Apoptosis, reactive oxygen species and follicular anti-Müllerian hormone in natural versus stimulated cycles

Age-related changes in Folliculogenesis and potential modifiers to improve fertility outcomes - A narrative review

Reproductive aging is characterized by a decline in oocyte quantity and quality, which is directly associated with a decline in reproductive potential, as well as poorer reproductive success and obstetrical outcomes. As women delay childbearing, understanding the mechanisms of ovarian aging and follicular depletion have become increasingly more relevant. Age-related meiotic errors in oocytes are well established. In addition, it is also important to understand how intraovarian regulators change with aging and how certain treatments can mitigate the impact of aging. Individual studies have demonstrated that reproductive pathways involving antimullerian hormone (AMH), vascular endothelial growth factor (VEGF), neurotropins, insulin-like growth factor 1 (IGF1), and mitochondrial function are pivotal for healthy oocyte and cumulus cell development and are altered with increasing age. We provide a comprehensive review of these individual studies and explain how these factors change in oocytes, cumulus cells, and follicular fluid. We also summarize how modifiers of folliculogenesis, such as vitamin D, coenzyme Q, and dehydroepiandrosterone (DHEA) may be used to potentially overcome age-related changes and enhance fertility outcomes of aged follicles, as evidenced by human and rodent studies.

Peroxiredoxin 4, a new favorable regulator, can protect oocytes against oxidative stress damage during in vitro maturation

BACKGROUND

Finding an effective regulator to avoid harmful effects caused by excessive reactive oxygen species (ROS) is a bottleneck during oocyte in vitro maturation (IVM). Previously, we found that peroxiredoxin 4 (Prdx4) expression is significantly higher in mature cumulus cell-oocyte complexes (COCs) than in immature COCs. Prdx4 belongs to the antioxidant enzyme family and can catalyze the reduction of H₂O₂.

RESULTS

In this study, we established an oxidative stress model with mouse COCs cultured in vitro. Treatment with H₂O₂ decreased cumulus expansion indexes and oocyte maturation in a concentration-dependent manner, indicating follicular development dysplasia. Infection with a Prdx4-overexpressing adenovirus significantly attenuated H₂O₂-induced changes, exhibiting effects similar to those of the intracellular ROS scavenger tiron (the positive control). Furthermore, the results confirmed that the protective effect of Prdx4 on oocyte maturation may be due to reductions in ROS levels and apoptosis. However, when the gap junctions between cumulus cells (CCs) and oocytes were destroyed, Prdx4 overexpression did not exert antiapoptotic effects. The expression levels of the gap junction marker protein CX43 were significantly recovered in the Prdx4-overexpressing group.

CONCLUSIONS

These results demonstrate that Prdx4 in CCs may be a new favorable regulator that improves in vitro-matured oocyte quality and enhances oocyte developmental competence by preventing CC apoptosis caused by oxidative stress through gap junctions. The findings expand the body of knowledge regarding follicle development, and the identification of Prdx4 as a new favorable regulator will aid in immature oocyte IVM.

Empty Zona Pellucida Only Case: A Critical Review of the Literature

The presence of empty zona pellucida (EZP) in oocytes following oocyte retrieval (OR) during an in vitro fertilization (IVF) cycle presents a major clinical and laboratory challenge in assisted reproduction. It has been attributed to several factors such as the ovarian stimulation protocol employed, the damaging of the follicles during oocyte retrieval (OR) mainly through the high aspiration pressure, during the denudation technique, and the degeneration of oolemma within the zona pellucida (ZP) through apoptosis. The role of ZP is pivotal from the early stages of follicular development up to the preimplantation embryo development and embryo hatching. Polymorphisms or alterations on the genes that encode ZP proteins may contribute to EZP. We present a critical review of the published literature hitherto on EZP and available options when encountered with the phenomenon of EZP. Concerning the former, we found that there is rare data on this phenomenon that merits documentation. The latter includes technical, genetic, and pathophysiological perspectives, along with specific treatment options. In conclusion, we identify the lack of a definitive management proposal for couples presenting with this phenomenon, we underline the need for an algorithm, and indicate the questions raised that point towards our goal for a strategy when addressing a previous finding of EZP.

