Activity of MPF and expression of its related genes in mouse MI oocytes exposed to cadmium

Fertility loss: negative effects of environmental toxicants on oogenesis

There has been a global decline in fertility rates, with ovulatory disorders emerging as the leading cause, contributing to a global lifetime infertility prevalence of 17.5%. Formation of the primordial follicle pool during early and further development of oocytes after puberty is crucial in determining female fertility and reproductive quality. However, the increasing exposure to environmental toxins (through occupational exposure and ubiquitous chemicals) in daily life is a growing concern; these toxins have been identified as significant risk factors for oogenesis in women. In light of this concern, this review aims to enhance our understanding of female reproductive system diseases and their implications. Specifically, we summarized and categorized the environmental toxins that can affect oogenesis. Here, we provide an overview of oogenesis, highlighting specific stages that may be susceptible to the influence of environmental toxins. Furthermore, we discuss the genetic and molecular mechanisms by which various environmental toxins, including metals, cigarette smoke, and agricultural and industrial toxins, affect female oogenesis. Raising awareness about the potential risks associated with toxin exposure is crucial. However, further research is needed to fully comprehend the mechanisms underlying these effects, including the identification of biomarkers to assess exposure levels and predict reproductive outcomes. By providing a comprehensive overview, this review aims to contribute to a better understanding of the impact of environmental toxins on female oogenesis and guide future research in this field.

Paternal genetic intergenerational and transgenerational effects of cadmium exposure on hormone synthesis disorders in progeny ovarian granulosa cells

To investigate the paternal genetic effects of cadmium (Cd) exposure on hormone synthesis disorders in the ovarian granulosa cells (GCs) of offspring. Here, male Sprague‒Dawley (SD) rats were gavaged with CdCl₂ (0, 0.5, 2, 8 mg/kg) from postnatal day (PND) 28-56, followed by mating with newly purchased healthy adult females to produce F1, and F1 adult males (PND 56) were mated with newly purchased healthy adult females to produce F2. The serum levels of estradiol (E₂) and progesterone (Pg) decreased in F1 but essentially returned to normal in F2. The levels of StAR, CYP11A1, CYP17A1, CYP19A1, and SF-1 showed different alterations in F1 and F2 ovarian GCs. The expression patterns of miRNAs and imprinted genes related to hormone synthesis in GCs of F1 and F2 differed, but methylation of hormone synthesis-related genes was not significantly altered (except for individual loci in F1). In addition, there were significant changes in the expression of imprinted genes and miRNAs in F0 and F1 sperm. We conclude that paternal Cd exposure causes intergenerational genetic effects (hormone synthesis disorders) and transgenerational effects (reparative changes in hormone synthesis function) in ovarian GCs. These genetic effects were related to the downregulation of StAR in F1 and the upregulation of CYP17A1, CYP19A1, StAR and SF-1 in F2. Important changes in miRNAs and imprinted genes were also observed, but not all alterations originated from paternal inheritance.

Melatonin protects oocytes from cadmium exposure-induced meiosis defects by changing epigenetic modification and enhancing mitochondrial morphology in the mouse

Cadmium (Cd) is one major environmental pollutant that can cause detrimental impacts on human as well as animal reproductive systems as a result of oxidative stress. It is widely acknowledged that melatonin secreted principally by the pineal gland is not only a natural potent antioxidant but also a free radical scavenger, whereas concerning how to alleviate the toxic effects of Cd on oocyte maturation remains elusive. In this investigation, it was the first time to explore the protective effects and potential mechanism of melatonin on meiotic maturation of mouse oocytes exposed to Cd in vitro medium. We found that Cd exerts adverse effects on meiotic maturation progression by disrupting the normal function of mitochondrion combined with the aberrant mitochondrial distribution and decreased membrane potential and altering epigenetic modification, including H3K9me2 and H3K4me2. Additionally, it was observed that Cd exposure disrupted the morphology of spindle organization and caused chromosome misalignment, which might be through changing the level of acetylated tubulin, whereas melatonin administration alleviated the toxic impacts of Cd on oocytes. Furthermore, the mitochondrial morphology-related genes mRNA expression and protein expression of autophagy-related genes was also investigated. The results suggested that melatonin supplementation significantly altered the mRNA expression of mitochondrial dynamics-related genes, rather than the expression of mitophagy-related proteins. Taken together, our results validated that melatonin administration has a certain protective impact against oocytes meiosis maturation defects induced by cadmium through changing epigenetic modification and enhancing mitochondrial morphology rather than mitophagy.

