Abstract 19390: Sirtuin 1 Modulates Cardiac Sodium Channels in vivo

The rapid upstroke in phase 0 of the cardiac action potential is the result of the inward sodium current (I Na ) carried by the cardiac voltage-gated sodium channel Na v 1.5 (SCN5A). We recently reported that the overexpression of Silent Information Regulator 1 (Sirtuin 1, SIRT1), an NAD + dependent protein deacetylase, deacetylated SCN5A, increased its cell surface expression, and increased I Na in HEK-293 cells and rat neonatal cardiac myocytes. Overexpression of a dominant negative SIRT1 construct decreased SCN5A cell surface expression and I Na . The role of acetylation of SCN5A and its regulation by SIRT1 has not been shown in vivo, however. We engineered cardiac specific Sirt1 knockout (cSirt1KO) mice by breeding Sirt1 flox/flox with α-MHC-cre mice on a C57BL-6 background. cSirt1KO compared to littermate Sirt1 flox/flox mice showed much less expression of Sirt1 mRNA (12±6%, n=3) and protein in the heart but not in the kidney, and Scn5a immunoprecipitated from cardiac membrane fractions of the cSirt1KO mice showed an ∼2-fold increase in acetylation (Figure A). At 3 months of age, EKGs from anesthetized cSirt1KO compared to littermate Sirt1 flox/flox mice showed PR prolongation (43±3 ms, n=4, vs. 37±2 ms, n=5; p<0.02) and telemetry from ambulatory cSirt1KO mice showed high degree heart block not seen in the controls (Figure B). Thus, our results show that Scn5a is acetylated in vivo in the mouse, that the degree of acetylation is regulated by cardiac-specific expression of Sirt1, and that decreases in Sirt1 lead to conduction disease similar to those seen in Scn5a +/- mice. These findings raise the possibility that pharmacological manipulation of Sirt1 may provide a means to modulate cardiac I Na and arrhythmias.