11beta-hydroxysteroid dehydrogenase 2 activity is elevated in severe obesity and negatively associated with insulin sensitivity

Alterations in glucocorticoid (GC) metabolism may contribute to the development of obesity and insulin resistance. We aimed to study the role of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) in human adiposity, paying special attention to the association between altered GC metabolism and insulin sensitivity. In 24-h urine samples of 72 extremely obese (mean BMI 45.5 +/- 1.1 kg/m(2)), but otherwise healthy patients urinary free cortisol (UFF), urinary free cortisone (UFE), tetrahydrocortisol (THF), 5alpha-tetrahydrocortisol (5alpha-THF), and tetrahydrocortisone (THE) were quantified by radioimmunoassay. The sum of the three major tetrahydrometabolites is an estimate for daily GC secretion, and the sum of UFF and UFE represents potentially bioactive-free-GCs. Thirty healthy lean subjects (BMI 22.3 +/- 0.3 kg/m(2)) served as controls. In obese subjects, absolute daily GC secretion and the potentially bioactive-free-GCs were significantly (P < 0.005) higher than in lean controls (11.8 +/- 0.7 vs. 8.0 +/- 0.6 mg/d; and 171.8 +/- 11.2 vs. 117.6 +/- 9.2 mug/d, respectively). However, when these values were corrected for body surface area (BSA), significant differences were no longer detectable. While enzyme activity indices for 5alpha-reductase and 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) were similar in lean and obese subjects, 11beta-HSD2 was markedly elevated in adiposity (3.7 +/- 0.2 vs. 2.1 +/- 0.1; P < 0.0001). This increase was accompanied by a significant reduction in UFF excretion corrected for BSA (16.5 +/- 1.2 vs. 21.7 +/- 2.0 mug/d/m(2); P = 0.0222). Besides, 11beta-HSD2 activity was significantly correlated with insulin sensitivity (P = 0.0262). When body size is accounted for, both adrenal GC secretion and potentially bioactive-free-GCs are indistinguishable between lean and extremely obese subjects. However in obesity, the kidney appears to intensify its supply of the direct substrate cortisone for extrarenal 11beta-HSD1, which may fuel visceral adiposity and insulin resistance.     

Polymorphisms within the Novel Type 2 Diabetes Risk Locus MTNR1B Determine β-Cell Function

Background

Very recently, a novel type 2 diabetes risk gene, i.e., MTNR1B, was identified and reported to affect fasting glycemia. Using our thoroughly phenotyped cohort of subjects at an increased risk for type 2 diabetes, we assessed the association of common genetic variation within the MTNR1B locus with obesity and prediabetes traits, namely impaired insulin secretion and insulin resistance.

Methodology/Principal Findings

We genotyped 1,578 non-diabetic subjects, metabolically characterized by oral glucose tolerance test, for five tagging single nucleotide polymorphisms (SNPs) covering 100% of common genetic variation (minor allele frequency >0.05) within the MTNR1B locus (rs10830962, rs4753426, rs12804291, rs10830963, rs3781638). In a subgroup (N = 513), insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp, and in a further subgroup (N = 301), glucose-stimulated insulin secretion was determined by intravenous glucose tolerance test. After appropriate adjustment for confounding variables and Bonferroni correction for multiple comparisons, none of the tagging SNPs was reliably associated with measures of adiposity. SNPs rs10830962, rs4753426, and rs10830963 were significantly associated with higher fasting plasma glucose concentrations (p<0.0001) and reduced OGTT- and IVGTT-induced insulin release (p≤0.0007 and p≤0.01, respectively). By contrast, SNP rs3781638 displayed significant association with lower fasting plasma glucose levels and increased OGTT-induced insulin release (p<0.0001 and p≤0.0002, respectively). Moreover, SNP rs3781638 revealed significant association with elevated fasting- and OGTT-derived insulin sensitivity (p≤0.0021). None of the MTNR1B tagging SNPs altered proinsulin-to-insulin conversion.

