Exposure to cadmium during in vitro maturation at environmental nanomolar levels impairs oocyte fertilization through oxidative damage: A large animal model study

Cadmium is a highly toxic heavy metal with negative effects on oocyte fertilization. The aim of this study was to analyse whether cadmium-induced impairment of fertilization is caused by mitochondria dysfunction and oxidative stress in the cumulus-oocyte complex (COC). Preliminarily, 19 trace element levels were measured in ovaries from juvenile and adult ewes and age-related cadmium ovarian bioaccumulation at nanomolar concentrations was found. COCs from juvenile and adult ewes, exposed during in vitro maturation to 1nM or 100nM CdCl₂, and subjected to in vitro fertilization showed significantly lower fertilization rates in exposed COCs compared with controls. In vitro matured exposed and control COCs underwent confocal microscopy analysis of mitochondria activity and reactive oxygen species (ROS) levels and lipid peroxidation (LPO) assay at cumulus cell and oocyte level. In both age groups, cadmium at nanomolar concentrations induced cumulus-oocyte mitochondria over-activity and oxidative damage which were related to impaired oocyte fertilization.

Differentiation of human neuroblastoma cells toward the osteogenic lineage by mTOR inhibitor

Current hypothesis suggest that tumors can originate from adult cells after a process of 'reprogramming' driven by genetic and epigenetic alterations. These cancer cells, called cancer stem cells (CSCs), are responsible for the tumor growth and metastases. To date, the research effort has been directed to the identification, isolation and manipulation of this cell population. Independently of whether tumors were triggered by a reprogramming of gene expression or seeded by stem cells, their energetic metabolism is altered compared with a normal cell, resulting in a high aerobic glycolytic 'Warburg' phenotype and dysregulation of mitochondrial activity. This metabolic alteration is intricately linked to cancer progression.The aim of this work has been to demonstrate the possibility of differentiating a neoplastic cell toward different germ layer lineages, by evaluating the morphological, metabolic and functional changes occurring in this process. The cellular differentiation reported in this study brings to different conclusions from those present in the current literature. We demonstrate that 'in vitro' neuroblastoma cancer cells (chosen as experimental model) are able to differentiate directly into osteoblastic (by rapamycin, an mTOR inhibitor) and hepatic lineage without an intermediate 'stem' cell step. This process seems owing to a synergy among few master molecules, metabolic changes and scaffold presence acting in a concerted way to control the cell fate.

The respiratory chains of four strains of the alkaliphilic Bacillus clausii

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It is important to understand how alkaliphilic prokaryotes thrive at high pH.

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An interesting issue is their ability to cope with bioenergetics at high pH.

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We show that four genetically similar strains adopt different biochemical behaviors.

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Two of the strains show a functional redundancy of the terminal part of the respiratory chain.

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Biochemical data correlate with the expression of cytochrome c oxidase and quinol oxidase genes (heme-copper types).

A comparative analysis of terminal respiratory enzymes has been performed on four strains of Bacillus clausii used for preparation of a European probiotic. These four strains originated most probably from a common ancestor through early selection of stable clones for industrial propagation. They exhibit a low level of intra-specific diversity and a high degree of genomic conservation, making them an attractive model to study the different bioenergetics behaviors of alkaliphilic bacilli. The analysis of the different bioenergetics responses has been carried out revealing striking differences among the strains. Two out of the four strains have shown a functional redundancy of the terminal part of the respiratory chain. The biochemical data correlate with the expression level of the mRNA of cytochrome c oxidase and quinol oxidase genes (heme-copper type). The consequences of these different bioenergetics behaviors are also discussed.

