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Small GTPases are molecular switches that participate in many essential cellular processes. Amongst them, human Rac1 was first described for its role in regulating actin cytoskeleton dynamics and cell migration, with a close relation to carcinogenesis. More recently, the role of Rac1 in regulating the production of reactive oxygen species (ROS), both as a subunit of NADPH oxidase complexes and through its association with mitochondrial functions, has drawn attention. Malfunctions in this context affect cellular plasticity and apoptosis, related to neurodegenerative diseases and diabetes. Some of these features of Rac1 are conserved in its yeast homologue Rho5. Here, we review the structural and functional similarities and differences between these two evolutionary distant proteins and propose yeast as a useful model and a device for high-throughput screens for specific drugs. [ABSTRACT FROM AUTHOR]

To decipher the mediator role of the grape Abscisic acid, Stress, Ripening (ASR) protein, VvMSA, in the pathways of glucose signaling through the regulation of its target, the promoter of hexose transporter VvHT1, we overexpressed and repressed VvMSA in embryogenic and non-embryogenic grapevine cells. The embryogenic cells with organized cell proliferation were chosen as an appropriate model for high sensitivity to the glucose signal, due to their very low intracellular glucose content and low glycolysis flux. In contrast, the non-embryogenic cells displaying anarchic cell proliferation, supported by high glycolysis flux and a partial switch to fermentation, appeared particularly sensitive to inhibitors of glucose metabolism. By using different glucose analogs to discriminate between distinct pathways of glucose signal transduction, we revealed VvMSA positioning as a transcriptional regulator of the glucose transporter gene VvHT1 in glycolysis-dependent glucose signaling. The effects of both the overexpression and repression of VvMSA on glucose transport and metabolism via glycolysis were analyzed, and the results demonstrated its role as a mediator in the interplay of glucose metabolism, transport and signaling. The overexpression of VvMSA in the Arabidopsis mutant abi8 provided evidence for its partial functional complementation by improving glucose absorption activity.

As photoautotrophic organisms, plants produce an incredible spectrum of pigments, anti-herbivory compounds, structural materials and energic intermediates. These biosynthetic routes help plants grow, reproduce and mitigate stress. HEXOKINASE1 (HXK1), a metabolic enzyme and glucose sensor, catalyzes the phosphorylation of hexoses, a key introductory step for many of these pathways. However, previous studies have largely focused on the glucose sensing and signaling functions of HXK1, and the importance of the enzyme's catalytic function is only recently being connected to plant development. In this brief Spotlight, we describe the developmental significance of plant HXK1 and its role in plant metabolic pathways, specifically in glucose-6-phosphate production. Furthermore, we describe the emerging connections between metabolism and development and suggest that HXK1 signaling and catalytic activity regulate discrete areas of plant development. [ABSTRACT FROM AUTHOR]

Small GTPases are molecular switches that participate in many essential cellular processes. Amongst them, human Rac1 was first described for its role in regulating actin cytoskeleton dynamics and cell migration, with a close relation to carcinogenesis. More recently, the role of Rac1 in regulating the production of reactive oxygen species (ROS), both as a subunit of NADPH oxidase complexes and through its association with mitochondrial functions, has drawn attention. Malfunctions in this context affect cellular plasticity and apoptosis, related to neurodegenerative diseases and diabetes. Some of these features of Rac1 are conserved in its yeast homologue Rho5. Here, we review the structural and functional similarities and differences between these two evolutionary distant proteins and propose yeast as a useful model and a device for high-throughput screens for specific drugs.

Aspergillus niger is the main industrial workhorse for global citric acid production. This fungus has complex sensing and signaling pathways to respond to environmental nutrient fluctuations. As the preferred primary carbon source, glucose also acts as a critical signal to trigger intracellular bioprocesses. Currently, however, there is still a knowledge gap in systems-level understanding of metabolic and cellular responses to this vital carbon source. In this study, we determined genome-wide transcriptional changes of citric acid-producing Aspergillus niger in response to external glucose gradient. It demonstrated that external glucose fluctuation led to transcriptional reprogramming of many genes encoding proteins involved in fundamental cellular process, including ribosomal biogenesis, carbon transport and catabolism, glucose sensing and signaling. The major glucose catabolism repressor creA maintained a stable expression independent of external glucose, while creB and creD showed significant downregulation and upregulation by the glucose increase. Notably, several high-affinity glucose transporters encoding genes, including mstA, were greatly upregulated when glucose was depleted, while the expression of low-affinity glucose transporter mstC was glucose-independent, which showed clear concordance with their protein levels detected by in situ fluorescence labeling assay. In addition, we also observed that the citric acid exporter cexA was observed to be transcriptionally regulated by glucose availability, which was correlated with extracellular citric acid secretion. These discoveries not only deepen our understanding of the transcriptional regulation of glucose but also shed new light on the adaptive evolutionary mechanism of citric acid production of A. niger.

Key message: Cytoplasm-localized RING ubiquitin E3 ligase AtCHYR2 involved in plant glucose responses during germination and post-germinative growth. CHY ZINC FINGER AND RING PROTEIN (CHYR) containing both a CHY zinc finger and a C3H2C3-type RING domain plays important roles in plant drought tolerance and the abscisic acid (ABA) response; however, their functions in sugar signaling pathways are less studied. Here, we report a glucose (Glc) response gene AtCHYR2, a homolog of RZFP34/CHYR1, which is induced by various abiotic stresses, ABA, and sugar treatments. In vitro, we demonstrated that AtCHYR2 is a cytoplasm-localized RING ubiquitin E3 ligase. Overexpression of AtCHYR2 led to hypersensitivity to Glc and enhanced Glc-mediated inhibition of cotyledon greening and post-germinative growth. Contrastingly, AtCHYR2 loss-of-function plants were insensitive to Glc-regulated seed germination and primary root growth, suggesting that AtCHYR2 is a positively regulator of the plant glucose response. Additionally, physiological analyses showed that overexpression AtCHYR2 increased stomata aperture and photosynthesis under normal condition, and promoted accumulation of endogenous soluble sugar and starch in response to high Glc. Genome-wide RNA sequencing analysis showed that AtCHYR2 affects a major proportion of Glc-responsive genes. Particularly, sugar marker gene expression analysis suggested that AtCHYR2 enhances the Glc response via a signaling pathway dependent on glucose metabolism. Taken together, our findings show that a novel RING ubiquitin E3 ligase, AtCHYR2, plays an important role in glucose responses in Arabidopsis. [ABSTRACT FROM AUTHOR]

Hexokinase1 (HXK1) is a bifunctional enzyme that plays indispensable roles in plant growth, nitrogen utilization, and stress resistance. However, information on the HXK family members of strawberries and their functions in glucose sensing and metabolic regulation is scarce. In the present study, four HXKs were firstly identified in the genome of Fragaria vesca and F. pentaphylla. The conserved domains of the HXK1s were confirmed, and a site-directed mutation (S177A) was introduced into the FpHXK1. FpHXK1, which shares the highest identity with the AtHXK1 was able to restore the glucose sensitivity and developmental defects of the Arabidopsis gin2-1 mutant, but not its kinase-activity-impaired mutant (FpHXK1S177A). The transcription of FpHXK1 was dramatically up-regulated under PEG-simulated drought stress conditions. The inhibition of the HXK kinase activity delayed the strawberry plant’s responses to drought stress. Transient overexpression of the FpHXK1 and its kinase-impaired mutant differentially affected the level of glucose, sucrose, anthocyanins, and total phenols in strawberry fruits. All these results indicated that the FpHXK1, acting as a glucose sensor, was involved in drought stress response and sugar metabolism depending on its kinase activity. [ABSTRACT FROM AUTHOR]

