Preantral follicular atresia occurs mainly through autophagy, while antral follicles degenerate mostly through apoptosis

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.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

Attenuation of sodium arsenite mediated ovarian DNA damage, follicular atresia, and oxidative injury by combined application of vitamin E and C in post pubertal Wistar rats

Arsenic being a toxic metalloid ubiquitously persists in environment and causes several health complications including female reproductive anomalies. Epidemiological studies documented birth anomalies due to arsenic exposure. Augmented reactive oxygen species (ROS) generation and quenched antioxidant pool are foremost consequences of arsenic threat. On the contrary, Vitamin E (VE) and C (VC) are persuasive antioxidants and conventionally used in toxicity management. Present study was designed to explore the extent of efficacy of combined VE and VC (VEC) against Sodium arsenite (NaAsO2) mediated ovarian damage. Thirty-six female Wistar rats were randomly divided into three groups (Grs) and treated for consecutive 30 days; Gr I (control) was vehicle fed, Gr II (treated) was gavaged with NaAsO2 (3 mg/kg/day), Gr III (supplement) was provided with VE (400 mg/kg/day) & VC (200 mg/kg/day) along with NaAsO2. Marked histological alterations were evidenced by disorganization in oocyte, granulosa cells and zona pellucida layers in treated group. Considerable reduction of different growing follicles along with increased atretic follicles was noted in treated group. Altered activities ofΔ5 3β-Hydroxysteroid dehydrogenase and 17β-Hydroxysteroid dehydrogenase accompanied by reduced luteinizing hormone, follicle-stimulating hormone and estradiol levels were observed in treated animals. Irregular estrous cyclicity pattern was also observed due to NaAsO2 threat. Surplus ROS production affected ovarian antioxidant strata as evidenced by altered oxidative stress markers. Provoked oxidative strain further affects DNA status of ovary. However, supplementation with VEC caused notable restoration from such disparaging effects of NaAsO2 toxicities. Antioxidant and antiapoptotic attributes of those vitamins might be liable for such restoration.

Androgen receptor signaling regulates follicular growth and steroidogenesis in interaction with gonadotropins in the ovary during mini-puberty in mice

In females, androgens contribute to ovarian diseases such as polycystic ovarian syndrome (PCOS), but their action is also crucial for ovarian physiology, i.e., follicular growth and estradiol (E2) synthesis during reproductive life, in interaction with the gonadotropins LH and FSH. However, it is unclear whether androgens already play a role in the ovary at mini-puberty, a phase of postnatal development with active follicular growth and high E2 levels. Therefore, we analyzed the potential actions of androgens on the ovary and their possible interaction with gonadotropins during this period in mice. We used molecular-based studies and pharmacological approaches in vivo and on cultured ovaries. We found that mini-pubertal ovaries produce significant amounts of testosterone and display androgen receptor (AR) expression in growing follicles, both under the control of LH. By blocking AR signaling either in vivo or in ovarian cultures, we found that this pathway may participate in the regulation of prepubertal E2 synthesis and follicular growth, possibly by regulating the expression of a number of key intra-ovarian regulators, including FSH receptor (Fshr), the aromatase enzyme converting androgens into estrogens (Cyp19a1) and the cell cycle inhibitor p27KIP1 (Cdkn1b). We further showed that AR may stimulate FSH-mediated regulation of Cyp19a1 through its action on Fshr mRNA abundance. Overall, this work supports the idea that AR signaling is already activated in mini-pubertal ovaries to regulate E2 synthesis and follicular growth, at the interplay with LH and FSH signaling. Its early action may, thus, contribute to the implementation of early ovarian function with possible impacts on reproductive function.

Effects of N-acetylcysteine on Growth, Viability, and Ultrastructure of In Vitro Cultured Bovine Secondary Follicles

This study aimed to investigate the effects of different concentrations of N-acetylcysteine (NAC) on the growth, antrum formation, viability, and ultrastructure of bovine secondary follicles cultured in vitro for 18 days. To this end, the follicles were cultured in TCM-199+ medium alone or supplemented with 1.0, 5.0, or 25.0 mM NAC. Follicular growth, antrum formation, viability (calcein-AM and ethidium homodimer-1) and ultrastructure were evaluated at the end of culture period. The results showed that 1.0 mM NAC increased the percentage of growing follicles and the fluorescence intensity for calcein-AM when compared to other treatments (p < 0.05). On the other hand, follicles cultured with 25.0 mM NAC had higher fluorescence intensity for ethidium homodimer-1, which is a sign of degeneration. Ultrastructural analysis showed that oocytes from follicles cultured in control medium alone or with 1 mM NAC had intact zonae pellucidae in close association with oolemmae, but the ooplasm showed mitochondria with a reduced number of cristae. On the other hand, oocytes from follicles cultured with 5 or 25 mM NAC had extremely vacuolated cytoplasm and no recognizable organelles. In conclusion, 1 mM NAC increases cytoplasmic calcein staining and the growth rate in bovine secondary follicles cultured in vitro, but the presence of 5 or 25 mM NAC causes damage in cellular membranes and organelles, as well as reducing the percentages of growing follicles.

