Glycolysis

About: Glycolysis is a research topic. Over the lifetime, 10593 publications have been published within this topic receiving 507460 citations. The topic is also known as: GO:0006096 & glycolysis.

Glucose and phosphate inhibit respiration and oxidative metabolism in cultured hamster eight-cell embryos : evidence for the "Crabtree effect"

Abstract: The development of hamster eight-cell embryos is inhibited by glucose in culture medium containing inorganic phosphate (Pi). This is hypothetically attributed to the "Crabtree effect," in which enhanced glycolysis inhibits respiratory activity and oxidative metabolism. To examine this hypothesis, oxygen consumption of hamster eight-cell embryos was measured using a microelectrode. A two- to three-fold decrease in oxygen consumption was observed in embryos cultured with glucose and Pi. Oxidizable substrates and intermediates of the Krebs cycle supported embryo development only in the absence of glucose and Pi; Krebs cycle inhibitors (fluoroacetate and arsenite) arrested embryo development. Under anaerobic conditions, pyruvate and lactate did not support embryo development. Inhibition of both respiration and oxidative activity in cultured hamster embryos by glucose and Pi is consistent with the existence of a Crabtree effect and indicates that the metabolic properties of preimplantation embryonic cells differ markedly from those of most somatic cells and resemble some cancer cells.

Muscle-specific loss of Bmal1 leads to disrupted tissue glucose metabolism and systemic glucose homeostasis.

Abstract: Diabetes is the seventh leading cause of death in the USA, and disruption of circadian rhythms is gaining recognition as a contributing factor to disease prevalence. This disease is characterized by hyperglycemia and glucose intolerance and symptoms caused by failure to produce and/or respond to insulin. The skeletal muscle is a key insulin-sensitive metabolic tissue, taking up ~80 % of postprandial glucose. To address the role of the skeletal muscle molecular clock to insulin sensitivity and glucose tolerance, we generated an inducible skeletal muscle-specific Bmal1 −/− mouse (iMSBmal1 −/−). Progressive changes in body composition (decreases in percent fat) were seen in the iMSBmal1 −/− mice from 3 to 12 weeks post-treatment as well as glucose intolerance and non-fasting hyperglycemia. Ex vivo analysis of glucose uptake revealed that the extensor digitorum longus (EDL) muscles did not respond to either insulin or 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) stimulation. RT-PCR and Western blot analyses demonstrated a significant decrease in mRNA expression and protein content of the muscle glucose transporter (Glut4). We also found that both mRNA expression and activity of two key rate-limiting enzymes of glycolysis, hexokinase 2 (Hk2) and phosphofructokinase 1 (Pfk1), were significantly reduced in the iMSBmal1 −/− muscle. Lastly, results from metabolomics analyses provided evidence of decreased glycolytic flux and uncovered decreases in some tricarboxylic acid (TCA) intermediates with increases in amino acid levels in the iMSBmal1 −/− muscle. These findings suggest that the muscle is relying predominantly on fat as a fuel with increased protein breakdown to support the TCA cycle. These data support a fundamental role for Bmal1, the endogenous circadian clock, in glucose metabolism in the skeletal muscle. Our findings have implicated altered molecular clock dictating significant changes in altered substrate metabolism in the absence of feeding or activity changes. The changes in body composition in our model also highlight the important role that changes in skeletal muscle carbohydrate, and fat metabolism can play in systemic metabolism.

Synaptosomal bioenergetics. The role of glycolysis, pyruvate oxidation and responses to hypoglycaemia.

