FSH protects mouse granulosa cells from oxidative damage by repressing mitophagy

Mitochondrial Quality Control in Ovarian Function: From Mechanisms to Therapeutic Strategies

Mitochondrial quality control plays a critical role in cytogenetic development by regulating various cell-death pathways and modulating the release of reactive oxygen species (ROS). Dysregulated mitochondrial quality control can lead to a broad spectrum of diseases, including reproductive disorders, particularly female infertility. Ovarian insufficiency is a significant contributor to female infertility, given its high prevalence, complex pathogenesis, and profound impact on women's health. Understanding the pathogenesis of ovarian insufficiency and devising treatment strategies based on this understanding are crucial. Oocytes and granulosa cells (GCs) are the primary ovarian cell types, with GCs regulated by oocytes, fulfilling their specific energy requirements prior to ovulation. Dysregulation of mitochondrial quality control through gene knockout or external stimuli can precipitate apoptosis, inflammatory responses, or ferroptosis in both oocytes and GCs, exacerbating ovarian insufficiency. This review aimed to delineate the regulatory mechanisms of mitochondrial quality control in GCs and oocytes during ovarian development. This study highlights the adverse consequences of dysregulated mitochondrial quality control on GCs and oocyte development and proposes therapeutic interventions for ovarian insufficiency based on mitochondrial quality control. These insights provide a foundation for future clinical approaches for treating ovarian insufficiency.

Mitophagy in mammalian follicle development and health

Mitophagy, the cellular process that removes damaged mitochondria, plays a crucial role in maintaining normal cell functions. It is deeply involved in the entire process of follicle development and is associated with various ovarian diseases. This review aims to provide a comprehensive overview of mitophagy regulation, emphasizing its role at different stages of follicular development. Additionally, the study illuminates the relationship between mitophagy and ovarian diseases, including ovary aging (OA), primary ovarian insufficiency (POI), and polycystic ovary syndrome (PCOS). A detailed understanding of mitophagy could reveal valuable insights and novel strategies for managing female ovarian reproductive health.

P62 promotes FSH-induced antral follicle formation by directing degradation of ubiquitinated WT1

In females, the pathophysiological mechanism of poor ovarian response (POR) is not fully understood. Considering the expression level of p62 was significantly reduced in the granulosa cells (GCs) of POR patients, this study focused on identifying the role of the selective autophagy receptor p62 in conducting the effect of follicle-stimulating hormone (FSH) on antral follicles (AFs) formation in female mice. The results showed that p62 in GCs was FSH responsive and that its level increased to a peak and then decreased time-dependently either in ovaries or in GCs after gonadotropin induction in vivo. GC-specific deletion of p62 resulted in subfertility, a significantly reduced number of AFs and irregular estrous cycles, which were same as pathophysiological symptom of POR. By conducting mass spectrum analysis, we found the ubiquitination of proteins was decreased, and autophagic flux was blocked in GCs. Specifically, the level of nonubiquitinated Wilms tumor 1 homolog (WT1), a transcription factor and negative controller of GC differentiation, increased steadily. Co-IP results showed that p62 deletion increased the level of ubiquitin-specific peptidase 5 (USP5), which blocked the ubiquitination of WT1. Furthermore, a joint analysis of RNA-seq and the spatial transcriptome sequencing data showed the expression of steroid metabolic genes and FSH receptors pivotal for GCs differentiation decreased unanimously. Accordingly, the accumulation of WT1 in GCs deficient of p62 decreased steroid hormone levels and reduced FSH responsiveness, while the availability of p62 in GCs simultaneously ensured the degradation of WT1 through the ubiquitin‒proteasome system and autophagolysosomal system. Therefore, p62 in GCs participates in GC differentiation and AF formation in FSH induction by dynamically controlling the degradation of WT1. The findings of the study contributes to further study the pathology of POR.

Reactive oxygen species signalling in the deterioration of quality of mammalian oocytes cultured in vitro: Protective effect of antioxidants

The in vitro fertilization (IVF) is the first choice of infertile couples worldwide to plan for conception. Besides having a significant advancement in IVF procedure, the success rate is still poor. Although several approaches have been tested to improve IVF protocol, minor changes in culture conditions, physical factors and/or drug treatment generate reactive oxygen species (ROS) in oocytes. Due to large size and huge number of mitochondria, oocyte is more susceptible towards ROS-mediated signalling under in vitro culture conditions. Elevation of ROS levels destabilize maturation promoting factor (MPF) that results in meiotic exit from diplotene as well as metaphase-II (M-II) arrest in vitro. Once meiotic exit occurs, these oocytes get further arrested at metaphase-I (M-I) stage or metaphase-III (M-III)-like stage under in vitro culture conditions. The M-I as well as M-III arrested oocytes are not fit for fertilization and limits IVF outcome. Further, the generation of excess levels of ROS cause oxidative stress (OS) that initiate downstream signalling to initiate various death pathways such as apoptosis, autophagy, necroptosis and deteriorates oocyte quality under in vitro culture conditions. The increase of cellular enzymatic antioxidants and/or supplementation of exogenous antioxidants in culture medium protect ROS-induced deterioration of oocyte quality in vitro. Although a growing body of evidence suggests the ROS and OS-mediated deterioration of oocyte quality in vitro, their downstream signalling and related mechanisms remain poorly understood. Hence, this review article summarizes the existing evidences concerning ROS and OS-mediated downstream signalling during deterioration of oocyte quality in vitro. The use of various antioxidants against ROS and OS-mediated impairment of oocyte quality in vitro has also been explored in order to increase the success rate of IVF during assisted reproductive health management.

A matter of new life and cell death: programmed cell death in the mammalian ovary

BACKGROUND

The mammalian ovary is a unique organ that displays a distinctive feature of cyclic changes throughout the entire reproductive period. The estrous/menstrual cycles are associated with drastic functional and morphological rearrangements of ovarian tissue, including follicular development and degeneration, and the formation and subsequent atrophy of the corpus luteum. The flawless execution of these reiterative processes is impossible without the involvement of programmed cell death (PCD).

MAIN TEXT

PCD is crucial for efficient and careful clearance of excessive, depleted, or obsolete ovarian structures for ovarian cycling. Moreover, PCD facilitates selection of high-quality oocytes and formation of the ovarian reserve during embryonic and juvenile development. Disruption of PCD regulation can heavily impact the ovarian functions and is associated with various pathologies, from a moderate decrease in fertility to severe hormonal disturbance, complete loss of reproductive function, and tumorigenesis. This comprehensive review aims to provide updated information on the role of PCD in various processes occurring in normal and pathologic ovaries. Three major events of PCD in the ovary-progenitor germ cell depletion, follicular atresia, and corpus luteum degradation-are described, alongside the detailed information on molecular regulation of these processes, highlighting the contribution of apoptosis, autophagy, necroptosis, and ferroptosis. Ultimately, the current knowledge of PCD aberrations associated with pathologies, such as polycystic ovarian syndrome, premature ovarian insufficiency, and tumors of ovarian origin, is outlined.

CONCLUSION

PCD is an essential element in ovarian development, functions and pathologies. A thorough understanding of molecular mechanisms regulating PCD events is required for future advances in the diagnosis and management of various disorders of the ovary and the female reproductive system in general.

The follicle-stimulating hormone triggers rapid changes in mitochondrial structure and function in porcine cumulus cells

Oocyte maturation is a key process during which the female germ cell undergoes resumption of meiosis and completes its preparation for embryonic development including cytoplasmic and epigenetic maturation. The cumulus cells directly surrounding the oocyte are involved in this process by transferring essential metabolites, such as pyruvate, to the oocyte. This process is controlled by cyclic adenosine monophosphate (cAMP)-dependent mechanisms recruited downstream of follicle-stimulating hormone (FSH) signaling in cumulus cells. As mitochondria have a critical but poorly understood contribution to this process, we defined the effects of FSH and high cAMP concentrations on mitochondrial dynamics and function in porcine cumulus cells. During in vitro maturation (IVM) of cumulus-oocyte complexes (COCs), we observed an FSH-dependent mitochondrial elongation shortly after stimulation that led to mitochondrial fragmentation 24 h later. Importantly, mitochondrial elongation was accompanied by decreased mitochondrial activity and a switch to glycolysis. During a pre-IVM culture step increasing intracellular cAMP, mitochondrial fragmentation was prevented. Altogether, the results demonstrate that FSH triggers rapid changes in mitochondrial structure and function in COCs involving cAMP.