Observation of Parthanatos Involvement in Diminished Ovarian Reserve Patients and Melatonin's Protective Function Through Inhibiting ADP-Ribose (PAR) Expression and Preventing AIF Translocation into the Nucleus

Diminished ovarian reserve (DOR) is characterized by the depletion of the ovarian pool, which leads to reductions in oocyte quality and quantity. Studies have suggested that ovarian reserve or ovarian aging is tightly related to apoptosis. However, the cell death mechanism is not comprehensively understood. Parthanatos, a type of poly [ADP-ribose] polymerase 1(PARP1)-dependent and apoptosis-inducing factor (AIF)-mediated cell death, plays a crucial role in various disorders. In the present study, we aimed to investigate whether parthanatos is involved in the pathogenesis of DOR. We recruited 40 patients (20 DOR patients and 20 normal ovarian reserve (NOR) patients) and examined PAR expression and AIF translocation in their isolated cumulus GCs (granulosa cells) by fluorescence microscopy. Our results demonstrated that PAR expression and AIF nuclear translocation were significantly higher in cumulus GCs of DOR patients, suggesting that PARP1-dependent cell death may be associated with DOR pathophysiology. Moreover, we tested the protective function of melatonin on hydrogen peroxide (H₂O₂)-induced parthanatos in human ovarian cancer (IGROV1) cells. Our results demonstrated that H₂O₂ treatment of IGROV1 cells led to excessive protein PARylation and AIF translocation into the nuclei. Melatonin effectively inhibits PARylation, blocks translocation of AIF into the nucleus, and consequently decreases the risk of parthanatos in cumulus GCs.

Ochratoxin A Exposure Impairs Porcine Granulosa Cell Growth via the PI3K/AKT Signaling Pathway

The mycotoxin ochratoxin A (OTA), a naturally occurring food contaminant, has a toxic effect on the growth and development of follicles in pigs. However, little is known regarding the specific toxic effects of OTA exposure on oocytes and granulosa cells (GCs). In this study, we cultured porcine ovarian GCs and exposed them to OTA in vitro in order to explore the mechanism causing the negative effects. Initially, it was found that OTA exposure inhibited cell viability in a time and dose dependent manner. We also showed that OTA exposure increased oxidative stress, decreased proliferation ratio, and increased apoptosis ratio in GCs. We revealed an important role for the PI3K/AKT signal pathway in GC proliferation and apoptosis by RNA-seq analysis. The results not only showed that OTA treatment significantly affected the expression of genes within the PI3K/AKT pathway but also demonstrated a concrete relationship between the PI3K/AKT pathway and GC cell proliferation and apoptosis. In conclusion, the results demonstrated that OTA exposure impaired porcine GC growth via the PI3K/AKT signaling pathway.

Effects of ovarian hyperstimulation on mitochondria in oocytes and early embryos

A mouse model was used to compare the number and function of mitochondria in oocytes and embryos obtained by superovulation and in a natural cycle (control group). The superovulation group had a higher number of total oocytes, MII oocytes, embryos with two pronuclei, 2-cell embryos and blastocysts than the control group (P<0.05 for all). The superovulation group had high proportion of MII oocytes with low number of mitochondrial (mt) DNA copies. The average number of mtDNA copies, ATP level and mitochondrial membrane potential ( Collapse

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Is AMH a regulator of follicular atresia?

We discuss the hypothesis that AMH is an intraovarian regulator that inhibits follicular atresia within the human ovary. Several indirect lines of evidence derived from clinical and basic science studies in a variety of different patient populations and model systems collectively support this hypothesis. Evidence presented herein include 1) timing of onset of menopause in women with polycystic ovary syndrome, 2) site of cellular origin and timing of AMH production, 3) AMH's influence on other critical growth factors and enzymes involved in folliculogenesis, and 4) AMH's inhibition of granulosa apoptosis. If this hypothesis is true, it may provide insight for treatment strategies for prevention and treatment of premature ovarian insufficiency, slowing natural ovarian aging, and/or delaying eventual ovarian failure. Such findings may lead to the development of 1) AMH agonists for retarding the onset of menopause and/or as a chemoprotectant prior to cancer therapy and 2) AMH antagonists for the treatment of PCOS.