The homeostasis of major macronutrient metabolism needs to be tightly regulated, especially when the availability of one or more nutrients fluctuates in the environment. Both sulfur metabolism and glucose signaling are important processes throughout plant growth and development, as well as during stress responses. Still, very little is known about how these processes affect each other, although they are positively connected. Here, we showed in Arabidopsis that the crucial transcription factor of sulfur metabolism, SLIM1, is involved in glucose signaling during shortage of sulfur. The germination rate of the slim1_KO mutant was severely affected by high glucose and osmotic stress. The expression of SLIM1-dependent genes in sulfur deficiency appeared to be additionally induced by a high concentration of either mannitol or glucose, but also by sucrose, which is not only the source of glucose but another signaling molecule. Additionally, SLIM1 affects PAP1 expression during sulfur deficiency by directly binding to its promoter. The lack of PAP1 induction in such conditions leads to much lower anthocyanin production. Taken together, our results indicate that SLIM1 is involved in the glucose response by modulating sulfur metabolism and directly controlling PAP1 expression in Arabidopsis during sulfur deficiency stress. [ABSTRACT FROM AUTHOR]

Summary: Low light intensities affect the outbreak of plant diseases. However, the underlying molecular mechanisms remain poorly understood.High‐performance liquid chromatography analysis of tomato (Solanum lycopersicum) revealed that apoplastic glucose (Glc) levels decreased in response to low light. Conversely, low‐light‐induced susceptibility to Pseudomonas syringae pv tomato (Pst) DC3000 was significantly alleviated by exogenous Glc treatment. Using cell‐based biolayer interferometry assays, we found that Glc specifically binds to the tomato regulator of G protein signaling 1 (RGS1). Laser scanning confocal microscopy imaging revealed that Glc triggers RGS1 endocytosis, which influences the uncoupling of the RGS1‐Gα (GPA1) and GPA1‐Gβ (SlGB1) proteins, in a dose‑ and duration‐dependent manner.Analysis of G protein single and double mutants revealed that RGS1 negatively regulates disease resistance under low light and is required for Glc‐enhanced defense. Downstream of RGS1‐Glc binding, GPA1 negatively mediates the light‐intensity‐regulated defense, whereas SlGB1 positively regulates this process.These results reveal a novel light‐intensity‐responsive defense system that is mediated by a Glc–RGS1–G protein signaling pathway. This information will be critical for future investigations of how plant cells sense extracellular sugars and adjust defense under different environments, as well as for genetic engineering approaches to improve stress resilience. [ABSTRACT FROM AUTHOR]

Biochemical signaling is one of the key mechanisms to coordinate a living organism in all aspects of its life. It is still enigmatic how exactly cells and organisms deal with environmental signals and irritations precisely because of the limited number of signaling proteins and a multitude of transitions inside and outside the cell. Many components of signaling pathways are functionally pleiotropic, which means they have several functions. A single stimulus often results in multiple responses, a distinct response can be triggered by numerous stimuli and signals initiated by different stimuli are often transduced via commonly used network components. This review sheds light on the most important molecular mechanisms of cellular signaling in fungi and consequently provides a comprehensive overview about the current state of research on the road to understand the impact of signal transduction in eukaryotic microorganisms. [ABSTRACT FROM AUTHOR]

Nutrients are vital to life through intertwined sensing, signaling, and metabolic processes. Emerging research focuses on how distinct nutrient signaling networks integrate and coordinate gene expression, metabolism, growth, and survival. We review the multifaceted roles of sugars, nitrate, and phosphate as essential plant nutrients in controlling complex molecular and cellular mechanisms of dynamic signaling networks. Key advances in central sugar and energy signaling mechanisms mediated by the evolutionarily conserved master regulators HEXOKINASE1 (HXK1), TARGET OF RAPAMYCIN (TOR), and SNF1-RELATED PROTEIN KINASE1 (SNRK1) are discussed. Significant progress in primary nitrate sensing, calcium signaling, transcriptome analysis, and root–shoot communication to shape plant biomass and architecture are elaborated. Discoveries on intracellular and extracellular phosphate signaling and the intimate connections with nitrate and sugar signaling are examined. This review highlights the dynamic nutrient, energy, growth, and stress signaling networks that orchestrate systemwide transcriptional, translational, and metabolic reprogramming, modulate growth and developmental programs, and respond to environmental cues. [ABSTRACT FROM AUTHOR]

Summary: CINV1, converting sucrose into glucose and fructose, is a key entry of carbon into cellular metabolism, and HXK1 functions as a pivotal sensor for glucose. Exogenous sugars trigger the Arabidopsis juvenile-to-adult phase transition via a miR156A/SPL module. However, the endogenous factors that regulate this process remain unclear. In this study, we show that sucrose specifically induced the PAP1 transcription factor directly and positively controls CINV1 activity. Furthermore, we identify a glucose feed-forward loop (sucrose-CINV1-glucose-HXK1-miR156-SPL9-PAP1-CINV1-glucose) that controls CINV1 activity to convert sucrose into glucose signaling to dynamically control the juvenile-to-adult phase transition. Moreover, PAP1 directly binds to the SPL9 promoter, activating SPL9 expression and triggering the sucrose-signaling-mediated juvenile-to-adult phase transition. Therefore, a glucose-signaling feed-forward loop and a sucrose-signaling pathway synergistically regulate the Arabidopsis juvenile-to-adult phase transition. Collectively, we identify a molecular link between the major photosynthate sucrose, the entry point of carbon into cellular metabolism, and the plant juvenile-to-adult phase transition.

To decipher the mediator role of the grape Abscisic acid, Stress, Ripening (ASR) protein, VvMSA, in the pathways of glucose signaling through the regulation of its target, the promoter of hexose transporter VvHT1, we overexpressed and repressed VvMSA in embryogenic and non-embryogenic grapevine cells. The embryogenic cells with organized cell proliferation were chosen as an appropriate model for high sensitivity to the glucose signal, due to their very low intracellular glucose content and low glycolysis flux. In contrast, the non-embryogenic cells displaying anarchic cell proliferation, supported by high glycolysis flux and a partial switch to fermentation, appeared particularly sensitive to inhibitors of glucose metabolism. By using different glucose analogs to discriminate between distinct pathways of glucose signal transduction, we revealed VvMSA positioning as a transcriptional regulator of the glucose transporter gene VvHT1 in glycolysis-dependent glucose signaling. The effects of both the overexpression and repression of VvMSA on glucose transport and metabolism via glycolysis were analyzed, and the results demonstrated its role as a mediator in the interplay of glucose metabolism, transport and signaling. The overexpression of VvMSA in the Arabidopsis mutant abi8 provided evidence for its partial functional complementation by improving glucose absorption activity.

My graduate and postdoctoral training in metabolism and enzymology eventually led me to study the short- and long-term regulation of glucose and lipid metabolism. In the early phase of my career, my trainees and I identified, purified, and characterized a variety of phosphofructokinase enzymes from mammalian tissues. These studies led us to discover fructose 2,6-P2, the most potent activator of phosphofructokinase and glycolysis. The discovery of fructose 2,6-P2 led to the identification and characterization of the tissue-specific bifunctional enzyme 6-phosphofructo-2-kinase:fructose 2,6-bisphosphatase. We discovered a glucose signaling mechanism by which the liver maintains glucose homeostasis by regulating the activities of this bifunctional enzyme. With a rise in glucose, a signaling metabolite, xylulose 5-phosphate, triggers rapid activation of a specific protein phosphatase (PP2ABδC), which dephosphorylates the bifunctional enzyme, thereby increasing fructose 2,6-P2 levels and upregulating glycolysis. These endeavors paved the way for us to initiate the later phase of my career in which we discovered a new transcription factor termed the carbohydrate response element binding protein (ChREBP). Now ChREBP is recognized as the masterregulator controlling conversion of excess carbohydrates to storage of fat in the liver. ChREBP functions as a central metabolic coordinator that responds to nutrients independently of insulin. The ChREBP transcription factor facilitates metabolic adaptation to excess glucose, leading to obesity and its associated diseases. [ABSTRACT FROM AUTHOR]

Hexokinases is a family of proteins that is found in all eukaryotes. Hexokinases play key roles in the primary carbon metabolism, where they catalyze the phosphorylation of glucose and fructose, but they have also been shown to be involved in glucose signaling in both yeast and plants. We have characterized the Klebsormidium nitens KnHXK1 gene, the only hexokinase-encoding gene in this charophyte alga. The encoded protein, KnHXK1, is a type B plant hexokinase with an N-terminal membrane anchor localizing the protein to the mitochondrial membranes. We found that KnHXK1 expressed in Arabidopsis thaliana can restore the glucose sensing and glucose repression defects of the glucose-insensitive hexokinase mutant gin2-1. Interestingly, both functions require a catalytically active enzyme, since an inactive double mutant was unable to complement gin2-1. These findings differ from previous results on Arabidopsis AtHXK1 and its orthologs in rice, where catalytic and glucose sensing functions could be separated, but are consistent with recent results on the rice cytoplasmic hexokinase OsHXK7. A model with both catalytic and non-catalytic roles for hexokinases in glucose sensing and glucose repression is discussed.