251 DEVELOPMENTAL AND BIOENERGY/OXIDATIVE CHARACTERIZATION OF PREPUBERTAL OVINE OOCYTES MATURED IN VITRO

Juvenile in vitro embryo transfer in farm animals reduces the generation interval and increases the rate of genetic gain. In human reproductive medicine, it enables the preservation of female fertility of young patients affected by cancer or by premature ovarian failure. The developmental competence of in vitro-produced juvenile embryos is strictly related to oocyte quality. The aim of the present study was to analyse the developmental potential and the mitochondrial/oxidative status of ovine prepubertal oocytes matured in vitro to clarify their suitability in juvenile in vitro embryo transfer programs. Oocytes from the ovaries of slaughtered prepubertal lambs (less than 6 months of age) were analysed after in vitro maturation. After cumulus cell removal, oocytes at the metaphase II stage (MII) underwent either IVF plus in vitro embryo culture (Experiment 1; n = 200; Bogliolo et al. 2011 Reprod. Fert. Dev. 23, 809–817) or confocal analysis of mitochondria (mt) and reactive oxygen species (ROS) fluorescence distribution, intensity, and colocalization (Experiment 2; n = 30; Martino et al. 2012 Fertil. Steril. 97, 720–728) or scavenger enzyme [superoxide dismutase (Ambruosi et al. 2011 PLoS ONE 6, e27452) and catalase (Beers and Sizer 1952 J. Biol. Chem. 195, 133–140)] activity analyses in cell lysates of individual oocytes (Experiment 3; n = 7). In Experiment 1, 150 of 200 MII oocytes (75%) cleaved after 30 h of in vitro embryo culture, and 36 of 150 2- to 4-cell-stage embryos (24%) reached the blastocyst stage at Day 8. In Experiment 2, 60 of 111 (54%) oocytes selected for in vitro maturation culture reached the MII stage, and 30 of them (50%) with a regular size (>150 µm in diameter) and morphology were analysed for bioenergy/redox parameters. Fourteen of 30 oocytes (47%) showed a heterogeneous (perinuclear, pericortical, or both) mt distribution pattern, and the remaining 16 of 30 oocytes (53%) showed a homogeneous distribution of small mt aggregates. Intracellular ROS were uniformly distributed, thus not corresponding to the mt distribution pattern. Fluorescent intensity of mt and ROS labelling, expressed as arbitrary densitometric units, were 821.4 ± 274.7 and 737.6 ± 226.5 in oocytes with a heterogeneous pattern and 723.7 ± 371.6 and 831.7 ± 263.7 in oocytes with a homogeneous pattern, respectively (not significant). The mt/ROS colocalization (Pearson correlation coefficient) did not differ between heterogeneous (0.47 ± 0.2) and homogeneous (0.51 ± 0.09; not significant) oocytes. In Experiment 3, superoxide dismutase (n = 4) and catalase activity (n = 3) values were 1.09 ± 0.03 and 10.63 ± 1.96 IU mg–1 of protein, respectively. This study provides basal values of bioenergy/redox parameters in prepubertal lamb MII oocytes as related to their developmental potential and may increase the knowledge of prepubertal oocyte physiology compared with their young adult counterparts.

247 ADENOSINE TRIPHOSPHATE CONTENT AND SUPEROXIDE DISMUTASE ACTIVITY IN SINGLE OOCYTES BEFORE AND AFTER IN VITRO MATURATION

The developmental competence of in vitro-produced embryos is strictly related to oocyte quality. Analyses of energy and redox status parameters are emerging technologies useful for further oocyte quality characterisation. Mitochondrial (mt) activity is a necessary feature involved in cytoplasmic maturation, and the primary function of mitochondria is adenosine triphosphate (ATP) production. Mitochondria distribution pattern and ATP content are important parameters in the evaluation of oocyte metabolic activity, particularly activities driving microtubules dynamics leading to chromosomes segregation. Superoxide dismutase (SOD), a first-line antioxidant enzyme, has also been hypothesised as being associated to oocyte quality. The aim of the present study was to analyse ATP content and SOD activity in single equine oocytes examined before and after in vitro maturation. Cumulus–oocyte complexes surrounded by a compact cumulus oophorus were recovered from the ovaries of slaughtered mares and analysed before or after in vitro maturation (Ambruosi et al. 2009 Theriogenology 71, 1093–1104). After cumulus cell removal, all oocytes underwent evaluation of signs of meiotic maturation, and only those oocytes showing cumulus expansion, regular ooplasmic size (>160 μm in diameter) and morphology, and 1st polar body extrusion were selected for analysis. Adenosine triphosphate intracellular levels were analysed by luciferin-luciferase bioluminescent reaction (ATPlite, PerkinElmer, Monza, Italy). Quantification of SOD activity was performed by spectrophotometrical assay with WST1 and by polyacrylamide native gel and nitro blue tetrazolium reduction method. Intracellular ATP levels were influenced by meiotic stage in that oocytes at the germinal vesicle stage (GV, n = 15) showed 1.25 ± 0.8 pmol cell–1, whereas metaphase II (MII) oocytes (n = 15) showed significantly higher levels (2.29 ± 1.69 pmol cell–1; P < 0.05). This is in line with our previous observations on mt distribution pattern analysed by Mitotracker Orange CMTM Ros staining and confocal microscopy (Ambruosi et al. 2009). In vitro-matured MII oocytes showed significantly higher rates of perinuclear mt distribution pattern, indicating mt aggregation around meiotic metaphase spindle, compared with GV oocytes (3/12, 25% v. 0/13, 0% in GV oocytes; P < 0.05). Superoxide dismutase spectrophotometrical activity was 0.72 ± 0.55 U mg–1 prot in GV oocytes (n = 4) and 2.33 ± 0.33 U mg–1 prot in MII oocytes (n = 2; P < 0.001). In native gel SOD activity was 16 285.05 arbitrary densitometric units (ADU) in a GV oocyte and 22 501.35 ADU in a MII oocyte. To our knowledge, this is the first study reporting intracellular SOD activity in single oocytes in mammals. Moreover, this is the first study reporting ATP content in single equine oocytes. Observed quantitative differences seem to be related to meiotic stage. Financial support was provided by MIUR PRIN 2007 Project Quota di Ateneo University of Bari, Italy, Resp. Sci. Pro M. E. DellAquila (prot. 2007S75KSE_003).

