Role of Rac1 GTPase activation in atrial fibrillation

Objectives We aimed to study the role of Rac1 GTPase in atrial fibrillation (AF). Background The signal transduction associated with AF is incompletely understood. We hypothesized that activation of Rac1 GTPase contributes to the pathogenesis of AF via activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and production of reactive oxygen species. Methods Old mice with cardiac-specific overexpression of constitutively active V12Rac1 (RacET) were compared with wild-type (WT) and WT undergoing transaortic constriction (TAC). In addition, samples of human left atrial appendages were analyzed in patients with sinus rhythm (SR) compared with patients with permanent AF matched for atrial diameter. Results At age 16 months, 75% of RacET but no WT or TAC mice showed AF. Treatment of RacET with statins for 10 months did not alter weight or fibrosis of atria or ventricles but decreased cardiac Rac1 and NADPH oxidase activity and reduced the incidence of AF by 50%. The left atria of patients with AF showed increased fibrosis, up-regulation of NADPH oxi dase activity, a 4-fold increase of Rac1 total protein and membrane expression as well as up-regulation of Rac1 activity. Conclusions Chronic cardiac overexpression of Rac1 represents a novel mouse model for AF. Rac1 GTPase contributes to the pathogenesis of AF and identifies a target for the prevention and treatment of AF. (J Am Coll Cardiol 2007;50: 359-67) (c) 2007 by the American College of Cardiology Foundation.