Mitochondrial and metabolic adjustments during the final phase of follicular development prior to IVM of bovine oocytes

HH5 double-carrier embryos fail to progress through early conceptus elongation

Massive genotyping in cattle has uncovered several deleterious haplotypes that cause preterm mortality. Holstein haplotype 5 (HH5) is a deleterious haplotype present in the Holstein Friesian population that involves the ablation of the transcription factor B1 mitochondrial (TFB1M) gene. The developmental stage at which HH5 double-carrier (DC, homozygous) embryos or fetuses die remains unknown and this is a relevant information to estimate the economic losses associated with the inadvertent cross between carriers. To determine whether HH5 DC survive to maternal recognition of pregnancy, embryonic day (E) 14 embryos were flushed from superovulated carrier cows inseminated with a carrier bull. Double-carrier E14 conceptuses were recovered at Mendelian rates but they failed to achieve early elongation, as evidenced by a drastic reduction of their extra-embryonic membranes, which were >26-fold shorter than those of carrier or noncarrier embryos. To assess development at earlier stages, TFB1M knockout (KO) embryos-functionally equivalent to DC embryos-were generated by clustered regularly interspaced short palindromic repeats (CRISPR) technology and cultured to the blastocyst stage, in vitro culture day (D) 8, and to the early embryonic disc stage, D12. No significant effect of TFB1M ablation was observed on the differentiation and proliferation of embryonic lineages and relative mitochondrial DNA (mtDNA) content up to D12. In conclusion, HH5 DC embryos are able to develop to early embryonic disc stage but fail to undergo early conceptus elongation, which is required for pregnancy recognition.

Preovulatory follicular fluid secretome added to in vitro maturation medium influences the metabolism of equine cumulus-oocyte complexes

BACKGROUND

In vitro embryo production is a highly demanded reproductive technology in horses, which requires the recovery (in vivo or post-mortem) and in vitro maturation (IVM) of oocytes. Oocytes subjected to IVM exhibit poor developmental competence compared to their in vivo counterparts, being this related to a suboptimal composition of commercial maturation media. The objective of this work was to study the effect of different concentrations of secretome obtained from equine preovulatory follicular fluid (FF) on cumulus-oocyte complexes (COCs) during IVM. COCs retrieved in vivo by ovum pick up (OPU) or post-mortem from a slaughterhouse (SLA) were subjected to IVM in the presence or absence of secretome (Control: 0 µg/ml, S20: 20 µg/ml or S40: 40 µg/ml). After IVM, the metabolome of the medium used for oocyte maturation prior (Pre-IVM) and after IVM (Post-IVM), COCs mRNA expression, and oocyte meiotic competence were analysed.

RESULTS

IVM leads to lactic acid production and an acetic acid consumption in COCs obtained from OPU and SLA. However, glucose consumption after IVM was higher in COCs from OPU when S40 was added (Control Pre-IVM vs. S40 Post-IVM: 117.24 ± 7.72 vs. 82.69 ± 4.24; Mean µM ± SEM; p < 0.05), while this was not observed in COCs from SLA. Likewise, secretome enhanced uptake of threonine (Control Pre-IVM vs. S20 Post-IVM vs. S40 Post-IVM: 4.93 ± 0.33 vs. 3.04 ± 0.25 vs. 2.84 ± 0.27; Mean µM ± SEM; p < 0.05) in COCs recovered by OPU. Regarding the relative mRNA expression of candidate genes related to metabolism, Lactate dehydrogenase A (LDHA) expression was significantly downregulated when secretome was added during IVM at 20-40 µg/ml in OPU-derived COCs (Control vs. S20 vs. S40: 1.77 ± 0.14 vs. 1 ± 0.25 vs. 1.23 ± 0.14; fold change ± SEM; p < 0.05), but not in SLA COCs.

CONCLUSIONS

The addition of secretome during in vitro maturation (IVM) affects the gene expression of LDHA, glucose metabolism, and amino acid turnover in equine cumulus-oocyte complexes (COCs), with diverging outcomes observed between COCs retrieved using ovum pick up (OPU) and slaughterhouse-derived COCs (SLA).

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.

Isoliquiritin can cause mitochondrial dysfunction and regulate Nrf2 to affect the development of mouse oocytes

IsoliQuirtigenin (ILG) has been widely studied in somatic cells and tissues, but less in reproductive development. It is a kind of widely used food additive. In this study, it was found that ILG could significantly increase the levels of ROS,GSH and MMP in mouse oocytes (P < 0.01). In order to explore the cause of this phenomenon, it was found that the abnormal distribution of mitochondria and ATP synthesis levels were significantly increased (P < 0.05). At this time, we made a reasonable hypothesis that ILG affected mitochondrial function. In subsequent studies, it was found that the endogenous ROS accumulation level in mitochondria was significantly increased. After continuous RT-PCR screening, it was found that the expression of Nrf2 was significantly inhibited (P < 0.01). Its upstream and downstream FOXO3 GPX1, CAT, SOD2, SIRT1 gene also appear different degree of significant change (P < 0.05), in which the lower expression of NADP + (P < 0.05) illustrates the mitochondrial ATP synthesis electronic chain were suppressed, it also has the reason, By inhibiting electron chain and ATP synthesis, ILG leads to oocyte apoptosis and initiation of autophagy, reducing oocyte and its subsequent developmental potential.

