Effect Of Glucose Deprivation Research Articles

The crosstalk among the physical tumor microenvironment and the effects of glucose deprivation on tumors in the past decade.

The occurrence and progression of tumors are inseparable from glucose metabolism. With the development of tumors, the volume increases gradually and the nutritional supply of tumors cannot be fully guaranteed. The tumor microenvironment changes and glucose deficiency becomes the common stress environment of tumors. Here, we discuss the mutual influences between glucose deprivation and other features of the tumor microenvironment, such as hypoxia, immune escape, low pH, and oxidative stress. In the face of a series of stress responses brought by glucose deficiency, different types of tumors have different coping mechanisms. We summarize the tumor studies on glucose deficiency in the last decade and review the genes and pathways that determine the fate of tumors under harsh conditions. It turns out that most of these genes help tumor cells survive in glucose-deprivation conditions. The development of related inhibitors may bring new opportunities for the treatment of tumors.

Targeting USP9X-AMPK Axis in ARID1A-Deficient Hepatocellular Carcinoma.

Background & AimsHepatocellular carcinoma (HCC) is a highly heterogeneous solid tumor with high morbidity and mortality. AT-rich interaction domain 1A (ARID1A) accounts for up to 10% of mutations in liver cancer, however, its role in HCC remains controversial, and no targeted therapy has been established.MethodsThe expression of ARID1A in clinical samples was examined by Western blot and immunohistochemical staining. ARID1A was knocked out by Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) in HCC cell lines, and the effects of glucose deprivation on cell viability, proliferation, and apoptosis were measured. Mass spectrometry analysis was used to find ARID1A-interacting proteins, and the result was verified by co-immunoprecipitation and Glutathione S Transferase (GST) pull-down. The regulation of ARID1A target gene USP9X was investigated by chromatin immunoprecipitation, Glutathione S Transferase (GST) pull-down, luciferase reporter assay, and so forth. Finally, drug treatments were performed to explore the therapeutic potential of the agents targeting ARID1A-deficient HCC in vitro and in vivo.ResultsOur study has shown that ARID1A loss protected cells from glucose deprivation–induced cell death. A mechanism study disclosed that AIRD1A recruited histone deacetylase 1 via its C-terminal region DUF3518 to the promoter of USP9X, resulting in down-regulation of USP9X and its target protein kinase AMP-activated catalytic subunit α2 (PRKAA2). ARID1A knockout and a 1989∗ truncation mutant in HCC abolished this effect, increased the levels of H3K9 and H3K27 acetylation at the USP9X promoter, and up-regulated the expression of USP9X and protein kinase AMP-activated catalytic subunit α2 (PRKAA2), which mediated the adaptation of tumor cells to glucose starvation. Compound C dramatically inhibited the growth of ARID1A-deficient tumors and prolongs the survival of tumor-bearing mice.ConclusionsHCC patients with ARID1A mutation may benefit from synthetic lethal therapy targeting the ubiquitin-specific peptidase 9 X-linked (USP9X)–adenosine 5‘-monophosphate–activated protein kinase (AMPK) axis.

Expression of IDE and PITRM1 genes in ERN1 knockdown U87 glioma cells: effect of hypoxia and glucose deprivation.

