We previously reported that a dual PI3K-mTOR inhibitor BEZ235 (BEZ) induced cardiac hypertrophy. Here, we investigated potential mechanisms.
Methods: three month old FVB/n female mice were treated with BEZ for five weeks. Cardiac function was monitored by serial echocardiography during the treatment and hemodynamic measurements at the end of the study. Cell signaling was analyzed by RT-PCR, Western blotting and ELISA.
Results: BEZ induced a dose-dependent increase of left ventricular (LV) wall thickness and systolic function. These were associated with increased hypertrophic markers ANP, BNP, β-MHC and α-skeletal actin in the heart. In addition, in chronic BEZ-treated mouse hearts, the activations of PI3Ks, mTOR and ERK were increased. We conducted further studies to understand these contradictory results. We found that BEZ induced an increase of hepatic gluconeogenesis gene expression which was associated with increased fasting glucose, increased serum insulin level, a worsened glucose and pyruvate tolerance and increased IGFR/Insulin receptor activation in the heart. Injections of insulin lowered blood glucose, improved glucose and pyruvate tolerance, but further aggravated BEZ-induced cardiac dysfunction. On the other hand, OSI-906 (an IGFR/IR inhibitor) normalized cardiac function in BEZ-treated mice.
Conclusions: Chronic BEZ treatment induced cardiac hypertrophy may be caused by increased insulin receptor activation in the heart.