Stimulation Of Uptake Research Articles

Stimulation of brain glucose uptake by cannabinoid CB2 receptors and its therapeutic potential in Alzheimer's disease

Cannabinoid CB2 receptors (CB2Rs) are emerging as important therapeutic targets in brain disorders that typically involve neurometabolic alterations. We here addressed the possible role of CB2Rs in the regulation of glucose uptake in the mouse brain. To that aim, we have undertaken 1) measurement of 3H-deoxyglucose uptake in cultured cortical astrocytes and neurons and in acute hippocampal slices; 2) real-time visualization of fluorescently labeled deoxyglucose uptake in superfused hippocampal slices; and 3) in vivo PET imaging of cerebral 18F-fluorodeoxyglucose uptake. We now show that both selective (JWH133 and GP1a) as well as non-selective (WIN55212-2) CB2R agonists, but not the CB1R-selective agonist, ACEA, stimulate glucose uptake, in a manner that is sensitive to the CB2R-selective antagonist, AM630. Glucose uptake is stimulated in astrocytes and neurons in culture, in acute hippocampal slices, in different brain areas of young adult male C57Bl/6j and CD-1 mice, as well as in middle-aged C57Bl/6j mice. Among the endocannabinoid metabolizing enzymes, the selective inhibition of COX-2, rather than that of FAAH, MAGL or α,βDH6/12, also stimulates the uptake of glucose in hippocampal slices of middle-aged mice, an effect that was again prevented by AM630. However, we found the levels of the endocannabinoid, anandamide reduced in the hippocampus of TgAPP-2576 mice (a model of β-amyloidosis), and likely as a consequence, COX-2 inhibition failed to stimulate glucose uptake in these mice. Together, these results reveal a novel general glucoregulatory role for CB2Rs in the brain, raising therapeutic interest in CB2R agonists as nootropic agents.

Diabetes-Associated Variation in TCF7L2 Is Not Associated With Hepatic or Extrahepatic Insulin Resistance.

A common genetic variation in TCF7L2 is associated with type 2 diabetes. However, the mechanism by which this occurs remains elusive. In addition to affecting insulin secretion, genetic variation at the TCF7L2 locus may alter insulin action or directly modify hepatic glucose metabolism. We sought to determine whether the diabetes-associated variant in this locus (the T allele of rs7903146) increases fasting endogenous glucose production (EGP), and impairs insulin-induced suppression of EGP and insulin-stimulated glucose disappearance. To address this, we studied individuals who were either homozygous for the diabetes-associated allele (TT) at rs7903146 or were homozygous for the protective allele (CC). Subjects were matched for other anthropometric characteristics and were studied using a euglycemic clamp. EGP and glucose uptake were measured using the tracer dilution technique, and the relative contribution of gluconeogenesis to EGP was quantitated using deuterated water corrected for transaldolase exchange. We report that the diabetes-associated variation in TCF7L2 did not associate with fasting EGP, insulin-induced suppression of EGP, and insulin-induced stimulation of glucose uptake. There was no association with the contribution of gluconeogenesis and glycogenolysis to EGP. These data indicate that genetic variation at TCF7L2 does not predispose an individual to type 2 diabetes by altering either hepatic or extrahepatic insulin action.

Carbohydrate mouth rinsing has no effect on power output during cycling in a glycogen-reduced state.

