title: Molecular basis of impaired glycogen metabolism during ischemic stroke and hypoxia.
abstract: BACKGROUND
  Ischemic stroke is the combinatorial effect of many pathological processes including the loss of energy supplies, excessive intracellular calcium accumulation, oxidative stress, and inflammatory responses. The brain's ability to maintain energy demand through this process involves metabolism of glycogen, which is critical for release of stored glucose. However, regulation of glycogen metabolism in ischemic stroke remains unknown. In the present study, we investigate the role and regulation of glycogen metabolizing enzymes and their effects on the fate of glycogen during ischemic stroke.
  
  
  RESULTS
  Ischemic stroke was induced in rats by peri-vascular application of the vasoconstrictor endothelin-1 and forebrains were collected at 1, 3, 6 and 24 hours post-stroke. Glycogen levels and the expression and activity of enzymes involved in glycogen metabolism were analyzed. We found elevated glycogen levels in the ipsilateral hemispheres compared with contralateral hemispheres at 6 and 24 hours (25% and 39% increase respectively; P<0.05). Glycogen synthase activity and glycogen branching enzyme expression were found to be similar between the ipsilateral, contralateral, and sham control hemispheres. In contrast, the rate-limiting enzyme for glycogen breakdown, glycogen phosphorylase, had 58% lower activity (P<0.01) in the ipsilateral hemisphere (24 hours post-stroke), which corresponded with a 48% reduction in cAMP-dependent protein kinase A (PKA) activity (P<0.01). In addition, glycogen debranching enzyme expression 24 hours post-stroke was 77% (P<0.01) and 72% lower (P<0.01) at the protein and mRNA level, respectively. In cultured rat primary cerebellar astrocytes, hypoxia and inhibition of PKA activity significantly reduced glycogen phosphorylase activity and increased glycogen accumulation but did not alter glycogen synthase activity. Furthermore, elevated glycogen levels provided metabolic support to astrocytes during hypoxia.
  
  
  CONCLUSIONS
  Our study has identified that glycogen breakdown is impaired during ischemic stroke, the molecular basis of which includes reduced glycogen debranching enzyme expression level together with reduced glycogen phosphorylase and PKA activity.
authors.affiliation: Department of Physiology, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Mohammed Iqbal
authors.initials: MI
authors.lastname: Hossain
authors.affiliation: Department of Medicine, St. Vincent's Campus, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Carli Lorraine
authors.initials: CL
authors.lastname: Roulston
authors.affiliation: Department of Physiology, St. Vincent's Campus, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: David Ian
authors.initials: DI
authors.lastname: Stapleton
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D002545:Brain Ischemia / Q000150:complications*; D015687:Cell Hypoxia / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006003:Glycogen / Q000378:metabolism*; D006004:Glycogen Debranching Enzyme System / Q000235:genetics; D024981:Glycogen Phosphorylase / Q000235:genetics; D008297:Male; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015424:Reperfusion; D020521:Stroke / Q000150:complications / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology
chemical_list: D006004:Glycogen Debranching Enzyme System; D047428:Protein Kinase Inhibitors; D006003:Glycogen; D024981:Glycogen Phosphorylase; D017868:Cyclic AMP-Dependent Protein Kinases