Mapping genetic variants associated with beta-adrenergic responses in inbred mice.

β-blockers and β-agonists are primarily used to treat cardiovascular diseases. Inter-individual variability in response to both drug classes is well recognized, yet the identity and relative contribution of the genetic players involved are poorly understood. This work is the first genome-wide association study (GWAS) addressing the values and susceptibility of cardiovascular-related traits to a selective β(1)-blocker, Atenolol (ate), and a β-agonist, Isoproterenol (iso). The phenotypic dataset consisted of 27 highly heritable traits, each measured across 22 inbred mouse strains and four pharmacological conditions. The genotypic panel comprised 79922 informative SNPs of the mouse HapMap resource. Associations were mapped by Efficient Mixed Model Association (EMMA), a method that corrects for the population structure and genetic relatedness of the various strains. A total of 205 separate genome-wide scans were analyzed. The most significant hits include three candidate loci related to cardiac and body weight, three loci for electrocardiographic (ECG) values, two loci for the susceptibility of atrial weight index to iso, four loci for the susceptibility of systolic blood pressure (SBP) to perturbations of the β-adrenergic system, and one locus for the responsiveness of QTc (p<10(-8)). An additional 60 loci were suggestive for one or the other of the 27 traits, while 46 others were suggestive for one or the other drug effects (p<10(-6)). Most hits tagged unexpected regions, yet at least two loci for the susceptibility of SBP to β-adrenergic drugs pointed at members of the hypothalamic-pituitary-thyroid axis. Loci for cardiac-related traits were preferentially enriched in genes expressed in the heart, while 23% of the testable loci were replicated with datasets of the Mouse Phenome Database (MPD). Altogether these data and validation tests indicate that the mapped loci are relevant to the traits and responses studied.

Glucagon-like peptide-1 increases beta-cell glucose competence and proliferation by translational induction of insulin-like growth factor-1 receptor expression.

Glucagon-like peptide-1 (GLP-1) protects beta-cells against apoptosis, increases their glucose competence, and induces their proliferation. We previously demonstrated that the anti-apoptotic effect was mediated by an increase in insulin-like growth factor-1 receptor (IGF-1R) expression and signaling, which was dependent on autocrine secretion of insulin-like growth factor 2 (IGF-2). Here, we further investigated how GLP-1 induces IGF-1R expression and whether the IGF-2/IGF-1R autocrine loop is also involved in mediating GLP-1-increase in glucose competence and proliferation. We show that GLP-1 up-regulated IGF-1R expression by a protein kinase A-dependent translational control mechanism, whereas isobutylmethylxanthine, which led to higher intracellular accumulation of cAMP than GLP-1, increased both IGF-1R transcription and translation. We then demonstrated, using MIN6 cells and primary islets, that the glucose competence of these cells was dependent on the level of IGF-1R expression and on IGF-2 secretion. We showed that GLP-1-induced primary beta-cell proliferation was suppressed by Igf-1r gene inactivation and by IGF-2 immunoneutralization or knockdown. Together our data show that regulation of beta-cell number and function by GLP-1 depends on the cAMP/protein kinase A mediated-induction of IGF-1R expression and the increased activity of an IGF-2/IGF-1R autocrine loop.

Modification of the monomer composition of polyhydroxyalkanoate synthesized in Saccharomyces cerevisiae expressing variants of the beta-oxidation-associated multifunctional enzyme.

Expression by Saccharomyces cerevisiae of a polyhydroxyalkanoate (PHA) synthase modified at the carboxy end by the addition of a peroxisome targeting signal derived from the last 34 amino acids of the Brassica napus isocitrate lyase (ICL) and containing the terminal tripeptide Ser-Arg-Met resulted in the synthesis of PHA. The ability of the terminal peptide Ser-Arg-Met and of the 34-amino-acid peptide from the B. napus ICL to target foreign proteins to the peroxisome of S. cerevisiae was demonstrated with green fluorescent protein fusions. PHA synthesis was found to be dependent on the presence of both the enzymes generating the beta-oxidation intermediate 3-hydroxyacyl-coenzyme A (3-hydroxyacyl-[CoA]) and the peroxin-encoding PEX5 gene, demonstrating the requirement for a functional peroxisome and a beta-oxidation cycle for PHA synthesis. Using a variant of the S. cerevisiae beta-oxidation multifunctional enzyme with a mutation inactivating the B domain of the R-3-hydroxyacyl-CoA dehydrogenase, it was possible to modify the PHA monomer composition through an increase in the proportion of the short-chain monomers of five and six carbons.