Metabolomics analysis of human cumulus cells obtained from cumulus-oocyte complexes with different developmental potential

STUDY QUESTION

Is the abundance of certain biochemical compounds in human cumulus cells (CCs) related to oocyte quality?

SUMMARY ANSWER

Malonate, 5-oxyproline, and erythronate were positively associated with pregnancy potential.

WHAT IS KNOWN ALREADY

CCs are removed and discarded prior to ICSI, thereby constituting an interesting biological material on which to perform molecular analysis aimed to predict oocyte developmental competence. Mitochondrial DNA content and transcriptional analyses in CC have been shown to provide a poor predictive value of oocyte competence, but the untargeted analysis of biochemical compounds (metabolomics) has been unexplored.

STUDY DESIGN, SIZE, DURATION

CCs were obtained from three groups of cumulus-oocyte complexes (COCs) of known developmental potential: oocytes not developing to blastocyst following ICSI (Bl-); oocytes developing to blastocyst but failing to establish pregnancy following embryo transfer (P-); and oocytes developing to blastocyst able to establish a pregnancy (P+). Metabolomics analyses were performed on 12 samples per group, each sample comprising the CC recovered from a single COC.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human CC samples were obtained from IVF treatments. Only unfrozen oocytes and embryos not submitted to preimplantation genetic testing were included in the analysis. Metabolomics analysis was performed by ultra-high performance liquid chromatography-tandem mass spectroscopy.

MAIN RESULTS AND THE ROLE OF CHANCE

The analysis identified 98 compounds, five of which were differentially abundant (P < 0.05) between groups: asparagine, proline, and malonate were less abundant in P- compared to Bl-, malonate and 5-oxoproline were less abundant in P- group compared to P+, and erythronate was less abundant in Bl- group compared to P+. No significant association between the abundance of the compounds identified and donor age or BMI was noted.

LIMITATIONS, REASONS FOR CAUTION

Data dispersion and the lack of coherence between developmental groups preclude the direct use of metabolic markers in clinical practice, where the uterine environment plays a major role in pregnancy outcome. The abundance of other compounds not detected by the analysis may be associated with oocyte competence. As donors were lean (only two with BMI > 30 kg/m2) and young (<34 years old), a possible effect of obesity or advanced age on the CC metabolome could not be determined.

WIDER IMPLICATIONS OF THE FINDINGS

The abundance of malonate, 5-oxyproline, and erythronate in CC was significantly higher in COCs ultimately establishing pregnancy, providing clues on the pathways required for oocyte competence. The untargeted analysis uncovered the presence of compounds that were not expected in CC, such as β-citrylglutamate and the neurotransmitter N-acetyl-aspartyl-glutamate, which may play roles in chromatin remodeling and signaling, respectively.

STUDY FUNDING/COMPETING INTEREST(S)

Research was supported by the Industrial Doctorate Project IND2017/BIO-7748 funded by Madrid Region Government. The authors declare no competing interest.

TRIAL REGISTRATION NUMBER

N/A.

Aging and oocyte competence: A molecular cell perspective

Follicular microenvironment is paramount in the acquisition of oocyte competence, which is dependent on two interconnected and interdependent processes: nuclear and cytoplasmic maturation. Extensive research conducted in human and model systems has provided evidence that those processes are disturbed with female aging. In fact, advanced maternal age (AMA) is associated with a lower chance of pregnancy and live birth, explained by the age-related decline in oocyte quality/competence. This decline has largely been attributed to mitochondria, essential for oocyte maturation, fertilization, and embryo development; with mitochondrial dysfunction leading to oxidative stress, responsible for nuclear and mitochondrial damage, suboptimal intracellular energy levels, calcium disturbance, and meiotic spindle alterations, that may result in oocyte aneuploidy. Nuclear-related mechanisms that justify increased oocyte aneuploidy include deoxyribonucleic acid (DNA) damage, loss of chromosomal cohesion, spindle assembly checkpoint dysfunction, meiotic recombination errors, and telomere attrition. On the other hand, age-dependent cytoplasmic maturation failure is related to mitochondrial dysfunction, altered mitochondrial biogenesis, altered mitochondrial morphology, distribution, activity, and dynamics, dysmorphic smooth endoplasmic reticulum and calcium disturbance, and alterations in the cytoskeleton. Furthermore, reproductive somatic cells also experience the effects of aging, including mitochondrial dysfunction and DNA damage, compromising the crosstalk between granulosa/cumulus cells and oocytes, also affected by a loss of gap junctions. Old oocytes seem therefore to mature in an altered microenvironment, with changes in metabolites, ribonucleic acid (RNA), proteins, and lipids. Overall, understanding the mechanisms implicated in the loss of oocyte quality will allow the establishment of emerging biomarkers and potential therapeutic anti-aging strategies. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.