Direct-Acting Antiviral Drug Modulates the Mitochondrial Biogenesis in Different Tissues of Young Female Rats

(1) Background: Hepatitis C virus (HCV) infection is endemic in Egypt, with the highest prevalence rate worldwide. Sofosbuvir (SOF) is a nucleos(t)ide analog that specifically inhibits HCV replication. This study aimed to explore the possible effects of the therapeutic dose of SOF on the mitochondrial biogenesis and functions of the liver, muscle, and ovarian tissues of young normal female rats. (2) Methods: This study was conducted on 20 female Wistar rats, classified into two groups, the control group and the exposed group; the latter was orally supplemented with 4 mg/kg/day of SOF for 3 months. (3) Results: The exposure to SOF impairs mitochondrial biogenesis via mitochondrial DNA copy number decline and suppressed mitochondrial biogenesis-regulated parameters at mRNA and protein levels. Also, SOF suppresses the DNA polymerase γ (POLG) expression, citrate synthase activity, and mitochondrial NADH dehydrogenase subunit-5 (ND5) content, which impairs mitochondrial functions. SOF increased lipid peroxidation and oxidative DNA damage markers and decreased tissue expression of nuclear factor erythroid 2-related factor 2 (Nfe2l2). (4) Conclusions: The present findings demonstrate the adverse effects of SOF on mitochondrial biogenesis and function in different tissues of young female rats, which mostly appeared in ovarian tissues.

C-type natriuretic peptide improves maternally aged oocytes quality by inhibiting excessive PINK1/Parkin-mediated mitophagy

The overall oocyte quality declines with aging, and this effect is strongly associated with a higher reactive oxygen species (ROS) level and the resultant oxidative damage. C-type natriuretic peptide (CNP) is a well-characterized physiological meiotic inhibitor that has been successfully used to improve immature oocyte quality during in vitro maturation. However, the underlying roles of CNP in maternally aged oocytes have not been reported. Here, we found that the age-related reduction in the serum CNP concentration was highly correlated with decreased oocyte quality. Treatment with exogenous CNP promoted follicle growth and ovulation in aged mice and enhanced meiotic competency and fertilization ability. Interestingly, the cytoplasmic maturation of aged oocytes was thoroughly improved by CNP treatment, as assessed by spindle/chromosome morphology and redistribution of organelles (mitochondria, the endoplasmic reticulum, cortical granules, and the Golgi apparatus). CNP treatment also ameliorated DNA damage and apoptosis caused by ROS accumulation in aged oocytes. Importantly, oocyte RNA-seq revealed that the beneficial effect of CNP on aged oocytes was mediated by restoration of mitochondrial oxidative phosphorylation, eliminating excessive mitophagy. CNP reversed the defective phenotypes in aged oocytes by alleviating oxidative damage and suppressing excessive PINK1/Parkin-mediated mitophagy. Mechanistically, CNP functioned as a cAMP/PKA pathway modulator to decrease PINK1 stability and inhibit Parkin recruitment. In summary, our results demonstrated that CNP supplementation constitutes an alternative therapeutic approach for advanced maternal age-related oocyte deterioration and may improve the overall success rates of clinically assisted reproduction in older women.

Melatonin Attenuates Sepsis-Induced Acute Lung Injury via Inhibiting Excessive Mitophagy

Background

Epidemiological studies have indicated that lung injury is a frequent complication of sepsis. Mitophagy is vital to multiple pathological processes and diseases; however, its influence on sepsis-induced acute lung injury remains elusive. Melatonin has multiple antioxidant action and anti-inflammatory effects, including regulating mitophagy and inflammatory cytokine expression. Whereas, little is known about the affection of melatonin and mitophagy on CLP-induced ALI.

Methods

The in vivo effect of melatonin on OPTN-mediated mitophagy was studied by CLP-induced ALI in a mouse model using C57BL/6 followed by treatment with vehicle and melatonin (30 mg/kg/d, intraperitoneal injection). ALI was assayed by lung wet /dry ratio, hematoxylin and eosin staining, and immunohistochemical staining. Signaling pathway changes were subsequently determined by Western blotting and immunofluorescence staining. The effects of melatonin on STAT3 activation and TNF-α production were detected by Western blotting, PCR, and immunohistochemical staining.

Results

Our results indicated that OPTN, mitophagy adaptors were significantly repressed in CLP-induced ALI, accompanied by overactivation of mitophagy and inflammation. At the same time, we found that melatonin treatment alleviated ALI caused by CLP, and the effect was highly correlated with OPTN-related mitophagy. Furthermore, we demonstrated that OPTN-related mitophagy, which was normalized by melatonin, blocked STAT3 involved epithelial barrier and inflammation in vivo.

Conclusion

Overall, our results confirm that mitophagy is adjusted by melatonin in the CLP-induced ALI. Moreover, manipulation of mitophagy through melatonin could be a possible treatment to reduce sepsis-associated lung injury.

The Ratio of cf-mtDNA vs. cf-nDNA in the Follicular Fluid of Women Undergoing IVF Is Positively Correlated with Age

Age-related mitochondrial markers may facilitate the prognosis of artificial reproductive technology outcomes. In this report, we present our study concerning the ratio of cf-mtDNA/cf-nDNA, namely the amount of cell-free mitochondrial DNA relative to cell-free nuclear DNA, in the follicular fluid (FF) of women undergoing IVF, aiming to generate a molecular fingerprint of oocyte quality. The values of this ratio were measured and compared among three groups of women (101 in total): (A) 31 women with polycystic ovary syndrome (PCOS), (B) 34 women younger than 36 years, and (C) 36 women older than 35 years of age. Real-time quantitative PCR (qPCR) was performed to quantify the ratio by using nuclear- and mitochondrial-specific primers and analyzed for potential correlation with age and pregnancy rate. Our analysis showed that the level of FF-cf-mtDNA was lower in the group of advanced-age women than in the groups of PCOS and non-PCOS women. Moreover, a significant positive correlation between FF-cf-mtDNA and the number of mature (MII) oocytes was observed. Collectively, the data show that the relative ratio of cf- mtDNA to cf-nDNA content in human FF can be an effective predictor for assessing the corresponding oocyte's age-related performance in IVF.

Effect of prolactin on cytotoxicity and oxidative stress in ovine ovarian granulosa cells

Background

Prolactin (PRL) has been reported to be associated with oxidative stress, which is an important contributor leading to cell apoptosis. However, little is known about the mechanisms underlying the effects of PRL on cytotoxicity and oxidative stress in ovine ovarian granulosa cells (GCs).

Methods

Ovine ovarian GCs were treated with 0, 4, 20, 100 and 500 ng/mL of PRL. Then, the cytotoxicity, cell viability, malondialdehyde (MDA), reactive oxygen species (ROS), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) of GCs were detected. Additionally, 500 ng/mL PRL was chosen as the high PRL concentration (HPC) due to its high cytotoxicity and oxidative stress. Proteomic and metabonomic were performed to examine the overall difference in proteins and metabolic pathways between C (control: 0 ng/mL PRL) and P groups (500 ng/mL PRL).

Results

The results indicated that GCs treated with 4 ng/mL PRL significantly decreased (P < 0.05) the cytotoxicity, ROS and MDA, increased (P < 0.05) the cell viability, SOD and T-AOC, and the GCs treated with 500 ng/mL PRL showed the opposite trend (P < 0.05). Supplementation with 500 ng/mL PRL significantly increased the proteins of MT-ND1, MAPK12, UBA52 and BCL2L1, which were enriched in ROS and mitophagy pathways. Pathway enrichment analysis showed that the pentose phosphate pathway was significantly enriched in the P group.