Network coupled cells, such as astrocytes, regulate their cellular homeostasis via Ca2+ signals spread between the cells through gap junctions. Intracellular Ca2+ release is controlled by different signaling pathways that can be stimulated by ATP, glutamate and serotonin (5-HT). Based on our findings, all these pathways are influenced by inflammatory agents and must be restored to fully recover the Ca2+ signaling network. An ultralow concentration of the local anesthetic agent bupivacaine reduced 5-HT-evoked intracellular Ca2+ release, and an ultralow concentration of the phosphodiesterase-5 inhibitor sildenafil in combination with vitamin D3 reduced ATP-evoked intracellular Ca2+ release. Combinations of these three substances downregulated 5-HT-, glutamate- and ATP-evoked intracellular Ca2+ release to a more normal Ca2+ signaling state. Furthermore, inflammatory Toll-like receptor 4 expression decreased with a combination of these three substances. Substance P receptor neurokinin (NK)-1 expression was reduced by ultralow concentrations of bupivacaine. Here, bupivacaine and sildenafil (at extremely low concentrations) combined with vitamin D3 have potential anti-inflammatory properties. According to the present study, drug combinations at the right concentrations, especially extremely low concentrations of bupivacaine and sildenafil, affect different cellular biochemical mechanisms and represent a potential solution for downregulating inflammatory parameters, thereby restoring cells or networks to normal physiological homeostasis. [ABSTRACT FROM AUTHOR]

Objective: The mechanism by which G-protein-coupled receptor 40 (GPR40) signaling amplifies glucose-stimulated insulin secretion through activation of protein kinase C (PKC) is unknown. We examined whether a GPR40 agonist, GW9508, could stimulate conventional and novel isoforms of PKC at two glucose concentrations (3 mM and 20 mM) in INS-1D cells. Methods: Using epifluorescence microscopy, we monitored relative changes in the cytosolic fluorescence intensity of Fura2 as a marker of change in intracellular Ca2+ ([Ca2+]i) and relative increases in green fluorescent protein (GFP)-tagged myristoylated alanine-rich C kinase substrate (MARCKS-GFP) as a marker of PKC activation in response to GW9508 at 3 mM and 20 mM glucose. To assess the activation of the two PKC isoforms, relative increases in membrane fluorescence intensity of PKCα-GFP and PKCε-GFP were measured by total internal reflection fluorescence microscopy. Specific inhibitors of each PKC isotype were constructed and synthesized as peptide fusions with the third α-helix of the homeodomain of Antennapedia. Results: At 3 mM glucose, GW9508 induced sustained MARCKS-GFP translocation to the cytosol, irrespective of changes in [Ca2+]i. At 20 mM glucose, GW9508 induced sustained MARCKS-GFP translocation but also transient translocation that followed sharp increases in [Ca2+]i. Although PKCα translocation was rarely observed, PKCε translocation to the plasma membrane was sustained by GW9508 at 3 mM glucose. At 20 mM glucose, GW9508 induced transient translocation of PKCα and sustained translocation as well as transient translocation of PKCε. While the inhibitors (75 μM) of each PKC isotype reduced GW9508-potentiated, glucose-stimulated insulin secretion in INS-1D cells, the PKCε inhibitor had a more potent effect. Conclusion: GW9508 activated PKCε but not PKCα at a substimulatory concentration of glucose. Both PKC isotypes were activated at a stimulatory concentration of glucose and contributed to glucose-stimulated insulin secretion in insulin-producing cells. [ABSTRACT FROM AUTHOR]

Cells and organisms have developed homeostatic mechanisms which protect them against a changing environment. How growth and homeostasis interact is still not well understood, but of increasing interest to the molecular and synthetic biology community to recognize and design control circuits which can oppose the diluting effects of cell growth. In this paper we describe the performance of selected negative feedback controllers in response to different applied growth laws and time dependent outflow perturbations of a controlled variable. The approach taken here is based on deterministic mass action kinetics assuming that cell content is instantaneously mixed. All controllers behave ideal in the sense that they for step-wise perturbations in volume and a controlled compound A are able to drive A precisely back to the controllers’ theoretical set-points. The applied growth kinetics reflect experimentally observed growth laws, which range from surface to volume ratio growth to linear and exponential growth. Our results show that the kinetic implementation of integral control and the structure of the negative feedback loop are two properties which affect controller performance. Best performance is observed for controllers based on derepression kinetics and controllers with an autocatalytic implementation of integral control. Both are able to defend exponential growth and perturbations, although the autocatalytic controller shows an offset from its theoretical set-point. Controllers with activating signaling using zero-order or bimolecular (antithetic) kinetics for integral control behave very similar but less well. Their performance can be improved by implementing negative feedback structures having repression/derepression steps or by increasing controller aggressiveness. Our results provide a guide what type of feedback structures and integral control kinetics are suitable to oppose the dilution effects by different growth laws and time dependent perturbations on a deterministic level. [ABSTRACT FROM AUTHOR]

Individuals with intrauterine growth retardation (IUGR) are prone to insulin resistance, whereas the underlying molecular mechanisms remain unclear. In this study, we investigated if the PI3K/Akt signaling pathway in skeletal muscle tissues involves insulin resistance in IUGR offsprings, particularly ones with catch-up growth. An IUGR rat model was established by feeding rats an isocaloric (30.50 Kcal/g) diet containing 8% protein (low-protein diet) from day 1 of pregnancy until the birth of their pups. Glucometabolic parameters were measured and compared. Quantitative PCR and western blot were performed to assess mRNA and protein expression changes of the PI3K/Akt related signals in skeletal muscle tissues. Pearson analysis was used to assess the correlation of the PI3K/Akt signaling level and catch-up growth with the insulin resistance index (IRI). The values of fasting plasma glucose, fasting insulin and IRI were significantly higher, whereas insulin sensitivity index was significantly lower in IUGR offsprings than those in the controls. The PI3K mRNA and protein levels as well as the phospho-AktSer473 levels were significantly lower in IUGR offsprings compared to the controls. Reductions of GLUT4 as well as increases of PTEN and nuclear fractional PPARγ were detected in IUGR offsprings. Catch-up growth IUGR rats were positively correlated with insulin resistance and underwent more remarkable alterations of the PI3K, PTEN and GLUT4 expressions. Our results demonstrated that rats born IUGR developed insulin resistance later in life, which was likely mediated by reductions of the PI3K/Akt related signaling activities, particularly in those with excess catch-up growth. [ABSTRACT FROM AUTHOR]

Published compact and extended models of the glucose-insulin physiologic control system are compared, in order to understand why a specific functional form of the compact model proved to be necessary for a satisfactory representation of acute perturbation experiments such as the Intra Venous Glucose Tolerance Test (IVGTT). A spectrum of IVGTT’s of virtual subjects ranging from normal to IFG to IGT to frank T2DM were simulated using an extended model incorporating the population-of-controllers paradigm originally hypothesized by Grodsky, and proven to be able to capture a wide array of experimental results from heterogeneous perturbation procedures. The simulated IVGTT’s were then fitted with the Single-Delay Model (SDM), a compact model with only six free parameters, previously shown to be very effective in delivering precise estimates of insulin sensitivity and secretion during an IVGTT. Comparison of the generating, extended-model parameter values with the obtained compact model estimates shows that the functional form of the nonlinear insulin-secretion term, empirically found to be necessary for the compact model to satisfactorily fit clinical observations, captures the pancreatic reserve level of the simulated virtual patients. This result supports the validity of the compact model as a meaningful analysis tool for the clinical assessment of insulin sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Energy acts as a primary prerequisite for plant growth like all the other organisms. Soluble sugars function in providing enough supply of nutrients which further helps in building macromolecules and energy to carry out specific and coordinated development. Sugars functions as nutrient as well as signaling molecule to promote cell division and differentiation in plants. Intriguingly, glucose has emerged as a crucial signaling molecule where hexokinase1 acts as the conserved glucose sensor. On the molecular scale, an extensive crosstalk between glucose and phytohormone signaling has been observed where glucose signals trigger multiple hexokinase1-dependent as well as hexokinase1-independent pathways to mediate diverse developmental, physiological and molecular mechanisms. Taken together, these findings this review focused on the glucose crosstalk with several classical plant hormonal-signaling pathways and the crucial role of hexokinase1 in modulating plant physiological processes. Highlights • Sugars act as a signaling molecule to facilitate plant growth. • Glucose has emerged as one of the crucial signaling molecule for the development of plant. • Glucose interact with phytohormones via hexokinase-dependent and independent pathways. [ABSTRACT FROM AUTHOR]

