Why Middle-Aged Listeners Have Trouble Hearing in Everyday Settings

Anecdotally, middle-aged listeners report difficulty conversing in social settings, even when they have normal audiometric thresholds [1-3]. Moreover, young adult listeners with normal hearing vary in their ability to selectively attend to speech amid similar streams of speech. Ignoring age, these individual differences correlate with physiological differences in temporal coding precision present in the auditory brainstem, suggesting that the fidelity of encoding of suprathreshold sound helps explain individual differences [4]. Here, we revisit the conundrum of whether early aging influences an individual's ability to communicate in everyday settings. Although absolute selective attention ability is not predicted by age, reverberant energy interferes more with selective attention as age increases. Breaking the brainstem response down into components corresponding to coding of?stimulus fine structure and envelope, we find that age alters which brainstem component predicts performance. Specifically, middle-aged listeners appear to rely heavily on temporal fine structure, which is more disrupted by reverberant energy than temporal envelope structure is. In contrast, the fidelity of envelope cues predicts performance in younger adults. These results hint that temporal envelope cues influence spatial hearing in reverberant settings more than is commonly appreciated and help explain why middle-aged listeners have particular difficulty communicating in daily life.     

A role for the vesicle-associated tubulin binding protein ARL6 (BBS3) in flagellum extension in Trypanosoma brucei

The small GTPase Arl6 is implicated in the ciliopathic human genetic disorder Bardet-Biedl syndrome, acting at primary cilia in recruitment of the octomeric BBSome complex, which is required for specific trafficking events to and from the cilium in eukaryotes. Here we describe functional characterisation of Arl6 in the flagellated model eukaryote Trypanosoma brucei, which requires motility for viability. Unlike human Arl6 which has a ciliary localisation, TbARL6 is associated with electron-dense vesicles throughout the cell body following co-translational modification by N-myristoylation. Similar to the related protein ARL-3A in T. brucei, modulation of expression of ARL6 by RNA interference does not prevent motility but causes a significant reduction in flagellum length. Tubulin is identified as an ARL6 interacting partner, suggesting that ARL6 may act as an anchor between vesicles and cytoplasmic microtubules. We provide evidence that the interaction between ARL6 and the BBSome is conserved in unicellular eukaryotes. Overexpression of BBS1 leads to translocation of endogenous ARL6 to the site of exogenous BBS1 at the flagellar pocket. Furthermore, a combination of BBS1 overexpression and ARL6 RNAi has a synergistic inhibitory effect on cell growth. Our findings indicate that ARL6 in trypanosomes contributes to flagellum biogenesis, most likely through an interaction with the BBSome.     

Niemann-Pick Type C2 protein contributes to the transport of endosomal cholesterol to mitochondria without interacting with NPC1

Mitochondrial cholesterol is maintained within a narrow range to regulate steroid and oxysterol synthesis and to ensure mitochondrial function. Mitochondria acquire cholesterol through several pathways from different cellular pools. Here we have characterized mitochondrial import of endosomal cholesterol using Chinese hamster ovary cells expressing a CYP11A1 fusion protein that converts cholesterol to pregnenolone at the mitochondrial inner membrane. RNA interference-mediated depletion of the voltage-dependent anion channel 1 in the mitochondrial outer membrane or of Niemann-Pick Type C2 (NPC2) in the endosome lumen decreased arrival of cholesterol at the mitochondrial inner membrane. Expression of NPC2 mutants unable to transfer cholesterol to NPC1 still restored mitochondrial cholesterol import in NPC2-depleted cells. Transport assays in semi-permeabilized cells showed nonvesicular cholesterol trafficking directly from endosomes to mitochondria that did not require cytosolic transport proteins but that was reduced in the absence of NPC2. Our findings indicate that NPC2 delivers cholesterol to the perimeter membrane of late endosomes, where it becomes available for transport to mitochondria without requiring NPC1.     

