ABSTRACT
Cerebral ischemia causes increased transcription of sulfonylurea receptor 1 (SUR1), which forms SUR1-regulated NC(Ca-ATP) channels linked to cerebral edema. We tested the hypothesis that hypoxia is an initial signal that stimulates transcription of Abcc8, the gene encoding SUR1, via activation of hypoxia-inducible factor 1 (HIF1). In the brain microvascular endothelial cells, hypoxia increased SUR1 abundance and expression of functional SUR1-regulated NC(Ca-ATP) channels. Luciferase reporter activity driven by the Abcc8 promoter was increased by hypoxia and by coexpression of HIF1α. Surprisingly, a series of luciferase reporter assays studying the Abcc8 promoter revealed that binding sites for specificity protein 1 (Sp1), but not for HIF, were required for stimulation of Abcc8 transcription by HIF1α. Luciferase reporter assays studying Sp1 promoters of three species, and chromatin immunoprecipitation analysis in rats after cerebral ischemia, indicated that HIF binds to HIF-binding sites on the Sp1 promoter to stimulate transcription of the Sp1 gene. We conclude that sequential activation of two transcription factors, HIF and Sp1, is required to stimulate transcription of Abcc8 following cerebral ischemia. Sequential gene activation in cerebral ischemia provides a plausible molecular explanation for the prolonged treatment window observed for inhibition of the end-target gene product, SUR1, by glibenclamide.
Subject(s)
ATP-Binding Cassette Transporters/genetics , Hypoxia-Inducible Factor 1/metabolism , Hypoxia-Ischemia, Brain/metabolism , Potassium Channels, Inwardly Rectifying/genetics , Receptors, Drug/genetics , Sp1 Transcription Factor/metabolism , Transcription, Genetic , ATP-Binding Cassette Transporters/antagonists & inhibitors , Action Potentials/drug effects , Action Potentials/physiology , Animals , Binding Sites , Brain/blood supply , Brain/metabolism , Calcium Channels/genetics , Calcium Channels/metabolism , Chromatin Immunoprecipitation , Disease Models, Animal , Endothelial Cells/metabolism , Glyburide/pharmacology , Glyburide/therapeutic use , Hep G2 Cells , Humans , Hypoglycemic Agents/pharmacology , Hypoglycemic Agents/therapeutic use , Hypoxia-Inducible Factor 1/antagonists & inhibitors , Hypoxia-Inducible Factor 1/genetics , Hypoxia-Ischemia, Brain/genetics , Hypoxia-Ischemia, Brain/prevention & control , Immunohistochemistry , KATP Channels/genetics , KATP Channels/metabolism , Luciferases/genetics , Male , Microvessels/cytology , Microvessels/metabolism , Patch-Clamp Techniques , Plasmids , Potassium Channels, Inwardly Rectifying/antagonists & inhibitors , Promoter Regions, Genetic , Protein Binding , Rats , Rats, Wistar , Receptors, Drug/antagonists & inhibitors , Reverse Transcriptase Polymerase Chain Reaction , Sp1 Transcription Factor/antagonists & inhibitors , Sp1 Transcription Factor/genetics , Sulfonylurea Receptors , TransfectionABSTRACT
Sulfonylurea receptor 1 (SUR1) is a molecule with more diverse and critically important functions than previously recognized. Long viewed simply as a subunit involved in formation of a subset of K(ATP) channels, accumulating evidence indicates that SUR1 is newly upregulated in CNS ischemia and injury and is surprisingly promiscuous in its association with different pore-forming subunits, which endow it with new roles not previously envisioned. In this review, we focus on the SUR1-regulated NC(Ca-ATP) channel, its emerging role in CNS ischemia and trauma, and the growing evidence from preclinical and clinical studies demonstrating the potential importance of block of SUR1 by sulfonylureas such as glibenclamide (glyburide) in conditions as seemingly diverse as stroke and spinal cord injury.
