SummaryMitochondrial disorders are highly heterogeneous conditions characterized by defects of the mitochondrial respiratory chain. Pharmacological activation of mitochondrial biogenesis has been proposed as an effective means to correct the biochemical defects and ameliorate the clinical phenotype in these severely disabling, often fatal, disorders. Pathways related to mitochondrial biogenesis are targets of Sirtuin1, a NAD+-dependent protein deacetylase. As NAD+ boosts the activity of Sirtuin1 and other sirtuins, intracellular levels of NAD+ play a key role in the homeostatic control of mitochondrial function by the metabolic status of the cell. We show here that supplementation with nicotinamide riboside, a natural NAD+ precursor, or reduction of NAD+ consumption by inhibiting the poly(ADP-ribose) polymerases, leads to marked improvement of the respiratory chain defect and exercise intolerance of the Sco2 knockout/knockin mouse, a mitochondrial disease model characterized by impaired cytochrome c oxidase biogenesis. This strategy is potentially translatable into therapy of mitochondrial disorders in humans.

SUMMARY Hematopoietic stem cells (HSCs) are the precursors of the hematopoietic system responsible for the lifelong production of blood and bone marrow. Given the emerging importance of epigenetic regulation in HSC fate decisions and malignant transformation, we investigated the role of the DNA methyltransferase Dnmt3b through genetic ablation in HSCs – either alone or in combinatorial deletion with its paralog Dnmt3a. While conditional inactivation of Dnmt3b alone in adult HSCs had minor functional impact, simultaneous deletion of Dnmt3a and Dnmt3b was synergistic resulting in a severe block in differentiation and enhanced HSC self-renewal. Dnmt3a/b-null HSCs displayed activated β-catenin signaling, partly accounting for the differentiation block. Loss of Dnmt3a in HSCs resulted in global DNA hypomethylation, but a paradoxical hypermethylation of CpG islands, most of which was eliminated in Dnmt3a/b-null HSCs. These data demonstrate distinct roles for Dnmt3b in HSC differentiation and provide unprecedented resolution into the epigenetic regulation of HSC fate decisions.

SUMMARY Intense noise exposure causes hearing loss by inducing degeneration of spiral ganglia neurites that innervate cochlear hair cells. Nicotinamide adenine dinucleotide (NAD+) exhibits axon-protective effects in cultured neurons, however, its ability to block degeneration in vivo has been difficult to establish due to its poor cell permeability and serum instability. Here, we describe a strategy to increase cochlear NAD+ levels in mice by administering nicotinamide riboside (NR), a recently described NAD+ precursor. We find that administration of NR, even after noise exposure, prevents noise-induced hearing loss (NIHL) and spiral ganglia neurite degeneration. These effects are mediated by the NAD+-dependent mitochondrial sirtuin, SIRT3, since SIRT3-overexpressing mice are resistant to NIHL and SIRT3 deletion abrogates the protective effects of NR and expression of NAD+ biosynthetic enzymes. These findings reveal that administration of NR activates a NAD+-SIRT3 pathway that reduces neurite degeneration caused by noise exposure.

We evaluated the in vivo fate and physiological behavior of quantum dots (QDs) in Caenorhabditis elegans by GFP transfection, fluorescent imaging, synchrotron radiation based elemental imaging, and speciation techniques. The in situ metabolism and degradation of QDs in the alimentary system and long-term toxicity on reproduction are fully assessed. This work highlights the utility of the C. elegans model as a multiflexible platform to allow noninvasively imaging and monitoring in vivo consequences of engineered nanomaterials.

p53, circRNAs and miRNAs are important components of the regulatory network that activates the EMT program in cancer metastasis. In prostate cancer (PCa), however, it has not been investigated whether and how p53 regulates EMT by circRNAs and miRNAs. Here we show that a Amotl1-derived circRNA, termed circAMOTL1L, is downregulated in human PCa, and that decreased circAMOTL1L facilitates PCa cell migration and invasion through downregulating E-cadherin and upregulating vimentin, thus leading to EMT and PCa progression. Mechanistically, we demonstrate that circAMOTL1L serves as a sponge for binding miR-193a-5p in PCa cells, relieving miR-193a-5p repression of Pcdha gene cluster (a subset of the cadherin superfamily members). Accordingly, dysregulation of the circAMOTL1L-miR-193a-5p-Pcdha8 regulatory pathway mediated by circAMOTL1L downregulation contributes to PCa growth in vivo. Further, we show that RBM25 binds directly to circAMOTL1L and induces its biogenesis, whereas p53 regulates EMT via direct activation of RBM25 gene. These findings have linked p53/RBM25-mediated circAMOTL1L-miR-193a-5p-Pcdha regulatory axis to EMT in metastatic progression of PCa. Targeting this newly identified regulatory axis provides a potential therapeutic strategy for aggressive PCa.