Conclusion

A low concentration of PRL inhibited cytotoxicity and oxidative stress. HPC induced oxidative stress in ovine ovarian GCs via the pentose phosphate pathway by modulating the associated proteins MT-ND1 in ROS pathway and UBA52, MAPK12 and BCL2L1 in mitophagy pathway, resulting in cytotoxicity.

Bendless is essential for PINK1-Park mediated Mitofusin degradation under mitochondrial stress caused by loss of LRPPRC

Cells under mitochondrial stress often co-opt mechanisms to maintain energy homeostasis, mitochondrial quality control and cell survival. A mechanistic understanding of such responses is crucial for further insight into mitochondrial biology and diseases. Through an unbiased genetic screen in Drosophila, we identify that mutations in lrpprc2, a homolog of the human LRPPRC gene that is linked to the French-Canadian Leigh syndrome, result in PINK1-Park activation. While the PINK1-Park pathway is well known to induce mitophagy, we show that PINK1-Park regulates mitochondrial dynamics by inducing the degradation of the mitochondrial fusion protein Mitofusin/Marf in lrpprc2 mutants. In our genetic screen, we also discover that Bendless, a K63-linked E2 conjugase, is a regulator of Marf, as loss of bendless results in increased Marf levels. We show that Bendless is required for PINK1 stability, and subsequently for PINK1-Park mediated Marf degradation under physiological conditions, and in response to mitochondrial stress as seen in lrpprc2. Additionally, we show that loss of bendless in lrpprc2 mutant eyes results in photoreceptor degeneration, indicating a neuroprotective role for Bendless-PINK1-Park mediated Marf degradation. Based on our observations, we propose that certain forms of mitochondrial stress activate Bendless-PINK1-Park to limit mitochondrial fusion, which is a cell-protective response.

Effects of Oxidative Stress on the Autophagy and Apoptosis of Granulosa Cells in Broody Geese

Broodiness is an unfavorable trait associated with the cessation of egg laying. Studies have found that excessive granulosa cell apoptosis and autophagy occur during goose broodiness. Other studies have also confirmed that oxidative stress is an important cause of apoptosis and autophagy. However, whether oxidative stress occurs during goose broodiness and whether this oxidative stress causes apoptosis and autophagy have not been fully elucidated. In this study, we investigated the effects of oxidative stress on the autophagy and apoptosis of granulosa cells in broody geese. The results showed higher mRNA expression of genes related to antioxidative stress responses (GPX, SOD-1, SOD-2, COX-2, CAT and hsp70) in pre-broody and broody geese than in laying birds. In addition, increased levels of granulosa cell apoptosis and autophagy were observed in pre-broody geese than in laying geese. Additionally, granulosa cells treated with H₂O₂ exhibited increased apoptosis and autophagy in vitro, and these effects were responsible for goose granulosa cell death. Moreover, vitamin E treatment effectively protected granulosa cells from H₂O₂-induced oxidative stress by inhibiting ROS production. Correspondingly, granulosa cell apoptosis and autophagy were greatly alleviated by vitamin E treatment. Together, our results demonstrated serious oxidative stress and granulosa cell apoptosis and autophagy in broody geese, and oxidative stress promoted apoptosis and autophagy. Vitamin E alleviated the autophagy and apoptosis of granulosa cells by inhibiting oxidative stress.

Apoptosis and autophagy-related gene transcription during ovarian follicular atresia in European hake (Merluccius merluccius)

Follicular atresia is an energy-saving oocyte resorption process that can allow the survival of female fish when environmental conditions are unfavourable and at the expense of fecundity. This study investigated the transcription levels of apoptosis and autophagy-related genes during atresia in the European hake that can show episodes of increased follicular atresia throughout the reproductive cycle. 169 female individuals were collected from the Bay of Biscay, and the ovaries were analysed using histological and molecular methods. Different levels of atresia were histologically detected in 73.7% of the ovaries analysed and the TUNEL assay identified apoptotic nuclei in follicles from both previtellogenic and vitellogenic stages. Transcripts of beclin-1 and ptenb were up-regulated in the ovaries containing atretic follicles, whereas p53, caspase-3, cathepsin D and dapk1 were up-regulated only in ovaries presenting vitellogenic atretic follicles. Our results indicate different implications of apoptotic vs autophagic processes leading to atresia during oocyte development, vitellogenesis being the moment of maximal apoptotic and autophagic activity in atretic hakes. The analysed genes could provide early warning biomarkers to identify follicular atresia in fish and evaluate fecundity in fish stocks.

Effect of High dose Gonadotropin Stimulation on Follicular Atresia through Light Chain 3B and Voltage Dependent Anion Channel 2

Background

Follicle development takes place under the control of hormonal and environmental stimuli. It suggested that to improve in vitro fertilisation outcomes in poor responders increasing gonadotropin doses be used. Excessive gonadotropin leads to atresia and impairs follicular development, but the molecular mechanisms of follicular atresia remain largely unknown. Recently, it was suggested that autophagy may be an alternative mechanism involved in follicle depletion.

Aims

In this study, we aimed to clarify the role of autophagic markers such as light chain (LC) 3B and voltage dependent anion channel 2 (VDAC2) in follicular atresia using the high dose gonadotropin stimulation.

Settings and Design

The female 24 BALB/c mice were employed in the present study under the Committee for the Purpose of Control and Supervision of Experiments on Animals guidelines with ethical clearance from the institutional ethical committee. These mice were categorised into four groups, with six rats in each as control and test animals.

Materials and Methods

Group 1 (control): no action will be taken. Group 2 (sham): only saline will be applied. Group 3: low-dose gonadotropin Pregnant mare's serum gonadotropin (PMSG) + human chorionic gonadotropin (HCG) will be applied. Group 4: high-dose gonadotropin + HCG will be applied. The animals were sacrificed 48 h after the last injection. For all group samples, both protein and mRNAs of the LC3B and VDAC2 were examined by immunohistochemical and reverse transcription-polymerase chain reaction techniques.

Statistical Analysis Used

All variables were analysed using GraphPad Prism 8. Kruskal-Wallis t-test and Mann-Whitney U test were used to compare immunohistochemical results; in addition to this, parametric one-way ANOVA test and Shapiro-Wilk test were applied for quantitative polymerase chain reaction statistics.

Results

An increased number of atretic follicles were observed in the high-dose gonadotropin + HCG group. LC3B immunoreactivity of the atretic secondary follicles in the high-dose group is higher than in other groups. The expression of VDAC2 protein in the secondary and Graafian follicles and also VDAC2 mRNA in the ovary were more highly expressed in the control and sham groups. The decrease in VDAC2 mRNA level and immunohistochemical expression was remarkable in the low-dose and high-dose follicle-stimulating hormone groups compared to the control and sham groups.

Conclusion

In this study, the increased LC3B and decreased VDAC2 expression, which are autophagy markers, were observed in both the gonadotropins groups, so we suggested that high doses of gonadotropins may cause ovarian atresia.

Yangjing Zhongyu decoction facilitates mitochondrial activity, estrogenesis, and energy metabolism in H2O2-induced human granulosa cell line KGN

ETHNOPHARMACOLOGICAL RELEVANT

Yangjing Zhongyu decoction (YJZYD) is a recipe from a Chinese classic medical work and has been empirically used in female infertility for hundreds of years, but the mechanisms of YJZYD on facilitating ovarian granulosa cells remain unfold.

AIM OF THE RESEARCH

The purpose of the study is to determine the rewarding effects of YJZYD on H₂O₂-induced KGN cells, involving mitochondrial activity, estradiol biosynthesis, and energy metabolism.

MATERIALS AND METHODS

The ingredients of YJZYD were investigated by UPLC-ESI-MS/MS analysis. The effects of YJZYD and H₂O₂ on cell viability were determined by CCK-8. Intracellular ROS were assessed by DCFH-DA. Intracellular Ca²⁺ was detected using Fura-4 AM. Mitochondrial membrane potential (MMP) was measured by JC-1. The production of energy was assessed by ATP. Apoptosis rate was analyzed by Annexin V-FITC/PI. Western blotting was used to evaluate the expression of proteins related to energy metabolism, apoptosis, mitochondrial mitophagy, and estrogen biosynthesis. E₂ levels were measured by ELISA.