The aim of the present investigation was to study the expression of genes encoding polyfunctional proteins insulinase (insulin degrading enzyme, IDE) and pitrilysin metallopeptidase 1 (PITRM1) in U87 glioma cells in response to inhibition of endoplasmic reticulum stress signaling mediated by ERN1/IRE1 (endoplasmic reticulum to nucleus signaling 1) for evaluation of their possible significance in the control of metabolism through ERN1 signaling as well as hypoxia, glucose and glutamine deprivations. The expression level of IDE and PITRM1 genes was studied in control and ERN1 knockdown U87 glioma cells under glucose and glutamine deprivations as well as hypoxia by quantitative polymerase chain reaction. It was found that the expression level of IDE and PITRM1 genes was down-regulated in ERN1 knockdown (without ERN1 protein kinase and endoribonuclease activity) glioma cells in comparison with the control glioma cells, being more significant for PITRM1 gene. We also found up-regulation of microRNA MIR7-2 and MIRLET7A2, which have specific binding sites in 3'-untranslated region of IDE and PITRM1 mRNAs, correspondingly, and can participate in posttranscriptional regulation of these mRNA expressions. Only inhibition of ERN1 endoribonuclease did not change significantly the expression of IDE and PITRM1 genes in glioma cells. The expression of IDE and PITRM1 genes is preferentially regulated by ERN1 protein kinase. We also showed that hypoxia down-regulated the expression of IDE and PITRM1 genes and that knockdown of ERN1 signaling enzyme function modified the response of these gene expressions to hypoxia. Glucose deprivation increased the expression level of IDE and PITRM1 genes, but ERN1 knockdown enhanced only the effect of glucose deprivation on PITRM1 gene expression. Glutamine deprivation did not affect the expression of IDE gene in both types of glioma cells, but up-regulated PITRM1 gene and this up-regulation was stronger in ERN1 knockdown cells. Results of this investigation demonstrate that ERN1 knockdown significantly decreases the expression of IDE and PITRM1 genes by ERN1 protein kinase mediated mechanism. The expression of both studied genes was sensitive to hypoxia as well as glucose deprivation and dependent on ERN1 signaling in gene-specific manner. It is possible that the level of these genes expression under hypoxia and glucose deprivation is a result of complex interaction of variable endoplasmic reticulum stress related and unrelated regulatory factors and contributed to the control of the cell metabolism.

Effects of Glucose Deprivation on ATP and Proteoglycan Production of Intervertebral Disc Cells under Hypoxia

As the most common cause of low back pain, the cascade of intervertebral disc (IVD) degeneration is initiated by the disappearance of notochordal cells and progressive loss of proteoglycan (PG). Limited nutrient supply in the avascular disc environment restricts the production of ATP which is an essential energy source for cell survival and function such as PG biosynthesis. The objective of this study was to examine ATP level and PG production of porcine IVD cells under prolonged exposure to hypoxia with physiological glucose concentrations. The results showed notochordal NP and AF cells responded differently to changes of oxygen and glucose. Metabolic activities (including PG production) of IVD cells are restricted under the in-vivo nutrient conditions while NP notochordal cells are likely to be more vulnerable to reduced nutrition supply. Moreover, provision of energy, together or not with genetic regulation, may govern PG production in the IVD under restricted nutrient supply. Therefore, maintaining essential levels of nutrients may reduce the loss of notochordal cells and PG in the IVD. This study provides a new insight into the metabolism of IVD cells under nutrient deprivation and the information for developing treatment strategies for disc degeneration.

Effect of glucose deprivation on the expression of genes encoding glucocorticoid receptor and some related factors in ERN1-knockdown U87 glioma cells

The aim of the present study was to examine the effect of glucose deprivation on the expression of genes encoded glucocorticoid receptor (NR3C1) and some related proteins (NR3C2, AHR, NRIP1, NNT, ARHGAP35, SGK1, and SGK3) in U87 glioma cells in response to inhibition of endoplasmic reticulum stress signaling mediated by ERN1/IRE1 (endoplasmic reticulum to nucleus signaling 1/inositol requiring enzyme 1) for evaluation of their possible significance in the control of glioma growth through endoplasmic reticulum stress signaling mediated by IRE1 and glucose deprivation. The expression of NR3C1, NR3C2, AHR, NRIP1, NNT, ARHGAP35, SGK1, and SGK3 genes in U87 glioma cells transfected by empty vector pcDNA3.1 (control cells) and cells without ERN1 signaling enzyme function (transfected by dnERN1) under glucose deprivation was studied by real time quantitative polymerase chain reaction. It was shown that the expression level of NR3C2, AHR, SGK1, SGK3, and NNT genes was up-regulated in control U87 glioma cells under glucose deprivation condition in comparison with the control cells growing with glucose. At the same time, the expression of NRIP1 gene is down-regulated in these glioma cells under glucose deprivation, but NR3C1 and ARHGAP35 genes was resistant to this experimental condition. We also showed that inhibition of ERN1 signaling enzyme function significantly modified the response of most studied gene expressions to glucose deprivation condition. Thus, effect of glucose deprivation on the expression level of NR3C2, AHR, and SGK1 genes was significantly stronger in ERN1 knockdown U87 glioma cells since the expression of NNT gene was resistant to glucose deprivation condition. Moreover, the inhibition of ERN1 enzymatic activities in U87 glioma cells led to up-regulation of ARHGAP35 gene expression and significant down-regulation of the expression of SGK3 gene in response to glucose deprivation condition. Results of this study demonstrated that glucose deprivation did not change the expression level of NR3C1 gene but it significantly affected the expression of NR3C2, AHR, NRIP, SGK1, SGK3, and NNT genes in vector-transfected U87 glioma cells in gene specific manner and possibly contributed to the control of glioma growth since the expression of most studied genes in glucose deprivation condition was significantly dependent on the functional activity of IRE1 signaling enzyme.

