glycogen and Glioblastoma

Channelling of glucose via glycogen, known as the glycogen shunt, may play an important role in the metabolism of brain tumours, especially in hypoxic conditions. We aimed to dissect the role of glycogen degradation in glioblastoma (GBM) response to ionising radiation (IR). Knockdown of the glycogen phosphorylase liver isoform (PYGL), but not the brain isoform (PYGB), decreased clonogenic growth and survival of GBM cell lines and sensitised them to IR doses of 10-12 Gy. Two to five days after IR exposure of PYGL knockdown GBM cells, mitotic catastrophy and a giant multinucleated cell morphology with senescence-like phenotype developed. The basal levels of the lysosomal enzyme alpha-acid glucosidase (GAA), essential for autolysosomal glycogen degradation, and the lipidated forms of gamma-aminobutyric acid receptor-associated protein-like (GABARAPL1 and GABARAPL2) increased in shPYGL U87MG cells, suggesting a compensatory mechanism of glycogen degradation. In response to IR, dysregulation of autophagy was shown by accumulation of the p62 and the lipidated form of GABARAPL1 and GABARAPL2 in shPYGL U87MG cells. IR increased the mitochondrial mass and the colocalisation of mitochondria with lysosomes in shPYGL cells, thereby indicating reduced mitophagy. These changes coincided with increased phosphorylation of AMP-activated protein kinase and acetyl-CoA carboxylase 2, slower ATP generation in response to glucose loading and progressive loss of oxidative phosphorylation. The resulting metabolic deficiencies affected the availability of ATP required for mitosis, resulting in the mitotic catastrophy observed in shPYGL cells following IR. PYGL mRNA and protein levels were higher in human GBM than in normal human brain tissues and high PYGL mRNA expression in GBM correlated with poor patient survival. In conclusion, we show a major new role for glycogen metabolism in GBM cancer. Inhibition of glycogen degradation sensitises GBM cells to high-dose IR indicating that PYGL is a potential novel target for the treatment of GBMs.

Topics: Adenosine Triphosphate; Glioblastoma; Glucose; Glycogen; Glycogen Phosphorylase; Humans; Liver; Protein Isoforms; RNA, Messenger

Hypoxia is a common feature of solid tumours and is associated with poor prognosis, resistance to radio- and chemotherapy, and tumour aggressiveness. For predictive purposes as well as for improved therapeutic intervention, it is increasingly needed to have direct and specific diagnostic tools in order to measure the extent of, and changes in, tumour hypoxia. In this article, we have investigated the potential of Fourier Transform Infrared (FTIR) microspectroscopy, at cellular and subcellular resolution, for detecting hypoxia-induced metabolic changes in brain tumour (glioblastoma) cell lines and in short term primary cultures derived from patient samples. The most prominent and common changes observed were the increase in glycogen (specifically in the U87MG cell line) and lipids (all cell lines studied). Additionally, each cell line presented specific individual metabolic fingerprints. The metabolic changes did not evolve markedly with time (from 1 to 5 days hypoxic incubation), and yet were harder to detect under chronic hypoxic conditions, which is consistent with cellular adaptation occurring upon long term changes in the microenvironment. The metabolic signature was similar regardless of the severity of the hypoxic insult and was replicated by the hypoxia mimetic drug dimethyloxalylglycine (DMOG). To investigate any specific changes at subcellular levels and to improve the sensitivity of the detection method, spectra were recorded separately in the cytoplasm and in the nucleus of D566 glioblastoma cells, thanks to the use of a synchrotron source. We show that this method provides improved detection in both cell compartments. Whilst there was a high spectral variability between cell lines, we show that FTIR microspectroscopy allowed the detection of the common metabolic changes triggered by hypoxia regardless of cell type, providing a potential new approach for the detection of hypoxic tumours.

