Conserved class B GPCR activation by a biased intracellular agonist.

Class B G-protein-coupled receptors (GPCRs), including glucagon-like peptide 1 receptor (GLP1R) and parathyroid hormone 1 receptor (PTH1R), are important drug targets1-5. Injectable peptide drugs targeting these receptors have been developed, but orally available small-molecule drugs remain under development6,7. Here we report the high-resolution structure of human PTH1R in complex with the stimulatory G protein (Gs) and a small-molecule agonist, PCO371, which reveals an unexpected binding mode of PCO371 at the cytoplasmic interface of PTH1R with Gs. The PCO371-binding site is totally different from all binding sites previously reported for small molecules or peptide ligands in GPCRs. The residues that make up the PCO371-binding pocket are conserved in class B GPCRs, and a single alteration in PTH2R and two residue alterations in GLP1R convert these receptors to respond to PCO371. Functional assays reveal that PCO371 is a G-protein-biased agonist that is defective in promoting PTH1R-mediated arrestin signalling. Together, these results uncover a distinct binding site for designing small-molecule agonists for PTH1R and possibly other members of the class B GPCRs and define a receptor conformation that is specific only for G-protein activation but not arrestin signalling. These insights should facilitate the design of distinct types of class B GPCR small-molecule agonist for various therapeutic indications.

Molecular Basis for Hormone Recognition and Activation of Corticotropin-Releasing Factor Receptors.

Corticotropin-releasing factor (CRF) and the three related peptides urocortins 1-3 (UCN1-UCN3) are endocrine hormones that control the stress responses by activating CRF1R and CRF2R, two members of class B G-protein-coupled receptors (GPCRs). Here, we present two cryoelectron microscopy (cryo-EM) structures of UCN1-bound CRF1R and CRF2R with the stimulatory G protein. In both structures, UCN1 adopts a single straight helix with its N terminus dipped into the receptor transmembrane bundle. Although the peptide-binding residues in CRF1R and CRF2R are different from other members of class B GPCRs, the residues involved in receptor activation and G protein coupling are conserved. In addition, both structures reveal bound cholesterol molecules to the receptor transmembrane helices. Our structures define the basis of ligand-binding specificity in the CRF receptor-hormone system, establish a common mechanism of class B GPCR activation and G protein coupling, and provide a paradigm for studying membrane protein-lipid interactions for class B GPCRs.

Structural basis for activation of somatostatin receptor 5 by cyclic neuropeptide agonists.

Somatostatin receptor 5 (SSTR5) is an important G protein-coupled receptor and drug target for neuroendocrine tumors and pituitary disorders. This study presents two high-resolution cryogenicelectron microscope structures of the SSTR5-Gi complexes bound to the cyclic neuropeptide agonists, cortistatin-17 (CST17) and octreotide, with resolutions of 2.7 Å and 2.9 Å, respectively. The structures reveal that binding of these peptides causes rearrangement of a "hydrophobic lock", consisting of residues from transmembrane helices TM3 and TM6. This rearrangement triggers outward movement of TM6, enabling Gαi protein engagement and receptor activation. In addition to hydrophobic interactions, CST17 forms conserved polar contacts similar to somatostatin-14 binding to SSTR2, while further structural and functional analysis shows that extracellular loops differently recognize CST17 and octreotide. These insights elucidate agonist selectivity and activation mechanisms of SSTR5, providing valuable guidance for structure-based drug development targeting this therapeutically relevant receptor.

A late eating midpoint is associated with increased risk of diabetic kidney disease: a cross-sectional study based on NHANES 2013-2020.

