Heat shock protein 70 regulates cellular redox status by modulating glutathione-related enzyme activities

Heat shock protein (Hsp) 70 has been reported to protect various cells and tissues from ischemic damage. However, the molecular mechanisms of the protection are incompletely understood. Ischemia induces significant alterations in cellular redox status that plays a critical role in cell survival/death pathways. We investigated the effects of Hsp70 overexpression on cellular redox status in Madin-Darby canine kidney (MDCK) cells under both hypoxic and ischemic conditions with 3 different approaches: reactive oxygen species (ROS) measurement by a fluorescence probe, redox environment evaluation by a hydroxylamine spin probe, and redox status assessment by the glutathione/glutathione disulfide (GSH/GSSG) ratio. Results from each of these approaches showed that the redox status in Hsp70 cells was more reducing than that in control cells under either hypoxic or oxygen and glucose deprivation (OGD) conditions. In order to determine the mechanisms that mediated the alterations in redox state in Hsp70 cells, we measured the activities of glutathione peroxidase (GPx) and glutathione reductase (GR), two GSH-related antioxidant enzymes. We found that OGD exposure increased GPx and GR activities 47% and 55% from their basal levels (no stress) in Hsp70 cells, compared to only 18% and 0% increase in control cells, respectively. These data, for the first time, indicate that Hsp70 modulates the activities of GPx and GR that regulate cellular redox status in response to ischemic stress, which may be important in Hsp70's cytoprotective effects.