The Dam1 complex is an essential component of the outer kinetochore that mediates attachments between spindle microtubules and chromosomes. Dam1p, a subunit of the Dam1 complex, binds to microtubules and is regulated by Aurora B/Ipl1p phosphorylation. We find that overexpression of cAMP-dependent protein kinase (PKA) catalytic subunits (i.e., TPK1, TPK2, TPK3) is lethal in DAM1 mutants and increases the rate of chromosome loss in wild-type cells. Replacing an evolutionarily conserved PKA site (S31) in Dam1p with a nonphosphorylatable alanine suppressed the high-copy PKA dosage lethality in dam1-1. Consistent with Dam1p as a target of PKA, we find that in vitro PKA can directly phosphorylate S31 in Dam1p and we observed phosphorylation of S31 in Dam1p purified from asynchronously growing yeast cells. Cells carrying high-copy TPK2 or a Dam1p phospho-mimetic S31D mutant displayed a reduction in Dam1p localization at the kinetochore, suggesting that PKA phosphorylation plays a role in assembly and/or stability of the Dam1 complex. Furthermore, we observed spindle defects associated with S31 phosphorylation. Finally, we find that phosphorylation of Dam1p on S31 is reduced when glucose is limiting as well as during a-factor arrest, conditions that inhibit PKA activity. These observations suggest that the PKA site of Dam1p participates in regulating kinetochore activity. While PKA is a wellestablished effector of glucose signaling, our work shows for the first time that glucose-dependent PKA activity has an important function in chromosome segregation. [ABSTRACT FROM AUTHOR]

We have previously shown that diabetes causes dysfunctional cerebral neovascularization that increases the risk for cerebrovascular disorders such as stroke and cognitive impairment. Pericytes (PCs) play a pivotal role in the angiogenic process through their interaction with the endothelial cells (EC). Yet, the role of PCs in dysfunctional cerebral neovascularization in diabetes is unclear. In the present study, we tested the hypothesis that the increased proangiogenic Ephrin-B2 signaling in PCs contributes to the dysfunctional cerebral neovascularization in diabetes. Type-II diabetes was induced by a combination of high fat diet and low dose streptozotocin injection in male Wistar rats. Selective in vivo Ephrin-B2 silencing in brain PCs was achieved using the stereotactic injection of adeno-associated virus (AAV) with NG2-promoter that expresses Ephrin-B2 shRNA. Neovascularization was assessed using vascular fluorescent dye stain. Novel object recognition (NOR) test was used to determine cognitive functions. Human brain microvascular pericytes HBMVPCs were grown in high glucose 25 mM and palmitate 200 uM (HG/Pal) to mimic diabetic conditions. Scratch migration and tube formation assays were conducted to evaluate PC/EC interaction and angiogenic functions in PC/EC co-culture. Diabetes increased the expression of Ephrin-B2 in the cerebrovasculature and pericytes. Concomitant increases in cerebral neovascularization parameters including vascular density, tortuosity and branching density in diabetic rats were accompanied by deterioration of cognitive function. Inhibition of Ephrin-B2 expression in PCs significantly restored cerebral vascularization and improved cognitive functions. HG/Pal increased PC/EC angiogenic properties in co-culture. Silencing Ephrin-B2 in PCs significantly reduced PC migration and PC/EC co-culture angiogenic properties. This study emphasizes the significant contribution of PCs to the pathological neovascularization in diabetes. Our findings introduce Ephrin-B2 signaling as a promising therapeutic target to improve cerebrovascular integrity in diabetes. [ABSTRACT FROM AUTHOR]

Key features for progression to pancreatic β-cell failure and disease are loss of glucose responsiveness and an increased ratio of secreted proinsulin to insulin. Proinsulin and insulin are stored in secretory granules (SGs) and the fine-tuning of hormone output requires signal-mediated recruitment of select SG populations according to intracellular location and age. The GTPase Rac1 coordinates multiple signaling pathways that specify SG release, and Rac1 activity is controlled in part by GDP/GTP exchange factors (GEFs). To explore the function of two large multidomain GEFs, Kalirin and Trio in β-cells, we manipulated their Rac1-specific GEF1 domain activity by using small-molecule inhibitors and by genetically ablating Kalirin. We examined age-related SG behavior employing radiolabeling protocols. Loss of Kalirin/Trio function attenuated radioactive proinsulin release by reducing constitutive-like secretion and exocytosis of 2-h-old granules. At later chase times or at steady state, Kalirin/Trio manipulations decreased glucosestimulated insulin output. Finally, use of a Rac1 FRET biosensor with cultured β-cell lines demonstrated that Kalirin/Trio GEF1 activity was required for normal rearrangement of Rac1 to the plasma membrane in response to glucose. Rac1 activa tion can be evoked by both glucose metabolism and signaling through the incretin glucagon-like peptide 1 (GLP-1) receptor. GLP-1 addition restored Rac1 localization/activity and insulin secretion in the absence of Kalirin, thereby assigning Kalirin's participation to stimulatory glucose signaling. [ABSTRACT FROM AUTHOR]

Macrophages are one of the major cell types that produce IL-1β. IL-1β maturation occurs via inflammasome activation, and mature IL-1β is then released from the cell. Secreted IL-1β mediates inflammatory reactions in various pathological environments, such as those in infectious, autoimmune, and cancerous diseases. Although the mechanism of IL-1β production has been discovered in infectious and autoimmune diseases, its production mechanism in the tumor microenvironment is unclear. Therefore, the mechanism of IL-1β production in macrophages in the tumor microenvironment was investigated in this study. First, bone marrow-derived macrophages obtained from C57BL/6 mice were treated with B16F10 tumor-conditioned media (TCM) in vitro. TCM increased the levels of IL-1β via glucose-mediated activation of the inflammasome. Moreover, TCM enhanced the activation of both NF-κB and mTOR pathways in a glucose-dependent manner. In particular, the expression levels of mTORC1 component proteins were dependent on the TCM-induced activation of NF-κB signaling. In addition, TCM affected ASC-ASC interactions through increasing intracellular reactive oxygen species levels. Finally, glucose inhibition by inoculation with 2-deoxy-D-glucose in vivo decreased the IL-1β levels in both the blood and tumor region of B16F10-bearing C57BL/6 mice relative to those in PBS-injected tumor-bearing mice. These results suggest that glucose supplied from blood vessels might be important for IL-1β production in tumor-associated macrophages via the integrated signals of the NF-κB and mTOR pathways in the tumor microenvironment. [ABSTRACT FROM AUTHOR]

Hexokinases is a family of proteins that is found in all eukaryotes. Hexokinases play key roles in the primary carbon metabolism, where they catalyze the phosphorylation of glucose and fructose, but they have also been shown to be involved in glucose signaling in both yeast and plants. We have characterized the Klebsormidium nitens KnHXK1 gene, the only hexokinase-encoding gene in this charophyte alga. The encoded protein, KnHXK1, is a type B plant hexokinase with an N-terminal membrane anchor localizing the protein to the mitochondrial membranes. We found that KnHXK1 expressed in Arabidopsis thaliana can restore the glucose sensing and glucose repression defects of the glucose-insensitive hexokinase mutant gin2-1. Interestingly, both functions require a catalytically active enzyme, since an inactive double mutant was unable to complement gin2-1. These findings differ from previous results on Arabidopsis AtHXK1 and its orthologs in rice, where catalytic and glucose sensing functions could be separated, but are consistent with recent results on the rice cytoplasmic hexokinase OsHXK7. A model with both catalytic and non-catalytic roles for hexokinases in glucose sensing and glucose repression is discussed. [ABSTRACT FROM AUTHOR]

