 BMP type I receptors are involved in BMP6-induced suppressive effects on Cx43 expression and GJIC activity in SVOG cells. Furthermore, these cellular activities are most likely mediated by the SMAD1/SMAD5-SMAD4-dependent signaling pathway. Notably, the ChIP analyses demonstrated that phosphorylated SMADs could bind to human Cx43 promoter. Our findings provide new insight into the molecular mechanisms by which an intrafollicular growth factor regulates cell-cell communication in human granulosa cells.

CCN2 Mediates S1P-Induced Upregulation of COX2 Expression in Human Granulosa-Lutein Cells

CCN1 and CCN2 are members of the CCN family and play essential roles in the regulation of multiple female reproductive functions, including ovulation. Cyclooxygenase-2 (COX2) is a critical mediator of ovulation and can be induced by sphingosine-1-phosphate (S1P) through the S1P_1/3-mediated Yes-associated protein (YAP) signaling. However, it is unclear whether CCN1 or CCN2 can mediate S1P-induced upregulation of COX2 expression and increase in prostaglandin E2 (PGE2) production in human granulosa-lutein (hGL) cells. In the present study, we investigated the effects of S1P on the expressions of CCN1 and CCN2 in hGL cells. Additionally, we used a dual inhibition approach (siRNA-mediated silencing and small molecular inhibitors) to investigate the molecular mechanisms of S1P effects. Our results showed that S1P treatment significantly upregulated the expression of CCN1 and CCN2 in a concentration-dependent manner in hGL cells. Additionally, inhibition or silencing of S1P₁, but not S1P₃, completely abolished the S1P-induced upregulation of CCN2 expression. Furthermore, we demonstrated that S1P-induced nuclear translocation of YAP and inhibition or silencing of YAP completely abolished the S1P-induced upregulation of CCN1 and CCN2 expression. Notably, silencing of CCN2, but not CCN1, completely reversed the S1P-induced upregulation of COX2 expression and the increase in PGE2 production. Thus, CCN2 mediates the S1P-induced upregulation of COX2 expression through the S1P₁-mediated signaling pathway in hGL cells. Our findings expand our understanding of the molecular mechanism underlying the S1P-mediated cellular activities in the human ovary.

Pluripotent Cell Models for Gonadal Research

Sex development is a complex process involving many genes and hormones. Defects in this process lead to Differences of Sex Development (DSD), a group of heterogeneous conditions not as rare as previously thought. Part of the obstacles in proper management of these patients is due to an incomplete understanding of the genetics programs and molecular pathways involved in sex development and DSD. Several challenges delay progress and the lack of a proper model system for the single patient severely hinders advances in understanding these diseases. The revolutionary techniques of cellular reprogramming and guided in vitro differentiation allow us now to exploit the versatility of induced pluripotent stem cells to create alternatives models for DSD, ideally on a patient-specific personalized basis.

TGF-β1 promotes hyaluronan synthesis by upregulating hyaluronan synthase 2 expression in human granulosa-lutein cells

Hyaluronan serves as a structural component of ovarian follicles, and hyaluronan-mediated signaling cascades lead to follicular development, oocyte maturation, and ovulation. Transforming growth factor-β (TGF-β1) is highly expressed in human oocytes and granulosa cells and involved in the regulation of follicular development and ovulation. Previous studies have shown the imperative role for TGF-β signaling in the regulation of hyaluronan-mediated cumulus expansion and ovulation in human granulosa-lutein (hGL) cells. However, the detailed underlying molecular mechanisms by which TGF-β regulates the synthesis of hyaluronan in hGL cells are not fully elucidated. Using both primary and immortalized hGL cells as study models, we provide the first data showing that TGF-β1 significantly promoted the synthesis of hyaluronan by upregulating the expression of hyaluronan synthase 2 in these cells. Additionally, using dual inhibition approaches, we show that the TGF-β type II (TβRII) receptor and TGF-β type I (ALK5) receptor are functional receptors that mediate stimulatory effects in response to TGF-β1. Moreover, we found that the canonical SMAD2/SMAD3-SMAD4 signaling pathway is the principal intracellular signaling pathway that upregulates the expressionhyaluronan synthase and subsequent hyaluronan synthesis. Notably, we showed that SNAIL transcription factor is a critical molecule mediating the TGF-β signaling, which contributes to the increase in hyaluronan synthesis. These results of our in vitro studies suggest that intraovarian TGF-β1 plays a functional role in the local regulation of hyaluronan synthesis in hGL cells.