Experimental hyperthermia: expression of proteins involved in the regulation of ovarian corpus luteum apoptosis in the acute and recovery periods

Background.Heat shock effects can initiate apoptosis of oocytes and corpus luteum cells in mammalian ovaries. During folliculogenesis, follicular apoptosis is regulated by Bcl-2 and BAX proteins which are key effectors of granular cell death. Mechanisms of disruption of the ovarian corpus luteum development under heat stress remain largely unclear.

Aim of the research: to identify the expression features of anti-apoptotic Bad and proapoptotic Bcl-2 proteins in the rat ovarian luteocytes in the acute (by day 3) and recovery (by days 7 and 14) periods after a single exposure of experimental hyperthermia (EH) (rectal temperature 43.5 °C).

Materials and methods. The expression of Bad and Bcl-2 was determined immunohistochemically using an indirect two-stage streptavidin-biotin method.

Results. On day 3 after EH, the expression areas of both Bad and Bcl-2 increased 2-fold, but the ratio of Bcl-2/Bad areas did not change, indicating that the intensity of apoptosis along the mitochondrial pathway in luteocytes in the acute period was  maintained within physiological values. On day  7, the Bad and Bcl-2 expression areas remained at the level of day 3, but the Bcl-2/Bad index decreased, indicating the activation of the apoptosis internal pathway in the ovarian corpus luteum cells. By day 14, the protein expression areas decreased (Bad – by 1.7 times, Bcl-2 – by 3.2 times) compared to the acute period, and the Bcl-2/Bad index decreased by 2 times compared to the control and the acute period group.

Conclusion. The observed predominance of proapoptotic Bad protein over antiapoptotic Bcl-2 in luteocytes on day 14 after EH indicates the anti-apoptotic protection violation, which leads to the apoptosis mitochondrial pathway activation of  the latter. A decrease in Bcl-2 expression can be regarded as a manifestation of the defective luteocytes removal mechanism and the body’s desire to normalize the ovarian-uterine cycle disrupted by high temperature exposure. 

Polycystic ovary syndrome: Identification of novel and hub biomarkers in the autophagy-associated mRNA-miRNA-lncRNA network

INTRODUCTION

Polycystic ovary syndrome (PCOS) is a common metabolic and endocrine disorder prevalent among women of reproductive age. Recent studies show that autophagy participated in the pathogenesis of PCOS, including anovulation, hyperandrogenism, and metabolic disturbances. This study was designed to screen autophagy-related genes (ATGs) that may play a pivotal role in PCOS, providing potential biomarkers and identifying new molecular subgroups for therapeutic intervention.

METHODS

Gene expression profiles of the PCOS and control samples were obtained from the publicly available Gene Expression Omnibus database. The gene lists of ATGs from databases were integrated. Then, the weighted gene co-expression network analysis was conducted to obtain functional modules and construct a multifactorial co-expression network. Gene Ontology and KEGG pathway enrichment analyses were performed for further exploration of ATG's function in the key modules. Differentially expressed ATGs were identified and validated in external datasets with the Limma R package. To provide guidance on PCOS phenotyping, the dysfunction module consists of a co-expression network mapped to PCOS patients. A PCOS-Autophagy-related co-expression network was established using Cytoscape, followed by identifying molecular subgroups using the Limma R package. ps. RNA-sequencing analysis was used to confirm the differential expression of hub ATGs, and the diagnostic value of hub ATGs was assessed by receiver operating characteristic curve analysis.

RESULTS

Three modules (Brown, Turquoise, and Green) in GSE8157, three modules (Blue, Red, and Green) in GSE43264, and four modules (Blue, Green, Black, and Yellow) in GSE106724 were identified to be PCOS-related by WGCNA analysis. 29 ATGs were found to be the hub genes that strongly correlated with PCOS. These hub ATGs were mainly enriched in autophagy-related functions and pathways such as autophagy, endocytosis, apoptosis, and mTOR signaling pathways. The mRNA-miRNA-lncRNA multifactorial network was successfully constructed. And three new molecular subgroups were identified via the K-means algorithm.