Oocyte-cumulus cells crosstalk: New comparative insights

Mammalian follicles are constituted of a complex structure composed of several layers of granulosa cells surrounding the oocyte and of theca cells that reside beneath its basement membrane. During folliculogenesis, granulosa cells separate into two anatomically and functionally distinct sub-types; the mural cells lining the follicle wall and the oocyte-surrounding cumulus cells, i.e. those in intimate metabolic contact with the oocyte. The cumulus cells connecting with the oocyte have trans-zonal cytoplasmic projections which, penetrating the zona pellucida, form the cumulus-oocyte complex. The connections through gap junctions allow the transfer of small molecules between oocyte and cumulus cells, such as ions, metabolites, and amino acids necessary for oocyte growth, as well as small regulatory molecules that control oocyte development. The bi-directional communication between the oocyte and cumulus cells is crucial for the development and functions of both cell types. Our current knowledge of the relationship between the oocyte and its surrounding cumulus cells continues to change as we gain a greater understanding of factors regulating oocyte development and folliculogenesis. This review will mainly focus on the reciprocal interaction between oocytes and cumulus cells during the latter stages of follicle development i.e. through antral development to periovulatory events including oocyte maturation, expansion, and degradation of the cumulus matrix.

Effects of adverse fertility-related factors on mitochondrial DNA in the oocyte: a comprehensive review

The decline of oocyte quality has profound impacts on fertilization, implantation, embryonic development, and the genetic quality of future generations. One factor that is often ignored but is involved in the decline of oocyte quality is mitochondrial DNA (mtDNA) abnormalities. Abnormalities in mtDNA affect the energy production of mitochondria, the dynamic balance of the mitochondrial network, and the pathogenesis of mtDNA diseases in offspring. In this review, we have detailed the characteristics of mtDNA in oocytes and the maternal inheritance of mtDNA. Next, we summarized the mtDNA abnormalities in oocytes derived from aging, diabetes, obesity, and assisted reproductive technology (ART) in an attempt to further elucidate the possible mechanisms underlying the decline in oocyte health. Because multiple infertility factors are often involved when an individual is infertile, a comprehensive understanding of the individual effects of each infertility-related factor on mtDNA is necessary. Herein, we consider the influence of infertility-related factors on the mtDNA of the oocyte as a collective perspective for the first time, providing a supplementary angle and reference for multi-directional improvement strategies of oocyte quality in the future. In addition, we highlight the importance of studying ART-derived mitochondrial abnormalities during every ART procedure.

Mitochondrial DNA content and developmental competence of blastocysts derived from pre-pubertal heifer oocytes

In the cattle-breeding industry, there is an increasing demand for in vitro embryo production from pre-pubertal heifers. In this study, we evaluated the differences in mitochondrial DNA content, oxidative stress, and developmental competence in blastocysts derived from pre-pubertal and pubertal heifers. We found higher mitochondrial DNA copy numbers in blastocysts produced from pre-pubertal heifers than from pubertal heifers. In the group of pre-pubertal animals, there was a significantly lower number of blastocysts produced in vitro from the same number of collected oocytes, and these blastocysts did not differ from those obtained from pubertal oocytes in terms of their morphological quality. The morphologically appropriate blastocysts derived from pre-pubertal heifers had higher concentrations of reactive oxygen species and glutathione. In blastocysts derived from pre-pubertal heifers, we found alterations in the expression of gene markers for developmental competence, which correlated with higher mitochondrial DNA content, suggesting a lower quality of blastocysts derived from pre-pubertal animals than from pubertal animals. The inadequate redox balance in blastocysts obtained from pre-pubertal females, along with higher mitochondrial DNA copy number, as well as differential gene expression of markers of developmental competence, elucidate the low quality of blastocysts derived from pre-pubertal animals, despite their unaltered morphology.

