Insulin regulates carboxypeptidase E by modulating translation initiation scaffolding protein eIF4G1 in pancreatic β cells

Insulin resistance, hyperinsulinemia, and hyperproinsulinemia occur early in the pathogenesis of type 2 diabetes (T2D). Elevated levels of proinsulin and proinsulin intermediates are markers of β-cell dysfunction and are strongly associated with development of T2D in humans. However, the mechanism(s) underlying β-cell dysfunction leading to hyperproinsulinemia is poorly understood. Here, we show that disruption of insulin receptor (IR) expression in β cells has a direct impact on the expression of the convertase enzyme carboxypeptidase E (CPE) by inhibition of the eukaryotic translation initiation factor 4 gamma 1 translation initiation complex scaffolding protein that is mediated by the key transcription factors pancreatic and duodenal homeobox 1 and sterol regulatory element-binding protein 1, together leading to poor proinsulin processing. Reexpression of IR or restoring CPE expression each independently reverses the phenotype. Our results reveal the identity of key players that establish a previously unknown link between insulin signaling, translation initiation, and proinsulin processing, and provide previously unidentified mechanistic insight into the development of hyperproinsulinemia in insulin-resistant states

Microbial Population Analysis of the Salivary Glands of Ticks; A Possible Strategy for the Surveillance of Bacterial Pathogens

<div><p>Ticks are one of the most important blood-sucking vectors for infectious microorganisms in humans and animals. When feeding they inject saliva, containing microbes, into the host to facilitate the uptake of blood. An understanding of the microbial populations within their salivary glands would provide a valuable insight when evaluating the vectorial capacity of ticks. Three tick species (<i>Ixodes ovatus</i>, <i>I. persulcatus</i> and <i>Haemaphysalis flava</i>) were collected in Shizuoka Prefecture of Japan between 2008 and 2011. Each tick was dissected and the salivary glands removed. Bacterial communities in each salivary gland were characterized by 16S amplicon pyrosequencing using a 454 GS-Junior Next Generation Sequencer. The Ribosomal Database Project (RDP) Classifier was used to classify sequence reads at the genus level. The composition of the microbial populations of each tick species were assessed by principal component analysis (PCA) using the Metagenomics RAST (MG-RAST) metagenomic analysis tool. <i>Rickettsia-</i>specific PCR was used for the characterization of rickettsial species. Almost full length of 16S rDNA was amplified in order to characterize unclassified bacterial sequences obtained in <i>I. persulcatus</i> female samples. The numbers of bacterial genera identified for the tick species were 71 (<i>I. ovatus</i>), 127 (<i>I. persulcatus</i>) and 59 (<i>H. flava</i>). Eighteen bacterial genera were commonly detected in all tick species. The predominant bacterial genus observed in all tick species was <i>Coxiella</i>. <i>Spiroplasma</i> was detected in <i>Ixodes</i>, and not in <i>H. flava</i>. PCA revealed that microbial populations in tick salivary glands were different between tick species, indicating that host specificities may play an important role in determining the microbial complement. Four female <i>I. persulcatus</i> samples contained a high abundance of several sequences belonging to Alphaproteobacteria symbionts. This study revealed the microbial populations within the salivary glands of three species of ticks, and the results will contribute to the knowledge and prediction of emerging tick-borne diseases.</p></div

Summary of <i>gltA</i> sequencing.

<p>Summary of <i>gltA</i> sequencing.</p

Relative abundances of different bacterial genera in the salivary glands of (A) <i>I. ovatus</i>, (B) <i>I. persulcatus</i> and (C) <i>H. flava</i>.

<p>All genera with less than 1.0% contribution were pooled into one group and labelled “others”.</p

Sequence results and number of detected genera.

<p>Sequence results and number of detected genera.</p

Alpha diversity calculated for each tick sample.

<p>The alpha diversity of each tick sample was calculated using the MG-RAST server. The mean value obtained for each tick group is represented by the horizontal line. Mean alpha diversity values: IOf (5.75), IOm (5.33), IPf (4.97), IPm (3.11), and HFf (2.14).</p

Venn diagram of all 163 identified genera distributed across the tick species and sex.

<p>Venn diagram of all 163 identified genera distributed across the tick species and sex.</p

Comparison of the relative abundance of rickettsial sequences estimated by 16S amplicon analysis and the results of <i>gltA</i> PCR.

<p>Vertical axis represents the relative abundance of rickettsial sequences calculated from the data obtained from 16S amplicon analysis. Blue dots represent samples in which <i>Rickettsia</i> was detected by both 16S amplicon analysis and <i>gltA</i> PCR. Red dots represent samples in which <i>Rickettsia</i> was detected by 16S amplicon analysis but not by <i>gltA</i> PCR. The plots with relative abundance values between 0% and 5% are shown in the magnified graph provided in the right column.</p