Effect of ammonium during in vitro maturation on oocyte nuclear maturation and subsequent embryonic development in pigs

The importance of optimal body condition to maximise reproductive health and perinatal outcomes in pigs

Overnutrition or undernutrition during all or part of the reproductive cycle predisposes sows to metabolic consequences and poor reproductive health which contributes to a decrease in sow longevity and an increase in perinatal mortality. This represents not only an economic problem for the pig industry but also results in poor animal welfare. To maximise profitability and increase sustainability in pig production, it is pivotal to provide researchers and practitioners with synthesised information about the repercussions of maternal obesity or malnutrition on reproductive health and perinatal outcomes, and to pinpoint currently available nutritional managements to keep sows' body condition in an optimal range. Thus, the present review summarises recent work on the consequences of maternal malnutrition and highlights new findings.

Increased ammonium in culture medium may promote cellular apoptosis and negatively affect pluripotency of human blastocysts

PURPOSE

To determine the association between ammonium concentration in culture medium and blastocyst development and to assess the influence of increased ammonium concentration on the expression of Bax, Bcl-2 and Oct4.

METHODS

A total of 254 cleavage-stage embryos were individually cultured in 30μL G2-plus medium on Day 3, and then culture media samples were collected on Day 5 for ammonium concentration determination immediately after evaluating the embryos morphology. Poor-quality blastocysts (combined score of CC) were used for gene expression analysis. The blastocyst formation rate, good-quality blastocyst rate and relative expression levels of Bax, Bcl-2 and Oct4 were analyzed.

RESULTS

Based on receiver operating characteristic curve, the cutoff value of ammonium concentration produced by embryos was 16.07 μmol/L (AUC = 0.722, 95% CI 0.637-0.807; P = 0.000), so all embryos were assigned to two groups according to the cutoff value: normal group (< 16.07 μmol/L) and increased group (≥ 16.07 μmol/L). There was a significant difference in blastocyst formation rate (80.5% vs 59.0%, P < 0.01) between normal group and increased group, as well as for good-quality blastocyst rate (21.0% vs 3.4%, P < 0.01). A significantly higher expression level of Bax (P < 0.05) and considerably lower expression level of Oct4 (P < 0.01) were observed in increased group compared to normal group.

CONCLUSION

Our data demonstrated for the first time that increased ammonium concentration in culture medium may promote cellular apoptosis and negatively affect pluripotency of human blastocyst.

The Calcium-Sensing Receptor Is Involved in Follicle-Stimulating Hormone-Induced Cumulus Expansion in in vitro Cultured Porcine Cumulus-Oocyte Complexes

The Calcium-Sensing Receptor (CASR) is a G protein-coupled receptor of the C family that reportedly promotes maturation of porcine oocytes. However, its role in cumulus expansion of cumulus-oocyte complexes (COCs) is not well known. This study was conducted to determine the role of CASR and potential mechanisms involved during in vitro maturation (IVM) of porcine COCs. After culture of COCs in follicle-stimulating hormone (FSH)-supplement maturation medium for 24 h, the time of breakdown of the germinal vesicle (GVBD), indicative of initiation of meiotic maturation, resulted in an increased (p < 0.05) CASR mRNA expression level in cumulus cells. Moreover, IVM of COCs in 10 μM of the CASR agonist NPS R-568 promoted (p < 0.05) cumulus expansion but only in FSH-containing medium. Conversely, 20 μM of the CASR inhibitor NPS2390 precluded cumulus expansion. We next tested the effect of the CASR agonist/inhibitor on the expression of cumulus expansion-related genes. The CASR agonist significantly upregulated the expression of hyaluronan acid synthase 2 (HAS2), whereas the CASR inhibitor downregulated the expression of all HAS2, prostaglandin-endoperoxide synthase 2 (PTGS2), and tumor necrosis factor a-induced protein 6 (TNFAIP6). Altogether, these results suggest that CASR activity is involved in FSH-stimulated porcine cumulus expansion.

