Improved cryotolerance and developmental potential of in vitro and in vivo matured mouse oocytes by supplementing with a glutathione donor prior to vitrification

Trapphoff T, Heiligentag M, Simon J, et al. Improved cryotolerance and developmental potential of in vitro and in vivo matured mouse oocytes by supplementing with a glutathione donor prior to vitrification. MOLECULAR HUMAN REPRODUCTION. 2016;22(12):867-881.STUDY QUESTION: Can supplementation of media with a glutathione (GSH) donor, glutathione ethyl ester (GEE), prior to vitrification protect the mouse oocyte from oxidative damage and critical changes in redox homeostasis, and thereby improve cryotolerance? SUMMARY ANSWER: GEE supplementation supported redox regulation, rapid recovery of spindle and chromosome alignment after vitrification/warming and improved preimplantation development of mouse metaphase II (MII) oocytes. WHAT IS KNOWN ALREADY: Cryopreservation may affect mitochondrial functionality, induce oxidative stress, and thereby affect spindle integrity, chromosome segregation and the quality of mammalian oocytes. GEE is a membrane permeable GSH donor that promoted fertilization and early embryonic development of macaque and bovine oocytes after IVM. STUDY DESIGN, SIZE, DURATION: Two experimental groups consisted of (i) denuded mouse germinal vesicle (GV) oocytes that were matured in vitro in the presence or absence of 1 mM GEE (IVM group 1) and (ii) in vivo ovulated (IVO) MII oocytes that were isolated from the ampullae and exposed to 1 mM GEE for 1 h prior to vitrification (IVO group 2). Recovery of oocytes from both groups was followed after CryoTop vitrification/warming for up to 2 h and parthenogenetic activation. PARTICIPANTS/MATERIALS, SETTING, METHODS: Reactive oxygen species (ROS), spindle morphology and chromosome alignment were analyzed by confocal laser scanning microscopy (CLSM) and polarization microscopy in control and GEE-supplemented MII oocytes. The relative overall intra-oocyte GSH content was assessed by analysis of monochlorobimane (MBC)-GSH adduct fluorescence in IVM MII oocytes. The GSH-dependent intra-mitochondrial redox potential (Em GSH) of IVM MII oocytes was determined after microinjection with specific mRNA at the GV stage to express a redox-sensitive probe within mitochondria (mito-Grx1-roGFP2). The absolute negative redox capacity (in millivolts) was determined by analysis of fluorescence of the oxidized versus the reduced form of sensor by CLSM and quantification according to Nernst equation. Proteome analysis was performed by quantitative 2D saturation gel electrophoresis (2D DIGE). Since microinjection and expression of redox sensor mRNA required removal of cumulus cells, and IVM of denuded mouse oocytes in group 1 induces zona hardening, the development to blastocysts was not assessed after IVF but instead after parthenogenetic activation of vitrified/warmed MII oocytes from both experimental groups. MAIN RESULTS AND ROLE OF CHANCE: IVM of denuded mouse oocytes in the presence of 1 mM GEE significantly increased intraoocyte GSH content. ROS was not increased by CryoTop vitrification but was significantly lower in the IVM GEE group compared to IVM without GEE before vitrification and after recovery from vitrification/warming (P < 0.001). Vitrification alone significantly increased the GSH-dependent intra-mitochondrial redox capacity after warming (E-GSH(m), P < 0.001) in IVM oocytes, presumably by diffusion/uptake of cytoplasmic GSH into mitochondria. The presence of 1 mM GEE during IVM increased the redox capacity before vitrification and there was no further increase after vitrification/warming. None of the reproducibly detected 1492 spots of 2D DIGE separated proteins were significantly altered by vitrification or GEE supplementation. However, IVM of denuded oocytes significantly affected spindle integrity and chromosome alignment right after warming from vitrification (0 h) in group 1 and spindle integrity in group 2 (P < 0.05). GEE improved recovery in IVM group as numbers of oocytes with unaligned chromosomes and aberrant spindles was not significantly increased compared to unvitrified controls. The supplementation with GEE for 1 h before vitrification also supported more rapid recovery of spindle birefringence. GEE improved significantly development to the 2-cell stage for MII oocytes that were activated directly after vitrification/warming in both experimental groups, and also the blastocyst rate in the IVO GEE-supplemented group compared to the controls (P < 0.05). LARGE SCALE DATA: None LIMITATIONS, REASONS FOR CAUTION: The studies were carried out in a mouse model, in IVM denuded rather than cumulus-enclosed oocytes, and in activated rather than IVF MII oocytes. Whether the increased GSH-dependent intra-mitochondrial redox capacity also improves male pronuclear formation needs to be studied further experimentally. The influence of GEE supplementation requires also further examination and optimization in human oocytes before it can be considered for clinical ART. WIDER IMPLICATIONS OF THE FINDINGS: Although GEE supplementation did not alter the proteome at MII, the GSH donor may support cellular homeostasis and redox regulation and, thus, increase developmental competence. While human MII oocyte vitrification is an established procedure, GEE might be particularly beneficial for oocytes that suffer from oxidative stress and reduced redox capacity (e.g. aged oocytes) or possess low GSH due to a reduced supply of GSH from cumulus. It might also be of relevance for immature human oocytes that develop without cumulus to MII in vitro (e.g. in ICSI cycles) for ART. STUDY FUNDING AND COMPETING INTERESTS: The study has been supported by the German Research Foundation (DFG FOR 1041; EI 199/3-2). There are no conflict of interests