RESULTS

121 compounds were identified in YJZYD by UPLC-ESI-MS/MS analysis. YJZYD could enhance mitochondrial activity by suppressing intracellular ROS and Ca²⁺, and increasing MMP and ATP content. YJZYD stimulated the expression of anti-apoptosis protein Bcl-2 and lowered the early apoptosis rate and the expression of Bax. Besides, YJZYD rescued E₂ secretion and improved the expression of FSHR, CYP19A1, and the ratio of p-CREB/CREB. In addition, YJZYD weakened H₂O₂-induced mitophagy by compromising the expression of PINK1, Parkin, Beclin1 and P62. Moreover, YJZYD strengthened energy metabolism by increasing ATP generation and the expression of SIRT1, PGC1α, NRF1, and COX IV. The combination of YJZYD and autophagy inhibitor had a stronger protective effect on energy metabolism.

CONCLUSION

This study evaluated the protective effects of YJZYD on H₂O₂-induced KGN cells. YJZYD could enhance mitochondrial activity, E₂ biosynthesis, and energy metabolism. These results strongly indicated that YJZYD might play a role in preserving ovarian granulosa cells and female fecundity.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Expression of ERβ induces Bovine Ovarian Granulosa Cell Autophagy via the AKT/mTOR Pathway

The aim of our study was to determine whether silencing or overexpression of Estrogen Receptor β (ERβ) regulates cell proliferation, steroidogenesis, autophagy and signaling pathways in bovine ovarian granulosa cells in vitro. In this study, bovine ovarian granulosa cells (BGCs) were cultured and transfected with ERβ siRNA (si-ERβ) or a plasmid overexpressing ERβ (oe-ERβ), and CCK-8 kit was used to assess cell proliferation. Real-time PCR was used to measure gene transcription. Western blotting was used to measure protein expression, and a specific kit was used to measure the production of steroid hormones. The results showed the expression level of ERβ affects BGC proliferation according to the gene transcription levels of FSHR, CYP19A1, HSD3β1 and STAR and the production of E2 and P4. ERβ was identified as an important nuclear receptor that induced BGC autophagy based on the mRNA and protein expression of autophagy-related genes. Furthermore, the role of ERβ in BGC autophagy was confirmed through treatment with rapamycin (RAPA) or 3-methyladenine (3-MA) in BGCs by cotransfection with si-ERβ or oe-ERβ in BGCs. The results related to AKT/mTOR signaling and phosphorylation suggested that ERβ induces BGC autophagy through attenuating AKT/mTOR signaling. In summary, this study demonstrates that silencing or overexpression of ERβ regulates BGC proliferation and function and induces BGC autophagy by targeting AKT/mTOR signaling. These data reveal a novel regulatory mechanism of autophagy via ERβ and provide insights into the role of autophagy in BGCs.

Acetaldehyde Induces Cytotoxicity via Triggering Mitochondrial Dysfunction and Overactive Mitophagy

Overconsumption of alcohol damages brain tissue and causes cognitive dysfunction. It has been suggested that the neurotoxicity caused by excessive alcohol consumption is largely mediated by acetaldehyde, the most toxic metabolite of ethanol. Evidence shows that acetaldehyde impairs mitochondrial function and induces cytotoxicity of neuronal cells; however, the exact mechanisms are not fully understood. The aim of this study was to investigate the role of mitophagy in acetaldehyde-induced cytotoxicity. It was found that acetaldehyde treatment induced mitophagic responses and caused cytotoxicity in SH-SY5Y cells. The levels of light chain 3 (LC3)-II, Beclin1, autophagy-related protein (Atg) 5 and Atg16L1, PTEN-induced putative kinase (PINK)1, and Parkin were significantly elevated, while the level of p62 was reduced in acetaldehyde-treated cells. Acetaldehyde also promoted the accumulation of PINK1 and Parkin on mitochondria and caused a remarkable decrease of mitochondrial mass. Treatment with autophagy inhibitors prevented the decline of mitochondrial mass and alleviated the cytotoxicity induced by acetaldehyde, suggesting that overactive mitophagy might be an important mechanism contributing to acetaldehyde-induced cytotoxicity. Antioxidant N-acetyl-L-cysteine significantly attenuated the mitophagic responses and alleviated the cytotoxicity induced by acetaldehyde, indicating that oxidative stress was a major mediator of the excessive mitophagy induced by acetaldehyde. Taken together, these findings provided new insights into the role of mitophagy and oxidative stress in acetaldehyde-induced cytotoxicity.

BPA and its analogs increase oxidative stress levels in in vitro cultured granulosa cells by altering anti-oxidant enzymes expression

Bisphenol A is a widespread endocrine disruptor with numerous effects on reproductive functions. Limitations on BPA in manufacturing has prompted the use of analogs, such as BPS and BPF, with limited research on their safety. The objective of this study was to evaluate the effects of BPA and its analogs on oxidative stress levels within bovine granulosa cells and to measure the expression of key antioxidant genes. Results indicate that BPA and BPF reduce cell viability and induce mitochondrial dysfunction and all three bisphenols increased production of reactive oxygen species as early as 12hrs post exposure. BPA increased the levels of antioxidants at 12hrs at the mRNA and protein levels, while these results were not significant at 48hrs. These results together suggest that BPA and its analogs can induce oxidative stress within bovine granulosa cells, although not necessarily through common mechanisms. Therefore, the use of BPA analogs may have to be re-considered.

Exposure to benzo(a)pyrene suppresses mitophagy via ANT1-PINK1-Parkin pathway in ovarian corpus luteum during early pregnancy

Exposure to benzo (a)pyrene (BaP) has been confirmed to interfere with embryo implantation. As the primary organ of progesterone synthesis during early pregnancy, the ovarian corpus luteum (CL) is essential for embryo implantation and pregnancy maintenance. We previously demonstrated that BaP impaired luteal function, but the molecular mechanism remains unclear. In CL cells, mitochondria are the main sites of progesterone synthesis. Mitophagy, a particular type of autophagy, regulates mitochondrial quality by degrading damaged mitochondria and ensuring the homeostasis of cell physiology. Therefore, the present study investigated the effects and the potential molecular mechanisms of BaP on ovarian mitophagy during early pregnancy. We found that BaP and its metabolite, BPDE, inhibited autophagy and PINK1/Parkin-mediated mitophagy in the pregnant ovaries and luteinized granulosa cell, KGN. Notably, adenine nucleotide translocator 1 (ANT1), a crucial mediator of PINK1-dependent mitophagy, was suppressed by BaP and BPDE both in vivo and in vitro. The inhibition of ANT1 leads to the decrease in the PINK1 bound to the outer membrane of mitochondria and consequently reduces recruitment of Parkin to the mitochondria, which is required for the subsequent clearance of mitochondria. Meanwhile, exposure to BPDE also damaged mitochondrial function, causing the reduction in mitochondrial potential and ATP production. Overexpression of ANT1 in KGN cells partially relieved the inhibition of mitophagy caused by BPDE, restored mitochondrial function and expression of hormone synthesis-associated genes. Collectively, our study firstly clarified that BaP and BPDE suppress mitophagy of CL cells via the ANT1-PINK1-Parkin pathway, which provides a new insight to explore the detailed mechanism of the BaP-induced ovarian toxicity.

