Increase In Glycogen Content Research Articles

Disruption of Polyhydroxybutyrate Synthesis Redirects Carbon Flow towards Glycogen Synthesis in Synechocystis sp. PCC 6803 Overexpressing glgC/glgA.

The photoautotrophic Synechocystis sp. PCC 6803 (hereafter Synechocystis) is known for its α-polyglucan (glycogen) synthesis to serve as a carbon storage compound. In this study, the glgC- and glgA-overexpressing Synechocystis strain with the disruption of polyhydroxybutyrate (PHB) synthesis (▴GCAX-ΔBK) showed an increased glycogen production. This engineered strain had a high glycogen content of 38.3% (g g-1 dry cell weight) as compared with 27.4% in the phaA knockout strain (ΔBK) and 34.8% in the glgC/glgA-overexpressing strain (▴GCAX) after 20 d growth. Under nitrogen-deprived growth conditions for 3 d, the ▴GCAX-ΔBK strain showed a further increase in glycogen content from 27.0% to 36.0%. Furthermore, the engineered strains grown under ionic, osmotic or oxidative stress conditions had an increase of glycogen accumulation, whereas no increase was observed in the wild type. The maximum glycogen content was 54.0% in the ▴GCAX-ΔBK strain treated with 3 mM H2O2. The overall results indicated that in the absence of PHB synthesis, Synechocystis cells redirected the carbon flow towards the synthesis of glycogen as an alternative physiological responsive compound especially under stress conditions.

Thorium-induced Anatomical and Histopathological Changes in Liver of Swiss Mice

Present study is aimed to investigate the anatomical and histopathological changes in liver tissues of Swiss albino male mice, one month after intravenous administration of thorium (232Th; 4 and 40 mg/kg). Synchrotron X-ray micro-CT imaging, CD31 immuno-cytochemistry, hematoxylin & eosin staining and Periodic acid-Schiff staining were performed to study changes in liver anatomy, blood vessels/capillaries, histology and glycogen content of liver, respectively. Synchrotron X-ray micro-CT imaging of liver showed loss of blood vessels in mice treated with thorium (4 mg/kg), which was more prominent at higher dose of thorium (40 mg/kg). These thorium-induced changes in liver were correlated with the decrease in CD31 positive cells and loss of tissue architecture. A dose-dependent increase in glycogen content was also observed in the liver of thorium-treated mice. Our results provide novel insight about the effects of thorium on liver, which may have significant implications in understanding the mechanism of thorium thorium-induced hepatotoxicity.

Activation of the IGF1 receptor stimulates glycogen synthesis by mink uterine epithelial cells.

Glycogen synthesis by mink uterine epithelial cells is stimulated by estradiol (E2 ) during estrus, although the mechanism/s through which the steroid promotes glycogen accumulation are unknown. Our aim was to determine if insulin is required for E2 induced glycogen synthesis by an immortalized mink uterine epithelial cell line (GMMe). We show that the cells expressed the genes for glycogen metabolizing enzymes (hexokinase 1, glucose-6-phosphatase 3, glycogen synthase 1, and glycogen phosphorylase-muscle), receptors for insulin, insulin-like growth factor 1 and E2 (Esr1). Interestingly, treatment of cells with E2 alone failed to stimulate glycogen production, whereas supraphysiological concentrations of insulin (50 μg/ml) only, significantly increased glycogen content. Moreover, insulin + E2 increased glycogen content when compared to insulin alone (p < 0.05), an affect that was blocked when cells were treated with the pure E2 receptor antagonist ICI 182,780. Glycogen synthesis in response to insulin was significantly inhibited when cells were pre-treated with picropodophyllotoxin, an IGF1R antagonist. Treatment of cells with LY294002, a phosphatidylinositol 3-kinase (PI3K) antagonist, blocked insulin's effects on glycogen production whereas treatment with U0126, an inhibitor of mitogen activated kinase-kinase (MEK1/2) was without effect. These findings suggest to us that the affects of E2 on glycogen synthesis by GMMe cells is mediated through Esr1 and increased responsiveness of the cells to insulin. Because picropodophylotoxin blocked the effects of insulin on glycogen production, and both insulin and IGF1 act through PI3K, it is possible that IGF1 plays a role in glycogen production by these cells.

