Decoding the molecular mechanism of selective autophagy of glycogen mediated by autophagy receptor STBD1.

Autophagy of glycogen (glycophagy) is crucial for the maintenance of cellular glucose homeostasis and physiology in mammals. STBD1 can serve as an autophagy receptor to mediate glycophagy by specifically recognizing glycogen and relevant key autophagic factors, but with poorly understood mechanisms. Here, we systematically characterize the interactions of STBD1 with glycogen and related saccharides, and determine the crystal structure of the STBD1 CBM20 domain with maltotetraose, uncovering a unique binding mode involving two different oligosaccharide-binding sites adopted by STBD1 CBM20 for recognizing glycogen. In addition, we demonstrate that the LC3-interacting region (LIR) motif of STBD1 can selectively bind to six mammalian ATG8 family members. We elucidate the detailed molecular mechanism underlying the selective interactions of STBD1 with ATG8 family proteins by solving the STBD1 LIR/GABARAPL1 complex structure. Importantly, our cell-based assays reveal that both the STBD1 LIR/GABARAPL1 interaction and the intact two oligosaccharide binding sites of STBD1 CBM20 are essential for the effective association of STBD1, GABARAPL1, and glycogen in cells. Finally, through mass spectrometry, biochemical, and structural modeling analyses, we unveil that STBD1 can directly bind to the Claw domain of RB1CC1 through its LIR, thereby recruiting the key autophagy initiation factor RB1CC1. In all, our findings provide mechanistic insights into the recognitions of glycogen, ATG8 family proteins, and RB1CC1 by STBD1 and shed light on the potential working mechanism of STBD1-mediated glycophagy.

Gluconeogenesis during development of the grass puffer (Takifugu niphobles).

During the development of teleost fish, the sole nutrient source is the egg yolk. The yolk consists mostly of proteins and lipids, with only trace amounts of carbohydrates such as glycogen and glucose. However, past evidence in some fishes showed transient increase in glucose during development, which may have supported the development of the embryos. Recently, we found in zebrafish that the yolk syncytial layer (YSL), an extraembryonic tissue surrounding the yolk, undergoes gluconeogenesis. However, in other teleost species, the knowledge on such gluconeogenic functions during early development is lacking. In this study, we used a marine fish, the grass puffer (Takifugu niphobles) and assessed possible gluconeogenic functions of their YSL, to understand the difference or shared features of gluconeogenesis between these species. A liquid chromatography (LC) / mass spectrometry (MS) analysis revealed that glucose and glycogen content significantly increased in the grass puffer during development. Subsequent real-time PCR results showed that most of the genes involved in gluconeogenesis increased in segmentation stages and/or during hatching. Among these genes, many were expressed in the YSL and liver, as shown by in situ hybridization analysis. In addition, glycogen immunostaining revealed that this carbohydrate source was accumulated in many tissues at segmentation stage but exclusively in the liver in hatched individuals. Taken together, these results suggest that developing grass puffer undergoes gluconeogenesis and glycogen synthesis during development, and that gluconeogenic activity is shared in YSL of zebrafish and grass puffer.

Expression of secretory calcium-binding phosphoprotein (scpp) genes in medaka during the formation and replacement of pharyngeal teeth.

BACKGROUND: Analyses of tooth families and tooth-forming units in medaka with regard to tooth replacement cycles and the localization of odontogenic stem cell niches in the pharyngeal dentition clearly indicate that continuous tooth replacement is maintained. The secretory calcium-binding phosphoprotein (scpp) gene cluster is involved in the formation of mineralized tissues, such as dental and bone tissues, and the genes encoding multiple SCPPs are conserved in fish, amphibians, reptiles, and mammals. In the present study, we examined the expression patterns of several scpp genes in the pharyngeal teeth of medaka to elucidate their roles during tooth formation and replacement. METHODS: Himedaka (Japanese medaka, Oryzias latipes) of both sexes (body length: 28 to 33 mm) were used in this study. Real-time quantitative reverse transcription-polymerase chain reaction (PCR) (qPCR) data were evaluated using one-way analysis of variance for multi-group comparisons, and the significance of differences was determined by Tukey's comparison test. The expression of scpp genes was examined using in situ hybridization (ISH) with a digoxigenin-labeled, single-stranded antisense probe. RESULTS: qPCR results showed that several scpp genes were strongly expressed in pharyngeal tissues. ISH analysis revealed specific expression of scpp1, scpp5, and sparc in tooth germ, and scpp5 was continually expressed in the odontoblasts of teeth attached to pedicles, but not in the osteoblasts of pedicles. In addition, many scpp genes were expressed in inner dental epithelium (ide), but not in odontoblasts, and scpp2 consistently showed epithelial-specific expression in the functional teeth. Taken together, these data indicate that specific expression of scpp2 and scpp5 may play a critical role in pharyngeal tooth formation in medaka. CONCLUSION: We characterized changes in the expression patterns of scpp genes in medaka during the formation and replacement of pharyngeal teeth.