Regulation by the cAMP cascade of oxygen free radical balance in mammalian cells

A study is presented of the effect of the cAMP cascade on oxygen metabolism in mammalian cell cultures. Serum-starvation of the cell cultures resulted in depression of the forward NADH-ubiquinone oxidoreductase activity of complex I, decreased content of glutathione, and enhancement of the cellular level of H2O2. Depressed transcription of cytosolic Cu/Zn-SOD 1, mitochondrial glutathione peroxidase and catalase was also observed. Activation of the cAMP cascade reversed the depression of the activity of complex I and the accumulation of H2O2. The effect of cAMP involved the cAMP-dependent protein kinase.

The NADH: ubiquinone oxidoreductase (complex I) of the mammalian respiratory chain and the cAMP cascade

Recent work has revealed cAMP-dependent phosphorylation of the 18-kDa IP subunit of the mammalian complex I of the respiratory chain, encoded by the nuclear NDUFS4 gene (chromosome 5). Phosphorylation of this protein has been shown to take place in fibroblast cultures in vivo, as well as in isolated mitochondria, which in addition to the cytosol also contain, in the inner-membrane matrix fraction, a cAMP-dependent protein kinase. Mitochondria appear to have a Ca2+-inhibited phosphatase, which dephosphorylates the 18-kDa phosphoprotein. In fibroblast and myoblast cultures cAMP-dependent phosphorylation of the 18-kDa protein is associated with potent stimulation of complex I and overall respiratory activity with NAD-linked substrates. Mutations in the human NDUFS4 gene have been found, which in the homozygous state are associated with deficiency of complex I and fatal neurological syndrome. In one case consisting of a 5 bp duplication, which destroyed the phosphorylation site, cAMP-dependent activation of complex I was abolished in the patient's fibroblast cultures. In another case consisting of a nonsense mutation, leading to termination of the protein after only 14 residues of the putative mitochondria targeting peptide, a defect in the assembly of complex I was found in fibroblast cultures.

Complex I and the cAMP cascade in human physiopathology

A cAMP-dependent protein kinase (PKA) is localized in mammalian mitochondria with the catalytic site at the matrix side of the membrane where it phosphorylates a number of proteins. One of these is the 18 kDa(IP) subunit of the mammalian complex I of the respiratory chain, encoded by the nuclear NDUFS4 gene. Mitochondria have a Ca(2+)-inhibited phosphatase, which dephosphorylates the 18 kDa phosphoprotein of complex I. In fibroblast and myoblast cultures cAMP-dependent phosphorylation of the 18 kDa protein is associated with stimulation of complex I and overall respiratory activity with NAD-linked substrates. Mutations in the human NDUFS4 gene have been found, which in the homozygous state are associated with deficiency of complex I and fatal neurological syndrome.

