Abstract 13459: Enhancement of Foxo Proteins Suppressing NaV1.5 Expression by Reactive Oxygen Species in Chronic Ischemic Heart Disease
Background: Our previous in vitro studies showed that Foxo1 negatively regulates SCN5a gene transcription. Reactive oxygen species, such as hydrogen peroxide (H2O2), were reported to be increased in ischemic heart disease (IHD) and to promote Foxo protein nuclear localization. Therefore, we determined if cardiac deletion of Foxo proteins increases cardiac INa by augmenting NaV1.5 expression and this deletion is able to prevent NaV1.5 downregulation in IHD, and if H2O2 promoting Foxo1 nuclear localization leads to decrease of NaV1.5 expression.
Methods: Adult mouse cardiac deletion of Foxo1,3,4 (Foxo1,3,4-/-) was induced by 4-hydroxytamoxifen (i.p. 40 mg/Kg) and confirmed by heart genetyping. INa was recorded from left ventricular cells using whole cell recording techniques. Myocardial infarction (MI) was induced by ligation of the left anterior descending artery (LADA) for 4 weeks; sham mice underwent the same procedure except LADA was not banded. Echocardiography and ECG were performed to determine cardiac function and electrical activity, respectively. HL-1 cells were exposed to H2O2 and Foxo1 nuclear translocation was determined by immunofluorescence. NaV1.5 and Foxo expression in mouse hearts and HL-1 cells were determined by RT-PCR and/or Western blot analysis.
Results: NaV1.5 mRNA and protein were significantly increased in mouse hearts with Foxo1,3,4-/- and peak INa densities at voltages from -40 to -5 mV were significantly increased in Foxo1,3,4-/- ventricular myocytes compared with those obtained from Foxo1,3,4+/+ ventricular cells. NaV1.5 mRNA was significantly decreased in 4 weeks MI hearts with cardiac failure and infarcted Q-wave while NaV1.5 mRNA was not reduced but significantly augmented in Foxo1,3,4-/- MI hearts. HL-1 cells were treated with 50 μ M H2O2 for 2 hours and Foxo1 was more localized in the nuclei after this treatment. NaV1.5 mRNA and protein were significantly decreased in HL-1 cells treated with 25 μ M H2O2 for 48 hours. siRNA-Foxo1 increased NaV1.5 expression and prevented NaV1.5 downregulation by H2O2.
Conclusions: Foxo proteins negatively regulate NaV1.5 expression and INa in the heart. Increase of ROS in chronic IHD promoting Foxo1 protein nuclear translocation leads to decreased NaV1.5 expression.
- © 2011 by American Heart Association, Inc.