A Novel Role for the Na‐K‐2Cl Cotransporter in Mitochondrial Respiration

A patient recruited by the undiagnosed disease program (UDP) at the NIH suffers from multi organ failure and deficits in energy homeostasis. The multi organ failure consists of complete gastrointestinal and bladder dysfunction, as well as thyroid, parathyroid, adrenal, and pancreatic deficiencies. The deficits in energy homeostasis were evidenced in lab tests conducted on the patient's muscle and liver biopsies, where there was an abnormal increase in glycogen content and mitochondrial DNA copy number. Whole exome sequencing showed that the patient expresses a de novo mutation in an allele of the Slc12a2 gene encoding the Na‐K‐2Cl cotransporter‐1 (NKCC1). Previous studies in the laboratory demonstrated that the 11 base pair deletion causing a truncation of the carboxyl‐terminus, leads to a non‐functional transporter. We have also demonstrated that the UDP patient's fibroblasts displayed reduced total NKCC1‐mediated K+ influx. Additionally, trafficking studies in transfected HEK293 cells expressing the NKCC1 truncation mutation have revealed that this mutated protein dimerizes with wild‐type (WT) NKCC1 and is trafficked to the plasma membrane along with WT NKCC1.To address a possible role of the cotransporter in metabolism, I utilized fibroblasts isolated from the patient and from healthy controls and performed mitochondrial respiration stress tests. I showed that mitochondrial respiration and ATP production was significantly higher in the patient's fibroblasts. Because the cells from the patient might carry additional mutations, I transfected MDCK cells with EGFP‐tagged wild‐type or mutant transporter, sorted the cells, and tested them. Cells expressing the mutant cotransporter also demonstrated higher mitochondrial respiration, compared to cells expressing wild‐type EGFP‐NKCC1.To further confirm the role of NKCC1 in mitochondrial respiration, I subjected control MDCK cells to bumetanide, a NKCC1 specific inhibitor. MDCK cells treated with 20 mM bumetanide for 20 min also demonstrated an increase in mitochondrial respiration. To further assess whether this effect in mitochondrial respiration is NKCC1 specific, I subjected bumetanide to two stable lines of MDCK cells (LK‐A3 and LK‐C1) that carry a distinct mutation in NKCC1, resulting in a non‐functional transporter. There was no change in mitochondrial respiration levels in these cells, which indicated that the rise in mitochondrial respiration levels in wild‐type cell is NKCC1 specific. These data reveal a novel role for NKCC1 in mitochondrial respiration. Future work will address the mechanism by which NKCC1 activity affects mitochondrial function.Support or Funding InformationSupported by NIH grants R21GM118944 and RO1DK093501This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Elevated GLUT4 and glycogenin protein abundance correspond to increased glycogen content in the soleus muscle of mdx mice with no benefit associated with taurine supplementation.

Duchenne muscular dystrophy (DMD) patients and the dystrophic mdx mouse have an elevated demand for ATP requiring processes, including Ca2+ regulation and skeletal muscle regeneration. As a key substrate for cellular ATP production, altered glycogen metabolism may contribute significantly to dystrophic pathology and explain reports of mild glucose intolerance. We compare the soleus and extensor digitorum longus (EDL) muscles of the mdx mouse during active muscle necrosis (at 28 days) and at 70 days where pathology is stable. We further investigate the impact of taurine (tau) on dystrophic glycogen metabolism to identify if the benefit seen with tau in a previous study (Barker et al. 2017) was in part owed to altered glycogen handling. The soleus muscle of 28‐ and 70‐day‐old mdx mice had elevated glucose transporter type 4 (GLUT4), glycogenin protein abundances and glycogen content compared to WT (C57BL10/ScSn) controls. Mdx tau mice exhibited modestly reduced glycogen compared to their respective mdx group. The EDL muscle of 28 days mdx tau mice had a ~70% increase in glycogenin protein abundance compared to the mdx but 50% less glycogen content. A twofold greater phosphorylated glycogen synthase (p‐GS) and glycogen phosphorylase (p‐GP) protein abundance was observed in the 70‐day‐old mdx soleus muscle than in the 28‐day‐old mdx soleus muscle. Glycogen debranching enzyme (GDE) protein abundance was elevated in both 28‐ and 70‐day‐old mdx soleus muscles compared to WT controls. We identified an increase in proteins associated with glucose uptake and utilization specific to the predominantly slow‐twitch soleus muscle of mdx mice regardless of age and that taurine affords no obvious benefit to glycogen metabolism in the mdx mouse.

