Simvastatin attenuates the c-Raf/Erk and calcineurin-NFATc2 pathways via inhibition of Hsp90 activity during the development of heart failure.

Hsp90 is a molecular chaperone that contributes to the activation and stabilization of client proteins. In our previous studies, we found that inhibition of Hsp90 delayed cardiac remodeling during the development of chronic heart failure in animal models. Simvastatin, an inhibitor of HMG-CoA reductase, has been shown to inhibit Hsp90. However, it is unclear whether simvastatin can prevent cardiac remodeling by inhibiting Hsp90. Therefore, the effects of simvastatin were examined in a rat model of chronic heart failure following myocardial infarction. The results showed that simvastatin reduced cardiac remodeling by inhibiting cardiac fibrosis. Furthermore, simvastatin decreased the expression of c-Raf and calcineurin, which are involved in intracellular signaling during the development of myocardial remodeling. In vitro, we found that the interaction of Hsp90 with c-Raf and calcineurin was reduced and the expression levels these client proteins were decreased in fibroblasts cultured in the presence of simvastatin. In addition, simvastatin also reduced proliferation, migration, and collagen production of fibroblasts. These results suggest that Hsp90 inhibition is partly responsible for the inhibitory effect of simvastatin on the development of myocardial remodeling.

Effects of 17-AAG on the RIP1/RIP3/MLKL pathway during the development of heart failure following myocardial infarction in rats.

In a previous study, we suggested that the Hsp90 inhibitor 17-AAG prevents cardiac dysfunction in the failing heart following myocardial infarction in rats. Although it is assumed that the RIP1/RIP3/MLKL necroptotic pathway, which comprises client proteins for Hsp90, is involved; however, the relationship between the cardioprotective effects of 17-AAG and the activity of the cardiac RIP1/RIP3/MLKL necrosome-associated proteins in the failing heart following myocardial infarction remained unclear. Therefore, the levels of phosphorylated MLKL after myocardial infarction with or without Hsp90 inhibitor treatment were measured. Myocardial infarction was induced by ligation of the coronary artery (CAL) in Wistar rats. 17-AAG was injected from the 2nd to the 8th week after myocardial infarction. The administration of 17-AAG attenuated the cardiac dysfunction, hypertrophy, and fibrosis at the 8th week after CAL, simultaneously lessening the increases in the expression and phosphorylation levels of RIP1, RIP3, and MLKL in the area of the left ventricular muscle without infarct. These results indicate that the activation of the RIP1/RIP3/MLKL pathway is a common event in the development of chronic heart failure. Furthermore, our findings suggest that the effects of 17-AAG treatment on the improvement of cardiac function in rats after myocardial infarction is related to the attenuation of this RIP1/RIP3/MLKL pathway.