Use of constant denaturant capillary electrophoresis of pooled blood samples to identify single-nucleotide polymorphisms in the genes (Scnn1a and Scnn1b) encoding the alpha and beta subunits of the epithelial sodium channel.

BACKGROUND: The epithelial sodium channel (ENaC) is composed of three homologous subunits: alpha, beta, and gamma. Mutations in the Scnn1b and Scnn1g genes, which encode the beta and the gamma subunits of ENaC, cause a severe form of hypertension (Liddle syndrome). The contribution of genetic variants within the Scnn1a gene, which codes for the alpha subunit, has not been investigated. METHODS: We screened for mutations in the COOH termini of the alpha and beta subunits of ENaC. Blood from 184 individuals from 31 families participating in a study on the genetics of hypertension were analyzed. Exons 13 of Scnn1a and Scnn1b, which encode the second transmembrane segment and the COOH termini of alpha- and beta-ENaC, respectively, were amplified from pooled DNA samples of members of each family by PCR. Constant denaturant capillary electrophoresis (CDCE) was used to detect mutations in PCR products of the pooled DNA samples. RESULTS: The detection limit of CDCE for ENaC variants was 1%, indicating that all members of any family or up to 100 individuals can be analyzed in one CDCE run. CDCE profiles of the COOH terminus of alpha-ENaC in pooled family members showed that the 31 families belonged to four groups and identified families with genetic variants. Using this approach, we analyzed 31 rather than 184 samples. Individual CDCE analysis of members from families with different pooled CDCE profiles revealed five genotypes containing 1853G-->T and 1987A-->G polymorphisms. The presence of the mutations was confirmed by DNA sequencing. For the COOH terminus of beta-ENaC, only one family showed a different CDCE profile. Two members of this family (n = 5) were heterozygous at 1781C-->T (T594M). CONCLUSION: CDCE rapidly detects point mutations in these candidate disease genes.

Complementary DNA cloning of complement C8 beta and its sequence homology to C9.

The complete amino acid sequence of mature C8 beta has been derived from the DNA sequence of a cDNA clone identified by expression screening of a human liver cDNA library. Comparison with the amino acid sequence of C9 shows an overall homology with few deletions and insertions. In particular, the cysteine-rich domains and membrane-inserting regions of C9 are well conserved. These findings are discussed in relation to a possible mechanism of membrane attack complex formation.

Paired activation of two components within muscarinic M3 receptor dimers is required for recruitment of beta-arrestin-1 to the plasma membrane.

beta-Arrestins regulate the functioning of G protein-coupled receptors in a variety of cellular processes including receptor-mediated endocytosis and activation of signaling molecules such as ERK. A key event in these processes is the G protein-coupled receptor-mediated recruitment of beta-arrestins to the plasma membrane. However, despite extensive knowledge in this field, it is still disputable whether activation of signaling pathways via beta-arrestin recruitment entails paired activation of receptor dimers. To address this question, we investigated the ability of different muscarinic receptor dimers to recruit beta-arrestin-1 using both co-immunoprecipitation and fluorescence microscopy in COS-7 cells. Experimentally, we first made use of a mutated muscarinic M(3) receptor, which is deleted in most of the third intracellular loop (M(3)-short). Although still capable of activating phospholipase C, this receptor loses almost completely the ability to recruit beta-arrestin-1 following carbachol stimulation in COS-7 cells. Subsequently, M(3)-short was co-expressed with the M(3) receptor. Under these conditions, the M(3)/M(3)-short heterodimer could not recruit beta-arrestin-1 to the plasma membrane, even though the control M(3)/M(3) homodimer could. We next tested the ability of chimeric adrenergic muscarinic alpha(2)/M(3) and M(3)/alpha(2) heterodimeric receptors to co-immunoprecipitate with beta-arrestin-1 following stimulation with adrenergic and muscarinic agonists. beta-Arrestin-1 co-immunoprecipitation could be induced only when carbachol or clonidine were given together and not when the two agonists were supplied separately. Finally, we tested the reciprocal influence that each receptor may exert on the M(2)/M(3) heterodimer to recruit beta-arrestin-1. Remarkably, we observed that M(2)/M(3) heterodimers recruit significantly greater amounts of beta-arrestin-1 than their respective M(3)/M(3) or M(2)/M(2) homodimers. Altogether, these findings provide strong evidence in favor of the view that binding of beta-arrestin-1 to muscarinic M(3) receptors requires paired stimulation of two receptor components within the same receptor dimer.

