Nitric oxide (NO)-induced protein S-nitrosylation triggers mitochondrial dysfunction and was related to cell senescence. However, the exact mechanism of these damages is not clear. In the present study, to investigate the relationship between in vitro aging and NO-induced protein S-nitrosylation, oocytes were treated with sodium nitroprusside dihydrate (SNP), and the resultant S-nitrosylated proteins were detected through biotin-switch assay. The results showed that levels of protein S-nitroso thiols (SNO)s and expression of S-nitrosoglutathione reductase (GSNOR) increased, while activity and function of mitochondria were impaired during oocyte aging. Addition of SNP, a NO donor, to the oocyte culture led to accelerated oocyte aging, increased mitochondrial dysfunction and damage, apoptosis, ATP deficiency, and enhanced ROS production. These results suggested that the increased NO signal during oocyte aging in vitro, accelerated oocyte degradation due to increased protein S-nitrosylation, and ROS-related redox signaling.

Connexin 43 (Cx43) is one of the gap junction proteins which are compounds of transmembrane proteins and transports the small-molecular-weight chemicals up to 2 kDa. Lacking of Cx43 influences the junctional protein, induces autophagy and apoptosis in somatic cells. However, the function of Cx43 in porcine early embryos is still unknown. Aim to find out the molecular mechanism of Cx43 on the developmental competence in early porcine embryos, Cx43 dsRNA (1 ㎍/㎕) was microinjected into the parthenogenetically activated porcine zygotes. Blastocyst rate (treatment, 8.8±1.6% vs. control, 38.6±4.3%) and total cell numbers in the blastocyst (treatment, 20.7±3.5 vs. control, 39.8±4.1) were significantly reduced following Cx43 knocking down. Results from FITC-dextran and Western blot assay show that knock down (KD) of Cx43 significantly increased membrane permeability through down regulation of genes which are component of both adherence and tight junction in the porcine blastocyst. Reactive oxygen species (ROS) was significantly increased in the Cx43 KD group compared to control. In addition, KD of Cx43 activated Caspase 3 and significantly increased ATG8 expression, induced autophagy and apoptosis. Results suggest that KD of Cx43 influences preimplantation porcine embryo development via increasing membrane permeability and ROS generation, and inducing autophagy and apoptosis.

Melatonin (N-aceyl-5-methoxytryptamine) is the major hormone of the pineal gland. Melatonin and its metabolic derivatives possess extensive free-radical scavenging abilities and played critical roles in antioxidative stress, resisting apoptotic cell death. Melatonin also could enhance mitochondrial biogenesis in rats with carbon tetrachloride-induced liver fibrosis. In addition, melatonin attenuates myocardial ischemia/reperfusion injury by reducing oxidative stress damage via activation of SIRT1 signaling in a melatonin receptor 2-dependent manner. Activation or overexpression of SIRT1 could enhance mitochondrial biogenesis and function by inducing PGC-1α expression and deacetylation. The aim of this study was to investigate if melatonin enhances mitochondrial biogenesis and function via activation of melatonin receptor 2/SIRT1/PGC1-α Pathway. The results showed that Melatonin rescued rotenone-induced impairment of porcine embryo development. Treatment with rotenone could increase oxidative stress and apoptosis. Rotenone impaired mitochondrial functions by disrupting mitochondrial membrane potential, reducing mitochondrial DNA copy number and ATP production. Melatonin could improve SIRT1 and PGC-1α expression, inducing mitochondrial biogenesis. Rotenone-induced mitochondrial dysfunction and ATP deficiency was rescued by melatonin treatment, the oxidative stress and apoptosis was significantly decreased. Inhibition of melatonin receptor 2 or Knockdown of SIRT1 abolished the protective effects of melatonin on rotenone-induced impairments. Therefore, melatonin enhanced mitochondrial biogenesis and function, protected against rotenone-induced impairments.

