Follicular localization of growth differentiation factor 8 and its receptors in normal and polycystic ovary syndrome ovaries

Dysregulated Liver Metabolism and Polycystic Ovarian Syndrome

A significant fraction of couples around the world suffer from polycystic ovarian syndrome (PCOS), a disease defined by the characteristics of enhanced androgen synthesis in ovarian theca cells, hyperandrogenemia, and ovarian dysfunction in women. Most of the clinically observable symptoms and altered blood biomarker levels in the patients indicate metabolic dysregulation and adaptive changes as the key underlying mechanisms. Since the liver is the metabolic hub of the body and is involved in steroid-hormonal detoxification, pathological changes in the liver may contribute to female endocrine disruption, potentially through the liver-to-ovary axis. Of particular interest are hyperglycemic challenges and the consequent changes in liver-secretory protein(s) and insulin sensitivity affecting the maturation of ovarian follicles, potentially leading to female infertility. The purpose of this review is to provide insight into emerging metabolic mechanisms underlying PCOS as the primary culprit, which promote its incidence and aggravation. Additionally, this review aims to summarize medications and new potential therapeutic approaches for the disease.

Myostatin: a multifunctional role in human female reproduction and fertility - a short review

Myostatin (MSTN) is member of the transforming growth factor β (TGF-β) superfamily and was originally identified in the musculoskeletal system as a negative regulator of skeletal muscle growth. The functional roles of MSTN outside of the musculoskeletal system have aroused researchers' interest in recent years, with an increasing number of studies being conducted in this area. Notably, the expression of MSTN and its potential activities in various reproductive organs, including the ovary, placenta, and uterus, have recently been examined. Numerous studies published in the last few years demonstrate that MSTN plays a critical role in human reproduction and fertility, including the regulation of follicular development, ovarian steroidogenesis, granule-cell proliferation, and oocyte maturation regulation. Furthermore, findings from clinical samples suggest that MSTN may play a key role in the pathogenesis of several reproductive disorders such as uterine myoma, preeclampsia (PE), ovary hyperstimulation syndrome (OHSS), and polycystic ovarian syndrome (PCOS). There is no comprehensive review regarding to MSTN related to the female reproductive system in the literature. This review serves as a summary of the genes in reproductive medicine and their potential influence. We summarized MSTN expression in different compartments of the female reproductive system. Subsequently, we discuss the role of MSTN in both physiological and several pathological conditions related to the female fertility and reproduction-related diseases.

Growth differentiation factor-11 downregulates steroidogenic acute regulatory protein expression through ALK5-mediated SMAD3 signaling pathway in human granulosa-lutein cells

BACKGROUND

Growth differentiation factor-11 (GDF-11) belongs to the transforming growth factor-β (TGF-β) superfamily. To date, the expression of GDF-11 in the ovary and its role in regulating ovarian function are completely unknown. Ovarian granulosa cell-mediated steroidogenesis plays a pivotal role in maintaining normal female reproductive function. GDF-11 and GDF-8 share high sequence similarity and exhibit many similar features and functions. Steroidogenic acute regulatory protein (StAR) regulates the rate-limiting step in steroidogenesis and its expression can be downregulated by GDF-8. Polycystic ovary syndrome (PCOS) is the most common cause of female infertility. The expression levels of GDF-8 are upregulated in the human follicular fluid and granulosa-lutein (hGL) cells of PCOS patients. However, whether similar results can be observed for the GDF-11 needs to be determined.

METHODS

The effect of GDF-11 on StAR expression and the underlying molecular mechanisms were explored by a series of in vitro experiments in a primary culture of hGL cells obtained from patients undergoing in vitro fertilization (IVF) treatment. Human follicular fluid samples were obtained from 36 non-PCOS patients and 36 PCOS patients. GDF-11 levels in follicular fluid were measured by ELISA.

RESULTS

GDF-11 downregulates StAR expression, whereas the expression levels of the P450 side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD) are not affected by GDF-11 in hGL cells. Using pharmacological inhibitors and a siRNA-mediated approach, we reveal that ALK5 but not ALK4 mediates the suppressive effect of GDF-11 on StAR expression. Although GDF-11 activates both SMAD2 and SMAD3 signaling pathways, only SMAD3 is involved in the GDF-11-induced downregulation of StAR expression. In addition, we show that SMAD1/5/8, ERK1/2, and PI3K/AKT signaling pathways are not activated by GDF-11 in hGL cells. RT-qPCR and ELISA detect GDF-11 mRNA expression in hGL cells and GDF-11 protein expression in human follicular fluid, respectively. Interestingly, unlike GDF-8, the expression levels of GDF-11 are not varied in hGL cells and follicular fluid between non-PCOS and PCOS patients.

CONCLUSIONS

This study increases the understanding of the biological function of GDF-11 and provides important insights into the regulation of ovarian steroidogenesis.

