MNNG-induced cell death is controlled by interactions between PARP-1, poly(ADP-ribose) glycohydrolase, and XRCC1

PARP-1 (poly(ADP-ribose) polymerases) modifies proteins with poly(ADP-ribose), which is an important signal for genomic stability. ADP-ribose polymers also mediate cell death and are degraded by poly(ADP-ribose) glycohydrolase (PARG). Here we show that the catalytic domain of PARG interacts with the automodification domain of PARP-1. Furthermore, PARG can directly down-regulate PARP-1 activity. PARG also interacts with XRCC1, a DNA repair factor that is recruited by DNA damage-activated PARP-1. We investigated the role of XRCC1 in cell death after treatment with supralethal doses of the alkylating agent MNNG. Only in XRCC1-proficient cells MNNG induced a considerable accumulation of poly(ADP-ribose). Similarly, extracts of XRCC1-deficient cells produced large ADP-ribose polymers if supplemented with XRCC1. Consequently, MNNG triggered in XRCC1-proficient cells the translocation of the apoptosis inducing factor from mitochondria to the nucleus followed by caspase-independent cell death. In XRCC1-deficient cells, the same MNNG treatment caused non-apoptotic cell death without accumulation of poly(ADP-ribose). Thus, XRCC1 seems to be involved in regulating a poly(ADP-ribose)-mediated apoptotic cell death.     

The db mutation improves memory in younger mice in a model of Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, while obesity is a major global public health problem associated with the metabolic disorder type 2 diabetes mellitus (T2DM). Chronic obesity and T2DM have been identified as invariant risk factors for dementia and late-onset AD, while their impacts on the occurrence and development of AD remain unclear. As shown in our previous study, the diabetic mutation (db, Lepr^db/db) induces mixed or vascular dementia in mature to middle-aged APP^ΔNL/ΔNL x PS1^P264L/P264L knock-in mice (db/AD). In the present study, the impacts of the db mutation on young AD mice at 10 weeks of age were evaluated. The db mutation not only conferred young AD mice with severe obesity, impaired glucose regulation and activated mammalian target of rapamycin (mTOR) signaling pathway in the mouse cortex, but lead to a surprising improvement in memory. At this young age, mice also had decreased cerebral Aβ content, which we have not observed at older ages. This was unlikely to be related to altered Aβ synthesis, as both β- and γ-secretase were unchanged. The db mutation also reduced the cortical IL-1β mRNA level and IBA1 protein level in young AD mice, with no significant effect on the activation of microglia and astrocytes. We conclude that the db mutation could transitorily improve the memory of young AD mice, a finding that may be partially explained by the relatively improved glucose homeostasis in the brains of db/AD mice compared to their counterpart AD mice, suggesting that glucose regulation could be a strategy for prevention and treatment of neurodegenerative diseases like AD.     

PECAM-Independent Thioglycollate Peritonitis Is Associated With a Locus on Murine Chromosome 2

Background

Previous studies have demonstrated that knockout or inhibition of Platelet/Endothelial Cell Adhesion Molecule (PECAM, CD31) in a number of murine strains results in impaired inflammatory responses, but that no such phenotype is seen in the C57BL/6 (B6) murine background.

Methodology/Principal Findings

We have undertaken a quantitative trait locus (QTL) mapping effort between FVB/n (FVB) and B6 mice deficient for PECAM to identify the gene or genes responsible for this unique feature of B6 mice. We have identified a locus on murine chromosome 2 at approximately 35.8 Mb that is strongly associated (LOD score = 9.0) with inflammatory responses in the absence of PECAM.

Conclusions/Significance

These data potentiate further study of the diapedesis machinery, as well as potential identification of new components of this machinery. As such, this study is an important step to better understanding the processes of inflammation.     

Isolation and Characterization of a Cold-Active Xylanase Enzyme from Flavobacterium sp.