RNA-sequencing reveals genes linked with oocyte developmental potential in bovine cumulus cells

Cumulus cells provide an interesting biological material to perform analyses to understand the molecular clues determining oocyte competence. The objective of this study was to analyze the transcriptional differences between cumulus cells from oocytes exhibiting different developmental potentials following individual in vitro embryo production by RNA-seq. Cumulus cells were allocated into three groups according to the developmental potential of the oocyte following fertilization: (1) oocytes developing to blastocysts (Bl+), (2) oocytes cleaving but arresting development before the blastocyst stage (Bl-), and (3) oocytes not cleaving (Cl-). RNAseq was performed on 4 (Cl-) or 5 samples (Bl+ and Bl-) of cumulus cells pooled from 10 cumulus-oocyte complexes per group. A total of 49, 50, and 18 differentially expressed genes (DEGs) were detected in the comparisons Bl+ versus Bl-, Bl+ versus Cl- and Bl- versus Cl-, respectively, showing a fold change greater than 1.5 at an adjusted p value <0.05. Focussing on DEGs in cumulus cells from Bl+ group, 10 DEGs were common to both comparisons (10/49 from Bl+ vs. Bl-, 10/50 from Bl+ vs. Cl-). These DEGs correspond to 6 upregulated genes (HBE1, ITGA1, PAPPA, AKAP12, ITGA5, and SLC1A4), and 4 downregulated genes (GSTA1, PSMB8, FMOD, and SFRP4) in Bl+ compared to the other groups, from which 7 were validated by quantitative PCR (HBE1, ITGA1, PAPPA, AKAP12, ITGA5, PSMB8 and SFRP4). These genes are involved in critical biological functions such as integrin-mediated cell adhesion, oxygen availability, IGF and Wnt signaling or PKA pathway, highlighting specific biological processes altered in incompetent in vitro maturation oocytes.

mtDNA content in cumulus cells does not predict development to blastocyst or implantation

STUDY QUESTION

Is relative mitochondrial DNA (mtDNA) content in cumulus cells (CCs) related to embryo developmental competence in humans and/or the bovine model?

SUMMARY ANSWER

mtDNA content in CCs provides a poor predictive value of oocyte developmental potential, both in vitro and following embryo transfer.

WHAT IS KNOWN ALREADY

CCs are closely connected to the oocyte through transzonal projections, serving essential metabolic functions during folliculogenesis. These oocyte-supporting cells are removed and discarded prior to ICSI, thereby providing interesting biological material on which to perform molecular analyses designed to identify markers that predict oocyte developmental competence. Previous studies have positively associated oocyte mtDNA content with developmental potential in animal models and women. However, it remains debatable whether mtDNA content in CCs could be used as a proxy to infer oocyte developmental potential.

STUDY DESIGN SIZE DURATION

mtDNA content was analyzed in CCs obtained from 109 human oocytes unable to develop to blastocyst, able to develop to blastocyst but failing to establish pregnancy or able to develop to blastocyst and to establish pregnancy. mtDNA analysis was also performed on bovine cumulus samples collected from 120 oocytes unable to cleave, oocytes developing into cleaved embryos but arresting development prior to the blastocyst stage or oocytes developing to blastocysts.

PARTICIPANTS/MATERIALS SETTING METHODS

Human CCs samples were obtained from women undergoing IVF. Only unfrozen oocytes and embryos not submitted to preimplantation genetic testing were included in the analysis. Bovine samples were obtained from slaughtered cattle and individually matured, fertilized and cultured in vitro. Relative mtDNA was assessed by quantitative PCR analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

mtDNA content in human and bovine CCs did not differ according to the developmental potential of their enclosed oocyte. Moreover, mtDNA content in bovine oocytes did not correlate with that of their corresponding CCs.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

The lack of correlation found between mtDNA content in human CCs and oocytes was also assessed in bovine samples. Although bovine folliculogenesis, mono-ovulatory ovulation and early embryo development exhibit considerable similarities with that of humans, they may not be fully comparable.

WIDER IMPLICATIONS OF THE FINDINGS

The use of molecular markers for oocyte developmental potential in CCs could be used to enhance success rates following single embryo transfer. However, our data indicate that mtDNA in CCs is not a good proxy for oocyte quality.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the Industrial Doctorate Project IND2017/BIO-7748 funded by the Madrid Region Government. The authors declare no competing interests.

Effect of season on germinal vesicle stage, quality, and subsequent in vitro developmental competence in bovine cumulus-oocyte complexes

Although the reproductive performance of grazing cattle is lower in summer compared to winter, the effect of season on oocyte developmental competence has not been thoroughly examined. We measured the effect of season on oocyte chromatin compaction, cumulus cell quality, and embryonic development after in vitro fertilization. Cumulus oocytes-complexes (COCs) were collected from abattoir cows' ovaries during the winter and summer months. First, we evaluated the degree of chromatin compaction in germinal vesicle (GV) oocytes (GV1 through GV3), which is associated with different degrees of developmental competence. Then, we determined the apoptotic index in cumulus cells from immature and in vitro matured COCs. Finally, in vitro matured oocytes were fertilized to determine blastocyst rate and embryo quality. During the summer months, we observed a significantly lower proportion of oocytes reaching the GV3 stage and higher levels of DNA fragmentation in cumulus cell. As a result, blastocyst yield and quality were reduced during the summer months. In conclusion, summer negatively affected oocyte GV stage progression, cumulus cell quality, and embryo development. Increased cumulus cell DNA fragmentation during summer, may partially explain the reduced oocyte maturation capacity, considering the relevance of cumulus-oocyte communication during this stage.