Myostatin increases human trophoblast cell invasion by upregulating N-cadherin via SMAD2/3-SMAD4 Signaling

Placental insufficiency disorders are major obstetric complications that share a common phenomenon of poor placental trophoblast cell invasion and remodeling of uterine tissues. Myostatin is a transforming growth factor (TGF)-β superfamily member well-known for its important role in muscle growth control. Myostatin is also produced in the placenta and has been shown to regulate some trophoblast functions. However, its roles in placental development are still poorly understood. In this study, we tested the hypothesis that myostatin increases trophoblast cell invasion by upregulating N-cadherin via SMAD2/3-SMAD4 signaling. Primary and immortalized (HTR8/SVneo) trophoblast cells were used as study models. Matrigel-coated transwell invasion assays were used to study the effects of recombinant human myostatin on trophoblast cell invasion. RT-qPCR and Western blot were used to measure myostatin effects on N-cadherin mRNA and protein levels, respectively. Small inhibitor molecules as well as siRNA-mediated knockdown were used to block myostatin receptor and downstream signaling, respectively. Data were analyzed either by unpaired Student T test or one-way ANOVA followed by Newman Keuls test for multiple group comparisons. Myostatin significantly increased primary and HTR8/SVneo trophoblast cell invasion. Moreover, myostatin upregulated N-cadherin mRNA and protein levels in a time dependent manner in both study models. These effects were blocked by inhibition of TGF-β type I receptors as well as siRNA-mediated knockdown of SMAD2/3 combined or common SMAD4. Importantly, myostatin-induced trophoblast cell invasion was abolished by knockdown of N-cadherin, SMAD2/3 or SMAD4. Myostatin may increase human trophoblast cell invasion by upregulating N-cadherin via SMAD2/3-SMAD4 signaling.

Regulatory Role and Potential Importance of GDF-8 in Ovarian Reproductive Activity

Growth differentiation factor-8 (GDF-8) is a member of the transforming growth factor-beta superfamily. Studies in vitro and in vivo have shown GDF-8 to be involved in the physiology and pathology of ovarian reproductive functions. In vitro experiments using a granulosa-cell model have demonstrated steroidogenesis, gonadotrophin responsiveness, glucose metabolism, cell proliferation as well as expression of lysyl oxidase and pentraxin 3 to be regulated by GDF-8 via the mothers against decapentaplegic homolog signaling pathway. Clinical data have shown that GDF-8 is expressed widely in the human ovary and has high expression in serum of obese women with polycystic ovary syndrome. GDF-8 expression in serum changes dynamically in patients undergoing controlled ovarian hyperstimulation. GDF-8 expression in serum and follicular fluid is correlated with the ovarian response and pregnancy outcome during in vitro fertilization. Blocking the GDF-8 signaling pathway is a potential therapeutic for ovarian hyperstimulation syndrome and ovulation disorders in polycystic ovary syndrome. GDF-8 has a regulatory role and potential importance in ovarian reproductive activity and may be involved in folliculogenesis, ovulation, and early embryo implantation.

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).

High ovarian GDF-8 levels contribute to elevated estradiol production in ovarian hyperstimulation syndrome by stimulating aromatase expression

Rationale: Growth differentiation factor-8 (GDF-8), also known as myostatin, belongs to the transforming growth factor-beta (TGF-β) superfamily. GDF-8 is expressed in the ovary and regulates various ovarian functions. Ovarian hyperstimulation syndrome (OHSS) is one of the most serious disorders during in vitro fertilization treatment. Aromatase, encoded by the CYP19A1 gene, is the enzyme that catalyzes the final step in estradiol (E2) biosynthesis. It has been demonstrated that high serum E2 levels are associated with the development of OHSS. However, the effects of GDF-8 on aromatase expression and its roles in the pathogenesis of OHSS remain unclear. Methods: The effect of GDF-8 on aromatase expression and the underlying mechanisms were explored by a series of in vitro experiments in primary human granulosa-lutein (hGL) and KGN cells. Rat OHSS model and human follicular fluid samples were used to examine the roles of the GDF-8 system in the pathogenesis of OHSS. Results: We demonstrate that GDF-8 stimulates aromatase expression and E2 production in hGL and KGN cells. In addition, TGF-β type I receptor ALK5-mediated SMAD2/3 signaling is required for GDF-8-induced aromatase expression and E2 production. Using a rat OHSS model, we show that the aromatase and GDF-8 levels are upregulated in the ovaries of OHSS rats. Blocking the function of ALK5 by the administration of its inhibitor, SB431542, alleviates OHSS symptoms and the upregulation of aromatase. Clinical results reveal that the protein levels of GDF-8 are upregulated in the follicular fluid of OHSS patients. Moreover, the expression of GDF-8 is increased in hGL cells of OHSS patients. Conclusions: This study helps to elucidate the mechanisms mediating the expression of aromatase in human granulosa cells, which may lead to the development of alternative therapeutic approaches for OHSS.