DISCUSSION

We provide a novel insight into the mechanisms behind autophagy in PCOS. BRCA1, LDLR, MAP1B, hsa-miR-92b-3p, hsa-miR-20b-5p, and NEAT1 might play a considerably important role in PCOS dysfunction. As a result, new potential biomarkers can be evaluated for use in PCOS diagnosis and treatment in the future.

The effect of fixed-time artificial insemination protocol initiated at different stages of the estrous cycle on follicle development and ovulation in gilts

Hormonal products have been developed for fixed-time artificial insemination (FTAI) to improve the efficiency of swine production. Here, we evaluated the effect of an FTAI protocol initiated during different phases of the estrous cycle on follicle development and ovulation in gilts. A total of 36 gilts were equally divided into three groups designated as the luteal (L), follicular (F), and post-ovulation (O) groups and fed with 20 mg of altrenogest for 18 days, followed by intramuscular injection of 1000 IU PMSG at 42 h after withdrawal of altrenogest, and 100 μg of GnRH after an 80-h interval. The L group had the highest number of follicles 4-6 mm in diameter, as well as corpora hemorrhagica. The mRNA expression of caspase-9 in the L group were significantly lower than those in the O and F groups (P < 0.05), while CYP11A1 and VEGF mRNA expression levels were significantly higher (P < 0.05). Moreover, FSHR mRNA levels were significantly higher in the O group than in the L, F, and control groups (P < 0.05). LHCGR and CYP19A1 mRNA levels were the highest in the F group (P < 0.05). Thus, the changes in the expression of genes associated with follicular development, maturation, and ovulation identified in this study indicated that initiation of the FTAI protocol during the luteal phase induced a better environment for follicle development and ovulation in gilts.

Protein Kinase A and 5' AMP-Activated Protein Kinase Signaling Pathways Exert Opposite Effects on Induction of Autophagy in Luteal Cells

In the absence of pregnancy the ovarian corpus luteum undergoes regression, a process characterized by decreased production of progesterone and structural luteolysis involving apoptosis. Autophagy has been observed in the corpus luteum during luteal regression. Autophagy is a self-degradative process important for balancing sources of cellular energy at critical times in development and in response to nutrient stress, but it can also lead to apoptosis. Mechanistic target of rapamycin (MTOR) and 5′ AMP-activated protein kinase (AMPK), key players in autophagy, are known to inhibit or activate autophagy, respectively. Here, we analyzed the signaling pathways regulating the initiation of autophagy in bovine luteal cells. In vivo studies showed increased activating phosphorylation of AMPKα (Thr172) and elevated content of LC3B, a known marker of autophagy, in luteal tissue during PGF2α-induced luteolysis. In vitro, AMPK activators 1) stimulated phosphorylation of regulatory associated protein of MTOR (RPTOR) leading to decreased activity of MTOR, 2) increased phosphorylation of Unc-51-Like Kinase 1 (ULK1) and Beclin 1 (BECN1), at sites specific for AMPK and required for autophagy initiation, 3) increased levels of LC3B, and 4) enhanced colocalization of autophagosomes with lysosomes indicating elevated autophagy. In contrast, LH/PKA signaling in luteal cells 1) reduced activation of AMPKα and phosphorylation of RPTOR, 2) elevated MTOR activity, 3) stimulated phosphorylation of ULK1 at site required for ULK1 inactivation, and 4) inhibited autophagosome formation as reflected by reduced content of LC3B-II. Pretreatment with AICAR, a pharmacological activator of AMPK, inhibited LH-mediated effects on RPTOR, ULK1 and BECN1. Our results indicate that luteotrophic signaling via LH/PKA/MTOR inhibits, while luteolytic signaling via PGF2α/Ca²⁺/AMPK activates key signaling pathways involved in luteal cell autophagy.

Luteinizing Hormone Regulation of Inter-Organelle Communication and Fate of the Corpus Luteum

The corpus luteum is an endocrine gland that synthesizes the steroid hormone progesterone. luteinizing hormone (LH) is a key luteotropic hormone that stimulates ovulation, luteal development, progesterone biosynthesis, and maintenance of the corpus luteum. Luteotropic and luteolytic factors precisely regulate luteal structure and function; yet, despite recent scientific progress within the past few years, the exact mechanisms remain largely unknown. In the present review, we summarize the recent progress towards understanding cellular changes induced by LH in steroidogenic luteal cells. Herein, we will focus on the effects of LH on inter-organelle communication and steroid biosynthesis, and how LH regulates key protein kinases (i.e., AMPK and MTOR) responsible for controlling steroidogenesis and autophagy in luteal cells.