Circadian clock regulates granulosa cell autophagy through NR1D1-mediated inhibition of ATG5

Autophagy of granulosa cells (GCs) is involved in follicular atresia, which occurs repeatedly during the ovarian development cycle. Several circadian clock genes are rhythmically expressed in both rodent ovarian tissues and GCs. Nuclear receptor subfamily 1 group D member 1 (NR1D1), an important component of the circadian clock system, is involved in the autophagy process through the regulation of autophagy-related genes. However, there are no reports illustrating the role of the circadian clock system in mouse GC autophagy. In the present study, we found that core circadian clock genes (Bmal1, Per2, Nr1d1, and Dbp) and an autophagy-related gene (Atg5) exhibited rhythmic expression patterns across 24 h in mouse ovaries and primary GCs. Treatment with SR9009, an agonist of NR1D1, significantly reduced the expression of Bmal1, Per2, and Dbp in mouse GCs. ATG5 expression was significantly attenuated by SR9009 treatment in mouse GCs. Conversely, Nr1d1 knockdown increased ATG5 expression in mouse GCs. Decreased NR1D1 expression at both the mRNA and protein levels was detected in the ovaries of Bmal1^-/- mice, along with elevated expression of ATG5. Dual-luciferase reporter assay and electrophoretic mobility shift assay showed that NR1D1 inhibited Atg5 transcription by binding to two putative retinoic acid-related orphan receptor response elements within the promoter. In addition, rapamycin-induced autophagy and ATG5 expression were partially reversed by SR9009 treatment in mouse GCs. Taken together, our current data demonstrated that the circadian clock regulates GC autophagy through NR1D1-mediated inhibition of ATG5 expression, and thus, plays a role in maintaining autophagy homeostasis in GCs.

Autophagy in ovary and polycystic ovary syndrome: role, dispute and future perspective

Polycystic ovary syndrome (PCOS) is a unification of endocrine and metabolic disorders and has become immensely prevalent among women of fertile age. The prime organ affected in PCOS is the ovary and its distressed functioning elicits disturbed reproductive outcomes. In the ovary, macroautophagy/autophagy performs a pivotal role in directing the chain of events starting from oocytes origin until its fertilization. Recent discoveries demonstrate a significant role of autophagy in the pathogenesis of PCOS. Defective autophagy in the follicular cells during different stages of follicles is observed in the PCOS ovary. Exploring different autophagy pathways provides a platform for predicting the possible cause of altered ovarian physiology in PCOS. In this review, we have emphasized autophagy's role in governing follicular development under normal circumstances and in PCOS, including significant abnormalities associated with PCOS such as anovulation, hyperandrogenemia, metabolic disturbances, and related abnormality. So far, few studies have linked autophagy and PCOS and propose its essential role in PCOS progression. However, detailed knowledge in this area is lacking. Here we have summarized the latest knowledge related to autophagy associated with PCOS. This review's main objective is to provide a background of autophagy in the ovary, its possible connection with PCOS and suggested a novel proposal for future studies to aid a better understanding of PCOS pathogenesis.Abbreviations: AE: androgen excess; AF: antral follicle; AKT/PKB: AKT serine/threonine kinase; AMH: anti-Mullerian hormone; AMPK: AMP-activated protein kinase; ATG: autophagy-related; BCL2: BCL2 apoptosis regulator; BECN1: beclin 1; BMP: bone morphogenetic protein; CASP3: caspase 3; CL: corpus luteum; CYP17A1/P450C17: cytochrome P450 family 17 subfamily A member 1; CYP19A1: cytochrome P450 family 19 subfamily A member 1; DHEA: dehydroepiandrosterone; EH: endometrial hyperplasia; FF: follicular fluid; FOXO: forkhead box O; FSH: follicle stimulating hormone; GC: granulosa cell; GDF: growth differentiation factor; HA: hyperandrogenemia; HMGB1: high mobility group box 1; IGF1: insulin like growth factor 1; INS: insulin; IR: insulin resistance; LHCGR/LHR: luteinizing hormone/choriogonadotropin receptor; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAPK/ERK: mitogen-activated protein kinase; MAPK8/JNK: mitogen-activated protein kinase 8; MTOR: mechanistic target of rapamycin kinase; MTORC: mechanistic target of rapamycin complex; NAFLD: nonalcoholic fatty liver disease; NFKB: nuclear factor kappa B; OLR1/LOX-1: oxidized low density lipoprotein receptor 1; oxLDL: oxidized low-density lipoproteins; PA: palmitic acid; PCOS: polycystic ovary syndrome; PF: primary follicle; PGC: primordial germ cell; PI3K: phosphoinositide 3-kinase; PMF: primordial follicle; ROS: reactive oxygen species; RP: resting pool; SIRT1: sirtuin 1; SQSTM1/p62: sequestosome 1; T2DM: type 2 diabetes mellitus; TC: theca cell; TUG1: taurine up-regulated 1.

Protective Mechanism of Luteinizing Hormone and Follicle-Stimulating Hormone Against Nicotine-Induced Damage of Mouse Early Folliculogenesis

Previous studies have shown that nicotine could impair the germ cell cyst breakdown and the primordial follicle assembly by autophagy. In this paper, we discovered that luteinizing hormone (LH) and follicle-stimulating hormone (FSH) could counteract the damage caused by nicotine of mouse germ cell cyst breakdown. The neonatal mice were separately intraperitoneally injected with nicotine, nicotine plus LH, nicotine plus FSH, and saline (control) for 4 days. Compared with the nicotine group, the quality of oocytes and the number of follicles were remarkably increased in the nicotine plus LH group or nicotine plus FSH group. LH and FSH could alleviate nicotine-induced oocyte autophagy by different pathways. LH reduced the nicotine-induced autophagy by restoring the phosphorylation level of adenosine 5′-monophosphate-activated protein kinase α-1, while FSH by downregulating the phosphorylation level of Forkhead box class O 1. In addition, in a subsequent study of 6-week mice in different treated groups, we found that LH and FSH supplementation significantly improved normal maturation rates, fertilization rates, and embryo’s developmental potential of oocytes in oocytes exposed to nicotine. Taken together, these results suggested that LH and FSH could counteract the damage caused by nicotine and finally ensure normal germ cell cyst breakdown and early embryo development.

Melatonin Represses Mitophagy to Protect Mouse Granulosa Cells from Oxidative Damage

Various environmental stimuli, including oxidative stress, could lead to granulosa cell (GC) death through mitophagy. Recently, it was reported that melatonin (MEL) has a significant effect on GC survival during oxidative damage. Here, we found that MEL inhibited oxidative stress-induced mitophagy to promote GC survival. The loss of cell viability upon H₂O₂ exposure was significantly restored after MEL treatment. Concomitantly, MEL inhibited the activation of mitophagy during oxidative stress. Notably, blocking mitophagy repressed GC death caused by oxidative stress. However, MEL cannot further restore viability of cells treated with mitophagy inhibitor. Moreover, PTEN-induced putative kinase 1 (PINK1), a mitochondrial serine/threonine-protein kinase, was inhibited by MEL during oxidative stress. As a result, the E3 ligase Parkin failed to translocate to mitochondria, leading to impaired mitochondria clearance. Using RNAi to knock down PINK1 expression, we further verified the role of the MEL-PINK1-Parkin (MPP) pathway in maintaining GC survival by suppressing mitophagy. Our findings not only clarify the protective mechanisms of MEL against oxidative damage in GCs, but also extend the understanding about how circadian rhythms might influence follicles development in the ovary. These findings reveal a new mechanism of melatonin in defense against oxidative damage to GCs by repressing mitophagy, which may be a potential therapeutic target for anovulatory disorders.

Celastrol Prevents Oxidative Stress Effects on FSHR, PAPP, and CYP19A1 Gene Expression in Cultured Human Granulosa-Lutein Cells

Regulation of oxidative stress (OS) is important to prevent damage to female reproductive physiology. While normal OS levels may have a regulatory role, high OS levels may negatively affect vital processes such as folliculogenesis or embryogenesis. The aim of this work was to study OS induced by glucose, a reactive oxygen species generator, or peroxynitrite, a reactive nitrogen species generator, in cultured human granulosa-lutein (hGL) cells from oocyte donors, analyzing expression of genes involved in oocyte maturation (FSHR, PAPP, and CYP19A1) and OS damage response (ALDH3A2). We also evaluated the effect of celastrol as an antioxidant. Our results showed that although both glucose and peroxynitrite produce OS increments in hGL cells, only peroxynitrite treatment increases ALDH3A2 and PAPP gene expression levels and decreases FSHR gene expression levels. Celastrol pre-treatment prevents this effect of peroxynitrite. Interestingly, when celastrol alone was added, we observed a reduction of the expression of all genes studied, which was independent of both OS inductors. In conclusion, regulation of OS imbalance by antioxidant substances such as celastrol may prevent negative effects of OS in female fertility. In addition to the antioxidant activity, celastrol may well have an independent role on regulation of gene expression in hGL cells.