Background: Type 2 diabetes is often linked with impaired proximal insulin signaling. Hence, a therapeutic agent that enhances cellular glucose uptake without requiring proximal insulin signaling would be desirable for improving glycemic control. The E4orf1 peptide (E4) derived from human adenovirus 36 (Ad36) promotes cellular glucose uptake in vitro and in vivo, independent of insulin. E4 bypasses a part of insulin signaling to upregulate cellular glucose uptake. We tested the hypothesis that E4 requires the distal but not proximal insulin signaling to enhance cellular glucose disposal. Methods: 3T3-L1 preadipocytes inducibly expressing E4 or a null vector (NV) were treated with inhibitor of insulin receptor (S961), inhibitor of insulin like growth factor-1receptor (IGF-1R) (Picropodophyllin, PPP), PPP+S961, or phosphatidyl inositol-3 kinase (PI3K) inhibitor (Wortmannin, WM). We used PPP and S961 to block the proximal insulin signaling, or WM to block the distal insulin signaling. Cells were exposed to 0 or 100nM insulin. Results: As expected, when the proximal or distal insulin signaling was blocked in NV cells, insulin could not enhance pAKT protein abundance, Glut4 translocation, or glucose uptake. Whereas, E4 cells significantly increased pAKT abundance, Glut4 translocation and glucose uptake independent of the presence of insulin or proximal insulin signaling. Enhanced glucose disposal in E4 cells was completely abrogated when the distal insulin signaling was blocked. Conclusions: E4 bypasses the proximal insulin signaling but uses the distal insulin signaling to activate pAkt and in turn Glut4 translocation to improve cellular glucose uptake. E4 offers a promising template to improve glycemic control when the proximal insulin signaling is impaired. [ABSTRACT FROM AUTHOR]

Key message: Trithorax-group Protein ARABIDOPSIS TRITHORAX5 modulates the glucose response.Abstract: Glucose is an evolutionarily conserved modulator from unicellular microorganisms to multicellular animals and plants. Extensive studies have shown that the Trithorax-group proteins (TrxGs) play essential roles in different biological processes by affecting histone modifications and chromatin structures. However, whether TrxGs function in the glucose response and how they achieve the control of target genes in response to glucose signaling in plants remain unknown. Here, we show that the Trithorax-group Protein ARABIDOPSIS TRITHORAX5 (ATX5) affects the glucose response and signaling. atx5 loss-of-function mutants display glucose-oversensitive phenotypes compared to the wild-type (WT). Genome-wide RNA-sequencing analyses have revealed that ATX5 impacts the expression of a subset of glucose signaling responsive genes. Intriguingly, we have established that ATX5 directly controls the expression of HY1 by trimethylating H3 lysine 4 of the Arabidopsis Heme Oxygenase1 (HY1) locus. Glucose signaling causes the suppression of ATX5 activity and subsequently reduces the H3K4me3 levels at the HY1 locus, thereby leading to the increased expression of ABSCISIC ACID-INSENSITIVE4 (ABI4). This result suggests that an important ATX5-HY1-ABI4 regulatory module governs the glucose response. This idea is further supported by genetic evidence showing that an atx5 hy1-100 abi4 triple mutant showed a similar glucose-insensitive phenotype as compared to that of the abi4 single mutant. Our findings show that a novel ATX5-HY1-ABI4 module controls the glucose response in Arabidopsis thaliana. [ABSTRACT FROM AUTHOR]

Target of Rapamycin Complex 1 (TORC1) is a conserved eukaryotic protein complex that links the presence of nutrients with cell growth. In Saccharomyces cerevisiae , TORC1 activity is positively regulated by the presence of amino acids and glucose in the medium. However, the mechanisms underlying nutrient-induced TORC1 activation remain poorly understood. By utilizing an in vivo TORC1 activation assay, we demonstrate that differential metabolism of glucose activates TORC1 through three distinct pathways in yeast. The first "canonical Rag guanosine triphosphatase (GTPase)-dependent pathway" requires conversion of glucose to fructose 1,6-bisphosphate, which activates TORC1 via the Rag GTPase heterodimer Gtr1GTP-Gtr2GDP. The second "non-canonical Rag GTPase-dependent pathway" requires conversion of glucose to glucose 6-phosphate, which activates TORC1 via a process that involves Gtr1GTP-Gtr2GTP and mitochondrial function. The third "Rag GTPase-independent pathway" requires complete glycolysis and vacuolar ATPase reassembly for TORC1 activation. We have established a roadmap to deconstruct the link between glucose metabolism and TORC1 activation. [Display omitted] • Glucose metabolism activates TORC1 in S. cerevisiae via at least three distinct pathways • Phosphorylation of glucose to G6P activates TORC1 through Gtr1GTP-Gtr2GTP • Conversion of glucose to FBP activates TORC1 through Gtr1GTP-Gtr2GDP • Complete glycolysis activates TORC1 independent of Rag GTPases (Gtr1/Gtr2) Alfatah et al. interrogate the relationship between glucose metabolism and TORC1 activation in Saccharomyces cerevisiae. They identify three distinct pathways for glucose-induced TORC1 activation, with each pathway requiring a different extent of glucose metabolism via the glycolytic pathway. [ABSTRACT FROM AUTHOR]

Plants lack 7-transmembrane, G-protein coupled receptors (GPCRs) because the G alpha subunit of the heterotrimeric G protein complex is “self-activating”—meaning that it spontaneously exchanges bound GDP for GTP without the need of a GPCR. In lieu of GPCRs, most plants have a seven transmembrane receptor-like regulator of G-protein signaling (RGS) protein, a component of the complex that keeps G-protein signaling in its non-activated state. The addition of glucose physically uncouples AtRGS1 from the complex through specific endocytosis leaving the activated G protein at the plasma membrane. The complement of proteins in the AtRGS1/G-protein complex over time from glucose-induced endocytosis was profiled by immunoprecipitation coupled to mass spectrometry (IP-MS). A total of 119 proteins in the AtRGS1 complex were identified. Several known interactors of the complex were identified, thus validating the approach, but the vast majority (93/119) were not known previously. AtRGS1 protein interactions were dynamically modulated by d-glucose. At low glucose levels, the AtRGS1 complex is comprised of proteins involved in transport, stress and metabolism. After glucose application, the AtRGS1 complex rapidly sheds many of these proteins and recruits other proteins involved in vesicular trafficking and signal transduction. The profile of the AtRGS1 components answers several questions about the type of coat protein and vesicular trafficking GTPases used in AtRGS1 endocytosis and the function of endocytic AtRGS1.

Aspergillus niger is the main industrial workhorse for global citric acid production. This fungus has complex sensing and signaling pathways to respond to environmental nutrient fluctuations. As the preferred primary carbon source, glucose also acts as a critical signal to trigger intracellular bioprocesses. Currently, however, there is still a knowledge gap in systems-level understanding of metabolic and cellular responses to this vital carbon source. In this study, we determined genome-wide transcriptional changes of citric acid-producing Aspergillus niger in response to external glucose gradient. It demonstrated that external glucose fluctuation led to transcriptional reprogramming of many genes encoding proteins involved in fundamental cellular process, including ribosomal biogenesis, carbon transport and catabolism, glucose sensing and signaling. The major glucose catabolism repressor creA maintained a stable expression independent of external glucose, while creB and creD showed significant downregulation and upregulation by the glucose increase. Notably, several high-affinity glucose transporters encoding genes, including mstA , were greatly upregulated when glucose was depleted, while the expression of low-affinity glucose transporter mstC was glucose-independent, which showed clear concordance with their protein levels detected by in situ fluorescence labeling assay. In addition, we also observed that the citric acid exporter cexA was observed to be transcriptionally regulated by glucose availability, which was correlated with extracellular citric acid secretion. These discoveries not only deepen our understanding of the transcriptional regulation of glucose but also shed new light on the adaptive evolutionary mechanism of citric acid production of A. niger ., Competing Interests: Author WZ was employed by Shan Dong Fuyang Biological Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Zheng, Du, Gao, Du, Cairns, Ni, Chen, Zhao, Ma, Yang, Zheng and Sun.)