BACKGROUND: Modifying diet is crucial for diabetes and complication management. Numerous studies have shown that adjusting eating habits to align with the circadian rhythm may positively affect metabolic health. However, eating midpoint, eating duration, and their associations with diabetic kidney disease (DKD) are poorly understood. METHODS: The National Health and Nutrition Examination Survey (2013-2020) was examined for information on diabetes and dietary habits. From the beginning and ending times of each meal, we calculated the eating midpoint and eating duration. Urinary albumin-to-creatinine ratio (UACR) ≥ 30 mg/g and/or estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 were the specific diagnostic criteria for DKD. RESULTS: In total, details of 2194 subjects with diabetes were collected for analysis. The overall population were divided into four subgroups based on the eating midpoint quartiles. The prevalence of DKD varied noticeably (P = 0.037) across the four categories. When comparing subjects in the second and fourth quartiles of eating midpoint to those in the first one, the odds ratios (ORs) of DKD were 1.31 (95% CI, 1.03 to 1.67) and 1.33 (95% CI, 1.05 to 1.70), respectively. And after controlling for potential confounders, the corresponding ORs of DKD in the second and fourth quartiles were 1.42 (95% CI, 1.07 to 1.90) and 1.39 (95% CI, 1.04 to 1.85), respectively. CONCLUSIONS: A strong correlation was found between an earlier eating midpoint and a reduced incidence of DKD. Eating early in the day may potentially improve renal outcomes in patients with diabetes.

Constitutive signal bias mediated by the human GHRHR splice variant 1.

Alternative splicing of G protein-coupled receptors has been observed, but their functions are largely unknown. Here, we report that a splice variant (SV1) of the human growth hormone-releasing hormone receptor (GHRHR) is capable of transducing biased signal. Differing only at the receptor N terminus, GHRHR predominantly activates Gs while SV1 selectively couples to ß-arrestins. Based on the cryogenic electron microscopy structures of SV1 in the apo state or GHRH-bound state in complex with the Gs protein, molecular dynamics simulations reveal that the N termini of GHRHR and SV1 differentiate the downstream signaling pathways, Gs versus ß-arrestins. As suggested by mutagenesis and functional studies, it appears that GHRH-elicited signal bias toward ß-arrestin recruitment is constitutively mediated by SV1. The level of SV1 expression in prostate cancer cells is also positively correlated with ERK1/2 phosphorylation but negatively correlated with cAMP response. Our findings imply that constitutive signal bias may be a mechanism that ensures cancer cell proliferation.

Molecular recognition of two endogenous hormones by the human parathyroid hormone receptor-1.

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) are two endogenous hormones recognized by PTH receptor-1 (PTH1R), a member of class B G protein- coupled receptors (GPCRs). Both PTH and PTHrP analogs including teriparatide and abaloparatide are approved drugs for osteoporosis, but they exhibit distinct pharmacology. Here we report two cryo-EM structures of human PTH1R bound to PTH and PTHrP in the G protein-bound state at resolutions of 2.62 Å and 3.25 Å, respectively. Detailed analysis of these structures uncovers both common and unique features for the agonism of PTH and PTHrP. Molecular dynamics (MD) simulation together with site-directed mutagenesis studies reveal the molecular basis of endogenous hormones recognition specificity and selectivity to PTH1R. These results provide a rational template for the clinical use of PTH and PTHrP analogs as an anabolic therapy for osteoporosis and other disorders.

The relationship between frailty and community-acquired pneumonia in older patients.

