Glucose metabolism during in vitro maturation of mouse oocytes: An study using RNA interference

Pyruvate Regulates the Expression of DLAT to Promote Follicular Growth

Increasing evidence has suggested that dihydrolipoamide S-acetyltransferase (DLAT), a subunit of the pyruvate dehydrogenase complex, is crucial for pyruvate metabolism and the regulation of cell death. The excessive death of granulosa cells (GCs) hinders the progression of follicular growth. However, the relationship between DLAT and follicular growth is poorly understood. Here, we found that pyruvate significantly shortened the age of pubertal initiation in mice and promoted follicular growth by promoting the proliferation of GCs. In addition, pyruvate up-regulated the expression of DLAT and the high level of DLAT was observed in large follicles, which were associated with follicular growth. Mechanistically, DLAT increased the mRNA and protein levels of proliferation pathways such as PCNA and MCL1 to promote GC proliferation. Additionally, DLAT bound to CASP3 and CASP9 proteins to inhibit the apoptosis of GCs. Taken together, these results reveal a mechanism that pyruvate regulated DLAT to promote follicular growth, and DLAT represents a promising target that supports new strategies for improving the growth of follicles.

Transcriptomic landscape of cumulus cells from patients <38 years old with a history of poor ovarian response (POR) treated with platelet-rich plasma (PRP)

Intraovarian injection of autologous platelet-rich plasma (PRP) has recently been investigated as a potential treatment for patients with diminished ovarian reserve. In the current study, differential gene expression in cumulus cells obtained from patients treated with PRP was compared to controls. RNA sequencing libraries were constructed from the cumulus cells, and differential expression analysis was performed with a false discovery rate threshold of p-value ≤0.05 and Log2 fold change ≥0.584. RNA sequencing of cumulus cells revealed significant differences in gene expression when comparing those treated with PRP and resulted in a live birth (n = 5) to controls with live birth (n = 5), or to controls with failed implantation (n = 5). Similarly, when all samples treated with PRP (those that resulted in live birth or arrested embryos (n = 10)) were compared to all samples from controls (those that resulted in live birth, no pregnancy, or arrested embryos (n = 13)), gene expression was significantly different. Several pathways were consistently affected by PRP treatment through multiple comparisons, including carbohydrate metabolism, cell death and survival, cell growth and proliferation, and cell-to-cell signaling, all of which have been implicated in human causes of infertility.

Downregulation of glucose-energy metabolism via AMPK signaling pathway in granulosa cells of diminished ovarian reserve patients

Glucose metabolism plays a crucial role in the function of granulosa cells (GCs) and the development of follicles. In cases of diminished ovarian reserve (DOR), alterations in these processes can impact female fertility. This study aims to investigate changes in glucose-energy metabolism in GCs of young DOR patients aged 20 to 35 years and their correlation with the onset and progression of DOR. 72 DOR cases and 75 women with normal ovarian reserve (NOR) as controls were included based on the POSEIDON and Bologna criteria. Samples of GCs and follicular fluid (FF) were collected for a comprehensive analysis involving transcriptomics, metabolomics, RT-qPCR, JC-1 staining, and flow cytometry. The study identified differentially expressed genes and metabolites in GCs of DOR and NOR groups, revealing 7 common pathways related to glucose-energy metabolism, along with 11 downregulated genes and 14 metabolites. Key substances in the glucose-energy metabolism pathway, such as succinate, lactate, NADP, ATP, and ADP, showed decreased levels, with the DOR group exhibiting a reduced ADP/ATP ratio. Downregulation of genes involved in glycolysis (HK, PGK, LDH1), the TCA cycle (CS), and gluconeogenesis (PCK) was observed, along with reduced glucose content and expression of glucose transporter genes (GLUT1 and GLUT3) in DOR GCs. Additionally, decreased AMPK pathway activity and impaired mitochondrial function in DOR suggest a connection between mitochondrial dysfunction and disrupted energy metabolism. Above all, the decline in glucose-energy metabolism in DOR is closely associated with its onset and progression. Reduced glucose uptake and impaired mitochondrial function in DOR GCs lead to internal energy imbalances, hindering the AMPK signaling pathway, limiting energy production and supply, and ultimately impacting follicle development and maturation.