The extracellular calcium-sensing receptor promotes porcine egg activation via calcium/calmodulin-dependent protein kinase II

Extracellular calcium is required for intracellular Ca²⁺ oscillations needed for egg activation, but the regulatory mechanism is still poorly understood. The present study was designed to demonstrate the function of calcium-sensing receptor (CASR), which could recognize extracellular calcium as first messenger, during porcine egg activation. CASR expression was markedly upregulated following egg activation. Functionally, the addition of CASR agonist NPS R-568 significantly enhanced pronuclear formation rate, while supplementation of CASR antagonist NPS2390 compromised egg activation. There was no change in NPS R-568 group compared with control group when the egg activation was performed without extracellular calcium addition. The addition of NPS2390 precluded the activation-dependent [Ca²⁺ ]_i rise. When egg activation was conducted in intracellular Ca²⁺ chelator BAPTA-AM and NPS R-568 containing medium, CASR function was abolished. Meanwhile, CASR activation increased the level of the [Ca²⁺ ]_i effector p-CAMKII, and the presence of KN-93, an inhibitor of CAMKII, significantly reduced the CASR-mediated increasement of pronuclear formation rate. Furthermore, the increase of CASR expression following activation was reversed by inhibiting CAMKII activity, supporting a positive feedback loop between CAMKII and CASR. Altogether, these findings provide a new pathway of egg activation about CASR, as the extracellular Ca²⁺ effector, promotes egg activation via its downstream effector and upstream regulator CAMKII.

Nutritional and metabolic stressors on ovine oocyte development and granulosa cell functions in vitro

The present study was undertaken to study the effect of ammonia, urea, non-esterified fatty acid (NEFA), and β-hydroxybutyric acid (β-OHB) on oocyte development and granulosa cell (GC) growth parameter of ovine (Ovis aries). Ovine oocytes were matured in vitro in the presence of different concentration of ammonia, urea, NEFA, and β-OHB for 24 h, in vitro inseminated and evaluated for cleavage and blastocyst yield. Same concentrations of ammonia, urea, NEFA, and β-OHB were examined on growth parameters and hormone secretion activity of granulosa cells in vitro. Real-time reverse transcription polymerase chain reaction was used to evaluate the expression of steroidogenic genes (steroidogenic cytochrome P-450 (CYP11A1, CYP19A1)), cell proliferation-related genes (GDF9, FSHr), and apoptosis-related genes (BCL-2 and BAX). The maturation, cleavage, and blastocyst production rates were significantly lowered in media containing either 200 μM ammonia or 5 mM urea or high combo NEFA or 1 μM β-OHB. Exposure of granulosa cell to 400 μM ammonia or 1 μM β-OHB or very high combo or 6 mM urea significantly decreased all the parameters examined compared to lower levels of all nutritional and metabolic stressors. Elevated concentration of metabolic stressors induced GC apoptosis through the BAX/BCL-2 pathway and reduced the steroidogenic gene messenger RNA (mRNA) expression and cell proliferation gene mRNA expression. These results suggested that the decreased function of GCs may cause ovarian dysfunction and offered an improved understanding of the molecular mechanism responsible for the low fertility in metabolic stressed condition.

Functional amino acids in the development of the pig placenta

The mammalian placenta is essential for supplying nutrients (e.g., amino acids and water) and oxygen from the mother to fetus and for removing fetal metabolites (e.g., ammonia and CO₂ ) from fetus to mother. Thus, placental growth and development are determinants of fetal survival, growth, and development. Indeed, low birth weight is closely associated with reduced placental growth. Providing gestating gilts or sows with dietary supplementation of arginine and glutamine, increases placental growth (including vascular growth), improves embryonic/fetal growth and survival, and reduces the large variation in birth weight among litters. These two amino acids serve as building blocks for tissue protein as well as substrates for the production of polyamines and nitric oxide, which stimulate DNA and protein synthesis and angiogenesis and vascular growth in the placenta. These recent findings not only greatly advance the field of mammalian amino acid metabolism and nutrition, but also provide practical, mechanism-based methods to enhance reproductive efficiency in swine. These results may also help improve embryonic/fetal survival and growth in other livestock species (e.g., sheep and cattle) and in humans.