ALK4-SMAD2/3-SMAD4 signaling mediates the activin A-induced suppression of PTX3 in human granulosa-lutein cells

As one of the members of the transforming growth factor-β (TGF-β) superfamily, activin A plays an important role in regulating follicular development and oocyte maturation. Pentraxin 3 (PTX3) is the key component that promotes the process of cumulus expansion during mammalian ovulation. At present, the regulation of PTX3 expression in human granulosa cells remains largely unknown. This study aimed to examine the effects of activin A on the expression of PTX3 in human granulosa-lutein (hGL) cells and to investigate the underlying molecular mechanisms. Using an established immortalized hGL cell line (SVOG) and primary hGL cells as study models, we demonstrated that activin A significantly increased the phosphorylation of SMAD2 and SMAD3, which suppressed the expression of PTX3 at both the mRNA and protein levels. Additionally, these effects induced by activin A were completely reversed by pretreatment with the TGF-β type I receptor inhibitor SB431542 and knockdown of ALK4. Furthermore, knockdown of SMAD2, SMAD3, or SMAD4 completely reversed the activin A-induced suppressive effects on PTX3 expression. Notably, the ChIP analyses demonstrated that phosphorylated SMADs could bind to human PTX3 promoter. Collectively, our results showed that the ALK4-SMAD2/3-SMAD4 signaling pathway most likely mediates the suppressive effect of activin A on PTX3 expression in hGL cells.

CDK4/6 inhibitor protects chemerin-induced human granulosa-lutein cells from apoptosis by inhibiting the p53/p21 waf pathway

Dysregulation of the cell cycle is common in human tumorigenesis. Therefore, CDK4/6 inhibitors targeting the cell cycle have been developed, and their antiapoptotic effects have been highly correlated with potential clinical therapies. The aim of this study was to identify the regulatory effect of the CDK4/6 inhibitor palbociclib on chemerin-induced apoptosis of immortalized human granulosa-lutein (hGL) cells and to elucidate its fundamental mechanism of action. Palbociclib enhanced antioxidative enzyme generation and diminished ROS generation in hGL cells. Furthermore, we found that palbociclib suppressed chemerin-induced apoptotic protein expression, reversing the Bcl-2/Bax ratio and inhibiting the p53/p21 ^waf pathway. Eventually, palbociclib decreased the level of cleaved caspase-3 and -9, hindering the apoptosis of hGL cells. In general, the antiapoptotic efficacy of palbociclib could be attributed in part to the modulation of the mitochondrial apoptotic pathway in hGL cells.

Characterization and identification of human immortalized granulosa cells derived from ovarian follicular fluid

Follicular fluid serves a crucial role in follicular development and oocyte maturation. Increasing evidence indicates that follicular fluid is rich in proteins and functional cells. In addition to oocyte cells, follicular fluid contains granulosa, thecal and ovarian surface epithelial cells. Granulosa cells (GCs) represent the predominant somatic cell type of the ovarian follicle and are involved in steroidogenesis and folliculogenesis. However, the long-term culture of GCs in vitro remains challenging. The present study aimed to extend the culture of GCs in vitro. Human GCs were collected from the follicular fluid of patients included in an in vitro fertilization program and cultured in the presence of conditioned medium obtained from mouse embryonic fibroblasts. GCs were cultured for over a year and 130 passages, and the population doubling time was ~22 h. Cells presented epithelial-like morphology and a cobblestone-like appearance when they reached confluence. Flow cytometric analysis demonstrated that cells expressed CD29, CD166 and CD49f but not CD31, CD34, CD45, CD90, CD105 or CD13. Immunofluorescence staining revealed that cells expressed follicle stimulating hormone receptor, luteinizing hormone receptor and cytochrome P450 aromatase, which was confirmed by reverse transcription-quantitative polymerase chain reaction. In the presence of androstenedione, cells secreted estradiol. In addition, estradiol level was further stimulated by dibutyryl cAMP treatment. In addition, intracellular cAMP and progesterone expression levels were upregulated by follicle stimulating hormone and/or human chorionic gonadotropin. Furthermore, cells survived in severe combined immunodeficiency mice following intra-ovarian injection. Histological analysis revealed that certain cells formed follicle-like structures. The results from the present study suggested that immortalized GCs may be a useful tool for further research on GC and improve the clinical application of drugs such as follicle-stimulating hormone or human chorionic gonadotropin.