Gluconeogenesis and glycogen metabolism during development of Pacific abalone, Haliotis discus hannai.

In lecithotrophic larvae, egg yolk nutrients are essential for development. Although yolk proteins and lipids are the major nutrient sources for most animal embryos and larvae, the contribution of carbohydrates to development has been less understood. In this study, we assessed glucose and glycogen metabolism in developing Pacific abalone, a marine gastropod mollusc caught and cultured in east Asia. We found that glucose and glycogen content gradually elevated in developing abalone larvae, and coincident expression increases of gluconeogenic genes and glycogen synthase suggested abalone larvae had activated gluconeogenesis and glycogenesis during this stage. At settling, however, glycogen sharply decreased, with concomitant increases in glucose content and expression of Pyg and G6pc, suggesting the settling larvae had enhanced glycogen conversion to glucose. A liquid chromatography-mass spectrometry (LC/MS)-based metabolomic approach that detected intermediates of these pathways further supported active metabolism of glycogen. Immunofluorescence staining and in situ hybridization suggested the digestive gland has an important role as glycogen storage tissue during settlement, while many other tissues also showed a capacity to metabolize glycogen. Finally, inhibition of glycolysis affected survival of the settling veliger larvae, revealing that glucose is, indeed, an important nutrient source in settling larvae. Our results suggest glucose and glycogen are required for proper energy balance in developing abalone and especially impact survival during settling.

Mouse Stbd1 is N-myristoylated and affects ER-mitochondria association and mitochondrial morphology.

Starch binding domain-containing protein 1 (Stbd1) is a carbohydrate-binding protein that has been proposed to be a selective autophagy receptor for glycogen. Here, we show that mouse Stbd1 is a transmembrane endoplasmic reticulum (ER)-resident protein with the capacity to induce the formation of organized ER structures in HeLa cells. In addition to bulk ER, Stbd1 was found to localize to mitochondria-associated membranes (MAMs), which represent regions of close apposition between the ER and mitochondria. We demonstrate that N-myristoylation and binding of Stbd1 to glycogen act as major determinants of its subcellular targeting. Moreover, overexpression of non-myristoylated Stbd1 enhanced the association between ER and mitochondria, and further induced prominent mitochondrial fragmentation and clustering. Conversely, shRNA-mediated Stbd1 silencing resulted in an increase in the spacing between ER and mitochondria, and an altered morphology of the mitochondrial network, suggesting elevated fusion and interconnectivity of mitochondria. Our data unravel the molecular mechanism underlying Stbd1 subcellular targeting, support and expand its proposed function as a selective autophagy receptor for glycogen and uncover a new role for the protein in the physical association between ER and mitochondria.

CGRP Induces Differential Regulation of Cytokines from Satellite Glial Cells in Trigeminal Ganglia and Orofacial Nociception.