PURPOSES: To explore the relationship between frailty and community-acquired pneumonia (CAP) in older patients. METHODS: A prospective observational study included 109 older patients(≥ 65 years) hospitalized with CAP in respiratory department of Fuxing hospital, Capital Medical University from June 2018 to December 2020. Frailty scores(Frail Scale, range 0-5) and pneumonia severity CURB-65 scale(mild = 1, modest = 2, and severe ≥ 3) were measured. We extracted clinical variables including white blood cell(WBC), neutrophil-to-lymphocyte ratio (NLR), C-reactive protein(CRP), hemoglobin, and albumin. Charlson Comorbidity Index(CCI) was calculated as well. The correlations between the variables and frailty scores were investigated, respectively. After adjusting for covariates, binomial logistic regression analysis was used to assess independent effect of frailty scores on the outcome(discharge or death/progression) in older CAP patients. RESULTS: The subjects had a median age 87(interquartile range,8.5) years, 60.6% male, 45.9% pre-frail, and 32.1% frail. There were positive correlations between frailty scores and CURB-65 scale (p = 0.000, r = 0.542), CCI(p = 0.000, r = 0.359) and NLR(p = 0.005, r = 0.268). Negative correlations were observed between frailty scores and hemoglobin (p = 0.002, r = - 0.298), albumin (p = 0.000, r = - 0.465). In multivariable logistic regression analysis, the factors associated with discharge or death/progression of CAP were frailty scores (OR = 1.623, p = 0.037), NLR (OR = 1.086, p = 0.008) and albumin (OR = 0.869, p = 0.034). CONCLUSIONS: Frailty is correlated with CURB-65 scale, CCI and hemoglobin, and albumin in older patients with CAP. Frailty is also a correlate of increased risk for death or progression in these older people.

Two new isoflavones from the roots of Sophora tonkinensis.

Two new isoflavones (1 and 2), as well as eight known ones were isolated from the roots of Sophora tonkinensis Gagnep. Compound 1 represents an unprecedented polymerization pattern constructed by isoflavone and cytisine. Their structures were elucidated by comprehensive spectroscopic data analysis, combined with ECD calculations. Compound 1 displayed significant anti-tobacco mosaic virus (TMV) activity compared with the positive control ningnanmycin. Moreover, compound 6 exhibited potent α-glucosidase inhibitory activity with IC50 value of 47.4 mg/L.

Oceanisphaera pacifica sp. nov., isolated from the intestine of Trichiurus japonicus.

A Gram-stain-negative, strictly aerobic, non-flagellated, oxidase- and catalase-positive, rod-shaped marine bacterium, designated strain DM8T, was isolated from the intestine of Trichiurus japonicus in Weihai, China. The strain optimally grew at 25-35℃, with 1.0-4.0% (w/v) NaCl and at pH 7.0-8.0. Its colonies were circular, slightly yellow, non-transparent, smooth, and approximately 0.8-1.5 mm in diameter, after being cultured for 48 h on marine agar 2216. Based on the result of phylogenetic analysis of 16S rRNA gene sequence, strain DM8T had close relationship with Oceanisphaera profunda SM1222T (96.9%) and the type strain DSM 15406 T of the type species Oceanisphaera litoralis (94.7%), respectively. Genome sequencing revealed a genome size of 3,109,059 bp and a G + C content of 46.9 mol%. It had Q-8 as the sole respiratory quinone and possessed C16:0, summed features 3 (C16:1ω7c/C16:1ω6c) and summed features 8 (C18:1ω7c/C18:1ω6c) as major fatty acids. The major polar lipid profile was composed of phosphatidylglycerol and phosphatidylethanolamine. Based on the phenotypic, chemotaxonomic characterizations, phylogenetic properties and genome analysis, strain DM8T should represent a novel species of the genus Oceanisphaera, for which the name Oceanisphaera pacifica sp. nov. is proposed. The type strain is DM8T (= KCTC 82764 T = MCCC 1K06133T).

Comparative genomic analysis of the genus Marinomonas and taxonomic study of Marinomonas algarum sp. nov., isolated from red algae Gelidium amansii.

Members of the genus Marinomonas are known for their environmental adaptation and metabolically versatility, with abundant proteins associated with antifreeze, osmotic pressure resistance, carbohydrase and multiple secondary metabolites. Comparative genomic analysis focusing on secondary metabolites and orthologue proteins was conducted with 30 reference genome sequences in the genus Marinomonas. In this study, a Gram-stain-negative, rod-shaped, non-flagellated and strictly aerobic bacterium, designated as strain E8T, was isolated from the red algae (Gelidium amansii) in the coastal of Weihai, China. Optimal growth of the strain E8T was observed at temperatures 25-30 °C, pH 6.5-8.0 and 1-3% (w/v) NaCl. The DNA G + C content was 42.8 mol%. The predominant isoprenoid quinone was Q-8 and the major fatty acids were C16:0, summed feature 3 and summed feature 8. The major polar lipids were phosphatidylglycerol (PG) and phosphatidylethanolamine (PE). Based on data obtained from this polyphasic taxonomic study, strain E8T should be considered as a novel species of the genus Marinomonas, for which the name Marinomonas algarum is proposed. The type strain is E8T (= KCTC 92201T = MCCC 1K07070T).