Environmentally relevant mixtures of phthalates and phthalate metabolites differentially alter the cell cycle and apoptosis in mouse neonatal ovaries†

Phthalates are a group of chemicals used as additives in various consumer products, medical equipment, and personal care products. Phthalates and their metabolites are consistently detected in humans, indicating widespread and continuous exposure to multiple phthalates. Thus, environmentally relevant mixtures of phthalates and phthalate metabolites were investigated to determine the effects of phthalates on the function of the ovary during the neonatal period of development. Neonatal ovaries from CD-1 mice were cultured with dimethyl sulphoxide (DMSO; vehicle control), phthalate mixture (0.1-100 μg/mL), or phthalate metabolite mixture (0.1-100 μg/mL). The phthalate mixture was composed of 35% diethyl phthalate, 21% di(2-ethylhexyl) phthalate, 15% dibutyl phthalate, 15% diisononyl phthalate, 8% diisobutyl phthalate, and 5% benzylbutyl phthalate. The phthalate metabolite mixture was composed of 37% monoethyl phthalate, 19% mono(2-ethylhexyl) phthalate, 15% monobutyl phthalate, 10% monoisononyl phthalate, 10% monoisobutyl phthalate, and 8% monobenzyl phthalate. After 96 h of culture, ovaries were harvested for histological analysis of folliculogenesis, gene expression analysis of cell cycle and apoptosis regulators, and immune staining for cell proliferation and apoptosis. The metabolite mixture significantly decreased the number and percentage of abnormal follicles (100 μg/mL) compared to controls. The metabolite mixture also significantly increased the expression of cell cycle inhibitors (100 μg/mL) and the antiapoptotic factor Bcl2l10 (10 μg/mL) compared to controls. The phthalate mixture did not significantly alter gene expression or follicle counts, but ovaries exposed to the phthalate mixture (0.1 μg/mL) exhibited marginally significantly increased apoptosis as revealed by DNA fragmentation staining. Overall, these data show that parent phthalates and phthalate metabolites differentially impact ovarian function.

Pseudo-Starvation Driven Energy Expenditure Negatively Affects Ovarian Follicle Development

In the present investigation, we examined whether a change in whole body energy fluxes could affect ovarian follicular development, employing mice ectopically expressing uncoupling protein 1 in skeletal muscle (UCP1-TG). Female UCP1-TG and wild-type (WT) mice were dissected at the age of 12 weeks. Energy intake and expenditure, activity, body weight and length, and body composition were measured. Plasma insulin, glucose, leptin, plasma fibroblast growth factor 21 (FGF21) and plasma insulin-like growth factor 1 (IGF1) levels were analyzed and ovarian follicle and corpus luteum numbers were counted. IGF1 signaling was analyzed by immunohistochemical staining for the activation of insulin receptor substrate 1/2 (IRS1/2) and AKT. UCP1-TG female mice had increased energy expenditure, reduced body size, maintained adiposity, and decreased IGF1 concentrations compared to their WT littermates, while preantral and antral follicle numbers were reduced by 40% and 60%, respectively. Corpora lutea were absent in 40% of the ovaries of UCP1-TG mice. Phospho-IRS1, phospho-AKT -Ser473 and -Thr308 immunostaining was present in the granulosa cells of antral follicles in WT ovaries, but faint to absent in the antral follicles of UCP1-TG mice. In conclusion, the reduction in circulating IGF1 levels due to the ectopic expression of UCP1 is associated with reduced immunostaining of the IRS1-PI3/AKT pathway, which may negatively affect ovarian follicle development and ovulation.

Characterization of Long Non-Coding RNA Profiles in Porcine Granulosa Cells of Healthy and Atretic Antral Follicles: Implications for a Potential Role in Apoptosis

