Impaired Glycogen Synthesis Research Articles

Sarcopenia Prevalence in Liver Cirrhosis Patients Using MRI and Handgrip Strength Measurements

Background: Cirrhosis, a leading cause of mortality worldwide, is histologically represented as formation of regenerative nodules encircled by fibrous bands caused by chronic liver injury. Nutritional status in cirrhotic patients is challenging to assess due to fluid accumulation resulting from impaired protein synthesis. Factors such as reduced food intake, malabsorption, and altered macronutrient metabolism negatively impact the nutritional status, leading to sarcopenia. The development of sarcopenia is multifactorial and is linked to lower survival rates. Aim: To assess sarcopenia prevalence in liver cirrhosis patients using MRI and handgrip strength measurements. Discussion: Impaired food intake in liver cirrhosis results from a combination of factors including loss of appetite, hormonal changes, early satiety, ascites, nausea, taste disturbances, and functional dyspepsia. Malabsorption can also occur due to portosystemic shunting, reduced bile production, chronic pancreatitis, and small intestinal bacterial overgrowth, all of which contribute to sarcopenia. It also arises from complex interactions involving impaired glycogen synthesis, inadequate nutrition, disrupted skeletal muscle protein synthesis and underlying hypermetabolism. Conclusion: MRI-based assessments indicate there is a significant occurrence of sarcopenia in individuals with cirrhosis. Our findings reveal that handgrip strength, when correlated with MRI results, is a reliable predictor of sarcopenia in these patients.

Berberine Ameliorates Hepatic Insulin Resistance by Regulating microRNA-146b/SIRT1 Pathway.

ObjectiveHepatic insulin resistance is a major initiating factor for type 2 diabetes mellitus. In previous study, Gegen Qinlian Decoction containing berberine could enhance hepatic insulin sensitivity by SIRT1-dependent deacetylation of FOXO1. However, it is not clear whether berberine also can improve hepatic insulin sensitivity by SIRT1/FOXO1 pathway. This study aimed to evaluate the efficacy of berberine for improving hepatic insulin resistance and the possible molecular mechanisms involved.MethodsIn vitro, HepG2 cells were induced with palmitic acid, and glycogen synthesis was examined. In vivo, a high-fat diet (HFD)-fed mouse model was established, and metabolic parameters were assessed. The expressions of miR-146b and sirtuin 1 (SIRT1) in liver were also examined. The relationship between miR-146b and SIRT1 was examined by the dual-luciferase reporter gene assay.ResultsSerum biochemical parameters, such as glucose and HOMA-IR index, were increased in HFD mice; miR-146b and SIRT1 were abnormally expressed in HFD mice and palmitic acid-treated HepG2 cells. Interestingly, berberine reduced body weight and caused a significant improvement in glucose tolerance and HOMA-IR index without altering food intake in mice. Overexpression of miR-146b abolished the protective effect of berberine on palmitic acid-induced impaired glycogen synthesis in HepG2 cells. Luciferase assay showed that miR-146b directly targeted SIRT1.ConclusionThe present findings suggest that berberine could attenuate hepatic insulin resistance through the miR-146b/SIRT1 pathway, which may represent a potential therapeutic target for the prevention and treatment of metabolic diseases, particularly diabetes.

Gene Expression of GSK3 in Type II Diabetics Compared to Non-Diabetics (ex vivo)

Background: GSK3 is a serine/threonine kinase that is involved in the storage of glucose into glycogen through the negative regulation of glycogen synthase. Defects in GSK3 and glycogen synthase function are early stages of the development of insulin resistance, which may cause impaired glycogen synthesis in Type II diabetes. Methods: In this cross-sectional study, the gene expression level of GSK3 from Type II diabetic and non-diabetic participants was compared via real-time RT-PCR. To investigate the relationships between GSK3 expression and indicators of insulin resistance, Pearson's correlation analysis was performed. To compare the differences between GSK3 expression levels based on BMI categories, one-way ANOVA was used. Results: Gene expression of GSK3 was slightly higher in diabetic participants compared to non-diabetics, but it was statistically insignificant. Also, no significant difference was found based on BMI categories in the two groups. No significant association between GSK3 expression and indicators of insulin resistance was observed in non-diabetic participants. There was only a positive significant correlation between GSK3 expression and FBS in diabetic participants. Conclusion: These results indicate that the regulation of GSK3 may occur at the translation level, as gene expression level was unaltered between diabetic and non-diabetic participants. Also, since circulating levels of both glucose and insulin regulate GSK3 activity, tissue specificity for the expression and post-translation regulations of GSK3 may exist, which cause hyperactivation or overexpression in some target tissues in diabetes. Furthermore, it is probable that glycogen synthase activity is also regulated by non-insulin mediated mechanisms like exercise or allosteric changes, independent of GSK3 expression.