α-Flavone glycosides have beneficial properties for applications in the pharmaceutical, cosmetic, and food industries. However, their chemical syntheses are often limited by a low efficiency or scarcity of substrates. In this study, α-flavone glucosides were enzymatically synthesized by amylosucrase from Deinococcus geothermalis (DGAS) using sucrose and various flavones as a donor for glucosyl units and acceptors, respectively. Luteolin was the most effective acceptor in the transglucosylation reaction using DGAS among nine flavone materials (apigenin, chrysin, 6,7-dihydroxyflavone, homoorientin, 7-hydroxyflavone, isorhoifolin, luteolin, luteolin-3′,7-diglucoside, and orientin). The highest production yield of luteolin glucoside was 86%, with a 7:1 molar ratio of donor to acceptor molecules, in 50 mM Tris-HCl buffer (pH 7) at 37°C for 24 h using 2 U of DGAS. The synthesized luteolin glucoside was identified as luteolin-4′-O-α-D-glucopyranoside with a glucose molecule linked to the C-4′ position on the B-ring of luteolin via an α-glucosidic bond, as determined by 1H and 13C nuclear magnetic resonance. This result clearly confirmed that the glucosylated luteolin was successfully synthesized by DGAS and it can be applied as a functional ingredient. Furthermore, this approach using DGAS has the potential to be utilized for the synthesis of various glucosylated products using different types of polyphenols to enhance their functionalities. [ABSTRACT FROM AUTHOR]

This study examined the effect of changes in body temperature during exercise on signal transduction-related glucose uptake in the skeletal muscle of type 2 diabetic rats. Otsuka Long-Evans Tokushima Fatty rats (25 weeks of age), which have type 2 diabetes, were divided into the following four weight-matched groups; control (CON, n = 6), exercised under warm temperature (WEx, n = 8), exercised under cold temperature (CEx, n = 8), and heat treatment (HT, n = 6). WEx and CEx animals were subjected to running on a treadmill at 20 m/min for 30 min under warm (25°C) or cold (4°C) temperature. HT animals were exposed to single heat treatment (40–41°C for 30 min) in a heat chamber. Rectal and muscle temperatures were measured immediately after exercise and heat treatment, and the gastrocnemius muscle was sampled under anesthesia. Rectal and muscle temperatures increased significantly in rats in the WEx and HT, but not the CEx, groups. The phosphorylation levels of Akt, AS160, and TBC1D1 (Thr590) were significantly higher in the WEx and HT groups than the CON group (p < 0.05). In contrast, the phosphorylation levels of AMP-activated protein kinase, ACC, and TBC1D1 (Ser660) were significantly higher in rats in the WEx and CEx groups than the CON group (p < 0.05) but did not differ significantly between rats in the WEx and CEx groups. Body temperature elevation by heat treatment did not activate the AMPK signaling. Our data suggest that body temperature elevation during exercise is essential for activating the Akt signaling pathway in the skeletal muscle of rats with type 2 diabetic rats. [ABSTRACT FROM AUTHOR]

Background: In diabetes research, the development of the artificial pancreas has been a major topic since continuous glucose monitoring became available in the early 2000’s. A prerequisite for an artificial pancreas is fast and reliable glucose sensing. However, subcutaneous continuous glucose monitoring carries the disadvantage of slow dynamics. As an alternative, we explored continuous glucose sensing in the peritoneal space, and investigated potential spatial differences in glucose dynamics within the peritoneal cavity. As a secondary outcome, we compared the glucose dynamics in the peritoneal space to the subcutaneous tissue. Material and methods: Eight-hour experiments were conducted on 12 anesthetised non-diabetic pigs. Four commercially available amperometric glucose sensors (FreeStyle Libre, Abbott Diabetes Care Ltd., Witney, UK) were inserted in four different locations of the peritoneal cavity and two sensors were inserted in the subcutaneous tissue. Meals were simulated by intravenous infusions of glucose, and frequent arterial blood and intraperitoneal fluid samples were collected for glucose reference. Results: No significant differences were discovered in glucose dynamics between the four quadrants of the peritoneal cavity. The intraperitoneal sensors responded faster to the glucose excursions than the subcutaneous sensors, and the time delay was significantly smaller for the intraperitoneal sensors, but we did not find significant results when comparing the other dynamic parameters. [ABSTRACT FROM AUTHOR]

Resveratrol, a non-flavonoid polyphenolic compound, is structurally and functionally similar to estrogen and has drawn great attention for its potentially beneficial effects on diabetes. However, it is not known whether it shares the same protective effect against diabetes as estrogen and the underlying mechanisms. The aim of the present study was to investigate the protective effects of phytoestrogen resveratrol and exogenous 17β-estradiol against streptozotocin (STZ)-induced type 1 diabetes. Female mice were ovariectomized (OVX) and chronically injected with different concentrations of resveratrol (0.1, 1 or 10 mg/kg) and 17β-estradiol (0.01, 0.1 or 1 mg/kg) subcutaneously for 4 weeks, and the levels of blood glucose, plasma insulin, plasma antioxidant capacity, the changes of pancreatic islet cells and the expressions of glucose transporter 4 (GLUT4), insulin receptor substrate 1 (IRS-1) and phosphorylation of extracellular signal-regulated kinase (p-ERK) were detected. Resveratrol and 17β-estradiol significantly inhibited the increase of the blood glucose level and the rise of plasma malondialdehyde in STZ-induced diabetic mice, improved the levels of plasma antioxidant capacity and plasma insulin, protected the pancreatic islet cells, and increased the expressions of GLUT4 and IRS-1, but decreased p-ERK expression in skeletal muscle and myocardial tissue. The results suggest that resveratrol or 17β-estradiol shows obvious protection against STZ-induced diabetes in OVX mice, the mechanisms probably involve their ameliorating antioxidant activities and islet function, promoting muscle glucose uptake and inhibiting the expression of p-ERK. [ABSTRACT FROM AUTHOR]

The yeast S. cerevisiae senses glucose through Snf3 and Rgt2, transmembrane proteins that generate an intracellular signal in response to glucose that leads to inhibition of the Rgt1 transcriptional repressor and consequently to derepression of HXT genes encoding glucose transporters. Snf3 and Rgt2 are thought to be glucose receptors because they are similar to glucose transporters. In contrast to glucose transporters, they have unusually long C-terminal tails that bind to Mth1 and Std1, paralogous proteins that regulate function of the Rgt1 transcription factor. We show that the C-terminal tail of Rgt2 is not responsible for its inability to transport glucose. To gain insight into how the glucose sensors generate an intracellular signal, we identified RGT2 mutations that cause constitutive signal generation. Most of the mutations alter evolutionarily-conserved amino acids in the transmembrane spanning regions of Rgt2 that are predicted to be involved in maintaining an outward-facing conformation or to be in the substrate binding site. Our analysis of these mutations suggests they cause Rgt2 to adopt inward-facing or occluded conformations that generate the glucose signal. These results support the idea that Rgt2 and Snf3 are glucose receptors that signal in response to binding of extracellular glucose and inform the basis of their signaling. [ABSTRACT FROM AUTHOR]

Bile acids are critical contributors to the regulation of whole body glucose homeostasis; however, the mechanisms remain incompletely defined. While the hydrophilic bile acid subtype, ursodeoxycholic acid, has been shown to attenuate hepatic endoplasmic reticulum (ER) stress and thereby improve glucose regulation in mice, the effect of hydrophobic bile acid subtypes on ER stress and glucose regulation in vivo is unknown. Therefore, we investigated the effect of the hydrophobic bile acid subtype, deoxycholic acid (DCA), on ER stress and glucose regulation. Eight week old C57BL/6J mice were fed a high fat diet supplemented with or without DCA. Glucose regulation was assessed by oral glucose tolerance and insulin tolerance testing. In addition, circulating bile acid profile and hepatic insulin and ER stress signaling were measured. DCA supplementation did not alter body weight or food intake, but did impair glucose regulation. Consistent with the impairment in glucose regulation, DCA increased the hydrophobicity of the circulating bile acid profile, decreased hepatic insulin signaling and increased hepatic ER stress signaling. Together, these data suggest that dietary supplementation of DCA impairs whole body glucose regulation by disrupting hepatic ER homeostasis in mice. [ABSTRACT FROM AUTHOR]