BackgroundThe effect of mouth rinsing with a carbohydrate (CHO) solution on exercise performance is inconclusive with no benefits observed in the fed state. This study examined the effect of CHO mouth rinse or CHO ingestion on performance in 9 moderately trained male cyclists.MethodsFour trials were undertaken, separated by 7 days, in a randomized, counterbalanced design. Each trial included a 90-min glycogen-reducing exercise protocol, immediately followed by a low CHO meal and subsequent overnight fast; the following morning a 1-h cycling time trial was conducted. The trials included 15 % CHO mouth rinse (CHOR), 7.5 % CHO ingestion (CHOI), placebo mouth rinse and placebo ingestion. Solutions were provided after every 12.5 % of completed exercise: 1.5 mL · kg−1 and 0.33 mL · kg−1 body mass during ingestion and rinse trials, respectively. During rinse trials participants swirled the solution for 8 s before expectorating. Blood samples were taken at regular intervals before and during exercise.ResultsPerformance time was not different between trials (P = 0.21) but the 4.5-5.2 % difference between CHOI and other trials showed moderate practical significance (Cohen’s d 0.57-0.65). Power output was higher in CHOI relative to other trials (P < 0.01). There were no differences between CHOR and placebo groups for any performance variables. Plasma glucose, insulin and lactate concentrations were higher in CHOI relative to other groups (P < 0.05).ConclusionsIn a fasted and glycogen-reduced state ingestion of a CHO solution during high-intensity exercise enhanced performance through stimulation of insulin-mediated glucose uptake. The CHO mouth rinsing had neither ergogenic effects nor changes in endocrine or metabolic responses relative to placebo.

Nanoparticle Delivered Human Biliverdin Reductase-Based Peptide Increases Glucose Uptake by Activating IRK/Akt/GSK3 Axis: The Peptide Is Effective in the Cell and Wild-Type and Diabetic Ob/Ob Mice.

Insulin's stimulation of glucose uptake by binding to the IRK extracellular domain is compromised in diabetes. We have recently described an unprecedented approach to stimulating glucose uptake. KYCCSRK (P2) peptide, corresponding to the C-terminal segment of hBVR, was effective in binding to and inducing conformational change in the IRK intracellular kinase domain. Although myristoylated P2, made of L-amino acids, was effective in cell culture, its use for animal studies was unsuitable. We developed a peptidase-resistant formulation of the peptide that was efficient in both mice and cell culture systems. The peptide was constructed of D-amino acids, in reverse order, and blocked at both termini. Delivery of the encapsulated peptide to HepG2 and HSKM cells was confirmed by its prolonged effect on stimulation of glucose uptake (>6 h). The peptide improved glucose clearance in both wild-type and Ob/Ob mice; it lowered blood glucose levels and suppressed glucose-stimulated insulin secretion. IRK activity was stimulated in the liver of treated mice and in cultured cells. The peptide potentiated function of IRK's downstream effector, Akt-GSK3-(α, β) axis. Thus, P2-based approach can be used for improving glucose uptake by cells. Also, it allows for screening peptides in vitro and in animal models for treatment of diabetes.

Acute stimulation of glucose influx upon mitoenergetic dysfunction requires LKB1, AMPK, Sirt2 and mTOR-RAPTOR.

Mitochondria play a central role in cellular energy production, and their dysfunction can trigger a compensatory increase in glycolytic flux to sustain cellular ATP levels. Here, we studied the mechanism of this homeostatic phenomenon in C2C12 myoblasts. Acute (30 min) mitoenergetic dysfunction induced by the mitochondrial inhibitors piericidin A and antimycin A stimulated Glut1-mediated glucose uptake without altering Glut1 (also known as SLC2A1) mRNA or plasma membrane levels. The serine/threonine liver kinase B1 (LKB1; also known as STK11) and AMP-activated protein kinase (AMPK) played a central role in this stimulation. In contrast, ataxia-telangiectasia mutated (ATM; a potential AMPK kinase) and hydroethidium (HEt)-oxidizing reactive oxygen species (ROS; increased in piericidin-A- and antimycin-A-treated cells) appeared not to be involved in the stimulation of glucose uptake. Treatment with mitochondrial inhibitors increased NAD+ and NADH levels (associated with a lower NAD+:NADH ratio) but did not affect the level of Glut1 acetylation. Stimulation of glucose uptake was greatly reduced by chemical inhibition of Sirt2 or mTOR-RAPTOR. We propose that mitochondrial dysfunction triggers LKB1-mediated AMPK activation, which stimulates Sirt2 phosphorylation, leading to activation of mTOR-RAPTOR and Glut1-mediated glucose uptake.

Neuregulin 1 Promotes Glutathione-Dependent Neuronal Cobalamin Metabolism by Stimulating Cysteine Uptake.