Dynamic Inventory of Intermediate Metabolites of Cyanobacteria in a Diurnal Cycle.

SummaryCyanobacteria are gaining importance both as hosts for photoautotrophic production of chemicals and as model systems for studies of diurnal lifestyle. The proteome and transcriptome of cyanobacteria have been closely examined under diurnal growth, whereas the downstream effects on the intermediary metabolism have not received sufficient attention. The present study focuses on identifying the cellular metabolites whose inventories undergo dramatic changes in a fast-growing cyanobacterium, Synechococcus elongatus PCC 11801. We identified and quantified 67 polar metabolites, whose inventory changes significantly during diurnal growth, with some metabolites changing by 100-fold. The Calvin-Benson-Bassham cycle intermediates peak at midday to support fast growth. The hitherto unexplored γ-glutamyl peptides act as reservoirs of amino acids. Interestingly, several storage molecules or their precursors accumulate during the dark phase, dispelling the notion that all biosynthetic activity takes place in the light phase. Our results will guide metabolic modeling and strain engineering of cyanobacteria.

CDK5RAP3 Deficiency Restrains Liver Regeneration after Partial Hepatectomy Triggering Endoplasmic Reticulum Stress

CDK5 regulatory subunit-associated protein 3 (CDK5RAP3) plays a crucial role in mammalian liver development and hepatic function by controlling hepatocyte proliferation and differentiation, glucose and lipid metabolism, UFMylation, and endoplasmic reticulum homeostasis. However, the role of CDK5RAP3 in liver regeneration remains unknown. A liver-specific Cdk5rap3 knockout (CKO) mouse model was used to study the function of CDK5RAP3 during liver regeneration induced by standard two-thirds partial hepatectomy (PHx). Twenty-four hours after PHx, the liver-to-body weight ratio was markedly higher in CKO mice than in wild-type mice. However, this ratio did not increase significantly and gradually over time after PHx in CKO mice. Hepatocyte proliferation was significantly delayed in CKO mice compared with wild-type mice. Meanwhile, CDK5RAP3 deficiency increased lipid accumulation, impaired glycogen synthesis, and lowered blood glucose levels after PHx. Critically, the absence of CDK5RAP3 seemed to promote an inflammatory response and induce apoptosis at a late stage of liver regeneration. In addition, CDK5RAP3 deficiency disrupted UFMylation homeostasis and aggravated endoplasmic reticulum stress in hepatocytes after PHx. Taken together, these data suggest that CDK5RAP3 enhances liver regeneration, at least partially via controlling cell cycle and glucose and lipid metabolism.

Loss of CLN3, the gene mutated in juvenile neuronal ceroid lipofuscinosis, leads to metabolic impairment and autophagy induction in retinal pigment epithelium

Juvenile neuronal ceroid lipofuscinosis (JNCL, aka. juvenile Batten disease or CLN3 disease) is a lysosomal storage disease characterized by progressive blindness, seizures, cognitive and motor failures, and premature death. JNCL is caused by mutations in the Ceroid Lipofuscinosis, Neuronal 3 (CLN3) gene, whose function is unclear. Although traditionally considered a neurodegenerative disease, CLN3 disease displays eye-specific effects: Vision loss not only is often one of the earliest symptoms of JNCL, but also has been reported in non-syndromic CLN3 disease. Here we described the roles of CLN3 protein in maintaining healthy retinal pigment epithelium (RPE) and normal vision. Using electroretinogram, fundoscopy and microscopy, we showed impaired visual function, retinal autofluorescent lesions, and RPE disintegration and metaplasia/hyperplasia in a Cln3 ~ 1 kb-deletion mouse model [1] on C57BL/6J background. Utilizing a combination of biochemical analyses, RNA-Seq, Seahorse XF bioenergetic analysis, and Stable Isotope Resolved Metabolomics (SIRM), we further demonstrated that loss of CLN3 increased autophagic flux, suppressed mTORC1 and Akt activities, enhanced AMPK activity, and up-regulated gene expression of the autophagy-lysosomal system in RPE-1 cells, suggesting autophagy induction. This CLN3 deficiency induced autophagy induction coincided with decreased mitochondrial oxygen consumption, glycolysis, the tricarboxylic acid (TCA) cycle, and ATP production. We also reported for the first time that loss of CLN3 led to glycogen accumulation despite of impaired glycogen synthesis. Our comprehensive analyses shed light on how loss of CLN3 affect autophagy and metabolism. This work suggests possible links among metabolic impairment, autophagy induction and lysosomal storage, as well as between RPE atrophy/degeneration and vision loss in JNCL.