Cyclic adenosine monophosphate-dependent phosphorylation of mammalian mitochondrial proteins: enzyme and substrate characterization and functional role

A study is presented on cyclic adenosine monophosphate- (cAMP-) dependent phosphorylation of mammalian mitochondrial proteins. Immunodetection with specific antibodies reveals the presence of the catalytic and the regulatory subunits of cAMP-dependent protein kinase (PKA) in the inner membrane and matrix of bovine heart mitochondria. The mitochondrial cAMP-dependent protein kinase phosphorylates mitochondrial proteins of 29, 18, and 6.5 kDa. With added histone as substrate, PKA exhibits affinities for ATP and cAMP and pH optimum comparable to those of the cytosolic PKA. Among the mitochondrial proteins phosphorylated by PKA, one is the nuclear-encoded (NDUFS4 gene) 18 kDa subunit of complex I, which has phosphorylation consensus sites in the C terminus and in the presequence. cAMP promotes phosphorylation of the 18 kDa subunit of complex I in myoblasts in culture and in their isolated mitoplast fraction. In both cases cAMP-dependent phosphorylation of the 18 kDa subunit of complex I is accompanied by enhancement of the activity of the complex. These results, and the finding of mutations in the NDUFS4 gene in patients with complex I deficiency, provide evidence showing that cAMP-dependent phosphorylation of the 18 kDa subunit of complex I plays a major role in the control of the mitochondrial respiratory activity.

Mutation in the NDUFS4 gene of complex I abolishes cAMP-dependent activation of the complex in a child with fatal neurological syndrome

Evidence is presented showing that in a patient with fatal neurological syndrome, the homozygous 5 bp duplication in the cDNA of the NDUFS4 18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of this protein and activation of the complex. These findings show for the first time that human complex I is regulated via phosphorylation of the subunit encoded by the NDUFS4 gene.

cAMP-dependent protein kinase and phosphoproteins in mammalian mitochondria. An extension of the cAMP-mediated intracellular signal transduction

Evidence has been obtained for the occurrence of a cAMP-dependent serine protein kinase associated with the inner membrane/matrix of mammalian mitochondria. The catalytic site of this kinase is localized at the inner side of the inner membrane, where it phosphorylates a number of mitochondrial proteins. One of these has been identified as the AQDQ subunit of complex I. cAMP-dependent phosphorylation of this protein promotes the activity of complex I and mitochondrial respiration. A 5 bp duplication in the nuclear gene encoding this protein has been found in a human patient, which eliminates the phosphorylation site. PKA anchoring proteins have recently been identified in the outer membrane of mammalian mitochondria, which could direct phosphorylation of proteins at contact sites with other cell structures.

Topology of the mitochondrial cAMP-dependent protein kinase and its substrates

In intact bovine heart mitochondria, cAMP-dependent phosphorylation of 42, 29, 18 and 6.5 kDa proteins was inhibited by carboxyatractyloside. This shows that both mitochondrial cAMP-dependent protein kinase (mtPKA) and its protein substrates are localized at the matrix side of the inner mitochondrial membrane. Proteins of 42, 29, 18, and 6.5 kDa were also bound at the outer surface of mitochondria where they were phosphorylated by the added purified catalytic subunit of PKA. In the cytosol from bovine heart proteins of the above molecular weights were phosphorylated by the cytosolic PKA.

The nuclear-encoded 18 kDa (IP) AQDQ subunit of bovine heart complex I is phosphorylated by the mitochondrial cAMP-dependent protein kinase

In bovine heart mitochondria a protein of M(r) 18 kDa, phosphorylated by mtPKA, is associated to the NADH-ubiquinone oxidoreductase in the inner membrane and is present in purified preparation of this complex. The 18 kDa phosphoprotein has now been isolated and sequenced. It is identified as the 18 kDa (IP) AQDQ subunit of complex I, a protein of 133 amino acids with a phosphorylation consensus site RVS at position 129-131.