Neuron-glia interactions contribute to pain initiation and sustainment. Intra-ganglionic (IG) secretion of calcitonin gene-related peptide (CGRP) in the trigeminal ganglion (TG) modulates pain transmission through neuron-glia signaling, contributing to various orofacial pain conditions. The present study aimed to investigate the role of satellite glial cells (SGC) in TG in causing cytokine-related orofacial nociception in response to IG administration of CGRP. For that purpose, CGRP alone (10 µL of 10-5 M), Minocycline (5 µL containing 10 µg) followed by CGRP with one hour gap (Min + CGRP) were administered directly inside the TG in independent experiments. Rats were evaluated for thermal hyperalgesia at 6 and 24 h post-injection using an operant orofacial pain assessment device (OPAD) at three temperatures (37, 45 and 10 °C). Quantitative real-time PCR was performed to evaluate the mRNA expression of IL-1ß, IL-6, TNF-α, IL-1 receptor antagonist (IL-1RA), sodium channel 1.7 (NaV 1.7, for assessment of neuronal activation) and glial fibrillary acidic protein (GFAP, a marker of glial activation). The cytokines released in culture media from purified glial cells were evaluated using antibody cytokine array. IG CGRP caused heat hyperalgesia between 6⁻24 h (paired-t test, p < 0.05). Between 1 to 6 h the mRNA and protein expressions of GFAP was increased in parallel with an increase in the mRNA expression of pro-inflammatory cytokines IL-1ß and anti-inflammatory cytokine IL-1RA and NaV1.7 (one-way ANOVA followed by Dunnett's post hoc test, p < 0.05). To investigate whether glial inhibition is useful to prevent nociception symptoms, Minocycline (glial inhibitor) was administered IG 1 h before CGRP injection. Minocycline reversed CGRP-induced thermal nociception, glial activity, and down-regulated IL-1ß and IL-6 cytokines significantly at 6 h (t-test, p < 0.05). Purified glial cells in culture showed an increase in release of 20 cytokines after stimulation with CGRP. Our findings demonstrate that SGCs in the sensory ganglia contribute to the occurrence of pain via cytokine expression and that glial inhibition can effectively control the development of nociception.

Changes in glycogen concentration and gene expression levels of glycogen-metabolizing enzymes in muscle and liver of developing masu salmon.

Glycogen, as an intracellular deposit of polysaccharide, takes important roles in energy balance of many animals. In fish, however, the role of glycogen during development is poorly understood. In the present study, we assessed changes in glycogen concentration and gene expression patterns of glycogen-metabolizing enzymes in developing masu salmon (Oncorhynchus masou masou), a salmonid species inhabiting west side of North Pacific Ocean. As we measured glycogen levels in the bodies and yolk sacs containing the liver separately, the glycogen concentration increased in both parts as the fish developed, whereas it transiently decreased in the yolk sac after hatching, implying glycogen synthesis and breakdown in these tissues. Immunofluorescence staining using anti-glycogen monoclonal antibody revealed localization of glycogen in the liver, muscle and yolk syncytial layer of the pre-hatching embryos and hatched larvae. In order to estimate glycogen metabolism in the fish, the genes encoding homologs of glycogen synthase (gys1 and gys2) and glycogen phosphorylase (pygma, pygmb and pygl) were cloned, and their expression patterns were assessed by quantitative PCR and in situ hybridization. In the fish, gys1 and gys2 were robustly expressed in the muscle and liver, respectively. Also, expression of pyg isoforms was found in muscle, liver and yolk syncytial layer during hatching. With changes in glycogen concentration and expression patterns of relevant genes, our results suggest, for the first time, possible involvement of glycogen in energy balance of fish embryos, especially during hatching.

Gross anatomical classification of the courses of the human lingual artery.

PURPOSE: There are many reports on the variation of origin site of the lingual artery branching from the external carotid artery. However, there are few reports systematically investigating the course of the lingual artery in detail from branching site to the body of tongue. The purpose of this study is to classify systematically the courses of the lingual artery including variations. METHODS: Using 111 body sides of 63 Japanese cadavers for dissection practices, the lingual artery and the surrounding structures were investigated gross anatomically. RESULTS: The courses of the lingual artery were classified into five types based on the positional relationships with the hyoglossus and the mylohyoid as follows; type M: coursing medial to the hyoglossus (normal course, 104 sides), type L: coursing lateral to the hyoglossus (2 sides), type T: transferring its course from lateral to medial to the hyoglossus (2 sides), type P: penetrating the mylohyoid (2 sides), and type C: the coinciding of types M and P (1 side). Types L, T, P, and C were considered to be variant lingual arteries. Types M and T, type L, and type P arose from the external carotid, facial, and submental arteries, respectively. In types L and P, adding to the variant lingual artery, the remnant of the normal lingual artery was also observed. CONCLUSION: The present study provides detailed information on the courses of lingual artery which will be of clinical importance especially in the super-selective arterial angiography.

