BLOCKING THE ENDOGENOUS INCREASE IN HSP-72 INCREASES SUSCEPTIBILITY TO HYPOXIA AND REOXYGENATION IN ISOLATED ADULT FELINE CARDIOCYTES

Background Heat shock protein (HSP) 72 is a ubiquitous protein that is rapidly induced in response to stress and is thought to constitute an endogenous protective response. Previously, work has focused on the e ffect of overexpression of HSP 72 in various cell types. We were inter ested in testing the hypothesis that blocking the increase in HSP 72 t hat occurs in response to hypoxia or ischemia would be deleterious, th us showing that the endogenous response in cells, particularly cardiac cells, is an important line of defense against cell injury. Methods a nd Results Isolated adult feline cardiocytes were treated with a 14-me r phosphorothioate antisense (AS) to HSP 72 and then exposed to mild ( 8 hours) or severe (12 hours) hypoxia. With mild hypoxia, an increase in LDH release, a decrease in MTT uptake, and a decrease in live-to-de ad ratios were seen in AS-treated cells compared with control cells an d cells treated with the complementary sense sequence or with AS to ma jor histocompatibility complex I. AS treatment converted mild hypoxic injury to a pattern of cell injury seen with severe injury. After seve re hypoxia, all treatment groups showed an increase in LDH, a decrease in MTT uptake, and a decrease in live-to-dead ratios; AS-treated cell s had the greatest increase in cell injury. AS treatment produced a 40 % decrease in HSP 72 levels after hypoxia compared with control cells treated with hypoxia. A dose-response study showed inhibition of the i ncrease in HSP 72 with as little as 5 mu g (1.24 mu mol/L) of AS. Conc lusions (1) Blocking an increase in HSP 72 with AS increases the susce ptibility of adult cardiac myocytes to hypoxic injury. (2) HSP 72 is a n important part of the normal cell response to stress and is importan t in protecting cardiac myocytes from hypoxia and reoxygenation.