AJP - Heart Calcium Transients and Cell-Sarcomere
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Am J Physiol Heart Circ Physiol (March 2, 2007). doi:10.1152/ajpheart.01098.2006
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Submitted on October 6, 2006
Accepted on February 25, 2007

Hypoxic Preconditioning Protects Human Brain Endothelium from Ischemic Apoptosis by Akt-Dependent Survivin Activation

Yunhong Zhang1, Tae Sung Park1, and Jeffrey M Gidday2*

1 Neurosurgery, Washington University School of Medicine, St. Louis, Missouri, United States
2 Neurosurgery, Washington University, St. Louis, Missouri, United States

* To whom correspondence should be addressed. E-mail: gidday{at}nsurg.wustl.edu.

Preconditioning-induced ischemic tolerance is well documented in brain, but cell-specific responses and mechanisms require further elucidation. The aim of this study was to develop an in vitro model of ischemic tolerance in human brain microvascular endothelial cells (HBMECs) and to examine the roles of PI3-kinase/Akt and the inhibitor-of-apoptosis protein Survivin in the ability of hypoxic preconditioning (HP) to protect endothelium from apoptotic cell death. Cultured HBMECs were subjected to HP, followed 16 h later by complete oxygen and glucose deprivation (OGD) for 8 h; cell viability was quantified at 20 h of reoxygenation (RO) by the MTT assay. HBMECs were examined at various times after HP or OGD/RO using immunoblotting and confocal laser scanning immunofluorescence microscopy for appearance of apoptotic markers, and expression of phosphorylated Akt (p-Akt) and phosphorylated survivin (p-survivin). Causal evidence for the participation of the PI3-kinase/Akt pathway in HP-induced protection and p-survivin upregulation was assessed by the PI3-kinase inhibitor LY294002. HP significantly reduced OGD/RO-induced injury by 50%, and also significantly reduced the OGD-induced translocation of apoptosis-inducing factor (AIF) from mitochondria to nucleus and the concomitant cleavage of poly(ADP-ribose) polymerase-1 (PARP-1). PI3-kinase inhibition blocked HP-induced increases in Akt phosphorylation, reversed the effects of HP on OGD-induced AIF translocation and PARP-1 cleavage, blocked HP-induced survivin phosphorylation, and ultimately attenuated HP-induced protection of HBMECs from OGD. Thus, HP promotes an antiapoptotic phenotype in HBMECs, in part by activating survivin via the PI3-kinase/Akt pathway. Survivin and other phosphorylation products of p-Akt may be therapeutic targets to protect cerebrovascular endothelium from apoptotic injury following cerebral ischemia.







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