Anatomical status of the human palatopharyngeal sphincter and its functional implications.

PURPOSE: The transition muscle between the palatopharyngeus (PP) and the superior constrictor of the pharynx (SCP) encircles the pharyngeal isthmus from behind and is designated as the palatopharyngeal sphincter (PPS). The PPS is inferred to play important roles for velopharyngeal closure, but its existence remains controversial and its roles have been regarded as being played by the SCP. The present study aimed to clarify the anatomical status and functional implications of the PPS. MATERIALS AND METHODS: Macroscopic and microscopic examinations were performed on 39 and 4 cadavers, respectively. In the former, the bilateral PPSs and their adjacent structures were exposed from outside and/or inside. In the latter, the velums embedded in paraffin were cut into frontal or sagittal sections and alternately processed with HE and Azan stains. RESULTS: The PPS originated from the nasal aspect of the lateral half of the palatine aponeurosis and the inferior margin of the medial pterygoid plate and was distinguishable from the PP descending in and along the palatopharyngeal arch and the cranialmost portion of the SCP in its origin. It passed dorsally on the lateral side of the levator veli palatini and traversed around the salpingopharyngeal fold running longitudinally. It then entered below the SCP and ran toward the pharyngeal raphe with SCP muscle fibers intermingled. CONCLUSIONS: The PPS is a muscle distinct from the SCP. Its contraction produces Passavant's ridge and conceivably enhances the efficiency of velopharyngeal closure by pressing the salpingopharyngeal fold and the musculus uvulae ridge against the velum.

Glycogen distribution in the microwave-fixed mouse brain reveals heterogeneous astrocytic patterns.

In the brain, glycogen metabolism has been implied in synaptic plasticity and learning, yet the distribution of this molecule has not been fully described. We investigated cerebral glycogen of the mouse by immunohistochemistry (IHC) using two monoclonal antibodies that have different affinities depending on the glycogen size. The use of focused microwave irradiation yielded well-defined glycogen immunoreactive signals compared with the conventional periodic acid-Schiff method. The IHC signals displayed a punctate distribution localized predominantly in astrocytic processes. Glycogen immunoreactivity (IR) was high in the hippocampus, striatum, cortex, and cerebellar molecular layer, whereas it was low in the white matter and most of the subcortical structures. Additionally, glycogen distribution in the hippocampal CA3-CA1 and striatum had a 'patchy' appearance with glycogen-rich and glycogen-poor astrocytes appearing in alternation. The glycogen patches were more evident with large-molecule glycogen in young adult mice but they were hardly observable in aged mice (1-2 years old). Our results reveal brain region-dependent glycogen accumulation and possibly metabolic heterogeneity of astrocytes. GLIA 2016;64:1532-1545.

Human muscle fibre type-specific regulation of AMPK and downstream targets by exercise.

AMP-activated protein kinase (AMPK) is a regulator of energy homeostasis during exercise. Studies suggest muscle fibre type-specific AMPK expression. However, fibre type-specific regulation of AMPK and downstream targets during exercise has not been demonstrated. We hypothesized that AMPK subunits are expressed in a fibre type-dependent manner and that fibre type-specific activation of AMPK and downstream targets is dependent on exercise intensity. Pools of type I and II fibres were prepared from biopsies of vastus lateralis muscle from healthy men before and after two exercise trials: (1) continuous cycling (CON) for 30 min at 69 ± 1% peak rate of O2 consumption (V̇O2 peak ) or (2) interval cycling (INT) for 30 min with 6 × 1.5 min high-intensity bouts peaking at 95 ± 2% V̇O2 peak . In type I vs. II fibres a higher ß1 AMPK (+215%) and lower γ3 AMPK expression (-71%) was found. α1 , α2 , ß2 and γ1 AMPK expression was similar between fibre types. In type I vs. II fibres phosphoregulation after CON was similar (AMPK(Thr172) , ACC(Ser221) , TBC1D1(Ser231) and GS(2+2a) ) or lower (TBC1D4(Ser704) ). Following INT, phosphoregulation in type I vs. II fibres was lower (AMPK(Thr172) , TBC1D1(Ser231) , TBC1D4(Ser704) and ACC(Ser221) ) or higher (GS(2+2a) ). Exercise-induced glycogen degradation in type I vs. II fibres was similar (CON) or lower (INT). In conclusion, a differentiated response to exercise of metabolic signalling/effector proteins in human type I and II fibres was evident during interval exercise. This could be important for exercise type-specific adaptations, i.e. insulin sensitivity and mitochondrial density, and highlights the potential for new discoveries when investigating fibre type-specific signalling.