Silymarin prevents lipid accumulation in the liver of rats with type 2 diabetes via sirtuin1 and SREBP-1c.

In this study, we have investigated whether silymarin intake influences lipid and glycogen content in conjunction with sirtuin1 (SIRT1) and sterol regulatory element-binding protein 1c (SREBP-1c) expressions in liver of type 2 diabetic rat. Thirty-six male Wistar rats were randomly divided into six groups: control groups (C) and diabetic groups (D); the control groups received 60 or 120 mg/kg silymarin (C+S60 or C+S120), and the diabetic groups received 60 or 120 mg/kg silymarin (D+S60 or D+S120) daily for 8 weeks. Serum biochemical parameters, as well as glycogen, lipid and oxidative stress biomarkers, in the liver tissue were measured by spectrophotometric methods. Additionally, SIRT1 and SREBP-1c messenger RNA (mRNA) expressions were evaluated by quantitative polymerase chain reaction. Diabetes caused a significantly increased fasting blood sugar, homeostasis model assessment for insulin resistance, liver total cholesterol and triglyceride (TG) content, which were attenuated after the administration of silymarin. Dietary silymarin caused the improvement of lipid content in the liver of diabetic rats. Moreover, silymarin administration promoted SIRT1, suppressed SREBP-1c mRNA expression, reduced liver nitric oxide and protein carbonyl content, and increased liver glycogen, catalase and glutathione peroxidase activity. Furthermore, histopathological changes were improved in the treated groups. Silymarin administration considerably restored hepatic changes induced by streptozotocin and nicotinamide. The upregulation of SIRT1 mRNA expression by silymarin may be associated with decreased lipid, increased glycogen content and downregulation of the SREBP-1c gene in the liver.

The evolution of eccrine sweat glands in human and nonhuman primates

Sweating is an unusual thermoregulatory strategy for most mammals, yet is critical for humans. This trait is commonly hypothesized to result from human ancestors moving from a forest to a warmer and drier open environment. As soft tissue traits do not typically fossilize, this idea has been difficult to test. Therefore, we used a comparative approach to examine 15 eccrine gland traits from 35 primate species. For each trait we measured phylogenetic signal, tested three evolutionary models to explain trait variation, and used phylogenetic models to examine how traits varied in response to climate variables. Phylogenetic signal in traits varied substantially, with the two traits exhibiting the highest values being gland distribution on the body and percent eccrine vs. apocrine glands on the body. Variation in most traits was best explained by an Ornstein-Uhlenbeck model suggesting the importance of natural selection. Two traits were strongly predicted by climate. First, species with high eccrine gland glycogen content were associated with habitats exhibiting warm temperatures and low rainfall. Second, species with increased capillarization were associated with high temperature. Glycogen is a primary energy substrate powering sweat production and sodium reabsorption in the eccrine gland, and increased capillarization permits greater oxygen, glucose and electrolyte delivery. Thus, our results are evidence of natural selection for increased sweating capacity in primate species with body surface eccrine glands living in hot and dry climates. We suggest that selection for increased glycogen content and capillarization may have been part of initial increases in hominin thermoregulatory sweating capacity.