Characterization of proteins phosphorylated by the cAMP-dependent protein kinase of bovine heart mitochondria

Characterization of two mitochondrial proteins of M(r) 42 and 18 kDa, respectively, phosphorylated by the cAMP-dependent protein kinase of bovine heart mitochondria (mtPKA), is presented. A 42 kDa protein is found to be loosely associated to complexes I, III and IV of the respiratory chain and complex V (ATP synthase) in the inner mitochondrial membrane. An 18 kDa protein is associated to complex I in the inner membrane and in a purified preparation of this complex where it can be phosphorylated by the isolated catalytic subunit of PKA.

cAMP-dependent protein phosphorylation in mitochondria of bovine heart

A study is presented of the cAMP-dependent phosphorylation in bovine heart mitochondria of three proteins of 42, 16 and 6.5 kDa associated to the inner membrane. These proteins are also phosphorylated by the cytosolic cAMP-dependent protein kinase and by the purified catalytic subunit of this enzyme. In the cytosol, proteins of 16 and 6.5 kDa are phosphorylated by the cAMP-dependent kinase. It is possible that cytosolic and mitochondrial cAMP-dependent kinases phosphorylate the same proteins in the two compartments.

Phosphorylation of mitochondrial proteins in bovine heart. Characterization of kinases and substrates

Protein phosphorylation by [gamma-32P]ATP in total extract and subfractions of bovine heart mitochondria has been studied. The results show that, in addition to pyruvate dehydrogenase, three mitochondrial proteins, with molecular weights of 44,000, 39,000 and 31,000 Da, are phosphorylated by a cAMP-independent mitochondrial protein kinase. Three other proteins associated with mitochondria, with molecular weights of 125,000, 19,000 and 6,500 Da, are phosphorylated by the cytoplasmic cAMP-dependent protein kinase (kinase A).

Spectrophotometric determination of functional characteristics of protein kinases with coupled enzymatic assay

The performance of enzyme-coupled spectrophotometric assay of protein kinases and its merits as compared with the radioisotopic method in characterizing functional activity of protein kinases are described. Kinetic parameters of protein kinase C and protein kinase A so obtained are presented. General application of the spectrophotometric assay in the study of protein kinases is recommended.

Interaction of Zn2+ with the bovine-heart mitochondrial bc1 complex

A study is presented of the effect of Zn2+ on the enzymatic properties of the bovine-heart cytochrome-bc1 complex. Micromolar concentrations of Zn2+ reversibly inhibit the cytochrome-c reductase activity of either the cholate-solubilized or liposome-reconstituted complex. Kinetic analysis of the redox reactions of the cytochromes indicate that Zn2+ affects the activity of the complex at the quinol oxidation site. The following have been determined: (a) Zn2+ inhibits the pre-steady-state reduction of cytochrome c1 by duroquinol either in the absence or in the presence of antimycin, (b) it does not inhibit the reduction of b cytochromes in the absence of antimycin or in the presence of myxothiazol, (c) it inhibits cytochrome-b reduction in the presence of antimycin. Furthermore Zn2+ inhibits the antimycin-promoted oxidant-induced extrareduction of b cytochromes. Addition of Zn2+ to reduced bc1 complex causes a red shift in the absorption spectrum of cytochrome b566 and a substantial decrease in the signal intensity of the EPR spectrum of the Fe-S protein. This is interpreted as an interaction of Zn2+ with the 2Fe-2S-cluster region of the Fe-S protein, thus giving rise to inhibition of the reductase activity and of the antimycin-insensitive reduction route of b cytochromes. A Scatchard-plot of 65Zn2+ binding to the native isolated complex gave a straight line from which a value of three binding sites and a single dissociation constant of 3 x 10(-6) M can be calculated, which is practically equal to the concentration causing 50% inhibition of electron flow.

Structural and functional characteristics of polypeptide subunits of the bovine heart ubiquinol--cytochrome-c reductase complex

Structural and functional characteristics of subunits of bovine heart cytochrome-c reductase have been investigated by controlled digestion of soluble and membrane-reconstituted purified bc1 complex and direct amino acid sequencing of native and digested protein subunits. The results obtained show that the N-terminal segments of core protein II and the 14-kDa protein extend at the periphery of the complex, protruding into the inner matrix space. The Fe-S protein, located at the outer C-periphery of the complex, is shown to be anchored to other subunits of the complex by the amphipathic N-terminal region. Proteolytic cleavage of 7-11 residues from the N-terminal segment of the 14-kDa protein is apparently associated with decoupling of redox-linked proton pumping. Partial digestion of core protein II, the 6.4-kDa protein, and the C-terminal region of the 9.2-kDa protein, is without effect on the redox and proton-motive activity of the complex.