Fulvivirga marina sp. nov. and Fulvivirga sediminis sp. nov., two novel Bacteroidetes isolated from the marine sediment.

Two novel, designated strains 29W222T and 2943T, were isolated from the marine sediment from Aoshan Bay, Jimo, PR China. Growth was observed at pH 6.0-8.5 (optimum, pH 7.5) for strain 29W222T, and pH 5.5-8.5 (pH 7.0) for strain 2943T. Both strains displayed growth in 0.5-6 % NaCl with an optimum at 1 % for 29W222T; 0.5 % for 2943T. Both strains grew optimally at 33 °C. The results of phylogenetic analyses based on 16S rRNA gene sequences indicated that 29W222T and 2943T represented members of the genus Fulvivirga and strain 29W222T was most closely related to Fulvivirga kasyanovii KMM 6220T (97.9 % sequence similarity) and Fulvivirga imtechensis AK7T (95.0 %), and 2943T to Fulvivirga imtechensis AK7T (95.7 %) and Fulvivirga kasyanovii KMM 6220T (94.8 %). The genomic DNA G+C contents of 29W222T and 2943T were 39.9 and 37.7 mol%, respectively. The results of chemotaxonomic analysis indicated that the sole respiratory quinone was menaquinone 7 (MK-7), and the major fatty acid was iso-C15 : 0 for both strains. Average nucleotide identity and average amino acid identity values between strain 29W222T and Fulvivirga kasyanovii KMM 6220T were 78.9 and 83.6 %, respectively; the corresponding values between 2943T and Fulvivirga imtechensis AK7T were 69.8 and 63.6 %, respectively. Therefore, strains 29W222T and 2943T represent to two novel species of the genus Fulvivirga, for which the names Fulvivirga marina sp. nov. (29W222T=KCTC 62848T=MCCC 1K05194T) and Fulvivirga sediminis sp. nov. (2943T=KCTC 62847T= MCCC 1K05144T) are proposed, respectively.

Maillard Reaction Products with Anti-Tobacco Mosaic Virus Activities Generated in Processed Thermopsis lanceolata R. Br. Seed Extract.

Six novel Maillard reaction products (MRPs) (1-6) were isolated from the processed Thermopsis lanceolata R. Br. seed extract, along with one biogenetically related intermediate (7). Compounds 1-4 possessed three rare dimerization patterns constructed by cytisine, whereas compounds 5 and 6 represented the first example of the addition products of cytisine and 5,6-dihydroxy-4-hexanolide. Their structures were elucidated by comprehensive spectroscopic data analysis and quantum chemistry calculations including GIAO 13C{1H} NMR and ECD calculation, combined with single-crystal X-ray diffraction analysis. Biologically, compound 3 displayed significant anti-tobacco mosaic virus activity compared with the positive control ningnanmycin.

Optimal cut-off value of serum procalcitonin in predicting bacterial infection induced acute exacerbation in chronic obstructive pulmonary disease: A prospective observational study.

