Diabetes is a global health problem caused primarily by the inability of pancreatic β-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of ...β-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic βV59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 β-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in β-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of β-cells in diabetes.
Abstract Stimulation of mitochondrial oxidative metabolism by Ca2+ is now generally recognised as important for the control of cellular ATP homeostasis. Here, we review the mechanisms through which ...Ca2+ regulates mitochondrial ATP synthesis. We focus on cardiac myocytes and pancreatic β-cells, where tight control of this process is likely to play an important role in the response to rapid changes in workload and to nutrient stimulation, respectively. We also describe a novel approach for imaging the Ca2+ -dependent regulation of ATP levels dynamically in single cells.
Strategies aimed at mimicking or enhancing the action of the incretin hormone glucagon-like peptide 1 (GLP-1) therapeutically improve glucose-stimulated insulin secretion (GSIS); however, it is not ...clear whether GLP-1 directly drives insulin secretion in pancreatic islets. Here, we examined the mechanisms by which GLP-1 stimulates insulin secretion in mouse and human islets. We found that GLP-1 enhances GSIS at a half-maximal effective concentration of 0.4 pM. Moreover, we determined that GLP-1 activates PLC, which increases submembrane diacylglycerol and thereby activates PKC, resulting in membrane depolarization and increased action potential firing and subsequent stimulation of insulin secretion. The depolarizing effect of GLP-1 on electrical activity was mimicked by the PKC activator PMA, occurred without activation of PKA, and persisted in the presence of PKA inhibitors, the KATP channel blocker tolbutamide, and the L-type Ca(2+) channel blocker isradipine; however, depolarization was abolished by lowering extracellular Na(+). The PKC-dependent effect of GLP-1 on membrane potential and electrical activity was mediated by activation of Na(+)-permeable TRPM4 and TRPM5 channels by mobilization of intracellular Ca(2+) from thapsigargin-sensitive Ca(2+) stores. Concordantly, GLP-1 effects were negligible in Trpm4 or Trpm5 KO islets. These data provide important insight into the therapeutic action of GLP-1 and suggest that circulating levels of this hormone directly stimulate insulin secretion by β cells.
Chronic hyperglycaemia causes a dramatic decrease in mitochondrial metabolism and insulin content in pancreatic β-cells. This underlies the progressive decline in β-cell function in diabetes. ...However, the molecular mechanisms by which hyperglycaemia produces these effects remain unresolved. Using isolated islets and INS-1 cells, we show here that one or more glycolytic metabolites downstream of phosphofructokinase and upstream of GAPDH mediates the effects of chronic hyperglycemia. This metabolite stimulates marked upregulation of mTORC1 and concomitant downregulation of AMPK. Increased mTORC1 activity causes inhibition of pyruvate dehydrogenase which reduces pyruvate entry into the tricarboxylic acid cycle and partially accounts for the hyperglycaemia-induced reduction in oxidative phosphorylation and insulin secretion. In addition, hyperglycaemia (or diabetes) dramatically inhibits GAPDH activity, thereby impairing glucose metabolism. Our data also reveal that restricting glucose metabolism during hyperglycaemia prevents these changes and thus may be of therapeutic benefit. In summary, we have identified a pathway by which chronic hyperglycaemia reduces β-cell function.
The article deals with the design of specialized VLSI designed for the construction of high-performance computing systems. Common options for building such systems are general-purpose processors ...(CPUs), graphics accelerators (GPUs) that work in the mode of general-purpose computing acceleration, and FPGAs that are configured to implement a specific task or a narrow class of tasks. If there is a demanded class of tasks with specific requirements for computing resources, it is possible to develop a specialized VLSI that is more effective than CPU and GPU in terms of the use of crystal resources, and more productive than FPGA due to the use of hardware-implemented connections instead of programmable cells and switched trace lines. Taking into account modern trends in microelectronics and existing technological lag from leading global manufacturers, an important role is played by the choice of VLSI architecture as well as the use of architectural and circuit design solutions that reduce technical risks and provide solutions to urgent problems for Russian companies.
Glucose induces insulin release from pancreatic β-cells by stimulating ATP synthesis, membrane depolarisation and Ca(2+) influx. As well as activating ATP-consuming processes, cytosolic Ca(2+) ...increases may also potentiate mitochondrial ATP synthesis. Until recently, the ability to study the role of mitochondrial Ca(2+) transport in glucose-stimulated insulin secretion has been hindered by the absence of suitable approaches either to suppress Ca(2+) uptake into these organelles, or to examine the impact on β-cell excitability. Here, we have combined patch-clamp electrophysiology with simultaneous real-time imaging of compartmentalised changes in Ca(2+) and ATP/ADP ratio in single primary mouse β-cells, using recombinant targeted (Pericam or Perceval, respectively) as well as entrapped intracellular (Fura-Red), probes. Through shRNA-mediated silencing we show that the recently-identified mitochondrial Ca(2+) uniporter, MCU, is required for depolarisation-induced mitochondrial Ca(2+) increases, and for a sustained increase in cytosolic ATP/ADP ratio. By contrast, silencing of the mitochondrial Na(+)-Ca(2+) exchanger NCLX affected the kinetics of glucose-induced changes in, but not steady state values of, cytosolic ATP/ADP. Exposure to gluco-lipotoxic conditions delayed both mitochondrial Ca(2+) uptake and cytosolic ATP/ADP ratio increases without affecting the expression of either gene. Mitochondrial Ca(2+) accumulation, mediated by MCU and modulated by NCLX, is thus required for normal glucose sensing by pancreatic β-cells, and becomes defective in conditions mimicking the diabetic milieu.
