Possible involvement of HSP90-HSF1 multichaperone complex in impairment of HSP72 induction in the failing heart following myocardial infarction in rats.

It is generally accepted that an increase in the myocardial level of heat-shock protein 72 (HSP72) protects viable cardiac tissue against myocardial infarction (MI)-induced stress. However, the induction of HSP72 after exposure to heat shock (HS) is blunted in the failing rat heart following MI. The mechanisms underlying this impairment in the HSP72 induction ability of the failing heart are not yet clearly defined. In the present study, we examined the involvement in heat-shock factor 1 (HSF1), a transcription factor of HSPs, in decreased ability for HSP72 induction in the failing rat heart following MI. In the failing heart, nuclear translocation of the HSF1 after exposure to hyperthermia was markedly reduced, whereas HSF1 in the cytosolic fraction and the HSP90 chaperone complex containing HSF1, a repressor of HSF1, were increased. Treatment with an HSP90 inhibitor, 17-allylamino-17-demethoxygel-danamycin, appeared to dissociate the interaction of HSF1 with HSP90, and then induced HSP72 in the failing heart after exposure to hyperthermia. These results suggest that an increase in the multichaperone complex, especially the HSF1-HSP90 interaction, associated with attenuation of HSF1 translocation into the nucleus, was involved in the impairment of HS-induced HSP72 induction in the failing heart following MI.

Possible involvement of phosphorylated heat-shock factor-1 in changes in heat shock protein 72 induction in the failing rat heart following myocardial infarction.

It is supposed that an increase in the level of heat shock protein 72 (HSP72) in the failing heart would be beneficial for reducing the myocardial damage. However, the induction of HSP72 after an exposure to heat shock is blunted in the failing rat heart following myocardial infarction. In this study, to clarify the possible mechanisms underlying this reduction in the ability for HSP72 induction in the failing heart, the possible involvement of heat-shock factor-1 (HSF1), an HSP transcription factor, in this reduction was examined. When hemodynamic parameters of rats with myocardial infarction 8 weeks after coronary artery ligation were measured, the animals showed the signs of chronic heart failure. The HSF1 content was increased in the viable myocardium in the failing heart. The ability to induce cardiac HSP72 was reduced after an exposure to hyperthermia. The level of HSF1 in the cytosolic fraction from the failing heart with or without exposure to hyperthermia was increased, whereas that of HSF1 in the nuclear fraction was reduced. In the failing heart, the level of HSF1 on its serine 303 (Ser303) residue, which phosphorylation represses HSF1, was increased. These findings suggest that HSF1 translocation from the cytosol into the nucleus was attenuated after an exposure to hyperthermia and that an increase in the phosphorylation of HSF1 Ser303 was involved in the impairment of heat shock-induced HSP72 induction in the failing heart following myocardial infarction.

Changes in small heat shock proteins HSPB1, HSPB5 and HSPB8 in mitochondria of the failing heart following myocardial infarction in rats.

The mechanisms underlying mitochondrial impairment in the failing heart are not yet clearly defined. In the present study, we examined the involvement of changes in small heat shock proteins (HSPs) such as HSPB1, HSPB5 and HSPB8 in mitochondrial dysfunction of the failing heart. Hemodynamic parameters of rats with myocardial infarction at the 2nd and 8th weeks (2W- and 8W-) after coronary artery ligation (CAL) were measured. The 8W-CAL rats, but not the 2W-CAL ones, showed the signs of the chronic heart failure concomitant with a reduced mitochondrial oxygen consumption rate. In the mitochondrial fraction prepared from the heart of the 2W-CAL animals, the contents of small HSPs and phosphorylated small HSPs were increased, suggesting that these increases contributed to the preservation of the mitochondrial energy-producing ability. In the failing heart, HSPB1 and HSPB8 contents and phosphorylated small HSP contents in the mitochondrial fraction were decreased, suggesting that a reduction in mitochondrial translocation of these small HSPs led to impaired mitochondrial energy-producing ability. To further define the submitochondrial locations of these small HSPs, we performed mitochondrial subfractionation. The contents of small HSPs in the 2W-CAL rats were increased in the mitochondrial inner-membrane fraction, whereas those of the 8W-CAL rats were reversed to those of the control animals. These findings suggest that small HSPs, at least in part, play an important role in the development of the impaired mitochondrial energy-producing ability that leads to heart failure after a myocardial infarction.