Ovarian aging: energy metabolism of oocytes

In women who are getting older, the quantity and quality of their follicles or oocytes and decline. This is characterized by decreased ovarian reserve function (DOR), fewer remaining oocytes, and lower quality oocytes. As more women choose to delay childbirth, the decline in fertility associated with age has become a significant concern for modern women. The decline in oocyte quality is a key indicator of ovarian aging. Many studies suggest that age-related changes in oocyte energy metabolism may impact oocyte quality. Changes in oocyte energy metabolism affect adenosine 5'-triphosphate (ATP) production, but how related products and proteins influence oocyte quality remains largely unknown. This review focuses on oocyte metabolism in age-related ovarian aging and its potential impact on oocyte quality, as well as therapeutic strategies that may partially influence oocyte metabolism. This research aims to enhance our understanding of age-related changes in oocyte energy metabolism, and the identification of biomarkers and treatment methods.

Role of miRNAs in glucose metabolism of mouse cumulus cells†

It is known that the oocyte has a limited capacity to acquire and metabolize glucose, and it must rely on cumulus cells (CCs) to take up glucose and produce pyruvate for use to produce ATP through oxidative phosphorylation. We therefore propose that miRNAs might regulate glucose metabolism (GM) in CCs and might be used as markers for oocyte quality assessment. Here, mouse CC models with impaired glycolysis or pentose phosphate pathway (PPP) were established, and miRNAs targeting the key enzymes in glycolysis/PPP were predicted using the miRNA target prediction databases. Expression of the predicted miRNAs was compared between CCs with normal and impaired glycolysis/PPP to identify candidate miRNAs. Function of the candidate miRNAs was validated by transfecting CCs or cumulus-oocyte-complexes (COCs) with miRNA inhibitors and observing effects on glucose metabolites of CCs and on competence of oocytes. The results validated that miR-23b-3p, let-7b-5p, 34b-5p and 145a-5p inhibited glycolysis, and miR-24-3p, 3078-3p,183-5p and 7001-5p inhibited PPP of CCs. Our observation using a more physiologically relevant model (intact cultured COCs) further validated the four glycolysis-targeting miRNAs we identified. Furthermore, miR-let-7b-5p, 34b-5p and 145a-5p may also inhibit PPP, as they decreased the production of glucose-6-phosphate. In conclusion, miRNAs play critical roles in GM of CCs and may be used as markers for oocyte quality assessment. Summary sentence:  We identified and validated eight new miRNAs that inhibit glycolysis and/or pentose phosphate pathways in cumulus cells (CCs) suggesting that miRNAs play critical roles in glucose metabolism of CCs and may be used for oocyte quality markers.

Altered Energy Metabolism, Mitochondrial Dysfunction, and Redox Imbalance Influencing Reproductive Performance in Granulosa Cells and Oocyte During Aging