Chaperone insufficiency links TLR4 signaling to endoplasmic reticulum stress.

Inflammation plays an important pathogenic role in a number of metabolic diseases such as obesity, type 2 diabetes, and atherosclerosis. The activation of inflammation in these diseases depends at least in part on the combined actions of TLR4 signaling and endoplasmic reticulum stress, which by acting in concert can boost the inflammatory response. Defining the mechanisms involved in this phenomenon may unveil potential targets for the treatment of metabolic/inflammatory diseases. Here we used LPS to induce endoplasmic reticulum stress in the human monocyte cell-line, THP-1. The unfolded protein response, produced after LPS, was dependent on CD14 activity but not on RNA-dependent protein kinase and could be inhibited by an exogenous chemical chaperone. The induction of the endoplasmic reticulum resident chaperones, GRP94 and GRP78, by LPS was of a much lower magnitude than the effect of LPS on TLR4 and MD-2 expression. In face of this apparent insufficiency of chaperone expression, we induced the expression of GRP94 and GRP78 by glucose deprivation. This approach completely reverted endoplasmic reticulum stress. The inhibition of either GRP94 or GRP78 with siRNA was sufficient to rescue the protective effect of glucose deprivation on LPS-induced endoplasmic reticulum stress. Thus, insufficient LPS-induced chaperone expression links TLR4 signaling to endoplasmic reticulum stress.

Effects of Glucose Deprivation on The Biological Phenotypes of Human Malignant Mesothelial Cells

Microenvironment is important in the maintenance of biological phenotypes such as survival, proliferation, and migration capacity in cancer cells. Decreased concentration of glucose is a common feature of the tumor microenvironment and has been reported to play a critical role in the acquirement of malignancy.Cancer cell metabolism is shifted toward glycolysis by the increased expression of glycolytic enzymes, glucose transporters, and inhibitors of mitochondrial metabolism. This study was performed to evaluate the effects of glucose‐free on the phenotypes of human malignant mesothelioma (HMM) cells. Glucose free media decreased the cell survival and proliferation of HMM cells. The mobility and invasion capacities were significantly decreased by glucose deprivation. These characteristics of cancer cells were resulted from the promotion of apoptosis. Gene expression level of ABCG2, an efflux transporter of cytotoxic drugs, was increased in glucose free media compared to normal media. The results suggest that deprivation of glucose from cancer cells affect their biological phenotypes due to lack of energy and increase multidrug resistance.

Activation of survival signals in melanoma cells in response to glucose deprivation (766.9)

Cancer’s use of alternate cellular pathways is necessary in order to proliferate and expand so aggressively but may make it possible to target using certain cancer therapies. We studied the effects that lowered glucose concentrations have on important cancer characteristics in WM266‐4 Melanoma cells. Changes to the cells included observable effects like morphology alteration and inhibition of growth as well as modification to internal signaling pathways. The cytoskeleton, being important for its interaction with insulin containing vesicles, altering of GLUT transporter translocation and glucose metabolism related enzymes, was disrupted after 48 hours which can be seen by the cells decreasing dendricity. Inhibition of growth was found to be correlated with decreasing glucose concentrations in medium, as was depletion of nutrients and changes in pH of the extracellular environment. Reduction in pH could be a mechanism of the cancer cells to proliferate and survive, the result of heavy production of lactic acid caused by increased rate of glycolysis, or both. Levels of p‐S6, p‐AMPK, p‐ERK and p‐MEK were shown to be increased by glucose deprivation at 6 hours showing that the cancer cells are fighting back in order to survive. S6 ribosomal protein as well p‐ACC decreased with glucose deprivation at 48 hours while p‐AMPK increased showing high levels of stress and eventually cellular shutdown. Finally, GLUT1 transporter expression as well as survivin, an anti‐apoptotic molecule, was shown to be increased at 24 hours under glucose deprivation. Collectively, our data suggest that the effects of glucose deprivation on melanoma are important in understanding the way these cells uptake their nutrients and may provide for therapeutic treatments in the future.Grant Funding Source: Supported by INBRE research grant