Xylan is the major component of hemicellulose, and xylan should be fully utilized to improve the efficiencies of a biobased economy. There are a variety of industrial reaction conditions in which an active xylanase enzyme would be desired. As a result, xylanase enzymes with different activity profiles are of great interest. We isolated a xylanase gene (xyn10) from a Flavobacterium sp. whose sequence suggests that it is a glycosyl hydrolase family 10 member. The enzyme has a temperature optimum of 30°C, is active at cold temperatures, and is thermolabile. The enzyme has an apparent K_m of 1.8 mg/ml and k_cat of 100 sec⁻¹ for beechwood xylan, attacks highly branched native xylan substrates, and does not have activity against glucans.     

c-Myc affects mRNA translation, cell proliferation and progenitor cell function in the mammary gland

Background  

The oncoprotein c-Myc has been intensely studied in breast cancer and mouse mammary tumor models, but relatively little is known about the normal physiological role of c-Myc in the mammary gland. Here we investigated functions of c-Myc during mouse mammary gland development using a conditional knockout approach.     

Acetylcholine turnover rates in rat brain regions during cocaine self-administration

The involvement of cholinergic neurons in the brain processes underlying reinforcement has been recently demonstrated. This experiment assessed the potential role of cholinergic neurons in cocaine reinforcement by measuring the turnover rates of acetylcholine in brain regions of rats self-administering cocaine and in yoked cocaine and yoked vehicle-infused controls. The activity of cholinergic innervations of and/or interneurons in the olfactory tubercle, caudate putamen, diagonal band-pre-optic region, ventral pallidum, lateral and medial hypothalamus, hippocampus, ventral tegmental area and visual cortices reflected by the turnover rates of acetylcholine were significantly altered in rats self-administering cocaine compared to yoked cocaine infused controls. These changes implicate the involvement of cholinergic neurons with cell bodies in the diagonal band-pre-optic region, the medial septum and several brainstem nuclei and interneurons in the caudate-putamen and ventral pallidum in the processes underlying cocaine self-administration. The identified cholinergic neuronal systems may have a broader role in the brain processes for natural reinforcers (i.e. food, water, etc.) since drugs of abuse are believed to produce reinforcing effects through these systems.     

Functional analysis of the split Synechocystis DnaE intein in plant tissues by biolistic particle bombardment

The DnaE intein of Synechocystis sp. PCC6803 (Ssp DnaE intein) is the first split intein identified in nature. Its N-terminal fragment (Int-n) is attached to the end of the N-terminal half of the DnaE protein (DnaE-n) to form the precursor DnaE-n/Int-n, while the C-terminal fragment (Int-c) precedes the C-terminal half of the DnaE protein (DnaE-c) to form the precursor Int-c/DnaE-c. Int-n and Int-c fragments in the separate precursors catalyze, in concert, a protein trans-splicing process to splice the flanking DnaE-n and DnaE-c into a functional catalytic subunit of DNA polymerase III. They then release themselves from the precursors. Previously, the Ssp DnaE intein has been used to reconstitute a protein trans-splicing mechanism in stably transformed Arabidopsis thaliana, resulting in successful reassembly of an intact and functional GUS from two halves of a split GUS protein. In this report, transient expression using a biolistic particle bombardment approach is described for functional analysis of Ssp DnaE intein. Analyses confirmed that the Ssp DnaE intein could catalyze protein trans-splicing not only in model plants but also in monocot and dicot crops. It also demonstrated that when up to 45 amino acid residues were removed from the C-terminus of the Int-n fragment, the Int-n fragment was still able to function in the protein trans-splicing process.     

Ketogenesis in the living rat followed by 13C-NMR spectroscopy. Infusion of [1,3-13C]octanoate

13C-NMR spectroscopy was used as a noninvasive approach to study the metabolism of [1,3-13C]octanoate in rat liver. Using a properly adjusted surface coil a liver selection of better than 90% was achieved in the intact animal without abdominal surgery. After infusion of [1,3-13C]octanoate via the jugular vein different patterns of metabolites were observed depending on the physiological state of the rat. In the fasted animal, the major metabolites were those of the Krebs cycle while in the diabetic animal ketogenic end products were predominant. As a fatty acid of medium chain length octanoate is imported into the inner mitochondrial space without control by the carnitine acyl transferase system. Hence, the metabolic differences observed between diabetic and fasted rats result from an intramitochondrial control mechanism. The in vivo 13C-NMR results therefore support previous biochemical in vitro studies which concluded that a major control of ketone body production occurs in the inner mitochondrial space, presumably via the redox potential of the liver. As an unexpected result, 13C-NMR provides evidence for the transitory esterification of the infused 13C-labeled octanoic acid. The corresponding 13C-NMR chemical shifts are typical for glycerides.