Abstract
BackgroundIschemic 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.ResultsIschemic 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.ConclusionOur 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.
Highlights
Stroke is the second most common cause of death and disability world-wide making it the most complex and devastating of all neurological diseases [1,2]
Glycogen is the principal endogenous source of cellular energy alternative to blood-derived glucose during periods of energydeficiency in the brain [4]. It is a complex branched polymer of glucose found predominantly in the liver and skeletal muscle where it maintains blood glucose homeostasis and provides energy for muscle contractions, respectively. It consists of glucose molecules covalently linked to a-1,4-glycosidic linkages attached to the polypeptide chain that are extended by the collaborative actions of glycogen synthase (GS) and glycogen branching enzyme (GBE) [5,6]
Glycogen is accumulated in contralateral hemisphere during ischemic stroke We first assessed the metabolic fate of glycogen in ischemic stroke-affected rat brains
Summary
Stroke is the second most common cause of death and disability world-wide making it the most complex and devastating of all neurological diseases [1,2]. Glycogen is the principal endogenous source of cellular energy alternative to blood-derived glucose during periods of energydeficiency in the brain [4]. It is a complex branched polymer of glucose found predominantly in the liver and skeletal muscle where it maintains blood glucose homeostasis and provides energy for muscle contractions, respectively. It consists of glucose molecules covalently linked to a-1,4-glycosidic linkages attached to the polypeptide chain that are extended by the collaborative actions of glycogen synthase (GS) and glycogen branching enzyme (GBE) [5,6]. We investigate the role and regulation of glycogen metabolizing enzymes and their effects on the fate of glycogen during ischemic stroke
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