Complotypes in individuals of African origin: frequencies and possible extended MHC haplotypes

We analyzed the frequency distribution of 106 complotypes [four allele sets of the major histocompatibility complex (MHC) genes for the complement proteins factor B, C2, C4A, and C4B] from 32 Black families residing in Boston and Washington, DC. Twenty-five different complotypes were identified, among which there were four complotypes that had not been previously observed in our large database of complotypes compiled from family studies of Boston Caucasians and that are, presumably, unique to individuals of African origin. These four African-derived complotypes areFC(1,90)0, FC63, S1C2,17, andSC(3,2,90)0. The frequencies of two of these four unique Black complotypes,FC(1,90)0 andFC63, were increased significantly when compared to Caucasians (p_corr <0.00042, p_corr=0.00294, respectively). The complotypeFC(1,90)0 was in positive linkage disequilibrium withHLA-DR3 haplotypes containing theB locus antigens Bw42, Bw52, Bw53, and Bw58, whileFC63 was associated withHLA-Bw70,-DR5. These findings demonstrate the extensive polymorphism of complotypes in Blacks, and also suggest that it may be possible to define unique extended haplotypes of African origin.     

The a2b adenosine receptor modulates glucose homeostasis and obesity

Background

High fat diet and its induced changes in glucose homeostasis, inflammation and obesity continue to be an epidemic in developed countries. The A2b adenosine receptor (A2bAR) is known to regulate inflammation. We used a diet-induced obesity murine knockout model to investigate the role of this receptor in mediating metabolic homeostasis, and correlated our findings in obese patient samples.

Methodology/Principal Findings

Administration of high fat, high cholesterol diet (HFD) for sixteen weeks vastly upregulated the expression of the A2bAR in control mice, while A2bAR knockout (KO) mice under this diet developed greater obesity and hallmarks of type 2 diabetes (T2D), assessed by delayed glucose clearance and augmented insulin levels compared to matching control mice. We identified a novel link between the expression of A2bAR, insulin receptor substrate 2 (IRS-2), and insulin signaling, determined by Western blotting for IRS-2 and tissue Akt phosphorylation. The latter is impaired in tissues of A2bAR KO mice, along with a greater inflammatory state. Additional mechanisms involved include A2bAR regulation of SREBP-1 expression, a repressor of IRS-2. Importantly, pharmacological activation of the A2bAR by injection of the A2bAR ligand BAY 60-6583 for four weeks post HFD restores IRS-2 levels, and ameliorates T2D. Finally, in obese human subjects A2bAR expression correlates strongly with IRS-2 expression.

Conclusions/Significance

Our study identified the A2bAR as a significant regulator of HFD-induced hallmarks of T2D, thereby pointing to its therapeutic potential.     

Linkage data suggesting allelic heterogeneity for paramyotonia congenita and hyperkalemic periodic paralysis on chromosome 17

Summary Paramyotonia congenita (PC), an autosomal dominant non-progressive muscle disorder, is characterised by cold-induced stiffness followed by muscle weakness. The weakness is caused by a dysfunction of the sodium channel in muscle fibre. Parts of the gene coding for the -subunit of the sodium channel of the adult human skeletal muscle (SCN4A) have been localised on chromosome 17. To investigate the role of this gene in the etiology of PC, a linkage analysis in 17 well-defined families was carried out. The results (z=20.61, =0.001) show that the mutant gene responsible for the disorder is indeed tightly linked to the SCN4A gene. The mutation causing hyperkalemic periodic paralysis (HyperPP) with myotonia has previously been mapped to this gene locus by the same candidate gene approach. Thus, our data suggest that PC and HyperPP are caused by allelic mutations at a single locus on chromosome 17.Dedicated to Professor P. E. Becker on the occasion of his 83rd birthday.     