Neuregulin 1 (NRG-1) is a key neurotrophic factor involved in energy homeostasis and CNS development, and impaired NRG-1 signaling is associated with neurological disorders. Cobalamin (Cbl), also known as vitamin B12, is an essential micronutrient which mammals must acquire through diet, and neurologic dysfunction is a primary clinical manifestation of Cbl deficiency. Here we show that NRG-1 stimulates synthesis of the two bioactive Cbl species adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) in human neuroblastoma cells by both promoting conversion of inactive to active Cbl species and increasing neuronal Cbl uptake. Formation of active Cbls is glutathione- (GSH-) dependent and the NRG-1-initiated increase is dependent upon its stimulation of cysteine uptake by excitatory amino acid transporter 3 (EAAT3), leading to increased GSH. The stimulatory effect of NRG-1 on cellular Cbl uptake is associated with increased expression of megalin, which is known to facilitate Cbl transport in ileum and kidney. MeCbl is a required cofactor for methionine synthase (MS) and we demonstrate the ability of NRG-1 to increase MS activity, and affect levels of methionine methylation cycle metabolites. Our results identify novel neuroprotective roles of NRG-1 including stimulating antioxidant synthesis and promoting active Cbl formation.

Impact of phosphate on glyphosate uptake and toxicity in willow

Phosphate (PO43−) has been shown to increase glyphosate uptake by willow, a plant species known for its phytoremediation potential. However, it remains unclear if this stimulation of glyphosate uptake can result in an elevated glyphosate toxicity to plants (which could prevent the use of willows in glyphosate-remediation programs). Consequently, we studied the effects of PO43− on glyphosate uptake and toxicity in a fast growing willow cultivar (Salix miyabeana SX64). Plants were grown in hydroponic solution with a combination of glyphosate (0, 0.001, 0.065 and 1mgl−1) and PO43− (0, 200 and 400mgl−1). We demonstrated that PO43− fertilization greatly increased glyphosate uptake by roots and its translocation to leaves, which resulted in increased shikimate concentration in leaves. In addition to its deleterious effects in photosynthesis, glyphosate induced oxidative stress through hydrogen peroxide accumulation. Although it has increased glyphosate accumulation, PO43− fertilization attenuated the herbicide’s deleterious effects by increasing the activity of antioxidant systems and alleviating glyphosate-induced oxidative stress. Our results indicate that in addition to the glyphosate uptake, PO43− is involved in glyphosate toxicity in willow by preventing glyphosate induced oxidative stress.

Vermicompost from municipal sewage sludge affects growth and mineral nutrition of winter rye (Secale cereale) plants

ABSTRACTThe aim of the study was to investigate sewage sludge vermicompost application effects on growth and mineral nutrition of winter rye (Secale cereale L.) plants as compared to two initial levels of mineral nutrient availability, pure sand and sand enriched with inorganic nutrients at the optimal level. Addition of sewage sludge vermicompost significantly inhibited rye seed germination at 20 to 50% sand substitution independently on mineral nutrient supplement. Growth inhibition was evident at early stages of plant development. However, at the later stages, sewage sludge vermicompost acted both as mineral fertilizer and plant growth-promoting agent. Significant stimulation of mineral uptake was seen only at high rates of vermicompost substitution (40 and 50%) already causing decrease in shoot dry matter accumulation. Vermicompost substitution resulted in a significant increase of leaf chlorophyll content. Beneficial effect of sewage sludge vermicompost in conditions of optimal mineral supply can result mainly from plant growth-promoting activity.