Muscles proteome analysis; irisin administration mimics some molecular effects of exercise in quadriceps muscle

Because of health-promoting effects, the adaptation of skeletal muscles to exercise is considered a therapeutic strategy for metabolic complications and musculoskeletal disabilities. Myokines display many beneficial effects of different exercise modalities. Among them, irisin is known as a systemic effector that positively influences several organs. There are a few studies about the effects of irisin on skeletal muscles, and irisin prosperities need to be well-defined for being an exercise mimetic. To aim this purpose, we assessed the proteome profile of mouse skeletal muscle after eight weeks of irisin injection comparing to resistance and endurance exercise treated groups. In the current study, two-dimensional gel electrophoresis was used to evaluate the protein content of the quadriceps muscle. The results were analyzed with Image Master 2D Platinum V6 software. Differentially expressed proteins were characterized by mass spectrometry (MALDI TOF/TOF) and interpreted using protein data banks and co-expression network. Irisin increases cellular ATP content by driving its overproduction through glycolysis and oxidative phosphorylation similar to two exercise protocols and as a specific property, decreases ATP consumption through creatine kinase downregulation. It also improves the microstructural properties of quadriceps muscle by increasing fiber proteins and might induce cellular proliferation and differentiation. Network analysis of differentially expressed proteins also revealed the co-expression of Irisin precursor with structural and metabolic-related proteins. The protein alterations after irisin administration display the potential of this myokine to mimic some molecular effects of exercise, suggesting it a promising candidate to improve muscle metabolism and structure.

Equine maternal aging affects oocyte lipid content, metabolic function and developmental potential

Advanced maternal age is associated with a decline in fertility and oocyte quality. We used novel metabolic microsensors to assess effects of mare age on single oocyte and embryo metabolic function, which has not yet been similarly investigated in mammalian species. We hypothesized that equine maternal aging affects the metabolic function of oocytes and in vitro-produced early embryos, oocyte mitochondrial DNA (mtDNA) copy number, and relative abundance of metabolites involved in energy metabolism in oocytes and cumulus cells. Samples were collected from preovulatory follicles from young (≤14 years) and old (≥20 years) mares. Relative abundance of metabolites in metaphase II oocytes (MII) and their respective cumulus cells, detected by liquid and gas chromatography coupled to mass spectrometry, revealed that free fatty acids were less abundant in oocytes and more abundant in cumulus cells from old vs young mares. Quantification of aerobic and anaerobic metabolism, respectively measured as oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in a microchamber containing oxygen and pH microsensors, demonstrated reduced metabolic function and capacity in oocytes and day-2 embryos originating from oocytes of old when compared to young mares. In mature oocytes, mtDNA was quantified by real-time PCR and was not different between the age groups and not indicative of mitochondrial function. Significantly more sperm-injected oocytes from young than old mares resulted in blastocysts. Our results demonstrate a decline in oocyte and embryo metabolic activity that potentially contributes to the impaired developmental competence and fertility in aged females.

Embryonic disc formation following post-hatching bovine embryo development in vitro

Failures during conceptus elongation are a major cause of pregnancy losses in ungulates, exerting a relevant economic impact on farming. The developmental events occurring during this period are poorly understood, mainly because this process cannot be recapitulated in vitro. Previous studies have established an in vitro post-hatching development (PHD) system that supports bovine embryo development beyond the blastocyst stage, based on agarose gel tunnels and serum- and glucose-enriched medium. Unfortunately, under this system embryonic disc formation is not achieved and embryos show notorious signs of apoptosis and necrosis. The objective of this study has been to develop an in vitro system able to support embryonic disc formation. We first compared post-hatching development inside agarose tunnels or free-floating over an agarose-coated dish in serum- and glucose-enriched medium (PHD medium). Culture inside agarose tunnels shaped embryo morphology by physical constriction, but it restricted embryo growth and did not provide any significant advantage in terms of development of hypoblast and epiblast lineages. In contrast to PHD medium, a chemically defined and enriched medium (N2B27) supported complete hypoblast migration and epiblast survival in vitro, even in the absence of agarose coating. Cells expressing the pluripotency marker SOX2 were observed in ~56% of the embryos and ~25% developed embryonic disc-like structures formed by SOX2+ cells. In summary, here we provide a culture system that supports trophectoderm proliferation, hypoblast migration and epiblast survival after the blastocyst stage.