microRNA-126 Is a Tumor Suppressor of Granulosa Cell Tumor Mediated by Its Host Gene EGFL7

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression at a post-transcriptional level. We examined the role of miR-126 in granulosa cell tumor (GCT) of the ovaries. In tissues from malignant GCT patients miR-126 expression was repressed. We showed that miR-126 could inhibit proliferation, migration, hormone production and promote apoptosis of cancerous granulosa cells (GCs) in vitro. The role of miR-126 as “tumor suppressor” was confirmed by using a tumor formation model in vivo. By RNA-seq, immunohistochemical staining (IHC), Western blot and luciferase reporter assay, we identified and confirmed EGFL7 as a direct functional target of miR-126 in cancer GCs. Furthermore, we found that the AKT signaling pathway was associated with miR-126 and EGFL7 in cancer GCs. Taken together, our results demonstrate a function of miR-126 in the suppression of GCT development via the regulation of EGFL7.

Palmitic acid causes insulin resistance in granulosa cells via activation of JNK

Obesity is a worldwide health problem with rising incidence and results in reproductive difficulties. Elevated saturated free fatty acids (FFAs) in obesity can cause insulin resistance (IR) in peripheral tissues. The high intra-follicular saturated FFAs may also account for IR in ovarian granulosa cells (GCs). In the present study, we investigated the relationship between saturated FFAs and IR in GCs by the use of palmitic acid (PA). We demonstrated that the glucose uptake in cultured GCs and lactate accumulation in the culture medium were stimulated by insulin, but the effects of insulin were attenuated by PA treatment. Besides, insulin-induced phosphorylation of Akt was reduced by PA in a dose- and time-dependent manner. Furthermore, PA increased phosphorylation of JNK and JNK blockage rescued the phosphorylation of Akt which was downregulated by PA. These findings highlighted the negative effect of PA on GCs metabolism and may partially account for the obesity-related reproductive disorders.

The HMGA2-IMP2 Pathway Promotes Granulosa Cell Proliferation in Polycystic Ovary Syndrome

CONTEXT

The high mobility group AT hook 2 (HMGA2) gene was previously identified in a genome-wide association study as a candidate risk gene that might be related to polycystic ovary syndrome (PCOS). Whether HMGA2 contributes to promoting granulosa cell (GC) proliferation in PCOS remains unknown.

OBJECTIVE

We sought to determine whether HMGA2 is involved in the ovarian dysfunction of PCOS and in the mechanism of increased GC proliferation.

PATIENTS AND CELLS

mRNA expression was analyzed in ovarian GCs from 96 women with PCOS and 58 healthy controls. Immortalized human GCs (KGN and SVOG cells) were used for the mechanism study.

MAIN OUTCOME MEASURES

mRNA expression in ovarian GCs was measured using quantitative RT-PCR, and KGN cells were cultured for proliferation assays after overexpression or knockdown of target genes. Protein expression analysis, luciferase assays, and RNA binding protein immunoprecipitation assays were used to confirm the mechanism study.

RESULTS

HMGA2 and IGF2 mRNA binding protein 2 (IMP2) were highly expressed in the GCs of women with PCOS, and the HMGA2/IMP2 pathway promoted GC proliferation. Cyclin D2 and SERPINE1 mRNA binding protein 1 were regulated by IMP2 and were highly expressed in women with PCOS.

CONCLUSIONS

The HMGA2/IMP2 pathway was activated in women with PCOS and promoted the proliferation of GCs. This might provide new insights into the dysfunction of GCs in PCOS.

Bone morphogenetic protein 2 increases lysyl oxidase activity via up-regulation of snail in human granulosa-lutein cells