GNIP1 E3 ubiquitin ligase is a novel player in regulating glycogen metabolism in skeletal muscle

BackgroundGlycogenin-interacting protein 1 (GNIP1) is a tripartite motif (TRIM) protein with E3 ubiquitin ligase activity that interacts with glycogenin. These data suggest that GNIP1 could play a major role in the control of glycogen metabolism. However, direct evidence based on functional analysis remains to be obtained. ObjectivesThe aim of this study was 1) to define the expression pattern of glycogenin-interacting protein/Tripartite motif containing protein 7 (GNIP/TRIM7) isoforms in humans, 2) to test their ubiquitin E3 ligase activity, and 3) to analyze the functional effects of GNIP1 on muscle glucose/glycogen metabolism both in human cultured cells and in vivo in mice. ResultsWe show that GNIP1 was the most abundant GNIP/TRIM7 isoform in human skeletal muscle, whereas in cardiac muscle only TRIM7 was expressed. GNIP1 and TRIM7 had autoubiquitination activity in vitro and were localized in the Golgi apparatus and cytosol respectively in LHCN-M2 myoblasts. GNIP1 overexpression increased glucose uptake in LHCN-M2 myotubes. Overexpression of GNIP1 in mouse muscle in vivo increased glycogen content, glycogen synthase (GS) activity and phospho-GSK-3α/β (Ser21/9) and phospho-Akt (Ser473) content, whereas decreased GS phosphorylation in Ser640. These modifications led to decreased blood glucose levels, lactate levels and body weight, without changing whole-body insulin or glucose tolerance in mouse. ConclusionGNIP1 is an ubiquitin ligase with a markedly glycogenic effect in skeletal muscle.

ВЛИЯНИЕ МНОГОКОМПОНЕНТНОГО РАСТИТЕЛЬНОГО СРЕДСТВА НА ФИЗИЧЕСКУЮ ВЫНОСЛИВОСТЬ В ТЕСТЕ ВЫНУЖДЕННОГО ПЛАВАНИЯ

The effect of preventive administration of the complex phytopreparation "tetraphyton" has been studied in experiments on rats. Tetraphyton developed on the base of Tibetan formula is the dry extract derived from species of plant material: roots of Inula helenium L., roots of Zingiber officinale Roscoe, fruits of Elletaria cardamomum (L.) Maton, offshoots of Caragana spinosa (L.) Wall. ex Hornem., characterized for the content of phenolic compounds, flavonoids, terpenoids. The preventive course introduction of tetraphyton in a dose 100 mg/kg for 7 days before experiment increases the potential for physical performance, increasing overall physical endurance against a background of intense physical exertion by 73 % (p < 0.05), prevents fatigue. It is shown that increase in the physical performance of rats in the experimental group is due to increase in the efficiency of the energy supply system in skeletal muscles and myocardium: a significant increase in the content of ATP (by 13 % and 2.5 times); decrease in lactate and pyruvate content (by 33 and 30 %; p < 0.05); increased glycogen content in the liver by 23 %, blood glucose by 19 %. The increase in catalase, SOD, and gSh levels (5 %, 19 %, 79 %; p < 0.05) indicates an increase in the power of the antioxidant defense of the organism and causes the cytoprotective effect of tetraphyton, confirmed by a decrease in fermentemia (lactate dehydrogenase, kreatinphosphokinase - 49 % and 43 %; p < 0.05). The main molecular-cellular mechanisms of the actoprotective action of the phytoadaptogen is the inhibition of the lipid peroxidation of cell membranes and a significant increase in the capacity of the endogenous antioxidant enzyme system that promotes the preservation of the integrity of skeletal muscles and the myocardium. This is due to the presence of phenolic compounds in the chemical composition that have direct antiradical action and increase the power endogenous antioxidant system.

Comparison betweent the Effects of Swimming and Treadmill-Based Aerobic Training Protocols in Diabetic Rats

