Energy failure in astrocytes increases the vulnerability of neurons to spreading depression.
A neuroprotective role of astrocytes has been hypothesized, but the mechanism is debated and in vivo evidence is limited. To test this hypothesis, a sublethal stressor (spreading depression) and fluorocitrate (FC), a selective inhibitor of the astrocytic Krebs cycle, were used in urethane-anaesthetized adult rats. Neuronal damage was assessed 24 h after treatment with silver stain and immunoreactivity for a 72-kDa heat-shock protein. ATP levels and mitochondrial aconitase activity, a marker indicating exposure to reactive oxygen species, were measured after 4 and 24 h. Spreading depression alone did not affect ATP levels, mitochondrial aconitase activity, or induce neuronal injury in the cortex. Local or intraventricular injection of FC significantly decreased ATP levels and mitochondrial aconitase activity, but did not produce neuronal damage. In animals receiving injections of FC and then spreading depression, there was evidence of significant neuronal stress and damage. Isocitrate, which bypasses the metabolic inhibition produced by FC, prevented all of the changes seen after the combination of FC and spreading depression. One-hour pretreatment with dimethyl sulfoxide (a scavenger of hydroxyl radicals), deferoxamine (an iron chelator) or fructose-1,6-bisphosphate also blocked inactivation of mitochondrial aconitase, ATP depletion and the neuronal damage induced by FC and spreading depression. These experiments demonstrate that inhibition of the metabolism of astrocytes, with a decrease in ATP levels, will increase the susceptibility of neurons to the stress induced by spreading depression. The neuroprotective effects of dimethyl sulfoxide, deferoxamine and fructose-1,6-bisphosphate suggest that oxidative stress contributes to the neurotoxicity in this situation.
Lian
Xiao-Yuan
XY
Department of Pharmacology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. xlian@bcm.tmc.edu
Stringer
Janet L
JL
D000154:Aconitate Hydratase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001253:Astrocytes / Q000187:drug effects*; D015153:Blotting, Western / Q000379:methods; D002470:Cell Survival / Q000187:drug effects; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D002951:Citrates / Q000008:administration & dosage*; D013181:Cortical Spreading Depression / Q000502:physiology*; D003676:Deferoxamine / Q000494:pharmacology; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D005635:Fructosediphosphates / Q000494:pharmacology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005973:Glutamine / Q000494:pharmacology; D050884:HSP72 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D007502:Iron Chelating Agents / Q000494:pharmacology; D007523:Isocitrates / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D009474:Neurons / Q000187:drug effects*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016622:Silver Staining / Q000379:methods
D002951:Citrates; D005635:Fructosediphosphates; D005904:Glial Fibrillary Acidic Protein; D050884:HSP72 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D007502:Iron Chelating Agents; D007523:Isocitrates; D005973:Glutamine; C007744:fluorocitrate; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; C034219:isocitric acid; D000154:Aconitate Hydratase; D003676:Deferoxamine; D004121:Dimethyl Sulfoxide