Lysyl oxidase (LOX) is a copper-dependent enzyme that maintains and stabilizes the extracellular matrix (ECM) by catalyzing the cross-linking of elastin and collagen. ECM within the ovarian follicle plays a crucial role in regulating follicular development and oocyte maturation. Bone morphogenetic protein 2 (BMP2) belongs to the BMP subfamily that has been shown to be involved in the process of ovarian folliculogenesis and luteal formation. To date, whether BMP2 regulates the activity of LOX during human follicular development remains to be elucidated. The aim of this study was to investigate the effect of BMP2 on the regulation of LOX expression and activity in human granulosa-lutein cells (hGL) and the underlying mechanisms. Using both primary and immortalized (SVOG cells) hGL cells, we demonstrated that BMP2 up-regulated the expression and activity of LOX and hence decreased the soluble collagens in cultured medium in hGL cells. Additionally, the mRNA and protein levels of two transcriptional factors, SNAIL and SLUG, were increased following cell exposure to BMP2. Knockdown of SNAIL, but not SLUG partially reversed BMP2-induced increases in LOX expression and activity. The BMP2-induced up-regulation of SNAIL expression was abolished by the pre-treatment with two BMP type I receptor inhibitors, dorsomorphin and DMH-1, but not SB431542. Moreover, knockdown of SMAD4 completely abolished BMP2-induced up-regulation of SNAIL expression and the subsequent increases in LOX expression and activity. Our results suggest that BMP2 increases LOX expression and activity via the up-regulation of SNAIL in hGL cells. These findings may provide insights into the functional role of BMP2 in the regulation of ECM formation during folliculogenesis.

BMP6 Downregulates GDNF Expression Through SMAD1/5 and ERK1/2 Signaling Pathways in Human Granulosa-Lutein Cells

Bone morphogenetic protein (BMP) 6 is a critical regulator of follicular development that is expressed in mammalian oocytes and granulosa cells. Glial cell line‒derived neurotrophic factor (GDNF) is an intraovarian neurotrophic factor that plays an essential role in regulating mammalian oocyte maturation. The aim of this study was to investigate the effect of BMP6 on the regulation of GDNF expression and the potential underlying mechanisms. We used an established immortalized human granulosa cell line (SVOG cells) and primary human granulosa-lutein (hGL) cells as in vitro cell models. Our results showed that BMP6 significantly downregulated the expression of GDNF in both SVOG and primary hGL cells. With dual inhibition approaches (kinase receptor inhibitor and small interfering RNA knockdown), our results showed that both activin receptor kinase-like (ALK) 2 and ALK3 are involved in BMP6-induced downregulation of GDNF. In addition, BMP6 induced the phosphorylation of Sma- and Mad-related protein (SMAD)1/5/8 and ERK1/2 but not AKT or p38. Among three downstream mediators, both SMAD1 and SMAD5 are involved in BMP6-induced downregulation of GDNF. Moreover, concomitant knockdown of endogenous SMAD4 and inhibition of ERK1/2 activity completely reversed BMP6-induced downregulation of GDNF, indicating that both SMAD and ERK1/2 signaling pathways are required for the regulatory effect of BMP6 on GDNF expression. Our findings suggest an additional role for an intrafollicular growth factor in regulating follicular function through paracrine interactions in human granulosa cells.

SNAIL Mediates TGF-β1-Induced Downregulation of Pentraxin 3 Expression in Human Granulosa Cells

Transforming growth factor-β (TGF-β) 1 plays a critical role in regulating follicular development, and its dysregulation has been shown to be involved in the pathogenesis of ovulation dysfunction. SNAIL is a well-known transcriptional repressor that mediates TGF-β1-induced cellular functions. Pentraxin 3 (PTX3) is a key enzyme for the assembly and stabilization of the cumulus oophorus extracellular matrix, which is essential for cumulus expansion during the periovulatory stage. The purpose of the present study was to investigate the roles of TGF-β1 and SNAIL in the regulation of PTX3 expression and to examine the underlying mechanism. An established immortalized human granulosa cell (GC) line (SVOG), a GC tumor cell line (KGN), and primary human granulosa-lutein cells were used as study models. We demonstrated that TGF-β1 treatment substantially decreased the messenger RNA and protein levels of PTX3. This suppressive effect was abolished by cotreatment with the soluble TGF-β type II receptor (TβRII) or the ALK4/5/7 inhibitor SB431542. Knockdown of ALK5, SMAD2/3, or SMAD4 reversed the effects of TGF-β1-induced SNAIL upregulation and PTX3 suppression. These results indicate that TGF-β1 upregulates SNAIL and downregulates PTX3 expression via a TβRII-ALK5-mediated SMAD-dependent signaling pathway in human GCs. Additionally, TGF-β1-induced PTX3 suppression was mediated by upregulation of the SNAIL transcription factor, as knockdown of SNAIL completely reversed the suppression of PTX3 in response to TGF-β1. These findings could inform the roles of TGF-β1 and SNAIL in the regulation of follicular function and might provide therapeutic targets for the treatment of ovulation dysfunction.