Chromosomal and cytoplasmic context determines predisposition to maternal age-related aneuploidy: brief overview and update on MCAK in mammalian oocytes

Eichenlaub-Ritter U, Staubach N, Trapphoff T. Chromosomal and cytoplasmic context determines predisposition to maternal age-related aneuploidy: brief overview and update on MCAK in mammalian oocytes. Biochemical Society Transactions. 2010;38(6):1681-1686.It has been known for more than half a century that the risk of conceiving a child with trisomy increases with advanced maternal age However the origin of the high susceptibility to nondisjunction of whole chromosomes and precocious separation of sister chromatids leading to aneuploidy in aged oocytes and embryos derived from them cannot be traced back to a single disturbance and mechanism Instead analysis of recombination patterns of meiotic chromosomes of spread oocytes from embryonal ovary and of origins and exchange patterns of extra chromosomes in trisomies as well as morphological and molecular studies of oocytes and somatic cells from young and aged females show chromosome specific risk patterns and cellular aberrations related to the chronological age of the female In addition analysis of the function of meiotic and cell cycle regulating genes in oogenesis and the study of the spindle and chromosomal status of maturing oocytes suggest that several events contribute synergistically to errors in chromosome segregation in aged oocytes in a chromosome specific fashion For instance loss of cohesion may differentially predispose chromosomes with distal or pericentromeric chiasmata to nondisjunction Studies on expression in young and aged oocytes from human or model organisms like the mouse indicate that the presence and functionality/activity of gene products involved in cell cycle regulation spindle formation and organelle integrity may be altered in aged oocytes thus contributing to a high risk of error in chromosome segregation in meiosis I and II Genes that are often altered in aged mouse oocytes include MCAK (mitotic centromere associated protein) a microtubule depolymerase and AURKB (Aurora kinase B) a protein of the chromosomal passenger complex that has many targets and can also phosphorylate and regulate MCAK localization and activity Therefore we explored the role of MCAK in maturing mouse oocytes by immunofluorescence overexpression of a MCAK-EGFP (enhanced green fluorescent protein) fusion protein knockdown of MCAK by RNA! (RNA interference) and inhibition of AURKB The observations suggest that MCAK is involved in spindle regulation chromosome congression and cell cycle control and that r ductions in mRNA and protein in a context of permissive SAC (spindle assembly checkpoint) predispose to aneuploidy I allure to recruit MCAK to centromeres and low expression patterns as well as disturbances in regulation of enzyme localization and activity e g due to alterations in activity of AURKB may therefore contribute to maternal age related rises in aneuploidy in mammalian oocyte