Beyond Body Weight-Loss: Dietary Strategies Targeting Intrahepatic Fat in NAFLD.

Non-alcoholic fatty liver disease (NAFLD) has emerged as the most prevalent liver disease in industrialized countries. It is regarded as the hepatic manifestation of the metabolic syndrome (MetS) resulting from insulin resistance. Moreover, insulin resistance impairs glycogen synthesis, postprandially diverting a substantial amount of carbohydrates to the liver and storing them there as fat. NAFLD has far-reaching metabolic consequences involving glucose and lipoprotein metabolism disorders and risk of cardiovascular disease, the leading cause of death worldwide. No pharmaceutical options are currently approved for the treatment of NAFLD. Exercise training and dietary interventions remain the cornerstone of NAFLD treatment. Current international guidelines state that the primary goal of nutritional therapy is to reduce energy intake to achieve a 7%–10% reduction in body weight. Meal replacement therapy (formula diets) results in more pronounced weight loss compared to conventional calorie-restricted diets. However, studies have shown that body mass index (BMI) or weight reduction is not obligatory for decreasing hepatic fat content or to restore normal liver function. Recent studies have achieved significant reductions in liver fat with eucaloric diets and without weight loss through macronutrient modifications. Based on this evidence, an integrative nutritional therapeutic concept was formulated that combines the most effective nutrition approaches termed “liver-fasting.” It involves the temporary use of a low calorie diet (total meal replacement with a specific high-protein, high-soluble fiber, lower-carbohydrate formula), followed by stepwise food reintroduction that implements a Mediterranean style low-carb diet as basic nutrition.

Heme Deficiency Causes Impaired Glycogen Synthesis in Skeletal Muscle Leading to Insulin Resistance

In vertebrates, the initial step in heme biosynthesis is the production of 5-aminolevulinic acid (ALA) by ALA synthase (ALAS). The ALAS1 gene encodes a ubiquitously expressed isozyme. Mice heterozygous null for ALAS1 (A1+/-s) experience mitochondrial dysfunction in skeletal muscle, impaired glucose tolerance (IGT) and insulin resistance (IR) past 20-weeks of age (aged A1+/-s) 1). IGT/IR in aged A1+/-s was remedied by oral administration of ALA for 1-week1). By contrast, mitochondrial dysfunction required 6-weeks of ALA administration before improvements could be observed, indicating the phenotype of IGT/ IR is not due to mitochondrial dysfunction1). We found no remarkable change in expressions and phosphorylation of proteins related to insulin signalling such as Akt and GSK3β in skeletal muscle of aged A1+/-s1). Rather, abnormal ultrastructure of glycogen granules and increased glycogen contents were observed in skeletal muscle of aged A1+/-s unlike of less than 15-weeks-old A1+/-s, and those abnormalities of glycogen were reversed after ALA-treatment for 1-week as well as IGT/IR. The quantification of glycogen contents showed that insulin-induced glycogen synthesis was impaired in skeletal muscle of aged A1+/-s, and the reduced de novo glycogen synthesis was recovered in ALA-administrated aged A1+/-s. Glycogen synthase (GS) activities were constitutively activated even at the low concentration of glucose 6-phosphate (G6P) and not augmented at the high concentration of G6P in extracts from skeletal muscle of aged A1+/-s, suggesting that GS fails to respond to allosteric activation by G6P. While, GS activities were normally regulated in those of ALA-administered aged A1+/-s. Taken together, our data suggest that impaired de novo glycogen synthesis in skeletal muscle is relevant to IGT/IR in aged A1+/-s due to constitutively activated GS without allosteric activation by G6P. Ref. 1) Saitoh et al. PLOS ONE in press. Disclosure O. Nakajima: None. S. Saitoh: Research Support; Spouse/Partner; Japan Society for the Promotion of Science, SBI Pharmaceuticals Co.,Ltd.. T. Kimura: None. T. Osaki: None. K.P. Vincent: Research Support; Self; Kora Healthcare. K. Takahashi: None. T. Tanaka: None. M. Nakajima: None.