Polysaccharides derived from mushrooms have potential to control blood sugar, reduce insulin resistance and prevent diabetic complications. The intracellular polysaccharopeptides of Trametes versicolor (TV) have been used as immunologic and oncologic adjuvants. The aim of this study was to investigate the potential activities and mechanisms of extracellular polysaccharopeptides (ePSP) obtained from TV strain LH-1 on regulating glucose homeostasis. Human hepatoma HepG2 cells incubated with normal glucose (5.5 mM, NG model), high glucose (33 mM, HG model), or high glucose (33 mM) plus high insulin (10−7 M, HGI model) concentrations were administered with TV LH-1 ePSP (50, 100, and 1000 μg/ml) for 24 hr. Glucose uptake of HepG2 cells, determined by flow cytometry, was significantly decreased in the HG and HGI models with insulin stimulation, suggesting insulin resistance of these cells; however, ePSP reversed this decrease in a dose-dependent manner (one-way ANOVA, p<0.05). In the HG and HGI models, ePSP significantly increased glycogen content, insulin receptor substrate-2 protein and phosphorylated AMP-activated protein kinase (AMPK), as determined by western blot analysis. In addition, ePSP significantly increased glucokinase in the NG and HG models, increased membrane glucose transporter-1 and decreased glycogen synthase kinase-3β in the HGI model, and increased glucose-6-phosphatase in the NG and HGI models (one-way ANOVA, p<0.05). In summary, TV LH-1 ePSP may elevate cellular glucose uptake to regulate glucose homeostasis via the activation of AMPK and glycogen synthesis in an insulin-independent manner. These results suggest that TV LH-1 ePSP may be a nutraceutical with anti-hyperglycemic activity. [ABSTRACT FROM AUTHOR]

High-glycemic-index diets, as well as a sedentary lifestyle are considered as determinant factors for the development of obesity, type 2 diabetes, and cardiovascular diseases in humans. These diets have been shown to shorten the life span of C. elegans in a manner that is dependent on insulin signaling, but the participation of other signaling pathways have not been addressed. In this study, we have determined that worms fed with high-glucose diets show alterations in glucose content and uptake, triglyceride content, body size, number of eggs laid, egg-laying defects, and signs of oxidative stress and accelerated aging. Additionally, we analyzed the participation of different key regulators of carbohydrate and lipid metabolism, oxidative stress and longevity such as SKN-1/NRF2, HIF-1/HIF1α, SBP-1/SREBP, CRH-1/CREB, CEP-1/p53, and DAF-16/FOXO, in the reduction of lifespan in glucose-fed worms. [ABSTRACT FROM AUTHOR]

One of the most ambitious endeavors in the field of diabetes technology is non-invasive glucose sensing. In the past decades, a number of different technologies have been assessed, but none of these have found its entry into general clinical use. We report on the development of a table-top confocal Raman spectrometer that was used in the home of patients with diabetes and operated for extended periods of time unsupervised and without recalibration. The system is based on measurement of glucose levels at a ‘critical depth’ in the skin, specifically in the interstitial fluid located below the stratum corneum but above the underlying adipose tissue layer. The region chosen for routine glucose measurements was the base of the thumb (the thenar). In a small clinical study, 35 patients with diabetes analyzed their interstitial fluid glucose for a period of 60 days using the new critical-depth Raman (CD-Raman) method and levels were correlated to reference capillary blood glucose values using a standard finger-stick and test strip product. The calibration of the CD-Raman system was stable for > 10 days. Measurement performance for glucose levels present at, or below, a depth of ~250μm below the skin surface was comparable to that reported for currently available invasive continuous glucose monitors. In summary, using the CD-Raman technology we have demonstrated the first successful use of a non-invasive glucose monitor in the home. [ABSTRACT FROM AUTHOR]

To identify genetic contributions to type 2 diabetes (T2D) and related glycemic traits (fasting glucose, fasting insulin, and HbA1c), we conducted genome-wide association analyses (GWAS) in up to 7,178 Chinese subjects from nine provinces in the China Health and Nutrition Survey (CHNS). We examined patterns of population structure within CHNS and found that allele frequencies differed across provinces, consistent with genetic drift and population substructure. We further validated 32 previously described T2D- and glycemic trait-loci, including G6PC2 and SIX3-SIX2 associated with fasting glucose. At G6PC2, we replicated a known fasting glucose-associated variant (rs34177044) and identified a second signal (rs2232326), a low-frequency (4%), probably damaging missense variant (S324P). A variant within the lead fasting glucose-associated signal at SIX3-SIX2 co-localized with pancreatic islet expression quantitative trait loci (eQTL) for SIX3, SIX2, and three noncoding transcripts. To identify variants functionally responsible for the fasting glucose association at SIX3-SIX2, we tested five candidate variants for allelic differences in regulatory function. The rs12712928-C allele, associated with higher fasting glucose and lower transcript expression level, showed lower transcriptional activity in reporter assays and increased binding to GABP compared to the rs12712928-G, suggesting that rs12712928-C contributes to elevated fasting glucose levels by disrupting an islet enhancer, resulting in reduced gene expression. Taken together, these analyses identified multiple loci associated with glycemic traits across China, and suggest a regulatory mechanism at the SIX3-SIX2 fasting glucose GWAS locus. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is associated with sensory abnormalities, including exacerbated responses to painful (hyperalgesia) or non-painful (allodynia) stimuli. These abnormalities are symptoms of diabetic peripheral neuropathy (DPN), which is the most common complication that affects approximately 50% of diabetic patients. Yet, the underlying mechanisms linking hyperglycemia and symptoms of DPN remain poorly understood. The transient receptor potential vanilloid 1 (TRPV1) channel plays a central role in such sensory abnormalities and shows elevated expression levels in animal models of diabetes. Here, we investigated the function of TRPV1 channels in sensory neurons cultured from the dorsal root ganglion (DRG) of neonatal mice, under control (5mM) and high glucose (25mM) conditions. After maintaining DRG neurons in high glucose for 1 week, we observed a significant increase in capsaicin (CAP)-evoked currents and CAP-evoked depolarizations, independent of TRPV1 channel expression. These functional changes were largely dependent on the expression of the receptor for Advanced Glycation End-products (RAGE), calcium influx, cytoplasmic ROS accumulation, PKC, and Src kinase activity. Like cultured neurons from neonates, mature neurons from adult mice also displayed a similar potentiation of CAP-evoked currents in the high glucose condition. Taken together, our data demonstrate that under the diabetic condition, DRG neurons are directly affected by elevated levels of glucose, independent of vascular or glial signals, and dependent on RAGE expression. These early cellular and molecular changes to sensory neurons in vitro are potential mechanisms that might contribute to sensory abnormalities that can occur in the very early stages of diabetes. [ABSTRACT FROM AUTHOR]

We previously demonstrated that infusion of an intestinal peptide called xenin-25 (Xen) amplifies the effects of glucose-dependent insulinotropic polypeptide (GIP) on insulin secretion rates (ISRs) and plasma glucagon levels in humans. However, these effects of Xen, but not GIP, were blunted in humans with type 2 diabetes. Thus, Xen rather than GIP signaling to islets fails early during development of type 2 diabetes. The current crossover study determines if cholinergic signaling relays the effects of Xen on insulin and glucagon release in humans as in mice. Fasted subjects with impaired glucose tolerance were studied. On eight separate occasions, each person underwent a single graded glucose infusion- two each with infusion of albumin, Xen, GIP, and GIP plus Xen. Each infusate was administered ± atropine. Heart rate and plasma glucose, insulin, C-peptide, glucagon, and pancreatic polypeptide (PP) levels were measured. ISRs were calculated from C-peptide levels. All peptides profoundly increased PP responses. From 0 to 40 min, peptide(s) infusions had little effect on plasma glucose concentrations. However, GIP, but not Xen, rapidly and transiently increased ISRs and glucagon levels. Both responses were further amplified when Xen was co-administered with GIP. From 40 to 240 min, glucose levels and ISRs continually increased while glucagon concentrations declined, regardless of infusate. Atropine increased resting heart rate and blocked all PP responses but did not affect ISRs or plasma glucagon levels during any of the peptide infusions. Thus, cholinergic signaling mediates the effects of Xen on insulin and glucagon release in mice but not humans. [ABSTRACT FROM AUTHOR]

