Parthenogenetic activation of pig oocytes using pulsatile treatment with a nitric oxide donor

S-nitrosoglutathione reductase maintains mitochondrial homeostasis by promoting clearance of damaged mitochondria in porcine preimplantation embryos

OBJECTIVES

S-nitrosoglutathione reductase (GSNOR), a protein denitrosylase, protects the mitochondria from mitochondrial nitrosative stress. Mammalian preimplantation embryos are mitochondria-rich, but the effects of GSNOR on mitochondrial function in preimplantation embryos are not well-studied. In the present study, we investigate whether GSNOR plays a role in mitochondrial regulation during porcine preimplantation embryo development.

MATERIALS AND METHODS

GSNOR dsRNA was employed to knock down the expression of GSNOR, and Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME), a pan-NOS inhibitor, was used to prevent protein S-nitrosylation. Mitochondrial amount and function in embryo development were assessed by performing immunofluorescence staining, Western blot, fluorescent probe and real-time reverse transcription PCR.

RESULTS

GSNOR knock-down significantly impaired blastocyst formation and quality and markedly induced the increase in protein S-nitrosylation. Notably, GSNOR knock-down-induced overproduction of S-nitrosylation caused mitochondrial dysfunction, including mitochondrial membrane potential depolarization, mitochondria-derived reactive oxygen species (ROS) increase and ATP deficiency. Interestingly, GSNOR knock-down-induced total mitochondrial amount increase, but the ratio of active mitochondria reduction, suggesting that the damaged mitochondria were accumulated and mitochondrial clearance was inhibited. In addition, damaged mitochondria produced more ROS, and caused DNA damage and apoptosis. Importantly, supplementation with L-NAME reverses the increase in S-nitrosylation, accumulation of damaged mitochondria, and oxidative stress-induced cell death. Interestingly, autophagy was downregulated after GSNOR knock-down, but reversed by L-NAME treatment. Thus, GSNOR maintains mitochondrial homeostasis by promoting autophagy and the clearing of damaged mitochondria in porcine preimplantation embryos.

Gasotransmitters in Gametogenesis and Early Development: Holy Trinity for Assisted Reproductive Technology-A Review

Creation of both gametes, sperm and oocyte, and their fusion during fertilization are essential step for beginning of life. Although molecular mechanisms regulating gametogenesis, fertilization, and early embryonic development are still subjected to intensive study, a lot of phenomena remain unclear. Based on our best knowledge and own results, we consider gasotransmitters to be essential for various signalisation in oocytes and embryos. In accordance with nitric oxide (NO) and hydrogen sulfide (H₂S) physiological necessity, their involvement during oocyte maturation and regulative role in fertilization followed by embryonic development have been described. During these processes, NO- and H₂S-derived posttranslational modifications represent the main mode of their regulative effect. While NO represent the most understood gasotransmitter and H₂S is still intensively studied gasotransmitter, appreciation of carbon monoxide (CO) role in reproduction is still missing. Overall understanding of gasotransmitters including their interaction is promising for reproductive medicine and assisted reproductive technologies (ART), because these approaches contend with failure of in vitro assisted reproduction.

The effect of protein kinase C activator and nitric oxide donor on oocyte activation and cortical granule exocytosis in porcine eggs

Nitric oxide (NO) and protein kinase C (PKC) are involved in the activation of mammalian oocytes, although their role in the exit from the metaphase II stage and cortical granule (CG) exocytosis is still not fully understood. The aim of this study was to verify whether the NO-donor together with specific PKC-activators induce the complete activation of porcine oocytes assessed as meiosis resumption and a cortical reaction. Pig maturated oocytes were treated with the NO-donor S-nitroso-N-acetylpenicillamine (SNAP, 2 mM) or PKC-activators such as phorbol-12-myristate-13-acetate (PMA, 100 nM), 1-oleoyl-2-acetyl-sn-glycerol (OAG, 400 μM) and l-α-phosphatidylinositol-3,4,5-trisphosphate dipalmitoyl heptaammonium salt (DPAM, 2 μM). To study the combined effect of NO-donor and PKC-activators, aliquots of oocytes were also incubated with SNAP (0.5 mM) together with PKC-activators at the same concentration as above (SNAP-DPAM, SNAP-OAG and SNAP-PMA groups). After in vitro maturation, an aliquot of oocytes was placed in a fresh medium without NO-donor or PKC-activators (Control group). Another aliquot of oocytes was activated by calcium ionophore A23187 (25 μM, 5 min). The results showed that 0% of the control oocytes reassumed meiosis. However, both the PKC-activators (DPAM 44.0 ± 10.0%, OAG 63.3 ± 1.0% and PMA 45.0 ± 16.5%) as well as the NO-donor alone (48.7 ± 21.0%) significantly induced exit from MII. Interestingly, the combination of PKC-activators and SNAP mainly restrained to the meiosis resumption (SNAP-OAG 0, SNAP-DPAM 17.4 ± 2.5% and SNAP-PMA 38.4 ± 8.5%). Control oocytes did not show a cortical reaction and the area occupied by CG reached 25.9 ± 1.7%, whereas CGs were partially released after Ca2+ ionophore treatment (13.0 ± 3.2%). Treatment with PKC-activators induced a cortical reaction compared with the control group (8.6 ± 2.5, 6.7 ± 1.9 and 0.7 ± 0.4%, respectively, for DPAM, OAG and PMA groups). However, treatment with the NO-donor alone (SNAP group 17.2 ± 2.2%) or combined with any PKC-activator prevented cortical reaction (SNAP-DPAM 20.7 ± 2.6%, SNAP-OAG 16.7 ± 2.9% or SNAP-PMA 20.0 ± 2.4%). Besides, meiosis resumption was not always accompanied by a cortical reaction, indicating that these two activation events are independent. In conclusion, PKC-activators alone induce CG exocytosis to the same degree as calcium ionophore. However, an NO-donor alone or combined with PKC-activators is not able to induce a cortical reaction in pig oocytes.

Effect of different activation modes on DNA integrity of porcine M II oocytes maturedin vitro

The effect of different activation protocols on DNA integrity of porcine oocytes maturedin vitrowas analysed using the comet assay. The oocytes from ovaries of slaughtered gilts were cultured for 48 h in modified M199 medium. They were then freed of cumulus cells and treated continuously or intermittently with a nitric oxide (NO) donor for 6 h. Standard activation with calcium ions (Ca2+) and culture without any treatment served as positive and negative controls, respectively. The activation was assessed according to the formation of pronuclei. Exposure of oocytes to Ca2+was associated with high activation efficiency, but decreased DNA integrity. The opposite, i.e. low activation efficiency but high DNA integrity was observed after continuous exposure to NO. Intermittent action of NO increased the activation rate, while the values of DNA damage remained at low levels. Our data suggest that an increased DNA instability could be the main reason compromising the further embryonic development of oocytes activated by the standard protocol. The intermittent treatment with NO thus represents a promising step to optimization of parthenogenetic activation of pig oocytes.