Lithium chloride inhibits StAR and progesterone production through GSK-3β and ERK1/2 signaling pathways in human granulosa-lutein cells

Lithium chloride (LiCl) is a widely-used medication to treat neurological disorders that has undesirable side effects on the female reproductive system. It has been show that LiCl can inhibit ovarian folliculogenesis, promote follicle atresia and suppress steroid hormone production in rodents. However, the effects of LiCl on human ovarian steroidogenesis remain completely unknown. In this study, both primary and immortalized human granulosa-lutein (hGL) cells were used to investigate the effects of LiCl on progesterone production and its related enzyme expression as well as the underlying mechanisms. Our results showed that LiCl significantly down-regulated the steroidogenic acute regulatory protein (StAR) expression and subsequent progesterone production in hGL cells. Additionally, LiCl induced the phosphorylation of GSK-3β and ERK1/2 but not AKT or CREB. Knockdown of endogenous GSK-3β or inhibition of ERK1/2 partially reversed LiCl-induced down-regulation of StAR. Furthermore, by using dual inhibition approaches, the results showed that both GSK-3β and ERK1/2 signaling mediated the regulatory effect of LiCl on StAR expression. Our findings deepen our understanding of the pathological effects and the underlying molecular mechanisms of how lithium might affect the female reproductive system.

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.

Bone morphogenetic protein 2 regulates cell-cell communication by down-regulating connexin43 expression in luteinized human granulosa cells

STUDY QUESTION

Does bone morphogenetic protein 2 (BMP2) regulate connexin43 (Cx43) and modulate cell-cell communication in luteinized human granulosa cells?

SUMMARY ANSWER

BMP2 decreases gap junction intercellular communication (GJIC) of luteinized human granulosa cells by down-regulating Cx43 expression through an activin receptor-like kinase (ALK)2/ALK3-mediated Sma- and Mad-related protein (SMAD)-dependent signaling pathway.

WHAT IS KNOWN ALREADY

BMP2 and its putative receptors are highly expressed in the human corpus luteum and are involved in the process of luteolysis. Cx43-coupled gap junctions play a critical role in the development and maintenance of corpus luteum.

STUDY DESIGN DURATION

This is a laboratory study conducted over a 1-year period. At least three independent experiments with three replicates were conducted and the experimental samples were compared with the appropriate vehicle controls for all of the inhibition-approach, concentration-dependent or time-course studies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

SVOG cell line (immortalized human granulosa-lutein cells derived from in vitro fertilization patients in an academic research center) was used as the study model. The changes of Cx43 expression and levels of phosphorylated SMAD1/5/8 protein were evaluated after exposure to recombinant human BMP2. Real-time quantitative PCR and Western blot analysis were used to examine the specific mRNA and protein levels, respectively. The BMP/TGF-β type I receptor inhibitors (Dorsomorphin, DMH-1 and SB431542) and target depletion small interfering RNAs (ALK2, ALK3, ALK6 and SMAD4) were used to investigate the underlying molecular mechanisms. A scrape loading and dye transfer assay was used to evaluate the GJIC between the SVOG cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Treatment with BMP2 down-regulated the expression of Cx43 and decreased the GJIC activity, whereas it increased the phosphorylated SMAD1/5/8 protein in SVOG cells (P < 0.05). These biological effects were abolished by pre-treatment with the BMP type I receptor inhibitors, Dorsomorphin and DMH-1 (P < 0.05), but not SB431542. Additionally, the individual or concomitant small interfering RNA-mediated knockdown of ALK2 and ALK3, but not ALK6 attenuated the BMP2-induced increases in phosphorylated SMAD1/5/8 and down-regulation of Cx43 expression (P < 0.05). The knockdown of SMAD4 completely abolished the BMP2-induced down-regulation of Cx43 expression (P < 0.05).

LIMITATIONS REASONS FOR CAUTION

This experimental study was conducted in an in vitro cell culture system, and may not reflect a realistic intra-ovarian environment.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggested that BMP2 may be involved in the local modulation of cell-cell communication in the luteal phase. This study also represents the first comprehensive research of molecular mechanisms of BMP2 in the down-regulation Cx43 in luteinized human granulosa cells. Such data may provide valuable insights into ovarian physiology and benefit the development of potential therapeutic methods for patients suffering from luteal insufficiency.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTEREST(s)

This research was supported by an operating grant from the China-Canadian Joint Health Research Initiative Grants Program to P.C.K. Leung and J.Z. Sheng. The authors declare no competing interest with the contents of this article.

