Heat-shock-induced cathepsin B activity during IVF and culture compromises the developmental competence of bovine embryos

The strong anti-hyaluronidase effect of ellagic acid markedly decreases polyspermy during in vitro fertilization, resulting in sustainment of the developmental potency in porcine oocytes

The present study investigated the effects of ellagic acid, a type of polyphenol that does not have a glycan and is composed of four hydroxyl groups and two lactone functional groups, on porcine in vitro fertilization (IVF) by focusing on its anti-hyaluronidase activity. A comparative analysis of ellagic acid and apigenin, which is commonly used as a hyaluronidase inhibitor, was performed. It compared the effects of ellagic acid and apigenin on hyaluronidase activity at different concentrations. The results showed that 10, 20, and 40 μM ellagic acid strongly reduced hyaluronidase activity (P < 0.05). The addition of 20 μM ellagic acid, but not apigenin, to porcine IVF medium effectively reduced polyspermy without decreasing sperm penetration or the formation rates of male pronuclei in cumulus-free oocytes. However, neither ellagic acid nor apigenin affected the number of sperm that bound to zona pellucida (ZP) or the induction of zona hardening and protease resistance. The percentage of acrosome-reacting sperm that bound to the ZP was markedly lower in the presence of 20 μM ellagic acid than in the untreated and apigenin-treated groups, even though the antioxidant capacity of ellagic acid was weaker than that of apigenin. Furthermore, a markedly higher percentage of embryos developed to the blastocyst stage in the ellagic acid-treated group, and the apoptotic indexes of expanded blastocysts produced by the ellagic acid treatment during IVF were significantly low. Therefore, the anti-hyaluronidase effect of ellagic acid markedly suppressed the induction of the acrosome reaction in sperm that bound to the ZP, resulting in a marked decrease in polyspermy under conditions that maintained high sperm penetrability during IVF and sustainment of the developmental potency in porcine oocytes.

Cathepsin L regulates oocyte meiosis and preimplantation embryo development

Early embryonic loss, caused by reduced embryo developmental competence, is the major cause of subfertility in humans and animals. This embryo developmental competence is determined during oocyte maturation and the first embryo divisions. Therefore, it is essential to identify the underlying molecules regulating these critical developmental stages. Cathepsin L (CTSL), a lysosomal cysteine protease, is involved in regulating cell cycle progression, proliferation and invasion of different cell types. However, CTSL role in mammalian embryo development is unknown. Using bovine in vitro maturation and culture systems, we show that CTSL is a key regulator for embryo developmental competence. We employed a specific CTSL detection assay in live cells to show that CTSL activity correlates with meiotic progression and early embryo development. Inhibiting CTSL activity during oocyte maturation or early embryo development significantly impaired oocyte and embryo developmental competence as evidenced by lower cleavage, blastocyst and hatched blastocyst rates. Moreover, enhancing CTSL activity, using recombinant CTSL (rCTSL), during oocyte maturation or early embryo development significantly improved oocyte and embryo developmental competence. Importantly, rCTSL supplementation during oocyte maturation and early embryo development significantly improved the developmental competence of heat-shocked oocytes/embryos which are notoriously known for reduced quality. Altogether, these results provide novel evidence that CTSL plays a pivotal role in regulating oocyte meiosis and early embryonic development.

Oxidative Stress in Assisted Reproductive Techniques, with a Focus on an Underestimated Risk Factor

Based on current findings, the presence of oxidative stress has a significant impact on the quality of gametes and embryos when performing assisted reproductive techniques (ART). Unfortunately, in vitro manipulation of these cells exposes them to a higher level of reactive oxygen species (ROS). The primary goal of this review is to provide a comprehensive overview of the development of oxidative stress in female and male reproductive systems, as well as in the case of the pre-implantation embryo and its environment. This review also focuses on the origins of ROS and the mechanisms of oxidative stress-induced damage during ART procedures. A well-known but underestimated hazard, light exposure-related photo-oxidation, is particularly concerning. The effect of oxidative stress on ART outcomes, as well as the various strategies for preventing it, are also discussed. We emphasize the role and significance of antioxidants and light protection including forms, functions, and mechanisms in the development of gametes and embryos in vivo and in vitro.

Effects of temperature on cathepsin B, cathepsin D and acid phosphatase during embryo development of the hard tick Haemaphysalis longicornis

The effects of temperature on the expression patterns and enzyme activity of cathepsin B (HlCatB), cathepsin D (HlCatD) and acid phosphatase (HlACP) during the embryo development of Haemaphysalis longicornis (bisexual population) were investigated in this study. Eggs were exposed to 20 °C (low temperature), 26 °C (normal temperature), and 30 °C (high temperature) immediately after laying, and collected on odd days of embryo development to measure HlCatB, HlCatD and HlACP gene expression using quantitative real-time PCR, as well as three enzyme activities using spectrophotometry. Then the associations between mRNA expression levels of three enzymes and their enzyme activities were assessed. Compared with normal temperature, the mRNA expression peaks of HlCatB were higher and appeared later at low and high temperatures and the activity of HlCatB increased on most days of embryonic development at high temperature. As for HlCatD, the expression peak appeared later at low temperature, but earlier at high temperature. The activity peaks of HlCatD were lower and appeared earlier at low and high temperatures. As for HlACP, the expression peak was higher and appeared later at low temperature, whereas it formed no prominent peak at high temperature. The activity peak of HlACP was higher at low temperature, but lower at high temperature. The linear regression analysis showed that activities of three enzymes were associated with their mRNA expression levels (P < 0.05). Three enzymes are involved in the embryo adaptation to temperature stress. Moreover, the mRNA expression level may be another factor affecting its enzyme activity.

