Signalling and Regulation of the Glucagon-like Peptide-1 receptor

Following nutrient ingestion, glucagon-like peptide 1 (GLP-1) secreted from intestinal L-cells mediates anti-diabetic effects, most notably stimulating glucose-dependent insulin release from pancreatic β-cells but also inhibiting glucagon release, promoting satiety and weight reduction and potentially enhancing or preserving β-cell mass. These effects are through the GLP-1 receptor (GLP-1R) which is a therapeutic target in type 2 diabetes. The present study focused on desensitisation and re-sensitisation of GLP-1R-mediated signalling and interactions of orthosteric and allosteric ligands. Data demonstrate GLP-1R desensitisation and subsequent re-sensitisation following removal of extracellular ligand with ligand-specific features. Following GLP-1-mediated desensitisation, re-sensitisation is dependent on receptor internalisation, endosomal acidification and receptor recycling. Re-sensitisation is also dependent on endothelin converting enzyme-1 (ECE-1) activity, possibly through proteolysis of GLP-1 in endosomes, facilitating disassociation of receptor-β-arrestin complexes leading to GLP-1R recycling and re-sensitisation. ECE-1 activity also regulates GLP-1-induced activation of extracellular signal regulated kinase (ERK) and generation of cAMP possibly through a G protein independent/β-arrestin dependent mechanism. By contrast, following GLP-1R activation by the orthosteric agonist, exendin-4, or allosteric agonist, compound 2, re-sensitisation was slow and independent of ECE-1 activity. Thus, different ligands depend on different events during GLP-1R trafficking which could be important for re-sensitisation and signalling, particularly that mediated by scaffolding around β-arrestin. As the GLP-1R is targeted therapeutically at orthosteric and allosteric sites, this study examined activation of the GLP-1R by orthosteric and allosteric agonists and in particular interactions between ligands of these sites. Challenging the GLP-1R with the allosteric ligand, compound 2, along with GLP-1 9-36 amide, a low affinity, low efficacy metabolite of GLP-1 7-36 amide, results in synergistic receptor activation. This may be important for therapeutic approaches with allosteric ligands, as metabolites of GLP-1 may be present in vivo at concentrations higher than the classic endogenous ligand. Indeed this could present a novel therapeutic approach

Theoretical Insight into Core–Shell Preference for Bimetallic Pt‑M (M = Ru, Rh, Os, and Ir) Cluster and Its Electronic Structure

Pt_<i>m</i>M_<i>n</i> (M = Ru, Rh, Os, and Ir; <i>m</i>+<i>n</i> = 38 and 55) clusters are systematically investigated using the DFT method. In an octahedral 38-atom cluster, core–shell structure M₆@- Pt₃₂ with M₆ core and Pt₃₂ shell is stable for Pt–Rh and Pt–Ir combinations but is not for Pt–Ru and Pt–Os combinations. In a 55-atom cluster, icosahedral M₁₃@Pt₄₂ structure is stable for all Pt-M combinations, indicating that a large cluster is more preferable to stabilizing the core–shell structure than a small cluster. The difference in cohesive energy (<i>E</i>_coh) between M₁₃ and Pt₁₃ and the distortion energy {<i>E</i>_dis(M₁₃)} of M₁₃ are parallel to the segregation energy (<i>E</i>_seg), indicating that these are important factors for stabilizing M₁₃@Pt₄₂. One more crucially important factor is the interaction energy (<i>E</i>_int) between M₁₃ core and Pt₄₂ shell, because <i>E</i>_int is parallel to <i>E</i>_seg and its absolute value is much larger than those of <i>E</i>_dis(M₁₃) and <i>E</i>_dis(Pt₄₂). The <i>E</i>_int depends on the energy gap between LUMO of M₁₃ core and HOMO of Pt₄₂ shell, indicating that LUMO energy of M₁₃ and HOMO energy of Pt₄₂ are good properties for understanding and predicting stability of core–shell structure. Pt atom is more positively charged in M₁₃@Pt₄₂ than in Pt₅₅ and the HOMO energy of M₁₃@Pt₄₂ is higher than that of Pt₅₅. The presence of these two contrary factors for O₂ binding suggests that M₁₃@Pt₄₂ is not bad for O₂ binding

Theoretical Insight into Core–Shell Preference for Bimetallic Pt‑M (M = Ru, Rh, Os, and Ir) Cluster and Its Electronic Structure