Accumulation of glycogen in axotomized adult rat facial motoneurons.

This study biochemically determined glycogen content in the axotomized facial nucleus of adult rats up to 35 days postinsult. The amounts of glycogen in the transected facial nucleus were significantly increased at 5 days postinsult, peaked at 7 days postinsult, and declined to the control levels at 21-35 days postinsult. Immunohistochemical analysis with antiglycogen antibody revealed that the quantity of glycogen granules in the axotomized facial nucleus was greater than that in the control nucleus at 7 days postinjury. Dual staining methods with antiglycogen antibody and a motoneuron marker clarified that the glycogen was localized mainly in motoneurons. Immunoblotting and quantification analysis revealed that the ratio of inactive glycogen synthase (GS) to total GS was significantly decreased in the injured nucleus at about 1-3 days postinsult and significantly increased from 7 to 14 days postinsult, suggesting that glycogen is actively synthesized in the early period postinjury but suppressed after 7 days postinsult. The enhanced glycogen at about 5-7 days postinsult is suggested to be responsible for the decrease in inactive GS levels, and the decrease of glycogen after 7 days postinsult is considered to be caused by increased inactive GS levels and possibly the increase in active glycogen phosphorylase.

A murine monoclonal antibody to glycogen: characterization of epitope-fine specificity by saturation transfer difference (STD) NMR spectroscopy and its use in mycobacterial capsular α-glucan research.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a major pathogen responsible for 1.5 million deaths annually. This bacterium is characterized by a highly unusual and impermeable cell envelope, which plays a key role in mycobacterial survival and virulence. Although many studies have focused on the composition and functioning of the mycobacterial cell envelope, the capsular α-glucan has received relatively minor attention. Here we show that a murine monoclonal antibody (Mab) directed against glycogen cross-reacts with mycobacterial α-glucans, polymers of α(1-4)-linked glucose residues with α(1-6)-branch points. We identified the Mab epitope specificity by saturation transfer difference NMR and show that the α(1-4)-linked glucose residues are important in glucan-Mab interaction. The minimal epitope is formed by (linear) maltotriose. Notably, a Mycobacterium mutant lacking the branching enzyme GlgB does not react with the Mab; this suggests that the α(1-6)-branches form part of the epitope. These seemingly conflicting data can be explained by the fact that in the mutant the linear form of the α-glucan (amylose) is insoluble. This Mab was subsequently used to develop several techniques helpful in capsular α-glucan research. By using a capsular glucan-screening methodology based on this Mab we were able to identify several unknown genes involved in capsular α-glucan biogenesis. Additionally, we developed two methods for the detection of capsular α-glucan levels. This study therefore opens new ways to study capsular α-glucan and to identify possible targets for further research.

Expression of transcripts for fibroblast growth factor 18 and its possible receptors during postnatal dentin formation in rat molars.