Female fertility decreases during aging. The development of effective therapeutic strategies to address the age-related decline in oocyte quality and quantity and its accurate diagnosis remain major challenges. In this review, we summarize our current understanding of the study of aging and infertility, focusing primarily on the molecular basis of energy metabolism, mitochondrial function, and redox homeostasis in granulosa cells and oocytes, and discuss perspectives on future research directions. Mitochondria serve as a central hub sensing a multitude of physiological processes, including energy production, cellular redox homeostasis, aging, and senescence. Young granulosa cells favor glycolysis and actively produce pyruvate, NADPH, and other metabolites. Oocytes rely on oxidative phosphorylation fueled by nutrients, metabolites, and antioxidants provided by the adjacent granulosa cells. A reduced cellular energy metabolism phenotype, including both aerobic glycolysis and mitochondrial respiration, is characteristic of older female granulosa cells compared with younger female granulosa cells. Aged oocytes become more susceptible to oxidative damage to cells and mitochondria because of further depletion of antioxidant-dependent ROS scavenging systems. Molecular perturbations of gene expression caused by a subtle change in the follicular fluid microenvironment adversely affect energy metabolism and mitochondrial dynamics in granulosa cells and oocytes, further causing redox imbalance and accelerating aging and senescence. Furthermore, recent advances in technology are beginning to identify biofluid molecular markers that may influence follicular development and oocyte quality. Accumulating evidence suggests that redox imbalance caused by abnormal energy metabolism and/or mitochondrial dysfunction is closely linked to the pathophysiology of age-related subfertility.

Transcriptomic profiles reveal the characteristics of oocytes and cumulus cells at GV, MI, and MII in follicles before ovulation

BACKGROUND

The oocyte and its surrounding cumulus cells (CCs) exist as an inseparable entity. The maturation of the oocyte relies on communication between the oocyte and the surrounding CCs. However, oocyte evaluation is primarily based on morphological parameters currently, which offer limited insight into the quality and competence of the oocyte. Here, we conducted transcriptomic profiling of oocytes and their CCs from 47 patients undergoing preimplantation genetic testing for aneuploidy (PGT-A). We aimed to investigate the molecular events occurring between oocytes and CCs at different stages of oocyte maturation (germinal vesicle [GV], metaphase I [MI], and metaphase II [MII]). Our goal is to provide new insights into in vitro oocyte maturation (IVM).

RESULTS

Our findings indicate that oocyte maturation is a complex and dynamic process and that MI oocytes can be further classified into two distinct subtypes: GV-like-MI oocytes and MII-like-MI oocytes. Human oocytes and cumulus cells at three different stages of maturation were analyzed using RNA-seq, which revealed unique transcriptional machinery, stage-specific genes and pathways, and transcription factor networks that displayed developmental stage-specific expression patterns. We have also identified that both lipid and cholesterol metabolism in cumulus cells is active during the late stage of oocyte maturation. Lipids may serve as a more efficient energy source for oocytes and even embryogenesis.

CONCLUSIONS

Overall, our study provides a relatively comprehensive overview of the transcriptional characteristics and potential interactions between human oocytes and cumulus cells at various stages of maturation before ovulation. This study may offer novel perspectives on IVM and provide a reliable reference data set for understanding the transcriptional regulation of follicular maturation.

Glucagon Promotes Gluconeogenesis through the GCGR/PKA/CREB/PGC-1α Pathway in Hepatocytes of the Japanese Flounder Paralichthys olivaceus

In order to investigate the mechanism of glucagon regulation of gluconeogenesis, primary hepatocytes of the Japanese flounder (Paralichthys olivaceus) were incubated with synthesized glucagon, and methods based on inhibitors and gene overexpression were employed. The results indicated that glucagon promoted glucose production and increased the mRNA levels of glucagon receptor (gcgr), guanine nucleotide-binding protein Gs α subunit (gnas), adenylate cyclase 2 (adcy2), protein kinase A (pka), cAMP response element-binding protein 1 (creb1), peroxisome proliferator-activated receptor-γ coactivator 1α (pgc-1α), phosphoenolpyruvate carboxykinase 1 (pck1), and glucose-6-phosphatase (g6pc) in the hepatocytes. An inhibitor of GCGR decreased the mRNA expression of gcgr, gnas, adcy2, pka, creb1, pgc-1α, pck1, g6pc, the protein expression of phosphorylated CREB and PGC-1α, and glucose production. The overexpression of gcgr caused the opposite results. An inhibitor of PKA decreased the mRNA expression of pgc-1α, pck1, g6pc, the protein expression of phosphorylated-CREB, and glucose production in hepatocytes. A CREB-targeted inhibitor significantly decreased the stimulation by glucagon of the mRNA expression of creb1, pgc-1α, and gluconeogenic genes, and glucose production decreased accordingly. After incubating the hepatocytes with an inhibitor of PGC-1α, the glucagon-activated mRNA expression of pck1 and g6pc was significantly down-regulated. Together, these results demonstrate that glucagon promotes gluconeogenesis through the GCGR/PKA/CREB/PGC-1α pathway in the Japanese flounder.