The environment and female reproduction: Potential mechanism of cadmium poisoning to the growth and development of ovarian follicle

Cadmium (Cd) is ubiquitous in our environment and can easily bioaccumulate into the organism after passage through the respiratory and digestive tracts. Long-term exposure to Cd can result in the significant bioaccumulation in organism because of its long biological high-life (10-30 years), which exerts irreversible damages on the health of animals and humans. Although there are increased evidence of impeding the normal function of female reproduction resulted from Cd exposure, the mechanism of the negative action of Cd on the growth and development of ovarian follicle remains enigmatic. Thus, the purpose of the presented study is to summarize available literature which describing Cd-related toxicity involved in the adverse effects on the growth and development of the ovarian follicle. In conclusion, it is suggested that Cd causes damage to the folliculogenesis of mammalians, which results in the decline in the number and quality of ovulated oocytes and the failure in the fertilization. The mechanism behinds that may be linked to the interference to the production of reproductive hormones and the augment of reactive oxygen species (ROS). Furthermore, the enhanced ROS, in turn, impairs various molecules including proteins, lipids and DNA, as well as the balance of the antioxidant defense system, mitochondrial homeostasis, endoplasmic reticulum, autophagy and epigenetic modification. This review is expected to elaborate the toxic mechanism of Cd exposure to the growth and development of ovarian follicles and provide essential remediation strategies to alleviate the damage of Cd to female reproductive health.

Ribonucleic Acid Export 1 Is a Kinetochore-Associated Protein That Participates in Chromosome Alignment in Mouse Oocytes

Ribonucleic acid export 1 (Rae1) is an important nucleoporin that participates in mRNA export during the interphase of higher eukaryotes and regulates the mitotic cell cycle. In this study, small RNA interference technology was used to knockdown Rae1, and immunofluorescence, immunoblotting, and chromosome spreading were used to study the role of Rae1 in mouse oocyte meiotic maturation. We found that Rae1 is a crucial regulator of meiotic maturation of mouse oocytes. After the resumption of meiosis (GVBD), Rae1 was concentrated on the kinetochore structure. The knockdown of Rae1 by a specific siRNA inhibited GVBD progression at 2 h, finally leading to a decreased 14 h polar body extrusion (PBE) rate. However, a comparable 14 h PBE rate was found in the control, and the Rae1 knockdown groups that had already undergone GVBD. Furthermore, we found elevated PBE after 9.5 h in the Rae1 knockdown oocytes. Further analysis revealed that Rae1 depletion significantly decreased the protein level of securin. In addition, we detected weakened kinetochore–microtubule (K-MT) attachments, misaligned chromosomes, and an increased incidence of aneuploidy in the Rae1 knockdown oocytes. Collectively, we propose that Rae1 modulates securin protein levels, which contribute to chromosome alignment, K-MT attachments, and aneuploidy in meiosis.

The role of miRNAs in regulating the effect of prenatal cadmium exposure on ovarian granulosa cells in a transgenerational manner in female rats

Cadmium (Cd) is known to affect ovarian granulosa cells (GCs), but no information on the transgenerational effects of Cd on GCs. In this study, pregnant Sprague-Dawley (SD) rats were orally dosed with Cd from gestation day 1 until birth. F1 or F2 female rats were mated with untreated males to produce the F2 or F3 generation. In the F1 generation, apoptotic cell bodies were observed in the Cd-treated group but not in the F2 generation. Moreover, significant changes in B-cell lymphoma 2 (Bcl2) expression were observed in both generations. Additionally, the expression of microRNAs (miRNAs) was significantly changed based on microarray analysis. Specifically, miR-16-5p and miR-181b-5p were upregulated in F1 and F2 rats, while miR-92a-2-5p demonstrated different expression patterns between the two generations. In F3 generation, miR-16-5p and miR-92a-2-5p were down-regulated. Further, another experiment was used to show that miR-16-5p and miR-92a-2-5p regulated the Bcl2-induced apoptotic effect of Cd on GCs by the Human ovarian GC tumor line (COV434 cell line) miRNA-knockdown model Overall, the results indicate that prenatal Cd exposure has epigenetic transgenerational effect on GCs, Moreover, the underlying mechanism may involve interference with miR-16-5p and miR-92a-2-5p-mediated regulation of Bcl2 genes in offspring.