3,4-Dihydroxybenzaldehyde Derived from Prunus mume Seed Inhibits Oxidative Stress and Enhances Estradiol Secretion in Human Ovarian Granulosa Tumor Cells

Granulosa cells form ovarian follicles and play important roles in the growth and maturation of oocytes. The protection of granulosa cells from cellular injury caused by oxidative stress is an effective therapy for female infertility. We here investigated an effective bioactive compound derived from Prunus mume seed extract that protects granulosa cells from hydrogen peroxide (H2O2)-induced apoptosis. We detected the bioactive compound, 3,4-dihydroxybenzaldehyde (3,4-DHBA), via bioactivity-guided isolation and found that it inhibited the H2O2-induced apoptosis of granulosa cells. We also showed that 3,4-DHBA promoted estradiol secretion in granulosa cells and enhanced the mRNA expression levels of steroidogenic factor 1, a promoter of key steroidogenic enzymes. These results suggest that P. mume seed extract may have clinical potential for the prevention and treatment of female infertility.

Elevated blood plasma antioxidant status is favourable for achieving IVF/ICSI pregnancy

The aim of the study was to determine the roles of intrafollicular and systemic oxidative stress and antioxidant response in ovarian stimulation and intracytoplasmic sperm injection (ICSI) outcomes. For this purpose, 102 ICSI patients undergoing controlled ovarian stimulation were enrolled and samples were collected on the day of follicle puncture. Total peroxide (TPX) concentrations and total antioxidant response (TAR) were measured in follicular fluid and blood plasma, and an oxidative stress index (OSI) was calculated based on these two parameters. Urinary concentrations of 8-iso-prostaglandin F2a (F2IsoP) were measured. Elevated intrafollicular oxidative stress was positively correlated with ovarian stimulation outcome: less FSH per retrieved oocyte was used, more oocytes were collected and higher serum oestradiol concentrations were measured in patients with higher follicular OSI. However, high urinary F2IsoP related to lower embryo quality and F2IsoP was also elevated in smoking patients. Patients with endometriosis had lower follicular antioxidant status. Most importantly, higher systemic blood TAR was significantly favourable for achieving clinical pregnancy (P=0.03). In conclusion, the findings suggest clear associations between oxidative stress, antioxidant status and several aspects of ovarian stimulation and IVF/ICSI outcome, including pregnancy rate. Several oxygen-dependent biochemical reactions produce reactive oxygen species as by-products that may eventually lead to oxidative stress, which is detrimental to cells and tissues. Total antioxidant status, on the other hand, comprises several agents that balance the excess of these reactive oxygen species and reduce potential damage to the body. The aim of the current work was to study this balance in 102 patients participating in an ICSI programme and to examine the degree to which total peroxide content and antioxidant status influence infertility and pregnancy outcome. During the study, several tests were performed to characterize oxidative stress levels in ovarian follicular fluid, blood plasma and urine. We found a significantly higher oxidative stress environment in the ovary when compared with blood plasma. This suggests a prominent role of oxidative stress in the ovaries of these patients. The elevated oxidative stress levels were correlated to a higher number of oocytes that could be obtained via the procedure and to a lower amount of FSH needed to mature the oocytes, suggesting that oxidative stress, to some degree, is favourable for hormone stimulation outcome. A high level of lipid peroxidation products in the urine, another marker of oxidative stress, was observed in smokers and this marker was elevated in patients with embryos that had lower developmental potential. A higher overall antioxidant status in blood plasma was advantageous for achieving pregnancy.

Sphingosine-1-phosphate inhibits H2O2-induced granulosa cell apoptosis via the PI3K/Akt signaling pathway

OBJECTIVE

To investigate the protective effect of sphingosine-1-phosphate (S1P) against H(2)O(2)-induced apoptosis in human granulosa cell cultures with freshly harvested granulosa cells.

DESIGN

Experimental study.

SETTING

Academic medical center for reproductive medicine.