Long non-coding RNAs (lncRNAs) play important roles in multiple biological processes including ovarian follicular development. Here we aimed to gain novel information regarding lncRNAs transcriptome profiles in porcine granulosa cells of advanced atretic antral (AA) and healthy antral (HA) follicles using RNA-seq. A total of 11,321 lncRNAs including 10,813 novel and 508 annotated lncRNAs were identified, of which 173 lncRNAs were differentially expressed (DE-lncRNAs); ten of these were confirmed by qRT-PCR. Gene Ontology indicated that DE-lncRNAs associated with developmental processes were highly enriched. Pathway analysis demonstrated predicted cis- and trans-targets of DE-lncRNAs. Potential mRNA targets of up-regulated DE-lncRNAs were mainly enriched in apoptosis related pathways, while targeted genes of downregulated DE-lncRNAs were primarily enriched in metabolism and ovarian steroidogenesis pathways. Linear regression analyses showed that expression of upregulated DE-lncRNAs was significantly associated with apoptosis related genes. NOVEL_00001850 is the most-downregulated DE-lncRNA (FDR = 0.04, FC = -6.53), of which miRNA binding sites were predicted. KEGG analysis of its downregulated target genes revealed that ovarian steroidogenesis was the second most highlighted pathway. qRT-PCR and linear regression analysis confirmed the expression and correlation of its potential targeted gene, CYP19A1, a key gene involved in estradiol synthesis. Our results indicate that lncRNAs may participate in granulosa cells apoptosis and thus antral follicular atresia.

Effect of Melatonin on Expression of Apoptosis Regulator Proteins Bcl-2 and Bad in Ovarian Follicular Apparatus after High Temperature Exposure

Expression of proapoptotic Bad and antiapoptotic Bcl-2 proteins in ovarian follicular apparatus of Wistar rats was evaluated on days 3, 7, and 14 after single experimental hyperthermia (EH) followed by therapeutic correction with subcutaneous melatonin (0.1 mg) dissolved in 0.2 ml physiological saline (PS) injected daily for 3 days. Duration of EH was less than 17 min; it was terminated when the rectal temperature attained 43.5°C. In acute posthyperthermia period (on experimental day 3), Bcl-2 and Bad expression area in folliculocytes of the experimental (EH+melatonin) and reference rats simultaneously increased in comparison with the corresponding values in control rats. At this, Bcl-2/Bad ratio of expression areas in experimental and reference rats did not differ from the control level. During the recovery period (on posthyperthermia day 7), Bad protein expression area significantly decreased in experimental rats resulting in elevation of Bcl-2/Bad ratio in comparison with control and reference groups on days 3 and 7. On day 14, Bcl-2 and Bad expression areas and Bcl-2/Bad ratio restored in experimental animals to the corresponding values assessed in control and reference groups. Thus, melatonin produced no effect on Bcl-2/Bad protein expression ratio during acute posthyperthermia period, but reduced the expression area of proapoptotic Bad protein and increased Bcl-2/Bad ratio on posthyperthermia day 7. Thus, melatonin can inhibit apoptosis via mitochondrial pathway in ovarian follicles on posthyperthermia day 7.

Transcriptome Analysis of Porcine Granulosa Cells in Healthy and Atretic Follicles: Role of Steroidogenesis and Oxidative Stress

One of the main causes of female infertility is a deregulated antral follicular atresia, a process of which the underlying molecular mechanisms are largely unknown. Our objective was therefore to characterize the complex transcriptome changes in porcine granulosa cells of healthy antral (HA) and advanced antral atretic (AA) follicles, using ELISA and RNA-Seq followed by qRT-PCR and immunohistochemistry. Granulosa cell RNA-Seq data revealed 2160 differentially expressed genes, 1483 with higher and 677 with lower mRNA concentrations in AA follicles. Bioinformatic analysis showed that the upregulated genes in AA follicles were highly enriched in inflammation and apoptosis processes, while the downregulated transcripts were mainly highlighted in the steroid biosynthesis pathway and response to oxidative stress processes including antioxidant genes (e.g., GSTA1, GCLC, GCLM, IDH1, GPX8) involved in the glutathione metabolism pathway and other redox-related genes (e.g., RRM2B, NDUFS4). These observations were confirmed by RT-qPCR and immunohistochemistry. Additionally, the granulosa cells of AA follicles express significantly stronger 8-OHdG immunostaining, a marker of oxidative DNA damage, implicating that oxidative stress may participate in follicular atresia. We hypothesize that the decrease in anti-apoptotic factors and steroid hormones coincides with increased oxidative stress markers and the expression of pro-apoptotic factors, all contributing to antral follicular atresia.