OBJECTIVE: To explore the optimal cut-off value of serum procalcitonin (PCT) level in predicting bacterial infection in hospitalized patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). METHODS: 204 hospitalized patients with AECOPD were enrolled in this study. Their diagnoses and treatments followed routine protocols in Fu-Xing Hospital affiliated to Capital Medical University, Beijing, China. Extra blood samples were taken for serum PCT level testing and the results were blinded to the treating physicians. On discharge, clinical data were collected and the treating physicians made comprehensive analyses to determine whether the AECOPD were triggered by respiratory tract bacterial infection or non-bacterial causes according to the "new diagnostic criteria" defined in this study. In the AECOPD patients with bacterial infection, treating physicians decided whether they had bacterial pneumonia based on imaging studies. Receiver operating characteristic curve (ROC) was used to analyze the accuracy of serum PCT level in predicting bacterial infection. RESULTS: In the 173 AECOPD patients who did not have pneumonia, 115 had evidences of bacterial infection while 58 did not. The median PCT levels were 0.1(0.08, 0.18) ng/ml and 0.07 (0.05, 0.08) ng/ml for each group, which were statistically different. The proposed optimal cut-off value of serum PCT level in predicting bacterial infection was 0.08 ng/mL according to this study, with a sensitivity of 81%, specificity of 67% and area under the ROC curve (AUC) of 0.794. There were 31 AECOPD patients diagnosed with pneumonia, their median PCT level was 0.23 ng/mL. CONCLUSIONS: The serum PCT levels slightly increased in the majority of hospitalized patients with AECOPD compared with reference range. When PCT level was ≥0.08 ng/mL, AECOPD was more likely to be caused by bacterial infection. A significantly elevated PCT levels may indicate combination of AECOPD and bacterial pneumonia.

Anti-tobacco mosaic virus (TMV) activity of chemical constituents from the seeds of Sophora tonkinensis.

Two new compounds, including one new arylbenzofuran (1) and one new pterocarpanoid (2), along with nine known ones, were isolated from the seeds of Sophora tonkinensis. The structures of the new compounds were elucidated based on a comprehensive spectroscopic data analysis. Compounds 2 and 3 exhibited good anti-tobacco mosaic virus (TMV) activities with the protective inhibition rate of 69.62% and 68.72% respectively, at concentration of 100 µg/ml.

Derivation of Porcine Extra-Embryonic Endoderm Cell Lines Reveals Distinct Signaling Pathway and Multipotency States.

The inner cell mass of the pre-implantation blastocyst consists of the epiblast and hypoblast from which embryonic stem cells (ESCs) and extra-embryonic endoderm (XEN) stem cells, respectively, can be derived. Importantly, each stem cell type retains the defining properties and lineage restriction of its in vivo tissue origin. We have developed a novel approach for deriving porcine XEN (pXEN) cells via culturing the blastocysts with a chemical cocktail culture system. The pXEN cells were positive for XEN markers, including Gata4, Gata6, Sox17, and Sall4, but not for pluripotent markers Oct4, Sox2, and Nanog. The pXEN cells also retained the ability to undergo visceral endoderm (VE) and parietal endoderm (PE) differentiation in vitro. The maintenance of pXEN required FGF/MEK+TGFß signaling pathways. The pXEN cells showed a stable phenotype through more than 50 passages in culture and could be established repeatedly from blastocysts or converted from the naïve-like ESCs established in our lab. These cells provide a new tool for exploring the pathways of porcine embryo development and differentiation and providing further reference to the establishment of porcine ESCs with potency of germline chimerism and gamete development.

Aeromicrobium piscarium sp. nov., isolated from the intestine of Collichthys lucidus.

A Gram-stain-positive, rod-shaped, whitesmoke-coloured and aerobic bacterium, designated strain Co35T, was isolated from the intestine of Collichthys lucidus collected from the Jiangmen Guangdong Chinese White Dolphin Provincial Nature Reserve. Strain Co35T was able to grow at 15-35 °C (optimal 28 °C), at pH 7.0-8.5 (optimal 8.0) and with 0-9 % (w/v) NaCl (optimal 0.5-1 %). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain Co35T was a member of the genus Aeromicrobium within the family Nocardioidaceae. The genomic DNA G+C content of strain Co35T was 68.4 mol%. Chemotaxonomic analysis showed that the sole respiratory quinone was menaquinone 9 (MK-9), and the major fatty acids included 10-methyl C18 : 0. The polar lipids were found to consist of phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylinositol (PI), two unidentified phospholipids (PL1-2) and two unidentified glycolipids (GL1-2). On the basis of its phylogenetic, phenotypic, chemotaxonomic, genotypic and genomic characteristics presented in this study, strain Co35T represents a novel species in the genus Aeromicrobium, for which the name Aeromicrobium piscarium sp. nov. is proposed. The type strain is Co35T (=KCTC 49280T=MCCC 1K03754T).