Melatonin loaded PLGA nanoparticles effectively ameliorate the in vitro maturation of deteriorated oocytes and the cryoprotective abilities during vitrification process

Almost all cells can be exposed to stress, but oocytes, which are female germ cells, are particularly vulnerable to damage. In this study, melatonin, a well-known antioxidant, was loaded into biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and delivered to damaged oocytes in order to improve their quality and restoration. Etoposide (ETP)-induced deteriorated oocytes show poor maturity, mitochondrial aggregation, and DNA damage. Treatment of NPs not only reduced DNA damage but also improved mitochondrial stability, as evidenced by increased ATP levels and mitochondrial homogeneity. When melatonin was added to the culture medium at the same concentration as that present in NPs, DNA and mitochondrial repair was insignificant due to the half-life of melatonin, whereas DNA repair in damaged oocytes upon multiple treatments with melatonin was similar to that observed with melatonin-loaded NPs. Next, we evaluated whether the oocytes treated with NPs could have cryoprotective abilities during vitrification/thawing. Vitrified-oocytes were stored at -196 °C for 0.25 h (T1) or 0.5 h (T2). After thawing, live oocytes were subjected to in vitro maturation. The NP-treated group showed maturity similar to the control group (77.8% in T1, 72.7% in T2) and the degree of DNA damage was reduced compared to the ETP-induced group (p < 0.05).

Selective autophagic degradation of ACLY (ATP citrate lyase) maintains citrate homeostasis and promotes oocyte maturation

Macroautophagy/autophagy is a cellular and energy homeostatic mechanism that contributes to maintain the number of primordial follicles, germ cell survival, and anti-ovarian aging. However, it remains unknown whether autophagy in granulosa cells affects oocyte maturation. Here, we show a clear tendency of reduced autophagy level in human granulosa cells from women of advanced maternal age, implying a potential negative correlation between autophagy levels and oocyte quality. We therefore established a co-culture system and show that either pharmacological inhibition or genetic ablation of autophagy in granulosa cells negatively affect oocyte quality and fertilization ability. Moreover, our metabolomics analysis indicates that the adverse impact of autophagy impairment on oocyte quality is mediated by downregulated citrate levels, while exogenous supplementation of citrate can significantly restore the oocyte maturation. Mechanistically, we found that ACLY (ATP citrate lyase), which is a crucial enzyme catalyzing the cleavage of citrate, was preferentially associated with K63-linked ubiquitin chains and recognized by the autophagy receptor protein SQSTM1/p62 for selective autophagic degradation. In human follicles, the autophagy level in granulosa cells was downregulated with maternal aging, accompanied by decreased citrate in the follicular fluid, implying a potential correlation between citrate metabolism and oocyte quality. We also show that elevated citrate levels in porcine follicular fluid promote oocyte maturation. Collectively, our data reveal that autophagy in granulosa cells is a beneficial mechanism to maintain a certain degree of citrate by selectively targeting ACLY during oocyte maturation.Abbreviations: 3-MA: 3-methyladenine; ACLY: ATP citrate lyase; AMA: advanced maternal age; CG: cortical granule; CHX: cycloheximide; CQ: chloroquine; CS: citrate synthase; COCs: cumulus-oocyte-complexes; GCM: granulosa cell monolayer; GV: germinal vesicle; MII: metaphase II stage of meiosis; PB1: first polar body; ROS: reactive oxygen species; shRNA: small hairpin RNA; SQSTM1/p62: sequestosome 1; TCA: tricarboxylic acid; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; UBA: ubiquitin-associated domain; Ub: ubiquitin; WT: wild-type.