Topics: Biomarkers, Tumor; Brain Neoplasms; Cell Hypoxia; Cell Nucleus; Cytoplasm; Fatty Acids, Unsaturated; Glioblastoma; Glycogen; HeLa Cells; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Microspectrophotometry; Phospholipids; Spectroscopy, Fourier Transform Infrared

Given the involvement of telomerase activation and dysregulated metabolism in glioma progression, the connection between these two critical players was investigated. Pharmacological inhibition of human Telomerase reverse transcriptase (hTERT) by Costunolide induced glioma cell apoptosis in a reactive oxygen species (ROS)-dependent manner. Costunolide induced an ROS-dependent increase in p53 abrogated telomerase activity. Costunolide decreased Nrf2 level; and ectopic Nrf2 expression decreased Costunolide-induced ROS generation. While TERT knock-down abrogated Nrf2 levels, overexpression of Nrf2 increased TERT expression. Inhibition of hTERT either by Costunolide, or by siRNA or dominant-negative hTERT (DN-hTERT) abrogated (i) expression of Glucose-6-phosphate dehydrogenase (G6PD) and Transketolase (TKT) - two major nodes in the pentose phosphate (PPP) pathway; and (ii) phosphorylation of glycogen synthase (GS). hTERT knock-down decreased TKT activity and increased glycogen accumulation. Interestingly, siRNA-mediated knock-down of TKT elevated glycogen accumulation. Coherent with the in vitro findings, Costunolide reduced tumor burden in heterotypic xenograft glioma mouse model. Costunolide-treated tumors exhibited diminished TKT activity, heightened glycogen accumulation, and increased senescence. Importantly, glioblastoma multiforme (GBM) patient tumors bearing TERT promoter mutations (C228T and C250T) known to be associated with increased telomerase activity; exhibited elevated Nrf2 and TKT expression and decreased glycogen accumulation. Taken together, our findings highlight the previously unknown (i) role of telomerase in the regulation of PPP and glycogen accumulation and (ii) the involvement of Nrf2-TERT loop in maintaining oxidative defense responses in glioma cells.

Topics: Animals; Antineoplastic Agents, Phytogenic; Brain Neoplasms; Cell Line, Tumor; Cellular Senescence; Gene Expression Regulation, Neoplastic; Glioblastoma; Glucosephosphate Dehydrogenase; Glycogen; Glycogen Synthase; Humans; Mice; Mice, Nude; NF-E2-Related Factor 2; Pentose Phosphate Pathway; Phosphorylation; Reactive Oxygen Species; RNA, Small Interfering; Sesquiterpenes; Signal Transduction; Telomerase; Transketolase; Tumor Suppressor Protein p53; Xenograft Model Antitumor Assays

Glioblastoma (GBM) remains the most aggressive primary brain cancer in adults. Similar to other cancers, GBM cells undergo metabolic reprogramming to promote proliferation and survival. Glycolytic inhibition is widely used to target such reprogramming. However, the stability of glycolytic inhibition in GBM remains unclear especially in a hypoxic tumor microenvironment. In this study, it was determined that glucose-6-phosphatase (G6PC/G6Pase) expression is elevated in GBM when compared with normal brain. Human-derived brain tumor-initiating cells (BTIC) use this enzyme to counteract glycolytic inhibition induced by 2-deoxy-d-glucose (2DG) and sustain malignant progression. Downregulation of G6PC renders the majority of these cells unable to survive glycolytic inhibition, and promotes glycogen accumulation through the activation of glycogen synthase (GYS1) and inhibition of glycogen phosphorylase (PYGL). Moreover, BTICs that survive G6PC knockdown are less aggressive (reduced migration, invasion, proliferation, and increased astrocytic differentiation). Collectively, these findings establish G6PC as a key enzyme with promalignant functional consequences that has not been previously reported in GBM and identify it as a potential therapeutic target.. This study is the first to demonstrate a functional relationship between the critical gluconeogenic and glycogenolytic enzyme G6PC with the metabolic adaptations during GBM invasion.