Effect of acteoside on the re-localization and abnormal morphology of mitochondria in porcine oocytes during in vitro maturation

PURPOSE

The aim of this study is to investigate the effect of acteoside, an antioxidant, on in vitro maturation (IVM) of oocytes to improve early parthenogenetic embryonic developmental competence.

METHODS

Porcine immature oocytes (total 770) were cultured in IVM medium with acteoside at various concentrations, 0 (control), 10, 30, and 50 μM. Each group was assessed for maturation and subsequent development rates, reactive oxygen species (ROS) level (15 oocytes per group and four independent experiments performed), ultrastructure observation (15 oocytes per group), mitochondrial activity (30 oocytes per groups and three independent experiments performed), and expression patterns of apoptosis-related genes (100 expended parthenogenetic embryos per group and three independent experiment performed). Main outcome measures were the rates of IVM, blastocyst formation, ROS, mitochondria, and expression of apoptosis-related genes in oocytes treated with acteoside.

RESULT(S)

Addition of acteoside during IVM did not change the maturation efficiency of oocytes but improved the rate of blastocyst formation with significantly decreased ROS level. Moreover, in acteoside-treated oocytes, cytoplasmic maturation was improved with morphologically uniform distribution of mitochondria and lipid droplets in cytoplasm. Acteoside supplementation also increased the mRNA expression levels of antiapoptotic genes and reduced those of pro-apoptotic genes.

CONCLUSION(S)

Acteoside supplementation in IVM medium improves the oocyte quality and subsequent development of pre-implantation embryos that would eventually contribute to produce embryos with high embryonic development competence.

Ammonium accumulation in commercially available embryo culture media and protein supplements during storage at 2-8°C and during incubation at 37°C

STUDY QUESTION

Does ammonium accumulate in commercially available culture media and protein supplements used for in vitro development of human pre-implantation embryos during storage and incubation?

SUMMARY ANSWER

Ammonium accumulates in ready-to-use in vitro fertilization (IVF) culture media during storage at 2-8°C and in ready-to-use IVF culture media and protein supplements during incubation at 37°C.

WHAT IS KNOWN ALREADY

Both animal and human studies have shown that the presence of ammonium in culture medium has detrimental effects on embryonic development and pregnancy rate. It is, therefore, important to assess the amount of ammonium accumulation in ready-to-use IVF culture media under conditions that are common in daily practice.

STUDY DESIGN, SIZE, DURATION

Ammonium accumulation was investigated in 15 ready-to-use media, 11 protein-free media and 8 protein supplements.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ammonium was measured by the use of an enzymatic method with glutamate dehydrogenase. To simulate the storage and incubation conditions during IVF treatments, ammonium concentrations were measured at different time-points during storage at 2-8°C for 6 weeks and during incubation at 37°C for 4 days.

MAIN RESULTS AND THE ROLE OF CHANCE

All ready-to-use, i.e. protein supplemented, culture media showed ammonium accumulation during storage for 6 weeks (ranging from 9.2 to 99.8 µM) and during incubation for 4 days (ranging from 8.4 to 138.6 µM), resulting in levels that might affect embryo development. The protein supplements also showed ammonium accumulation, while the culture media without protein supplementation did not. The main sources of ammonium buildup in ready-to-use culture media were unstable glutamine and the protein supplements. No additional ammonium buildup was found during incubation when using an oil overlay or with the presence of an embryo in the culture droplet.

LIMITATIONS, REASONS FOR CAUTION

In addition to the unstable glutamine and the protein supplements, other free amino acids might contribute to the ammonium buildup. We did not investigate the deterioration of other components in the media.