l-Carnitine Supplementation during In Vitro Maturation and In Vitro Culture Does not Affect the Survival Rates after Vitrification and Warming but Alters Inf-T and ptgs2 Gene Expression

l-carnitine is a potent antioxidant used for in vitro culture systems. Controversial results have been reported using l-carnitine in culture medium at different stages of in vitro bovine embryo production. Cumulus-oocyte complexes (n = 843) were in vitro-fertilized and cultured and added (treatment group) or not added (control group) with l-carnitine. At day three of culture, each group was subdivided into two subgroups receiving no l-carnitine (group 1), 3.8 mM l-carnitine added during in vitro maturation (group 2), 1.5 mM added during the in vitro culture (group 3), and 3.8 mM and 1.5 mM added during the maturation and culture, respectively (group 4). At day 8, blastocyst embryos were examined for mitochondrial activity, the presence of lipid droplets, total cell number, gene expression, and cryotolerance by vitrification. The data were analyzed with a one-way analysis of variance. l-carnitine added in the late in vitro culture significantly reduced mitochondrial activity and lipid content, and upregulated ifn-τ and ptgs2 gene expression compared to controls (p < 0.05). l-carnitine supplementation did not significantly affect the embryo rate production or survival rate after vitrification and warming (p > 0.05). l-carnitine supplementation significantly improved embryo potential to develop viable pregnancies in agreement with a study reporting improved pregnancy rates.

Combined use of Diane-35 and metformin improves the ovulation in the PCOS rat model possibly via regulating glycolysis pathway

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex endocrine and metabolic disease with unknown pathogenesis. However, the treatment of Diane-35 combined with metformin can improve the endocrine and ovulation of PCOS. In this study, we investigated the effects of Diane-35 combined with metformin (DM) treatment on ovulation and glucose metabolism in a PCOS rat model.

METHODS

Sprague Dawley rats were divided into 3 groups, control group, model group (PCOS group) and Diane-35 combined with metformin (PCOS + DM group). The mRNA expression levels were determined by qRT-PCR. The hormone levels were determined by enzyme-linked immunosorbent assay. Immunostaining detected the protein levels of lactate dehydrogenase A (LDH-A), pyruvate kinase isozyme M2 (PKM2) and sirtuin 1 (SIRT1) in the ovarian tissues. TNUEL assay was performed to determine cell apoptosis in the PCOS rats. The metabolites in the ovarian tissues were analyzed by liquid chromatography with tandem mass spectrometry.

RESULTS

PCOS rats showed an increased in body weight, levels of luteinizing hormone and testosterone and insulin resistance, which was significantly attenuated by the DM treatment. The DM treatment improved disrupted estrous cycle and increased the granulosa cells of the ovary in the PCOS rats. The decreased proliferation and increased cell apoptosis of granulosa cells in the ovarian tissues of PCOS rats were significantly reversed by the DM treatment. The analysis of metabolics revealed that ATP and lactate levels were significantly decreased in PCOS rats, which was recovered by the DM treatment. Furthermore, the expression of LDH-A, PKM2 and SIRT1 was significantly down-regulated in ovarian tissues of the PCOS rats; while the DM treatment significantly increased the expression of LDH-A, PKM2 and SIRT1 in the ovarian tissues of the PCOS rats.

CONCLUSION

In conclusion, our study demonstrated that Diane-35 plus metformin treatment improved the pathological changes in the PCOS rats. Further studies suggest that Diane-35 plus metformin can improve the energy metabolism of the ovary via regulating the glycolysis pathway. The mechanistic studies indicated that the therapeutic effects of Diane-35 plus metformin treatment in the PCOS rats may be associated with the regulation of glycolysis-related mediators including PKM2, LDH-A and SIRT1.

Intraovarian influence of bovine corpus luteum on oocyte morphometry and developmental competence, embryo production and cryotolerance

Three experiments were conducted to determine influence of the bovine corpus luteum (CL) on morphometric and functional characteristics of oocytes, and subsequent embryonic development. Cumulus-oocyte complexes were aspirated from two types of cows: 1) with a CL in one ovary (CL+) and without a CL in the contralateral ovary (CL-), 2) and from cows without CL in either ovary (C). Intracellular activity of the enzyme glucose-6-phosphate dehydrogenase (G6PDH), oocyte diameter and thickness of the zona pellucida were determined (Experiment 1). Then, the rate of in vitro oocyte maturation for each ovarian category was evaluated and oocyte diameter and zona pellucida thickness were measured after maturation (Experiment 2). In Experiment 3, in vitro embryo production and cryotolerance were assessed. The oocyte diameter was greater (P < 0.01) and the zona pellucida was thinner in CL+ than in CL- (P > 0.05) or C (P = 0.0131) ovaries. Activity of G6PDH was lower in oocytes from CL+ than CL- (P < 0.01) and C (P = 0.0148) ovaries. Rate of oocyte maturation, oocyte diameter and thickness of the zona pellucida after maturation did not differ among groups. Rate of cleavage was greater in zygotes from CL+ than from CL- or C (P < 0.01); and CL+ ovaries produced more total embryos on day 7 (P < 0.05) and more blastocysts (P < 0.01) than CL- and C ovaries. Rate of expansion and hatching of day-7 vitrified-warmed blastocysts at 24 and 48 h of culture did not differ among groups. In conclusion, oocytes collected from CL+ ovaries were larger and metabolically more prepared to continue maturation than those from ovaries lacking a CL. Also, rates of cleavage and yield of blastocysts were greater for oocytes from CL+ ovaries than from CL- and C ovaries. These findings indicate that a CL influenced oocyte developmental competence and embryonic development, presumably through intraovarian interactions.