Conclusions/Significance

In conclusion, common genetic variation within MTNR1B determines glucose-stimulated insulin secretion and plasma glucose concentrations. Their impact on β-cell function might represent the prevailing pathomechanism how MTNR1B variants increase the type 2 diabetes risk.     

Synthesis of rhamnogalacturonan I fragments by a modular design principle

The improved syntheses of methyl 2-O-acetyl-3-O-benzyl-alpha-L-rhamnopyranoside (12) and 1,2-di-O-acetyl-3-O-benzyl-alpha-L-rhamnopyranose (15), which were used as glycosyl acceptor and donor, respectively, are described. Glycosylation of the O-4 position of both rhamnose derivatives with 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl bromide (26) provided disaccharides 27 and 29. After partial deprotection of 27 and coupling of the resulting 28 with disaccharide 19, tetrasaccharide 31 was obtained. Furthermore, transforming of 29 into the corresponding bromide 30 and coupling with galacturonates 16 and 32 provided trisaccharides 33 and 34, respectively, which could be regarded as building blocks of ramified rhamnogalacturonan fragments. The preparation of tetra- (21) and hexasaccharide (25) of rhamnogalacturonan I is reported to demonstrate the feasibility of the synthesis of larger pectin fragments using the modular design principle with this type of building blocks.     

Expression of somite segmentation genes in amphioxus: a clock without a wavefront?

In the basal chordate amphioxus (Branchiostoma), somites extend the full length of the body. The anteriormost somites segment during the gastrula and neurula stages from dorsolateral grooves of the archenteron. The remaining ones pinch off, one at a time, from the tail bud. These posterior somites appear to be homologous to those of vertebrates, even though the latter pinch off from the anterior end of bands of presomitic mesoderm rather than directly from the tail bud. To gain insights into the evolution of mesodermal segmentation in chordates, we determined the expression of ten genes in nascent amphioxus somites. Five (Uncx4.1, NeuroD/atonal-related, IrxA, Pcdhdelta2-17/18, and Hey1) are expressed in stripes in the dorsolateral mesoderm at the gastrula stage and in the tail bud while three (Paraxis, Lcx, and Axin) are expressed in the posterior mesendoderm at the gastrula and neurula stages and in the tail bud at later stages. Expression of two genes (Pbx and OligA) suggests roles in the anterior somites that may be unrelated to initial segmentation. Together with previous data, our results indicate that, with the exception that Engrailed is only segmentally expressed in the anterior somites, the genetic mechanisms controlling formation of both the anterior and posterior somites are probably largely identical. Thus, the fundamental pathways for mesodermal segmentation involving Notch-Delta, Wnt/beta-catenin, and Fgf signaling were already in place in the common ancestor of amphioxus and vertebrates although budding of somites from bands of presomitic mesoderm exhibiting waves of expression of Notch, Wnt, and Fgf target genes was likely a vertebrate novelty. Given the conservation of segmentation gene expression between amphioxus and vertebrate somites, we propose that the clock mechanism may have been established in the basal chordate, while the wavefront evolved later in the vertebrate lineage.     

Structural Requirements for Cub Domain Containing Protein 1 (CDCP1) and Src Dependent Cell Transformation

Cub domain containing protein 1 (CDCP1) is strongly expressed in tumors derived from lung, colon, ovary, or kidney. It is a membrane protein that is phosphorylated and then bound by Src family kinases. Although expression and phosphorylation of CDCP1 have been investigated in many tumor cell lines, the CDCP1 features responsible for transformation have not been fully evaluated. This is in part due to the lack of an experimental system in which cellular transformation depends on expression of exogenous CDCP1 and Src. Here we use retrovirus mediated co-overexpression of c-Src and CDCP1 to induce focus formation of NIH3T3 cells. Employing different mutants of CDCP1 we show that for a full transformation capacity, the intact amino- and carboxy-termini of CDCP1 are essential. Mutation of any of the core intracellular tyrosine residues (Y734, Y743, or Y762) abolished transformation, and mutation of a palmitoylation motif (C689,690G) strongly reduced it. Src kinase binding to CDCP1 was not required since Src with a defective SH2 domain generated even more CDCP1 dependent foci whereas Src myristoylation was necessary. Taken together, the focus formation assay allowed us to define structural requirements of CDCP1/Src dependent transformation and to characterize the interaction of CDCP1 and Src.     