2,5-Hexanedione influences primordial follicular development in cultured neonatal mouse ovaries by interfering with the PI3K signaling pathway via miR-214-3p

The mechanisms by which 2,5-hexanedione (2,5-HD) exposure adversely affects reproduction are unclear. In the present study, whole neonatal mouse ovaries were exposed to 2,5-HD in vitro and then assessed for progesterone levels to determine the effects of this compound on ovary function. Ovarian histomorphological analyses were performed to assess the effects of 2,5-HD on follicular development, and PI3K signaling pathway was evaluated to elucidate the molecular mechanisms of 2,5-HD-mediated toxicity on follicular development. The results showed that after ovarian exposure to 2,5-HD in vitro, the percentage of secondary follicles decreased, while the progesterone levels and the percentage of unhealthy follicles increased, with oocytes identified as the target of damage. The 2,5-HD treatment significantly decreased the of the gene encoding the apoptosis-related protein caspase-8, and PI3K/AKT/FOXO3 pathway signaling was also altered. Furthermore, the effects of 2,5-HD on the gene expression of the PI3K/AKT/FOXO3 and follicular development were blocked by 740Y-P (a PI3K activator), miR-214-3p was abnormally expressed, and luciferase reporter assay results demonstrated that the 3' untranslated region of PI3K was a direct target of miR-214-3p. Overall, the results of the present study indicate that 2,5-HD exposure inhibits follicular development, and the underlying mechanism may involve interference with miR-214-3p-mediated regulation of the PI3K signaling pathway.

Elevation of MPF and MAPK gene expression, GSH content and mitochondrial distribution quality induced by melatonin promotes porcine oocyte maturation and development in vitro

The MPF and MAPK genes play crucial roles during oocyte maturation processes. However, the pattern of MPF and MAPK gene expression induced by melatonin (MT) and its correlation to oocyte maturation quality during the process of porcine oocyte maturation in vitro remains unexplored. To unravel it, in this study, we cultured the porcine oocytes in maturation medium supplemented with 0, 10⁻⁶, 10⁻⁹, and 10⁻¹² mol/L melatonin. Later, we analyzed the MPF and MAPK gene expression levels by RT-PCR and determined the maturation index (survival and maturation rate of oocytes). The GSH content in the single oocyte, and cytoplasmic mitochondrial maturation distribution after porcine oocyte maturation in vitro was also evaluated. We also assessed the effects of these changes on parthenogenetic embryonic developmental potential. The oocytes cultured with 10⁻⁹mol/L melatonin concentration showed higher oocyte maturation rate, and MPF and MAPK genes expression levels along with better mitochondrial distribution than the 0, 10⁻⁶, and 10⁻¹² mol/L melatonin concentrations (p < 0.05). No significant difference was observed in the survival rates when the oocytes were cultured with different melatonin concentrations. The expression of the MPF gene in the oocytes cultured with 10⁻⁶ mol/L melatonin was higher than with 10⁻¹² and 0 mol/L melatonin, and the expression of the MAPK gene in 10⁻⁶ and 10⁻¹² group was higher than the control (p < 0.05). As far as the embryonic developmental potential is concerned, the cleavage and blastocyst rate of oocytes cultured with 10⁻⁶ and 10⁻⁹ mol/L melatonin was significantly higher than the 10⁻¹² mol/L melatonin and control. In conclusion, 10⁻⁹–10⁻⁶ mol/L melatonin significantly induced the MPF and MAPK gene expression; besides, it could also be correlated with GSH content of single oocyte, mitochondrial maturation distribution, and the first polar body expulsion. These changes were also found to be associated with parthenogenetic embryo developmental potential in vitro.

Cadmium exposure during prenatal development causes progesterone disruptors in multiple generations via steroidogenic enzymes in rat ovarian granulosa cells

Exposure to the heavy metal cadmium (Cd) in the environment is linked to adverse health. To fully understand the adverse effects of this important endocrine-disrupting compound (EDC) requires studies that address multigenerational effects and epigenetic mechanisms. The present study orally dosed pregnant SD rats with Cd from gestation day 1 until birth. First filial generation (F1) female rats were mated with untreated males to generate the secondary filial generation (F2). Ovarian granulosa cells (OGCs) were collected at postnatal day (PND) 56 from both generations after prenatal Cd exposure, and hormone secretion examinations showed a progesterone disorder. Significant decreases in steroidogenic enzymes (steroidogenic acute regulatory protein (StAR) and P450 cholesterol side-chain cleavage enzyme (CYP11A1)) were observed in F1 and F2 rats. However, F1 and F2 rats had different patterns of mRNA and protein expression of steroidogenic factor 1 (SF-1). We also found that microRNAs were significantly changed using a microarray, and miR-10b-5p and miR-27a-3p were upregulated in F1 and F2 rats. The COV434 cell line microRNA-knockdown model showed that these two important microRNAs regulated the StAR-induced Cd effect on progesterone secretion. Overall, the results of this study indicate that prenatal Cd exposure causes cytotoxicity problems, progesterone disorder and microRNAs expression changed in a multigenerational manner. And progesterone disorder may interfere with the steroidogenic enzymes in offspring. The present study also revealed that environmental pollution produces multigenerational effects.