Fatty acid transport and transporters in muscle are critically regulated by Akt2

Muscle contains various fatty acid transporters (CD36, FABPpm, FATP1, FATP4). Physiological stimuli (insulin, contraction) induce the translocation of all four transporters to the sarcolemma to enhance fatty acid uptake similarly to glucose uptake stimulation via glucose transporter-4 (GLUT4) translocation. Akt2 mediates insulin-induced, but not contraction-induced, GLUT4 translocation, but its role in muscle fatty acid transporter translocation is unknown. In muscle from Akt2-knockout mice, we observed that Akt2 is critically involved in both insulin-induced and contraction-induced fatty acid transport and translocation of fatty acid translocase/CD36 (CD36) and FATP1, but not of translocation of fatty acid-binding protein (FABPpm) and FATP4. Instead, Akt2 mediates intracellular retention of both latter transporters. Collectively, our observations reveal novel complexities in signaling mechanisms regulating the translocation of fatty acid transporters in muscle.

Lactobacillus acidophilus counteracts enteropathogenic E. coli-induced inhibition of butyrate uptake in intestinal epithelial cells.

Butyrate, a key short-chain fatty acid metabolite of colonic luminal bacterial action on dietary fiber, serves as a primary fuel for the colonocytes, ameliorates mucosal inflammation, and stimulates NaCl absorption. Absorption of butyrate into the colonocytes is essential for these intracellular effects. Monocarboxylate transporter 1 (MCT1) plays a major role in colonic luminal butyrate absorption. Previous studies (Tan J, McKenzie C, Potamitis M, Thorburn AN, Mackay CR, Macia L. Adv Immunol 121: 91-119, 2014.) showed decreased MCT1 expression and function in intestinal inflammation. We have previously shown (Borthakur A, Gill RK, Hodges K, Ramaswamy K, Hecht G, Dudeja PK. Am J Physiol Gastrointest Liver Physiol 290: G30-G35, 2006.) impaired butyrate absorption in human intestinal epithelial Caco-2 cells due to decreased MCT1 level at the apical cell surface following enteropathogenic E. coli (EPEC) infection. Current studies, therefore, examined the potential role of probiotic Lactobacilli in stimulating MCT1-mediated butyrate uptake and counteracting EPEC inhibition of MCT1 function. Of the five species of Lactobacilli, short-term (3 h) treatment with L. acidophilus (LA) significantly increased MCT1-mediated butyrate uptake in Caco-2 cells. Heat-killed LA was ineffective, whereas the conditioned culture supernatant of LA (LA-CS) was equally effective in stimulating MCT1 function, indicating that the effects are mediated by LA-secreted soluble factor(s). Furthermore, LA-CS increased apical membrane levels of MCT1 protein via decreasing its basal endocytosis, suggesting that LA-CS stimulation of butyrate uptake could be secondary to increased levels of MCT1 on the apical cell surface. LA-CS also attenuated EPEC inhibition of butyrate uptake and EPEC-mediated endocytosis of MCT1. Our studies highlight distinct role of specific LA-secreted molecules in modulating colonic butyrate absorption.

Is the β-cell the key for remission of diabetes after bariatric surgery?

Type 2 diabetes (T2D) is a major complication of obesity and an important global health problem, because of its high prevalence, causal relationship with serious medical complications, adverse effects on quality-of-life and economic impact due to increased health care costs and loss of productivity. The pathogenesis of T2D involves multi-organ insulin resistance, particularly insulin-resistant glucose metabolism in skeletal muscle (impaired insulin-mediated stimulation of glucose uptake) and the liver (impaired insulin-mediated suppression of glucose production), in conjunction with inadequate insulin secretion from pancreatic β-cells. Even though a large number of effective medications are available to treat T2D, approximately half of patients fail to achieve adequate glycaemic control, defined by the American Diabetes Association as HbA1c < 7%.

Mannitol alleviates chromium toxicity in wheat plants in relation to growth, yield, stimulation of anti-oxidative enzymes, oxidative stress and Cr uptake in sand and soil media

