Complex Patterns of Metabolic and Ca²⁺ Entrainment in Pancreatic Islets by Oscillatory Glucose

Glucose-stimulated insulin secretion is pulsatile and driven by intrinsic oscillations in metabolism, electrical activity, and Ca(2+) in pancreatic islets. Periodic variations in glucose can entrain islet Ca(2+) and insulin secretion, possibly promoting interislet synchronization. Here, we used fluorescence microscopy to demonstrate that glucose oscillations can induce distinct 1:1 and 1:2 entrainment of oscillations (one and two oscillations for each period of exogenous stimulus, respectively) in islet Ca(2+), NAD(P)H, and mitochondrial membrane potential. To our knowledge, this is the first demonstration of metabolic entrainment in islets, and we found that entrainment of metabolic oscillations requires voltage-gated Ca(2+) influx. We identified diverse patterns of 1:2 entrainment and showed that islet synchronization during entrainment involves adjustments of both oscillatory phase and period. All experimental findings could be recapitulated by our recently developed mathematical model, and simulations suggested that interislet variability in 1:2 entrainment patterns reflects differences in their glucose sensitivity. Finally, our simulations and recordings showed that a heterogeneous group of islets synchronized during 1:2 entrainment, resulting in a clear oscillatory response from the collective. In summary, we demonstrate that oscillatory glucose can induce complex modes of entrainment of metabolically driven oscillations in islets, and provide additional support for the notion that entrainment promotes interislet synchrony in the pancreas

Complex Patterns of Metabolic and Ca²⁺ Entrainment in Pancreatic Islets by Oscillatory Glucose

Glucose-stimulated insulin secretion is pulsatile and driven by intrinsic oscillations in metabolism, electrical activity, and Ca(2+) in pancreatic islets. Periodic variations in glucose can entrain islet Ca(2+) and insulin secretion, possibly promoting interislet synchronization. Here, we used fluorescence microscopy to demonstrate that glucose oscillations can induce distinct 1:1 and 1:2 entrainment of oscillations (one and two oscillations for each period of exogenous stimulus, respectively) in islet Ca(2+), NAD(P)H, and mitochondrial membrane potential. To our knowledge, this is the first demonstration of metabolic entrainment in islets, and we found that entrainment of metabolic oscillations requires voltage-gated Ca(2+) influx. We identified diverse patterns of 1:2 entrainment and showed that islet synchronization during entrainment involves adjustments of both oscillatory phase and period. All experimental findings could be recapitulated by our recently developed mathematical model, and simulations suggested that interislet variability in 1:2 entrainment patterns reflects differences in their glucose sensitivity. Finally, our simulations and recordings showed that a heterogeneous group of islets synchronized during 1:2 entrainment, resulting in a clear oscillatory response from the collective. In summary, we demonstrate that oscillatory glucose can induce complex modes of entrainment of metabolically driven oscillations in islets, and provide additional support for the notion that entrainment promotes interislet synchrony in the pancreas

Cellular metabolism constrains innate immune responses in early human ontogeny

Pathogen immune responses are profoundly attenuated in fetuses and premature infants, yet the mechanisms underlying this developmental immaturity remain unclear. Here we show transcriptomic, metabolic and polysome profiling and find that monocytes isolated from infants born early in gestation display perturbations in PPAR-γ-regulated metabolic pathways, limited glycolytic capacity and reduced ribosomal activity. These metabolic changes are linked to a lack of translation of most cytokines and of MALT1 signalosome genes essential to respond to the neonatal pathogen Candida. In contrast, they have little impact on house-keeping phagocytosis functions. Transcriptome analyses further indicate a role for mTOR and its putative negative regulator DNA Damage Inducible Transcript 4-Like in regulating these metabolic constraints. Our results provide a molecular basis for the broad susceptibility to multiple pathogens in these infants, and suggest that the fetal immune system is metabolically programmed to avoid energetically costly, dispensable and potentially harmful immune responses during ontogeny

A Multi-Parameter, High-Content, High-Throughput Screening Platform to Identify Natural Compounds that Modulate Insulin and Pdx1 Expression