Chloroplast migration: A new circadian rhythm inAcetabularia

Summary Young cells ofAcetabularia mediterranea were studied by time lapse cinematography. Rhythmic changes were observed in the optical transmission of the rhizoid and the apex of the cells, respectively. Transmission changes were determined photometrically by single frame analysis. Optical density is at the maximum in the rhizoid, when it is in the minimum in the apex, andvice versa. The rhythm is endogenous, since it persists under constant conditions. The length of the periods is typically circadian. The changes of optical density are caused by chloroplast migrations which are directed towards the apex of the cell at the beginning of the circadian day and towards the rhizoid at the beginning of the circadian night. This new rhythm, which is probably circadian, is discussed in terms of cytoplasmic streaming and of other circadian rhythms, known to occur inAcetabularia.     

Syntheses and stabilities of proteins related to the polyoma small T antigen in Escherichia coli.

We compared the syntheses and turnovers of two proteins related to the polyoma small T antigen synthesized in Escherichia coli from plasmids containing polyoma genomic segments joined to lac control elements. A protein with an authentic polyoma N terminus was more unstable than a protein with N-terminal amino acids derived from beta-galactosidase. Both were more unstable than most bacterial proteins.     

Stachybotrychromenes A–C: novel cytotoxic meroterpenoids from <Emphasis Type="Italic">Stachybotrys</Emphasis> sp.

In the course of gaining new insights into the secondary metabolite profile of various Stachybotrys strains, in particular concerning triprenyl phenol-like compounds, so far, unknown metabolites with analogous structural features were discovered. Three novel meroterpenoids containing a chromene ring moiety, namely stachybotrychromenes A–C, were isolated from solid culture of the filamentous fungus Stachybotrys chartarum DSMZ 12880 (chemotype S). Their structures were elucidated by means of comprehensive spectroscopic analysis (1D and 2D NMR, ESI-HRMS, and CD) as well as by comparison with spectroscopic data of structural analogues described in literature. Stachybotrychromenes A and B exhibited moderate cytotoxic effects on HepG2 cells after 24 h with corresponding IC₅₀ values of 73.7 and 28.2 μM, respectively. Stachybotrychromene C showed no significant cytotoxic activity up to 100 μM. Moreover, it is noteworthy that stachybotrychromenes A–C are produced not only by S. chartarum chemotype S but also S. chartarum chemotype A and Stachybotrys chlorohalonata.     

Evolution of duplicated growth hormone genes in autotetraploid salmonid fishes.

A defining character of the piscine family Salmonidae is autotetraploidy resulting from a genome-doubling event some 25-100 million years ago. Initially, duplicated genes may have undergone concerted evolution and tetrasomic inheritance. Homeologous chromosomes eventually diverged and the resulting reduction in recombination and gene conversion between paralogous genes allowed the re-establishment of disomic inheritance. Among extant salmonine fishes (e.g. salmon, trout, char) the growth hormone (GH) gene is generally represented by two functional paralogs, GH1 and GH2. Sequence analyses of salmonid GH genes from species of subfamilies Coregoninae (whitefish, ciscos) and Salmoninae were used to examine the evolutionary history of the duplicated GH genes. Two divergent GH gene paralogs were also identified in Coregoninae, but they were not assignable to the GH1 and GH2 categories. The average sequence divergence between the coregonine GH genes was more than twofold lower than the corresponding divergence between the salmonine GH1 and GH2. Phylogenetic analysis of the coregonine GH paralogs did not resolve their relationship to the salmonine paralogs. These findings suggest that disomic inheritance of two GH genes was established by different mechanisms in these two subfamilies.