Chromium (Cr) is one of the most phytotoxic metals in the agricultural soils and its concentration is continuously increasing mainly through anthropogenic activities. Little is known on the role of mannitol (M) on plant growth and physiology under metal stress. The aim of this study was to investigate the mechanism of growth amelioration and antioxidant enzyme activities in Cr-stressed wheat (Triticum aestivum L. cv. Lasani 2008) by exogenously applied mannitol. For this, wheat seedlings were sown in pots containing soil or sand and subjected to increasing Cr concentration (0, 0.25 and 0.5mM) in the form of of K2Cr2O7 with and without foliar application of 100mM mannitol. Plants were harvested after four months and data regarding growth characteristics, biomass, photosynthetic pigments, and antioxidant enzymes were recorded. Mannitol application increased plant biomass, photosynthetic pigments and antioxidant enzymes while decreased Cr uptake and accumulation in plants as compared to Cr treatments alone. In this study, we observed that M applied exogenously to Cr-stressed wheat plants, which normally cannot synthesize M, improved their Cr tolerance by increasing growth, photosynthetic pigments and enhancing activities of antioxidant enzymes and by decreasing Cr uptake and translocation in wheat plants. From this study, it can be concluded that M could be used to grow crops on marginally contaminated soils for which separate remediation techniques are time consuming and not cost effective.

Unexpected stimulation of soil methane uptake as emergent property of agricultural soils following bio-based residue application.

Intensification of agriculture to meet the global food, feed, and bioenergy demand entail increasing re-investment of carbon compounds (residues) into agro-systems to prevent decline of soil quality and fertility. However, agricultural intensification decreases soil methane uptake, reducing, and even causing the loss of the methane sink function. In contrast to wetland agricultural soils (rice paddies), the methanotrophic potential in well-aerated agricultural soils have received little attention, presumably due to the anticipated low or negligible methane uptake capacity in these soils. Consequently, a detailed study verifying or refuting this assumption is still lacking. Exemplifying a typical agricultural practice, we determined the impact of bio-based residue application on soil methane flux, and determined the methanotrophic potential, including a qualitative (diagnostic microarray) and quantitative (group-specific qPCR assays) analysis of the methanotrophic community after residue amendments over 2months. Unexpectedly, after amendments with specific residues, we detected a significant transient stimulation of methane uptake confirmed by both the methane flux measurements and methane oxidation assay. This stimulation was apparently a result of induced cell-specific activity, rather than growth of the methanotroph population. Although transient, the heightened methane uptake offsets up to 16% of total gaseous CO2 emitted during the incubation. The methanotrophic community, predominantly comprised of Methylosinus may facilitate methane oxidation in the agricultural soils. While agricultural soils are generally regarded as a net methane source or a relatively weak methane sink, our results show that methane oxidation rate can be stimulated, leading to higher soil methane uptake. Hence, even if agriculture exerts an adverse impact on soil methane uptake, implementing carefully designed management strategies (e.g. repeated application of specific residues) may compensate for the loss of the methane sink function following land-use change.

Transcriptional remodeling in response to transfer upon carbon-limited or metformin-supplemented media in S. cerevisiae and its effect on chronological life span

One of the factors affecting chronological life span (CLS) in budding yeast is nutrient, especially carbon limitation. Aside from metabolites in the growth medium such as glucose, amino acids, and acetic acid, many pharmaceuticals have also been proven to alter CLS. Besides their impact on life span, these drugs are also prospective chemicals to treat the age-associated diseases, so the identification of their action mechanism and their potential side effects is of crucial importance. In this study, the effects of caloric restriction and metformin, a dietary mimetic pharmaceutical, on yeast CLS are compared. Saccharomyces cerevisiae cells grown in synthetic dextrose complete (SDC) up to mid-exponential phase were either treated with metformin or were subjected to glucose limitation. The impacts of these perturbations were analyzed via transcriptomics, and the common (stimulation of glucose uptake, induction of mitochondrial maintenance, and reduction of protein translation) and divergent (stimulation of aerobic respiration and reprogramming of respiratory electron transport chain (ETC)) cellular responses specific to each treatment were determined. These results revealed that both glucose limitation and metformin treatment stimulate CLS extension and involve the mitochondrial function, probably by creating an efficient mitochondria-to-nucleus signaling of either aerobic respiration or ETC signaling stimulation, respectively.