Fibroblast growth factors (FGFs) regulate the proliferation and differentiation of various cells via their respective receptors (FGFRs). During the early stages of tooth development in fetal mice, FGFs and FGFRs have been shown to be expressed in dental epithelia and mesenchymal cells at the initial stages of odontogenesis and to regulate cell proliferation and differentiation. However, little is known about the expression patterns of FGFs in the advanced stages of tooth development. In the present study, we focused on FGF18 expression in the rat mandibular first molar (M1) during the postnatal crown and root formation stages. FGF18 signals by RT-PCR using cDNAs from M1 were very weak at postnatal day 5 and were significantly up-regulated at days 7, 9 and 15. Transcripts were undetectable by in situ hybridization (ISH) but could be detected by in situ RT-PCR in the differentiated odontoblasts and cells of the sub-odontoblastic layer in both crown and root portions of M1 at day 15. The transcripts of FGFR2c and FGFR3, possible candidate receptors of FGF18, were detected by RT-PCR and ISH in differentiated odontoblasts throughout postnatal development. These results suggest the continual involvement of FGF18 signaling in the regulation of odontoblasts during root formation where it may contribute to dentin matrix formation and/or mineralization.

Glucose uptake mediated by glucose transporter 1 is essential for early tooth morphogenesis and size determination of murine molars.

Glucose is an essential source of energy for body metabolism and is transported into cells by glucose transporters (GLUTs). Well-characterized class I GLUT is subdivided into GLUTs1-4, which are selectively expressed depending on tissue glucose requirements. However, there is no available data on the role of GLUTs during tooth development. This study aims to clarify the functional significance of class I GLUT during murine tooth development using immunohistochemistry and an in vitro organ culture experiment with an inhibitor of GLUTs1/2, phloretin, and Glut1 and Glut2 short interfering RNA (siRNA). An intense GLUT1-immunoreaction was localized in the enamel organ of bud-stage molar tooth germs, where the active cell proliferation occurred. By the bell stage, the expression of GLUT1 in the dental epithelium was dramatically decreased in intensity, and subsequently began to appear in the stratum intermedium at the late bell stage. On the other hand, GLUT2-immunoreactivity was weakly observed in the whole tooth germs throughout all stages. The inhibition of GLUTs1/2 by phloretin in the bud-stage tooth germs induced the disturbance of primary enamel knot formation, resulting in the developmental arrest of the explants and the squamous metaplasia of dental epithelial cells. Furthermore, the inhibition of GLUTs1/2 in cap-to-bell-stage tooth germs reduced tooth size in a dose dependent manner. These findings suggest that the expression of GLUT1 and GLUT2 in the dental epithelial and mesenchymal cells seems to be precisely and spatiotemporally controlled, and the glucose uptake mediated by GLUT1 plays a crucial role in the early tooth morphogenesis and tooth size determination.

Polyglucosan neurotoxicity caused by glycogen branching enzyme deficiency can be reversed by inhibition of glycogen synthase.

Uncontrolled elongation of glycogen chains, not adequately balanced by their branching, leads to the formation of an insoluble, presumably neurotoxic, form of glycogen called polyglucosan. To test the suspected pathogenicity of polyglucosans in neurological glycogenoses, we have modeled the typical glycogenosis Adult Polyglucosan Body Disease (APBD) by suppressing glycogen branching enzyme 1 (GBE1, EC 2.4.1.18) expression using lentiviruses harboring short hairpin RNA (shRNA). GBE1 suppression in embryonic cortical neurons led to polyglucosan accumulation and associated apoptosis, which were reversible by rapamycin or starvation treatments. Further analysis revealed that rapamycin and starvation led to phosphorylation and inactivation of glycogen synthase (GS, EC 2.4.1.11), dephosphorylated and activated in the GBE1-suppressed neurons. These protective effects of rapamycin and starvation were reversed by overexpression of phosphorylation site mutant GS only if its glycogen binding site was intact. While rapamycin and starvation induce autophagy, autophagic maturation was not required for their corrective effects, which prevailed even if autophagic flux was inhibited by vinblastine. Furthermore, polyglucosans were not observed in any compartment along the autophagic pathway. Our data suggest that glycogen branching enzyme repression in glycogenoses can cause pathogenic polyglucosan buildup, which might be corrected by GS inhibition.

Histological demonstration of glucose transporters, fructose-1,6-bisphosphatase, and glycogen in gas gland cells of the swimbladder: is a metabolic futile cycle operating?