Topics: Animals; Astrocytes; Brain Neoplasms; Cell Differentiation; Cell Line, Tumor; Cell Movement; Cell Survival; Gene Knockdown Techniques; Glioblastoma; Glucose-6-Phosphatase; Glycogen; Glycogen Phosphorylase; Glycogen Synthase; Glycolysis; Humans; Male; Mice, Nude; Neoplasm Invasiveness; Neoplastic Stem Cells; Phenotype; RNA, Small Interfering; Up-Regulation

Glioblastoma Multiforme (GBM) is an aggressive form of brain Tumor that has few cures. In this study, we analyze the anti-proliferative effects of a new molecule JQ1 against GBMs induced in Wistar Rats. JQ1 is essentially a Myc inhibitor. c-Myc is also known for altering the biochemistry of a tumor cell. Therefore, the study is intended to analyze certain other oncogenes associated with c-Myc and also the change in cellular biochemistry upon c-Myc inhibition. The quantitative analysis of gene expression gave a co-expressive pattern for all the three genes involved namely; c-Myc, Bcl-2, and Akt. The cellular biochemistry analysis by transmission electron microscopy revealed high glycogen and lipid aggregation in Myc inhibited cells and excessive autophagy. The study demonstrates the role of c-Myc as a central metabolic regulator and Bcl-2 and Akt assisting in extending c-Myc half-life as well as in regulation of autophagy, so as to regulate cell survival on the whole. The study also demonstrates that transient treatment by JQ1 leads to aggressive development of tumor and therefore, accelerating death, emphasizing the importance of dosage fixation, and duration for clinical use in future.

Topics: Animals; Azepines; Brain Neoplasms; Cell Line, Tumor; Down-Regulation; Gene Expression Regulation, Neoplastic; Gene Silencing; Glioblastoma; Glycogen; Immunohistochemistry; Lipid Metabolism; Male; Proto-Oncogene Proteins c-myc; Rats, Wistar; Survival Analysis; Triazoles

The addition of norepinephrine to cultured glioblastoma cells results in an inhibition of uptake of radioactivity from D-[2-(3)H]glucose, D-[1-(14)C]glucose, D-[2-(14)C]glucose, and D-[6-(14)C]glucose. In addition, if the glioblastoma cells are previously labeled with these substrates, norepinephrine causes an increase in the release of radioactivity. These effects were not observed with cultured neuroblastoma cells. It is suggested that the breakdown of glycogen is activated by norepinephrine as a result of an increase in 3':5'-cyclic AMP.

Topics: Animals; Biological Transport; Carbon Dioxide; Carbon Isotopes; Clone Cells; Cyclic AMP; Depression, Chemical; Glioblastoma; Glucose; Glycogen; Mice; Micropore Filters; Neuroblastoma; Norepinephrine; Rats; Theophylline; Tritium

Topics: Adenosine Triphosphate; Animals; Brain Neoplasms; Disease Models, Animal; Fluorometry; Freezing; Glioblastoma; Glucose; Glycogen; Histocytochemistry; Lactates; Mice; NAD; NADP; Neoplasm Transplantation; Neoplasms, Experimental; Neuroglia; Oxygen Consumption; Pentoses; Phosphates; Phosphocreatine; Transplantation, Homologous

Topics: Animals; Brain Neoplasms; Cerebral Cortex; Glioblastoma; Glycogen; Humans; Meningioma; Microscopy, Electron; Neuroglia; Neurons; Rabbits

Topics: Astrocytoma; Brain Neoplasms; Ependymoma; Ganglioneuroma; Glioblastoma; Glycogen; Histocytochemistry; Humans; Medulloblastoma; Neurilemmoma; Oligodendroglioma; Papilloma; Tuberous Sclerosis

Topics: Adenosine Triphosphate; Animals; Brain Neoplasms; Creatine Kinase; Glioblastoma; Glucose; Glucosephosphate Dehydrogenase; Glucosyltransferases; Glutamate Dehydrogenase; Glycogen; Glycolysis; Hexokinase; Histocytochemistry; Ischemia; Lactates; Mice; NAD; NADP; Neoplasms, Experimental; Phosphates; Phosphocreatine; Phosphoglucomutase; Phosphogluconate Dehydrogenase

Topics: Adult; Animals; Brain Chemistry; Female; Glioblastoma; Glycogen; Humans; Liver; Male; Meningioma; Mice; Microscopy, Electron; Middle Aged; Neoplasms, Experimental