Coordinated Regulation of Vasopressin Inactivation and Glucose Uptake by Action of TUG Protein in Muscle

In adipose and muscle cells, insulin stimulates the exocytic translocation of vesicles containing GLUT4, a glucose transporter, and insulin-regulated aminopeptidase (IRAP), a transmembrane aminopeptidase. A substrate of IRAP is vasopressin, which controls water homeostasis. The physiological importance of IRAP translocation to inactivate vasopressin remains uncertain. We previously showed that in skeletal muscle, insulin stimulates proteolytic processing of the GLUT4 retention protein, TUG, to promote GLUT4 translocation and glucose uptake. Here we show that TUG proteolysis also controls IRAP targeting and regulates vasopressin action in vivo. Transgenic mice with constitutive TUG proteolysis in muscle consumed much more water than wild-type control mice. The transgenic mice lost more body weight during water restriction, and the abundance of renal AQP2 water channels was reduced, implying that vasopressin activity is decreased. To compensate for accelerated vasopressin degradation, vasopressin secretion was increased, as assessed by the cosecreted protein copeptin. IRAP abundance was increased in T-tubule fractions of fasting transgenic mice, when compared with controls. Recombinant IRAP bound to TUG, and this interaction was mapped to a short peptide in IRAP that was previously shown to be critical for GLUT4 intracellular retention. In cultured 3T3-L1 adipocytes, IRAP was present in TUG-bound membranes and was released by insulin stimulation. Together with previous results, these data support a model in which TUG controls vesicle translocation by interacting with IRAP as well as GLUT4. Furthermore, the effect of IRAP to reduce vasopressin activity is a physiologically important consequence of vesicle translocation, which is coordinated with the stimulation of glucose uptake.

Protective effect of butanol extracts of skin of Anguilla japonica against endoplasmic reticulum stress-induced insulin resistance via the AMPK pathway in L6 myotubes

The effect of butanol extracts of the skin of Anguilla japonica (BESA) on endoplasmic reticulum (ER) stress-induced insulin resistance in L6 myotubes was investigated. Western blotting revealed that BESA increased phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase, and stimulated glucose uptake in L6 myotubes. Stimulation of AMPK and glucose uptake by BESA were significantly (p<0.05) reduced by siRNA LKB1 or siRNA AMPK, compared with controls, suggesting that enhanced glucose uptake by BESA was predominantly accomplished via an LKB1-mediated AMPK activation pathway. In addition, BESA effectively reduced phosphorylation of ER stress markers, RNA-activated protein kinase-like ER resident kinase, JNK, and significantly (p<0.01) increased glucose uptake via AMPK activation in tunicamycin-treated L6 myotubes, compared with controls. Improvement of insulin sensitivity under ER stress conditions by BESA is predominantly accomplished via an LKB1-AMPK-dependent pathway.

6]-Gingerol Affects Glucose Metabolism by Dual Regulation via the AMPKα2-Mediated AS160-Rab5 Pathway and AMPK-Mediated Insulin Sensitizing Effects.

[6]-Gingerol has been used to control diabetes and dyslipidemia; however, its metabolic role is poorly understood. In this study, [6]-gingerol increased adenosine monophosphate (AMP)-activated protein kinase (AMPK) phosphorylation in mouse skeletal muscle C2C12 cells. Stimulation of glucose uptake by [6]-gingerol was dependent on AMPKα2. Moreover, both Inhibition and knockdown of AMPKα2 blocked [6]-gingerol-induced glucose uptake. [6]-Gingerol significantly decreased the activity of protein phosphatase 2A (PP2A). Inhibition of PP2A activity with okadaic acid enhanced the phosphorylation of AMPKα2. Moreover, the interaction between AMPKα2 and PP2A was increased by [6]-gingerol, suggesting that PP2A mediates the effect of [6]-gingerol on AMPK phosphorylation. In addition, [6]-gingerol increased the phosphorylation of Akt-substrate 160 (AS160), which is a Rab GTPase-activating protein. Inhibition of AMPKα2 blocked [6]-gingerol-induced AS160 phosphorylation. [6]-gingerol increased the Rab5, and AMPKα2 knockdown blocked [6]-gingerol-induced expression of Rab5, indicating AMPK play as an upstream of Rab5. It also increased glucose transporter 4 (GLUT4) mRNA and protein expression and stimulated GLUT4 translocation. Furthermore, insulin-mediated glucose uptake and Akt phosphorylation were further potentiated by [6]-gingerol treatment. This potentiation was not observed in the presence of AMPK inhibitor compound C. In summary, our results suggest that [6]-gingerol plays an important role in glucose metabolism via the AMPKα2-mediated AS160-Rab5 pathway and through potentiation of insulin-mediated glucose regulation.