Integrin‐Linked Kinase is Necessary for Normal Hepatic Glycogen Storage and Energy Metabolism

A recently established characteristic of obesity and its associated insulin resistance is altered extracellular matrix (ECM) in a broad range of tissues, including adipose tissue, skeletal muscle, heart, kidney and liver. This results in increased ECM and abnormal morphology. The cell is informed of the state of the ECM by interaction of ECM with integrin receptors. In recent years the contribution of these receptors to the development of insulin resistance has been realized using a high fat fed mouse model of diet-induced obesity (DIO). Integrin receptor signaling occurs through a number of distinct intracellular signaling nodes. Among the critical hubs of integrin signaling is integrin-linked kinase (ILK). Hepatocyte-specific knockout of ILK (hILK-KO) is beneficial in models of hepatic damage, regeneration, and insulin resistance. It has also been reported that hILK causes age-dependent effects on hepatic gene expression and signaling. It remains to be determined whether the age-dependence of hepatic gene expression is associated with distinct metabolic responses during times of metabolic stress. Thus, it was the initial aim of these studies to determine glucose tolerance and body composition of hILK-KO mice during the growth phase of the mouse as specific hepatic genes are deficient. We hypothesized beneficial effects of hILK-KO on glucose tolerance in young mice (6-wk old). This hypothesis was confirmed as hILK-KO mice presented with improved glucose tolerance relative to wild type (WT) mice at 6-weeks of age. We further investigated the underlying metabolic drivers of altered glucose homeostasis in these mice. Despite lower glucose concentrations after a 5-hour fast, gluconeogenic processes are accelerated in 6-week old hILK-KO mice. Decreased hepatic glycogen content coincides with lower 5 h fasting glucose and improved glucose tolerance. Impaired glycogen synthesis also occurs in these mice during a refeeding challenge. This occurs despite intact insulin-stimulated glycogen synthesis signaling. hILK-KO livers also possess decreased energy in the adenine nucleotide pool during metabolic flux analyses. Hepatocytes isolated from hILK-KO livers also have lower respiration metrics on a per cell basis, but increased mitochondrial content indicated by VDAC protein levels. These attributes are also accompanied by decreased Bnip3 and increased p62 protein levels indicating impaired autophagy/mitophagy. In summary we demonstrate that hILK-KO leads to an impaired energy buffering system in hepatocytes, possibly through deficient autophagy. Studies in hepatocytes suggest that this accelerates glycolysis as an energy-producing process, which limits the availability of glucose for glycogenesis. This inability to store glycogen also accelerates fasting transitions and increases reliance on gluconeogenesis to buffer circulating glucose, which compounds energy demand of hepatocytes. Therefore, ILK is required for establishment of normal energy and glucose metabolism in the liver of mice in the growth phase. This indicates ILK as a potential intermediary signal for integrin-mediated effects on metabolism in hepatic physiology. Support or Funding Information DK050277, DK007563, DK112553, DK059637 Graphical summary of the metabolic effects of hepatocyte specific knockout of integrin-linked kinase. Abbreviations: ILK- integrin-linked kinase; ATP- adenosine triphosphate; GS- glycogen synthase. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Short-term heat stress altered metabolism and insulin signaling in skeletal muscle.