Equine Aging and the Oocyte: A Potential Model for Reproductive Aging in Women

Numerous similarities in reproductive aging have been documented between the mare and woman. Aging is associated with a decline in fertility. In mares and women, oocyte transfer procedures were initially used to establish that oocyte donor age is associated with oocyte quality. Age-associated differences in oocytes include altered morphology, gene expression, and developmental potential. Reactive oxygen species and mitochondrial dysfunction are thought to be important contributors to loss of oocyte quality. In the woman, aneuploidy is a primary consideration with maternal aging. Although misalignment of chromosomes during meiosis has been observed in the mare, less is known in this area. Reproductive aging will be reviewed in the mare and compared with the woman with emphasis on factors that affect oocyte quality and developmental potential. Areas in which the mare could be used as a research model to study reproductive aging in women will be highlighted.

Oxidative homeostasis in oocyte competence for in vitro embryo development

The objective of this study was to evaluate the levels of reactive oxygen species (ROS) and glutathione (GSH) in oocytes from follicles of different diameters and their relevance in the in vitro production of embryos (IVPE). Bovine ovaries were aspirated according to the diameter of the follicle [2-8 (general), 4-8 (large), and 2 < 4 mm (small)]. The oocytes were evaluated for levels of ROS, GSH, in vitro maturation, and IVPE. Higher levels of ROS and GSH were observed (p < 0.05) in oocytes of the large group (85.6 ± 7.2 and 140.0 ± 9.6) followed by those in the general (81.1 ± 10.5 and 134.3 ± 7.8) and small (73.5 ± 10.1 and 125.0 ± 10.6) groups. However, the proportion of ROS/GSH did not differ (p > 0.05) between the general, large, and small groups. The maturation was higher (p < 0.05) in the large group (87.8 ± 3.0%) than in the small group (72.2 ± 5.8%), but both were similar (p > 0.05) to that in the general group (82.2 ± 2.5%), whereas the IVPE of the large group (57.3 ± 3.0%) was higher (p < 0.05) than those in the general (44.7 ± 4.4%) and small (34.0 ± 4.0%) groups. We report that oocytes from large follicles are more competent for IVPE, whereas higher levels of ROS and GSH appear to be correlated with oocyte competence, as long as oxidative homeostasis is retained.

Biphasic in vitro maturation with C-type natriuretic peptide enhances the developmental competence of juvenile-goat oocytes

In vitro embryo production success in juvenile animals is compromised due to their intrinsic lower oocyte quality. Conventional in vitro maturation (IVM) impairs oocyte competence by inducing spontaneous meiotic resumption. A series of experiments were performed to determine if maintaining meiotic arrest during a pre-maturation culture phase (pre-IVM) prior to conventional IVM improves oocyte competence of juvenile-goat (2 months old) cumulus-oocyte complexes (COCs). In experiment 1, COCs were cultured with C-type natriuretic peptide (CNP; 0, 50, 100, 200 nM) for 6 and 8 h. Nuclear stage was assessed, revealing no differences in the incidence of germinal vesicle (GV) breakdown. In experiment 2, the same CNP concentrations were assessed plus 10 nM estradiol, the known upstream agonist activating expression of NPR2, the exclusive receptor of CNP. CNP (200 nM) plus estradiol increased the rate of oocytes at GV stage at 6 h compared to control group (74.7% vs 28.3%; P<0.05) with predominantly condensed chromatin configuration. In experiment 3, relative mRNA quantification revealed NPR2 expression was down-regulated after pre-IVM (6 h). In experiment 4, analysis of transzonal projections indicated that pre-IVM maintained cumulus-oocyte communication after oocyte recovery. For experiments 5 and 6, biphasic IVM (6 h pre-IVM with CNP and estradiol, plus 24 h IVM) and control IVM (24 h) were compared. Biphasic IVM increased intra-oocyte glutathione and decreased ROS, up-regulated DNA-methyltransferase 1 and pentraxin 3 expression and led to an increase in rate of blastocyst development compared to control group (30.2% vs 17.2%; P<0.05). In conclusion, a biphasic IVM, including a pre-IVM with CNP, maintains oocyte meiotic arrest for 6 h and enhances the embryo developmental competence of oocytes from juvenile goats.