Експресія генів IGFBP1, IGFBP2 та IGF2BP3 у клітинах гліоми з пригніченою функцією сигнального ензиму ERN1 за умов дефіциту глутаміну і глюкози

Insulin-like growth factor binding proteins play an important role in the regulation of cell proliferation and malignant tumor growth. It was shown that blockade of both enzymatic functions of sensor and signaling enzyme ERN1 (from endoplasmic reticulum to nuclei-1), the major component of endoplasmic reticulum stress signaling, decreases the expression level of IGFBP1, IGFBP2 and IGF2BP3 genes in U87 glioma cell. The decreased level of these gene expressions in glioma cells with ERN1 signaling enzyme loss of function correlates with suppression of cell proliferation. It was shown that glutamine deprivation condition leads to enhance the expression of IGFBP1 gene, but did not change significantly the expression of IGFBP2 and IGF2BP3 genes in both types of glioma cells. Moreover, this effect of glutamine deprivation did not depend from suppression of ERN1 enzyme function. At the same time, the expression of IGFBP2 and IGF2BP3 genes is decreased in glucose deprivation condition in both types of glioma cells and blockade of ERN1 signaling enzyme enhanced this effect. Thus, results of this investigation demonstrated that the expression of IGFBP1, IGFBP2 and IGF2BP3 genes in U87 glioma cells is dependent from signaling enzyme ERN1 and is changed in glutamine and glucose deprivation conditions, but only effect of glucose deprivation was depended of ERN1 signaling enzyme function. Moreover, the decreasing of IGFBP1, IGFBP2 and IGF2BP3 gene expressions in glioma cells with blockade of both enzymatic activities of ERN1 is possibly related to suppression of these cells proliferation.

Membrane lipid profile alterations are associated with the metabolic adaptation of the Caco-2 cells to aglycemic nutritional condition

Cancer cells can adapt their metabolic activity under nutritional hostile conditions in order to ensure both bioenergetics and biosynthetic requirements to survive. In this study, the effect of glucose deprivation on Caco-2 cells bioenergetics activity and putative relationship with membrane lipid changes were investigated. Glucose deprivation induces a metabolic remodeling characterized at mitochondrial level by an increase of oxygen consumption, arising from an improvement of complex II and complex IV activities and an inhibition of complex I activity. This effect is accompanied by changes in cellular membrane phospholipid profile. Caco-2 cells grown under glucose deprivation show higher phosphatidylethanolamine content and decreased phosphatidic acid content. Considering fatty acid profile of all cell phospholipids, glucose deprivation induces a decrease of monounsaturated fatty acid (MUFA) and n-3 polyunsaturated fatty acids (PUFA) simultaneously with an increase of n-6 PUFA, with consequent drop of n-3/n-6 ratio. Additionally, glucose deprivation affects significantly the fatty acid profile of all individual phospholipid classes, reflected by an increase of peroxidability index in zwitterionic phospholipids and a decrease in all anionic phospholipids, including mitochondrial cardiolipin. These data indicate that Caco-2 cells metabolic remodeling induced by glucose deprivation actively involves membrane lipid changes associated with a specific bioenergetics profile which ensure cell survival.

