Relationship between ischemia duration and expression of heat shock protein 70 in ischemia-reperfusion canine hearts

Background Heat shock protein 70 (HSP70) has been shown to exert a protective effect in hearts subjected to ischemia-reperfusion and alleviate adverse effects of myocardial ischemia-reperfusion injury (MIRI). However, little is known about the influence of ischemia time on HSP70 expression. The effects of ischemic duration on the content of HSP70 transcripts in ischemia-reperfusion myocardium were investigated in this study. Methods Male mongrel dogs underwent a 15-or 60-min occlusion of the left anterior descending coronary artery, followed by a 120-min reperfusion. Additionally, a sham-operation group was assigned. The animals were killed after 120-min reperfusion and the heart was quickly removed. The myocardium was examined pathologically by electron microscopy. HSP70 mRNA expressions both in intact and ischemic myocardium were measured by a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method using complementary DNA normalized against the housekeeping gene β-actin. Results (1) No ultrastructural changes of microvessels and myocardial cells except for a slight loss of mitochondrial granules were noted in reperfusion myocardium from dogs in 15-min ischemia group. In 60-min ischemia group, endothelial cells of capillaries showed slight swelling, and the intercellular linking gaps of endothelial cells slightly widened. As for myocardial cells, intercellular, intermyofibrillar, and intermyofilament edemas were present. Besides, the fractures of a few myofilaments, the granule loss and swelling of mitochondria were also seen. (2) HSP70 mRNA expression level in both ischemia-reperfusion zone and intact myocardium was markedly higher in 15- min ischemia group than in sham-operation group (36.2 ± 6.5 vs 22.0 ± 4.0, P = 0.005; 29.8 ± 4.5 vs 22.2 ± 4.7, P = 0.050). Compared with sham-operation group, however, no changes in mRNA HSP70 levels were seen in 60 min ischemia group (25.7 ± 7.5 vs 22.0 ± 4.0, P = 0.681; 28.5 ± 4.7 vs 22.2 ± 4.7, P = 0.118). The ratio of HSP70 mRNA expression content in ischemia-reperfusion zone to that in intact myocardium in 15-min ischemia group was not significantly different from sham-operation group (1.22 ± 0.16 vs 1.01 ± 0.22, P = 0.233), but remarkably higher than 60-min ischemia group (1.22 ± 0.16 vs 0.89 ± 0.17, P = 0.019).Conclusions The change of HSP70 expression in ischemia-reperfusion myocardium is associated with ischemia time, that is, short duration ischemia promotes HSP70 expression , whereas long time ischemia does not. Furthermore, the HSP 70 expression changes consist with the protective extent of myocardial ultrastructures.