Glucose sparing by glycogenolysis (GSG) determines the relationship between brain metabolism and neurotransmission

Over the last two decades, it has been established that glucose metabolic fluxes in neurons and astrocytes are proportional to the rates of the glutamate/GABA-glutamine neurotransmitter cycles in close to 1:1 stoichiometries across a wide range of functional energy demands. However, there is presently no mechanistic explanation for these relationships. We present here a theoretical meta-analysis that tests whether the brain’s unique compartmentation of glycogen metabolism in the astrocyte and the requirement for neuronal glucose homeostasis lead to the observed stoichiometries. We found that blood-brain barrier glucose transport can be limiting during activation and that the energy demand could only be met if glycogenolysis supports neuronal glucose metabolism by replacing the glucose consumed by astrocytes, a mechanism we call Glucose Sparing by Glycogenolysis (GSG). The predictions of the GSG model are in excellent agreement with a wide range of experimental results from rats, mice, tree shrews, and humans, which were previously unexplained. Glycogenolysis and glucose sparing dictate the energy available to support neuronal activity, thus playing a fundamental role in brain function in health and disease.

Preliminary Study to Investigate the Distribution and Effects of Certain Metals After Inhalation of Welding Fumes in Mice

The most important welding processes used are the Gas Metal Arc (GMA) welding, the Tungsten Inert Gas (TIG) welding, and the Manual Metal Arc (MMA) welding processes. The goal of our investigation was to monitor the distribution of iron (Fe), manganese (Mn), calcium (Ca) and magnesium (Mg) in the lung, spleen, liver, and kidney of mice after inhalation exposure of different welding methods using different steel base materials. The treatment groups were the following: MMA-mild steel, MMA-molybdenum-manganese (MoMn) alloy, TIG-mild steel, and TIG-stainless steel. The samples were taken 24- and 96 hours after the treatments.Most importantly, it was found that the Mn concentration in the lung’ samples of the MMA-mild steel and the MMA-MoMn groups was increased extremely at both sampling times and in the spleen’ samples also. In the TIG groups, the rise of the Mn concentration was only considerable in the lungs and spleens at 24h, and emerged concentration was found in the liver in 96h samples. Histopathology demonstrated emerged siderin content in the spleens of the treated animals and in siderin filled macrophages in the lungs mostly in all treated groups. Traces of high-level glycogen retention was found in the MMA groups at both sampling times. Similar glycogen retention in TIG-Ms and TIG stainless group’s liver samples and emerged number of vacuoles, especially in the hepatocytes of the TIG-stainless steel 96h group were also found.The mentioned results raise the consequence that there is a considerable difference in the kinetics of the Mn distribution between the MMA- and the TIG-fume treated groups. Hence, the result suggests that manganese has a particle-size dependent toxico-kinetics property. The anomaly of the glycogen metabolism indicates the systemic effect of the welding fumes. Also, the numerous vacuoles mentioned above show a possible liver-specific adverse effect of some components of the TIG-stainless steel welding fumes.

Preclinical Research in McArdle Disease: A Review of Research Models and Therapeutic Strategies

McArdle disease is an autosomal recessive disorder of muscle glycogen metabolism caused by pathogenic mutations in the PYGM gene, which encodes the skeletal muscle-specific isoform of glycogen phosphorylase. Clinical symptoms are mainly characterized by transient acute “crises” of early fatigue, myalgia and contractures, which can be accompanied by rhabdomyolysis. Owing to the difficulty of performing mechanistic studies in patients that often rely on invasive techniques, preclinical models have been used for decades, thereby contributing to gain insight into the pathophysiology and pathobiology of human diseases. In the present work, we describe the existing in vitro and in vivo preclinical models for McArdle disease and review the insights these models have provided. In addition, despite presenting some differences with the typical patient’s phenotype, these models allow for a deep study of the different features of the disease while representing a necessary preclinical step to assess the efficacy and safety of possible treatments before they are tested in patients.

GSK3β Activity in Reward Circuit Functioning and Addiction

Glycogen synthase kinase-3β (GSK3β), primarily described as a regulator of glycogen metabolism, is a molecular hub linking numerous signaling pathways and regulates many cellular processes like cytoskeletal rearrangement, cell migration, apoptosis, and proliferation. In neurons, the kinase is engaged in molecular events related to the strengthening and weakening of synapses, which is a subcellular manifestation of neuroplasticity. Dysregulation of GSK3β activity has been reported in many neuropsychiatric conditions, like schizophrenia, major depressive disorder, bipolar disorder, and Alzheimer’s disease. In this review, we describe the kinase action in reward circuit-related structures in health and disease. The effect of pharmaceuticals used in the treatment of addiction in the context of GSK3β activity is also discussed.