Abstract: The bioenergetic interaction between glycolysis and oxidative phosphorylation in isolated nerve terminals (synaptosomes) from guinea-pig cerebral cortex is characterized. 1 Essentially all synaptosomes contain functioning mitochondria. 2 There is a tight coupling between glycolytic rate and respiration: uncoupler causes a tenfold increase in glycolysis and a sixfold increase in respiration. 3 Synaptosomes contain little endogenous glycolytic substrate and glycolysis is dependent on external glucose. 4 In glucose-free media, or following addition of iodoacetate, synaptosomes continue to respire and to maintain high ATP/ADP ratios. 5 In contrast to glucose, the endogenous substrate can neither maintain high respiration in the presence of uncoupler nor generate ATP in the presence of cyanide. 6 Pyruvate, but not succinate, is an excellent substrate for intact synaptosomes. 7 The in-situ mitochondrial membrane potential (ΔΨm) is highly dependent upon the availability of glycolytic or exogenous pyruvate; glucose deprivation causes a 20-mV depolarization, while added pyruvate causes a 6-mV hyperpolarization even in the presence of glucose. 8 Inhibition of pyruvate dehydrogenase by arsenite or pyruvate transport by α-cyano-4-hydroxycinnamate has little effect on ATP/ADP ratios; however respiratory capacity is severely restricted. 9 It is concluded that synaptosomes are valuable models for studying the control of mitochondrial substrate supply in situ.

Metabolic and Proliferative State of Vascular Adventitial Fibroblasts in Pulmonary Hypertension Is Regulated Through a MicroRNA-124/PTBP1 (Polypyrimidine Tract Binding Protein 1)/Pyruvate Kinase Muscle Axis

Abstract: Background: An emerging metabolic theory of pulmonary hypertension (PH) suggests that cellular and mitochondrial metabolic dysfunction underlies the pathology of this disease. We and others have previously demonstrated the existence of hyperproliferative, apoptosis-resistant, proinflammatory adventitial fibroblasts from human and bovine hypertensive pulmonary arterial walls (PH-Fibs) that exhibit constitutive reprogramming of glycolytic and mitochondrial metabolism, accompanied by an increased ratio of glucose catabolism through glycolysis versus the tricarboxylic acid cycle. However, the mechanisms responsible for these metabolic alterations in PH-Fibs remain unknown. We hypothesized that in PH-Fibs microRNA-124 (miR-124) regulates PTBP1 (polypyrimidine tract binding protein 1) expression to control alternative splicing of pyruvate kinase muscle (PKM) isoforms 1 and 2, resulting in an increased PKM2/PKM1 ratio, which promotes glycolysis and proliferation even in aerobic environments. Methods: Pulmonary adventitial fibroblasts were isolated from calves and humans with severe PH (PH-Fibs) and from normal subjects. PTBP1 gene knockdown was achieved via PTBP1-siRNA; restoration of miR-124 was performed with miR-124 mimic. TEPP-46 and shikonin were used to manipulate PKM2 glycolytic function. Histone deacetylase inhibitors were used to treat cells. Metabolic products were determined by mass spectrometry–based metabolomics analyses, and mitochondrial function was analyzed by confocal microscopy and spectrofluorometry. Results: We detected an increased PKM2/PKM1 ratio in PH-Fibs compared with normal subjects. PKM2 inhibition reversed the glycolytic status of PH-Fibs, decreased their cell proliferation, and attenuated macrophage interleukin-1β expression. Furthermore, normalizing the PKM2/PKM1 ratio in PH-Fibs by miR-124 overexpression or PTBP1 knockdown reversed the glycolytic phenotype (decreased the production of glycolytic intermediates and byproducts, ie, lactate), rescued mitochondrial reprogramming, and decreased cell proliferation. Pharmacological manipulation of PKM2 activity with TEPP-46 and shikonin or treatment with histone deacetylase inhibitors produced similar results. Conclusions: In PH, miR-124, through the alternative splicing factor PTBP1, regulates the PKM2/PKM1 ratio, the overall metabolic, proliferative, and inflammatory state of cells. This PH phenotype can be rescued with interventions at various levels of the metabolic cascade. These findings suggest a more integrated view of vascular cell metabolism, which may open unique therapeutic prospects in targeting the dynamic glycolytic and mitochondrial interactions and between mesenchymal inflammatory cells in PH.