Ultrastructure of Granulosa Cells of Bovine Ovarian Antral Follicles in Relation to Atresia

The aim of this study was to describe the most common forms of ovarian follicle atresia in large antral follicles of cows and quantify the occurrence of different cell structures in each form. Atresia of antral follicles in ovaries was determined on the basis of ultrastructural images acquired by electron microscopy of ultrathin sections contrasted with uranyl acetate and lead citrate to visualize cell organelles. All forms of atresia in large follicles are accompanied by regressive changes of the granulosa cells. The initial form of atresia is characterized by enlarged intercellular spaces after the disruption of the gap junctions and desmosomes. Small collapsed cells with pyknotic nuclei, substantially reduced the cytoplasm and a higher incidence of lysosomes are located on the surface of the granulosa layer. The stratum granulosum wall collapses and the basal membrane is swollen with a rupture of the lamina basalis. Obliterative atresia is characterized by a multiplied loose connective tissue consisting of collagen fibers, fibroblasts, histiocytes, blood capillaries and sporadically granulocytes. The cystic form of atresia is characterized by small collapsed, pyknotic granulosa cells settled in one or two layers. In luteinization-associated atresia, granulosa cells are hypertrophied, their cytoplasm contains smooth endoplasmic reticulum and mitochondria with tubules. In conclusion, the initial atresia of large antral ovarian follicles is associated with processes of cell death, followed by multiplication of the loose connective tissue cells, its dystrophy and hyalinization of the collagen fibers. Ultrastructural examination could be used as a complementary method to improve histopathological diagnostics of cow reproductive organs in veterinary practice.

A review of the physiology behind letrozole applications in infertility: are current protocols optimal?

Letrozole is a targeted aromatase inhibitor which has primarily been used in post-menopausal women with breast cancer. Recently, it has been utilized in infertile pre-menopausal women because of its ability to enhance FSH production for ovulation induction. However, the ovarian follicle’s response to FSH is only a part of the endocrine events occurring in a developing follicle. The health of the small antral follicles is driven primarily by androgens, which contribute to granulosa cell mitosis, sensitivity to FSH, and resistance to atresia. In contrast, elevated androgens in the late antral to pre-ovulatory follicle have a negative impact on follicle health and lead to atresia and cystic follicle formation. This ovarian physiologic data suggests that current applications of letrozole to infertility may be squandering some of the primary benefits available in using letrozole to promote follicle development. Four applications of letrozole to infertility that have appeared in the medical literature are reviewed. Androgen-related benefits are reviewed and various questions put forward about how letrozole could be more effectively used to help patients in these settings.

Characteristics of Circular RNA Expression Profiles of Porcine Granulosa Cells in Healthy and Atretic Antral Follicles

Circular RNAs (circRNAs) are thought to play essential roles in multiple biological processes, including apoptosis, an important process in antral follicle atresia. We aimed to investigate the potential involvement of circRNAs in granulosa cell apoptosis and thus antral follicle atresia. CircRNA expression profiles were generated from porcine granulosa cells isolated from healthy antral (HA) and atretic antral (AA) follicles. Over 9632 circRNAs were identified, of which 62 circRNAs were differentially expressed (DE-circRNAs). Back-splicing, RNase R resistance, and stability of DE-circRNAs were validated, and miRNA binding sites and related target genes were predicted. Two exonic circRNAs with low false discovery rate (FDR) high fold change, miRNA binding sites, and relevant biological functions—circ_CBFA2T2 and circ_KIF16B—were selected for further characterization. qRT-PCR and linear regression analysis confirmed expression and correlation of the targeted genes—the antioxidant gene GCLC (potential target of circ_CBFA2T2) and the apoptotic gene TP53 (potential target of circ_KIF16B). Increased mRNA content of TP53 in granulosa cells of AA follicles was further confirmed by strong immunostaining of both p53 and its downstream target pleckstrin homology like domain family a member 3 (PHLDA3) in AA follicles compared to negligible staining in granulosa cells of HA follicles. Therefore, we concluded that aberrantly expressed circRNAs presumably play a potential role in antral follicular atresia.

Thyroid Hormones and Functional Ovarian Reserve: Systemic vs. Peripheral Dysfunctions

Thyroid hormones (THs) exert pleiotropic effects in different mammalian organs, including gonads. Genetic and non-genetic factors, such as ageing and environmental stressors (e.g., low-iodine intake, exposure to endocrine disruptors, etc.), can alter T4/T3 synthesis by the thyroid. In any case, peripheral T3, controlled by tissue-specific enzymes (deiodinases), receptors and transporters, ensures organ homeostasis. Conflicting reports suggest that both hypothyroidism and hyperthyroidism, assessed by mean of circulating T4, T3 and Thyroid-Stimulating Hormone (TSH), could affect the functionality of the ovarian reserve determining infertility. The relationship between ovarian T3 level and functional ovarian reserve (FOR) is poorly understood despite that the modifications of local T3 metabolism and signalling have been associated with dysfunctions of several organs. Here, we will summarize the current knowledge on the role of TH signalling and its crosstalk with other pathways in controlling the physiological and premature ovarian ageing and, finally, in preserving FOR. We will consider separately the reports describing the effects of circulating and local THs on the ovarian health to elucidate their role in ovarian dysfunctions.