Autophagy is systematically regulated by upstream factors and nutrients. Recent studies reported that telomerase and hexokinase 2 [HK2) regulate autophagy through mTOR and that telomerase has the capacity to bind to the HK2 promoter. However, the molecular linkage among telomerase, HK2, and autophagy is not fully understood. Here, we show that HK2 connects telomerase to autophagy. HK2 inhibition in HepG2 cells suppressed TERT-induced autophagy activation and further enhancement by glucose deprivation. The HK2 downstream factor mTOR was responsible for the TERT-induced autophagy activation under glucose deprivation, implying that TERT promotes autophagy through an HK2-mTOR pathway. TERC played a role similar to that of TERT, and simultaneous expression of TERT and TERC synergistically enhanced HK2 expression and autophagy. At the gene level, TERT bound to the HK2 promoter at a specific region harboring the telomerase-responsive sequence ‘.’ Mutagenesis of TERC and the TERT-responsive element in the HK2 promoter revealed that TERC is required for the binding of TERT to the HK2 promoter. We demonstrate the existence of a telomerase-HK2-mTOR-autophagy axis and suggest that inhibition of the interaction between telomerase and the HK2 promoter diminishes glucose starvation-induced autophagy. [ABSTRACT FROM AUTHOR]

Background: The pathophysiologic processes underlying the regulation of glucose homeostasis are considerably complex at both cellular and systemic level. A comprehensive and structured specification for the several layers of abstraction of glucose metabolism is often elusive, an issue currently solvable with the hierarchical description provided by multi-level models. In this study we propose a multi-level closed-loop model of whole-body glucose homeostasis, coupled with the molecular specifications of the insulin signaling cascade in adipocytes, under the experimental conditions of normal glucose regulation and type 2 diabetes. Methodology/Principal findings: The ordinary differential equations of the model, describing the dynamics of glucose and key regulatory hormones and their reciprocal interactions among gut, liver, muscle and adipose tissue, were designed for being embedded in a modular, hierarchical structure. The closed-loop model structure allowed self-sustained simulations to represent an ideal in silico subject that adjusts its own metabolism to the fasting and feeding states, depending on the hormonal context and invariant to circadian fluctuations. The cellular level of the model provided a seamless dynamic description of the molecular mechanisms downstream the insulin receptor in the adipocytes by accounting for variations in the surrounding metabolic context. Conclusions/Significance: The combination of a multi-level and closed-loop modeling approach provided a fair dynamic description of the core determinants of glucose homeostasis at both cellular and systemic scales. This model architecture is intrinsically open to incorporate supplementary layers of specifications describing further individual components influencing glucose metabolism. [ABSTRACT FROM AUTHOR]

Zinc is a metal ion that is an essential cell signaling molecule. Highlighting this, zinc is an insulin mimetic, activating cellular pathways that regulate cellular homeostasis and physiological responses. Previous studies have linked dysfunctional zinc signaling with several disease states including cancer, obesity, cardiovascular disease and type 2 diabetes. The present study evaluated the insulin-like effects of zinc on cell signaling molecules including tyrosine, PRSA40, Akt, ERK1/2, SHP-2, GSK-3β and p38, and glucose oxidation in human and mouse skeletal muscle cells. Insulin and zinc independently led to the phosphorylation of these proteins over a 60-minute time course in both mouse and human skeletal muscle cells. Similarly, utilizing a protein array we identified that zinc could active the phosphorylation of p38, ERK1/2 and GSK-3B in human and ERK1/2 and GSK-3B in mouse skeletal muscle cells. Glucose oxidation assays were performed on skeletal muscle cells treated with insulin, zinc, or a combination of both and resulted in a significant induction of glucose consumption in mouse (p<0.01) and human (p<0.05) skeletal muscle cells when treated with zinc alone. Insulin, as expected, increased glucose oxidation in mouse (p<0.001) and human (0.001) skeletal muscle cells, however the combination of zinc and insulin did not augment glucose consumption in these cells. Zinc acts as an insulin mimetic, activating key molecules implicated in cell signaling to maintain glucose homeostasis in mouse and human skeletal muscle cells. Zinc is an important metal ion implicated in several biological processes. The role of zinc as an insulin memetic in activating key signaling molecules involved in glucose homeostasis could provide opportunities to utilize this ion therapeutically in treating disorders associated with dysfunctional zinc signaling. [ABSTRACT FROM AUTHOR]

Müller cells are key to metabolic and ionic regulation in the retina. They also produce a number of inflammatory mediators and are significantly affected in diabetic retinopathy. To investigate the role of toll-like receptor 4 (TLR4) in retinal Müller cells, we crossed TLR4 floxed with PDGFRα-Cre mice to eliminate TLR4 in retinal Müller cells. We performed Western blotting and ELISA analyses to determine whether loss of TLR4 affected myeloid differentiation primary response protein (MyD88)-dependent or –independent signaling, leading to reduced levels of tumor necrosis factor alpha (TNFα) and interleukin 1 beta (IL1β) in whole retinal lysates from the TLR4 floxed and TLR4-PDGFRα-Cre mice. Data show that TLR4-PDGFRα-Cre mice have reduced levels of both the MyD88-dependent and -independent signaling pathways. These studies confirm successful development of a Müller cell-specific TLR4 knockout mouse colony. These mice have reduced MyD88-dependent and –independent signaling pathway proteins, as well as reduced TNFα and IL1β levels. These mice can be used to dissect TLR4 signaling in disorders affecting retinal Müller cells. [ABSTRACT FROM AUTHOR]

In animal cells, activation of heterotrimeric G protein signaling generally occurs when the system’s cognate signal exceeds a threshold, whereas in plant cells, both the amount and the exposure time of at least one signal, D-glucose, are used toward activation. This unusual signaling property called Dose-Duration Reciprocity, first elucidated in the genetic model Arabidopsis thaliana, is achieved by a complex that is comprised of a 7-transmembrane REGULATOR OF G SIGNALING (RGS) protein (AtRGS1), a Gα subunit that binds and hydrolyzes nucleotide, a Gβγ dimer, and three WITH NO LYSINE (WNK) kinases. D-glucose is one of several signals such as salt and pathogen-derived molecular patterns that operates through this protein complex to activate G protein signaling by WNK kinase transphosphorylation of AtRGS1. Because WNK kinases compete for the same substrate, AtRGS1, we hypothesize that activation is sensitive to the AtRGS1 amount and that modulation of the AtRGS1 pool affects the response to the stimulant. Mathematical simulation revealed that the ratio of AtRGS1 to the kinase affects system sensitivity to D-glucose, and therefore illustrates how modulation of the cellular AtRGS1 level is a means to change signal-induced activation. AtRGS1 levels change under tested conditions that mimic physiological conditions therefore, we propose a previously-unknown mechanism by which plants react to changes in their environment. [ABSTRACT FROM AUTHOR]

Survival of cancer cells in the harsh tumor microenvironment, characterized by oxygen and glucose deprivation, requires rapid initiation of cytoprotective measures. Metabolites whose levels change during stress are ideal signaling cues, particularly if used in post-translational modifications of stress-responsive signal transducers. In cancer cells exposed to oxygen or glucose deprivation, there is an increase in cellular levels of acetate, a substrate for acetate-dependent acetyl CoA synthetase 2 (Acss2) that also stimulates translocation of Acss2 from the cytosol to the nucleus. Nuclear, but not cytosolic, Acss2 promotes acetylation of the stress-responsive Hypoxia Inducible Factor 2α (HIF-2α) subunit by the acetyltransferase/coactivator Creb binding protein (Cbp), a process that facilitates stable Cbp/HIF-2α complex formation. In addition to promoting de novo transcription, Cbp and HIF-2α act in concert to regulate local histone 3 epigenetic marks. Exogenous acetate augments Acss2/HIF-2 dependent cancer growth and metastasis in cell culture and mouse models. Thus, an acetate switch in mammals links nutrient intake and stress signaling with tumor growth and metastasis. [ABSTRACT FROM AUTHOR]