Cadmium induces ovarian granulosa cell damage by activating PERK-eIF2α-ATF4 through endoplasmic reticulum stress

This study aimed to investigate whether cadmium induces ovarian granulosa cell damage by activating protein kinase R-like endoplasmic reticulum kinase (PERK)-eIF2α-ATF4 through endoplasmic reticulum (ER) stress and to elucidate the underlying regulation mechanism. Two models of cadmium exposure were established. In one model, ovarian granulosa cells isolated from 21-day-old female Sprague Dawley rats were cultured in vitro for 36 h and exposed to CdCl2 (0, 5, 10, and 20 μM), and in another model, a human ovarian granulosa tumor cell line (COV434) was used to construct the binding immunoglobulin protein (BIP)-knockdown cell line sh-BIP and exposed to 0 and 20 μM CdCl2. After exposure to cadmium for 12 h, the expression mRNA and protein levels of BIP, p-PERK, and p-eIF2α were determined in the two models. miRNAs related to BIP were also detected in granulosa cells after cadmium exposure. We found that mRNA and protein levels of all factors were upregulated in each cadmium-dose group, except for BIP mRNA expression in the 5 μM Cd group. The BIP gene was knocked down in COV434 cells before exposure to cadmium. All factors were upregulated in COV434 cells exposed to Cd, and the expression of the p-eIF2α protein was downregulated in sh-BIP cells exposed to Cd. In addition, no differences in BIP-related miRNAs were detected in cadmium-exposed rat ovarian granulosa cells versus the control group. Cadmium induces ovarian granulosa cell damage by inducing ER stress.

Cadmium overload modulates piroxicam-regulated oxidative damage and apoptotic pathways

Cadmium (Cd) is a common environmental pollutant that threatens humans' and animals' health. Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used drugs due to their wide therapeutic action; however, they have significant side effects. Since, under many circumstances, humans and animals may be co-exposed to Cd and NSAIDs, the current investigation was assigned to explore the intertwining relationship between Cd and NSAIDs. Four groups of male Wister rats were used: control group: rats received saline; Cd group: rats received cadmium (Cd, 2 mg/kg) orally; Px group: rats received a NSAID (piroxicam, Px, 7 mg/kg, i.p.); and Cd+Px group: rats received both Cd+Px. All treatments were given once a day for 28 consecutive days. Then, blood samples, stomach, liver, and kidney tissues were collected. The results indicated that Px provoked gastric ulcer indicated by high ulcer index, while Cd had no effect on the gastric mucosa. In addition, treatment with Cd or Px alone significantly induced liver and kidney injuries indicated by serum elevations of AST, ALT, ALP, ALB, total protein, creatinine, and urea along with histopathological alterations. Significant increases in malondialdehyde and reduction in GSH and CAT contents were reported along with up-regulated expression of Bax and Bcl-2 after Cd or Px exposure. However, when Cd and Px were given in a combination, Cd obviously potentiated the Px-inflicted cellular injury and death in the liver and kidney but not in the stomach when compared to their individual exposure. This study concluded that oxidative stress mechanisms were supposed to be the main modulator in promoting Cd and Px toxicities when given in combination.

Nucleus, Cytoskeleton, and Mitogen-Activated Protein Kinase p38 Dynamics during In Vitro Maturation of Porcine Oocytes

The mitogen-activated kinase (MAPK) p38, a member of the MAPK subfamily, is conserved in all mammalian cells and plays important roles in response to various physiologic cues, including mitogens and heat shock. In the present study, MAPK p38 protein expression in porcine oocytes was analyzed during in vitro maturation (IVM) by Western blotting and immunocytochemistry. The levels of p-p38 or activated p38 and p38 expression were at the lowest in the germinal vesicle (GV) stage oocyte, gradually rising at the germinal vesicle breakdown (GVBD) and then reaching a plateau throughout the IVM culture (p < 0.05). Similarly, the expression level of total p38 was also lower in the GV oocyte than in the oocyte of other meiotic stages and uprising after GVBD and remained high until the metaphase III (MII) stage (p < 0.05). In the GV stage, phosphorylated p38 (p-p38) was initially detectable in the ooplasm and subsequently became clear around the nucleus and localized in the ooplasm at GVBD (18 h post-culture). During the metaphase I (MI) and metaphase II (MII) stages, p-p38 was evenly distributed throughout the ooplasm after IVM for 30 or 42 h. We found that the subcellular localization increased in p-p38 expression throughout oocyte maturation (p < 0.05) and that dynamic reorganization of the cytoskeleton, including microfilaments and microtubules, was progressively changed during the course of meiotic maturation which was likely to be associated with the activation or networking of p38 with other proteins in supporting oocyte development. In conclusion, the alteration of p38 activation is essential for the regulation of porcine oocyte maturation, accompanied by the progressive reorganization and redistribution of the cytoskeleton and MAPK p38, respectively, in the ooplasm.