Abstract 070: Interaction between Mena, Connexin43, and Rac1 at the Intercalated Disc

Abstract

Background: We previously reported that Mena, a member of Ena/VASP family of actin regulatory protein, is associated with heart failure (HF). Mena is localized to the intercalated disc (ICD) and interacts with ICD proteins implicated in HF. The ICD mediates force transmission and electrical coupling between cardiomyocytes. Slowed conduction in HF is associated with Cx43 remodeling, the predominant connexin isoform in the heart. Mena-/- mice develop cardiac dysfunction, conduction abnormalities, ICD disorganization, and Cx43 lateralization. We hypothesized that: 1) Mena’s interaction with the cytoskeleton is critical for ICD stabilization and maintenance of electrical function; 2) Mena may modulate signal(s) from the cardiac sarcolemma to the ICD for control of expression and localization of Cx43 through the regulation of the small GTPase Rac1. Methods and Results: Interaction of Mena with Cx43 and Rac1 was evaluated in neonatal rat ventricular myocytes (NRVM), HeLa cells, and in transgenic mice overexpressing constitutively active V12Rac1 (RacET). Pull down assay using GST-PAK1 demonstrated a direct association of Mena with active Rac1-GTP in vitro. In NRVMs, siRNA knockdown of Mena significantly increased activity of Rac1-GTPase by 2-fold (p=0.05, n=5). Western blot analysis revealed increased total Cx43 expression in Mena siRNA (1.11±0.2) compared to scramble (0.33±0.1, p<0.01, n=5). Enhanced Cx43 expression was associated with increased rate of recovery after photobleaching between cardiomyocytes by gap-FRAP analysis (Tau 153.0±4.8 vs. 73.0±1.8 sec, p<0.0001). Ongoing experiments with optical mapping of NRVM monolayers will determine whether conduction velocity may be enhanced after Mena knockdown. Confocal imaging revealed altered Cx43 trafficking and localization with Mena knockdown. Additionally in ventricles of RacET hearts, Mena expression was increased by 59% (p=0.01, n=4) compared to control, along with lateral redistribution of Cx43. Conclusions: Our results suggest that Mena is a critical regulator of the ICD at the intersection of Cx43 and Rac1. Increased Rac1 activation is associated with lateralized Cx43, and enhanced cellular coupling. Mena may modulate Cx43 localization through the regulation of Rac1 activity.