Hypoxia Antagonizes Glucose Deprivation on Interleukin 6 Expression in an Akt Dependent, but HIF-1/2α Independent Manner

Although both glucose deprivation and hypoxia have been reported to promote cascades of biological alterations that lead to induction of inflammatory mediators, we hypothesized that glucose deprivation and hypoxia might show neutral, synergistic or antagonistic effects to each other on gene expression of inflammatory mediators depending on the regulatory components in their promoters. Gene expression of interleukin 6 (IL-6) was analyzed by real-time PCR, ELISA, or Western blot. Effects of glucose deprivation and/or hypoxia on activation of signaling pathways were analyzed by time-dependent phosphorylation patterns of signaling molecules. We demonstrate that hypoxia antagonized the effects of glucose deprivation on induction of IL-6 gene expression in microglia, macrophages, and monocytes. Hypoxia also antagonized thapsigargin-induced IL-6 gene expression. Hypoxia enhanced phosphorylation of Akt, and inhibition of Akt was able to reverse the effects of hypoxia on IL-6 gene expression. However, inhibition of HIF-1/2α did not reverse the effects of hypoxia on IL-6 gene expression. In addition, phosphorylation of p38, but not JNK, was responsible for the effects of glucose deprivation on IL-6 gene expression.

Reactive Oxygen Species and p38 Mitogen-activated Protein Kinase Mediate Exercise-induced Skeletal Muscle-derived Interleukin-6 Expression

Interleukin-6 (IL-6) is a pleiotropic cytokine secreted by many different cell types, and skeletal muscle is an important source of IL-6 during exercise. Here, we studied the effects of glucose deprivation in vitro on skeletal muscle-derived IL-6 expression and release in C2C12 myocytes, as well as its regulation by p38 mitogen-activated protein kinase (p38MAPK) and reactive oxygen species (ROS). C2C12 myotubes were cultured in DMEM medium containing 4.5 g · L−1 glucose (glucose control, GC) or DMEM medium containing no glucose (glucose deprivation, GD) for 0, 6, 12, 18 and 24 hours, and then incubated with 10mM NAC (a ROS scavenger) or 10 μM SB203580 (a p38MAPK inhibitor) under either GC or GD conditions for 24 hours. IL-6 expression levels were subsequently analyzed using RT–PCR, and IL-6 protein levels in the medium were measured using ELISA. Glucose deprivation significantly enhanced IL-6 expression at 18 and 24 hours compared to the glucose control, and caused IL-6 protein levels to increase significantly over the entire 24-hour measurement period. The ROS scavenger NAC inhibited the glucose deprivation-induced release of IL-6 protein almost completely, while the p38MAPK inhibitor SB203580 inhibited glucose deprivation-induced IL-6 protein release to a lesser extent. Our study suggests that glucose deprivation in C2C12 myocytes induces IL-6 expression and release, and that this IL-6 release is mainly mediated via ROS signaling. Skeletal muscle-derived IL-6 may thus play an important role in energy metabolism during exercise.

Galactose Counteracts Hypoglycemia-Induced Decline of Cholinergic Neurons at Low pH in Organotypic Rat Brain Slices of the Basal Nucleus of Meynert

A growing body of evidence indicates that hypoglycemia and acidosis may contribute to the development of Alzheimer’s disease (AD). The cell death of basal forebrain cholinergic neurons constitutes a hallmark of AD and directly correlates with cognitive impairment. The aim of the present study was to investigate, in an organotypic rat brain slice model of the basal nucleus of Meynert, the effects of glucose deprivation on cholinergic neurons under normal and acidic conditions. Furthermore, we were interested to explore whether different saccharides (galactose, fructose, saccharose, lactose) can replace glucose under low pH conditions. Our data show a pH-dependent survival of cholinergic neurons at a high (37.1 mmol/l) glucose level, which was markedly decreased at a low (5.6 mmol/l) glucose level. Galactose (+31.5 mmol/l) significantly counteracted the loss of choline acetyltransferase-positive neurons in low-glucose-treated slices, while fructose, lactose and saccharose only partly protected cholinergic neurons. In conclusion, our results indicate that replacement of glucose with different saccharides, but most potently with galactose, protects cholinergic neurons against hypoglycemia at a low pH.