Mitochondria as a biomarker for IVF outcome

Mitochondria play an essential role in generating energy for embryo development and maintaining embryo metabolism through key cellular functions including ion homeostasis, amino acid metabolism, glycolysis, fatty acid metabolism, signal transduction and apoptotic regulation. Recent literature suggests that mitochondrial content and function may be related to implantation success and embryo viability. Some studies have linked increased levels of mitochondrial DNA to aneuploidy, advanced maternal age and euploid blastocyst with implantation failure, while others have failed to demonstrate similar findings. This review aims to provide an overview of the current literature surrounding the possibilities of using mitochondria as an additional biomarker for infertility treatment outcome and summarize the reasons as to why there are inconsistencies in these studies.

Temporal expression pattern of steroid-metabolizing enzymes in bovine COC during in vitro maturation employing different gonadotropin concentrations

Steroid hormones are regulators in the fine-tuned process of follicular development. During final maturation in vivo a switch from oestradiol (E2) to progesterone (P4) dominance within the follicle is well-described. This change is accompanied by the resumption of meiosis and results in the maturation of the oocyte. It also suggests the important role of these hormones. However, present in vitro maturation (IVM) systems do not completely mimic the in vivo situation, resulting in oocytes of reduced quality. Aim of the study was to determine the temporal pattern of steroid hormone concentrations in the IVM medium of bovine cumulus-oocyte-complexes (COC) at defined time points. The influence of different gonadotropin supplementations during IVM on oocyte maturation, as well as the molecular quality of the oocytes and their corresponding cumulus cells was investigated. COCs were obtained from abattoir-derived ovaries and matured in medium added with different compounds of gonadotropins (eCG/hCG; FSH/LH, each at 0.05 IU or 0.01 IU; only FSH; without gonadotropins) employing a standard protocol without oil overlay. In experiment 1, medium, oocytes and cumulus cells were collected at different time points (0 h [control], 4 h, 8 h, 12 h, 16 h, 20 h, 24 h) after IVM in just eCG/hCG-supplemented medium. In experiment 2, medium, oocytes and cumulus cells were collected at 0 h (control) and after 24 h of IVM with all above-named supplements. The E2 concentration remained similar during IVM whereas P4 concentration increased during experiment 1. No significant changes could be determined after the addition of different gonadotropins (experiment 2). These results suggest that during IVM the temporal pattern of E2 and P4 did not correspond with the pattern during final maturation in vivo. RT-qPCR was used to assess the relative abundance of developmentally important genes in oocytes (BMP15; GDF9; ZAR1; PGR; PGRMC1/2; G6PD; StAR; ESR1/2; SULT1E1; STS; SOAT) and cumulus cells (ESR1/2; FSHR; LHCGR; CYP19A1; HSD3B1; PGR; PGRMC1/2; SULT1E1; STS; SOAT) at all collection points in both experiments. Most transcripts follow a time-regulated mRNA expression pattern during the entire in vitro maturation period. In addition, the expression of the analyzed transcripts was not influenced by the different gonadotropin supplementations during the IVM period. In all, this underlines that present conditions of IVM do not reflect the in vivo situation and require further optimisation.

Resveratrol supplementation during in vitro maturation improves embryo development of prepubertal goat oocytes selected by brilliant cresyl blue staining

This study aimed to investigate the effect of resveratrol supplementation in maturation medium on the developmental ability and bioenergetic\oxidative status of prepubertal goat oocytes selected by brilliant cresyl blue (BCB). Oocytes collected from slaughterhouse-derived ovaries were selected by 13 µM BCB staining and classified as grown BCB+ and growing BCB- oocytes. All oocytes were matured in vitro in our conventional maturation medium and supplemented with 1 µM (BCB+R and BCB-R) and without (Control groups: BCB+C and BCB-C) resveratrol. After 24 h, IVM-oocytes were fertilized with fresh semen and presumptive zygotes were in vitro cultured for 8 days. Oocytes were assessed for blastocyst development and quality, mitochondrial activity and distribution, and levels of GSH, ROS, and ATP. BCB+R (28.3%) oocytes matured with resveratrol presented significantly higher blastocyst development than BCB+C (13.0%) and BCB- groups (BCB-R: 8.3% and BCB-C: 4.7%). Resveratrol improved blastocyst development of BCB-R oocytes at the same rate as BCB+C oocytes. No differences were observed in blastocyst quality among groups. GSH levels were significantly higher in resveratrol groups (BCB+R: 36554.6; BCB-R: 34946.7 pixels/oocyte) than in control groups (BCB+C: 27624.0; BCB-C: 27655.4 pixels/oocyte). No differences were found in mitochondrial activity, ROS level, and ATP content among the groups. Resveratrol-treated oocytes had a higher proportion of clustered active mitochondria in both BCB groups (BCB+R: 73.07%; BCB-R: 79.16%) than control groups (BCB+C: 19.35%; BCB-C: 40%). In conclusion, resveratrol increased blastocyst production from oocytes of prepubertal goats, particularly in better quality oocytes (BCB+).