Adverse effect of superoxide-induced mitochondrial damage in granulosa cells on follicular development in mouse ovaries

High mitochondrial oxidative phosphorylation (mt-OXPHOS) levels are required to supply the ATP necessary for follicle-stimulating hormone (FSH)-induced granulosa cell proliferation during the follicular development process. Consequently, excessive reactive oxygen species (ROS) might be generated and have an adverse effect on follicular health. This study aimed to elucidate the negative effects of ROS on mitochondrial functions in FSH-stimulated granulosa cells during the follicular development process and to investigate whether pyrroloquinoline quinone (PQQ) treatment could accelerate this process by ameliorating the adverse effects. To do this, both in vitro and in vivo experiments were performed with granulosa cells from superovulated immature (3-week-old) mice that were pretreated with or without PQQ, and a natural mating study was also performed. The ROS level in FSH-/eCG-stimulated granulosa cells was significantly increased. Moreover, high oxidative stress and mtDNA damage levels were evident in the granulosa cells. PQQ treatment not only reduced the ROS and oxidative stress levels but also ameliorated mtDNA damage, accelerated FSH-/eCG-induced ATP production, and increased the mitochondrial membrane potential and the expression levels of mitochondrial genes (Nd1, Cytb, Cox1, ATPase6) and the mt-ND1 protein. Accordingly, the proliferation and viability of granulosa cells, numbers of healthy preovulatory follicles and ovulated oocytes and serum estrogen level were significantly improved, while the apoptosis of granulosa cells was reduced. However, PQQ treatment did not change the fertility parameters in mature mice with natural cycles but did significantly increased the number of offspring born per delivery. These results revealed that ROS-associated damage in FSH-stimulated granulosa cells adversely affects their physiology and follicular health during the follicular development process. Treatment with PQQ is a beneficial tool to increase both the number of ovulated oocytes and pups per delivery.

Ovarian Aging: Role of Pituitary-Ovarian Axis Hormones and ncRNAs in Regulating Ovarian Mitochondrial Activity

The number of mitochondria in the oocyte along with their functions (e.g., energy production, scavenger activity) decline with age progression. Such multifaceted functions support several processes during oocyte maturation, ranging from energy supply to synthesis of the steroid hormones. Hence, it is hardly surprising that their impairment has been reported in both physiological and premature ovarian aging, wherein they are crucial players in the apoptotic processes that arise in aged ovaries. In any form, ovarian aging implies the progressive damage of the mitochondrial structure and activities as regards to ovarian germ and somatic cells. The imbalance in the circulating hormones and peptides (e.g., gonadotropins, estrogens, AMH, activins, and inhibins), active along the pituitary-ovarian axis, represents the biochemical sign of ovarian aging. Despite the progress accomplished in determining the key role of the mitochondria in preserving ovarian follicular number and health, their modulation by the hormonal signalling pathways involved in ovarian aging has been poorly and randomly explored. Yet characterizing this mechanism is pivotal to molecularly define the implication of mitochondrial dysfunction in physiological and premature ovarian aging, respectively. However, it is fairly difficult considering that the pathways associated with ovarian aging might affect mitochondria directly or by altering the activity, stability and localization of proteins controlling mitochondrial dynamics and functions, either unbalancing other cellular mediators, released by the mitochondria, such as non-coding RNAs (ncRNAs). We will focus on the mitochondrial ncRNAs (i.e., mitomiRs and mtlncRNAs), that retranslocate from the mitochondria to the nucleus, as active players in aging and describe their role in the nuclear-mitochondrial crosstalk and its modulation by the pituitary-ovarian hormone dependent pathways. In this review, we will illustrate mitochondria as targets of the signaling pathways dependent on hormones and peptides active along the pituitary/ovarian axis and as transducers, with a particular focus on the molecules retrieved in the mitochondria, mainly ncRNAs. Given their regulatory function in cellular activities we propose them as potential diagnostic markers and/or therapeutic targets.

High doses of FSH induce autophagy in bovine ovarian granulosa cells via the AKT/mTOR pathway

Follicle-stimulating hormone (FSH) plays a critical role in follicular growth and granulosa cell function; however, the mechanism by which the aggressive stimulation of FSH leads to poorer oocyte quality and embryo development potential is unclear. In this study, bovine ovarian granulosa cells (BGCs) were challenged with FSH doses (vehicle, 0.1, 1, 10 and 100 ng/ml) to investigate the effects of FSH on BGCs. The results indicated that the relative viability of BGCs was significantly increased in cells challenged with 1 ng/ml FSH, whereas the viability was significantly decreased with 100 ng/ml FSH treatment. The mRNA abundance of FSHR, CYP19, StAR and BAX was significantly upregulated with 1, 10 and 100 ng/ml of FSH, while the BCL-2 mRNA level was downregulated with higher concentrations of FSH (10 and 100 ng/ml). Furthermore, BGC autophagy was detected in cells treated with 10 and 100 ng/ml FSH by MDC staining, and the mRNA abundance of LC3, BECN1, BNIP3, ATG3 and ATG7 was upregulated with increasing FSH concentration. Meanwhile, the protein expression of LC3 was increased in cells treated with 10 and 100 ng/ml FSH. 1 and 10 ng/ml FSH significantly increased E2 production, whereas 10 and 100 ng/ml FSH significantly increased P4 production. FSH significantly inhibited the phosphorylation of AKT in cells treated with higher concentrations (1, 10 and 100 ng/ml), while activating mTOR phosphorylation at concentrations of 10 and 100 ng/ml of FSH. In summary, we can conclude that higher doses of FSH (10 and 100 ng/ml) induce BGC autophagy via the AKT/mTOR signalling pathway.

Effect of mitophagy in oocytes and granulosa cells on oocyte quality†

Mitophagy is the process by which cells selectively remove supernumerary or damaged mitochondria through autophagy, and is crucial for mitochondrial homeostasis and cell survival. Mitochondria play vital roles in determining the developmental competence of oocytes. During the early stages of oogenesis, aberrant mitochondria can be removed by mitophagy. After oocyte formation, mitophagy is not actively initiated to clear damaged mitochondria despite the presence of mitophagy regulators in oocytes, which leads to the transmission of dysfunctional mitochondria from the oocyte to the embryo. However, granulosa cells around oocytes can improve mitochondrial function through mitophagy, thereby improving oocyte developmental capacity. Furthermore, this review discusses recent work on the substances and environmental conditions that affect mitophagy in oocytes and granulosa cells, thus providing new directions for improving oocyte quality during assisted reproductive technology treatment.

FSHR ablation induces depression-like behaviors

Alteration in reproductive hormones profile is associated with the increasing risk of menopausal depression in women. Serum follicle-stimulating hormone (FSH) level is changed during the menopause transition, while the effect of FSH on menopausal depression has remained undefined. In this study we investigated whether or how FSH affected menopausal depression in postmenopausal (ovariectomized) FSHR knockout mice (Fshr^−/−). We found that Fshr^−/− mice displayed aggravated depression-like behaviors, accompanied by severe oxidative stress in the whole brain, resulted from significantly reduced glutamate cysteine ligase modifier subunit (GCLm) in glutathione synthesis and glucose-6-phosphate dehydrogenase (G6PD) in NADP/NADPH transition. Importantly, administration of ROS scavenger N-acetyl cysteine (NAC, 150 mg · kg⁻¹ · d⁻¹, i.p. for 12 weeks) attenuated the depression-like behaviors of Fshr^−/− mice. Consistent with these in vivo experiment results, we found that pretreatment with FSH (50, 100 ng/mL) dose-dependently increased protein levels of GCLm and G6PD, and decreased the ROS production in N2a mouse neuroblastoma cells. These findings demonstrate that FSH signaling is involved in pathogenesis of menopausal depression, and likely to maintain the redox-optimized ROS balance in neurons.