WIDER IMPLICATIONS OF THE FINDINGS

Break-down of components into ammonium is more pronounced during incubation at 37°C, however, it is not negligible during storage at 2-8°C. This results in increasing ammonium levels in culture media over time that may affect embryo development. Therefore, it is important that the use of free l-glutamine in human embryo culture media is stopped and that the use of protein supplements is thoroughly evaluated.

STUDY FUNDING/COMPETING INTERESTS

No funding or no competing interests declared.

TRIAL REGISTRATION NUMBER

Not applicable.

The Extracellular Calcium-Sensing Receptor (CASR) Regulates Gonadotropins-Induced Meiotic Maturation of Porcine Oocytes

Gonadotropins and epidermal growth factor (EGF) play crucial roles in promoting oocyte maturation. The regulatory network downstream of these key factors is not well understood. The present study was designed to investigate the role of the calcium-sensing receptor (CASR) in porcine oocyte in vitro maturation. CASR expression was up-regulated in oocytes matured in gonadotropin-containing medium. Cortical distribution of CASR was enhanced with gonadotropins but not EGF. Supplementation of a CASR agonist (NPS R-568) in the gonadotropin (FSH and/or LH)-containing maturation medium significantly enhanced oocyte nuclear maturation. Addition of NPS2390, a CASR antagonist, compromised oocyte nuclear maturation. Furthermore, increased cortical distribution and decreased expression of CASR was observed after the NPS R-568 treatment. Oocytes treated with NPS R-568 had higher concentration of CYCLIN B1, decreased reactive oxygen species, and increased glutathione levels, indicative of advanced cytoplasmic maturation. In contrast, NPS2390 treatment compromised oocyte cytoplasmic maturation. A higher blastocyst formation rate after parthenogenetic activation was observed when oocytes were matured in the presence of the CASR agonist, NPS R-568. MAPK3/1 phosphorylation was increased during in vitro maturation and after NPS R-568 treatment, and decreased following CASR antagonist supplementation. Taken together, our data showed that the CASR is a gonadotropin-regulated factor that promotes porcine oocyte maturation in a MAPK-dependent manner.

Mitochondrial SIRT5 is present in follicular cells and is altered by reduced ovarian reserve and advanced maternal age

Women with reduced ovarian reserve or advanced maternal age have an altered metabolic follicular microenvironment. As sirtuin 5 (SIRT5) senses cellular metabolic state and post-translationally alters protein function, its activity may directly impact on oocyte viability and pregnancy outcome. Therefore, we investigated the role of SIRT5 in relation to ovarian reserve and maternal age. Women (n=47) undergoing routine IVF treatment were recruited and allocated to one of three cohorts based on ovarian reserve and maternal age. Surplus follicular fluid, granulosa and cumulus cells were collected. SIRT5 mRNA, protein and protein activity was confirmed in granulosa and cumulus cells via qPCR, immunohistochemistry, western blotting and desuccinylation activity. The presence of carbamoyl phosphate synthase I (CPS1), a target of SIRT5, was investigated by immunohistochemistry and follicular-fluid ammonium concentrations determined via microfluorometry. Women with reduced ovarian reserve or advanced maternal age had decreased SIRT5 mRNA, protein and desuccinylation activity in granulosa and cumulus cells resulting in an accumulation of follicular-fluid ammonium, presumably via alterations in activity of a SIRT5 target, CPS1, which was present in granulosa and cumulus cells. This suggests a role for SIRT5 in influencing oocyte quality and IVF outcomes.

Comparison of Quinn's Advantage fertilization medium and tissue culture medium 199 for in vitro maturation of oocytes

OBJECTIVE

The purpose of the study was to compare the Quinn's Advantage fertilization medium (Q1) and the tissue culture medium 199 (TCM199) for in vitro maturation (IVM) of oocytes and ammonium production during IVM.

MATERIALS AND METHODS

The immature murine oocytes were randomly added into Q1 and TCM199. Ammonium concentrations were measured at the start and after 18 hours of IVM, and the mature oocytes were fertilized and cultured into blastocysts. The blastocysts were then stained for inner cell mass (ICM) and trophectoderm.