The forgotten role of glucose effectiveness in the regulation of glucose tolerance.

Glucose effectiveness (SG) is the ability of glucose per se to stimulate its own uptake and to suppress its own production under basal/constant insulin concentrations. In an individual, glucose tolerance is a function of insulin secretion, insulin action and SG. Under conditions of declining insulin secretion and action (e.g. type 2 diabetes), the degree of SG assumes increasing significance in determining the level of glucose tolerance both in fasted and postprandial states. Although the importance of SG has been recognized for years, mechanisms that contribute to SG are poorly understood. Research data on modulation of SG and its impact in glucose intolerance is limited. In this review, we will focus on the role of SG in the regulation of glucose tolerance, its evaluation, and potential advantages of therapies that can enhance glucose-induced stimulation of glucose uptake and suppression of its own production in conditions of impaired insulin secretion and action.

The effect of different nitrogen sources on the symbiotic interaction between Sorghum bicolor and Glomus intraradices: Expression of plant and fungal genes involved in nitrogen assimilation

In the arbuscular mycorrhizal (AM) symbiosis, plants take up part of the nitrogen (N) through a mycorrhizal pathway. In this study, we assessed the effect of different N sources on the expression of genes coding for enzymes and transporters of the mycorrhizal N uptake pathway, using Sorghum bicolor and Glomus intraradices as a model. Some of the genes investigated were differentially regulated in the intraradical and in the extraradical mycelium depending on the N source. In AM roots, some fungal and plant genes were co-regulated, suggesting an interdependence of both partners in the mycorrhizal N uptake pathway. Mycorrhizal N transfer may have a preference for glycine (plant growth and N uptake stimulation).

Abnormalities of AMPK activation and glucose uptake in cultured skeletal muscle cells from individuals with chronic fatigue syndrome.

BackgroundPost exertional muscle fatigue is a key feature in Chronic Fatigue Syndrome (CFS). Abnormalities of skeletal muscle function have been identified in some but not all patients with CFS. To try to limit potential confounders that might contribute to this clinical heterogeneity, we developed a novel in vitro system that allows comparison of AMP kinase (AMPK) activation and metabolic responses to exercise in cultured skeletal muscle cells from CFS patients and control subjects.MethodsSkeletal muscle cell cultures were established from 10 subjects with CFS and 7 age-matched controls, subjected to electrical pulse stimulation (EPS) for up to 24h and examined for changes associated with exercise.ResultsIn the basal state, CFS cultures showed increased myogenin expression but decreased IL6 secretion during differentiation compared with control cultures. Control cultures subjected to 16h EPS showed a significant increase in both AMPK phosphorylation and glucose uptake compared with unstimulated cells. In contrast, CFS cultures showed no increase in AMPK phosphorylation or glucose uptake after 16h EPS. However, glucose uptake remained responsive to insulin in the CFS cells pointing to an exercise-related defect. IL6 secretion in response to EPS was significantly reduced in CFS compared with control cultures at all time points measured.ConclusionEPS is an effective model for eliciting muscle contraction and the metabolic changes associated with exercise in cultured skeletal muscle cells. We found four main differences in cultured skeletal muscle cells from subjects with CFS; increased myogenin expression in the basal state, impaired activation of AMPK, impaired stimulation of glucose uptake and diminished release of IL6. The retention of these differences in cultured muscle cells from CFS subjects points to a genetic/epigenetic mechanism, and provides a system to identify novel therapeutic targets.