Glycogen autophagy in glucose homeostasis.

Department of Anatomy, Histology and Embryology, Medical School, University of Ioannina, Ioannina, Greece.
Pathology - Research and Practice (Impact Factor: 1.21). 02/2006; 202(9):631-8. DOI: 10.1016/j.prp.2006.04.001
Source: PubMed

ABSTRACT Glycogen autophagy, the sequestration and degradation of cell glycogen in the autophagic vacuoles, is a selective, hormonally controlled and highly regulated process, representing a mechanism of glucose homeostasis under conditions of demand for the production of this sugar. In the newborn animals, this process is induced by glucagon secreted during the postnatal hypoglycemia and inhibited by insulin and parenteral glucose, which abolishes glucagon secretion. Hormonal action is mediated by the cAMP/protein kinase A (induction) and phosphoinositides/mTOR (inhibition) pathways that converge on common targets, such as the protein phosphatase 2A to regulate autophgosomal glycogen-hydrolyzing acid glucosidase and glycogen autophagy. Intralysosomal phosphate exchange reactions, which are affected by changes in the calcium levels and acid mannose 6- and acid glucose 6-phosphatase activities, can modify the intralysosomal composition in phosphorylated and nonphosphorylated glucose and promote the exit of free glucose through the lysosomal membrane. Glycogen autophagy-derived nonphosphorylated glucose assists the hyaloplasmic glycogen degradation-derived glucose 6-phosphate to combat postnatal hypoglycemia and participates in other metabolic pathways to secure the fine tuning of glucose homeostasis during the neonatal period.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT Extranuclear DNA (enDNA) is not well studied ultrastructurally in the retinal pigment epithelium (RPE). We analyzed the retina and vastus medialis muscle of four mouse strains that are related to focal retinal degeneration by transmission electron microscopy (TEM) and EM immunolabeling. Evaluation of enDNA would imply the involvements of enDNA is either limited to the affected tissue or generalized in the whole body. Ultrastructural analysis and EM immunolabeling revealed that enDNA was present in the RPE cells but not in the muscle. These data suggest that enDNA could be unique to unhealthy RPE and a potential biomarker for cellular abnormality.
    Ultrastructural Pathology 06/2014; · 0.98 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Autophagy recently has been shown to be involved in normal hepatic function and in pathological conditions such as non-alcoholic fatty liver disease. Adrenergic signalling also is an important regulator of hepatic metabolism and function. However, currently little is known about the potential role of adrenergic signaling on hepatic autophagy, and whether the β-adrenergic receptor itself may be a key regulator of autophagy. To address these issues, we investigated the actions of the β2-adrenergic receptor agonist, clenbuterol on hepatic autophagy. Surprisingly, we found that clenbuterol stimulated autophagy and autophagic flux in hepatoma cells, primary hepatocytes and in vivo. Similar effects also were observed with epinephrine treatment. Interestingly, propranolol caused a late block in autophagy in the absence and presence of clenbuterol, both in cell culture and in vivo. Thus, our results demonstrate that the β2- adrenergic receptor is a key regulator of hepatic autophagy, and that the β-blocker propranolol can independently induce a late block in autophagy.
    PLoS ONE 01/2014; 9(6):e98155. · 3.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, we tested the hypothesis that NAC administration leads to reduced oxidative stress and thus to decreased expression of autophagy markers in young mice. Our results reveal that NAC administration results in reduced muscle mRNA levels of several autophagy markers, including Beclin-1, Atg7, LC3, Atg9, and LAMP2. However, NAC supplement fails to block the activation of skeletal muscle autophagy in response to fasting, because fasting significantly increases the mRNA level of several autophagy markers and LC3 lipidation. We further examined the effects of NAC administration on mitochondrial antioxidant capacity in fed and 24-hour fasted mice. Our results clearly show that NAC administration depresses the expression of manganese superoxide dismutase (MnSOD) and TP53-induced glycolysis and apoptosis regulator (TIGAR), both of which play a predominant antioxidant role in mitochondria by reducing ROS level. In addition, we found no beneficial effect of NAC supplement on muscle mass but it can protect from muscle loss in response to fasting. Collectively, our findings indicate that ROS is required for skeletal muscle constitutive autophagy, rather than starvation-induced autophagy, and that antioxidant NAC inhibits constitutive autophagy by the regulation of mitochondrial ROS production and antioxidant capacity.
    Oxidative medicine and cellular longevity. 01/2014; 2014:315896.