Abstract Background: Type 1 diabetes mellitus (DM1) can cause damage to several physiological systems. Objectives: To compare and characterize the effects of aerobic exercise training (ET) performed by swimming with those of ET performed on a treadmill on the skeletal muscle and heart of rats with DM1. Methods: 41 male Wistar rats were randomized into four groups: nondiabetic control (CTR), diabetic control (DMC), diabetic trained on the treadmill (DMT), and diabetic trained by swimming (DMS). The trained groups performed aerobic exercise training for 8 weeks, 5 times a week, 60 min per day. Exercise tolerance, blood glucose, body weight, wet weight of the skeletal muscles and left ventricle (LV), muscle glycogen, cross-sectional area of skeletal muscles, and cross-sectional diameter and collagen volume fraction of the LV were evaluated. Results: The results were expressed as mean ± standard deviation of the mean and submitted to two-way ANOVA with post-hoc Bonferroni test. Aerobic ET protocols applied to animals with DM1, regardless of the ergometer, showed satisfactory results (p < 0.05) when compared to the control groups: improved exercise tolerance, increased glycogen content of the soleus and extensor digitorum longus (EDL) muscles and increased cross-sectional diameter of the left ventricular cardiomyocytes. In some variables, such as exercise tolerance and cross-sectional area of the soleus and EDL muscles, DMT showed better results than DMS (p < 0.05). On the other hand, DMS showed increased cross-sectional diameter of cardiomyocytes when compared with the DMT group. Conclusion: Both aerobic ET protocols offered benefits to animals with diabetes; however, due to the specific characteristics of each modality, different physiological adaptations were observed between the trained groups.

No Superior Adaptations to Carbohydrate Periodization in Elite Endurance Athletes.

The present study investigated the effects of periodic carbohydrate (CHO) restriction on endurance performance and metabolic markers in elite endurance athletes. Twenty-six male elite endurance athletes (maximal oxygen consumption (V˙O2max), 65.0 mL O2·kg·min) completed 4 wk of regular endurance training while being matched and randomized into two groups training with (low) or without (high) CHO manipulation 3 d·wk. The CHO manipulation days consisted of a 1-h high-intensity bike session in the morning, recovery for 7 h while consuming isocaloric diets containing either high CHO (414 ± 2.4 g) or low CHO (79.5 ± 1.0 g), and a 2-h moderate bike session in the afternoon with or without CHO. V˙O2max, maximal fat oxidation, and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 min of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and β-hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b), and phosphorylated acetyl-CoA carboxylase (pACC). The training effects were similar in both groups for all parameters. On average, V˙O2max and power output during the 30-min TT increased by 5% ± 1% (P < 0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18% ± 5%), CS activity (11% ± 5%), and pACC (38% ± 19%; P < 0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged. Superimposing periodic CHO restriction to 4 wk of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.

In ovo feeding of nutrients and its impact on post-hatching water and feed deprivation up to 48hr, energy status and jejunal morphology of chicks using response surface models.

A Box-Behnken design (BBD) in a response surface methodology (RSM) was used to investigate the response of broiler chicks to in ovo feeding (IOF) of beta-hydroxy beta-methylbutyrate (HMB), dextrin and the timing of the first water and feed deprivation. On day 18th of incubation, 1,500 eggs were randomly assigned to 15 experimental runs of BBD, each with 4 replicates, as 3 levels IOF of HMB (0%, 0.5% and 1%) and dextrin (0%, 20% and 40%), and 3 levels of the first water and feed deprivation (6, 27 and 48hr). Day-old chicks from each replicate were then used to assess the effect of IOF and time first water and feed access on chick's responses. The IOF of dextrin leads to respectively 9.7%-15.5% lower hatchability for 20% and 40% inclusion (p<.05), whereas HMB inclusion appeared with no effect on hatchability (p>.05). Administration of dextrin or HMB into the amnion of embryos elevated length, width and surface area of villus, and increased glycogen content of liver and breast (p<.05). In all parameter models, the linear terms showed highest contribution (R2 =0.81-0.97) to explain existing variation in chick's responses. The first water and feed deprivation had largest effect on BW2 and glycogen content of liver and breast. It is concluded that if possible, place chicks before 7hr of hatch to preserve BW loss and have maximum response from IOF. If not possible, use IOF with 40% dextrin+0.5% HMB to preserve gut integrity and energy status up to 48hr. This should give advantage to chicks to recover fast after feeding, but that would have to be confirmed by trials growing birds to slaughter age.