The Exploration of Poor Ovarian Response-Related Risk Factors: A Potential Role of Growth Differentiation Factor 8 in Predicting Ovarian Response in IVF-ET Patient

Controlled ovarian hyperstimulation (COH) is the most common therapeutic protocol to obtain a considerable number of oocytes in IVF-ET cycles. To date, the risk factors affecting COH outcomes remain elusive. Growth differentiation factor 8 (GDF-8), a member of transforming growth factor β (TGF-β) superfamily, has been long discerned as a crucial growth factor in folliculogenesis, and the aberrant expression of GDF-8 is closely correlated with the reproductive diseases. However, less is known about the level of GDF-8 in IVF-ET patients with different ovarian response. In the present study, the potential risk factors correlated with ovarian response were explored using logistic regression analysis methods. Meanwhile, the expression changes of GDF-8 and its responsible cellular receptors in various ovarian response patients were determined. Our results showed that several factors were intensely related to poor ovarian response (POR), including aging, obesity, endometriosis, surgery history, and IVF treatment, while irregular menstrual cycles and PCOS contribute to hyperovarian response (HOR). Furthermore, POR patients exhibited a decrease in numbers of MII oocytes and available embryos, thereby manifesting a lower clinical pregnancy rate. The levels of GDF-8, ALK5, and ACVR2B in POR patients were higher compared with those in control groups, whereas the expression level of ACVR2A decreased in poor ovarian response patients. In addition, clinical correlation analysis results showed that the concentration of GDF-8 was negatively correlated with LH and estradiol concentration and antral follicle count. Collectively, our observations provide a novel insight of ovarian response-associated risk factors, highlighting the potential role of GDF-8 levels in ovarian response during COH process.

Aberrant elevation of GDF8 impairs granulosa cell glucose metabolism via upregulating SERPINE1 expression in patients with PCOS

Clinical investigations have demonstrated that polycystic ovary syndrome (PCOS) is often accompanied by insulin resistance (IR) in more than 70% of women with PCOS. However, the etiology of PCOS with IR remains to be characterized. Growth differentiation factor 8 (GDF8) is an intraovarian factor that plays a vital role in the regulation of follicle development and ovulation. Previous studies have reported that GDF8 is a pathogenic factor in glucose metabolism disorder in IR patients. To date, the role of GDF8 on glucose metabolism of granulosa cell in PCOS patients remains to be determined. In the current study, we demonstrated that the expression and accumulation of GDF8 in human granulosa-lutein (hGL) cells and follicular fluid from PCOS patients were higher compared with those of non-PCOS women. GDF8 treatment caused glucose metabolism defects in hGL cells. Transcriptome sequencing results showed that SERPINE1 mediated GDF8-induced impairment of hGL glucose metabolism defects. Using pharmacological and small interfering RNA (siRNA)-mediated knockdown approaches, we demonstrated that GDF8 upregulated the expression of SERPINE1 via the ALK5-mediated SMAD2/3-SMAD4 signaling pathway. Interestingly, the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway was also activated with GDF8 treatment but did not participate in the effect of GDF8 on SERPINE1 expression. Our results also showed that TP53 was required for the GDF8-stimulated increase in SERPINE1 expression. Importantly, our study demonstrated that SB-431542 treatment significantly improved DHEA-induced PCOS-like ovaries. These findings support a potential role for GDF8 in metabolic disorders in PCOS.

Identification of potential metabolic biomarkers of polycystic ovary syndrome in follicular fluid by SWATH mass spectrometry

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex disorder associated with multiple metabolic disturbance, including defective glucose metabolism and insulin resistance. The altered metabolites caused by the related metabolic disturbance may affect ovarian follicles, which can be reflected in follicular fluid composition. The aim of this study is to investigate follicular fluid metabolic profiles in women with PCOS using an advanced sequential window acquisition of all theoretical fragment-ion spectra (SWATH) mass spectrometry.

MATERIALS AND METHODS

Nineteen women with PCOS and twenty-one healthy controls undergoing IVF/ET were recruited, and their follicular fluid samples were collected for metabolomic study. Follicular fluid metabolic profiles, including steroid hormones, free fatty acids, bioactive lipids, and amino acids were analyzed using the principal component analysis (PCA) and partial least squares to latent structure-discriminant analysis (PLS-DA) model.

RESULTS

Levels of free fatty acids, 3-hydroxynonanoyl carnitine and eicosapentaenoic acid were significantly increased (P < 0.05), whereas those of bioactive lipids, lysophosphatidylcholines (LysoPC) (16:0), phytosphingosine, LysoPC (14:0) and LysoPC (18:0) were significantly decreased in women with PCOS (P < 0.05). Additionally, levels of steroid hormone deoxycorticosterone and two amino acids, phenylalanine and leucine were higher in the PCOS patients (P < 0.05).

CONCLUSION

Women with PCOS display unique metabolic profiles in their follicular fluid, and this data may provide us with important biochemical information and metabolic signatures that enable a better understanding of the pathogenesis of PCOS.