Solution structure of the C-terminal DUF1000 domain of the human thioredoxin-like 1 protein

Solution structure of the C-terminal DUF1000 domain of the human thioredoxin-like 1 protein

Glucose Deprivation Regulates KATP Channel Trafficking via AMP-Activated Protein Kinase in Pancreatic β-Cells

OBJECTIVEAMP-activated protein kinase (AMPK) and the ATP-sensitive K+ (KATP) channel are metabolic sensors that become activated during metabolic stress. AMPK is an important regulator of metabolism, whereas the KATP channel is a regulator of cellular excitability. Cross talk between these systems is poorly understood.RESEARCH DESIGN AND METHODSRat pancreatic β-cells or INS-1 cells were pretreated for 2 h at various concentrations of glucose. Maximum KATP conductance (Gmax) was monitored by whole-cell measurements after intracellular ATP washout using ATP-free internal solutions. KATP channel activity (NPo) was monitored by inside-out patch recordings in the presence of diazoxide. Distributions of KATP channel proteins (Kir6.2 and SUR1) were examined using immunofluorescence imaging and surface biotinylation studies. Insulin secretion from rat pancreatic islets was measured using an enzyme immunoassay.RESULTSGmax and NPo in cells pretreated with glucose-free or 3 mmol/l glucose solutions were significantly higher than in cells pretreated in 11.1 mmol/l glucose solutions. Immunofluorescence imaging and biotinylation studies revealed that glucose deprivation induced an increase in the surface level of Kir6.2 without affecting the total cellular amount. Increases in Gmax and the surface level of Kir6.2 were inhibited by compound C, an AMPK inhibitor, and siAMPK transfection. The effects of glucose deprivation on KATP channels were mimicked by an AMPK activator. Glucose deprivation reduced insulin secretion, but this response was attenuated by compound C.CONCLUSIONSKATP channel trafficking is regulated by energy status via AMPK, and this mechanism may play a key role in inhibiting insulin secretion under low energy status.

Molecular mechanisms involved in Sertoli cell adaptation to glucose deprivation

Sertoli cells provide the physical support and the necessary environment for germ cell development. Among the products secreted by Sertoli cells, lactate, the preferred energy substrate for spermatocytes and spermatids, is present. Considering the essential role of lactate on germ cell metabolism, it is supposed that Sertoli cells must ensure its production even in adverse conditions, such as those that would result from a decrease in glucose levels in the extracellular milieu. The aim of the present study was to investigate 1) a possible effect of glucose deprivation on glucose uptake and on the expression of glucose transporters in rat Sertoli cells and 2) the participation of different signal transduction pathways in the above-mentioned regulation. Results obtained show that decreasing glucose levels in Sertoli cell culture medium provokes 1) an increase in glucose uptake accompanied by only a slight decrease in lactate production, 2) an increase in GLUT1 and a decrease in GLUT3 expression, and 3) an activation of AMP-activated protein kinase (AMPK)-, phosphatidylinositol 3-kinase (PI3K)/PKB-, and p38 MAPK-dependent pathways. Additionally, by using specific inhibitors of these pathways, a possible participation of AMPK- and p38MAPK-dependent pathways in the regulation of glucose uptake and GLUT1 expression is shown. These results suggest that Sertoli cells adapt to conditions of glucose deprivation to ensure an adequate lactate concentration in the microenvironment where germ cell development occurs.

The effect of glucose deprivation on collagen synthesis in fibroblast cultures

It was decided to study the effect of glucose deprivation on collagen synthesis and degradation in fibroblast cultures and a correlation of these processes with the expression of oxygen/glucose regulated proteins (ORP150/GRP170). The incorporation of radiolabeled proline into collagenase-sensitive and hydroxyproline-containing proteins was used as an index of collagen synthesis, whereas pulse-chase technique was employed to evaluate the degradation of newly synthesised proteins. We demonstrated that fibroblasts incubated in high-glucose medium synthesised detectable amounts of collagenous proteins. Most of them were secreted into the culture medium. The shortage of glucose resulted in about 30% reduction in synthesis of collagenous proteins, both those secreted into culture medium and remaining in the cell layer. The pulse-chase experiments demonstrated that the reduced amount of newly synthesised collagen was protected against intracellular degradation. Proportionally less collagen was degraded in cultures incubated in low-glucose than in high-glucose media. These phenomena were accompanied by an increase in the expression of chaperon-ORP150 in cultures growing in low-glucose medium. We suggest that the increased expression of ORP150 is a factor which protects collagen against intracellular degradation induced by glucose deprivation.