Thiamethoxam (TMX) is a neonicotinoid insecticide. Residues of TMX have been detected in various crops. Although it has specific high toxicity to insects and is designed to exterminate them, the toxicity has also found in mammals recently. Differ from acetylcholine toxicity, TMX has peroxide toxicity in mammals. Matured oocytes have the capacity of fertilization, but oocytes own abundant mitochondria and its maturation is vulnerable to reactive oxygen species (ROS). Excessive production of reactive oxygen species (ROS) can override antioxidant defenses, produce oxidative stress and DNA damage that triggers apoptosis and necrosis in organisms. However little is known about the harm of ROS induced by TMX during oocytes maturation. Here, bovine germ-vesicle (GV) oocytes were cultured to metaphase of the second meiosis (MII) stage in vitro with or without TMX. During this process, oocytes were evaluated by various methods. Microscopic examination showed that 1.6 mM TMX significantly inhibited the maturation process in which oocytes were arrested before MI stage or between MI and MII stage. Correspond to this two periods, immunofluorescence staining and enzyme activity analysis showed that active CDC25 and CDC2 reduced in TMX group compared to control; time lapse and immunofluorescence staining gave results that Cyclin B could not be degraded, actin cap could not form, and Bub3 could not be removed from kinetochores. In addition, MII oocytes exposed to TMX showed disordered chromosomes and spindle. To study further, oocytes cultured for 24 h were analyzed. On the one hand, these oocytes in TMX group accumulated more ROS and produced significantly decreased mitochondrial membrane potential and increased apoptotic signal compared to control by methods of quantities for dichlorodihydrofluorescein diacetate (DCHFDA), 5,5′,6,6′-Tetrachloro-1,1′,3,3′-tetraethyl-imidacarbocyanine iodide and Annexin-V, but the level of γH2AX protein in TMX group did not decline significantly compared with control. On the another hand, these oocytes were activated to be parthenogenetic embryos and cultured. Assessment for embryo development showed decreased rates of cleavage, morula and blastocyst in TMX group compared to control in vitro. In conclusion, these results suggest that ROS induced by TMX results in dysfunction of mitochondria and apoptosis, which block bovine oocytes to MI stage, trap them at AI/TI stage and trigger disordered chromosomes and spindle at MII stage. Additionally, MII oocytes with poor qualities result from TMX lose abilities to cleavage and develop to be morulae and blastocysts.

The porcine zygotic genome activation occurs along with global epigenetic remolding at the 4-cell stage. The histone acetylation, regulating DNA transcription, replication and so on, requires adequate acetyl-CoA. Acetyl-CoA produced by translocated pyruvate dehydrogenase in the nucleus of mammalian cells has been reported, which is commonly considered locating in the mitochondria. To find out whether the nuclear pyruvate dehydrogenase regulating the histone acetylation by controlling generation of acetyl-CoA, a multiple sgRNAs-CRISPR/Cas9 targeting strategy was employed to generate a pyruvate dehydrogenase E1 alpha1 (Pdha1) knockout (KO) parthenogenetic embryo model. Results showed that the targeting efficiency of Pdha1 reached more than 90%. Hence, this model was used in the subsequent experiments. Furthermore, a translocation of Pdha1 during zygotic genome activation was found by immunofluorescent staining and was significantly inhibited by Pdha1 KO. Meanwhile, the 8-cell stage embryo rate significantly decreased after 72 h (24.19% vs 12.53%, control vs Pdha1 KO), indicating a 4-cell arrest. In addition, the nuclear histone acetylation level significantly decreased when Pdha1 was KO. To determine whether the zygotic genome transcription was affected, the qPCR was performed and showed that the mRNA level of Eif1A, Acly, Sqle and Pdha1 all dropped significantly in the Pdha1 KO group compared to the control. In conclusion, the translocated Pdha1 generates acetyl-CoA for histone acetylation inside the nucleus of porcine embryos, which promotes the zygotic genome activation of porcine embryos.