Bcl-2 prevents hypoxia/reoxygenation-induced cell death through suppressed generation of reactive oxygen species and upregulation of Bcl-2 proteins.
The function of bcl-2 in preventing cell death is well known, but the mechanisms whereby bcl-2 functions are not well characterized. One mechanism whereby bcl-2 is thought to function is by alleviating the effects of oxidative stress upon the cell. To examine whether Bcl-2 can protect cells against oxidative injury resulting from post-hypoxic reoxygenation (H/R), we subjected rat fibroblasts Rat-1 and their bcl-2 transfectants b5 to hypoxia (5% CO2, 95% N2) followed by reoxygenation (5% CO2, 95% air). The bcl-2 transfectants exhibited the cell viability superior to that of their parent non-transfectants upon treatment with reoxygenation after 24-, 48-, or 72-h hypoxia, but not upon normoxic serum-deprivation or upon serum-supplied hypoxic treatment alone. Thus bcl-2 transfection can prevent cell death of some types, which occurred during H/R but yet not appreciably until termination of hypoxia. The time-sequential events of H/R-induced cell death were shown to be executed via (1) reactive oxygen species (ROS) production at 1-12 h after H/R, (2) activation of caspases-1 and -3, at 1-3 h and 3-6 h after H/R, respectively, and (3) loss of mitochondrial membrane potential (DeltaPsi) at 3-12 h after H/R. These cell death-associated events were prevented entirely except caspase-1 activation by bcl-2 transfection, and were preceded by Bcl-2 upregulation which was executed as early as at 0-1 h after H/R for the bcl-2 transfectants but not their non-transfected counterpart cells. Thus upregulation of Bcl-2 proteins may play a role in prevention of H/R-induced diminishment of cell viability, but may be executed not yet during hypoxia itself and be actually operated as promptly as ready to go immediately after beginning of H/R, resulting in cytoprotection through blockage of either ROS generation, caspase-3 activation, or DeltaPsi decline.
Saitoh
Yasukazu
Y
Division of Cell Biochemistry, Hiroshima Prefectural University School of BioSciences, Shobara, Hiroshima 727-0023, Japan.
Ouchida
Rika
R
Miwa
Nobuhiko
N
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology*; D002470:Cell Survival; D002478:Cells, Cultured; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014162:Transfection; D015854:Up-Regulation
D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D020169:Caspases; D010100:Oxygen