A simple and rapid method for the preparation of pure delphinidin-3-O-sambubioside from Roselle and its antioxidant and hypoglycemic activity

The present study aimed to establish a simple and rapid method for the preparation of pure delphinidin-3-O-sambubioside (D3S) from Roselle and then investigate its antioxidant and hypoglycemic activity. According to our results, 60 mg of D3S with the purity of 96.1% was finally isolated from 500 g of Roselle by combination of macroporous resins and C18 Sep-Pak cartridge techniques. Further studies revealed that D3S could significantly attenuate H2O2-induced oxidative stress by inhibiting H2O2-induced ROS overproduction, GSH depletion, mitochondrial membrane potential decrease and mitochondrial membrane peroxidation. In addition, we also found that D3S at the concentrations of 20 μg/mL and 40 μg/mL are able to promote glucose consumption and increase glycogen content in human liver HepG2 cells. These results indicated that D3S possesses potent antioxidant activity and hypoglycemic activity. Overall, our studies suggest that D3S could be a valuable material for designing functional foods against oxidative stress-related diseases and diabetes.

Glycogen phosphorylase inhibition improves beta cell function.

Glycogen phosphorylase (GP) is the key enzyme for glycogen degradation. GP inhibitors (GPi-s) are glucose lowering agents that cause the accumulation of glucose in the liver as glycogen. Glycogen metabolism has implications in beta cell function. Glycogen degradation can maintain cellular glucose levels, which feeds into catabolism to maintain insulin secretion, and elevated glycogen degradation levels contribute to glucotoxicity. The purpose of this study was to assess whether influencing glycogen metabolism in beta cells by GPi-s affects the function of these cells. The effects of structurally different GPi-s were investigated on MIN6 insulinoma cells and in a mouse model of diabetes. GPi treatment increased glycogen content and, consequently, the surface area of glycogen in MIN6 cells. Furthermore, GPi treatment induced insulin receptor β (InsRβ), Akt and p70S6K phosphorylation, as well as pancreatic and duodenal homeobox 1(PDX1) and insulin expression. In line with these findings, GPi-s enhanced non-stimulated and glucose-stimulated insulin secretion in MIN6 cells. The InsRβ was shown to co-localize with glycogen particles as confirmed by in silico screening, where components of InsR signalling were identified as glycogen-bound proteins. GPi-s also activated the pathway of insulin secretion, indicated by enhanced glycolysis, mitochondrial oxidation and calcium signalling. Finally, GPi-s increased the size of islets of Langerhans and improved glucose-induced insulin release in mice. These data suggest that GPi-s also target beta cells and can be repurposed as agents to preserve beta cell function or even ameliorate beta cell dysfunction in different forms of diabetes. This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Supplementation of glycerol or fructose via drinking water to grazing lambs on tissue glycogen level and lipogenesis.

Lambs ( = 18; 40.1 ± 7.4 kg BW) were used to assess supplementation of glycerol or fructose via drinking water on growth, tissue glycogen levels, postmortem glycolysis, and lipogenesis. Lambs were blocked by BW and allocated to alfalfa paddocks (2 lambs/paddock and 3 paddocks/treatment). Each paddock within a block was assigned randomly to drinking water treatments for 30 d: 1) control (CON), 2) 120 g fructose/L of drinking water (FRU), or 3) 120 g glycerol/L of drinking water (GLY). Lambs grazed alfalfa with free access to water treatments for 28 d and then were fasted in indoor pens for a final 2 d with access to only water treatments. Data were analyzed using the MIXED procedure of SAS with water treatment and time (when appropriate) in the model. During the 28-d grazing period, ADG was greater ( < 0.05) for GLY than for CON or FRU. During the 2-d fasting period, BW shrink was lower ( < 0.05) for GLY compared with CON or FRU. Hot carcass weight was greater ( < 0.05) for GLY than for FRU. The interaction for glycogen content × postmortem time was significant ( = 0.003) in LM and semitendinosus (ST) muscles. Glycogen content in the LM was greater ( < 0.05) for GLY at 2 and 3 h and for FRU at 1 h postmortem compared with CON. Glycogen content in ST did not differ between treatments ( > 0.05). Liver glycogen content was over 14-fold greater ( < 0.05) for GLY compared with FRU or CON. Liver free glucose was greater ( < 0.05) for GLY than for CON, whereas liver lipid content was higher ( < 0.05) for CON than for GLY. Supplementation with GLY increased ( < 0.05) odd-chain fatty acids in LM, subcutaneous fat (SQ), and the liver. Stearic acid (C18:0) concentrations were reduced in LM ( = 0.064) and subcutaneous adipose tissue (SQ; = 0.018), whereas oleic acid (C18:1 -9) concentration tended to be increased ( = 0.066) in SQ with FRU and GLY. Linolenic acid (C18:3 -3) was reduced ( = 0.031) and all long-chain -3 fatty acid (eicosapentaenoic acid, docosapentaenoic acid, and docosahexaenoic acid) concentrations were increased ( < 0.05) with FRU and GLY compared with CON. Glycerol supplementation upregulated ( < 0.05) stearoyl-CoA desaturate () and fatty acid synthase () mRNA by over 40-fold in the SQ and 5-fold in the liver. Glycerol supplementation also upregulated ( < 0.05) glucose transporters and glycogen branching enzyme in the liver. Overall, glycerol supplementation improved growth, reduced BW shrink during fasting, increased glycogen content in muscle and the liver, and stimulated de novo lipogenesis.