Heat-related complications continue to be a major health concern for humans and animals and lead to potentially life-threatening conditions. Heat stress (HS) alters metabolic parameters and may alter glucose metabolism and insulin signaling. Therefore, the purpose of this investigation was to determine the extent to which 12 h of HS-altered energetic metabolism in oxidative skeletal muscle. To address this, crossbred gilts (n = 8/group) were assigned to one of three environmental treatments for 12 h: thermoneutral (TN; 21 °C), HS (37 °C), or pair-fed to HS counterparts but housed in TN conditions (PFTN). Following treatment, animals were euthanized and the semitendinosus red (STR) was recovered. Despite increased relative protein abundance of the insulin receptor, insulin receptor substrate (IRS1) phosphorylation was increased (P = 0.0005) at S307, an inhibitory site, and phosphorylated protein kinase B (AKT) (S473) was decreased (P = 0.03) likely serving to impair insulin signaling following 12 h of HS. Further, HS increased phosphorylated protein kinase C (PKC) ζ/λ (P = 0.02) and phosphorylated PKCδ/θ protein abundance (P = 0.02), which are known to regulate inhibitory serine phosphorylation of IRS1 (S307). Sarcolemmal glucose transporter 4 (Glut4) was decreased (P = 0.04) in the membrane fraction of HS skeletal muscle suggesting diminished glucose uptake capacity. HS-mediated increases (P = 0.04) in mechanistic target of rapamycin (mTOR) were not accompanied by phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1). HS decreased (P = 0.0006) glycogen synthase (GS) and increased (P = 0.02) phosphorylated GS suggesting impaired glycogen synthesis. In addition, HS altered fatty acid metabolic signaling by increasing (P = 0.02) Acetyl-CoA carboxylase (ACC), decreasing (P = 0.005) phosphorylated ATP-citrate lyase (pATPCL) and fatty acid synthase (P = 0.01) (FAS). These data suggest that 12 h of HS blunted insulin signaling, decreased protein synthesis, and altered glycogen and fatty acid metabolism.

AJS1669, a novel small-molecule muscle glycogen synthase activator, improves glucose metabolism and reduces body fat mass in mice.

Impaired glycogen synthesis and turnover are common in insulin resistance and type 2 diabetes. As glycogen synthase (GS) is a key enzyme involved in the synthetic process, it presents a promising therapeutic target for the treatment of type 2 diabetes. In the present study, we identified a novel, potent and orally available GS activator AJS1669 {sodium 2-[[5-[[4-(4,5-difluoro-2-methylsulfanyl-phenyl) phenoxy] methyl]furan-2-carbonyl]-(2-furylmethyl)amino] acetate}. In vitro, we performed a glycogen synthase 1 (GYS1) activation assay for screening GS activators and identified that the activity of AJS1669 was further potentiated in the presence of glucose-6-phosphate (G6P). In vivo, we used ob/ob mice to evaluate the novel anti-diabetic effects of AJS1669 by measuring basal blood glucose levels, glucose tolerance and body fat mass index. Repeated administration of AJS1669 over 4 weeks reduced blood glucose and hemoglobin A1c (HbA1c) levels in ob/ob mice. AJS1669 also improved glucose tolerance in a dose-dependent manner, and decreased body fat mass. The mRNA levels of genes involved in mitochondrial fatty acid oxidation and mitochondrial biogenesis were elevated in skeletal muscle tissue following AJS1669 treatment. Hepatic tissue of treated mice also exhibited elevated expression of genes associated with fatty acid oxidation. In contrast to ob/ob mice, in C57Bl/6 mice AJS1669 administration did not alter body weight or reduce glucose levels. These results demonstrate that pharmacological agents that activate GYS1, the main GS subtype found in skeletal muscle, have potential for use as novel treatments for diabetes that improve glucose metabolism in skeletal muscle.

Hepatic mTORC1 Opposes Impaired Insulin Action to Control Mitochondrial Metabolism in Obesity

Dysregulated mitochondrial metabolism during hepatic insulin resistance may contribute to pathophysiologies ranging from elevated glucose production to hepatocellular oxidative stress and inflammation. Given that obesity impairs insulin action but paradoxically activates mTORC1, we tested whether insulin action and mammalian target of rapamycin complex 1 (mTORC1) contribute to altered invivo hepatic mitochondrial metabolism. Loss of hepatic insulin action for 2weeks caused increased gluconeogenesis, mitochondrial anaplerosis, tricarboxylic acid (TCA) cycle oxidation, and ketogenesis. However, activation of mTORC1, induced by the loss of hepatic Tsc1, suppressed these fluxes. Only glycogen synthesis was impaired by both loss of insulin receptor and mTORC1 activation. Mice with a double knockout of the insulin receptor and Tsc1 had larger livers, hyperglycemia, severely impaired glycogen storage, and suppressed ketogenesis, as compared to those with loss of the liver insulin receptor alone. Thus, activation of hepatic mTORC1 opposes the catabolic effects of impaired insulin action under some nutritional states.