Autophagy participates in germline cyst breakdown and follicular formation by modulating glycolysis switch via Akt signaling in newly-hatched chicken ovaries

In females, the establishment of the primordial follicle pool is accompanied by a remarkable programmed oocyte loss for unclear reasons. In this study, the role of autophagy was investigated to serve as a protective mechanism for oocyte survival during chicken folliculogenesis. Inhibition of autophagy by 3-methyladenine (3-MA) led to a remarkable delay in germ cell cyst breakdown that resulted in fewer primordial follicles and retarded sequent follicular development either in vivo or in the ovarian organ culture. Furthermore, the glycolysis level was downregulated in ovaries treated with 3-MA, while Recilisib (a specific activator of Akt) reversed this inhibiting effect of 3-MA on primordial folliculogenesis. Collectively, these data indicate that autophagy functions to maintain germ cell cyst breakdown and primordial follicle assembly by regulating ovarian glycolysis involving Akt signaling in the ovaries of newly-hatched chickens.

Metabolic control of oocyte development

Well balanced and timed metabolism is essential for oocyte development. The effects of extrinsic nutrients on oocyte maturation have been widely reported. In contrast, intrinsic control of oogenesis by intracellular metabolites and metabolic enzymes has received little attention. The comprehensive characterization of metabolic patterns could lead to more complete understanding of regulatory mechanisms underlying oocyte development. A cell's metabolic state is integrated with epigenetic regulation. Epigenetic modifications in germ cells are therefore sensitive to parental environmental exposures. Nevertheless, direct genetic evidence for metabolites involvement in epigenetic establishment during oocyte development is still lacking. Moreover, metabolic disorder-induced epigenetic perturbations during oogenesis might mediate the inter/transgenerational effects of environmental insults. The molecular mechanisms responsible for this deserve further investigation. Here, we summarize the findings on metabolic regulation in oocyte maturation, and how it contributes to oocyte epigenetic modification. Finally, we propose a mouse model that metabolic disorder in oocyte serves as a potential factor mediating the maternal environment effects on offspring health.

PCOS and Role of Cumulus Gene Expression in Assessing Oocytes Quality

The global infertility rate has been declining from year to year. PCOS is one of the treatable accountable causes contributing to anovulatory infertility. Nevertheless, the success rate of treatments and live-birth outcomes especially involving assisted reproductive techniques is still not very promising. There is a reduction in the development potential of oocytes and high-quality embryos in PCOS patients compared to non-PCOS patients. A critical step in IVF treatment is the assessment of oocyte and embryo competence before embryo transfer. Oocytes in metaphase II are very fragile. Repeated morphological assessment on these oocytes may directly impair the quality and affect the whole process. Identification of potential biomarkers especially in the cumulus cells oocytes complex will help to predict the outcome and may create space for improvement. This review has explored gene expression in cumulus cells with regards to oocytes quality in both normal and PCOS women. The gene expression was classified according to their physiological function such as the contribution on cumulus expansion, cumulus cells apoptosis, and glucose metabolism. Collectively, the review suggested that positive expression of HAS2, PTX3, GREM1, and VCAN may correlate with good quality oocytes and can be used as an indicator among PCOS women.