The galactose-induced decrease in phosphate levels leads to toxicity in yeast models of galactosemia

Classic galactosemia is an inborn error of metabolism caused by deleterious mutations in the GALT gene. A number of evidences indicate that the galactose-1-phosphate accumulation observed in patient cells is a cause of toxicity in this disease. Nevertheless, the consequent molecular events caused by the galactose-1-phosphate accumulation remain elusive. Here we show that intracellular inorganic phosphate levels decreased when yeast models of classic galactosemia were exposed to galactose. The decrease in phosphate levels is probably due to the trapping of phosphate in the accumulated galactose-1-phosphate since the deletion of the galactokinase encoding gene GAL1 suppressed this phenotype. Galactose-induced phosphate depletion caused an increase in glycogen content, an expected result since glycogen breakdown by the enzyme glycogen phosphorylase is dependent on inorganic phosphate. Accordingly, an increase in intracellular phosphate levels suppressed the galactose effect on glycogen content and conferred galactose tolerance to yeast models of galactosemia. These results support the hypothesis that the galactose-induced decrease in phosphate levels leads to toxicity in galactosemia and opens new possibilities for the development of better treatments for this disease.

Effects of glucose and insulin administration on glucose transporter expression in the North Pacific spiny dogfish (Squalus suckleyi)

Elasmobranchs (sharks, skates, and rays) are a primarily carnivorous group of fish, consuming few carbohydrates. Further, they tend to exhibit delayed responses to glucose and insulin administration in vivo relative to mammals, leading to a presumption of glucose-intolerance. To investigate the glucoregulatory capabilities of the spiny dogfish (Squalus suckleyi), plasma glucose concentration, muscle and liver glycogen content, and glucose transporter (glut1 and 4) mRNA levels were measured following intra-arterial administration of bovine insulin (10ngkg−1) or an approximate doubling of fasting plasma glucose concentration. Within 6h, following glucose administration, approximately half of the introduced glucose load had been cleared, with control levels being restored by 24h post-injection. It was determined that plasma clearance was due in part to increased uptake by the tissues as muscle and liver glycogen content increased significantly, correlating with an upregulation of glut mRNA levels. Following administration of bovine insulin, plasma glucose steadily decreased through 18h before returning toward control levels. Observed decreases in plasma glucose following insulin injection were, however, relatively minor, and no increases in tissue glycogen content were observed. glut4 and glycogen synthase mRNA levels did significantly increase in the muscle in response to insulin, but no changes occurred in the liver. The responses observed mimic what occurs in mammals and teleosts, thus suggesting a conserved mechanism for glucose homeostasis in vertebrates and a high degree of glucose tolerance in these predominantly carnivorous fish.