PVHL is a regulator of glucose metabolism and insulin secretion in pancreatic beta cells.

Insulin secretion from pancreatic beta cells is stimulated by glucose metabolism. However, the relative importance of metabolizing glucose via mitochondrial oxidative phosphorylation versus glycolysis for insulin secretion remains unclear. von Hippel-Lindau (VHL) tumor suppressor protein, pVHL, negatively regulates hypoxia-inducible factor HIF1alpha, a transcription factor implicated in promoting a glycolytic form of metabolism. Here we report a central role for the pVHL-HIF1alpha pathway in the control of beta-cell glucose utilization, insulin secretion, and glucose homeostasis. Conditional inactivation of Vhlh in beta cells promoted a diversion of glucose away from mitochondria into lactate production, causing cells to produce high levels of glycolytically derived ATP and to secrete elevated levels of insulin at low glucose concentrations. Vhlh-deficient mice exhibited diminished glucose-stimulated changes in cytoplasmic Ca(2+) concentration, electrical activity, and insulin secretion, which culminate in impaired systemic glucose tolerance. Importantly, combined deletion of Vhlh and Hif1alpha rescued these phenotypes, implying that they are the result of HIF1alpha activation. Together, these results identify pVHL and HIF1alpha as key regulators of insulin secretion from pancreatic beta cells. They further suggest that changes in the metabolic strategy of glucose metabolism in beta cells have profound effects on whole-body glucose homeostasis.

Quinupristin-dalfopristin combined with beta-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolide-lincosamide-streptogramin B antibiotics.

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin active against most gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). In experimental endocarditis, however, Q-D was less efficacious against MRSA isolates constitutively resistant to macrolide-lincosamide-streptogram B (C-MLS(B)) than against MLS(B)-susceptible isolates. To circumvent this problem, we used the checkerboard method to screen drug combinations that would increase the efficacy of Q-D against such bacteria. beta-Lactams consistently exhibited additive or synergistic activity with Q-D. Glycopeptides, quinolones, and aminoglycosides were indifferent. No drugs were antagonistic. The positive Q-D-beta-lactam interaction was independent of MLS(B) or beta-lactam resistance. Moreover, addition of Q-D at one-fourth the MIC to flucloxacillin-containing plates decreased the flucloxacillin MIC for MRSA from 500 to 1,000 mg/liter to 30 to 60 mg/liter. Yet, Q-D-beta-lactam combinations were not synergistic in bactericidal tests. Rats with aortic vegetations were infected with two C-MLS(B)-resistant MRSA isolates (isolates AW7 and P8) and were treated for 3 or 5 days with drug dosages simulating the following treatments in humans: (i) Q-D at 7 mg/kg two times a day (b.i.d.) (a relatively low dosage purposely used to help detect positive drug interactions), (ii) cefamandole at constant levels in serum of 30 mg/liter, (iii) cefepime at 2 g b.i.d., (iv) Q-D combined with either cefamandole or cefepime. Any of the drugs used alone resulted in treatment failure. In contrast, Q-D plus either cefamandole or cefepime significantly decreased valve infection compared to the levels of infection for both untreated controls and those that received monotherapy (P &lt; 0.05). Importantly, Q-D prevented the growth of highly beta-lactam-resistant MRSA in vivo. The mechanism of this beneficial drug interaction is unknown. However, Q-D-beta-lactam combinations might be useful for the treatment of complicated infections caused by multiple organisms, including MRSA.