Regulation of AMH, AMHR-II, and BMPs (2,6) Genes of Bovine Granulosa Cells Treated with Exogenous FSH and Their Association with Protein Hormones

Anti-Mullerian hormone (AMH) is an important reproductive marker of ovarian reserve produced by granulosa cells (GCs) of pre-antral and early-antral ovarian follicles in several species, including cattle. This hormone plays a vital role during the recruitment of primordial follicles and follicle stimulating hormone (FSH)-dependent follicular growth. However, the regulatory mechanism of AMH expression in follicles is still unclear. In this study, we compared the expression of AMH, AMHR-II, BMP2, BMP6, FSHR, and LHCGR genes during follicular development. In-vitro expression study was performed with and without FSH for AMH, AMHR-II, BMP2, and BMP6 genes in bovine GCs which were isolated from 3–8 mm follicles. Association among the mRNA expression and hormone level was estimated. GCs were collected from small (3–8 mm), medium (9–12 mm) and large size (13 to 24 mm) follicles before, during onset, and after deviation, respectively. Further, mRNA expression, hormones (AMH, FSH, and LH), apoptosis of GCs, and cell viability were detected by qRT-PCR, ELISA, flow cytometry, and spectrophotometry. AMH, AMHR-II, BMP2, and FSHR genes were highly expressed in small and medium follicles as compared to large ones. In addition, the highest level of AMH protein (84.14 ± 5.41 ng/mL) was found in medium-size follicles. Lower doses of FSH increased the viability of bovine GCs while higher doses repressed them. In-vitro cultured GCs treated with FSH significantly increased the AMH, AMHR-II, and BMP2 expression levels at lower doses, while expression levels decreased at higher doses. We found an optimum level of FSH (25 ng/mL) which can significantly enhance AMH and BMP2 abundance (p < 0.05). In summary, AMH, AMHR-II, and BMP2 genes showed a higher expression in follicles developed in the presence of FSH. However, lower doses of FSH demonstrated a stimulatory effect on AMH and BMP2 expression, while expression started to decline at the maximum dose. In this study, we have provided a better understanding of the mechanisms regulating AMH, AMHR II, and BMP2 signaling in GCs during folliculogenesis, which would improve the outcomes of conventional assisted reproductive technologies (ARTs), such as superovulation and oestrus synchronization in bovines.

Corticosterone Injection Impairs Follicular Development, Ovulation and Steroidogenesis Capacity in Mice Ovary

Simple Summary

Researchers have hitherto established hundreds of animal stress models. However, these models have some limitations due to the complexity in operation and large differences between individual animals. In particular, there are few stress models that are specifically applied in mammalian ovaries. In this study, using intraperitoneal injection of cortisol/corticosterone (CORT), we successfully established a stress model that acts on the ovarian function. Our data showed that CORT inhibits ovarian and follicular development and blocks ovulation. The establishment of this model might provide a living platform for studying ovarian stress in future research.

Abstract

The aim of this study is to establish an ovarian stress model, and to investigate the effects of stress on follicular development. Our data showed that continuous intraperitoneal injection of CORT successfully created a stressful environment in the ovary. To assess the effects of CORT on ovarian functions, 80 three-week-old ICR (Institute of Cancer Research) female mice were randomly divided into control group and treatment group. All mice were injected intraperitoneally with pregnant horse serum gonadotropin (PMSG). At the same time, the treatment group were injected with CORT (1 mg/mouse) at intervals of 8 h; while the control group was injected with same volume of methyl sulfoxide (DMSO). Blood, ovaries, or ovarian granulosa cell samples were collected at 24 h, 48 h, and 55 h after PMSG injection. The results showed that, compared with the control group, CORT-injected mice revealed a significant decrease in ovulation rates, ovarian weight, ovarian index, the number of secondary follicles and mature follicles, levels of estrogen and progesterone, and mRNA expression of steroid synthase-related genes. Collectively, our findings clearly demonstrated that CORT injection could represent an effective practice to simulate stresses that inhibit ovarian functions by reducing follicular development and ovulation.

Immunohistochemical Detection of Vasa Antigen and Apoptosis-Related DNA Fragmentation in Ovaries of Sheep Fetuses Prenatally Exposed to Vitamin D Deficiency

The primordial germ cells (PGCs) in female animals are comprised of diplotene oocytes arrested in the first meiotic prophase. Expression of Vasa is one of the key factors required for subsequent resumption of development and recruitment of PGCs into the growing follicle class. Since vitamin D regulates recruitment of PGCs and developmental competence of ovarian follicles, this study was designed to investigate the expression of Vasa and rate of apoptosis in foetal ovaries prenatally restricted from dietary vitamin D. Nineteen sexually mature Welsh mountain ewes were randomly assigned to vitamin D deficient (VDD) and vitamin D control (VDC) diets from 17d before mating, up to 125d of gestation, when fetal ovaries were collected and fixed in formalin for immunohistochemistry and TUNEL assay. VDD ovaries had fewer healthy oocytes that could stain positive for Vasa as well as a lower integrated density value for DAB staining intensity. Conversely, TUNNEL staining in VDD animals showed a higher integrated density value and percentage of affected area (P<0.05). The present findings indicate that Vasa expression is decreased, while the rate of apoptosis increased in VDD fetal ovaries, and this may adversely affect resumption of growth and development of PGCs reserve.

Autophagy in hypoxic ovary

Oxygen deprivation affects human health by modulating system as well as cellular physiology. Hypoxia generates reactive oxygen species (ROS), causes oxidative stress and affects female reproductive health by altering ovarian as well as oocyte physiology in mammals. Hypoxic conditions lead to several degenerative changes by inducing various cell death pathways like autophagy, apoptosis and necrosis in the follicle of mammalian ovary. The encircling somatic cell death interrupts supply of nutrients to the oocyte and nutrient deprivation may result in the generation of ROS. Increased level of ROS could induce granulosa cells as well as oocyte autophagy. Although autophagy removes damaged proteins and subcellular organelles to maintain the cell survival, irreparable damages could induce cell death within intra-follicular microenvironment. Hypoxia-induced autophagy is operated through 5' AMP activated protein kinase-mammalian target of rapamycin, endoplasmic reticulum stress/unfolded protein response and protein kinase C delta-c-junN terminal kinase 1 pathways in a wide variety of somatic cell types. Similar to somatic cells, we propose that hypoxia may induce granulosa cell as well as oocyte autophagy and it could be responsible at least in part for germ cell elimination from mammalian ovary. Hypoxia-mediated germ cell depletion may cause several reproductive impairments including early menopause in mammals.

The role of FSH and TGF-β superfamily in follicle atresia

Most of the mammalian follicles undergo a degenerative process called “follicle atresia”. Apoptosis of granulosa cells is the main characteristic of follicle atresia. Follicle stimulating hormone (FSH) and the transforming growth factor β (TGF-β) superfamily have important regulatory functions in this process. FSH activates protein kinase A and cooperating with insulin receptor substrates, it promotes the PI3K/Akt pathway which weakens apoptosis. Both Smad or non-Smad signaling of the transforming growth factor β superfamily seem to be related to follicle atresia, and the effect of several important family members on follicle atresia is concluded in this article. FSH and TGF-β are likely to mutually influence each other and what we have already known about the possible underlying molecular mechanism is also discussed below.

Autophagy in Ovarian Follicular Development and Atresia

Autophagy is a mechanism that exists in all eukaryotes under a variety of physiological and pathological conditions. In the mammalian ovaries, less than 1% of follicles ovulate, whereas the remaining 99% undergo follicular atresia. Autophagy and apoptosis have been previously found to be involved in the regulation of both primordial follicular development as well as atresia. The relationship between autophagy, follicular development, and atresia have been summarized in this review with the aim to obtain a more comprehensive understanding of the role played by autophagy in follicular development and atresia.