Diastolic Dysfunction in Diabetic Cardiomyopathy is Linked with Cardiomyocyte Glucose Storage and Metabolic Signalling Abnormality

Diabetic cardiomyopathy is characterised by diastolic dysfunction but the underlying mechanisms remain unknown. Dysregulated cardiomyocyte glucose handling and metabolism in diabetes plays an important role in the cardiac pathology. The aim of this study was to investigate the role of disturbances in cardiac glucose handling and AMPK (key metabolic regulator) signalling in the development of diabetic cardiomyopathy. Mice with diet-induced obesity and insulin resistance (high fat diet (HFD) vs AIN93G control, 15 weeks) were evaluated for systemic glucose tolerance, cardiac function (echocardiography), cardiac glycogen (enzymatic assay) and protein expression (immunoblot). Neonatal rat ventricular myocytes (NRVMs) were cultured in normal (5 mM) or high (30 mM) glucose for 24 hours with AMPK agonist treatment (AICAR, 1 mM, 30 min). HFD-fed mice exhibited increased body weight (27%, p < 0.01) and decreased glucose tolerance. Diastolic dysfunction in HFD mice was evidenced by increased E/E’ (39%, p < 0.05) and positively correlated with body weight and glucose intolerance. Glycogen content was increased in the hearts of HFD mice (46%, p < 0.05), associated with decreased phosphorylation of AMPK (Thr172, 23%, p < 0,05). No changes in glycogen synthase or phosphorylase protein expression/phosphorylation were observed. NRVMs exposed to high glucose similarly exhibited increased glycogen content (36%, p < 0.05) which was unaffected by AMPK activation via AICAR. This study is the first to show that diastolic dysfunction correlates with cardiomyocyte glucose metabolism in an obese, insulin resistant setting. These findings identify that disturbance of cardiomyocyte glucose storage plays a role in diabetic cardiopathology. Further investigation of AMPK and alternative (novel) signalling pathways in this setting is warranted.

Long-term treatment with insulin and retinoic acid increased glucose utilization in L6 muscle cells via glycogenesis.

The skeletal muscle regulates glucose homeostasis. Here, the effects of vitamin A metabolites including retinoic acid (RA) alone, and in combination with insulin, on glucose utilization were investigated in rat L6 muscle cells during the differentiation process. L6 cells were treated with differentiation medium containing retinol, retinal, RA, and (or) insulin. The glucose levels and pH values in the medium were measured every 2 days. The expression levels of insulin signaling and glycogen synthesis proteins, as well as glycogen content were determined. Retinal and RA reduced the glucose content and pH levels in the medium of the L6 cells. RA acted synergistically with insulin to reduce glucose and pH levels in the medium. The RA- and insulin-mediated reduction of glucose in the medium only occurred when glucose levels were at or above 15 mmol/L. Insulin-induced phosphorylation of Akt Thr308 was further enhanced by RA treatment through the activation of retinoic acid receptor. RA acted synergistically with insulin to phosphorylate glycogen synthase kinase 3β, and dephosphorylate glycogen synthase (GS), which was associated with increases in the protein and mRNA levels of GS. Increases in glycogen content were induced by insulin, and was further enhanced in the presence of RA. We conclude that activation of the RA signaling pathway enhanced insulin-induced glucose utilization in differentiating L6 cells through increases in glycogenesis.

Optic nerve energy metabolism: the role of astrocyte glycogen

SummaryGlycogen is a glucose storage molecule. We studied the physiology and functions of glycogen in CNS white matter using acutely isolated mouse optic nerve (MON), a typical CNS white matter tract. Glycogen is present in MON astrocytes. Aglycemia caused loss of the stimulus evoked compound action potential (CAP) after ~15 min. CAP decline coincided with exhaustion of usable tissue glycogen. Increasing glycogen content prolonged the latency to decline onset and, conversely, decreasing glycogen shortened this latency. Metabolic support provided by glycogen during aglycemia was abolished by an inhibitor of glycogen breakdown (DAB). The MON has a high resting level of extracellular lactate (~0.6 mM). The metabolic support provided by glycogen during aglycemia is abolished by an inhibitor of glycogen breakdown (DAB) in MON. Both tissues exhibit high levels of extracellular lactate ([Lactate−]o), up to 50% of which derives from glycogen. During aglycemia, glycogen in astrocytes is metabolized to lactate and ‘shuttled’ to axons (and possibly oligodendrocytes) to support oxidative energy metabolism. Glycogen breakdown and lactate transport to axons is also needed to sustain brief periods of intense axonal discharge.