An explanation of the mechanisms underlying fragile X-associated premature ovarian insufficiency

Fragile X and fragile X-associated tremor-ataxia syndrome (FXTAS) are caused by mutations of the FMR1 gene. The mutations causing FXTAS can expand in a generation to a "full mutation" causing fragile X syndrome. The mutations causing FXTAS and the phenotype, fragile X-associated premature ovarian insufficiency (FXPOI), are referred to as the FMR1 premutation (PM). The objective of this paper was to formulate a theory to explain the Mechanism for FXPOI.Recent research on fragile X syndrome and FXTAS has led to sophisticated theories about the mechanisms underlying these diseases. It has been proposed that similar mechanisms underlie FXPOI. Utilizing recent research on FXTAS, but a more detailed application of ovarian physiology, we present a more ovarian specific theory as to the primary mechanism explaining the development of FXPOI.The FXPOI phenotype may best be viewed as derivative of the observation that fragile X PM carriers experience menopause an average of 5 years earlier than non-carriers. Women carrying the PM experience an earlier menopause because of an accelerated activation of their primordial follicle pool. This acceleration of primordial follicle activation occurs, in part, because of diminished AMH production. AMH production is diminished because of accelerated atresia of early antral follicles. This accelerated atresia likely occurs because the fragile X PM leads to a slowing of the rate of granulosa cell mitosis in some follicles.

Assessing the practice of LuPOR for poor responders: a prospective study evaluating follicular fluid cfDNA levels during natural IVF cycles

PURPOSE

The aim of this study is to provide data on the practice of Luteal Phase Oocyte Retrieval (LuPOR). The authors assess cell-free DNA levels in follicular fluid (ff cfDNA) from poor responders undergoing natural cycles, and comparing it to respective data originating from follicular phase oocyte retrievals.

METHODS

Forty-seven women were eligible for this prospective study. Participants were classified as poor responders based on Bologna criteria while being detected with a second follicular wave. Follicular fluid was collected and prepared for cfDNA extraction. Levels of cfDNA were quantified via Q-PCR employing the ALU115 and ALU247 primers. These primers are associated with apoptotic and necrotic events. Levels of ff cfDNA resulting from follicular phase oocyte retrieval (FoPOR) and LuPOR-performed in a single menstrual cycle were associated with the number and maturation status of yielded oocytes and the number and fertilization status of resulting zygotes. Survival rate following thawing of cryopreserved zygotes, along with the resulting number of cleavage stage and blastocyst stage embryos are provided.

RESULTS

Mean levels of ALU115 were significantly lower during FoPOR when compared to LuPOR (0.79 ± 0.72 vs 1.46 ± 1.59 ng/μl, p = 0.02). Regarding the FoPOR group, a significant positive correlation of serum estradiol and ALU115 concentration (p = 0.04) was revealed. A significant negative correlation between serum estradiol and cfDNA integrity was observed both during FoPOR (p = 0.03) and LuPOR (p = 0.03). A significant lower number of retrieved (1.09 ± 0.28 vs 1.29 ± 0.58, p = 0.02) and MII oocytes (0.77 ± 0.55 vs 1.08 ± 0.61, p = 0.02) was observed when comparing the FoPOR to LuPOR groups respectively. The integrity of cfDNA was observed to be higher in FoPOR originating embryos that arrested either prior to cleavage (0.28 ± 0.13 vs 0.17 ± 0.10, p = 0.006) or prior to blastocyst formation (0.28 ± 0.12 vs 0.13 ± 0.06, p = 0.04). In the case of LuPOR originating embryos, cfDNA integrity was observed to be higher in embryos that arrested only prior to the blastocyst stage (0.27 ± 0.20 vs 0.11 ± 0.07, p = 0.008). Similarly, cfDNA integrity was observed to be lower in top quality blastocysts originating from FoPOR (0.07 ± 0.04 vs 0.17 ± 0.05, p = 0.03) and in top quality cleavage stage embryos (0.09 ± 0.06 vs 0.31 ± 0.22, p = 0.01) and blastocysts (0.06 ± 0.02 vs 0.14 ± 0.06, p = 0.02) originating from LuPOR.