Thermogenic effect of the new beta-adrenoreceptor agonist Ro 16-8714 in healthy male volunteers.

Previous investigations in experimental animals have shown that a new type of beta-adrenoceptor agonist (Ro 16-8714) possesses both thermogenic and antihyperglycemic properties. The aim of the study was to assess the thermogenic capacity of the compound in man after acute administration. Following an overnight fast three different doses (5, 10 and 20 mg) and a placebo were given per os to six normal-weight young men. The rate of energy expenditure (EE) and substrate utilization were determined by indirect calorimetry (hood system) before and for 6 h following the drug administration. Heart rate and blood pressure as well as plasma glucose, insulin and free fatty acid (FFA) concentrations were also measured at regular intervals throughout the study. The increment relative to base-line (mean +/- s.e.m.) in EE with placebo, 5, 10 and 20 mg was 4 +/- 3, 10 +/- 2, 11 +/- 2 and 21 +/- 2 percent respectively whereas heart rate was enhanced by 2 +/- 2, 8 +/- 3, 22 +/- 2, and 49 +/- 8 percent. Systolic blood pressure increased less (1 +/- 2, 8 +/- 1, 11 +/- 1 and 13 +/- 2 percent), and diastolic blood pressure did not change significantly. Simultaneously we observed a slight and transient increase in blood glucose, insulin and FFA concentrations. It is concluded that in lean individuals Ro 16-8714 is a potent thermogenic agent; however, new beta-adrenoceptor agonists should be developed in order to avoid the tachycardia associated with the thermogenic effect.

Horizontal transfer of exosomal microRNAs transduce apoptotic signals between pancreatic beta-cells.

BACKGROUND: Diabetes mellitus is a common metabolic disorder characterized by dysfunction of insulin-secreting pancreatic beta-cells. MicroRNAs are important regulators of beta-cell activities. These non-coding RNAs have recently been discovered to exert their effects not only inside the cell producing them but, upon exosome-mediated transfer, also in other recipient cells. This novel communication mode remains unexplored in pancreatic beta-cells. In the present study, the microRNA content of exosomes released by beta-cells in physiological and physiopathological conditions was analyzed and the biological impact of their transfer to recipient cells investigated. RESULTS: Exosomes were isolated from the culture media of MIN6B1 and INS-1 derived 832/13 beta-cell lines and from mice, rat or human islets. Global profiling revealed that the microRNAs released in MIN6B1 exosomes do not simply reflect the content of the cells of origin. Indeed, while a subset of microRNAs was preferentially released in exosomes others were selectively retained in the cells. Moreover, exposure of MIN6B1 cells to inflammatory cytokines changed the release of several microRNAs. The dynamics of microRNA secretion and their potential transfer to recipient cells were next investigated. As a proof-of-concept, we demonstrate that if cel-miR-238, a C. Elegans microRNA not present in mammalian cells, is expressed in MIN6B1 cells a fraction of it is released in exosomes and is transferred to recipient beta-cells. Furthermore, incubation of untreated MIN6B1 or mice islet cells in the presence of microRNA-containing exosomes isolated from the culture media of cytokine-treated MIN6B1 cells triggers apoptosis of recipient cells. In contrast, exosomes originating from cells not exposed to cytokines have no impact on cell survival. Apoptosis induced by exosomes produced by cytokine-treated cells was prevented by down-regulation of the microRNA-mediating silencing protein Ago2 in recipient cells, suggesting that the effect is mediated by the non-coding RNAs. CONCLUSIONS: Taken together, our results suggest that beta-cells secrete microRNAs that can be transferred to neighboring beta-cells. Exposure of donor cells to pathophysiological conditions commonly associated with diabetes modifies the release of microRNAs and affects survival of recipient beta-cells. Our results support the concept that exosomal microRNAs transfer constitutes a novel cell-to-cell communication mechanism regulating the activity of pancreatic beta-cells.