Increased Environment-Related Metabolism and Genetic Expression in the In Vitro Matured Mouse Oocytes by Transcriptome Analysis

Infertility in humans at their reproductive age is a world-wide problem. Oocyte in vitro maturation (IVM) is generally used in such cases to acquire the embryo in assisted reproductive technology (ART). However, the differences between an in vivo (IVO) and IVM culture environment in the RNA expression profile in oocytes, remains unclear. In this study, we compared the global RNA transcription pattern of oocytes from in vitro and in vivo maturation. Our results showed that 1,864 genes differentially expressed between the IVO and IVM oocytes. Among these, 1,638 genes were up-regulated, and 226 genes were down-regulated, and these changes were mainly divided into environmental adaption, metabolism, and genetic expression. Our detailed analysis showed that the expression of genes that belonged to metabolism-related processes such as energy metabolism, nucleotide metabolism, and carbohydrate metabolism was changed; and these genes also belonged to organismal systems including environmental adaptation and the circulatory system; moreover, we also found that the relative gene expression of genetic expression processes, such as protein synthesis, modification, and DNA replication and repair were also altered. In conclusion, our data suggests that in vitro maturation of mouse oocyte resulted in metabolism and genetic expression changes due to environmental changes compared with in vivo matured oocytes.

Effect of aging on mitochondria and metabolism of bovine granulosa cells

This study investigated the effect of aging on mitochondria in granulosa cells (GCs) collected from the antral follicles of young and aged cows (25–50 months and over 140 months in age, respectively). When GCs were cultured under 20% O₂ for 4 days, mitochondrial DNA copy number (Mt-number), determined by real-time PCR, increased throughout the culture period, and the extent of increase was greater in the GCs of young cows than in those of old cows. In a second experiment, GCs were cultured under 20% O₂ for 24 h. Protein levels of TOMM20 and TFAM in GCs were lower in aged cows than in young cows, and the amount of reactive oxygen species and the mitochondrial membrane potential were higher, whereas ATP content and proliferation activity were lower, respectively. Glucose consumption and lactate production were higher in the GCs of aged cows than in those of young cows. When GCs were cultured under 5% or 20% O₂ for 24 h, low O₂ decreased ATP content and increased glucose consumption in GCs of both age groups compared with high O₂; however, low O₂ decreased the Mt-number only in the GCs of young cows. In conclusion, we show that aging affects mitochondrial quantity, function, and response to differential O₂ tensions in GCs.

Mitochondrial Pyruvate Carrier Function in Health and Disease across the Lifespan

As a nodal mediator of pyruvate metabolism, the mitochondrial pyruvate carrier (MPC) plays a pivotal role in many physiological and pathological processes across the human lifespan, from embryonic development to aging-associated neurodegeneration. Emerging research highlights the importance of the MPC in diverse conditions, such as immune cell activation, cancer cell stemness, and dopamine production in Parkinson’s disease models. Whether MPC function ameliorates or contributes to disease is highly specific to tissue and cell type. Cell- and tissue-specific differences in MPC content and activity suggest that MPC function is tightly regulated as a mechanism of metabolic, cellular, and organismal control. Accordingly, recent studies on cancer and diabetes have identified protein–protein interactions, post-translational processes, and transcriptional factors that modulate MPC function. This growing body of literature demonstrates that the MPC and other mitochondrial carriers comprise a versatile and dynamic network undergirding the metabolism of health and disease.

Thioredoxin-interacting protein regulates glucose metabolism and improves the intracellular redox state in bovine oocytes during in vitro maturation