CONCLUSIONS

Our results indicate that ff originating from LuPOR presents with higher levels of cfDNA. The higher cfDNA levels are attributed to mainly apoptotic events, as the ALU247 levels and DNA integrity did not differ statistically significantly between FoPOR and LuPOR. The absolute mean level of ALU247 corresponding to necrotic events was higher in LuPOR. Regarding embryological data, cfDNA integrity was correlated with both number and quality of cleavage stage embryos in both FoPOR and LuPOR, along with blastocyst stage embryos in LuPOR. Necrotic events were associated with poorer blastocyst formation rate and blastocyst quality in LuPOR. As the comparison between FoPOR and LuPOR results to similar IVF laboratory data, the practice of LuPOR may stand as a promising approach for poor responders, while it merits further investigation.

Cytotoxicity and DNA Damage Caused from Diazinon Exposure by Inhibiting the PI3K-AKT Pathway in Porcine Ovarian Granulosa Cells

Organophosphorus insecticide diazinon (DZN) is diffusely used in agriculture, home gardening, and crop peats. Much work so far has focused on the link between DZN exposure and the occurrence of neurological diseases, while little is known on the reproductive toxicological assessment on DZN exposure. This research aimed to investigate the underlying mechanisms of toxic hazards for DZN exposure on cultured porcine ovarian granulosa cells. We analyzed the oxidative stress, energy metabolism, DNA damage, apoptosis, and autophagy by using high-throughput RNA-seq, immunofluorescence, Western blotting, and real-time PCR. The combined data demonstrated that DZN exposure could cause excessive ROS and DNA damage, which induced apoptosis and autophagy by inhibiting the PI3K-AKT pathway. The down-regulated CYP19A1 protein and granulosa cell deaths increase the risk for developing premature ovarian failure and follicular atresia. In conclusion, DZN exposure has obvious reproductive toxicity by induction of granulosa cell death through pathways connected to DNA damage and oxidative stress by inhibiting the PI3K-AKT pathway.

The Role of microRNAs in Ovarian Granulosa Cells in Health and Disease

The granulosa cell (GC) is a critical somatic component of the ovary. It is essential for follicle development by supporting the developing oocyte, proliferating and producing sex steroids and disparate growth factors. Knowledge of the GC's function in normal ovarian development and function, and reproductive disorders, such as polycystic ovary syndrome (PCOS) and premature ovarian failure (POF), is largely acquired through clinical studies and preclinical animal models. Recently, microRNAs have been recognized to play important regulatory roles in GC pathophysiology. Here, we examine the recent findings on the role of miRNAs in the GC, including four related signaling pathways (Transforming growth factor-β pathway, Follicle-stimulating hormones pathway, hormone-related miRNAs, Apoptosis-related pathways) and relevant diseases. Therefore, miRNAs appear to be important regulators of GC function in both physiological and pathological conditions. We suggest that targeting specific microRNAs is a potential therapeutic option for treating ovary-related diseases, such as PCOS, POF, and GCT.

Mathematical model to study the aging of the human follicle according to the telomerase activity

The aim of this work is to study the aging rate at which human follicles reach the preovulatory state. To this end, both telomere length and telomerase activity effects on granulosa cells (GCs) aging has been studied. GCs are somatic cells which determine the development of the oocyte. A human preantral follicle takes approximately 85 days to achieve the preovulatory size, going through several stages (Gougeon, 1996). The telomere length of GCs of each class of follicles, during folliculogenesis, are modelled using a chemical master equation formalism similar to the one in Wesch et al. (2016). Seven differential ordinary systems of equations, corresponding to seven stages of the follicule maturation, concatenated in time, are considered. The mitotic and death rates are approximated by using the mean number of GCs in each class of follicles and the time they remain on each stage. The influence of different telomerase activity rates and the telomere shortening of the preovulatory follicle is studied. Some cases of infertility are associated with low levels of telomerase activity and short telomeres in GCs. The method aims at understanding how low levels of telomerase activity in preovulatory stages lead to the accumulation of aged GCs. In the case of higher telomerase activities, the mathematical model predicts a more juvenile outcome in preovulatory follicles. Juvenile GCs, could be critical for embryo development if the oocyte were fertilized, since GCs, transformed in corpus luteum, must divide and increase their size (Alila and Hansel, 1984) to sustain early pregnancy (Csapo et al., 1972).

Ovarian ageing and the impact on female fertility

Female fertility decreases with increasing age, a reflection of declining oocyte quantity and quality. The menopausal transition occurs when the oocyte quantity falls below a threshold level. The pattern of follicular depletion as well as the factors, timing and mechanisms surrounding both declining oocyte number and oocyte quality remain incompletely understood. Further studies are needed to examine the factors involved and develop predictive models and biomarkers to assist in the management of age-related subfertility. This review summarises the current knowledge addressing the ageing ovary and its impact on fertility.