Luminal surface of the swimbladder is covered by gas gland epithelial cells and is responsible for inflating the swimbladder by generating O(2) from Root-effect hemoglobin that releases O(2) under acidic conditions. Acidification of blood is achieved by lactic acid secreted from gas gland cells, which are poor in mitochondria but rich in the glycolytic activity. The acidic conditions are locally maintained by a countercurrent capillary system called rete mirabile. To understand the regulation of anaerobic metabolism of glucose in the gas gland cells, we analyzed the glucose transporter expressed there and the fate of ATP generated by glycolysis. The latter is important because the ATP should be immediately consumed otherwise it strongly inhibits the glycolysis rendering the cells unable to produce lactic acid anymore. Expression analyses of glucose transporter (glut) genes in the swimbladder of fugu (Takifugu rubripes) by RT-PCR and in situ hybridization demonstrated that glut1a and glut6 are expressed in gas gland cells. Immunohistochemical analyses of metabolic enzymes demonstrated that a gluconeogenesis enzyme fructose-1,6-bisphosphatase (Fbp1) and a glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Gapdh) are highly expressed in gas gland cells. The simultaneous catalyses of glycolysis and gluconeogenesis reactions suggest the presence of a futile cycle in gas gland cells to maintain the levels of ATP low and to generate heat that helps reduce the solubility of O(2).

Ultrastructural characteristics of oligodendrocyte precursor cells in the early postnatal mouse optic nerve observed by serial block-face scanning electron microscopy.

Oligodendrocyte precursor cells (OPC) arise from restricted regions of the central nervous system (CNS) and differentiate into myelin-forming cells after migration, but their ultrastructural characteristics have not been fully elucidated. This study examined the three-dimensional ultrastructure of OPCs in comparison with other glial cells in the early postnatal optic nerve by serial block-face scanning electron microscopy. We examined 70 putative OPCs (pOPC) that were distinct from other glial cells according to established morphological criteria. The pOPCs were unipolar in shape with relatively few processes, and their Golgi apparatus were localized in the perinuclear region with a single cisterna. Astrocytes abundant in the optic nerve were distinct from pOPCs and had a greater number of processes and more complicated Golgi apparatus morphology. All pOPCs and astrocytes contained a pair of centrioles (basal bodies). Among them, 45% of pOPCs extended a short cilium, and 20% of pOPCs had centrioles accompanied by vesicles, whereas all astrocytes with basal bodies had cilia with invaginated ciliary pockets. These results suggest that the fine structures of pOPCs during the developing and immature stages may account for their distinct behavior. Additionally, the vesicular transport of the centrioles, along with a short cilium length, suggests active ciliogenesis in pOPCs.

Liver glycogen phosphorylase is upregulated in glioblastoma and provides a metabolic vulnerability to high dose radiation.

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.

Identification of mycobacterial alpha-glucan as a novel ligand for DC-SIGN: involvement of mycobacterial capsular polysaccharides in host immune modulation.

Mycobacterium tuberculosis possesses a variety of immunomodulatory factors that influence the host immune response. When the bacillus encounters its target cell, the outermost components of its cell envelope are the first to interact. Mycobacteria, including M. tuberculosis, are surrounded by a loosely attached capsule that is mainly composed of proteins and polysaccharides. Although the chemical composition of the capsule is relatively well studied, its biological function is only poorly understood. The aim of this study was to further assess the functional role of the mycobacterial capsule by identifying host receptors that recognize its constituents. We focused on alpha-glucan, which is the dominant capsular polysaccharide. Here we demonstrate that M. tuberculosis alpha-glucan is a novel ligand for the C-type lectin DC-SIGN (dendritic cell-specific ICAM-3-grabbing nonintegrin). By using related glycogen structures, we show that recognition of alpha-glucans by DC-SIGN is a general feature and that the interaction is mediated by internal glucosyl residues. As for mannose-capped lipoarabinomannan, an abundant mycobacterial cell wall-associated glycolipid, binding of alpha-glucan to DC-SIGN stimulated the production of immunosuppressive IL-10 by LPS-activated monocyte-derived dendritic cells. By using specific inhibitors, we show that this IL-10 induction was DC-SIGN-dependent and also required acetylation of NF-kappaB. Finally, we demonstrate that purified M. tuberculosis alpha-glucan, in contrast to what has been reported for fungal alpha-glucan, was unable to activate TLR2.