Fasting serum total bile acid levels are associated with insulin sensitivity, islet ß-cell function and glucagon levels in response to glucose challenge in patients with type 2 diabetes.

Type 2 diabetes (T2D) is characterized by islet ß-cell dysfunction and impaired suppression of glucagon secretion of α-cells in response to oral hyperglycaemia. Bile acid (BA) metabolism plays a dominant role in maintaining glucose homeostasis. So we evaluated the association of fasting serum total bile acids (S-TBAs) with insulin sensitivity, islet ß-cell function and glucagon levels in T2D. Total 2,952 T2D patients with fasting S-TBAs in the normal range were recruited and received oral glucose tolerance tests for determination of fasting and postchallenge glucose, C-peptide and glucagon. Fasting and systemic insulin sensitivity were assessed by homeostasis model assessment (HOMA) and Matsuda index using C-peptide, i.e., ISHOMA-cp and ISIM-cp, respectively. Islet ß-cell function was assessed by the insulin-secretion-sensitivity-index-2 using C-peptide (ISSI2cp). The area under the glucagon curve (AUCgla) was used to assess postchallenge glucagon. The results showed ISHOMA-cp, ISIM-cp and ISSI2cp decreased, while AUCgla notably increased, across ascending quartiles of S-TBAs but not fasting glucagon. Moreover, S-TBAs were inversely correlated with ISHOMA-cp, ISIM-cp and ISSI2cp (r = -0.21, -0.15 and -0.25, respectively, p < 0.001) and positively correlated with AUCgla (r = 0.32, p < 0.001) but not with fasting glucagon (r = 0.033, p = 0.070). Furthermore, after adjusting for other clinical covariates by multiple linear regression analyses, the S-TBAs were independently associated with ISHOMA-cp (ß = -0.04, t = -2.82, p = 0.005), ISIM-cp (ß = -0.11, t = -7.05, p < 0.001), ISSI2cp (ß = -0.15, t = -10.26, p < 0.001) and AUCgla (ß = 0.29, t = 19.08, p < 0.001). Increased fasting S-TBAs are associated with blunted fasting and systemic insulin sensitivity, impaired islet ß-cell function and increased glucagon levels in response to glucose challenge in T2D.

Rearrangement of a polar core provides a conserved mechanism for constitutive activation of class B G protein-coupled receptors.

The glucagon receptor (GCGR) belongs to the secretin-like (class B) family of G protein-coupled receptors (GPCRs) and is activated by the peptide hormone glucagon. The structures of an activated class B GPCR have remained unsolved, preventing a mechanistic understanding of how these receptors are activated. Using a combination of structural modeling and mutagenesis studies, we present here two modes of ligand-independent activation of GCGR. First, we identified a GCGR-specific hydrophobic lock comprising Met-338 and Phe-345 within the IC3 loop and transmembrane helix 6 (TM6) and found that this lock stabilizes the TM6 helix in the inactive conformation. Disruption of this hydrophobic lock led to constitutive G protein and arrestin signaling. Second, we discovered a polar core comprising conserved residues in TM2, TM3, TM6, and TM7, and mutations that disrupt this polar core led to constitutive GCGR activity. On the basis of these results, we propose a mechanistic model of GCGR activation in which TM6 is held in an inactive conformation by the conserved polar core and the hydrophobic lock. Mutations that disrupt these inhibitory elements allow TM6 to swing outward to adopt an active TM6 conformation similar to that of the canonical ß2-adrenergic receptor complexed with G protein and to that of rhodopsin complexed with arrestin. Importantly, mutations in the corresponding polar core of several other members of class B GPCRs, including PTH1R, PAC1R, VIP1R, and CRFR1, also induce constitutive G protein signaling, suggesting that the rearrangement of the polar core is a conserved mechanism for class B GPCR activation.