PATIENT(S)

Cultures of primary granulosa cells isolated from women undergoing in vitro fertilization (IVF).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Cell apoptosis and Western blot analysis of signaling pathway proteins.

RESULT(S)

We found that S1P (1 and 10 mM) statistically significantly decreased granulosa cell apoptosis after H(2)O(2) treatment. The decreased cell apoptosis induced by S1P was abolished after treatment with VPC23019, an inhibitor of S1P1 and S1P3 receptors, W146, an inhibitor of S1P1 receptors, and CAY10444, an inhibitor of S1P3 receptors. A Western blot analysis revealed that the level of phospho-Akt increased and peaked at 10 minutes after 10 mM S1P exposure.

CONCLUSION(S)

Treatment with S1P can inhibit the apoptosis of granulosa cells in response to oxidative stress induced by H(2)O(2). The protective effect of S1P is mediated by activating the PI3K/Akt pathway, and the antiapoptotic effect of S1P is mainly mediated through the S1P1 and S1P3 receptor.

Increased female fertility in aquaporin 8-deficient mice

Aquaporin-8 (AQP8) is a water channel expressed extensively in male and female reproductive systems. But its physiological functions are largely unknown. In the present study, we first found significantly increased number of offspring delivered by AQP8(-/-) mothers compared with wild-type mothers in cross-mating experiments. Comparison of ovulation in the two genotypes demonstrated that AQP8(-/-) ovaries released more oocytes (9.5 ± 1.9 vs. 7.1 ± 2.1 in normal ovulation and 37.8 ± 6.7 vs. 27.9 ± 5.7 in superovulation). Histological analysis showed increased number of corpus luteums in mature AQP8(-/-) ovaries, suggesting increased maturation and ovulation of follicles. By RT-PCR, western blot and immunohistochemistry analyses, we determined the expression of AQP8 in mouse ovarian granulosa cells. Granulosa cells isolated from AQP8(-/-) mice showed 45% of decreased membrane water permeability than wild-type mice. As the atresia of ovarian follicles is primarily due to apoptosis of granulosa cells, we analyzed the apoptosis of isolated granulosa cells from wild-type and AQP8(-/-) mice. The results indicated significantly lower apoptosis rate in AQP8(-/-) granulosa cells (21.3 ± 3.6% vs. 32.6 ± 4.3% in AQP8(+/+) granulosa cells). Taken together, we conclude that AQP8 deficiency increases the number of mature follicles by reducing the apoptosis of granulosa cells, thus increasing the fertility of female mice. This discovery may offer new insight of improving female fertility by reducing granulosa cell apoptosis through AQP8 inhibition.

Peroxiredoxin 2 inhibits granulosa cell apoptosis during follicle atresia through the NFKB pathway in mice

Peroxiredoxin 2 (PRDX2) has been known to act as an antioxidant enzyme whose main function is H(2)O(2) reduction in cells. We aimed to study the expression patterns of PRDX2 in mouse ovaries and explore the function of this protein in apoptosis of granulosa cells (GCs). We found that the expression of the PRDX2 protein in atretic follicle GCs was markedly higher than in healthy follicle GCs. In vitro, the transfection of siRNA targeting the Prdx2 gene inhibited the proliferation and induced the apoptosis of primary cultured GCs. Furthermore, suppression of PRDX2 resulted in the augmentation of endogenous H(2)O(2), and the ability to eliminate the exogenous H(2)O(2) was attenuated. The expression of PRDX2 and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB), whose activity was inhibited by binding to IKB, increased in GCs treated with various concentrations of H(2)O(2) for 30 min. However, no significant change in cytoplasmic IKB expression was observed. At 2 h after treatment with H(2)O(2), nuclear NFKB expression level was reduced, cytoplasmic IKB expression was increased, and PRDX2 expression was unchanged. Silencing of the Prdx2 gene caused early changes in NFKB and IKB expression in the primary cultured GCs compared to that in control cells. Taken together, these data suggest that PRDX2 plays an important role in inhibiting apoptosis in GCs and that PRDX2 actions may be related to the expression of NFKB and IKB.