Distribution of glycosylphosphatidylinositol-specific phospholipase D mRNA in bovine tissue sections

It has been reported that mammalian serum, and to a lower extent mammalian liver, brain, pancreas, udder, and milk, contain glycosylphosphatidylinositolspecific phospholipase D activity. However, the sites of synthesis have not been determined. In order to study in which cells(s) of the organism synthesis of glycosylphosphatidylinositol-specific phospholipase D takes place, we undertook a systematic screening of 12 different bovine tissues. In situ hybridization experiments with a specific anti-sense RNA probe, derived from a bovine liver cDNA, revealed that glycosylphosphatidylinositol-specific phospholipase D mRNA is present in mast cells of the adrenal gland, lung, and liver. On the other hand, our specific probe detected no mRNA in bovine pancreas, brain, and udder, although enzyme activity has been reported in these tissues. Northern blot analysis of total bovine liver RNA demonstrated two distinct glycosylphosphatidylinositol-specific phospholipse D mRNAs of approximately 3.3 kb and 4 kb length suggesting that two forms of the enzyme may exist.     

The pseudorabies virus UL11 protein is a virion component involved in secondary envelopment in the cytoplasm

Homologs of the small tegument protein encoded by the UL11 gene of herpes simplex virus type 1 are conserved throughout all herpesvirus subfamilies. However, their function during viral replication has not yet been conclusively shown. Using a monospecific antiserum and an appropriate viral deletion and rescue mutant, we identified and functionally characterized the UL11 protein of the alphaherpesvirus pseudorabies virus (PrV). PrV UL11 encodes a protein with an apparent molecular mass of 10 to 13 kDa that is primarily detected at cytoplasmic membranes during viral replication. In the absence of the UL11 protein, viral titers were decreased approximately 10-fold and plaque sizes were reduced by 60% compared to wild-type virus. Intranuclear capsid maturation and nuclear egress resulting in translocation of DNA-containing capsids into the cytoplasm were not detectably affected. However, in the absence of the UL11 protein, intracytoplasmic membranes were distorted. Moreover, in PrV-DeltaUL11-infected cells, capsids accumulated in the cytoplasm and were often found associated with tegument in aggregated structures such as had previously been demonstrated in cells infected with a PrV triple-mutant virus lacking glycoproteins E, I, and M (A. R. Brack, J. M. Dijkstra, H. Granzow, B. G. Klupp, and T. C. Mettenleiter, J. Virol. 73:5364-5372, 1999). Thus, the PrV UL11 protein, like glycoproteins E, I, and M, appears to be involved in secondary envelopment.     

Anomalies in the enumeration of starved bacteria on culture media containing nalidic acid and tetracycline

Culturable counts of antibiotic resistant, genetically engineeredPseudomonas fluorescens were determined on antibiotic-containing plate count agar during starvation in water. Prior to starvation, colony counts obtained on all media separated into two groups. The mean of the colony counts on plate count agar with or without tetracycline (4.9 × 10⁶ ml⁻¹) was significantly higher than the mean colony counts on plate count agar containing either nalidixic acid or nalidixic acid plus tetraclycline (2.5×10⁶ ml⁻¹). After 20 days of starvation the highest mean colony counts continued to be obtained on plate count agar (7.2 × 10⁶ ml⁻¹) with slightly, but significantly, lower counts obtained on plate count agar containing either nalidixic acid (5.6 × 10⁶ ml⁻¹) or tetraclycline (1.5×10⁶ ml⁻¹). A combination of nalidixic acid and tetracycline in plate count agar, however, dramatically reduced colony counts (8.3 × 10² ml⁻¹) after this starvation period. The addition of catalase to plate count agar containing nalidixic acid and tetracycline negated the effect caused by this combination of antibiotics. When colony counts obtained over the entire 20 day incubation were considered, the addition of MgSO₄ to plate count agar containing nalidixic acid and tetracycline resulted in a significant increase in colony counts. Other combinations of antibiotics, nalidixic acid+carbenicillin, nalidixic acid+kanamycin, streptomycin+tetracycline, streptomycin+carbenicillin, rifampicin+tetracycline, rifampicin+carbenicillin, and rifampicin+kanamycin, did not inhibit colony formation of starved cells. Antibiotic resistant strains ofP. putida andEscherichia coli also displayed sensitivity to the combination of nalidixic acid and tetracycline in plate count agar after starvation.