HbA1c variability and diabetic peripheral neuropathy in type 2 diabetic patients.

BACKGROUND: Diabetic complications may be associated with impaired time-dependent glycemic control. Therefore, long-term glycemic variability, assessed by variations in haemoglobin A1c (HbA1c), may be a potential risk factor for microvascular complications, such as diabetic peripheral neuropathy (DPN). We investigated the association of HbA1c variability with DPN in patients with type 2 diabetes. METHODS: In this cross-sectional study, 563 type 2 diabetic patients who had been screened for DPN and undergone quarterly HbA1c measurements during the year preceding enrolment were recruited. DPN was confirmed in patients displaying both clinical manifestations of neuropathy and abnormalities in a nerve conduction evaluation. HbA1c variability was assessed by the coefficient of variation of HbA1c (CV-HbA1c), and the mean of HbA1c (M-HbA1c) was calculated. In addition, medical history and clinical data were collected. RESULTS: Among the recruited patients, 18.1% (n = 102) were found to have DPN, and these patients also presented with a higher CV-HbA1c than the patients without DPN (p < 0.001). The proportion of patients with DPN increased significantly from 6.9% in the first to 19.1% in the second and 28.5% in the third tertile of CV-HbA1c (p for trend < 0.001). After adjusting for initial HbA1c, M-HbA1c and other clinical factors via multiple logistic regression analysis, the odds ratios (ORs) for DPN in the second and third versus those in the first CV-HbA1c tertile were 3.61 (95% CI 1.62-8.04) and 6.48 (2.86-14.72), respectively. The area under the receiver operating characteristic (ROC) curve of CV-HbA1c was larger than that of M-HbA1c, at 0.711 (95% CI 0.659-0.763) and 0.662 (0.604-0.721), respectively. ROC analysis also revealed that the optimal cutoff value of CV-HbA1c to indicate DPN was 15.15%, and its corresponding sensitivity and specificity were 66.67% and 65.73%, respectively. CONCLUSIONS: Increased HbA1c variability is closely associated with DPN in type 2 diabetic patients and could be considered as a potent indicator for DPN in these patients.

Differential Requirement of the Extracellular Domain in Activation of Class B G Protein-coupled Receptors.

G protein-coupled receptors (GPCRs) from the secretin-like (class B) family are key players in hormonal homeostasis and are important drug targets for the treatment of metabolic disorders and neuronal diseases. They consist of a large N-terminal extracellular domain (ECD) and a transmembrane domain (TMD) with the GPCR signature of seven transmembrane helices. Class B GPCRs are activated by peptide hormones with their C termini bound to the receptor ECD and their N termini bound to the TMD. It is thought that the ECD functions as an affinity trap to bind and localize the hormone to the receptor. This in turn would allow the hormone N terminus to insert into the TMD and induce conformational changes of the TMD to activate downstream signaling. In contrast to this prevailing model, we demonstrate that human class B GPCRs vary widely in their requirement of the ECD for activation. In one group, represented by corticotrophin-releasing factor receptor 1 (CRF1R), parathyroid hormone receptor (PTH1R), and pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R), the ECD requirement for high affinity hormone binding can be bypassed by induced proximity and mass action effects, whereas in the other group, represented by glucagon receptor (GCGR) and glucagon-like peptide-1 receptor (GLP-1R), the ECD is required for signaling even when the hormone is covalently linked to the TMD. Furthermore, the activation of GLP-1R by small molecules that interact with the intracellular side of the receptor is dependent on the presence of its ECD, suggesting a direct role of the ECD in GLP-1R activation.