Subject(s)
ATP-Binding Cassette Transporters/antagonists & inhibitors , Brain Ischemia/drug therapy , Potassium Channel Blockers/therapeutic use , Potassium Channels, Inwardly Rectifying/antagonists & inhibitors , Receptors, Drug/antagonists & inhibitors , Spinal Cord Injuries/drug therapy , Stroke/drug therapy , ATP-Binding Cassette Transporters/physiology , Animals , Humans , KATP Channels/physiology , Potassium Channels/physiology , Potassium Channels, Inwardly Rectifying/physiology , Receptors, Drug/physiology , Sulfonylurea ReceptorsABSTRACT
Acute spinal cord injury (SCI) causes progressive hemorrhagic necrosis (PHN), a poorly understood pathological process characterized by hemorrhage and necrosis that leads to devastating loss of spinal cord tissue, cystic cavitation of the cord, and debilitating neurological dysfunction. Using a rodent model of severe cervical SCI, we tested the hypothesis that sulfonylurea receptor 1-regulated (SUR1-regulated) Ca(2+)-activated, [ATP](i)-sensitive nonspecific cation (NC(Ca-ATP)) channels are involved in PHN. In control rats, SCI caused a progressively expansive lesion with fragmentation of capillaries, hemorrhage that doubled in volume over 12 hours, tissue necrosis, and severe neurological dysfunction. SUR1 expression was upregulated in capillaries and neurons surrounding necrotic lesions. Patch clamp of cultured endothelial cells exposed to hypoxia showed that upregulation of SUR1 was associated with expression of functional SUR1-regulated NC(Ca-ATP) channels. Following SCI, block of SUR1 by glibenclamide or repaglinide or suppression of Abcc8, which encodes for SUR1 by phosphorothioated antisense oligodeoxynucleotide essentially eliminated capillary fragmentation and progressive accumulation of blood, was associated with significant sparing of white matter tracts and a 3-fold reduction in lesion volume, and resulted in marked neurobehavioral functional improvement compared with controls. We conclude that SUR1-regulated NC(Ca-ATP) channels in capillary endothelium are critical to development of PHN and constitute a major target for therapy in SCI.
Subject(s)
ATP-Binding Cassette Transporters/biosynthesis , Calcium Channels/metabolism , Endothelial Cells/metabolism , Hemorrhage/metabolism , Multidrug Resistance-Associated Proteins/biosynthesis , Sodium Channels/metabolism , Spinal Cord Injuries/metabolism , ATP-Binding Cassette Transporters/antagonists & inhibitors , Animals , Behavior, Animal/drug effects , Capillaries/metabolism , Capillaries/pathology , Cells, Cultured , Disease Models, Animal , Endothelial Cells/pathology , Female , Gene Expression Regulation/drug effects , Glyburide/pharmacology , Hemorrhage/drug therapy , Hemorrhage/etiology , Hemorrhage/pathology , Hypoglycemic Agents/pharmacology , Multidrug Resistance-Associated Proteins/antagonists & inhibitors , Necrosis/drug therapy , Necrosis/etiology , Necrosis/metabolism , Necrosis/pathology , Oligodeoxyribonucleotides, Antisense , Patch-Clamp Techniques , Potassium Channels, Inwardly Rectifying , Rats , Rats, Long-Evans , Receptors, Drug , Spinal Cord Injuries/complications , Spinal Cord Injuries/drug therapy , Spinal Cord Injuries/pathology , Sulfonylurea Receptors , Time FactorsABSTRACT
Cerebral edema is caused by a variety of pathological conditions that affect the brain. It is associated with two separate pathophysiological processes with distinct molecular and physiological antecedents: those related to cytotoxic (cellular) edema of neurons and astrocytes, and those related to transcapillary flux of Na+ and other ions, water, and serum macromolecules. In this review, the authors focus exclusively on the first of these two processes. Cytotoxic edema results from unchecked or uncompensated influx of cations, mainly Na+, through cation channels. The authors review the different cation channels that have been implicated in the formation of cytotoxic edema of astrocytes and neurons in different pathological states. A better understanding of these molecular mechanisms holds the promise of improved treatments of cerebral edema and of the secondary injury produced by this pathological process.
Subject(s)
Brain Edema/etiology , Brain Edema/pathology , Ion Channels/physiology , Animals , Astrocytes/pathology , Electrolytes/metabolism , Humans , Neurons/pathologyABSTRACT
Pathological conditions in the central nervous system, including stroke and trauma, are often exacerbated by cerebral edema. We recently identified a nonselective cation channel, the NC(Ca-ATP) channel, in ischemic astrocytes that is regulated by sulfonylurea receptor 1 (SUR1), is opened by depletion of ATP and, when opened, causes cytotoxic edema. Here, we evaluated involvement of this channel in rodent models of stroke. SUR1 protein and mRNA were newly expressed in ischemic neurons, astrocytes and capillaries. Upregulation of SUR1 was linked to activation of the transcription factor Sp1 and was associated with expression of functional NC(Ca-ATP) but not K(ATP) channels. Block of SUR1 with low-dose glibenclamide reduced cerebral edema, infarct volume and mortality by 50%, with the reduction in infarct volume being associated with cortical sparing. Our findings indicate that the NC(Ca-ATP) channel is crucially involved in development of cerebral edema, and that targeting SUR1 may provide a new therapeutic approach to stroke.