Cellular metabolism is regulated over space and time to ensure that energy production is efficiently matched with consumption. Fluorescent biosensors are useful tools for studying metabolism as they ...enable real-time detection of metabolite abundance with single-cell resolution. For monitoring glycolysis, the intermediate fructose 1,6-bisphosphate (FBP) is a particularly informative signal as its concentration is strongly correlated with flux through the whole pathway. Using GFP insertion into the ligand-binding domain of the
transcriptional regulator CggR, we developed a fluorescent biosensor for FBP termed HYlight. We demonstrate that HYlight can reliably report the real-time dynamics of glycolysis in living cells and tissues, driven by various metabolic or pharmacological perturbations, alone or in combination with other physiologically relevant signals. Using this sensor, we uncovered previously unknown aspects of β-cell glycolytic heterogeneity and dynamics.
How is β-cell mass adjusted to changes in the functional insulin requirements? The answer to this question is central to the understanding of the causes and (potentially) the therapy of type 2 ...diabetes. In this issue of Cell Metabolism, El Ouaamari et al. (2016) report that increased production of the protease inhibitor SerpinB1 in the liver links insulin resistance to stimulation of β-cell proliferation.
How is β-cell mass adjusted to changes in the functional insulin requirements? The answer to this question is central to the understanding of the causes and (potentially) the therapy of type 2 diabetes. In this issue of Cell Metabolism, El Ouaamari et al. report that increased production of the protease inhibitor SerpinB1 in the liver links insulin resistance to stimulation of β-cell proliferation.
Diabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their β cells (Fh1βKO mice) develop progressive hyperglycemia and ...dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na+ accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in α cells from hyperglycemic Fh1βKO and β-V59M gain-of-function KATP channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1βKO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.
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•Chronic hyperglycemia inhibits fumarase and glucagon secretion by α cells•Hyperglycemia causes SGLT-dependent reduction of cytoplasmic pH and ATP production•SGLT inhibitors normalize cytoplasmic pH, ATP production, and glucagon secretion•The Na-dependent mechanism may impair ATP production in other SGLT-expressing cells
In diabetes, glucagon secretion is dysregulated but the underlying mechanisms are not fully understood. Knudsen et al. report that hyperglycemia impairs glucagon secretion by SGLT-dependent elevation of intracellular Na+, leading to acidification, reduced ATP production, and dysregulated KATP channel activity in α cells. The SGLT mechanism may also impair heart and kidney cell ATP production.
The semi‐essential ubiquitous amino acid taurine has been shown to alleviate obesity and hyperglycemia in humans; however, the pathways underlying the antidiabetic actions have not been ...characterized. We explored the effect of chronic taurine exposure on cell biology of pancreatic islets, in degenerative type 1‐like diabetes. The latter was modeled by small dose of streptozotocin (STZ) injection for 5 days in mice, followed by a 10‐day administration of taurine (2% w/v, orally) in the drinking water. Taurine treatment opposed the detrimental changes in islet morphology and β‐/α‐cell ratio, induced by STZ diabetes, coincidentally with a significant 3.9 ± 0.7‐fold enhancement of proliferation and 40 ± 5% reduction of apoptosis in β‐cells. In line with these findings, the treatment counteracted an upregulation of antioxidant (Sod1, Sod2, Cat, Gpx1) and downregulation of islet expansion (Ngn3, Itgb1) genes induced by STZ, in a pancreatic β‐cell line. At the same time, taurine enhanced the transdifferentiation of α‐cells into β‐cells by 2.3 ± 0.8‐fold, echoed in strong non‐metabolic elevation of cytosolic Ca2+ levels in pancreatic α‐cells. Our data suggest a bimodal effect of dietary taurine on islet β‐cell biology, which combines the augmentation of α‐/β‐cell transdifferentiation with downregulation of apoptosis. The dualism of action, stemming presumably from the intra‐ and extracellular modality of the signal, is likely to explain the antidiabetic potential of taurine supplementation.
Dietary amino acid taurine preferentially targets pancreatic alpha‐cells to induce their transdifferentiation into beta‐cells, upon the condition of depletion of the latter.
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