Tpbpa-Cre-mediated deletion of TFAP2C leads to deregulation of Cdkn1a, Akt1 and the ERK pathway, causing placental growth arrest.

Loss of TFAP2C in mouse leads to developmental defects in the extra-embryonic compartment with lethality at embryonic day (E)7.5. To investigate the requirement of TFAP2C in later placental development, deletion of TFAP2C was induced throughout extra-embryonic ectoderm at E6.5, leading to severe placental abnormalities caused by reduced trophoblast population and resulting in embryonic retardation by E8.5. Deletion of TFAP2C in TPBPA(+) progenitors at E8.5 results in growth arrest of the junctional zone. TFAP2C regulates its target genes Cdkn1a (previously p21) and Dusp6, which are involved in repression of MAPK signaling. Loss of TFAP2C reduces activation of ERK1/2 in the placenta. Downregulation of Akt1 and reduced activation of phosphorylated AKT in the mutant placenta are accompanied by impaired glycogen synthesis. Loss of TFAP2C led to upregulation of imprinted gene H19 and downregulation of Slc38a4 and Ascl2. The placental insufficiency post E16.5 causes fetal growth restriction, with 19% lighter mutant pups. Knockdown of TFAP2C in human trophoblast choriocarcinoma JAr cells inhibited MAPK and AKT signaling. Thus, we present a model where TFAP2C in trophoblasts controls proliferation by repressing Cdkn1a and activating the MAPK pathway, further supporting differentiation of glycogen cells by activating the AKT pathway.

Abstract B41: Post-transcriptional regulation of IDH1 by the RNA-binding protein HuR is important for pancreatic cancer cell survival under nutrient deprivation

Abstract Introduction: Isocitrate dehydrogenase 1(IDH1) has been prioritized in the recent cancer biology literature because of mutations occurring in some tumor types. Additionally the wild type isoenzyme is important for metabolic reprogramming under hypoxic stress. Importantly, the role of IDH1 under other forms of metabolic stress, such as nutrient deprivation (hallmark of the PDA microenvironment) has not been explored, and the regulatory mechanism of IDH1 expression remains unknown. We recently showed that the regulatory RNA binding protein, HuR, binds and directly regulates IDH1 expression in multiple PDA cell lines. The regulatory protein becomes biologically engaged under nutrient deprivation by translocating with the IDH1 transcript form the nucleus to the cytoplasm under glucose deprivation, and HuR silencing sensitized cells under these conditions. Here, we hone in on the regulatory HuR binding site to the IDH1 transcript, explore the importance of HuR in the context of additional metabolic stressors and utilize stable isotope metabolomic profiling to gain mechanistic insight into how HuR is protective under nutrient deprivation. Methods: IDH1 and HuR expression were knocked down by siRNA, and cell viability was determined by PicoGreen and Trypan blue exclusion assays. Immunofluorescence was used to image HuR subcellular localization under glutamine deprivation. Based on computational predictions of 5 HuR binding sites in the IDH1 mRNA 3'UTR, we subcloned this entire region into a luciferase reporter construct to further study this regulatory interaction. In order to determine the impact of HuR expression in cellular metabolism targeted tracer fate association studies were performed using GC-MS of pellets from cells cultured with 13C-labeled glucose and glutamine in BxPC3 pancreatic cancer cells that differed only in HuR expression. We calculated Pearson correlations of measured metabolites after HuR silencing. Results: Cell viability was impaired by depletion of both IDH1 and HuR (vs. controls) upon glutamine and glucose withdrawal. Moreover, HuR silencing resulted in potent suppression of IDH1 at the mRNA and protein levels. HuR silencing substantially decremented luciferase activity in the IDH1 3'UTR construct compared to the control (> 2-fold decrease). HuR translocated to the cytoplasm under glutamine deprivation, as previously published observed with glucose deprivation by our group. Metabolic tracer fate association studies revealed that HuR silencing impaired carbon flux from glutamine into fatty acid end products (myristate and palmitate, > 0.9-Pearson's Correlation) under low glucose conditions, implicating HuR's regulatory role in the IDH1-mediated reductive carboxylation step of this metabolic pathway. Additionally, HuR silencing impaired ribose and glycogen synthesis from glucose, and futile carbon exchange fluxes were prevalent. Conclusions: HuR is important for pancreatic cancer cell survival under glutamine deprivation, as previously observed for glucose deprivation. Carbon flux from glutamine to fatty acid end products suggests a role for HuR in reductive carboxylation of glutamine-derived α-ketoglutarate by IDH1, as a way to maintain adequate lipid synthesis under glucose deprivation. Our Studies provide a rationale to pursue pharmacologic strategies that target HuR or its regulation of IDH1 as a novel treatment of PDA. Citation Format: Mahsa Zarei, Fernando F. Blanco, Laszlo G. Boros, Charles J. Yeo, Jonathan R. Brody, Jordan M. Winter. Post-transcriptional regulation of IDH1 by the RNA-binding protein HuR is important for pancreatic cancer cell survival under nutrient deprivation. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B41.