RESULTS

The maturation rate was higher in Q1 than in TCM199 (85.7% vs. 76.6%, p = 0.024). The fertilization and blastocyst rates were slightly higher in Q1, but not significant. Differential staining of the blastocysts showed slightly higher ICM ratio in the blastocysts derived from Q1. Mean ammonium concentrations in Q1 and TCM199 at Time 0 were 184.9 and 339.2 μg/dL, respectively (p = 0.05), and after 18 hours of IVM were 268.7 and 443.6 μg/dL, respectively (p = 0.045). Addition of ammonium chloride into Q1 adversely affects IVM.

CONCLUSION

Q1 is superior to TCM199 in terms of oocyte maturation, which may be due to lower ammonium concentration.

Effect of Dipeptides on In vitro Maturation, Fertilization and Subsequent Embryonic Development of Porcine Oocytes

The effects of amino acids and dipeptides on in vitro production of porcine embryos and accumulation of ammonia in culture medium during developmental stages were examined in this study. The maturation, fertilization and development of embryonic cultures were performed in modified Tissue culture medium (mTCM)-199 supplemented with 10% (v/v) porcine follicular fluid, modified Tyrode's albumin lactate pyruvate (mTALP) medium, and modified North Carolina State University (mNCSU)-23 medium, respectively. In addition, amino acids and dipeptides of different concentrations and combinations were used to treat the embryos. The addition of L-alanyl-L-glutamine (AlnGln)+L-glycyl-L-glutamine (GlyGln) significantly (p<0.05) improved oocyte maturation, fertilization and the incorporation and oxidation of (14)C(U)-glucose when compared to the control group and other treatment groups. Additionally, 2-4 cell, 8-16 cell, morula and blastocyst development increased significantly (p<0.05) following treatment with AlnGln+GlyGln when compared to the control group and other treatment groups, while this treatment reduced the accumulation of ammonia. Taken together, these findings suggest that treatment with AlnGln+GlyGln may play an important role in increasing the rate of porcine oocyte maturation, fertilization and embryonic development by reducing the level of accumulated ammonia measured in the culture media.

Small RNA profile of the cumulus-oocyte complex and early embryos in the pig

Small RNA represent several unique noncoding RNA classes that have important function in the development of germ cells and early embryonic development. Deep sequencing was performed on small RNA from cumulus cells (recovered from germinal vesicle [GV] and metaphase II-arrested [MII] oocytes), GV and MII oocytes, in vitro fertilization-derived embryos at 60 h postfertilization (4- to 8-cell stage), and Day 6 blastocysts. Additionally, a heterologous miRNA microarray method was also used to identify miRNA expressed in the oocyte during in vitro maturation. Similar to the results of expression analysis of other species, these data demonstrate dynamic expression regulation of multiple classes of noncoding RNA during oocyte maturation and development to the blastocyst stage. Mapping small RNA to the pig genome indicates dynamic distribution of small RNA organization across the genome. Additionally, a cluster of miRNA and Piwi-interacting RNA (piRNA) was discovered on chromosome 6. Many of the small RNA mapped to annotated repetitive elements in the pig genome, of which the SINE/tRNA-Glu and LINE/L1 elements represented a large proportion. Two piRNA (piR84651 and piR16993) and seven miRNA (MIR574, MIR24, LET7E, MIR23B, MIR30D, MIR320, and MIR30C) were further characterized using quantitative RT-PCR. Secretory carrier membrane protein 4 (SCAMP4) was predicted to be subject to posttranscriptional gene regulation mediated by small RNA, by annotating small RNA reads mapped to exonic regions in the pig genome. Consistent with the prediction results, SCAMP4 was further confirmed to be differentially expressed at both transcriptional and translational levels. These data establish a small RNA expression profile of the pig cumulus-oocyte complex and early embryos and demonstrate their potential capacity to be utilized for predictions of functional posttranscriptional regulatory events.