Diabetes is a devastating disease that is ultimately caused by the malfunction or loss of insulin-producing pancreatic beta-cells. Drugs capable of inducing the development of new beta-cells or improving the function or survival of existing beta-cells could conceivably cure this disease. We report a novel high-throughput screening platform that exploits multi-parameter high-content analysis to determine the effect of compounds on beta-cell survival, as well as the promoter activity of two key beta-cell genes, insulin and pdx1. Dispersed human pancreatic islets and MIN6 beta-cells were infected with a dual reporter lentivirus containing both eGFP driven by the insulin promoter and mRFP driven by the pdx1 promoter. B-score statistical transformation was used to correct systemic row and column biases. Using this approach and 5 replicate screens, we identified 7 extracts that reproducibly changed insulin and/or pdx1 promoter activity from a library of 1319 marine invertebrate extracts. The ability of compounds purified from these extracts to significantly modulate insulin mRNA levels was confirmed with real-time PCR. Insulin secretion was analyzed by RIA. Follow-up studies focused on two lead compounds, one that stimulates insulin gene expression and one that inhibits insulin gene expression. Thus, we demonstrate that multi-parameter, high-content screening can identify novel regulators of beta-cell gene expression, such as bivittoside D. This work represents an important step towards the development of drugs to increase insulin expression in diabetes and during in vitro differentiation of beta-cell replacements

MISC-1/OGC Links Mitochondrial Metabolism, Apoptosis and Insulin Secretion

We identified MISC-1 (Mitochondrial Solute Carrier) as the C. elegans orthologue of mammalian OGC (2-oxoglutarate carrier). OGC was originally identified for its ability to transfer α-ketoglutarate across the inner mitochondrial membrane. However, we found that MISC-1 and OGC are not solely involved in metabolic control. Our data show that these orthologous proteins participate in phylogenetically conserved cellular processes, like control of mitochondrial morphology and induction of apoptosis. We show that MISC-1/OGC is required for proper mitochondrial fusion and fission events in both C. elegans and human cells. Transmission electron microscopy reveals that loss of MISC-1 results in a decreased number of mitochondrial cristae, which have a blebbed appearance. Furthermore, our pull-down experiments show that MISC-1 and OGC interact with the anti-apoptotic proteins CED-9 and Bcl-xL, respectively, and with the pro-apoptotic protein ANT. Knock-down of misc-1 in C. elegans and OGC in mouse cells induces apoptosis through the caspase cascade. Genetic analysis suggests that MISC-1 controls apoptosis through the physiological pathway mediated by the LIN-35/Rb-like protein. We provide genetic and molecular evidence that absence of MISC-1 increases insulin secretion and enhances germline stem cell proliferation in C. elegans. Our study suggests that the mitochondrial metabolic protein MISC-1/OGC integrates metabolic, apoptotic and insulin secretion functions. We propose a novel mechanism by which mitochondria integrate metabolic and cell survival signals. Our data suggest that MISC-1/OGC functions by sensing the metabolic status of mitochondria and directly activate the apoptotic program when required. Our results suggest that controlling MISC-1/OGC function allows regulation of mitochondrial morphology and cell survival decisions by the metabolic needs of the cell

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

A Simplified Model for Mitochondrial ATP Production

Most of the adenosine triphosphate (ATP) synthesized during glucose metabolism is produced in the mitochondria through oxidative phosphorylation. This is a complex reaction powered by the proton gradient across the mitochondrial inner membrane, which is generated by mitochondrial respiration. A detailed model of this reaction, which includes dynamic equations for the key mitochondrial variables, was developed earlier by Magnus and Keizer. However, this model is extraordinarily complicated. We develop a simpler model that captures the behavior of the original model but is easier to use and to understand. We then use it to investigate the mitochondrial responses to glycolytic and calcium input. We use the model to explain experimental observations of the opposite effects of raising cytosolic Ca 2þ in low and high glucose, and to predict the effects of a mutation in the mitochondrial enzyme nicotinamide nucleotide transhydrogenase (Nnt) in pancreatic b-cells

Type 2 diabetes susceptibility gene GRK5 regulates physiological pancreatic β-cell proliferation via phosphorylation of HDAC5

Summary: Restoring functional β cell mass is a potential therapy for those with diabetes. However, the pathways regulating β cell mass are not fully understood. Previously, we demonstrated that Sox4 is required for β cell proliferation during prediabetes. Here, we report that Sox4 regulates β cell mass through modulating expression of the type 2 diabetes (T2D) susceptibility gene GRK5. β cell-specific Grk5 knockout mice showed impaired glucose tolerance with reduced β cell mass, which was accompanied by upregulation of cell cycle inhibitor gene Cdkn1a. Furthermore, we found that Grk5 may drive β cell proliferation through a pathway that includes phosphorylation of HDAC5 and subsequent transcription of immediate-early genes (IEGs) such as Nr4a1, Fosb, Junb, Arc, Egr1, and Srf. Together, these studies suggest GRK5 is linked to T2D through regulation of β cell growth and that it may be a target to preserve β cells during the development of T2D