Investigation and management of the hepatic glycogen storage diseases.

The glycogen storage diseases (GSD) comprise a group of disorders that involve the disruption of metabolism of glycogen. Glycogen is stored in various organs including skeletal muscle, the kidneys and liver. The liver stores glycogen to supply the rest of the body with glucose when required. Therefore, disruption of this process can lead to hypoglycaemia. If glycogen is not broken down effectively, this can lead to hepatomegaly. Glycogen synthase deficiency leads to impaired glycogen synthesis and consequently the liver is small. Glycogen brancher deficiency can lead to abnormal glycogen being stored in the liver leading to a quite different disorder of progressive liver dysfunction. Understanding the physiology of GSD I, III, VI and IX guides dietary treatments and the provision of appropriate amounts and types of carbohydrates. There has been recent re-emergence in the literature of the use of ketones in therapy, either in the form of the salt D,L-3-hydroxybutyrate or medium chain triglyceride (MCT). High protein diets have also been advocated. Alternative waxy maize based starches seem to show promising early data of efficacy. There are many complications of each of these disorders and they need to be prospectively surveyed and managed. Liver and kidney transplantation is still indicated in severe refractory disease.

Glycogen accumulation underlies neurodegeneration and autophagy impairment in Lafora disease

Lafora disease is a fatal neurodegenerative condition characterized by the accumulation of abnormal glycogen inclusions known as Lafora bodies. It is an autosomal recessive disorder caused by mutations in either the laforin or malin gene. To study whether glycogen is primarily responsible for the neurodegeneration in Lafora disease, we generated malin knockout mice with impaired (totally or partially) glycogen synthesis. These animals did not show the increase in markers of neurodegeneration, the impairments in electrophysiological properties of hippocampal synapses, nor the susceptibility to kainate-induced epilepsy seen in the malin knockout model. Interestingly, the autophagy impairment that has been described in malin knockout animals was also rescued in this double knockout model. Conversely, two other mouse models in which glycogen is over-accumulated in the brain independently of the lack of malin showed impairment in autophagy. Our findings reveal that glycogen accumulation accounts for the neurodegeneration and functional consequences seen in the malin knockout model, as well as the impaired autophagy. These results identify the regulation of glycogen synthesis as a key target for the treatment of Lafora disease.

The induction of miR-96 by mitochondrial dysfunction causes impaired glycogen synthesis through translational repression of IRS-1 in SK-Hep1 cells

MicroRNA (miRNA) is a class of endogenous small noncoding RNA that negatively regulates gene expression at the post-transcriptional level and plays an important role in the pathogenesis of various diseases. However, the identity and role of miRNAs involved in the development of insulin resistance resulting from mitochondrial dysfunction are largely unknown. In this study, mitochondrial dysfunction by genetic or metabolic inhibition induced an impairment of insulin signaling in SK-Hep1 cells via a reduction in the expression of IRS-1 protein. Significant up-regulation of miR-96, which was presumed to target IRS-1 3′UTR, was found in SK-Hep1 cells with mitochondrial dysfunction. Using reporter gene assay we confirmed that miR-96 authentically targeted IRS-1 3′UTR. Furthermore, the ectopic expression of miR-96 caused a substantial decrease in IRS-1 protein expression, and a consequent impairment in insulin signaling. These findings suggest that the up-regulation of miR-96 by mitochondrial dysfunction contributes to the development of insulin resistance by targeting IRS-1 in SK-Hep1 cells.