ALK2/ALK3-BMPR2/ACVR2A Mediate BMP2-Induced Downregulation of Pentraxin 3 Expression in Human Granulosa-Lutein Cells

Bone morphogenetic protein 2 (BMP2) belongs to the transforming growth factor-β superfamily and plays a critical role in regulating ovarian follicle function. Currently, the role of BMP2 during cumulus expansion remains to be determined. The aim of this study was to investigate the effect of BMP2 on the regulation of pentraxin 3 (PTX3) expression (the major component of cumulus expansion) and the underlying mechanisms in human granulosa-lutein (hGL) cells. Both primary and immortalized hGL cells were used as research models. Our results showed that treatment with BMP2 significantly suppressed the basal and luteinizing hormone-induced upregulation of PTX3. In addition, BMP2 stimulated the phosphorylation of SMAD1/5/8, and this effect was abolished by the addition of BMP type I receptor inhibitors, dorsomorphin homolog 1, and dorsomorphin but not SB431542. Moreover, the knockdown of activin receptorlike kinase 2/3 or BMP receptor type II/activin receptor type IIB receptors completely reversed the BMP2-induced phosphorylation of SMAD1/5/8 and restored PTX3 expression. Similarly, the knockdown of SMAD4 completely reversed the suppressive effect of BMP2 on the expression of PTX3. These results improve our understanding of the molecular mechanisms of BMP2 signaling. Our findings suggest that BMP2 may be involved in the regulation of cumulus expansion during the periovulatory stage.

Lithium Chloride Increases COX-2 Expression and PGE2 Production in a Human Granulosa-Lutein SVOG Cell Line Via a GSK-3β/β-Catenin Signaling Pathway

Lithium chloride (LiCl) is widely prescribed for the treatment of bipolar disorders and is associated with a higher incidence of reproductive adverse effects. Cyclooxygenase (COX)-2 and its derivative, prostaglandin E2 (PGE2), play regulatory roles in the human ovulatory process. Whether LiCl affects ovulation by regulating COX2 expression and PGE2 production in the human ovary is still largely unknown. The aim of this study was to investigate the effect of LiCl on the expression of COX-2 and production of PGE2 in human granulosa-lutein (hGL) cells, as well as the mechanisms underlying this effect. Both immortalized and primary hGL cells were used as research models. Using dual inhibition approaches, our results show that LiCl initiates the hGL cellular action by inhibiting the activity of glycogen synthase kinase-3β [GSK-3β (phosphorylation of GSK-3β)] and activation of extracellular signal-regulated kinase 1/2 (ERK1/2), but not by affecting protein kinase B or cAMP response element binding protein signaling. Additionally, the phosphorylation of GSK-3β, but not ERK1/2, resulted in the stabilization and nuclear localization of β-catenin. Furthermore, knockdown of either β-catenin or GSK-3β reversed the LiCl-induced upregulation of COX-2 expression. These results indicate that LiCl upregulates the expression of COX-2 and the subsequent production of PGE2 through the canonical GSK-3β/β-catenin signaling pathway in hGL cells.

SMAD1/5 mediates bone morphogenetic protein 2-induced up-regulation of BAMBI expression in human granulosa-lutein cells

Bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) is a transforming growth factor β (TGF-β) type I receptor antagonist that negatively regulates TGF-β and bone morphogenetic protein (BMP) signaling. BAMBI has been shown to be regulated by TGF-β signaling; however, whether BAMBI can be regulated by BMP signaling remains to be determined. The aim of this study was to investigate the effect of BMP2 on the regulation of BAMBI expression in human granulosa-lutein cells and the underlying mechanisms. Both primary and immortalized human granulosa-lutein cells were used as research models. Using dual inhibition approaches, our results showed that BMP2 activated SMAD1/5/8 phosphorylation and up-regulated BAMBI mRNA levels, which was reversed by the BMP type I receptor inhibitors, DMH-1 and dorsomorphin, but not by SB431542 (activin/TGF-β type I receptor inhibitor). Moreover, the combined knockdown of SMAD1 and SMAD5 completely abolished the BMP2-induced up-regulation of BAMBI. Similarly, knockdown of SMAD4 reversed the BMP2-induced up-regulation of BAMBI. Pre-treatment with BMP2 inhibited the TGF-β1-induced phosphorylation of SMAD2/3 and up-regulation of MMP2, and these inhibitory effects were reversed by knockdown of endogenous BAMBI. Our findings indicate that BAMBI is a BMP-responsive gene and that BAMBI participates in the negative feedback regulation of TGF-β signaling in the human ovary.