The global gene expression outline of the bovine blastocyst: reflector of environmental conditions and predictor of developmental capacity

Background

Morphological evaluation of embryos has been used to screen embryos for transfer. However, the repeatability and accuracy of this method remains low. Thus, evaluation of an embryo’s gene expression signature with respect to its developmental capacity could provide new opportunities for embryo selection. Since the gene expression outline of an embryo is considered as an aggregate of its intrinsic characteristics and culture conditions, we have compared transcriptome profiles of in vivo and in vitro derived blastocysts in relation to pregnancy outcome to unravel the discrete effects of developmental competence and environmental conditions on bovine embryo gene expression outlines. To understand whether the gene expression patterns could be associated with blastocyst developmental competency, the global transcriptome profile of in vivo (CVO) and in vitro (CVT) derived competent blastocysts that resulted in pregnancy was investigated relative to that of in vivo (NVO) and in vitro (NVT) derived blastocysts which did not establish initial pregnancy, respectively while to unravel the effects of culture condition on the transcriptome profile of embryos, the transcriptional activity of the CVO group was compared to the CVT group and the NVO group was compared to the NVT ones.

Results

A total of 700 differentially expressed genes (DEGs) were identified between CVO and NVO blastocysts. These gene transcripts represent constitutive regions, indel variants, 3′-UTR sequence variants and novel transcript regions. The majority (82%) of these DEGs, including gene clusters like ATP synthases, eukaryotic translation initiation factors, ribosomal proteins, mitochondrial ribosomal proteins, NADH dehydrogenase and cytochrome c oxidase subunits were enriched in the CVO group. These DEGs were involved in pathways associated with glycolysis/glycogenesis, citrate acid cycle, pyruvate metabolism and oxidative phosphorylation. Similarly, a total of 218 genes were differentially expressed between CVT and NVT groups. Of these, 89%, including TPT1, PDIA6, HSP90AA1 and CALM, were downregulated in the CVT group and those DEGs were overrepresented in pathways related to protein processing, endoplasmic reticulum, spliceasome, ubiquitone mediated proteolysis and steroid biosynthesis. On the other hand, although both the CVT and CVO blastocyst groups resulted in pregnancy, a total of 937 genes were differential expressed between the two groups. Compared to CVO embryos, the CVT ones exhibited downregulation of gene clusters including ribosomal proteins, mitochondrial ribosomal protein, eukaryotic translation initiation factors, ATP synthases, NADH dehydrogenase and cytochrome c oxidases. Nonetheless, downregulation of these genes could be associated with pre and postnatal abnormalities observed after transfer of in vitro embryos.

Conclusion

The present study provides a detailed inventory of differentially expressed gene signatures and pathways specifically reflective of the developmental environment and future developmental capacities of bovine embryos suggesting that transcriptome activity observed in blastocysts could be indicative of further pregnancy success but also adaptation to culture environment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07693-0.

Heat stress on oocyte or zygote compromises embryo development, impairs interferon tau production and increases reactive oxygen species and oxidative stress in bovine embryos produced in vitro

Interferon tau (IFNT) is the cytokine responsible for the maternal recognition of pregnancy in ruminants and plays a role modulating embryo-maternal communication in the oviduct inducing a local response from immune cells. We aimed to investigate IFNT production, reactive oxygen species, and oxidative stress under the influence of heat stress (HS) during different stages of bovine in vitro embryo production. HS was established when the temperature was gradually raised from 38.5°C to 40.5°C in laboratory incubator, sustained for 6 hr, and decreased back to 38.5°C. To address the HS effects on IFNT production, reactive oxygen species, and oxidative stress, ovaries from a slaughterhouse were used according to treatments: control group (38.5°C); oocytes matured under HS; oocytes fertilized under HS; zygotes cultured in the first day under HS; and cells submitted to HS at oocyte maturation, fertilization, and the first day of zygote culture. The HS negatively affected cleavage and blastocyst rates, in all HS groups. On Day 7, all HS-treated embryos showed decrease IFNT gene and protein expressions, whereas reactive oxygen species were increased in comparison to the control. In conclusion, the compromised early embryo development due to higher temperatures during in vitro oocyte maturation, fertilization, and/or zygote stage have diminished IFNT expression and increased reactive oxygen species in bovine.