Resistance Training for Diabetes Prevention and Therapy: Experimental Findings and Molecular Mechanisms

Type 2 diabetes mellitus (T2D) is characterized by insulin resistance, impaired glycogen synthesis, lipid accumulation, and impaired mitochondrial function. Exercise training has received increasing recognition as a cornerstone in the prevention and treatment of T2D. Emerging research suggests that resistance training (RT) has the power to combat metabolic dysfunction in patients with T2D and seems to be an effective measure to improve overall metabolic health and reduce metabolic risk factors in diabetic patients. However, there is limited mechanistic insight into how these adaptations occur. This review provides an overview of the intervention data on the impact of RT on glucose metabolism. In addition, the molecular mechanisms that lead to adaptation in skeletal muscle in response to RT and that are associated with possible beneficial metabolic responses are discussed. Some of the beneficial adaptations exerted by RT include increased GLUT4 translocation in skeletal muscle, increased insulin sensitivity and hence restored metabolic flexibility. Increased energy expenditure and excess postexercise oxygen consumption in response to RT may be other beneficial effects. RT is increasingly establishing itself as an effective measure to improve overall metabolic health and reduce metabolic risk factors in diabetic patients.

Liver Glycogen Loading Dampens Glycogen Synthesis Seen in Response to Either Hyperinsulinemia or Intraportal Glucose Infusion

The purpose of this study was to determine the effect of liver glycogen loading on net hepatic glycogen synthesis during hyperinsulinemia or hepatic portal vein glucose infusion in vivo. Liver glycogen levels were supercompensated (SCGly) in two groups (using intraportal fructose infusion) but not in two others (Gly) during hyperglycemic-normoinsulinemia. Following a 2-h control period during which fructose infusion was stopped, there was a 2-h experimental period in which the response to hyperglycemia plus either 4× basal insulin (INS) or portal vein glucose infusion (PoG) was measured. Increased hepatic glycogen reduced the percent of glucose taken up by the liver that was deposited in glycogen (74 ± 3 vs. 53 ± 5% in Gly+INS and SCGly+INS, respectively, and 72 ± 3 vs. 50 ± 6% in Gly+PoG and SCGly+PoG, respectively). The reduction in liver glycogen synthesis in SCGly+INS was accompanied by a decrease in both insulin signaling and an increase in AMPK activation, whereas only the latter was observed in SCGly+PoG. These data indicate that liver glycogen loading impairs glycogen synthesis regardless of the signal used to stimulate it.

Impaired glycogen synthesis causes metabolic overflow reactions and affects stress responses in the cyanobacterium Synechocystis sp. PCC 6803

The biosynthesis of glycogen or starch is one of the main strategies developed by living organisms for the intracellular storage of carbon and energy. In phototrophic organisms, such polyglucans accumulate due to carbon fixation during photosynthesis and are used to provide maintenance energy for cell integrity, function and viability in dark periods. Moreover, it is assumed that glycogen enables cyanobacteria to cope with transient starvation conditions, as observed in most micro-organisms. Here, glycogen accumulates when an appropriate carbon source is available in sufficient amounts but growth is inhibited by lack of other nutrients. In this study, the role of glycogen in energy and carbon metabolism of phototrophic cyanobacteria was first analysed via a comparative physiological and metabolic characterization of knockout mutants defective in glycogen synthesis. We first proved the role of glycogen as a respiratory substrate in periods of darkness, the role of glycogen as a reserve to survive starvation periods such as nitrogen depletion and the role of glycogen synthesis as an ameliorator of carbon excess conditions in the model organism Synechocystis sp. PCC 6803. We provide striking new insights into the complex carbon and nitrogen metabolism of non-diazotrophic cyanobacteria: a phenotype of sensitivity to photomixotrophic conditions and of reduced glucose uptake, a non-bleaching phenotype based on an impaired acclimation response to nitrogen depletion and furthermore a phenotype of energy spilling. This study shows that the analysis of deficiencies in glycogen metabolism is a valuable tool for the identification of metabolic regulatory principles and signals.