Mechanism of glycogen synthase inactivation and interaction with glycogenin

The macromolecule glycogen is the major glucose reserve in eukaryotes and defects of glycogen metabolism and structure lead to glycogen storage diseases and neurodegeneration. Glycogenesis begins with self-glucosylation of glycogenin (GN), which recruits glycogen synthase (GS). GS is activated by glucose-6-phosphate (G6P) and inactivated by phosphorylation, but how these opposing processes are coupled is unclear. We provide the first structure of phosphorylated human GS-GN complex revealing an autoinhibited GS tetramer flanked by two GN dimers. Phosphorylated N- and C-terminal tails from two GS protomers converge to form dynamic "spike" regions, which are buttressed against GS regulatory helices. This keeps GS in a constrained "tense" conformation that is inactive and more resistant to G6P activation. Mutagenesis that weaken the interaction between the regulatory helix and phosphorylated tails leads to a moderate increase in basal/unstimulated GS activity, supporting the idea that phosphorylation contributes to GS inactivation by constraining GS inter-subunit movement. We propose that multivalent phosphorylation supports GS autoinhibition through interactions from a dynamic "spike" region, thus allowing a "tuneable rheostat" for regulating GS activity. Our structures of human GS-GN provide new insights into the regulation of glycogen synthesis, facilitating future studies of glycogen storage diseases.

Histochemical Study of Human Placental Tissues in Gestational Diabetic Mellitus

Gestational diabetes mellitus (GDM) is a serious pregnancy complication in which a woman who has never had diabetes develops chronic hyperglycemia during her pregnancy. Normal placental function is essential for optimal fetal growth. The transport of glucose from the mother to the fetus is critical for fetal nutrient demands and can be stored as glycogen in the placenta. However, the function of this glycogen deposition is unknown: It may well be a source of fuel for a placenta itself or the storage reservoir for the later use by the fetus in times of need. While the significance of the placental glycogen remains unknown, the mounting evidence indicates that the altered glycogen metabolism and/or deposition is associated with many pregnancy complications, such as gestational diabetes, that adversely affect fetal development. The aim of this study is to assess glycogen deposition using Histochemical staining of Periodic Acid Schiff (PAS) stain. The placenta tissue collected from 50 women were enrolled in this study (25 women with no complications) and (25 women with gestational diabetes). The placentas of the two groups were compared in this study based on glycogen deposition with periodic acid-Schiff stain. The results of a histochemical investigation using PAS stain revealed a significant increase in the glycogen deposition (p≤0.001) in diabetic women's placentas within the intervillous core, around fetal vessels, and the basement membranes.

Proteomic characterization of GSK3β knockout shows altered cell adhesion and metabolic pathway utilisation in colorectal cancer cells

Glycogen-specific kinase (GSK3β) is an integral regulator of the Wnt signalling pathway as well as many other diverse signalling pathways and processes. Dys-regulation of GSK3β is implicated in many different pathologies, including neurodegenerative disorders as well as many different tumour types. In the context of tumour development, GSK3β has been shown to play both oncogenic and tumour suppressor roles, depending upon tissue, signalling environment or disease progression. Although multiple substrates of the GSK3β kinase have been identified, the wider protein networks within which GSK3β participates are not well known, and the consequences of these interactions not well understood. In this study, LC-MS/MS expression analysis was performed using knockout GSK3β colorectal cancer cells and isogenic controls in colorectal cancer cell lines carrying dominant stabilizing mutations of β-catenin. Consistent with the role of GSK3β, we found that β-catenin levels and canonical Wnt activity are unaffected by knockout of GSK3β and therefore used this knockout cell model to identify other processes in which GSK3β is implicated. Quantitative proteomic analysis revealed perturbation of proteins involved in cell-cell adhesion, and we characterized the phenotype and altered proteomic profiles associated with this. We also characterized the perturbation of metabolic pathways resulting from GSK3β knockout and identified defects in glycogen metabolism. In summary, using a precision colorectal cancer cell-line knockout model with constitutively activated β-catenin we identified several of the diverse pathways and processes associated with GSK3β function.

LUBAC: a new player in polyglucosan body disease

Altered protein ubiquitination is associated with the pathobiology of numerous diseases; however, its involvement in glycogen metabolism and associated polyglucosan body (PB) disease has not been investigated in depth. In PB disease, excessively long and less branched glycogen chains (polyglucosan bodies, PBs) are formed, which precipitate in different tissues causing myopathy, cardiomyopathy and/or neurodegeneration. Linear ubiquitin chain assembly complex (LUBAC) is a multi-protein complex composed of two E3 ubiquitin ligases HOIL-1L and HOIP and an adaptor protein SHARPIN. Together they are responsible for M1-linked ubiquitination of substrates primarily related to immune signaling and cell death pathways. Consequently, severe immunodeficiency is a hallmark of many LUBAC deficient patients. Remarkably, all HOIL-1L deficient patients exhibit accumulation of PBs in different organs especially skeletal and cardiac muscle resulting in myopathy and cardiomyopathy with heart failure. This emphasizes LUBAC's important role in glycogen metabolism. To date, neither a glycogen metabolism-related LUBAC substrate nor the molecular mechanism are known. Hence, current reviews on LUBAC's involvement in glycogen metabolism are lacking. Here, we aim to fill this gap by describing LUBAC's involvement in PB disease. We present a comprehensive review of LUBAC structure, its role in M1-linked and other types of atypical ubiquitination, PB pathology in human patients and findings in new mouse models to study the disease. We conclude the review with recent drug developments and near-future gene-based therapeutic approaches to treat LUBAC related PB disease.