Small and Large Ribosomal Subunit Deficiencies Lead to Distinct Gene Expression Signatures that Reflect Cellular Growth Rate

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RNA Editing Genes Associated with Extreme Old Age in Humans and with Lifespan in C. elegans

Background

The strong familiality of living to extreme ages suggests that human longevity is genetically regulated. The majority of genes found thus far to be associated with longevity primarily function in lipoprotein metabolism and insulin/IGF-1 signaling. There are likely many more genetic modifiers of human longevity that remain to be discovered.

Methodology/Principal Findings

Here, we first show that 18 single nucleotide polymorphisms (SNPs) in the RNA editing genes ADARB1 and ADARB2 are associated with extreme old age in a U.S. based study of centenarians, the New England Centenarian Study. We describe replications of these findings in three independently conducted centenarian studies with different genetic backgrounds (Italian, Ashkenazi Jewish and Japanese) that collectively support an association of ADARB1 and ADARB2 with longevity. Some SNPs in ADARB2 replicate consistently in the four populations and suggest a strong effect that is independent of the different genetic backgrounds and environments. To evaluate the functional association of these genes with lifespan, we demonstrate that inactivation of their orthologues adr-1 and adr-2 in C. elegans reduces median survival by 50%. We further demonstrate that inactivation of the argonaute gene, rde-1, a critical regulator of RNA interference, completely restores lifespan to normal levels in the context of adr-1 and adr-2 loss of function.

Conclusions/Significance

Our results suggest that RNA editors may be an important regulator of aging in humans and that, when evaluated in C. elegans, this pathway may interact with the RNA interference machinery to regulate lifespan.     

SHMTool: a webserver for comparative analysis of somatic hypermutation datasets

The somatic hypermutation (SHM) of Immunoglobulin variable (V) regions is a key process in the generation of antibody diversity. The growing number of datasets of point mutations that occur during SHM in mice and humans often include comparisons between wild-type and individuals or strains genetically defective in the repair mechanisms that contribute to SHM. However, it has been difficult to compare the results of different studies because the analyses have not been standardized for criteria such as correction for base composition and the inclusion of unique mutations. If many mutations are involved, the analysis can also be time consuming. To overcome these problems and facilitate a standardized analysis and display of similar data, we present a webserver (SHMTool) for comparing SHM datasets, available at http://scb.aecom.yu.edu/shmtool.     

DNA repeat rearrangements mediated by DnaK-dependent replication fork repair

We propose that rearrangements between short tandem repeated sequences occur by errors made during a replication fork repair pathway involving a replication template switch. We provide evidence here that the DnaK chaperone of E. coli controls this template switch repair process. Mutants in dnaK are sensitive to replication fork damage and exhibit high expression of the SOS response, indicative of repair deficiency. Deletion and expansion of tandem repeats that occur by replication misalignment ("slippage") are also DnaK dependent. Because mutations in dnaX encoding the gamma and tau subunits of DNA polymerase III mimic dnaK phenotypes and are genetically epistatic, we propose that the DnaKJ chaperone remodels the replisome to facilitate repair. The fork remains largely intact because PriA or PriC restart proteins are not required. We also suggest that the poorly defined RAD6-RAD18-RAD5 mechanism of postreplication repair in eukaryotes occurs by an analogous mechanism to the DnaK template-switch pathway in prokaryotes.     

Enhancement of antral contractions and vagal afferent signaling with synchronized electrical stimulation

Gastric filling activates vagal afferents involved in peripheral signaling to the central nervous system (CNS) for food intake. It is not known whether these afferents linearly encode increasing contractions of the antrum during antral distension (AD). The aim of this study was to investigate effects of AD and electrically enhanced antral contractions on responses of vagal afferents innervating the antrum. Single-fiber recordings were made from the vagal afferents in anesthetized male Long-Evans rats. Antral contractions were measured with a solid-state probe placed in the antrum. A nonexcitatory electrical stimulation (NES) inducing no smooth muscle contractions was applied during the ascending phase of antral contractions to enhance subsequent antral contractions. Fifty-six fibers identified during AD (1 ml for 30 s) were studied through different types of mechanical stimuli. Under normal conditions, one group of fibers exhibited rhythmic firing in phase with antral contractions. Another group of fibers had nonrhythmic spontaneous firing. Responses of 15 fibers were tested with NES during multiple-step distension (MSD). NES produced a mean increase in antral contraction amplitude (177.1 +/- 35.3%) and vagal afferent firing (21.6 +/- 2.6%). Results show that both passive distension and enhanced antral contractions activate distension-sensitive vagal afferents. Responses of these fibers increase linearly to enhanced antral contraction induced by NES or MSD up to a distending volume of 0.6 ml. However, responses reached a plateau at a distending volume >0.8 ml. We concluded that enhanced contraction of the antrum can activate vagal afferents signaling to the CNS.     

Nitric oxide attenuates insulin- or IGF-I-stimulated aortic smooth muscle cell motility by decreasing H2O2 levels: essential role of cGMP

Insulin and insulin-like growth factor I (IGF-I) both play important roles in vascular remodeling. Moreover, nitric oxide (NO) is well established as a counterregulatory agent that opposes the actions of several vascular agonists, in part by decreasing smooth muscle motility. We tested the hypothesis that NO blocks insulin or IGF-I-induced rat aortic smooth muscle cell motility via a mechanism involving the attenuation of agonist-induced elevation of hydrogen peroxide levels and cGMP as mediator. Insulin or IGF-I induced an increase of hydrogen peroxide levels and cell motility. Both effects were blocked by catalase or diphenyleneiodonium, indicating that hydrogen peroxide elevation is necessary for induction of cell motility. Two NO donors mimicked the effects of catalase, indicating that NO decreases cell motility by suppressing agonist-induced elevation of hydrogen peroxide. A cGMP analogue mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked the effect of NO on hydrogen peroxide levels, indicating that elevation of cGMP is both necessary and sufficient to account for the reduction of hydrogen peroxide levels. A NO donor as well as a cGMP analogue attenuated insulin-stimulated NADPH activity, indicating that NO decreases hydrogen peroxide levels by inhibiting the generation of superoxide, via a cGMP-mediated mechanism. Finally, exogenous hydrogen peroxide increased cell motility and reversed the inhibitory effect of cGMP. These results support the view that NO plays an antioxidant role via reduction of hydrogen peroxide in cultured rat aortic smooth muscle cells and that this effect is both necessary and sufficient to account for its capacity to decrease cell motility.