The extent of glucose metabolism during oocyte maturation is closely related to oocyte developmental potential. Thioredoxin-interacting protein (TXNIP) is an α-arrestin family protein that negatively regulates glucose uptake into cells. However, little information is available regarding the function of TXNIP in bovine oocytes. Accordingly, the present study was performed to investigate the influence of TXNIP on glucose metabolism in bovine oocytes during in vitro maturation. Pharmacological inhibition of TXNIP by azaserine enhanced glucose uptake and imparted a specific metabolic effect on glycolysis and pentose phosphate pathway (PPP). RNA interference (RNAi) was adopted to further determine the biological significance of TXNIP in regulating glucose metabolism. The maturation rate and the developmental competence of TXNIP siRNA-treated oocytes were significantly improved. Knockdown of TXNIP in bovine oocytes significantly increased glycolysis by increasing the activities of phosphofructokinase (PFK), pyruvate kinase, and lactate dehydrogenase; pyruvate and lactate production; and intracellular ATP level, as well as mitochondrial activity. Furthermore, glucose metabolism through PPP was also enhanced by TXNIP depletion, as TXNIP siRNA treatment promoted glucose-6-phosphate dehydrogenase (G6PDH) activity and NADPH content, and helped maintain a high level of glutathione and a low level of reactive oxygen species within the oocytes. Further studies revealed that inhibition of TXNIP resulted increases in glucose transporter 1 (GLUT1) expression, as well as PFK1 platelet isoform (PFKP) and G6PDH mRNA levels. These results reveal that TXNIP depletion promotes oocyte maturation by enhancing both glycolysis and the PPP. During in vitro maturation of bovine oocytes, TXNIP serves as a key regulator of glucose uptake by controlling GLUT1 expression.

Effects of glucose metabolism pathways on nuclear and cytoplasmic maturation of pig oocytes

The developmental competence of IVM porcine oocytes is still low compared with that in their in vivo counterparts. Although many studies reported effects of glucose metabolism (GM) on oocyte nuclear maturation, few reported on cytoplasmic maturation. Previous studies could not differentiate whether GM of cumulus cells (CCs) or that of cumulus-denuded oocytes (DOs) supported oocyte maturation. Furthermore, species differences in oocyte GM are largely unknown. Our aim was to address these issues by using enzyme activity inhibitors, RNAi gene silencing and special media that could support nuclear but not cytoplasmic maturation when GM was inhibited. The results showed that GM in CCs promoted pig oocyte maturation by releasing metabolites from both pentose phosphate pathway and glycolysis. Both pyruvate and lactate were transferred into pig DOs by monocarboxylate transporter and pyruvate was further delivered into mitochondria by mitochondrial pyruvate carrier in both pig DOs and CCs. In both pig DOs and CCs, pyruvate and lactate were utilized through mitochondrial electron transport and LDH-catalyzed oxidation to pyruvate, respectively. Pig and mouse DOs differed in their CC dependency for glucose, pyruvate and lactate utilization. While mouse DOs could not, pig DOs could use the lactate-derived pyruvate.

SIRT2 Inhibition Results in Meiotic Arrest, Mitochondrial Dysfunction, and Disturbance of Redox Homeostasis during Bovine Oocyte Maturation

SIRT2, a member of the sirtuin family, has been recently shown to exert important effects on mitosis and/or metabolism. However, its roles in oocyte maturation have not been fully clarified. In this study, SIRT2, located in the cytoplasm and nucleus, was found in abundance in the meiotic stage, and its expression gradually decreased until the blastocyst stage. Treatment with SIRT2 inhibitors resulted in the prevention of oocyte maturation and the formation of poor-quality oocytes. By performing confocal scanning and quantitative analysis, the results showed that SIRT2 inhibition induced prominent defects in spindle/chromosome morphology, and led to the hyperacetylation of α-tubulin and H4K16. In particular, SIRT2 inhibition impeded cytoplasmic maturation by disturbing the normal distribution of cortical granules, endoplasmic reticulum, and mitochondria during oocyte meiosis. Meanwhile, exposure to SirReal2 led to elevated intracellular reactive oxygen species (ROS) accumulation, low ATP production, and reduced mitochondrial membrane potential in oocytes. Further analysis revealed that SIRT2 inhibition modulated mitochondrial biogenesis and dynamics via the downregulation of TFAM and Mfn2, and the upregulation of DRP1. Mechanistically, SIRT2 inhibition blocked the nuclear translocation of FoxO3a by increasing FoxO3a acetylation, thereby downregulating the expression of FoxO3a-dependent antioxidant genes SOD2 and Cat. These results provide insights into the potential mechanisms by which SIRT2-dependent deacetylation activity exerts its effects on oocyte quality.