Abstract 17271: Foxo1 Regulates Cardiac Sodium Channel (NaV1.5) Expression in Mouse Ventricular Hypertrophy and Failure Induced by Transverse Aortic Constriction
Background: In heart failure, intracellular Na+ is increased, which leads to Na+/Ca2+-exchanger mediated increase in [Ca2+]i, reduced contractility and increased propensity to arrhythmias. Increase of cardiac Na+ currents is considered to contribute to this process. The mechanisms of Na+ channel alteration are poorly understood. It has been shown that Foxo1 transcriptional activity is inhibited in cardiac hypertrophy through its phosphorylation and the promoter region of SCN5A encoding NaV1.5 has Foxo1 binding sites. Therefore, we determined if Foxo1 control NaV1.5 expression and how its phosphorylation influence this process in heart hypertrophy and failure.
Methods: Left ventricular (LV) hypertrophy and failure were induced in adult C57BLC/6J mice by transverse aortic constriction (TAC). Sham mice underwent the same operation, except the aorta was not banded. LV hypertrophy and function were determined by echocardiography at 4 weeks after TAC. Na+ currents were recorded from the LV cells using whole cell recording techniques. Western blot was performed to determine NaV1.5 protein and phosphorylated Foxo1 levels. SCN5A promoter activity was assessed by luciferase assay.
Results: TAC produced a significant increase in heart to body weight ratio. Echocardiography showed a significant LV wall thickening. Both LV ejection fraction and fractional shortening were significantly reduced in TAC mice. Na+ current density was significantly increased (p <0.05) (TAC: 19.4±1.8, n=10; sham:15.0±1.0, n=13 at −20 mV) without alteration of voltage-dependent activation. Increased Na+ current density was associated with higher Nav1.5 protein levels and increased Foxo1 phosphorylation at Tyr24 and Ser256. Expression of Foxo1 in both Hela and HL-1 cells caused depression of SCN5A promoter activity, whereas siRNA targeting to Foxo1 increased NaV1.5 protein expression in HL-1 cells. Decrease in Nav1.5 protein expression was observed in HL-1 cells infected with constitutively activated GFP-Foxo1-AAA and Foxo-1-ADA.
Conclusions: Foxo1 negatively regulates SCN5A transcription and this effect is attenuated by its phosphorylation contributing to increased NaV1.5 protein expression and Na+ current density in heart hypertrophy and failure.
- © 2010 by American Heart Association, Inc.