Molecular Mechanisms of Action of FSH

The glycoprotein follicle-stimulating hormone (FSH) acts on gonadal target cells, hence regulating gametogenesis. The transduction of the hormone-induced signal is mediated by the FSH-specific G protein-coupled receptor (FSHR), of which the action relies on the interaction with a number of intracellular effectors. The stimulatory Gαs protein is a long-time known transducer of FSH signaling, mainly leading to intracellular cAMP increase and protein kinase A (PKA) activation, the latter acting as a master regulator of cell metabolism and sex steroid production. While in vivo data clearly demonstrate the relevance of PKA activation in mediating gametogenesis by triggering proliferative signals, some in vitro data suggest that pro-apoptotic pathways may be awakened as a "dark side" of cAMP/PKA-dependent steroidogenesis, in certain conditions. P38 mitogen-activated protein kinases (MAPK) are players of death signals in steroidogenic cells, involving downstream p53 and caspases. Although it could be hypothesized that pro-apoptotic signals, if relevant, may be required for regulating atresia of non-dominant ovarian follicles, they should be transient and counterbalanced by mitogenic signals upon FSHR interaction with opposing transducers, such as Gαi proteins and β-arrestins. These molecules modulate the steroidogenic pathway via extracellular-regulated kinases (ERK1/2), phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3K)/protein kinase B (AKT), calcium signaling and other intracellular signaling effectors, resulting in a complex and dynamic signaling network characterizing sex- and stage-specific gamete maturation. Even if the FSH-mediated signaling network is not yet entirely deciphered, its full comprehension is of high physiological and clinical relevance due to the crucial role covered by the hormone in regulating human development and reproduction.

FSH Receptor Signaling: Complexity of Interactions and Signal Diversity

FSH is synthesized in the pituitary by gonadotrope cells. By binding to and interacting with its cognate receptor [FSH receptor (FSHR)] in the gonads, this gonadotropin plays a key role in the control of gonadal function and reproduction. Upon activation, the FSHR undergoes conformational changes leading to transduction of intracellular signals, including dissociation of G protein complexes into components and activation of several associated interacting partners, which concertedly regulate downstream effectors. The canonical Gs/cAMP/protein kinase A pathway, considered for a long time as the sole effector of FSHR-mediated signaling, is now viewed as one of several mechanisms employed by this receptor to transduce intracellular signals in response to the FSH stimulus. This complex network of signaling pathways allows for a fine-tuning regulation of the gonadotropic stimulus, where activation/inhibition of its multiple components vary depending on the cell context, cell developmental stage, and concentration of associated receptors and corresponding ligands. Activation of these multiple signaling modules eventually converge to the hormone-integrated biological response, including survival, proliferation and differentiation of target cells, synthesis and secretion of paracrine/autocrine regulators, and, at the molecular level, functional selectivity and differential gene expression. In this mini-review, we discuss the complexity of FSHR-mediated intracellular signals activated in response to ligand stimulation. A better understanding of the signaling pathways involved in FSH action might potentially influence the development of new therapeutic strategies for reproductive disorders.

Melatonin protects mouse granulosa cells against oxidative damage by inhibiting FOXO1-mediated autophagy: Implication of an antioxidation-independent mechanism

Oxidative stress has been described as a prime driver of granulosa cell (GCs) death during follicular atresia. Increasing evidence suggests potential roles of melatonin in protecting GCs from oxidative injury, though the underlying mechanisms remain largely undetermined. Here we first proposed that the inhibition of autophagy through some novel regulators contributes to melatonin-mediated GCs survival under conditions of oxidative stress. Oxidant-induced loss of GCs viability was significantly reduced after melatonin administration, which was correlated with attenuated autophagic signals upon oxidative stimulation both in vivo and in vitro. Compared with melatonin treatment, suppression of autophagy displayed similar preventive effect on GCs death during oxidative stress, but melatonin provided no additional protection in GCs pretreated with autophagy inhibitors. Notably, we found that melatonin-directed regulation of autophagic death was independent of its antioxidation/radical scavenging ability. Further investigations identified FOXO1 as a critical downstream effector of melatonin in promoting GCs survival from oxidative stress-induced autophagy. Specifically, suppression of FOXO1 via the melatonin-phosphatidylinositol 3-kinase (PI3K)-AKT axis not only improved GCs resistance to oxidative stress, but also abolished the autophagic response, from genes expression to the formation of autophagic vacuoles. Moreover, the activation of SIRT1 signaling was required for melatonin-mediated deacetylation of FOXO1 and its interaction with ATG proteins, as well as the inhibition of autophagic death in GCs suffering oxidative stress. These findings reveal a brand new mechanism of melatonin in defense against oxidative damage to GCs by repressing FOXO1, which may be a potential therapeutic target for anovulatory disorders.

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Melatonin inhibits oxidative damage in GC without scavenging oxidative stress itself.

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Melatonin protects GC from oxidative damage via inhibiting autophagic cell death.

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Inhibition of FOXO1-dependent autophagy by melatonin reduces oxidative damage in GC.

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Suppression of autophagy through melatonin-PI3K-AKT-FOXO1 axis improves GC survival.

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Melatonin reduces oxidative injury by inhibiting SIRT1-FOXO1-ATG7-dependent autophagy.

Melatonin reduces oxidative damage in mouse granulosa cells via restraining JNK-dependent autophagy

Oxidative stress-induced granulosa cell (GCs) injury is believed to be a common trigger for follicular atresia. Emerging evidence indicates that excessive autophagy occurs in mammalian cells with oxidative damage. N-acetyl-5-methoxytrypamine (melatonin) has been shown to prevent GCs from oxidative injury, although the exact mechanism remains to be elucidated. Here, we first demonstrated that the suppression of autophagy through the JNK/BCL-2/BECN1 signaling is engaged in melatonin-mediated GCs protection against oxidative damage. Melatonin inhibited the loss of GCs viability, formation of GFP-MAP1LC3B puncta, accumulation of MAP1LC3B-II blots, degradation of SQSTM1 and the expression of BECN1, which was correlated with impaired activation of JNK during oxidative stress. On the other hand, blocking of autophagy and/or JNK also reduced the level of H2O2-induced GCs death, but failed to further restore GCs viability in the presence of melatonin. Particularly, the suppression of autophagy provided no additional protective effects when GCs were pretreated with JNK inhibitor and/or melatonin. Importantly, we found that the enhanced interaction between BCL-2 and BECN1 might be a responsive mechanism for autophagy suppression via the melatonin/JNK pathway. Moreover, blocking the downstream antioxidant system of melatonin using specific inhibitors further confirmed a direct role of melatonin/JNK/autophagy axis in preserving GCs survival without scavenging reactive oxygen species (ROS). Taken together, our findings uncover a novel function of melatonin in preventing GCs from oxidative damage by targeting JNK-mediated autophagy, which might contribute to develop therapeutic strategies for patients with ovulation failure-related disorders.

Protective mechanism of FSH against oxidative damage in mouse ovarian granulosa cells by repressing autophagy

Oxidative stress-induced granulosa cell (GCs) death represents a common reason for follicular atresia. Follicle-stimulating hormone (FSH) has been shown to prevent GCs from oxidative injury, although the underlying mechanism remains to be elucidated. Here we first report that the suppression of autophagic cell death via some novel signaling effectors is engaged in FSH-mediated GCs protection against oxidative damage. The decline in GCs viability caused by oxidant injury was remarkably reduced following FSH treatment, along with impaired macroautophagic/autophagic flux under conditions of oxidative stress both in vivo and in vitro. Blocking of autophagy displayed similar levels of suppression in oxidant-induced cell death compared with FSH treatment, but FSH did not further improve survival of GCs pretreated with autophagy inhibitors. Further investigations revealed that activation of the phosphoinositide 3-kinase (PI3K)-AKT-MTOR (mechanistic target of rapamycin [serine/threonine kinase]) signaling pathway was required for FSH-mediated GCs survival from oxidative stress-induced autophagy. Additionally, the FSH-PI3K-AKT axis also downregulated the autophagic response by targeting FOXO1, whereas constitutive activation of FOXO1 in GCs not only abolished the protection from FSH, but also emancipated the autophagic process, from the protein level of MAP1LC3B-II to autophagic gene expression. Furthermore, FSH inhibited the production of acetylated FOXO1 and its interaction with Atg proteins, followed by a decreased level of autophagic cell death upon oxidative stress. Taken together, our findings suggest a new mechanism involving FSH-FOXO1 signaling in defense against oxidative damage to GCs by restraining autophagy, which may be a potential avenue for the clinical treatment of anovulatory disorders.