Abstract
Cell death induced by the combined insult of hypoxia-ischemia in neonatal rodents has been extensively investigated. Ischemia-only-induced cell death, however, has been much less characterized. Based on the notion that 1) ischemic stroke is a relatively common disorder in human neonates, and 2) developing cells are more susceptible to apoptosis, the present study examined whether typical apoptosis was induced by cerebral ischemia in a new neonatal rat model. Erythropoietin (EPO; Epoetin) was tested for its protective effect against ischemia-induced cell death. Postnatal day 7 rats were subjected to permanent occlusion of the middle cerebral artery branch supplying the right whisker-barrel cortex. Terminal deoxynucleotidyl transferase biotin-dUTP nick end-labeled-positive cells in the ischemic region were detectable 4 h after ischemia and reached a peak level 16 h later. The cell death was preceded by caspase activation and cytochrome c release. Cell body shrinkage was evident among damaged cells. Agarose gel electrophoresis showed DNA damage with a smear pattern as well as DNA laddering. Electron microscopy demonstrated apoptotic features such as cell shrinkage, chromatin condensation, and fragmentation; meanwhile, necrotic alterations coexisted in the cytoplasm. EPO treatment increased signal transducers and activators of transcription-5 and Bcl-2 levels, markedly attenuated apoptotic cell death, and reduced ischemic infarct in the cortex. It is suggested that focal ischemia in the developing brain causes cell death with prominent apoptotic features coexisting with some characteristics of necrosis. This is consistent with the concept of hybrid death described previously in cultures and adult or developing brain. EPO may be explored as a potential therapy for neonatal ischemic stroke.
Footnotes
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This study was supported by National Institutes of Health Grants NS35902 (to D.M.H.), NS37337, NS42236, NS045155, and NS045810, and American Heart Association and Bugher Foundation Awards 0170064N and 0170063N.
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doi:10.1124/jpet.105.094391.
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ABBREVIATIONS: MCA, middle cerebral artery; P7, postnatal day-7; EPO, erythropoietin; EPOR, erythropoietin receptor; JAK, Janus tyrosine kinase; STAT-5, signal transducers and activators of transcription-5; CCA, common carotid artery; TTC, triphenyl tetrazolium chloride; TUNEL, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling.
- Received August 18, 2005.
- Accepted December 14, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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