Expression of Heat Shock Protein mRNA Induced by Ischemia-Reperfusion in Skeletal Muscles

ABSTRACT

The heat shock response is an important homeostatic mechanism that enables cells of animals, plants, and bacteria to survive a variety of environmental stresses. In all organisms a small set of proteins(heat shock proteins, hsps) is preferentially synthesized in response to stress. By seeking the expression of mRNA of hsps to tissue ischemia-reperfusion injury, a guideline can be provided in its application. A total of 100 Sprague-Dawley rats weighing about 200 to 300 gm were used. The rats were divided into three groups; group1 sham operation group, group 2 ischemia induced only, and group 3 ischemia-reperfusion group. The ischemia group(group 2) was subdivided according to the duration of ischemia. 1, 2, 4, 8, and 12 hours each. Ischemia-reperfusion group(group 3) was subdivided according to the duration of ischemic insult lasting 1, 2, and 4 hours each(group 3-1, 2, 3). Samples were taken from both subgroups 15 min, 30 min, 1, 2, 4, 8 hours after reperfusion. Creatine phosphokinase levels were measured and mRNA expression was observed using in situ hydridization histochemistry. The elevation of creatine phosphokinase was correlated to the duration of ischemic insult and to the duration of reperfusion time. This postulated the fact that the amount of muscle injury had direct connection with time of ischemia and the injury continued even after reperfusion. The overall mRNA of hsp in the ischemia-reperfusion group showed faster and stronger expression compared to that of the ischemia-only group. Among the ischemia-reperfusion subgroups, as the ischemic time was increased, the mRNA expression demonstrated faster but with decreased amount. This findings suggest that there can be a limit in expression of hsp based on the extent of ischemic insult. This can be helpful in clinical applications. When the gastrocnemius and soleus muscle are compared, white muscle group(gastrocnemius) revealed faster and stronger expression of mRNA of hsps. This is most likely due to the fact that red muscle group has abundant blood supply and mitochondria, and implies decreased injury after ischemia-reperfusion. Although the precisive mechanism of hsp is not yet known, heat shock induced protection increases flap survival dramatically. But by demonstrating the pattern of expression based on ischemia time and reperfusion, this paper suggests a possible limit of hsp against ischemia- reperfusion injury.