Glucose Deprivation Regulates KATP Channel Trafficking via AMPK in Pancreatic Beta-Cells

AMP-activated protein kinase (AMPK) and ATP-sensitive K+ channel (KATP channel) are metabolic sensors that are activated during metabolic stress. The importance of AMPK has been appreciated by its role as a regulator of metabolism, whereas KATP channel is known as a regulator of cellular excitability. Cross-talks between two systems are not well understood. In pancreatic β-cells or INS-1 cells, we measured KATP currents by the patch clamp technique and examined distributions of KATP channel proteins (Kir6.2 and SUR1) using immunofluorescence imaging and surface biotinylation studies. When KATP channels were activated by washout of intracellular ATP using a ATP- and Mg2+-free internal solution, the increase in whole cell conductance was surprisingly small in cells incubated in 11.1 mM glucose medium, but the increase was significantly higher in cells pre-incubated in glucose-free medium for 2 hrs. We confirmed that KATP channel proteins were mostly internalized in 11.1 mM glucose, but recruited to the plasma membrane by glucose deprivation without changes in total levels. The effects of glucose deprivation on KATP channels were abolished by an AMPK inhibitor or a knockdown of AMPK using siRNA, but mimicked by an AMPK activator. These results suggest that regulation of KATP channel trafficking by AMPK is a prerequisite for KATP channel activation in pancreatic β-cells in response to glucose deprivation. The interplay between AMPK and KATP channels may play a key role in inhibiting cellular excitability and insulin secretion under low energy status.

Sex-specific effects of glucose deprivation on cell-mediated immunity and reproduction in Siberian hamsters (Phodopus sungorus)

In most species, sexes differ in levels of parasitism. These differences have traditionally been believed to be static, but a capacity for adjusting anti-parasite investments would allow sexes to allocate resources adaptively contingent on environmental conditions. During stressful periods, such as a food shortage, allocation decisions would be mandated in males and females, but the biasing of resources may differ depending on the value of various physiological alternatives to the fitness of each sex. To determine whether sexes sacrifice immune or reproductive capacity when stressed, male and female Siberian hamsters (Phodopus sungorus) were pharmacologically deprived of glucose. Glucose deprivation was expected to compromise immune activity (delayed-type hypersensitivity) more than reproductive capacity in males because male fitness is limited by reproductive opportunities. The opposite was predicted for females because of the greater value of surviving to breed in favorable conditions. Contrary to expectations, glucoprivation compromised immune activity in female, but not male, hamsters. Conversely, glucoprivation reduced male, but not female, reproductive organ masses. These results may reflect the adjustments made by wild hamsters during food shortages, or they may be influenced by the study design; neither sex was permitted to incur other behavioral and physiological costs, such as lactation and parental care. Regardless, our results indicate that sex differences in parasitism are likely to be plastic in many circumstances, but further work in free-living animals is critical to ascertain whether results of the present study are naturally representative.

Increased ATP-sensitive K + channel expression during acute glucose deprivation

ATP-sensitive potassium (K ATP) channels play a central role in glucose-stimulated insulin secretion (GSIS) by pancreatic β-cells. Activity of these channels is determined by their open probability ( P o) and the number of channels present in a cell. Glucose is known to reduce P o, but whether it also affects the channel density is unknown. Using INS-1 model β-cell line, we show that the expression of K ATP channel subunits, Kir6.2 and SUR1, is high at low glucose, but declines sharply when the ambient glucose concentration exceeds 5 mM. In response to glucose deprivation, channel synthesis increases rapidly by up-regulating translation of existing mRNAs. The effects of glucose deprivation could be mimicked by pharmacological activation of 5′-AMP-activated protein kinase with 5-aminoimidazole-4-carboxamide ribonucleotide and metformin. Pancreatic β-cells which have lost their ability for GSIS do not show such changes implicating a possible (patho-)physiological link between glucose-regulated K ATP channel expression and the capacity for normal GSIS.