Association of heat shock protein 70 expression with rat myocardial cell damage during heat stress in vitro and in vivo.

To investigate the mechanism of sudden death as a result of stress-induced damage to heart tissue and myocardial cells and to investigate the cardioprotective role of Hsp70 during heat stress, the distribution and expression of Hsp70 was evaluated in the heart cells of heat-stressed rats in vivo and heat-stressed H9c2 cells in vitro. After exposure to heat stress at 42°C for different durations, we observed a significant induction of CK, CK-MB, and LDH as well as pathologic lesions characterized by acute degeneration, suggesting that cell damage occurs from the onset of heat stress. Immunocytochemistry showed that Hsp70 was distributed mainly in the cytoplasm of myocardial cells in vivo and in vitro. Hsp70-positive signals in the cytoplasm were more prominent in intact areas than in degenerated areas after 60 min of heat stress. Hsp70 protein levels in myocardial cells in vitro decreased from the beginning to the end of heat stress. Hsp70 protein levels in rat heart tissues in vivo decreased gradually with prolonged heat stress, with a slight increase at the beginning of heat stress. These results indicate that Hsp70 plays a role in the response of cardiac cells to heat stress and that decreased Hsp70 levels are associated with damage to rat myocardial cells in vitro and in vivo. Significant differences were found in hsp70 mRNA, which began to increase after 20 min of heat stress in vitro and after 40 min in vivo. This indicates that hysteresis is involved in mRNA expression after heat stress in vivo.

Association of Hsp60 expression with damage to rat myocardial cells exposed to heat stress in vivo and in vitro.

To investigate the protective role of Hsp60 against stress damage and its role in the sudden death of stressed animals, changes in the levels of Hsp60 protein and hsp60 mRNA of myocardial cells in vivo and in vitro were studied. In addition, the relationship between Hsp60 expression and heat-induced damage was also studied. Rats were exposed to a temperature of 42° ± 1°C for 0, 20, 40, 60, 80, or 100 min. More than 50% of the rats died suddenly within 100 min. With increasing heat stress duration, hsp60 mRNA levels significantly increased in both in vivo and in vitro rat myocardial cells; however, a similar trend was not observed for Hsp60 protein levels. Although the changes observed in Hsp60 expression in myocardial cells in vitro were inconsistent with those of rat heart tissues in vivo, Hsp60 expression levels were consistent with the histopathological damage observed in myocardial cells both in vivo and in vitro. Differences in Hsp60 expression may reflect the degree of injury sustained by myocardial cells in vivo and in vitro. As a mitochondrial protein, Hsp60 represents a potential biomarker of heat stress, and may protect against heat stress induced myocardial cellular damage both in vivo and in vitro.

Evaluation of Hsp47 expression in heat-stressed rat myocardial cells in vitro and in vivo.

The aim of the present study was to identify the correlation between expression of heat shock protein 47 (Hsp47) and stress injury in heat-stressed myocardial cells and to compare variations in Hsp47 expression in rat myocardial cells exposed to different heat stress for varying periods in vitro and in vivo. Exposure to heat stress at 42°C resulted in similar induction patterns of the heart damage-related enzyme aspartate aminotransferase in the supernatants of H9c2 cells and in the serum of rats. Histological analysis revealed that both H9c2 cells and heart tissues displayed cellular degeneration in response to different periods of heat stress. Hsp47 was constitutively expressed in the cytoplasm of H9c2 cells at all time points during heat stress, which was consistent with observations in heart fibers in vivo. Immunoblotting analysis revealed no significant difference between the expression of Hsp47 in H9c2 cells and heart tissue. However, the expression of hsp47 mRNA in response to heat stress was significantly increased in H9c2 cells at 60 min (P < 0.01) and 100 min (P < 0.01), which was comparable to that at 100 min (P < 0.01) in the rat heart. Thus, Hsp47 was elevated significantly after hyperthermia at the mRNA level but not at the protein level both in vitro and in vivo. The results suggest that Hsp47 turnover may increase during heat stress or that Hsp47 consumption exceeds its production.