β-arrestins regulate gonadotropin receptor-mediated cell proliferation and apoptosis by controlling different FSHR or LHCGR intracellular signaling in the hGL5 cell line

Gonadotropin signaling classically involves proliferative, steroidogenic and apoptotic stimuli. In this study, we used the human granulosa cell line hGL5 to demonstrate how follicle-stimulating hormone (FSH) and luteinizing hormone (LH) differently control proliferative or apoptotic signals, revealing novel intrinsic properties of their receptors (FSHR, LHCGR). We found that, in this tumor-like cell line, the expression of endogenous FSHR and LHCGR is serum-dependent, but both receptors were unable to activate the canonical cAMP/PKA pathway upon gonadotropin stimulation, failing to produce cAMP, progesterone and G protein-coupled receptor (GPCR)-mediated apoptosis in vitro. Conversely, ligand treatment resulted in FSHR- and LHCGR-mediated ERK1/2 phosphorylation and cell proliferation due to receptor coupling to β-arrestins. The inactive cAMP/PKA pathway was unlocked by siRNA-mediated knock-down of β-arrestin 1 and 2, leading to progesterone synthesis and apoptosis. Surprisingly, FSH, but not LH treatment accelerated the cAMP/PKA-mediated apoptosis after β-arrestin silencing, an effect which could be reproduced by overexpressing the FSHR, but not the LHCGR. This work demonstrates that the expression of FSHR and LHCGR can be induced in hGL5 cells but that the FSHR-dependent cAMP/PKA pathway is constitutively silenced, possibly to protect cells from FSHR-cAMP-PKA-induced apoptosis. Also, we revealed previously unrecognized features intrinsic to the two structurally similar gonadotropin receptors, oppositely resulting in the regulation of life and death signals in vitro.

Activin A upregulates PTGS2 expression and increases PGE2 production in human granulosa-lutein cells

Activin A is one of the members of transforming growth factor-β superfamily that is expressed in human large luteal cells, and may act in an autocrine/paracrine manner to regulate luteal function. Prostaglandin-endoperoxide synthase 2 (PTGS2) enzyme and its derivative, prostaglandin E2 (PGE2), play significant roles in the regulation of corpus luteum formation and maintenance. To date, whether activin A can induce the expression of PTGS2 and the production of PGE2 in human granulosa-lutein cells is largely unknown. The aim of this study was to examine the effects of activin A on the regulation of PTGS2 expression and PGE2 production in human granulosa-lutein cells, and to investigate the underlying signal transduction mechanisms. In this study, the immortalized (SVOG cells) and primary human granulosa-lutein cells were used as the cell models. A TGF-β/activin type I receptor inhibitor, SB431542 and small interfering RNAs were used to investigate the activin A-induced downstream signaling pathway. We have demonstrated that activin A upregulated the expression of PTGS2 and increased the production of PGE2 via an ACVR1B-mediated SMAD2/3–SMAD4 signaling pathway. Our results suggest that activin A may be involved in the modulation of human corpus luteum formation via the induction of PTGS2 expression and PGE2 production.

Oocyte-somatic cell interactions in the human ovary-novel role of bone morphogenetic proteins and growth differentiation factors

BACKGROUND

Initially identified for their capability to induce heterotopic bone formation, bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor β superfamily. Using cellular and molecular genetic approaches, recent studies have implicated intra-ovarian BMPs as potent regulators of ovarian follicular function. The bi-directional communication of oocytes and the surrounding somatic cells is mandatory for normal follicle development and oocyte maturation. This review summarizes the current knowledge on the physiological role and molecular determinants of these ovarian regulatory factors within the human germline-somatic regulatory loop.

OBJECTIVE AND RATIONALE

The regulation of ovarian function remains poorly characterized in humans because, while the fundamental process of follicular development and oocyte maturation is highly similar across species, most information on the regulation of ovarian function is obtained from studies using rodent models. Thus, this review focuses on the studies that used human biological materials to gain knowledge about human ovarian biology and disorders and to develop strategies for preventing, diagnosing and treating these abnormalities.