Pt_<i>m</i>M_<i>n</i> (M = Ru, Rh, Os, and Ir; <i>m</i>+<i>n</i> = 38 and 55) clusters are systematically investigated using the DFT method. In an octahedral 38-atom cluster, core–shell structure M₆@- Pt₃₂ with M₆ core and Pt₃₂ shell is stable for Pt–Rh and Pt–Ir combinations but is not for Pt–Ru and Pt–Os combinations. In a 55-atom cluster, icosahedral M₁₃@Pt₄₂ structure is stable for all Pt-M combinations, indicating that a large cluster is more preferable to stabilizing the core–shell structure than a small cluster. The difference in cohesive energy (<i>E</i>_coh) between M₁₃ and Pt₁₃ and the distortion energy {<i>E</i>_dis(M₁₃)} of M₁₃ are parallel to the segregation energy (<i>E</i>_seg), indicating that these are important factors for stabilizing M₁₃@Pt₄₂. One more crucially important factor is the interaction energy (<i>E</i>_int) between M₁₃ core and Pt₄₂ shell, because <i>E</i>_int is parallel to <i>E</i>_seg and its absolute value is much larger than those of <i>E</i>_dis(M₁₃) and <i>E</i>_dis(Pt₄₂). The <i>E</i>_int depends on the energy gap between LUMO of M₁₃ core and HOMO of Pt₄₂ shell, indicating that LUMO energy of M₁₃ and HOMO energy of Pt₄₂ are good properties for understanding and predicting stability of core–shell structure. Pt atom is more positively charged in M₁₃@Pt₄₂ than in Pt₅₅ and the HOMO energy of M₁₃@Pt₄₂ is higher than that of Pt₅₅. The presence of these two contrary factors for O₂ binding suggests that M₁₃@Pt₄₂ is not bad for O₂ binding

Functional interaction between ligands on GLP-1R-mediated cAMP generation in HEK-GLP-1R cells.

<p>HEK-GLP-1R cells were pretreated (Pre-) for 10 min with 1 µM GLP-1 9–36 amide in the presence of IBMX before challenge for 15 min with the indicated concentrations of agonists. Where no pre-treatment is indicated, an equivalent volume of buffer (KHB) was added for 10 min in the presence of IBMX prior to ligand addition for 15 min. Levels of intracellular cAMP were then determined relative to the cellular protein content. The final concentration of DMSO (vehicle) for the 15 min treatment period was 5% v/v in all cases. Data are mean±s.e.m., n = 3.</p

Time course of cAMP generation in response to GLP-1 9–36 amide, compound 2 or co-stimulation in HEK-GLP-1R cells.

<p>HEK-GLP-1R cells were either untreated (Basal; not visible) or treated for the indicated times with GLP-1 9–36 amide (1 µM), compound 2 (1 µM) or the two in combination (Co-addition) in the presence of IBMX. The final concentration of DMSO (vehicle) was 5% v/v in all cases. In addition to the measured levels of cAMP generation, the numerical sum of cAMP generation in response to GLP-1 9–36 amide and compound 2 alone are presented (Numerical). Data are mean±s.e.m., n = 3, ** P<0.01 and *** P<0.001 by Bonferroni's multiple range test following oneway ANOVA. For clarity, only differences between ‘numerical’ and ‘co-addition’ conditions are shown.</p

High Molecular Weight Polyesters Derived from Biobased 1,5-Pentanediol and a Variety of Aliphatic Diacids: Synthesis, Characterization, and Thermo-Mechanical Properties

High molecular weight aliphatic polyesters were synthesized from biobased 1,5-pentanediol and aliphatic diacids with 4, 5, 6, 9, 10, or 12 carbon atoms via melt polycondensation. The poly­(1,5-pentylene dicarboxylate)­s were characterized with intrinsic viscosity, gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), and tensile testing. The effects of dicarboxylate chain length on crystalline structure and thermo-mechanical properties were investigated. All the polyesters had weight-average molecular weight over 100,000 g/mol or intrinsic viscosity over 1.05 dL/g except poly­(1,5-pentylene adipate) (PPeA), which was less thermally stable than others. As semicrystalline polymers, they have a polyethylene-like crystal structure and crystallize rapidly except poly­(1,5-pentylene succinate) (PPeS). As a whole, the crystallizability and melting temperature (<i>T</i>_m) increase with dicarboxylate chain length, and the “even–odd” effect exists to a certain extent. Among them, poly­(1,5-pentylene azelate) (PPeAz), poly­(1,5-pentylene sebacate) (PPeSe), and poly­(1,5-pentylene dodecanedioate) (PPeDo) have <i>T</i>_m of 50–62 °C, good thermal stability, and exhibit comparable or even superior tensile properties in comparison with polyethylene and the well-known biodegradable copolyester, poly­(butylene adipate-<i>co</i>-terephthalate) (PBAT). These biobased and potentially biodegradable polyesters appear to be promising materials for practical applications