Lys-48-linked polyubiquitination regulates a variety of cellular processes by targeting ubiquitinated proteins to the proteasome for degradation. Although polyubiquitination had been presumed to occur by transferring ubiquitin molecules, one at a time, from an E2 active site to a substrate, we recently showed that the endoplasmic reticulum-associated RING finger ubiquitin ligase gp78 can mediate the preassembly of Lys-48-linked polyubiquitin chains on the catalytic cysteine of its cognate E2 Ube2g2 and subsequent transfer to a substrate. Active site-linked polyubiquitin chains are detected in cells on Ube2g2 and its yeast homolog Ubc7p, but how these chains are assembled is unclear. Here, we show that gp78 forms an oligomer via 2 oligomerization sites, one of which is a hydrophobic segment located in the gp78 cytosolic domain. We further demonstrate that a gp78 oligomer can simultaneously associate with multiple Ube2g2 molecules. This interaction is mediated by a novel Ube2g2 surface distinct from the predicted RING binding site. Our data suggest that a large gp78 -Ube2g2 heterooligomer brings multiple Ube2g2 molecules into close proximity, allowing ubiquitin moieties to be transferred between neighboring Ube2g2s to form active site-linked polyubiquitin chains.crystallography ͉ endoplasmic reticulum-associated protein degradation ͉ gp78 ͉ polyubiquitin chain C ovalent attachment of the 76-residue ubiquitin to polypeptides regulates the stability, localization, or activity of the modified proteins (1-3). This modification requires concerted actions of 3 types of enzymes: an activating enzyme (E1) that forms a thioester linkage (designated herein as ''ϳ'') between its catalytic cysteine and the carboxyl group of the Gly-76 in ubiquitin; a conjugating enzyme (E2) that receives ubiquitin from an E1; and an ubiquitin ligase (E3) that catalyzes the transfer of ubiquitin from the E2 active-site cysteine to a substrate (4). To date, 2 E1s and dozens of E2 enzymes have been identified in mammals, whereas the number of E3s is in the range of several hundreds (5-8). Many E3 enzymes contain a RING finger domain that interacts transiently with a cognate E2 to mediate polyubiquitination reactions (4, 9-12).Ubiquitination often occurs in the form of a polymer whereby the C-terminal Gly-76 in an ubiquitin moiety is linked to a lysine residue in another ubiquitin molecule. It had been presumed that polyubiquitin chains are formed by conjugating ubiquitin moieties, one at a time, first to a lysine residue in a substrate, and then to a lysine in the previously-attached ubiquitin molecule. This appears to be the case for some E2s (13-15). However, we and several other groups recently found that ubiquitin chains can also be preassembled on the catalytic cysteine of the E2 enzyme Ube2g2 and its yeast homologue Ubc7p both in vitro and in vivo (16)(17)(18)(19). These ubiquitin-conjugating enzymes are associated with endoplasmic reticulum (ER) membranes to modify misfolded polypeptides that have been exported from the ER lumen in a proc...

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Various challenging constraints must be satisfied in railway alignment design for topographically complex mountainous regions. The alignment design for such environments is so challenging that existing methodologies have great difficulties in automatically generating viable railway alignment alternatives. We solve this problem with a hybrid method in which a bidirectional distance transform (DT) algorithm automatically selects control points before a genetic algorithm (GA) refines the alignment. This approach solves the problems of (1) determining the appropriate distribution of control points in the GA and (2) producing alignments that deviate significantly from the DT‐optimized paths. Automatic design of backtracking curves and dynamic generation of vertical points of intersection handling multiple constraints are developed to improve the GA performance. This method has been applied to a real case on the Sichuan–Tibet Railway where excessively severe natural gradients must be overcome. It automatically finds an alignment optimized for the given objectives and complex constraints, as well as various promising alternatives.