SEARCH METHODS

Relevant English-language publications describing the roles of BMPs or growth differentiation factors (GDFs) in human ovarian biology and phenotypes were comprehensively searched using PubMed and the Google Scholar database. The publications included those published since the initial identification of BMPs in the mammalian ovary in 1999 through July 2016.

OUTCOMES

Studies using human biological materials have revealed the expression of BMPs, GDFs and their putative receptors as well as their molecular signaling in the fundamental cells (oocyte, cumulus/granulosa cells (GCs) and theca/stroma cells) of the ovarian follicles throughout follicle development. With the availability of recombinant human BMPs/GDFs and the development of immortalized human cell lines, functional studies have demonstrated the physiological role of intra-ovarian BMPs/GDFs in all aspects of ovarian functions, from follicle development to steroidogenesis, cell–cell communication, oocyte maturation, ovulation and luteal function. Furthermore, there is crosstalk between these potent ovarian regulators and the endocrine signaling system. Dysregulation or naturally occurring mutations within the BMP system may lead to several female reproductive diseases. The latest development of recombinant BMPs, synthetic BMP inhibitors, gene therapy and tools for BMP-ligand sequestration has made the BMP pathway a potential therapeutic target in certain human fertility disorders; however, further clinical trials are needed. Recent studies have indicated that GDF8 is an intra-ovarian factor that may play a novel role in regulating ovarian functions in the human ovary.

WIDER IMPLICATIONS

Intra-ovarian BMPs/GDFs are critical regulators of folliculogenesis and human ovarian functions. Any dysregulation or variations in these ligands or their receptors may affect the related intracellular signaling and influence ovarian functions, which accounts for several reproductive pathologies and infertility. Understanding the normal and pathological roles of intra-ovarian BMPs/GDFs, especially as related to GC functions and follicular fluid levels, will inform innovative approaches to fertility regulation and improve the diagnosis and treatment of ovarian disorders.

Connective tissue growth factor mediates growth differentiation factor 8-induced increase of lysyl oxidase activity in human granulosa-lutein cells

Lysyl oxidase (LOX) is an essential enzyme for the stabilization of the extracellular matrix (ECM) and the subsequent follicle and oocyte maturation. Currently, there is limited information pertaining to the regulation of LOX activity in human ovarian tissue. Growth differentiation factor 8 (GDF8) is a unique member of the transforming growth factor-β superfamily that is expressed in human granulosa cells and has important roles in regulating a variety of ovarian functions. The aim of the present study was to investigate the effects of GDF8 on the regulation of LOX expression and activity in human granulosa cells and to examine the underlying molecular determinants. An established immortalized human granulosa cell line (SVOG) and primary granulosa-lutein cells were used as study models. Using dual inhibition approaches (TGF-β type I inhibitor SB505124 and small interfering RNAs) and ChIP analyses, we have demonstrated that GDF8 up-regulated the expression of connective tissue growth factor (CTGF) through the activin receptor-like kinase 5-mediated SMAD2/3-SMAD4 signaling pathways. In addition, the increase in CTGF expression contributed to the GDF8-induced increase in LOX expression and activity. Our findings suggest that GDF8 and CTGF may play critical roles in the regulation of ECM formation in human granulosa cells.

Activin A-induced increase in LOX activity in human granulosa–lutein cells is mediated by CTGF

Lysyl oxidase (LOX) is the key enzyme involved in the crosslinking of collagen and elastin that is essential for the formation of extracellular matrix (ECM). LOX-mediated ECM remodeling plays a critical role in follicle development, oocyte maturation and corpus luteum formation. To date, the regulation of LOX in human ovary has never been elucidated. Activin A and its functional receptors are highly expressed in ovarian follicles from an early developmental stage. They locally regulate follicle progression. The aim of this study was to investigate the effects of activin A on the expression of LOX and its extracellular enzyme activity in primary and immortalized human granulosa–lutein cells obtained from patients undergoing anin vitrofertilization procedure. We demonstrated that activin A significantly upregulated the expression of connective tissue growth factor (CTGF) and LOX via an activin/TGF-β type I receptor mediated-signaling pathway. Using a target depletion small interfering RNA knockdown approach, we further confirmed that the upregulation of CTGF expression resulted in an activin-A-induced increases in LOX expression and activity. These findings may provide insight into the mechanisms by which intrafollicular growth factors regulate the expression of LOX for ECM formation and tissue remodeling in the human ovary.